Continuous desulfurization process based on metal oxide-based regenerable sorbents
a desulfurization process and metal oxide technology, applied in the direction of combustible gas purification/modification, other chemical processes, separation processes, etc., can solve the problems of additional capital and operating costs for the removal of other sulfur species, cos, and other sulfur species, so as to reduce the cost, reduce the effect of sulfur species and minimizing side reactions
Active Publication Date: 2022-01-20
SUSTEON INC
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Benefits of technology
The present disclosure is about a continuous desulfurization process for gas mixtures containing sulfur. It uses a fixed-bed reactor with a regenerable metal oxide-based sorbent to remove sulfur from the gas mixture. The process includes a regeneration process sequence that optimizes the conversion of metal sulfide back into active metal oxide while minimizing side reactions. Combined with a functional process scheme, the process achieves effective desulfurization and regeneration for at least 100 cycles, reducing replacement costs for disposable sorbents. The main technical effect is the higher efficiency and reduced cost of sulfur removal compared to conventional processes.
Problems solved by technology
The presence of these reduced sulfur species in gas mixtures adversely impacts processes designed to extract energy or convert these gas mixtures into value-added chemicals.
The Selexol™ sulfur removal process is very selective for H2S, but struggles to remove other sulfur species, particularly COS.
With a Selexol™-based desulfurization process, an additional preprocessing step, to convert the COS into H2S via a hydrolysis reaction, may be required, resulting in additional capital and operating costs for removal of sulfur species besides H2S.
Not all solvent-based desulfurization processes have this issue, but most do.
The cost associated with continuously replenishing this caustic is a significant operating cost, which increases proportionally to the concentration of reduced sulfur species.
In addition, separation and conversion of the captured sulfur species into a suitable form that is acceptable for disposal requires significant additional processing.
These disadvantages make caustic wash cost prohibitive when the sulfur concentration in the gas mixture is high.
These disadvantages also reduce commercial applications for caustic washing to a few niche applications for which better alternative technologies are not available.
However, the use of this process for syngas is limited due to highly flammable nature of the syngas components, namely H2 and CO.
Furthermore, this process suffers from a number of technical issues, including degradation of chelating agents, high chemical make-up costs, formation of sulfur oxo-anions, and plugging of the absorber due to salt formation.
For small quantities of sulfur removal , typically below 5 ton / day, this process is not cost-competitive.
For gas mixtures comprising sulfur in a range of from about 5 ppmv to about 5,000 ppmv, existing commercial sulfur removal processes generally are not very cost-effective, a circumstance which creates a significant economic penalty for utilization of these gas mixtures, particularly to produce value-added chemicals and fuels.
This catalytic hydrodesulfurization process requires significant amounts of hydrogen to drive the process.
However, for straight-run fractions such as straight run naphtha, which have lower sulfur concentrations, dedicated caustic wash systems are frequently used, because the H2S in this process stream is relatively small and the value of the product derived can tolerate higher operating costs associated with continuous consumption of caustic solution.
In addition, the caustic wash systems are problematic and challenging for operators to operate and maintain, which escalates the already high operating costs, as well as producing substantial amounts of spent caustic solution that must be safely disposed of In some instances, the H2S-containing H2 stream from the hydrodesulfurization unit is recycled without any H2S removal, except for purging it from the recycle loop to maintain a desired H2S concentration at the inlet of the hydrodesulfurization reactor.
This is typically achieved by purging part of the recycle stream resulting in higher than necessary operating cost for hydrogen consumption, which adversely and unacceptably affects the overall profitability of the process facility.
This processing adds additional processing equipment and process complexity, which increases capital and operating cost of the AGR system.
Because of the small concentrations of sulfur in these tail gas streams, the high level of sulfur removal required, and the overall small amount of sulfur being treated, solvent-based processes are complex and cost-prohibitive.
Although regeneration reactions can be proposed for almost any metal oxide / metal sulfide combination, the key differentiator for the regenerable sorbent from the generic sulfur guard bed sorbent is its ability to be regenerated numerous times. If a sorbent cannot be effectively regenerated more than 50 times without deteriorating desulfurization and regeneration performance, then the sorbent will not be cost-effective in comparison to a generic sulfur guard bed sorbent that is non-regenerable in character, and is intended to be utilized without regeneration until the sorbent is loaded to a final or predetermined extent, following which the guard bed is removed for disposal, and replaced by a fresh guard bed.
High porosity generally provides faster kinetics for the desulfurization reaction; it however leads to poor crush strength and hence should be carefully controlled to get the proper balance of kinetics and crush strength.
Thermal and chemical cycling during the desulfurization and regeneration cycles may lead to sintering and changes in the physical properties that can have an adverse effect on sorbent performance.
