Overview The value of condensate Condensate corrosion Condensate treatment Condensate monitoring, sampling and control
Condensate System
Condensate Treatment Technology is the Implementation of an Integrated Chemical, Mechanical and Monitoring Program to Derive Significant Operating Cost Savings in Plant Operation
The Value of Returning Condensate Condensate is Hot Water! Most Industrial Condensate Systems are pressurized Utilities and some process systems are under vacuum Condensate is (reasonably) Pure Water! Low conductivity water replaces additional demineralized makeup water for boiler feedwater Replaces softened water and allows boiler to operate at higher cycles of concentration
Typical Condensate ReturnIndustry Chemical Cogen Paper Petrochemical Power Refining Steel Typical % Return 30-60 20-80 40-65 65-85 95-99 10-60 5-50
The Risks of Returning Condensate Process Contamination Oil Process Constituents Raw Water Constituents Oxygen Hardness Corrosion Products Iron Copper
Why is Condensate Treatment Needed?Condensate Treatment is the Battle Against Three Dissolved Gases: CO2 O2 NH3
Carbon Dioxide SourcesBreakdown of feedwater alkalinity 2 HCO3 Bicarbonate heat Carbonate heat
CO3 -2 + H 2O + CO 2Water
Carbon Dioxide
CO3 -2 + H2OCarbonate
Water
2OH - + CO 2Hydroxide
Carbon Dioxide
Air inleakage Breakdown of organic compounds present in the feedwater
Where CO2 Corrosion Occurs
CO2(g) + H2O(g) --> No Reaction CO2(g) + H2O(l) --> H2CO3(l) (carbonic acid) Then, H2CO3(l) H+ + HCO3-
Wastage Caused by CO2
Softened Water used for Boiler Makeup produces a considerable CO2 concentration in the condensate. Consider revising the external treatment system to reduce the CO2 loading. Demineralized Water greatly reduces the CO2 loading in the system, but there is still sufficient present to depress condensate pH and still require treatment.
Feedwater Alkalinity Reduction To Control CO2 Generation Lime softening Dealkalization Degasification Demineralization Increased condensate return
Oxygen Corrosion in Condensate
Sources of Oxygen in Condensate Systems Systems under vacuum Intrusion into Batch Processes In and out of Service Equipment Leakage past Pump Seals Service water used to Quench Alternate heating/cooling cycles
Mechanical Corrections to Oxygen IntrusionCauses of O2 Entry Into Vacuum Systems Out-of-Service Systems Open Receivers Pump Seal Leakage Quench Water Alternate Heating/Cooling Means of Detection Check Gauges Test at Start-up Identify Test In-Service Test/Observe Identify Remedy Repair Leaks Dump Condensate Repipe Below Liquid Level Repack, or Install New Seals Remove Source Dump Condensate
Ammonia is the Third Dissolved Gas to be Considered Ammonia only attacks copper alloys Sources of Ammonia Ammonia added as a treatment Amine-based treatment decomposition Thermal decomposition of hydrazine Nitrogen containing organics present in make water
Mechanism of Ammonia Attack Ammonia Dissolution in Liquid Phase NH3(g) + H2O(l) --> NH4OH Ammonia Ionization NH4OH NH4+ + OHCopper/Ammonia Complexation Cu+2 + 6NH4+ --> Cu(NH4)6
AmmoniaDissolved oxygen ppb 0 to 20 20 to 50 >50 Maximum allowable ammonia, ppm 0.5 0.3 Any level may be a problem
Remedies for Ammonia Attack Alloy Selection (Youll never see copper piping in an ammonia plant) Consider a hydrazine substitute Evaluate neutralizing amine selection Sewer contaminated condensate (i.e. air injector drains) There is no treatment for ammonia attack
System SurveyS te a m / o n d e n s aS y ste m s C a n B e E x te n s iv e C teM a ke - up Pr o ce s s
x R e b o iler s d an x K et tl es e ttl
Id e n tify E q u ip m en t h e at ex c h a n g ers a n d re a cto r s
P r o ce s s
P r o ce s s Low p re s su re st e a m B low d ow n fl a s h t a nk F l a sh t a nk C o nd e n s a te R e c e iv e r
x C o n d en s e rs se x Tank x S t ea m x F la sh
h ea ter s tr ap s ta n k s a n d re ce ive rs ta
A complete system survey is the key to any effective treatment strategy The survey defines system needs and limitations
Steam Traps
Condensate Treatment
Condensate Treatment Alternatives Neutralizing Amines Distribute throughout systems Neutralize CO2 Elevate condensate pH Filming Agents Both amines and non-amines are used Create a barrier between condensate and piping Scavenger/Passivating Agents Primarily condition metal surfaces
Neutralizing Amines Neutralizing amines are the most universally used chemical treaments to prevent CO2 corrosion Neutralizing amines are organic compounds with an amino functionality attached (-NH2; NHR; -NR2) The organic group may be cyclic, a straight chain or a branched chain.
