Hybrid dual-fuel combined cycle power plants employ two or more different fuels (one of which is typically a solid fuel), utilized by two or more different prime movers with a thermal coupling in between. Major thermodynamic and economic advantages of hybrid combined cycle configurations have been pointed out by various authors in previous studies. The present investigation considers the performance of natural gas and biomass hybrid combined cycles in small scale, with an internal combustion engine as topping cycle and a steam boiler/turbine as bottoming cycle. A parametric analysis evaluates the impact of natural gas to biomass fuel energy ratio on the electrical efficiency of various hybrid configurations. Results show that significant performance improvements with standard technology can be achieved by these hybrid configurations when compared to the reference (two independent, single-fuel power plants at the relevant scales). Electrical efficiency of natural gas energy conversion can reach up to 57–58% LHV, while the efficiency attributed to the bottoming fuel rises with up to 4 percentage points. In contrast to hybrid cycles with gas turbines as topping cycle, hybrid configurations with internal combustion engines show remarkably similar performance independent of type of configuration, at low shares of natural gas fuel input.

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