Rankine Cycle Efficiency via Expander Inlet Temperature Control
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Solution Overview
Problem
Existing Rankine cycle apparatuses face a trade-off between improving electricity generation efficiency and increasing in size, limiting their application to large-scale facilities, and there is a need to reduce the size while maintaining efficiency for smaller-scale combined heat and power systems.
Innovation Solution
The method involves setting the temperature of the working fluid at the inlet of the expander higher than the saturation temperature on the high-pressure side, enabling efficient heat exchange in the internal heat exchanger, which enhances the efficiency of electricity generation without increasing the size of the apparatus, and includes the use of sensors for precise temperature control and organic working fluids with low boiling points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the expansion ratio of the expander is increased to increase the enthalpy recovered and electricity generated, then the electricity generation efficiency is improved, but the size of the Rankine cycle apparatus increases
Solution Approach 1:
The invention changes the operating parameters of the Rankine cycle by setting the working fluid temperature at the expander inlet to a specific range (higher than saturation temperature but not excessively high). This parameter optimization allows the system to achieve high electricity generation efficiency without requiring an oversized expander or other components, thus resolving the contradiction between productivity and apparatus size.
2Productivity
If an internal heat exchanger is provided to reduce thermal input to the evaporator, then the electricity generation efficiency is improved, but the size of the Rankine cycle apparatus increases
Solution Approach 1:
The invention optimizes the temperature parameters of the working fluid at various points in the cycle, particularly setting the expander inlet temperature within a specific range. This parameter optimization enables the system to achieve high efficiency without requiring a large internal heat exchanger, as the thermodynamic conditions are optimized to maximize heat recovery effectiveness within a compact footprint.
3Productivity
If the evaporator is designed to correspond exactly to the targeted difference in enthalpy on the boiling curve, then the overall energy efficiency is improved, but the size of the Rankine cycle apparatus increases
Solution Approach 1:
The invention changes the temperature parameter of the working fluid at the expander inlet to a specific range, which optimizes the enthalpy difference utilization in the evaporator. This allows the evaporator to be designed with a smaller size while still achieving the targeted enthalpy difference and maintaining high overall energy efficiency.
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 approach allows for improved electricity generation efficiency while minimizing the size of the Rankine cycle apparatus, maintaining efficiency even with low pump efficiency, and enhancing controllability and design flexibility, making it suitable for smaller-scale combined heat and power systems.
Implementation Method 1
an internal heat exchanger that allows heat exchange to take place between the working fluid discharged from the expander and the working fluid discharged from the pump
Implementation Method 2
an evaporator that heats the working fluid pressurized by the pump
Implementation Method 3
a condenser that cools the working fluid discharged from the expander
Implementation Method 4
an expander that converts expansion energy of the working fluid heated in the evaporator into rotary power
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
A Rankine cycle apparatus (20A) includes a pump (23), an evaporator (24), an expander (21), a condenser (22), and an internal heat exchanger (25). The internal heat exchanger (25) allows heat exchange to take place between the working fluid discharged from the expander (21) and a working fluid discharged from the pump (23). A temperature of the working fluid at an inlet of the expander (21) is set so that a temperature of the working fluid at an outlet of the expander (21) be higher than a saturation temperature on a high-pressure side of the cycle.