FORMATION OF IMPURITIES IN SYNTHESIS GAS AT STAGE OF CONVERSION OF CARBON MONOXIDE TO HYDROGEN IN AMMONIA PRODUCTION

Abstract

The article analyzes the work of the department for the conversion of carbon monoxide with water vapor to hydrogen as part of the ammonia synthesis unit. The effect of temperature and duration of operation of the medium-temperature conversion catalyst on the technical and technological parameters of the process is shown. The catalytic conversion of carbon monoxide is an important component of the hydrogen production process in the industrial technology of deep processing of natural gas. In modern ammonia synthesis units, the conversion process takes place in two stages: first, at a temperature of 360 – 430 °C on iron-chromium, and then at 190 – 260 °C on a copper-containing catalyst. It was found that along with the main products (H2, CO2), the presence of undesirable impurities of ammonia, amines, alcohols, acetates and formates was detected in the synthesis gas. It is shown that the main by-product at the stage of medium-temperature conversion is ammonia, the content of which in the condensate reaches 80-85%. Methanol is formed as a by-product both at the stage of medium-temperature (9-13%) and low-temperature conversion (87-91%). Most of the methanol generated during the conversion process is condensed with water in separators, while the rest goes to the CO2 removal system. In the separator, where the temperature is 160-162 °C, on average 68% of methanol remains in the gas phase, and in the separator, where deeper gas cooling is applied to 72 °C, about 81% of methanol remains in the condensate. To decrease the methanol content, it is necessary to lower the conversion temperature and increase the gas space velocity. Under the conditions of ammonia production from methanol and ammonia, a mixture of amines of varying degrees of substitution is formed, predominantly methylamine (CH3)NH2 and demytylamine (CH3)2NH2. Moreover, about 35-40% of the formed amines goes into condensate, and most of it remains in the gas phase and goes to the stage of cleaning from CO2. In the production of ammonia, solutions based on potash - K2CO3 are used to clean the converted gas from CO2, which absorb organic impurities, which are formed mainly at the stage of low-temperature conversion. Impurities impair the operation of the purification stage and cause foaming of solutions. One of the reasons for foaming is the presence of organic matter degradation products in the solution.