1. Key steps
2.Consideration factors
3.Methods of caustic soda production
4. How to choose the right electrolytic cell when customizing a caustic soda plant?
5.What is the cost structure of producing caustic soda by ion exchange membrane method?
Process selection: There are two methods for industrial production of caustic soda: causticization and electrolysis (including mercury method, diaphragm method and ion membrane method). At present, ion membrane electrolysis is widely used. Because of its advantages of low investment, low energy consumption, good quality of sodium hydroxide, no pollution and low production cost, it is usually given priority when building, renovating and expanding production equipment; caustic soda produced by causticization has low purity and poor economic benefits, and is only produced on a small scale in a few countries. my country mainly uses diaphragm method and ion membrane method.
Site selection: Consider being close to the raw material production area (such as the raw salt production area) to reduce the raw material transportation cost; have convenient transportation conditions to facilitate product transportation; have sufficient and qualified water sources, because the production process requires a lot of water; at the same time, consider local infrastructure, policies and regulations, environmental capacity and other factors.
Factory design: According to the selected process and production scale, the overall layout of the factory is designed, including the planning of production workshops, storage facilities, public works (such as power supply, water supply, gas supply), office areas, etc.; the selection and configuration of each process and equipment in the design production process, such as brine refining equipment, electrolyzers, evaporators, etc., to ensure the continuity and stability of production.
Equipment procurement and installation: According to the design requirements, equipment that meets the quality standards and production capacity is purchased, such as electrolyzers, pumps, pipelines, storage tanks, etc.; after the equipment arrives, professional personnel are organized to install and debug to ensure that the equipment can operate normally.
Personnel recruitment and training: Recruit managers, technicians, operators, etc. with relevant knowledge and skills in chemical production; conduct pre-job training for employees, including production technology, equipment operation, safety and environmental protection, so that they are familiar with the factory's production process and operating procedures.
Implementation of safety and environmental protection measures: formulate a complete safety management system and operating procedures, and equip necessary safety facilities and protective equipment, such as fire-fighting equipment, protective equipment, emergency rescue equipment, etc.; design and build corresponding environmental protection treatment facilities, such as sewage treatment systems, waste gas treatment devices, etc., to ensure that the "three wastes" emissions in the production process meet national and local environmental protection standards.
Trial production and acceptance: After completing the installation and commissioning of the equipment, conduct trial production to test the rationality of the production process, the stability of the equipment and the quality of the product; after the trial production is qualified, conduct project acceptance in accordance with relevant standards and regulations, and obtain the necessary production licenses and qualifications.
Market demand: Understand the demand situation, price trends, major consumption areas and future development trends of the caustic soda market, and ensure that the product has a stable market sales. For example, my country's downstream consumption of caustic soda is concentrated in metallurgy, chemical industry, textile, light industry and other industries, among which the alumina industry is the largest demand area.
Cost factors: Comprehensively consider the cost of raw materials (such as raw salt prices), energy costs (electricity, steam, etc.), transportation costs, labor costs, etc., and reduce production costs and improve economic benefits by optimizing processes and selecting reasonable sites.
Advanced technology and equipment: Select advanced and reliable production technology and equipment to improve production efficiency, product quality and automation, reduce energy consumption and labor intensity, and consider the maintenance and update costs of equipment.
Policies and regulations: Comply with national and local policies, regulations and standards on chemical project construction, production safety, environmental protection, etc., such as project approval procedures, environmental emission indicators, safety supervision regulations, etc., to ensure that the factory operates legally and in compliance with regulations.
Safety risks: Fully evaluate the safety risks in the caustic soda production process, such as the strong corrosiveness of caustic soda, electrical safety during electrolysis, and the risks of flammable and explosive gases such as hydrogen, etc., and take effective prevention and response measures to ensure the safety of personnel and equipment.
Sustainable development: Focus on energy conservation and emission reduction and comprehensive utilization of resources, adopt advanced energy-saving technologies and environmental protection processes, reduce the emission of "three wastes", reduce the impact on the environment, and achieve sustainable development of the enterprise.
3.Methods of caustic soda production
There are two main methods for producing caustic soda: causticization and electrolysis. The electrolysis method is the mainstream method at present:
Causticization method: using soda ash solution and lime (solid or lime milk) as raw materials, it is divided into soda ash causticization method and natural soda causticization method according to different raw materials. Before the emergence of electrolysis in the late 19th century, it has always been the main method for producing caustic soda in the world. However, due to the low purity and poor economic benefits of the produced caustic soda, only a few countries currently produce it on a small scale. Taking the natural soda causticization method as an example, the natural soda is crushed, dissolved (or alkaline brine), clarified, and then added with lime milk for causticization at 95-100℃. The causticized liquid is clarified, evaporated and concentrated to a NaOH concentration of about 46%. The clear liquid is cooled, salted and further boiled to obtain a solid caustic soda product. The causticized mud is washed with water, and the washing water is used to dissolve the natural soda.
Electrolysis method: The main raw material is raw salt. According to the different electrolytic cell structures, electrolytic materials and diaphragm materials, it is divided into mercury method, diaphragm method and ion exchange membrane method:
Mercury method: It has been eliminated due to its high environmental pollution.
