Effect of carbon dioxide on the removal of hydrogen sulfide from high-temperature gas
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It is well known that both hydrogen sulfide and carbon dioxide are acidic gases, and the active components of desulfurization agents are generally metal oxides. This leads to competitive adsorption by carbon dioxide, resulting in a decrease in the sulfur capacity of the desulfurization agent. How can the selectivity of such agents for hydrogen sulfide be improved? :o :o
What you’re saying is a bit unclear; I’m not sure what desulfurization and decarbonization technology you’re using – could you explain? If it’s low-temperature methanol washing, then this issue wouldn’t arise.
Hydrogen sulfide and carbon dioxide – how can the selectivity of desulfurizers for hydrogen sulfide be improved? This is determined by the properties of the reaction and is difficult to change, unless efforts are made to reduce carbon dioxide levels. As for what you mentioned about “removing hydrogen sulfide using high-temperature gas,” I find it very difficult to understand! The gas before entering the desulfurization unit must pass through a cooling tower to ensure that its temperature does not exceed 42°C. Since the solubility of gases is inversely proportional to temperature, the amount of O2 dissolved in an aqueous solution decreases as the temperature rises. For example, at normal pressure, the saturated oxygen content in water is 7.5 mg/L at 30°C and 5.4 mg/L at 50°C. As the temperature rises, the amount of O2 absorbed from the desulfurization solution through the injector decreases, which hinders the activation of the desulfurizing agent by oxygen absorption during regeneration. A decrease in O2 adsorption affects the catalytic activity of the desulfurization agent, which may lead to an increase in H2S levels and a higher requirement for desulfurization agents. Moreover, at high temperatures, side reactions accelerate and alkali consumption increases. Furthermore, at high temperatures, the air inside the sulfur foam expands, causing the bubbles to burst and preventing the formation of a sulfur foam layer, which affects the separation of sulfur. Therefore, the temperature of the solution should not exceed 42°C; it is better to keep it between 30-40°C.
In wet desulfurization of semi-water gas, the CO2 content is not too high; therefore, CO2 has little effect on the selective absorption of H2S by alkaline solutions. The significant impact of CO2 on the selective absorption of H2S by alkaline solutions occurs mainly during the desulfurization of shift gas, as the CO2 content in that case is around 28%. Some factories now add a flash tank to flash out the CO2 from the desulfurization liquid coming out of the desulfurization tower before it enters the spray regenerator. The fundamental solution to this problem lies in minimizing the gas-liquid contact time as much as possible. Since the reaction of alkaline solution absorbing H2S is a rapid one, reducing the gas-liquid contact time allows the impact of CO2 to be minimized while still ensuring effective absorption of H2S. To reduce the gas-liquid contact time, solutions must be found in terms of the tower’s structure. Generally, the gas-liquid contact time in a packed tower is 80 seconds. However, with a plate tower, such as the QYD mass transfer internals developed by our company and successfully applied in the stripping towers of various enterprises, the gas-liquid contact time is only 15–20 seconds, yielding excellent performance. As for high-temperature gas, I fully agree with the opinion from the 3rd floor: if wet desulfurization is used, it’s impossible for the system to operate properly at such high temperatures. This post was last edited by Dongshi Zhang Tong on 2009-3-28 at 11:23.]
The efficiency of absorbing different gases varies at different temperatures and pressures.