Fuel requirements, ammonia plant

High temperature steam reforming of natural gas accounts for 97% of the hydrogen used for ammonia synthesis in the United States. Hydrogen requirement for ammonia synthesis is about 336 m /t of ammonia produced for a typical 1000 t/d ammonia plant. The near-term demand for ammonia remains stagnant. Methanol production requires 560 m of hydrogen for each ton produced, based on a 2500-t/d methanol plant. Methanol demand is expected to increase in response to an increased use of the fuel—oxygenate methyl /-butyl ether (MTBE). 

Current Ammonia Plant Feed And Fuel Requirements... 

Their thermal efficiency is not very different and in a top-fired furnace can be as high as 95 %. The enthalpy difference between inlet and exit, often referred to as reformer duty, is made up of the heat required to raise the temperature to the level at the tube exit and the enthalpy of the reforming reaction. In a typical tubular steam reforming furnace, about 50% of the heat generated by combustion of fuel in the burners is transferred through the reformer tube walls and absorbed by the process gas (in a conventional ammonia plant primary reformer 60 % for reaction, 40% for temperature increase). 

In nearly all ammonia plants the same material is used as both feedstock and fuel. The fuel requirements may be 40% of the total or mcwe, depending on the ext t to which heat recovery equipment is used. In previous years when fuel was inexpensive, many ammonia plante were built with minimum heat recovery facilities. Buividas et al. give an example of how the fuel requirement (natural gas) was decreased by 34% through more efficient energy use, which primarily included high-pressure steam generation and preheating combustion air to the reformers I7I, The decrease in total fuel plus feedstock reqiure-ment was about 15%. The increase in fuel efficiency was obtained at the expense of about 6% increase in plant investment costs. Table 6.8 shows the requirements for fuel plus feedstock that assume efficient heat recovery. 

In a natural gas-based plant 20%-30% of the gas is used for fuel and the balance for feedstock. The lower fuel values are for plants equipped with good energy-recovery systems. Fuel requirements do not include electric power generation or steam generation other than that connected with heat recovery. Modern ammonia... 

The low-temperature fuel cells (PEMFC and PAFC) require pure hydrogen, as carbon monoxide is a poison to the platinum anode. A PSA unit as used in large-scale hydrogen plants (Figure 2.4) carmot be used at the small scale in question, and the final purifrcation is made either by methanation (as used in ammonia plants, Section 2.5) or by preferential partial oxidation (PROX) of carbon monoxide to carbon dioxide over a... 

Site-Specific Condderations. The proper specification of an SCR system requires consideration of site specific information. This information includes type of fuel, flue gas flow rate and temperature, initial NO, concentrations, ash quantity and characteristics, SO2 and SO3 concentrations in the flue gas, water vapor concentration, excess oxygen concentration, plant mode of opieration, emission compliance requirements, catalyst life requirements, ammonia slip requirements, and data on the existing equipment in the flue gas train. 

Economics Simplification over conventional processes gives important savings such as investment, catalyst-replacement costs, maintenance costs, etc. Total feed requirement (process feed plus fuel) is approximately 7 Gcal/metric ton (mt) ammonia (25.2 MMBtu/short ton) depending on plant design and location. 

The capital cost and the specific energy requirement (i.e., feed and fuel, and so the manufacturing cost) largely depend on the raw material employed [411], [412], Table 22 shows the relative capital cost and the relative energy requirement for a plant with a capacity of 1800 t/d ammonia. For the natural gas based plant the current best value of 28 GJ/t NH3 is used. 

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