Fluidized Bed Torrefaction and Grinding of Biomass
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Solution Overview
Problem
Current processes for preparing lignocellulosic biomass for gasification or combustion are inefficient due to the need for separate torrefaction and grinding steps, which are not effectively integrated, especially for particles with dimensions and densities in the range of 2 cm to 5 cm and 300 to 800 kg/m3, and lack a fluidized bed technology for simultaneous torrefaction and size reduction.
Innovation Solution
A fluidized bed torrefaction and grinding unit that simultaneously reduces the size of lignocellulosic biomass particles from 2 cm to less than 1 mm and lowers water content to below 10% by performing mild pyrolysis at 230° C to 300° C, allowing for optimized operating conditions and easy treatment of mixed biomass and coal or coke particles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If separate torrefaction and grinding steps are used, then each step can be optimized independently, but the overall process complexity and time consumption increase
Solution Approach 1:
The patent combines torrefaction and grinding operations into a single integrated device where biomass particles undergo mild pyrolysis and size reduction simultaneously in the same reactor vessel. This eliminates the need for separate torrefaction and grinding equipment, reducing overall process complexity while maintaining the quality benefits of controlled torrefiction at 230-300°C.
Solution Approach 2:
The reactor serves multiple functions simultaneously: it acts as both a torrefaction reactor for thermal treatment and a grinding chamber for size reduction. The fluidized bed system enables both heating and mechanical breakdown of particles within the same operational environment, making the device multi-functional and eliminating the need for separate unit operations.
2Manufacturing precision
If separate torrefaction and grinding steps are used, then each step can be optimized independently, but the total processing time increases
Solution Approach 1:
The integrated fluidized bed system enables continuous simultaneous torrefaction and grinding of biomass particles. As particles are fluidized and heated, they undergo size reduction and drying in the same continuous process stream, eliminating idle time between separate operations and achieving continuous production of processed biomass material.
Solution Approach 2:
The torrefiction process softens and deconstructs the lignocellulosic structure of biomass particles before significant size reduction occurs, making the subsequent grinding much more efficient. This preliminary thermal treatment weakens the material structure, allowing faster and easier size reduction to achieve the desired particle dimensions.
3Quantity of substance
If traditional drying and grinding methods are used, then equipment is simple, but water content reduction to below 10% and particle size to less than 1 mm is difficult to achieve simultaneously
Solution Approach 1:
The system changes the physical and chemical parameters of biomass particles through controlled thermal treatment at 230-300°C in an inert atmosphere. This mild pyrolysis causes moisture evaporation, hemicellulose degradation, and structural softening, which simultaneously reduces water content to below 10% and prepares the material for efficient size reduction to particles smaller than 1 mm.
Solution Approach 2:
The torrefiction process induces phase transitions in the biomass components, including evaporation of free and bound water, decomposition of hemicellulose, and structural rearrangement of cellulose and lignin. These phase changes fundamentally alter the material properties, making it easier to grind to the required fine particle size while maintaining low moisture content.
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
The unit achieves a synergistic effect by integrating torrefaction and grinding, facilitating the production of small-sized, dry biomass particles suitable for entrained bed gasification, enhancing the efficiency of subsequent treatment processes and allowing direct transfer to gasification units.
Implementation Method 1
Torrefiction can be defined as moderate temperature pyrolysis with a controlled residence time. Typical operating conditions for torrefiction correspond to a temperature in the range 230° C. to 300° C. in the absence of air.
Implementation Method 2
The present invention describes a unit which can carry out the torrefiction step and the grinding step simultaneously in the same vessel. This produces a synergistic effect between the operating conditions for torrefiction, which means that the conditions under which the grinder functions can be optimized. Further, since the unit functions as a fluidized bed, it is very easy to treat, as a mixture with the biomass particles, other solid particles such as oil coke or coal particles.
Implementation Method 3
The size reduction step is generally carried out in a grinder, said grinding step being greatly facilitated by the upstream torrefiction step since torrefiction is not only accompanied by drying but also by partial destructuring of the lignocellulosic material.
Data Source
AI summary
A process and a unit for fluidized bed torrefaction and grinding of particles of a biomass with a largest dimension of 2 cm to 5 cm, and which unit contains an envelope having a general shape of a sector having a) two substantially vertical walls delimiting that sector; and b) at least one inclined wall defining three zones, from bottom to top: a lower zone provided with a fluidization means, and provided with a grinder placed at the bottom of that zone; an intermediate zone (2) provided with a fluidization means; and an upper zone (3) provided with a fluidization means; and a pipe (11) for introducing the particles reaching into the unit to the level of the intermediate zone.