Detailed study of the impact of co-utilization of biomass in a natural gas combined cycle power plant through perturbation analysis

Co-utilization of fossil fuels and biomass is a successful way to make efficient use of biomass for power
production. When replacing only a limited amount of fossil fuel by biomass, measurements of net output
power and input fuel rates will however not suffice to accurately determine the marginal efficiency of the
newly introduced alternative fuel. The present paper therefore proposes a technique to determine the
marginal biomass efficiency with more accuracy. The process simulation model for co-utilization of natural
gas and a small perturbing fraction of biomass in an existing combined cycle plant (500MWth Drogenbos,
Belgium) is taken as case study. In this particular plant, biomass is introduced into the cycle as
fuel for a primary steam reforming process of the input natural gas.
This paper proposes a perturbation analysis that has been developed to allow for an accurate assessment
of the marginal efficiency of biomass by using only accurately measurable variables. To achieve this,
effects of co-utilization were studied in each component of the gas turbine down to its steam bottom
cycle to identify the components most affected by the limited perturbing amount of biomass. The procedure
is validated through process simulation, where accurate marginal efficiencies can be compared with
the efficiency obtained from the perturbation analysis. A full off-design simulation is required to achieve
this result. Through the use of process simulation, the accuracy of the mathematical model could be verified
for each formula and each assumption. Compared to process simulation data, the model was found
to accurately predict marginal efficiencies of the introduced biomass for biomass shares as low as 0.1%.