What is hydrogen recovery technology in the ammonia process?

Hydrogen is recovered from the synthesis off-gas and returned to the ammonia synthesis system to increase production or reduce consumption. Hydrogen recovery methods commonly used at present include variable pressure adsorption, membrane separation and deep cooling separation. Variable pressure adsorption method is characterised by high product purity, high recovery rate, low operating costs, the disadvantage is that the valve is frequently switched, so the performance of the valve, the level of self-control and high reliability requirements.

Membrane separation method and hollow fibre separation technology is characterized by investment, low operating costs, product recovery and pressure adsorption method is comparable, but the product purity is not as high as pressure adsorption.

Deep cooling separation method is based on the differences in the condensation and liquefaction temperature of the components of the gas mixture and the gas mixture is cooled to a certain temperature, so that the condensation temperature is higher than the temperature of the gas liquefaction to achieve the purpose of separation, which is characterised by a high recovery rate, but the investment is large.

Three methods in China have examples, the Southwest Chemical Industry Research Institute developed pressure adsorption and the Chinese Academy of Sciences Dalian Institute of Physical and Chemical Technology developed membrane separation technology, have been widely used in China, deep cooling separation device can also be produced in China, but only for small plant examples, the three comparisons are shown in the table below.

From the above analysis, it can be seen that both variable pressure adsorption and membrane separation can be considered as options for saving investment, operational reliability and land use.