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I N D E X________________________________________________________________________ PAGE NO.________________________________________________________________________
I. GENERAL BASIC PRINCIPLES…………………………………
II. PROCESS DESCRIPTION ………………………………………..
III. DEFROSTING OF PLANT ………………………………………..
IV. START UP AFTER DEFROST …………………………………….
V. START UP AFTER SHORT SHUT DOWN ……………………….
VI. PLANT SHUT DOWN ………………………………………………
VII. NORMAL RUNNING OF PLANT ………………………………….
VIII. MOLECULAR SIEVE DRYERS ………………………………………
IX. EXPANSION ENGINE ………………………………………………….
X. LIQUID OXYGEN PUMP ………………………………………………
XI. SAFETY PRECAUTIONS FOR AIR SEPARATION PLANT ………..
XII. OXYGEN TEST SET …………………………………………………….
XIII. TEST PROCEDURE ……………………………………………………..
XIV. ACETYLENE SPOT TEST ………………………………………………
XV. NITROGEN TEST SET (PHOSPHORUS) ………………………………..
XVI OPTIONAL (NITROGEN PRODUCTION) ………………………………
XVII. VALVE INDEX AND NOMENCLATURE ……………………………..
XVIII. INSTRUMENTS INDEX AND NOMENCLATURE …………………….
XIX. ABBREVIATIONS ……………………………………………………….
________________________________________________________________________
Note : This Manual has been made as comprehensive and detailed as possible. However, due to constant developments, introduction/deletion of optional items from plant to plant etc. there might be certain instances of unclarity. Please do refer to the manufacturer in such cases.
I. GENERAL BASIC PRINCIPLES
Atmospheric air is used to produce oxygen and nitrogen in most industrial processes. Atmospheric air mainly contains the following elements. :
ELEMENT % COMPOSITIONBY VOLUME
BOILING POINT ATATMOSPHERIC PRESSURE
Nitrogen (N2) 78.03% 195.5 deg. C.Oxygen (O2) 20.99% 182.7 deg. C.Argon (A) 0.93% 185.5 deg. C.Carbondioxide (CO2) 0.03% 78.5 deg. C.
The other constituents of air are hydrogen and rare gases, such as Neon, Helium, Krypton and Xenon (in traces).
The major impurities are dust particles and moisture which will be present as per atmospheric conditions.
Air is composed principally of oxygen and nitrogen and its physical properties lie between the two but closer to those of nitrogen. In its normal atmospheric condition, air is a colourless odorless gas. Air which is normally in gaseous state can be liquefied, as steam from gaseous state can be condensed to form water in liquid state.
Air is liquefied in this process by expansion in an expansion engine and in a Joule Thompson Expansion Valve. As we use an expansion engine, the air is to be compressed only to a medium pressure of 35 kgs./cm2 (500 PSIG) whereas other processes need about 200 kgs./cm2 air pressure. Expansion Engine is a single acting reciprocating engine with inlet and outlet valves, set to open at particular time intervals of stroke cycle. Thus, air entering expansion engine through inlet valve with a high pressure is expanded during the downward stroke of piston. The expanded air will be drawn out through the outlet valve during upward stroke of piston. During such expansion, air gets cooled.The expanded air from Expansion Engine and Expansion Valve will enter the lower part of Distillation Column. This Air will mostly be liquid.
Distillation is an operation of separating two components having two different boiling points. Thus at a particular temperature in between the two boiling points, one component will be volatile (Thus vapour) and the other component will be liquid. Thus, the component which is more volatile can be drawn out of a distillation column as vapour. The component which is less volatile can be drawn out as liquid. Oxygen and Nitrogen have a difference of about 13 deg. C. in boiling points and therefore, can be separated in a distillation column. Nitrogen will be drawn out as vapour. Oxygen will be collected as liquid and can be pumped upto 150 kgs./cm2 by a liquid oxygen pump.
II. PROCESS DESCRIPTION________________________________________________________________________
Air is drawn from atmosphere through Suction Air Filter (1) where dust particles are removed. The air should not be drawn from a location near an Acetylene Gas Plant.
The air is then compressed in an Air Compressor (2) to a maximum pressure of 60 kgs/cm2 for plant starting condition and to a pressure of 35 kgs/cm2 for normal running condition. Air Compressor has inter coolers between stages and an after cooler. For further details on Air Compressor, please refer to Air Compressor Manual. The air compressor should be maintained always in good condition as it is the main source of air supply to the plant.
The air then enters an Evaporation Cooler (5) where it gets cooled by about 10-12 deg. C. This cooler is an elliptical vessel split into two compartments. In each compartment, there is a pipe coil and is inter connected. The coils are half submerged in water in the vessel. Dry Nitrogen will be bubbled through this water to become wet gas. As the water vapourises, it requires latent heat which is absorbed from water itself. So water gets cooled. Thus, air inside the pipe coil will get cooled. Compressed air, cooled in Evaporation Cooler will enter a Moisture Separator (6). Moisture condensed as water will be separated and drained once in an hour (ensure that water is always present in the cascade cooler. If no water is present, cascade cooler will not work and the air entering battery will remain warm. Co2 may be carried into the column).
The air will then pass through an Oil Separator (7) packed with Activated Carbon/Alumina. Here the oil vapour carried over from Air Compressor will be removed. If this oil vapour is not removed sufficiently, (due to spent carbon or due to high temperature of process air ) the oil vapour will damage molecular sieves. To obtain a long life of Molecular Sieve ensure that carbon filter is well maintained. Change carbon/alumina every 2 years or even earlier.
The air then enters one of the Molecular Sieve vessels (8). The Moisture and Carbon Dioxide in the air will be removed in the drier. If they are not removed before entry to Cold Box, they will form Ice and dry ice which will choke the Heat Exchanger Tubes and other equipments. There are two dryers. One will be (on line with the process air) in operation for approximately 10 hours and the other will be under regeneration. Regeneration will be done by heating and cooling by out going nitrogen. An electric regeneration gas heater (9) is used for regeneration. For further details refer separate Chapter on Molecular Sieve Dryers.
The dry air is again filtered in a Ceramic Filter (10) before entry to Cold Box to avoid any dust entry to Cold Box. (The Filter must be checked every six months. If element is damaged must be replaced at once to prevent Molecular Sieve from entering column and causing permanent damage). The compressed air, cooled and without moisture and carbon dioxide will enter the Cold Box (11). It initially passes through a Heat Exchanger No.1, a multi pass coil type heat exchanger. The incoming air will be cooled by the outgoing oxygen and nitrogen. The air will be cooled to – 100 deg.C. in this heat exchanger.
The air will then be bifurcated into two streams. The main air stream will enter Expansion Engine (14) at 35 kgs./cm2 and will be expanded to 5 kgs./cm2 and 150 deg. C.The rest of the air will pass through Heat Exchanger No.2 or liquefier to be cooled to about – 155 deg.C. by the outgoing oxygen and nitrogen. This air will then be expanded by an Expansion Valve R1 to form liquid air. Both the air streams will now enter bottom portion of the Pressure Column. An additional expansion valve R4 is generally provided to be used only for start-up.
As the air enters the Pressure Column, after the Expansion Engine, and after Air Expansion Valve R1, a part of this air condenses into liquid and falls at the bottom of the Column. This liquid is about 40% oxygen and 60% nitrogen and is usually called the “Rich Liquid”.
A part of the air in this column evaporates and rises to the top of the Column touching the Condenser which is cooler than the Lower Column. As this air touches the Condenser, it condenses into a liquid on top of the Lower Column. This liquid is generally 99% nitrogen and being poor in oxygen, it is called “Poor Liquid”.
Final separation of the 2 fraction is achieved in the Upper Column. Both the Poor Liquid and the Rich Liquid are carried into the Upper Column by two Expansion Valves and the pressure drops from approx. 4.5 kgs./cm2 in the pressure column to 0.6 kgs./cm2 in the upper column. This Rich Liquid enters the middle of the Upper Column and as it flows down, nitrogen evaporates and oxygen continues down as liquid. The Liquid Nitrogen (Poor Liquid) enters the top of the column and as it flows down the column, it comes in contact with any evaporating oxygen and condenses the same into a liquid, while the nitrogen itself becomes a Gas as it is more volatile. This process takes place in each tray. The entire gaseous nitrogen is piped out from the top of the column through the Heat Exchangers. Similarly, the liquid oxygen at the bottom of the column is carried away to a liquid oxygen pump from which it is compressed and again passed through the Heat Exchangers into the Gas Cylinders. As the Liquid oxygen travels through the Heat Exchangers, it evaporates into gaseous oxygen filling the Cylinder with gas and giving up its cold to the incoming air.
Generally the purity of oxygen will be 99.6% and nitrogen about 96%, when the plant is operated exclusively for oxygen production. If pure nitrogen is also required, a part of the air (Mixture gas) is bled out from the center of the Upper Column. By doing so, waste nitrogen purity will gradually increase to 99.6% and the oxygen production will fall. The nitrogen so produced can be compressed by means of a standard nitrogen compressor. This purity can be achieved only on plants with outlet for mixture gas.
The plant operation should be such that it is not too cold or too warm. If the cold box is too cold, the nitrogen will condenses into liquid oxygen and the oxygen purity will fall.
If the plant is too warm oxygen will evaporates with the nitrogen, and the quantity of oxygen produced will go down substantially and the waste nitrogen will carry more and more oxygen. To obtain optimum result of the plant, therefore, check the purity of the waste nitrogen which should not fall below 96%. Purity of approx. 97% is normally easy to maintain. The plant should be operated to achieve max. waste N2 purity without loosing oxygen purity. This will maximise oxygen production.
When the plant works continuously for a few months, it tends to accumulate Carbon Dioxide and moisture in its internal parts. These are to be removed once in about ten to twelve months. For details, refer Chapter on Defrosting of Plant.
Similarly, the L.O. Pump alone can be defrosted in case of trouble in pumping (refer L.O. Pump Chapter).
It is advised to give Carbon Tetra Chloride wash to the Cold Box equipments once in two years to ensure protection against Hydro Carbon contamination. Before starting plant, it is generally defrosted and blown out. Then the cooling/starting is done which will take about 7-8 hours. When the plant is stopped for short intervals, the plant need not be defrosted, but all the Cold Line Valves are to be closed to prevent outside moisture from entering the Cold Box.
