Biomass co-firing potentials for electricity generation in Poland—Matching supply and co-firing opportunities

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32 (2008) 865 – 879

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Biomass co-firing potentials for electricity generation in Poland—Matching supply and co-firing opportunities Ma˚rten Berggren, Emil Ljunggren, Filip Johnsson Department of Energy Conversion, Chalmers University of Technology, SE 412 96 Go¨teborg, Sweden

art i cle info

ab st rac t

Article history:

As part of the European Union (EU) accession treaty, Poland is obliged to increase the share

Received 20 December 2007

of renewable electricity production to 7.5% by 2010 (from a present share of about 2% in

Accepted 23 December 2007

2002). Most of this increase is expected to be covered by biomass-based electricity

Available online 20 February 2008

generation. This paper investigates the potential for co-firing of biomass and coal in the

Keywords: Co-firing Biomass Power generation Renewable electricity Bioenergy Poland Modelling

Polish power-generation system. More specifically, this study focuses on matching potentials in biomass supply with opportunities for co-firing biomass in existing coalfired power plants. Available estimates of biomass supply and information on the power plant infrastructure are used as input for modelling the co-firing potential for each of the 16 regions in Poland (‘‘Voivodship’’). The modelling also gives the additional cost of the electricity and the CO2-avoidance cost for the co-firing. The result shows a potential of electricity produced from biomass in co-firing of 1.6–4.6% (2.3–6.6 TWhe) of the total electricity production in 2010. Adding this potential to the existing production of about 2% electricity from renewable energy sources (RES-E) gives an overall contribution of RES-E in the range 3.6–6.6%. The additional cost for the implementation of co-firing is less than h20 per MWhe (the average electricity price in Poland in 2003 was h96 per MWhe) corresponding to a CO2-avoidance cost of less than h20 per tonne CO2. In summary it can be concluded that although co-firing can serve as a low-cost option for near-term increase of RES-E, there is still an additional 0.9–3.9% of other RES-E production required to be developed to reach the 2010 target of 7.5% RES-E. The results call for quick action with respect to implementation of co-firing, if Poland should have any chance to reach the RES-E target by 2010. & 2008 Elsevier Ltd. All rights reserved.

1.

Introduction

The environmental impact from the use of fossil fuels has induced the European Union (EU) to take action in order to increase the share of renewable energy sources (RES) on the energy market. The ‘‘White Paper on Renewable Energy’’[1] set the target of doubling the share of renewable energy from the (1997) level of 6% to 12% by 2010. As Poland has entered the EU, the document ‘‘The Treaty of Accession’’ [2] was signed in which Poland undertakes to reach a 7.5% share of electricity from Corresponding author. Tel.: +46 31 772 1449; fax: +46 31 772 3592.

E-mail address: [email protected] (F. Johnsson). 0961-9534/$ - see front matter & 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2007.12.017

renewable energy sources (RES-E) in its gross national production of electricity in 2010. Near-future options available to reach this target are co-firing of biomass in large coal-fired power boilers, wind power, hydropower, biogas plants and biomass-fuelled power plants. According to the document ‘‘Development strategy of renewable energy sector’’ [3], the share of RES-E from wind, hydro and biogas in 2010 is expected to be about 2.7% (4 TWhe). The remainder (4.8%) must come from biomass. To reach the 7.5% RES-E target the Polish government has introduced a ‘‘quota obligation system’’ [4], which obliges

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companies that trade with electricity to keep a portion of RES-E in their portfolios, this portion increases each year until the year 2010 when the portion should be 7.5% of RES-E. Presently available options for generating electricity from biomass are small- and medium-sized biomass-fired power plants and combined heat and power plants (CHP) and cofiring biomass with fossil fuels in large power boilers. The cofiring option is the least expensive of these. There is currently no developed market for biomass in Poland. This creates uncertainty with respect to supply and price, but implementation of co-firing should therefore be a comparatively lowrisk path for power-generating companies (utilities), as they can then still rely on the use of fossil fuel as base fuel in case of disturbances on the biomass supply side. Also 2010, the year the target must be reached, is not far away and the producers of electricity must soon find ways to increase their investments in renewable power generation and co-firing will not require building new plants, as would be the case with small- and medium-sized plants and CHP plants. The advantages associated with co-firing raises the interest for an estimation of the potential for co-firing in the Polish power-generation sector. Several studies have been carried out that estimate the current and potential supply of biomass for energy purposes on a global scale, e.g. [5–7]. These studies have analysed available amounts of biomass for energy supply over a 50 years time frame from now, indirectly assuming demanddriven scenarios. Berndes et al. [6] compared 17 such studies given in literature and found the estimates of biomass supply in the future global energy supply to vary with a factor of about 4. Other studies have presented potentials or problems with using biomass in different combustion systems, e.g. [8,9]. However, there is a lack of studies that determine the potential of electricity from biomass by matching the supply of biomass on a regional level including the power plant infrastructure and thereby get more accurate estimates of the potentials, i.e. not assuming the market to be demand driven. Thus, by focusing on regional supply of biomass, electricity as the only energy carrier, current power plant infrastructure and a relatively short time perspective, it should therefore be possible to obtain a better estimate of biomass potentials. Hence, there is a need to find a methodology which can be used for national estimates of electricity production from biomass. The aim of this paper is to illustrate such an approach by finding the potential for co-firing biomass with coal in the Polish power-generation system in 2010. More specifically, the work focuses on matching biomass supply with the potential for co-firing in the existing power plant infrastructure. The matching is carried out by reviewing experiences in the field of co-firing together with data estimating the biomass supply, combined with applying a database on the existing power plants. Furthermore, the purpose is to estimate the cost of implementing the co-firing potential together with the reduction in emissions. The estimated co-firing potential will be compared with the Polish 2010 target of 7.5% RES-E.

32 (2008) 865 – 879

model has been established. The inputs for the LP model are estimates on the biomass supply potential and data on the power plant infrastructure. The biomass supply and the power plants are matched by the model which gives the potential of electricity in 2010 from co-firing, the total cost for implementing the co-firing potential together with the CO2avoidance cost.

2.1.

