Advantages and disadvantages of water-coal slurry gasification

I. The oxygen consumption in coal water slurry gasification is high; it is generally above 400 Nm3/1000 Nm3 (CO+H2). To reduce this oxygen consumption, it is necessary to choose coal with low ash content and low ash melting point, as well as coal that has good slurry-forming properties, so that high-concentration coal slurries can be produced and the amount of oxygen consumed due to the evaporation of large quantities of water in the gasifier can be reduced. II. For gasifiers that are required to be in a hot standby state, they generally need to be shut down for maintenance after operating for about two months, or when faults occur and planned shutdowns are necessary. The standby unit must be at a temperature of over 1000°C before it can be used for processing materials. If the cold standby unit is temporarily raised to a temperature above 1000°C, it will inevitably affect the production of the entire system; hence, there is a requirement that standby units always remain in a hot standby state. Maintaining a hot standby furnace requires significant energy; it needs 150–1500 Nm3/h of gas, 150–1500 Nm3/h of air, as well as some extracted steam and cooling water. By strengthening management, optimizing operations to ensure long-duration operation of each furnace, carrying out planned shutdowns, and raising the temperature of the backup furnace before maintenance, it becomes unnecessary to have a hot standby furnace. III. Short service life of refractory materials in gasification furnaces: The bricks on the fire-facing side of the refractory materials are one of the key materials that determine whether a gasification furnace can operate for a long time and help reduce production costs. Currently, the most widely used bricks in the world are French bricks, Austrian bricks, and American bricks. The characteristic of French bricks is that they perform well at low operating temperatures and can adapt to large fluctuations in operating temperature ； Austrian bricks and American bricks perform well at high operating temperatures, but they tend to become brittle when the operating temperature varies greatly. Our country has chosen French bricks (Safefire Refractories Company), with a service life of 1 to 1.5 years. Among them, the Weihe Fertilizer Plant replaced all the refractory bricks on the combustion surfaces of its three gasification furnaces over the course of one year; each furnace required 750,000 dollars in terms of brick replacement costs, and the replacement process for each furnace took a long time, disrupting production for two months. At present, our country is developing refractory materials that are inexpensive, resistant to high-temperature erosion, and have a long service life. At the same time, during installation we must ensure the quality of furnace construction, and strengthen management in operations to reduce fluctuations in furnace temperature, thereby artificially extending the lifespan of the bricks exposed to the flame. IV. The short lifespan of the thermocouples in the gasification furnace’s furnace chamber is due to the mutual shear forces that occur as a result of the different expansion coefficients of the furnace shell and the refractory bricks when heated, which in turn affects the thermocouples. Each time the furnace temperature changes during startup and shutdown, we strive to control the temperatures of the enclosure and the furnace chamber properly, in order to prevent damage to the thermocouples and to guide our subsequent actions. If the thermocouple fails, we can determine the furnace temperature by observing changes in the CH4 content in the syngas, as well as the color of the slag discharged from the furnace, as well as the size and shape of its particles. This requires a high level of expertise and experience; additionally, other process parameters in the system can be used to control the furnace temperature and ensure normal operation of the system. V. Short lifespan of the process burner: Proper operation of the gasifier during the stable operation of the burner is another important factor. The burners have a short lifespan (about 1.5 months) and are expensive (80,000 dollars per unit). According to data from Ube in Japan, burners are the main cause of frequent shutdowns of gasification furnaces; therefore, it is essential to closely monitor their operation during use. In Russia, we are able to assess the operating condition of the burners every year by examining factors such as the cooling water system for the burners, the pressure difference in the gasification furnace, and the composition of the gases. We have also implemented interlocks specifically for the burner systems; if the operating conditions deteriorate, the gasification furnace stops operating. Otherwise, in mild cases, the uneven combustion from the burners can cause erosion of the refractory bricks, while in severe cases, the burners themselves may be damaged. VI. High investment in gasification equipment: We use the Texaco gasification process, which requires us to pay patent fees to Texaco Development Company. In addition, many special materials, equipment, valves, instruments, etc. need to be imported from abroad, and their prices are usually several times higher than those in the domestic market. Regarding design issues, most people in the country believe that with the successive commissioning of projects in Lunan, Shanghai, Weihua, and Huaihua, we have accumulated extensive design experience and production skills, and domestic design institutes are fully reliable for undertaking such projects. VII. Short lifespan of the quenching ring: The quenching ring has a short service life (about 1 year), and it requires efforts from many enthusiastic individuals to develop improvements for it. This post was last edited by Ma Hai on 2009-3-28 19:59.]

So as operators, does our workload are much more complicated than that in the Shell process?