DISTRICT HEATING SYSTEMS FROM LIGNITE FIRED POWER PLANTS TEN YEARS EXPERIENCE IN GREECE

Transcription

1 DISTRICT HEATING SYSTEMS FROM LIGNITE FIRED POWER PLANTS TEN YEARS EXPERIENCE IN GREECE E. Karlopoulos 1, D. Pekopoulos 2, E. Kakaras 1 1. Centre for Research and Technology Hellas/Institute for Solid Fuels Technology and Applications 4 th km N.R.Ptolemaida-Kozani P.O. BOX 95, 50200, Ptolemaida, Greece Tel: Fax: karlopoulos@lignite.gr 2. Regional Development Agency of West Macedonia S.A. 1-3, Fon Karagianni Str. GR50100, Kozani, Greece Tel: Fax: engin@anko.gr Abstract Roughly, a 70% of the total electricity production in Greece is covered by the combustion of domestic lignites. The major part of the lignite thermal power plants is assembled in northern Greece, where the climatic conditions require considerable heating loads to meet the demands in heating and hot water for use in the domestic and tertiary sector. Since 1993, these needs are covered in the city of Kozani through the modern installation of a district heating system. The system utilises part of the produced steam in the 1200 MW el lignite power station of Agios Dimitrios, which is located 18 km from the entrance of the city. The peak heating load exceeds the 125 MW th, with an annual demand of roughly MWh. The annual amount of heat is produced by 90% in the lignite power plant and by 10% in an 80 MW th peak load unit, feeding with oil or alternatively LPG. The aim of this paper is to present the installation of the district heating system in Kozani, focusing on the systems of rational management of energy, on the environmental and economic benefits from the operation to date, as well as on the prospects of the dissemination of experience to other cities in Greece. 1. Introduction District heating is an efficient and environmentally friendly energy technology which involves the production, transportation and distribution of hot water for domestic heating. It has been used in Greece since 1993 and two installations are today in operation in Kozani and Ptolemaida, while two more installations are under construction in the towns of Aminteo and Megalopolis. The main characteristics of the urban areas served by this technology are the adverse climate conditions due to their high altitude and also their vicinity to lignite fired power plants which are the main source of thermal energy used for district heating installations in Greece. Up to now, the most common practice of heating in Greece has been individual central heating. Each system serves only one building and uses in the vast majority of buildings, heating oil. The development of District Heating (DH) systems and consequently the reduction of the atmospheric emissions in the cities of Ptolemaida and Kozani (as well as in Aminteo and Megalopolis in the near future) during the winter time are significant for environmental improvement of in the area concerned. The aim of this paper is to present the experience gained from more than ten years of district heating system in the city of Kozani, as well as to present briefly the current status of district heating sector in Greece.

2 2. Current Status of District Heating Sector in Greece Greece lies between the latitudes 35 and 42. In general, the climate is mild Mediterranean, although it varies according to the latitude, the vicinity to the sea and the geomorphology of each region. The segregation of the country into three geographical zones, considering their climatic conditions and according to existing regulations for heat insulation, as defined by the Presidential Decree, 362/4.7.79, is shown in figure 1. Taking 18 0 C as basic temperature, the number of heating degree-days in Zone A, which is the warmest zone, is below 900, in Zone B it ranges between 900 and 1300, and in Zone C it is above Figure 1: The three geographical zones of Greece according to their climatic conditions Heating requirements in Greece are covered mainly by the use of diesel oil. Only recently has the use of natural gas begun to be promoted in big cities situated near the main distribution pipe line (Athens, Thessalonica, Komotini) with a view to reducing environmental impact and administration costs. The mean value of the energy required for the heating and hot water production in the oldest of the existing buildings, due to their insufficient insulation, is significantly increased compared to the energy requirements of new buildings, which are constructed in accordance with new regulations. In Greece, district heating is used almost exclusively for heating private and public buildings in urban areas with relatively high population density. From 1994 to 2002 the total heat capacity covered by district heating networks has increased significantly and by over 65% in the last 5 years [2]. The heating load covered by district systems is shown in figure 2.

3 Even though there are available data for the annual consumption of heavy oil for heating, they cannot be considered reliable because large proportions of heavy oil, due to their low price, are used for other applications apart from heating. However, the data for heating diesel sales are reliable. During 1999 a total of 3,173,401 tons were used, covering about 51.5% of the heating energy requirements MWth Year Figure 2: Heating Load covered by District heating systems in Greece The cooling loads are almost exclusively covered by electricity. There are no available data for the individual housing consumption of electricity. Assuming that approximately 1/3 of the total electricity consumed by the houses and office buildings concerns the conditioning of the area and the production of hot water, its participation in the coverage of conditioning loads, in 1998, is estimated at 12.0%. 3. District Heating System of Kozani 3.1 General description Kozani s district heating system started in 1993 and today serves more than customers who rent or own their apartments ( citizens, approximately). The total surface area heated amounts today to m 2. The contracted heat capacity amounts to Mcal/h, of which about 5% covers the public sector. The installed thermal power for serving the base load today is 70 ΜWth which comes from units 3 and 4 of Ag. Dimitrios lignite fired power station located 18 km outside the town. The hot water distributed by the primary network has outgoing return temperatures of C 65 0 C respectively. The transport and distribution to the customers thermal substations is carried out with the help of 3 pump stations. The peak load is covered by 3 boilers equipped with oil and LPG burners with a capacity of 10 MW th each and another two with a capacity of 27.5 MW th each. The total distribution network has a length