Ion exchange membrane method: It is the mainstream production method in the world today, accounting for about 99%. The specific production process is divided into six steps: rectification, brine refining, electrolysis, chlorine hydrogen treatment, liquid alkali evaporation, and solid alkali production (optional). The production of 1 ton of caustic soda requires about 2300-2400 kWh of electricity and 1.4-1.6 tons of raw salt, which account for 60% and 20% of the caustic soda production cost respectively. At the same time, the production of 1 ton of caustic soda will be accompanied by 0.886 tons of chlorine and 0.025 tons of hydrogen. Chlor-alkali enterprises usually have chlorine-consuming devices. PVC is the main chlorine-consuming product, accounting for about 40% of chlorine consumption.
4. How to choose the right electrolytic cell when customizing a caustic soda plant?
When customizing a caustic soda plant, you can choose a suitable electrolyzer from the following aspects:
Type selection
Ion membrane electrolyzer cell types are basically divided into two types: monopolar and bipolar. Bipolar cells generally operate under high voltage and low current conditions, while monopolar cells operate under low voltage and high current conditions. At present, bipolar cell technology is mostly used in caustic soda production, especially natural circulation and high current density bipolar cells are widely used.
Performance indicators
Production capacity: It needs to be selected according to the caustic soda production scale of the factory. The caustic soda production capacity of a single cell is generally 20,000 tons/year, and the maximum can reach 25,000 tons/year. It is necessary to ensure that the selected electrolyzer can meet the planned production requirements.
Current distribution: An electrolyzer with reasonable current distribution can make the electrolysis process more stable and efficient. For example, the electrolyzer of the chlorine project performs well in this regard.
Power consumption index: This is one of the important factors affecting production costs. Electrolyzers with lower power consumption indicators should be selected to reduce energy consumption. For example, the electrolyzers of Asahi Kasei and Beihua Machinery have similar and better performance in power consumption indicators and service life.
Equipment maintenance
Structural design: Consider the convenience of maintenance. For example, Wood Company uses small unit cells, which are relatively easy to maintain.
Stability: Select electrolytic cells with mature technology and stable operation to reduce downtime. Early domestic repolarization cells had problems such as unit cell leakage and electrode puncture membrane. After improvement, they achieved long-term stable operation.
5.What is the cost structure of producing caustic soda by ion exchange membrane method?
Raw material cost
Raw salt: Raw salt is the main raw material for producing caustic soda. Generally, about 1.4-1.6 tons of raw salt are needed to produce 1 ton of caustic soda. The price fluctuation of raw salt will have an important impact on the production cost of caustic soda. Its cost ratio is relatively high, usually reaching about 20% of the total cost.
Chemicals: Some other chemicals are also needed in the production process, such as soda ash, caustic soda, barium chloride, sodium sulfite, etc. for brine refining to remove impurities in brine. Although the cost of these chemicals is relatively lower than that of raw salt, they are also part of the cost structure.
Energy cost
Electricity: The ion exchange membrane electrolysis process consumes a lot of electricity. The electricity cost is an important part of the production cost of caustic soda, accounting for about 60%. It takes about 2300-2400 kWh of electricity to produce 1 ton of caustic soda. The price of electricity directly affects the production cost of caustic soda.
Steam: Steam is required in processes such as brine heating and alkali evaporation and concentration. Steam costs also account for a certain proportion of the total cost, and the specific proportion will vary depending on the production process and energy utilization efficiency.
Equipment and depreciation costs
Equipment purchase: The construction of an ion exchange membrane caustic soda production unit requires the purchase of a large number of equipment, such as electrolyzers, rectifiers, evaporators, pumps, pipelines, etc. The investment amount of these equipment is large, and the selection and quality of the equipment will affect the price and service life of the equipment.
Depreciation: The equipment will gradually wear and age during use, and the purchase cost of the equipment needs to be allocated to the annual production cost according to a certain depreciation method. In addition, the factory's fixed assets such as plant buildings also need to be depreciated.
Labor costs
The caustic soda production process requires a certain number of operators, technicians and managers. Labor costs include employee wages, bonuses, benefits, social insurance and other expenses. The level of labor costs is related to factors such as local labor market prices, corporate salary policies, and the degree of production automation. With the improvement of production automation, the proportion of labor costs in total costs may decline.
Environmental protection costs
Pollution control: A certain amount of wastewater, waste gas and waste residue will be generated during the production of caustic soda by the ion exchange membrane method, and corresponding environmental protection treatment facilities need to be built, such as sewage treatment systems, waste gas treatment devices, waste residue treatment facilities, etc. The construction, operation and maintenance of these facilities require a large amount of capital.
Environmental monitoring and compliance costs: Enterprises need to regularly monitor pollutant emissions to ensure that various emission indicators meet national and local environmental protection standards. At the same time, enterprises also need to bear environmental compliance costs, such as paying sewage fees and environmental taxes.
Other costs
Repair and maintenance: In order to ensure the normal operation of production equipment, it is necessary to regularly repair and maintain the equipment, including daily maintenance, overhaul, replacement of parts and other expenses.
Management and sales: The company's management expenses (such as office expenses, travel expenses, management personnel salaries, etc.) and sales expenses (such as advertising expenses, transportation costs, sales commissions, etc.) will also be allocated to product costs.
