Applied Thermal Engineering Vol. 17, Nos. 8-10, pp. 993-1003, 1997 ‘0 European Communities 1997. Published bv Elsevier Science Ltd Pergamon

A B c CW D E F GCC H HP IP LP MP Q S& T TSI TSP VHP VLP W

PII: S1359-4311(96)00087-7 Printed in Great Britain

1359-4311197 $17.00 + 0.00

TARGETING AND DESIGN METHODOLOGY FOR REDUCTION OF FUEL, POWER AND CO, ON TOTAL

SITES

J. KlemeS,* V. R. Dhole,* K. Raissi,* S. J. Perry* and L. Puigjanerl_ *University of Manchester Institute of Science and Technology (UMIST). Manchester, M60 IQD.

UK and tUniversitat Politecnica de Catahmya (UPC), Barcelona, Spain

Abstract-Simultaneous optimisation of production processes and total site utility systems provides a novel methodology that can reduce energy demands and emissions on a total factory site whilst simultaneously avoiding loss of cogeneration efficiency. This paper reports on the results of studies of total sites where the application of the methodology has achieved savings in fuel of up to 20%, along with improvements in global CO? levels and other emissions levels of at least 50% when compared to those achieved by application to individual operational processes. The novel methodology took into account the specific features of semi-continuous and batch operations and also the opportunities offered by the multi-objective optimisation of the design strategy for the total site. The environmental costs and potential for regulatory action were also incorporated. Software tools were developed to support the total site approach which was subsequently tested and its capabilities validated by successfully solving various case studies from different industrial sectors. [cs European Communities 1997. Published by Elsevier Science Ltd.

Keywords-Energy efficiency, process integration, total site, environmental aspects, design tools, paper industry, refinery, hydrocracking, polymer manufacturing.

NOTATION

VHP generated by the central boiler HP required by the site MP representing the remaining site demand cooling water MP generated by site source profile and consumed by site sink profile cooling water required to satisfy the site cooling fuel requirement grand composite curve enthalpy high-pressure steam intermediate-pressure steam low-pressure steam medium-pressure steam heat recovered site composite curve temperature total site integration total site profiles very-high-pressure steam very-low-pressure steam cogenerated shaftwork power

Greek letfers

; first plant of a site second plant of a site

Ar,,, minimum temperature approach ; third plant of a site 6 fourth plant of a site ilc Carnot factor

INTRODUCTION

The paper describes results achieved by a research team of collaborators from the University of Manchester Institute of Science and Technology (UMIST); Ecole des Mines (ARMINES), Paris; Universitat Politecnica de Catalunya (UPC), Barcelona; Courtaulds Espafia S A (CE); SPEC S A,

993

994 J. Klemei et nl.

Athens; Hellenic Aspropyrgos Refinery S A (HAR); Linnhoff March Ltd (LM), Northwich, UK; TU Hamburg-Harburg (TUHH) and Pulp and Paper Research Institute (PPRI), Bratislava, Slovakia.

In this study pinch technology has been considerably extended to site-wide applications. As a result it is now possible to set targets for improvement and expansion opportunities in individual process units, as well as in an overall production site, whilst simultaneously improving the site’s infrastructure. The combined targets provided the user with strategies that could tackle an apparently overwhelmingly complex problem.

A valuable and viable industrial procedure for targeting and planning the reduction of energy costs and emissions at the factory site level has now been developed. ARMINES incorporated the environmental costs and the possible regulatory actions. UPC adopted the newly developed approach and applied it to continuous/semicontinuous and batch operations. CE collected data and conducted a case study, which emphasised energy and water minimisation. SPEC further developed methodologies at the total site level, incorporating the overall economic impact of process modifications; they also participated in conducting and validating the case studies. HAR specified the requirements for the application of the methodology, collected data on the total site refinery and conducted the case studies. LM developed prototype software in the optimum form in which the methodology will be delivered to industry; they also applied the new procedures and the prototype software to industrial applications. TUHH developed the multi-objective optimisation into a design and control strategy for total sites. PPRI selected and conducted a case study on a paper mill, with the aim of reducing energy and water consumption.

