Occupational hazards in soda ash production

1# ggyf2008 Safety in soda ash production 　Soda ash, whose chemical name is sodium carbonate (Na2CO3), is commonly known as soda or alkali ash. Its pure form is a white powder that dissolves easily in water to form a strongly alkaline solution. Soda ash is an important basic chemical raw material, widely used in industries such as petroleum, chemicals, papermaking, glass manufacturing, textiles, metallurgy, leather processing, and detergents; it is also used as an edible alkali. 　　The main industrial methods for producing soda ash are the ammonia-soda process and the combined soda ash process. The process flow of the ammonia-alkali method is as follows: raw salt is converted into saturated brine; after magnesium salts are removed using lime milk, the mixture is sent to a calcium removal tower where it is treated with carbonation tower exhaust gas (containing ammonia and carbon dioxide), thereby precipitating the calcium salts in the form of calcium carbonate. The refined brine is sent to the ammonia absorption tower to produce ammonia-brine, which is then fed into a carbonation tower where it is carbonated using carbon dioxide gas (gas from lime kilns and calcination furnaces), resulting in sodium bicarbonate crystals. After filtration, separation, and calcination, soda ash is obtained. The reactions at each step are as follows: Mg2+ + Ca(OH)2 → Mg(OH)2↓ + Ca2+ (removal of magnesium); Ca2+ + (NH4)2CO3 → CaCO3↓ + NH4+ (removal of calcium); NaCl + NH4HCO3 → NaHCO3↓ + NH4Cl (carbonation); NaHCO3 → Na2CO3 + CO2↑ + H2O↑ (calcination). The combined alkali production method eliminates the need for lime, thereby removing bulky equipment such as lime kilns, scrubbers, and ammonia distillation towers. It increases ammonia synthesis and allows for the co-production of ammonium chloride, which is an excellent nitrogen fertilizer for rice cultivation. 　　Occupational hazards: Soda ash production is an industry within the chemical sector where occupational hazards are relatively mild. The main hazards include mechanical injuries, burns from dust, and noise exposure; however, there is also a possibility of explosions and poisoning. 　　Mechanical injuries – During the transportation and processing of raw materials such as limestone, coal, and salt, as well as in processes like compression, filtration, calcination, packaging, and transportation, moving machinery often causes mechanical injuries that can result in harm, disability, or death. 　　Burns — Accidents of alkaline burns to the eyes and skin caused by lime, lime milk, ammonia solutions, and ammonia mother liquor occur frequently. Even small amounts of lime or lime milk entering the eyes often cause conjunctival edema and congestion. The effect of lime paste on eye tissues is prolonged, and since it tends to adhere to the moist eyeball, it has a significant impact on vision. When the area of alkaline skin burns is large, failure to provide timely or appropriate treatment can lead to death. The chronic effects of lime on the skin can include dryness, hardening, and cracking. 　　Dust – The handling of raw materials and the packaging of finished products involve significant dust hazards; alkaline dust can irritate the respiratory tract, causing rhinitis, tracheitis, and even chemical pneumonia. 　　Noise – Blowers, compressors, centrifuges (filters), and crushers generate significant noise, which can lead to hearing loss and nervous exhaustion among workers in these positions; in severe cases, it can cause deafness. 　　Explosions and poisoning – although uncommon, conditions that could lead to explosions and poisoning may arise. If the carbonization off-gases used for calcium removal in saline water contain large amounts of ammonia, they may also carry small amounts of other flammable gases such as carbon monoxide and methane; all of these can form explosive mixtures with air. They can accumulate in the dead corners of tanks, vessels, and towers, and an explosion can occur when exposed to a source of ignition. In addition to the calcium removal, ammonia absorption, and carbonization units (especially during maintenance), attention should be paid to ammonia poisoning and carbon dioxide asphyxiation. 　　Safety measures 　　1. Workers who come into contact with lime, ammonia solutions, ammonia mother liquor, and lime milk should wear alkali-resistant work clothes and gloves, as well as protective glasses while working. When working in areas with high levels of lime and soda ash dust, it is also necessary to wear protective goggles with a windshield frame. 　　2. Install water spray and eye wash facilities at the aforementioned positions. If it contacts the skin or eyes, rinse the affected area immediately with plenty of clean water for at least 15 minutes. 　　3. All rotating and transmission equipment shall be equipped with protective covers or guards to prevent mechanical injuries; it is advisable to install safety limit devices as well. 　　4. Comprehensive control of toxic gas leaks and dust. In all areas where ammonia or carbon dioxide is used, or where such gases are generated, the production equipment must be enclosed to prevent any leaks or spills. It is best to implement automated remote control while carrying out production in a closed environment. Dust from limestone, coal, etc. can be controlled through humidification methods, while dust removal at packaging stations is achieved using measures such as ventilated bag filters. 　　5. Strictly adhere to the process safety regulations during production, especially by carefully controlling the liquid levels in the ammonia absorption tower and ammonia vaporization tower, to prevent ammonia leaks that could lead to explosions and poisoning. 　　6. Pay attention to safety during maintenance work, and strictly implement the permit system for entering towers and cylinders, performing safe welding operations, and working at heights. Before entering the tower or tank and carrying out hot work, the system must be isolated (using blind flanges or by disconnecting pipelines; valves cannot be used for isolation), and inert gas purging analysis as well as air purging analysis must be conducted. Work can only begin once the levels of flammable and toxic gases are within acceptable limits (usually below 0.5%), and the oxygen level is also within the required range (usually above 19%). Someone must be assigned to supervise the process and monitor any changes in conditions at all times.

