ORC Heat Engine Startup Control via Switchable Expander
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Solution Overview
Problem
ORC heat engines face challenges in starting up efficiently, leading to high initial pressure requirements, potential pump overheating, and dry-running issues, which affect component lifetime and performance, and they struggle to operate across varying temperatures and heat demands like conventional gas boilers.
Innovation Solution
An ORC heat engine with a control system that includes a switchable mechanism between drivable and non-drivable states, using sensing means and processing to manage the expander-generator's operation, allowing the system to transition from inverter-driven startup to fluid-driven operation, thereby reducing initial pressure needs and preventing dry-running.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large initial inlet pressure is supplied by the pump to overcome stiction and start expander rotation, then the expander-generator can begin to rotate, but the pump overheats and lubrication is reduced due to very little working fluid flowing through the pump
Solution Approach 1:
The system pre-pressurizes the working fluid in the evaporator before starting the expander-generator, so that when the expander starts, there is already sufficient pressure differential to drive rotation without requiring the pump to operate at high pressure with minimal flow
Solution Approach 2:
The control system dynamically adjusts pump operation based on expander-generator rotation status, reducing pump pressure and flow during start-up when the expander is not rotating, and normalizing operation once rotation begins, thereby preventing pump overheating
2Stress or pressure
If the pump operates to provide high pressure and flow into the evaporator at start-up when the expander-generator is not rotating, then the working fluid circulates, but the pump may run dry causing increased wear and reduced lifetime
Solution Approach 1:
The control system continuously monitors expander-generator rotation status and working fluid levels, providing feedback to adjust pump operation. When the expander is not rotating or fluid levels are low, the pump operation is modulated to prevent dry-running conditions
Solution Approach 2:
The system ensures sufficient working fluid is present in the circuit before pump operation begins, and maintains appropriate fluid levels during start-up, preventing the pump from running dry and extending its lifetime
3Adaptability or versatility
If the ORC heat engine operates across a range of temperatures and heat demands like conventional gas boilers, then the system versatility increases, but the control complexity and component adaptability requirements increase
Solution Approach 1:
The control system dynamically adjusts operating parameters including pump speed, evaporator heating rate, and expander load based on real-time temperature and heat demand conditions, enabling the system to adapt across a wide operational range without requiring multiple fixed-configuration systems
Solution Approach 2:
The ORC heat engine components are designed with multi-functionality to handle varying temperatures and heat demands. The same core components (pump, evaporator, expander, condenser) operate across different conditions rather than requiring specialized components for each operating mode, reducing overall system complexity
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 solution improves start-up time, extends component lifetime, enhances operational efficiency, and allows the ORC heat engine to operate effectively across a range of temperatures and heat demands, similar to conventional gas boilers, with reduced mechanical components and increased reliability.
Implementation Method 1
an evaporator for heating and evaporating a working fluid
Implementation Method 2
an evaporator for heating and evaporating a working fluid
Implementation Method 3
a condenser for cooling and condensing the working fluid
Implementation Method 4
a positive displacement expander-generator... The evaporated gas phase fluid is then expanded through the expander-generator thus producing electrical energy
Data Source
AI summary
An ORC heat engine including a working fluid circuit having an evaporator for heating and evaporating a working fluid, a condenser for cooling and condensing the working fluid, and a positive displacement expander-generator having an inlet in fluid communication with the evaporator and an outlet in fluid communication with the condenser. The ORC heat engine further includes a control system coupled to the positive displacement expander-generator having a switch and driving means, the switch being switchable between a first state and a second state, wherein in the first state the switch is coupled to the driving means, and the positive displacement expander-generator is drivable by the driving means, and in the second state the switch is not coupled to the driving means or the driving means is switched off, and the positive displacement expander-generator is not drivable by the driving means.