PROCESSING STATIONDESIGN & SCREW PRESS

PART 1

Ir. AMIN BUHARI MD ZAIN

SIME DARBY PLANTATIONS SDN BHD

INTRODUCTION

• The equipments that make up the pressing station in Palm Oil Mill– Fruit Elevator/Scrapper conveyor– Fruit Distribution Conveyor– Fruit Return Conveyor– Press Station Structure complete with platform,

handrails and walkways– Hot water tank for press station– Digesters normally of type 3500L-5000L

capacity– Twin Hydraulic Screw Press – normally P15 or

P9 type. New Press P20-P30 type

• Crude oil collection gutter – preferably SS

(New Mill used 10-12” slanting pipe)

• Desanding Tank (sand trap)

• Sand Removal conveyor for sand trap

• Sand Removal Elevator with screen buckets

• Hopper with support for sand waste

• Vibrating Screen – 60” circular double deck type c/w ms structure, platform & walkway

• Screen waste conveyor• Crude Oil Tank with auto steam heating• Crude Oil Transfer Pumps with auto level switch.• Manpower – Should not be more than 2 persons per

shift • Maintenance – 20% of the total maintenance hours

goes towards pressing station and out of this 20%, almost more then 50% for press maintenance.

• Total maintenance cost in the region of 85 – 90 cents/ton ffb processed (depend on locations)

PRESSING STATION LAYOUT

• A Satisfactory layout of pressing station could be achieved in many different ways

• Each case of layout will definitely having special reasons incorporated in the design

• New approach in arranging press station layout is to meet the user friendly concept, easy maintenance, easy supervision and etc.

Presentation Title

MAIN PROCESS STATION

BOILER HOUSEE

NG

INE

RO

OM

OIL

RO

OM

KERNEL PLANT

SHELL BUNKER

MACHINERY LAYOUT

PRESSING STATION

Digester

Crude Oil Collection Gutter

Screw Press

Sand TrapVib Screen

Crude Oil Tank

Fruit Distribution / Return Conveyor

Fruit Elevator /Scrapper Conveyor

Hot Water Tank/Dilution

Cake Breaker Conveyor

1 2 3 4

Press Platform

Digester Platform

FRONT ELEVATION

Digester

Screw Press

Hot Water Tank/Dilution

Cake Breaker Conveyor

Crude Oil Collection Gutter

Fruit Elevator /Scrapper Conveyor

Fruit Distribution / Return Conveyor

Sand Trap

PRESSING STATION

SIDE ELEVATION

PRESSING STATION

• Fruit Conveyor– Normally for bigger capacity mills, two units

will be installed adjacent to each other

• Fruit Elevators– Two of this unit normally one is a standby– Shaftless conveyor is now started been used to

replace this bucket elevator

• Top Fruit Conveyor

• Crude Oil Screening Station

• Sand Trap Tank

• Crude Oil Pump

1) Fruit Elevator• Elevators are the simplest and most reliable units

for making vertical lift and widely used in Palm Oil Mill.

• There are 2 main types– Chains and Buckets ; Buckets are carried on one or two

chain (chain from malleable cast iron or mild steel)– Belt and Buckets; Buckets are attached to the canvas

rubber or synthetic fabric belting.

• Most common types of elevator used in POM is the spaced buckets with centrifugal discharge, the contents of the buckets are thrown out at the head shaft by centrifugal force.

Elevator Design

• This type of elevator can handle most of the free flowing fine or small lump materials.

• The buckets are loaded partly by the material flow and partly by scooping-up material from the elevator boot.

• The limiting factor for the elevator height is the strength of the chain.

• Normally elevators rarely exceed 22m height.• Inclined single chain elevators are limited to 30o C• Double chain type elevators can exceed 30 degrees if roller

chains are used. • Choice of chain is very important as the wrong choice will

almost lead to increase in maintenance, high upkeep cost and lost of production.