TOTAL SITE METHODOLOGY

Traditional pinch analysis assesses the minimum practical energy needs for a process through a systematic design procedure [l] using the following five steps:

1. 2. 3. 4. 5.

Collect plant data. Set targets for the minimum practical energy needs. Examine process changes that contribute to meeting the target. Obtain a minimum energy design that achieves the target. Optimise by trading-off energy costs against capital costs.

This methodology [2] produces integrated process designs coupled to logical investment strategies that result in major energy savings, which could reach up to 50%.

A total site

This paper extends the pinch analysis methodology to total site plant, which therefore incorporates multiple processes linked by a common central utility system. In other words, to the complete factory. Total site integration (TSI) is a fundamental methodology which has evolved from the original applications of pinch analysis (Fig. 1).

However, TSI extends considerably beyond the boundaries of the individual process. It addresses the task of optimising the design of each process and the utility infrastructure in the context of the complete factory. Some details have already been described in several recent publications [3-61, whilst this paper introduces an overall description of the development of that methodology and several extensions of its applications.

Several of the processes have their own utilities, whilst others are served by common central utilities, which in some cases are on site and in others external. They use either local or imported fuel and imported or cogenerated power. Usually, the individual processes are designed and operated on a one-off basis by company engineers or external contractors, whilst central services are managed by other engineers. The plant infrastructure evolves with little or no development overview. A number of separate units may occupy different subsections of a site and operate independently as separate business units.

This situation leads to a waste of resources. In order to improve performance, it is necessary to implement a simultaneous approach to process design, retrofit and site utility planning, with the single objective of manufacturing products with minimum use of energy and capital.

Methodology for reduction of fuel, power and CO: on total sites 995

n&ions , ,

F”e, ,[i\ E’OyHp

I

Emissions

A HP

hAI3

IE

Fuel 3- -Plant O! 1 1 Plant p 1 1 Plant y 1

I i 4 COOUNG

Fig. 1. Typical process industry total site.

Total site proJiles By plotting enthalpy differences, in order to produce the grand composite curve (GCC) [l], the

hot and cold utilities are considered. This diagram demonstrates the effects of utility mix and therefore achieves an optimum integrated design for both process and utilities [7].

Figure 2 shows three processes in the form of their GCC. The GCC of a process represents the heat available at every temperature level after all feasible intra-process heat integrations have been carried out. The profile above the process pinch represents a heat sink, whereas the profile below the process pinch represents a heat source [3].

FUEL UTILITIES POWER

H I_- Plant a

H

Want p H

Plant y

Fig. 2. Three processes in the form of their Grand Composite Curves.

996 J. KlemeS ef al.

Process a . H

T .

Site Source Profile

Site Sink Profile

0

Total Site Profiles

Fig. 3. Construction of Site Sources-Sink Profiles for two processes.

The site source profile is then constructed by combining the heat source information from all the available processes into a single profile which is analogous to the hot composite curve for a single process (Fig. 3).

In a similar way, the site sink profile is formed by combining the heat sink information from all available processes, and is analogous to the cold composite curve. Together, the total site profiles give a simultaneous view of surplus heat, and heat deficit, for all the processes on the site.

Figure 4 shows the location of utilities (steam mains) in the total site profiles (TSP), indicating also the various utility levels. Using the Carnot factor qcenthalpy H plot, a simulation is avoided, since explicit cogeneration and fuel targets can be derived [3].

The above TSP provide the designer with valuable information about the medium-pressure (MP) steam generation from all processes, shown in Fig. 4 as D. This generated steam precisely meets some of the heating requirements of the processes (D). The remaining MP demand C is provided by the turbine system. The high-pressure (HP) steam demand of all processes, as targeted from TSP, is B. In order to satisfy the HP steam demand and demand of the processes (B) and the remaining MP steam demand (C), the central boiler is required to produce A units of VHP steam. Additional VHP steam is provided to meet cogeneration requirements.

The fuel requirement is calculated from the projection of the fuel profile on the enthalpy axis as F. The cooling requirements of the site can again be found from the TSP, in Fig. 4 shown as E. In this case the cooling duties are met by cooling water CW.

