Simultaneous synthesis of heat exchanger networks with pressure recovery: Optimal integration between heat and work (original) (raw)
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MINLP Model for the synthesis of heat exchanger networks with handling pressure of process streams
2014
This paper introduces a new mathematical model for the simultaneous synthesis of heat exchanger networks (HENs), wherein the handling pressure of process streams is used to enhance the heat integration. The proposed approach combines generalized disjunctive programming (GDP) and mixed-integer nonlinear programming (MINLP) formulation, in order to minimize the total annualized cost composed by operational and capital expenses. A multi-stage superstructure is developed for the HEN synthesis, assuming constant heat capacity flow rates and isothermal mixing, and allowing for streams splits. In this model, the pressure and temperature of streams must be treated as optimization variables, increasing further the complexity and difficulty to solve the problem. In addition, the model allows for coupling of compressors and turbines to save energy. A case study is performed to verify the accuracy of the proposed model. In this example, the optimal integration between the heat and work decreases the need for thermal utilities in the HEN design. As a result, the total annualized cost is also reduced due to the decrease in the operational expenses related to the heating and cooling of the streams.
Energy Conversion and Management, 2015
Generalized disjunctive programming (GDP) Mixed-integer nonlinear programming (MINLP) Retrofit Heat exchanger network (HEN) Pressure recovery Sub-ambient processes a b s t r a c t This paper presents a new mathematical programming model for the retrofit of heat exchanger networks (HENs), wherein the pressure recovery of process streams is conducted to enhance heat integration. Particularly applied to cryogenic processes, HENs retrofit with combined heat and work integration is mainly aimed at reducing the use of expensive cold services. The proposed multi-stage superstructure allows the increment of the existing heat transfer area, as well as the use of new equipment for both heat exchange and pressure manipulation. The pressure recovery of streams is carried out simultaneously with the HEN design, such that the process conditions (streams pressure and temperature) are variables of optimization. The mathematical model is formulated using generalized disjunctive programming (GDP) and is optimized via mixed-integer nonlinear programming (MINLP), through the minimization of the retrofit total annualized cost, considering the turbine and compressor coupling with a helper motor. Three case studies are performed to assess the accuracy of the developed approach, including a real industrial example related to liquefied natural gas (LNG) production. The results show that the pressure recovery of streams is efficient for energy savings and, consequently, for decreasing the HEN retrofit total cost especially in sub-ambient processes.
MINLP optimization algorithm for the synthesis of heat and work exchange networks
2014
This paper introduces a new optimization model for the simultaneous synthesis of heat and work exchange networks. The work integration is performed in the work exchange network (WEN), while the heat integration is carried out in the heat exchanger network (HEN). In the WEN synthesis, streams at high-pressure (HP) and low-pressure (LP) are subjected to pressure manipulation stages, via turbines and compressors running on common shafts and stand-alone equipment. The model allows the use of several units of single-shaft-turbine-compressor (SSTC), as well as helper motors and generators to respond to any shortage and/or excess of energy, respectively, in the SSTC axes. The heat integration of the streams occurs in the HEN between each WEN stage. Thus, as the inlet and outlet streams temperatures in the HEN are dependent of the WEN design, they must be considered as optimization variables. The proposed multi-stage superstructure is formulated in mixed-integer nonlinear programming (MINLP), in order to minimize the total annualized cost composed by capital and operational expenses. A case study is conducted to verify the accuracy of the proposed approach. The results indicate that the heat integration between the WEN stages is essential to enhance the work integration, and to reduce the total cost of process due the need of a smaller amount of hot and cold utilities.
