Industrial energy-flow management

APPLIED ENERGY

Applied Energy 84 (2007) 781–794

www.elsevier.com/locate/apenergy

Industrial energy-flow management Marko Lampret a, Venceslav Bukovec a, Andrej Paternost a, Srecko Krizman a, Vito Lojk b, Iztok Golobic b,* b

a Krka Pharmaceutical Company, Smarjeska cesta 6, 8000 Novo mesto, Slovenia University of Ljubljana, Faculty of Mechanical Engineering, Askerceva 6, 1000 Ljubljana, Slovenia

Available online 29 March 2007

Abstract Deregulation of the energy market has created new opportunities for the development of new energy-management methods based on energy assets, risk management, energy efficiency and sustainable development. Industrial energy-flow management in pharmaceutical systems, with a responsible approach to sustainable development, is a complex task. For this reason, an energy-information centre, with over 14,000 online measured data/nodes, was implemented. This paper presents the energy-flow rate, exergy-flow rate and cost-flow rate diagrams, with emphasis on cost-flow rate per energy unit or exergy unit of complex pharmaceutical systems.  2007 Elsevier Ltd. All rights reserved. Keywords: Energy management; Energy-flow rate; Exergy-flow rate; Cost-flow rate

1. Introduction In industrial environments, the main goal of energy management is reliable, high quality and efficient use of energy in the light of sustainable development of companies [1–5]. Naturally, global factors should be considered as well as local specificities in the energysupply scene. This is of special importance when large changes occur in the market, as we are presently witnessing in Slovenia. On 1 May, 2004, Slovenia became a full member of the EU. New directives and a role of regulator in the process of energy market liberalisation in Slovenia are reflected in the fact that energy has become a commodity with specific requirements, quality and price. *

Corresponding author. Tel.: +386 1 4771420; fax: +386 1 4771773. E-mail address: [email protected] (I. Golobic).

0306-2619/$ - see front matter  2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2007.01.009

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Directives 96/92/EC and 2003/54/EC setting forth general rules that govern the inner market for electricity and Directives 98/30/EC and 2003/55/EC for natural gas have provided a transparent and undiscriminating access to electricity supply and natural-gas pipeline networks. Therefore, all consumers, with the exception of households, have been able to freely select their supplier from 1 July, 2004 onward. A complete opening of the electrical energy and natural gas market by 1 July, 2007 will require further development, taking into account the Slovene transitional period and ownership relationships, which have changed towards greater protection of more vulnerable consumers, provision of high-quality supply and sustainable development. The regulatory framework in the field of electricity and natural gas indicates guidelines for achieving the regulatory goals and exerting an adequate influence on the energy market for all those involved. The goals of Slovene energy-policy [6,7] are merged into three pillars of sustainable development, which define the reliability and competitiveness of energy supply and the effects that management of energy resources and energy have on the environment. The aspect of energy-supply reliability is expressed via long-term preservation of energy resource availability at a level comparable with the present level of electrical-energy supply from domestic energy resources, i.e. at least 75% of the present consumption. The installed power of power-supply plants within the power-supply system in the Slovene territory should be at least 45% higher than the maximum peak power of consumption over the long term. Constant increases in the technical reliability of the energy-network operation will be necessary, along with the implementation of measures for efficient energy use and use of renewable energy-resources, and maintaining the present ownership share, or at least a majority state ownership in companies of state importance in the field of energy supply. Provision of competitive energy-supply will continue in the direction of accelerated opening of electrical energy and natural-gas markets, separation of the pricing policy from mechanisms for promoting the development of energy companies via professional and independent regulation of energy markets, with legal and functional separation of the manufacturers and suppliers of electrical energy and natural gas, as well as by providing favourable conditions for a transparent, clear, safe and effective operation of organised energy-markets. Sustainable development is based on improving the efficiency of energy use by AD 2010 by between 10% and 15% relative to the year AD 2004, which should take place in the industrial and service sectors and in the field of energy consumption in buildings. In the public sector and in traffic, a 10% improvement should be achieved compared with 2004. The share of electrical energy from cogeneration should be doubled from 800 GWh in AD 2000 to 1600 GWh in AD 2010, and the share of renewable energy resources in primary energy balance from 8.8% in 2002 to 12% in AD 2010, whereby their share in heat supply would increase from 22% to 25% in AD 2010 and in the production of electrical energy from 32% to 33.6% in AD 2010, with up to a 2% share of biofuels being achieved for transportation by the end of AD 2005. The strategy of energy supply in Slovenia is based on a lower growth rate of the GDP and the implementation of measures for efficient energy-use, renewable energy-resources and more intensive supply of natural-gas. Thus, the total natural-gas consumption is expected to increase from 930 million Sm3 in AD 1997 or 1012 million Sm3 in AD 2000 to 1187 million Sm3 in AD 2005 or 1434 million Sm3 in AD 2010. The anticipated increase in industry alone is from 732 million Sm3 in AD 1997 or 696 million Sm3 in AD 2000 to 764 million Sm3 in AD 2005 or 786 million Sm3 in AD 2010.