Site composite curves and site utility grand composite curves

The amount of heat recovery that can take place in the total site through the steam mains can be derived from the total site profile (Figs 3 and 4). By moving the sink profile towards the source profile the amount of overlap of the profiles represents the amount of heat recovery Qr,, that can be obtained through the steam mains. The limit to heat recovery is reached when a sink profile steam main touches the source profile. The final representation is the site composite curve [S] (Fig. 5).

The position of the ‘total site pinch’ indicates that heat recovery on the site is at a maximum. The remaining site sink profile heat demand is met by the supply of steam from a central boiler (VHP). Below the site pinch the excess heat is removed by cooling water (CW) or produces VLP

H

Methodology for reduction of fuel, power and CO? on total sites 997

Fig. 4. Utility Location in Total Site.

which is vented or condensed cooling water (CW). The shaded area enclosed by the steam profiles ( W) is proportional to the potential cogeneration realised by the site utility system. The steam levels are marked as high pressure HP, medium MP, intermediate IP and low pressure LP.

The formation of the site composites represents a new and unique analytical tool which can be used to obtain targets for fuel calculated from central boiler VHP supply, heat recovery and potential cogeneration, for a total site.

T t

H- Enthalpy

Fig. 5. Development of Site Composite Curve (SCC) and Total Site Pinch.

J. KlemeS et al.

Heat In

rl VHP

Total Site Pinch

WICW

3

Heat Out

VHP VHP

Enthalpy H Fig. 6. Site Composite Curves and Site Utility Grand Composite Curves.

The ‘site utility GCC’ is another form of the site composites (Fig. 6) and provides the designer with a tool to determine different potentials for cogeneration. The designer can readily screen options for both utilities and processes that are the most promising at the targeting stage. All designs are expressed in terms of fuel and power at the full extent of the site boundaries.

Semi-continuous and batch plants at total sites

A strategy to optimise energy consumption in batch processes was developed by UPC [9-l 11. It enables simultaneous optimisation of processes and site-wide utility systems. It results in smoothing consumption peaks in order to reach uniform utility demand profiles that would match the available utility resources at any time.

The energy integration methodology is based on: (a) the selection and analysis of the best potential matches between hot and cold streams; (b) the evaluation of heat exchange in every potential match; (c) the matching of each stream until the energy requirements are satisfied if more than two streams are simultaneously available; (d) a feasibility study for each potential match in the real industrial environment.

The methodology identifies the worst product changeovers and proposes an alternative configuration which improves the global objective function; that includes a penalty waste component expressing the pollution index associated with product changes in each unit.

ENVIRONMENTAL ASPECTS

By balancing the needs for on-site fuel and imported energy it is possible to target for global emissions. Figure 7 shows the overall site targeting procedure. Economic decisions and trade-offs are made for process changes, fuel and steam demands, infrastructure changes and are used to set targets. The decisions are tested in the global context, revised as required and the procedure is repeated to establish a set of planning scenarios which meet different criteria. As the targets meet specific conditions and constraints, the designer can, with confidence, produce strategies for site

Methodology for reduction of fuel, power and CO? on total sites 999

development packages that take into account long- and short-term investment/benefit functions. Arguments for local and global control measures can then be rationally assessed.

For the management of a site, the environmental impacts are of concern to the extent that they reflect responsible care and that there are government regulations (current or expected) which will have to be met. In some situations, a company may take additional steps to protect the environment beyond regulations, for the sake of public relations. Of course, it is also important to identify the environmental impacts that have not yet been addressed to meet these regulations.

Therefore, the methodology addresses impacts that are not of direct concern to the site, such as data on the environmental impact in power plants of the national utility grid, or pollution created by the supply of fuel upstream of the site (Fig. 8).

The pollutants taken into account which are of prime importance for the present work are listed in ref. [ 121; these are typical for emissions from fossil-fuel-fired equipment, such as boilers, furnaces, gas turbines and engines.

Pollution indexes have been defined in order to assess the environmental impact created by the substances used in preparatory/cleaning tasks. Their values express the hazard potential, toxicity and treatment cost of these exit streams. For this purpose, the toxicity indices of ref. [13] may be useful. Pollution indexes depend on the features of the current and the future load on each piece of equipment. A detailed description has been provided in ref. [ 121.

