1. Process Gas Swwetening Principles.pptx

gas process sweetening

1. Amine Treating 1-Day Course for Starborn Chemical 17 July, 2017

2. Amine Treating Course Topics

3. Process Principles Chemistry and Amine Selection

4. Typical Sour Gas Plant – Flow Diagram

5. Feed Components Hydrocarbons C 1 to C 7+ , aromatics, NGL Acid Gas CO 2 and H 2 S Sulphur bearing gases COS , RSH Water and others H 2 O, N 2, O 2, S Transients Compressor oil, upstream chemicals, fracture acids, FeS , silica (sand)

6. Amine Plant Flowsheet

7. Purpose of the Amine Plant Recover CO 2 from natural gas Minimize CO 2 emissions CO 2 to be incinerated Optional : sell to other industries or re-inject into ground

8. Amine Treating : Gas Plants Single absorber for each generator Wide range of both H 2 S and CO 2 in gas feed Potential for oxygen in feed gas – solution gas treaters Problems with amine degradations Typical specification sales specifications : 4 ppm H 2 S, 2 % CO 2

9. Amine Treating : Refinery Both Gas and Liquid Streams Multiple absorbers with common regenerator Predominantly H 2 S removal Some CO 2 removal Complication of inlet contaminants Organic acids, ammonia, etc. Problems with Heat Stable Salts

10. Typical Amine Treating Plant – Refinary

11. Amine Treating : Tail Gas Used to minimize Sulphur emissions on sour plants Low pressure absorption 7- 28 kPag ( 1-4 psig ) Low H 2 S specification Low CO 2 removal (High Slip) Potential inlet Contaminants – SO 2

12. Other Treating Schemes Acid gas enrichment CO 2 slip important Low pressure operation CO 2 only removal (ammonia plants) Degradation and corrosion are big issues Syngas treating H 2 and CO ; no hydrocarbons in feed so amine temperatures can be very low Carbon capture Extremely low pressure; high oxygen content in feed; CO 2 only, loose spec

13. Types of Amines Used for Gas / Liquid Treating

14. Amine Samples - Refinery Amine Samples – Gas Plant

15. Gas Treating Solvents Primary amines MEA, DGA® Secondary amines DEA, DIPA Tertiary Amines MDEA, formulated MDEA Sterically hindered amines ( Flexsorb ) Physical Solvents Mixed Amines ( Sulfinol )

16. Molecular Structures of Amines Ammonia Too volatile N H H H

17. Primary Amines MEA Monoethanolamine M.wt = 61 DGA Diglycolamine M.wt = 105 N H H – CH 2 – CH 2 – OH N H H – CH 2 – CH 2 – O – CH 2 – CH 2 – OH

18. Primary Amines MEA Strong base ; high heat of reaction More energy required to strip acid gas Degradation (corrosion, high usage) Will degrade in the presence of CO 2 Can be reclaimed on-site (in process) Degradation products have higher boiling points than MEA Nearly total removal of CO 2 at any operating pressure High vapour pressure so significant vaporization losses Lowest HC solubility MEA typically used at 15 – 20 wt %.

19. Primary Amines DGA ® , ADEG ® Strong base ; high heat of reaction However, high solution strength reduces circulation rate as well as energy required to strip acid gases Comparable lean loadings to secondary amines High acid gas holding capacity per unit volume Degrades in the presence of CO 2 , COS Degradation products (urea and thiourea ) can be converted back to DGA in reclaimer Higher HC solubility than MEA Perform well at high temperatures typically used at 50 wt %.