Poland is divided into 16 administrative districts, named Voivodships. Table 1 lists key figures for these districts. The capital, Warsaw is situated in the Voivodship Mazowieckie, which is the largest and most populated district, while the largest installed capacity for power production is found in the south-central districts Slaskie and Lodzkie. Table 1 also lists straw production, timber harvest and area of fallow and contaminated land, i.e. these figures give potentials of straw, wood and unused areas for the cultivation of energy crops in the districts. The districts with least potentials for energy crops are in the south of Poland where also a large share of the installed power capacity can be found. The biomass supply potential for Poland was mainly taken from a recent report assessing the biomass potentials for various types of biomass feedstock [10]. It was concluded that these data are the most up to date on biomass supply in Poland. However, alternative estimates (e.g. [11–13]) of the biomass supply potential have been gathered to create a maximum and a minimum biomass supply estimate, and thereby examining the influence of the biomass supply on the co-firing potential. Also, two different scenarios of the transportation of biomass cross-regional boundaries have been analysed (between ‘‘Voivodships’’), the first scenario does not allow cross-borders transport of biomass, the second scenario allows cross-border transport of biomass.

2.2.

Boiler infrastructure

The available boiler capacity for co-firing is mainly based on the Chalmers Power Plant database which contains all power plants in Europe (EU25) with a capacity generally exceeding 10 MWe, and which is described elsewhere [14]. The database includes the name, position and fuel type of all powerproducing units, in the case of Poland down to a capacity of 1 MWe. Some additional information for each boiler with respect to boiler type, capacity and commissioning year was gathered from other sources [15,16]. A technical assessment was made with respect to possible co-firing fraction for the different boiler types with the assessment based on current and previous experience of co-firing in Europe and the USA, with special attention to Swedish experiences since co-firing has a comparatively long history in Sweden and since information on the experiences gained in Sweden was easily accessed.

2.3.

2.

Biomass supply potential

Modelling

Method

To find the potential for co-firing of biomass with coal in Poland, a simple cost optimising linear programming (LP)

A schematic view of the LP model for estimating the co-firing potential is shown in Fig. 1. The model minimises the cost for implementation of co-firing with respect to combining the

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Table 1 – Key figures for the districts (Voivodships) in Poland Voivodship

Area (km2)a

Population Year 2004a

Installed power capacity (MW)b

Straw production (Thous ton/y)c

Timber harvest (dam3/y)c

Fallow and contaminated land (thous ha)d

Dolnos´la˛skie Kujawsko-pomorskie Lubelskie Lubuskie Ło´dzkie Ma"opolskie Mazowieckie Opolskie Podkarpackie Podlaskie Pomorskie Sla˛skie S´wietokrzyskie ˛ Warmin´sko-mazurskie Wielkopolskie Zachodnio-pomorskie

19,948 17,970 25,114 13,984 18,219 15,144 35,598 9,412 17,926 20,180 18,293 12,294 11,672 24,203 29,826 22,901

2,895,729 2,067,548 2,187,918 1,009,177 2,592,568 3,256,171 5,139,545 1,053,723 2,097,325 1,204,036 2,192,404 4,707,825 1,290,176 1,428,385 3,362,011 1,695,708

2775 550 343 388 5414 2020 4306 1659 559 158 444 7006 1692 62 2924 1885

2180 2212 2609 653 1571 870 2722 1448 856 1164 1484 755 843 1616 3767 1835

2106 1366 1033 2390 759 696 1370 827 1627 1261 1941 1033 654 2709 2335 2936

249 191 296 215 226 152 410 103 226 199 230 163 143 345 307 346

Total

312,685

38,180,249

32,182

26,585

25,043

3800

a

[40]. Based on the Chalmers Power Plant database. c [10]. d [18]. b

supply and conversion route (type of biomass and boiler) which gives the lowest cost. This gives as a result a co-firing potential which is either limited by the capacity on the supply side or on the conversion side. This work focuses entirely on the co-firing option and, consequently, the modelling does not compare co-firing to other RES-E technologies (such as biomass-based CHP), which obviously have to be implemented over a longer time than to 2010. Here, it is assumed that co-firing is the least costly option until 2010. As mentioned above, two different scenarios are investigated. The first is based on that each of the 16 regions (‘‘Voivodships’’) in Poland is treated individually, i.e. there is no cross-border transportation of biomass between these regions. The results for the 16 regions are then summarised to produce aggregated results for the entire Poland. In the second scenario, the available biomass within a region is allowed to be transported to neighbouring regions. In practice, this results in different average allowable biomass transportation distances with the first scenario yielding an average transportation distance of 60 km and in the second scenario an average transportation distance of 100 km. As indicated above the LP model matches the biomass supply and the boiler structure in a way that minimises the total cost for the implementation of co-firing with the total cost being the sum of the cost for each boiler which is retrofitted for co-firing. The cost for each boiler consists of investment costs for retrofit, generation costs (mainly fuel) and additional operation and maintenance costs (O&M) resulting from the co-firing. Table 2 lists these costs for each

boiler type considered in this work. The O&M cost is divided into a fixed part (percentage of the total investment) and a variable part which is assumed to depend on the amount of biomass fuel co-fired. The investment costs for retrofitting are assumed to be limited to costs for building a new parallel fuel-handling system. The fuel costs include the transportation cost. The cost figures used are based on previous projects for various boiler types. Yet, retrofitting different boilers may lead to different costs and costs other than those used here (e.g. large boilers or boilers which are older than those applied in this work may lead to higher retrofitting costs). An assessment of the existing boilers in the Power Plant database was made with respect to co-firing possibilities, i.e. type and amount of biomass fuels which can be co-fired in different boiler types. The electricity efficiency applied in the model depends on age and type of power plant, i.e. if the plant only produces power or is a CHP plant. Emission factors from IPCC [17] were used to calculate the emissions of CO2 for the different coals used. The CO2-avoidance cost was obtained by comparing the additional cost of producing electricity with biomass in co-firing (including investment, extra O&M and fuel costs) divided by the amount of CO2 reductions, yielding a cost expressed in h/tonne CO2. In the model, all boilers in a region are made available for co-firing. The boilers are then evaluated and boilers which are not feasible (older than 30 years and non-coal-fired) are excluded as options. The remaining boilers are then categorised into three different technologies as each technology has its own limitations, e.g. with respect to the fraction of

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Fuel Supply

32 (2008) 865 – 879

Conversion

Type

Boiler-

Cost

-Type

Heat value

-Cost

Availibility

-Size

Electricity production from biomass in co-firing

Emissions

-Age -Main fuel

Cost for implementing co-firing

-Location

Cost optimisation Fig. 1 – Schematic view of the model used for the matching of biomass supply with suitable boilers.

