Have any experts done simulations of phosphoric acid recovery of ammonia from coking exhaust gas?

Is the poster talking about the legendary anhydrous ammonia? The process is very mature and several coking plants in China adopt this process.

The anhydrous ammonia produced by the Fosam unit has high purity, high output value and good economic benefits. Because it is a liquid product, it is inconvenient to store and transport it. The principle of absorbing ammonia by the Fossum method is to use aqueous solutions of monoammonium salt and diammonium salt of phosphoric acid to selectively absorb ammonia from coke oven gas. The ammonium phosphate mother liquor that has absorbed ammonia is stripped with steam under the pressure of the regeneration process to obtain ammonia vapor containing about 20% ammonia. The regenerated ammonium phosphate mother liquor is returned to the absorption part for recycling. Ammonia vapor containing 20% ​​ammonia is distilled to obtain 99.98% anhydrous ammonia. This method consists of three parts: absorption, analysis, and distillation. 1) Absorption of ammonia. Coke oven gas enters from the bottom of the absorption tower. The absorption tower is an upper and lower air spray tower. The absorption liquid contacts the gas in countercurrent. The absorption liquid is sprayed in separate cycles in the upper and lower sections. The NH3/H3PO4 molecular ratio of the upper absorption liquid is 1.25. It absorbs ammonia in the gas during its own circulation. The molecular ratio of the circulating liquid increases to 1.35. Part of the upper circulating liquid overflows from the tower to the lower section as a supplement for the lower absorbing liquid. After the lower-stage absorption liquid circulates to absorb ammonia, the molecular number ratio reaches 1.85, and 3% of the circulating amount is extracted and sent to the regeneration process. The operating temperature of the tower is 55°C, and the ammonia content in the gas behind the tower can reach 0. lg/m3. The resistance of the absorption tower is 1.0~1.5kPa. The material of the tower is SUS304L. 2) Regeneration of ammonium phosphate mother liquor. The ammonium phosphate mother liquor that has absorbed ammonia enters the desorption tower. It must first undergo pretreatment to remove oil, and then exchange heat with the lean liquid at the bottom of the desorption tower to reach 104°C before entering the contactor. The rich liquid oil removal method adopts foam flotation tar remover. Since the ammonium phosphate mother liquor absorbs trace amounts of acidic gases (H2S, HCN, CO2, etc.) and reacts with the ammonia in the absorption liquid during the process of absorbing ammonia, the ammonium salts generated can easily cause accumulation in the subsequent distillation tower and block the tower. Therefore, the acidic gas must be evaporated from the absorption liquid, which is the purpose of the contactor. The 104°C rich liquid is heated to the boiling point by the waste steam from the distillation process in the contactor, and the acidic gas dissolved in the absorption liquid is evaporated. These ammonia-containing acidic gases are discharged from the contactor and returned to the absorption tower. The contactor material is SUS316L. After passing through the contactor, the rich liquid is pumped through a gas-liquid heat exchanger to exchange heat with the concentrated ammonia vapor at the top of the analysis tower. It is then heated to 187°C by a heater and then enters the top of the analysis tower. Direct steam is introduced at the bottom of the tower. The operating pressure of the tower is about 1.4MPa. The ammonia-containing gas leaves the top of the tower at 184°C. After heat exchange, cooling and adjustment to 131°C, it enters the receiving tank as the raw material for the distillation tower. The lean liquid at 195°C after deamination has a molecular ratio of 1.25 and is drawn from the bottom of the tower. After heat exchange and cooling to 55°C, it is sent to the upper section of the absorption tower for recycling. The entire absorption and regeneration form a complete system. The amount of phosphoric acid retained in the system is certain, and the moisture in the system must be kept balanced. Part of the moisture in the absorption liquid evaporates into the gas during the absorption process, and part of the moisture is taken away with the concentrated ammonia vapor from the top of the analysis tower. The key to maintaining the moisture balance of the system is to control the phosphoric acid concentration in the regeneration liquid (number of molecules ratio 1.25) at the bottom of the analysis tower to 31% (W). The material of the analysis tower is SUS304L. 3) Distillation of ammonia. The ammonia liquid at 131°C and containing about 20% ammonia from the receiving tank of the desorption tower is sent to the middle part of the rectification tower for rectification. 99.98% pure ammonia vapor is obtained at the top of the tower. After cooling, part of it is sent to the top of the tower as reflux. The temperature at the top of the tower is controlled at 33-34°C, and the rest is used as product. The operating pressure of the distillation tower is 1.7MPa, the condensation cooling water temperature is 30°C, the wastewater discharged from the bottom of the distillation tower contains ammonia <0.1% (W), direct steam is introduced at the bottom of the tower, and the operating temperature is about 194°C. Feed 20% (W) NaOH aqueous solution near the feed layer of the distillation tower to remove trace amounts of acidic components such as CO2 and H2S in the feed to prevent ammonium salts from being produced and causing clogging. In addition, oil may accumulate near the feed layer of the distillation tower, which must be led out from the side line at an appropriate height and returned to the absorption tower gas. 4) Comparison of semi-direct method and indirect method for producing anhydrous ammonia. Semi-direct Faversum produces anhydrous ammonia, that is, the ammonium phosphate mother liquor absorption tower is installed in the gas system. There are following problems with this approach. First, due to direct contact with coal gas, it is easy to contaminate the absorbing liquid, and a tar removal device must be installed in the post-process, which complicates the analysis and distillation operations. ； Secondly, the operating temperature of the Fossum absorption tower is about 40°C, and a final cooling system must be connected behind it. The gas system consumes high energy. Moreover, the lean liquid coming out of the bottom of the analytical tower must be cooled to the corresponding temperature after heat exchange, which requires a large cooling area and high energy consumption. The absorption tower has a lot of circulating absorption liquid (spray density requirements) and high power consumption. ； In addition, due to the large diameter of the absorption tower, a lot of special steel is required and the investment is high. The indirect method produces anhydrous ammonia. The absorption tower is installed after the deacidification tower to recover ammonia from the acidic gas. The acidic gas has been distilled and has relatively few impurities. There is no need to add an oil removal device. The relative amount of acidic gas is much smaller, the ammonia concentration is high, the diameter of the absorption tower is small, and the circulating liquid volume is small. The shortcomings of the semi-direct method can be completely avoided. The operating temperature of absorbing ammonia from acid gas is high, and the poor absorption liquid returned from the bottom of the analysis tower does not need to be cooled to a low temperature as in the semi-direct method, which is beneficial to energy saving.