-
35 Languages:
Heating - Biomass system - Multiple buildings / Slovenia
Case study assignment
You have been hired by a municipality in Slovenia to investigate the reduction of greenhouse gases and to see if locally produced biomass could be used to heat the community. Gornji Grad's current district energy system is fired by #2 oil and serves 90% of the households and municipal buildings in the community. A wood products company, which is currently not part of the district energy system, has proposed to supply free biomass (wood waste) to the town. In return, the town is to provide the company a free connection to the district heating system and a 50% discount on fuel cost compared to the company's current use of #2 oil. This 50% reduction in fuel cost is roughly equivalent to $73/tonne of wood from the perspective of the municipality.
Site information
Gornji Grad is a community of 2,700 people located in the northeastern part of Slovenia; the nearest meteorological station is in Ljubljana, 50 km to the southeast. Approximately 60 km to the northwest is the Austrian weather station of Klagenfurt. The typical weather in Gornji Grad is considered to be somewhere in between these two cities.
The peak heating load on Gornji Grad's district energy system, adjusted for a normal year, is 1.5 MW. The heating load for its building stock (21,500 m²) is estimated to be 70 W/m². You can assume that the existing connection to the district energy system is 1 building cluster, with the wood company as a 2nd building cluster.
The wood products company has a peak heating load of 750 kW. The company's building has a floor area of 7,500 m² and is located 100 m away from a 100 mm distribution pipe and 250 m from the district heating system's main boiler plant. Only minor modifications within the boiler plant are required to connect the company to the district heating system. In addition to the wood products building heating load, it also has a substantial process heat load. To estimate this load assume that it is equivalent to a 51% "Domestic hot water heating base load."
Case study assignment
You have been hired by a municipality in Slovenia to investigate the reduction of greenhouse gases and to see if locally produced biomass could be used to heat the community. Gornji Grad's current district energy system is fired by #2 oil and serves 90% of the households and municipal buildings in the community. A wood products company, which is currently not part of the district energy system, has proposed to supply free biomass (wood waste) to the town. In return, the town is to provide the company a free connection to the district heating system and a 50% discount on fuel cost compared to the company's current use of #2 oil. This 50% reduction in fuel cost is roughly equivalent to $73/tonne of wood from the perspective of the municipality.
Site information
Gornji Grad is a community of 2,700 people located in the northeastern part of Slovenia; the nearest meteorological station is in Ljubljana, 50 km to the southeast. Approximately 60 km to the northwest is the Austrian weather station of Klagenfurt. The typical weather in Gornji Grad is considered to be somewhere in between these two cities.
The peak heating load on Gornji Grad's district energy system, adjusted for a normal year, is 1.5 MW. The heating load for its building stock (21,500 m²) is estimated to be 70 W/m². You can assume that the existing connection to the district energy system is 1 building cluster, with the wood company as a 2nd building cluster.
The wood products company has a peak heating load of 750 kW. The company's building has a floor area of 7,500 m² and is located 100 m away from a 100 mm distribution pipe and 250 m from the district heating system's main boiler plant. Only minor modifications within the boiler plant are required to connect the company to the district heating system. In addition to the wood products building heating load, it also has a substantial process heat load. To estimate this load assume that it is equivalent to a 51% "Domestic hot water heating base load."
The district heating system is a typical medium temperature system. The pipes were designed with a 25% oversizing factor.
The new, high-efficiency biomass boiler (85% seasonal efficiency) is to be located at the city's existing district heating plant. The community also wants to install a second biomass boiler so that the plant will have 100% standby capacity. The existing heating plant lacks sufficient space for the 2 new biomass boilers.
Tests of the company's wood waste show a dry calorific value of almost 19,000 MJ/tonne with typical moisture content of 40%. The extra electricity demand for the biomass system and circulation pumps is estimated to be 60,000 kWh. Electricity in Slovenia is mostly produced by coal fired power stations. The old oil-fired boilers at both the heating plant and the wood products company have seasonal efficiencies around 60%.
For the greenhouse gas analysis, assume that coal is the fuel for the base case electricity system.
Financial information
Typical financial figures for the analysis are provided by the community: inflation of 1%, debt ratio of 80%, debt interest rate of 6%, debt term of 15 years and a discount rate of 10%. This project will be implemented via a public/private company which has an effective income tax of 28%. Losses can be carried forward. Depreciation is calculated via the declining balance method with a 75% tax basis and a depreciation rate of 25%. The system is assumed to last 25 years. A local supplier quoted €370,000 per biomass boiler.