Chemical engineering transactions, 2018
Heat integration by means of Heat Exchanger Network (HEN) synthesis is fundamental in Process Engineering. There are aspects and design options that so far have been scarcely explored in this area. That is the case of heat and work integration. Recent literature shows that the simultaneous optimization of HEN with pressure recovery units can yield substantial gains. Superstructure based mathematical models for HEN synthesis are usually extended for dealing with heat and work integration formulations. Those models are complex to solve, containing nonlinearities and non-convexities that need to be overcome with simplifying assumptions (e.g., isothermal mixing after stream splitting or limiting the structural possibilities) and efficient solution approaches. An important trend in the heat integration literature is the use of meta-heuristic methods. These have arisen as an interesting alternative to the deterministic approaches. Meta-heuristics are attractive since they do not require a...
Synthesis of Work and Heat Exchange Networks Considering Practical Operating Constraints
2019
The synthesis of work and heat exchange networks (WHEN) has drawn much attention from process synthesis researchers in the present decade, arising as a promising field of study. The current literature has shown that simultaneously integrating heat and work may lead to substantial savings in utilities usage in highly energy-demanding processes. The problem, however, comprises highly nonlinear constraints and efficient solutions are difficult to obtain. Optimisation-based approaches have presented interesting solutions. However, in some cases, they may not be practical. When coupling several compressors and turbines via one single-shaft for work exchange, it may become technically difficult to maintain the same rotation speed. Moreover, discharge temperatures in compressors/turbines in some literature solutions may be considered impractically high/low. In order to address the first issue, the number of units that can be coupled via single-shaft was limited, and the use of multiple axe...
Simultaneous synthesis of work exchange networks with heat integration
Chemical Engineering Science, 2014
New MINLP model for the synthesis of work exchange networks with heat integration. Work integration of streams at high and low-pressure in a multi-stage superstructure. Pressure manipulation equipment acting on several shafts and stand-alone equipment. Heat integration between pressure manipulation stages in the work exchange network. Use of a smaller amount of utilities reducing capital cost and operational expenses. Mixed-integer nonlinear programming (MINLP) Work exchange network (WEN) Heat exchanger network (HEN) Heat integration Pressure recovery a b s t r a c t
Almmzt~Tbe ~m~/heat exchanger network synthesis (HENS) probkm is very complex and involves combinatorial in~oblems in the '*matching" between hot and cold streams to enhance heat mmve~, teml~tme dqm~ant physical and transport properties, the choice of flow conflt~aeon and nme~l, of ~on for the heat esdmnge~ the mmbinalion of"hard" and "soft" problem data (some target tmnptnturm must be met, while others may be varied within limiu if this is of advanta~ for the total prcom ~onomy), various kinds of ~nmalnts (forbidden and oompui~ry marcia) and diffamn typm of ~ (liquid, vaponr and mixed phase). Pressure drop limitatima and the cost of ~ are aim important.
Applied Thermal Engineering, 2011
This paper presents a mathematical programming formulation for the synthesis of heat exchanger networks minimizing simultaneously the total annual cost and the environmental impact. The proposed model consists of a Multiobjective Mixed Integer Non-Linear programming problem that considers the optimal location and use of different types of hot and cold utilities available through disjunctive formulations. The total annual cost objective function considers the minimization of the cost for the utilities and capital for the heat exchanger units, whereas the environmental impact objective function is calculated through the eco-indicator 99 for the different types of utilities using the life cycle analysis methodology. Three example problems are presented to show the applicability of the proposed methodology without numerical complications.
Computers & Chemical Engineering, 2011
Heat exchanger network synthesis Synheat model Bilevel optimization MINLP Grouping of process streams Aggregate streams a b s t r a c t In this work we present a bilevel optimization method for simultaneous synthesis of heat exchanger networks (HENS). The results show that compared to a similar method using the same superstructure the presented method can provide comparative solutions to HENS problems with reduced calculation effort especially for larger problems. Hence the value of this work is a good way of simplifying a HENS problem so that HENS problems can be solved efficiently with good results. The presented method combines four submodels into an overall method by using grouping of streams, aggregate streams and bilevel optimization. The idea of the method is to decompose the set of binary variables i.e. the variables that define the existence of heat exchanger matches, into two separate problems. Three different HENS examples from the literature are solved.