How to select a cold slag extractor for circulating fluidized bed boilers?

I. Purpose: It is a new generation of high-efficiency, environmentally friendly patented product developed by our company based on years of experience in manufacturing drum-type slag coolers (Patent No.: ZL 02 2 19855.5). The SGT type sleeve-type drum slag coolers and the SGP(FSL) type sleeve-type (air) water-cooled slag coolers can rapidly cool high-temperature slag while recovering efficient thermal energy. They are widely used for the cooling and transportation of ash and slag from circulating fluidized bed boilers, bubbling bed boilers, fluidized bed boilers, and waste incineration boilers. They have been used in conjunction with boilers produced by various boiler manufacturers, including Wuxi Boiler Factory, and have received high praise from users. II. Working principle: The slag cooler consists of a feeding and discharging device, a rotating cylinder, a driving device, a rotary joint, and a base, among other components. When the power is turned on, the motor starts to operate; through a reducer, it drives the friction wheel, causing the rotating cylinder to spin. The water inlet valve is opened, allowing cooling water to fill the cooling layer inside the rotating cylinder while ensuring smooth flow of water. The high-temperature material entering from the feeding device goes into the inner cylinder of the rotating cylinder. As the cylinder continues to rotate, the material is continuously transported forward by the spiral guide plates inside the inner cylinder. During this process, the heat emitted by the high-temperature material is transferred from the inner wall of the cylinder to its outer wall, and from there to the cooling water. This causes the cooling water to warm up. Due to the continuous inflow of cooling water, the heated water is constantly discharged, thereby ensuring that the high-temperature material entering through the feeding device is rapidly cooled by the time it reaches the discharge device. III. Structural features: 1. The base of the slag cooler is constructed as an integral structure by welding steel sections together, offering good stiffness, high strength, and strong integrity, which facilitates transportation and installation. 2. The drive system uses variable-frequency speed control or slip control, and a friction drive device is employed to rotate the cylindrical tank, ensuring its smooth and reliable operation. 3. The SGT type slag cooler employs a multi-tube water cooling system, which reduces the size of the equipment, decreases the thickness of the slag layer, **increases the heat transfer area, and enhances the turbulence of the cooling water, thereby improving the cooling efficiency. 4. The slag inlet is equipped with a labyrinth and slag guiding type of sealing, while the slag outlet features a fully enclosed structure and is connected to the conveyor via flanges. Thus, the problem of slag and ash leakage was effectively resolved. 5. The inlet and outlet connections for cooling water utilize new types of rotary joints, along with products from Johnson Company, which effectively solve the problem of leaks at these connections; leaks generally do not occur within one year. 6. The slag inlet section is designed in a gradually expanding shape, which reduces the risk of slag blockage; an emergency drainage hole can be installed at the slag inlet, and guide vanes are provided in the slag transition chamber to ensure that the slag is diverted promptly. 7. Considering the possibility of scaling in the cooling circulating water inside the jacket, the cold slag machine is equipped with a sewage discharge port on its cylinder body for discharging waste water and cleaning off scale. IV. Technical specifications: 1. The slag discharge machine is designed according to the user’s requirements; it has sufficient capacity in terms of slag discharge volume and cooling ability, ensuring continuous slag discharge even when the boiler is operating at full load. The slag discharge temperature ranges from 100 to 250°C, and the machine can operate safely over a long period of time. 2. The cooling water volume for the slag cooler is 3–6 tons of water per ton of slag. The water source used is desalinated water, softened water, or pure water from the power plant; the inlet water temperature is below 30 degrees Celsius, with a temperature difference between inlet and outlet water of 30–60°C. The inlet water pressure is 0.3–0.5 Mpa. 3. The slag inlet pipe of the slag cooler, as well as the spiral plates used for guiding slag in the high-temperature section at the slag inlet, are made of heat-resistant and wear-resistant steels such as 12Cr1MoV and 1Cr18Ni9Ti. This reduces equipment deformation and wear, thereby extending its service life; the designed service life of this equipment is 5 years. 4. The slag cooler employs variable-frequency speed control and slip speed control methods, offering a wide range of output adjustment capabilities; it can be adjusted to any value within the rated output range. The motor is equipped with an overload protection device, ensuring normal startup even under full load conditions. 5. Subject to meeting the cooling requirements, the external dimensions of the slag cooler, as well as the distance between the slag inlet and outlet, can be designed and arranged according to the customer’s requirements. V. Installation, Use, and Maintenance: (I) Installation: Before installation, count the components (including spare parts) and accompanying documents, check the flatness and strength of the equipment foundation, and verify whether the positions of the embedded plates or bolts meet the design requirements and those of the equipment. Then proceed with installation according to the following steps: 1. After the equipment is in place, adjust its level so that the centerline of the cylinder is horizontal, and fix the foot bolts. 