Nitric Acid abatement

NO Abatement. Source performance standards for nitric acid plants in the United States were introduced by the U.S. EPA in 1971 (55). These imposed a discharge limit of 1.5 kg of NO as equivalent nitrogen dioxide per 1000 kg of contained nitric acid, which corresponds to about 200—230... 

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. 

Adipic acid historically has been manufactured predominantly from cyclohexane and, to a lesser extent, phenol. During the 1970s and 1980s, however, much research has been directed to alternative feedstocks, especially butadiene and cyclohexene, as dictated by shifts in hydrocarbon markets. All current industrial processes use nitric acid in the final oxidation stage. Growing concern with air quality may exert further pressure for alternative routes as manufacturers seek to avoid NO, abatement costs, a necessary part of processes dial use nitric acid. 

J. Neiss, Particulate Removal from NOx Abatement Off-Gas in a Nitric Acid Plant , Ammonia P/ant Safety, Volume 21, pp.171-172, AlChE, New York (1979). 

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. 

Adsorption Abatement uses acid-resistant molecular sieves to absorb the NOx from the tail gas. The adsorbent is periodically regenerated and the NOx recovered, converted to NOj and recycled to the plant for recovery as nitric acid. The tail gas may also be mixed with a reducing agent (usually natural gas or ammonia) and passed through a catalyst to reduce the NOx to elemental nitrogen. When natural gas is used, conditions must be carefully controlled and facilities installed to control the heat released by natural gas that reacts with both the NOx and the oxygen91. 

The primary pollution problem in nitric acid manufacture is the abatement of nitrogen oxides (NOx) in tail gases. In the United States, gaseous emissions from newly constructed nitric acid plants must be limited to 1.5 kilograms of NOx per tonne of nitric acid (100% basis) produced, with a maximum stack opacity of 10 percent. Modem acid towers, with extended sections, can reduce NOx emissions to less than 200 parts per million. 5... 

Adsorption abatement uses acid-resistant molecular sieves to absorb the NOx from the tail gas. The adsorbant is periodically regenerated and the NOx recovered, converted to N02 and recycled for recovery as nitric acid.91... 

As the last nitric acid evaporates, the nuclear boiling of the liquid may change to effervescence again, which may become vigorous. If the reaction rate appears to be increasing too quickly for comfort, remove the beaker from the hotplate. If the reaction does not abate in 30 to 60 s, add 1—2 ml of nitric acid to lower the temperature and hence the redox potential, and then allow the reaction to proceed again it may be necessary to heat the solution if the reaction has subsided too far. 

Whereas no reaction occurred in the absence of catalyst, ruthenium catalysts were able to remove most of the Total Organic Carbon (TOC) of p-HBZ acid aqueous solutions at relatively mild conditions after 7h. The most important intermediates detected were phenol, hydroquinone and maleic acid. The results related to the study of the effects of the acid used for the preparation of aerogel supports (TiOa, ZrOa) and the nature of ruthenium precursor on the catalytic properties of the samples are gathered in the Tables 4 and 5. As shown in Table 4, the use of nitric acid during the synthesis of the Ti02 support and Ru(N0)(N03)3 as the metal precursor leads to the more efficient Ru/TiOa catalyst (63.8% TOC abatment). 

NOx abatement of tail gases from nitric acid plants and other NOx sources (e.g., adipic acid, nicotinic acid, nitrates calcination, etc.) has been implemented during the past 10 years in about 40 projects in 18 countries by applying two processes ... 

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. 

At present the target technology is a nitric acid plant vwthout a special abatement process unit with an NOx concentration of 200 ppmv in the tail gas. Medium-pressure plants can vent 500-800 ppmv of NOx in tail... 

Pate KT, Langer SH (1985) Electrogenerative reduction of nitric acid for pollution abatement. Environ Sci Technol 19 371-373... 

Figure 6.4.23 Single-pressure nitric acid plant (high pressure) using selective catalytic reduction (SCR) for NO f abatement (BFW boiler feed water). Adapted from Moulijn, Makkee, and Van Diepen (2004).

The Abatement of NjO From Nitric Acid Plant A Case Study 1613... 

Figure 27.3 Flow sheet of a dual-pressure nitric acid plant, with different locations for abatement measures. (Reproduced with permission from Ref. [9].)...

The Abatement of Nfi From Nitric Acid Piant A Case Study 1623... 

Many attempts at the lab scale were devoted to the catalytic abatement of N2O, and the technology is now available at the industrial scale even if some problems persist related to the catalyst stability at high temperature inside the ammonia burner. In the particular case of nitric acid plant, the simultaneous removal of low concentration of N2O and NO, is still of interest, since no technology is viable especially end-of-pipe systems for which the low temperatures of the exhaust gas do not allow the simultaneous conversion of N2O and NO. The implementation of a process running at medium temperatures is technologically... 

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