Type coal gasification technology

In recent years, due to the rising prices of smokeless lump coal and coke, many enterprises that use fixed-bed batch gasifiers for coal gasification have turned to using briquetted coal as a substitute for lump coal and coke in order to survive and thrive, thereby producing semi-water gas and water gas. In actual production, without modifying the existing gas stoves, using briquetted coal often fails to achieve the desired results. The current situation is: declining production, rising consumption, and poor production stability. Although the price of briquettes is low, the overall efficiency is not satisfactory. In such cases, most companies simply attribute this phenomenon to poor performance of briquette gasification, failing to identify appropriate process conditions; they focus too much on operational factors while ignoring the more important issue: the original gasifiers were designed for burning lump coal and coke, and switching to briquettes results in incompatibilities within the gasifier equipment itself. Fixed-bed batch gasifiers, whether it is the UGI type used in the United States, the 03.6 m type from the former Soviet Union, or the domestically developed 12.6 m type in China, are all designed to use lump coal coke as raw material. For the gas stove’s height-to-diameter ratio, jacketed boilers, ash plows, ash discharge ports, ash transition zones, central ash boxes, upper air passages, and other related aspects, the parameters used in design, as well as the process models and simulation tests, along with the raw materials employed in industrial trials, are all metallurgical coke and high-quality lump coal – materials that differ significantly in their industrial properties from briquetted coal. The calorific value of briquetted coal is relatively low, accounting for 70% to 80% of that of metallurgical coke or high-quality lump coal ； The bulk density of briquetted coal is equivalent to 75% that of lump coal, and 105% that of metallurgical coke. When switching to coal briquettes, if the original designed gas furnace is still used, the height of the carbon layer inside the furnace must be much greater than that in furnaces using metallurgical coke or lump coal in order to provide enough heat for proper gasification. Therefore, it is impossible for conventional gasifiers that use briquettes as raw material to improve the quality of the gas; the CO2 content is usually between 9% and 12%, and the gas production volume is also low, with the production volume of semi-water gas being around 700 m3/(mz·h). The thermal stability of metallurgical coke reaches 98%, while that of high-quality lump coal is 92%. The thermal stability and heat strength of briquetted coal are much lower than those of lump coal coals; generally, the thermal stability of coal balls is 70% and that of coal sticks is 75%. The aforementioned differences result in vastly different control of process parameters. Regarding the temperature parameters at the furnace, metallurgical coke can reach 750°C, high-quality lump coal can reach 550°C, while briquetted coal can only operate at temperatures below 400°C. The ash fusion point and ash content of briquetted coal differ significantly from those of coal coke; therefore, the design of components such as grates, ash scrapers, ash discharge ports, and the ash transition zone also varies greatly. If nothing is changed, it will inevitably result in either the ash tray and ash discharge ports under the gas stove being clogged with ash or having ash in a powdered form that flows around, making stable operation difficult. Based on empirical data, fixed-bed gasifiers using high-quality lump coal produce 1 m3 of semi-water gas per 0.95–1.05 m3 of air per unit of furnace. Using briquettes as raw material, due to their lower calorific value, the heat storage capacity in the carbon layer is relatively low; often, every 1. 15–1. It takes 1.25 m3 of air to produce 1 m3 of qualified semi-water gas. Therefore, to achieve an ideal production rate in gasification using briquetted coal, the amount of air required to supply heat must be higher than that for lump coal; in other words, the demand for blast air is relatively greater compared to lump coal. However, in actual production, fixed-bed gasifiers use briquetted coal as the feed gas for gasification, and the amount of air blown in is reduced; otherwise, it may cause the material to be blown over. To achieve an ideal production rate in coal gasification, it is necessary to redesign the blast system of the gasifier, increasing the amount of primary air supplied compared to that used for lump coal, while ensuring that the material does not get blown over. From the above comparison, it can be seen that the process conditions for coal briquette gasification differ significantly from those for lump coal coke. Using a gasifier designed for lump coal coke to burn coal briquettes will definitely lead to incompatibility, preventing the advantage of lower costs associated with coal briquettes from being utilized. This is precisely the fundamental reason why some enterprises that produce briquetted coal achieve unsatisfactory results. To burn briquettes properly, a gas stove suitable for burning briquettes is necessary. The characteristics of this gas stove should be consistent with those of the briquettes.

I am very grateful for the explanations provided on the second floor. The processing of coal briquettes, from coal powder to a form suitable for use in furnaces, requires a great deal of labor, which contributes to higher costs for these briquettes. Additionally, poor gasification leads to even higher costs for synthetic ammonia production. At present, the price of lump coal is indeed high, and it’s impossible to obtain lump coal in areas far away from the mining sites. Therefore, using coal briquettes as raw material remains the choice of some nitrogen fertilizer manufacturers. Otherwise, they either have to shut down or invest heavily in powder coal gasification. I would like to ask everyone to share more technical knowledge in this regard.