The average price of electricity is €0.065/kWh and #2 oil is delivered for €0.63/L. The fuel cost escalation is expected to be the same as inflation. As a simplification, you may assume that the price that the city will charge its regular district heating customers for the delivered heat energy will remain unchanged and is the same as what one would pay for conventional oil heat.
Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis.
Solution
The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.
Teacher's notes
Real project
Results
In 1998, the town of Gornji Grad, a community of 2,700 people in northeastern Slovenia, began implementing a biomass-fired community energy system with the connection of 50 buildings to a biomass-fired district heating system. By the end of 2001 over 86% of all buildings were connected to the system. The expected greenhouse gas reductions have been estimated at 40% as compared to the displaced heating fuels. The project will not only produce cleaner air but also increased employment in the area.
Gornji Grad is the first community in Slovenia to use municipally-generated wood waste for heating. The project is held out as a model for other similar communities in Slovenia and other countries. The heating systems that were replaced utilized wood, coal and oil. The main biomass (wood waste) supplier is a minority shareholder (25%) in the town's energy supply company ENGO Ltd.
Total project cost was €4.1 million. A grant for 25% of the costs was received from the Slovenian government and the Phare program of the European Union (EU). Another grant of 15% was given by the government of Austria. The Phare program is one of the three "pre-accession instruments" financed by the European Community to assist applicant countries from central Europe in their preparations for joining the European Union.
The project was recognised as "the climate project of the month" in October 2000, by the Climate Alliance, an association of European cities and municipalities.
System description
The systems consists of two 2 MW biomass-fired boilers designed by Järnforsen Energi in Sweden and built by Järnforsen International in Celje, Slovenia. Wood waste, sawdust and wood chips are mainly supplied by a local company and stored in a silo with automatic discharge system. The biomass is fed into the combustion chambers with a transfer auger. The combustion chambers consist of a sloping reciprocating grate system. Underfire air is introduced through the grate and flue gas is re-circulated to reduce NOX emissions. Overfire air is controlled in different zones to minimize CO emissions. The hot flue-gas then enters the integrated boiler located behind the combustion chamber. The system efficiency is estimated to be 90% when using fuel with 40% moisture content on a wet basis.
The plant is equipped with multi cyclones for particulate removal. The system meets all EU emission criteria for particulate, CO and NOX.
During the summer months only one boiler is used. The control system automatically sets the system output depending on load, time of day and weather conditions.
The district heating system consists of approximately 8,000 m of pipe. The energy consumption of individual customers is calculated automatically and heating bills are issued on a monthly basis.
Lessons learned
The big picture
Roughly 55% of Slovenia is covered by forest, making the country rich in biomass potential. Three other municipalities in Slovenia have now also developed similar biomass community energy systems. The mayors of these cities started the initiatives by establishing a common consortium to become part of the EU's Phare development fund. The mayors believe that the projects will stimulate regional development by providing new jobs, by improving the local environment and by promoting tourism.
Photo
Boiler - Biomass system - District energy - Wood waste, Gornji Grad, Slovenia
References
The new, high-efficiency biomass boiler (85% seasonal efficiency) is to be located at the city's existing district heating plant. The community also wants to install a second biomass boiler so that the plant will have 100% standby capacity. The existing heating plant lacks sufficient space for the 2 new biomass boilers.
Tests of the company's wood waste show a dry calorific value of almost 19,000 MJ/tonne with typical moisture content of 40%. The extra electricity demand for the biomass system and circulation pumps is estimated to be 60,000 kWh. Electricity in Slovenia is mostly produced by coal fired power stations. The old oil-fired boilers at both the heating plant and the wood products company have seasonal efficiencies around 60%.
For the greenhouse gas analysis, assume that coal is the fuel for the base case electricity system.
Financial information
Typical financial figures for the analysis are provided by the community: inflation of 1%, debt ratio of 80%, debt interest rate of 6%, debt term of 15 years and a discount rate of 10%. This project will be implemented via a public/private company which has an effective income tax of 28%. Losses can be carried forward. Depreciation is calculated via the declining balance method with a 75% tax basis and a depreciation rate of 25%. The system is assumed to last 25 years. A local supplier quoted €370,000 per biomass boiler.
The average price of electricity is €0.065/kWh and #2 oil is delivered for €0.63/L. The fuel cost escalation is expected to be the same as inflation. As a simplification, you may assume that the price that the city will charge its regular district heating customers for the delivered heat energy will remain unchanged and is the same as what one would pay for conventional oil heat.
Prepare a RETScreen study, documenting any assumptions that you are required to make, and report on the significant conclusions from this analysis.
