Heat Pump Decoupling for Stable Heat Recovery
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Solution Overview
Problem
Existing heat recovery systems in cogeneration plants face inefficiencies due to variable fluid temperatures from thermal users, which negatively impact heat pump performance and overall plant efficiency, leading to suboptimal heat recovery and environmental effects.
Innovation Solution
A closed circuit connecting the heat pump to the cogeneration plant, decoupled from the fluid distribution circuit, using a separation exchanger to maintain a constant fluid temperature for the heat pump, and a low-temperature gas exchanger to recover residual heat from combustion gases, with a heat pump loop optimizing thermal exchange and heat recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the heat pump is connected to the return branch from thermal users, then heat recovery is enabled, but the variable fluid temperature (oscillating more than 10°C) negatively impacts heat pump performance
Solution Approach 1:
The system is divided into two separate circuits: a primary circuit connecting the heat pump to the cogeneration plant, and a secondary distribution circuit serving thermal users. The separation exchanger connects these circuits, allowing heat transfer while maintaining independent operation of each circuit. This segmentation isolates the heat pump from temperature variations in the user distribution system.
Solution Approach 2:
The separation exchanger acts as an intermediary device between the heat pump's primary circuit and the user distribution circuit. It enables thermal energy transfer while preventing direct fluid mixing and temperature coupling, thereby stabilizing the heat pump operating conditions while still allowing heat recovery from combustion gases.
2Loss of energy
If the fluid temperature to users is adjusted according to climatic curves, then energy efficiency improves, but temperature variation over time prevents optimal plant utilization
Solution Approach 1:
The system pre-cools the circulation fluid in the primary circuit before it enters the separation exchanger, preparing it at optimal temperature conditions in advance. This preliminary cooling action ensures that the heat pump operates at peak efficiency regardless of subsequent temperature variations in the user distribution system.
Solution Approach 2:
The system dynamically adjusts the cooling degree in the primary circuit based on real-time operating conditions, combining the benefits of climatic curve adjustment with continuous optimization. This dynamic control allows the plant to maintain optimal utilization while still adapting to external temperature variations.
3Loss of energy
If a second exchanger is added downstream of the recovery boiler, then residual heat recovery is enabled, but the system complexity increases
Solution Approach 1:
The separation exchanger serves multiple functions simultaneously: it acts as a heat transfer interface between primary and secondary circuits, a temperature stabilization device for the heat pump, and a system decoupling point. This multi-functionality reduces the need for additional dedicated components, managing system complexity while enabling residual heat recovery.
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 configuration doubles the recoverable heat from combustion gases, stabilizes the heat pump operation, and increases the overall efficiency of the plant by maintaining a controlled temperature gradient, enhancing thermal recovery and reducing environmental impact.
Implementation Method 1
downstream of said primary cycle gas exchanger a second exchanger is connected, connected to the evaporator of the heat pump by a circuit... such heat pump to cool the fluid flow before it enters into said second exchanger
Implementation Method 2
The circulating technical fluid in the heat pump (18), after absorbing heat from the working fluid in the secondary circuit (20), may transfer the heat to the working fluid in the primary circuit (10) through the condenser (19b)
Implementation Method 3
a separation exchanger to maintain a constant fluid temperature for the heat pump
Implementation Method 4
a low-temperature gas exchanger to recover residual heat from combustion gases
Data Source
Figure 1
AI summary
A system for heat recovery from combustion gases comprises a primary circuit (10), which is associated with a cogeneration unit (12), a heat pump (18), and a pair of respective exchangers (14, 22), and a separation exchanger (11c) for thermally decoupling said primary circuit (10) from the heat distribution circuit to the users (HC), and supplying a constant temperature inlet flow to the condenser (19b) of the heat pump (18).