Application of air cooler in rotary kiln tail of cement industry

The air cooler is a device that uses air as a cooling medium to cool the high temperature flue gas to the desired temperature. Since 1930s, air cooler has been widely used in large petrochemical enterprises after many improvements. In recent years, due to the promotion of new dry cement production line, air cooler also began to be applied in the cement industry, and achieved good economic benefits. The powder in high-temperature flue gas has different physical properties between at dry-process cement kiln head and kiln tail, thus kiln head and tail adopt different cooling meatures. The powder in kiln head flue gas has larger particle size, small viscosity, so air cooler is used more. However, due to the viscosity and concentration of the dust contained in the kiln tail flue gas are big, it is easy to cause the heat transfer tube to be clogged, therefore, there is a general use of humidifying tower.

But the humidifying tower has the following disadvantages:

1) the tower takes too much space and is too high, so it is difficult to operate and maintain.

2) the consumption of water resources is too large, the spraying is too frequent, the automation is low, the nozzle is easy to plug and difficult to clean.

3) low reliability, easy to happen wet bottom, affect the process production.

In view of the above shortcomings, it is urgent to use the air cooler to cool down the flue gas at the kiln end. This paper mainly discusses and introduces the application of kiln air cooler in cement industry.

1. Conventional air cooler problems

Kiln tail flue gas is characterized by: large flue gas, high temperature, high concentration and contains acid and alkali oxides and other corrosive ingredients. In addition, more than 60% of the dust particle size is less than 2.5 μm, making the dust viscosity. Flue gas through the cooling of the steel pipe easily lead to clogging. In fact, at first when the dry cement production line was introduced into China, the kiln tail flue gas treatment has indeed tried the air cooler. At that time the cooling pipe diameter of air cooler was less than Φ60 mm. Shortly after put into use, due to the nature of the kiln tail flue gas, serious obstruction within the tube happened, affecting the normal operation of the process. So solving the steel cooling pipe blockage is the key to decided success or failure of air cooler application in kiln tail.

Usually there are three ways to prevent and clear the blockage:

1) By reducing the inner diameter of the steel pipe or reducing the number of steel pipes to improve the speed of flue gas into the cooling steel pipe, so that smoke quickly through the tube to reduce the fouling time. Disadvantages: high-speed flue gas will flush and wear the nozzle, reducing the life of the cooling pipe, and increase the resistance of the tube and exhaust fan energy consumption.

2) Expand the diameter of the cooling steel pipe. Disadvantages: cooling pipe diameter to expand, resulting in a sharp decline in heat transfer efficiency, need to increase the cooling fan air volume and power.

3) direct removal of the cooling tube fouling, when the popular gas box pulse or anti-blowing cleaning technology, low efficiency, low strength, making clear the block is very difficult.

Neither of these 3 methods can solve the problem effectively. The blockage of the cooling steel tube seriously affects the normal process production, which has led to the stagnation of the air cooler in the kiln for many years.

With the development of new technology in dust removal field, after years of development, pulse jet cleaning technology has become the mainstream, with high efficiency, high strength, one to one injection characteristics. It has been widely used in all walks of life dust removal equipment. Can we combine the pulse jet blowing and soot cleaning technology to improve the air cooler again so that it can be applied to the flue gas field at the kiln end? After careful analysis, each cooling tube is like a filter bag, which can be used as a dust collector, so that each cooling pipe is pulsed by the pulse air flow to remove the dust attached to the inner wall of the cooling pipe.

After analysis and demonstration by dust removal test: for an upright cooling pipe, one end is fixed, one end is articulated, use high voltage (0.5~0.7 MPa) gas pulse to inject the interior of the pipe, and the cooling pipe vibrates to a certain extent, accompanied by the gravity and downward gas flow driven, to make the dust off the tube wall, so as to eliminate dust tube blockage.

2. Characteristics and application of new air cooler

According to the above analysis, a new type of air cooler with pulse dust cleaning device is developed for the heat exchange of cement kiln flue gas (hereinafter referred to as new air cooler, which is used to distinguish traditional air cooler). Under the premise that the heat exchange efficiency is guaranteed, the inner wall ash accumulation of the heat exchanger tube can be removed and the overall area and height of the air cooler can be reduced without increasing the caliber of the heat exchange tube.

2.1 structural features

The new air cooler consists of dust cleaning system (gas storage tank, blow pipe, nozzle, pulse valve, Dan Xiangfa), cooling pipe and axial fan. It has the following characteristics:

1) the heat transfer steel pipe is arranged in a row arrangement, each pulse valve corresponds to a spray tube, each spray pipe is corresponding to a row of heat exchange tubes, and a nozzle on a spray pipe is corresponding to a heat exchange pipe opening.

2) the flue gas passes through the interior of the heat exchange tube, and the inner wall of the heat exchange tube is gradually accumulated ash.

3) the gas storage tank and the blowing pipe are connected by a one-way valve, and only the high-pressure jet flow is allowed to pass one-way, and the pulse valve is not damaged by the reverse passing of the high temperature smoke stream.

2.2 Operation and maintenance

To ensure the normal operation of the air cooler at the kiln end, we should pay attention to the following points:

1) the normal operation of the dust cleaning program

Check the working state of the pulse jet device, according to the dust concentration, set the time gathering 2mm-thick dust inside the pipe wall as the dust pulse cleaning cycle. In actual operation, if the resistance of air cooler is increased, the ash cleaning period can be reduced accordingly. Once the blowing device fails, it needs to be dealt with in time to prevent the failure of the pulse cleaning in the cooling pipe.

2) Check the inner seal of the air cooler

Air tightness leakage of welding seam or manhole will cause water vapor into the air cooler. The corrosive components in the flue gas of the kiln will aggravate the fouling of the dust when it meets the water vapor, leading to the weakening of the effect of cleaning the cooling pipe.

3) the normal operation of axial fan

The axial fan provides a forced heat exchange between the ambient air and the cooling pipe, which ensures the performance of the air cooler. Therefore, the reliability of the axial fan influences the cooling and cooling effect of the air cooler. In order to ensure the continuous and reliable operation of axial fans, proper maintenance procedures should be carried out.

In addition, during the operation of air cooler, it is necessary to check and record the temperature data regularly. Compared with the normal temperature, the system error is found in time, and the alarm is given and handled in a timely manner.

Under the condition of more and more shortage of water resources, the use of air coolers to cool high temperature smoke is the direction of the development of flue gas cooling. The successful application of the above cases proves the feasibility of the application of the new air cooler at the cement kiln end. This will greatly expand the range of the use of air coolers, especially in the field of flue gas cooling with high viscosity and high concentration dust.