Caustic Soda Evaporation Saving Technological Transformation

Caustic soda, an important basic raw material for chemical industry, is widely used in all areas of the national economy, and it occupies a very important position especially in industrial and agricultural production and people's lives . Alkali production of caustic soda used in our country is mainly divided into diaphragm process alkali and ion-exchange membrane process alkali. By the end of 2005, the capacity of caustic soda production had reached 15746000 t/a, in which the capacity of diaphragm caustic soda production is 8364000 t/a , accounting for the production of caustic soda 53.2%. The capacity of caustic soda is 100000 t/a in Zunyi Alkali Factory, in which the capacity of diaphragm caustic soda production is about 60000 t/a.Evaporation of caustic soda is a key piont in the technological process of diaphragm caustic soda. The process needs much energy. The evaporation which is from heating vapor into liquid evaporation materials equals to calorific value, the energy consumption of caustic soda occupies about 25% ~ 35% which is next to electrolysis process. Therefore, the use of advanced application of energy-saving technology in caustic soda evaporation process , has a direct impact on production of caustic soda production and the economic efficiency of enterprises." Three effect and five compartment" process was adopted in the. original diaphragm caustic soda evaporation system of Zunyi Alkali Factory. At that time , the production capacity was 35000 t/a before the technological transformation(2000 year). The capacity of electrolysis system in 2001 was 56000 t/a after innovation. The evaporation system was constrainted by limited space and other factors for the corresponding transformations of the the diaphragm caustic soda production. So reforming the original evaporation system on the basis of technology and equipment, through energy-saving technology, which allows expansion of caustic soda evaporation system to meet the requirements and lowers consumption, has become the target of this technological transformation. After careful analysis and examination, the original evaporation system of Zunyi Alkali Factory has the main problem as follows :feed into effective low temperature, concentration fluctuations;feed salt evaporation process seriously;evaporation equipment disposition unreasonable;errors in the end effect vacuum devices, vacuum was too low. errors in the cooling devices, pass rate of caustic soda was too low.Heat transfer process is a controlling factor in the evaporation of caustic soda. From basic heat transfer equation Q= KAΔt , focusing on the heat transfer coefficient K and the heat transfer range of temperature At factors . According to careful analysis and comparison, we determined key factors such as the vacuum system, salt-extracting system and other key systems , and provided a theoretical basis for energy saving program.Aiming at the original evaporation system, we put forward technological transformation as follows :use the heating chamber for scraped preheating feeding preheater transformation process into improving feeding efficiency . Enhance cell operation and management control the concentration of alkali electrolysis in 120~135g/L.change the doubl evaporator heating chamber into single evaporator heating chamber to rise evaporator heating chamber to increase heat transfer area.change salt-extracting process to reverse process adding the original liquor additional sub-salt devices, reducing the salinity of orginal liquor.the use of air-tower combination of vacuum condenser device end absorb the second steam , improving vacuum tube road to rise vacuum. Use waste heating chamber for a set of additional product base cooling device to lower the temperature and raise the crystallization rate of salt.After modification measures putting into operation, evaporation system performanced stabbly and controlling of the main indicators of technology improved markedly. After technological transformation, evaporation capacity increased from 35,070 t/a to 57,383 t/a. The summary of typical average steam consumption dropped from 5. 37 t/t 100% NaOH to 4. 19 t/t 100% NaOH. Finished passing rate rised from 75% to 95～100%. The technological transformation has successfully achieved the expected goal of a significant reduction in energy consumption, and increase the economic efficiency of enterprises.