Evaluation of Environmental Loads for the Synthesis of a Trigeneration System

This paper details the calculation of the environmental loads associated with the construction of each piece of equipment (considering that the materials were not reused at the end of the equipment’s lifetime, which is the worst case scenario) and operation of a trigeneration system. The purpose of a trigeneration system is to meet the demands of a consumer center — in this case, a medium-sized hospital located in Zaragoza, Spain. The evaluation extended over a period of one year, considering previously specified energy service demands (electricity, heat - sanitary hot water and heating -, and cooling). The system interacted with the economic environment (market) through the purchase of natural gas and electricity from the grid, and also through the sale of autogenerated electricity to the grid, according to Spanish regulations. Therefore, the environmental loads regarding the operation of the system were associated with the consumption of natural gas and electricity purchased/sold from/to the grid. Technical information on each piece of equipment was obtained from catalogs and from consultation with manufacturers. Regarding natural gas, special care was taken to correctly identify the natural gas supplied to a user in Spain (it was considered that the gas comes from Algeria, transported in Liquefied Natural Gas (LNG) carriers, including pipeline transportation to the user and controlled burning). The electricity supplied by the Spanish electric grid was also properly specified and characterized. The environmental loads were calculated utilizing SimaPro, a specialized Life Cycle Assessment tool, and then incorporated into a linear programming model, solved by LINGO optimization software. Environmental criteria were used to obtain the optimal configuration and operation of the system simultaneously.