Ammonia Process Flow Diagram

Figure 4. Compressors with interstage cooling. (Used with permission of Simulation Sciences Inc.)

excess of 21 bar are required to achieve sufficient conversion. Conversions of 20%-25% ammonia per pass are achieved. However, the conversion of hydrogen per pass is still less than 30%, therefore, the process requires a large recycle of unreacted gases. The converted vapor product is cooled by ammonia refrigeration in the primary separator to condense the ammonia product. A purge is removed from the remaining gases to prevent the buildup up of inerts (in particular, CH4 and Ar) in the synthesis reactor. Figure 5 shows the process flow diagram of the conversion and Figure 6 illustrates the complete ammonia plant process flow diagram.

Recently, the price of ammonia has nearly doubled as global supplies have been tightened and are now in line with the demands. Ammonia process licensors are employing new technologies that can be retrofitted to existing plants to increase the capacity by 20%-40% [3]. A wide range of newer more reactive catalysts are now replacing the iron-based catalysts. These catalysts are found to be advantageous in operating at lower synthesis pressures. Iron-titanium metals, rutheniumalkali metals, or ruthenium promoted by potassium and barium on activated carbon have exhibited high efficiency. The raw material hydrogen must be free from the oxides of carbon, which degrade the catalyst activity. Additionally, phosphorus, sulfur, and arsenic compounds tend to poison the catalyst in the subsequent reaction.

Free Process Flow Diagrams
Figure 5. Process flow diagram of the conversion unit. (Used with permission of Simulation Sciences Inc.)
Flow Diagram Ammonia Plant
Figure 6. A complete ammonia plant process flow diagram. (Used with permission of Simulation Sciences Inc.)

M. W. Kellogg has developed a new technology in the synthesis of ammonia. They employ a ruthenium on graphite as the catalyst on Kellogg Advanced Ammonia Process (KAAP). The process is the first to employ a non-iron based catalyst and was co-developed with British Petroleum Ventures. The KAAP has been commercialized since 1994, and has been used in an increasing number of projects.

Process technology licensors have developed alternative techniques to the primary and secondary reformer processes. These technologies integrate process units with steam and power systems, thereby using heat exchange networks to capture waste heat. Additionally, they provide the energy required for reforming methane. M.W. Kellogg has employed a system where the desulfurized natural gas and steam are first divided into two streams and heated. The mixed feed is then fed to a tubular reforming exchanger and an autothermal reformer. Enriched air at 600°C is then passed to the autothermal reformer and the effluent at 1,000°C flows to the shell side of the reforming heat exchanger. In the autothermal reformer, which contains conventional secondary

Kellogg Ammonia Process Flow Diagram
Figure 7. Kellogg's new ruthenium-catalyst based advanced ammonia process combined with the reforming exchange system. (Used with permission of Chemical Engineering.)
Ammonia Reactor Bed Diagram

Figure 8. Designs of ammonia synthesis converters (a) Principle of the autothermal ammonia synthesis reactor; (b) Radial flow converter with capacities of 1,800 tpd; (c) Horizontal three-bed converter and detail of the catalyst cartridge. (Source: Walas, M. S., Chemical Process Equipment, Selection and Design, Butterworth Series in Chemical Engineering, 1988.)

Figure 8. Designs of ammonia synthesis converters (a) Principle of the autothermal ammonia synthesis reactor; (b) Radial flow converter with capacities of 1,800 tpd; (c) Horizontal three-bed converter and detail of the catalyst cartridge. (Source: Walas, M. S., Chemical Process Equipment, Selection and Design, Butterworth Series in Chemical Engineering, 1988.)

reforming catalyst, the feed gas is partially oxidized. The mixed stream is then sent to the reforming exchanger consisting of tubes filled with catalysts. This is designed to minimize the buildup of pressure and to expand separately without any constraint. Finally, the heat for reforming comes from an autothermal reformer effluent. Figure 7 shows the designs features in an integrated system. Figure 8 shows a selection of ammonia reactors.

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Responses

  • mari
    What is the % conversion of ammonia on ruthenium catalysts for kaap plants?
    6 years ago
  • Saku
    What is an ammonia converter reactor?
    5 years ago

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