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One of the by-products from bioethanol production using woody materials is lignin solids, which can be utilized as feedstock for combined heat and power (CHP) production. In this paper, the influence of integrating a drying process into a biomass-based polygeneration system is studied, where the exhaust flue gas is used to dry the lignin solids instead of direct condensation in the flue gas condenser (FGC). The evaporated water vapor from the lignin solids is mixed with the drying medium for consequent condensation. Thus, the exhaust flue gas after the drying still has enough humidity to produce roughly the same amount of condensation heat as direct condensation in the existing configuration. The influence of a drying process and how it interacts with the FGC in CHP production as a part of the  polygeneration system is analyzed and evaluated. If a drying process is integrated with the polygeneration system, overall energyefficiency is only increased by 3.1% for CHP plant, though the power output can be increased by 5.5% compared with the simulated system using only FGC.

Abstract: Bioethanol is considered an alternative to fossil fuels in the transportation sector. The use of pellets for heating is another efficient way to mitigate greenhouse gas emissions. This paper evaluates the techno-economic performance of a biorefinery system in which an existing combined heat and power plant integrates with the productions of bioethanol and pellets using straw as feedstock. A two-stage acid hydrolysis process for bioethanol production is used, and two different drying technologies are chosen for drying hydrolysis solid residues. A sensitivity analysis on critical parameters, such as the bioethanol selling price and feedstock price, is performed. The bioethanol production cost is also calculated for two cases at the conditions of ten-year and five-year payback time. The results show that the first case is a more feasible economic configuration at present, having an over 30% production cost reduction compared with the conventional cogeneration plants of bioethanol and solid fuel.

Three optional pellet production processes integrated with an existing biomass-based CHP plant using different raw materials (wood chips and solid hydrolysis residues) are studied. The year is divided into 12 periods, and the integrated biorefinery systems are modeled and simulated for each period. The annual economic performance of three integrated biorefinery systems is analyzed based on the simulation results. The option of pellet production integrated with the existing CHP plant with the exhaust flue gas and superheated steam as drying mediums has the lowest specific pellet production cost of 105 €/tpellet, the shortest payback time of less than 2 years and the greatest CO2 reduction of the three options. An advantage in common among the three options is a dramatic increase of the total annual power production and significant CO2 reduction in spite of a small decrease of power efficiency.

Conversion of wastes to energy by different technologies can contribute greatly to treating waste sustainably, reducing dependency on imported fossil fuels and protecting environment. A static model of energy balance for a certain region is constructed to simulate and optimize the energy system with the purpose to minimize the total costs, including collection, transportation and conversion or treatment of wastes, distribution of energy products as well as import and export of wastes and energy products. The objective is to find optimum positions for building new energy plants and planting energy crops for two scenarios. How to achieve a regional fossil-fuel-free energy system is also analyzed through a case study of the County of Västmanland in central Sweden. The boundary conditions are assumed to be the limit of local waste generation, capacity of energy plants, and the demands of energy products.