Reheater Dense Bed Combustion and Particle Separation
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Solution Overview
Problem
In pyrolysis systems, afterburning of combustible solid particles and loss of entrained solid particles in combustion product flue gas during regeneration of the heat transfer medium lead to reduced operating efficiency and increased production costs, as conventional separation methods are inadequate in preventing ash buildup and particle loss.
Innovation Solution
Implementing a process that includes a fluidized dense bed reheater with an internal gas-solids separator, such as a cyclone or vortex separator, to separate and return combustible and inert/catalytic solid particles to the dense bed, optimizing superficial gas velocity, and using a flue gas-solids separator to manage flue gas and solid particle flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the superficial gas velocity is increased to enhance combustion efficiency in the reheater, then the combustion of combustible solid particles is improved, but more solid particles become entrained in the flue gas and are lost
Solution Approach 1:
The system divides the combustion process into two distinct zones: a dense bed region for primary combustion and a dilute phase region for secondary combustion. This segmentation allows optimized gas velocity in each zone - high velocity in the dilute phase for combustion completeness while the dense bed retains particles through fluidization control, preventing excessive entrainment loss
Solution Approach 2:
The system implements a feedback loop where entrained particles are separated from flue gas using cyclone separators and returned to the dense bed. This feedback mechanism recovers lost particles, maintains combustion efficiency, and reduces net particle loss while allowing optimized gas velocity for combustion
2Reliability
If the residence time of flue gas in the reheater is extended to ensure complete combustion, then combustion completeness is improved, but the risk of afterburning in downstream equipment increases
Solution Approach 1:
The combustion process is segmented into controlled stages: primary combustion in the dense bed with controlled oxygen supply, and secondary combustion in the dilute phase. This staged approach ensures complete combustion through progressive oxidation while controlling the rate and location of heat release, preventing uncontrolled afterburning downstream
Solution Approach 2:
The system performs preliminary combustion actions in the reheater by ensuring complete burning of combustible particles before flue gas exits. The dense bed pre-combustion and dilute phase oxidation work together to eliminate remaining combustibles upstream, preventing downstream afterburning hazards
3Loss of substance
If a conventional external separator is used to separate solid particles from flue gas, then particle separation is achieved, but the separation efficiency is insufficient and ash buildup occurs in the reheater
Solution Approach 1:
The system merges the combustion process with particle separation by using the combustion dynamics themselves to facilitate separation. The transition from dense bed to dilute phase creates natural particle-gas separation, and cyclone separators integrated into the system provide high-efficiency separation that conventional external separators cannot achieve, preventing ash buildup while recovering particles
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 process effectively controls afterburn and reduces solid particle loss, enhancing heat transfer to the reheater dense bed, preserving solid particles for recycling, and optimizing throughput and cost efficiency.
Implementation Method 1
an internal gas-solids separator, such as a cyclone or vortex separator
Implementation Method 2
an internal gas-solids separator, such as a cyclone or vortex separator
Implementation Method 3
a fluidized dense bed reheater
Data Source
AI summary
Processes for controlling afterburn in a reheater and loss of entrained solid particles in reheater flue gas are provided. Carbonaceous biomass feedstock is pyrolyzed using a heat transfer medium forming pyrolysis products and a spent heat transfer medium comprising combustible solid particles. The spent heat transfer medium is introduced into a fluidizing dense bed. The combustible solid particles of the spent heat transfer medium are combusted forming combustion product flue gas in a dilute phase above the fluidizing dense bed. The combustion product flue gas comprises flue gas and solid particles entrained therein. The solid particles are separated from the combustion product flue gas to form separated solid particles. At least a portion of the separated solid particles are returned to the fludizing dense bed.