Nitric plant types

Ammonia from coal gasification has been used for fertilizer production at Sasol since the beginning of operations in 1955. In 1964 a dedicated coal-based ammonia synthesis plant was brought on stream. This plant has now been deactivated, and is being replaced with a new faciUty with three times the production capacity. Nitric acid is produced by oxidation and is converted with additional ammonia into ammonium nitrate fertilizers. The products are marketed either as a Hquid or in a soHd form known as Limestone Ammonium Nitrate. Also, two types of explosives are produced from ammonium nitrate. The first is a mixture of fuel oil and porous ammonium nitrate granules. The second type is produced by emulsifying small droplets of ammonium nitrate solution in oil. 

Nonetheless, production and use of nitric phosphates ia Europe are continuing to grow. In general, nitric phosphate processes are somewhat more compHcated than sulfur-based processes and requite higher investment. In the past, several attempts have been made to estabHsh commercial acceptance of this type process ia the United States, but plant operations have been relatively short Hved because of low sulfur prices and resultant competition from sulfur-based processes. 

Figure 3.14. Connections of a nitric add plant, intermediate pressure type...

While vanadia- on titania-based catalysts can be used for both the classes of applications, there are other types of catalysts such as those based on copper [31b], which show good performances in case of mixtures of N0/N02 (nitric acid plants), while performances are worse when applied to emissions from catalytic processes. 

Although often it is considered that a single reaction mechanism occurs in the selective reduction of NO by ammonia, data show that instead different mechanisms are possible and that too depending on the type of catalyst and reaction conditions (feed composition, reaction temperature) - one mechanism may prevail over the others [31b], However, not considering this aspect and making extrapolation regarding the reaction mechanism from one catalyst to another or to different reaction conditions may lead to erroneous conclusions. In addition, it is important to consider all possible opportunities to develop new kinds of catalysts, for example, for the combined removal of NO and N20 from nitric acid plant emissions [25],... 

Other metal oxide catalysts studied for the SCR-NH3 reaction include iron, copper, chromium and manganese oxides supported on various oxides, introduced into zeolite cavities or added to pillared-type clays. Copper catalysts and copper-nickel catalysts, in particular, show some advantages when NO—N02 mixtures are present in the feed and S02 is absent [31b], such as in the case of nitric acid plant tail emissions. The mechanism of NO reduction over copper- and manganese-based catalysts is different from that over vanadia—titania based catalysts. Scheme 1.1 reports the proposed mechanism of SCR-NH3 over Cu-alumina catalysts [31b],... 

PuraSiv N A process for removing nitrogen oxides from the tail gases from nitric acid plants, using an acid-resistant zeolite molecular sieve. Developed by the Union Carbide Corporation in 1971. Not to be confused with PuraSiv HR, Type N (see previous entry). 

In a plant of this type nitric arid of about 90% and sulphuric acid of 70% are obtained. In the absorption towers nitric acid of 30-60% is produced. 

Biocorrosion in well-oxygenated cooling systems can also involve other types of bacteria, such as nitrifying bacteria, which are commonly found where ammonia is present (say from refinery or fertilizer plant leaks). They are principally aerobic and oxidize ammonia to nitrate, causing serious local falls in pH that result in nitric acid corrosion. Examples are Nitrosomonas sp. and Nitrobacter sp. 

A TANK is required to store the one week production capacity from the nitric acid plant. This storage buffer allows the plant to continue operation for up to one week in the event of an unforeseen shutdown in the adjacent ammonium nitrate plant. The tank is a fixed cone-roof cylindrical-type design,... 

A storage tank for product nitric acid is a necessity on this plant. The tank should have the capacity to store one week of full acid production to allow for continued supply in the event of unscheduled shutdowns in the adjacent ammonium nitrate plant. This requires a minimum tank capacity of 1500 m3. However, it is recommended to increase the tank capacity so that an inventory of 450 m3 of product acid is always available within the tank for outside sales. This extra volume is equivalent to 20 standard road-tanker loads. The tank must be constructed of stainless steel type 304L ( nitric acid grade ), the specification of this material is given in Appendix D. The design data required for this unit are specified below. 