Although many regenerable metal oxide sorbent have been proposed and tested at laboratory scale, adaptation of the lab-scale production processes into commercial processes that can produce the sorbent at a suitable cost for commercial application of a fixed-bed regenerable sorbent process has not been achieved in practice for many of these sorbents.
The impact of this sulfur during use of sulfur-laden hydrocarbon-based fuels include mechanical problems associated with corrosion of downstream process equipment, detrimental poisoning of catalysts, and / or environmental issues associated with the release of SOx to the environment.
For low concentrations of H2S, typically <1 ppm, the cost of replacing the sorbent, when all or a major amount of the metal oxide has been converted to a sulfide, is an acceptable operating expense.
When the H2S concentration substantially exceeds 1 ppm, the cost of replacing the sorbent, when the metal oxide has been converted to metal sulfide, becomes prohibitive.
However, sufficient amounts of the diluents are not usually readily available at low enough cost to support generation of a cost-effective oxidizing mixture for regeneration.
As for diluting air to generate the regeneration gas, the volumetric flow of these inerts available at a plant is limited.
Method used
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[0171]A fixed bed sorbent material manufactured by Clariant Corporation (Charlotte, N.C., USA) with trade name T-2716 was tested at the University of North Dakota Energy and Environmental Re search Center (UNDEERC) in Grand Forks, N. Dak. A slipstream with a flow rate of 555 std. cubic feet per hour (SCFH) from UNDEERC's pilot-scale gasifier using Illinois #6 coal was sent to a fixed bed reactor that was loaded with 27.1 lbs. of the T-2716 sorbent. The desulfurization was carried out at 600° F. (316° C.) at a space velocity of about 1,400 per hour (at STP conditions). The sorbent reduced the inlet sulfur content of the syngas from 10,920 ppmv to less than 2 ppmv in a residence time of 1.9 seconds. Prior to breakthrough, the sulfur loading on the sorbent was about 10 wt %. Once the sorbent in the desulfurization reactor was saturated with sulfur, it was switched to the regeneration mode and the sorbent was regenerated at 1000° F. (538° C.) with an oxygen- containing stream. Multiple ...
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Abstract
A continuous desulfurization process and process system are described for removal of reduced sulfur species at gas stream concentrations in a range of from about 5 to about 5000 ppmv, using fixed beds containing regenerable sorbents, and for regeneration of such regenerable sorbents. The desulfurization removes the reduced sulfur species of hydrogen sulfide, carbonyl sulfide, carbon disulfide, and / or thiols and disulfides with four or less carbon atoms, to ppbv concentrations. In specific disclosed implementations, regenerable metal oxide-based sorbents are integrated along with a functional and effective process to control the regeneration reaction and process while maintaining a stable dynamic sulfur capacity . A membrane-based process and system is described for producing regeneration and purge gas for the desulfurization.
Description
CROSS-REFERENCE TO RELATED APPLICATION[0001]The benefit under 35 USC § 119 of U.S. Provisional Patent Application Ser. No. 62 / 797,541 filed Jan. 28, 2019 in the names of Raghubir Prasad Gupta and Brian Scott Turk for CONTINUOUS DESULFURIZATION PROCESS BASED ON METAL OXIDE-BASED REGENERABLE SORBENTS is hereby claimed. The disclosure of U.S. Provisional Patent Application Ser. No. 62 / 797,541 is hereby incorporated herein by reference, in its entirety, for all purposes.BACKGROUNDTechnical Field[0002]The present disclosure relates to a process and apparatus for the removal of hydrogen sulfide, carbonyl sulfide, carbon disulfide, and / or thiols and disulfides with four or less carbon atoms, from gas mixtures containing same. The process and apparatus in various embodiments herein described particularly relate to sorbent requirements, commercial sorbent production processes and sorbent compositions, process design, processing conditions, and target applications for the continuous removal o...
Claims
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IPC IPC(8): C10K1/32B01J8/02B01J20/30B01J20/28B01J19/00C10K1/26C10K1/00B01J20/02B01D53/82B01D53/52B01D53/96B01D53/34B01D53/22
CPCC10K1/32B01D2257/306B01J20/3078B01J20/28071B01J20/28073B01J20/28059B01J20/28011B01J19/0033C10K1/26C10K1/004B01J20/0203B01D53/82B01D53/52B01D53/96B01D53/346B01D53/22B01J2219/00051B01J2219/00162B01J2219/00164B01J2219/00186B01J2220/56B01D2253/1124B01D2257/304B01D2257/308B01D2253/311B01D2253/306B01J8/02B01D2259/40086B01D2251/102B01D2253/104B01D53/265B01D2258/06B01D2053/221B01D2256/12B01D2257/102B01D2256/24B01D53/04B01D2257/104B01D53/0462B01D2259/40056B01D53/0438B01D53/0446
InventorGUPTA, RAGHUBIR PRASADTURK, BRIAN SCOTT
OwnerSUSTEON INC