High-Moisture Fuel Drying Before Steam Boiler Combustion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The efficient use of biomass and low-rank coal in steam generating boilers is limited by high fuel moisture, leading to reduced flame temperature, poor fuel utilization, and low boiler efficiency due to increased flue gas volume and latent heat loss, resulting in steam generation below design expectations.
Innovation Solution
A process that thermally integrates a dryer with a boiler, using an oxygen-depleted gas stream for drying high-moisture fuel, combined with oxygen enrichment of the combustion air to improve combustion efficiency, and includes bypass mechanisms to control heat transfer and moisture levels, utilizing recirculating thermal fluids and inert atmospheres for safe operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If high-moisture fuel is combusted directly in the boiler, then fuel utilization is poor and flame temperature is reduced, but steam generation capacity falls below design expectations
Solution Approach 1:
The patent applies preliminary action by drying the high-moisture fuel before combustion in the boiler. A dryer is integrated with the boiler system to remove excess moisture from the fuel prior to burning, ensuring that the fuel reaches the boiler at an optimal moisture content level. This preliminary drying action prevents the suppression of flame temperature and maintains steam generation capacity at or above design expectations.
2Loss of energy
If high-moisture fuel is combusted, then fuel utilization deteriorates with high unburned carbon levels, but combustion efficiency remains low
Solution Approach 1:
The patent applies preliminary action by drying the high-moisture fuel before combustion in the boiler. A dryer is integrated with the boiler system to remove excess moisture from the fuel prior to burning, ensuring that the fuel reaches the boiler at an optimal moisture content level. This preliminary drying action prevents the suppression of flame temperature and maintains steam generation capacity at or above design expectations.
3Quantity of substance
If high-moisture fuel is combusted, then flue gas volume flow increases, but latent heat loss in exhaust gases increases
Solution Approach 1:
The patent applies preliminary action by drying the high-moisture fuel before combustion in the boiler. A dryer is integrated with the boiler system to remove excess moisture from the fuel prior to burning, ensuring that the fuel reaches the boiler at an optimal moisture content level. This preliminary drying action prevents the suppression of flame temperature and maintains steam generation capacity at or above design expectations.
4Temperature
If oxygen enrichment is applied to combustion air, then flame temperature and combustion kinetics increase, but combustion air flow rate requirement decreases
Solution Approach 1:
The patent applies parameter changes by enriching the combustion air with oxygen. An oxygen enrichment system is integrated into the boiler to increase the oxygen concentration in the combustion air supplied to the furnace. This parameter change in the combustion air composition enhances flame temperature and combustion kinetics, allowing for reduced combustion air flow rates while maintaining or improving combustion efficiency.
5Loss of energy
If a dryer is integrated with the boiler, then fuel moisture is reduced and combustion efficiency improves, but system complexity increases
Solution Approach 1:
The patent applies merging by integrating the dryer directly with the boiler system. The dryer and boiler are combined into a unified system where the dryer is positioned upstream of the boiler, sharing common structures, supports, and operational controls. This merging approach reduces the overall system complexity compared to having separate standalone units, while still achieving the benefits of fuel moisture reduction and improved combustion efficiency.
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 approach enhances boiler efficiency and steam generation by reducing fuel moisture, increasing flame temperature, and optimizing steam production, while ensuring safe and flexible operation.
Implementation Method 1
heating the high-moisture solid fuel by indirect heat exchange with a recirculating thermal fluid
Implementation Method 2
recirculating thermal fluid provides process heat in the form of a recirculating thermal fluid to dry the wet fuel
Implementation Method 3
transferring a first portion of the amount of heat to generate steam by indirect heat exchange with the combustion products stream
Implementation Method 4
generate steam
Implementation Method 5
transferring a second portion of the amount of heat to preheat the combustion air by indirect heat exchange with the combustion products stream
Implementation Method 6
transferring a third portion of the amount of heat to the recirculating thermal fluid by indirect heat exchange with the combustion products stream
Implementation Method 7
contacting a high-moisture solid fuel with an oxygen-depleted gas stream while heating the high-moisture solid fuel to produce a dried solid fuel
Implementation Method 8
contacting a high-moisture solid fuel with an oxygen-depleted gas stream
Implementation Method 9
combusting the dried solid fuel with a combustion air stream to produce a combustion products stream having an amount of heat
Implementation Method 10
bypassing one or both of a portion of the combustion air stream to avoid the indirect heat exchange with the combustion products stream and a portion of the combustion products stream to avoid the indirect heat exchange with the combustion air stream
Data Source
AI summary
A process for combusting a high-moisture fuel to generate steam in which the high-moisture solid fuel is first dried by contacting with an oxygen-depleted gas stream while being heated by indirect heat exchange with a recirculating thermal fluid. The dried fuel is then combusted with a combustion air stream to produce a combustion products stream whose heat first is used to generate steam, and then to preheat the combustion air stream by indirect heat exchange in which a portion of the combustion air stream and/or a portion of the combustion products stream bypasses the heat exchanger. The combustion products stream also provides heat to dry the solid fuel via the recirculating thermal fluid.