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A Swedish integrated pulp and paper mill—Energy optimisation and local heat cooperation
ARTICLE IN PRESS Energy Policy 37 (2009) 2514–2524
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Energy Policy journal homepage: www.elsevier.com/locate/enpol
A Swedish integrated pulp and paper mill—Energy optimisation and local heat cooperation S. Klugman a, M. Karlsson b,, B. Moshfegh b a b
¨vle, SE-80 176 Ga ¨vle, Sweden Department of Technology and Building Environment, University of Ga ¨ping University, SE-581 83 Linko ¨ping, Sweden Department of Management and Engineering, Division of Energy Systems, Linko
a r t i c l e in f o
a b s t r a c t
Article history: Received 27 November 2007 Accepted 23 September 2008 Available online 14 April 2009
Heat cooperation between industries and district heating companies is often economically and environmentally beneficial. In this paper, energy cooperation between an integrated Swedish pulp and paper mill and two nearby energy companies was analysed through economic optimisations. The synergies of cooperation were evaluated through optimisations with different system perspectives. Three changes of the energy system and combinations of them were analysed. The changes were process integration, extending biofuel boiler and turbine capacity and connection to a local heat market. The results show that the single most promising system change is extending biofuel and turbine capacity. Process integration within the pulp and paper mill would take place through installing evaporation units that yield less excess heat but must in this particular case be combined with extended biofuel combustion capacity in order to be beneficial. Connecting to the local heat market would be beneficial for the pulp and paper mill, while the studied energy company needs to extend its biofuel capacity in order to benefit from the local heat market. Furthermore, the potential of reducing CO2 emissions through the energy cooperation is shown to be extensive; particularly if biofuel and turbine capacity is increased. & 2009 Published by Elsevier Ltd.
Keywords: Industrial energy system Optimisation Cooperation
1. Introduction Cooperation between industries and energy companies regarding energy is rather extensive in Sweden. Of the total energy supply of 60 TWh for production of district heating, which heats buildings and tap water during 2004, 6 TWh originated from industrial excess heat (Swedish District Heating Association, 2006). Still, the potential for increased excess heat deliveries from the industries is large, especially in regions where the industries are situated close to cities (Swedish District Heating Association, 2006). This kind of energy cooperation has a potential to be both economically and environmentally beneficial, because energy resources are more efficiently used. Economically favourable due to, among other things, decreased use of expensive fuels, and environmentally since exhausts from fuel combustion may be reduced, including CO2 emissions and, hence, the decreased influence on the greenhouse effect (IPCC, 2007). Seen from the industrial perspective, heat delivery to district heating systems is a way to decrease cooling costs in cases where otherwise active cooling would have been necessary. In addition, selling heat creates an income. However, selling industrial excess
Corresponding author. Tel.: +46 13285739; fax: +46 13281788.
E-mail address: [email protected] (M. Karlsson). 0301-4215/$ - see front matter & 2009 Published by Elsevier Ltd. doi:10.1016/j.enpol.2008.09.097
heat is not always the best solution seen from an energy saving perspective. Using the heat within an industry through so-called process integration is often the first alternative that should be considered (Bengtsson et al., 2002). Still, if the possible process integration measures require other temperatures than needed in the district heating system, there is little or no conflict between the two alternatives. Cooperation between industries and energy companies is not always initiated even though it would be both economically beneficial and resource efficient. Other parameters, such as different business cycles, believed advantages of being independent and historical conflicts are examples of barriers to cooperation. The purpose of this paper is to contribute to the understanding of local energy cooperation regarding technical and economical aspects, in order to facilitate future cooperation. The purpose of this paper is divided into two tasks: Firstly, to find synergies in the cooperation between a pulp and paper mill and two closely situated energy companies. The second task is to evaluate energy system changes on a general level for the total system, for example increased industrial excess heat deliveries, process integration, increased biofuel boiler capacity and increased electricity generation. Previous studies point at the economical potential of cooperation between industries and energy companies. For example Sundberg and Sjo¨din (2003) and Gebremedhin (2003) show how a mechanical pulp mill and a
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municipally owned energy company increase cost-effectiveness through cooperation. Moreover, Karlsson and Wolf (2008), show economic benefits when integrating a pulp mill, a saw mill and a biofuel upgrade plant with a district heating system to different extents, and in Wolf and Karlsson (2008) potential reduction of CO2 emissions in the same system has been shown. The study was performed within a research project which aimed at optimising the regional energy system through a local deregulated heat market, which in the following is referred to as ‘‘the heat market’’ (Gebremedhin and Moshfegh, 2004; Karlsson et al., 2009). Normally, only one operator produces and delivers heat in each district heating system. In the study of a local deregulated heat market, four energy companies and three industries within three municipalities are given the opportunity to sell and buy heat in a joint district heating system. The heat use in the region, including steam use in the industries and district heating, equals 7 TWh/year. In this paper, one of the three ¨vle, which is situated at the municipalities is studied, namely Ga east coast of Sweden, 170 km north of Stockholm. Two of the energy companies and one industry, an integrated pulp and paper mill, are situated in the municipality and have existing heat cooperation.
2. Method Different economic perspectives and changes in the energy system were evaluated and compared through optimisations performed with mixed integer linear programming. In the following, the analysis tool is described followed by a description of the implementation of modelling.
2.1. Analysis tool The method for analysis of industrial energy systems (MIND) method is used for the analysis (Nilsson, 1993). The MIND method is based on mixed integer linear programming and minimises the system cost, which includes costs for fuel and electricity, among others. The method is flexible both when it comes to representing time dynamics and the structure. Time is divided into time steps to reflect diurnal, weekly, monthly and long-run variations occurring in e.g. energy prices. The structure of the system is represented by nodes and branches, where the nodes represent a component, process line or the total plant and the branches represent the flows in the system, such as material and energy flows. The MIND method has been used as the basis for analyses in more than 30 scientific articles, ranging from dairies to steelworks (Gong et al., 2002). The energy system optimisation software reMIND, which is based on the MIND method, is used in this paper.
2.2. Implementation of modelling The input data originates from an earlier analysis (Klugman et al., 2006), interviews with staff at the studied companies and results from optimisations of the heat market (Karlsson et al., 2009). Several cases were modelled and optimised. The optimisations were carried out by minimising the system cost, i.e. the total energy cost for electricity, heat and fuel purchase minus energy revenues from sales of heat, fuel, electricity and tradable green certificates. Maintenance costs are also included. The latter are obtained for electricity generation from renewable energy sources (here: biofuel) (Swedish Government Energy Bill, 2003), and can be sold on a market.
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The energy system changes aim at an efficient resource use and were compared in two groups of cases: with only the heat connections of today and with the heat market. In order to evaluate synergies from energy cooperation between the companies, two comparisons were made. First an optimisation was made where the existing heat pipe to the municipal energy company from the other companies was disconnected. The result was compared to the connected system with a joint perspective of all three operators. Secondly, the total system was modelled with five different system boundaries in order to illustrate different system perspectives. In these optimisations, which illustrate the perspective of a single operator, only the costs and revenues that concern the specific operator were accounted for. Thus, the use of boilers, turbines etc., run by other operators, neither provided costs nor rendered revenues if it did not affect the operator in question. Consequently, the facilities of other operators were chosen randomly. The results for each operator were compared to his results extracted from the joint perspective optimisation. The comparisons were made regarding system costs, fuel use and electricity generation. One year’s energy supply and use were calculated in the optimisations. The year was divided into several time steps in order to recognise the seasonal and diurnal variations in heat demand and energy prices. The investment costs were not included in the investigation. Instead, the suggested investments were evaluated regarding the contribution to the annual benefit.
3. Participating companies ¨s mill is an integrated pulp and paper industry with The Korsna primary sulphate pulp production. The production during 2004 was 6,34,000 metric tonnes of board and paper and 69,000 tonnes of fluff pulp. Total electricity use was 896 GWh and process steam use was 3170 GWh during 2004. The bark from the Korsna¨s mill is ¨r Energi AB (KEAB), which is burnt by the energy company Karska partly owned by Korsna¨s and has its boilers at the same industrial area as the Korsna¨s mill. The generated steam from the bark combustion is used by the paper mill but most of the steam load at the paper mill, 83%, is covered by black liquor recovery boilers. The main part of the steam that is used by the pulp and paper mill passes through a back-pressure turbine which is owned by KEAB. Korsna¨s receives a minor part of the revenues from electricity sale. Heat is delivered to the district heating system of Ga¨vle from KEAB and Korsna¨s. From Korsna¨s, the heat delivered to town originates from the evaporation unit, which is constructed to produce heat at a temperature suitable for the district heating system. The special design is called ‘‘back-pressure evaporation plant’’ and demands about 140 GWh/year (23%) more steam than a conventional evaporation plant would have demanded. Since the fuel is mainly biofuel, tradable green certificates are obtained for the generated electricity but the small fraction produced with oil. The district heating system in Ga¨vle is operated by the ¨vle Energi AB (GEAB). Besides the municipal energy company Ga heat that is delivered from KEAB and the Korsna¨s mill to GEAB, the company also has its own boilers and a turbine. The steam load at Korsna¨s and the maximum heat load in Ga¨vle are presented in Fig. 1. The steam load at Korsna¨s is rather constant while the heat load in Ga¨vle varies greatly: from 25 MW during summer via 130 MW on average in winter to peak loads above 300 MW during the coldest days. The boiler capacities of the three companies are also presented in Fig. 1. There are electric boilers at Korsna¨s and KEAB. The district heating load in Ga¨vle could be covered by GEAB’s own boilers during most of the year, except the very coldest days. Korsna¨s has boiler capacity enough to be self-sufficient and KEAB is able to supply both the steam load at Korsna¨s and the
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900 800
Oil and electricity
700
Biofuels
MW
600 500 400 300 200 100 0 Steam load Korsnäs
Maximum district heating load GEAB
Steam boilers Korsnäs
Steam and hot water boilers KEAB
Hot water boilers GEAB
Fig. 1. Steam and district heating loads are shown by the two bars to the left. Boiler capacities of the three companies are shown by the bars to the right. Biofuel capacity is pointed out particularly.
district heating load in Ga¨vle on its own. As can be seen in Fig. 1, the biofuel boiler capacity in the region is not large enough to support the steam and heat loads; therefore, during the coldest months, heat pumps, oil and electric boilers must be used.
