Micro Gas Turbine Prevaporizing Combustor and Ejector Cooling
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Solution Overview
Problem
Current microturbines, especially those under 25 kW, are inefficient and have short lifetimes due to inadequate heat transfer control, leading to fuel coking and increased maintenance requirements, and they struggle with maintaining performance across varying operating conditions.
Innovation Solution
The microturbine design incorporates a prevaporizing combustor with a combustor air bypass system and a generator cooling system, allowing controlled fuel vaporization and air-fuel mixing, along with a radial inflow compressor turbine and axial free power turbine to optimize performance and efficiency, while the ejector cooling scheme uses hot exhaust gas to cool the generator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If hot combustion products are used to directly heat the fuel stream before injection into the combustor, then fuel vaporization is achieved, but fuel temperature varies considerably causing fuel coking and increased combustor maintenance requirements
Solution Approach 1:
A heat exchanger is introduced as an intermediary component between the combustion products and the fuel stream. The heat exchanger transfers heat from the combustion products to the fuel indirectly, allowing temperature control while preventing direct contact that causes coking. This mediator enables reliable heat transfer without the harmful effects of direct heating.
Solution Approach 2:
The system changes the temperature parameter of the fuel stream through controlled heat exchange before injection. By regulating the heat transfer process through the heat exchanger, the fuel temperature is maintained within optimal ranges, preventing coking while ensuring proper vaporization for reliable combustion.
2Weight of moving object
If microturbines are designed to be smaller and lighter than reciprocating engines, then compactness and weight reduction are achieved, but efficiency decreases and lifetime is reduced to less than 100 hours
Solution Approach 1:
Fuel is pre-vaporized and pre-heated in the heat exchanger before entering the combustor. This preliminary action ensures that fuel is properly prepared for combustion, improving combustion efficiency and reducing operational stresses on turbine components, thereby extending microturbine lifetime while maintaining compact size.
Solution Approach 2:
The patent replaces direct mechanical heating methods with a thermal field-based heat exchanger system. This substitution allows for more controlled and efficient heat transfer, improving overall system efficiency and reliability while maintaining the compact, lightweight design of the microturbine.
3Productivity
If fuel is vaporized in a small amount of air using hot combustion products, then fuel vaporization is achieved, but inadequate control of heat transfer allows temperature variation and fuel coking
Solution Approach 1:
The heat exchanger serves as an intermediary that enables controlled heat transfer from combustion products to fuel. This intermediary component provides the necessary control mechanism, allowing high vaporization rates while maintaining stable fuel temperature through regulated thermal exchange, eliminating the coking problem.
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 design achieves a thermal efficiency of 15% and extends the microturbine's lifetime to over 1,000 hours, while maintaining high combustion efficiency and reducing maintenance needs by controlling fuel temperature and air-fuel ratios.
Implementation Method 1
a centrifugal compressor comprising a compressor rotor to provide a continuous flow of compressed air
Implementation Method 2
a prevaporizing combustor for mixing the compressed air with fuel, wherein the compressed air is mixed with fuel in a specific ratio to produce a high-pressure hot gas
Implementation Method 3
a radial inflow compressor turbine to extract power from the high-pressure hot gas produced by the prevaporizing combustor
Implementation Method 4
an axial free power turbine to extract power from the high-pressure hot gas exiting the radial inflow compressor turbine to power an attached load
Implementation Method 5
a generator having a stator installed in the housing and a rotor fixed to the second end of the power output shaft so as to be rotated together
Implementation Method 6
a generator cooling system to provide cooling air to the generator, the system comprising a passage surrounding the generator
Data Source
AI summary
A unique, small microturbine engine adapted to integrate with an electrical generator for producing electrical power has been developed. The microturbine includes an ejector cooling scheme, a prevaporizing combustor, and a combustor air bypass. The ejector cooling scheme uses energy in the hot exhaust gas stream of the microturbine to entrain a flow of ambient air that cools the generator. The prevaporizing combustor of the present invention allows liquid fuel to be vaporized in a small amount of air prior to combustion, thereby increasing combustion efficiency and decreasing combustor size requirements. The combustor air bypass allows a fraction of the compressor discharge air to bypass the prevaporizing combustor under certain operating conditions. This permits control of the overall equivalence ratio and the fuel/air mixing process in the combustion zone, improving efficiency and operability.