1. Crude oil Treatment process
Hydrotreatment
Amine recovery
Sulfur recovery

2. Hydrotreater
BP-UK

3. Hydrotreatment What is hydrotreatment?
It is a process to catalytically stabilize and/or remove undesirable elements from products or feedstocks by reacting them with hydrogen.
 Stabilization usually involves converting unsaturated hydrocarbons such as olefins to paraffins.
Undesirable elements removed by hydrotreating include sulfur, nitrogen, oxygen, halides, and metals.

6. Difference between Hydrotreating and Hydrocracking
Hydrotreating and hydrocracking both can be called Hydroprocessing

8. PROCESS VARIABLES
The principal operating variables are temperature, hydrogen partial pressure, and space velocity.
Liquid Hourly Space Velocity (LHSV)= Volumetric flow rate/catalyst volume
Weight Hourly Space Velocity (WHSV)= Mass flow rate/catalyst mass
Increasing temperature and hydrogen partial pressure increases sulfur and nitrogen removal and hydrogen consumption.
Increasing hydrogen partial pressure also increases hydrogen saturation and reduces coke formation.
Increasing space velocity reduces conversion, hydrogen consumption, and coke formation.
Although increasing temperature improves sulfur and nitrogen removal, excessive temperatures must be avoided because of the increased coke formation.

9. PROCESS VARIABLES
Typical ranges of process variables in hydrotreating operations are

14. Hydrotreatent Reactions
Convert Organic S to Hydrogen Sulfide
Convert Organic N to Ammonia
Convert Organic O to Water
Convert Organic halides to Hydrogen Halides
Saturate Olefins
Saturate Aromatics
Remove Metals

15. Desulfurization
Increasing Difficulty

17. Denitrogenation
Denitrogenation is usually more complex than desulfurization.

18. Oxygen Removal

19. Olefin Saturation
Olefins are unstable components and they polymerize in presence of oxygen
Olefin saturation is very rapid and exothermic reaction

20. Aromatic Saturation
Aromatics present as 1, 2, 3 or more rings structure
Aromatic saturation is a stepwise reaction
Aromatic saturation is an exothermic reaction

21. Aromatic Saturation

22. Halide Removal

23. Metals Removal
Lead, mercury, arsenic, silicon, nickel, vanadium, sodium
Compounds that contain metals decompose in reactor and deactivate catalyst
The metal deposited on catalyst cannot be removed by regeneration

24. Lead poisoning effect on catalyst activity

25. Arsenic poisoning effect on catalyst activity

26. Sodium poisoning effect on catalyst activity

27. Ease of hydrotreatment reactions

32. Guard Reactor

33. Hydrotreatment Catalyst
Solid consisting of a base alumina impregnated with metal oxides
Pellets shaped as cylindrical or pills
For Desulfurization, Co-Mb catalyst is used
For Desulfurization, Denitrogenation and Aromatic saturation, Ni-Mb catalyst is used

34. Sulfur recovery
Hydrogen sulfide created from hydrotreating is a toxic gas that needs further treatment
Solvent extraction: using diethanolamine (DEA) dissolved in water separates the H2S gas from the process stream (DEA should be recovered) 34

35. H2S separation_ Amine Unit35

36. DEA Chemistry
DEA: weak organic base to absorb acid gases of H2S and CO2 from gas streams.
Chemical Structure: DEA = [HO(CH2)2]2 - NH
C2H4OH \
N - H /
The reaction of DEA with H2S and CO2 are equilibrium reactions:
H2S: R2NH + H2S ⇋ R2NH2SH
CO2: 2R2NH + H2O + CO2 ⇋ (R2NH2)2CO3
where R = HO(CH2)2
Absorption
Absorption is favoured by high pressures and low temperatures 36

37. Amine Regeneration Regeneration is favoured: low P and high T
Acid gas components are boiled out of the amine solution
The required heat input to the reboiler:
Sensible heat required to bring the rich amine from the inlet temperature (~95°C) to the column base temperature (~127°C) 
Heat of reaction to desorb the acid gas components.  
Heat of vapourisation to generate sufficient water vapour within the column to strip the acid gas components in the amine
Need to ensure that temperatures are maintained below 130°C to prevent amine degradation and subsequent amine corrosion 37

38. DEA Properties Amine Strength: Amine Loading: Ideally 25-27wt% DEA
Higher amine concentrations = higher regenerator boiling temperatures and increased corrosion rates
Lower amine concentrations = higher circulation rates and thus increase energy requirements for pumping and regeneration
Amine Loading:
Amine Loading = mol (H2S) + mol (CO2) mol (DEA)
Target is an amine loading of 0.3 – 0.5 mol/mol 38

39. Sulfur Recovery Unit_Flowsheet Based on Claus Process
Muffle furnace
Catalytic reaction
Thermal reaction

40. Equipment Roles_ Muffle Furnace
H2S
Air
Thermal Reaction
Muffle Furnace
925 – 1300 C
Muffle Furnace:
1/3 of the H2S in the acid gas stream is partially oxidised to sulphur dioxide to produce a 2:1 molar ratio of H2S to SO2.
3H2S + 3/2 O2  SO2 + H2O + 2H2S DH = kJ/mol H2S
This reaction occurs at ~1100oC and the energy released is used to generate steam in a waste heat boiler and the first sulphur condenser. 40