4. Systems analysis Korsnäs
In this section, the models that were used for the system analysis are described. First, the use of different system perspectives is presented. Thereafter, the energy system changes which were analysed are described followed by a description of the model input data. Finally, the method for calculation of CO2 emissions is presented.
GEAB District heating
KEAB
4.1. System perspectives As illustrated in Fig. 2 five different economic system boundaries were analysed and compared in order to find synergisms. The five different cases are also listed in Table 1, except the cases where each system is analysed separately based on the local district heating system, i.e. LKorsna¨s, LKEAB and LGEAB. First, the boundary was put around what the Korsna¨s mill controls. Hence, only the costs and revenues which concern the mill were taken into account. Secondly, the corresponding calculation was made for KEAB. Then, the two companies Korsna¨s and KEAB (KK) were seen as a single operator in order to find synergisms between them. Furthermore, the perspective of the municipal energy company, GEAB, is evaluated and finally all the three operators Korsna¨s, KEAB and GEAB (KKG) are taken into account at the same time, which extends the economic system boundary to a local energy system in which possible synergisms can be found. The case with all three operator’s joint perspective is used as a reference case to which the other cases are compared. In all cases, the technical energy systems of all three companies were included in the analysis, that is, the technical system boundary is always the outer circle in Fig. 2. In addition to the changes of economic system boundary, the total system was evaluated, with no heat deliveries allowed from Korsna¨s and KEAB to GEAB, Case DKKG. With this condition, the model was optimised for the joint perspective of Korsna¨s and KEAB, Case LKK, while GEAB’s costs and revenues were calculated separately and added to the system cost obtained through the optimisation of Case LKK.
Fig. 2. The economic system boundaries for the five different perspectives from which the changes in the energy system were analysed.
4.2. Energy system changes Besides optimisations for each of the five perspectives and the disconnected system, a number of changes in the energy system were evaluated through optimisations, as listed in Table 1 and also pointed out with grey colour in Fig. 3. Connection to the heat market was one of the studied system changes. Further, the back-pressure evaporation plant was evaluated by replacing it by a conventional evaporation unit with less excess heat in some cases. Also, a new biofuel-fired boiler and a turbine at KEAB were examined. In addition, two combinations of energy system changes were analysed as well: the new boiler and turbine at KEAB and either connection to the heat market or replacement of the back-pressure evaporation plant. The energy system changes are evaluated from two perspectives: the joint perspective of all operators, and the joint perspective of Korsna¨s and KEAB. The cases with changes are compared to the reference cases LKKG and LKK, respectively. In the analysis of the disconnected system, Case DKKG, the back-pressure evaporation unit was not replaced by a conventional evaporation unit because the purpose was to just study the effect of a
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Korsnäs mill
Oil boilers
Steam demand Gas boiler
Hot water
Steam distribution Evaporation plant
Electric boiler
Steam
Existing units
Added or changed units Recovery boilers
Biofuel boiler
Oil boiler
GEAB
Turbine
Biofuel boiler Turbine Turbine
Bark boiler
Electric boiler
Hot water condensor Flue gas heat recovery District heating delivery
Oil hot water boiler Heat pumps
KEAB
Fig. 3. Schematic of the model of Korsna¨s and KEAB. Electricity purchase and demand at Korsna¨s is not included in the picture. Also, the steam demand in the model is divided into 0.4 MPa, 1.2 MPa.
disconnection without any other changes in the system. If a connection between the mill and the district heating system had never been made, a conventional evaporation unit would have been invested in and 140 GWh/year less steam would be required. The heat market cases are only studied from the joint perspective of Korsna¨s and KEAB. The reason that the common perspective is not applied is that the focus of this paper regarding the heat market is to evaluate how Korsna¨s and KEAB, not the municipal energy company, would be affected by it. The heat market cases are compared to an adjustment of Case LKKG. The costs and revenues for Korsna¨s and KEAB are extracted from the result of Case LKKG and heat delivery prices according to the current agreement are used. How the heat market would affect GEAB and other municipal energy companies is studied by Karlsson et al. (2009).
4.3. Model input data The models include the KEAB plant and the energyrelated equipment at the Korsna¨s mill, e.g. boilers, turbines, heat pumps and steam condensers, and GEAB’s biofuel boiler and turbine. These are listed in Table 2 and in Fig. 3, a schematic of the
Table 1 Cases that are evaluated with the MIND method. Variation
Present systema Disconnected system Heat market Replace the back-pressure evaporation plant New boiler and turbine at KEAB Heat market+new boiler and turbine at KEAB New boiler and turbine at KEAB+replace the backpressure evaporation plant
System boundary Korsna¨s mill+KEAB
Korsna¨s mill+KEAB+GEAB
LKK – HMKK BPEKK BTKK HM,BTKK BPE,BTKK
LKKG DKKG – BPEKKG BTKKG – BPE,BTKKG
Five different system boundaries and seven variations of the model are used. The designation for each case is also presented in the table. a Except the cases shown in the table each system is analyzed separately based on the local district heating system, i.e. LKorsna¨s, LKEAB and LGEAB.
model is shown where possible changes are pointed out with grey colour. In the figure, fuel and electricity supply is not indicated.
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Table 2 Energy-related facilities in the modela. Operator
Facility
Capacity (MW)
Korsna¨s
Recovery boilers Gas boiler Oil boilers Electric boiler
GEAB's alternative price Heat market marginal price, Case HMKK Heat market marginal price, Case HM,BTKK
Output
KEAB
Oil/bark boiler Oil boiler Heat pump Electric boiler New biofuel boiler Old turbine New turbine
540/60 120 12 40 70 48 24
Steam
Euros/MWh
60 350 3 14 15
40
20
Hot water
0 0
3000
6000
9000
Hours GEAB
a
Biofuel boiler Turbine
76 24
Electricity
Input data for the facilities are collected from staff at the different sites.
Table 3 Korsna¨s’ steam load, electricity load and paper production in the modela.
400 350
District heating load in Gävle
300
Delivery to the heat market, case HMKK Delivery to the heat market, case HM,BTKK
250 MW
Fig. 5. Heat prices in the heat market and GEAB’s alternative heat price for the hours of the year chronologically from January to December. Explanations regarding the abbreviations are found in Table 1.
150 100 50 0 3000
6000
Value
Unit
Steam 0.4 MPa Steam 1.2 MPa Electricity Paper production
196 150 102 80
MW MW MW Tonnes/h
a Input data for production and the different loads are collected from staff at Korsna¨s mill.
200
0
Entity
9000
Hours Fig. 4. Duration curve for the district heating load in the model. Three loads are used: the total delivery to the district heating system in Ga¨vle and, in two cases, the heat deliveries from Korsna¨s and KEAB to the heat market, with two load variations depending on case. Explanations regarding the abbreviations are found in Table 1.
The steam and electricity use at the mill are basically modelled as single loads, proportional to the paper production, according to Table 3. The paper production in tonnes per hour is modelled as fixed and cannot be changed by the optimisation, but the choice of boilers to support the steam load in the production is up to the optimisation to decide. Also, there is a possibility to dump steam of 0.4 MPa, for example, when the steam produced in the recovery boilers exceeds the demand. The district heating load is fixed for each time step and can be supported by any of the operators. The calculations are made for one year’s operation and the year is divided into 104 time steps of varying length which correspond to different heat load levels in the district heating system according to season of the year and hour of the day. Fig. 4 shows the duration curve for the three district heating loads in the model. The price for district heating is set as GEAB’s alternative price, i.e. the cost GEAB would have if they had to produce all heat for district heating by themselves. As long as the capacity of the biofuel boiler is sufficient, it is used for heat production, which
also generates electricity sales revenues for GEAB. When all the biofuel boiler capacity is used, oil boilers are taken into operation. Because of this, the heat price ranges between 6 and 71 euro1/MWh, as illustrated in Fig. 5. In the cases with the heat market, the magnitude of the heat delivery from each company was predetermined according to the results from optimisations of the heat market (Karlsson et al., 2009). Thereby, the use of the back-pressure evaporation plant was predetermined, but the priority of KEAB’s boilers was up to the optimisation to decide. The heat price was set according to the marginal price, which was also a result of the above-mentioned analysis, and varies within the range 6–41 euro/MWh, as shown in Fig. 5. The energy carrier prices that are used in the model are presented in Table 4. The prices for electricity, both purchase and sales, are market prices (Nordpool, 2006). The price for tradable green certificates is the average price for 2005 (Svenska kraftna¨t, 2007). In addition to the fuel price, energy and carbon dioxide taxes according to the Swedish legislation in 2005 are considered for fossil fuels (Swedish Tax Agency, 2006).
4.4. CO2 emission calculations The effect of the energy system changes on the CO2 emissions are calculated using the values in Tables 5 and 6. Two ways of calculating the CO2 emissions due to electricity are used. First, electricity is regarded as produced in coal-fired condensing power plants, which are the marginal electricity production units in Northern Europe. Secondly, the average Swedish electricity production was accounted for, which consists of 47% hydropower 1
1 euro ¼ 9 SEK (assumed value).
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400
Table 4 Prices used in the model. Entity
Euro/MWh
Electricity purchase/sale Tradable green certificates Oil Bark
25–38/24–36a 24b 28c,d 14d
Oil, via the turbine Bark, directly from steam boiler Heat pumps
350
Bark, via the turbine Flue gas condensation Back-pressure evaporation
250 MW
a Price range within which the monthly average prices varies around the year. Monthly market prices (Nordpool, 2006) for the years 2001–2005 are used. Also, there are different prices for purchase and sale on the market. b Average price for 2005 (Svenska kraftna¨t, 2007). c Including energy and carbon dioxide taxes (Swedish Tax Agency, 2006). d Oil and bark prices are based on discussions with the participating companies.
GEAB’s biofuel boiler
300
200 150 100 50
Table 5 CO2 emissions from different fuels (SCB, 2007).
0 0
Fuel
CO2 emissions (kg CO2/MWh of fuel)
Residual fuel oil Biofuel
267 0
Table 6 CO2 emissions from external electricity for different accounting models. Model
CO2 emissions (kg CO2/MWh of electricity)
Marginal coal Average Swedish power production
974a 11b
a b
Calculated from Gro¨nkvist et al. (2003). According to the Swedish Energy Agency (2000).
and 45% nuclear power and of which only a small fraction is produced by fossil fuels (Swedish Energy Agency, 2006). Average Swedish power production is included to reflect the traditional accounting method used in Sweden, but also to have a possibility to compare an average accounting method to a marginal accounting method.