DESIGN TOOLS

Development of software

A systematic approach to TSI has been developed at UMIST. This technique allows a better understanding of the interactions between fuel demands, power generation and heat recovery in

‘---3 Site Fuel

Emissions I

Site Composlte c&s

Recess Power

Net Site Power

Emissions

RochLs Fuel Emissions

Fig. 7. Overall Site Targeting.

.I. Klemeg et al.

Fig. 8. Environmental Impact of a Site.

the total site. This, in turn, can result in energy savings, harmful emissions abatement, and reductions in capital costs. The implementation of the total site methodology has two distinct parts: data preparation; and targeting (Fig. 9).

The data preparation for total site methodology consists of the following:

Provision of process stream data. Setting the AT,, for the process data. Generating the initial grand composite curve (GCC). Modifying GCC in order to remove heat transfer from process to process. Finding remaining heating requirements to be supplied by total site. Adding extracted data to a file of cumulative information from other processes. Repeating the total procedure for the other processes on site.

The targeting phase consists of producing the following tools:

??The production of the balanced site profiles. This is made up of the sink/source profiles (the total heat sinks and sources from the processes) which provide the cumulative heat sources and sinks for the entire site and the location of utilities to satisfy heating and cooling demands. These can be drawn on a temperature/enthalpy plot or a Carnot factor/enthalpy plot. ??The production of the total site composite curves. This provides information on the maximum

steam recovery in the system and also on the potential for cogeneration. In addition, the total site pinch is found. As before, this can be drawn on a temperature/enthalpy or enthalpy/Carnot factor plot. ??The production of the site utility curve. This is directly related to the total site composite curves

and provides information on utility loads and cogeneration.

The targeting tools are required to be highly interactive in their production and use, thereby allowing the user to have the greatest degree of flexibility in the choice of the utility systems and the modification of the utility system. These tools also allow the user to take account of any process changes. The final software, incorporating data preparation, targeting tools and highly interactive user interfaces, allows the implementation of the methodology.

Super-target

Linnhoff March used its SuperTargetTM software as a source of fundamental Pinch Technology calculations. It, therefore, incorporated the prototype software codes within the SuperTargetTM environment. LM developed a prototype user interface design that satisfies the software

Methodology for reduction of fuel, power and CO? on total sites 1001

specifications. The calculation and user interface have been integrated together and incorporated into SuperTargetTM to produce a prototype software product. This software tool was used to test the developed methodology in industry. A specification was drawn so that third-party software products can generate suitable data files that can be read by the prototype software for inclusion into the total site analysis.

Generic process model, configurer, linker and total site optimiser

A two-layer approach has been adopted by SPEC using the total site methodology. In the higher layer, the plant is represented as a network with the processes being the nodes and the material and energy flows being the arcs. In the lower layer, each one of the processes is in turn represented by a similar network structure, with overall input-output being the same as that of the corresponding node in the higher level. An assembly of basic modules will be used to realise the approach: the generic process mode; the process model configurer; the process model linker; and the total site optimiser. A detailed description can be found in ref. [12]. This approach has been validated with the HAR case study.

Multi-objective optimisation with uncertain parameters

TUHH created several tools for the solution of the multi-objective optimisation problem by applying the developed methodology. For conflicting objectives, a compromise solution set, instead of one solution, is obtained. The ‘selfish’ extrema of the compromise solution between production and energy objectives provided information about the utility demands of the process. The simulation and optimisation of processes are connected with inaccuracies due to uncertainties in

SITE PROCESSES

\ _____________

SITE UTILITY SYSTEM

J DATA PREPARATION __-____________

“RNANCED SITE Pf?OFlLES” ‘TOTAL SITE COWOSI~S’ ‘SITE UTILITY GUY

(Pr-) (Procf3ss + utility System) (Utility System) L I . 1

TARGETING Fig. 9. Data Preparation and Targeting.

1002 J. KlemeS et al.

the model parameters. An interval-mathematical approach is used for the formulation of the new concept. Furthermore, the sensitivity of the objective function towards changes in the uncertain parameters is introduced.

