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Uniform ventilation is the basic way to solve the problems of gas generator grates. At present, the large-diameter gas generator grates used by fertilizer companies are all fan-shaped grates. There are many problems with this grate, and the results are not ideal despite repeated modifications. THL-I type furnace grate is a new type of furnace grate used in our factory's φ13.6-meter fixed bed gas generator. This furnace grate has been installed and used in July 1998 and has achieved good results. Compared with the old grate: Gas production increased by 24% ； Back focus reduced by 9.12% ； Vapor decomposition rate increased by 6.14% ； 74% reduction in carry-out ； The slag formation rate is 75%. Moreover, it has great operational flexibility, strong adaptability, and significant economic benefits, which completely solves many problems that have plagued the φ3.6-meter gas generator for many years. 1 Problem raised Uniform ventilation is one of the important factors for stable production of fixed-layer gas generators. It requires: The grate evenly distributes air volume ； There should be no large pieces of slag and too much fine dust in the slag. ； The slag formation rate is high, the slag particles are uniform in size, and the air permeability in the slag is uniform. Uniform ventilation ensures a stable ash layer, fire layer and carbon layer in the furnace, and forms a stable reduction layer above the fire layer. Uniform ventilation allows the coal and coke in the fire layer to be fully burned. When the temperature of the fire layer increases, the steam decomposition rate increases. ； Gas quality and production are improved and back-coking is reduced. The full combustion of coal and coke increases the slag formation rate, and the air paths between the slag particles are smooth and evenly ventilated, which further promotes uniform ventilation in the furnace and forms a stable circulation system. There are several factors in the structure of the old grate that affect the uniform ventilation, such as: The slag breaking ability is poor, and the large slag blocks generated in the slag are difficult to break, causing blockage of the grate and seriously affecting the uniform ventilation in the furnace. And the downward blowing brings out a lot of materials, which causes serious wear and tear on subsequent equipment and pipelines. Local overburning often occurs ； The fire layer burns incompletely and the amount of burnt back is large. ； When the furnace temperature is low, it is difficult to improve gas quality and output. Moreover, the operation is intensive, and it is often necessary to stop the machine to remove large pieces of slag and clear blocked grates. 2 Grate structure with uniform ventilation 2.1 Determine the main structure of the furnace to ensure uniform ventilation in the furnace. First, the furnace grate must distribute air evenly. The operating conditions allow the maximum height of the grate to be 1.80m. In order to increase operating flexibility, the total height of the grate is limited to 1.60~1.70m. Its structure is a laminated grate plate shape, which is composed of a base and several grate plates with angles. The outer diameter circle of the grate plate divides the cross section of the furnace body into several annular wind control areas. The size of each wind control area is proportional to the ventilation volume in that area. ； The inner diameter circle of the grate plate controls the distribution of the air inlet volume, and the ventilation area of the inner diameter circle is determined by the furnace section controlled by the outer diameter of each grate plate. After reasonable design, the wind speed and air volume of the furnace body section controlled by the grate plates of each layer of the furnace grate are basically the same, so that the air distribution of the furnace grate can be achieved uniformly. 2.2 Problems with carried-out objects and grate clogging. The ventilation of the old grate does not have slag-blocking measures. When encountering downward blowing, a large amount of slag and ash is brought out, causing serious wear and tear on subsequent equipment and pipelines. The main reason for the blockage of the grate is that the slag and ash are not discharged smoothly during the rotation of the grate, so that slag and ash of different particle sizes are constantly squeezed into the grate plates, gradually blocking the air duct of the entire grate plate and losing the ventilation capacity. In the laminated grate plate-shaped furnace grate, since each layer of grate plates is tapered upward, and there is a stroke distance of about 300 to 500mm between the outer edge of each layer of grate plates (in contact with the slag) and the inner diameter of the lower layer of grate plates (or base), the slag particles settle during this distance. In order to make the settlement more effective and prevent larger slag blocks from squeezing into the space between the two grate plates and blocking the grate ventilation channels, there are upward and downward folds at the inner and outer diameter circles of the grate plates respectively, and an annular settling chamber is formed between any two grate plates. When blowing down, slag particles and ash are brought in by the wind along the outer diameter of the grate plate. Because there is a downward fold at the outer diameter and the annular area is small, the slag particles pass through it at a high speed. Once the high-speed slag particles pass through the outer diameter section, they encounter a settlement zone with a large annular area, and the slag particles partially settle due to the reduced speed. Due to the obstruction of the upward folding edge at the inner diameter circle, most of the slag particles are blocked in the settlement zone, and a small amount of slag particles are brought out by the accelerated wind speed at the inner diameter, so the carry-out is greatly reduced. When blowing occurs, due to the acceleration effect of the folding edge at the outer diameter of the grate plate, part of the settled slag particles are blown out again. In this cycle, the space between the grate plates is no longer blocked due to the settling of slag particles. Secondly, due to the obstruction of the outer folding edge of the grate plate, slightly larger slag blocks are not easy to squeeze into the annulus between the grate plates and block the air duct, and the grate air duct is unobstructed. 