2. Adjust the position of the feed hopper so that it is aligned with the slag discharge pipe of the boiler, with the slag discharge pipe extending about 30 cm into the feed hopper. 3. Install the rotating water joint; at the connection point with this joint, both the inlet and outlet pipes should be fitted with flexible hoses or metal hoses. Shut-off valves, pressure gauges, flow meters, and thermometers should be installed on all external pipelines as well as the inlet and outlet pipes. Due to the differences in the water supply pipelines at each user’s site, the gauge valves are the responsibility of the user; they should be arranged in accordance with the <Water Circulation System Diagram>. The specifications and models shall be selected by the user based on the pipelines available at the site that can meet the equipment’s operational requirements, or the company can provide such specifications and model parameters. The operating pressure of the inlet water is 0.3～0.5 Mpa. 4. Electrical wiring (including the enclosure and protective grounding of the box), and check the insulation level according to Class E standards. 5. Inject lubricating grease into the lubricated areas to ensure an adequate supply of lubricant. (II) No-load testing: Before feeding materials, rotate the cylinder so that the vent hole is at the highest point of the cylinder. Unscrew the bolt of the vent hole, open the water inlet valve; once air is released from the vent hole, tighten the bolt of the vent hole and then open the water outlet valve ； Check whether the wiring of the speed control motor is correct. Try to power it on and start the drive motor; once it reaches the normal operating speed, use the speed control controller to adjust the desired speed ； When shutting down, first disconnect the power to the speed control controller for 2-3 minutes, and then cut off the power to the drive motor. Perform the power-on test 2-3 times as mentioned above; once everything is working properly, use it thereafter. 1. Conduct a thorough inspection and no-load test run before commissioning: Thoroughly inspect the inside and outside of the slag cooler; there should be no debris in the drive mechanism area, which must be cleaned thoroughly ； Check the tightness of all components ； Connect the cooling water and check whether the water pressure and flow rate are normal ； After confirming that the cooling water is functioning properly, start the speed control motor at high speed and run the system under no-load conditions at different speeds for 2–4 hours. After shutting down the system and checking that there are no abnormalities in any parts, proceed with trial operations at partial to full load, with the operation time being no less than 4 hours. 2. The trial operation shall meet the following requirements; otherwise, the cause shall be identified and addressed: (1) There shall be no leakage points in any part. (2) It operates smoothly, with no abnormal vibrations or noises. (3) There is no oil leakage from the reducer. (4) The motor temperature rise is within the range specified on its nameplate. (5) The temperatures of the bearings in each section are normal, generally not exceeding 65°C. 3. Before starting the slag cooler, the following checks should be carried out, and appropriate actions should be taken based on the actual conditions: (1) Check for any abnormalities in various parts of the slag cooler. (2) Tightness of various parts of the slag cooler. (3) Check for any foreign objects in the slag cooler, especially in the rotating parts of the drive mechanism. (4) Check for leaks in the water supply pipe of the slag cooler. (5) Is the water flow rate of the slag cooler normal, and is the inlet temperature within the specified range? 4. The slag cooler can be started only after confirming that the cooling water flow is normal; it is advisable to start it at high speed. Adjust the speed according to the amount of slag to be discharged. 5. Before shutting down the slag cooler, feeding should be stopped first; once there is no material coming out of the discharge port, and all parts of the slag cooler have reached normal temperature, then the water supply should be turned off. That is, turn off the water outlet valve. 6. The reducer and all bearings should be inspected regularly, and oil should be added or replaced as necessary. After the slag cooler has been in operation for three months, all the lubricating oil in the reducer should be replaced (90# lubricating oil and 40# engine oil). 7. In cold regions during winter, if the cool slag machine is not in use for an extended period of time, the cooling water should be drained to prevent it from freezing and cracking. 8. The cooling water pipes should be connected using flexible pipes and rotary joints. 9. Cooling water used is demineralized or softened water; after heat exchange, it can directly enter the deaerator, with 100% recovery of waste heat. If industrial water is used, descaling should be carried out regularly (usually once a month). (III) During no-load testing, check the following items: 1. The rotation direction of the cylinder – it should rotate in the direction indicated by the arrow on the product (if no arrow is indicated, it rotates counterclockwise when viewed from the feed end); otherwise, the wiring of the drive motor should be reversed. 2. First, zero the tachometer, then slowly turn the main potentiometer on the speed control controller to determine whether the speed control range meets the requirements. 3. Check for leaks in the water connection; maintain an inlet water pressure of 0.3–0.5 Mpa, and adjust the inlet and outlet valves to control the pressure difference

