Is this appropriate treatment of sulfur recovery tail gas?
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Everyone knows that no matter what sulfur recovery process, sulfur particles will inevitably be carried in the exhaust gas, and there will always be hydrogen sulfide or sulfur dioxide in the exhaust gas, causing the exhaust gas to exceed the standard and difficult to meet environmental protection requirements. Although the reaction conversion rate can be raised to a high level in the design of the sulfur recovery process, and the exhaust gas meets environmental protection requirements, it is always difficult to achieve such a high conversion rate in actual operation! In order to meet the tail gas emission standards, a company sprays the sulfur recovery tail gas (after washing with water) with lean methanol to remove the water and hydrogen sulfide in the tail gas, and then cools it through an ammonia cooler to further reduce the temperature of the tail gas. It enters a separation tank and uses lean methanol (spray methanol again in the separation tank) to remove the hydrogen sulfide and dioxide. For sulfur and other gases, the separated gas enters the hydrogen sulfide concentration tower (using a low-temperature methanol washing process) and uses the lowest-temperature methanol in the entire system to wash out the substandard gases again. The tail gas after washing enters the torch together with the tail gas from the hydrogen sulfide concentration tower for venting, and the separated rich methanol is pressurized and then enters the methanol-water separation tower for methanol-water separation operation! It can be seen that after this design, the hydrogen sulfide gas in the exhaust gas can be completely guaranteed to meet the emission standards after being washed many times, but there is a problem! 1. The sulfur particles carried in the exhaust gas will be deposited in the pipeline when cooled, and may enter the ammonia cooler tube, causing the tube to be clogged and damaging the equipment, resulting in overpressure of sulfur recovery, which is not conducive to operation. It will also cause overpressure of the thermal regeneration tower, which is not conducive to methanol regeneration, affecting the absorption effect, causing the purified gas to exceed the standard. ； Second, the tail gas may also bring sulfur particles into the hydrogen sulfide concentration tower or the methanol-water separation tower, causing the inlet filters of the regeneration tower feed pump and wastewater pump to be often blocked by sulfur particles, so the frequency of cleaning of the pump inlet filters is very high. ； Third, due to the intervention of air in the sulfur recovery process, oxygen in the air enters the hydrogen sulfide concentration tower together with the tail gas. Part of the oxygen dissolves into methanol at low temperatures. The release of oxygen after thermal regeneration of methanol may cause serious corrosion in the thermal regeneration tower, which will have a greater impact on the entire system! Of course, this enterprise has not yet been put into production, and we don’t know what the specific results will be in the future. Here are just some of my personal opinions. Please discuss and express your opinions together!
In the future, the result will be the same as the poster expected. I have seen several devices with this process. The exhaust gas is not recycled into the concentration tower, but is directly sent to the torch for incineration. This technology is not very mature and will cause many problems, including the 1, 2, and 3 situations you mentioned.
Since the exhaust gas contains sulfur particles, hydrogen sulfide or sulfur dioxide and oxygen, activated carbon can be used to remove sulfur and hydrogen sulfide, but may have little effect on sulfur dioxide. The cost is not high either.
But you have to think about using activated carbon to remove sulfur, so that the sulfur will be deposited on the surface of the activated carbon, making the adsorption surface smaller and smaller, and the removal effect will be worse! I don’t think it will work in industry either! Welcome to continue the discussion!
Our sulfur recovery exhaust gas enters the circulating fluidized bed boiler for combustion, but problems arise again. First, there is a slight positive pressure in the lower part of the furnace. The pressure of the sulfur recovery exhaust gas is only 0.03MPa. In addition, the pipeline is relatively long, 1,000 meters, making it difficult to enter the furnace. Second, the pipeline needs to be heated throughout the entire process, and it is easy to be blocked after sulfur condensation. I wonder if that gentleman knows if it is possible to increase the fan pressure before entering the boiler. In this way, the requirements for the fan are relatively high. Corrosion-resistant, leak-proof, etc.
