At present, there are mainly two methods of sulfur recovery, wet method and dry method. The wet method includes Lurgi’s low and high temperature condensation process, Topsoe’s WSA process, etc. The dry method includes the traditional Claus process, sub-dew point Claus process, reduction absorption process, direct oxidation Claus process, oxygen-enriched Claus process, and oxidation absorption Claus process.
Dry desulfurization
(1) Conventional Claus process
The Claus process is a relatively mature multi-unit treatment technology and is currently the most widely used sulfur recovery process.
The process is as follows: acidic gas containing hydrogen sulfide is burned in a Claus furnace to oxidize part of the hydrogen sulfide into sulfur dioxide, which then reacts with the remaining unreacted hydrogen sulfide on a catalyst to form sulfur.
The characteristics of the traditional Claus process are:
Control n(O2):n(H2S)=1:2. If the oxygen content is too high, SO2 will overflow. If it is too low, the removal efficiency of H2S will be reduced.
A demister needs to be installed to remove sulfur from the gas flow to increase the sulfur recovery.
The total sulfur recovery rate of the Claus process is 94%-96%.
The Claus process is not suitable for gases containing combustible components such as coal gas, or when the sulfur mass fraction is less than 40%.
(2) Sub-dew point Claus process
The so-called sub-dew point process is characterized by the Claus reaction at a temperature below the sulfur dew point. It mainly includes Sulfreen, Hydrosulfreen, Carbonsulfreen, Oxysulfreen, CBA, ULTRA, MCRC, Clauspol 1500, Clauspol 300, Clisulf SDP, ER Claus, Maxisulf and other processes.
(3) Reduction absorption process
The reduction absorption process converts organic sulfur and SO2 into H2S and then absorbs it, so the total sulfur recovery rate can reach more than 99.5%. It mainly includes SCOT, Super-SCOT, LS-SCOT, BSR/Amine, BSR/WetOxidation, Resulf, AGE/Dual Solve, HCR, Parsons/BOC Recycle, Sulfcycle and ELSE processes.
(4) Direct oxidation process
Direct oxidation refers to the direct oxidation of H2S to sulfur on a solid catalyst. It is actually a new development of the Claus prototype process. The key to the direct oxidation process technology is to develop a highly active catalyst with good selectivity and insensitivity to H2O and excess O2. At present, it is prepared using different mixtures of iron-based metal oxides. The main selective catalytic oxidation sulfur recovery technologies include: Seleclox, BSR/Selectox, BSR/Hi-Activity claus, MODOP, Superclaus, Catasulf and ClinsulfDO.
Take the Superclaus process as an example for a brief introduction. There are two types of Super Claus processes: Super Claus-99 and Super Claus-99.5. In the Super Claus process, the gas does not need to be dehydrated. During selective oxidation, excess oxygen can be added without significant effect on selectivity. The process is simple and easy to operate. The process is continuous without cycle switching, the sulfur recovery rate is high, the investment is low, the energy consumption and raw material costs are low, and the application scale is unlimited and the scope of use is wide.
(5) Oxygen-enriched Claus process
Using oxygen-enriched air or even pure oxygen instead of air in the Claus unit can reduce the amount of inert component N2 accordingly, thereby improving the processing capacity of the unit. The industrialized oxygen-enriched Claus processes include COPE, SuRe and Oxyclaus; to solve the operating cost problem, PS Claus, which supplies oxygen by pressure swing adsorption, has emerged; to solve the furnace temperature problem, NOTICE process has been produced.
(6) Oxidation absorption process
This process oxidizes sulfur in the tail gas into SO2, absorbs and desorbs it, and then reuses it. It is rarely used in the Claus process. This type of process mainly includes Wellmawn-Lord, Elsorb and Cominco de Sox processes.