One of the remedies for inevitable worldwide decarbonisation, would be offered by a negative CO2 emission power plant. The negative emission effect can be achieved by using a renewable energy source as fuel and capturing carbon dioxide. The syngas from sewage sludge is considered as a renewable energy source. Analysis assumes two types of fuel: mentioned syngas and methane. In order to achieve a positive environmental effect, the thermodynamic cycle must be equipped with a carbon capture installation, while producing electricity. On the other hand, if there is no such an installation, it is said to be zero-emission - analogous to wind farms or photovoltaic farms. The shown thermodynamic cycle will ultimately be powered by syngas produced in a sewage sludge gasifier. The calculations carried out for methane are comparative calculations. Other assumptions are: combustion process in presence of pure oxygen, stoichiometric combustion and water injection to the combustion chamber. Research was carried out with Ebsilon®Professional software. In the calculations thermodynamical tables for steam were used. Presented are studies of two thermodynamic cycle cases of negative CO2 emission gas – steam turbine combinations. First of them is a basic combined cycle with Carbon Capture and Storage (CCS) installation, whereas the second one consists of the first cycle additionally integrated with an ASU. The aim of the examined problem was to investigate the influence of the ASU on generated power and efficiency. Both cycles feature the same power output from considered turbines, i.e. 155,02 kW for syngas, what results in the same gross efficiency equal 51,98 %. On the other hand, power for own needs is markedly different for both cases, that has a pronounced effect on the net efficiency. Simulation results showed that the net efficiency of the negative CO2 emission power plant achieved 37,40 %, but efficiency of the cycle integrated with the ASU was reduced to 24.83 %. The power value congenial to 160 kW is an effect of the fact, that calculations were carried out for a demonstrative installation. In the system, two devices will be specially designed: the combustion chamber (WCC) and the spray- ejector condenser (SEC). Their functionality needs to be proved in a measuring campaign. Presented calculations are one of the first studies of an impact of the ASU on performance of the negative emission CO2 power plant.