20. Secondary Amines DEA Diethanolamine M.wt = 105 DIPA Diisopropanolamine M.wt = 133 N H – CH 2 – CH 2 – OH HO – CH 2 – CH 2 – N H – CH 2 – CH – OH HO – CH – CH 2 – CH 3 CH 3

21. Secondary Amines Less basic so lower heat of reaction than primary amines Degradation less prevalent Removes CO 2 but requires deeper level of regeneration to get similar performance DEA not reclaimable in-situ, not normally required DEA typically used 25 – 30 wt % DIPA typically used from 40 – 50 wt %

22. Tertiary amines MDEA Methyldiethanolamine M.wt = 119 N CH 3 – CH 2 – CH 2 – OH HO – CH 2 – CH 2 –

23. Tertiary amines Weakest base so lowest heat of reaction Lowest reboiler duty of the amines Virtually no CO 2 degradation Capable of CO 2 slip while removing all the H 2 S Poor COS, CS 2 , mercaptan , removal from inlet gas MDEA used at 35 – 50 wt % strength Higher HC solubility than MEA or DEA Weak base means the importance of all other operating parameters become amplified

24. Reboiler Steam Requirements (SI) (Reaction Heat Only – highest conc.) Amine Type kJ/kg H 2 S kJ/kg CO 2 15 % MDEA 1500 1902 60 % DGA 1570 1972 30 % DEA 1140 1510 40 % DIPA 1230 1750 50 % MDEA 1045 1340

25. Formulated Tertiary Amines All major vendors have some form of formulated MDEA solvent Generally, formulations contain stronger “base” additives to enhance CO 2 absorption – can custom design a slip Some formulations contain stripping enhancers to achieve low lean loadings Some additives improve CO 2 slip

26. Activated MDEA ( aMDEA ) Developed by BASF, features a “activator” molecule ( piperazine ) mixed with MDEA solution Capable of very high removal of CO 2 Low corrosion rates, low reboiler duty, high rich loadings capability Competitive formulations now available

27. Why So Many MDEA – Based Solvents Today ? Stability MDEA ▷ only slight degradation Reactivity with CO 2 MDEA < DEA < MEA Enhancement MDEA + additive  enhanced CO 2 slip MDEA + additive  improved CO 2 removal Lower CO 2 related corrosion rates  

28. Types of Amine - Summary Primary Effective low pressure removal Strong acid gas removal Secondary Good all-purpose sweetening Tertiary CO 2 slip Formulated Customized CO 2 removal

29. Types of Amine – Summary Con’t Hindered Extremely high CO 2 slip TGTU / AGE Physical Bulk H 2 S and Sulphur Species Removal Mixed Mercaptan and Trace Sulphur Removal

30. Molarity Is a measure of the “potency” of the solvent – the number of moles of amine per liter of solution

31. Molarity vs Solution Strength Amine mole weight vary from 133 - 61 DIPA 133 MDEA 119 DEA 105 DGA® 105 MEA 61 So a 30 wt % amine solution yields a ?? Molarity (300 g/L/ M.wt )

32. Molarity For example, at typical operating strengths, the amines have the following molarities : Amine Strength Molarity MEA 15 wt % 2.48 DEA 30 wt % 2.90 DGA® 50 wt % 5.10 MDEA 50 wt % 4.40 DIPA 40 wt % 3.30

33. Amine Plant Flowsheet

34. Gas Mixtures – Partial Pressure Dalton’s Law P = pp i P = system total pressure pp i = partial pressure component i pp i = x i . P Where x i = mole fraction component i Partial Pressure is the driving force to get a gas into a solution  

35. Partial Pressure It is the partial pressure of the 21 % oxygen in the air that forces the oxygen into our blood when we breathe pp O2 = 100 kPa X 0.21 = 21 kPa ( 3 psia ) At higher elevation (low pressure) we become oxygen starved (climbing Mt. Everest) When we take in pure oxygen to our lungs, the higher concentration means a higher partial pressure and easier absorption into the blood

36. Gas Mixtures – Partial Pressure Total system pressure P = 10000 kPa Partial pressure of : Methane = 10000 kPa x 0.75 = 7500 kPa CO 2 = 10000 kPa x 0.20 = 2000 kPa H 2 S = 10000 kPa x 0.03 = 300 kPa H 2 O = 10000 kPa x 0.02 = 200 kPa Note : i = 10000 kPa = P  