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Because of its specificities and large returns, the pharmaceutical industry operating in such an environment is especially vulnerable in the field of energy management. The goal of industrial energy-management is to establish such management of energy and process supply as to ensure the unimpeded course of manufacturing processes and high efficiency of the energy system in the light of the sustainable development of companies. This paper presents the development of an energy information centre of a company, which enables upgrading with the energy-flow rate, exergy-flow rate and cost-flow rate diagrams, with emphasis on cost-flow rate per energy unit or exergy unit for complex pharmaceutical systems. 2. Energy information centre In the analysed case of a pharmaceutical company with 3000 employees, energy costs in the year 2002 accounted for 1.75% of the company’s total business expenditures. In the case of industrial energy-flow management, only the following areas were selected: supplied of electricity, natural gas, heat, compressed air, cooling water and cooled water. Table 1 presents the consumption of natural resources during the period from AD 1998 to 2002. It should be emphasised here that natural gas is used for the cogeneration of electrical energy and heat. In the year 2002, the following amounts of energy and water were prepared for the basic site: 5,521,776 kWh of electrical energy, 137,414 tons of steam for technological processes and heating, 128,934,000 m3 of compressed air at an absolute pressure of 3 bar, 15,926,000 m3 of compressed air at an absolute pressure of 9 bar, 23,037,055 kWh of cooled water at a temperature of 6/12 C, 253,932 m3 of industrially prepared water, 243 m3 of a pyrogenic water, 31,783 m3 of purified water and 8247 m3 of water for injections. Fig. 1 presents the energy consumption and specific energy consumption per unit of net sales revenues. In accordance with the company’s internal standard, software FIX and iFIX devised by Intellution were used for the Energy Information Centre, as well as peripheral control equipment MISTIC manufactured by OPTO, and SIMATIC manufactured by Siemens. Measuring sensors for individual parameters, such as temperature, pressure, flow, moisture, etc. are connected to a measuring loop and together with control elements they form a SCADA system for the regulation and monitoring of process data. Individual data are archived in historical files. In this case, the FIX DMACS software-package was used. The following function was used for its integration into the application: F ðntf ; Time; Date; Duration; Interval; PathÞ

ð1Þ

Table 1 Resources in years 1998–2002

Electricity, kWh Natural gas, Sm3 Fuel, ton Drink water, m3 River water, m3

1998

1999

2000

2001

2002

47.229.100 11.781.137 16.46 260.096 1.014.910

47.007.300 11.538.191 31.73 247.058 2.012.120

45.556.500 11.715.281 42.96 248.686 3.398.993

53.286.500 11.871.139 49.80 233.079 4.372.662

56.469.386 12.445.522 0 236.581 3.472.501

M. Lampret et al. / Applied Energy 84 (2007) 781–794 25,00

700.000 600.000

Energy (GJ)

20,00 500.000 400.000

15,00

300.000

10,00

200.000 5,00 100.000

2002

2001

2000

1999

1998

1997

1996

1995

1994

0,00 1993

0

Specific energy use (kJ/SIT) April 2004: 1 = 238 SIT

784

Year Fig. 1. Energy and specific energy consumption in the period between AD 1993 and 2002.

Fig. 2. Block diagram of a reducing station for steam.

