Can the sulfur recovery off-gas be sent to a methanol scrubber?
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High H2S-containing exhaust gases from low-temperature methanol washing are usually sent to the Claus process for sulfur recovery, but the exhaust gases generated by the Claus process do not meet the emission standards. Is it possible to send them back to the methanol washing process? Is there any design or practice based on such an approach? Also, if the H2S exhaust concentration is 15%, can ammonia-based desulfurization be used to produce ammonium sulfate?
It’s not possible, because the main component of Klaus exhaust is no longer H2S but SO2. If the H2S exhaust concentration is around 15%, the Topsox acid production process can be considered, although the construction period is longer and the investment is slightly higher.
Reply to 2# wgonline: But I’ve seen it designed this way, so there must be a reason for it, right? Methanol also absorbs SO2, and it returns to the H2S concentration tower at the lowest temperature, making it the most suitable place for absorption; the main concern is that the exhaust gas may not meet the required standards.
This does exist, but what is returned is not the sulfur recovery off-gas; rather, it is H2S generated as a result of the hydrogenation reduction of the sulfur recovery off-gas, which is then sent back to the methanol washing unit. By choosing this process, you need to install an additional hydrogenation unit after sulfur recovery, which involves high investment costs; moreover, a suitable hydrogenation fuel gas is required, adding to the expenses. This approach can increase the sulfur recovery rate to 99.8%, but the investment required is significant... If the investment for incinerating the exhaust gases in the third-stage Claus unit is considered 100%, then the additional investment for hydrogenation amounts to 200%... In fact, sending the exhaust gases after incineration to the boiler’s waste gas recovery system is more than sufficient to meet the required emission standards.
Instead of going through all this trouble, it’s better to just use Super Claus; the investment required is around 120%, yet a sulfur conversion rate of 99.8% can still be achieved. But in practice, it just means spending a lot of money...
The Claus off-gases undergo hydrogenation reduction, during which SO2, COS, and S react with H2 to form hydrogen sulfide; this gas is then pressurized using a compressor, cooled down in an ammonia cooler, and subsequently returned to the hydrogen sulfide concentration tower. New Energy Co., Ltd. is designed in this way; of course, the exhaust can also be burned in an exhaust incinerator before being released.
Sulfur recovery is an environmental protection project, and it’s difficult to make a profit from it. Our company has designed a three-stage Claus process, which, according to the design, is capable of meeting the emission requirements. Our factory has very strict environmental protection requirements. I’m not sure if the design is correct I’ve actually installed an exhaust gas combustion furnace in my plant; theirs is a two-stage Claus system with a conversion rate of 97%. However, if it is burned, the sulfur compound emissions are likely to exceed the limits. To achieve a high conversion rate, it’s not cost-effective to use that many devices, unless the devices are large enough to yield significant benefits. If environmental regulations are too strict, there’s nothing that can be done. If the environmental impact assessment is not approved, the project cannot proceed.
It is said that the sulfur recovery catalysts produced by some factories today are capable of recovering sulfur even at an H2S concentration of 5%, ensuring that the exhaust gases meet regulatory standards. I don’t know if it’s true