Luciana Savulescu

Direct and indirect heat transfer in water network systems

Abstract This paper addresses direct/indirect heat recovery network design for water network systems. A particular water network case of two different temperature fresh water sources is analysed. A new systematic heat recovery design approach based on thermodynamics is proposed for water stream sets leading to energy pinch problems. The concept of direct/indirect heat transfer decomposition is introduced to explore the design of heat exchanger network (indirect heat transfer) and non-isothermal mixing. This concept is illustrated through a new graphical segregation of the composite curves. To overcome the limitations associated with the representation of stream mixing in the composite curves, a new tool, source–demand energy composite curves, is introduced to evaluate the complexity of direct heat recovery and design different mixing scenarios.

DESIGN OF COOLING SYSTEMS FOR EFFLUENT TEMPERATURE REDUCTION

Temperature restrictions on aqueous effluents dictate that streams with a temperature higher than the permitted level needed to pass through cooling systems to reduce the effluent temperature before discharge. This paper introduces methods for the design of effluent cooling systems. Inappropriate mixing of effluents with different temperatures reduces opportunities to recover heat from effluents and degrades driving forces for cooling systems. A new systematic method is introduced for the segregation strategy for effluents to deal with effluent temperature problems most effectively by a combination of heat recovery and effluent cooling. This can lead to distributed effluent cooling systems. The design procedure sets targets before design. A design procedure then allows the targets to be achieved by following design rules for distributed cooling. An optimisation model has been developed to search for the most economic design of cooling systems. A case study involving retrofit is presented to illustrate the design methodology and the optimisation model of cooling systems.

On Minimization of the Number of Heat Exchangers in Water Networks

This article addresses the problem of minimizing the number of heat exchangers for heat recovery as well as the number of mixing and splitting junctions within water networks while maintaining the energy targets determined by the classical pinch analysis. A new systematic approach is proposed to eliminate the kink points and linearize the composite curves. This is based on a systematic strategy that indicates how to mix and split the water streams in order to modify the shape of the initial composite curves. A new graphical thermodynamic rule that avoids the deterioration of energy targets while minimizing the number of heat transfer units as well as the mixing and splitting network complexity has been formalized. This rule permits the control of the procedure of mixing and splitting on the T-H diagram in order to guarantee the pre-established targets. The proposed approach can be used for either the manual design of heat recovery within water networks or the building of a superstructure with a limited number of feasible design options.

An Improved Linear Programming Approach for Simultaneous Optimization of Water and Energy

An optimization method based on Mixed Integer Linear Programming (MILP) has been developed for simultaneous optimization of water and energy (SOWE) in industrial processes. The superstructure integrates process thermal streams and optimizes the consumption of water while maximizing internal heat recovery to reduce thermal utility consumption. In this paper, additional concepts have been implemented in the superstructure to target the issues of the pulp and paper processes. Non-Isothermal Mixing (NIM) has been considered at different locations in order to reduce the number of thermal streams and decrease the investment cost by avoiding unnecessary investment on heat exchangers. The concepts of restricted matches and water tanks have been added to the superstructure to adapt it to the pulp and paper case studies. The Integer-Cut Constraint (ICC) technique has been combined with the MILP model to generate systematically a set of optimal solutions to support the decision-making for cost-effective configurations.

A novel MILP approach for simultaneous optimization of water and energy: Application to a Canadian softwood Kraft pulping mill

Abstract An optimization methodology based on Mixed Integer Linear Programming (MILP) has been developed for simultaneous optimization of water and energy (SOWE) in industrial processes. The superstructure integrates non-water process thermal streams and optimizes the consumption of water, while maximizing internal heat recovery to reduce thermal utility consumption. To address the complexity of water and energy stream distribution in pulp and paper processes, three features have been incorporated in the proposed SOWE method: (a) Non-Isothermal Mixing (NIM) has been considered through different locations to reduce the number of thermal streams and decrease the investment cost by avoiding unnecessary investment on heat exchangers; (b) the concept of restricted matches combined with water tanks has been added to the superstructure; and (c) the Integer-Cut Constraint technique has been combined with the MILP model to systematically generate a set of optimal solutions to support the decision-making for cost-effective configurations. The performance of the proposed improved MILP approach has been evaluated using several examples from the literature and applied to a Canadian softwood Kraft pulping mill as an industrial case study. The results indicate that this approach provides enhanced key performance indicators as compared to conceptual and non-linear complex mathematical optimization approaches.

Process Integration Concepts for Combined Energy and Water Integration

Abstract: All sectors of the process industries depend on water and energy resources to transform raw materials into a large number of products demanded by society. The sustainability issue is an essential consideration in process design, which drives significant efforts to improve both water and energy efficiency. Most of these processes display strong interactions between water and energy use such that any changes to the energy network often impact the water network, although this impact is seldom followed in any systematic way by process-design engineers. Due to a number of market externalities, the economic balance between energy and water is heavily inclined towards energy. However, with water shortages becoming more frequent throughout the world, it is likely that the balance will change in the near future. Other environmental aspects associated with chemical process design include energy-related issues such as greenhouse gas and other air emissions as well as water quality. This chapter reviews several useful Process Integration (PI)-based concepts recently developed across a number of worldwide research teams, in support of process-design applications dealing with problems characterised by strong energy and water interactions.

Novel methods for combined energy and water minimisation in the food industry

Publisher Summary The food processing industry consumes significant amounts of water and energy. Due to increasing energy costs and concerns regarding climate change, there is an urgent need to improve energy efficiency. Similarly, the availability, quality, and cost of fresh water resources must be taken into account as a part of a life-cycle analysis for ensuring sustainability and cost-effective operation. There exist housekeeping rules and best practice guidelines in the management of water and energy in the food industry. However, a systematic and integrated approach that allows simultaneous design and/or optimization of water and energy systems while minimizing the economic and environmental burden should be employed to fully consider the interactions between these major resources and their efficient use. This chapter provides an introduction to integrated design concepts to present a systematic approach that the food processing industry can adopt when performing plant water and energy assessments. It discusses available conceptual design tools as well as design guidelines within the context of combined energy and water minimization analysis. It also describes the complexity of the water network, defined in part by process water demands and its associated energy requirements and highlights the need for a global and integrated investigation of overall-plant water and energy profiles, rather than a local non-integrated approach.

Simultaneous Water and Energy Minimization for Brown Stock Washing System

Abstract Pulp and paper mills are huge consumers of water and energy. Hence, much research works have been dedicated to simultaneous reduction of water and energy in the past decades. However, none of those works are addressing the brown stock washing system (BSWS), which is the core processing section that determines the amount of energy required in black liquor (BL) concentration. The latter is the largest energy consumption in a typical pulp and paper mill. Therefore, minimizing water consumption in the BSWS will lead to energy saving too. In this work, mass balances of the BSWS is first analyzed in a process simulation software (Cadsim), and adopted as the base case model for the study. Next, a mixed integer non-linear programming (MINLP) optimization model is developed to minimize the total annualized cost incurred in the project. The synthesized water network features significant reduction in both energy and water consumption in the BSWS.