Non-Condensable Gas in the Process of Batch-Type Pyrolysis Oil Refining Equipment

Non-Condensable Gas in the Process of Batch-Type Pyrolysis Oil Refining Equipment

In the operation of batch-type waste tire pyrolysis oil refining equipment, non-condensable gas (NCG) is one of the core by-products of the process. Its generation, composition, characteristics, treatment and utilization are directly related to the safety, economic efficiency and environmental compliance of the project. The key details are as follows:

Generation Stage

NCG is gradually produced throughout the pyrolysis process. In the preheating stage (200–250℃), it is mainly formed by the vaporization of light volatile components in waste tires. When entering the main pyrolysis stage (450–550℃), low-carbon hydrocarbon gases generated by the cleavage of rubber macromolecular chains become its primary source, accounting for over 80% of the total NCG output. In the later stage of pyrolysis, as the temperature drops, the gas production rate gradually decreases. The overall output accounts for approximately 3%–5% of the mass of waste tire raw materials.

Core Composition

NCG is a mixture of flammable gases, mainly composed of C1–C4 low-carbon hydrocarbons including methane, ethane, propane and butane, along with small amounts of hydrogen and carbon monoxide, as well as trace hydrogen sulfide (derived from sulfides in rubber). Its explosion limit ranges from about 5% to 15%, classifying it as a flammable and explosive gas. Moreover, its sulfur-containing components are corrosive, requiring pretreatment before utilization.

Storage and Treatment Methods

In the batch-type process, NCG is not stored for a long period of time and is only temporarily stored in a buffer tank with a volume of less than 1 m³. The buffer tank is equipped with pressure monitoring and explosion-proof pressure relief devices to maintain a stable pressure within the safe range. The produced NCG must first undergo desulfurization and dehydration pretreatment to remove hydrogen sulfide and moisture. After that, it is preferentially fed into the external heating chamber of the pyrolysis reactor for combustion as fuel to achieve heat energy recovery. If there is excess output, it can be compressed and liquefied for sale as industrial fuel gas, or disposed of safely by burning in a supporting torch system.

Safety and Environmental Precautions

Emergency shut-off valves must be installed on the conveying pipelines to prevent gas leakage. Gas leak detection probes should be equipped in the pretreatment and combustion sections to avoid safety accidents caused by the accumulation of flammable gases. During the combustion of NCG, a small amount of sulfur dioxide and nitrogen oxides will be generated, which need to be sent to the flue gas purification system for desulfurization and denitrification treatment before being discharged up to standard.