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Core Production Process
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Equipment & Innovation
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Quality Control Standards
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Safety & Environmental Protection
1.Core Production Process
Preparation of Raw Materials
Limestone Calcination: Limestone (calcium carbonate, ) is first calcined in a kiln at high temperatures (around 900 - 1200°C). The chemical reaction is as follows: . The resulting quicklime (calcium oxide, ) is then used in the subsequent steps.
Slaking of Quicklime: The quicklime is mixed with water in a slaking tank. The reaction is highly exothermic and forms calcium hydroxide (slaked lime, ): . The slaked lime is usually prepared as a fine suspension or paste for better reaction in the next stage.
2. Chlorination Reaction
Reactor Setup: The slaked lime suspension or paste is transferred to a chlorination reactor. This reactor is typically made of materials that can withstand the corrosive effects of chlorine gas (), such as steel lined with rubber or other corrosion-resistant materials.
Chlorination Process: Chlorine gas is introduced into the reactor containing the slaked lime. The chemical reaction that occurs is a complex one, mainly resulting in the formation of calcium hypochlorite (), calcium chloride (), and water (). The overall reaction can be approximated as: .
Reaction Control: The reaction temperature, pressure, and the flow rate of chlorine gas need to be carefully controlled. Usually, the reaction is carried out at a relatively low temperature (around 40 - 60°C) to ensure the formation of the desired product and to prevent the decomposition of calcium hypochlorite. The reaction time also varies depending on the scale of production and the reaction conditions, but it generally takes several hours to complete.
3. Separation and Drying
Separation: After the chlorination reaction is complete, the resulting mixture contains a suspension of solid bleaching powder particles along with some unreacted slaked lime and other impurities. This mixture is then subjected to a separation process, such as filtration or centrifugation. Filtration using filter presses or centrifuges helps to separate the solid bleaching powder from the liquid phase, which mainly contains water and dissolved salts.
Drying: The separated wet bleaching powder is then dried to remove the remaining moisture. Drying can be carried out in a rotary dryer or a flash dryer. In a rotary dryer, hot air is passed through the moving bleaching powder particles, evaporating the moisture. In a flash dryer, the wet powder is dispersed in a stream of hot gas, which quickly dries the particles. The final moisture content of the bleaching powder is typically controlled to be very low (usually less than 5%) to ensure its stability and shelf life.
4. Packaging and Quality Control
Packaging: The dried bleaching powder is then packaged in suitable containers, such as airtight plastic bags or metal drums. The packaging is designed to prevent the entry of moisture and air, as bleaching powder can react with moisture and carbon dioxide in the air over time, leading to a decrease in its active chlorine content.
Quality Control: Samples of the packaged bleaching powder are taken for quality control tests. The main quality 指标 include the active chlorine content, which is a measure of the bleaching and disinfecting power of the product. Other tests may include checking the particle size distribution, the presence of impurities, and the pH value of the solution made from the bleaching powder. Only products that meet the specified quality standards are released for sale and use.
2.Equipment & Innovation
(1) Reactor Design
Advantages of tower reactor: The multi-layer tray structure improves gas distribution efficiency and reduces dead-angle reactions; the tail gas scrubbing system equipped with alkaline solution (NaOH) neutralizes residual chlorine.
Intelligent monitoring: Internet of Things (IoT) sensors monitor the corrosion status of equipment in real time, predict maintenance cycles, and reduce downtime risks.
(2) Green Manufacturing
On-site preparation of chlorine: The electrochemical method is used to electrolyze brine to generate Cl₂, reducing transportation risks.
By-product recovery: The by-product calcium chloride (CaCl₂) is used for road deicing or industrial desiccant, and hydrogen (H₂) is used for power generation to achieve resource recycling.
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3.Quality Control Standards
1. Active Chlorine Content
Definition and Significance: Active chlorine is the most crucial indicator of bleaching powder's quality as it represents the substance's bleaching and disinfecting power. It is the amount of available chlorine that can participate in oxidation reactions. Higher active chlorine content generally indicates stronger bleaching and disinfecting capabilities.
Standard Range: Typically, the active chlorine content in high-quality bleaching powder (calcium hypochlorite-based) should be in the range of 30% - 40% by weight. However, for some specialized or high-purity products, the active chlorine content may be even higher, up to 60% or more. The specific standard may vary depending on the intended application of the bleaching powder. For example, bleaching powder used in drinking water disinfection often requires a more strictly controlled and relatively high active chlorine content to ensure effective pathogen removal while maintaining safety standards.
