What Is Biomass Gasification?

Biomass gasification, as a sustainable energy solution, provides a method to extract energy from readily available organic resources while significantly reducing carbon footprint compared to traditional methods. In today’s world, where concerns about climate change, environmental pollution, energy crises, and more continue to deepen, biomass gasification, as an emerging technology, has seen rapid development and application, with considerable market potential.

Biomass gasification is a technology for converting biomass materials into syngas, which can be used for energy and chemical production. This technology is versatile and highly adaptable in terms of feedstock types and scale. It serves as an effective approach for distributed biomass utilization and the treatment of combustible solid waste. It can partially substitute fossil fuels, promote energy efficiency, and reduce emissions, and contribute to sustainable development. Today, it has already been widely applied around the globe.

The principle of biomass gasification is based on the composition and chemical reactions of biomass. Biomass is a natural material composed of carbohydrates, proteins, fats, and other organic compounds, with its main components being cellulose, hemicellulose, and lignin, among others. Common biomass sources include agricultural residues, wood, and fruit peels. The working process of biomass gasification is to subject biomass to high-temperature, oxygen-depleted conditions in a closed system, resulting in partial oxidation or pyrolysis of materials. This process ultimately transforms the biomass into syngas rich in H2, CO, and CH4. Syngas can be used as a gaseous fuel or for the production of liquid fuels and chemical products.

How Biomass Gasification Works

The biomass gasification process involves complex thermochemical reactions that result in the conversion of gaseous and solid substances. The key stages include drying, pyrolysis, partial oxidation, and reduction. When biomass enters the gasifier, it is first heated to remove surface moisture, a relatively simple process in which the chemical composition of the material remains unchanged. The drying process is relatively slow and absorbs heat, reducing the reaction temperature. As the temperature inside the gasifier increases, the biomass begins to undergo pyrolysis, releasing volatile components. Higher temperatures lead to more intense reactions.

The biomass material, after releasing volatile components, forms the bed for the next stage of reactions. The volatile gases released during pyrolysis participate in the subsequent oxidation-reduction reactions. The oxidation reaction between the pyrolysis gases and oxygen is a highly exothermic reaction.

biomass fixed bed gasifier working principle
Fixed-bed biomass gasifier

Drying Stage:

At the initial stage after biomass enters the gasifier, moisture within the biomass is evaporated due to the surrounding temperature. This process involves the removal of internal moisture in the biomass and is considered a physical change. It primarily occurs in the temperature range of 100-200°C.

Pyrolysis Stage:

When the temperature of the biomass is raised above 160°C, large organic molecules like cellulose within the biomass undergo carbon-hydrogen bond cleavage, releasing volatile components. Major products of this stage include char particles, CO, CO2, H2, CH4, H2O, and tar compounds, among others.

Oxidation Stage:

Also known as the combustion stage, it primarily involves the incomplete combustion of the volatile components produced during pyrolysis, as well as char particles, with oxygen from the gasifying agent. This results in the production of CO2, H2O, and CO formed through partial oxidation. Since the oxidation stage is an exothermic reaction, it generates a significant amount of heat and raises the temperature inside the gasifier.

Reduction Stage:

The reduction stage mainly refers to the process where char particles generated from biomass pyrolysis react in a reducing atmosphere with substances like CO2 and water vapor to produce combustible gases. Because the reduction process is endothermic, the reaction zone temperature decreases to approximately 700-900°C.

In the four gasification stages, drying, pyrolysis, and reduction reactions are all endothermic processes, meaning they absorb heat. The oxidation reaction is the driving force of the entire gasification process, sustaining these reactions. The reduction stage occurs after the gasification reactions, where water vapor and carbon dioxide produced during combustion react with carbon to produce hydrogen and carbon monoxide, completing the transition of biomass from solid fuel to gaseous fuel.

In actual gasification reactions, these processes are not relatively independent but rather interrelated and distributed in an intertwined manner. As the gasification temperature increases, the gas production gradually increases, and the content of carbon dioxide, hydrogen, methane, and hydrocarbon gases all increases to varying degrees. This is especially true for the concentration of combustible components, which improves the quality of the produced gas.

Preprocessing of Biomass for Gasification

Forestry biomass has relatively low ash content and high heating value, making it the primary feedstock for gasification processes in many countries. Non-woody biomass, such as straw, bagasse, and herbal residues from agriculture and agricultural processing by-products, is considered low-quality fuel due to its higher ash content, lower heating value, lower density, higher moisture content, and complex composition.

High ash content in biomass can lead to particle agglomeration in fluidized-bed gasifiers and slagging in the high-temperature zone of fixed-bed gasifiers. Low-density raw materials can lead to bridging and arching issues, making them unsuitable for direct use in fixed-bed gasification. To make use of low-quality biomass materials, various preprocessing methods are typically employed to enhance their quality. These methods may include drying, grinding, shaping, or roasting to improve the material characteristics. Additionally, the gasification reactor needs to be designed in a way that accommodates the specific properties of the fuel.

Co-gasification with wood-based materials or coal is another effective approach for utilizing low-quality biomass. This can help improve the overall gasification process and maximize the use of available resources.

Applications of Biomass Gasification

Biomass gasification technology is currently experiencing rapid development, and its applications are continually expanding. Some mature biomass gasification practices include biomass gasification for combined heat and power (CHP), distributed biomass gasification energy stations, biomass hydrogen production, and biochar production.

biomass gasification combined heat and power plant
Biomass gasification for combined heat and power

GEMCO ENERGY is continuously researching and developing in the field of pyrolysis and gasification technology. The company can provide a range of energy solutions based on biomass gasification. If you are interested in more detailed information and pricing for these solutions, please feel free to drop us an email.

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