Ammonia primary pollutant

The primary pollution problem in nitric add manufacture is the abatement of nitrogen oxides (NOx) in tail gases. In the United States in 1998, gaseous emissions from newly constructed nitric add plants must be limited to 1.5 kilograms of NOx per tonne of nitric add (100% basis) produced, with a maximum stack opacity of 10%. Modern add towers, with extended sections, can reduce NOx emissions to less than 200 parts per million35. Production of ammonia also involves the combustion of hydrocarbons so NOx abatement must also be addressed for this product as well. 

Emissions to the atmosphere from ammonia plants include sulfur dioxide (SOj), nitrogen oxides (NOJ, carbon monoxide (CO), carbon dioxide (COj), hydrogen sulfide (HjS), volatile organic compounds (VOCs), particulate matter, methane, hydrogen cyanide, and ammonia. The two primary sources of pollutants, with typical reported values, in kilograms per ton (kg/t) for the important pollutants, are as follows ... 

Not all catalysts need the extended smface provided by a porous structure, however. Some are sufficiently active so that the effort required to create a porous catalyst would be wasted. For such situations one type of catalyst is the monolithic catalyst. Monolithic catalysts are normally encountered in processes where pressure drop and heat removal are major considerations. Typical examples include the platinum gauze reactor used in the ammonia oxidation portion of nitric acid manufacture and catalytic converters used to oxidize pollutants in automobile exhaust. They can be porous (honeycomb) or non-porous (wire gauze). A photograph of a automotive catalytic converter is shown in Figure CD 11-2. Platinum is a primary catalytic material in the monolith. 

In the atmosphere, ammonia is estimated to have a half-life of several days. The primary fate process is reaction of ammonia with acid air pollutants and removal of the resulting ammonium compounds by dry or wet deposition. Rain washout and reaction with photochemically produced hydroxyl radicals are also expected to contribute to the atmospheric fate of vapor-phase ammonia. In water and soil, ammonia will volatilize to the atmosphere and be removed by microbial processes, by adsorption to sediment and soil matrices as well as by plant uptake. 

The profitability of this process is highly dependent on energy cost and capital investment. Energy and capital cost penalties associated with pollution control systems must therefore be minimized as far as practicable. The first step is to reduce the sulfur concentration in the ammonia plant feedstock to less than 0.1 ppmv to prevent poisoning the reformer catalyst. Once desulfurized, the feedstock is partially reacted with steam in a primary reformer to... 

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