Nitric Acid absorption abatement

Process Licensors. Some of the well-known nitric acid technology licensors are fisted in Table 3. Espindesa, Grande Paroisse, Humphreys and Glasgow, Rhfyne Poulenc, Uhde, and Weatherly are all reported to be licensors of weak acid technology. Most weak acid plant licensors offer extended absorption for NO abatement. Espindesa, Rhfyne Poulenc, Weatherly, and Uhde are also reported (53,57) to offer selective catalytic reduction (SCR) technology. 

The primary pollution problem in nitric acid plants is the abatement of NOx in tail gases. Three options exist to reduce these emissions to acceptable levels 1) Capture the NOx and convert it to additional nitric acid, 2) Capture the NOx and convert it to nitrate-nitrite sales, or 3) Render the NOx harmless by converting it to non-polluting compounds. The processes that have been developed to reduce emissions at existing and new plants can be classified into four general categories Absorption, Adsorption, Selective Catalytic Reduction (SCR) and Non-Selective Catalytic Reduction91. 

In an economic comparison of abatement systems, a 1991 EPA study indicates that extended absorption to be the most cost-effective method for NOx removal. Selective Reduction matches its performance only in small-capacity plants of about 200 to 250 tonnes per day. Nonselective abatement systems were indicated to be the least cost-effective method of abatement. The results of any comparison depend on the cost of capital versus variable operating costs. A low capital cost for SCR is offset by the ammonia required to remove the NOx. Higher tail gas NOx concentrations make this method less attractive. The investment for extended absorption is partially recovered by increased yield of nitric acid product104. 

Absorption Abatement or extended absorption refers to modifications that involve the addition of increased absorption capacity or optimization of the existing absorption system to oxidize and react the nitrogen oxides with water to form acid.. Tail gases are passed through an absorber containing either water or an aqueous solution of ammonia, urea or sodium hydroxide. When water is used as the absorbent, the resultant weak acid is recycled. This increases nitric acid yields by 1% to 3%. When other absorbents are used, the recovered NOx is typically consumed in the production of nitrogen solutions for fertilizer use. If sodium hydroxide is the absorbent, pure sodium nitrite and sodium nitrate may be recovered91,104. 

The cost of NOx pollution abatement depends on the efficiency of the original absorption system estimated costs for a 365-tpd nitric acid unit are given in Table 19.4 [191. 

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