Air Compressor Waste Heat Recovery Using a Low-Boiling-Point Cycle
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Solution Overview
Problem
Existing waste heat recovery methods for air compressors, such as those disclosed in Japanese Patent Applications, suffer from inefficient heat recovery rates and do not directly reduce power consumption, as they involve multiple heat exchange operations and do not effectively convert the potential heat of compressed air into usable energy.
Innovation Solution
A waste heat utilization device that includes a circulation path for a low boiling point medium, an evaporator for heat exchange with compressed air or lubricating oil, an expansion machine to generate rotary power, and a condenser to cool and condense the medium, allowing efficient conversion of compressed air heat into rotary power, which can be used to reduce air compressor power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If cooling water is used to cool compressed air in an aftercooler and then a refrigeration type dryer is used to further cool the air, then the compressed air can be effectively cooled and moisture can be condensed, but the heat recovery rate deteriorates due to multiple heat exchange operations
Solution Approach 1:
The invention extracts the heat recovery function from the traditional multi-stage cooling system by introducing a separate heat recovery unit that captures waste heat from the compressed air before it enters the aftercooler. This allows the main cooling path to remain simple while recovering energy through a dedicated extraction system, thus improving heat recovery rate without compromising cooling effectiveness.
Solution Approach 2:
The heat recovery operation is performed preliminarily before the compressed air undergoes cooling in the aftercooler and dryer. By recovering heat in advance from the high-temperature compressed air, the system maximizes energy recovery while the subsequent cooling stages only need to remove the remaining heat, reducing the overall energy loss of the system.
2Loss of energy
If the potential heat of compressed air is recovered as steam energy in a boiler, then thermal energy can be utilized, but this does not lead directly to a reduction in the power consumption of the air compressor
Solution Approach 1:
The invention replaces the traditional steam generation approach with a direct mechanical energy recovery system. Instead of converting thermal energy to steam, the system uses a heat-driven mechanical device (such as a thermodynamic expansion machine) that directly converts the thermal energy of compressed air into mechanical work, which can be used to drive the air compressor or other mechanical loads, thereby directly reducing power consumption.
Solution Approach 2:
The invention introduces an intermediary heat recovery unit that acts as a bridge between the compressed air and the power consumption reduction goal. This intermediary device captures waste heat from the compressed air and converts it into useful work through a thermodynamic cycle, which can then be applied to reduce the power input required by the air compressor or other factory equipment.
3Power
If a reheater is provided to reheat compressed air using cooling water, then the pressure of compressed air increases and load on the air compressor is reduced, but two heat exchange operations are required which deteriorates heat recovery rate
Solution Approach 1:
The invention merges the heat recovery function with the power generation function by using a single heat-driven expansion machine that both recovers heat from the compressed air and generates mechanical work to reduce compressor load. This combined approach eliminates the need for separate reheater and heat recovery units, reducing the number of heat exchange operations while achieving both objectives simultaneously.
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 device efficiently recovers potential heat from compressed air, converting it into rotary power to reduce the air compressor's power consumption by operating the expansion machine, thereby lowering the overall energy usage of the compressor.
Implementation Method 1
an evaporator interposed on the discharge path and the circulation path to evaporate the low boiling point medium by performing heat exchange between the low boiling point medium and compressed air discharged from the air compressor or lubricating oil included in the compressed air
Implementation Method 2
to evaporate the low boiling point medium by performing heat exchange between the low boiling point medium and compressed air discharged from the air compressor
Implementation Method 3
an expansion machine into which the low boiling point medium evaporated by the evaporator is introduced such that a rotary force is applied thereto by the low boiling point medium
Implementation Method 4
a condenser that cools and condenses the low boiling point medium discharged from the expansion machine
Data Source
AI summary
A waste heat utilization device for an air compressor includes: a discharge path of an oil free air compressor; a circulation path along which a low boiling point medium circulates; an evaporator provided on the circulation path to heat and evaporate the low boiling point medium using the potential heat of the compressed air; and a preheater provided on an upstream side of the evaporator to preheat the low boiling point medium using the potential heat of the compressed air. A scroll type expansion machine is rotated by the low boiling point medium evaporated by the evaporator and increased in pressure, and power is generated by a power generator connected to a rotary shaft of the scroll type expansion machine. The low boiling point medium discharged from the scroll type expansion machine is then cooled and condensed by a condenser.