Abstract: The slag cooler is one of the main sources of failure for auxiliary equipment in domestic CFB systems. As CFB boilers become larger in scale, drum-type slag coolers exhibit the greatest capacity limitations, and they have become a major bottleneck in the development of CFB technology. Starting from the heat transfer characteristics of ash slag, this paper explores the development direction of drum-type slag coolers by analyzing the factors affecting their output, and proposes medium-sized (WWR-E series with an output of 2–5 t/h) and large-sized (WWR-X series with an output of 5–15 t/h) slag coolers. 1. What are the main types of drum-type slag coolers? With the widespread use of CFB boilers, drum-type slag coolers have become the primary type of slag cooling equipment. Currently, the drum-type slag coolers used in CFB systems mainly fall into four series: 1) O-type drum slag coolers: Their main feature is the use of an internal spiral structure; they were first approved for use in Pingdingshan in 1992. Currently, dozens of manufacturers in China are producing this type of slag cooler, and it has become the most widely used slag cooler in the country. The output at temperatures below 200°C (for lengths of 8m or less) is less than 5 t/h. 2) M-type slag cooler: commonly known as multi-tube slag cooler. It can be regarded as a collection of multiple miniature O-type slag coolers. The key advantage is the low slag discharge temperature. The main weakness is low power output. 3) Type E cold slag extractor: The internal spiral blade structure has been eliminated, and a dispersed louver-type blade structure is used instead. For temperatures below 200°C, the output range is 2–10 t/h. 4) X-type slag coolers: They can be considered as a combination of multiple independent E-type slag coolers; for temperatures below 200°C, their output range is 2–20 t/h. 2. Analysis of ways to improve the drum-type slag cooler based on heat transfer principles. The heat dissipation of ash and slag inside the slag cooler occurs through three processes: the slag, the inner cylinder, and water. According to the principles of heat transfer, the following relationship holds: 1/K = 1/Kz + 1/Kg + 1/Ks. Here, K represents the overall heat transfer coefficient; Kz is the heat transfer coefficient of the slag, Kg is the heat transfer coefficient of the inner cylinder (steel), and Ks is the heat transfer coefficient of water. Since both Kg and Ks are much larger than Kz (by tens to hundreds of times), their impact on K is minimal. In heat transfer calculations, it can be approximated as K ≈ Kz. In other words, the heat transfer in the slag cooling machine depends on the heat transfer properties of the slag. The heat transfer of slag includes two aspects: conduction and radiation. That is: Q1 = (T1 – T2)F1λ/δ and Q2 = C0F1[(T1/100)4 – (T2/100)4]/[1/Ar1 + (F1/F2)(1/Ar1 – 1)]. From the above formulas, it can be seen that 1. The conduction heat transfer in the slag cooling machine is proportional to the heat transfer area of the slag ； It is negatively correlated with the thickness of the ash slag. 2. As for the radiation heat transfer of slag, the ratio of the total radiant surface area of the slag to the surface area of the inner cylinder is the most important factor. Making the slag in a scattered state is an effective means to increase the ratio of slag surface area to the inner cylinder’s surface area, thereby enhancing radiation heat loss. The ash heat exchange curve obtained through