Elevator Capacity

• The capacity of a bucket elevator can be estimated as

– Theoretical Capacity = C x V x 60 P

C = Capacity Bucket, V = Chain Speed (feet/minute) P = Spacing or pitch of buckets (feet)

Elevator Capacity contd.• The actual capacity will normally less than theoretical

figure and the following formula will give the actual capacity

Actual Capacity = C x W x V x B P x 36.7 where; C = Capacity of Bucket (ft3) W = Density of material (lb/ft3) V = Chain Speed (ft/min) B = Bucket Loading Factor (vary between 0.6 – 0.85) P = Buckets spacing or pitch of buckets (ft)

POWER REQUIRED FOR ELEVATOR

• The simplest formula to calculate power required to drive elevators is to take the theoretical power and increase the figure by 50 to 100% to cover friction

• Theoretical HP = C x W x V x B x H• 33000 x P• Where

• HP = Horsepower• C = Capacity of Bucket (ft3)• W = Density of material (lb/ft3)• V = Chain speed (ft/min)• B = Bucket Loading Factor• H = Lift (ft)• P = Spacing or pitch of buckets (ft)

Fruit Elevator Operation Cost

• Normal operation cost where no chain replacement is required is in the region of not more than 4 – 5 cents/ton ffb

• When chain replacement is necessary / (major overhaul) than operation cost will vary to between 12 – 18 cents/ton ffb

2) Fruit Conveyor

• Another method of materials handling commonly used to transport fruitlets in the pressing station – feeding the fruit elevator and digester / return conveyor etc.

• It is a common type screw conveyor and consists of – a helicoid (helix rolled from flat steel bar) or– Sectional flight (individual sections pressed and

formed into a helix from flat plate)

Mounted on a pipe or shaft and turning it through.

Screw Conveyor (600mm Dia)

• Screw conveyors standard pitch is approximately equal to the diameter and is generally suitable for horizontal installation and inclined up to 20 degree.

• For inclines greater than 20 deg half standard pitch of the screw is adopted.

• For moving difficult material and controlling feed rate, double and triple flights, variable pitch and stepped diameter screws are adopted.

• Ribbon screw are used for wet and sticky substances. Wear problem at flight outer edge normally is reduced by doubling strip on the edges.

Interlocking System

• Since almost any conveyor can jam for some reason, Interlocking system in a conveyor system are obviously important to stop all incoming materials if the conveyor trips/stop thus will avoiding spillage.

Screw Conveyor Capacity• Theoretical capacity can be calculated by

– C(ft3/hr) = ((D2 – d2) x P x RPM)/36.7• Where

– D = Screw diameter (in)– d = Shaft diameter (in)– P = Screw Pitch (in)– RPM = Revolutions of screw

• Actual capacity normally a lot less than that given by the above formula.

• Recommended that when specific operating data is not available figure of between 30 – 50% of the theoretical capacity be adopted.

Simple Calculation – Fuel Conveyor

• Mill Capacity : 60,000kg/hr

• % of fibre : 12%

• Quantity fibre : 7200kg/hr

• Fibre bulk density : 250kg/m3

• Volume of fibre : 28.80m3/hr (1016.64cu.ft/hr)

• % of shells : 6%

• Quantity shells : 3600kg/hr

• Shell bulk density : 500kg/m3

• Total volume of shell : 7.20 m3/hr (254.16 cu.ft/hr)

• Total volume fibre+shell : 36.00m3/hr (1270.80 cu.ft/hr)

• Diameter of screw : 22 in (0.56m)

• Shaft diameter : 4 in (0.102m)

• Screw Pitch : 22 in (0.56m)

• Conveyor RPM : 40

• Theoretical Capacity

• C (cu.ft/hr) = ((D2 – d2) x P x RPM)/36.7

CAPACITY DATA FOR HORIZONTAL STANDARD PITCH SCREW CONVEYORS

Filled Screw Screw Dia Maximum Recommended Capacity at One RPM% in speed (RPM) Cu ft / hour

6 165 2.27 9 150 8.00

12 140 9.30 45 14 130 30.80

16 120 46.60 18 115 66.10 20 105 95.00 24 95 164.80

6 120 1.50 9 100 5.60

12 90 13.30 30 14 85 21.10

16 80 31.40 18 75 45.40 20 70 62.10 24 65 109.90

Conveyor Horsepower

• The required Hp made up of two components – Hp necessary to move the empty screw

(function of conveyor length, rotation speed and friction in conveyor bearings)

– Hp that to move the material (function of total weight of material conveyed per unit time, conveyor length and depth to which the trough is loaded.

