Design and construction of torrefaction system integrated with parabolic trough solar collector and determination of optimum operating conditions for different biomass

Technologies for the thermochemical conversion of biomass are a priority for R&D funding in Turkey. These methods have applications in different fields such as energy, environmental science and chemistry. The most important advantage is to obtain the required form (solid, liquid or gas) of a product. Products can be used as a fuel for heating and electricity or sold as chemical substances. Biochar is a solid product produced by a thermal process which is known as "torrefaction". Nowadays, biochar can be used for amending soil, as an alternative fuel to lignite or a component of other processes. The process has a low level of pyrolysis and it is carried out under anaerobic conditions in the temperature range of 200°C to 300°C depending on the characteristics of the biomass. The desired results are the degradation of structure by breaking hydrogen bonds, the removal of moisture and minimum loss of volatiles. Solar energy is also one of renewable energy sources used in both heating and electricity generation. Due to accelerating of photovoltaic sector and cheapening investment costs of it, concentrated solar power systems is economically preferable rather the production of superheated steam than electricity generation. Concentrated solar energy can also be transferred to a solid material as water and oil. In this thesis, torrefaction process was used with parabolic though solar concentrator in that produced the high temperature fluid. Thus, it is aimed to reduce investment and operating costs of torrefaction. The required energy for biochar production was directly supplied by parabolic concentrator, and the designed system was carried out differently from CSP systems. In this regard, the torrefaction reactor was positioned to the focus line of concentrator and lab-scale prototype was established. Optical efficiency of the system and the heat transfer coefficient of receiver were found approximately 0.73 and 1.04W/m2K, respectively. Furthermore, cotton stalk, pine chips and chicken litter were carbonized in lab-scale electrical torrefaction system. The effects of important parameters such as temperature, particle size, bulk density and retention time were investigated for each biomass, and optimum process conditions were determined. The optimum conditions for each biomass were used for the experiments in designed and established CSP assisted torrefaction system (prototype system). Finally, the biochar production yield was compared. Whole biochar obtained was consistent with the results in the literature. The ANOVA statistical analysis was performed by using the mass loss, energy yield, carbon content, higher heating values (HHV), H/C and O/C ratios, thus temperature was found to be the most important parameter. The optimum process conditions of cotton stalk was the temperature of 318°C, retention time of 60 minutes and density of 155kg/m3. For the biochar of pine chips, the particle size of 5mm in retention time of 10 minutes at the temperature of 350°C were determined as optimum condition. In addition the optimum condition for chicken litter was found 300°C, 60 minutes and the density of 200kg/m3. CSP assisted torrefaction system was designed with copper selective surface reactor that was most effective receiver. The experiments carried out in optimum conditions at prototype system were compared with the lab-scale electrical system, and the average difference between response variables was found at %5.1.