Key Precautions for Fuel Heating System

Key Precautions for Fuel Heating System

The heating method uses non-condensable gas (NCG) generated during pyrolysis as the primary fuel, with diesel or natural gas as backup fuels. The fuel is fully combusted in the external heating chamber of the pyrolysis reactor to produce high-temperature flue gas, which then transfers heat to the inner pyrolysis chamber for raw material heating. This heating method enables recycling of self-generated by-products, features low energy consumption costs, and is suitable for large-scale batch-type pyrolysis equipment. It should be noted that this heating method must be equipped with a complete flue gas purification system (including desulfurization, denitrification, and dust removal units) to meet emission standards.

Key precautions are as follows:

Fuel Conveyance and Safety Control

The non-condensable gas must undergo pre-treatment for desulfurization and dehydration to remove hydrogen sulfide and moisture, preventing corrosion of pipelines, valves and burners, as well as excessive sulfide emission during combustion.

The non-condensable gas conveying pipelines shall be equipped with pressure monitoring devices and emergency shut-off valves. Pressure fluctuations shall be controlled within a safe range (usually 0.05–0.1 MPa) to avoid leakage caused by overpressure or burner flameout caused by insufficient pressure.

Backup fuel (diesel or natural gas) storage tanks shall be kept at a safe distance from the heating chamber. Natural gas pipelines shall pass air tightness tests, and diesel storage tanks shall be fitted with anti-leakage bunds to prevent fire hazards from fuel leakage.

Precise Control of Combustion Process

The heating chamber shall maintain the optimal fuel-air ratio (with excess air coefficient controlled at 1.1–1.3) to ensure complete fuel combustion, reduce the formation of pollutants such as carbon monoxide and unburned hydrocarbons; meanwhile, excessive air supply shall be avoided to prevent increased nitrogen oxide content in flue gas.

Strictly follow the stage-by-stage temperature control requirements of the batch-type process: heat up slowly during the preheating stage (10–15℃/h), maintain a stable temperature of 450–550℃ during the main pyrolysis stage, and prohibit over-temperature operation (＞600℃) to prevent aging of reactor materials and excessive gasification of pyrolysis products.

Equip with flame monitors. In case of flameout, immediately cut off fuel supply, purge the heating chamber with inert gas to remove residual combustible gas, and only then perform re-ignition to eliminate the risk of flashback and explosion.

Stable Operation of Flue Gas Purification System

The desulfurization unit shall preferably adopt the lye spray method. Real-time monitoring of lye concentration (maintaining a 20% sodium hydroxide aqueous solution) shall be carried out, and lye shall be replenished in a timely manner to ensure a desulfurization efficiency of ≥90% and reduce sulfur dioxide content in flue gas.

The denitrification unit can adopt the selective non-catalytic reduction (SNCR) method, control the reaction temperature at 850–1100℃, and inject reducing agents precisely to reduce nitrogen oxide emissions; the dust removal unit shall clean the filter bags or electrodes regularly to prevent excessive flue gas emission resistance caused by dust clogging.

Regularly monitor flue gas emission indicators (sulfur dioxide, nitrogen oxides, particulate matter) to ensure compliance with the Emission Standard of Pollutants for Coking Chemical Industry or more stringent local emission standards, and keep test records for inspection.

Equipment Maintenance and Emergency Management

Regularly inspect the refractory brick lining of the heating chamber. If spalling or cracking is found, repair it promptly to prevent damage to the reactor body caused by high-temperature flue gas leakage; clean ash deposits and coking on the inner wall of the heating chamber to avoid affecting heat transfer efficiency.

Formulate emergency response plans, clarify emergency procedures and responsible persons for scenarios such as fuel leakage, burner flameout and flue gas purification system failure; equip with emergency equipment such as fire extinguishers and inert gas generators, and conduct regular drills.

Regularly clean the heat exchange tubes of the waste heat recovery device to prevent reduced heat exchange efficiency caused by dust accumulation; at the same time, check its sealing performance to avoid energy waste or safety hazards caused by leakage of the waste heat recovery system.