Integration of Biomass into District Energy Systems with Methanol Production Based on a MINLP Optimization Methodology

The international energy consumption has considerably increased due to the demographic and economic growth in recent decades. In this framework, polygeneration represents an innovative and promising concept. The purpose of this study is to provide a generic modelling and optimization framework to evaluate the polygeneration systems in urban areas. An integrated biomass-based polygeneration scheme with CCHP (combined cooling, heating and power) system, providing electricity, heating and cooling as well as methanol product, is proposed and evaluated in this work. The potential of integrating the system into a district energy system is also investigated by case study. A mixed-integer nonlinear programming (MINLP) approach has been formulated in GAMS (General Algebraic Modeling System) to address the following issues: a) selection of technologies, types and numbers of equipment to match the energy demand of end users; b) strategic planning and process designing from both economic and environmental perspectives; c) representation of the relationships and trade-offs between the trigeneration and chemical conversion steps; d) operation strategies for the dynamic energy systems with time dependent components and boundary conditions. Moreover, the proposed system is compared to the conventional natural gas based CCHP system as the reference.