III. DEFROSTING OF PLANT________________________________________________________________________
Despite air purification by Molecular Sieve, traces of water vapour and Carbon Dioxide will get past the Molecular Sieve Driers and enter the Cold Box. In due course, any Carbon Dioxide or water vapour that gets past through the Molecular Sieve Driers will be deposited as solid carbon dioxide (dry Ice – Sublimation temperature of - 80 deg.C.) or Ice (water ice – freezing temperature 0 deg. C.) within the tubes of Heat Exchangers, inside the Valves, Expansion Valve, L.O.Pump Filter and inside the holes in sieve trays. These solid deposits will restrict the flow of air and will be evidenced by gradual increasing difference between Air Compressor discharge pressure and Air Pressure before R1. In case of excess carbon dioxide the L.O.Pump Suction Filter will get chocked. Other symptoms of frosting are fluctuations of pressure and an increasing difficulty in maintaining the required purity and rate of production. Ultimately the pipes become so restricted that even when the compressor is working at its rated pressure and flow, the amount of air that can enter the plant is not sufficient to maintain production and purity. When the above occurs, the plant must be defrosted which is the process of melting out all of these accumulated deposits.
A. Complete Defrost of Plant
1. Initially drain all the liquid from the plant through D-1, D-2 and D-3.
2. Check before defrosting that any one of the molecular sieve driers A or B is completely reactivated. This reactivated drier should be kept as standby for final cooling and production of plant after defrost. The other spent drier is to be used for complete defrosting. Incase no drier is kept reactivated, one of the driers will have to be heated for 4-5 hours by passing air through A-15 with heater on and 4-5 hours after switch of the heater. Take care pressure on heater does not cross 0.5 kgs./cm2. This will reactivate the battery and keep ready for plant start up.
3. Then keep the following valves setting (assume drier ‘A’ is ready)
a. Valve Close R1, A3, A5, A7, A8, A9, A11, A12, A15, A16, N2, N4, N5, N6, N7, N8, N9,
N10.
b. Valves Open
A1, A2, A4, A6, A10, A13, A14, A17, A18, A19, N1, N3, N11, 01, 02, 03, B1, B2,B5,D1, D2, D3, G1,G2,G3,G4,G5,G6,B4,B3 and Liquid Level Indicator Valves VL22, VL23, VL20 & VL21.
4. In Expansion Engine, lift the inlet and outlet valve push rods by a lever. Place a metallic piece of about 4mm. thickness in between Pestal plunger and push rod.
5. Start the air compressor after ensuring cooling water circulation as per air compressor manual and adjust air pressure to about 30 kgs./cm2 initially by closing valves A, A1, A2, A10 and compressor drain valves. Adjust air pressure by A1.
6. Gradually open air inlet to defrost heater valve A16 watching pressure in P-13. The pressure should not be more than 0.5 kgs./cm2.
7. Check flow of air in all drain valves D1 to D4 Blow out valves B-1 to B-5 and Analysis valves G-1 to G-6
8. After about 1 ½ hour switch on the defrost air heater and watch temperature of air, after heater. It should not exceed 65 deg. C. under any circumstances.
9. Disconnect the out let nut of the Liquid Indicator Valves (VL22, VL23, VL20 & VL21) to check the air flow connect the out let nuts after defrosting.
10. Check outlet temperature at all defrost outlets. They should be hand warm. The process of defrost may take approx. 6 to 8 hours.
11. After the outlet air at all points are hand warm switch off the defrost heater.
12. After about 30 minutes, close defrost air inlet valve A-16. Open air drains A1 and A2.
13. Stop air compressor. Depressurise all lines and vessels and close all valves of the plant.
14. Do not over heat the plant (max. 65 deg. C). If you do so the soldering in the cold box may melt and result in the total destruction of the cold box.
IV. START UP AFTER DEFROST
_____________________________________________________________________
1. Ensure availability of electricity at normal voltage and enough water level in Cooling Towers. Check oil levels of all running machineries are normal.
2. Start cooling water circulation to Air Compressor and ensure continuous water flow at all outlets.
3. Rotate flywheel of all running machineries by hand at least one turn for free rotation. Ensure Expansion Engine inlet valve A13 is closed.
4. Keep the following valve setting : - (assume drier ‘A’ on line)
Valve Open.
A-1, A-2, A-5, A-14, N-1, N-3, N-6, N-8, N-9, N-10, D-1, B-1, B-2, B-3, B-4, R-2 & R-3 & R-4 to be kept 10 turns open. Valve close
R-1, A-3, A-4, A-6, A-7, A-8, A-9, A-10, A-11, A-12, A-13, A-15, A-16, A-17, A-18, A-19, N-2, N-4, N-5, N-7, 0-1, 0-2, 0-3, B-5, D-1 to D-4 and G-1 to G-6.
All pressure gauge isolation valves should be kept slightly open.
5. Start the Air Compressor as per Compressor Manual. After attaining full speed, close the inter stage separator drain valves. Close A-2 completely. Close A-1 partially, watching air pressure in P-4, to be about 40 kgs./cm2. Ensure that oil feed to each cylinder is as prescribed in compressor manual. If oil is fed more than required, it will form hydrocarbons and cause explosion of distillation column. Excess air temperature in cylinders also can cause hydrocarbon formation.
6. Gradually pressurise Molecular Sieve Drier, which is ready for operating
(Assume ‘A’) through pressurising valve A-7, watching P-5. When P-5 is almost near P-4, open air inlet to Drier A-3. Due to sudden pressurising and depressurising Molecular Sieve pellets become powder and its life will reduce.
7. Now air is ready to be admitted to Cold Box. Open A-11, slowly watching P-1 pressure. Now air will be blown through drains B-1 and B-2. Blow the air lines a few times by closing and opening A-11.
8. Similarly blow Mixed Air Line by opening and closing A-12.
9. Thereafter close A-11, A-12, B-1 and B-2.
10. Now again open A-11 slowly watching Air Pressure in P-1. After pressurising, open A-1 fully.
11. Now the expansion engine should be started electrically. Keep the inlet valve hydraulic system lever in “stop” position. Oil Pressure in P-15 should be atleast 1.2 kgs./cm2. Then release all air locks in hydraulic system. Keep the inlet cam in ‘7x’ positions. Bring the inlet valve hydraulic lever to run positions. Now both inlet and outlet valve pestles should work. Open the air inlet valve A-13, slowly watching P-7 and P-8 pressure gauges. Then A-13 should be opened fully.
12. The lower column pressure P-2 also will go up. During initial start up, the pressure will be about 3 to 4 kgs./cm2 in lower column and about 0.4 to 0.5 kgs./cm2 in upper column. Now the air will blow through B-3 and B-4, blow out air for few minutes and close B-3 and B-4.
13. After reaching a steady upper column pressure in P-3, regeneration should be started to regenerate off the line drier. After checking drier cycles, heating should be started.
14. Then Nitrogen to the evaporation cooler should be admitted by opening valve N-2. Valve N-3 must be closed watching upper column pressure. If there is excess water in evaporation cooler, it will generate a back pressure on Upper Column P-3, which should not exceed 0.6 kgs./cm2. Ensure that Nitrogen pipe dips into water.
15. Now watch air pressure in P-1, P-2, P-3 and P-4. They should be steady. Slowly increase air pressure in P-4 by closing A-1 gradually, so that, discharge pressure in P-4, is about 55 to 60 kgs./cm2. Take care that P-2 and P-3 does not go up. Also watch warmth of expansion engine cylinder if new piston rings have been used. If it is warm, reduce air pressure slightly.
16. Now watch temperature, Expansion Engine outlet T-2 and Expansion Engine Inlet T-1. These will start cooling. After about 2 ½ to 3 hours T-1 will reach–90 deg.C. and T-2 will reach – 140 deg. C.
17. When T-1 is – 90 deg.C. to -100 deg.C. and when T-2 is -140 deg.C. open R-1 valve slightly. Then watch T-3 temperature. This will start cooling down.
18. By now, we would have advanced the Expansion Engine Cam position from 7 to about 5 or 4 depending upon the increase in air pressure in P-2 and P-3. When we reduce cam position, the inlet pressure will go up and outlet pressure will come down and vice versa. But in higher cam position, more air will be handled by Expansion Engine but the temperature drop will be less and vice versa. When starting the plant, even when the expansion machine is operated in cam 7, the pressure will be very high. The pressure at P-1 will be high (50 kgs./cm2) as the warm air volume is large. As air contracts due to cooling after the first heat exchanger, the pressure at P-1 will drop gradually and the cam positions are adjusted to maintain a high P-1 pressure. After about five hours operation, the liquid will appear in Lower Column and P-1 pressure will continue to drop. The
cams are then shifted to positions 3, 2 ……. etc. to adjust, to sustain high pressure at P-1 and obtain maximum purity, when the plant is sufficiently cool.
19. When T-3 temperature before R1 reaches – 140 deg.C./ -150 deg.C. open R1 slightly more without upsetting T3. Half an hour after this, liquid air will start forming in Lower Column.
20. 1 or 1 ½ hours after this, liquid oxygen will start forming in Main condenser.
21. It is a good practice to drain a little amount of R.L. and L.O. initially to flush lines by opening D1 and D2.
22. Now line up Upper Column level gauge (L1) by opening VL20 and VL21 gradually. The level of liquid oxygen will start increasing.
23. When Upper Column level in L1 had increased to about 50 cms. (start closing R-2, R-3 and R-4 valves. Gradually close the R-4 fully). Level will fall down and again rise.
24. When R-2 is about 2 turns open and R-3 is about 1 turn open, Oxygen purity is to be analysed collecting a sample from G-6.
25. Oxygen purity should be more than 99% before starting production.
26. To increase oxygen purity, R-2 is to be slightly closed.
27. After attaining good oxygen purity and having good level, open oxygen valve R-5 and then R-6 valve gradually. Now Liquid Oxygen is allowed to enter L.O. Pump.
28. When level has again risen after a drop, we are ready to start L.O. Pump.
29. Open valve 0-1 and close valve 0-2 & 0-3.
30. Before starting L.O.Pump, check free rotation by hand. Clean the L.O. Pump Piston with C.T.C.
31. Start the L.O. Pump and check oil pressure for crank lubrication in P-16 pressure gauge. It should be about 0.7 kgs./cm2.
32. Now check for flow of oxygen in vent vis 0-1.
33. Then open 0-2, 0-3 and loosen all bull nose connections to cylinders. Close 0-1. Now, product oxygen lines will be purged.
34. Thereafter close 0-2, 0-3 and tighten bull nose connection. Keep open cylinder valves, individual connection valves and open 0-2.
35. Filling in main manifold lines can be started.
36. Rate of production can be checked by time taken for filling a set of known capacity cylinders.
V. START UP AFTER SHORT SHUT DOWN________________________________________________________________________
1. When plant is stopped for shot time, either due to electricity or Maintenance or Cooling water failure, the start up is not very lengthy as earlier.