Table 2 – Key parameters used in the modelling of the potential of electricity from biomass in co-firing in Poland Parameter

Unit

Value

Retrofit cost Fluidised beda PCb Gratea

h/kWe h/kWe h/kWe

60 180 60

Extra operation and maintenance cost Variable costc Fixed percentage costc Fuel cost including transportd Hard coal Lignite Straw Forest residue Fuel wood Energy crops

h/TJbiofuel % of investment

0.7 2

ined, corresponding to a high and a low biomass supply potential. The model first chooses the boilers with the lowest investment cost, depending on the type of boiler, and then it ranks the boilers with respect to their age (i.e. a new boiler is used before an old boiler).

2.4.

Restrictions and assumptions

The following restrictions and assumptions have been made in the modelling:

 All power plants that are documented in the Chalmers h/GJ h/GJ h/GJ h/GJ h/GJ h/GJ

Maximum share of biomass in co-firinge Fluidised bed (woody biomass) % (energy basis) PC (woody biomass) % (energy basis) Grate (straw) % (energy basis)

1.94 2.03 2.75 2.28 2.23 2.32



15 10 10

The parameters are based on previous projects and should be seen as approximate (e.g. for each boiler technology, retrofit cost may vary between projects due to difference in local conditions for retrofitting). a [35,36]. b [37]. c [29]. d [38,39]. e Based on co-firing experience and estimates for Poland made in this work.

biomass which can be co-fired. This potential of biomass cofiring for each boiler is then matched with the estimated biomass supply in the region. The matching produces an amount of biomass that can be used in each boiler with respect to both the boiler technology and the biomass supply. This amount of biomass is then converted into potential of electricity production by using estimated electrical efficiency. Two different biomass supply estimations have been exam-



 



Power Plant Database for Poland are considered. These are the ones built up to the year 2000 and with a capacity above 1 MWe. Only co-firing in coal-fired boilers is included in this study. More than 95% of the installed electricity production capacity in Poland is fuelled with coal and coal-fired boilers are assumed to be the most cost effective for cofiring. Boilers fuelled with natural gas and oil make up for less than 5% of the installed capacity. Thus, these boilers represent a minor potential for co-firing to a higher cost (since this require gasification of biomass or major reconstruction of boilers fuelled with oil). Only boilers with a commissioning year after 1974 (o30 years old) are considered to be economically feasible for investing in co-firing. The electricity production in each region will be the same in 2010 as in 2002.1 Pulverised coal (PC) and fluidised bed (FB) boilers are allowed to use 10% and 15% respectively of forest residue, fuel wood and energy crops (woody fuels). These figures have been estimated from the experience gathered in this work. Also, a current co-firing project (FB) in Poland has limited the co-firing tests to 5–15%, of biomass and this is viewed as an indication of possible shares in FB boilers. Grate-fired boilers are allowed to use 10% straw. No other biomass is allowed in grate boilers. Straw is a rather problematic fuel to use in co-firing and due to technical and logistical (the low density of straw creates large

1 Most of the basic data collection of this study was carried out in the year 2002.

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3.

volumes) issues straw has been designated for grate boilers. The investment for co-firing is limited to a separate fuelhandling system for biomass. This, since the share of biomass co-fired is comparatively low (typically less then 15%). The installation of co-firing does not change the capacity or the efficiency of the plant. Again, this should be a reasonable assumption due to the rather low share of co-firing. The potential of biomass supply within each region is distributed evenly. All boilers have the same operating time (load factor). This operating time was calculated by using figures from [18] for installed electricity capacity and annual production in Poland. The average load factor was calculated to 4450 h/year for the year 2002 figures. This load factor has been used for production in all boilers. An average load factor was needed in order to calculate the technical potential on a yearly basis.

Biomass supply potential

The biomass supplies in Poland considered in this work are straw, forest residue, fuel wood and energy crops. For the modelling in this work, the maximum and the minimum supply potential of these fuels in the year 2010 are based on the work reported in [10–13,19] and estimates by the authors. The figures are divided according to region and expressed in

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energy units (Joule). Figs. 2 and 3 show the result of these estimates, which have been used as input for the calculations. Fig. 2 shows the straw potential and Fig. 3 shows the total potential estimate of forest residue, fuel wood and energy crops. From Figs. 2 and 3 it can be seen that there are considerable variations in straw potential between the regions whereas the potential of forest residue, fuel wood and energy crops are more evenly distributed over the country.

3.1.

Straw

It is assumed that the amount of straw available for energy use in 2010 will be the same as today, as the agricultural sector is assumed to be similar in 2010 as it is at present. The figures for the current surplus vary between 4 million tonnes [11] and 11 million tonnes [10]. These values have been presented on a regional level in [10] and represent the maximum and minimum supply potential applied in the present modelling.

3.2.

Forest residues

There is only one figure found for the present potential of supply from forest residues. It is assumed that this potential will be the same in the year 2010. This figure is 2.5 million m3/yr [10] and is the only estimate used, i.e. maximum and minimum potential are set equal in this case.

3.3.

Fuel wood

National figures for the present potential of fuel wood vary between 2.5 [10] and 4.9 million m3/yr [12]. These figures are

6100 10300 3300

9200

4800 8700 0

0

7200 13300

1000 9200

9600 20000

700 2300

1500 6500 100 5500

2000 16200 3900 9800

Low straw supply estimate (TJ/year)

0

1300 4500

0

800

3200

0

2300

High straw supply estimate (TJ/year) Fig. 2 – Minimum and maximum straw supply potentials in Polish regions (PJ/yr) in the year 2010. The left bar represents the minimum straw supply potential and the right bar the maximum supply potential of straw. Values based on [10,19] and own estimates.

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1600 4800 1900 6300 2100 6600 1400 4300 1100 3500

2000 7100

1900 6000

1700 4800

1000 3700 1400 5100

2100 5300 800 2700

600 2000 1400 3600 Low wood supply estimate (TJ/year)

1200 3400

2000 5200

High wood supply estimate (TJ/year) Fig. 3 – Minimum and maximum supply potentials for woody biomass in Polish regions (PJ/yr) in the year 2010. The left bar represents the minimum woody-biomass supply potential and the right bar the maximum woody-biomass supply potential. Values based on [10,19] and own estimates.

assumed to be the same in the year 2010 and are used as minimum and maximum potentials in this work. It is assumed that the regional share of the national potential of fuel wood can be distributed in proportion to the forested area in each region. Figures on the forested area in the regions are gathered from [18].

3.4.

