Introduction
Company originally had a pre-decomposition kiln clinker production line designed for 4500t/d, and was equipped with a pure low-temperature waste heat power station with an 8.1Mw. As the output of cement kilns continues to increase, the temperature of the outlet waste gas of C1 cyclone is gradually decreasing, that is, the gas temperature of the SP waste heat boiler population decreases year by year with the increase of the thermal efficiency of cement kilns. The reduction of waste heat resources at the end of the kiln leads to the reduction of the power generation of waste heat power stations.
Faced with this reality, the company has carried out a series of optimization and transformation work in order to increase the residual heat power generation at the end of the kiln. This article summarizes the technical transformation of waste heat power stations, especially waste heat boilers, for reference.
01
Technical transformation of low-frequency acoustic clean system of kiln tail SP waste heat boiler
At the beginning of 2020, the company transformed the original vibration and ash cleaning system of kiln tail SP waste heat boiler into a low-frequency acoustic clean system.
1.1 Main defects of the vibration and cleaning system
(1)Original SP waste heat boiler vibrating and cleaning device Maintenance and maintenance . The hammer head, pin and the vibration and drill rod are all consumable parts and must be replaced frequently. The vibration and drill rod is very easy to deform and stuck and cannot be replaced online.
(2) vibration device causes interrupted impact on the heated surface heat exchange pipe, which can easily damage the welds on the heated surface and cause boiler water leakage and other accidents. boiler heating surfaces are closely arranged, and the repair of damaged welds is insufficient. Often, the entire group of heating surfaces can only be shortened at in container. Often, more than a dozen heat transfer pipes are shortened to deal with a weld port. This causes the boiler heating surface to continue to decrease, indirectly reducing waste heat generation, and increasing maintenance workload and maintenance costs.
(3) vibrating rod has air leakage problem , which not only increases the power consumption of high-temperature fan , but also has no effective solution. Moreover, the vibration hammer and vibration rod are rigidly collided, and the noise pollution problem of is more serious .
(4) Kiln tail boiler system has large dust content, and the dust particles are finer. It is not timely or clean, which is very easy to cause large-scale ash accumulation or instantaneous material collapse, seriously affecting the heat exchange effect and causing instantaneous overflow of high-temperature fans, affecting the stable operation of the kiln system.
1.2 Advantages of low-frequency sound wave cleaning system
(1) Low-frequency sound wave cleaning system is simple (see Figure 1), daily operation is simple, just follow the debug settings to remotely control, and the on-site equipment is almost zero maintenance.
Figure 1 Low-frequency sound wave clean system
(2) The driving force comes from the existing compressed air, and can save electricity for vibration and activate about 7.7~9.9kWh/h.
(3) Low-frequency acoustic cleaner uses the inherent low vibration frequency . The dust particles are evenly discharged, and will not form large-area dust accumulation or collapse of materials. It will prevent the instantaneous overflow of high-temperature fans from , ensuring that the kiln system can operate stably; clean the dust.
(4) Low-frequency sound cleaner is sealed and welded between the furnace wall, and there is no air leakage problem , and the ash cleaner loudspeaker is facing the inside of the boiler, and the noise pollution is low.
02
Kiln tail waste heat power generation system sealing transformation
Kiln tail waste heat power generation system is mostly above 6000Pa due to negative pressure, whether it is the waste heat boiler bypass valve, the boiler body furnace wall, or the ash bucket and the ash unloading valve system, it is easy to cause the system to be sealed due to problems such as sealing device design selection, design structure, welding quality, thermal expansion and contraction, causing the high-temperature wind to run away from the bypass in vain or the waste heat quality is reduced due to leakage of cold air, which has a great impact on the waste heat power generation and additionally increases the operating load of the high-temperature fan.
(1) Replace the kiln tail flue gas valve with a double-axis double butterfly valve to solve the problem of air leakage by the boiler.The flue gas bypass valve of the kiln tail waste heat boiler originally used the louver valve . The valve sealing performance is relatively poor. Under high-temperature operating conditions, the valve plate has been deformed, it is not closed tightly, and it is not flexible to open and close easily. A large amount of high-temperature flue gas leaks directly from the bypass into the high-temperature fan, causing a lot of waste heat and affecting the power generation. During peak-off maintenance in winter, the louver valve is replaced with a new double-axis double-disc flue shutoff valve. The actual air leakage volume is less than 3%, so that high-temperature flue gas can enter the kiln tail waste heat boiler more, improve waste heat recovery efficiency, and significantly increase the power generation. In addition, the valve plate does not accumulate dust when it is closed, which avoids the problem of a large amount of dust accumulation entering the high-temperature fan causing the fan to jump and stop.
