What is syngas refining in the synthesis ammonia process?

The feed gas after shift and desulfurization and decarburization contains small amounts of impurities such as CO and CO2. In order to prevent them from damaging the synthesis catalyst, a final purification process, called refining, is required before the raw gas is sent to the synthesis section. After purification, the carbon content is less than 10 ppm.

For the purification of trace CO and C02 in the ammonia fresh gas, most of the small and medium-sized nitrogen fertilizer enterprises in China still use the traditional "copper washing" purification process, which is basically not used in the new ammonia synthesis system due to the disadvantages of high operation cost, unstable operation and easy to cause environmental pollution, etc. Another purification method is CO depth purification, which is the most effective way to purify the ammonia. Another purification method is CO depth conversion - methanation process, the process can ensure that the purity of the synthetic fresh gas, the operation is relatively stable, but its shortcomings are also more obvious, the conversion section of the steam consumption is large (low change of the CO content of the exit in 0.3% or so), the decarbonization system requires a high degree of purification (decarbonization of the exit of the CO2 content of 0.2% or so); the synthesis of the fresh gas of the CH4 content is high, the synthesis of ammonia High CH4 content in synthesized fresh gas, high volume of air release in synthesized ammonia section, and increased fresh gas consumption. At present, China's representative ammonia feedstock gas refining processes are alcohol alkylation process and alcohol alkylation refining process. Alcohol alkylation refining process is an upgraded technology of bimethanol refining process, and the hydrocarbon catalyst is a kind of iron catalyst, in which carbon monoxide and carbon dioxide react with hydrogen to form hydrocarbon compounds, which are condensed into liquid at room temperature, and the methane generated is very little, and the methane entering the ammonia synthesis system is greatly reduced. Alcohol alkylation process is the organic combination of the process and methanation purification process, so that the conversion and decarbonization system outlet of the harmful components of the ammonia synthesis feedstock gas, such as CO and CO2, react with hydrogen to generate a higher value of methanol, into the alkylation catalyst gas in the CO and CO2 of 50 ~ 200 PPm, ammonia feedstock gas CH4 basically did not increase. Alcohol alkylation refining purification process, is the use of methanolization reaction will be in the raw gas CO, CO2 under the action of the catalyst and H2 reaction to generate methanol. The CO+CO2 of the methanolization outlet is controlled at about 0.3~0.5%, and then the post-alcohol gas enters into the hydrocarbonization reactor, where a small amount of CO+CO2 in the gas reacts with H2 to generate alcohols and hydrocarbons and a small amount of methane under the action of the catalyst, respectively. The CO+CO2 in the hydrocarbonization outlet gas is <10ppm and sent to the synthesis process.

International and domestic large-scale ammonia synthesis plant is mostly used in low-temperature liquid nitrogen wash process, the process is a typical physical low-temperature absorption process, is the best way to remove CO. At the same time, the process can remove all the impurities in the gas, such as methane, liquid nitrogen cleaning gas is almost pure hydrogen and nitrogen, synthesis section without the need to discharge air, the disadvantage of high investment.