Energy crops

An estimate of the long-term supply potential for energy crop cultivation concludes that there are 1.2 million hectares of fallow land and 2.6 million hectares of contaminated agricultural land available for energy crops [10]. Today the amount of land used for energy crops is only about 2000 ha and to reach the potential (3.8 million hectares) in 2010 does not seem realistic [19]. Swedish experience has therefore been used as basis to estimate the maximum and minimum potential for energy crops in 2010. At present, 15,000 ha of energy crops are being cultivated in Sweden out of an estimated potential of 300,000 ha, which means that 5% of the total potential is being used [13]. Assuming Poland will reach the same proportion in 2010, this would mean a cultivated area of 190,000 ha. Also, according to [20] it is expected that the area utilised for energy crops plantation in EU15 will be 0.9 million hectares in the year 2010, these plantations will mainly be allocated to land previously used for cereal production. This means that 2.3% of the area used for cereals will substituted with energy crops in EU15 by the year 2010, applying the same share for Poland yields a potential of 190,000 ha of energy crops. This figure is used as the maximum potential, i.e. assumed to be a realistic to reach

within 5–10 years from now [19]. Furthermore, it is estimated that the amount of energy crop cultivation in Sweden will increase by 15,000 ha by 2010, the main driving force for this increase is decreasing prices of cereal products and increasing prices of wood chips [13,19]. Adding this figure to the current 2000 ha of energy crops in Poland, assuming that the driving forces in Sweden also applies in Poland, yields 17,000 ha (equal to 0.45% of total potential), which is taken as the minimum potential and is viewed as a quite low potential [19]. These national figures were distributed regionally in proportion to the amount of fallow and agriculture land in each region, i.e. in each Voivodship [18].

3.5. Comments on the forest residue and fuel wood supply potential To evaluate the above estimates on potential supply of forest residue and fuel wood a comparison of Swedish and Polish biomass supply potentials was conducted, similar to that made for energy crops above. Since there is almost no utilisation of straw in Sweden, the potential of straw was therefore not evaluated. Sweden has 22.7 million hectares of productive forest [21] compared with 8.9 million hectares in Poland [10]. Forest covers about 55.4% of the area of Sweden [21] whilst for Poland this figure is 28.5% [10]. The forest in Sweden consists of 81% coniferous and 17% deciduous trees [21] whereas in Poland the corresponding figures are 77% coniferous and 23% deciduous trees [10]. The amount of woody biomass produced in Sweden is about 70 million m3 each year [22] and in Poland about 24 million m3 [10]. Of 75 million m3 cut in final felling in

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Sweden, 30 million m3 of forest residue is produced, of which 4 m3 is utilised as fuel wood, mostly for district heating purposes [22]. In Sweden, 90% of the production of wood goes to the timber industry and 10% is used as fuel wood [22]. Translating the Swedish figures to Polish figures indicates that the amount of forest residue that could be utilised in Poland is about 1.4 million m3 and the amount of fuel wood production could be around 2.4 million m3. The estimates given in the above sections are 2.5 million m3 of forest residue [10] and 2.5–4.9 million m3 fuel wood [10,12]. Thus, the value from [10] for forest residue is slightly higher than expected when making a comparison with Swedish conditions. The estimate of fuel wood in Poland [10,12] is similar to what is predicted when compared with Swedish utilisation. The differences are considered small enough to assume that the estimates by [10,13], used in this work, are reasonable. There are probably some good reasons for the differences between Swedish and Polish conditions which result in this difference, but more exact estimates would be beyond the scope of this paper.

4.

Co-firing capacity

Figs. 4a and b clearly show that the vast majority of the boilers used for electricity production in Poland are PC boilers, both in terms of number and installed capacity. The size of the PC boilers varies significantly, with an average size of 279 MWth, consisting of boilers of various age. Figs. 4a and b also show that 11 FB boilers have been installed. The number is quite low but the installed capacity of the FB boilers is rather high, 3572 MWth, and these consists of mainly new boilers (e.g. the lignite-fired CFB boilers in Turow near Bogatynia). This means that the average size of an FB boiler in Poland is 325 MWth. The figures for grate boilers are the reverse, with a high number of installed boilers but with a low installed average capacity, and mostly old boilers. The average size of grate boilers in Poland is 27 MWth and they are therefore probably best suited to local biomass fuels. Figs. 4c and d show the number of boilers in Poland divided into type of main fuel and installed thermal capacity. About 92% of the boilers and more than 95% of the installed capacity of all boilers have coal as the main fuel. There is a possibility of using co-firing of biomass in natural gas-fired boilers, which involves gasification of biomass, but this is expensive and not considered in this work. Experience from Sweden opens up the possibility of re-powering oil-fired plants for co-firing of coal and biofuel, but this is not considered in this work, also in this case due to higher cost than co-firing in existing boilers and, even if neglecting the costs, this option would only concern a limited number of boilers. Figs. 4e and f show the age structure of the boilers. There are no significant differences between the age structure if represented as number of boilers or as installed capacity. The average commissioning year for a boiler in Poland is 1968. As mentioned above, only boilers commissioned after the year 1974 are considered suitable for co-firing. This age assumption is due to the fact that old boilers are estimated to have low efficiency and shorter remaining lifetime. Consequently, it is less economical to retrofit an old boiler with co-firing and

32 (2008) 865 – 879

871

the age limit has therefore been set at 30 years (which is still assumed to be an optimistic figure). This means that in the model co-firing is assumed economically viable in 233 out of the 585 boilers or in 44.6 GWth out of 78.9 GWth.

4.1.

