Why do desulfurizers reduce the effect of sulfur

Mechanism of activated carbon desulfurizer
Activated carbon desulfurizer is one of the earliest dry desulfurizers, which has been used for more than 70 years. The previous activated carbon desulfurization technology has a huge equipment, complex regeneration and sulfur recovery process, and the operation is troublesome. In the 1950s, it was gradually replaced by wet process. In recent years, due to the improvement and simplification of regeneration method, activated carbon desulfurizer and room temperature fine desulfurization technology for fine desulfurization have been developed, Many small and medium-sized ammonia plants, urea plants and combined alcohol plants use activated carbon desulfurizer to remove some organic sulfur in feed gas by dry process. This method has the advantages of large sulfur capacity, strong adaptability, low operating temperature, renewable and repeated use, and can recover sulfur. Moreover, the price of active carbon desulfurizer is relatively low. However, the activated carbon desulfurizer is only limited to the case of oxygen, In terms of water resistance, activated carbon desulfurizer is better than iron oxide desulfurizer
The desulfurization mechanism of activated carbon is to accelerate the reaction of H2S and O2 in the gas by the catalysis of active groups on the surface of activated carbon
2H2S+ O2 →2H2O+2S ΔH= -434.3kJ/mol
In fact, the reaction of H2S and O2 on the surface of activated carbon is divided into two steps. First, the surface oxide of active center is formed by adsorbing oxygen on the surface of activated carbon. Then, the hydrogen sulfide molecule in the gas reacts with chemically adsorbed oxygen, and the generated sulfur is deposited in the micropores of activated carbon ash. In order to accelerate the reaction and improve the desulfurization effect, the actual O2 / H2S ratio should be greater than the theoretical value of 0.5, The ratio is better than 3
Activated carbon desulfurizer may introduce active metals such as copper, alkali metal and alkaline earth metal to improve its catalytic activity by over impregnation. The crude desulfurizer of activated carbon can deal with high content of sulfur, but the outlet gas still contains 20-30? G / g sulfur, If a small ammonia plant purifies the semi water gas containing 1.72 g / m3 of sulfur (H2S) under normal pressure, 33 ℃ and 195 H-1, the sulfur can be removed to 54 mg / m3. The consumption of activated carbon, ammonia and steam per ton of ammonia is 0.63 kg, 0.25 kg and 62 kg respectively. The regeneration cycle is 26 days
The sulfur capacity of activated carbon fine desulfurizer is 4-6 times that of activated carbon crude desulfurizer. T103 is a food grade carbon dioxide fine desulfurizer, which has a certain sulfur capacity for organic sulfur, and can be used at 60-80 ℃
The calculation shows that the equilibrium constant of H2S oxidation on activated carbon desulfurizer is much larger than that on Zinc Oxide Desulfurizer at 30 ℃, while the equilibrium concentration of H2S is about 10-17 lower than that on Zinc Oxide Desulfurizer at 30 ℃. This is also confirmed by the kinetic characteristics of T101 type activated carbon desulfurizer, The sulfur capacity of the original particle size of the activated carbon fine desulfurizer is three times higher than that of the zinc oxide desulfurizer, and its penetration space velocity is two times higher than that of the zinc oxide desulfurizer,
It will decrease because sulfur will precipitate with many metal ions