(2) Solve the serious problem of expansion joint leakage of the kiln tail boiler ventilation beam. The expansion joint of the original ventilation beam adopts spliced simple expansion joint, which cannot completely eliminate the thermal expansion and contraction of the ventilation beam itself. Cracks often appear in the welds between the expansion joint and the ventilation beam. Due to the limited position of the expansion joint, welding is very difficult. After each repair and welding, the weld will be pulled open again within a few days. This repeatedly becomes a difficult technical problem. During the renovation, we removed the original spliced square expansion joint and replaced it with an integrated circular expansion joint. Judging from the operation for one year, the problem of ventilation beam expansion and leakage air outlet has been completely solved and the effect is good.
(3)Kiln tail boiler furnace wall expansion joint original structure is difficult to achieve sealing welding, and air leakage between the furnace walls is serious. Due to the huge size of the kiln tail boiler, the two-layer boiler furnace walls are mostly connected by welding expansion joints. The disadvantage of this structure is that it is difficult to welding on site, which leads to the fact that most kiln tail boilers cannot achieve complete sealing between the two-layer furnace walls. You can often hear a leaking sound on the spot, but repeated welding is useless. The company adopts an integrally bent sealed expansion joint structure, and completely solves the problem of air leakage in the boiler furnace wall through transformation.
(4) Boiler ash bucket unloader (original double reprint valve) has internal air leakage, and it is replaced with star rotary discharger , solving the internal air leakage problem.
03
Kiln tail waste heat boiler cooling and efficiency improvement
3.1 Reason for transformation
Company waste heat power generation system kiln tail SP waste heat boiler smoke exhaust temperature is higher than the design value (210℃), and the inlet temperature of the high-temperature fan fluctuates around 235℃. When the raw material mill is shut down, in order to reduce the flue gas temperature to meet the allowable operating temperature of the tail dust collector , the humidification tower needs to start running when the raw material mill is shut down, with a daily running time of about 4 to 5 hours. The resulting water consumption is about 15 to 20t/h and an electricity consumption of 200kWh/d. So how to solve the problem of how to solve the problem of excessive flue gas temperature at the outlet of the original SP waste heat boiler, reduce the smoke air temperature at the inlet of the high-temperature fan, and shut down the operation and humidity increase tower. If the boiler heating surface is increased to reduce the smoke exhaust temperature of the SP boiler by about 15℃, it can effectively increase the waste heat generation by more than 600kWh, and it can also reduce the operation output power of the high-temperature fan, saving about 60kWh of power consumption. Related calculation parameters are shown in Table 1.
Table 1 Calculation of power saving value of high-temperature fan motor after the flue gas temperature of SP boiler is reduced by 15°C
3.2 Renovation content
Adjust and increase the heat transfer area of SP waste heat boiler economizer heat transfer area (see Figure 2). original boiler economizer heat transfer area was 1411m², which was increased to 2686m² after adjustment. This transformation can reduce the smoke exhaust temperature of the waste heat boiler by about 15°C, that is, the fluctuation range of the boiler smoke exhaust temperature is reduced to about 216°C. After the renovation, the steam production of the waste heat boiler will increase by 3.5t/h, and the power generation can be increased by about 600kWh/h.
Figure 2 Increase the heat transfer area of the economizer of the SP waste heat boiler
04
Conclusion
In the process of continuous improvement of cement kiln production and continuous improvement of heat exchange efficiency, the reduction of waste heat resources at the kiln tail has led to a decrease in the power generation of waste heat power stations.In order to change this situation, the company transformed the original vibration and cleaning system of the kiln-tail SP waste heat boiler into a low-frequency acoustic cleaning system; strengthened the seal of the power generation system; increased the boiler heating surface, and reduced the smoke exhaust temperature of the SP boiler by about 15℃. After the renovation, the steam production of the waste heat boiler will increase by 3.5t/h, and the power generation can be increased by about 600kWh/h. Practice has proved that technological transformation that is practical and adaptable to local conditions has small investment and good benefits, which is worth summarizing and exchanging.
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