Amine Unit Antifoam Injection Points and Flow Rate Calculation

Step by step procedure:

1. Lean amine flow rate shall be used to calculate antifoam injection flow rate

2. Target the available injection point to identify the stream flow rate, use that stream not entire lean amine inventory from system

3. Set the pure antifoam concentration in identified lean amine stream at 3-5 ppm for lower foaming / 10-20 ppm medium / 25-35 ppm heavy

4. Formula: liters/hr of pure antifoam flow rate = (ppm pure antifoam * m3/h lean amine rate * 1000) / 1000000

5. Numerical example: liters/hr of pure antifoam = (25 * 100 *1000) / 1000000 = 2.5 l/hr

6. Antifoam dillution ratio with water is 3 : 1 then the total l/hr of pure antifoam needed to be injected is: 2.5 * 4 = 10 l/hr

7. Antifoam dillution ratio with water is X : 1 then the total l/hr of pure antifoam needed to be injected is: 2.5 * (X+1) = Y l/hr

8. Remember that 25 ppm of pure antifoam shall be targeted in the identified lean amine stream!

9. If foaming is occuring for first time use a schock dose of pure antifoam: target 30 ppm for 10-15 minutes

10. If foaming is occuring on continuous base, use lower dose: target 3-5 ppm continuous injection to keep the product specification.

Foaming
a) Plant symptoms:
- operating pressure of Absorber / Stripper shall fluctuate and pressure drop shall increase
- amine/Solvent carryover from Absorber / Stripper / Rich Flash Drum shall increase
- foam test shall be positive
- amine / Solvent shall be poorly stripped
- H2S / CO2 shall pass with treated gas (off spec gas).

b) What can generate / enhance foaming?
- presence of hydrocarbons which react with organic acids and form amine soaps due to poor inlet gas separation in Feed Gas KO and / or lean amine / solvent temperature too low
- oil, inhibitors from improperly cleaned equipment
- suspended solids: carbon fines, colloidal iron oxide due to improper inlet gas separation in Feed gas KO or malfunction of filtration system or due to improper selection of filter material
- make-up water quality: presence of corrosion inhibitors from steam condensate system
- increased particulates levels due to corrosion / erosion.

c) What can we do? What are the knobs to be used?
- lean amine / solvent temperature 5-10 C above inlet gas temperature to minimize hydrocarbon condensation
- efficient inlet separation to minimize carryover in Absorber of liquid hydrocarbons, iron sulfide / suspended particles and well treating chemicals: separator efficiency shall be 99% for 10 microns droplets
- proper clean-out procedure in place for new equipment prior to start-up
- good filtration of lean amine / solvent using carbon and mechanical filtration: the temperature shall be higher than 50C for an efficient filtration
foam test with make-up water
- the recommended amine concentration kept in ranges
- the stripper maximum bottom temperature shall be 130°C and if steam is - the reboiler heating medium must be desuperheated to maximum 155°C to avoid amine degradation (during the operation / design the reboiler heat flux shall not be exceeded especially for kettle type – control the pressure or temperature of steam instead of flooding the tubes, for thermosiphon is not applicable)
- before to add a corrosion inhibitor / additives do a test: add in a bottle solvent and the specified quantity of corrosion inhibitor to achieve desire concentration and observe foaming tendency
- add antifoaming agents, but this shall be use until the root cause shall be identify (typical antifoaming agents: silicone, polyglycol, high molecular weight alcohols)
- proper maintain the filtration system changing the elements, prefilter, carbon filter and postfilter
- before start-up clean the unit with water to remove any detergent
- if the temperature of solvent is decreasing, then the viscosity and foaming tendency increase
- implement a corrosion / monitoring program

Amine color tips:
- Clear and Bright: solvent quality is superior. If a yellowish or greenish tinge is observed, this is normal
- Blue Tinge is an indication of cyanide, Regenerator overhead system shall be affected by corrosion
- Translucent black, if after standing 10-15 minutes a lower amount of sediment is visible, erosion / corrosion is developing
- Black: If you can’t see through solvent, this is indication that the level of particulates and chemical contaminants is very high – a lot of particulates shall settle in the bottle test. This also indicates the presence of heat stable salts.

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