OPERATIONAL STRATEGIES OF 2-SPOOL MICRO GAS TURBINE WITH ALTERNATIVE FUELS: A PERFORMANCE ASSESSMENT

The demand for efficient, cost-effective, and low-emission decentralized electricity and heat production is rapidly increasing. Micro Gas Turbines (mGT) have not yet succeeded in conquering the small-scale combined heat and power (CHP) market. The main reason is that their electrical efficiency is not high enough to maintain a cost-effective operation at low heat demand. A two-shaft intercooled mGT has the potential to meet the current market demand for decentralized power generation. This technology maintains a high level of electrical efficiency even at part load and coupled with its fuel-flexible combustion chamber, makes it an ideal candidate for CHP concepts in a renewable future. The energy transition however also requires mGTs to be able to run on alternative fuels, such as hydrogen and syngas, which shifts its operating conditions and requires significant modification in the cycle's part-load control to ensure the stable operation of the components such as the compressor. Therefore, in this paper, performance analysis on a 2-spool mGT is carried out using a mixture of natural gas, syngas, and hydrogen as a fuel. Specific attention is given to the low-pressure and high-pressure compressors and the variation of surge margin by adding hydrogen and syngas into the fuel. Two control strategies of the 2-spool mGT are adopted. In the first scenario, the two shafts have the same rotational speed while in the second one, the shaft speeds are controlled independently. In both part-load strategies, the specific performance of the two compressors keeps high isentropic efficiency which leads to high electrical efficiency at nominal power when natural gas-syngas mixture is used as fuel. When the engine is operated with equal shaft speeds, the maximum performance with 100 vol.% of syngas is observed at 85% of the nominal load while 100 vol.% of hydrogen shows maximum efficiency at an electric load of 63.7%. Also, at electric power lower than 60% of the nominal and for high amounts of syngas in natural gas, the low-pressure compressor (LPC) operates closely to surge line. In the second part-load strategy, the efficiency increases as the load decreases and the LPC runs in an efficient and safe operating region. Moreover, the performance of the 2-spool mGT is significantly influenced by the amount of nitrogen in syngas. At 200 kW, 45 vol.% of nitrogen decreases the airflow rate of the cycle by 7.4 % compared to 0 vol.%. The results indicate that the amount of nitrogen in syngas and also the part-load strategies significantly influence the safe operation of the LPC component.