CASE STUDIES

The case studies solved problems in different industrial sectors using tools developed within this project [14]. They included synthetic fibre textiles, oil refineries and a paper mill. Environmental impacts were taken into consideration using pollution indexes specified by the developed methodology.

Acrylic polymer manufacturing plant The specific problems to be examined were: product changeover; high energy consumption in

solvent recovery process; hot and cold streams when simultaneous in time; location of heat exchangers when some of them were very disperse; production stops; and start-ups to be avoided due to the power costs. Process waste minimisation had to be taken into consideration. Energy and pollution reduction both reached 15%.

Refinery total sites

Lindsey Oil Rejinery. The selected industrial site for testing the developed total site technique was Lindsey Oil Refinery at Killingholme in England. Data were collected from 26 process units in order to carry out pinch analyses of these processes. From these 26 units, five were ‘black boxes’ because they either had low utilisation or because detailed data were not available. Results showed that nine out of the 21 units studied in detail accounted for 12.4% out of the total potential energy savings. The energy savings in the hot utilities were of the order of 20%, while the reduction of the emissions on the site was 27%.

Hellenic Aspropyrgos Rejnery. HAR is a petroleum refinery that produces about 6 million tons of petroleum products and covers approximately 55% of Greece’s needs. The size of energy costs amounts to about 30 million US$ p.a. The steam and power networks have been used in order to perform detailed energy efficiency studies for various modes of operation and identify the potential for further energy efficiency improvement through tighter heat and power integration, either as retrofit projects or as load reallocation. The case study has shown that even if the site operated at a high level of efficiency, energy savings up to 28% are possible.

Leuna Hydrocracking Plant . TUHH presented compromise solutions of the multi-objective optimisation problem for the hydrocracking plant. The compromise set between production and energy objectives was shown in the optimisation criteria space. The model of the hydrocracking plant was also extended to include equations for the utility consumptions of the separation units. Based on a maximum energy recovery design for the whole process, the utility demands were estimated by exergy efficiency coefficients. The energy savings reached up to 6 MW, depending on the level of cogeneration, and an electric power surplus of 2.2 MW was generated [12].

Tissue paper mill. The Total Site in Zilina, Slovakia, comprising a waste paper line and two paper machines (with pulp stock preparation lines) was studied [15]. As an extension of the site, a power station was also considered. As an integrated site, savings up to 7.15 MW (24.5%) were found. This results in a reduction in emissions of nearly 30%.

CONCLUSIONS

This project created the novel methodology and design tools for further substantial savings of energy and reduction of pollution on large industrial total sites. The application of this concept resulted in both a considerable reduction of energy use in processes and preservation or enhancement of the internal production of power.

As a consequence, the consumption of fuel is reduced, as is the net difference between imported and exported power. The emissions from local combustion units and the stations of external suppliers are also reduced. However, in addition to the expected reduction in energy operating costs, the capital investment requirements are also reduced. Thus, in one comprehensive

Methodology for reduction of fuel, power and CO? on total sites 1003

improvement, benefits of reductions in energy, pollution and capital investment are achieved at the same time.

The primary application of the new techniques is to large industrial complexes, such as chemical process factories and oil refineries. The application of total site pinch technology has already produced spectacular economies with 30% energy and 10% capital savings.

AcknoMledgemenrs~The main contributors to the presented research were B. Linnhoff, V. R. Dhole, K. Raissi, S. J. Perry, University of Manchester Institute of Science and Technology (UMIST); A. Rabl, Ecole des Mines (ARMINES), Paris; L. Puigjaner, A. Espuiia, .I. Cuxart, J. Corominas, R. Grau, Universitat Polit&cnica de Catalunya (UPC); F. Senar, J. Font, E. Martinez, Courtaulds Espafia S A (CE); G. J. Prokopakis, SPEC S A, Athens; A. Lygeros, A. Stephanakis, Hellenic Aspropyrgos Refinery S A (HAR); M. Yell, E.-A. Petela, Linnhoff March Ltd (LM), Northwich, UK; G. Gruhn, J. Rosenkranz, TU Hamburg-Harburg (TUHH); S. BohBEek, M. GerulovB, Pulp and Paper Research Institute (PPRI), Bratislava. Slovakia.

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