2. Keep the following starting conditions : (Assume Drier “A” on line)
Valves open
A-1, A-5, A-14, N-1, N-3, N-6, N-8, N-9, N-10,R-5, R-6, 0-1 - R2 and R3 Turns open.
Valves close
R1, A-2, A-3, A-4, A-6, A-7, A-8, A-9, A-10,A-11, A-12, A-13, A-15, A-16, A-17, A-18.A-19, N-2, N-4, N-5, N-7, 0-2, 0-3,Blow out Valves B-1 to B-5Drain Valves D-1 to D-4
All pressure gauge isolation valves should be slightly opened and level gauge valves are to be opened.
3. Start the air compressor after ensuring cooling water supply. Close inter stage drain valves and adjust air pressure in P-4 to about 40 kgs.cm2 by valve a1.
4. Pressurise drier which was on operating (Assume “A”) by opening A-7, after pressurising open A-3 fully and close A-7.
5. After pressurising Drier, gradually open A-11 and pressurise Heat Exchangers watching P-1 pressure. After pressurising open A-11 completely.
6. Start Expansion Engine. Set hydraulic system and pressure properly. Keep cam around three positions. Open air inlet valve A-13.
7. Watch P-2 and P-3 pressures. When pressures are normal start drier regeneration, start drier heater if required.
8. Admit nitrogen to evaporation cooler by opening N2 and closing N3.
9. Watch temperatures T-1 and T-2 when they are – 90 / -100 deg.C. and – 140 deg.C. respectively and open R-1 valve.
10. Close R-2 and R-3 valves watching Upper Column level in L-1 to be within limits.
11. Check oxygen purity after setting R-1, R-2, R-3 valves and Expansion Engine cam setting.
12. When purity is normal start L.O. pump and start filling cylinders as mentioned earlier.
VI. PLANT SHUT DOWN_____________________________________________________________________
Plant can be shut down under various circumstances. Therefore the same is instructed under different categories, such as, (a) normal (planned) shut down (b) emergency shut down in case of power failure, cooling water failure or air compressor trouble or any other running machinery failure and (c) shut down incase of only expansion engine failure.
(a) Normal planned shut down :-
1. Stop oxygen cylinder filling when a particular batch is over and vent oxygen close valves, 0-2, 0-3, and open 0-1 valve.
2. Stop L.O. pump and close R-5 and R-6 valves and open D-3.
3. Open nitrogen vent N-2 and then close N-3.
4. Stop drier heater.
5. Reduce air pressure by opening A-1 by about 1/2 to 1 turn.
6. Close A-13 and stop expansion engine.
7. Close A-11 air inlet valve.
8. Close drier air inlet and outlet valve.
9. Open all separator drains and interstage drains of air compressor.
10. Stop the air compressor.
11. When air pressure in P-1 had come down close R-1 valve and close level gauge valves VL-22, VL-23, and VL-20, VL-21.
12. Stop cooling water circulation after 15 minutes.
(b) Emergency shut down :
1. Stop drier heater.
2. Open valve N-3 and close N-2.
3. Stop expansion engine electrically and bring hydraulic system lever to stop position. Open A-1 valve.
4. Stop L.O. pump electrically and close 0-2, and open 0-1.
5. Open air drain valves A-1 and A-2 and stop air compressor.
6. Close valves A-11, A-13, R-1, drier air valves.
(c) Shut down in case of trouble in expansion engine :-
1. Open air drain valve A-1, by one turn.
2. Stop drier heater.
3. Open N-3 and close N-2.
4. Stop L.O. pump electrically and close 0-2 & 0-3 and open 0-1.
5. Exp. engine inlet valve hydraulic system lever is to be brought to stop position.
6. Stop expansion engine electrically.
7. Watch air pressure not to exceed limits.
8. Close R-1 valve.
9. In case of short maintenance A-11 and drier air valves need not be closed and air compressor can be kept running otherwise they are to be shut.
VII. NORMAL RUNNING OF PLANT________________________________________________________________________
In case of operation of any oxygen plant, it is better not to disturb operation much. Normal operation of plant is best known by experience in individual plants. However, the following are guidelines :-
Air Compressor inter stage separator drains and moisture separator drains are to be opened and closed, every hour, to let out condensed moisture. All readings should be noted in a prescribed log sheet. Molecular Sieve Drier Heating and Cooling cycles are to be taken care (refer M.S. Drier Chapter).The rare gas vent valve G-2 should be kept slightly open to allow non condensed rare gases to escape from Lower Column. It is better to be bubbled through water kept in a bottle or through a small rotamater.
After starting the plant, the air pressure is to be brought down slowly to about 35 kgs./cm2, by further opening R-1 or by bringing up the inlet cam position of expansion engine to 3 or 2, from 1. This will increase production slightly. However, the upper column level L-1 and purities should be maintained. The plant can be maintained steadily if the upper column liquid level, column pressure, air pressure are maintained properly. Every half an hour product oxygen purity should be checked by drawing sample gas from G-6.
If any Hydrocarbon (particularly Acetylene) is present, in the atmospheric air, or is found due to excessive heating of the air compressor oil, the acetylene will settle as solid crystal, in the condenser liquid. Acetylene crystals in liquid oxygen can explode spontaneously, causing serious accidents. Therefore, once in 8 hours liquid oxygen and liquid air should be drained a little in order to avoid accumulation of acetylene. Excess presence of acetylene in liquid oxygen can cause explosion. In 5 liters of liquid oxygen, presence of more than 5 milligrams of acetylene (C2H2) or 200 mgs. of other Hydrocarbons are hazardous. Analysis for presence of acetylene is explained separately, and analysis should be done in each shift.If Acetylene is found to be present, the liquid is to be drained to reduce contamination. If acetylene still persists in the liquid oxygen, the plant must be stopped immediately. All liquid should be drained and the plant should be defrosted.
The standard operating conditions are the following, but they differ from plant to plant.
P-1 35-40 KGS./CM2 T-1 - 100 DEG.C.P-2 4.8 – 5.0 “ T-2 - 158 DEG.C.P-3 0.5 “ T-3 - 150 DEG.C.
“ T-4 + 25 DEG.C.P-4 42-47 “ T-7 - 150 DEG.C.P-13 1.5 “P-14 0.2 “
Exp. engine inlet cam-1 to 3
R-1 VALVE -0/4R-2 “ -1/10R-3 “ -0/10
L-1 40-55 CMS T-5 +22 DEG.C.T-6 +18 DEG.C
If liquid levels drop and if the plant is getting warmed up, throttle R-1 valve and bring down expansion engine cam position to increase cold production. When cam position is brought down from upper number to lower number, the air inlet pressure will go up and outlet pressure will come down. The air throughput will also come down. Therefore, temperature drop across expansion engine will go up. Similarly, if inlet cam number is brought up to higher number, air inlet pressure will come down and outlet pressure will go up. Air throughput will go up but temperature drop across expansion engine will be less.
The purity of oxygen should always be maintained. To increase oxygen purity, the plant can be slightly warmed up or R-2 can be slightly closed. When upper column level is consistent, the purity also will be constant.
Cylinder filling should be checked. There should not be any gas leaks. Avoid using only waste or oil in filling procedure.
Water level should be maintained at half in Evaporation cooler.
VIII. MOLECULAR SIEVE DRIERS________________________________________________________________________
DESCRIPTION
Each vessel of the molecular battery is filled with about 150 kgs. of molecular sieve of 1.5mm or 3mm. (Type 13 X). As the process air passes through the molecular sieve the molecular sieve will absorb water vapour and co2 from the air. After some 10 hours the molecular sieve becomes saturated, and it will have to be regenerated.
If hot air at low pressure is passed through the saturated molecular sieve, the molecular sieve will discharge the co2 and water vapour is ready for use again. The absorbing capacity of the molecular sieve drops rapidly if the process air is warm. Therefore, ensure that the compressed air entering into the molecular sieve is below 30 degree centigrade and that the molecular sieve is thoroughly cooled after regeneration, before the process air is passed through it again. Cooler air inlet temperature will result in better absorption of moisture and Co2.
REGENERATION
The waste nitrogen from the cold box is passed through an electrical heater of about 9 KW and then passed through the vessel to be regenerated. The temperature at the inlet of the vessel rise rapidly, while the outlet temperature will rise very slowly. If the inlet temperature exceeds 350 degree centigrade, the heater must be put off, and put on again after 10 minutes. When the outlet temperature reaches 180 degree centigrade (for about one hour) the molecular sieve is regenerated. This process is known as the heating cycle, which will take 4.1/2 hours. At this stage, the heater must be put off, but the cold nitrogen will continue to pass through the vessel cooling the molecular sieve. Generally a by pass of the heater is provided which should be opened and heater line closed so that heater does not have to be cooled. This decreases the cooling time. This process is known as the cooling cycle which will last about 4 hours. After cooling, the vessel is ready for use when required for purifying the process air.
Molecular Sieve is a very expensive material, and should carefully used. The following will ensure its long life :
a. Oil vapour will destroy the molecular sieve and therefore ensure that the carbon filter is in good condition and the process air is as cool as possible, that maximum oil and moisture condenses out before the air enters the vessel.
b. While changing from one vessel to the other, pressurise the vessel very slowly, by opening the valve A-7 or A-8. It may take half an hour for the vessel to pressurise. If the main valves are opened rapidly, the molecular sieve may break up, due to high pressure air propelling the molecular sieve in the vessel.
c. When charging fresh molecular sieve, lower the same slowly through a pipe, so that it does not break on falling at the bottom.
Most of the plant operating problems are caused by the carry-over of co2 into the cold box and its blocking the heat exchangers. Satisfactory working of the molecular sieve will avert all these problems. Therefore, maintain and operate this equipment carefully.
The drier valve seats should be in perfect condition and if the air pass through valve seat both production of plant and regeneration of driers will be affected.
DRIER CHANGE OVER :-
When cooling is complete, the regenerated drier is to be lined up, as the other drier would have become saturated by now. The nitrogen valves of regenerated drier are to be closed. Then the regenerated drier will first be pressurised through pressurising valve. The pressurising should not be sudden and hence not through main air inlet valve. The molecular sieve pallets will get disintegrated soon if pressurising and depressurising is sudden.
After pressurising open air inlet valve completely. Open air outlet valve gradually, watching the outlet air temperature. This temperate will initially go up and thereafter will cool down. Then open the outlet valve completely. Start closing the outlet of the drier on line, taking care of common air outlet temperature. Then close air outlet and inlet valves of drier which was on line tightly. Depressurise the drier by depressurising valve. Then open the nitrogen valves of the drier to be regenerated. Check flow of gas at the regeneration nitrogen vent. Then switch on the drier heater for starting heating cycle of drier. Check for proper performance of drier heater.
