In this work, the production of power using a combined cycle gas turbine/steam turbine, which operates
with biogas as fuel, is evaluated. The process begins with the production of biogas from pig and/or cattle
slurry manure(s) using anaerobic digestion. Afterwards, the gas is cleaned up to remove humidity, hydrogen
sulfide, carbon dioxide and ammonia. The cleaned gas (biomethane) is then used in a Brayton cycle
(gas turbine) to produce energy. The flue gas that exits the Brayton cycle is typically at high temperature
and it is further utilized to produce steam that generates power in a regenerative Rankine cycle (steam
turbine). Two alternative steam production schemes are evaluated: either splitting the flue gas to have
high temperature gas for the reheating step of the steam or sequential heating up. The model is formulated
as a Mixer Integer Nonlinear Programming (MINLP) solved in GAMS for the optimal production of
power. For a typical production capacity of manure in farms, 2.6 MW are produced. The investment for
the plant turns out to be 26 M€ and the production cost of the electricity is 0.35 €/kW h before including
the credit from the conditioned digestate, that could be sold as fertilizer. The electricity cost goes down to
0.15 €/kW h considering a reasonable credit from the digestate, whose composition depends on the feedstock
processed in the facility.