second-by-second calculation is as follows. It can be seen that the heat dissipation of the cold slag machine, especially in the high-temperature section, relies primarily on radiation cooling. From the above analysis, we can see that effective ways to increase the output of the cold slag machine are: 1) To make the ash and slag in a scattered state; 2) To increase the heat exchange area: for example, by increasing the diameter and length of the inner cylinder, and by installing as many heat dissipation fins as possible on it. 3) Increase the adhesion rate of slag to the inner cylinder, thereby increasing the heat exchange area. 4) Reduce the thickness of the ash sludge. 3. Comparison of the output capacity of various types of drum-type slag coolers: Although the types and specifications of slag coolers manufactured by different companies vary, for a given application site, the space required for installing such coolers remains the same. Moreover, the design of various drum-type slag coolers (the outer cylinder and accessories) is basically the same; therefore, we chose slag coolers with identical outer and inner cylinder diameters for a simple comparison: 1) O-type slag cooler: It allows for a small amount of slag dispersion through a scattering plate (or scraper), with a slag accumulation thickness of 150–300 mm and a wall-adhesion rate of 0.2–0.3 (which decreases as the cylinder diameter increases), resulting in the smallest heat dissipation area. This is precisely the main factor contributing to the insufficient output of cold slag machines in China at present. Although there are many manufacturers claiming a capacity of 20 t/h, both theory and practice show that below 200°C, the capacity cannot exceed 5 t/h. 2) M-type cold slag extractor: Almost no spillage; the slag accumulation thickness is 30–50 mm, and the wall-adhesion rate is 0.25–0.3 (decreasing as the diameter of the small cylinder increases); it has a larger heat dissipation area than the O-type. However, since the ash slag needs to be dispersed into multiple inner cylinders, blockage at the slag inlet is likely to occur ； Furthermore, since the blades cannot be fully welded to the inner wall of the inner cylinder, they are prone to deformation under high-temperature operation, which poses a risk of ash and slag blocking the small cylinder. Type E cold slag conveyor: The ash and slag are dispersed in a fully scattered manner during operation, achieving maximum radiation cooling efficiency. The slag accumulation thickness is below 50 mm, with a wall-adhesion rate of 0.45–0.50 (varying depending on the tangent deviation angle of the blades); the heat dissipation area increases by over 80%, and a capacity of 8 t/h can be achieved in the temperature range below 200°C (for units with a length of 8 meters or less). 3) X-type cold slag conveyor: The ash and slag are dispersed in a fully scattered state during operation, achieving maximum radiative heat dissipation efficiency. The slag accumulation thickness is below 50 mm, with a wall-adhesion rate of 0.45~0.50 (varying depending on the tangent deviation angle of the blades). The total heat dissipation area is 1.955~3.55 times that of an O-type slag cooler, while the wall-adhesion area is 5~8 times that of an O-type slag cooler. It can be said that this is a major breakthrough for China’s cold slag cooler industry! It laid the theoretical and practical foundation for a slag cooler with an output of 30–50 t/h (slag discharge temperature of 150°C).

