THE PINCH-ANALYSIS AND OPTIMIZATION OF INDUSTRIAL FACILITIES. S.V. Zhulaev Gazprom neftekhim Salavat JSC, Salavat, Russia

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1 399 UDC THE PINCH-ANALYSIS AND OPTIMIZATION OF INDUSTRIAL FACILITIES S.V. Zhulaev Gazprom neftekhim Salavat JSC, Salavat, Russia Abstract. The existing methods of heat saving in the designed and operating industrial units, and also methods of designing of heat exchange networks are reviewed. The efficiency of the pinch method in heat saving, its convenience for designing of heat exchange systems, and its advantages in comparison with alternative methods are shown. The basic principles of pinch analysis, the sequence of performing of pinch analysis in an industrial unit, and difficulties possible during carrying out of pinch analysis are described. Data concerning saving rate of pinch analysis in the leading world companies are presented. Modern upgrades to this method are reviewed. Keywords: process integration, pinch analysis, pinch method, heat recuperation, heat exchange layout, heat exchange network, heat saving, energy saving Rise of prices of gas and oil and toughening of ecological standards have led to a significant growth of the operational costs connected with power consumption, and revealed the necessity to raise the efficiency of energy usage. This work presents a review of application of pinch analysis for optimization of energy consumption of industrial facilities. The basic methods [1] of optimization of power consumption at an industrial enterprise are the following: the operational improvements, which allow to optimize the technological process; higher rate of heat regeneration due to improvements in heat integration of the technological process (the pinch analysis belongs to this group); introduction of new technologies, which raise the efficiency of operation of the equipment. Table 1 reveals the potential effect of decisions suggested by the company Honeywell to increase the efficiency of power consumption for a standard oil refinery with the capacity of barrels per day [1]. These methods can be applied together as well as separately. But the data presented in the table show that improvement of heat regeneration is one of the most effective methods of power consumption decreasing.

2 400 Field of economy Table 1. Comparative efficiency of various methods of power consumption optimization [1] Increase of efficiency of power consumption, % Power savings, mln $ / year Reduction of CO 2 emissions, th.t. /year Improvement of quality of operation and management 2-4 1, More rational heat regeneration Introduction of advanced technologies of process conduction 3-8 2, Optimisation of the plant s energy department facilities 2-3 1,5-2, Improvement of planning , Using renewable energy sources (introducing a unit of ecological treatment, 2000 barrels per day) Carbon quota Всего , Improvement of heat regeneration is directly connected with optimization and reconstruction of heat exchange systems. The choice of an optimum variant (that is connected with the least costs of additional heat exchange surface and of changing of the network structure) from set of alternatives is an important component of designing. The existing methods of reconstruction of the heat exchange systems use either the pinch method or methods of mathematical programming. A designing procedure which uses the pinch method consists of two stages: determination of targets and design stage. The main advantage of this method consists in interactive character of procedure of designing. The drawbacks of it are the necessity to carry out long-duration manual calculations, and, besides, a possibility of generating of too complicated alternative projects because of the implicit accounting of cost criteria during the calculation. If we use the methods of mathematical programming, the problem of designing of the optimum HES is formulated as the problem of nonlinear mathematical programming, which consists of a set of equations and restrictions. The advantage of such methods is the possibility to automate the calculations, and the drawbacks are the limited possibilities for active participation of the designer and the necessity of a number of considerable simplifications to estimate the cost of the project. Applying of a highly effective method of integration of heat exchange processes based on the pinch analysis, offered and developed by professor Linnhoff and the researchers from University of the Manchester Institute of Science and Technology (UMIST), allows to reach unique results in designing and redesigning of heat and mass exchange networks in many enterprises. Using pinch-technology in operating refining and petrochemical plants, the majority of which has been operating since , allows to decrease power con-

