Life cycle assessment of combined bioheat and biopower production and cost: Simulated case studies based on combustion utilizing turkish oak (Quercus cerris L.) coppices

Combined heat and power (CHP) or cogeneration involves two or more secondary energy carriers such as useful heat and electricity, using a single fuel in one conversion process. Biomass is an alternative fuel for CHP systems. The name Combined BioHeat and BioPower (CBHBP) emphasizes that a biomass source is used as the feedstock for the production of CHP. Turkey is a country with rich biomass potential; however, traditional utilization is predominant. The high technical potential of biomass offers a strategic source for energy supply diversification in Turkey. As an indigenous energy source, biomass could help to minimize fuel import dependency and greenhouse gas (GHG) emissions, and to increase local development. Moreover, biomass is actually an effective means to further develop CHP investments in the country, which would contribute significantly to energy saving measures in Turkey. Although electricity licenses using renewables have been growing based on many investments in Turkey, biopower applications are in the developmental stage and sector growth is slower than anticipated. A challenging further increase in biopower development is needed, not only to reach the national targets, but also to adhere to international commitments. The growth in biopower production has mainly involved biochemical conversion technologies to produce landfill gas and biogas, which are applicable to wet biomass sources. However, biopower production through thermochemical conversion technologies that require solid biomass sources is still at an early stage and therefore limited in the country. In addition, most plants only generate biopower, and CBHBP applications are too few. The majority of the global biopower generated comes from CBHBP plants, and in other countries, CBHBP production through distributed generation (DG) is seen as a viable way of taking advantage of local biomass sources. Moreover, a sustainable supply of feedstock is crucial for biomass energy applications. Modern utilization of solid biomass sources through distributed CBHBP production, including the efficient application of thermochemical conversion technologies, could be put into use for future development of biopower in Turkey. Oak coppice forests are among the biomass treasures of Turkey and are readily available solid biomass sources for production of biomass energy. Initiating modern energy forestry applications starting with unproductive or poorly productive oak coppice forests in the areas near these biomass treasures that are also near settlements where there is a constant heating/cooling and power demand, distributed CBHBP plants could be implemented rapidly and become widespread in the country. Forest villages, where wood is already often used as a source of energy for heating and cooking, which practice results in a serious threat to forest sustainability, are the best opportunities for distributed CBHBP deployment. This would provide not only environmental, but also technological, social, and economic benefits. If renewable-based energy technologies are to compete with conventional energy technologies, they must be sustainable. Life Cycle Assessment (LCA) is a preferred key tool to estimate environmental sustainability of biomass energy applications. It is a standardized tool that uses a life cycle approach. An LCA provides a way of looking at any product to determine its resource consumption and the environmental consequences of releases throughout its life cycle, from raw material acquisition to final waste disposal. LCA can also be used as an eco-design (green design) tool. Eco-design aims to minimize environmental life cycle impacts of a product at its design stage. In cases of CBHBP implementation, LCA can be used as the fundamental basis to determine environmental sustainability of the project, including an eco-design approach for CBHBP production. In this study, the first aim is to conduct an LCA study with an eco-design approach to determine the environmental sustainability of combustion-based in situ CBHBP plants based on simulated case studies. To achieve this aim, the simulated case studies have different scales, all utilize Turkish oak (herein TR-Oak) (Quercus cerris L.) coppices, consider CBHBP eco-design parameters, and also take into account current commercial CBHBP plants worldwide. The results of the LCA study include a contribution analysis of midpoint and endpoint impacts for different stages of biomass-to-CBHBP value chain. This helps to figure out the relative importance of the stages in the system boundary. The results also include a sensitivity analysis on LCA results. In order to present an eco-design approach, the LCA study demonstrates the effect of the most fundamental CBHBP design parameters on LCA results. In addition, the LCA study quantifies the most important environmental benefits of CBHBP production compared to Turkish lignite coal-fueled power production. The next aim of the study is to finalize the research with CBHBP production representative cost estimates that could be used to facilitate decision making for investors interested in CBHBP technologies in Turkey. This thesis research is the first attempt, to our knowledge, to conduct an LCA in coordination with process simulation, and to introduce an eco-design approach for sustainable CBHBP production. This study, being the first