Power plant co-firing potential

As mentioned above, the term ‘‘technical potential’’ refers to available boiler capacity for burning biomass in co-firing. To calculate the potential for co-firing in the above mentioned 233 boilers, the possible shares of biomass in co-firing were analysed from a technical perspective. Experience of co-firing were found in many countries and especially in the Nordic countries Denmark, Sweden and Finland, which have a good biomass supply, contributing to favourable conditions for co-firing. Many power plants, especially in Sweden, have now switched from co-firing to 100% biofuelled plants due to changes in legislation. Examples of other countries that are using co-firing are the USA, Italy, Germany, Austria, The Netherlands and Switzerland. The reason for using co-firing in Sweden has mainly been the taxation on heat and electricity production, which depends on the fuel used (biomass or fossil fuel). Until recently, the taxation gave a reduced tax if the share of biomass used as fuel was equal to the share of heat relative to the total energy production. The share of biomass in the fuel mix with coal in a Swedish CHP plant has therefore been equal to the factor between heat and electricity production in the CHP plants, which is about 3 to 1. Today, taxation has changed so that the fuel mix used must be calculated for both heat and electricity production. In Poland, the existing ‘‘quota obligation system’’ could create a similar driving force to use co-firing, but with a lower share of biomass. As observed in Sweden, the share of biomass in co-firing is highly dependent on the driving force (i.e. policy/economic and legislation) for using biomass in electricity production. In Poland the ‘‘quota obligation system’’ is currently the most important driving force for the introduction of RES-E. It is reasonable to assume that some of the 233 boilers mentioned above will not be converted to co-firing, which means that the target of biomass share in the others must be slightly above what is required to meet the ‘‘quota obligation system’’ of 7.5% RES-E. This assumption is based on the previously mentioned assumption that most of the increased RES-E production until 2010 will originate from biomass in co-firing and that, consequently, the assumption that each boiler suitable for co-firing at least will be targeted to reach a biomass fraction of 7.5%. Thus, this work will show to what extent the overall 7.5% target can be met, considering constraints with respect to technical limitations and biomass supply. Furthermore, it is assumed that a separate transportation system for the biofuel from the unloading area to the boiler will be built. With a separate system, the capacity decrease in the boiler is limited and the reliability of the plant will be kept at the same level [23]. With a small share of biomass, it can also be assumed that the reduction in efficiency when introducing biomass will be negligible. Finally, it is desirable to keep the share of biomass low in order not to affect the ash quality as the ash is often used in the cement industry. In the

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50

24

11

26

19

PC

w n

4

G

no

1

1

U

600

90 77

80

493

Thermal capacity (GW)

500 Number of boilers

5

4

U nk

G as

G ra

O il

te

FB

PC

0

n

100

nk no w

150

as

178

200

G

250

91

il

Number of boilers

300

110 100 90 80 70 60 50 40 30 20 10 0

O

325

Thermal capacity (GW)

350

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ra te

BIOMASS AND BIOENERGY

FB

872

400 300 200 100

42

25

18

70 60 50 40 30

23

20 10

7

0

4

1

0

Gas

Unknown

0 Hard coal

Brown coal

Oil

Gas

Unknown

Hard coal

Brown coal

Oil

40 133

140 Number of boilers

149

147

120 100 80 52

60 36

40 20

25

29

12

Thermal capacity (GW)

160

34

35 29

30 25 20

15

16

15 9

10 5 0

1

2

0

0 1923- 1934- 1944- 1954- 1964- 1974- 1984- 19941933 1943 1953 1963 1973 1983 1993 2000

1923- 1934- 1944- 1954- 1964- 1974- 1984- 19941933 1943 1953 1963 1973 1983 1993 2000

Fig. 4 – The number (a) and the thermal capacities (b) of different types of boiler in Poland. Number (c) of boilers and the installed capacity (d) in Poland that use a certain fuel. Number (e) and installed capacity (f) of boilers in Poland and the commissioning years. The black bars, in (e) and (f), show the boilers that are less than 30 years old. Based on the Chalmers Power Plant Database and [15,16].

Netherlands and Germany a small share of a secondary fuel in the plants, from which the cement companies collect their ash, is accepted. It is clear from experiences, mainly in Sweden and Finland, that FB boilers are especially suitable for co-firing. The Polish Power Company Elektrocieplownie Warszawskie is planning to implement co-firing in an FB boiler with a share of 5–15%

biomass [24]. The experiences of co-firing in Sweden together with the assumptions discussed above can be summarised in suitable co-firing shares of biomass in FB and PC boilers for Polish conditions, with p15% biomass in FB boiler and p10% in a PC boiler. Experience of straw co-firing is primarily from Denmark, where the PC boilers mainly use straw pellets, which result in

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a higher fuel cost than for unprocessed straw. Many of the PC boilers in Poland are large, which creates logistical problems. These two factors have resulted in PC boilers being considered not suitable for using straw in co-firing. FB boilers are sensitive to sintering problems when using straw and are therefore not considered for co-firing with straw. Grate boilers, however, should be suitable for straw co-firing in Poland, due to their relatively small size, which does not cause logistical problems on the supply side, and the fact that there are existing strawfired grate boilers in operation in Poland. These are heat-only boilers but represent good examples of efficient straw-fire systems [25]. The co-firing limit for grate boilers has been estimated from experience at the Studstrup power plant [26] in Denmark. A possible problem when using straw is corrosion of superheater tubes. According to [26], co-firing of straw in a PC boiler with up to 10% straw does not result in any increase in superheater corrosion rate. However, when using around 20% straw, corrosion rate increased by 100–200% [26]. Suitable co-firing shares of straw in grate boilers are therefore estimated to be p10%. Table 3 summarises suitable co-firing shares of biomass for the modelling employed in this work. These shares have in this work been used as maximum shares of biomass which can be applied in the different types of boiler. In order to calculate the technical potential on a yearly basis, the above mentioned average load hour of 4450 h/year was applied.

4.2.

Technical potential for burning biomass in co-firing

By applying the figures for the maximum share of biomass in co-firing and the operation time (average load factor of

Table 3 – Potential of producing electricity from biomass in co-firing in the year 2010 (% of total electricity production)

With no transport of biomass between the regions. Gives an average transport distance of 60 km Allowing transport of wood fuels (forest residue, fuel wood and energy crops) between the regions. This gives an average transport distance of 81 km for the minimum calculation and 97 km for the maximum calculation (all woody biomass supply is used) Unlimited import of biomass (all the technical potential is used)

Minimum biomass supply potential

Maximum biomass supply potential

1.3

2.8

1.6

4.6

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4450 h/year as given above) to the 233 boilers, a technical potential for burning biomass is obtained for each region. The result is shown in Fig. 5. The figure shows that the major capacity is in the central-southern part of Poland and consists mostly of PC boilers. The FB boilers are situated in three regions: Dolnoslaskie, Slaskie and Mazowieckie. It is also clear that the installed capacity in grate boilers is much lower than for PC and FB boilers.

5.

5.4

Three different limitations for biomass transport. Based on the model calculations.

