Large-scale thermal power plants are still dominated by pulverized coal boilers. There are many powder grinding stations on the market to produce qualified quality pulverized coal to meet the daily power generation needs of thermal power plants. The main production equipments for pulverized coal mills mainly include coal mills, coal transportation equipment, coal unloading equipment and reclaimer equipment. The coal grinding system is the core of the entire coal grinding station.

However, due to the flammable and explosive characteristics of pulverized coal, and the requirement for fineness, many pulverized coal mill have high technical requirements for the preparation of pulverized coal.

As the first-class supplier of grinding system integration in China, CHAENG has devoted itself to the research and production of pulverized coal preparation systems for many years. The project engineer of Xinxiang Great Wall Machinery Coal Pulverized Coal Preparation System introduced us in detail.

1. Pulverized coal fineness is a must for coal mills

For power plant pulverized coal boilers, the fineness of pulverized coal not only has a great impact on the economic performance of the operation, but also has an important impact on the safe operation of the boiler, especially for the boilers that use poor coal and anthracite. If the pulverized coal becomes thick, it will easily cause a series of problems such as boiler fire extinguishing, coking, high-temperature corrosion, reheater over-temperature explosion tube, wear of the tail heating surface, and low combustion efficiency.

Only finer pulverized coal can be burnt quickly and the boilers have less incomplete combustion losses. Accordingly, the efficiency of the boiler can be increased accordingly. (If the boiler is operated under the fineness of pulverized coal, each 600MW boiler can save hundreds of millions of tons per year. coal).

At present, pulverized coal is a common problem in power plants. The main reasons for the pulverized coal are:

1 The problem of the coal mill itself and the quality of the inspections make it difficult for the pulverizing system to reduce the pulverized coal fineness. Pulverizer seal system is poor, the differential pressure at the inlet and outlet of the coal mill is relatively small (usually 1500-2000Pa), and the amount of coal is small. Once the coal is added to the coal mill, the phenomenon of coal mill will occur, resulting in a serious shortage of the milling system. At full load, the entire mill needs to run continuously. If you want to reduce the fineness of pulverized coal, it will cause the powder level to decrease and affect the load.

2 The ball load of the coal mill, the proportion of steel balls with different diameters, and the quality of the steel ball are also important factors affecting the fineness of the pulverized coal. Each pulverizer has its best ball load (the best ball load is determined by tests), and steel ball should be replenished regularly to prevent the steel ball from being too small and affecting its output. The addition of different diameter steel balls in the coal mill is to maintain the fullness of its steel balls to ensure the best grinding effect.

3 The coarse powder separator is an important equipment that affects the fineness of pulverized coal, and it is also a device with many problems. At present, the wear of the coarse powder separator is a very serious problem. In order to prevent the wear, many power plants have installed anti-wear materials inside the coarse separator. Generally, 50 mm thickness is installed on the outer and inner walls of the inner and outer sleeves. Anti-wear material. This problem of wear has been alleviated, but at the same time it has brought about other problems. The flow area of ​​the coarse powder separator has been reduced, the flow state of the air flow has been disturbed, the original design conditions have been destroyed, and the separation effect has deteriorated, resulting in insufficient output. The separator efficiency is reduced. In addition, there are other common problems with the coarse dust separator, such as the air leakage of the access door, the lack of scale on the coarse separator to the outside of the baffle, the inconsistency of the inner and outer openings, the inflexible baffle movement, and the local wear of the coarse powder separator baffles. Severe, folded gaps on both sides of the baffle are too large, etc. These common problems affect the fineness of pulverized coal.

4 The influence of milling air flow rate on the fineness of coal fines is quite obvious. The air flow of the milling process increases, the output of the milling system increases, and the pulverized coal becomes thicker. Sometimes the operating personnel can not adjust the air flow rate of the powder in a timely manner, resulting in excessive air flow in the milling process and the pulverized coal is very thick. 5 Coal quality is an important factor that affects the fineness of pulverized coal. The difference in the erosive coefficient and the ash content of coal will affect the output of the pulverizing system and the pulverized coal fineness. Sometimes the operating personnel cannot adjust the ventilation volume of the pulverizing system according to the change of coal quality, and it will also affect the pulverized coal fineness. Human factors are also an important cause of pulverized coal, and the influence of pulverized coal fineness on equipment and operation is often not immediately apparent. Therefore, the importance of pulverized coal fines is often not given much attention. The manual detection of pulverized coal fineness is difficult to ensure timely. According to the provisions of sampling, testing, adjustment.

To solve the problem of excessive pulverized coal, Xinxiang Changcheng Machinery Co., Ltd. launched a roller coal mill, which is a new energy-saving and energy-saving vertical mill that Great Wall Machinery has combined with senior experts and research institutes at home and abroad to develop. The coal vertical mill adopts an optimized grinding process to ensure high fineness and uniformity of the pulverized coal, and its compound separator also greatly improves the efficiency of powder separation. The mill has a large diameter and a small rolling resistance, so it has good output characteristics and low power consumption. It is the first choice for a new type of coal mill.

Pulverized Coal Preparation System Great Wall Machinery has sold the hottest products for many years. The main machine is a wind sweeping coal mill. This equipment is mainly composed of feeding device, main bearing, rotating part, transmission device, helium device, high pressure starting device and lubrication system. The raw materials are fed into the mill through the feed equipment. The hot air enters the mill through the air inlet pipe. With the rotation of the mill barrel, the coal exchanges heat with the hot air in the mill. The coal is crushed and ground in the mill. While the coal is being ground, the fine powder is carried through the hot air in the mill and out of the mill via the discharge device.

2. The coal grinding station must use various measures to prevent explosion during the preparation of pulverized coal

In the pulverizing system, pulverized coal is transported by gas, and the gas powder mixture encounters a spark that may cause explosion of pulverized coal. In a closed system, the pressure generated by pulverized coal explosion can reach 0.35 MPa, so once the explosion occurs, the consequences are very serious.

So how should we prevent it?

(1) The higher the temperature of the gas mixture, the easier it is to explode. Therefore, during the operation of the pulverizing system, the temperature of the gas mixture at the outlet of the pulverizer should be strictly controlled. The pulverized coal moisture is often reflected in the coal mill outlet air temperature. In actual operation, the coal mill outlet gas mixture temperature should be selected according to different coal types.

(2) The pulverized coal pipeline in the pulverizing system should have a certain inclination angle during installation. Try to avoid horizontal pipelines and dead angles. The flow rate of the gas-powder mixture should not be too low. In the pulverized coal gas flow pipeline, the throttling is reduced. Sedimentation to prevent spontaneous combustion of pulverized coal and causing an explosion.

(3) CO detection device can be used to predict spontaneous combustion and explosion of pulverized coal.