Tube furnace biomass cracking

The application of tube furnace in biomass cracking is mainly reflected in its role as the core equipment of pyrolysis reactor, which achieves efficient conversion of biomass into biochar, bio oil and combustible gas through precise control of temperature, residence time and reaction atmosphere. The following analysis will be conducted from three aspects: technical principles, application scenarios, and optimization directions:

1. Technical principle: Core concept of tube furnace cracking
The core of biomass cracking in a tube furnace is through inter wall heat transfer (fuel combustion heats the outer wall of the furnace tube, transferring heat to the material inside the tube), under inert gas (such as nitrogen) or steam dilution conditions, to cause thermochemical decomposition of biomass. The typical process includes:
Preheating stage: Biomass raw materials (such as rice husks and sawdust) are fed into a tube furnace through a screw feeder and heated to 500-600 ℃ in the convection section.
Cracking reaction: The raw materials enter the radiation section and undergo rapid pyrolysis at high temperatures of 750-900 ℃, producing biochar (solid), bio oil (liquid), and combustible gases (CO, H ₂, CH ₄, etc.).
Product separation: The cracking gas is terminated by a rapid cooling boiler to prevent secondary cracking; Collect biochar and bio oil separately.
Key parameters:

Temperature: directly affects the distribution of products. For example, when rice husks are cracked at 550-850 ℃, the hydrogen content increases significantly with increasing temperature, while the carbon dioxide content decreases.
Staying time: too short leads to insufficient cracking (with more solid residue), while too long can cause secondary cracking of tar (increased gas production and decreased bio oil yield).
Reaction atmosphere: Inert gases (such as nitrogen) can reduce oxidation reactions, while water vapor dilution can inhibit coking and increase gas yield.

2. Application scenario: Diversified practice of tube furnace cracking
Preparation of Biochar
Case: Pre treated cork was pyrolyzed at 550 ℃ for 60 minutes to produce biochar with improved adsorption performance. The adsorption capacity of biochar pre treated with expansion for methyl blue and Congo red increased by 50.0% and 67.6% respectively compared to untreated samples.
Advantages: The tube furnace can accurately control the temperature gradient and optimize the pore structure of biochar.
Upgrading of bio oil
Case: Through a three-stage cracking process (pyrolysis+chemical chain gasification+catalytic reforming), high-quality synthesis gas (H ₂ yield 0.46Nm ³/kg) was produced from pine sawdust using Fe ₂ O ∝/Al ₂ O ∝ composite oxygen carrier at 800 ℃.
Advantages: The segmented temperature control capability of the tube furnace supports multi-step reaction coupling and improves product selectivity.
Combustible gas production
Case: Under vacuum conditions, the optimal reaction temperature for cracking wood chips is 500-600 ℃, with a residence time of 1 hour. The yield of bio oil reaches 58.56%, and the calorific value of gas products increases with temperature.
Advantages: Vacuum environment reduces gas diffusion resistance and improves reaction efficiency.

3. Optimization direction: Improve the cracking efficiency of tube furnace
Temperature control optimization
Strategy: CFD simulation is used to optimize the axial temperature gradient of the furnace tube, ensuring that the first 30% of the tube length is mainly used for raw material heating, and the latter section maintains a vigorous reaction temperature.
Effect: The yield error of the product can be controlled within 5%, and the yield of target products such as ethylene can be improved.
Reduced dwell time
Strategy: Use small-diameter (<50mm) furnace tubes to enhance heat transfer, combined with millisecond level residence time design (such as USRT furnace).
Effect: Increasing the cracking temperature to 880-900 ℃ significantly improves the ethylene yield.
Reaction atmosphere regulation
Strategy: Introduce steam dilution (dilution ratio 0.3-1.0) to suppress coking and remove the generated carbon.
Effect: Extend the service life of furnace tubes and increase the operating cycle.
Catalyst integration
Strategy: Load type solid base catalysts (such as NiO modified oxygen carriers) promote cracking reactions.
Effect: Improved carbon conversion rate and high gasification efficiency.