Circulating Fluidized Bed Boiler Return Duct Design
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Solution Overview
Problem
Large circulating fluidized bed boilers face challenges in controlling and distributing solid particles due to complex and space-consuming return ducts and separate fuel feeding channels, leading to inefficient heat exchange and potential clogging issues.
Innovation Solution
The implementation of a compact design featuring downpipes connected to lift channels with overflow conduits, allowing for even distribution of solid particles and adjustable heat exchange efficiency, where solid particles are guided through heat exchange surfaces for cooling before returning to the furnace, and fuel is introduced into the downpipes to facilitate homogeneous distribution and ignition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If separate return ducts for cooled and uncooled particles as well as separate fuel feeding channels are used, then the distribution of solid particles can be controlled, but the arrangement becomes complicated and space consuming
Solution Approach 1:
The patent combines multiple functions into a single integrated return duct structure. The return duct simultaneously handles both cooled and uncooled particle return, and includes integrated fuel feeding channels within the same structure. This merging eliminates the need for separate dedicated ducts for each function, reducing spatial complexity while maintaining distribution control capabilities through internal positioning and flow dynamics.
Solution Approach 2:
The return duct is designed as a multi-functional component that performs particle return, fuel feeding, and flow distribution simultaneously. By making the return duct universal in its functions rather than specialized for single purposes, the patent reduces the total number of components needed while achieving comprehensive control over the fluidized bed operation.
2Ease of operation
If multiple separate channels and ducts are used for particle return and fuel feeding, then material distribution can be managed, but the lower portion of the furnace requires more wall space
Solution Approach 1:
The fuel feeding channels are nested within the return duct structure itself. The return duct contains internal passages or channels that guide fuel into the particle flow, creating a nested configuration where one system is embedded within another. This nesting allows fuel feeding functionality to be incorporated without occupying additional external wall space.
Solution Approach 2:
Instead of arranging fuel feeding channels and particle return paths in separate spatial dimensions that require additional wall area, the patent utilizes the internal cross-sectional dimension of the return duct. By distributing fuel injection points and particle flow paths within the cross-section of the return duct, the design achieves material distribution control without increasing the external footprint or wall space requirements.
3Power
If fluidizing velocity is increased to improve heat exchange efficiency, then heat transfer improves, but particle distribution homogeneity may be affected
Solution Approach 1:
The patent employs different fluidizing velocity conditions in different regions of the heat exchange chamber. By creating local variations in fluidization intensity, the system achieves high heat exchange efficiency in regions where high velocity enhances heat transfer, while maintaining particle distribution homogeneity in regions where controlled fluidization prevents excessive mixing or segregation. This spatial differentiation of fluidization quality resolves the contradiction between heat transfer and distribution uniformity.
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 design enhances the homogeneous distribution of solid particles and fuel within the furnace, improving combustion efficiency and reducing emissions while minimizing the complexity and space requirements of the boiler's lower portion, allowing for efficient heat exchange and fuel distribution.
Implementation Method 1
solid particles are guided through heat exchange surfaces for cooling before returning to the furnace
Implementation Method 2
The heat exchange chamber is a fluidized chamber, which means that there are means provided in the lower portion of the chamber, especially nozzles and inlet piping for fluidization gas, by means of which the bed of solid particles being formed in the chamber can be fluidized
Implementation Method 3
said return duct being provided with a gas seal
Implementation Method 4
a furnace for combusting carbonaceous fuel
Data Source
Figure 1
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Figure 3
AI summary
A circulating fluidized bed boiler (10), comprising a furnace (12) for combusting carbonaceous fuel, at least one outlet channel (14) connected to the upper portion of the furnace for removing flue gas and solid particles generating in the combustion of fuel, each outlet channel provided with a particle separator (16) attached with a flue gas channel (18) for transferring cleaned flue gas and a return duct (20) for transferring separated solid particles to the lower portion of the furnace. The return duct is provided with a gas seal (22), a heat exchange chamber (24), a lift channel (34) and an overflow conduit (44), in which solid particles exiting the gas seal are guided to the upper portion of the heat exchange chamber (24) and from the lower portion of the heat exchange chamber through the lift channel (34) to the furnace or directly from the upper portion of the heat exchange chamber through the overflow conduit (44) to the furnace, and there is at least one downpipe (42), which is connected from the upper portion to flow connection with the upper portion of the lift channel (44) and from the lower portion to flow connection with the lower portion of the furnace and additionally the overflow conduit (44) is connected to the upper portion of the downpipe. The downpipe (42) is preferably also connected to an inlet for fuel (50).