Overview of the main occupational hazards in caustic soda production. The processes of ammonia synthesis and caustic soda production involve harsh operating conditions such as high temperatures and pressures. The main hazardous materials involved in these processes include semi-water gas, shift gas, syngas, liquid ammonia/ammonia water, carbon dioxide, soda ash and its dust, ammonium chloride and its dust, etc. As a result, there are risks of fires, explosions, corrosion, chemical burns, carbon monoxide poisoning, and suffocation during production. Dust and toxic fumes may pose hazards during the drying and packaging stages. In addition, various rotating equipment, electrical equipment, as well as equipment and pipelines for handling high-temperature materials used in production can also pose risks such as mechanical injuries, electric shock, and burns from high temperatures. The hazard characteristics of the main harmful substances in the caustic soda production process are as follows: 1) Carbon monoxide (one of the components of the conversion gas). Carbon monoxide is a colorless and odorless gas. It is flammable and explosive, with a auto-ignition temperature of 610°C and a specific gravity of approximately 0.97. Its explosive limit in air is 12.5–74.2%. This substance can bind to hemoglobin in the blood, causing tissue hypoxia and posing a serious threat to the human body. After inhalation, one should immediately go to a place with fresh air; in severe cases, artificial respiration and chest compressions should be performed, and medical attention sought. The maximum allowable concentration in the air is 30 mg/m3. When extinguishing a fire, first cool the surrounding objects with water, and only then proceed with extinguishing the fire after cutting off the gas supply. 2) Hydrogen (one of the components of conversion gas, shift gas, decarburization gas, and syngas). Hydrogen is a colorless and odorless gas. It is flammable and explosive, with a auto-ignition temperature of 400°C and a specific gravity of 0.0694. It reacts violently with halogens such as chlorine, fluorine, and bromine, and its explosive limit in air is 4.1–74.1%. This product is non-toxic to humans; it only causes oxygen deprivation and suffocation at high concentrations, thereby exhibiting its **effects**. When extinguishing a fire, first cool the surrounding objects with water, and only then proceed with extinguishing the fire after cutting off the gas supply. Attention should be paid to openings in the roof during storage. 3) Ammonia/gaseous ammonia/ammonium hydroxide: Ammonia is a colorless gas with a pungent, unpleasant odor. The explosive limits are 15.7-27.4%, and the relative density (to air) is 0.6 ； Low concentrations of ammonia irritate the mucous membranes, while high concentrations can cause tissue necrosis. Mild exposure to ammonia gas leads to symptoms such as tearing, coughing, mucosal congestion, and bronchitis; in severe cases, it can result in pulmonary edema, respiratory distress, coma, and shock. Liquid ammonia, ammonia solution, or high-concentration ammonia gas can cause eye burns, and liquid ammonia can also cause skin burns ； Classification of the degree of hazard from occupational exposure to toxins: Grade IV (mild hazard). 4) Ammonium chloride: Ammonium chloride is a white crystal that is odorless; it sublimes at 338 degrees, with a relative density (with respect to water) of 1.5 ； Contact with ammonium chloride and its dust causes mild irritation to the skin, eyes, and respiratory system; ingestion can lead to mild poisoning ； In case of skin or eye contact, rinse immediately with plenty of water. 5) Soda ash: Soda ash is a white powdery crystal that is corrosive and can cause mild irritation to the skin, eyes, and respiratory system. In case of skin or eye contact, rinse immediately with plenty of water. 6) Sodium sulfide: Colorless or yellow granular crystals; in its industrial form, it appears as reddish-brown or brick-red lumps. Flammable, with a relative density of 1.86 and a melting point of 1180°C. This product decomposes in the presence of acids, releasing highly toxic and flammable hydrogen sulfide gas; its aqueous solution is corrosive. Additionally, the anhydrous form of this product can catch fire on its own, so caution is required. In case of skin or eye contact, rinse immediately with plenty of water.

