Circulating fluidized bed boilers rely on coal's clean combustion technology and good adaptability to coal types. They have the characteristics of high combustion efficiency, difficulty in extinguishing fires, and good ash availability. They are widely used in small and medium-sized thermal power plants in my country. It has been rapidly promoted in enterprises and is developing in the direction of large-scale development. However, there is indeed considerable lag in the application and development of slag discharge equipment and systems as auxiliary equipment of CFB boilers. Almost none of the 75t/h and 130t/h CFB boilers that have been put into production in China has a slag discharge system that can operate continuously for a long time. Therefore, it is imperative to develop, develop and promote a new complete set of slag discharge equipment.
2. Differences in the application of CFB boiler slagging equipment at home and abroad
Foreign CFB boilers are equipped with ash cooling devices and ash conveying equipment to cool high-temperature ash and transport low-temperature ash The application of these devices and equipment is basically successful, which is not only related to their design, manufacturing and operation level, but also related to their fuel characteristics (low ash content, small particle size), etc. Since the amount of ash and slag is small and the particle size is small, the cooling and transportation of ash and slag are easy to achieve. Most of my country's CFB boilers use coal with high ash and low calorific value, which has a large amount of ash and coarse particles. The problems of cold slag and slag transportation have not been fundamentally solved. Very few of the 75t/h and 130t/h CFB boilers currently operating in our country have well-formed and complete dry-type slag cooling and slag conveying equipment. Most of them only have slag cooling equipment but no slag conveying equipment. A few CFB boilers also use completely artificial discharge of hot slag, natural stack cooling or direct cooling with water. It not only increases the heat loss of ash and slag, but also pollutes the environment and is not conducive to the comprehensive utilization of ash and slag.
3. Current status of domestic CFB boiler slag removal equipment
The slag removal methods of circulating fluidized bed boilers can be divided into two forms: wet slag removal and dry slag removal.
3.1 Wet slag removal system
It is a hydraulic slag removal system composed of industrial water circulation system, slag ditch, slag flushing water pump, sediment tank and other equipment. It is a typical slag discharge method for large power plants. Although the application technology is passable, when applied to CFB boilers, the activity of ash and slag after water quenching becomes poor, which is not suitable for comprehensive utilization of ash and slag. It also occupies a large area and causes physical heat loss of ash and slag. larger. At the same time, it also brings water pollution and waste of water resources. Therefore, the application of wet slag removal to CFB boilers is not a reasonable slag removal method and will not be promoted.
3.2 Dry slag discharge system
Dry slag discharge is the main slag discharge method promoted by CFB boilers. Generally, dry slag discharge system consists of slag cooling equipment, slag conveying equipment, It consists of a slag storage bin, a slag cooler feed valve, a slag storage bin discharge valve and other equipment. At present, the dry slag cooling and slag conveying equipment used in 75t/h and 130t/h CFB boilers operating in China mainly include the following types.
3.2.1 Spiral water-cooled slag cooler
Commonly known as water-cooled slag cooler, the hot slag advances along the spiral channel, and cooling water with a certain pressure flows in the water jacket of the casing and the shaft The two media flow in the water jacket of the core and blades, and the two media flow in opposite directions for heat exchange. The hot slag can be cooled from 850°C to about 200°C, and the speed-regulating motor can adjust the number of revolutions to achieve automatic control. Its advantages are large heat exchange, low re-ignition, stable operation, convenient adjustment, and small overall size. The disadvantages are that the main shaft and blades wear a lot and are prone to leakage. The blade wear protection tiles need to be replaced every year and require a lot of maintenance. The cooling water quality requirements are high (demineralized water or softened water) and a water circulation system should be set up reasonably. There are still many users using it. use.
3.2.2 Drum water-air-cooled slag cooler
After entering the drum, the hot slag advances along the spiral channel of the inner drum wall. Cooling water and heat pass through the inner and outer drum jackets. The slag undergoes surface reverse heat exchange and can be connected to an air cooling system to cool the 850°C hot slag to 200~300°C. The advantages of the drum slag cooler are small wear, low maintenance, long service life, simple structure and reliable operation. The cooling water quality requirements are not high (softened water or industrial water is enough). The disadvantage is that the heat exchange rate is slightly lower, so the overall size is slightly larger. Currently, it has a wide range of applications.
3.2.3 Steel belt air-cooled slag cooler
This equipment is a new type of dry slag discharge equipment used on 220t/h pulverized coal furnaces. It can also be used For large CFB boilers.