Drier changeover (in short)
Imagine No.1 drier is ready after regeneration. (In case of No.2 Drier adjust the valves given in brackets.)
1. Close N-5 and N-7 (N-6 & N-8)2. Close A-9 and open A-7 and A-83. Watch P-5 to increase gradually for ½ an hour (P-6)4. When P-5 and P-6 are almost equal, open A-3 (A-4)5. Close A-7, A-8 and A-96. Open A-5 slowly.7. After 15 minutes open A-5 fully and start closing A-6 slowly. (A-6, A-5)8. After 15 minutes close A-6 and A-4 completely (A-5, A-3)9. Open A-9 and A-8 (A-9, A-7)10. P-6 will come down (P-5)11. When P-6 reads minimum, open N-6 & N-8 (P-5, N-5, N-7)12. Start drier heater and watch T-13
Replacement of Molecular Sieve :-
Molecular Sieve is to be replaced if :
(a) it becomes powder(b) if it gets contaminated by oil, or(c) if it looses its absorption capacity ;
The above will be known by frequent checking of cold box equipments.
To change Molecular Sieve, open the top and bottom flanges of drier vessel. Remove the filter at the bottom, Collect the old Molecular Sieve, which will fall down. Clean the filters, below the drier vessel.
Fit the bottom filter. Charge about 10 kgs. of Alumina/Silica Gel. Then charge Molecular Sieve type 13-X, 1.5mm or 3mm size about 150 kgs. the Molecular Sieve should be sieved and be free of all smaller size particles. It is better to charge through a long funnel so that Molecular Sieve does not fall with a force and break. Charging is normally done by hand. When level of Molecular Sieve is just at the brim of dish end of drier vessel, stop charging. Then fill up the doomed portion with Alumina/Silica Gel. Fit the top filter after cleaning.
IX. EXPANSION ENGINE________________________________________________________________________
DESCRIPTION
The Expansion Engine is a vertical single acting reciprocating type engine. This produces the cold required for operating the plant. The high pressure air enters through inlet valve at the start of downward stroke of the piston. On further downward motion, the inlet valve closes and entrapped air expands. During upward stroke, outlet valve remains open and inlet valve remains closed.
Therefore, in downward stroke air enters the cylinder and expands. In the upward stroke the expanded air is pushed outside. The electric motor is used initially to start the machine. Thereafter the engine is moved by the air pressure itself and during which time, the engine motor retains the speed by acting as a brake. Since work is done by air in rotating the flywheel, it loses its heat content (enthalpy). Thus the air gets cooled. This cooling is more than that of an expansion in an expansion valve.
An elementary factor for functions of expansion engine is to use dry and carbon dioxide free air, as otherwise, ice and dry ice will form or valve seats, causing mal-function.
The approximate temperature drop across expansion engine is 50 to 70 degree centigrade depending upon inlet air pressure, temperature and inlet cam position.
The expansion engine can be considered as three major units :(a) the drive unit(b) the cylinder unit or air expansion ; and (c) the hydraulic system for operating the valves.
The drive unit is similar to any reciprocating machine with usual parts, such as, crank case, crank shaft, connecting rod, crosshead etc. The expansion engine has an extended crankshaft to enable to accommodate the cams for valve lifting and is housed by a cam box. The moving parts are lubricated through a hole in crank shaft. Oil scrapper rings are provided to prevent oil escape to cylinder unit.
The cylinder unit handling process air consists of cylinder, piston, inlet and outlet isolation valves, pressure gauges and the ball valve assemblies. The ball valves are actuated mechanically by a push rod as per the timing transmitted by the cam. The push rods are housed in a stuffing box to avoid air leakage and is actuated by the hydraulic system.
The hydraulic system is the control system. The hydraulic oil is fed by a pump to (a) pressurised oil container for valve actuation (b) to lubricate crankshaft and drive unit parts, and (c) to lubricate the rolled holders. Oil pressure at P-15 should be 1.5 to 2 kgs/cm2 and can be adjusted by a valve mounted on the pump. The oil specification should be viscosity 6.5 degree centigrade. angler at +50 degree centigrade and specific gravity 0.91 kgs/cm2. Flash point of at least +175 degree centigrade solidifying point of
atleast -5 degree centigrade. This requires an addition of silicon defoaming agent of 1-2 drops per litre of oil.
Oil from pressurised oil container is fed to two control oil push pumps for inlet and outlet. The outlet valve cam rigid with one cam position creates a to-and-fro motion on the roll holder of the push pump. This motion is received by the pistons of the push pump and develops and pressure pulsation. This pulsation is transmitted to valve piston through a piping. The piston in valve pestle again transmits the pressure pulsation into a mechanical to and fro suction. As the piston of valve pestle is in line with the push rod, the ball valves are operated. Similarly, the inlet valve push pump operates the inlet ball valves as per the cam settings and the required cam setting is set by the selector arrangement. To change cam position : (a) release locking device of cam setting ; (b) unload expansion engine by unloder valves ; (c) change cam position by turning cam selector wheel ; (d) check cam position by noting the pointer on cam number ; (e) load expansion engine and (f) lock cam setting device by tightening lock handle on cam selector. The effects of different cam settings are mentioned in the plant start up procedure.
The expansion engine inlet ball valve is brought to close position by passing oil pressure pulsation/displacement from inlet push pump to pressurise oil container by an unloader valve or by a solenoid valve electrically.
There are air release valve at each valve pestle. During initial start up, air should be released ; (a) at air release plug of oil pressure container ; (b) at oil pressure gauge valve VP-15 ; and (c) at air release valves of valve pestles.
There should be no leaks in hydraulic system for best performance of engine.
SAFETY :-
If the power supply to the expansion engine should fail, there would be no breaking of the engine speed, which will rise rapidly. To prevent such contingencies, the following two safety features have been provided :-
(a) If the power supply fails, a solenoid valve will operate in oil system, closing the inlet valve to the expansion engine.
(b) A lever load/unload valve is provided in the expansion engine, which can be operated by hand. This too will close the air inlet to the engine and can be operated by the operator when required.
A safety valve (bursting disc) is provided in the air outlet line before air out isolation valve A-14. This safety is set to blow at 8 kgs./cm2.
Nitrogen purge is provided in distance piece below cylinder and in valve pestle housing to prevent atmospheric moist air to form frost on colder parts.
OPERATION :-
(A) Start Up
1. Check oil level in crank case, cam case and pressure oil container.
2. Open air outlet valve, Nitrogen purge valve and oil feed valve to control push pumps.
3. Start the motor and check direction of rotation.
4. Observe oil pressure ad release air locks.
5. Check outlet valve lifting and inlet valve lifting by changing lever of ball valve.
6. Open air inlet isolation valve slowly.
(B) Normal Run
1. Check for oil levels, oil pressure, oil leaks, air lock in oil system and malfunction of hydraulic system and set right.
2. Check if valve lifting is normal.
3. If stuffing box of valve push rods are leaking, the engine is to be stopped and attended to.
4. Avoid temperature less than -165 deg.C.
5. Check that the cooling is proper by seeing temperatures T1 and T2.
6. Change inlet valve cam position, if necessary, as detailed in plant start up.
(C) Shut Down
1. Unload inlet valve pestle by operating load/unload valve in hydraulic system.
2. Stop Motor.
3. Close air inlet valve.
MAINTENANCE
(a) Changing of Piston Rings :- Normally the expansion engine piston rings wear out in about 6 months time. They have to be changed. The rings wearing out can be noticed by excessive air leak at the bottom of engine cyl leak can be felt.Isolate engine by closing the main inlet and outlet isolation valves (A-13 & A-14). Open the cylinder head on top of the engine. Remove the oil scrapper rings. Its housing is to be dismantled from the crank case, and is to be kept lifted up. Rotate the fly wheel to attain top dead centre. Remove the stud nuts of the piston rod bottom mounting flange. Hold the piston in position by lever and rotate the fly wheel, so that the cross head gets disconnected from piston rod. Unscrew the piston rod mounting flange from piston and also remove the oil scrapper housing. Now, the piston can be lifted from the top using eye bolt threaded to the top of the piston. The piston rings and the guide rings are to be changed if worn out. While placing the new rings, take care that the play between bud joints of a ring is about 0.4 to 0.5 mm. The ring gaps are to be staggered at a degree of 120. Now the piston with piston rings should be inserted in a liner provided for the purpose of maintenance. This liner with piston ring assembly inside is to be placed on the top of cylinder, such that, the liner is in line with the cylinder. Now push the piston rod alongwith the rings, so that, the rings slide from the liner to main cylinder without distortion or expansion. After the piston has been pushed completely inside the main cylinder, the liner provided for the purpose of ring insertion is to be removed.
Insert the scrapper ring housing inside the piston rod and then thread in the mounting flange on the piston. Tight the flange with stud bolts of the cross head. Fix the oil scrapper ring housing and oils scrapper ring.
Rotate the flywheel and check for free rotation. Place the small piece of lead on top of the piston and fix cylinder head. Now rotate the flywheel for atleast two rotations. Remove the cylinder head, check the thickness of lead which indicates the head end clearance. This should be above 1mm. and less than 2 mm.
(b) Valve Maintenance :-
The inlet and outlet ball valve should be maintained properly for efficient performance of the expansion engine. The valves can be opened by opening the cap nut of the press screw. Then loosen the press screw. Remove the valve top block by unscrewing. The ball valve assembly can now be taken out by using a small eye bolt. The ball valve assembly is to be dismantled. Check for spring tension, for no scratches either on the ball or on the ball seat. Reassemble the valve after cleaning with CTC. The whole assembly can be assembled as it was opened.
The clearance between the valve hydraulic pestle and the push rod of the ball valve should be such that it has 4mm in inlet and 0.3mm in outlet. To check the same, remove the spring in the ball valve assembly and fix a solid wooden piece and tighten the valve assembly. Also tighten the valve top block. Using a lever, lift the push rod. Measure the clearance between the push rod and the piston of the hydraulic valve pestle, using a feeler gauge. To vary the clearance, the checknut of the screw on top of the piston of the hydraulic valve pestle is to be loosened. Then either by tightening the screw or loosening the screw, the clearance can be varied. After setting the clearance, the checknut of the
screw is to be tightened. After every maintenance of the ball valve, it is better to check the clearance of the push rod.
X. LIQUID OXYGEN PUMP________________________________________________________________________
1. DESCRIPTION
The liquid oxygen pump is a single stage, single acting piston pump. It is used for filling oxygen into cylinders upto a pressure of 165 kg/cm2.
The pump is designed for assembly in air separation unit that works by pumping liquid oxygen and gasifying the same in heat exchangers for final filling as gas in cylinders. Control of liquid feed is not necessary, because the pump is designed in accordance with the plant size and the liquid produced is constantly pumped off.
