Composition and Use of Pyrolysis Gas

Pyrolysis gas is a gaseous product formed during the pyrolysis process. It is generated by the decomposition of organic matter (such as waste tires, plastics, wood, food waste, etc.) after high-temperature heating in an oxygen-free or oxygen-deficient environment. Pyrolysis gas contains carbon monoxide (CO), hydrogen (H₂), methane (CH₄), carbon dioxide (CO₂), a small amount of hydrocarbons and other volatile organic compounds. Its rich composition makes it have a certain fuel value, and it can also be further applied as a chemical raw material. This article will discuss the composition characteristics, generation mechanism and use of pyrolysis gas in different fields.

1. Composition Analysis of Pyrolysis Gas

The composition of pyrolysis gas depends on the type of raw materials, pyrolysis temperature, heating rate and reaction environment. The following are the main components of pyrolysis gas:

Carbon Monoxide (CO)

Cause of Generation: Carbon monoxide is generated during the pyrolysis process due to the incomplete combustion reaction between carbon and oxygen. The higher the temperature, the greater the proportion of carbon monoxide.

Features: Carbon monoxide has a high calorific value, is flammable and has a certain degree of toxicity.

Uses: Carbon monoxide can be used as an important component of synthesis gas for the preparation of chemical products (such as methanol) or as fuel gas.

Hydrogen (H₂)

Cause of formation: Under high temperature conditions, water molecules and hydrocarbons contained in the raw materials decompose to generate hydrogen.

Features: Hydrogen is an efficient and clean fuel that only produces water after combustion and no carbon dioxide emissions.

Uses: Hydrogen can be used in fuel cells, industrial hydrogenation processes, and chemical production such as synthetic ammonia.

Methane (CH₄)

Cause of formation: When organic matter is pyrolyzed, the carbon-hydrogen chain breaks to generate methane, especially in the low-temperature pyrolysis process.

Features: Methane has a high calorific value and good combustion characteristics, and is the main component of natural gas.

Uses: Methane can be used as a household and industrial fuel, and can also be used for power generation or further converted into liquid fuels and chemical raw materials.

Carbon dioxide (CO₂)

Cause of formation: The oxygen-containing components in organic matter decompose to generate carbon dioxide, and decarboxylation reactions at high temperatures also produce CO₂.

Features: Carbon dioxide has no fuel value, but can be used to enhance oil and gas recovery in certain industrial fields.

Uses: Carbon dioxide can be used for gas shielded welding, oil field production enhancement, agricultural greenhouse gas regulation, etc.

Light hydrocarbons (ethylene, propylene, etc.)

Causes of formation: During high-temperature pyrolysis, hydrocarbon decomposition produces light hydrocarbons, especially in the pyrolysis of plastics and rubber.

Features: Light hydrocarbons have high economic value and are important chemical raw materials.

Uses: These light hydrocarbons can be used to produce ethylene, propylene, etc., and further used in the production of plastics and chemical products.

2. Uses of pyrolysis gas

Pyrolysis gas has a high utilization value because it contains a variety of combustible gases and chemical raw materials. Its main application directions include fuel, power generation, chemical raw materials and greenhouse gas management.

Fuel and heating

Pyrolysis gas has a high calorific value and can be directly used as fuel for industrial heating, boiler heating or kiln heating.

Specifically, it can be:

Industrial fuel: A mixture of carbon monoxide, hydrogen and methane can be directly burned in an industrial boiler to provide a heat source for the factory.

Boiler heating: After cleaning and impurity removal, pyrolysis gas can be used as boiler fuel to heat various industrial heating systems.

Kiln heating: Pyrolysis gas can also provide heat sources for high-temperature processes such as steel and cement, reducing dependence on fossil fuels.

Power generation

Pyrolysis gas has broad application prospects in power generation. It can generate electricity through internal combustion engines, gas turbines or fuel cells to achieve efficient use of energy:

Internal combustion engine power generation: Pyrolysis gas can be directly used for internal combustion engine power generation, which is particularly suitable for small-scale distributed energy systems and has strong adaptability.

Gas turbine power generation: The compressed and purified pyrolysis gas can enter the gas turbine for power generation, which is suitable for medium and large-scale power generation needs.

Fuel cell power generation: The hydrogen in it can be used as fuel for fuel cells to achieve zero-emission clean power generation, especially suitable for cities or areas with high environmental protection requirements.

Chemical raw materials

Carbon monoxide, hydrogen, methane and light hydrocarbons in pyrolysis gas can be used as basic raw materials for chemical production and are widely used in synthesis, catalysis and polymerization processes:

Synthetic methanol: A mixture of carbon monoxide and hydrogen (i.e., synthesis gas) can be used for methanol production and further processed into chemical products such as formaldehyde and acetic acid.

Synthetic ammonia: Hydrogen in pyrolysis gas can be used for synthetic ammonia, which is the basic raw material for the production of fertilizers and chemicals.

Ethylene and propylene production: Light hydrocarbons (such as ethylene and propylene) are the main raw materials for the production of plastics such as polyethylene and polypropylene, and are the key to the modern chemical industry.

Greenhouse gas management

Carbon dioxide in pyrolysis gas can be used for greenhouse gas management to achieve effective resource utilization and carbon emission reduction:

Utilization of carbon dioxide: Carbon dioxide can be collected and stored, or used in agricultural greenhouse gas regulation and carbonated beverage production.

Geological storage: Treated carbon dioxide can be injected underground for storage to help achieve carbon neutrality goals.

Oil field production enhancement: Carbon dioxide gas is injected into oil fields to increase oil recovery and increase oil production, while achieving carbon dioxide fixation and emission reduction.

3. Challenges in the application of pyrolysis gas

Although pyrolysis gas has a variety of uses, it still faces some challenges in practical applications:

Gas purification and treatment

Pyrolysis gas contains tar and impurities, and direct use will lead to equipment corrosion and reduced efficiency. The cost of cleaning, purifying and removing impurities from the gas is high, and more efficient purification technologies need to be developed.

Storage and transportation

The storage and transportation of pyrolysis gas requires special gas equipment, especially hydrogen-containing gas. Establishing an efficient storage and transportation system is a prerequisite for the widespread application of pyrolysis gas.

Fluctuating gas composition

Different raw materials and process conditions will cause fluctuations in the composition of pyrolysis gas, affecting the quality stability of the gas. Therefore, it is necessary to strictly monitor and adjust the gas composition during the application process.