3 401 sumption and, accordingly, financial payments for it by %, and in some cases on certain units up to 70 % [2]. Also the payback period of redesign projects, developed using the pinch-analysis method, does not exceed two years. The pinch method is based on the thermodynamic analysis of the system of technological streams, and uses nonmonotonic dependence of the general annual operation cost of the project on the least temperature difference over the heat exchanging equipment. Using the pinch method allows to achieve considerable financial savings due to minimization of consumption of external energy resources (both the ones that bring energy and take it away), by the maximum heat regeneration in the considered technological system. Besides, this method allows to minimize the heat exchange surface and number of heat exchange units, to optimize the pressure drop in the network and the arrangement of power units, to minimize the quantity of sewage and emission of carbon dioxide. In case of retrofitting of existing enterprises pinch technology makes it possible to use already installed equipment at maximum performance in new networks and to reduce the investments into reconstruction this way. Moreover, the methods of pinch analysis make it possible to define the compromise in cost between all the listed factors and capital investments at the set pay-back period of the project. Let's note two more very important properties, which are an integral part of the pinch analysis. Firstly, it is the possibility to determine the project targets before the starting the designing. The second important property is the possibility to integrate of processes within a big industrial complex. As a result we can prepare investment plans, define the energy targets and the targets of decreasing of the emissions of harmful substances, both for the existing processes, and for the newly designed ones. Let's present the sequence of performing the pinch-analysis in the plant [3]. 1. Data extraction; 2. Targeting; 3. Design; 4. Optimization, where the original chemical engineering system is improved in terms of economics. In the beginning of the analysis the initial data are collected and the table of initial design data is compiled. Then the graph is drawn in coordinates «heat flows of hot and cold streams temperatures»: firstly for individual apparatuses and streams, then for summed up (integrated) streams. The example is given on the Fig. 1.

4 402 Fig. 1. Composite curves determine energy targets before designing The point of the closest approaching of the curves represents the least temperature difference of the chosen heat exchange circuit, that is the bottleneck of the heat exchange system. It is called "pinch". Then the graphical analysis of these results is performed: The relation between the hot and cold energy targets (i.e. consumption of hot and cold utilities) and the value of the temperature between the hot and cold composite curves in the pinch point is defined. There are also the geometrical method of energy targeting [4], the method of energy targeting with simultaneous definition of necessary temperatures of utilities [5], the STEP graphical method, allowing to simplify and combine the determination of the pinch point, calculation of the energy targets and allocation of the heat exchangers [6]. Designing of the heat exchange network, disposing of the heat exchangers and utilities, simplification of the heat exchange network. If necessary, the work of combined heat and power generation systems (steam or gas turbines, heat pumps, refrigeration cycles) can be analyzed. Consideration of possibility of changing the process parameters (particularly in reactors, distillation columns, evaporators, dryers, etc.) to increase power saving [7]. The pinch analysis can be applied both for designing of a new enterprise, and at redesigning of an existing unit [8]. But in the latter case, of course, there are features and restrictions concerning energy targeting, disposing of heat exchangers, stream splitting, etc. The method of double-level approach to pinch [9] can be applied for redesigning of the units, allowing to upgrade the heat regeneration in case of streams with the properties varying with temperature. Some results of application of the pinch analysis are presented in Tables 2-4 [8].

5 403 Table 2. Results of application of the pinch technology in «UnionCarbide» [8] Type of the Capital Pay-back Process Energy saving, $/year project investments, $ period, months Petrochemistry Revamping Special chemistry Revamping Special chemistry Revamping License unit New Saving Organic bulk chemistry Revamping Organic bulk chemistry Revamping Organic bulk chemistry Revamping Special chemistry Revamping Table 3. Results of application of the pinch technology in «ICI» [8] Type of the Capital investments, Process Energy saving, $/year project $ Organic bulk chemistry New Special chemistry New Saving Crude processing Revamping Saving Inorganic bulk chemistry New Saving Special chemistry Revamping New plant New 30-40% 30 % saving Non-specialized Revamping Petrochemistry Revamping phase I phase II Table 4. The Analysis of application of the pinch technology in various industries [8] Branch Saving Pay-back period Petrochemistry 40 % of consumed fuel months Inorganic chemistry 30 % of total energy 9-16 months Chemistry 30 % of total energy 15 months Pharmacology % of total energy 2-2,5 years Polymers 25 % + increase of productivity Up to 2,5 years Dyes 15 % of total energy 15 months Metallurgy 50 % increase of capacity 2 years Food production 35 % of total energy 1-2 years

