Analysis of a biorefinery integration: application to a sulfite wood pulping process

The pulp and paper (P&P) industry in industrially mature countries is facing a long-term crisis. Large and modern manufacturing facilities in tropical regions emerge as new competitors. The constant increase of energy costs has also contributed to the financial difficulties encountered in the industry. To stay viable and sustainable, P&P mills need to elaborate new strategies to increase their revenues. In this context, converting a P&P mill into an integrated forest biorefinery could be the solution to restore the health of the industry and overcome the crisis. Diversifying the industry's product mix by producing bio-energy and bio-materials could be a way to penetrate new markets while maintaining its core production of pulp and paper. Producing bio-materials implies energy consumption and waste heat. The energy management cannot therefore be dissociate from the biorefinery integration in a P&P mill: both energy and mass integration must be considered. The objective of this work is to illustrate the trade-off between conversion of materials and of energy and shows the importance of considering simultaneously the heat recovery through heat exchangers and the combined heat and power production. Process integration techniques have been applied to study a bisulfite mill which produces pulp and three additional by-products: bioethanol, lignosulfonate and yeast. Particular attention was devoted to the integration of the chemical recycling loops which have a significant impact on the process energy balances and therefore influence the choice of biorefinery integration strategies. A key element of the process integration pathway was to consider the heat cascade as a model of the heat exchanger network by decoupling the installed heat exchangers network when analysing the potential effects of the recycling and production strategies at the plant level. Using this model, the optimal integration of a combined heat and power production unit was determined taking into account the simultaneous maximisation of process internal heat recovery. To facilitate the computational formulation of the problem, the overall process was subdivided into several production sub-systems with flow diagrams and flow rates dependant on the main product being manufactured in each sub-system. Mass balance constraints were introduced to model the flow distribution between sub-systems and the hot and cold streams were computed by means of a conventional flowsheeting software. The corresponding hot and cold streams were subsequently integrated at the mill scale level. The pulp production line and energy conversion equipment such as the sulphur boiler, lignin boiler and the biomass boilers were simultaneously optimized.

Analysis of a biorefinery integration in a bisulfite pulp process

François Maréchal, Zoé Périn-Levasseur

Process integration techniques have been applied to study a bisulfite mill which produces pulp and three additional by- products: bioethanol, lignosulfonate and yeast. Particular attention was devoted to the integration of the chemical recycling loops which have a significant impact on the process energy balances and therefore influence the choice of biorefinery integration strategies. This analysis illustrates the trade-off between conversion of materials and of energy and shows the importance of considering simultaneously the heat recovery through heat exchangers and the combined heat and power production.

2009

Energy efficiency and conversion in complex integrated industrial sites

Zoé Périn-Levasseur

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.

EPFL2009

Energy and Exergy Analysis of a Cruise Ship

Karin Andersson, Francesco Baldi, Tuong-Van Nguyen

In recent years, the International Maritime Organization agreed on aiming to reduce shipping’s greenhouse gas emissions by 50% with respect to 2009 levels. Meanwhile, cruise ship tourism is growing at a fast pace, making the challenge of achieving this goal even harder. The complexity of the energy system of these ships makes them of particular interest from an energy systems perspective. To illustrate this, we analyzed the energy and exergy flow rates of a cruise ship sailing in the Baltic Sea based on measurements from one year of the ship’s operations. The energy analysis allows identifying propulsion as the main energy user (46% of the total) followed by heat (27%) and electric power (27%) generation; the exergy analysis allowed instead identifying the main inefficiencies of the system: while exergy is primarily destroyed in all processes involving combustion (76% of the total), the other main causes of exergy destruction are the turbochargers, the heat recovery steam generators, the steam heaters, the preheater in the accommodation heating systems, the sea water coolers, and the electric generators; the main exergy losses take place in the exhaust gas of the engines not equipped with heat recovery devices. The application of clustering of the ship’s operations based on the concept of typical operational days suggests that the use of five typical days provides a good approximation of the yearly ship’s operations and can hence be used for the design and optimization of the energy systems of the ship.

2018

Energy efficiency and conversion in complex integrated industrial sites

Zoé Périn-Levasseur

EPFL2009