of its kind in Turkey, should be helpful to all dealing with biomass energy applications in the country. This thesis starts with a comprehensive review of CBHBP production technology already used. Then, based on the review study, Case Study-1 (CS-1), CS-2, and CS-3 were proposed to characterize distributed CBHBP production. The focus was on a steam turbine system based on direct combustion technology, the conventional Rankine cycle, in line with worldwide biopower developments. CS-1, CS-2, and CS-3 have 2, 5, and 10 megawatt electrical (MWe) biopower output, respectively. Meanwhile, the biomass feedstock selected for use in CBHBP production was TR-Oak chips from TR-Oak coppice forests in the Marmara region of Turkey. Samples were taken and experiments were carried out to characterize TR-Oak chips. Later, process simulations of CS-1, -2, and -3 utilizing the characterized TR-Oak chips were carried out using Aspen Plus V8.4 process simulation software. The relevant process parameters, requirements, and environmental impacts of the CBHBP plants were quantified based on the simulated case studies considering eco-design parameters. Next, based on CBHBP process simulation outputs and eco-design parameters, the LCA study was conducted using SimaPro V8.1.1.16 LCA software. After defining the goal and scope, and completing the inventory analysis phase of the LCA study, a Life Cycle Inventory (LCI) was prepared using SimaPro software. In the LCA study, the system boundary starts with harvesting of TR-Oak coppices, and ends with biopower to an electrical grid and bioheat to a district heating network. Three energy output-related functional units were chosen: 1 kilowatt-hour (kWh) biopower, 1 kWh bioheat, and 1 kWh (combined) energy production. The modeling approach used was a unit process-based attributional LCA. Exergy-based allocation was used between biopower and bioheat. While CML-IA baseline V3.03 (with the World 2000 normalization set) was the midpoint impact assessment method chosen, it was ReCiPe Endpoint (H) V1.12, (with World ReCiPe H/A and H/H weighting sets) that was chosen as the endpoint impact assessment method. Then, the LCA results were obtained by following the impact assessment methods provided in the SimaPro software. The LCA results of the study include comparative characterization, normalization, and weighting results. In addition, there is a detailed contribution analysis for midpoint and endpoint impacts. For this, the system boundary (and hence the LCA results) was arranged in the stages of TR-Oak chip supply chain, CBHBP plant operation, TR-Oak ash transport and spreading, and construction and decommissioning. The results also include the effect of feedstock properties and process conditions on LCA results to implement the eco-design approach, a sensitivity analysis of the most uncertain assumptions and choices, and finally, a comparison of TR-Oak chip-fueled biopower production with Turkish lignite-based power production in terms air emissions from combustion. The study ends with CBHBP production cost estimates. The LCA results showed that when deciding on a scale of CBHBP production, there should always be a trade-off between scale and annual environmental impacts. Moreover, reducing feedstock demand and strain on the biomass supply chain of CBHBP plants is another issue to consider. The chosen characterization results are within the ranges reported in literature. Normalization results revealed the importance of background waste treatment processes on the TR-Oak chip supply chain as well as the construction and decommissioning operations. Weighting results showed that human health has the highest importance followed by resources. The importance of impacts on ecosystems is insignificant relative to those on human health and resources. Contribution analysis showed the relative importance of different stages in the system boundary. Both CBHBP plant operation and TR-Oak chip supply chain are stages that need to be designed with the highest care to minimize environmental loading and to achieve sustainable CBHBP production. To achieve a sense of overall perspective, the TR-Oak chip supply chain contributes ~ 43–52% to the single score, and operation of the CBHBP plant contributes ~ 42–52%. Thus, one is not more or less important than the other is. The TR-Oak chip supply chain is the stage most affected by increases in moisture content due to the consequent higher transportation requirements. Excess air ratio and furnace temperature affected the importance of CBHBP plant operation mostly due to nitrogen oxides (NOx) emission increases. Sensitivity analysis enabled estimation of the effects of variation in transport distance between roadside and CBHBP plant, equipment productivity, CBHBP plant lifetime, and allocation procedure. In addition, the significance of explaining all the methodological choices and inventory data prepared for an LCA study in as much detail and as transparently as possible, was revealed. Under the current framework conditions in Turkey, the CBHBP cost estimates provided in the thesis are economically feasible. Biopower unit costs were found to be 8.7–9.5 US Dollar cent (cent) per kWh. Comparison of TR-Oak chip-fueled biopower production with Turkish lignite-based power production, when considered in terms of the effects of air emissions from combustion on human health, the single score for 1 kWh of Turkish lignite-fueled power production is 15 times higher than that for 1 kWh of TR-Oak chip-fueled biopower production.