• Formula for approximate Hp figure• Hp = (ALN + CWLF) x 10-6

– Hp = Horsepower at conveyor shaft– A = Factor for size of conveyor– L = Conveyor Length (ft)– N = Speed RPM– C = Capacity (ft3/hr)– W = Material density (lb/ft3)– F = Factor for materials

• The above formula gives the approx. conveyor shaft Hp and for the size of driving motor. It is recommended that– If HP<1 to multiply by factor 2, – 1<hp<2 to multiply by factor 1.5– 2<hp<4 to multiply by factor 1.25– 4<hp<5 to multiply by factor 1.1 and if Hp above 5 no correction is

necessary

TABLE FOR FACTOR "A"SCREW DIAMETER FACTOR A

IN

6 549 96

10 11412 17114 25516 33618 41420 51024 690

APPROXIMATE VALUE FOR "F"PALM FRUITS 0.4 PALM NUTS & KERNELS 0.5 FLUE DUST 4.0 SILICA SAND AND CLAY 2.0

Screw Conveyor Operation Cost

• Screw conveyors require minimum maintenance and the normal cost of spare parts, consumables and labour for upkeep of a screw conveyor is comparatively very low between 1 – 2 cents/ton ffb

PRESS STRUCTURE• Press structure in oil mill usually varies between

3m to 6m for press platform and 9m – 12m height for digester platform.

• Reasons of the engineers designing this platform height was to allow smooth gravity flow of mesh and crude oil from press for further process.

• If the height too low than the gravity flow of oil to vibrating screen and entry point press cake to depericarper is not sufficient-

• In most cases, press were installed at about 4-5m height from ground level

• There were also mills the press were at Ground Level with slight modification to the process flow.

DIGESTER• The digester is an essential part of the continuous twin

screwpress.• It is matched in every respect to the screw press.• It is supplied as a complete extraction unit.• This extraction unit is unsurpassed in oil extraction

efficiency and in continuous trouble free pressing operation

• Design ranging from 600 litres to 3500 litres and exceptionally to 5500 litres

• Commonly used matching the twin screwpress are 2,800 / 3,200 and 3,500 litres model.

• The digesters are supplied either with wear rings in front of the arms or more frequently with complete liners

SIDE AND TOP VIEWS OF TYPICAL DIGESTER

Digester contd

• The standard digesters are supplied either with a steam injection device or less often with a steam jacket (42 – 45psi)

• The digesters can be fitted with a stainless steel liner and stainless steel bottom instead of mild steel parts.

Digester system

• Optional system for Digester – Temperature regulator– Hydro-flow coupling slip ring motor– Level Indicator– Hour counter– Various types of control panel for digester

alone also combined for press & digester

Function of Digester

• The rupturing of all oil bearing cells• The complete loosening of the pericarp from nuts• To prepare mash for efficient oil extraction by the

press• The mash to be made homogeneous I.e. fibre and

nuts mixed evenly• The temperature of the mesh to be raised to not

less than 95 C

Normal Operation The digester is supplied fitted with 4 sets of digesting

arms and one set of expeller arms. In practice only 3 sets of digesting arm is usually used.

It is normal to remove the top set and keep them as spares in store.

For normal operation the digester should be kept completely full at all times.

The digester temperature should be maintained high at 95oC.

Steam valve to the digester steam jacket should be kept fully opened during the operation of the digester. The temperature of the fruit in the digester should be adjusted by controlling the steam to the live steam jets.

•

Bottom Digester Oil Drainage• There are 2 valves connecting the bottom of

digester for bottom oil drainage. These valve should be checked from time to time to ensure that they are not blocked.

