Indirect Cooling

Ammonia synthesis reactors differ in the method used to recover the reaction heat and control the temperature of the reactants. There are two methods used; the quenching and the indirect cooling methods. 

In the quenching method (direct cooling), a part of the recycle gas enters the first catalyst bed at about 400oC and exits at 500oC. The gas temperature is then lowered (quenched) prior to its entrance into the following catalyst beds, by the insertion of a cooler (150-200oC) recycle gas (cold shot) (UNIDO, 1979 p.173). The introduction of the cooling gas lowers the ammonia concentrations and decreases the temperatures at the exit of the reactor. 

In the indirect cooling method, heat exchangers are used to cool the gas and recover heat out of each catalyst bed. The heat recovered can then be used to produce high-pressure steam, preheat the boiler feed-water and even heat the incoming syngas to the desired inlet temperature. Reactors employing the indirect cooling method have lower energy requirements than reactors employing the quenching method (ECCJ, 1999, p.149)

Other possible benefits from adopting the indirect cooling method are higher conversion rate per pass and lower requirements in catalyst volumes (IPTS/EC, 2007 p.84).

This measure is applicable for all feedstocks and for both retrofit and new plants.

Development Status Products

Indirect CoolingCosts & Benefits

Parent Process: Ammonia Synthesis
Energy Savings Potential
CO2 Emission Reduction Potential

The investment cost for a 300,000 tonne per year reactor is 150 million yen, and the payback period is 1.5 years (1999 figures) (ECCJ, 1999, p. 149).

Indirect CoolingSchematic

Indirect Cooling Publications

Directory of Energy Conservation Technology in Japan - Section 3: Chemical Industry

Prepared by New Energy and Industrial Technology Development Organization and the Energy Conservation Center, Japan, this extensive directory covers an extensive list of energy saving measures applicable to diverse range of industries. Section 3 concentrates on measures applicable to chemical industry, including ammonia production.

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Indirect Cooling Reference Documents

Reference Document on Best Available Techniques for the Manufacture of Large Volume Inorganic Chemicals - Ammonia, Acids and Fertilisers

Prepared by the Institute for Prospective Technical Studies of European Commision, this document provides detalied information on Best Available Technologies applicable to Ammonia production – as well as on the production of Acids and Fertilizers.  

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