5. Results The optimisation result of the joint perspective, Case LKKG, is shown to be the case which is most similar to today’s operation, which is regulated through agreements between the three companies. In the following result presentation, Case LKKG is used as the base case to which the other cases are compared. The priority of boilers etc. for district heating deliveries is the same in Case LKKG as in the present operation, except that in today’s operation KEAB’s flue gas condensation is partly used without committing the back-pressure evaporation plant and partly when this is fully used. Also, the size of heat delivery from Korsna¨s and KEAB to GEAB corresponds well with operation at present. A difference though, is that the heat from KEAB to GEAB origins to a greater extent from biofuel on the expense of flue gas condensation in the model result. This is explained by the fact that the heat from flue gas condensation depends on the use of the biofuel boiler, and that in today’s operation the biofuel boiler supports the steam demand at Korsna¨s to a higher degree than in the optimisation results. Therefore it is necessary for KEAB to increase its use of the biofuel boiler for heat delivery to GEAB, in order to be able to produce heat from flue gas condensation in the model. Furthermore, the electricity generation in Case LKKG is similar to the electricity generation of today.
3000
6000
9000
Hour Fig. 6. Duration curve for district heating deliveries during a year in Case LKKG.
As seen in Fig. 6, the base for district heating production is the back-pressure evaporation plant. As the heat load increases, flue gas condensation and then the biofuel boiler at GEAB are taken into operation. Next, the heat pumps and the steam from the bark boiler that has passed through the turbine are used. When the district heating load exceeds 150 MW, steam from the bark boiler is also used directly without passing the turbine. In order to supply the peak heat load, the oil boiler is used for cogeneration. Regarding steam to support Korsna¨s’ steam demand, the result from LKKG is that, besides steam from recovery and gas boilers, bark and electricity are used. No oil is used for Korsna¨s, though. The steam from the recovery boilers passes through the turbine most of the time because it generates revenues from electricity sales. Only when the district heating load is very high, steam from KEAB passes through the turbine instead. A difference between today’s system and the model is that the pricing of heat deliveries differ. Instead of the agreed prices, which depend on which fuel is used, GEAB’s alternative price is used in the model. Analysis of Case LKKG shows that the heat delivery from Korsna¨s and KEAB to GEAB according to model results would give revenues of about 9 million euro if the prices from the agreements are used, but with GEAB’s alternative price the revenue is about 20 million euro. However, since the pricing is the same for all the modelled cases the economical results are still relevant when comparing different cases.
5.1. Cooperation synergism In order to find the synergism for cooperation between Korsna¨s and KEAB on one hand and GEAB on the other hand, calculations were made for a disconnected system, DKKG. In this case, GEAB needs to produce all heat itself. The biofuel boiler supports the basic heat demand, but during the winter oil boilers need to be taken into operation as well. Except the fuel costs, GEAB’s revenue from electricity generation was also taken into account. The result is shown in Fig. 7. In total, about 30 million euro/year are saved through the cooperation. This is due to the cheaper fuel that can be used for hot water production for district heating (Fig. 8). Particularly, GEAB needs to combust a great deal of oil during the winter if they cannot buy heat from Korsna¨s and KEAB. The electricity generation does not change much between the cases, amounting to around 400 GWh/year.
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8 GEAB
60
7
KK
50
Million euros/year
Million euros/year
70
40 30 20 10 0
6 5 4 3 2 1
LKKG
DKKG
0
Fig. 7. System cost for the joint perspective (LKKG) and for the disconnected system (DKKG). The costs for Korsna¨s and KEAB (KK) and GEAB, respectively, are pointed out in the two cases. Explanations regarding the abbreviations are found in Table 1.
LKK
LKorsnäs
LKEAB
LGEAB
Fig. 9. Decrease of system revenue from the optimisation with joint perspective (LKKG) in comparison with the system revenue from the optimisations with separate perspectives (LKEAB, LKorsna¨s, LGEAB) and the joint perspective of Korsna¨s and KEAB (LKK). Explanations regarding the abbreviations are found in Table 1.
1400 LKKG DKKG
1200
450 350 GWh/year
GWh/year
GEAB's turbine KEAB's turbine
400
1000 800 600 400
300 250 200 150 100 50
200
0 LKKG
0 Oil
Bark
Electricity for boilers and heat pumps
Fig. 8. Energy use for boilers and heat pumps in Case LKKG and if Korsna¨s and KEAB (KK) and GEAB were disconnected (Case DKKG). Explanations regarding the abbreviations are found in Table 1.
LKorsnäs
LKEAB
LGEAB
Fig. 10. Electricity generation in the five optimisations with different economic system boundaries. Note that the use of GEAB’s turbine is random in the cases in which GEAB’s costs and revenues are not accounted for, i.e. LKK, LKorsna¨s, LKEAB. Analogically, the use of KEAB’s turbine is random in Case LGEAB. Explanations regarding the abbreviations are found in Table 1.
1200
5.2. Applying different system perspectives
Oil Bark
1000
Electricity for electric boilers and heat pumps
800 GWh/year
The fuel priority for district heating production varies largely depending on system perspective. The use of turbines also varies. In order to calculate how the joint perspective affects each operator, the system costs of the optimisations with single (LKEAB, LKorsna¨s, LGEAB) and two (Korsna¨s and KEAB, LKK) actor perspectives are compared to the system cost of each operator in the optimisation with overall perspective LKKG. The comparison indicates how cooperation influences each company. It is found that the separate perspectives give a more beneficial result for each operator, though a very small change is found in GEAB’s case, as seen in Fig. 9. This is because the separate perspectives make the other companies operate in order to benefit one single company. GEAB has the smallest loss, which indicates that today’s operation is made close to GEAB’s optimal operation. KEAB makes the greatest loss and Korsna¨s is in between. The electricity generation is highest in Case LKKG; both GEAB’s and KEAB’s turbines are used almost all the time (Fig. 10). This is because the benefits from both GEAB’s and KEAB’s turbines are taken into account. The oil use is lowest in Case LKKG; instead, bark is used to the highest extent (Fig. 11). In the separate perspective cases, the fuel use of the companies whose costs are not taken into account does not affect the optimisation result. Hence, when there are no costs for the fuels used in different boilers, the use of the boilers is chosen randomly. The steam and heat demands are still fixed though. However, Korsna¨s and KEAB share the interest in using KEAB’s turbine, and therefore the boilers in which high pressure steam is produced are prioritised in all cases but LGEAB. In no case is the possibility of dumping steam used, since the cost of
LKK
600 400 200 0 LKKG
LKK
LKorsnäs
LKEAB
LGEAB
Fig. 11. Fuel use for steam and hot water production in the whole system with different economic perspectives. Black liquor and foul gases that need to be burnt by Korsna¨s are exempted. Korsna¨s’ electricity use for processes is also excluded. Explanations regarding the abbreviations are found in Table 1.
extra fuel is too high in comparison to the benefit of the extra electricity generation that would have been possible. Besides for fuel costs, this is also due to low turbine efficiency. In all cases where Korsna¨s’ costs are accounted for, no oil is used for the steam demand at Korsna¨s because both electricity and bark are less expensive. In Case LKorsna¨s, less of the steam from the recovery boiler passes through the turbine in comparison to Case LKKG, since Korsna¨s only gains a small part of the revenue for electricity sale. Therefore, less additional steam is required in Case LKorsna¨s. The bark use for supplying Korsna¨s is greater in Case LKKG
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than in Case LKK because GEAB’s boiler is used more in Case LKKG, instead of KEAB’s burning of bark for district heating. That releases bark boiler capacity at KEAB that can be used for Korsna¨s.
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6 HMKK
5
HM,BTKK
In Fig. 12, the result from the optimisations made with system changes and overall perspective are presented (cf. Table 3). The system cost is compared to the reference case, LKKG. It is found that a new biofuel boiler and turbine at KEAB (Case BTKKG) gives the lowest system cost. This is because cheap biofuel replaces oil and electricity to a large extent. The case that gives the highest electricity generation is to additionally switch from back-pressure to conventional evaporation, BPE,BTKKG. In none of the cases is the possibility of dumping steam used. Comparison of the cases where the system changes are seen from the joint perspective of Korsna¨s and KEAB, BPEKK, BTKK and BPE,BTKK and LKK, confirm these result. For the cases in which the back-pressure evaporation plant is replaced, BPEKKG and BPEKK, the system cost increases. This is because the hot water that fails to come from the backpressure evaporation plant needs to be covered by something else, which to a large extent is bark but during the coldest months oil needs to be used as well. For the cases where replacing the backpressure evaporation plant is combined with extended biofuel capacity, the loss is decreased. The heat market is shown to be beneficial for Korsna¨s, with or without new biofuel boiler and turbine at KEAB, see Fig. 13. The result of the heat market for KEAB is not unambiguously positive. In Case HMKK, where no system changes are made, KEAB even makes a loss from connecting to the heat market though in Case HM,BTKK with a new boiler and turbine, KEAB makes good profit from it. The loss for KEAB in Case HMKK is explained by the lower revenue for selling heat in comparison to current prices. In Case HM,BTKK the heat price is still low, but that is compensated by a greater heat delivery and even more by the additional electricity generation in the new turbine. 5.3.1. Electricity generation The results from the optimisations of cases with system changes show that the electricity generation is remarkably higher in the cases with a new boiler and turbine at KEAB (Fig. 14). The case that gives the highest electricity generation is BPE,BTKKG, in which replacing the back-pressure evaporation plant and expanding the biofuel boiler and turbine capacity are combined.
10
Million euros/year
8 6 4 2
3 2 1 0 -1 -2 -3 Korsnäs
KEAB
Fig. 13. Reduced cost for Korsna¨s and KEAB, respectively, in the cases with heat market, in comparison to the results for each operator in LKKG recalculated with agreed prices of today. Explanations regarding the abbreviations are found in Table 1.