Its structure is mainly composed of a large number of strip-shaped heat-resistant steel plates. Chains on both sides drive it forward at a low speed. The hot slag falls on the steel plates and is cooled to 200°C by negative pressure ventilation over a large area. The cold air absorbs heat and heats up to 300~400°C. It can be used as a conveyor. Wind utilization, the advantages of this equipment are clean and hygienic, stable and reliable operation, good heat energy utilization, and easy to control. However, the equipment cost is too high, the investment is large, and the equipment is bulky, so it is only suitable for large CFB boilers.
3.2.4 Moving bed slag cooler
The ash and slag in the moving bed slag cooler moves from top to bottom due to gravity, and contacts the heating surface or air for heat exchange and cooling. The final slag is discharged from the lower slag port. There are water-cooled, air-cooled and Feng Shui-cooled moving bed slag coolers. The equipment has the advantages of simple structure, reliable operation and easy operation. The disadvantages are large size, poor heat exchange effect, and few applications. It is only used in small-capacity or low-ash fluidized beds.
3.2.5 Fengshui ***-cooled fluidized bed slag cooler
This slag cooler utilizes the gas-solid two-phase flow characteristics of the fluidized bed to transfer heat and is air-cooled. Mainly, water cooling is supplementary. The cooling slag temperature decreases with the increase of air volume and the decrease of slag amount, and the cooling slag effect is the best. Adopting reasonable Feng Shui, the cooled fluidized bed slag cooler has no mechanical equipment, simple structure and low maintenance cost. It does not need to set up a separate fan to save energy. When the outlet air temperature is higher than 200℃, it can be used as secondary or tertiary air into the furnace, cooling Low-temperature water supply or other condensed water can be selected for slag water. The slag discharge temperature is around 120°C. The heat energy recovery is good and the energy saving effect is the best. The supporting slag conveying equipment works safely and reliably, and has good sealing performance. The disadvantage is that the volume is slightly larger. It is a promising ash cooling equipment and should be widely promoted and applied.
3.2.6 Slag conveying equipment for CFB boilers
The slag conveying equipment currently used in China mainly includes scraper slag conveying machines, temperature-resistant belt slag conveying machines, bucket elevators, and chains. Bucket conveyor, positive and negative pressure pneumatic slag conveying equipment, etc. Scraper and bucket lift slag conveyors have a high failure rate, the belt has poor high temperature resistance, can only withstand a temperature of 150°C, and has a small lifting angle, while chain buckets and pneumatic conveying have better results than them.
3.3 Several typical domestic slag discharge systems
3.3.1 It consists of a drum or water-cooled cage slag cooler, an ash scraper, a bucket elevator, a slag storage bin, etc. The mechanical slag discharge system
This system was put into use at Jinzhou Erhe at the end of 1993. The scraper and bucket lift have been modified many times and can operate for a long time and have a large output. However, when the slag discharge temperature is 200 to 300°C, the scraper expands due to heat, the total scraper transmission distance is long, there are many mechanical failures, the bucket lift shell and bucket are greatly worn, the transmission chain link distance is long, the tensile load is large and easy to break, and the amount of maintenance is It is large, has poor operation continuity, and causes great environmental pollution, so it is not promoted for use.
3.3.2 A mechanical slag discharge system consisting of a roller or water-cooled winch, a chain bucket conveyor, and a slag storage bin.
The system uses a chain bucket conveyor to improve its operating conditions. The chain bucket operation is more stable and the output is larger. However, at higher slag temperatures, the rotating parts are also easily damaged and need further improvement. However, the lifting angle of the chain bucket can reach 60 degrees, which is suitable for high-level transmission and can be used for long or short distances. Currently, it is widely used.
3.3.3 The relatively complete dry slagging system developed by Guodian Construction Research Institute for 220t/h pulverized coal furnace
Can be applied to large CFB boilers, the original temperature-resistant belt The slag conveyor was changed to a chain bucket due to burnout. The operation condition is relatively stable, the equipment is clean, and it meets environmental protection requirements. However, the equipment investment is too large and is not suitable for small and medium-sized CFB boilers.
3.3.4 Drum or water-cooled cage slag cooler
The supporting pneumatic slag conveying system has been running in Shenyang Xinbei Thermal Power Company for four years. After various transformations, it has gradually formed a reasonable , complete dry slag discharge system, with certain successful experience.
For more information about engineering/service/purchasing tender document writing and production to improve the bid winning rate, you can click on the official website customer service at the bottom for free consultation: /#/bid