Process for preparing substitute natural gas from synthesis gas

Abstract

The invention relates to a process for preparing substitute natural gas from synthesis gas, which comprises the following steps that: after being subjected to detoxification and desulfuration, the raw materials are subjected to heat exchange and are mixed with recycle gas from a third methanator and the obtained mixture is divided into two strands, wherein the first strand enters a first methanator to be subjected to the methanation reaction; all high-temperature first synthesis gas obtained after the first strand of raw material gas reacts in the first methanator is sequentially fed into a steam superheater and a first waste heat boiler to be subjected to heat exchange and then is fed into a second methanator to be subjected to the further methanation reaction to obtain second synthesis gas; after being subjected to heat exchange, the second synthesis gas is mixed with the second strand of raw material gas, and then the mixture is fed into the third methanator; and third synthesis gas discharged out of the third methanator is divided into two strands after being subjected to heat exchange compression, one strand of the third synthesis gas serving as the recycle gas is mixed with the raw material gas, the rest of the third synthesis gas enters a fourth methanator to enable the unreacted raw material gas to be synthesized into methane so as to obtain the synthesis gas capable of replacing the natural gas. The process has the characteristics that the reaction temperature rise is easy to control; the utilization of system energy is optimized; and the like.

Description

technical field [0001] The invention relates to a chemical process, in particular to a process for producing substitute natural gas from synthetic gas. Background technique [0002] The development of high-temperature methanation technology can be traced back to the 1970s. Due to the oil crisis, the United States, Britain and other countries began to study the application of alternative energy sources, including the technology research and development of coal-based high calorific value city gas and alternative natural gas. In 1984, the world's first and only commercial coal-to-natural gas plant put into operation was built. In 1978, a Danish company also built a 7200m 3 / d's synthetic natural gas pilot plant, which has been tested for 3 years. In addition, there are many plants in Europe that use similar technology to produce city gas. Since the 1980s, my country has started the research on gas methanation, but it is mainly the partial methanation of water gas to produce ...

AI Technical Summary

Problems solved by technology

The former puts the superheater behind, resulting in insufficient steam superheat, or can only produce superheated medium-pressure steam by-product, resulting in the high-temperature waste heat of the process gas cannot be well utilized, and the process flow setting is not reasonable

In the latter, since the superheater is placed in front, and the outlet temperature of the first reactor is generally 620-670°C, the manufacturing of the steam superheater is difficult and costly

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