Full-temperature-range simulated rotating moving bed pressure swing adsorption process for extracting H2 and NH3 from synthetic ammonia purge gas

Abstract

The invention discloses a full-temperature-range simulated rotating moving bed pressure swing adsorption (FTrSRMPSA) process for extracting H2 and NH3 from synthetic ammonia purge gas. The middle-high temperature pressure swing adsorption ammonia concentration system and the middle gas pressure swing adsorption hydrogen extraction system are formed by a plurality of axial flow fixed bed adsorption towers and a rotating speed mechanism, wherein the axial flow fixed bed adsorption towers are arranged in the center of an upper multi-channel rotating valve and a lower multi-channel rotating valve, and are arranged on a circular ring-shaped rotating tray around the multi-channel rotating valve; gas flowing through a rotary valve channel, pipelines at the inlet and outlet ends of the adsorption towers and the adsorption bed layers can complete mass transfer of respective adsorption and desorption steps at the inlet and outlet positions of each adsorption tower and at each adsorption bed layer while rotating, so that a pressure swing adsorption process of simulating a rotary moving bed is formed; according to the invention, a simulated rotating moving bed pressure swing adsorption process on the basis of axial flow fixed bed pressure swing adsorption is realized, and H2 and NH3 products are obtained with high purity and high yield and are returned to a synthetic ammonia production process for recycling.

Description

technical field [0001] The invention relates to the field of recovery and reuse of synthetic ammonia purge gas, in particular to a method for extracting H from synthetic ammonia purge gas 2 with NH 3 The full temperature range of a rotary moving bed pressure swing adsorption process is simulated. Background technique [0002] During the production of synthetic ammonia, hydrogen (H 2 ) and nitrogen (N 2 ) under the action of high temperature and high pressure and catalyst to generate synthetic ammonia (NH 3 ), but the conversion rate of synthetic ammonia is only 1 / 3. In order to improve the yield of synthetic ammonia, the unreacted hydrogen-nitrogen mixture is returned to the synthetic ammonia production process as a circulating gas to continue to participate in the reaction. During the circulation process, some inert gas components such as argon (Ar), helium ( He), etc. will continue to accumulate resulting in the reaction gas hydrogen (H 2 ) and nitrogen (N 2 ) decre...

AI Technical Summary

Problems solved by technology

However, the traditional PSA separation method still has some significant defects: first, the size and fluctuation of the ammonia content in the purge gas seriously restricts the separation and extraction of H by PSA. 2 s efficiency

However, the RWPSA process also has obvious limitations and disadvantages: First, the diameter and height (thickness) of the adsorption wheel are relatively limited, resulting in an insufficient scale of adsorption treatment. This is because the RWPSA is essentially a moving bed, and similar cycle In the "steady state" mass transfer of these typical moving bed adsorption processes such as bed or fluidized bed, the axial mass transfer diffusion or radial mass transfer diffusion capacity must be limited, and thus cannot meet the requirements for the removal of ammonia or water to balance adsorption. Purification Requirements for Mechanism-Based Adsorbate Components

This feature is an advantage for the axial flow or radial flow fixed bed process; second, the manufacturing of the rotary PSA equipment is complicated, especially the equipment with equalization is more complicated, and the number of equalization is not more than 2 times. Therefore, it is not suitable for high-pressure purge gas PSA purification of H 2 Working conditions, because for the high-pressure purge gas, the pressure equalization two times makes the pressure change too large, which will cause the air flow in the adsorption tower to be too fast and bring out the solid adsorbent particles, which will cause the process control valve and regulating valve or Rotary valves bring erosion and wear, coupled with the influence of the rotational shear force of the adsorbent itself, the pulverization of the adsorbent particles will be quite serious, which will cause leakage and safety hazards in the corresponding rotary valves or control valves

At present, the rotary PSA equipment is mostly manufactured or monopolized by foreign companies, and the cost is relatively high; third, it is more suitable for the rapid adsorption and rapid desorption of a single adsorbate component, and the adsorption mechanism of the adsorbate component is mainly kinetic adsorption. working conditions, such as the purification of exhaust gas containing VOCs, etc.

For the deamination process based on equilibrium adsorption, the RWPSA process is not suitable, especially when the synthetic ammonia release gas contains more NH with strong polarity. 3 , CO 2 Impurity components such as water, hydrocarbons, etc. require a long enough mass transfer path for adsorption. The too short adsorbent bed height in the RWPSA process cannot fully absorb these impurity components, resulting in deamination and impurity removal not up to standard. At the same time, the adsorbent cannot form a composite bed filled with various adsorbents in a fixed bed for treatment, and is especially vulnerable to water droplets in the vent gas, high hydrocarbons and other easily polluted droplets such as compressors; Fourth, the adsorbent in the RWPSA is prone to throwing due to the existence of shear force when rotating, resulting in partial flow or short flow of the process gas in the adsorption bed, which greatly reduces the mass transfer efficiency and makes the adsorbent easier to absorb. Pulverization leads to shortened adsorbent life

In the rotary pressure swing adsorption method, regular adsorbents are also commonly used instead of granular granular adsorbents, which can reduce the alternating stress and loss of adsorbent particles, but for the deamination purification and purification of synthetic ammonia purge gas 2 For this type of regular adsorbent, especially composite structured adsorbent, there are few reports at home and abroad.

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