All nitric acid plants are based on the same basic chemical operations 1) Oxidation of ammonia with air to give nitric oxide, 2) Oxidation of the nitric oxide to nitrogen dioxide and 3) Absorption in water to give a solution of nitric acid. The efficiency of the first step is favored by low pressure whereas that of the second step is favored by high pressure. These considerations, combined with economic reasons give rise to two types of nitric acid plants - single pressure and dual pressure97. 

The main unit operations in nitric acid plants are the same for all types of operating pressures. These steps are97 1) Ammonia Evaporation, 2) Ammonia Filtration, 3) Air Filtration, 4) Air Compression, 5) Air/Ammonia Mixing, 6)... 

The capital cost of an integrated SCR unit for a new 1,000 tonne/day plant is estimated to be 1.5% of the total capital cost of the nitric acid plant. This cost includes the cost of the SCR catalyst but excludes spare parts. The capital cost of an end-of-pipe SCR unit for an existing 1,000 tonne/day plant is estimated to be 3% to 6% of the total capital cost of the nitric acid plant. But this is very dependent on the type of nitric acid process. The SCR will increase operating costs by 1.1% when NOx in the tail gas is reduced from 1,000 ppmv to 200 ppmv. The maintenance cost of the SCR unit is typically 2.5% of the capital cost97. 

As discussed above the preferred technology for NOx removal in nitric add plants is selective catalytic reduction (SCR) using ammonia as a reductant and in many cases vanadium-pentoxide-type catalysts. Unfortunately, this process does not remove of N2O (nitrous oxide)221. 

Nitric Phosphate. Fertilizers that are referred to as nitric phosphate or nitrophos-phate are produced by acidulation of phosphate rock with nitric acid or with mixtures of nitric and sulfuric or phosphoric acids. The primary advantage of nitric phosphate processes is that no sulfur or less sulfur is required as compared with superphosphates or ammonium phosphates this is particularly important during a shortage of sulfur, or in locations where sulfur must be shipped long distances. A variety of processes and equipment have been used in Europe since the late 1930s.3,12 Also there are a number of plants in Central and South America and in Asia. The production of nitric phosphates is complex. Simple substitution of nitric acid in a superphosphate-type acid-rock reaction is not feasible because (1) decomposition of the nitric acid would occur and cause noxious fumes and loss of nitrogen and (2) the product would be extremely hygroscopic and unstable. 

Typically foods, feedstuffs, leaves, plants, biological solids, tissue, polymers, etc. Prior to solubilisation these types of sample generally require destruction via wet digestion or ashing in a muffle furnace. A typical procedure featuring a nitric/perchloric acid mixture is reproduced below. 

A few classicaV studies on the reactivity of HCs to reduce NOx with catalysts indicated that the use of such reductants for controlling mobile NOx emissions was quite attractive to the automotive industry, thereby the advent of a new type of HC-SCR technology in the mid-1980s. An example may be the treatment process of the tail gas from nitric acid production plant via ammonia oxida-tion. The process includes the usual injection of excessive amounts of HCs over supported noble metals such as Pt, Pd and Rh to eliminate the yellowish stack plume due to 0.1 - 0.5% NOx, mainly NO2, from the nitric acid plant. 

The current tendency in the nitric acid industry is to ever larger plants (capacities up to 1500 t of 100% HNO /d) and to ever higher pressures both in the combustion and in the absorption stages to solve emission and other problems. The developments in the USA and in Western Europe are somewhat different 90% of the plants in the USA being monopressure/high pressure plants (H/H-type), whereas in Western Europe many plants operate in the medium pressure and medium/high pressure ranges (M/M-types and M/H-types respectively). 

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