The drive unit is similar to any reciprocating machine with the crank shaft, flywheel, connecting rod, cross head etc.
The liquid oxygen pump consists of a stainless steel inside liner with liquid inlet and evaporated gas outlet port. There are no valves on these ports, which are closed by the piston itself on the pressure stroke. The third outlet is the main discharge outlet with the two non-return ball valves. The two valves remain firmly closed during suction stroke due to high pressure in partly filled cylinders.
To ensure that these valves are fully closed, a positive pressure of about 60 kgs/cm2 must be maintained on it. When a fresh batch of cylinders is taken for filling open the manifold valve slowly or use a spare batch of cylinders to ensure a positive pressure on these valves. Most malfunctions of the pump are due to these valves not closing properly.
When the pump is operated liquid oxygen from the main condenser enters the outer jacket of the pump. Some of this liquid evaporates due to heat produced in pumping and the vapour is passed out through the upper port back into the upper column as gas. The main stream of liquid oxygen is taken into the pump cylinder and compressed out by the piston in the pressure stroke. This high pressure liquid oxygen passes through two non-return valves into the heat exchangers and then to the cylinder filling rack.
If the Molecular Sieve is not functioning properly, some carbon dioxide and moisture will condense into the condenser and will travel to the L.O. Pump inlet where a filter is provided. The solid co2 may block the filter and the pump will not operate efficiently.
In such an event the L.O. pump should be defrosted. This way, the solid carbon dioxide will be removed and the pump will now work satisfactorily unless there is a continuous carryover of CO2. Drain a little L.O. in a double glass vessel and check against light. If the liquid is turbid, there are co2 crystals in it. If it is clear the fault is elsewhere.
ERECTION
During despatch of the plant, the drive unit is removed from the inside pump unit and is detached from cold box. The inside pump unit itself will come installed within the cold box. The drive unit should be placed on its foundation. The bolts connecting the drive unit mounting flange to the cold box should be loosely tightened. The four stuffing box retaining bolts should be loosely tightened. The piston rod is to be rightly connected to the cross head. Now, the alignment should be such as the piston rod is in the dead centre of stuffing box. This can be checked by means of a feeler gauge, around the piston rod in stuffing box casing. This clearance should be same for any forward and backward position of piston. When this is centralised, the piston moves smoothly. The connecting bolts can be tightened without upsetting alignment and the drive unit is to be grouted.
LUBRICATION
Before starting, the crank case is to be filled with oil at two thirds (2/3) of oil level gauge through the breather in the back side. The oil specifications are : viscosity 6.5, engine at +50 deg. centigrade, specific gravity 0.91 kg/cm2. Flash point +175 deg. centigrade and solidification point max. -5 deg. centigrade. The oil is to be changed in 1000 hours.
Oil is sucked from crank case through magnetic mesh filter by gear oil pump, which is directly driven by crank shaft. There is a pressure regulating valve in the pump. The pressurised oil enters a pressurised chamber and enters oil holes drilled through crank shaft, big end bearing, connecting rod, cross head pin and cross head. An oil pressure gauge P-16 is provided which should normally be 0.5 to 1.0 kg/cm2.
The end bearings of crank shaft or the two roller bearings are lubricated by splash of oil by the crank shaft. To avoid any escape of lubricating oil along the piston rod, a rubber “O” ring is provided around the piston rod. This “O” ring is held in position by a cover plate at front side (piston end side) of crank case.
In spite of this precaution, oil wetting of piston rod is to be checked often. Remove oil film if any by spraying carbon tetrachloride. Any escape of oil from drive unit to pump side should immediately be attended to. As a precaution, before starting the pump, the piston rod should be cleaned with CTC.
OPERATION
1. Open return oxygen gas vent valve (R-6) gradually, watching upper column P-3 pressure.
2. Open liquid oxygen inlet valve R-5 gradually. The level in upper column 1-2, will fall down initially and then wait till it again builds up.
3. Check for liquid – flow by opening valve D-3.
4. Open valve 0-1.
5. Check free rotation of flywheel by hand. Clean L.O. pump piston with CTC. Open nitrogen purge for stuffing lox.
6. Start L.O. pump motor. Check for right direction of rotation. It should be anti-clockwise when viewed from flywheel side.
7. Oil pressure P-16 should build upto 1.0 kg/cm2. If not release air through pressure gauge valve P-16.
8. Check for flow of oxygen in vent after 0-1.
9. Open 0-2, 0-3 and loosen all bull nose connections and purge the product oxygen.
10. Thereafter close 0-1 then close 0-3 and tighten bull nose connections. Keep cylinders valves open on filling manifold and start filling on one side.
During normal run, check for any gland leaks of liquid oxygen in the piston rod of stuffing box. If it leaks, tighten glandnut after warming with warm water. If it further leaks, stuffing box asbestos packing are to be changed.
CAUTION Always keep the L.O. pump parts of pump unit free from oil and grease. Refer chapter on safety.
SHUT DOWN AND DEFROST
1. To stop L.O. pump, stop the motor electrically.
2. Close valves R-5, R-6, 0-2 & 0-3 and open 0-1
3. Open liquid drain valve D-3 and drain liquid oxygen
4. Open defrost outlet valve of L.O. pump B-5
5. Open Defrost air inlet to pump A-19
6. Defrost air is to be drawn from process air through A-16 and watch pressure at P-13 to be less than 0.5 kg/cm2.
7. L.O. pump can be defrosted even when plant is in operation.
8. Check for flow of air at B-5 and D-3
9. After 15 minutes, switch on heater to maintain max. of 65 deg. centigrade.
10. When outlet air is hand warm defrosting is complete and switch off the defrost heater.
11. Close valve A-16, A-19, B-5 and D-3.
MAINTENANCE
a. FILTER
Remove cold box cover plate on right side in L.O. pump housing. Remove slag wool. The filter and cover can be removed by opening its outer flange. An insert made of sintered bronze is fixed inside. It can be cleaned by initial blowing with high pressure nitrogen, then CTC washing and again blowing with nitrogen. While fixing back make sure there are no gas leaks, by conducting a pressure test.
b. CYLINDER PISTON AND PISTON RINGS
The inside liner can be removed alongwith piston rod and rings. Detach piston rod from cross head by opening cross head cap remove. Remove stuffing box cover nut, lantern ring and packings. Remove non-return valve on pump end side and cap nut. Pull out inside liner with a small puller. The liner with piston rod will come out.
Remove piston rod from liner and inspect piston rings. There are four sets of teflon rings, and one guide ring. If the rings are damaged, replace them. Clean with CTC all parts. Fix new teflon asbestos rope of 3mm O.D., around liner. Push piston rod with rings inside liner. They should not be cut by port holes in to-and-fro motion. Insert the assembly as it was removed. Connect piston rod to cross head. Check head end clearance of pump to be not less than 1mm. Fix cap remove on pump end. Assemble stuffing box with new graphite impregnated asbestos packings, cut the form of rings.
XI. SAFETY PRECAUTIONS FOR AIR SEPARATION PLANTS
________________________________________________________________________
All personnel being employed for work in connections with oxygen/rich air, should be cautioned concerning the hazards involved and precautions to be observed.
WARNING
Oil grease or similar substances must not be allowed to come into contact with compressed oxygen or liquid oxygen. Contact of these substances with oxygen may result in an explosion.
Personnel working in an area of possible oxygen concentration, such as near an oxygen vent or a liquid oxygen spillage or in a trench where oxygen seepage and concentration might occur, must ensure that their clothing is free from contaminations of oxygen before lighting a cigarette or approaching a naked flame. It is essential that the clothes be aired for at least 15 minutes before approaching a flame after any such contamination.
The following precautions must be strictly observed at all times.
1. Thoroughly wash all oxygen fittings, valves and parts with clean trichloro ethylene carbon tetra chloride (CTC) before installation. Never use petrol, kerosene or other hydrocarbon solvents for this purpose. All tubing, lines, valves etc. to be used in oxygen service must be of an approved type and must be thoroughly degreased and blown out with clean oil-free compressed air or nitrogen before being placed in service.
2. Do not permit the release of acetylene or other flammable gases in the vicinity of the plant air intake. A concentration of acetylene exceeding 5 parts per million in liquid oxygen may explode with extreme violence. The plant is equipped with adsorber which give protection against accidental contamination. Strict supervision is essential to minimise the possibility of contamination.
3. The plant and the plant vicinity must be kept clean and free from obstructions at all times. Any oil leaks within the plant surroundings must be rectified without delay. Oil spillage must be cleaned up immediately using rag and carbon tetra chloride or TEC.
4. Do not lubricate oxygen valves, regulators, gauges or fittings with oil or any other substance.
5. Ensure that insulation removed from the air separator jacket is not contaminated with oil or other inflammable materials. Personnel carrying out maintenance on the air separation plant equipment must wear clean overalls and their hands and tools must be free of oil. This ensures that the insulation and equipment within the jacket is not contaminate with oil. Should
contamination take place the affected material must be discarded and replaced by clean new material.
6. Do not fasten electric conduits to the plant or its pipelines.
7. Do not use oxygen as a substitute for compressed air, spark present in an atmosphere of oxygen will immediately burst into flame.
8. Do not fill any container or pipe line with oxygen unless it has been thoroughly degreased.
9. When discharging liquid oxygen/rich liquid from drains, valves or pipe lines, open valves slowly to avoid the possibility of being splashed. In particular ensure that liquid does not run into shoes or gloves. Contact with liquid oxygen/rich liquid will cause frostbite evidenced by whiteness and numbness of the skin. The affected parts must be bathed at once in cold (not hot) water and seek medical attention immediately.
10. Do not breathe cold oxygen vapour. The temperature of the vapour rising from liquid oxygen is approximately -180 deg. centigrade. A deep breath of vapour at this temperature can result in frost-bitten lungs with resultant serious illness and permanent disability or death.
11. Do not experiment with liquid oxygen by putting solids or liquid into it for the purpose of watching the effect of the cold liquid. The object placed in the oxygen may catch fire or explode.
12. Do not pour liquid oxygen on the floor of the shop or around any object that can catch fire. As the liquid oxygen vaporises, the cold vapours may be swept alongwith ground into contact with combustible material. The whole floor of an office is known to have caught fire when oxygen vapours contacted a lighted cigarette butt. Spillage of liquid oxygen must be avoided especially in the vicinity of lubricated machinery, asphalt paving, concrete surface containing bitumen joints or where the liquid oxygen can flow into drains or sewers.
13. Do not use any pipe jointing on oxygen pipe threads except the jointing approved for oxygen service. Ordinary pipe jointing contains grease as a lubricant and will catch fire.
