Main Causes of High Coke Discharge Temperature in Dry Coke Quenching and Corresponding Solutions

01 Process Overview
Dry coke quenching utilizes a circulation fan to blow cooler inert gas (nitrogen) from the bottom to the top of the dry quenching furnace. Meanwhile, hot coke descends through the furnace under the force of gravity. Direct heat exchange occurs between the hot coke and the cool inert gas within the furnace, raising the gas temperature while lowering the coke temperature. The heated inert gas then exchanges heat with water in a boiler, generating steam. After cooling down, the inert gas is recirculated by the fan to exchange heat with the hot coke again. This continuous cycle achieves the objectives of lowering the coke discharge temperature and recovering the sensible heat from the hot coke.

02 Adverse Effects of High Coke Discharge Temperatures
In actual production, poor control of the coke discharge temperature—causing it to exceed the design maximum of 205°C—can result from factors such as prolonged use of the dry coke quenching system, uneven contact between the inert gas and the coke, or delayed operator response. Excessively high discharge temperatures have the following impact:
(1) Impact on conveyor belt service life: During transport, the coke comes into direct contact with the conveyor belt. Excessively high discharge temperatures cause thermal damage to the belt; prolonged operation under these conditions significantly reduces the belt's service life and increases production costs.

⑵ Inadequate recovery of sensible heat from hot coke: Dry coke quenching is a system designed to recover sensible heat from hot coke; however, high coke discharge temperatures result in some heat being carried out of the system along with the coke. This means a portion of the sensible heat remains unrecovered, thereby reducing the economic efficiency of the dry quenching system.
⑶ Increased coke burn-off within the quenching chamber: High discharge temperatures cause the layer of hot coke inside the chamber to shift downward, increasing the rate of coke burn-off and reducing coke yield.

03 Analysis of Factors Affecting Coke Discharge Temperature
(1) Suboptimal Furnace Design
The ventilation area in the flue section is insufficient; increasing the system's circulating gas volume causes excessive gas velocity in this area, lifting the coke inside the dry quenching furnace. This causes coke particles to clog the ventilation openings between the flue corbels, further reducing the ventilation area and creating a vicious cycle—a phenomenon known as "coke lifting." This makes it difficult to increase the circulating gas volume or meet the design specifications for the system's gas-to-coke ratio (the ratio of circulating gas volume to the rate of coke discharge). Consequently, insufficient heat exchange between the inert gas and the coke results in an excessively high discharge temperature. For the No. 3 and No. 4 coke oven dry quenching units at JISCO, the design gas-to-coke ratio was 1,240 m³/t of coke, yet actual production figures fall far short of this requirement.
(2) Impact of Accumulated Coke Dust on Circulating Gas Volume During Long-Term Operation
After exiting the dry quenching furnace, the circulating gas undergoes primary dust removal before entering the boiler. Although the dust content drops below 50 mg/m³ after this stage, some fine coke particles still enter the boiler; some accumulate inside, while others exit with the gas stream. A secondary dust removal process reduces the dust content to below 5 mg/m³, but residual dust passes through the circulating fan and accumulates within the heat pipe heat exchanger. Over prolonged operation, coke dust builds up throughout the circulating gas ducts. These accumulations not only obstruct the ducts—increasing system resistance and reducing circulating gas flow—but also deposit on boiler tubes and heat exchanger pipes. This impairs heat transfer between the circulating gas and water, causing the temperature of the cool inert gas entering the furnace to rise, thereby preventing effective coke cooling.

⑶ Uneven descent of coke within the dry quenching furnace and delayed adjustment
Hot coke moves downward through the dry quenching furnace while the circulating cooling gas moves upward; direct heat exchange occurs between the hot coke and the gas within the furnace. However, in actual production, factors such as non-uniform coke bulk density and varying friction between the coke and the furnace walls lead to uneven coke descent. Consequently, the coke descends more rapidly in some areas and more slowly in others. In areas of rapid descent, the contact time between the coke and the circulating cooling gas is insufficient for effective heat exchange; the heat remains within the hot coke rather than being transferred to the gas, resulting in an excessively high coke discharge temperature. The dry quenching system design addresses this issue by incorporating adjustment rods at the bottom of the furnace; the uniformity of the coke's descent is regulated by adjusting the depth to which these rods are inserted into the furnace. Yet, after prolonged use, the adjustment rods undergo wear, rendering them ineffective at regulating the uniformity of the coke's descent.

⑷ After prolonged use, the valve plugs of the dry quenching furnace control valves become clogged with coke dust, preventing flexible valve adjustment.
During normal operation, three main control valves regulate the system parameters: the system air intake valve (which introduces air into the circulating gas to control CO and H₂ levels), the circulating gas recirculation valve (which directs cooler gas—having passed through the boiler—into the flue zone to mix with the high-temperature gas from the furnace, thereby controlling the boiler inlet temperature and protecting the boiler tubes), and the pre-chamber pressure control valve (which vents gas from the circulation duct to regulate pressure within the furnace's pre-chamber). Currently, these valves lack responsiveness and precision, making fine adjustments impossible. This prevents timely regulation of key parameters—such as circulating gas flow rate, boiler inlet negative pressure, and boiler inlet temperature—thereby affecting the discharge temperature of the coke.

04 Solutions for High Coke Discharge Temperatures
⑴ Modify the corbels in the flue section of the dry quenching furnace. Modifying the corbels increases the ventilation area between them and reduces airflow velocity in the flue section, effectively resolving the issue of coke floating.
⑵ Remove coke fines from the circulating gas ducts of the dry quenching furnace. Clearing coke fines from the system effectively reduces flow resistance, increases the circulating gas volume, enhances the coke cooling effect, and lowers the coke discharge temperature.

⑶ Inspect and replace the adjustment rods at the bottom of the dry quenching furnace. After replacement, adjust the rods based on temperature variations around the upper and lower sections of the furnace: shift the rods inward toward the furnace center where temperatures are high, and outward toward the furnace periphery where temperatures are low. Continuously monitor the temperatures surrounding the rods during the adjustment process until the temperature distribution becomes uniform.
⑷ Take advantage of the annual maintenance shutdown to inspect the three adjustment valves of the dry quenching furnace. Identify the causes of any sluggish valve response and formulate appropriate corrective measures. Overhaul the three valves to ensure that, following maintenance, they allow for fine adjustments and effectively control the various process parameters.

05 Conclusion
Following the implementation of the aforementioned measures, the coke discharge temperature for JISCO’s No. 3 and No. 4 coke dry quenching units dropped from 190°C to approximately 150°C. Therefore, controlling the discharge temperature hinges on maximizing the system's circulating gas flow—without causing the coke to float—while ensuring uniform contact and efficient heat exchange between the inert gas and the hot coke within the quenching chamber, as well as properly regulating the oxygen content in the circulating gas.

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