Solution
The worked-out solution is the data file selected from within the RETScreen Project Database. The user automatically downloads the Project Database file while downloading the RETScreen software.
Teacher's notes
- If the wood products company were to be connected to the existing distribution pipe (via 100 m of new pipe), RETScreen calculates that the existing distribution pipe would have to be 125 mm in diameter to handle the load. The existing pipe is only 100 mm however and therefore cannot handle the extra demand. Consequently, the longer piping route (250 m) has to be used to connect the company directly to the heating plant.
- The biomass is nominally free for the city, but the city needs to deliver heat to the wood products company for 50% of the company's previous fuel cost. Therefore, the value of the 50% discount is essentially the price paid by the city for the biomass.
- The annual "O&M" and the "Periodic Costs" that are shown are incremental relative to the corresponding costs for a conventional oil-fired heating plant.
- The real project, as described in the Results section, differs from the one modelled in RETScreen. This is due to the fact that a simplified project scenario is presented for the purposes of this case study.
- There are no "Credits" for displacing existing oil-fired equipment as there was no mention in the case study that they had to be replaced. If this was the case then the financial viability of the project would improve.
Real project
Results
In 1998, the town of Gornji Grad, a community of 2,700 people in northeastern Slovenia, began implementing a biomass-fired community energy system with the connection of 50 buildings to a biomass-fired district heating system. By the end of 2001 over 86% of all buildings were connected to the system. The expected greenhouse gas reductions have been estimated at 40% as compared to the displaced heating fuels. The project will not only produce cleaner air but also increased employment in the area.
Gornji Grad is the first community in Slovenia to use municipally-generated wood waste for heating. The project is held out as a model for other similar communities in Slovenia and other countries. The heating systems that were replaced utilized wood, coal and oil. The main biomass (wood waste) supplier is a minority shareholder (25%) in the town's energy supply company ENGO Ltd.
Total project cost was €4.1 million. A grant for 25% of the costs was received from the Slovenian government and the Phare program of the European Union (EU). Another grant of 15% was given by the government of Austria. The Phare program is one of the three "pre-accession instruments" financed by the European Community to assist applicant countries from central Europe in their preparations for joining the European Union.
The project was recognised as "the climate project of the month" in October 2000, by the Climate Alliance, an association of European cities and municipalities.
System description
The systems consists of two 2 MW biomass-fired boilers designed by Järnforsen Energi in Sweden and built by Järnforsen International in Celje, Slovenia. Wood waste, sawdust and wood chips are mainly supplied by a local company and stored in a silo with automatic discharge system. The biomass is fed into the combustion chambers with a transfer auger. The combustion chambers consist of a sloping reciprocating grate system. Underfire air is introduced through the grate and flue gas is re-circulated to reduce NOX emissions. Overfire air is controlled in different zones to minimize CO emissions. The hot flue-gas then enters the integrated boiler located behind the combustion chamber. The system efficiency is estimated to be 90% when using fuel with 40% moisture content on a wet basis.
The plant is equipped with multi cyclones for particulate removal. The system meets all EU emission criteria for particulate, CO and NOX.
During the summer months only one boiler is used. The control system automatically sets the system output depending on load, time of day and weather conditions.
The district heating system consists of approximately 8,000 m of pipe. The energy consumption of individual customers is calculated automatically and heating bills are issued on a monthly basis.
Lessons learned
- The implementation of this project would have been very difficult without the participation of motivated municipal officials.
- Involvement of domestic equipment suppliers increases the project's potential for success.
- Transfer of project management and technical know-how from similar projects is essential.
- Small municipalities often have limited capabilities concerning energy data collection and planning, energy management, engineering finances and management of technical projects.
- Without proper supervision, consultants and engineering companies can have a tendancy to exceed the optimal financial costs of projects by primarily considering technical issues instead of the overall financial performance.
The big picture
Roughly 55% of Slovenia is covered by forest, making the country rich in biomass potential. Three other municipalities in Slovenia have now also developed similar biomass community energy systems. The mayors of these cities started the initiatives by establishing a common consortium to become part of the EU's Phare development fund. The mayors believe that the projects will stimulate regional development by providing new jobs, by improving the local environment and by promoting tourism.
Photo
Boiler - Biomass system - District energy - Wood waste, Gornji Grad, Slovenia
References
- Granstrand, Mats, "Personal communication," Järnforsen Energi, 2002.
- Öko-Institut, Instruments and Options for Environmental Policy during the Accession Process of EU Associated Countries in the Area of Environment and Energy, Germany, April 2000.
- Ziegler, Urban, "Personal communication," PEMtec, 2002.