600 500
GWh/year
5.3. Energy system changes
Million euros/year
4
KEAB's new turbine KEAB's old turbine GEAB
400 300 200 100 0 LKKG
BPEKKG
BTKKG
BPE,BTKKG
Fig. 14. Electricity generation in the cases with system changes and the joint perspective of Korsna¨s, KEAB and GEAB. Explanations regarding the abbreviations are found in Table 1.
5.3.2. Fuel use Biofuel boilers at KEAB and GEAB supply the base district heating demand for most cases, along with the back-pressure evaporation plant in the cases in which it is possible, see Figs. 15–17. In these figures, for the cases including the new biofuel boiler and turbine, cases BTKKG, BPE,BTKKG, BTKK, BPE,BTKK and HM,BTKK, the entities ‘‘Oil, via turbine’’ and ‘‘Bark, via turbine’’ include both the steam which passes through the old and the new turbine. In the cases in which the back-pressure evaporation plant is replaced, the oil use is higher. The heat production for district heating in the heat market cases is also based on the back-pressure evaporation plant, see Fig. 18. In Case HM,BTKK the new bio fuel boiler is used to a great extent which reduces the need for heat pumps and oil.
0 -2 -4 BPEKKG
BTKKG
BPE,BTKKG
Fig. 12. Decreased system cost for the system changes, in comparison to LKKG. Explanations regarding the abbreviations are found in Table 1.
5.3.3. CO2 emission reduction Figs. 18 and 19 show the change in CO2 emissions in the cases with system changes. Two ways of regarding CO2 emissions are implemented: electricity is either regarded as the marginal electricity production units in Northern Europe, which are coalfired condensing power plants, or it is regarded as the average Swedish electricity production, which mainly is hydro power and nuclear power.
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900 800 Electric boiler
700 GWh/year
Oil, directly
600
Oil, via turbine
500
Bark, directly Bark, via turbine
400
Flue gas condensation
300
Heat pumps BPE
200
GEAB
100 0 LKKG
BPEKKG
BTKKG
BPE,BTKKG
Fig. 15. Boiler use for district heating production in the reference case (left) and the cases with system changes and the joint perspective of Korsna¨s, KEAB and GEAB. Explanations regarding the abbreviations are found in Table 1.
900 800 Electric boiler
700 GWh/year
Oil, directly
600
Oil, via turbine
500
Bark, directly Bark, via turbine
400
Flue gas condensation
300
Heat pumps BPE
200
GEAB
100 0 LKK
BPEKK
BTKK
BPE,BTKK
Fig. 16. Boiler use for district-heating production in the reference case (left) and the cases with system changes and the joint perspective of Korsna¨s and KEAB. Explanations regarding the abbreviations are found in Table 1.
600 Electric boiler
500 GWh/year
Oil, directly
400
Oil, via turbine Bark, directly
300
Bark, via turbine
200
Flue gas condensation Heat pumps
100
BPE
0 KK from LKKG
HMKK
HM,BTKK
Fig. 17. Boiler use from the joint perspective of Korsna¨s and KEAB, extracted from the LKKG optimisation, and for the heat market cases. Explanations regarding the abbreviations are found in Table 1.
Connection to the heat market will reduce the CO2 emissions from KEAB and Korsna¨s seen as a joint unit, particularly if coal condensing power is seen as the marginal electricity production units. This is due to the reduced heat deliveries, which require less fuel. To replace the back-pressure evaporation plant would slightly reduce the CO2 emissions if electricity is seen as coal condensing power. If replacement of evaporation plant is combined with a
new biofuel boiler, the reduction is much greater though. If the average electricity production in Sweden is considered instead, the CO2 emissions increase when the back-pressure evaporation plant is replaced. This is due to the increased use of oil. A new biofuel boiler and turbine at KEAB largely reduces the CO2 emissions if electricity is regarded as coal condensing power. If the average electricity production in Sweden is considered instead, the CO2 emission reduction is smaller.
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50
Thousand tonnes CO2/year
0 -50 -100 -150 -200 -250
Marginal coal condensing power Average Swedish
-300 -350 -400 BPEKKG
BTKKG
BPE,BTKKG
Fig. 18. CO2 emissions in comparison to LKKG (common perspective) for two ways of accounting CO2 for electricity. Explanations regarding the abbreviations are found in Table 1.
Thousand tonnes CO2/year
100 0 -100 -200 -300 -400 Marginal coal condensing power
-500
Average Swedish
-600 HMKK
HM,BTKK
BPEKK
BTKK
BPE,BTKK
Fig. 19. CO2 emissions in comparison to LKK (Korsna¨s–KEAB perspective) for two ways of accounting CO2 for electricity. Explanations regarding the abbreviations are found in Table 1.
6. Concluding discussion From the analysis of the energy system with different economic system boundaries it is found that there is a competition within the energy cooperation regarding boiler use. In total, there is an overcapacity among the companies, which make each operator strive to use their own equipment to a higher degree. Regarding the system from a joint perspective, benefits of cooperation are pointed out. The oil demand could be reduced and the electricity generation could be extended. The results show that the operation of the system today is similar to the optimisation with a joint perspective. The analysis of a disconnection of today’s heat deliveries shows that the cooperation of today greatly reduces the system cost, particularly through reduction of the oil demand. The benefit of regarding extended system boundaries is applicable in any case where geographically close systems are physically connected or such a connection is possible to realize. In all cases, except when only the district heating utility GEAB’s perspective is applied, there is a possibility of dumping lowpressure steam and thereby using KEAB’s turbine in a similar way to a condensing turbine instead of as a back-pressure turbine. Whether this opportunity is chosen to be used by the optimisation or not indicates whether condensing power is a beneficial
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alternative for the industry or not. The dumping opportunity is never used, though. This indicates that condensing power is not beneficial for the industries in question, or at least that the condensing turbine needs to be more efficient than KEAB’s backpressure turbine. Among the system changes that were analysed, process integration was shown to be not beneficial if it is not combined with extended biofuel boiler capacity. This is because the process integration measure that was analysed reduces the excess heat that can be delivered for district heating. The heat therefore needs to be replaced and the biofuel boiler capacity of today is not sufficient. In reality, a greater benefit would possibly be shown for the pulp and paper mill Korsna¨s, since the oil and electricity, which are used to support the steam demand at the mill today, would be reduced through the process integration. In the optimisations though, no oil is used; not even in the reference case. The process integration results emphasise the importance of regarding extended system boundaries in any system analysis of closely connected companies. Even though process integration is an energy efficiency measure within one company’s system, the consequences for the connected companies need to be taken into account. In this case it was shown that process integration needs to be combined with extended biofuel boiler capacity in order not to cause a sub-optimisation of the regional energy system. The single most beneficial energy system change was shown to be expanding the capacity for biofuel combustion. This result is due to the high prices for oil and electricity, which biofuel replaces. Furthermore, the electricity generation is extended by increased biofuel boiler capacity and adds to the benefit of the measure. The industrial energy company KEAB has already decided to build a new biofuel-fired boiler with turbine. Connecting to the local heat market is beneficial for Korsna¨s. The main reason is the higher price they would obtain for selling heat. For KEAB, the benefits of connecting to the heat market depend on the investment in expanded biofuel boiler and turbine capacity. Without that investment, KEAB would make a loss by connecting to the heat market. The reason is the lower price they would obtain for selling heat. Changing the price on the heat market would make some operators become losers in the heat market, whereas other operators would gain even more. Generally, net receivers of heat from the heat market would gain on a lower heat market price and the contrary for net suppliers. For example, if the price in the heat market is about half the price of today the breakpoint between winning and loosing on connecting to the heat market for Korsna¨s is found. For KEAB, revenues from extended electricity production are dominating incomes and therefore the price in the heat market is not that influential on total revenues. There is a potential to reduce CO2 emissions through the studied energy cooperation. Particularly if electricity is calculated according to the marginal power generation in Northern Europe, which is coal condensing power, the investment in a new biofuel boiler and turbine reduces the CO2 emissions greatly.
Acknowledgements The work has been carried out under the auspices of the RESO project, which is financed by the Swedish Energy Agency, the companies mentioned in this study as well as Sandvik, Sandviken Energi, Skutska¨r and A¨lvkarleby Fja¨rrva¨rme. The authors are grateful to Ha˚kan Yderling at Korsna¨s AB and Ingemar Hemlin, Maria Carendi and Peter Holmstro¨m at Karska¨r energi AB for valuable assistance in this study. We would also like to thank Alemayehu Gebremedhin, Ph.D., for preparing data that was
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necessary for the study. We are also grateful to Associate Professor Dag Henning for useful comments. References Bengtsson, C., Nordman, R., Berntsson, T., 2002. Utilization of excess heat in the pulp and paper industry—a case study of technical and economic opportunities. Applied Thermal Engineering 22 (9), 1069–1081. Gebremedhin, A., 2003. The role of a paper mill in a merged district heating system. Applied Thermal Engineering 23 (6), 769–778. Gebremedhin, A., Moshfegh, B., 2004. Modelling and optimisation of district heating and industrial energy system. An approach to a locally deregulated heat market. The International Journal of Energy Research 28 (5), 411–422. Gong, M., Karlsson, M., So¨derstro¨m, M., 2002. Industry and the energy market: Optimal choice of measures using the MIND method. In: Proceedings of the CRIS (International Institute for Critical Infrastructures) Conference on Power Systems and Communications Infrastructures for the Future. Beijing. Gro¨nkvist, S., Sjo¨din, J., Westermark, M., 2003. Models for assessing net CO2 emissions applied on district heating technologies. International Journal of Energy Research 27, 601–613. IPCC, A., 2007. Climate change 2007: the physical science basis. In: Solomon, S., Qin, D., Manning, M., Marquis, M., Averyt, K., Tignor, M.M.B., LeRoy Miller, Jr., H., Chen, Z. (Eds.), Contribution of Working Group I to the Fourth Assessment Report of the International Panel on Climate Changes. Cambridge University Press, New York, USA. Karlsson, M., Wolf, A., 2008. Using an optimization model to evaluate the economic benefits of industrial symbiosis in the forest industry. Journal of Cleaner Production 16 (14), 1536–1544. Karlsson, M., Gebremedhin, A., Klugman, S., Henning, D., Moshfegh, B., 2009. Regional energy system optimization—Potential for a regional heat market. Applied Energy 86 (4), 441–451.
