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Summary of the Renovation and Operation of the 10×104 t/a Briquette Plant 1 Overview As the price of bituminous coal continues to rise, the cost of anthracite in fertilizer production is becoming increasingly significant. Reducing the cost of raw materials and lowering consumption are the most direct ways for enterprises to increase profitability. Yankuang Yishan Chemical Co., Ltd. has a synthetic ammonia production capacity of 30×104 tons per year; it consumes over 400,000 tons of anthracite each year, and the coal dust generated during processing amounts to 7×104 tons. If this white coal dust is shaped into briquettes to be used as raw material for gas production in furnaces, it is possible to reduce the amount of anthracite that needs to be purchased, thereby saving coal resources and improving the utilization rate of anthracite. As a result, briquette technology has been rapidly adopted and applied. Selection of the briquette manufacturing process: Our company originally had 8 coal rod machines. Due to the frequent damage to the heads of these machines, which required regular replacements, the quality of the coal rods was poor. This also increased the workload for the workers, led to high electricity consumption, and reduced production efficiency. To save energy and reduce consumption, a 10×104 t/a coal ball production line with more reliable equipment and simpler operation has been installed. Utilize the existing coal stick production line. By adding just a coal ball machine and a drying kiln, it can be converted into a coal ball production line. Compared to coal sticks, dried coal balls have a lower moisture content when fed into the furnace (around 1.5%), as compared to the moisture content of coal sticks used in this manner ； Coal balls have higher mechanical strength than coal sticks; they are less likely to expand, burst, or break down once placed in the furnace, which reduces the impurities in the semi-water gas ； In particular, the workload on workers **is reduced, ensuring orderly production. Description of the coal ball production process: The raw coal powder first enters a crusher, where the particles are crushed to a certain size. It then goes into a twin-shaft mixer for further crushing; at the same time, binders (including sodium humate and clay) are added in specific proportions, and everything is thoroughly mixed. After mixing evenly, the mixture is conveyed via a belt conveyor to a storage bin for soaking ； The retting time is generally required to be >48 hours. After retting, the raw material is thoroughly mixed using a vertical mixer or a twin-shaft mixer, after which it enters a coal ball forming machine. The coal balls produced by this machine pass through a sieve and are conveyed by a belt to the first layer of chain plates in the drying kiln; they undergo continuous drying across the second, third, and fourth layers of chain plates before being removed from the kiln. The drying time is adjusted based on the speed of the chain plate mechanism, with a duration of 2–3 hours. After leaving the kiln, the coal balls are conveyed to a coal ball storage tank using a belt conveyor with a large inclination angle, where they await transport to the gas production section for use in gasification. Sifting is provided before and after each conveyor belt for the shaped coal balls, to ensure that as much coal dust as possible attached to the coal balls is separated. The coal ball drying process uses a hot air furnace for heating and drying. Bituminous coal is burned inside the hot air furnace, and the hot flue gas enters the drying kiln through gates that connect the hot air furnace to the kiln. The flue gas is distributed through the gaps in the cast iron covers on the flue ducts, thereby controlling the temperature inside the kiln. After drying the coal balls in the kiln, the flue gas enters the exhaust fan via pipes at the top of the kiln’s rear end; the exhaust fan then sends this gas to a chimney for discharge. If there is a lot of dust and smoke, a cyclone dust collector can be installed in front of the exhaust fan to separate the dust from the exhaust gases before they are released, which will yield better results. The temperature inside the kiln is controlled by adjusting the opening degree of the inlet valve of the exhaust fan. The production process flow for coal balls is shown in Figure 1. file:///E:/DOCUME~1/zzjjaa/LOCALS~1/Temp/ksohtml/wps_clip_image1.jpg The selection of main equipment is shown in Table 1. file:///E:/DOCUME~1/zzjjaa/LOCALS~1/Temp/ksohtml/wps_clip_image2.jpg 3 Key points for production control: (1) Control the grinding particle size to be <3 mm. (2) The moisture content of coal powder should be <8%, while the moisture content of the formed coal balls should be maintained between 8% and 10%. (3) The adhesive must be thoroughly mixed with the raw coal, and this can be ensured by measures such as increasing the speed of the mixer. The amount of adhesive used is kept below 8.5%, and clay is added in an appropriate amount based on the mass of the coal balls. (4) The speed of the coal ball machine is adjusted by controlling the frequency converter, thereby regulating the coal ball production volume and achieving better results. (5) It is necessary to select an appropriate belt conveyor speed; too high a speed increases the impact force of the coal balls, which can easily cause them to break. (6) The temperature control in the drying kiln should be appropriate; the temperature at the kiln inlet should be above 200 °C, and the temperature at the kiln outlet should be above 100 °C. Temperatures that are too high or too low can result in poor drying of the coal balls, preventing them from reaching the desired moisture content or causing cracks in the coal balls. (7) After the drying kiln has been in operation for a certain period, it must be stopped to clean the ash accumulated inside. 4 Operating Results: The 10×104 t/a briquette production plant began construction and installation in May 2007, with installation completed by the end of June. Testing was carried out in July, and the plant went into official operation in August. Both the output and the quality of the coal balls met the design requirements, and the operation performance was good. After drying, the coal balls meet the following specification requirements upon testing. Moisture ≤ 1.5%, fixed carbon ≥ 65%, volatile matter ≤ 11.0%, ash content ≤ 23.0%, sulfur content ≤ 0.8%, humic acid ≤ 1.5%, coal dust content ≤ 1.0%. Balling efficiency ≥ 90%, cold strength ≥ 45 kg per ball. 5 Issues exist: (1) When this production line had produced 8,000 tons of coal balls, the surface of the rollers used in the balling machine was covered with pitting, which caused the rollers to stick to the coal balls and prevented them from breaking free, forcing the production to stop. Through consultations with companies in the same industry and manufacturers, as well as thorough analysis, it is inferred that the following reasons may be to blame: first, the adhesive formula was not prepared properly, resulting in a high pH value that caused mild corrosion of the roller coating ； Second is the quality defect of the roller skins in coal ball formers, resulting from inadequate heat treatment during the manufacturing process. To address the above issues, a solution has been developed: adjust the adhesive formula to keep the pH value below 8.5 ； Since the rolls of the coal ball forming machine are manufactured through overall heat treatment, fine coal cinders are used to roll them through the machine 5 to 8 times, and they are polished with a bar grinder (bar grinding wheel) until all corrosion spots are removed. Afterwards, the bar grinder is used to gently shape corners at 45 degrees along the edges of each ball socket, in order to reduce pitting and eliminate the problem of balls sticking in those sockets. (2) Coal ball production is affected by weather conditions, and the moisture content of white coal powder directly impacts the quality of the coal balls; therefore, a dry coal storage area should be established to ensure stable coal ball quality. (3) The chain conveyor in the drying kiln tends to break the coal balls when turning them, which reduces the proportion of intact coal balls; this aspect requires further improvement. 6 Summary (1) In the current situation of increasingly tight supply and rising prices of anthracite, using briquetted coal as a substitute for anthracite in gas production not only reduces dependence on anthracite but also makes full use of coal dust. This is an energy-saving and cost-reducing measure that deserves widespread adoption. As briquetted coal technology continues to improve and evolve, its advantages become more evident. (2) Once the coal balls are fed into the furnace, they can be used either in combination with other fuels or alone, depending on the specific conditions of gas production in each plant. Practice has shown that it is more effective to use coal balls alone in four gas production furnaces that share one fan; this makes it easier to adjust the operation of the furnaces, thereby achieving optimal performance and proper regulation of their operation