The explosion-proof design of a direct-fired furnace for waste gas treatment equipment requires the coordinated action of multiple safety devices to construct a three-dimensional protection system, encompassing flame blocking, pressure relief, and temperature monitoring. Its core logic lies in eliminating the three elements of an explosion (combustible material, oxidizer, and ignition source) through a combination of physical isolation, mechanical pressure relief, and electronic monitoring.
The flame arrester is the first line of defense for a direct-fired furnace, its core function being to prevent flame backflash within the piping. When combustion occurs in the waste gas piping due to static electricity, friction, or high temperature, the corrugated metal or honeycomb structure within the flame arrester reduces the flame temperature below the ignition point through the "wall effect." Specifically, after the flame enters the flame arrester, the airflow is divided into numerous tiny streams. When these streams contact the flame arrester wall, heat is rapidly conducted, causing a sharp drop in flame temperature, ultimately extinguishing the flame due to the inability to sustain the combustion chain reaction. For example, in chemical waste gas treatment, the flame arrester prevents flames from an explosion in the reaction vessel from spreading along the piping to the direct-fired furnace, avoiding the risk of a secondary explosion.
Pressure relief devices are critical components in preventing equipment overpressure explosions, and their design must meet the requirements of rapid pressure relief and directional discharge. Direct-fired furnaces are typically equipped with a dual combination of rupture discs and pressure relief valves: the rupture disc is a one-time pressure relief element; when the furnace pressure exceeds a set value, the diaphragm ruptures instantaneously, creating a pressure relief channel; the pressure relief valve, on the other hand, achieves dynamic adjustment through spring or gravity, automatically opening when the pressure is abnormal and closing again when the pressure returns to normal. For example, the pressure relief valve of a petrochemical company's direct-fired furnace is designed for a pressure of 5 kPa. When the furnace pressure rises to a critical value due to excessively high exhaust gas concentration or uncontrolled combustion, the pressure relief valve can open within 0.1 seconds, releasing the pressure to a safe range.
Temperature monitoring systems achieve precise control of the combustion process through multi-point sensors and interlocking controls. Direct-fired furnaces require thermocouples or infrared thermometers to be installed in key locations such as the combustion chamber, heat exchanger, and exhaust gas inlet to monitor temperature changes in real time. When the temperature exceeds a set threshold (e.g., 850℃), the system automatically triggers an interlocking mechanism: on the one hand, it reduces fuel supply to decrease combustion intensity; on the other hand, it activates a nitrogen dilution device to inject inert gas into the furnace to reduce oxygen concentration. For example, the temperature control system of a direct-fired furnace in an automotive painting company can achieve precise control of ±5℃, ensuring that organic matter in the exhaust gas is completely decomposed within the optimal temperature range, avoiding equipment damage due to excessively high temperatures or incomplete combustion due to insufficient temperatures.
Explosion-proof electrical devices eliminate the risk of electrical sparks, blocking the generation of ignition sources. The motor, fan, and control system of a direct-fired furnace must be explosion-proof, with its enclosure meeting an IP65 protection rating to prevent dust and moisture intrusion; internal wiring must use explosion-proof junction boxes to prevent sparks caused by aging wiring or short circuits. For example, the explosion-proof motor of a direct-fired furnace in a pharmaceutical company adopts an increased safety design, ensuring safe operation in explosive gas environments by limiting the motor surface temperature (below 135℃) and strengthening insulation performance.
Explosion-proof structural design enhances overall explosion resistance by optimizing equipment materials and layout. The combustion chamber of a direct-fired furnace must be made of high-temperature resistant alloy steel or ceramic fiber materials, with a temperature resistance exceeding 1000℃ to withstand the direct impact of high-temperature flames. The furnace structure must be equipped with reinforcing ribs and explosion-proof doors that automatically open to release energy in the event of a sudden increase in internal pressure. For example, the explosion-proof door design pressure of a direct-fired furnace in a chemical plant is 10 kPa, employing a spring-loaded opening mechanism that can complete the pressure relief action within 0.3 seconds, preventing the furnace body from deforming due to excessive pressure.
The waste gas pretreatment system reduces the risk of explosion by lowering the concentration of waste gas and removing impurities. Direct-fired furnaces require dust removal, demisting, and concentration regulation of the waste gas: dust removal devices remove particulate matter from the waste gas, preventing it from generating localized high temperatures during combustion; demisting devices eliminate liquid droplets in the waste gas, preventing a sudden increase in concentration due to droplet evaporation; and concentration regulation devices control the waste gas concentration below the lower explosive limit through nitrogen dilution or air supplementation. For example, the pretreatment system of a direct-fired furnace in an electronics company can dilute the exhaust gas concentration from 5000 mg/m³ to 2000 mg/m³, ensuring a safe and controllable combustion process.
The explosion-proof design of a direct-fired furnace is a comprehensive application of flame arresters, pressure relief devices, temperature control, explosion-proof electrical systems, structural reinforcement, and pretreatment technologies. By using flame arresters to block flame propagation, pressure relief devices to release overpressure energy, temperature control systems to precisely regulate combustion, explosion-proof electrical systems to eliminate ignition sources, structural reinforcement to enhance explosion resistance, and pretreatment to reduce explosion risks, direct-fired furnaces can achieve efficient and safe exhaust gas treatment, providing reliable environmental protection solutions for industries such as chemical, coating, and pharmaceutical manufacturing.