Klugman, S., Karlsson, M., Moshfegh, B., 2006. An integrated chemical pulp and paper mill-energy audit and perspectives on regional cooperation. In: Proceedings of the 19th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, ECOS 2006. Aghia Pelagia, Crete, Greece. Nilsson, K., 1993. Cost-effective industrial energy systems: multiperiod optimization of operating strategies and structural choices. Linko¨ping Studies in Science and Technology, Dissertation No. 315. Linko¨ping University, Linko¨ping, Sweden. Nordpool, 2006. /http://www.nordpool.com/S. Visited 2006-05-31. SCB, 2007. Emissionsfaktorer fo¨r CO2, kg/MWh, /http://www.scb.se/templates/ tableOrChart____24672.aspS. Accessed November 2007. Sundberg, G., Sjo¨din, J., 2003. Project financing consequences on cogeneration: industrial plant and municipal utility co-operation in Sweden. Energy Policy 31 (6), 491–503. Svenska kraftna¨t, 2007. Price statistics available at /http://elcertifikat.svk.se/S. Accessed November 2007. Swedish District Heating Association, 2006. Statistics 2004. Swedish District Heating Association, Stockholm (Svensk Fja¨rrva¨rme AB. Olof Palmes gata 31. 101 53 Stockholm, Sweden). Swedish Energy Agency, 2000. Electricity market 2000. Report ET 18:2000. Swedish Energy Agency, Eskilstuna, Sweden. Swedish Energy Agency, 2006. Energy in Sweden 2006 Facts and Figures, ET2006:44. Eskilstuna: STEM. Swedish Government Energy Bill, 2003. Electricity certificates to promote renewable energy sources. 2002/03:40, Sweden (in Swedish). Swedish Tax Agency, 2006. Taxes in Sweden 2006. Available at /http://www. skatteverket.se/S. Wolf, A., Karlsson, M., 2008. Evaluating the environmental benefits of Industrial Symbiosis—Discussion and demonstration of a new approach. Progress in Industrial Ecology—An International Journal 5 (5–6), 502–517.
Contents lists available at ScienceDirect
Energy Policy journal homepage: www.elsevier.com/locate/enpol
A Swedish integrated pulp and paper mill—Energy optimisation and local heat cooperation S. Klugman a, M. Karlsson b,, B. Moshfegh b a b
¨vle, SE-80 176 Ga ¨vle, Sweden Department of Technology and Building Environment, University of Ga ¨ping University, SE-581 83 Linko ¨ping, Sweden Department of Management and Engineering, Division of Energy Systems, Linko
a r t i c l e in f o
a b s t r a c t
Article history: Received 27 November 2007 Accepted 23 September 2008 Available online 14 April 2009
Heat cooperation between industries and district heating companies is often economically and environmentally beneficial. In this paper, energy cooperation between an integrated Swedish pulp and paper mill and two nearby energy companies was analysed through economic optimisations. The synergies of cooperation were evaluated through optimisations with different system perspectives. Three changes of the energy system and combinations of them were analysed. The changes were process integration, extending biofuel boiler and turbine capacity and connection to a local heat market. The results show that the single most promising system change is extending biofuel and turbine capacity. Process integration within the pulp and paper mill would take place through installing evaporation units that yield less excess heat but must in this particular case be combined with extended biofuel combustion capacity in order to be beneficial. Connecting to the local heat market would be beneficial for the pulp and paper mill, while the studied energy company needs to extend its biofuel capacity in order to benefit from the local heat market. Furthermore, the potential of reducing CO2 emissions through the energy cooperation is shown to be extensive; particularly if biofuel and turbine capacity is increased. & 2009 Published by Elsevier Ltd.
Keywords: Industrial energy system Optimisation Cooperation
1. Introduction Cooperation between industries and energy companies regarding energy is rather extensive in Sweden. Of the total energy supply of 60 TWh for production of district heating, which heats buildings and tap water during 2004, 6 TWh originated from industrial excess heat (Swedish District Heating Association, 2006). Still, the potential for increased excess heat deliveries from the industries is large, especially in regions where the industries are situated close to cities (Swedish District Heating Association, 2006). This kind of energy cooperation has a potential to be both economically and environmentally beneficial, because energy resources are more efficiently used. Economically favourable due to, among other things, decreased use of expensive fuels, and environmentally since exhausts from fuel combustion may be reduced, including CO2 emissions and, hence, the decreased influence on the greenhouse effect (IPCC, 2007). Seen from the industrial perspective, heat delivery to district heating systems is a way to decrease cooling costs in cases where otherwise active cooling would have been necessary. In addition, selling heat creates an income. However, selling industrial excess
Corresponding author. Tel.: +46 13285739; fax: +46 13281788.
E-mail address: [email protected] (M. Karlsson). 0301-4215/$ - see front matter & 2009 Published by Elsevier Ltd. doi:10.1016/j.enpol.2008.09.097
heat is not always the best solution seen from an energy saving perspective. Using the heat within an industry through so-called process integration is often the first alternative that should be considered (Bengtsson et al., 2002). Still, if the possible process integration measures require other temperatures than needed in the district heating system, there is little or no conflict between the two alternatives. Cooperation between industries and energy companies is not always initiated even though it would be both economically beneficial and resource efficient. Other parameters, such as different business cycles, believed advantages of being independent and historical conflicts are examples of barriers to cooperation. The purpose of this paper is to contribute to the understanding of local energy cooperation regarding technical and economical aspects, in order to facilitate future cooperation. The purpose of this paper is divided into two tasks: Firstly, to find synergies in the cooperation between a pulp and paper mill and two closely situated energy companies. The second task is to evaluate energy system changes on a general level for the total system, for example increased industrial excess heat deliveries, process integration, increased biofuel boiler capacity and increased electricity generation. Previous studies point at the economical potential of cooperation between industries and energy companies. For example Sundberg and Sjo¨din (2003) and Gebremedhin (2003) show how a mechanical pulp mill and a
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municipally owned energy company increase cost-effectiveness through cooperation. Moreover, Karlsson and Wolf (2008), show economic benefits when integrating a pulp mill, a saw mill and a biofuel upgrade plant with a district heating system to different extents, and in Wolf and Karlsson (2008) potential reduction of CO2 emissions in the same system has been shown. The study was performed within a research project which aimed at optimising the regional energy system through a local deregulated heat market, which in the following is referred to as ‘‘the heat market’’ (Gebremedhin and Moshfegh, 2004; Karlsson et al., 2009). Normally, only one operator produces and delivers heat in each district heating system. In the study of a local deregulated heat market, four energy companies and three industries within three municipalities are given the opportunity to sell and buy heat in a joint district heating system. The heat use in the region, including steam use in the industries and district heating, equals 7 TWh/year. In this paper, one of the three ¨vle, which is situated at the municipalities is studied, namely Ga east coast of Sweden, 170 km north of Stockholm. Two of the energy companies and one industry, an integrated pulp and paper mill, are situated in the municipality and have existing heat cooperation.
2. Method Different economic perspectives and changes in the energy system were evaluated and compared through optimisations performed with mixed integer linear programming. In the following, the analysis tool is described followed by a description of the implementation of modelling.
2.1. Analysis tool The method for analysis of industrial energy systems (MIND) method is used for the analysis (Nilsson, 1993). The MIND method is based on mixed integer linear programming and minimises the system cost, which includes costs for fuel and electricity, among others. The method is flexible both when it comes to representing time dynamics and the structure. Time is divided into time steps to reflect diurnal, weekly, monthly and long-run variations occurring in e.g. energy prices. The structure of the system is represented by nodes and branches, where the nodes represent a component, process line or the total plant and the branches represent the flows in the system, such as material and energy flows. The MIND method has been used as the basis for analyses in more than 30 scientific articles, ranging from dairies to steelworks (Gong et al., 2002). The energy system optimisation software reMIND, which is based on the MIND method, is used in this paper.
2.2. Implementation of modelling The input data originates from an earlier analysis (Klugman et al., 2006), interviews with staff at the studied companies and results from optimisations of the heat market (Karlsson et al., 2009). Several cases were modelled and optimised. The optimisations were carried out by minimising the system cost, i.e. the total energy cost for electricity, heat and fuel purchase minus energy revenues from sales of heat, fuel, electricity and tradable green certificates. Maintenance costs are also included. The latter are obtained for electricity generation from renewable energy sources (here: biofuel) (Swedish Government Energy Bill, 2003), and can be sold on a market.
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The energy system changes aim at an efficient resource use and were compared in two groups of cases: with only the heat connections of today and with the heat market. In order to evaluate synergies from energy cooperation between the companies, two comparisons were made. First an optimisation was made where the existing heat pipe to the municipal energy company from the other companies was disconnected. The result was compared to the connected system with a joint perspective of all three operators. Secondly, the total system was modelled with five different system boundaries in order to illustrate different system perspectives. In these optimisations, which illustrate the perspective of a single operator, only the costs and revenues that concern the specific operator were accounted for. Thus, the use of boilers, turbines etc., run by other operators, neither provided costs nor rendered revenues if it did not affect the operator in question. Consequently, the facilities of other operators were chosen randomly. The results for each operator were compared to his results extracted from the joint perspective optimisation. The comparisons were made regarding system costs, fuel use and electricity generation. One year’s energy supply and use were calculated in the optimisations. The year was divided into several time steps in order to recognise the seasonal and diurnal variations in heat demand and energy prices. The investment costs were not included in the investigation. Instead, the suggested investments were evaluated regarding the contribution to the annual benefit.