14. Compressor and expander lubricating oil consumption must be regularly checked. Any excessive consumption must be investigated immediately and the cause rectified.
15. The cold box atmosphere must be checked atleast once in a week. If local frost spots occur or if liquid level is inaccountably lost in the plant, and if any check indicates oxygen concentration above 21%, immediate action should be taken to locate and rectify the leaks.
16. The use of a flame (eg. for welding or cutting) in the immediate vicinity of the air separation plant or oxygen piping must be permitted only when the plant has been shut down and defrosted and when the oxygen content of the air within the equipment concerned does not exceed the atmospheric normal of 21%.
17. Do not attempt repair until all pressure is released from the section to be dismandled.
18. Remember that pressure alone is not dangerous. A boiler at 0.7 kg/cm2 may be more destructive in the event of an explosion than a smaller container of 220 kg/cm2 owing to the greater mass of metal involved. In general, fluid at high pressure and moving at a high velocity are the most dangerous.
19. Use a face shield or chemical type safety goggles when using the oxygen or nitrogen test set to prevent possible injury to the operator in the event of a blow-back of the reagent.
20. Check safety valves and bursting discs every 3 months.
XII. OXYGEN TEST SET________________________________________________________________________
The purity of the pure oxygen product and the oxygen content of the crude nitrogen gas is measured volumetrically by the chemical reaction between the oxygen in a measured sample of gas and a highly activated form of copper contained in a saturated solution of Ammonium Chloride in Ammonium Hydroxide. The reaction is affected in a glass tube which is contained in a cylindrical reservoir. The sample of gas is passed into the burette and measured. The sample is then drawn through the interconnecting rubber and glass tubing into the reaction chamber where the oxygen reacts with copper to form copper oxide (cu.0). The oxide formed is immediately dissolved by the solution of ammonium chloride in ammonium hydroxide. When the reaction is complete, the residual gas is returned to the burette for measurement. The apparatus is calibrated to give a direct reading for oxygen purity, in the region of 99.6%.
TEST APPARATUS
The test apparatus is as per sketch enclosed.
There is a gas entry (I) at the right extreme where sample gas can be hosed. There is a 3-way stop cock “G” to permit the gas to be bubbled through glass tube inserted in a purging vessel (or to be burette as desired). There is a graduated burette “A” in the middle, connected on one side with the purging vessel and the other side with the reaction chamber “D” through a 3 way stop cock “H”. The burette is connected with a levelling bottle by a rubber pipe. The reaction chamber is enclosed by a reservoir “E”. There is a rubber bung fitted in the bottom of the reservoir which also partly closes the reaction chamber bottom to avoid the copper wire coming out of the chamber.
PREPARATION OF TEST SET
Prepare the test solution of mixing one volume of Sp.gr.0.90 Ammonium Hydroxide (NH4OH) with two volumes of distilled water and add Ammonium Chloride (NH4CL) until solid crystals remain undissolved at the bottom of the container.
Invert the reaction chamber set, remove the rubber bung “F” and fill the reaction chamber “D” with copper wire in spiral form. Replace the bung and return it in an upright position and connect with the burette tubing.
Fill the reservoir and the reaction chamber three quarter with fresh test solution. With the levelling bottle “B” held below the level of the burette, half fill the bottle with the test solution.
Draw the test solution from the reservoir in the reaction chamber by turning the burette stop cock “H” to connect the burette with the reaction chamber and then lowering the levelling bottle. Squeeze the rubber pipe to expel all the air and then close the stop cock,
it so heat the reaction chamber and the interconnecting rubber pipe is completely filled with test solution.
The purging vessel (lute) is half filled with water and the sample gas to be tested is allowed to bubble through water to atmosphere.
Fill the burette with fresh solution by turning the stop cocks “G” and “H” to connect with the purging vessel, so that, all the air gets expelled. Repeat it till all the air bubbles are removed. When solution commences to flow from the burette to glass tube, close the stop cock “G” close the cock it and replace the levelling bottle in the holder.
TEST PROCEDURE
Open the stop cock “G” adjust the gas flow and allow the sample gas to bubble through the purging vessel for one or two minutes. Check that the burette and test connection tube are completely filled with the solution. Turn the stop cock, open to the burette connection. Then slowly open the cock “H” and allow the oxygen to pass into the burette (not to the reacting chamber), controlling the oxygen flow. When the burette is filled below the bottom mark, close the stop cocks “H” & “G”.
Adjust the level of the gas in the burette to the 100 cc. mark by holding the levelling bottle at the level of the liquid in the burette and carefully open cocks “G” and “H” to bubble through the purging vessel to atmosphere.
Pass the gas sample into the reaction chamber by turning the burette stop cock “H” to connect with the reaction chamber and raising the levelling bottle. The sample should be passed between the burette and the chamber several times.
On the first passage into the reaction chamber, the volume of gas sample is greatly diminished. The oxygen in the sample react with the copper to form an oxide which dissolve in the solution. After the first passage of the sample, the valve diminution becomes progressively less until all the oxygen has been absorbed by the copper and only the unreactive impurities remain unabsorbed.
Transfer the unabsorbed gas from the reaction chamber to the burette by lowering the levelling bottle. Do it a few times to ensure that gas bubbles are not trapped in the tubing. When all the unabsorbed gas has been passed into the burette, close the stop cock “H” equalise the levels of the solution in the burette and the levelling bottle and observe the amount of unabsorbed gas which represents the percentage of impurity of the sample.
XIII. TEST PROCEDURE
________________________________________________________________________
Crack the nitrogen purity test valve, open the stop cock “G” adjust the gas flow and allow the sample gas to bubbles through the purging vessel for one or two minutes. Check that the burette, the reaction chamber and the test connection tube are completely filled with water. Turn the stop cock open to the burette connection. Then slowly open the cock “H” to allow the oxygen to pass into the burette (not the reacting chamber), controlling the nitrogen flow. When the burette is filled below the bottom mark, close the stop cocks “G” and “H” and disconnect the nitrogen sample tube. Close the test valve. Adjust the level of the gas in the burette to the 100 cc. mark, by holding the levelling bottle at the level of the water in the burette and carefully opening the cocks “G” & “H” to bubble through the purging vessel to atmosphere.
NOTE :-
1. When first passed into the burette, the nitrogen sample will be colder than the room temperature and will expand as it warms. Therefore, the sample should be allowed to warm to room temperature for several minutes before the level is adjusted to the zero mark.
Pass the gas sample into the reaction chamber by turning the burette stop cock “H”, to connect it to the reaction chamber, then raising the levelling bottle. Close the stop cock, replace the levelling bottle in the holder and allow the oxygen in the sample to react with the Phosphorus. The reaction results in the emission of a white smoke consisting of Phosphorus Pentoxide (P205), suspend in nitrogen. The Phosphorus Pentoxide subsequently dissolve in water to form Phosphoric acid.
When the reaction is complete, as indicated by smoke ceasing the emit, open the cock and lower the levelling bottle to pass the unabsorbed gas from the reacting tube into the burette, pinch the rubber tube to ensure no bubbles are trapped in it.
Level the liquid in the burette and the levelling bottle and note the reducing indicated on the burette scale at the liquid level. This reading is equal to the percentage of purity of the original nitrogen sample.
2. The gas sample may be warm due to the reaction of the oxygen impurity with the Phosphorus. Allow it to cool to room temperature for several minutes before adjusting the level to the zero mark.
XIV. ACETYLENE SPOT TEST
________________________________________________________________________
INTRODUCTION
In the operation of air separation plants, trace quantities of certain gaseous contaminations can pass through the Heat Exchangers and the distillation column and accumulate in the liquid oxygen within the condenser. The source of these contaminants is generally the air fed into the plant or to a minor degree, the cracking of lubricating oil in the air compressor cylinders. Acetylene is a contaminant of liquid oxygen which becomes dangerous if the quantity present exceed two parts per million. The danger of an excessive concentration of acetylene can be prevented by use of clean air a operation and maintenance of the air compressor.
OPERATING SUPPLIES :-
The following chemicals are required for the acetylene spot check. The quantities stated are sufficient to permit 5 tests per day for a period of 150 days.
Concentrated Ammonium Hydroxide(specific gravity 0.9)
: 1.4 lit.
Soluble starch : 30 grms.Hydroxylamine Hydrochloride : 500 grms.Copper Sulphate : 250 grms.Distilled water : 11 lit.
DESCRIPTION
The test equipment comprises a one litre silvered glass, Dewar flask which is used to obtain and hold liquid oxygen sample a rack for five eight inch Pyrex test tubes each calibrated at 3, 10 and 20 cc. levels, a test tube holder and a dropping bottle by which Hydroxylamine Hydrochloride droops may be added to the test tube in use. Also included in the equipment are two reagent bottles for storage of the acetylene test solution, a test solution addition bottle to enable addition of reagent to the test tube, and a colour standards and rack.
TEST FREQUENCY
The frequency of testing for trace of acetylene will largely depend on the location of the plant with respect to sources of contamination ; the greater the chance of acetylene contamination, the greater the need for frequent testing.
On initial start up, the test should be carried out at least every 4 hours. The test results must be recorded. After testes have been carried out for several months, the records must be closed examined to determine the average acetylene contaminant level in the product liquid oxygen. If the level has remained at a steady low average, (below 0.25 ppm.
acetylene) the period of test may be extended to 24 hours, if fluctuations in the levels are noted, the test must continue at 4 hours periods.
TEST PROCEDURE The Acetylene content of the liquid oxygen is determined from the colour intensity produced by a chemical reaction with the Acetylene. The residue remaining just before the evaporation of the final traces of liquid oxygen sample is reacted with an Acetylene test solution. A reddish colour resulting from this reaction indicates an Acetylene concentration in the liquid oxygen.
Proceed as follows :-
1. Open valve D-2 and purge the sample line before taking a liquid oxygen sample. Precool the Dewar Flash by filling with liquid oxygen from the sample line. Allow to stand for about one minute. Discard contents of flask and refill from sample line.
2. Precool a clean test tube by filling it with liquid oxygen from the Dewar flask. Allow the tube to cool and discard the contents. Use a clamp to hold the test tube to prevent contact with the fingers. Refill the test tube to the 20 cc. mark with liquid oxygen from the flask.
3. Allow the oxygen to evaporate from the tube without agitating the tube. Immediately before the last drop of liquid oxygen evaporates, add acetylene test solution to the test tube until the 3 cc. mark is reached. Close the test tube with a finger and warm the solution by holding the tube in the hand. Add exactly 12 drops of the Hydroxylamine Hydrochloride solution to eliminate the blue colour of the acetylene test solution and allow the colour reaction to proceed for approx. one minute.
