Energy efficiency and conversion in complex integrated industrial sites : application to a sulfite pulping facility

This thesis presents a methodology to analyse the integration of heat recovery energy conversion technologies and biorefinery concepts in existing pulp and paper facilities. By using innovative process integration techniques and thermo-economic optimisation tools, efficient energy saving opportunities can be obtained and guidelines can be applied to implement energy efficiency enhancing measures. The objective is to provide engineers a decision support tool for the design of heat exchangers networks. The system approach used in this work is based on the development of a framework that implements existing simulation tools and process integration methods. The first contribution of this work resides in the establishment of a reconciled model of a complex pulping facility where utility and process measurements are studied simultaneously. Derived operating nominal conditions are validated through a complete sensitivity analysis. The resulting base case model is considered to be representative of the original process and constitutes the basis of the process energy integration definition problem. The core of the methodology consists in the application of two successive approaches: the top-down and the bottom-up approach. The top-down approach allows to identify which sub-systems of the facility consume more energy and could eventually lead to large energy savings. Conversion technologies used to produce utilities and their distribution to the process are also identified. The bottom-up approach benefits from the results of the top-down approach in order to evaluate the energy saving potentials. Systematic definition of the process heat transfer requirement defined as hot and cold streams is obtained according to different heat-temperature profiles. The exergy concept is employed to explain how using different heat-temperature profiles of the same energy requirement is changing the perspective of the energy use in the facility and therefore make possible the identification of energy saving opportunities with different levels of process modifications. An innovative way of considering the steam producers using as a main feed process materials in the definition of the process integration problem is also presented. The development of scenarios using systematically all energy requirement definitions is done and allows the elaboration of a decision support tool that point out the critical process modifications necessary to achieve interesting energy savings. A detailed example of the complete methodology developed in this thesis is illustrated using the multi-effect evaporator. The optimal integration of combined heat and power production and heat pumps is also presented. Finally, the interest of using this methodology is demonstrated in the case of a biorefinery integration by the development of a trade-off between the conversion of lignocellulosic materials into bio-materials and energy.