6 404 It is necessary to take into account possible problems and side effects which may appear during the implementation of power saving projects. The paper [10] lists the following typical problems which need to be settled while taking energy saving measures, first of all while organizing heat or mass exchange between the streams, which makes all processes and equipment interconnected, depending on each other: the issues of start-up of the equipment or switching it to other modes when there is still no heat-transfer agents from other apparatuses of the CES, which will appear only after the unit is switched to the operating mode; another similar type of problems pauses in operation of individual apparatuses of the CES, while the work of all CES is interdependent; a possible inequality of the thermal balances of apparatuses consuming and producing heat; to compensate the shortage or excess of heat special engineering solutions are necessary, such as additional heat exchangers, passes, sections, coolers or heaters, heat accumulators, etc.; interdependent automatic control of interconnected apparatuses; undesirably long distances between apparatuses are possible, causing difficulties with tracing of pipelines, significant pressure and temperature losses, necessity in additional pumps, etc.; heat losses in additional communication lines, necessity to insulate them; a number of processes (evaporation, rectification, absorption, etc.) need significant pressure changes in the apparatuses, vacuumizing, etc. to provide the necessary temperature differences; Thus, despite possible difficulties, the pinch analysis is highly effective and relatively cheap method of power savings. Besides, application of the pinch analysis considerably simplifies the work of designers of heat exchange networks, allowing to reach the compromise between the capital investments and power consumption. References 1. Brendan P. Shikhan, Sin' (Frenk) Zhu, V. Rybkin. Optimizatsiya energozatrat tekhnologicheskikh protsessov (Energy optimization in plant processes), Territoriya Neftegaz, 2009, Issue 8, pp Kustova A.A. Pochemu zapadnaya energoservisnaya sistema ne rabotaet v Rosii? (Why is the Western power energy service system is not working in Russia?), Energrgosberezhenie, 2008, Issue Konovalov V.I., Kudra T., Pakhomov A.N., Orlov A.Yu. Sovremennye analiticheskie podkhody k energosberezheniyu. Integrirovannyi podkhod. Pinch-analiz. Lukovichnaya model' (Present-day analytical approaches to energy saving. Integrated approach. Pinch analysis. Onion model), Vestnik TGTU, 2008, Volume 14, Issue 3, pp

7 Salama A.I.A. Determination of the optimal heat energy targets in heat pinch analysis using a geometry-based approach, Computers & Chemical Engineering, 2006, Volume 30, Issue 4, pp DOI: /j.compchemeng Marcelo Castier. Pinch analysis revisited: New rules for utility targeting, Applied Thermal Engineering, Volume 27, Issue 8-9, pp DOI: /j.applthermaleng Sharifah R. Wan Alwi, Zainuddin A. Manan. STEP A new graphical tool for simultaneous targeting and design of a heat exchanger network, Chemical Engineering Journal, Volume 162, Issue 1, pp DOI: /j.cej Kemp, Ian C. Pinch analysis and process integration A user guide on process integration for the efficient use of energy (2nd Ed.). Elsevier Ltd, p. 8. Smit R., Klemesh I., Tovazhnyanskii L.L., Kapustenko P.A., Ul'ev L.M. Osnovy integratsii teplovykh protsessov (Fundamentals of thermal processes integration). Khar'kov: NTU KhPI, p. 9. Robin Smith, Megan Jobson, Lu Chen. Recent development in the retrofit of heat exchanger networks, Applied Thermal Engineering, 2010, Volume 30, Issue 16, p DOI: /j.applthermaleng Konovalov V.I., Gatapova N.Ts. Osnovnye puti energosberezheniya i optimizatsii v teplo- i massoobmennykh protsessakh i oborudovanii (General ways of energysaving and optimization in heat and mass transfer processes and equipment), Vestnik TGTU, 2008, Volume 14, Issue 4. pp