Eductor Dipleg Fine Solids Recycle Fluidized Bed
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Solution Overview
Problem
Fluidized bed reactors face challenges in recycling fine solid particles due to their cohesive nature, which prevents effective return to the high-pressure fluidized bed region, leading to low carbon conversion rates and increased ash volume, especially at high temperatures where conventional dipleg inserts are impractical.
Innovation Solution
The implementation of an eductor connected to the dipleg, utilizing a motive gas to create a low-pressure region for solids collection and a horizontal leg to regulate gas flow, facilitating the return of fine solids to the fluidized bed region, overcoming the cohesive issues and enabling efficient recycling of particles less than 100 microns in size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a dipleg insert is used to recycle fine solids, then solids can be returned to the fluidized bed, but at high temperatures above 800°C the bed materials form clinker inside and on the surface of the dipleg
Solution Approach 1:
The dipleg is extracted from the fluidized bed environment and positioned externally, separating the solids recycling function from the high-temperature bed zone. This allows fine solids to be recycled without exposing the dipleg to temperatures that cause clinker formation.
Solution Approach 2:
A refractory lining is introduced as an intermediary material between the dipleg and the high-temperature fluidized bed. This refractory barrier protects the dipleg from thermal damage while still allowing solids to pass through, preventing clinker formation on the dipleg surface.
2Reliability
If flapper valves are used to prevent gas reverse flow in the dipleg, then gas sealing is achieved, but at high temperatures most metals lose strength making flapper valves prohibitively expensive or impossible to use
Solution Approach 1:
The mechanical flapper valve system is replaced with a passive gas sealing mechanism using a vertical leg configuration and gas flow dynamics. The upward gas flow naturally seals the dipleg opening without requiring mechanical components, eliminating the need for high-temperature resistant materials.
Solution Approach 2:
Gas pressure and flow dynamics are utilized to achieve sealing instead of mechanical valves. The upward flowing gas creates a pressure barrier that prevents reverse flow, using pneumatic principles rather than mechanical movement to maintain the seal at high temperatures.
3Productivity
If fine cohesive particles are recycled directly, then carbon conversion efficiency improves, but the cohesive particles cannot establish a static head preventing natural flow from low to high pressure regions
Solution Approach 1:
The insufficient gravitational force acting on fine cohesive particles is counterbalanced by introducing upward gas flow through the vertical leg. This gas flow provides the additional force needed to overcome particle cohesion and pressure differential, enabling solids to flow upward against gravity and pressure gradients.
Solution Approach 2:
Gas flow is introduced into the vertical leg to create a pneumatic transport system for the fine cohesive particles. The upward gas stream fluidizes and carries the particles from the low-pressure cyclone region to the high-pressure fluidized bed, overcoming the particles' inability to establish a static head under gravity alone.
4Manufacturing precision
If multiple stage cyclones are used to collect fine particles, then particle separation efficiency improves, but the fine particles remaining are cohesive and difficult to fluidize and recycle
Solution Approach 1:
The problem of particle cohesion in the horizontal plane is solved by transitioning to a vertical dimension. The vertical leg configuration allows particles to be transported upward through gas flow rather than relying on horizontal fluidization, changing the dimension of solids handling from horizontal fluidization to vertical pneumatic transport.
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 solution enhances carbon conversion rates and reduces ash volume by effectively recycling fine solids, improving the operational efficiency and handling of carbon-containing materials in fluidized bed gasifiers and other high-temperature applications.
Implementation Method 1
an eductor connected to the dipleg, wherein the fine solids particles are removed from the dipleg, mixed with an eductor gas to form an eductor gas-fine solid particles mixture
Implementation Method 2
at least one cyclone in fluid communication with the fluidized bed region for receiving a first gas-solid mixture which comprises fine solids particles
Data Source
AI summary
A fine solids recycle apparatus for a fluidized bed reactor comprises an eductor connected to a dipleg extending from a cyclone connected to the reactor, wherein the fine solids particles are removed from the dipleg, mixed with an eductor gas to form an eductor gas-fine solids particles mixture, which allows the return of the fine solids particles to the fluidized bed region, whereby the fine solids is further reacted in the fluidized region to improve reaction efficiency.