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High efficiency recuperator

Development and manufacture of a gas turbine recuperator of 100 kw(e) with high efficiency exceeding 90% based on primary surfaces for temperatures of 650-700 degrees celsius. Development of stamping and welding technology for very thin special steel foils with 0.08mm thickness.

The main aim of the project is the development of high efficiency gas-turbine recuperators. The project will be divided into the following tasks: 1. Design of the whole concept of the recuperator, including inlet and outlet ports. 2. Design of the heat transfer surface with a high overall heat transfer coefficient with as low as possible pressure losses. 3. Selection of available and suitable material with high creep resistance at high temperatures of 650 to 700 degrees Celsius. 4. Welding technology development. 5. Long-term testing of recuperators to assess durability between major overhauls and the service life. 1. Design of the whole concept of the recuperator, including inlet and outlet ports. Increasing demand for small energy sources (approximate power ranges from 5 kW to 400 kW) are expected as a result of the deregulation of electricity markets in many countries around the world. There are only a few solutions which can meet different customer's requirements for small energy sources, i.e. high efficiency, low operating costs, high durability and ecological aspects. One of these solutions is the small gas turbine (microturbines) designed for combined heat and power generation (CHP), however the efficiency of the basic cycle turbine is low. According to FORECAST INTERNATIONAL, it is expected that the number of installations will peak around 2011, more than doubling the number of installations when compared with 2002. Specific requirements for microturbines are: fuel-to-electricity conversion efficiency of at least 40 %, costs of electricity that are competitive with alternatives (including grid-connected power) for market applications, and the option of using multiple fuels including natural gas, diesel, ethanol, landfill gas, and other biomass-derived liquids and gases, 11,000 hours of operation between major overhauls and a service life of at least 45,000 hours with NOx emissions lower than 7 ppm for natural gas. In order to increase microturbine efficiency and hence decrease fuel consumption and electricity cost, a recuperator is mandatory. The recuperator is a heat exchanger, which takes heat from exhaust gas and preheats the compressor-discharged air before it enters the combustion chamber. The result is higher thermal efficiency. There is a significant relationship between the recuperator parameters and the thermal efficiency of the microturbine which affects the recuperator construction. The requirements of recuperators may be summarized as: high effectiveness, low-pressure losses, minimum volume and weight, high reliability and durability, and low cost. These requirements can only be fulfilled by counter flow heat exchangers with high compactness. 2. Design of heat transfer surfaces with high overall heat transfer coefficients and as low as possible pressure losses As the recuperator represents 25-30 percent of the overall machine cost, efforts are being focused on establishing new low cost recuperator designs for gas turbine engines. The heat transfer surfaces in these recuperator designs are of the plate-fin and primary surface types and all types can be manufactured with high compactness, i.e., high heat transfer surface area to volume ratio. As a parameter for the evaluation, volume and area factors are used. Normally 4 unique categories or configurations of heat transfer surfaces are used: plate-fin type, cross-corrugated (CC), corrugated-undulated (CU) and cross-wavy (CW). All surfaces except for plate-fin are considered as primary surfaces as they have the lowest number of parts and are easier to manufacture. Of these the CU surface is not currently in use in the industry and the CC surface is not commercially available in any gas turbine recuperator. From evaluations carried out by UTRIAINEN and SUNDEN, it is shown that the Cross Corrugated (CC) surface has the best potential for use in compact recuperators of the future. 3. Selection of available and suitable material with high creep resistance at high temperatures of 650 to 700 degrees Celsius. A standard material, AISI T347 austenitic steel is currently used for the recuperator core in very thin foils of thickness 0.08 to 0.12 mm. Oxidation/corrosion testing at 650 degrees Celsius indicates very severe attacks after only a few thousand hours, indicating that alloys with significantly better behaviour are needed at 650-700 degrees Celsius. Research is being conducted at OAK RIDGE NL in cooperation with ALLEGHENY-LUDLUM TECHNICAL CENTRE in the U.S.A. to develop cost effective alloys with improved performance and high creep resistance and temperature capability. The near term goal is better performance at or above 704 degrees Celsius for 2004. The modified T347 is T347CR (now designated AL347HP), which was creep tested at 704 degrees Celsius and found to have improvements of 75% for the foil compared to T347. 4. Welding technology development A principal issue in developing the above mentioned recuperator is the welding technology of very thin austenitic steel with thickness of 0.08 to 0.15 mm. In the CZECH REPUBLIC no company currently offers such technology, especially for welding in very thin gaps between individual plates. The company PRECISION TUBES has developed its own technology for welding very thin tubes of small diameters. The company has the potential to develop a similar welding technology for the aforementioned recuperator. 5. Long-term testing of recuperators to assess durability between major overhauls and the service life The recuperator needs be tested for long-term durability. These tests will be conducted at microturbine manufacturer sites where the microturbine will be operated. Keywords: primary surface recuperator, high efficiency, welding technology.
Acronym: 
HEFRECA
Project ID: 
3 436
Start date: 
01-01-2005
Project Duration: 
42months
Project costs: 
1 080 000.00€
Technological Area: 
Turbines, fluid machinery, reciprocating engines, combined heat and power
Market Area: 

Raising the productivity and competitiveness of European businesses through technology. Boosting national economies on the international market, and strengthening the basis for sustainable prosperity and employment.