• In general, bottom digester oil drainage tends to directly increase clarification difficulties and at the same time introduce the bad effect of over digestion

• When there is excessive oil visible at the digester chute window, a limited amount of bottom drainage is desirable

• Bottom oil drainage should not be so great that no surplus oil is seen at the window.

• It should be borne in mind that excessive bottom drainage is sometimes the result of operation at too low temperature.

• Low temperature operation impedes the proper passage of the oil through screw press cage and strainer.

• The Digester should never be left full overnight

Effect of Over Digestion

• Increase Iron Contamination of the palm oil

• Increase the Clarification loss

• Increase Upkeep Cost

• Increase Power Consumption

Maintenance cost for digester is in the range of 8-12 cents/ton ffb

SCREW PRESS

• Details about this screw press will be cover in the next lecture after tea break

• There were few well established press in the market with the throughput ranging from 10ton ffb/hr – 20ton ffb/hr

• The Screw press were named after their designed capacity I.e. P9, P15 and P20

• Operation and maintenance cost are vary between 25 to 55 cents/ton ffb processed depend to the condition of the press itself.

CAKE BREAKER CONVEYOR

• It serves the purpose of taking the cake of pericarp residue delivered by the press to the depericarper.

• The cake is given a preliminary treatment as it is transported, I.e the fibre and nuts are loosen after the lumps of cake have been deposited into the conveyor through the chute at the press, being broken down by the adjustable paddles fitted on the conveyor shaft or by the screw outer edge cut into paddle type.

• Earlier design was equipped with steam jacketted to dried out the cake moisture for efficient separation of fibres at the depericarper

• As the efficiency of hydraulic twin screw press improved, there is a growing tendency of the mill engineers to remove or isolate steam from the jacketted conveyor.

• Most of new mills, CBC was no longer equipped with steam jacketted.

• Padle arm has been phased out and was replaced with full ribbon screw type.

• To ensure screw conveyor still performing function as CBC, some engineers has weld flat bars at the outer screw edge

• New innovation was to cut the outer edge of the ribbon.

• CBC usually fitted with renewable liner plate to combat the heavy wear takes place in this conveyor.

CBC

• It is a reliable peace of equipment and most of the maintenance is due to the abrasive wear plate, shaft and screw

• The cost of maintaining the CBC is in the region of 5 – 8 cents/ton ffb

Vibrating Screen

• Performing a useful function in an oil mill by screening out the large fibre particles in the crude oil.

• Require continuous attention and it is not a very pleasant equipments because of the splashing of crude oil in and around the screens.

• It is not really an ideal equipments for this particles screening due to the fact that fibre can pass through the holes in the screens and the crude oil is exposed to air when passed over screen.

• Normal cost to maintain this double deck vibrating screen is in between 5 – 7 cents/ ton ffb.

Crude Oil Tank• Common practice the tank is installed below the vibrating

screen. This should be avoided as the hot vapour emitted from the tank make it impossible to carry out maintenance.

• Different design had been tried out from the closed tank and now an open tank with a sloping bottom towards the suction.

• Fitted with open steam injection coil to keep it homogeneous and to keep crude oil temperature at desired level of 90 0C and above.

• Maintenance cost is about 1 cents/ton ffb.• Trend todays is fabricating this tank from stainless steel.

Crude Oil Pump

• Various type of pumps are used for the purpose pumping the crude oil to clarification station.

• Whatever pump type is used, wear and tear rates are high due to abrasive nature of the fibre and sand particles in the crude oil.

Types of Pumps

• Centrifugal Pump– Since crude oil is a viscous liquid which contains solid

materials. Pump with an open or semi-open type impeller should be used.

– Pumps for crude oil usually has a volute casing.

– This casing take the form of a volute increasing in cross sectional area as the outlet is approached.

– The volute converts the velocity energy imparted to the liquid by the impeller into pressure energy with comparatively low losses.

• A continuous cavity pump– Made up of male metal rotor rotates with

minimum clearance in an elastometric female stator. The screw pumps are ideal for handling viscous liquids but they must be operated at relatively low speed in order to attain best performance from this type of pump

Maintenance cost = 10 – 12 cents/ton ffb.