Carbon black production

Thread Content

Application of Coke Oven Gas as a Fuel in the Production of Wet-Granulated Carbon Black Authors: Zhao Bin, Wang Yuhong Date: 2008-12-3 14:17:13 Application of Coke Oven Gas as a Fuel in the Production of Wet-Granulated Carbon Black Zhao Bin, Wang Yuhong (Henan Tianhong Coking Company, Pingdingshan 467021, Henan) Our company’s current carbon black production line is a dry-granulation carbon black production line developed in the early 1980s; the fuel used is coal tar, and the raw materials include coal tar, ethylene tar, anthracene oil, etc., making it an oil-to-oil production process. The existing problems include aging equipment, low production capacity per furnace, poor stability of the plants, low level of automation, large fluctuations in quality, a limited range of products, as well as high energy consumption and costs. As the company’s coke production scale continues to expand, a large amount of coke oven gas is generated in excess; approximately 90,000 m3/day of this gas is burned off, which not only results in significant energy waste but also causes air pollution. To address this issue, we have developed a new oil-gas production process that uses excess coke oven gas as fuel and coal tar, ethylene tar, anthracene oil, etc. as raw materials, thereby enabling the comprehensive utilization of excess gas and improving the technological level of carbon black production. 1 Comparison between dry granulation and wet granulation: Dry granulation involves passing carbon black continuously through a rotating cylinder, causing the powdered carbon black to form spherical particles due to its physical cohesion. Dry granulation uses simple equipment and results in low granulation costs, but the particles have low strength, making them prone to breaking during bulk transportation. Wet granulation involves mixing carbon black with a certain proportion of granulation water; in a gear-type wet granulator, the mixture undergoes mixing, wetting, and stirring to form pellets, which are then dried to produce granular carbon black products. This method provides good particle strength, allowing for bulk transportation. 2 Process flow and characteristics of wet granulation 2.1 Process flow The production of carbon black via wet granulation uses coal tar, ethylene tar, anthracene oil, etc. as raw materials, and coke oven gas as fuel. The product is obtained through processes such as combustion, cracking reactions, rapid cooling and activation, collection and crushing, wet granulation, and packaging. That is, the dehydrated crude oil is sent to the crude oil storage tank. Coke oven gas mixes with air supplied by the main fan and preheated to 650°C in an air preheater, and the two burn together in the combustion section of the reactor, generating a high-temperature flue gas stream at 1850°C. The crude oil is pumped to the crude oil preheater, where it is preheated to 180°C before being injected into the reactor’s throat section, where it mixes with the high-temperature flue gas stream and undergoes rapid cracking to produce carbon black. At the rear of the reaction furnace, water is sprayed directly into the high-temperature carbon black flue gas, rapidly lowering its temperature and terminating the carbon black reaction. The carbon black fumes generated by the reaction are collected using a cyclone separator and a bag filter; the collected carbon black is then crushed and sent to the powdered carbon black storage tank. The exhaust gas discharged from the bag filter is pressurized by a fan; a small portion of it (about 20%) is sent to an exhaust gas combustion furnace for burning as a heat source for the dryer, while the majority is sent to the coal drying system as fuel. Powdered carbon black is granulated using a wet granulator, then dried in a rotary dryer. After that, it goes through lifting, screening, and magnetic separation before being stored in product storage tanks. The finished products are packaged, stored, and delivered to the customers. Part of the hot air stream used for the indirect drying of wet carbon black particles is discharged into the atmosphere through a 30 m high dryer and chimney. The air flow entering the drying cylinder is pumped by an exhaust fan to an exhaust bag filter for filtration and purification; the carbon black filtered out enters the carbon black supply system, while the purified gas is discharged directly into the atmosphere through a chimney. In the carbon black production process, the equipment cooling water is reused. Oily wastewater, boiler drainage, ground washing water containing carbon black, and water seal drainage are all sent to a biochemical treatment station for centralized treatment before being discharged. 2.2 Technical Features: The process technology is advanced, production is stable, and product quality is high. Excess gas is made use of effectively, which helps to improve the factory environment. The production technology is at an advanced level in China, featuring low energy consumption and high yields. An advanced distributed computer control system is employed, ensuring good reliability and a high degree of automation. 3 Main contents of the research The core of the wet granulation process for producing carbon black using coke oven gas as fuel lies in developing a combustion model for the combustion chamber. A combustion model refers to the relationship between the ratio of fuel to air fed into the furnace and the temperature of the air at the exit of the air preheater, as well as the fuel temperature and fuel composition. (1) Research on combustion models. Using computer programming for calculation, control models for five types of carbon black—N234, N229, N326, N339, and N351—were developed for the production of carbon black using coke oven gas as fuel, with ethylene tar, coal tar, and anthracene oil serving as the raw materials along with various mixture ratios. Analysis and calculations were carried out based on relevant data. (2) Material and heat balance. After thoroughly studying the process data of oil-gas processes using natural gas as fuel, we carried out extensive development work focusing on three key parameters: the overall combustion rate in the combustion chamber, the combustion temperature, and the total heat generated. As a result, we determined a series of important process parameters and control indicators for facilities that produce carbon black using coke oven gas as fuel, including the amount of air supplied to the furnace, the carbon black output, the amount of fuel consumed, the amount of coke oven gas used, and the yield; these data were then used for analysis and calculations. (3) Research on the reaction model of carbon black in new processes. A new combustion model for coke oven gas has been developed; based on calculations of the chemical reactions involved, a theoretical combustion model for coke oven gas in the combustion chamber was obtained. Through repeated experimentation during the trial operation, a reliable mathematical model of the combustion reaction temperature was developed, and reaction models for different product types were established. Practice has shown that not only is a high and stable combustion rate maintained, but also good and stable product quality is achieved. (4) Research on gas combustion nozzles. An efficient gas combustion nozzle has been developed. Taking into account the characteristics of gas, the length of the burner was increased, and coaxial dual-swirl grooves were used in its air distribution structure, along with two air inlets, thereby increasing the turbulence level of the air distribution at the burner’s combustion nozzle and making the combustion flame more stable. (5) Research on new methods for constructing reaction furnaces. Based on the existing technology for constructing furnaces for carbon black production, and by incorporating advanced furnace construction techniques from domestic manufacturers, a reactor lining was designed for a process that uses coke oven gas as fuel to produce carbon black. All the refractory materials used were of domestic origin; furthermore, improvements were made in terms of refractory material selection, furnace design, and construction methods, with a new approach of internal lining followed by external pouring being adopted for furnace construction. Production practice has proven that this method is feasible. 4 Performance of the production unit (1) Easy to operate, with improved furnace temperature stability. (2) It eliminates burning and coking, reduces impurities, improves product quality, and avoids shutdowns for coke blowing. (3) It reduced the fuel consumption of carbon black products and increased the yield of these products. Compared to using coal tar as fuel before, the fuel consumption per unit of carbon black product has decreased by 500 kg/t. (4) An increase in product varieties, stable quality, good performance, and enhanced ability to meet market demands. (5) It makes full use of excess gas, reduces environmental pollution, and lowers production costs.