Ammonia removal process

Figure 4-10. Basic steps in ammonia removal processes.

Direct hydrogen cyanide (HCN) gas in a fuel oil gasification plant to a combustion unit to prevent its release. 4. Consider using purge gases from the synthesis process to fire the reformer strip condensates to reduce ammonia and methanol. 5. Use carbon dioxide removal processes that do not release toxics to the environment. When monoethanolamine (MEA) or other processes, such as hot potassium carbonate, are used in carbon dioxide removal, proper operation and maintenance procedures should be followed to minimize releases to the environment. 

The Catalytic Wet Air Oxidation (CWAO) process is capable of converting all organic contaminants ultimately to carbon dioxide and water, and can also remove oxidizable inorganic components such as cyanides and ammonia. The process uses air as the oxidant, which is mixed with the effluent and passed over a catalyst at elevated temperatures and pressures. If complete COD removal is not required, the air rate, temperature and pressure can be reduced, therefore reducing the operating cost. CWAO is particularly cost-effective for effluents that are highly concentrated... 

Ammonia. Ammonia interferes with existing acid gas removal processes because it can pass on through the scrubbers and then solidify on cyrogenic surfaces or it can go with the acid gases and poison the sulfur conversion catalysts. If ammonia is absorbed into an aqueous stream, then this aqueous stream must be... 

Figure 13 Chevron WWT process. Acid is used in first stage to enhance hydrogen sulfide removal. Caustic is used in second stage to enhance ammonia removal. (From Ref. 20.)...

In the case of the scrubberless approach, the damaged layer is in practice generally removed during the underetch particle removal process (ammonia... 

J. J. Watts and W. A. Richards patented the preparation of this salt by removing the proper quantity of carbon dioxide from sodium hydrocarbonate by adding sodium hydroxide, sodium carbonate, or the hydroxides of the alkaline earths, and crystallizing the soln. at about 35° C. Winkler obtained it from carbonated liquor of the ammonia-soda process and T. M. Chatard by the spontaneous evaporation of soln. of normal sodium carbonate which had been exposed to the air some time and thereby absorbed carbon dioxide. There is a fairly general agreement that a temp, below 35° is not favourable to the formation of trona and that the crystals develop better in sodium chloride soln. and excess of the normal carbonate also favours the formation of trona. J. J. Watts and W. A. Richards say that if an excess of the hydrocarbonate be used, it crystallizes out unchanged. T. M. Chatard studied the influence of the composition of the soln. on the formation of trona, and obtained the results indicated in Table LIV with soln. containing a mol. of the normal carbonate. H. N. McCoy and C. D. Test have studied the conditions under which the sesquiearbonate is formed, and their results are summarized in Fig. 73. 

Purification of Synthesis Gas. This involves the removal of carbon oxides to prevent poisoning of the NIT3 catalyst. An absorption process is used to remove the bulk of the C02, followed by methanation of the residual carbon oxides in the methanator, Modern ammonia plants use a variety of C02-removal processes with effective absorbent solutions. The principal absorbent solutions currently in use are hot carbonates and cthanolamincs. Other solutions used include methanol, acetone, liquid nitrogen, glycols, and other organic solvents. 

The BYAS (Bypass Ammonia Synthesis) process can be used for economical expansion of existing ammonia synthesis plants. This process introduces additional natural gas at an intermediate stage in the process. The additional nitrogen in the air, which also has to be introduced, is removed by PSA (pressure swing absorption). The process was developed and offered by Humphreys and Glasgow in the UK1. 

Figure 19.2. Andrussow HCN Process with Ammonia Removal. (This material is used by permission of John Wiley and Sons, Inc.))...

Ammonia removal is the next step in the gas cleanup process. A typical approach is to contact the coke-oven gas with a solution of sulfuric acid to form ammonium sulfate, which is then recovered by crystallization, dried, and sold as fertilizer. More modem processes for ammonia removal include the water wash process, in which the coke-oven gas is scrubbed with water that dissolves the ammonia along... 

The final step is desulfurization. A number of processes have been developed which are suitable for removing H2S from coke-oven gas. These include using solutions of potassium carbonate, monoethanolamine (MEA), or ammonia to absorb the H2S. If ammonia solution is used as the absorbent, desulfurization is frequently combined with the ammonia removal step. Recovered H2S can be converted to elemental sulfur or sulftiric acid. The product remaining after all the above steps is cleaned coke-oven gas, some of which is used to heat the coke ovens and produce more coke with the rest going to the boiler house and/or the blast furnace for direct injection. 

Fig. 22.30. Andrussow HCN process with ammonia removal.129 (Copyright by John Wiley Sons, Inc. and reproduced by permission of copyright owner.)...

Dual Pressure An ammonia synthesis process, based on the AMV process but providing more capacity by removing some of the product at an intermediate stage. Developed by Krupp Uhde in 2001-2002. 

Purifier An ammonia synthesis process, developed C.F. Braun and now licensed by Kellog Brown and Root. An important feature is the cryogenic removal of inert gases from the system. Seventeen plants were operating in 2005. 

---