The appearance of reddish colour in the sample, in the test tube indicates the presence of acetylene. To determine the approx. acetylene concentration present in the sample, compare the colour developed against the colour standards. The two colour standards 0.25 and 1.0 ppm, are for tests that are carried out using a 20 cc. sample. In the event that the test indicates contamination exceeding 0.25 ppm. repeat the test using a 10 cc. sample in place of the 20 cc. sample normally taken. A colour intensity equal to 0.25 ppm. in the 20 cc. sample will indicate 0.5 ppm. in the 10 cc. sample. Similarly the same procedure enables the 1 ppm. colour standard to be used to determine a 2 ppm. concentration.
WARNING
ACETYLENE CONCENTRATION OF 2 PPM OR HIGHER ARE DANGEROUS. STOP THE PLANT IMMEDIATELY AND PROCEED AS DETAILED BELOW TO AVOID POSSIBLE INJURY TO PERSONNEL AND DAMAGE TO EQUIPMENT.
PREPARATION OF SOLUTIONS AND COLOUR STANDARDS.
ACETYLENE TEST SOLUTION
Prepare the test solution as follows :
1. Add one gram of soluble starch to 10 cc. of distilled water and stir into a thin paste. Pour the paste into the vessel containing 20 cc. of boiling distilled water. Stir the solution and allow to cool.
2. Dissolve 5 grams of Copper Sulphate (CuSO4 5 H2O) in approx. 500 cc. of distilled water in one litre flaks.
3. Add 50 cc. of concentrated Ammonium Hydroxide (26.4% NH3, specific gravity 0.900 st 60 deg. F.) to the cooper Sulphate solution.
4. Add the prepared starch solution to the Copper Ammonia solution and dilute to the one litre mark with distilled water. Store in flask bottle.
NOTE : The Acetylene test solution has a deep blue colour.
Preparing Hydroxylamine Hydrochloride Solution Add 2 cc. concentrated Hydrochloric acid (37.7. NC1, specific gravity 1.191 at 60 deg.F.) to 150 cc. of distilled water contained in a beaker. Add the following and stir until dissolved ;
Cobaltous Chloride Hexhydrate CoCL2 .. 6H2O – 10.00 gms.Cupric Sulphate Pentahydrate CuSO4 .. 5H2O - 2.00 gms.Ferric Chloride Hexhydrate FECL3 .. 6H2O - 0.30 gms.
Transfer all of the solution to a 200 cc. flask and make upto 200 cc. with distilled water and shake well. Tube 15 cc. of this solution to a test tube and seal the tube. The colour and colour Intensity when viewed from the side of the tube against a white back ground should be equivalent to that produced by liquid oxygen containing 1 ppm. Acetylene when tested in accordance with the procedure described.
0.25 PP. COLOUR STANDARD
The solution is as for the 1 ppm. standard except that the quantities of chemicals used is as follows :-
Cobaltous Chloride Pentahydrate COCL2 .. 6H2O – 1.90 gms.Cupric Sulphate Pentahydrate CUSO4 .. 5H2O - 1.30 gms.Ferric Chloride Hexhydrate FeCL3 .. 6H2O - 0.20 gms.
The colour and colour intensity of the solution when viewed from the side of the tube against a white background is essentially equivalent to that produced by liquid oxygen containing 0.25 ppm. acetylene when tested in accordance with the procedure, detailed.
TEST SET PART LIST
SR.NO. DESCRIPTION QTY. REQUIRED.
1. Dewar Flask, one litre thermos 12. Test Tube Rack 13. Test Tube Holder 14. Test Tubes, Pyres, 8 in x 5/8 in graduated 3 cc.
10 cc. & 20 cc.5
5. Dropper bottle, 4 oz. Polyethylene with dropper 16. Reagent bottle, 16 oz. narrow mouth, storage 27. Carrying case 18. Reagent bottle, 16 oz. Polyethylene for test
Solution addition. 1
9. Colour standards 0.25 ppm. And 1.0 ppm. 2
ACTION IN THE EVENT OF ACETYLENE CONTAMINATION
1. Contamination less than 0.5 ppm.The plant may continue to be operated normally.
2. Contamination greater than 0.5 ppm. but less than 2 ppm.
The plant may continue to be operated but the source of contamination must be ascertained and eliminated and the following action must be taken to reduce the level of contamination in the condenser.
Operate the plant at the maximum liquid production rate and as quickly as it is produced, withdraw liquid oxygen from the condenser through drain valve D-2. Dispose of the contaminated liquid oxygen. Continue thus until the contamination is less than 0.5 ppm.
3. Contamination greater than 2 ppm.
If the maximum operating limit of 2 ppm. is reached the plant must be shut down. Immediately drain off and dispose of all liquid oxygen from valves (D-1, D-2, D-3) and defrost the plant. The source of contamination must be ascertained and eliminated before the plant is again started.
XV. NITROGEN TEST SET (PHOSPHEROUS)________________________________________________________________________
The oxygen test set can also be used as a nitrogen test set by using stick phosperous in place of copper wire and water in place of ammonium chloride solution. Yellow or white phospherous submerged in water is used for absorbing the oxygen (which is the principal impurity in the nitrogen gas) to form prosperous pantoxide, which is soluable in water. The volume of remaining gas nitrogen) is then measured in the burette. A downward graduated burette may be used for easy reading.
WARNING It is dangerous to pass gas containing more than 7% oxygen into the phospherous test set.
Phospherous is highly combustible when exposed to air. Always keep it completely immersed in water both in the test set and in storage. Use tongs when handling phospherous. Do not handle with the fingers.
PREPARATION OF THE TEST SETInvert the reaction chamber set, remove the rubber bung “F” pinch the rubber tube to close it and fill the chamber and the reservoir with water. Using tong, fill the chamber with 3/16 or ¼ inch diameter stick phospherous.
Cork the reaction chamber and connect the chamber to the stop cock “H”. Fill the levelling bottle and the purging vessel half with water. Turn the stop cock to connect the reaction chamber with the burette and lower the levelling bottle. The water from the reservoir will rise in the reaction chamber and will flow down in the burette through stop cock “H”. Then turn the stop cock “H” to open to the purging vessel, at the same time, turn open cock “G” also. Raise the levelling bottle so that water will rise through the burette, cock “H”, the rubber tube connection and the cock “G” and finally it will tickle down to the purging vessel. By raising and lowering the levelling bottle a few times, all the air present in the burette and the rubber tubing connections including the cocks “G” & “H” should be expelled. After checking for air bubbles in the chamber and the burette, close the cock “H” and turn open the cock “G” for sample gas connection. The sample gas to be tested is allowed to bubble through water to atmosphere.
XVI . OPTIONAL (NITROGEN PRODUCTION)________________________________________________________________________
Note : Please note that the following options given below are with specified order only.
OPTION I : SIMULTANEOUS OXYGEN & NITROGEN PRODUCTION
To get simultaneous Oxygen and Nitrogen production, gradually open mixed gas outlet valve to half turn. Also open mixed air valve gradually to half turn, watch temperature T-7 and it should be around -150 degree centigrade. Adjust poor liquid, (lower column Nitrogen) purity by closing R-3 valve, to just about half turn open. The lower column Nitrogen purity should be about 99 to 99.5%.
After about 1/2 hour, the upper column nitrogen purity also will increase. Keep checking oxygen purity also. If oxygen purity is dropping close R-2 valve also slightly.
The oxygen production will drop down by about 6 to 10 m3/hr. The mixed gas flow should be maintained to about 40 m3/hr.
During defrosting, mixed gas line and mixed air line also should be defrosted.
OPTION II : NITROGEN PUMPING
The plant can produce nitrogen compressed through pump with additional equipments like Cryogenic Control Valves (R7, R8 and R9), liquid Nitrogen Vessel, Level Indicator and extra pipe lines. The optional items which can be installed at party site also depending upon the Nitrogen requirement in the local market.
Controlling Purity And Filling of NitrogenGradually increase closing of Control Valve R3 until liquid Nitrogen purity (analysis G-4) improve to 0.1% by volume is (99.90%).
Open the Control Valve R7 according to R3 setting and close R3. Check the purity of Nitrogen (Analysis D-9) and adjust the Control Valve R7 accordingly.
Operate the Liquid Nitrogen level indicator by opening the valve of VL22 x VL23. When the level of the Liquid Nitrogen reaches about 300mm, gradually start opening control valve R8 (Liquid Nitrogen to pump) so that the Liquid Level is maintained at 300mm. Open R9 (Vapour back from pump). Check the Nitrogen purity at the pump through the drain valve D-4.
Maintain the T-3 temperature more than -160oC by controlling the control valve R-1. Frequently check analysis (G-4) and adjust control valve R-7 purity decreases.
After completing the Nitrogen filling stop the pump, close R-8 and R-9. Close R-7 and open R3 according to R-7 setting, so that Oxygen purity does not disturb.
OPTION III : LIQUID NITROGEN PRODUCTION
The plant can produce Liquid Nitrogen with additional equipments like Cryogenic Control Valves, Liquid Nitrogen Vessel, Level Indicators and extra pipe lines which can be installed at party site also depending upon the Liquid Nitrogen requirement in the local market.
Controlling Purity at Liquid Nitrogen production
Gradually increase closing of control valve R3 until Liquid Nitrogen Purity (analysis at D9) improve to 0.1% by volume.
Stop the 02 production when the condenser level reaches about 500mm gradually start opening of control valve R7. Operate the Liquid Nitrogen level indicator by opening the valves VL 22 & VL 23 When the level of the Liquid Nitrogen reaches about 300mm, gradually start opening control valve R10 so that the liquid level maintained at 300mm.
Frequently check analysis G-4 and adjust control valves R3 by closing if purity decreases.
After completing the Liquid Nitrogen filling close R7 and R10. Open R3 gradually without disturbing the Oxygen purity and start the oxygen production.
OPTION IV : HIGH PURITY NITROGEN PRODUCTION
Do the plant control as per Option II above. High Purity Nitrogen can be achieved by further fine control of R-3 and R-7. Check the purity by a PPM – Oxygen Analyser as per requirement.
