Organic Rankine Cycle with Intermediate Steam Extraction
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Solution Overview
Problem
Organic Rankine cycles face inefficiencies in heat recovery due to high molecular mass working fluids generating high volumetric flows and overheating during expansion, leading to significant losses in exergy and reduced thermodynamic efficiency.
Innovation Solution
The proposed solution involves separating steam expansion within the turbine into two flows, with one flow tapped at an intermediate pressure for heat supply to external users and the remaining expanded to a lower pressure matching the heat absorption temperature, utilizing two recuperators to recover heat and preheat the organic fluid, thereby maximizing electrical efficiency and allowing flexible heat detachment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If organic working fluid is used in ORC cycle, then thermal energy can be exploited at low-medium temperatures, but high volumetric flows are generated in the turbine reducing bleeding efficiency
Solution Approach 1:
The turbine is divided into multiple expansion stages with intermediate extractions. The expansion process is segmented into distinct pressure levels, allowing heat to be detached at multiple points along the expansion path rather than as a single extraction, thereby improving overall heat recovery efficiency while maintaining compatibility with high volumetric flow organic fluids.
Solution Approach 2:
Intermediate pressure extraction points are introduced as mediators between the high-pressure inlet and low-pressure outlet of the turbine. These intermediate stages allow heat to be transferred to thermal users at pressures that match their requirements, optimizing heat exchange efficiency without compromising the turbine's ability to handle high volumetric flows.
2Power
If working fluid is overheated during expansion, then electrical efficiency is improved, but significant exergy loss occurs during heat transfer to thermal users
Solution Approach 1:
The overheating process is segmented into multiple stages corresponding to different expansion pressures. Heat is detached at each intermediate stage at temperatures better matched to thermal user requirements, reducing the temperature difference during heat transfer and minimizing exergy loss while still maintaining sufficient overheating to preserve electrical efficiency.
Solution Approach 2:
The temperature and pressure parameters of the working fluid are dynamically adjusted at each extraction stage to optimize the balance between electrical efficiency and heat transfer efficiency. By changing these parameters progressively through intermediate extractions, the system achieves both high power generation and low exergy loss.
3Power
If heat is transferred to thermal users from overheated vapor, then electrical power is generated, but high temperature difference causes significant efficiency loss
Solution Approach 1:
Heat transfer to thermal users is segmented into multiple extractions at different pressure levels rather than a single extraction from fully expanded vapor. This allows heat to be transferred at higher temperatures that are better matched to thermal user requirements, reducing the temperature difference and improving heat transfer efficiency while still generating electrical power.
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 enhances electrical efficiency and flexible heat recovery by optimizing heat utilization, reducing exergy loss, and adapting to varying heat demands without significant loss of efficiency.
Implementation Method 1
an expander (turbine) 2 where the fluid expanding (in an ideal iso-entropic manner) transfers the useful work of the cycle to the outside
Implementation Method 2
a first condenser 4 at high temperature, of the water-steam or other heat transfer fluid cooled type, suitable for transferring heat to the thermal user
Implementation Method 3
suitable for transferring heat to the thermal user
Implementation Method 4
a pump 5, 5' where the liquid is returned by the pressure of the condenser 4, 4' up to the pressure of the evaporator 1
Implementation Method 5
an evaporator 1, where the pressurized fluid is heated, vaporized and possibly overheated or brought to supercritical conditions by using heat from an external source
Data Source
Figure 1
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AI summary
Organic Rankine cycle (300, 400, 500) comprising: - an evaporator (1) where the pressurized fluid is heated, vaporized and brought into subcritical or supercritical conditions using the heat of a source; - a turbine (2) where the fluid while expanding provides the useful work of the cycle; - at least one pump (5, 5 ') where the liquid is brought from the pressure of at least one condenser (4, 4') to the evaporator pressure (1); - a pre-heater (6), which using the same source supplies heat to the working fluid, bringing it to a temperature close to the vaporization temperature, said organic Rankine cycle (300, 400, 500) further comprising - a first recuperator (3) which receives a first portion of organic fluid vapor extracted from the turbine (2), and is connected to a first condenser (4), by means of a first circuit (10) at medium pressure; - at least one second recuperator (3 ', 403', 404 ') which receives a second portion organic fluid vapor leaving the turbine (2) and is connected to a second condenser (4'), by means of a second low pressure circuit (11), said organic Rankine cycle (300, 400, 500) being characterized by at least one further pre-heater (301, 301') positioned in parallel with one or both of said first and second recuperator (3, 3').