Results

The results from the modelling of the co-firing potential in 2010 show that this can amount to between 1.3% and 2.8% of the total electricity production in Poland, corresponding to minimum and maximum biomass supply potential in the first scenario (limited transportation). The second scenario calculation, where the biomass is allowed to flow over regional boundaries, gives a potential between 1.6% and 4.6%. Figs. 6 and 7 show the co-firing potential for each region for the first scenario for the minimum and maximum biomass supply potential, respectively. The potential is given in absolute figures (TJ) and as a percentage of the total electricity production as obtained from the model. Figs. 8 and 9 show the results expressed as a surplus of either technical potential or woody-biomass supply potential (not straw), in the first scenario calculation. A surplus of biomass in Figs. 8 or 9 means that the limiting factor for the co-firing potential, in that region, is the boiler capacities for burning biomass. A technical surplus states that the limiting factor is the biomass supply.

5.1.

Straw

In almost all regions, the supply potential for straw is much higher than the technical potential on the conversion side, i.e. the number of grate-fired boilers for power production is too low and the total capacity too small to be able to use the available straw. Consequently, most of the available straw is not being used. However, for the minimum estimate of the straw supply there are four regions with no supply of straw. In two of these (Swietokrzyskie and Podkarpackie), grate boilers are available for co-firing and there is therefore a surplus of technical potential in these regions. If all surplus straw were to be used for electricity production 3–10 TWhe (2–7% of total electricity production) could be produced. It should be noted that in this work no boilers have been found where this surplus straw can be used.

5.2.

5.4

873

Woody biomass

In the case of woody fuels (forest residue, fuel wood and energy crops), it differs from district to district whether the technical or the biomass potential is the limiting factor. Fig. 8 shows that, in the minimum supply estimation, there is a shortage of biomass supply in most regions. In the maximum supply estimation, the location of the biomass is the limiting factor, as can be seen in Fig. 9.

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2360 100 7940

90 1030

2120 740

9660 290 1020

2400 90

400 230

21150 3400 930

610 90

4210

PC boilers

7300

6940 70

80

12710 290 2880 Grate boilers 4660 90

470

FB boilers

Fig. 5 – Total boiler capacity for burning biomass in co-firing with coal in TJ/yr in each region. The capacities are shown for FB, Grate and PC boilers. Based on the Chalmers Power Plant Database, [15,16] and own estimates.

9

2500 TJ % 2000

8 7 6

1500 %

TJ

5 4 1000 3 2

500

1 0

D o Ku ln. j.P om . Lu be l Lu . bu s. Lo dz M . al op . M az ow . O po l. Po dk . Po dl . Po m Sl . as k. Sw W iet. ar .M az W . ie lk . Za ch .

0

Fig. 6 – The potential production of electricity (in TJ and as percentage of total electricity production) from biomass in co-firing in each region for the first scenario calculation (no transport of biomass between regions). Minimum values are used for the biomass supply potential. Based on model calculations.

5.3.

Cross-border transport of biomass

Because the borders between the regions in reality are transparent, the restriction in the first model calculation to keep the supply within the districts is a strong limitation. This is especially so when the results of the first calculation show that in almost all cases a surplus of biomass in one district could be used in a neighbouring district (note that biomass in this case does not include straw, as this fuel is not

economical to transport over long distances). Therefore, the second scenario calculation, in which biomass supply is allowed to flow from one region to neighbouring regions, shows that all biomass supply potential can be used in cofiring. The result is shown in Table 3. The same table also shows the maximum potential of produced electricity from biomass in co-firing if unlimited amounts of biomass are allowed to be imported into Poland, i.e. all the technical potential for co-firing is used.

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875

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2500

9 TJ %

2000

8 7 6

1500

%

TJ

5 4

1000

3 2

500

1 0 Ku j

D

ol n. .P om . Lu be l Lu . bu s. Lo dz M . al o M p. az ow . O po l. Po dk . Po dl . Po m . Sl k. as Sw k. W iet. ar .M az W . ie lk . Za ch .

0

Fig. 7 – The potential production of electricity (in TJ and as percentage of total electricity production) from biomass in co-firing in each region for the first scenario calculation (no transport of biomass between regions). Maximum values are used for the biomass supply potential. Based on model calculations.

750 1820

5820

400

760 20180

9130

490

1250

3050 6310

3430 Boiler capacity surplus

810

6500

14200

1990

Woody biomass supply surplus

Fig. 8 – The surplus of either technical or wood fuel potential in TJ, when minimum values are used for biomass potential, in each region. Based on the first scenario model calculations (no transport of biomass between regions).

5.4.

Emissions and costs

In the reference case (before the implementation of co-firing) the model calculates the total amount of CO2 emissions from power plants to be 165.4 million tonnes. The emissions of CO2 from combustion installations in the energy sector were 164.7 million tonnes in the year 2000 [27]. In September (2004) the Ministry of Environment in Poland, presented a national allocation plan for CO2, in March (2005) the European Commission accepted this allocation plan but the total volume of allowances was decreased from 858.6 to 717.3 million tonnes of CO2 for the 2005–2007 trading period [27,28]. This means that the annual CO2 allowances for electricityproducing plants, for the 2005–2007 trading period, is about

160 million tonnes. When applying co-firing according to the first scenario, the CO2 emissions from fossil fuels will be reduced from 165.4 to between 163.2 and 161.2 million tonnes (minimum and maximum biomass supply potential), equivalent to a decrease in CO2 emissions of 1.3% and 2.6%. The corresponding decrease in the second scenario calculation is between 1.6% and 4.4%. Table 4 displays the reduction in emissions. The emissions of SO2 are not given in absolute figures, the reason being that a large proportion of the flue gases are assumed to have been scrubbed for SO2, which has not been taken into account in the model. Table 5 shows the overall cost obtained from the model for the implementation of co-firing. This cost is shown in relation to capacity (MWe) and produced electricity (kWhe), together with the

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2450 6170 1320

3230 1680 4060

17490 3600

4370

4450 180 4940

4650

12030

5170 930

Boiler capacity surplus Woody biomass surplus

Fig. 9 – The surplus of either technical or wood fuel potential in TJ, when maximum values are used for biomass potential, in each region. Based on the first scenario model calculations (no transport of biomass between regions). Table 4 – Emission reductions in the first scenario calculation (no transport of biomass between regions) when using biomass in co-firing Emission reductions in the first calculation

Minimum biomass potential

Maximum biomass potential

2.2 1.3 1.0

4.3 2.6 2.4

CO2 (million tonnes) CO2 (%) SO2 (%) Based on the model calculations.

investment cost for a new biofuelled CHP and the current electricity price in Poland. The table also gives the calculated CO2-avoidance cost which is around h20 per tonne CO2. The figures in Table 5 are averages of the calculations.

5.5.

