Solution for detecting explosive dust concentration in feed and food workshops

In recent years, with the increase in factory production capacity in various regions, combustion and explosion accidents caused by combustible dust have occurred multiple times, resulting in serious casualties and property losses, which has attracted widespread attention from all sectors of society.

Common dust explosions include flour mill dust explosion, dairy refrigerator explosion, grain dust explosion, plastic dust explosion, cheese factory spray dryer explosion, sugar explosion, cement factory dust explosion, polishing dust explosion, etc., especially flour mill and grain industry dust explosion is particularly high. How to comprehensively detect the dust content in hazardous process sections is a problem that every dust related enterprise must consider.

What is a dust explosion

Dust explosion is caused by the high pressure generated by the combustion of combustible dust suspended in the air. Dust is a tiny particle of solid matter, with a much larger surface area compared to block like substances of the same weight, making it prone to ignition. If it is suspended in the air and reaches a certain concentration, it forms an explosive mixture.

Dust explosion is very dangerous because when encountering a heat source (open flame or temperature), the flame instantly spreads throughout the mixed dust space, the chemical reaction speed is extremely fast, and a large amount of heat is released, forming high temperature and pressure. The energy of the system is converted into mechanical work and radiation of light and heat, which has strong destructive power.

At present, seven types of material dust are explosive: metals (such as magnesium aluminum powder); Coal; Grain (such as wheat, starch); Feed (such as blood meal, fish meal); Agricultural and sideline products (such as cotton, tobacco); Forest products (such as paper powder, wood powder); Synthetic materials (such as plastics, dyes).

Dust fire and explosion accidents often occur in coal mines, flour mills, sugar mills, textile mills, sulfur mills, feed, plastic, metal processing plants, grain depots and other mining enterprises. This is related to the conditions required for dust explosions. Dust explosion itself is a special type of combustion phenomenon, which also requires three conditions: combustibles, combustion aids, and ignition sources.

There are generally three conditions that are prone to dust explosions: (1) combustible dust is suspended in the air at an appropriate concentration, forming what people commonly refer to as a dust cloud; (2) Having sufficient air and oxidants; (3) There is a fire source or strong vibration and friction.

It is generally believed that as long as explosive dust meets conditions (1) and (2), it means that there are signs of potential accidents.

The main hazards of dust explosion

(1) Has extremely strong destructive power

Dust explosions involve a wide range of sectors, including coal, chemical, pharmaceutical processing, wood processing, grain and feed processing, etc. In recent years, the frequency of dust explosions in China has been 150-300 local explosions and 1-3 system explosions per year, with an increasing trend. The dust explosions, especially system explosions, that have occurred in our country have caused serious losses. In 1987, the flax dust explosion accident at Harbin Linen Factory resulted in 58 deaths, 177 minor injuries, and a direct economic loss of 8.82 million yuan.

(2) Easy to cause secondary explosions

The first explosion wave blows up the dust deposited on the equipment or ground. In a short period of time after the explosion, negative pressure is formed in the central area of the explosion, and fresh air around fills in from the outside to the inside, forming a so-called "return wind". It mixes with the raised dust and ignites the second explosion under the residual fire of the first explosion. During the second explosion, the dust concentration is generally much higher than during the first explosion, so the power of the second explosion is much greater than that of the first one.

(3) Can produce toxic gases

One is carbon monoxide; Another type is the toxic gas produced by the decomposition of explosives (such as plastics) themselves. The production of toxic gases often causes a large number of casualties and injuries to humans and animals after explosions, which must be fully taken seriously.

Selection of dust detector

(1) Selection of dust detector principle

At present, the main principles of dust detection include weighing method, beta ray method, and laser backscatter method. The weighing method uses a filter screen to filter and weigh, which is often used for portable detectors. The beta ray method utilizes the absorption effect of dust and is generally adopted by detection institutions due to its large volume and high radiation hazard. Laser backscatter is used to detect the backscattering of dust from a light source. Due to its fast detection and high accuracy, it is the most suitable detection principle for factory workshop environments.

(2) Selection of dust analyzer

The main products on the market are portable pump suction and laser online detection. Portable pump suction is commonly used for miners to carry around when going underground, and is not suitable for continuous testing in workshop environments. Laser online testing is the most suitable testing method for on-site needs.

(3) Selection of dust detector functions

Due to the fact that production workshops are mostly explosion-proof places, the first consideration when choosing a dust detection system is to have an explosion-proof type. From a safety perspective, it is best to require dual certification for gas explosion and dust explosion prevention.

The lower explosive limit varies depending on the dust medium in different places, and the appropriate range should be selected according to the specific medium. For example, feed mills, flour mills, and breweries often produce grain dust, and it is recommended to choose a range of 0-3000 milligrams per cubic meter.

A comprehensive and safe dust monitoring system not only has the ability to detect dust concentration, but also has other functions that need to be considered. When the dust exceeds the standard, it can provide sound and light alarms, automatic ventilation, and multi-point aggregation to the host for monitoring, etc.

Aiyi Technology Solution

Aiyi Technology has specially designed various solutions suitable for various enterprises to address the dust situation in the feed and food industries. This scheme consists of a dust detection unit (laser dust detector), a display unit (explosion-proof display controller, sound and light alarm), and a linkage unit (industrial computer, linkage system), and the scheme can be flexibly changed according to the customer's factory size and functional requirements.

The dust detection unit adopts AGA6050 explosion-proof laser dust analyzer, which uses the principle of laser backscatter for detection. It can measure the dust content in a space of about 5-10m, and the range can be selected from 100~40000mg/m3. Compared to pump suction dust detectors, it has the advantages of large measurement range, high detection accuracy, and maintenance free.

The dust detector is equipped with an explosion-proof box with a window, which can see the real-time dust concentration value on site. When the dust concentration value exceeds the preset alarm value, it will automatically sound and light an alarm to remind the on-site staff. At the same time, the controller will automatically control the workshop exhaust system to replace the exhaust.

For situations where multiple workshops and locations require centralized control, Aiyi Technology can configure an industrial computer for centralized display. The industrial computer has functions such as concentration display, data curve, and historical record.