2.3 The formation of large slag blocks, slag breaking and ash discharge problems The formation of large slag blocks, slag breaking and poor ash discharge are interrelated problems. Uneven ventilation is the main reason for the formation of large slag blocks, and the existence of large slag blocks in the furnace directly affects the uniform ventilation. The formation of large slag blocks is due to local overheating in the furnace, which causes local coal and coke to burn into larger molten slag. When the molten slag fails to break in time, the molten slag falls to the ash layer along with the slag ash, and gradually cools to form large slag blocks. The large slag blocks in the furnace cannot be broken and can only move irregularly in the ash layer as the grate rotates. Due to the large volume of large slag blocks, local ventilation in the furnace is uneven. When there are many large slag blocks in the furnace, the ventilation conditions in the furnace deteriorate, and the furnace has to stop and dig out the slag blocks from the manholes, which seriously affects normal production. From the above analysis, it can be seen that the key point to eliminate large slag blocks is to break larger molten slag before it is formed. Therefore, the slag breaking structure should be considered based on the characteristics of molten slag formation. In terms of the grate structure, all the exposed parts of the ash discharge ribs of each layer of grate plates are raised to a height sufficient to stir the slag layer (shaped like an ingot). The slag body is evenly stirred, so that the coke and slag in the furnace continue to squirm with the rotation of the grate, so that the formed molten slag is broken first when it is molten, and large slag blocks will not form. In addition, heightening the extended ends of the ribs also enhances the slag discharge effect. Since the ribs are arranged evenly and clockwise on the grate plate, the slag and ash are continuously pushed by the ribs, and the height of the ribs increases, which will inevitably increase the amount of ash discharge. Therefore, the selection of rib radian should meet the requirements of ash discharge speed and slag creep frequency. The slag breaking and ash discharge structures at the bottom of the furnace are integrated. If the slag and ash at the bottom of the furnace cannot be discharged into the ash box in time, it will cause dead ash. The slag and ash that is constantly pushed down from the top will be blocked by the dead ash, and the gas generator will not be able to operate normally. If the slag blocks that follow the slag and ash cannot be broken and discharged into the ash box in time, they will be blocked and the ash discharge will also be blocked. Therefore, the slag-breaking and ash-discharging structure of the grate base is more important. In order to enable the slag blocks to smoothly fall into the slag breaking area of the base, the outer edge of the grate base and the upper grate plate connected to the base is designed as a wavy quadrilateral. The two parts have similar wavy shapes, and the wavy part and the circular diameter section each account for half of the outer diameter circle. The maximum gap between the grate plate and the furnace body jacket is about 350mm, and the minimum is about 250mm. This structure can ensure that slag blocks within φ350mm can smoothly fall into the base and be broken. The entrance height of the ash box is 300mm, and the height of the outer diameter round section of the base should exceed 300mm, so that the base and the furnace bottom protection plate area form an effective slag block extrusion area. The wavy base strengthens the outward pushing force of the slag and ash, so that the slag and ash is continuously pushed into the ash box without accumulation of dead ash, ensuring that the slag and ash in the furnace are evenly discharged outward along the layers. According to actual measurement, the slag blocks with a diameter of 100~200mm in the gray box account for (50~60)% of the total slag volume. The smooth progress of slag breaking and ash removal makes the bed in the furnace stable, the air permeability in the slag is good and the ventilation is uniform, the temperature of the fire layer is increased (about 1400°C), the gas quality is improved, the output is increased, and a virtuous cycle is achieved in the entire furnace. http://www.zaoqiwang.com/upload/060516940161856.jpg 3 Summary of the actual measured data of the φ3.6m gas generator after using the THL-I type furnace grate (the data in brackets are those using the old furnace grate): Gas production: 11 446m3/h (9203 m3/h) ； Vapor decomposition rate: 42.71%(36.56%) ； Slagging rate: 74.3% (55.9%) ； Bring out things: 0.233m3/class (0.813 m3/class) ； back focus: 8.23% (18.26%). The THL-I grate was installed and put into use in July 1998 with good results. Completely solved many problems existing in the φ13.6m grate. According to estimates, the use of this furnace grate will generate benefits of 648,000 yuan per year per unit. There are more than 40 φ3.6-meter gas furnaces in the country. If all THL-I type furnace grates are used, the annual economic benefit can be directly created at 26 million yuan. At the same time, due to the reduction in carry-out, the reduction in refocus rate can create certain social benefits.