Age structure

Fig. 10 gives the age structure of the boilers used for co-firing as obtained in the first scenario calculation for the minimum and maximum biomass supply estimations. The age structure is shown in relation to the total number of boilers built from 1974 and onwards. The boilers not used for co-firing built in late 1990s are mostly natural gas and oil-fired boilers. The figure also shows that for the newest boilers the difference between the maximum and minimum supply estimation is small. For older boilers there is a significant difference. This is due to the fact that almost all new boilers are used in the minimum biomass supply estimation modelling. The maximum biomass supply estimation yields a higher biomass supply and this extra supply is matched with older boilers. It is also possible to see that about 50% of the boilers are used for co-firing in the maximum biomass supply estimation.

Table 5 – The costs for implementing co-firing of biomass and coal in the first scenario calculation (no transport of biomass between regions)

Co-firing Co-firing New biofuelled CHP Electricity price in Poland (2003) CO2-avoidance cost

Unit

Value

Million h/MWe h/MWhe Million h/MWe h/MWhe h/tonne CO2

0.5 18 1.3a 96 16

Based on the model calculations. a [30].

6.

Discussion

The resulting potential for co-firing of biomass with coal is a sensitivity analysis in itself, with one high and one low estimate of the biomass supply potential given in this work. The high estimate is considered as an optimistic estimate, which means that the real potential in 2010 is not likely to exceed this estimate. The most probable outcome is that the biomass supply potential will be somewhere in between the low and the high estimate. In most regions the supply of forest residue, fuel wood and energy crops limit the co-firing potential in FB and PC boilers. At the same time, there is a large supply potential of straw that is not being used in the grate boilers. The surplus of straw is in the range 39–119 PJ/yr. Because straw is a problematic fuel, and more expensive than wood chips in Poland, it has not been used in FB or PC boilers in this work. However, straw constitutes a large RES in Poland that should be used, for example, in heat-only boilers. In the first scenario calculation, the model does not allow biomass supply to be transported across the borders. This

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45 40

Total number of boilers

35

Maximum biomass supply estimate

30

Minimum biomass supply estimate

25 20 15 10 5

2000

1999

1998

1996

1997

1995

1994

1993

1992

1991

1990

1989

1988

1986

1987

1985

1983

1984

1981

1982

1979

1980

1978

1977

1975

1976

1974

0

Fig. 10 – Age structure of the boilers used for co-firing in the two estimates of biomass supply. The total number of boilers commissioned each year is shown together with the number of boilers used by the model. Based on first scenario model calculations (no transport of biomass between regions).

limitation results in an average transport distance of 60 km. Based on the results in Figs. 8 and 9 it is possible to conclude that allowing the woody biomass to cross-regional borders means that the woody biomass will only be transported to a neighbouring region and not across the country. This conclusion is based on the assumption that most regions with a technical surplus have one neighbouring region that has a woody-biomass supply surplus potential. The average transport distance in the second scenario calculation is 81 km for the minimum supply estimation and 97 km for the maximum supply estimation. These transport distances are reasonable and a cross-border flow of woody biomass, as in the second scenario calculation, gives a realistic estimation of the cofiring potential in both biomass supply estimations. This means that between 1.6% and 4.6% of the total electricity in Poland could be produced from biomass in co-firing in the year 2010. If the woody biomass were not allowed to cross-regional borders, the corresponding figures would be 1.3–2.8%. Because of uncertainty in the development of electricity production, it has been assumed that electricity production in Poland will be the same in the year 2010 as in 2002. It is likely that electricity production will increase slightly and this increase will come from new built boilers. These boilers will provide new capacity for biomass co-firing. However, it has already been concluded that the biomass supply is the limiting factor in most regions. This means that an increase in electricity production will lead to a minor percentage decrease in potential of electricity from the biomass share in co-firing, compared to the modelling results. The restriction on biomass combustion in coal-fired plants in this work has been in the commissioning year of the plant and the maximum share of biomass in the boilers. As stated previously, the co-firing capacity is often higher than the biomass supply potential. However, in the first scenario calculation, with no cross-border transport of biomass, there are some regions where the co-firing capacity is the limiting factor. The restriction on the commissioning year was therefore tested with an increase from 30 to 35 years, i.e. all plants

built from the year 1969 until 2000 were made available for cofiring. This resulted in a limited increase in the potential for electricity production from biomass in co-firing by 0.04–0.22 percentage points, in the first scenario calculation. The maximum share of biomass in co-firing was also tested by an increase of five percentage points, which gave an increase of 0.10–0.26% points in the results. These changes are thus low and it was concluded that the results are not sensitive to changes in these restrictions. The results obtained from the cost calculations in the model show an average investment cost of h0.5 million per MWe; an additional cost of producing electricity from biomass in co-firing of h17 per MWhe; and a CO2-avoidance cost of h16 per tonne CO2. The investment cost is a result from the input investment cost/MWfuel and the power plant efficiencies. It is difficult to give an averaged investment cost for all boilers in Poland and the efficiency may vary considerably from one plant to another. However, the resulting figure is about a third of the investment cost for a biofuelled CHP [29]. The additional cost for the electricity produced from biomass co-firing is about 18% of the average electricity price in 2003 [30]. More than 50% of the additional cost originates from a higher biomass fuel cost compared with coal. The development of these costs, including transport, is difficult to determine, especially for biomass as this market is only on the verge of being established. If the Polish government succeeds in the promotion of renewable energy, it can be expected that the demand for biomass will increase and the price will follow. The energy companies that invest in biomass combustion should therefore consider the choice of signing contracts with biomass traders that run over long periods. About one-third of the additional cost is from O&M. The input values for O&M are taken from calculations from a new biofuelled CHP in Sweden. It can be assumed that there are synergies between coal and biomass in co-firing and the O&M costs for biomass in co-firing are therefore lower than for a 100% biofuelled plant. The personnel costs in Poland are also lower than in Sweden, which should reduce the O&M cost.

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The CO2-avoidance cost is calculated from the same additional cost as the extra electricity cost, together with calculations for CO2 emissions from coal combustion (combustion of biomass is assumed to be CO2-neutral). The emissions are based on the carbon content in coal, which may vary for different qualities. However, this variation is seen as a minor source of error.

7.

