Question: Requirements for CO2 in the combined alkali production process
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Gentle experts, I work in gasification and know nothing about the alkali production process. I would like to ask where the CO2 used in the alkali production process is applied, and what are the requirements regarding its quality and pressure? Apart from use as a raw material for *pure CO2, are there any other applications that require impure CO2? How low can the concentration of impurities be? Is there any experience that can help estimate how much pure CO2 and how much impure CO2 is needed per ton of soda ash? The question is quite general; I hope experts will kindly share their insights. Thank you!
This post was last edited by chen3jun on 2010-7-16 at 15:43. Carbon dioxide is sent to the carbonization tower for carbonization reaction; the equation is as follows； CO2 + NaCl + NH3 + H2O ---- NaHCO3 + NH4Cl; the resulting heavy alkali is then sent for calcination and heating to be decomposed into soda ash, as shown in the chemical equation ； 2NaHCO3 ---- Na2CO3 + H2O + CO2. For the carbonization reaction, a higher concentration of carbon dioxide is preferable, but the concentration of carbon dioxide in the conversion gas is generally around 28%. At this point, the pressure is increased to raise the partial pressure of carbon dioxide. In the case of concentrated gas soda production (where the conversion gas is first decarburized to obtain a high-concentration carbon dioxide), the pressure is generally 3 kilograms. Otherwise, the pressure is 6–12 kilograms.
This post was last edited by chen3jun on 2010-7-16 at 15:41. The amount of carbon dioxide required for one ton of soda ash needs to be considered in two different scenarios. 1. Soda production from furnace gas, that is, the recovery of carbon dioxide decomposed in the calcination furnace; the above two formulas can be combined into ； NaCl + H2O + CO2 + NH3 ---- NaCO3 + NH4Cl. From this, the required amount of carbon dioxide can be calculated ； V=1000/106 *22.4=211.32 (m3), assuming that 99% pure soda ash is produced. Considering also certain losses of carbon dioxide (some is carried away in the exhaust gases, and it’s not possible to recover all of the carbon dioxide inside the calcination furnace), let’s assume a utilization rate of 90% for carbon dioxide. Thus, the actual amount of carbon dioxide required is ； 211.32*0.99/0.9=232.5 (m3). Next, calculate the amount of shift gas required for one ton of soda ash; assuming that the carbon dioxide content in the shift gas is 28%, then V_shift = 232.5/0.28 = 830 (m3). 2. If the furnace gas is not recycled, then the overall equation is as follows: ； 2CO2 + 2NaCl + 2NH3 + 2H2O ---- Na2CO3 + H2O + CO2 + NH4Cl Similarly, if 99% pure soda ash is produced, ignoring the carbon dioxide carried away by the exhaust gases ； V=2*1000/106*22.4*0.99=418.4 (m3); V’=418.4/0.28=1494 (m3)