Thank you to the moderator for providing the information. Could you please let us know the performance of these users, so that we can send someone to conduct an inspection?

This post was last edited by dongjiang1001 on 2012-5-5 at 16:04. The sealing mechanism of this device utilizes Natural’s patented technology; it is a telescopic and fully dynamic sealing system designed specifically for handling powdered substances such as dust from boilers. It offers excellent sealing performance, good air permeability, prevents dust leakage, does not affect the telescoping and swinging of the boiler’s ash discharge pipes, and completely eliminates dust leakage during ash discharge. The ash feeding and cooling section is made of 16Mn wear-resistant steel plates, and the distributor ensures that the high-temperature ash from the boiler is evenly distributed across the needle-shaped tube cooling units, thereby improving the cooling effect. The water cooling tank for the ash inlet fabric cooling section is located outside, to prevent water leakage from entering the cold ash machine. The high-efficiency pin-tube heat exchange unit utilizes Danish Opel’s patented technology for marine boiler heat exchange, and boasts advantages such as high heat exchange efficiency, large heat exchange area, resistance to ash blockage, and a long service life due to its wear resistance. All of the welds on this unit are located outside the housing, which prevents water leakage from entering the cold ash chamber. The ash discharge valve can be an adjustable, leak-proof shaft-sealed ash discharge valve, which features good sealing performance, flexible control, simple structure, and easy maintenance; the specific type is selected based on the actual requirements of the user. Since this device uses water as an indirect cooling medium, its operation is dependent on water; the amount of cooling water must meet the requirements specified for the device’s parameters, and it is strictly prohibited to operate the device in the absence of water supply. To ensure safe operation, safety valves and water-outage alarm devices are installed on the return water pipeline. The entire system of this machine does not rely on electricity, pneumatics, or anything similar; as a result, there is no power loss, which is another of its notable features. IV. Main economic and technical indicators and expected economic and social benefits: Taking the LHJ150–5 fluidized bed boiler ash cooler as an example: (1) Power loss: 0 Kw – 0.75 Kw. ⑵Recyclable waste heat: The cold ash cooler of the LHJ150–5 fluidized bed boiler is capable of heating 30 m3 of water from 20°C to 80°C within 1 hour. The amount of heat that can be recovered is: Q = C x M × (T2 – T1) = 4200 × 30000 × 60 = 7560000000 (J) = 151200 kilocalories. The energy recovered per day is: 151200 x 24 = 3628800 kilocalories. 300 per year: 3628800 x 300 = 1088640000 kilocalories. This is equivalent to 155.52 tons of standard coal. 300 yuan per ton: 155.52 x 300 = 46,656 yuan. ⑶Ash recovery: 120 tons of high-quality fine powder ash with excellent activity is recovered each day; this ash can be directly added to cement. At a conservative estimate of 3 yuan per ton, the daily revenue from this activity amounts to 120 x 3 = 360 yuan. Assuming 300 operating days per year, the total annual revenue would be approximately 360 x 300 = 108,000 yuan, which is equivalent to 108,000 yuan. ⑷This results in a water savings of about 60 tons per day; over 300 days in a year, that amounts to 18,000 tons of water saved. At a cost of 1 yuan per ton, this translates to annual savings of 18,000 yuan. In summary, a LHJ150–5 fluidized bed boiler ash cooler can save nearly 160,000 yuan in economic benefits per year. The social benefits it brings, such as those in terms of environmental protection, are also immeasurable and enormous.

For fluidized bed slag coolers, air-water combined slag coolers are used, while drum slag coolers are more common. Air-water combined slag coolers tend to have more problems; currently, drum slag coolers seem to be more widely used

I would like to use the cooling water from the slag cooling machine to supply heating for the factory premises. Do any experts have any good suggestions? It would be even better if there are existing solutions available; please share them with me. Thank you in advance

The selection of elements is very comprehensive; great material

Reply to 1# fendi: We use a drum-type cold slag extractor

The original poster’s description is very detailed, and the explanation regarding the selection of slag coolers is accurate as well. At present, the domestic market for slag coolers is rather chaotic; the manufacturing processes are simple, and there are concerns about shoddy quality. It is hoped that standards can be established to regulate this area.

Henan Shenghuo Company produces cold slag removers of various design types (multi-tube type, Songling-enhanced louvered drum cold slag remover, membrane drum cold slag remover). These products offer excellent performance, high reliability, and a long service life. For inquiries, please contact Mr. Li at 13383856060.