Conclusions

The modelling in this work estimates the potential in electricity production from co-firing biomass in existing units in the year 2010 to range from 2.3 to 6.6 TWhe. These values correspond to 1.6–4.6% of the total electricity production in Poland. In the year 2010, 7.5% of the electricity produced in Poland is set to come from RES. The current share is about 2%. Thus, the present modelling results show that the biomass share in co-firing could, together with the current share, reach about 3.6–6.6% of the total electricity production. This means that other RES must contribute with about 0.9–3.9% of the total electricity production in the year 2010. Considering this result and the short time left to 2010, it seems unlikely that Poland will reach its RES target by 2010. The variation in the calculated potential of electricity from biomass in co-firing depends on the estimates of the biomass supply potential, which is found to be the limiting factor except in the case of straw. Straw represents a large amount of unused supply, although the use of straw in co-firing is difficult but may be suitable for heat production. Optimising the use of the biomass supply potential gives an increase in electricity price to h17 per MWhe, which is about 18% of the current electricity price (2003). This corresponds to a CO2-avoidance cost of about h16 per tonne CO2. Experience from co-firing in Europe and the USA shows that typically 10–15% biomass (on energy base) can be co-fired in coal plants (which is of interest for Poland today) without any major problems in corrosion, slagging, fouling, fuel handling and fuel feeding [31–34]. A new handling system for biomass should be used in order to ensure the reliability of the plant [33]. R E F E R E N C E S

[1] European Commission White Paper for a Community Strategy and Action Plan COM(97)599 final (26/11/1997). [2] European Commission. The treaty of accession 2003. Brussels: Belgium; 2003. [3] Council of Ministers, Development strategy of renewable energy sector. Warsaw, Poland, 2000. [4] EC Baltic Renewable Energy Centre, European Renewable Energy Council. Renewable Energy Policy review Poland. Altener Programme, 2004. [5] Hoogwijk M, Faaij A, van den Broek R, Berndes G, Gielen D, Turkenburg W. Exploration of the ranges of the global potential of biomass for energy. Biomass and Bioenergy 2003;25:119–33. [6] Berndes G, Hoogwijk M, van den Broek R. The contribution of biomass in the future global energy supply: a review of 17 studies. Biomass and Bioenergy 2003;25:1–28.

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[7] Fischer G, Schrattenholzer L. Global bioenergy potentials through 2050. Biomass and Bioenergy 2001;20:151–9. [8] Pronobis M. Evaluation of the influence of biomass co-firing on boiler furnace slagging by means of fusibility correlations. Biomass and Bioenergy 2005;28:375–83. [9] Hartmann D, Kaltschmitt M. Electricity generation from solid biomass via co-combustion with coal: energy and emission balances from a German case study. Biomass and Bioenergy 1999;16:397–406. [10] Pisarek M, Kunikowski G, Hunder M, Smilgiewicz T, Ganko E, Oniszk-Poplawska A. The comprehensive assessment of the bio-energy development prospects in Poland. Review of biomass resources and potentials. Warsaw, Poland: EC Baltic Renewable Energy Centre; 2004. [11] Smagcz J. The possibilities for energetic utilisation of biomass in Poland. Pamietnik ˛ Pu"awski zeszyt 132 Instituet of Soil Science and Plant cultivation, Pulawy, Poland, 2003. [12] Wo´jcik T. Renewable energy sources in State Forests and programmes of their development. Conference proceedings: Moz˙liwos´ci wykorzystania biomasy na cele energetyczne. Malino´wka, Poland: State Forest National Forest Holding; 2003. [13] Agrobra¨nsle. Willow statistics, 2004. Available at /www. agrobransle.seS. [14] Kja¨rstad J, Johnsson F. Simulating future paths of the European power generation—applying the Chalmers power plant database to the British and German power generation system. In: Proceedings of the seventh international conference on greenhouse gas control technologies, Vancouver, 2004. [15] Agencja Rynku Energii SA. Katalog- Elektrowni i elektrocieplowni przemyslowych. Poland: Warsaw; 2000. [16] Agencja Rynku Energii SA. Public thermal power plants in Poland. Poland: Warsaw; 2002. [17] IPCC. Emission factor database, 2005. Available at /www. ipcc-nggip.iges.or.jp/EFDBS. [18] Central Statistical Office in Warsaw. Poland statistics, 2004. Available at: /http://www.stat.gov.plS. [19] Jansson M. Personal communication on potential willow ¨ rebro, Sweden: Agrobra¨nsle AB; production in Poland. O 2004. [20] European Commission. Reform of the common agricultural policy: a long term perspective for sustainable agriculture: impact analysis. Directorate-General for Agriculture, 2003. [21] Skogsstyrelsen. Skogsstatistisk a˚rsbok 2004. Sweden: Jo¨nko¨ping; 2004. [22] Hillring B. Energi fra˚n skogen. Sweden: Uppsala; 1999. [23] Swiatkowski J. Personal communication Polish power plants. Warsaw, Poland: Energy Office (IEN); 2004. [24] Hinderson A. Personal communication on Polish power plants. Stockholm, Sweden: Vattenfall Utveckling AB; 2004. [25] Okonek M, Pisarek M. Personal communication. Warsaw, Poland: EC Baltic Renewable Energy Centre; 2004. [26] Wieck-Hansen K, Overgaard P, Hede Larson O. Cofiring coal and straw in a 150 MWe power boiler experiences. Biomass and Bioenergy 2000;19:395–409. [27] The Republic of Poland, Ministry of the Environment. National allocation plan for CO2 emission allowances 2005–2007 trading period. Poland: Warsaw; 2004. [28] European Commission. Press release, Emissions trading: Commission decides on Polish allocation plan. IP/05/269, 2005. [29] Ba¨rring M, Nystro¨m O, Nilsson P-A, Olsson F, Egard M, Jonsson P. El fra˚n nya anla¨ggningar. Report no. 03:14, Elforsk, Sweden, 2003. [30] Okonek M. Evaluation of the policy and legal framework and barriers of biomass CHP/DHP in Poland. Warsaw, Poland: EC Baltic Renewable Energy Centre; 2003.

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[31] Tillman DA. Biomass co-firing: the technology, the experience, the combustion consequences. Biomass and Bioenergy 2000;19:365–84. [32] Tillman DA, editor. Co-firing benefits for coal and biomass. Biomass and Bioenergy 2000;19:363–4. [33] Alakangas E, Ja¨rvinen T. Cofiring of biomass—evaluation of fuel procurement and handling in selected existing plants and exchange of information. Final report—part 2. VTT Energy, Jyva¨skyla¨, Finland, 2001. [34] Union of the Electricity Industry. Co-firing of biomass and waste with coal. Ref: 02003Ren9770, Brussels, Belgium, 1997.

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