Coalfield Fire Thermal Extraction Using Dual-Medium Borehole System
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Solution Overview
Problem
Current methods for extracting thermal energy from underground high-temperature coalfield fire areas face inefficiencies due to small pipeline radii, high engineering costs, and poor gas permeability, which limits thermal extraction efficiency and applicability in areas with compact coal rocks and uneven gas flowability.
Innovation Solution
A method involving the use of a low-temperature gaseous thermal medium injected through boreholes, followed by extraction and subsequent thermal exchange with liquid medium in casing-type borehole exchangers, targeting areas with high natural potential anomalies to enhance thermal energy extraction efficiency, especially in regions with poor gas permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If horizontal steel pipes are arranged in the fire area to extract thermal energy, then thermal energy can be extracted, but the pipeline radius is small and thermal extraction efficiency is low
Solution Approach 1:
The patent uses a gaseous thermal medium (inert gas) instead of liquid carriers in steel pipes to extract thermal energy. The gas is injected into the coalfield fire area, absorbs heat from the burning coal, and is then extracted to generate power. This pneumatic approach eliminates the need for extensive steel pipe networks while improving thermal extraction efficiency through better gas flow and heat transfer characteristics in the porous coal structure.
Solution Approach 2:
The patent changes the physical state of the thermal medium from liquid (in steel pipes) to gas, which can flow more effectively through the porous coal rock structure. The gaseous medium can penetrate deeper into the fire area and exchange heat more efficiently with the burning coal, thereby improving thermal extraction efficiency without requiring large amounts of piping infrastructure.
2Area of stationary object
If a large number of steel pipes are buried for large-area thermal recovery, then thermal extraction control range increases, but engineering amount increases and horizontal drilling becomes difficult
Solution Approach 1:
The patent replaces the complex steel pipe burial system with a gas injection and extraction system. Gas can be easily injected through boreholes into large areas of the coalfield fire zone without requiring extensive horizontal drilling or pipe laying. This pneumatic approach dramatically reduces engineering difficulty while maintaining or expanding the thermal extraction control range.
3Adaptability or versatility
If gaseous thermal medium is used for thermal recovery, then thermal exchange control range increases and gas flowability improves, but injected gas cannot enter areas with high coal rocks compactness and poor gas permeability
Solution Approach 1:
The patent divides the coalfield fire area into different zones based on gas permeability characteristics. In areas with poor gas permeability and high compactness, the system uses liquid thermal medium injection through thermal exchangers, while in areas with better permeability, it uses gaseous thermal medium. This segmentation allows the system to adapt to different geological conditions and ensure effective thermal extraction across the entire fire area.
Solution Approach 2:
The patent applies different thermal medium types (gas or liquid) to different local areas based on their specific permeability characteristics. This localized approach ensures that each area receives the most appropriate thermal extraction method for its geological conditions, thereby improving overall system reliability and effectiveness.
4Productivity
If gaseous thermal medium is injected into areas with poor gas permeability, then thermal extraction can be attempted, but gas flow is blocked and effective thermal exchange with high temperature coal rocks cannot be achieved
Solution Approach 1:
The patent changes the physical parameter of the thermal medium from gas to liquid in areas with poor gas permeability. Liquid thermal medium can flow through compact coal rock structures more effectively than gas, enabling thermal exchange in previously inaccessible areas. This parameter change ensures reliable thermal extraction across diverse geological conditions.
Solution Approach 2:
The patent introduces thermal exchangers as intermediary devices in areas with poor gas permeability. These exchangers facilitate heat transfer between the thermal medium and the coal rocks without requiring direct gas flow through the compact formation. The thermal exchanger acts as a mediator that enables thermal extraction where direct gas injection would fail.
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 method improves thermal energy extraction efficiency by targeting specific high-temperature areas with uneven gas permeability, controlling coal fire development, and effectively screening geological regions for enhanced thermal energy recovery.
Implementation Method 1
after the thermal exchange between the gaseous thermal medium and the high temperature coal rock mass in the fire area
Implementation Method 2
the injection borehole is used to send a low temperature gaseous thermal medium to the underground high temperature area... the high temperature gaseous thermal medium is extracted from the earth surface through the extraction borehole
Implementation Method 3
a casing-type borehole thermal exchanger is arranged in a potential anomaly region persistently existing in the thermal extraction target area to complete the thermal exchange between the high temperature coal rocks and the liquid thermal medium
Data Source
AI summary
A method for extracting thermal energy in an underground high temperature area of a coalfield fire area, including: determining a thermal extraction target area by a natural potential method and a ground detecting borehole; using an injection borehole to send a gaseous thermal medium to an underground high temperature area of the thermal extraction target area; after the thermal exchange between the gaseous thermal medium and a high temperature coal rock mass, the gaseous thermal medium is extracted through an extraction borehole; continuously monitoring a natural potential of the thermal extraction target area; arranging a casing-type borehole thermal exchanger in a potential anomaly region to complete the thermal exchange between the high temperature coal rocks and a liquid thermal medium; stopping the thermal extraction operations when the temperatures of the extracted gaseous thermal medium and the liquid thermal medium reach 70° C. or below.