Compressor Waste-Heat Recovery for Stable Hot Water at Low Load
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Solution Overview
Problem
Existing waste-heat recovery systems for oil-cooled gas compressors face challenges in supplying hot water at requested temperatures and maintaining efficient heat recovery rates, especially during low compressor load factors and no-load operations, due to inadequate heat management and reduced heat exchange rates.
Innovation Solution
A waste-heat recovery system that includes a waste-heat-recovery heat exchanger connected to a stored hot water tank, with a circulation pump and control device to manage the circulation of heat medium, allowing multi-pass heat exchange and controlling the cooling fan's rotational frequency to maintain target temperatures and optimize heat recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a waste-heat-recovery heat exchanger is provided to an oil-cooled gas compressor to recover waste-heat from oil or compressed air, then waste-heat recovery is enabled, but the system cannot supply hot water at requested temperatures during low compressor load factors and no-load operations
Solution Approach 1:
The system preheats feed water using waste-heat from the compressor before it enters the boiler. By performing this heat exchange in advance, the system ensures that hot water can be supplied at requested temperatures even when compressor load varies, as the preheated water can be stored and used when needed.
Solution Approach 2:
The invention introduces a heat exchanger as an intermediary device between the compressor waste-heat and the water system. This mediator enables efficient heat transfer from the compressed air and oil to the feed water, ensuring stable hot water supply temperature regardless of compressor load conditions.
2Temperature
If cooling water is used to absorb heat from the compressor, then the compressor is cooled effectively, but the heat exchange rate decreases during low load operations
Solution Approach 1:
The cooling water system serves dual functions: it cools the compressor during high-load operations and acts as a heat recovery medium during low-load operations. This multi-functionality allows the system to maintain effective cooling while enabling waste-heat recovery across varying operational conditions.
Solution Approach 2:
The system dynamically adjusts the heat exchange process based on compressor load conditions. During low-load operations, the cooling water flow and heat exchanger operation are optimized to maintain adequate cooling while maximizing heat recovery potential, thereby adapting the heat exchange rate to match operational demands.
3Reliability
If the circulation pump operates continuously to maintain hot water temperature, then hot water supply is stable, but energy consumption increases
Solution Approach 1:
Instead of continuous operation, the circulation pump operates periodically based on temperature sensor feedback. When the hot water tank temperature drops below the requested temperature, the pump activates to circulate water through the heat exchanger for reheating. When the temperature is sufficient, the pump stops, reducing energy consumption while maintaining temperature stability.
Solution Approach 2:
The system incorporates temperature sensors that provide feedback to the circulation pump control. The sensors monitor hot water tank temperature and compressor operating conditions, enabling the pump to operate only when necessary to maintain requested temperature levels, thereby optimizing energy usage while ensuring reliable hot water supply.
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 effectively supplies hot water at requested temperatures and improves waste-heat recovery rates by restraining heat emission from the recovery apparatus, even during low compressor load factors, and maintains efficient heat exchange across varying operational conditions.
Implementation Method 1
a waste-heat-recovery heat exchanger for recovering heat from at least either of the compressed gas flowing through the gas piping or the oil flowing through the oil piping
Implementation Method 2
a circulation pump provided at the circulation circuit
Implementation Method 3
a control device for controlling to stop the circulation pump or reduce the rotational frequency thereof
Implementation Method 4
a stored hot water tank for storing the heat from the waste-heat-recovery heat exchanger in a form of hot water
Data Source
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AI summary
The purpose of the present invention is to enable hot water at a required temperature to be supplied, even in cases when compressor load factor is low; to suppress heat dissipation from a waste-heat recovery device; and to improve waste-heat recovery rate. A waste-heat recovery system in an oil-cooled gas compressor is provided with: a compressor main body (3); an oil separator (6); gas piping (8) which supplies compressed gas separated from oil by the oil separator; oil piping (7) which returns, to the compressor main body, the separated oil; and a waste-heat-recovery heat exchanger (10) which recovers heat from the compressed gas. The waste-heat recovery system is also provided with: a hot-water storage tank (19); circulation circuits (17, 18); a circulation pump (22) provided to these circulation circuits; and a control device (32) which stops the circulation pump or reduces the rotational frequency of the circulation pump.