As we all know, the dry-process cement production line is commonly used in the cement industry. The new type of dry-process cement production process includes four main sections: Pre-homogenization of raw materials, homogenization of raw materials, clinker firing, cement grinding, etc.
Raw material conveying system
The raw material, including limestone, dolomite was crushed and conveyed to the cement factory, then sent to storage by liftfork and lifted to the raw material warehouse, after calculation, the qualified limestone with the size of 10-50mm will be conveyed to the top silo of the preheater. The feed particle size is 10∽50mm, and the finished product particle size is 5∽40mm to reach more than 90%.
Active lime calcination system
Active lime calcination system is composed of a vertical preheater, rotary kiln, cooler, and other auxiliary equipment.
Vertical preheater: The vertical preheater is composed of the preheater body, storage bin, feeding pipe, hydraulic push rod device, etc. The polygonal and round preheaters adopt compartment partition devices to gradually heat the limestone to avoid rapid temperature rises and explosions that would produce a large amount of powder. The decomposition rate of the limestone entering the kiln reaches 30%∽40%, and the average temperature of the discharged gas is 230℃∽ 260℃, thereby reducing system heat consumption.
Rotary kiln: The rotary kiln consists of a cylinder, a support device, a variable speed transmission device, a wheel blocking device, a kiln tail and kiln head seal, and a kiln head cover. The kiln body is placed at an inclination of 3.5% to the horizontal. Equipped with two sets of support devices, the supporting wheel bearing is a water-cooled oil spoon-lubricated sliding bearing and has spherical tiles that can be automatically aligned. There is also a hydraulic gear wheel near the large ring gear. A variable-frequency speed motor is used to drive the kiln body, and an auxiliary transmission is provided to drive the kiln body. The kiln head and kiln tail adopt a spring leaf sealing device. The frequency conversion motor is used to drive the kiln body, and the decomposition rate of the preheater is used to effectively control the calcination time and temperature to meet the raw and over-burning index requirements. The burner adopts a four-channel burner with mixed combustion of coal and gas. The adjustment is flexible and convenient, and the operation is free. The ejection speed of each air duct can be adjusted at will during operation, and any flame required under different kiln conditions can be adjusted. The kiln calcining temperature is easy to control.
Vertical cooler: The vertical cooler is composed of a cooler body, a fixed screen, a cooling air device, an electric vibration unloader, etc. The vertical cooler is divided into several cooling and discharging areas. The discharging speed of each area can be controlled independently according to the material temperature; the cooling air directly contacts the hot lime in the cooler, and the cooling effect is good; the ash discharging temperature is low; and the ash discharging temperature is low. At approximately 40℃ higher than the ambient temperature, after cooling the lime, the temperature of the cooling air can be preheated to above 600℃. Part of it is used as the secondary combustion-supporting air of the rotary kiln, and the other part is used to dry the pulverized coal. The cooler has no moving parts, a simple structure, a good cooling effect, and requires less equipment maintenance.
Pulverized coal preparation system
Pulverized coal preparation is an important part of the active lime rotary kiln system using coal. There are generally two systems. One is a pulverized coal preparation system consisting of an air-swept tube coal mill and a bag dust collector. This system has the advantages of easy operation and a clean environment. Its production process is as follows:
Coal lumps with a lumpiness of ≤25mm are supplied to the belt by the process bucket lift, then input into the raw coal bunker through the belt and fed into the coal mill through the disk feeder or electromagnetic vibration feeder at the bottom of the raw coal bunker. It is equipment that integrates grinding and drying. During grinding, hot air from the rotary kiln system or hot flue gas from the auxiliary combustion chamber is introduced for drying. The pulverized coal gas coming out of the coal mill enters the pulverizer for separation under the action of the exhaust fan. The coarse pulverized coal is returned to the mill through the automatic ash discharge valve for re-grinding, while the fine powder is in the air flow. It is driven into the bag dust collector to collect dust to achieve the purpose of powder and gas separation. The gas coming out of the powder separator is discharged by the exhaust fan after dust collection and purification. Part of the waste gas is blown into the coal mill for recycling, and the other part of the waste gas is discharged into the atmosphere through the chimney. The pulverized coal collected by the dust collector is discharged into the pulverized coal storage bin in front of the kiln. According to the needs, the pulverized coal is sent to the burner in front of the kiln through a Roots blower, and the burner combustion fan supplies air for combustion and is used for calcining limestone.
Finished product conveying system
The finished lime is transported from the cooler to the elevator through the chain bucket machine, and is sent to the top of the silo through the bucket elevator. After screening, the qualified products with a particle size of more than 5mm are sent to the finished product silo by the belt conveyor, and the powder smaller than 5mm is sent to the powder bin. There are electric discharge valves under the silo, finished product silo, and the powder silo. The main function of the finished product warehouse here is to buffer and measure. The finished products should be sent to the steel factory and calcium carbide factory in time to reduce powdering.
Flue gas treatment system
The high-temperature flue gas generated by the combustion of the rotary kiln undergoes heat exchange with the limestone in the preheater, and the temperature drops below 260°C. It is cooled by the multi-tube cooler and then enters the high-temperature bag dust collector. After dust removal, it is discharged through the chimney by a high-temperature fan. into the atmosphere, and the dust concentration of the flue gas discharged into the atmosphere is less than 30mg/Nm³. To meet the process requirements of the modern activated lime pre-decomposition rotary kiln production line, ensure reliable operation of process equipment, stabilize process parameters, ensure product quality, save energy, and improve the operation rate of the production line. The entire line adopts advanced technology and full process control, adding DCS control based on PLC control, centralized monitoring, operation, and decentralized control of the main production line, and controlling the rotary kiln operating system to improve product quality and reduce consumption. Improve the reliability and maintainability of electronic control equipment to realize the modernization of control, monitoring, and operation.
Cement grinding station
The cement grinding station is a finished cement production unit that separates the final finished product stage in cement production. At this stage, the cement clinker is added to an appropriate amount of mixed materials for powdering to produce finished cement. The production of cement can generally be divided into three processes: raw material preparation, clinker calcination, and cement production. The production process of Portland cement is representative of cement production. It uses limestone and clay as the main raw materials, which are lifted to the silo by a bucket elevator, connected to a hot blast furnace through a dryer, and then lifted by a bucket elevator. After arriving at the homogenization bin, it enters the ball mill and then enters the powder separator through a bucket elevator. The fine materials then enter the screw conveyor through a bucket elevator and are transported to the cement warehouse respectively. Each cement warehouse is equipped with a screw conveyor for finished product transportation.