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where: ntf is the site record in the SCADA system in the form of Node:TagÆField; Time – hour for the archived data; Date – day for the archived data; Duration – length of observation, which varies in individual databases; Interval – time interval at which sampling is performed during the monitored observation period; and Path – path to the file in the computer’s memory or any other memory unit. Function F always yields only one value for a certain moment in the site’s history. If this piece of information is not available, as is the case with non-operational measuring devices or measurement systems, the function will report an impossible value, e.g. 12.34. As an example of control, Fig. 2 shows a schematic of a system for controlling and monitoring the pressure of technological steam in a distribution station.

Fig. 3. Block diagram of a reducing station for steam.

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Preparation of technological steam, at an absolute pressure of 3 bar, takes place at four reducing stations, the control of which has a significant influence on the operation of the entire heating-plant. Using the principle of Direct Digital Control (DDC), other process parameters are also taken into account in addition to the pressure behind the reducing valve, such as the flow of steam and the loading of the steam boilers. Fig. 3 presents the block diagram from Fig. 2, supplemented with the photographs of individual elements. Under normal circumstances, the digital signal from a programmable logical controller (PLC) has a direct influence on the executive part, which in this case is the reducing valve. Since all measurement signals of the boiler plant converge to the controller, the DDC mode enables the simple control of several loops and in extreme cases also concurrent changing of the dynamics, i.e. the controller’s parameters. In the case of critical control-loops, there is an additional BACK UP controller in the conventional version of SIPARD DR21, which operates in a stand-by mode. When three-position three-point regulation control is used, switching between the controllers in case of problems is nonHeat power station

Electricity

Purifying plant

units Pumps station

TGA

measure

Air cond.

CHS

measure

controler

measure

Compr.air system

measure

controler

measure

controler

Useful water

measure

measure

measure

measure

controler

controler

controler

controler

FIX DMACS in iFIX SCADA-e

History data

Data from balance ( Excel files )

Momentary data

A PL I C A T I O N

energy diagram

exergy diagram

economic diagram

Fig. 4. Energy information centre.

cost and consumption

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problematic, in spite of discontinuous regulator output. Via the ARCNET serial communication, the programmable logical controller exchanges data with the SCADA system, which enables visualisation of the process and the capture, storage and transfer of process data via Fix DMACS, which then enables authorised persons access to data and their further processing via an Internet-based business network. Of 30 archived databases with over 14,000 points, 11 databases (from which 500 points were captured) were used for the application of industrial energy-flow management in Visual Basic 6.0, as shown in Fig. 4. Additional 120 points were used via a monthly energy bill, where various measuring sensors of cumulative values are also used. The value of these data is constant for the observed month. If the current month is observed, known values of the previous month’s flow and the observed trend during the past year for example are used: m_ April 2003 m_ April 2004 ¼ m_ March 2004 : ð2Þ m_ March 2003 If data on energy flow distribution are not available, an estimate based on knowledge of the manufacturing processes is used. 3. Energy-flow rate, exergy-flow rate and cost-flow rate diagrams The heat flow of an individual medium is determined on the basis of mass flow, specific heat and the temperature difference between the inlet and outlet sides:

Table 2 Constants for water-vapour saturation pressure n

dn

n

dn

n

dn

1 2 3 4 5

5.6745359 · 103 6.3925247 · 10 9.6778430 · 103 6.2215701 · 107 2.0747825 · 109

6 7 8 9

9.4840240 · 1013 4.1635019 · 10 5.8002206 · 103 1.3914993 · 10

10 11 12 13

4.8640239 · 102 4.1764768 · 105 1.4452093 · 108 6.5459673 Æ 10

1.2 1

ΔE / Q

0.8 0.6 0.4 0.2

Water 5/10 oC

Water 90/60 oC

Sat. steam 4 bar

Gasoline

Fuel oil

Town gas

Natural gas

Electricity

0

Fig. 5. Exergy versus energy price of some common energy forms.

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_ p ðT in  T out Þ Q_ ¼ mc

ð3Þ

or via the mass flow and the difference between the inlet and outlet specific enthalpies

Natural gas( /GJ) / Electricity( /GJ)

_ in  hout Þ: Q_ ¼ mðh

ð4Þ

0,60 0,50 0,40 0,30 0,20 0,10 0,00 1998

1999

2000

2001

2002

2003

Year

Fig. 6. Ratio of Slovene industrial actual prices of natural gas and electricity per unit of energy.

