With the continuous improvement of people’s living standards, people’s demand for plywood is increasing. According to the data provided by the China Timber Circulation Association, my country’s plywood industry has developed rapidly. In 2003, my country’s plywood output was 455.34 million cubic meters. A large number of plywood factories have been put into production. How to define the fire hazard of industrial formaldehyde storage tanks and glue workshops in plywood factories, and how to eliminate the danger of dust explosion in production, all of these are very annoying. This article discusses these two aspects, taking the CUZI Industry factory as an example.
Ⅰ.Fire hazards of industrial formaldehyde storage tanks and glue-making workshops
Take CUZI Industry as an example. Its glue-making workshop uses industrial formaldehyde (37% concentration), urea, a small amount of formic acid and liquid sodium hydroxide to produce urea-formaldehyde resin glue, which is used as a bonding agent for composite boards. Therefore, plywood factories are equipped with raw material industrial formaldehyde storage tanks. So, do industrial formaldehyde storage tanks belong to Class A fire hazard, Class B fire hazard or Class C fire hazard?
1.Physical and chemical properties of formaldehyde
Formaldehyde, chemical formula HCHO, molecular weight: 30.03, is a colorless gas with a strong pungent odor. It is gaseous at room temperature, with a flash point of 50℃ (37%), a lower explosion limit of 7.0%, and an upper explosion limit of 73.0%. Its vapor forms an explosive mixture with air, which can cause combustion and explosion when exposed to open flames and high heat. If exposed to high heat, the internal pressure of the container increases, and there is a risk of cracking and explosion. It is easily soluble in water, alcohol and ether. According to the lower explosion limit classification, it should be classified as a Class A dangerous item.
2.Formaldehyde production process
The raw material methanol is mixed with air and water vapor in a certain ratio through a heater and a filter into a gasifier, and the methanol is oxidized into formaldehyde by a catalyst. The formaldehyde gas and water vapor are condensed and cooled and absorbed by an absorption tower to form a 37% concentration formaldehyde solution. Because industrial formaldehyde is easy to polymerize into polyoxymethylene when the temperature is below 6°C, and methanol has a certain anti-condensation effect, industrial formaldehyde generally contains a certain amount of methanol with Class A fire hazard.
3.Physical and chemical properties of industrial formaldehyde
In industry, formaldehyde is produced and consumed in aqueous solutions containing different amounts of methanol, commonly known as industrial formaldehyde, commonly known as formalin. Formaldehyde usually appears in the form of an aqueous solution. Its 37% aqueous solution is called formalin, and the boiling point of this solution is 19 ℃. It is very volatile at room temperature, and the evaporation rate increases with the increase of temperature.
The implementation standards in my country are as follows:
Article 2.2.2 of the “Design Specifications for Synthetic Resins for Wood Industry” LYJ122-92 stipulates that in the industrial formaldehyde solution storage tank area, according to the current national standards, the methanol content in the industrial formaldehyde solution shall not exceed 12%. According to the upper limit, the flash point is about 55°C, which is a Class B liquid. However, due to the improvement of the process and the use of new inhibitors to replace methanol in formaldehyde production, the methanol content in the factory products is generally less than 7%, and the corresponding flash point is higher than 60°C.
In summary, since the methanol content index in formaldehyde in the national standard can be determined through negotiation with the manufacturer, the fire hazard of industrial formaldehyde is uncertain. Therefore, the fire department should pay attention to requiring the factory to use industrial formaldehyde with a low methanol content during the audit. Only when the methanol content in the industrial formaldehyde is less than 7%, can the industrial formaldehyde storage tank and glue making workshop be audited according to the Class C fire hazard requirements.
Ⅱ.How to eliminate the danger of dust explosion in production
In the production of plywood factories, dust fires and explosions often occur in filter devices, silos and drying equipment. It not only causes huge property losses, but also endangers personal safety, and even causes the company to stop work and production. The cause of dust fires and explosions is the sparks or residual burning debris entrained in the combustible materials being processed or dried when they are transported to the dangerous areas of the factory that are prone to fire by pneumatic or mechanical transportation. Therefore, it is recommended that plywood factories should install automatic detection and fire extinguishing systems in production equipment.
Taking Cuzi Industry as an example, it has installed GreCon spark detection and extinguishing systems on dust filter devices, silos, drying equipment and grinding equipment, which are specifically used to detect and extinguish those fire sources existing in pneumatic dust collection systems, so that the fire sources can be extinguished before they reach the filter devices, silos and working areas that are prone to fire and explosion.
1.Dust filtration device and silo protection
GreCon spark detection device is installed on the wall of the dust collection pipe to detect the infrared radiation emitted by the spark. Once the spark is detected, a water spray device that sprays mist will be activated immediately, and the spark will be extinguished. The water spray fire extinguishing device consists of a quick-start solenoid valve and one or more spray nozzles. According to the speed of the transported material, the water spray fire extinguishing device is installed on the pipe wall about 4 to 6 meters (12 to 18 feet) away from the spark detection device along the direction of the logistics. The water spray fire extinguishing device can be activated in an instant. The water mist sprayed by the special water spray fire extinguishing nozzle covers the entire pipe section. The correct arrangement of the water spray fire extinguishing device can make the fire source be completely enveloped in the water mist, so that it can be extinguished in an instant.
2.Protection of drying equipment
When drying combustible materials, sparks and burning embers may appear at any time. The root cause is the emergency brake shutdown, or the presence of over-dried materials in the drying equipment, or the presence of overheated materials in the pipeline. Once the overheated particles left in the drying equipment come into contact with oxygen in the air, the risk of fire and explosion is greatly increased. All areas of the factory connected by pneumatic transportation and the drying equipment itself will be threatened by fire or explosion. Since the temperature in this area exceeds the standard detection temperature of the spark detection device, the spark detection device must be equipped with a light guide search device. The GreCon spark detection device can detect sparks in the pneumatic conveying pipeline of the drying equipment, or in the discharge chute, or in the mechanical transmission equipment. Once a spark is detected, the computer-programmed control device is automatically activated immediately. For example, the water spraying device is activated; or the pneumatic conveying pipeline is closed and cut off; or in extremely urgent moments and when necessary, the drying equipment is stopped urgently, or the entire drying equipment is sprayed with water.
3.Protection of grinding equipment
Grinding equipment requires a very high speed when running. When foreign objects, such as metal chips, stones, etc., fly into the mill, or when the equipment has a mechanical failure, violent sparks are often generated. The GreCon spark detection device can detect these violent sparks and start the fire extinguishing device to extinguish them, thereby protecting the mechanical settings connected behind. The GreCon spark detection and extinguishing system can detect and count each spark with the help of a spark resolution counting device, and can extinguish the sparks one by one without interrupting production. Only when the number of sparks counted exceeds the pre-set number of sparks, or when violent sparks occur, the machine is braked and stopped. This feature avoids severe damage to the machine due to foreign objects flying into the mill or mechanical failure of the equipment.
In short, there are a lot of combustibles in the plywood factory, and the consequences of a fire are unpredictable. Therefore, while doing a good job in approval, the plywood factory should also establish and improve fire management agencies and various rules and regulations at all levels, and continuously improve the fire safety awareness of enterprise cadres and employees, so as to fundamentally reduce the occurrence of fire accidents and ensure the healthy development of the plywood factory.
