A STUDY OF 50MW HYDROGEN COMBUSTION TURBINES
INTRODUCTIONA Hydrogen combustion turbine system has been proposed by Mitsubishi Heavy Industries, Ltd. (MHI) which is the Closed Circuit Cooled Topping Recuperation Cycle (CCCTR cycle) and this studies are administrated through the New Energy and Industrial Technology Development Organization (NEDO) as a part of International Clean Energy Network Using Hydrogen Conversion (so-called WE-NET) program with funding from the Agency of Industrial Science and Technology (AIST) in Ministry of International Trade and Industry (MITI) of Japan. This cycle uses hydrogen and oxygen combustion and is composed of closed Brayton and Rankin cycle. 50MW test plant is planned in advance of 500MW electricity generating commercial plant. In case of 500MW plant the first stage vane and blade height is 85mm and efficiency is more than 60% HHV at combustion exit temp. (CET) 1700C. According to scale principle the first vane and blade height for 50MW is 28mm which is too small for cooling design. Therefore we redesigned this height to 38mm without decrease of efficiency. Then we conclude 50MW plant efficiency is near 60% HHV. Besides as a test method, methane fuel and oxygen application based on CCCTR cycle is analyzed and verified. In this case plant efficiency is near 60% HHV including CO2 extraction work. This also can supply economical configuration of test plant.
2. Closed Circuit Cooled Topping Recuperation Cycle (CCCTR cycle)The base cycle at combustion exit temp. (CET) 1500C which MHI called "Topping extraction cycle" was proposed by GRAZ Technical Instututes . This cycle is shown in Figure 1. MHI modified this base cycle to get "Topping recuperation cycle" (CCCTR) at combustion exit temp. 1700C as shown in Figure 2  . This cycle is suitable for a high CET (1700C) from the point of view of both the thermal efficiency and the feasibility of manufacture. Figure 3 shows that in case that CET is less than 1500C, "Topping extraction cycle" is the best selection and in case that CET is more than 1500C, "Topping recuperation cycle" is the best selection.
3. Study of 500MW plantFigure 2 shows the CCCTR cycle of 500MW plant which efficiency is 61.8% HHV. Figure 4 shows the design of the first blade which height is 85mm. This height size is enough to design cooling passage in vane and blade.
4. Study of 50MW plant as test plantScale down machine of CCCTR as 50MW test plant
Figure 5 shows the CCCTR cycle of 50MW plant which efficiency is 59.6% HHV. As a test plant in advance of 500MW, this 50MW plant should be tested for verification of elementary technics of 500MW commercial plant. According to scale principle the first vane and blade height for 50MW is 28mm. But this height is too small for design of cooling passage in blade and vane. Therefore MHI redesigned this height to 38mm without decrease of efficiency as shown in Figure 6.
Simpler cycle or methane fuel cycle based on CCCTR as 50MW test plant
Table 1 : Studies of 50MW cycle
Table 1 : Studies of 50MW cycle
Figure 8 shows the most economical configuration which uses methane fuel (Natural gas) and oxygen application based on CCCTR cycle. In this case plant efficiency is near 60% HHV including CO2 extraction work. This also can supply economical configuration of test plant because hydrogen is more expensive than natural gas in price. Besides this plant is also useful as countermeasure for withdrawal of CO2 with low energy because of its high efficiency in spite of including extraction work of CO2. Similar cycle which shows high efficiency was studied by GRAZ Techinical Institutes . In Figure 8, MHI uses actual elementary efficiency of turbine & compressor etc. to get reasonable efficiency 58.8% HHV, but no cooling. In the meantime this system needs another work for production of Oxygen which assumed 10-20% of output power. Decrease of work for production of Oxygen is a subject to be developed. In future if storing method of CO2 will be developed, this cycle would have much effect on prevention from CO2 increase on earth.
5. Conclusion(1)We estimate it will take about 30 years that hydrogen energy will be popular. Therfore MHI believes that there is needs to develop Hydrogen Combustion Turbines which output is about 500MW by that time. MHI selected CCCTR as the best cycle for Hydrogen/Oxygen combustion cycle from the point of view of both the thermal efficiency and the feasibility of manufacture.
(2)Simple and economical test plant which output is 50MW was studied. Scale down of CCCTR is a strong candidate. Therefore MHI studied 1st vane & blade height for easy design. Simpler cycle based on CCCTR, but not high efficiency is second candidate. Methane fuel and Oxygen cycle based on CCCTR is third candidate because of its economy as a test plant. Besides other cycles based on CCCTR will be studied in future for seaching more economical test cost and future application.
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