3. Participating companies ¨s mill is an integrated pulp and paper industry with The Korsna primary sulphate pulp production. The production during 2004 was 6,34,000 metric tonnes of board and paper and 69,000 tonnes of fluff pulp. Total electricity use was 896 GWh and process steam use was 3170 GWh during 2004. The bark from the Korsna¨s mill is ¨r Energi AB (KEAB), which is burnt by the energy company Karska partly owned by Korsna¨s and has its boilers at the same industrial area as the Korsna¨s mill. The generated steam from the bark combustion is used by the paper mill but most of the steam load at the paper mill, 83%, is covered by black liquor recovery boilers. The main part of the steam that is used by the pulp and paper mill passes through a back-pressure turbine which is owned by KEAB. Korsna¨s receives a minor part of the revenues from electricity sale. Heat is delivered to the district heating system of Ga¨vle from KEAB and Korsna¨s. From Korsna¨s, the heat delivered to town originates from the evaporation unit, which is constructed to produce heat at a temperature suitable for the district heating system. The special design is called ‘‘back-pressure evaporation plant’’ and demands about 140 GWh/year (23%) more steam than a conventional evaporation plant would have demanded. Since the fuel is mainly biofuel, tradable green certificates are obtained for the generated electricity but the small fraction produced with oil. The district heating system in Ga¨vle is operated by the ¨vle Energi AB (GEAB). Besides the municipal energy company Ga heat that is delivered from KEAB and the Korsna¨s mill to GEAB, the company also has its own boilers and a turbine. The steam load at Korsna¨s and the maximum heat load in Ga¨vle are presented in Fig. 1. The steam load at Korsna¨s is rather constant while the heat load in Ga¨vle varies greatly: from 25 MW during summer via 130 MW on average in winter to peak loads above 300 MW during the coldest days. The boiler capacities of the three companies are also presented in Fig. 1. There are electric boilers at Korsna¨s and KEAB. The district heating load in Ga¨vle could be covered by GEAB’s own boilers during most of the year, except the very coldest days. Korsna¨s has boiler capacity enough to be self-sufficient and KEAB is able to supply both the steam load at Korsna¨s and the
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900 800
Oil and electricity
700
Biofuels
MW
600 500 400 300 200 100 0 Steam load Korsnäs
Maximum district heating load GEAB
Steam boilers Korsnäs
Steam and hot water boilers KEAB
Hot water boilers GEAB
Fig. 1. Steam and district heating loads are shown by the two bars to the left. Boiler capacities of the three companies are shown by the bars to the right. Biofuel capacity is pointed out particularly.
district heating load in Ga¨vle on its own. As can be seen in Fig. 1, the biofuel boiler capacity in the region is not large enough to support the steam and heat loads; therefore, during the coldest months, heat pumps, oil and electric boilers must be used.
4. Systems analysis Korsnäs
In this section, the models that were used for the system analysis are described. First, the use of different system perspectives is presented. Thereafter, the energy system changes which were analysed are described followed by a description of the model input data. Finally, the method for calculation of CO2 emissions is presented.
GEAB District heating
KEAB
4.1. System perspectives As illustrated in Fig. 2 five different economic system boundaries were analysed and compared in order to find synergisms. The five different cases are also listed in Table 1, except the cases where each system is analysed separately based on the local district heating system, i.e. LKorsna¨s, LKEAB and LGEAB. First, the boundary was put around what the Korsna¨s mill controls. Hence, only the costs and revenues which concern the mill were taken into account. Secondly, the corresponding calculation was made for KEAB. Then, the two companies Korsna¨s and KEAB (KK) were seen as a single operator in order to find synergisms between them. Furthermore, the perspective of the municipal energy company, GEAB, is evaluated and finally all the three operators Korsna¨s, KEAB and GEAB (KKG) are taken into account at the same time, which extends the economic system boundary to a local energy system in which possible synergisms can be found. The case with all three operator’s joint perspective is used as a reference case to which the other cases are compared. In all cases, the technical energy systems of all three companies were included in the analysis, that is, the technical system boundary is always the outer circle in Fig. 2. In addition to the changes of economic system boundary, the total system was evaluated, with no heat deliveries allowed from Korsna¨s and KEAB to GEAB, Case DKKG. With this condition, the model was optimised for the joint perspective of Korsna¨s and KEAB, Case LKK, while GEAB’s costs and revenues were calculated separately and added to the system cost obtained through the optimisation of Case LKK.
Fig. 2. The economic system boundaries for the five different perspectives from which the changes in the energy system were analysed.
4.2. Energy system changes Besides optimisations for each of the five perspectives and the disconnected system, a number of changes in the energy system were evaluated through optimisations, as listed in Table 1 and also pointed out with grey colour in Fig. 3. Connection to the heat market was one of the studied system changes. Further, the back-pressure evaporation plant was evaluated by replacing it by a conventional evaporation unit with less excess heat in some cases. Also, a new biofuel-fired boiler and a turbine at KEAB were examined. In addition, two combinations of energy system changes were analysed as well: the new boiler and turbine at KEAB and either connection to the heat market or replacement of the back-pressure evaporation plant. The energy system changes are evaluated from two perspectives: the joint perspective of all operators, and the joint perspective of Korsna¨s and KEAB. The cases with changes are compared to the reference cases LKKG and LKK, respectively. In the analysis of the disconnected system, Case DKKG, the back-pressure evaporation unit was not replaced by a conventional evaporation unit because the purpose was to just study the effect of a
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Korsnäs mill
Oil boilers
Steam demand Gas boiler
Hot water
Steam distribution Evaporation plant
Electric boiler
Steam
Existing units
Added or changed units Recovery boilers
Biofuel boiler
Oil boiler
GEAB
Turbine
Biofuel boiler Turbine Turbine
Bark boiler
Electric boiler
Hot water condensor Flue gas heat recovery District heating delivery
Oil hot water boiler Heat pumps
KEAB
Fig. 3. Schematic of the model of Korsna¨s and KEAB. Electricity purchase and demand at Korsna¨s is not included in the picture. Also, the steam demand in the model is divided into 0.4 MPa, 1.2 MPa.
disconnection without any other changes in the system. If a connection between the mill and the district heating system had never been made, a conventional evaporation unit would have been invested in and 140 GWh/year less steam would be required. The heat market cases are only studied from the joint perspective of Korsna¨s and KEAB. The reason that the common perspective is not applied is that the focus of this paper regarding the heat market is to evaluate how Korsna¨s and KEAB, not the municipal energy company, would be affected by it. The heat market cases are compared to an adjustment of Case LKKG. The costs and revenues for Korsna¨s and KEAB are extracted from the result of Case LKKG and heat delivery prices according to the current agreement are used. How the heat market would affect GEAB and other municipal energy companies is studied by Karlsson et al. (2009).
4.3. Model input data The models include the KEAB plant and the energyrelated equipment at the Korsna¨s mill, e.g. boilers, turbines, heat pumps and steam condensers, and GEAB’s biofuel boiler and turbine. These are listed in Table 2 and in Fig. 3, a schematic of the
Table 1 Cases that are evaluated with the MIND method. Variation
Present systema Disconnected system Heat market Replace the back-pressure evaporation plant New boiler and turbine at KEAB Heat market+new boiler and turbine at KEAB New boiler and turbine at KEAB+replace the backpressure evaporation plant
System boundary Korsna¨s mill+KEAB
Korsna¨s mill+KEAB+GEAB
LKK – HMKK BPEKK BTKK HM,BTKK BPE,BTKK
LKKG DKKG – BPEKKG BTKKG – BPE,BTKKG
Five different system boundaries and seven variations of the model are used. The designation for each case is also presented in the table. a Except the cases shown in the table each system is analyzed separately based on the local district heating system, i.e. LKorsna¨s, LKEAB and LGEAB.
model is shown where possible changes are pointed out with grey colour. In the figure, fuel and electricity supply is not indicated.
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Table 2 Energy-related facilities in the modela. Operator
Facility
Capacity (MW)
Korsna¨s
Recovery boilers Gas boiler Oil boilers Electric boiler
GEAB's alternative price Heat market marginal price, Case HMKK Heat market marginal price, Case HM,BTKK
Output
KEAB
Oil/bark boiler Oil boiler Heat pump Electric boiler New biofuel boiler Old turbine New turbine
540/60 120 12 40 70 48 24
Steam
Euros/MWh
60 350 3 14 15
40
20
Hot water
0 0
3000
6000
9000
Hours GEAB
a
Biofuel boiler Turbine
76 24
Electricity
Input data for the facilities are collected from staff at the different sites.
Table 3 Korsna¨s’ steam load, electricity load and paper production in the modela.
400 350
District heating load in Gävle
300
Delivery to the heat market, case HMKK Delivery to the heat market, case HM,BTKK
250 MW
Fig. 5. Heat prices in the heat market and GEAB’s alternative heat price for the hours of the year chronologically from January to December. Explanations regarding the abbreviations are found in Table 1.
150 100 50 0 3000
6000
Value
Unit
Steam 0.4 MPa Steam 1.2 MPa Electricity Paper production
196 150 102 80
MW MW MW Tonnes/h
a Input data for production and the different loads are collected from staff at Korsna¨s mill.
200
0
Entity
9000
Hours Fig. 4. Duration curve for the district heating load in the model. Three loads are used: the total delivery to the district heating system in Ga¨vle and, in two cases, the heat deliveries from Korsna¨s and KEAB to the heat market, with two load variations depending on case. Explanations regarding the abbreviations are found in Table 1.
The steam and electricity use at the mill are basically modelled as single loads, proportional to the paper production, according to Table 3. The paper production in tonnes per hour is modelled as fixed and cannot be changed by the optimisation, but the choice of boilers to support the steam load in the production is up to the optimisation to decide. Also, there is a possibility to dump steam of 0.4 MPa, for example, when the steam produced in the recovery boilers exceeds the demand. The district heating load is fixed for each time step and can be supported by any of the operators. The calculations are made for one year’s operation and the year is divided into 104 time steps of varying length which correspond to different heat load levels in the district heating system according to season of the year and hour of the day. Fig. 4 shows the duration curve for the three district heating loads in the model. The price for district heating is set as GEAB’s alternative price, i.e. the cost GEAB would have if they had to produce all heat for district heating by themselves. As long as the capacity of the biofuel boiler is sufficient, it is used for heat production, which
also generates electricity sales revenues for GEAB. When all the biofuel boiler capacity is used, oil boilers are taken into operation. Because of this, the heat price ranges between 6 and 71 euro1/MWh, as illustrated in Fig. 5. In the cases with the heat market, the magnitude of the heat delivery from each company was predetermined according to the results from optimisations of the heat market (Karlsson et al., 2009). Thereby, the use of the back-pressure evaporation plant was predetermined, but the priority of KEAB’s boilers was up to the optimisation to decide. The heat price was set according to the marginal price, which was also a result of the above-mentioned analysis, and varies within the range 6–41 euro/MWh, as shown in Fig. 5. The energy carrier prices that are used in the model are presented in Table 4. The prices for electricity, both purchase and sales, are market prices (Nordpool, 2006). The price for tradable green certificates is the average price for 2005 (Svenska kraftna¨t, 2007). In addition to the fuel price, energy and carbon dioxide taxes according to the Swedish legislation in 2005 are considered for fossil fuels (Swedish Tax Agency, 2006).
