Biogas upgrading for removing CO₂ and other trace components from the raw biogas is a necessary step to obtain biomethane. Because of the fact that the biogas is obtained from the biomass, the finally use of the biomethane implies a good environmental impact. This fuel could be used in many energetic applications as vehicle fuel or be supplied to the natural gas grid.
Several techniques have been developed to achieve this objective, in this thesis a chemical absorption method will be studied. The chemical absorption process in biogas upgrading exploit the reversible nature of the chemical reaction of an aqueous alkaline solvent, usually an amine, specifically the monoethanolamine (MEA).
The main goal of this thesis is to carry out the exergo-economic analysis and optimization of a biogas upgrading plant. In order to do it, the software Aspen Plus 8.8 version is used. Firstly, the methodology needed to develop the analysis is explained, basically, an exergy study is done in order to know where the exergy destruction is more considerable and the final value achieves in the biogas upgrading process. After that, the exergo-economic analysis computes the unitary cost of the different streams and the cost of the components from the plant in order to characterize the cost-rate of the different streams of the process. Finally, an optimization methodology is explained and apply into the process in order to know in which components the optimization is more necessary and also, to understand the nature of the optimization itself that is to say if the optimization is need to be done regarding the efficiency or the cost of the component.
Furthermore, the biogas upgrading plant is study in order to calculate the efficiency of the whole process taking into account the energy generated and the energy consumption. The energy consumption is obtained and compared with the bibliography values collected in order to verify the value. However, the thermodynamic part is not only studied, also an economic study is carried out to the biogas upgrading plant.
The economic study is done in order to guarantee that the biogas upgrading plant is a feasible project. Because of that, the Net Present Value (NPV), the Benefic-cost ratio (BCR), the Internal Rate of Return (IRR) and the Payback Time (PBT) have been calculated. Moreover, a sensitivity analysis has been done varying different parameters of the plant. It is important to comment that the monetary benefits are given due to the sale of the biomethane. Because of that, the incentives given by the government are a significant parameter that needs to be defined.
Not only a base case has been studied, different cases have been also defined in order to understand in a more complete way the biogas upgrading process through a chemical absorption. These cases are: the variation of the final purity of the biomethane, the variation of the capacity of the plant varying the volume flow of biogas and the variation of the operational parameters of the absorber.
After the final discussion of the obtained results, the future lines of research have been defined at the end of the project in order to identify the following steps that can be done to continue the development of the biogas upgrading process.