Why Amines are So Popular Direct Neutralization of CO2 Direct elevation of pH Easy to feed Easy to Control Many options available Few Side Effects Compatible with other system treatments Treatment Recycles Blends Available
Weaknesses of Amines Selection requires system knowledge Presumed performance doesnt always occur Can be expensive if CO2 loading is high No impact on oxygen contamination Some systems cannot tolerate nitrogen Adds conductivity to condensate
Amine Selection in a Simple SystemAmine Volatility is not as big an issue when condensation is one and done External Treatment System
CondenserEconomizer Makeup Water Boiler Deaerating Heater Boiler Feedwater Pump
Steam Turbine
Superheater
A Typical Paper Machine Dryer Configuration Represents a Complex Condensate System
Neutralizing Amine Selection Criteria Need for Volatility Amount of CO2 Expected FDA Regulations Applicable? Pressure of Steam System Process Considerations Direct Contact with Process? Steam used for Humidification
Neutralizing Amine Operating Mechanism Volatility - As measured by Distribution Ratio at the pressure of two phase conditions Neutralizing Capacity - As determined by the molecular weight of the amine molecules present pH Elevation - As determined by the basicity constant of the molecules present
The Importance of Volatility Volatility positions the amines in complex systems Amine volatility is always compared to CO2 Volatility is measured by V/L Ratio or Distribution Ratio Volatility is not as important in simple systems
Amine Volatility is Very Temperature & Pressure Dependent
Amine Volatility vs. PressureName 0 CO 2 NH3 MEA A min o m e th y lp r o p a n o l Mo r p h o lin e MO PA DEA E DMA IP Cy c lo h e x y la m in e 4 .0 3 .0 ** Ex p e r ime n ta l B o ile r Re s u lts 0 .4 0 0 .4 4 3 V /L R a i t o v s B o i l e r p r e ssu r e ( p si g ) ** 50 4 .8 150 8 .5 6 .7 0 .1 1 0 .6 5 0 .9 9 2 .1 5 .8 7 .3 9 .0 450 8 .5 7 .0 0 .1 7 0 .6 5 1 .1 0 2 .0 6 .3 4 .8 9 .4 600 1 5 .8 5 .0 0 .2 4 0 .7 7 1 .2 2 2 .3 5 .2 4 .9 8 .2 900 >9 9 .0 4 .3 0 .2 5 0 .8 6 1 .2 2 2 .0 4 .5 4 .2 7 .0
Using Concept of Volatility Evaluate System to determine if volatility matters Amine blends provide for most comprehensive coverage Look for places of steam venting (flashed steam), and pick amine to avoid loss Focus on amines in locations of maximum condensate return
Neutralizing Amines Neutralizing capacity determines amount of CO2 (actually carbonic acid) that the amine can counteract Neutralizing capacity is specified by the molecular weight of the amine
Molecular Weight of AminesAmine Morpholine Cyclohexylamine MOPA DEAE MEA MW 87 99 89 119 61
Corrosion of Carbon Steel and Copper Depends on pH of WaterAfter neutralization, the final function of the amine is to boost condensate pH into the range where total metal solubility is minimized. The measure of an amines capability to boost pH is specified by its basicity constant.PH Control Ranges Mixed iron-copper metallurgy Ferrous Metallurgy Typical 8.5-9.2 8.5-9.5 For Neutralizing Amines Preferred 8.8-9.2 9.0-9.5
Amine IonizationR-NH2 RNH3+ + OHAmines that stay in the R-NH2 form contribute little to pH elevation. Amines that ionize more completely are more cost-effective.
Ionization Properties of Different Amines, NH3 and CO 2Name pKa* CO2 4.3 NH3 9.3 Monoethanolamine, MEA or EA Aminomethylpropanol, AMP Morpholine 8.4 Methoxypropylamine, MOPA Diethylaminoethanol, DEAE Cyclohexylamine 10.6 Dimethylamino-2-propanol, DMAIP Diethanolamine, DEA 8.9 Dimethylpropylamine, DMPA Dimethylaminoethanol, DMAE 9.5 9.5 10.1 9.6 9.6 10.7 9.6
* pKa indicates base strength of the amine. The higher the pKa the stronger the base.
Amine Neutralizing Ability11
9 pH 7 5 0.0 0.5 1.0 1.5 2.0 2.5 ppm Amine / ppm CO2 Morpholine 3.0 3.5 4.0
Cyclohexylamine
Diethylaminoethanol
Regulatory Issues
FDA Applications Amines cannot be used to treat steam which could contact milk or milk products
Cyclohexylamine Diethylaminoethanol
10 ppm 15 ppm 10 ppm 3 ppm
q
Only four amines are FDA approved Steam concentrations are limited
Morpholine Octadecylamine
q
OSHA* RestrictionsOSHA PEL Limits
Morpholine Diethylaminoethanol Cyclohexylamine
20 ppm 10 ppm 10 ppm
Establishes the concentration of amines in air to which a healthy worker could be exposed for an eight hour period Known as the PEL (Permissible Exposure Limit)
* Occupational Safety and Health Administration
Summary of Neutralizing Amine Use Determine the regulatory limitations Determine type of system - single pressure(simple) or multiple flash (complex) Select Amine Volatility to get Treatment where needed Ascertain amount of CO2 to justify selection based on Neutralization Capacity Select condensate pH control range on basicity of amines in use Satellite fed maybe necessary Monitor throughout the system