4.4. CO2 emission calculations The effect of the energy system changes on the CO2 emissions are calculated using the values in Tables 5 and 6. Two ways of calculating the CO2 emissions due to electricity are used. First, electricity is regarded as produced in coal-fired condensing power plants, which are the marginal electricity production units in Northern Europe. Secondly, the average Swedish electricity production was accounted for, which consists of 47% hydropower 1
1 euro ¼ 9 SEK (assumed value).
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400
Table 4 Prices used in the model. Entity
Euro/MWh
Electricity purchase/sale Tradable green certificates Oil Bark
25–38/24–36a 24b 28c,d 14d
Oil, via the turbine Bark, directly from steam boiler Heat pumps
350
Bark, via the turbine Flue gas condensation Back-pressure evaporation
250 MW
a Price range within which the monthly average prices varies around the year. Monthly market prices (Nordpool, 2006) for the years 2001–2005 are used. Also, there are different prices for purchase and sale on the market. b Average price for 2005 (Svenska kraftna¨t, 2007). c Including energy and carbon dioxide taxes (Swedish Tax Agency, 2006). d Oil and bark prices are based on discussions with the participating companies.
GEAB’s biofuel boiler
300
200 150 100 50
Table 5 CO2 emissions from different fuels (SCB, 2007).
0 0
Fuel
CO2 emissions (kg CO2/MWh of fuel)
Residual fuel oil Biofuel
267 0
Table 6 CO2 emissions from external electricity for different accounting models. Model
CO2 emissions (kg CO2/MWh of electricity)
Marginal coal Average Swedish power production
974a 11b
a b
Calculated from Gro¨nkvist et al. (2003). According to the Swedish Energy Agency (2000).
and 45% nuclear power and of which only a small fraction is produced by fossil fuels (Swedish Energy Agency, 2006). Average Swedish power production is included to reflect the traditional accounting method used in Sweden, but also to have a possibility to compare an average accounting method to a marginal accounting method.
5. Results The optimisation result of the joint perspective, Case LKKG, is shown to be the case which is most similar to today’s operation, which is regulated through agreements between the three companies. In the following result presentation, Case LKKG is used as the base case to which the other cases are compared. The priority of boilers etc. for district heating deliveries is the same in Case LKKG as in the present operation, except that in today’s operation KEAB’s flue gas condensation is partly used without committing the back-pressure evaporation plant and partly when this is fully used. Also, the size of heat delivery from Korsna¨s and KEAB to GEAB corresponds well with operation at present. A difference though, is that the heat from KEAB to GEAB origins to a greater extent from biofuel on the expense of flue gas condensation in the model result. This is explained by the fact that the heat from flue gas condensation depends on the use of the biofuel boiler, and that in today’s operation the biofuel boiler supports the steam demand at Korsna¨s to a higher degree than in the optimisation results. Therefore it is necessary for KEAB to increase its use of the biofuel boiler for heat delivery to GEAB, in order to be able to produce heat from flue gas condensation in the model. Furthermore, the electricity generation in Case LKKG is similar to the electricity generation of today.
3000
6000
9000
Hour Fig. 6. Duration curve for district heating deliveries during a year in Case LKKG.
As seen in Fig. 6, the base for district heating production is the back-pressure evaporation plant. As the heat load increases, flue gas condensation and then the biofuel boiler at GEAB are taken into operation. Next, the heat pumps and the steam from the bark boiler that has passed through the turbine are used. When the district heating load exceeds 150 MW, steam from the bark boiler is also used directly without passing the turbine. In order to supply the peak heat load, the oil boiler is used for cogeneration. Regarding steam to support Korsna¨s’ steam demand, the result from LKKG is that, besides steam from recovery and gas boilers, bark and electricity are used. No oil is used for Korsna¨s, though. The steam from the recovery boilers passes through the turbine most of the time because it generates revenues from electricity sales. Only when the district heating load is very high, steam from KEAB passes through the turbine instead. A difference between today’s system and the model is that the pricing of heat deliveries differ. Instead of the agreed prices, which depend on which fuel is used, GEAB’s alternative price is used in the model. Analysis of Case LKKG shows that the heat delivery from Korsna¨s and KEAB to GEAB according to model results would give revenues of about 9 million euro if the prices from the agreements are used, but with GEAB’s alternative price the revenue is about 20 million euro. However, since the pricing is the same for all the modelled cases the economical results are still relevant when comparing different cases.
5.1. Cooperation synergism In order to find the synergism for cooperation between Korsna¨s and KEAB on one hand and GEAB on the other hand, calculations were made for a disconnected system, DKKG. In this case, GEAB needs to produce all heat itself. The biofuel boiler supports the basic heat demand, but during the winter oil boilers need to be taken into operation as well. Except the fuel costs, GEAB’s revenue from electricity generation was also taken into account. The result is shown in Fig. 7. In total, about 30 million euro/year are saved through the cooperation. This is due to the cheaper fuel that can be used for hot water production for district heating (Fig. 8). Particularly, GEAB needs to combust a great deal of oil during the winter if they cannot buy heat from Korsna¨s and KEAB. The electricity generation does not change much between the cases, amounting to around 400 GWh/year.
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8 GEAB
60
7
KK
50
Million euros/year
Million euros/year
70
40 30 20 10 0
6 5 4 3 2 1
LKKG
DKKG
0
Fig. 7. System cost for the joint perspective (LKKG) and for the disconnected system (DKKG). The costs for Korsna¨s and KEAB (KK) and GEAB, respectively, are pointed out in the two cases. Explanations regarding the abbreviations are found in Table 1.
LKK
LKorsnäs
LKEAB
LGEAB
Fig. 9. Decrease of system revenue from the optimisation with joint perspective (LKKG) in comparison with the system revenue from the optimisations with separate perspectives (LKEAB, LKorsna¨s, LGEAB) and the joint perspective of Korsna¨s and KEAB (LKK). Explanations regarding the abbreviations are found in Table 1.
1400 LKKG DKKG
1200
450 350 GWh/year
GWh/year
GEAB's turbine KEAB's turbine
400
1000 800 600 400
300 250 200 150 100 50
200
0 LKKG
0 Oil
Bark
Electricity for boilers and heat pumps
Fig. 8. Energy use for boilers and heat pumps in Case LKKG and if Korsna¨s and KEAB (KK) and GEAB were disconnected (Case DKKG). Explanations regarding the abbreviations are found in Table 1.
LKorsnäs
LKEAB
LGEAB
Fig. 10. Electricity generation in the five optimisations with different economic system boundaries. Note that the use of GEAB’s turbine is random in the cases in which GEAB’s costs and revenues are not accounted for, i.e. LKK, LKorsna¨s, LKEAB. Analogically, the use of KEAB’s turbine is random in Case LGEAB. Explanations regarding the abbreviations are found in Table 1.
1200
5.2. Applying different system perspectives
Oil Bark
1000
Electricity for electric boilers and heat pumps
800 GWh/year
The fuel priority for district heating production varies largely depending on system perspective. The use of turbines also varies. In order to calculate how the joint perspective affects each operator, the system costs of the optimisations with single (LKEAB, LKorsna¨s, LGEAB) and two (Korsna¨s and KEAB, LKK) actor perspectives are compared to the system cost of each operator in the optimisation with overall perspective LKKG. The comparison indicates how cooperation influences each company. It is found that the separate perspectives give a more beneficial result for each operator, though a very small change is found in GEAB’s case, as seen in Fig. 9. This is because the separate perspectives make the other companies operate in order to benefit one single company. GEAB has the smallest loss, which indicates that today’s operation is made close to GEAB’s optimal operation. KEAB makes the greatest loss and Korsna¨s is in between. The electricity generation is highest in Case LKKG; both GEAB’s and KEAB’s turbines are used almost all the time (Fig. 10). This is because the benefits from both GEAB’s and KEAB’s turbines are taken into account. The oil use is lowest in Case LKKG; instead, bark is used to the highest extent (Fig. 11). In the separate perspective cases, the fuel use of the companies whose costs are not taken into account does not affect the optimisation result. Hence, when there are no costs for the fuels used in different boilers, the use of the boilers is chosen randomly. The steam and heat demands are still fixed though. However, Korsna¨s and KEAB share the interest in using KEAB’s turbine, and therefore the boilers in which high pressure steam is produced are prioritised in all cases but LGEAB. In no case is the possibility of dumping steam used, since the cost of
LKK
600 400 200 0 LKKG
LKK
LKorsnäs
LKEAB
LGEAB
Fig. 11. Fuel use for steam and hot water production in the whole system with different economic perspectives. Black liquor and foul gases that need to be burnt by Korsna¨s are exempted. Korsna¨s’ electricity use for processes is also excluded. Explanations regarding the abbreviations are found in Table 1.
extra fuel is too high in comparison to the benefit of the extra electricity generation that would have been possible. Besides for fuel costs, this is also due to low turbine efficiency. In all cases where Korsna¨s’ costs are accounted for, no oil is used for the steam demand at Korsna¨s because both electricity and bark are less expensive. In Case LKorsna¨s, less of the steam from the recovery boiler passes through the turbine in comparison to Case LKKG, since Korsna¨s only gains a small part of the revenue for electricity sale. Therefore, less additional steam is required in Case LKorsna¨s. The bark use for supplying Korsna¨s is greater in Case LKKG
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than in Case LKK because GEAB’s boiler is used more in Case LKKG, instead of KEAB’s burning of bark for district heating. That releases bark boiler capacity at KEAB that can be used for Korsna¨s.