Fig. 7. Energy-flow diagram of the company.

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If a time period is analysed, the heat is determined on the basis of data for individual ith time-intervals stored in the database Q¼

i¼ik X

m_ i cp ðT in;i  T out;i ÞDt

ð5Þ

m_ i ðhin;i  hout;i ÞDt:

ð6Þ

i¼1

or Q¼

i¼ik X i¼1

Exergy flows are determined by knowing the mass flows, their specific exergies and surrounding conditions: _  ho  T o ðs  so Þ: E_ ¼ m½h

ð7Þ

Surrounding conditions were taken into account via the selected surrounding temperature of To = 288 K, surrounding pressure of po = 1 bar and moisture of the surrounding air, xo = 0.0018 kg/kg. Exergy of the medium in a certain time-period can be determined in a similar way as heat, via sums for each time-interval. Specific enthalpies and entropy of water and steam are determined on the basis of known temperature and pressure [8]. The specific enthalpy and exergy of moist air are determined, taking into account the surrounding conditions [9]:

Fig. 8. Energy-costs flow diagram of the company.

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h1þx ¼ cpa T þ xðDhlvw þ cpwv T Þ  cpa T o  xo ðDhlvw þ cpwv T o Þ:   T pð0:622 þ xÞ e1þx ¼ cpa ðT  T o Þ  T o ln þ Ra T o ln To po ð0:622 þ xÞ     T pxð0:622 þ xo Þ þ x cpwv ðT  T o Þ  T o ln þ Rw T o ln To po xo ð0:622 þ xÞ

ð8Þ

ð9Þ

where the specific heat of dry air can be taken to be cpa 1006 J/kg K; specific heat of water vapour cpwv 1805 J/kg K; evaporation heat for water Dhlvw 2501 · 103 J/kg; and the gas constant of dry air Ra 287.055 J/kg K and for water Rw 461.520 J/kg K. The compressed-air pressure function must be included in the enthalpy and exergy functions [7]. The humidity ratio of moist air is upws x ¼ 0:622 : ð10Þ p  upws where p is the absolute air-pressure, u the relative humidity and psw the saturation pressure of the water vapour, which is determined for the temperature interval between 100 and 0 C [10]:

Fig. 9. Energy-flow diagram of a heat power-station.

M. Lampret et al. / Applied Energy 84 (2007) 781–794

psw

  d1 2 3 4 þ d 2 þ d 3 T þ d 4 T þ d 5 T þ d 6 T þ d 7 lnðT Þ ; ¼ exp T

791

ð11Þ

and for the temperature interval between 0 and 200 C: psw

  d8 2 3 þ d 9 þ d 10 T þ d 11 T þ d 12 T þ d 13 lnðT Þ : ¼ exp T

ð12Þ

Constants in Eqs. (11) and (12) for the water vapour saturation pressure are given in Table 2. In order to achieve both savings in operating costs and sustainable development, it is recommended that an energy-management programme be established, and key elements of such a programme based on experience in implementing energy-conservation strategies are highlighted. Exergy analysis is said, by many researchers [1–4,7], to be a powerful tool for assessing the thermodynamic efficiencies and loss of systems and processes. Unfortunately, because of a lack of understanding or considerable complexity of this issue, the responses of industry to such efforts are all too frequently poor.

Fig. 10. Exergy diagram of a heat power-station.

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The price of an energy medium is calculated as: C EM ¼ C TN þ C AD

ð13Þ

where CEM is the price of the energy medium, CTN the price based on technical norms and CAD the price of various additional factors, such as maintenance, depreciation, insurance premiums and labour costs. For electrical energy as a type of energy that is totally convertible to work, the energy price equals its exergy price. As an example, for district heating, exergy of a given quality of district heat can be written as a function of temperature DE ¼ Qð1  T o Þ=ð½T in  T o  lnðT in =T out ÞÞ

ð14Þ

where the outdoor temperature is To, supply temperature Tin and return temperature Tout. Fig. 5 presents the relationships between the exergy and energy values of some commonenergy-forms based on CEM. Because of the complexity of pharmaceutical systems, in our case the price of an energy medium is still based on the energy price, but upgrading to the exergy price will be possible in the future. Fig. 6 shows the ratio of achieved prices of natural gas and electricity per unit of energy over a period of a few years for Slovene pharmaceutical companies. This ratio is especially important in the case of cogeneration, where stimulative values are supposed to be below 0.3 at a given level of sustainable development. Control over energy flows is performed via the energy-flow rate, exergy-flow rate and cost-flow rate diagrams or over a time interval. In this way, energy and cost flow-rates, or the amount of energy and costs of energy media in an observed period can be observed.

