Pyrolysis Gas Tar Reduction via Filtration and Partial Oxidation
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Solution Overview
Problem
Existing methods for producing clean product gas from biomass or coal are inefficient and costly due to difficulties in removing tar and dust from pyrolysis gas, particularly when using fuels like straw material that generate fine ash and small particles, leading to problematic deposits and slag formations.
Innovation Solution
A method involving guiding pyrolysis gas through filters to remove particles down to 7μ or 4μ, followed by partial oxidation and passage through a coke bed, ensuring efficient tar decomposition while preventing deposits and slag formations, with a two-stage gasifier process to control temperature and oxygen levels for effective tar removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If pyrolysis gas is filtered through a cyclone filter only, then the system is simpler, but fine ash and small particles pass through causing problematic deposits and slag formations
Solution Approach 1:
The filtering system is divided into multiple stages: a cyclone filter for coarse particle removal followed by a high-efficiency filter for fine particle removal. This segmentation allows each filter to specialize in removing particles of specific size ranges, preventing deposits and slag formations while maintaining system manageability.
Solution Approach 2:
The cyclone filter performs preliminary filtering of larger particles before the gas enters the high-efficiency filter. This preliminary action reduces the load on the subsequent fine particle filter and prevents large particles from causing deposits in downstream equipment.
2Productivity
If temperature is raised above 1000°C for tar decomposition, then tar removal efficiency improves, but ash and dust melt causing problematic deposits
Solution Approach 1:
Particle filtration is performed before the partial oxidation step that raises temperature to 1000-1200°C. By removing fine particles and ash in advance through the multi-stage filtering system, the gas is prepared so that high temperature processing does not result in melted deposits.
Solution Approach 2:
The filtered gas acts as an intermediary medium that has been prepared (particles removed) before undergoing the high-temperature partial oxidation process. This intermediary state allows the temperature to be raised sufficiently for tar decomposition without the harmful effect of melted ash and dust.
3Productivity
If thorough filtering removing particles down to 4μ is implemented, then tar decomposition efficiency improves, but the filtering system becomes more complex and costly
Solution Approach 1:
The filtering task is segmented into two stages: coarse filtering by cyclone (removing larger particles) and fine filtering by high-efficiency filter (removing particles down to 4μ). This segmentation achieves thorough filtering necessary for efficient tar decomposition while keeping each individual filtering stage relatively simple.
Solution Approach 2:
The cyclone filter performs preliminary removal of larger particles, reducing the concentration of particles that the subsequent high-efficiency filter must handle. This preliminary action makes the fine particle removal more feasible and cost-effective.
4Temperature
If partial oxidation is performed externally in a separate reactor, then temperature control is better, but the system complexity increases
Solution Approach 1:
The gasification system is segmented into distinct functional units: a pyrolysis reactor for biomass conversion, a separate partial oxidation reactor for temperature control and tar decomposition, and a coke bed for final gas cleaning. This segmentation allows each unit to be optimized for its specific function, particularly temperature control in the partial oxidation reactor.
Solution Approach 2:
The partial oxidation reactor serves as an intermediary unit between the pyrolysis reactor and the coke bed. It receives pyrolysis gas, performs controlled oxidation to raise temperature to 1000-1200°C for tar decomposition, and then passes the treated gas to the coke bed, thereby mediating the temperature and composition of the gas stream.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method significantly reduces tar content in pyrolysis gas, ensuring a clean product gas while minimizing the risk of deposits and slag formations, thus providing a cost-efficient and controlled tar decomposition process.
Implementation Method 1
guiding the pyrolysis gas through one or more filters to remove at least 90% of all the particles in the pyrolysis gas having a particle size down to 7μ
Implementation Method 2
partially oxidizing the pyrolysis gas in a partial oxidation reactor to remove tar from the pyrolysis gas
Implementation Method 3
the temperature of the gas is raised to over 1000° C. during the partially oxidizing process
Implementation Method 4
guiding the pyrolysis gas through a coke bed to further remove tar from the pyrolysis gas
Implementation Method 5
guiding the filtered and partial oxidized pyrolysis gas through a coke bed will ensure an even more efficient tar decomposition
Data Source
AI summary
Disclosed is a method for reducing the tar content in pyrolysis gas generated in a pyrolysis reactor (1). The method comprises the steps of: guiding the pyrolysis gas through a filter (2) to remove at least 90% of all the particles in the pyrolysis gas having a particle size down to 7μ and preferably down to 4μ from the pyrolysis gas, partially oxidizing the pyrolysis gas in a partial oxidation reactor (3) to remove tar from the pyrolysis gas, and guiding the pyrolysis gas through a coke bed (4) to further remove tar from the pyrolysis gas. Furthermore, a two-stage gasifier (6) is disclosed.