SODA ASH PLANT

Next to sulfuric acid and ammonia, soda ash (sodium carbonate) is the third largest manufactured chemical in the world. Comparatively, baking soda (Sodium bicarbonate), a byproduct of the soda ash industry also enjoys good market demand. While soda ash is commercially used for the production of glass, inorganic chemicals, soaps, synthetic detergents and processed food, baking soda is primarily used as a leavening agent and in medicines. The world production capacity of soda ash and baking soda is estimated to be 42 million tons in 2005 (Web 1) and 1 million tons in 2001 respectively. Today, more than 90% of soda ash and baking soda are manufactured using Solvay’s process.

Despite being cost effective for the manufacture of both soda ash and baking soda, Solvay’s process is disadvantageous from the pollution abatement perspective. Solvay’s process produces huge quantities of CaCl2 which does not have much market value. Other waste streams produced in the process contain lower quantities of CaCO3 and other impurities of limestone. In addition, magnesium and calciumions in the brine solution are removed as carbonates which are also regarded as additional waste products. An alternative for the Solvay’s process is the Dual and Hou’s process in which ammonia is not recovered, but is transformed into ammonium chloride product, which can be sold as a fertilizer component. In addition, it is important to note that apart from enhanced utility usage, the Dual process requires purer brine solution and does not eliminate the generation of waste carbonate products in the brine purification step.

Existing trends in chemical process industries indicate a strong bias towards integrated processing, co-generation, and minimization of waste product generation. Process intensification coupled with techno-economic analysis enables the selection of most potential physical and chemical transformation routes that maximize process efficiency and minimize waste generation and energy consumption. Considering the necessity to address theoretical and experimental investigations for the alternative route, this work presents a preliminary techno-economic analysis of soda ash and baking soda production from sodium sulfate. Amongst several alternate routes for soda ash and baking soda production, a critical review of the industrial processes for soda ash indicates a partial utilization of the modified Leblanc process to initially produce Na2SO4 and HCl from NaCl and H2SO4.

Eventually, Na2SO4 can be used as the source for the production of baking soda (and soda ash) and (NH4)2SO4 (Bichel et al., 2008). Compared to the Solvay’s process, the alternate process has certain advantages. Firstly, pure chemicals are used as raw materials and therefore, further purification steps are eliminated, and waste generation is reduced. Secondly, all products namely HCl, baking soda, soda ash and ammonium sulfate have good market value compared to their raw-materials. Thirdly, the process allows the simultaneous removal of SOx and NOx from flue gases using regenerated sodium bicarbonate/carbonate solutions along with the production of fertilizers.