High-Moisture Fuel Combustion via Integrated Drying
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Solution Overview
Problem
The efficient use of high-moisture, low-BTU solid fuels in reaction vessels like steam generating boilers is limited due to high fuel moisture, leading to reduced boiler efficiency, steam generation capacity, and increased flue gas volume.
Innovation Solution
A process that thermally integrates a dryer with a boiler, using the combustion products stream as a recirculating thermal fluid to dry the wet fuel, and optionally enriching the combustion air with oxygen to control the steam generation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-moisture solid fuel is combusted directly in a boiler, then fuel utilization is reduced with high unburned carbon levels and steam generation capacity below design expectations, but adding a separate drying system increases device complexity
Solution Approach 1:
The patent combines the fuel drying function and combustion function into a single integrated system. The boiler serves dual purposes: generating steam while simultaneously drying high-moisture fuel through direct contact with combustion gases. This eliminates the need for a separate drying system, reducing device complexity while maintaining high steam generation capacity.
Solution Approach 2:
The boiler is designed to perform multiple functions: steam generation, fuel drying, and heat recovery. By making the boiler a multi-functional device that handles both combustion and drying operations, the system avoids adding extra equipment while improving overall fuel utilization and steam production.
2Loss of energy
If high-moisture fuel is combusted, then flue gas volume flow increases and latent heat is lost in exhaust gases, but increasing combustion air flow to compensate increases energy loss
Solution Approach 1:
The patent converts the harmful effect of high flue gas volume flow into a beneficial drying medium. The large volume of combustion gases, which would normally represent energy loss, is instead used to dry the high-moisture fuel directly in the combustion chamber. This transforms waste heat into a useful drying function, reducing latent heat loss while maintaining combustion efficiency.
Solution Approach 2:
The system recovers energy that would otherwise be discarded in the exhaust gases. By using the combustion products to dry the fuel in-situ, the latent heat in the flue gases is utilized for moisture evaporation rather than being lost to the atmosphere, thereby improving overall energy efficiency.
3Productivity
If oxygen enrichment is added to improve combustion efficiency and steam generation rate, then flame temperature and combustion kinetics increase, but system complexity and cost increase
Solution Approach 1:
The system uses its own combustion products to provide the drying function, eliminating the need for external drying equipment. The combustion gases automatically serve the dual purpose of sustaining combustion and removing moisture from fuel, creating a self-sufficient system that improves steam generation without adding complex oxygen enrichment infrastructure.
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 improves boiler efficiency, increases steam generation rate, and reduces the cost of steam and power production by effectively reducing fuel moisture and optimizing combustion conditions.
Implementation Method 1
transferring heat to generate steam by indirect heat exchange with the combustion products stream
Implementation Method 2
transferring heat to the recirculating thermal fluid by indirect heat exchange with the first portion of the combustion products stream
Implementation Method 3
combusting the dried solid fuel with a combustion air stream to produce a combustion products stream
Implementation Method 4
transferring heat to preheat the combustion air stream by indirect heat exchange with the second portion of the combustion products stream
Data Source
AI summary
A process for combusting a high-moisture fuel to generate steam, the process comprising heating a high-moisture solid fuel while contacting the high-moisture solid fuel with an oxygen-depleted gas stream to produce a dried solid fuel and a moist oxygen-depleted gas stream; combusting the dried solid fuel with a combustion air stream to produce a combustion products stream; transferring heat to generate steam by indirect heat exchange with the combustion products stream; dividing the combustion products stream into a first portion and a second portion; transferring heat to the recirculating thermal fluid by indirect heat exchange with the first portion of the combustion products stream; and transferring heat to preheat the combustion air stream by indirect heat exchange with the second portion of the combustion products stream; and recombining the first portion of combustion products stream and the second portion of the combustion products stream.