Compressor Waste-Heat Recovery Pump Control for Stable Hot Water
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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, especially during low compressor load factors and unload or stoppage states, due to inefficient heat exchange and reduced waste-heat recovery rates.
Innovation Solution
A waste-heat recovery system that includes an oil separator, a waste-heat-recovery heat exchanger, a stored hot water tank, a circulation circuit with a pump, and a control device to manage the circulation pump's operation based on temperature differences between the heat exchanger outputs and the hot water tank, ensuring hot water is supplied at the required temperature and optimizing heat recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the water amount is reduced to elevate the temperature of replenished water, then the temperature of hot water is improved, but the heat exchange rate is deteriorated
Solution Approach 1:
The system performs preliminary heating by circulating cooling water through the waste-heat-recovery heat exchanger before the water is supplied to the hot water tank. This preliminary action allows the water to be preheated by compressor waste heat, and then further heated in the hot water tank if needed, thereby achieving the requested temperature while maintaining adequate heat exchange rate
Solution Approach 2:
The circulation pump continuously circulates cooling water through the waste-heat-recovery heat exchanger to maximize heat recovery from the compressor. This continuous circulation ensures that heat exchange occurs throughout the operating cycle, improving overall heat recovery efficiency without requiring excessive water flow rates
2Loss of energy
If the circulation pump operates continuously to maximize heat recovery, then the waste-heat recovery rate is improved, but energy consumption of the circulation pump increases
Solution Approach 1:
The circulation pump operates dynamically based on real-time temperature conditions. The control device adjusts the pump operation to run when the temperature difference between cooling water and hot water tank is favorable for heat recovery, and stops or reduces operation when the temperature difference is insufficient or when hot water demand is low, thereby optimizing the balance between waste-heat recovery rate and pump energy consumption
Solution Approach 2:
The control device monitors temperatures of cooling water from the waste-heat-recovery heat exchanger and hot water in the tank, using this feedback to intelligently control the circulation pump. This feedback mechanism ensures the pump operates only when it can contribute to effective heat recovery, avoiding unnecessary energy consumption while maintaining high waste-heat recovery rates when conditions are favorable
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 controlling the circulation pump's frequency and heat exchange processes, even during low compressor load conditions, thereby reducing heat emission and maintaining efficient operation.
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
Data Source
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, to a demanded destination, compressed gas separated from oil by the oil separator; oil piping (7) which returns, to the compressor main body, the oil separated by the oil separator; and a waste-heat-recovery heat exchanger (10) which recovers heat from the compressed gas and/or the oil. The waste-heat recovery system is also provided with: a hot-water storage tank (19); circulation circuits (17, 18) in which a heat medium is made to circulate between the waste-heat-recovery heat exchanger and the hot-water storage tank; a circulation pump (22) provided to these circulation circuits; and a control device (32) which, in cases when the temperature of the oil or the compressed gas subjected to heat exchange in the waste-heat-recovery heat exchanger is equal to or less than the temperature of the hot water in the hot-water storage tank, stops the circulation pump or reduces the rotational frequency of the circulation pump.