Closed Loop Coal Drying System Using Inert Gas Recirculation
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Solution Overview
Problem
Existing coal drying methods face challenges such as high energy consumption, production of fines that can spontaneously combust, and inefficiencies in using waste heat streams, particularly when drying lower-rank coals, which limits their economic viability and safety.
Innovation Solution
A closed loop coal drying system utilizing a fluidized bed with an inert fluidizing gas, where the gas is recycled and heated using waste heat sources, and oxygen levels are tightly controlled to prevent combustion, allowing for low-temperature drying and efficient moisture removal, while also reducing particle size for cost-effective processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high temperature and pressure drying methods are used, then drying efficiency is improved, but energy consumption increases significantly
Solution Approach 1:
The patent changes the temperature and pressure parameters from high to low range, using low temperature (below 200°C) and atmospheric pressure drying conditions. This is achieved by using a fluidized bed dryer with inert gas circulation, allowing efficient drying without the high energy input required by conventional high temperature methods.
Solution Approach 2:
The system uses waste heat streams from the power plant (such as flue gas or cooling water heat) to provide the drying energy, making the system self-sufficient regarding energy input. The waste heat that would otherwise be discarded is utilized to heat the inert gas for drying coal, eliminating the need for additional high energy consumption.
2Productivity
If fluidized bed drying is used to remove moisture, then drying efficiency is improved, but fine particulates become entrained and can spontaneously combust
Solution Approach 1:
The patent replaces air with inert gas (such as nitrogen or carbon dioxide) as the fluidizing medium in the dryer. This inert atmosphere prevents oxygen from contacting the fine coal particulates, eliminating the risk of spontaneous combustion while maintaining the efficient moisture removal capabilities of fluidized bed drying.
Solution Approach 2:
The inert gas acts as an intermediary substance that performs the dual function of fluidizing the coal bed for efficient drying and simultaneously preventing combustion by displacing oxygen. This mediator enables the drying process to proceed efficiently without the harmful side effect of fine particulate ignition.
3Reliability
If inert gas is used to prevent combustion, then safety is improved, but system complexity increases due to gas recycling requirements
Solution Approach 1:
The system recovers and recycles the inert gas after it exits the dryer. The gas is condensed to remove moisture, then reused as fresh fluidizing gas. This recovery process eliminates the need for continuous inert gas consumption and reduces overall system complexity by creating a closed-loop system rather than requiring large continuous supplies of inert gas.
Solution Approach 2:
The inert gas circulates continuously through the system in a closed loop, repeatedly performing the useful functions of drying and combustion prevention. The continuous circulation and recycling of the same gas stream maintains safety while avoiding the complexity of multiple gas supply systems.
4Quantity of substance
If lower-rank coals are dried using conventional methods, then moisture removal is achieved, but economic viability deteriorates due to high operating costs
Solution Approach 1:
The drying system uses waste heat from the power plant's own operations to dry the coal, making the process economically viable. By utilizing already-generated heat that would otherwise be wasted, the system avoids additional fuel costs and operating expenses, enabling profitable drying of lower-rank coals with higher moisture content.
Solution Approach 2:
The patent changes the operating parameters to low temperature and atmospheric pressure conditions, which significantly reduces energy consumption and operating costs compared to high temperature methods. This parameter change makes the drying of lower-rank coals economically feasible by reducing the cost burden on power plant operations.
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
The system achieves efficient coal drying with reduced energy consumption, minimized risk of spontaneous combustion, and lower operational costs by recycling the fluidizing gas and controlling oxygen levels, leading to significant savings for power plants.
Implementation Method 1
circulating a fluidizing gas through the dryer to fluidize the coal
Implementation Method 2
heating the particulate matter in the dryer to remove water from the particulate matter
Implementation Method 3
heating the particulate matter in the dryer to remove water from the particulate matter
Implementation Method 4
removing water vapor and fluidizing gas from the dryer, removing fine particulates and water vapor from the fluidizing gas
Data Source
AI summary
A drying system includes a fluidized bed dryer and fluidizing gas loop. The system is a closed loop so that fluidizing gas used to dry particulate matter can be reconditioned and recycled to fluidize and dry additional particulate matter. The fluidizing gas is reconditioned by removing fine particulates and water vapor. The drying system includes oxygen control features to prevent oxygen from entering the system. A method for drying particulate matter includes fluidizing the particulate matter in a dryer with a fluidizing gas, heating the particulate matter to remove water, removing water vapor and fluidizing gas from the dryer, removing fines and water vapor from the fluidizing gas, recirculating the fluidizing gas to the dryer to fluidize additional particulate matter and removing dried particulate matter from the dryer. A modular drying system reduces the amount of construction necessary at the installation site.