Small scale CO2 capture.

As a consequence of anthropological processes, the environment needs more concerns and regulations. One of the challenges is the capture of carbon dioxide (CO2) which has been elaborated to reduce the greenhouse effect. At this moment the use of CO2 capture systems is mainly envisaged in large scale plants. In this thesis, some of the most diffused technologies have been studied and compared to each other for application to small-scale CO2 emitters. In fact, there are many small or medium-sized plants that do not pay sufficient attention to the emission of carbon dioxide but which, on the whole, have a significant impact on the greenhouse effect. Usually, the installation of big amine plant, for example, is not interesting for this kind of industries, then small-scale CO2 capture could be an alternative, also if they do not achieve the same performances of larger plants. The present study has taken as example a cogeneration unit installed in Liegì University, which gave the possibility to have real data, used as input for computations. It is powered by a biomass boiler of 12 MW produce 257 kg of CO2 per MWhth and 457 kg of CO2 per MWhel for a total of 12800 kg on CO2 per year. The technologies analyzed are Post-Combustion Carbon Capture (PCCC) and are amine solvents and membrane separation. The global work wants to point out which one of them is the most profitable from energy and cost point of view and convenient for small scale use. After a general introduction about carbon capture technologies, the first part regards the description of membrane technology and physical phenomena that govern it. Membrane use for CO2 capture is less widespread than others method and many researchers are still working on it. The biggest drawback of this technology is the brief lifetime of membrane (around 3-4 years) and the relatively low purity of v in the permeate stream which makes it impossible to use only in one stage configuration. Despite their drawbacks, the membrane is interesting because they only imply a minor consumption of energy and their modularity allows to save much space. The base module of the membrane has been produced with the help of Aspen Custom Modeler (ACM) software, which permitted to insert the physical law which governs the phenomena. The base module was then implemented in Aspen Plus software which gave the possibility to build different configuration. The study of configuration regarded both the use of compression or vacuum condition. At the end of the analysis, two configurations demonstrated to achieve 99% of CO2 purity with almost 87% of CO2 separated. Then most convenient between them has been chosen for the comparison with Amine technology and it uses 400 m2 of polymeric membrane area (Polaris) and needs 2.65 MWe. The second part instead interests the use of CO2 absorption with amine solvents, one of the most common and mature technologies is the post-combustion process. This one achieves a higher separation rate, but also induces a higher consumption of energy. In particular, a pre-existing model in Aspen Plus software has been studied and adopted to our case of study. The used model allows the evaluation of the process energy requirement and studies the oxidative degradation in the absorber which is the cause of most of the solvent loss. Also, in this case as well as a membrane the operating conditions are analysed to check when the efficiency of separation is maximum and when energy consumption is minor.