• Energy Research

Abstract Sewage sludge is a residue of wastewater processing that is biologically active and consists of water, organic matter, including dead and alive pathogens, as well as organic and inorganic contaminants such as polycyclic aromatic hydrocarbons (PAHs) and heavy metals. Due to the nature of sewage sludge and its possible influence on human health and wellbeing, it is a subject of various regulations. Currently, sewage sludge is considered as biomass, according to the new Polish act on renewable energy sources of February 20, 2015 and its novel version of July 19, 2019. This study presents a novel model, along with a comparison with experimental results. The model could be used for sewage sludge gasification modelling for accurate assessment of the performance of novel concepts bioenergy with carbon capture and storage (BECCS) installations, using sewage sludge as a fuel. The composition of the dry produced gas, determined experimentally, yields: XCO = 0.093, XCO2 = 0.264, XCH4 = 0.139, XCxHy = 0.035, and XH2 = 0.468. Performed modifications to the original Deringer-with-Gumz-modification gasification model allowed to obtain good agreement with the experimental results, reaching XCO = 0.071, XCO2 = 0.243, XCH4 = 0.139, XC3H8 = 0.035, and XH2 = 0.512. The main novelty in the formulas of the internal model was due to propane inclusion, which was not found in the literature before. Additionally, sulphur dioxide was applied in exchange for other sulphur components presented in the original model. Equilibrium constants were adjusted to suit the experimental model. For ease of calculation, the own code was used to iterate multiple temperatures. Included was the energy balance equation that is essential for verification.

The article presents results of thermodynamic analysis using a zero-dimensional mathematical models of a negative CO2 emission power plant. The developed cycle of a negative CO2 emission power plant allows the production of electricity using gasified sewage sludge as a main fuel. The negative emission can be achieved by the use this type of fuel which is already a “zero-emissive” energy source. Together with carbon capture installation, there is a possibility to decrease CO2 emission below the “zero” level. Developed models of a novel gas cycle which use selected codes allow the prediction of basic parameters of thermodynamic cycles such as output power, efficiency, combustion composition, exhaust temperature, etc. The paper presents results of thermodynamic analysis of two novel cycles, called PDF0 and PFD1, by using different thermodynamic codes. A comparison of results obtained by three different codes offered the chance to verify results because the experimental data are currently not available. The comparison of predictions between three different software in the literature is something new, according to studies made by authors. For gross efficiency (54.74%, 55.18%, and 52.00%), there is a similar relationship for turbine power output (155.9 kW, 157.19 kW, and 148.16 kW). Additionally, the chemical energy rate of the fuel is taken into account, which ultimately results in higher efficiencies for flue gases with increased steam production. A similar trend is assessed for increased CO2 in the flue gas. The developed precise models are particularly important for a carbon capture and storage (CCS) energy system, where relatively new devices mutually cooperate and their thermodynamic parameters affect those devices. Proposed software employs extended a gas–steam turbine cycle to determine the effect of cycle into environment. First of all, it should be stated that there is a slight influence of the software used on the results obtained, but the basic tendencies are the same, which makes it possible to analyze various types of thermodynamic cycles. Secondly, the possibility of a negative CO2 emission power plant and the positive environmental impact of the proposed solution has been demonstrated, which is also a novelty in the area of thermodynamic cycles.

In the face of tightening climate regulations, the adoption of carbon dioxide recovery systems is inevitable. Modular process skid units have been widely adopted across the industry. The gas-steam power plant skid unit with the carbon dioxide recovery system was described. The proposed skid module consists of the compact cycle with the oxy-combustion and the carbon dioxide capture skid unit producing pure compressed CO2. The compactness of the suggested skid can be achieved due to a novel small size designs of the wet combustion chamber and the spray-ejector condenser.