No data available for recovery and horizontal coke ovens

Thread Content

I. Non-recycling coke ovens (or heat-recycling coke ovens): Non-(heat)-recycling coke ovens introduce an appropriate amount of air during the coking process, allowing all the gas generated in the oven to burn in order to heat the coal for coking, without recovering the chemical products contained in that gas. The hot flue gas is used by the boiler to recover heat, generating steam for power generation. 1. International situation: Non-recycling coke ovens or heat-recycling coke ovens are a type of oven that first appeared in the United States in the 1960s. In 1963, the first batch of 250 Mitchell-type coke ovens without coke recovery systems came online, with an annual coke production capacity of 250,000 tons; by the end of the 1960s, the total annual coke production capacity had reached 500,000 tons. In the early 1970s, a new type of Jewell–Thompson reactor was developed. Due to the increased size of the furnace openings, as well as the addition of composite flues and chimneys at the furnace bottom and other components in the combustion chamber, the output per unit of the furnace has increased, resulting in a substantial reduction in air pollution. By the 1980s, further improvements were made to the structure of the furnace and to the control of combustion within it, which led to a further reduction in air pollution, an improvement in the quality of coke, and lower maintenance costs for coke ovens. At the end of the 1980s and the beginning of the 1990s, the temperature of the entire furnace was controlled through continuous temperature simulation adjustments, ultimately achieving temperature control over the coking cycle. To date, the coke oven technology without (heat) recovery has reached a mature stage, been introduced to the international market, and has received recognition from the U.S. Environmental Protection Agency. The investment per ton of coke produced in U.S. non-recycling coke ovens is approximately $270. Currently, apart from the United States, **non-recycling coke ovens are in use in Germany, Australia, India, Brazil, and other countries.** In the United States, coke ovens without recycling systems generally use top-loading coal, while in Germany top-loading coal is commonly used as well. 2. Domestic situation: There are no coke ovens for recycling in the country; such ovens were first built at the end of the 1990s, mainly for the transformation of traditional coke ovens. To date, several coke ovens without a recycling system have been built in Shanxi Province, and this practice has spread to regions such as Inner Mongolia, Liaoning, and Shandong; there are now over 30 such facilities, with an annual coke production capacity of around 20 million tons. The domestically designed and constructed non-recycling coke ovens are of horizontal bed type, with coal being compacted and fed into the oven; they operate under negative pressure. Raw gas is introduced to the bottom of the oven through side flues for indirect heating, and a portion of the raw gas at the oven top is also burned. The coking time is generally 65–72 hours, with wet quenching. The exhaust hot gases have their waste heat recovered in a waste heat boiler, and the steam generated is used for power generation. Thanks to the ramming technique, lower-quality coking coal can be used, thereby improving the quality of coke. Taking China’s JNR-2 type non-recycling coke oven as an example: Charring chamber dimensions: length × width × height = 13,334 × 2,888 × 3,598 mm; cycle time: 70 hours; coal loading per chamber: 50 tons (wet); production capacity: 1.2 million tons of coke per year (12 sets × 24 chambers); investment cost: 750 million yuan; cost per ton of coke: 625 yuan/ton. 3. Characteristics of non-recycling (heat) recovery coke ovens: (1) Environmental aspects: (a) Due to their operation under negative pressure, non-recycling coke ovens enable control over continuous dust emissions, but preventive measures are still necessary to address intermittent pollution issues; otherwise, pollution problems will persist. (b) Since there is no chemical recovery system, no coking phenol-cyanide wastewater is generated; however, the problem of desulfurizing combustion exhaust gases and the disposal of the desulfurizer after desulfurization still remain to be addressed (currently lime milk is used for desulfurization, and an appropriate method is also needed to handle the waste residue resulting from this process). (2) In terms of resource utilization: (a) China is relatively short of petroleum resources. Therefore, extracting chemical raw materials and fuel oil through coal carbonization is not only an important source of chemical products and a supplement to the petroleum industry, but also some chemical products cannot be produced by the petroleum industry. As such, coal chemistry still holds an important position in the national economy. Burning the gas produced by carbonization entirely as a heat source represents, in a sense, a waste of resources. (b) In the production process of coke ovens without recycling, there is some loss of coke, and the coking rate decreases by approximately 1% to 3%, resulting in waste of coal resources. (c) If the gas is not recovered, the residual heat after combustion can be utilized, which can also be considered as an exploitation of resources. However, the large number of coke ovens being built at present often fail to install waste heat boilers and power generation equipment due to limited investment or a desire for quick results, resulting in significant waste of resources. (d) Cokers without recycling occupy large areas and require flat ground, which is also a waste of land resources. (3) In terms of technical level: (a) Furnace temperature control: Currently, abroad, furnace temperature control in coke ovens without recycling has reached a very high level, with control applied not only to the overall furnace temperature but also to the temperature during the coking process. In domestic coke ovens without recycling systems, due to outdated monitoring and control methods, the temperature inside the oven remains unregulated; the high-temperature areas keep changing, and in severe cases this can lead to damage to the oven structure. It is currently difficult to determine exactly how long a generation of reactors can remain in service. (b) Flue gas desulfurization: The issue of flue gas desulfurization has not yet been fully resolved, and there are still many technical problems associated with using lime milk for desulfurization. China’s coking industry policies stipulate that, given the limited land and natural resources in the country, coal resources need to be utilized comprehensively, and the technical level of non-recycling coke ovens is still far behind that of foreign countries. Taking market demand into account as well, non-recycling coke ovens are permitted to exist at present, but they should not be promoted or encouraged. This process technology must be further improved, enhanced, and standardized. II. Horizontal coke ovens: There is no direct experience with horizontal coke ovens; very little is known about them, and there is also scarce information available on them. Horizontal coke ovens began to appear in Shanxi, China, at the end of the 1990s, but in very small numbers. Take a certain furnace type as an example. Charging chamber dimensions: length × width × height = 13290×3000×2701 mm. Coal cake dimensions: 12440×2810×1200 mm. Cycle time: 80 hours. Operating time: 35 minutes. Coal loading per chamber: 50 t (wet). Characteristics of horizontal coke ovens: Compared to vertical coke ovens in existing technology, horizontal coke ovens have a different method of coke extraction, as well as different equipment for receiving and removing coke. They suffer from problems such as high levels of dust during coke extraction, environmental pollution, and high construction costs. Coke unloading also requires a fixed coke pushing station, which has the disadvantages of poor structural reliability, high investment costs, and large space requirements. Due to its long coking time and operation duration, its production capacity is low.