Co-firing from woody biomass feedstock is one of the alternatives toward increased use of renewable feedstock in existing coal power plants. However, the economic level of co-firing at a particular power plant depends on several site-specific factors. Torrefaction has been identified recently as a promising biomass pretreatment option to lead to reduction of the feedstock delivered cost, and thus facilitate an increase in the co-firing ratio. In this study, a mixed integer linear program (MILP) is developed to integrate supply chain of co-firing and torrefaction process and find the optimal level of biomass co-firing in terms of minimized transportation and logistics costs, with or without tax credits. A case study of 26 existing coal power plants in three Great Lakes States of the US is used to test the model. The results reveal that torrefaction process can lead to higher levels of co-firing, but without the tax credit, the effect is limited to the low capacity of power plants. The sensitivity analysis shows that co-firing ratio has higher sensitivity to variation in capital and operation costs of torrefaction than to the variation in the transportation and feedstock purchase costs.
One of the core decisions on securing the supply of biomass to co-firing power plants is the design of a proper logistics system. Though technologies have been developed to improve the characteristics of feedstock, their effects in the logistics systems have received less attention. This paper compares the conventional woody biomass logistics system with the advanced woody biomass logistics system that includes the torrefaction process to upgrade the feedstock. More specifically, this study uses a mixed integer linear program to integrate conventional and advanced biomass logistics and applies them to a case study of 26 coal power plants in the Great Lakes states to determine the most feasible logistics system for each plant. The results revealed that the amount of cost savings from the advanced woody biomass logistics depends on the capacity and location of the power plant. To categorize the cost savings of individual plants, it was found that plants can be divided into seven groups based on three parameters: 1) annual coal tonnage shipped (total capacity), 2) availability of biomass in the vicinity, and 3) average distance from biomass collecting sites. Overall savings from advanced logistics were small, but plants within each of the groups demonstrated similar cost reductions. The sensitivity analysis showed that trucking costs and feedstock purchasing costs were most sensitive to variation. From torrefaction effects, energy content after torrefaction had more significance than mass reduction.
Rapid demographic ageing is a global challenge and has tremendous implications for transportation planning, because the mobility of elderly people is an essential element for active ageing. Although many studies have been conducted on this issue, most of them have been focused on aggregated travel patterns of the elderly, limited in spatiotemporal analysis, and most importantly primarily relied on sampled (2–3%) household travel surveys, omitting some trips and having concerns of quality and credibility. The objectives of this study are to present more in-depth analysis of the elderly’s spatiotemporal activity and travel behaviors, to compare them with other age and gender groups, and to draw implications for sustainable transportation for the elderly. For our analysis, we used locational trajectory-based mobile phone data in Gangnam, Korea. The data differs from sampled household travel survey data, as mobile phone data represents the entire population and can capture comprehensive travelers’ movements, including peculiarities. Consistent with previous researches, the results of this study showed that there were differences in activity and travel patterns between age and gender groups. However, some different results were obtained as well: for instance, the average nonhome activity time per person for the elderly was shorter than that of the nonelderly, but the average numbers of nonhome activities and trips were rather higher than those of nonelderly people. The results of this study and advantage of using mobile phone data will help policymakers understand the activities and movements of the elderly and prepare future sustainable transportation.
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