2521
6 HMKK
5
HM,BTKK
In Fig. 12, the result from the optimisations made with system changes and overall perspective are presented (cf. Table 3). The system cost is compared to the reference case, LKKG. It is found that a new biofuel boiler and turbine at KEAB (Case BTKKG) gives the lowest system cost. This is because cheap biofuel replaces oil and electricity to a large extent. The case that gives the highest electricity generation is to additionally switch from back-pressure to conventional evaporation, BPE,BTKKG. In none of the cases is the possibility of dumping steam used. Comparison of the cases where the system changes are seen from the joint perspective of Korsna¨s and KEAB, BPEKK, BTKK and BPE,BTKK and LKK, confirm these result. For the cases in which the back-pressure evaporation plant is replaced, BPEKKG and BPEKK, the system cost increases. This is because the hot water that fails to come from the backpressure evaporation plant needs to be covered by something else, which to a large extent is bark but during the coldest months oil needs to be used as well. For the cases where replacing the backpressure evaporation plant is combined with extended biofuel capacity, the loss is decreased. The heat market is shown to be beneficial for Korsna¨s, with or without new biofuel boiler and turbine at KEAB, see Fig. 13. The result of the heat market for KEAB is not unambiguously positive. In Case HMKK, where no system changes are made, KEAB even makes a loss from connecting to the heat market though in Case HM,BTKK with a new boiler and turbine, KEAB makes good profit from it. The loss for KEAB in Case HMKK is explained by the lower revenue for selling heat in comparison to current prices. In Case HM,BTKK the heat price is still low, but that is compensated by a greater heat delivery and even more by the additional electricity generation in the new turbine. 5.3.1. Electricity generation The results from the optimisations of cases with system changes show that the electricity generation is remarkably higher in the cases with a new boiler and turbine at KEAB (Fig. 14). The case that gives the highest electricity generation is BPE,BTKKG, in which replacing the back-pressure evaporation plant and expanding the biofuel boiler and turbine capacity are combined.
10
Million euros/year
8 6 4 2
3 2 1 0 -1 -2 -3 Korsnäs
KEAB
Fig. 13. Reduced cost for Korsna¨s and KEAB, respectively, in the cases with heat market, in comparison to the results for each operator in LKKG recalculated with agreed prices of today. Explanations regarding the abbreviations are found in Table 1.
600 500
GWh/year
5.3. Energy system changes
Million euros/year
4
KEAB's new turbine KEAB's old turbine GEAB
400 300 200 100 0 LKKG
BPEKKG
BTKKG
BPE,BTKKG
Fig. 14. Electricity generation in the cases with system changes and the joint perspective of Korsna¨s, KEAB and GEAB. Explanations regarding the abbreviations are found in Table 1.
5.3.2. Fuel use Biofuel boilers at KEAB and GEAB supply the base district heating demand for most cases, along with the back-pressure evaporation plant in the cases in which it is possible, see Figs. 15–17. In these figures, for the cases including the new biofuel boiler and turbine, cases BTKKG, BPE,BTKKG, BTKK, BPE,BTKK and HM,BTKK, the entities ‘‘Oil, via turbine’’ and ‘‘Bark, via turbine’’ include both the steam which passes through the old and the new turbine. In the cases in which the back-pressure evaporation plant is replaced, the oil use is higher. The heat production for district heating in the heat market cases is also based on the back-pressure evaporation plant, see Fig. 18. In Case HM,BTKK the new bio fuel boiler is used to a great extent which reduces the need for heat pumps and oil.
0 -2 -4 BPEKKG
BTKKG
BPE,BTKKG
Fig. 12. Decreased system cost for the system changes, in comparison to LKKG. Explanations regarding the abbreviations are found in Table 1.
5.3.3. CO2 emission reduction Figs. 18 and 19 show the change in CO2 emissions in the cases with system changes. Two ways of regarding CO2 emissions are implemented: electricity is either regarded as the marginal electricity production units in Northern Europe, which are coalfired condensing power plants, or it is regarded as the average Swedish electricity production, which mainly is hydro power and nuclear power.
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900 800 Electric boiler
700 GWh/year
Oil, directly
600
Oil, via turbine
500
Bark, directly Bark, via turbine
400
Flue gas condensation
300
Heat pumps BPE
200
GEAB
100 0 LKKG
BPEKKG
BTKKG
BPE,BTKKG
Fig. 15. Boiler use for district heating production in the reference case (left) and the cases with system changes and the joint perspective of Korsna¨s, KEAB and GEAB. Explanations regarding the abbreviations are found in Table 1.
900 800 Electric boiler
700 GWh/year
Oil, directly
600
Oil, via turbine
500
Bark, directly Bark, via turbine
400
Flue gas condensation
300
Heat pumps BPE
200
GEAB
100 0 LKK
BPEKK
BTKK
BPE,BTKK
Fig. 16. Boiler use for district-heating production in the reference case (left) and the cases with system changes and the joint perspective of Korsna¨s and KEAB. Explanations regarding the abbreviations are found in Table 1.
600 Electric boiler
500 GWh/year
Oil, directly
400
Oil, via turbine Bark, directly
300
Bark, via turbine
200
Flue gas condensation Heat pumps
100
BPE
0 KK from LKKG
HMKK
HM,BTKK
Fig. 17. Boiler use from the joint perspective of Korsna¨s and KEAB, extracted from the LKKG optimisation, and for the heat market cases. Explanations regarding the abbreviations are found in Table 1.
Connection to the heat market will reduce the CO2 emissions from KEAB and Korsna¨s seen as a joint unit, particularly if coal condensing power is seen as the marginal electricity production units. This is due to the reduced heat deliveries, which require less fuel. To replace the back-pressure evaporation plant would slightly reduce the CO2 emissions if electricity is seen as coal condensing power. If replacement of evaporation plant is combined with a
new biofuel boiler, the reduction is much greater though. If the average electricity production in Sweden is considered instead, the CO2 emissions increase when the back-pressure evaporation plant is replaced. This is due to the increased use of oil. A new biofuel boiler and turbine at KEAB largely reduces the CO2 emissions if electricity is regarded as coal condensing power. If the average electricity production in Sweden is considered instead, the CO2 emission reduction is smaller.
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50
Thousand tonnes CO2/year
0 -50 -100 -150 -200 -250
Marginal coal condensing power Average Swedish
-300 -350 -400 BPEKKG
BTKKG
BPE,BTKKG
Fig. 18. CO2 emissions in comparison to LKKG (common perspective) for two ways of accounting CO2 for electricity. Explanations regarding the abbreviations are found in Table 1.
Thousand tonnes CO2/year
100 0 -100 -200 -300 -400 Marginal coal condensing power
-500
Average Swedish
-600 HMKK
HM,BTKK
BPEKK
BTKK
BPE,BTKK
Fig. 19. CO2 emissions in comparison to LKK (Korsna¨s–KEAB perspective) for two ways of accounting CO2 for electricity. Explanations regarding the abbreviations are found in Table 1.
6. Concluding discussion From the analysis of the energy system with different economic system boundaries it is found that there is a competition within the energy cooperation regarding boiler use. In total, there is an overcapacity among the companies, which make each operator strive to use their own equipment to a higher degree. Regarding the system from a joint perspective, benefits of cooperation are pointed out. The oil demand could be reduced and the electricity generation could be extended. The results show that the operation of the system today is similar to the optimisation with a joint perspective. The analysis of a disconnection of today’s heat deliveries shows that the cooperation of today greatly reduces the system cost, particularly through reduction of the oil demand. The benefit of regarding extended system boundaries is applicable in any case where geographically close systems are physically connected or such a connection is possible to realize. In all cases, except when only the district heating utility GEAB’s perspective is applied, there is a possibility of dumping lowpressure steam and thereby using KEAB’s turbine in a similar way to a condensing turbine instead of as a back-pressure turbine. Whether this opportunity is chosen to be used by the optimisation or not indicates whether condensing power is a beneficial
2523
alternative for the industry or not. The dumping opportunity is never used, though. This indicates that condensing power is not beneficial for the industries in question, or at least that the condensing turbine needs to be more efficient than KEAB’s backpressure turbine. Among the system changes that were analysed, process integration was shown to be not beneficial if it is not combined with extended biofuel boiler capacity. This is because the process integration measure that was analysed reduces the excess heat that can be delivered for district heating. The heat therefore needs to be replaced and the biofuel boiler capacity of today is not sufficient. In reality, a greater benefit would possibly be shown for the pulp and paper mill Korsna¨s, since the oil and electricity, which are used to support the steam demand at the mill today, would be reduced through the process integration. In the optimisations though, no oil is used; not even in the reference case. The process integration results emphasise the importance of regarding extended system boundaries in any system analysis of closely connected companies. Even though process integration is an energy efficiency measure within one company’s system, the consequences for the connected companies need to be taken into account. In this case it was shown that process integration needs to be combined with extended biofuel boiler capacity in order not to cause a sub-optimisation of the regional energy system. The single most beneficial energy system change was shown to be expanding the capacity for biofuel combustion. This result is due to the high prices for oil and electricity, which biofuel replaces. Furthermore, the electricity generation is extended by increased biofuel boiler capacity and adds to the benefit of the measure. The industrial energy company KEAB has already decided to build a new biofuel-fired boiler with turbine. Connecting to the local heat market is beneficial for Korsna¨s. The main reason is the higher price they would obtain for selling heat. For KEAB, the benefits of connecting to the heat market depend on the investment in expanded biofuel boiler and turbine capacity. Without that investment, KEAB would make a loss by connecting to the heat market. The reason is the lower price they would obtain for selling heat. Changing the price on the heat market would make some operators become losers in the heat market, whereas other operators would gain even more. Generally, net receivers of heat from the heat market would gain on a lower heat market price and the contrary for net suppliers. For example, if the price in the heat market is about half the price of today the breakpoint between winning and loosing on connecting to the heat market for Korsna¨s is found. For KEAB, revenues from extended electricity production are dominating incomes and therefore the price in the heat market is not that influential on total revenues. There is a potential to reduce CO2 emissions through the studied energy cooperation. Particularly if electricity is calculated according to the marginal power generation in Northern Europe, which is coal condensing power, the investment in a new biofuel boiler and turbine reduces the CO2 emissions greatly.
Acknowledgements The work has been carried out under the auspices of the RESO project, which is financed by the Swedish Energy Agency, the companies mentioned in this study as well as Sandvik, Sandviken Energi, Skutska¨r and A¨lvkarleby Fja¨rrva¨rme. The authors are grateful to Ha˚kan Yderling at Korsna¨s AB and Ingemar Hemlin, Maria Carendi and Peter Holmstro¨m at Karska¨r energi AB for valuable assistance in this study. We would also like to thank Alemayehu Gebremedhin, Ph.D., for preparing data that was
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