Synthesis single-train plants

Application To produce ammonia from natural gas, LNG, LPG or naphtha. Other hydrocarbons—coal, oil, residues or methanol purge gas— are possible feedstocks with an adapted front-end. The process uses conventional steam reforming synthesis gas generation (front-end) and a medium-pressure (MP) ammonia synthesis loop. It is optimized with respect to low energy consumption and maximum reliability. The largest single-train plant built by Uhde with a conventional synthesis has a nameplate capacity of 2,000 metric tons per day (mtpd). For higher capacities refer to Uhde Dual Pressure Process. 

Fig. 1.4-1. Flow chart of a single-train plant for the synthesis of ammonia using the Steam-...

Steam-Reforming Natural Gas. Natural gas is the single most common raw material for the manufacture of ammonia. A typical flow sheet for a high capacity single-train ammonia plant is iadicated ia Figure 12. The important process steps are feedstock purification, primary and secondary reforming, shift conversion, carbon dioxide removal, synthesis gas purification, ammonia synthesis, and recovery. 

The hydrogen-to-carbon monoxide mole ratio for the product gas is usually 4 to 9 however, it can be increased if additional steam is used in the reaction. This will reduce the demand in the carbon monoxide-shift converters, which follow the secondary reformer. Steam sometimes is introduced after the reformer before the gas is fed to the carbon monoxide-shift converters. In the single-train ammonia plants, the natural gas is reformed in two steps. In the first step, the reaction takes place in the primary reformer in tubes suspended in a refractory-lined furnace. The large amount of endothermic heat is supplied by burning natural gas with air in the furnace. The heat flux in the tubes can be as high as 35,000 Btu/hr sq ft. The methane leakage is about 10 percent in the effluent dry gas, or about 60 to 65 percent of the feed methane is converted to synthesis gas. 

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