Gas Field Processing Troubleshooting
As I mentioned in the previous post ; part 1 Sour Gas Sweetening , the Amine sweetening unit consists of two major parts :
The absorber tower (Contactor) where acid gases (H2S and CO2) are removed from the feed gas by using amine solution (sweetening step) and the regenerator where these acid gases are removed from the rich amine (Regeneration step) .
The Key Factors of Amine unit are :
- Amine consumption
- Amine circulation rate
- Amine strength
- Temperature deference between lean amine and the inlet gas .
- Reboiler temperature .
- Filters ?p .
- Flash separator hydrocarbon liquid level .
- Corrosion .
There are three major process problems that generally occur :
1) Residue gas off specification with too high acid gases content .- Observed by means of Lab or On-stream analyzers .
2) Amine foaming .
- Observed by how much the pressure deference across the contactor is . Or , - By liquid carry over with the residue gas . Or ,- By liquid level increasing within contactor
Corrosion .
- Observed by corrosion coupons analysis .
1) Residue gas off-specification with too high acid gases content .
The causes of this problem may be as follows , I will mention only some of them as they are much more :
a) Low lean amine circulation rate .- Check the lean amine circulation rate with the design figures
b) Low lean amine strength .The strength may have been lowered to the point insufficient amine is present to do the complete removal of the acid gases. -Rich/lean amine heat exchanger leakage . - Insufficient stripping of the amine still . Check the still trays if dirty , partially plugged or lost . Check the stripping gas rate .Or - Make up the system with pure lean amine .
c)The inlet gas H2S content increasing . - Inlet gas composition should be checked to determine if the inlet acid gas concentration has increased to overload the amine . Then , Adjust amine circulation rate as per the new H2S values .
d) The contactor temperature .The contactor temperature of both amine and gas should be kept between 32–55 °C .Inlet gas and rich amine temp. below 32 °C can reduce the efficiency of the chemical reaction and give off spec. residue gas . Lower temp. down about 15 °C is acceptable for MDEA and DGA .
2) Amine foaming :
Amine foaming is the major problem of amine plants operation . It can be caused by large amount of solids floating around in the liquid such as iron sulfide , scale , drilling mud , dirt , corrosion inhibitors and etc .Sock filters and charcoal filters should be used to reduce foam .When Foam is severe enough , foam will be carried out the contactor . Some will be caught in the residue gas scrubber but some can also blow down stream to the next process causing reduction of the amine load and problem and possibly harm downstream .When foam is not great enough to carry over it will reduce the efficiency of the contactor .
What to do when foam appears ?
- Inject anti-foam chemical into the lean amine to the contactor .- Regenerate the charcoal filter or replace .- Prevent hydrocarbon condensation within the contactor , the lean amine inlet temperature should always be from 10–20 °F higher than the inlet gas temp.- High amine strength increases foaming tendency .The amine strength should be carried as low as operation and plant load will allow . Amines have lower surface tension than water , As the amine solution is a water solution , the higher the concentration of amine the lower the solution surface tension will be . Low surface tension promotes and increases foam ,Thus , the lower the concentration can be held , the less tendency to foam .
3) Corrosion :
Amine systems with high CO2 and very little H2S will have corrosion within the still condenser , line to the reflux accumulator and in the accumulator.When free liquid water condenses it absorbs CO2 and produces a very corrosive acid .Stainless steel tubes are recommended for the still overhead condenser unit , whether air cooled or water cooled . If carbon steel tubes are used they should be seamless tubes with a corrosion allowance and be stress relieved .A method to help reduce the corrosiveness of the overhead system is to inject a small amount of lean amine into still overhead line a short distance before the condenser . This amine will mix with the reflux and raise the PH reducing the corrosiveness .Units with H2S will have a coating of iron sulfide form on the piping and vessel walls which will reduce considerably the corrosion effect of the CO2-water acid .
Best Practices and troubleshooting lesson learnt in the gas field processing is the key of success for the current process operation
Operation and process specialist
8 年I agree , we can prevent foaming by adequate inlet gas separation to minimze liquid hydrocarbons, iron sulfide/ suspended particles and well treating chemicals from entering the amine system. Proper clean-out of new equipment prior to start-up. Adequate carbon and mechanical filtration. Foam test with proposed make-up or initial fill-water,proper mechanical filter material selection,temporary use of antifoams.
Sales Manager @ GALDABINI ???? | Straightening machines
8 年In order to minimize the foaming issue, it can be helpful to install a liquid-gas coalescer in the gas feed line upstream of the amine contactor in order to remove all of the entrained liquids. In the same way it is recommendable to install a liquid-gas coalescer downstream of the unit, in order to recover the carried over amine, enhance the quality of the gas and protect the downstream equipment. Another important point is to keep the recirculating amine system clean. The solids concentration in the loop gradually increases unless removed by an efficient filter, and the high solids result in equipment fouling and stabilize foaming. The circulating amine should contain less than 1 ppm by weight of suspended solids and should be filtered to an efficiency of at least 10μm ABSOLUTE. Finally the conventional amine unit design calls for filtration of a 10% slipstream of the recirculating amine (based on little or no scientific evaluation!) which often is not enough.
Senior Mechanical Engineer di PT Perta Daya Gas
8 年Trimakasih pak sangat bermanfaat
Plant Operations Senior Manager 9-LNG / 4-Petrochemicals / OR&A LNG Saipem Chiyoda Daewoo JV ,APCI ,CasCade ,Chart IPSMR SsLNG Plants , Organisation Establishment. ISO L. Auditor Erika , CAMS Assessor OPITO
8 年One important reason for foaming ,the heavy hydrocarbons associated the feed gas and contaminated the amine system. The best solution to overweening and skimming the HC. Taking samples until to get red of its.