The design of our plant is the same as the design idea mentioned by the poster. The key to this technology is to add a hydrogenation reaction device behind Claus sulfur recovery to completely react impurities such as elemental sulfur, sulfur dioxide, and oxygen to generate hydrogen sulfide. After water washing, cooling, and pressurization, it is sent to a low-temperature methanol washing device. Methanol is injected, cryogenically separated, and then sent to a hydrogen sulfide concentration tower for processing. If the sulfur dioxide and other components exceed the standard after the hydrogenation reaction, it will be discharged to the torch to ensure the smooth operation of the low-temperature methanol washing.
I agree with the 6th floor's point of view. Add a hydrogenation device to the exhaust gas. The hydrogenation device can convert all SO2, Sx, and organic sulfur into H2S. This solves the problem of solid sulfur in the exhaust gas very well, and there is no major change in the current process. The only flaw that has not been solved is the corrosion of the regeneration tower by oxygen. ； But I think this problem should not be difficult to solve. First of all, the O2 content in the tail gas is very small. If there is too much, it cannot be added to the concentration tower. If O2 enters the process gas, wouldn't it be a very dangerous thing? ； Secondly, the absorption capacity of methanol for O2 should be relatively poor, and less of it will enter the methanol cycle. Of course, trace amounts of O2 will also corrode the regeneration tower. Improving the material of the regeneration tower can effectively prevent corrosion, and the increase in costs should not be too obvious. The corrosion we are worried about may not occur in actual operation, and I don't know what the situation would be like in a similar site. I think this is a better choice without changing the current overall process flow. Of course, another idea is to add a tower and use lean methanol to absorb the current exhaust gas instead of injecting methanol. This is because I saw that your current process absorbs the washed exhaust gas three times. Obviously, including the first two injections of methanol, it does not make your exhaust gas meet the emission standards. So why not directly wash the exhaust gas with methanol? Wouldn't it be simpler to use a methanol-rich regeneration system where the washed methanol is directly pumped and washed with low-temperature methanol? For sulfur particles in the exhaust gas, an automatic regeneration and filtration system can be added to the methanol-rich pipeline. If you feel that this process is unstable or uneasy, then use the above method and add a hydrogenation device. The same goes for O2. This idea may not be very mature and has many problems. In my humble opinion, it is for reference only!
You all have good water skills, and one more thing is: If the previous hydrogenation is not complete, SO2 will be brought into the H2S concentration tower, and the low-temperature methanol washing process will be affected.
One idea is to add hydrogen after the Claus reaction, but this requires post-processing, a water washing tower, and a separator. The problem of water and sulfur is not serious. After the water washing tower, there is a cooling process, and the water and sulfur become liquid and separated. It only consumes power and is not very efficient. For your reference
What types of hydrogenation catalysts are currently available?:handshake
Such a design can indeed meet environmental protection requirements and can easily pass environmental impact assessments, but how many manufacturers will do this after it is actually put into production? Will the torch be discharged directly? It’s worth thinking about! ! ! ! !
I think SSR technology is better: Two-stage Claus + exhaust gas hydrogenation reduction + physical absorption (the absorbing liquid absorbs H2S in the absorption tower and becomes rich liquid, the absorbed gas is burned in the incinerator to recover heat and then discharged, the rich liquid goes to the regeneration tower, H2S is desorbed in the tower and goes to the Claus unit, and the lean liquid is returned to the absorption tower for recycling).
Now there is a process: The acid gas is partially burned, passes through two stages of Claus, and then is directly sent to the boiler for combustion after exhaust gas incineration, and finally enters wet desulfurization. However, there are problems in the process. The exhaust gas is not incinerated completely, resulting in the failure of wet desulfurization to crystallize (due to the low temperature of the exhaust gas incinerator, organic sulfur and hydrocarbons cannot be completely burned). May I ask if there is a solution?