XVII. VALVE INDEX AND NOMENCLATURE
VALVE NOMENCLATURE VALVE NO. TYPE
Main regulating valves
Main Air Expansion R1 ExpansionR.L. Expansion R2 “P.L. Expansion R3 “Air By Pass Valve R4 “Liquid Oxygen Inlet to Pump R5 “Vapour Oxygen from Pump R6 “Liquid Nitrogen to Vessel R7 “Liquid Nitrogen to Pump R8 “Vapour Nitrogen from Pump R9 “Liquid Nitrogen Outlet R10 “
Air ValveMoisture Separation Drain A1 Blow OffOil Absorber Drain A2 “Mol. Sieve Drier “A” Air Inlet A3 Globe Mol. Sieve Drier “B” Air Inlet A4 “Mol. Sieve Drier “A” Air Outlet A5 “Mol. Sieve Drier “B” Air Outlet A6 “ Mol. Sieve Drier “A” Pressurising A7 Needle Mol. Sieve Drier “B” Pressurising A8 “Mol. Sieve Drier Pressure releaser A9 “Air Filter after drier drain A10 “Main air inlet to cold box A11 GlobeMixed air to Cold Box A12 Blow OffAir Inlet to Expansion Engine A13 Cryogenic GlobeAir Outlet from Expansion Engine A14 Cryogenic GlobeAir by pass to Mol. Battery heaterfor start-up regeneration
A15 Blow Off
Defrost Main Air Inlet A16 Blow off Defrost Air in Lower Column A17 Globe Defrost Air in Upper Column A18 “Defrost Air in L.O.Pump A19 “
Nitrogen Valves
Nitrogen heater by pass N-1 GateNitrogen from Evaporation cooler N-2 “Nitrogen to Atmosphere N-3 “Nitrogen through heater N-4 “Mol. Sieve Drier “A” N2 Inlet N-5 GlobeMol. Sieve Drier “B” N2 Inlet N-6 “Mol. Sieve Drier “A” N2 Outlet N-7 “
Mol. Sieve Drier “B” N2 Outlet N-8 “Nitrogen Purge for Exp.Engine N-9 Gate Nitrogen Purge for L.O. Pump N-10 “Mix. Gas out N-11 GlobeNitrogen Purge for L. N2 Pump N-12 “
Oxygen Valve
H. Press oxygen Vent 0-1 Manifold Manifold “A” isolation 0-2 “Manifold “B” isolation 0-3 “
Drain, Analysis and Blow Out Valves
Air blow out from distribution pieces (air line between heat exchanger No.1and No.2)
B-1 Blow Off
Air blow before R1 B-2 “Upper column blow out B-3 “Lower column blow out B-4 Cryogenic drainDefrost out of L.O. Pump / Drain B-5 “Lower / Pressure column Drain D-1 “Main Condensor Drain D-2 Analysis Liquid Oxygen Pump Drain D-3 “Liquid Nitrogen Pump Drain D-4 “Rich Liquid Analysis G-1 “Rare Gases G-2Waste Nitrogen Analysis G-3P.L. Analysis G-4Mix Gas Analysis G-5Oxygen Analysis G-6
“Pressure gauge & Instrument Isolation Valves
Air Pressure gauge (P-1) before R-1 VP-1Lower column Pr. gauge (P-2) VP-2Upper column Pr. Gauge (P-3) VP-3Air Pr. before moisture Separator (Air Compressor) 4th stage pressure - (P-4) VP-4Mol. Sieve drier “A” Pr. gauge (P-5) VP-5Mol. Sieve drier “B” Pr. gauge (P-6) VP-6Air pressure gauge InletExp. engine (P-7) VP-7Air pressure gauge outletExp. Engine (P-8) VP-8L.O. Pump discharge oxygen pressure (P-9) VP-9
Oxygen Filing manifold “A”Pressure gauge (P-10) VP-11Filling manifold “B” (P -11) VP-12L.N2 Pump Discharge Nitrogen Pressure (P-12)Defrost air press gauge (P-13) VP-13Regeneration N2 press gauge (P-14) VP-14Exp. engine oil press gauge (P-15) VP-15Condenser liquid level L.P. isolation VL-20“ “ H.P. isolation VL-21N2 – Manifold – AN2 – Manifold – B
(P-16)(P-17)
Liquid Nitrogen LevelL.P. IsolationH.P. Isolation
VL-22VL-23
Other Valves
Upper column safety S-1Lower column safety S-2High pressure oxygen safety S-3Defrost air safety S-4Air Compressor Discharge Safety S-5High Pressure Nitrogen Safety S-6
XVIII. INSTRUMENTS INDEX AND NOMENCLATURE
PRESSURE GAUGE :
PRESSURE GAUGE NOMENCLATURE
PRESSURE GAUGE NO.
TYPE
Air before R1 P-1 Panel mounted back connection Lower column P-2 “ “Upper column P-3 “ “Air after air compressor P-4 Bottom connectionMolecular Sieve drier “A” P-5 “ “Molecular Sieve drier “B” P-6 “ “Air inlet expansion engine P-7 “ “Air outlet expansion engine P-8 “ “L.O. Pump discharge oxygen P-9 Panel mounted back connectionFilling manifold “A” P-10 “ “Filling manifold “B” P-11 “ “Liquid N2 Pump discharge Nitrogen Pressure P-12 “ “Defrost Air P-13 “ “Regeneration Nitrogen P-14 “ “Expansion engine oil pressure P-15 “ “
TEMPERATURE INDICATORS
TEMPERATURE INDICATOR NOMENCLATURE NO. TYPE
Air In Expansion Engine T-1 Panel PT. 100Air Out Expansion Engine T-2 “Air before R1 T-3 “Air Out Heat Exchanger I T-4 “Nitrogen Out Heat Exchanger I T-5 “Oxygen Out Heat Exchanger I T-6 “N. Air Out H. Exchanger II T-7 “Defrost Air Out Def. Heater T-8 DialNitrogen Outlet Heat Exchanger – 1 T-9Regeneration N2 out Mol. Sieve PT. 100 Drier Heater out let T-10 “ “ drier A & B T-11 “
LEVEL GAUGES :
________________________________________________________________________
LEVEL GUAGE NOMENCLATURE NO. TYPE________________________________________________________________________
Liquid Oxygen L-1 Panel D.P. Manometer
Liquid Nitrogen L-2 “ “
________________________________________________________________________
XIX. ABBREVIATIONS________________________________________________________________________
Dgn.Pr. - Design PressureHyd. T.Pr. - Hydraulic Test PressurePn.T.Pr. - Pneumatic Test PressureTemp. - Temperature
*************************
I. PLANT SPECIFICATIONS
1. Production Capacity :
The plant is very versatile and can be set for a cycle to produce any one of the following alternatives :
________________________________________________________________________OXYGEN PRODUCTION NITROGEN PRODUCTION
OPTIONALS
Alternative Gas Qty. Gas Purity
ProductPressure
Gas Qty. Gas Purity
ProductPressure
1. 110 m3/hr. 99.6% 150 kgs/cm2 400 m3/hr. 96%(Waste)
0.5 kg/cm2
2. 90 m3/hr. 99.6% 150 kgs/cm2 375 m3/hr. 99.6% 0.5 kg/cm2
________________________________________________________________________
* About 150 m3/hr. of Nitrogen will be used for regeneration of dryers.
The above product capacities are based on ambient conditions of 10 deg. cent. temperature, 760mm of High pressure and 50% relative humidity and 0.03% of carbon dioxide is allowed as impurity.
2. Other Specifications.
Air Pressure (starting) : 60 kgs./cm2
Air Pressure (normal) : 35 kgs./cm2
Starting time (after defrost) : 7-8 hoursStarting time (for short stop) : 1-2 hoursDefrost time : 8 hoursDefrosting cycle at normal conditions : 6 monthsCylinder filling manifold connections : 2 x 8 Nos.Cooling water requirement : 35 m3/hr.Inlet cooling water temperature : 20 deg. C.Total Weight (about) : 25 tonsAssembly height : 9 mtrs.Area required : 15 x 12 Mtrs.Air input : 600 m3/hr.Power supply required : 440 volts and
220 volts.
3. Power Requirement :
H.P. K.W.
Air Compressor 200.0 150.0Drier Heater - 15.0Expansion Engine 10 7.5L.O. Pump 3 2.2Defrost Heater - 9/12Cooling Water Pump 7.5 5.7
MOLECULAR SIEVE
TECHNICAL DATA
:
:Type of Absorbent : Molecular Sieve Type 13-XQuantity of Molecular Sieve : Approx. 200 kgs. per each drierQuantity of air handled : 600 m3/hr. for 10 hours.Heating time : 4.1/2 hoursCooling time : 4 hoursChangeover time : 1.1/2 hoursHeating inlet temperature : min.280 deg. cent to
max.350 deg. CentigradeHeating outlet temperature : min.130 deg. cent. to
max.200 deg. CentigradeCooling outlet temperature : min. 30 deg. cent. to
max. 50 deg. CentigradeMain air inlet temperature : min. 8 deg. cent. To
max. 30 deg. centigradeAir Pressure : min. 35 kgs/cm2 to
max. 60 kgs/cm2
Max. permissible carbon-Dioxide in atm. air Max.moisture content allowable in atm.air
:
:
0.03 %
50% relative humidity at 10 deg. Centigrade.
Heater capacity : 15 KWHeater voltage supply : 440V.Heater individual ammeterreading
: 22 ampe. Each
EXPANSION ENGINE
TECHNICAL DATA :-
Type of Expansion Engine : SEM 0.5/1No. of Cylinders : 1Dia. of cylinder bore : 80 mmPiston stroke : 125 mmSpeed : 200 RPMInlet air pressure : 60 kgs/cm2/35kgs/cm2
Outlet air pressure : 5 kgs/cm2
Throughput volume at 60 kgs/cm2 :and 8 degree centigrade. about : 420 nm3/hr.Throughput volume at 50 kgs/cm2 :and -75 deg. centigrade about. : 150-480 nm3/hr.Inlet valve opening time :Cam setting positions : 8Power required or supplied : 7.5 KW./10 H.P.Piston head clearance : 1.2 + -0.2 mmInlet valve pestle clearance : 0.4 to 0.5 mmOutlet valve pestle clearance : 0.3 to 0.4 mm
LIQUID OXYGEN PUMP
TECHNICAL DATA
Type of pump : IL/IL/100/22Number of cylinders : 1Cylinder dia. : 22mmPiston stroke : 100mmSpeed : 125/150 RPMSuction pressure : 0.5 kg/cm2
Disc. Pressure (final max.) : 165 kg/cm2
Operating temperature : -183 deg. centigradeNormal delivery : 100 nm3/hr.Driving capacity required : 1.5 KW
OPERATION MANUAL
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OXYGEN PLANT--------------------------------------------------
DALAL MCKENNA PVT. LTD.Sanghi Centre, Ground Floor, 11/21 Mani Mahal, Mathew Road, Opera House, Mumbai-400 004.
Tel (91-22) 23634852/ 54 Fax: (91-22) 23631559E-mail : [email protected] ****** Website : www.sanghioxygen.com
1st July 2008