Safety technical measures: 1) Flame arresters are installed on the natural gas pipelines, liquid ammonia storage tanks, and flammable gas vent lines of this project to prevent fires and explosions. 2) For the exposed conductive parts of the power distribution installations and electrical equipment that are normally de-energized but may become energized in case of an accident, this project installs reliable grounding systems in accordance with the requirements of the \"Code for Design of Grounding of Industrial and Civil Electrical Installations\" (GBJ65). 3) Determine the structural type, fire resistance rating, fire separation distances, building materials, etc., for each newly constructed structure based on the fire and explosion hazards associated with production and storage. At the same time, necessary safety evacuation and protection facilities shall be installed within various buildings. Such as safety exits and guardrails, to enable on-site personnel to evacuate urgently in the event of an accident. At the same time, emergency lighting and safety evacuation signs should be installed in buildings with crowded populations and at production sites. 4) Safety devices such as barriers and protective covers shall be installed on the exposed parts of various rotating equipment and belt conveyor systems. At those operational positions within these areas where there is a risk of falling, auxiliary facilities such as escalators, work platforms, and fences shall be installed in accordance with relevant standards. In areas prone to accidents, various safety signs are installed in accordance with regulations, and the corresponding safety colors are applied. Industrial hygiene measures: 1) This project will employ the currently mature and reliable technologies for ammonia synthesis and caustic soda production, featuring a high level of automation and mechanization. The equipment is well-sealed, and most operators work from control rooms; there are few personnel conducting on-site inspections, which effectively reduces the chances of exposure to toxic and harmful substances. 2) All installations and equipment will be designed to be either outdoor or semi-outdoor in order to prevent the accumulation of flammable and toxic gases. To address the potential hazards of dust and toxins in the calcination process of the double-alkali plant, as well as in the ammonium chloride production and packaging processes, the production site will enhance equipment sealing and ventilation; local ventilation systems will be installed in certain areas to ensure that dust concentrations in the workshops remain within acceptable levels. Meanwhile, appropriate personal protective equipment will be provided for the operators. 3) In areas where operators may be exposed to toxic substances such as liquid ammonia, ammonia water, soda ash, and ammonium chloride, a set of emergency showers and eyewash stations will be installed to minimize the potential harm caused by these corrosive materials to the operators. 4) In the design, silencers are installed at appropriate locations on the steam and gas vent lines to reduce the noise generated by gas venting. When calculating the pump, it is necessary to ensure that NPSH available > NPSH required, thereby preventing vibration and noise caused by cavitation in the pump. Select the fluid flow velocity within the pipeline appropriately to reduce pipeline vibration. The noise level of various pumps and motors is specified clearly in the design specifications and ordering instructions; such noise levels must meet **the standard. The pipe support for this pipeline is carefully designed to prevent and reduce vibration. 5) In accordance with the requirements for personal protection, for the material pipelines and equipment in this project that are permitted to dissipate heat, thermal insulation measures are applied when the temperature of the fluid flowing through them is ≥60°C. The heat protection zone includes the localized areas of equipment and pipes that operators might come into contact with, within 2 meters below the ground level or operating platform, or within 0.6 meters of the edge of the platform. 6) All production and living facilities such as changing rooms, washrooms, toilets, and rest rooms required for the various units of this project will be newly constructed. 7) This project will involve the construction of a small gas protection station, equipped with the necessary facilities and personnel to meet the requirements for gas protection and emergency response.

During the production process, proper use of personal PPE is important. Things like gloves, glasses, masks, etc