Loop Seal with Eductor for Cyclone Solids Recycling
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Solution Overview
Problem
Fluidized bed gasifiers face significant challenges in collecting and recycling fine particles, which leads to carbon loss and caking issues due to the small size and low density of particles, as well as pressure fluctuations causing gas reverse flow, resulting in inefficient cyclone operation and clinker formation.
Innovation Solution
The implementation of a loop seal with aeration gas and an eductor to induce gas underflow from the cyclone, using recycled gas and feeding fuel fines to the eductor motive gas nozzles to break caking, ensuring efficient particle collection and return to the fluidized bed while preventing gas reverse flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If conventional cyclones are used for particle collection in fluidized bed gasifiers, then particles can be separated from gas stream, but fine particles are not effectively collected and gas reverse flow occurs due to pressure fluctuations
Solution Approach 1:
A U-shaped dipleg with loop seal acts as an intermediary component between the cyclone and fluidized bed. The loop seal creates a gas-tight barrier that prevents reverse flow while allowing solids to pass through. The U-shaped geometry with downward inclination ensures gas cannot flow back into the cyclone, solving the reliability issue while maintaining particle collection efficiency.
Solution Approach 2:
The dipleg is configured with a U-shaped vertical geometry instead of a simple straight connection. This dimensional change creates a loop seal effect where the vertical upward section blocks gas reverse flow, while the downward inclined section allows solids to gravitate back to the bed. This geometric transformation resolves the contradiction between preventing gas leakage and maintaining solids transport.
2Reliability
If aeration gas is added to the dipleg to prevent gas reverse flow, then gas sealing is improved, but caking of fine particles occurs
Solution Approach 1:
The harmful effect of caking is separated from the necessary function of gas sealing. Instead of adding aeration gas directly to the dipleg where it would cause caking, the system uses the U-shaped geometry and downward inclination to achieve gas sealing through physical configuration. The aeration gas is extracted from the dipleg environment and redirected to the oxidation zone where it serves a useful function without causing harm.
Solution Approach 2:
The fine particles that would normally cake in the dipleg are instead directed to the oxidation zone where they undergo combustion. The potential harm of caking is converted into benefit by using the same particles as fuel in the oxidation zone, improving carbon conversion while eliminating the caking problem.
3Productivity
If fine particles are fed to the gasifier, then carbon conversion can be improved, but caking occurs when particles are heated
Solution Approach 1:
The loop seal and dipleg configuration act as an intermediary transport system that directs fine particles away from the fluidized bed heating zone. Instead of allowing particles to cake in the bed, they are channeled through the downward inclined dipleg to the oxidation zone, where combustion occurs rapidly before caking can develop. This intermediary transport path resolves the contradiction between utilizing fine particles for carbon conversion and preventing caking.
4Productivity
If the dipleg is configured for solids return, then particle recycling is achieved, but gas can flow upwards through the dipleg causing cyclone inefficiency
Solution Approach 1:
The dipleg is configured with a U-shaped vertical geometry and downward inclination rather than a simple horizontal or upward connection. This dimensional change creates a one-way valve effect where gravity and geometry prevent gas from flowing back into the cyclone while still allowing solids to return to the bed. The vertical loop creates a gas seal without requiring additional sealing mechanisms.
Solution Approach 2:
The downward inclination of the dipleg creates a gravitational counterweight effect that opposes upward gas flow. The geometry is designed so that solids naturally flow downward under gravity while gas pressure fluctuations cannot overcome the gravitational head to force gas upward into the cyclone. This passive gravitational barrier prevents carbon loss while maintaining particle recycling.
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 cyclone collection efficiency, reduces carbon loss, and prevents caking by ensuring all aeration gas flows downwards, improving the overall operation and carbon conversion efficiency of the fluidized bed gasifier.
Implementation Method 1
an eductor to induce gas underflow from the cyclone
Implementation Method 2
loop seal with aeration gas
Implementation Method 3
at least one cyclone in fluid communication with the fluidized bed region for receiving a first gas-solid mixture
Implementation Method 4
some gas, mainly steam and oxygen, is provided to the bed through a distributor, also called grid. The lifting force of the gas makes the whole bed materials act like fluids
Data Source
AI summary
A loop seal for a fluidized bed reactor comprising a vertical downcomer segment connected to a dipleg for receiving solids particles from the dipleg, a horizontal segment downstream of the downcomer, a riser segment downstream of the horizontal segment, and a downwardly inclined segment downstream of the riser, whereby the solids are entrained to the fluidized bed reactor. An eductor is added to the angled leg to induce the underflow gas from the cyclone; one of the preferred motive fluids to the eductor is the fines from fuel preparation and the carrying gas for the fines. Also provided are a fluidized bed reactor comprising the loop seal, and a method for producing syngas from coal and steam using the same.