Fig. 11. Rant’s diagram for the same situation as Fig. 10.

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Data in the diagrams are divided into several quality categories with respect to the availability and reliability of data, with accompanying annotations. Various types of loss are presented as flows exiting the observed control volume and are divided into electrical loss, loss on conversion of natural gas, heat loss with water vapour, loss during the distribution of various qualities of water and loss of compressed air. Fig. 7 shows the energy diagram of the company and Fig. 8 the energy-cost flow diagram of the entire site. Fig. 9 shows the energy-flow diagram of a heat power-station. For a better understanding, designations and arrangements from control systems are used here as well, but this has primarily caused a disadvantage of lower transparency, as can be seen from the comparison of the exergy diagram of a heat power-station in Fig. 10 and Rant’s diagram for the same situation in Fig. 11. Fig. 12 show the diagrams of energy, exergy and energy cost-flows for individual plants. Cumulative presentations of energy use and costs by individual energy resources in a plant or the division of consumption and consumer costs for a selected energy-source can be performed in a similar way.

Fig. 12. Energy, exergy and energy costs flow diagrams for individual plants.

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4. Conclusion In industrial environments, it is essential to gradually implement energy-flow management, with a clear presentation of its beneficial effects. This paper presents such implementation, which is introduced as much as possible into the existing graphical monitoring presentation, while emphasising the relevance with the current situation of energy and cash flows in the company. The benefits of such an approach are reflected in the promotion of energy management and the waste-heat recovery in individual plant and the implementation of a spiral of permanent improvements in the field of efficient energy-use, gradually involving all employees in accordance with their competencies and abilities. By establishing a new tool, an opportunity is provided for introducing a more transparent system for calculating the costs of energy consumption and, at the same time, for greater care on part of the consumers to implement measures for efficient energy use. This is the way to achieve cost optimisation, which is the basic purpose of targeted monitoring of energy consumption. Through the relationship between exergy on one hand and both energy and environment on the other, it is clear that exergy is related to sustainable development. These efforts should be supplemented by studies of cases in which exergy has been applied successfully, as well as promotional activities. It is critical that the potential benefits of exergy be exploited: therefore the emphasis of our further work will be on the cost-flow rate per energy unit and the exergy unit of complex pharmaceutical systems. References [1] Bejan A. Method of entropy-generation minimization, or modelling and optimization based on combined heat transfer and thermodynamics. Revue Ge´ne´rale de Thermique 1996;35:637–46. [2] Rosen MA, Dincer I. Exergy cost, energy-mass analysis of thermal systems and processes. Energy Convers Manage 2003;44:1633–51. [3] Hammond GP. Towards sustainability: energy efficiency, thermodynamic analysis, and the ‘two cultures’. Energy Policy 2004;32:1789–98. [4] Rosen MA, Dincer I. Exergoeconomic analysis of power plants operating on various fuels. Appl Therm Eng 2003;23:643–58. [5] Al-Mansour F, Merse S, Tomsic M. Comparison of energy-efficiency strategies in the industrial sector of Slovenia. Energy 2003;28:421–40. [6] Resolution of National Energy Programme, Porocevalec Drzavnega zbora RS, no. 98, November; 2003 [in Slovene language]. [7] Zagozen D. National Energy Programme. In: Proceedings of 7th meeting of SDDE, 14–16 March, 2004, Portoroz, Slovenia, 2004, p.11–18 [in Slovene language]. [8] Haar L, Gallagher JS, Kell GS. Steam tables. Washington: Hemisphere; 1984. [9] Fratzsher W, Brodjanskij WM, Michalek K. Exergie Theorie und Anweldung. Leipzig, VEB Deutscher Verlag fur Grundstoffindustrie; 1986. [10] ASHRAE Handbook, Fundamentals. Atlanta: American Society of Heating, Refrigerating and AirConditioning Engineers; 2001.