37. Partial Pressure – CO 2 For example, the partial pressure of a gas containing 1 % CO 2 at various pressures would be : At 7000 kPa (1000 psi) pp co2 = 70 kPa ( 10 psi) At 700 kPa (100 psi) pp co2 = 7 kPa ( 1 psi) At 60 bar a, 2 % of CO 2 has a partial pressure of 1.2 bar (this would be equivalent to the top packaging partial pressure)

38. CO 2 removal profile – Simulation Output

39. Mass Transfer

40. Reaction Rates The chemical reaction between the acid gases and the amine is affected by both mass transfer and reaction kinetics Viscosity of the fluid (mass transfer) Residence time in the fluid (mass transfer) Contamination of the fluid/layers (mass transfer) Temperature of the fluid (kinetics)

41. Basic Chemistry Amine Treating

42. Absorption Fundamentals Absorption is the transfer of gas phase component (CO 2 ) to a liquid phase (amine) The tendency of a component to move from the gas to the liquid phase is determined by the partial pressure of that component Absorption favored by low temperature

43. Absorption Chemistry Acid gases react with weak liquid bases to form thermally regenerable salts acid + base  salt + heat Caustic ( NaOH or KOH)  too strong Ammonia (NH 3 )  too volatile Alkanolamines  good balance + amine  salt + heat H 2 S CO 2

44. Regeneration Chemistry Adding energy (heat) to the salts reverses the reaction to form the original bases and acids acid + base salt + heat CO 2 + amine rich amine + heat  

45. Reaction Mechanism CO 2 reactions (primary and secondary amines) – carbamate formation 2 [R 1 R 2 NH] + CO 2 [R 1 R 2 NH]H + + [R 1 R 2 N-COO] – (fast) “carbamate reaction”  

46. Reactions Mechanism CO 2 (primary and secondary) Acid- base reaction (slow) CO 2 + H 2 O H 2 CO 3 (carbonic acid) H 2 CO 3 H + + HCO 3 - (bicarbonate) H + + R 1 R 2 NH R 1 R 2 NH 2 + CO 2 + H 2 O + R 1 R 2 NH R 1 R 2 NH 2 + + HCO 3 -  

47. Reactions Mechanism CO 2 reactions Tertiary Amines CO 2 + H 2 O H 2 CO 3 (slow) [R 1 R 2 NR 3 ] + H 2 CO 3 [R 1 R 2 NR 3 ]H + + HCO 3 - (fast)  

48. Activated MDEA ( aMDEA ) MDEA solution formulated with piperazine Capable of very high removal of CO 2 Amine Reaction rate constant (L mol -1 s -1 ) MEA DGA DEA DIPA Piperazine MMEA MDEA 6000 4500 1300 100 59000 7100 4 Table 1. Reaction Rate constants with CO 2 of common gas treating amines

49. CO 2 Absorption in Amine Solvent Reaction between weak acid and weak base is thermally reversible.     Tertiary Amine do not have a labial H available to react. CO2 must hydrolyze to react with Tertiary Amine

50. CO 2 Absorption in Amine Solvent CO 2 hydrolysis is rate limiting CO 2 must hydrolyze to carbamate before it can react as a base CO 2 hydrolysis is slow, therefore rate limits CO 2 removal Tertiary Amine (MDEA, TEA) do not have labial H needed to form an amine carbamate , therefore only react with carbonic acid     Using chemistry to advantage: The slow hydrolysis reaction can be used to advantage, preferential H 2 S removal is possible with tertiary amines Reaction accelerators/activator have been developed to increase rate of CO 2 reaction Suitable activator should have ability to enhance the reaction rate with low heat of reaction

51. CO 2 Absorption in Promoted Amine Solvent Because of the low reaction rate of the CO 2 removal by alkanolamines or alkaline salts, promotors or activators are needed to improve the absorption process. The following compounds can be used to increase the reaction rate: Formaldehyde Methanol Phenol Ethanolamine Glycine Hindered amine The art of activated MDEA formulation is to find the suitable chemistry which gives higher CO 2 absorption rate, lower heat of reaction, and higher selectivity to benefit the total treating cost.