Ammonia generation from coal

Whereas near-term appHcation of coal gasification is expected to be in the production of electricity through combined cycle power generation systems, longer term appHcations show considerable potential for producing chemicals from coal using syngas chemistry (45). Products could include ammonia, methanol, synthetic natural gas, and conventional transportation fuels. 

In the water-gas process, hydrogen and carbon monoxide are generated from the reaction between steam and high-temperature coke in a two-step process. In the first step, the coal bed is heated to about 1300 °C with upward blown air. The reactant gas is then switched to steam, creating the syngas and cooling the coal bed. To make optimum use of the heat in the system, steam is blown first upward then downward. When the bed temperature drops to about 900 °C, the steam is stopped and the next cycle is started. The product from the water-gas process can be used for ammonia or methanol synthesis. 

Modem production methods of ammonia are very efficient, even from coal, and the existing production process involves inherent CO2 separation, enabling CO2 sequestration to be employed without additional CO2 scmbbing. Hansen et al. (2010) have studied the potential well-to-power efficiency of electricity generation using an NH3-fuelled SOFC plant from various feedstocks, and fourtd the overall efficiency of an energy chain with CO2 sequestration, even from coal feedstock, could be as high as 40%. 

Sustainably generated hydrogen has many uses in chemical synthesis and in synthetic fuels manufacture. In addition to its applications in fuel cells, it can be burned directly in gas turbines and internal combustion engines. It is the fuel of choice for fuel cells and, combined chanically with N2 from air, it is used to make ammonia for fertilizer and synthetic nitrogen compounds. It is a key feedstock for processes to convert biomass materials, such as sugars, to useful synthetic chemicals. And elemental H2 is a key ingredient in making synthetic fnels from coal, biomass, and even CO2. 

The combination of chemical and fuel production results in a type of synergism that can benefit the economics of both end products. Thus, some chemicals that cannot be produced economically as primary products from coal may be obtained as revenue-generating coproducts that enhance the overall economics of fuel production. This concept has prompted efforts at Great Plains and Sasol to increase the recovery of chemical by-products from these facilities. At Great Plains, ammonia and sulfur now are recovered, but facilities are... 

As world deposits of petroleum and coal are exhausted, new sources of hydrogen will have to be developed for use as a fuel and in the production of ammonia for fertilizer. At present, most hydrogen gas is produced from hydrocarbons, but hydrogen gas can also be generated by the electrolysis of water. Figure 19-23 shows an electrolytic cell set up to decompose water. Two platinum electrodes are dipped in a dilute solution of sulfuric acid. The cell requires just one compartment because hydrogen and oxygen escape from the cell much more rapidly than they react with each other. 

A minor part of mined fossil fuels is used as a raw material for the chemical industry (e.g., plastics, synthetic fabrics, carbon black, ammonia, and fertilizers). The major part supplies the energy needs for modem society. Fossil fuels supply about 86% of global primary energy consumption (39% oil, 24% coal, and 23% natural gas), providing energy for transportation, electricity generation, and industrial, commercial, and residential uses (El A 2001). Coal, and to a lesser extent oil, combustion leaves a significant amount of solid waste. The treatment of solid waste from fossil fuel combustion is treated in different chapters of this book. In this chapter we focus on air emissions of fossil fuel combustion, and their impact on human health and the environment. 

The fluid-bed combustion method (2) has been chosen, however, for process development in the regeneration of spent melts from the hydrocracking of coal. In this method, from one to two parts by weight of spent melt is generated for each part of coal fed to the hydrocracking process. The carbonaceous residue, sulfur, and ammonia retained in the melt are burned out with air in a fluidized bed of inert solids. The zinc chloride is simultaneously vaporized, the ash separated from the overhead vapors, and the zinc chloride vapor is condensed as pure liquid for return to the process. 

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. 

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