41. COS and CS2
Formation
The presence of CO2 and HC in the feed gases to the Claus plant gives rise to carbonyl sulphide (COS) and carbon disulphide (CS2) in the Muffle Furnace and Waste Heat Boiler
If these compounds are not hydrolysed back to H2S they will proceed through the catalytic reactors unreacted
This results in reduced sulphur conversion and decreased SRU efficiency. 41

42. COS and CS2 COS and CS2 Destruction
The hydrolysis reactions can be written as:
COS + H2O  CO2 + H2S
CS H2O  CO H2S
Hydrolysis is favoured by high temperatures (>310C)
The ability of the catalyst to carry out the COS/CS2 hydrolysis reactions depends on:
1.         the catalyst formulation
2.         the operating temperatures in the first reactor
3.         the state of deactivation of the catalyst
Destruction
The hydrolysis reactions can be written as:
COS + H2O  CO2 + H2S
CS H2O  CO H2S
Hydrolysis is favoured by high temperatures (>310C)
The ability of the catalyst to carry out the COS/CS2 hydrolysis reactions depends on:
1.         the catalyst formulation
2.         the operating temperatures in the first reactor
3.         the state of deactivation of the catalyst 42

43. Equipment Roles_ Waste Heat Boiler
HP Steam – 3.4 MPa
Waste Heat Boiler:
Cools process stream
Recovers energy in a useful form (HP Steam) for use in the preheaters
Reactions also take place in the WHB 43

44. Equipment Roles_ Reactors
Catalytic Reaction
170 – 350 C
The Two Reactors
Reactor 1:
COS and CS2 destruction / hydrolysis at temps > 310 C
Operation at elevated temperatures compromises Claus reaction equilibrium
Reactor 2:
Maximise Claus Reaction
Operate at as lower temperature as practicable above the sulphur dewpoint to prevent dropping sulphur onto the catalyst bed
Catalytic Reaction: The remaining 2/3 of the H2S is reacted over a catalyst with SO2 produced in thermal reaction to form elemental sulphur.
2H2S + SO2  3S + 2H2O DH = -31 kJ/mol H2S 44

45. Equipment Roles_ Condensers
Sulphur Condensers
LP Steam – 345 kPa
Liquid Sulphur
Sulphur Condensers:
Recover produced sulphur 45

46. Equipment Roles_ Incinerator
Incineration or Further Treatment
Incinerator:
Combust unreacted H2S to SO2 prior to emission of tail gas to the environment 46

47. The Claus Process_ Thermodynamics Equilibrium
1.  Thermal Reaction:
3H2S + 3/2 O2  SO2 + H2O + 2H2S DH = kJ/mol H2S
2. Catalytic Reaction:
2H2S + SO2  3S + 2H2O DH = -31 kJ/mol H2S
Thermal and catalytic reactions are Reversible reactions
Thermodynamic Equilibrium 47

48. The Claus Process_ Thermodynamics Equilibrium
There are 2 regions of high conversion of H2S to elemental sulphur
High Temperatures – thermal reaction
Low Temperatures – catalytic reaction
Often the Claus process is kinetically limited due to residence time and mixing issues, especially in the the Muffle Furnace 48

49. SRU Catalyst Standard Catalyst Promoted Catalyst
Activated alumina (Al2O3) – (Co-Mb)
Average life in a refinery SRU is 3-5 years
Important catalyst properties
Surface area: 320 – 390 m2/g
Pore volume distribution: to ensure bulk diffusion to internal surface area
Physical and mechanical properties: crush strength
Promoted Catalyst
Titanium dioxide (TiO2)
COS / CS2 hydrolysis, O2 scavenger, deactivation resistance
Poor crush strength
Expensive 49

50. SRU Efficiency
Sulphur recovery efficiency is a measure of the percentage of sulphur present in SRU feed as H2S, that is converted and recovered as liquid elemental sulphur.
SRU recovery efficiency is:
dependent upon all significant operating conditions
a direct measure of sulphur plant performance
is independent of plant size
can be measured accurately 50

51. SRU Efficiency It can be represented by the following equation:
Recovery = SPRODUCED/SFEED(as H2S)
The efficiency of a conventional Claus plant is limited by:
the efficiency of COS/CS2 hydrolysis in the first catalytic reactor
the equilibrium conversion of H2S and SO2 to elemental sulphur at the minimum safe operating temperature
the saturation vapour pressure of sulphur at the minimum safe condenser operating temperature. 51

52. To Maximise SRU Efficiency
Minimise impurity level in the feed
Impurities all reduce the partial pressures of the Claus Reactants
CO2 acts as a ‘fire extinguisher’ in the Muffle Furnace decreasing temperatures, decreases plant capacity and leads to the production of COS
Natural Gas/HC leads to the production of CS2, increases air demand, and cause possible downstream contamination
H2O is a product of the Claus Reaction
NH3 increases air demand, and can lead to plugging from ammonium salts 52

53. To Maximise SRU Efficiency
Maximise product removal at earliest opportunity
Use 3 catalytic stages with active catalyst
Maximise Reactor 1 temperatures to maximise COS and CS2 destruction
Optimal air control
H2S and O2 should be delivered to the muffle furnace in the correct stoichiometric ratio
Excess O2 can result in sulphation of the catalyst = deactivation 53

54. End of Chapter Nine