Modeling of a Two-Flow Gas Purification From Carbon Oxides (IV) by Methyldiethanolamine Solution

The object of research is the stage of purification of process gas of ammonia production with a capacity of 1360–1500 t/day in a two-section plate absorber. The paper substantiates the possibility to replace the monoethanolamine (MEA) absorbent solution with the activated solution of methyl diethanolamine (aMDEA) on the example of the Ukrainian multi-tonnage production, working under the two-flow purification scheme. One of the most problematic areas is the lack of a mathematical model for the absorption of carbon monoxide (IV) by a new absorbent for two-flow purification schemes. In the course of the study, the method of compiling the material balance was used, which takes into account the peculiarities of the interaction of the aMDEA components with CO2, and numerical integration to calculate the number of plates.

An algorithm for calculating material and heat balances for finely and roughly regenerated solutions has been developed and implemented in Excel. The algorithm and the program provide for multivariate calculations with varying concentration parameters for gas and solution and their temperature. Thermal calculations take into account the adiabatic heating due to the exothermic absorption reaction and determine the temperature of the solutions at the outlet of each part of the absorber. Analysis of the material balance calculations in comparison with the data on the MEA solution shows a decrease in the solution consumption by 5.5 % when using aMDEA, which will help to reduce the energy costs for pumping and regeneration. By kinetic calculation, the number of plates for the absorber was determined to be 13. With the number of 15 in a standard absorber, the calculated number of plates allows the gas to be purified to a content of 0.01 % CO2. An increase in the temperature of the solutions at the inlet to both sections by 10 degrees does not significantly affect the number of plates. Thus, mathematical modeling of a two-section plate absorber showed a real possibility of replacing an 18 % MEA solution with a 40 % aMDEA solution. It is proposed to implement this on existing equipment without changing the technological scheme.