Testing Method: The active chlorine content is usually determined through a chemical titration method. Commonly, the bleaching powder sample is first dissolved in an appropriate acidic medium, which releases the available chlorine in the form of free chlorine. Then, a standardized reducing agent (such as sodium thiosulfate) is titrated against the solution, and the amount of reducing agent consumed is used to calculate the active chlorine content based on the stoichiometry of the reaction.
2. Purity and Impurity Levels
Main Impurities: Bleaching powder may contain various impurities such as unreacted calcium hydroxide (), calcium chloride (), and other trace elements. Excessive levels of these impurities can affect the performance and stability of the bleaching powder.
Calcium Hydroxide: The presence of unreacted calcium hydroxide should be minimized as it can react with carbon dioxide in the air over time, leading to the formation of calcium carbonate () and reducing the active chlorine content. Generally, the maximum allowable content of calcium hydroxide is often set at a few percent (e.g., less than 5% by weight) depending on the product specification.
Calcium Chloride: While calcium chloride is a by-product of the manufacturing process, its content should also be controlled within a reasonable range. Excessive calcium chloride can cause the bleaching powder to be more hygroscopic, leading to caking and degradation of the product.
Typically, the acceptable range for calcium chloride content is around 10% - 20% by weight, but this can vary based on different quality requirements.
Trace Elements: Trace elements such as heavy metals (e.g., lead, mercury, cadmium) should be present at extremely low levels. These heavy metals can pose health risks if the bleaching powder is used in applications related to food processing, water treatment, or disinfection of areas in contact with humans. The maximum allowable limits for heavy metals are often set in accordance with strict environmental and health regulations, usually in the parts per million (ppm) or even parts per billion (ppb) range.
3. Particle Size and Physical Properties
Particle Size Distribution: The particle size of bleaching powder affects its solubility and usability. A suitable particle size distribution is desired to ensure rapid dissolution and uniform dispersion during use. Generally, the particles should be within a certain range, for example, with a median particle size of around 50 - 200 micrometers. If the particles are too large, they may dissolve slowly, reducing the effectiveness of the bleaching or disinfection process. On the other hand, if the particles are too fine, they may cause dusting problems during handling, which can be a safety hazard and also lead to product loss.
Moisture Content: The moisture content of bleaching powder is a critical physical property. Excessive moisture can cause the bleaching powder to cake, which not only affects its flowability and usability but also accelerates the decomposition of calcium hypochlorite, reducing the active chlorine content over time. The acceptable moisture content is typically kept below 5% by weight. Special packaging and storage conditions are often implemented to maintain the low moisture level.
Appearance and Color: Bleaching powder should have a consistent and characteristic appearance. It is usually a white or slightly yellowish powder. Any significant deviation in color, such as the presence of dark spots or discoloration, may indicate the presence of impurities or degradation of the product.
4. Stability and Shelf Life
Stability Testing: Bleaching powder should be stable under normal storage conditions. Stability tests are conducted to evaluate how the product's properties change over time. This includes measuring the change in active chlorine content, the formation of any new impurities, and the physical integrity of the powder. The product should maintain its specified quality parameters (such as a minimum active chlorine content) within a certain period, usually defined as the shelf life.
Shelf Life: The shelf life of bleaching powder is typically specified as 6 - 12 months under proper storage conditions (e.g., in a cool, dry, and well-ventilated place, away from direct sunlight and sources of heat and moisture). However, the actual shelf life may vary depending on the manufacturing process, packaging quality, and storage environment. Quality control measures ensure that the product meets the required standards throughout its shelf life.
5. Safety and Regulatory Compliance
Safety Standards: Bleaching powder is a hazardous chemical due to its strong oxidizing properties and potential toxicity. It must comply with safety standards related to handling, storage, and transportation. This includes proper labeling with hazard warnings (such as "corrosive," "oxidizing agent," and "toxic if ingested or inhaled"), and the provision of safety data sheets (SDS) that detail the chemical's properties, potential hazards, and appropriate safety precautions.
Regulatory Compliance: The manufacturing of bleaching powder must adhere to relevant national and international regulations. These regulations cover aspects such as environmental protection (e.g., proper disposal of waste generated during production), product quality control, and workplace safety. For example, in the food and water treatment industries, bleaching powder used for disinfection must meet specific regulatory requirements to ensure the safety of the end products.
4.Safety & Environmental Protection
(1) Worker Safety
Mandatory equipment: Gas Mask, Acid-Resistant Gloves, Emergency Ventilation System.
Leakage Treatment: Use lime slurry to neutralize chlorine gas leaks.
(2) Waste Management
Wastewater: Discharged after neutralization with lime to pH 6–8.
Waste Gas: Catalytic oxidation technology converts residual Cl₂ into harmless salts.