4 of 285 km while in the town of Kozani consumer thermal substations have been placed. The company responsible for operating the system is the Municipal District Heating Company of Kozani. 3.2 Heat demand The heat demand, as well as the fluctuation between mean monthly and peak load daily demand are presented in figures 3 and 4 respectively. The total degree-days are about 2500, while the district heating system serves the costumers from October until the end of April. Heat load (%) Duration (h/year) Figure 3: Annual heat load duration curve PEAK LOAD (%) Time of day PEAK LOAD OCTOBER NOVEMBER DECEMBER JANUARY FEBRUARY MARCH APRIL MAY Figure 4: Mean monthly and peak load fluctuation The peak heating load exceeds 125 MW th, with an annual demand of roughly MWh. The annual amount of heat is produced by 90% in the lignite power plant and by 10% in a 80 MW th peak load unit, feeding with oil or alternatively LPG.

5 3.3 Basic technology characteristics The main technical characteristics of the basic load system, the lignite fired power plant, are presented in table 1: Table 1: Technical parameters of the basic load system Parameter Nominal thermal load Supply temperature of hot water Return temperature of hot water Value 70 MW th C 65 0 C The heat extraction from the lignite fired thermal power plant takes place through a two-stage steam extraction for the feeding of two condensers /heat exchangers, connected in a series. 3.4 Transmission and distribution system The transmission and distribution system is affected through a two-pipe system in closed circulation. The pipes are installed in parallel, one pipe for the supply of the hot water to the consumers and the other pipe for the return of the hot water for reheating, as it is shown in picture 1. Picture 1: A Two-pipe distribution system for supply and return of the hot water. In each building there is a thermal substation with indirect connection. The primary side is the district heating distribution network and the secondary side is the central heating building s network. Each building s thermal substation consists of the heat exchanger, a control unit, a load control valve, a flow limitation valve and an energy meter. The basic process diagram is presented in figure 5.

6 Figure 5: Basic process diagram of Kozani s DH System

7 4. Energy Taxation & Prizing Policy 4.1 Pricing policy The pricing policy followed by the district heating company in the town of Kozani since it started operating was determined by the following factors: The legal status and the public welfare character of the companies, Their economic viability, The attraction of new customers to their district heating networks, The covering of the financial and operating requirements of the companies, and finally The parameters which determine the energy market on a national level and especially the cost of diesel oil Bearing in mind the above, the selling price of thermal energy for the companies consumers is about 65% of its production cost using heating oil. To determine the final cost, the length of the heating period 7 months and the efficiency of boilers ( %) were taken into consideration. In practice, the benefit for consumers so far form the operation of the installation has been more than 40% if we take into account the fact that the boilers which were replaced were old and poorly maintained and therefore inefficient. Table 2: Fuel types used for domestic space heating in Greece (prices are for 2000) Cost per MWh Fuel Type Lower Heating Value Without VAT 18% VAT 18% Included District Heating 25,30 29,85 Briquettes KJ/kg 11,20 13,22 Firewood KJ/kg 13,00 15,34 Diesel / LT 27,82 32,83 LPG / Kg 29,90 35,28 Natural Gas / Nm3 38,19 45,06 As is indicated in the table above [3], the cost of the district heating systems operation is significantly low. This cost results from the low cost energy supplied from the Public Power Cooperation (PPC), owner of the lignite fired power plant, to the Municipal Enterprises, which carry out the management of the systems, and also from the attempt of Municipality Enterprises to attract the interest of consumers. With the improvement of the living standard, although they show lower prices, solid fuels are not preferable due to the difficulties of using and storing. The fuel that is almost exclusively used in the central heating of Greek buildings is heating oil, which has a significantly lower price than electricity and the installations for heating production are not expensive. The utilization of a cheap night electricity rate for heating is possible only if serious investments for the enhancement of the electrical installations and the purchase of heat accumulator take place. It is expected that natural gas will cover, in the near future; significant conditioning loads, substituting heating oil and electricity.

8 5. Environmental Aspects It has been proved that the district heating systems have made significant contribution to reductions of gas emissions in the cities of Kozani and Ptolemaida during the winter period. Based on data collected from the Municipal enterprise of Ptolemaida, the average smoke concentration in the air during January 1988 (before DH) was 58 µg/m 3, while in January 1995 (after DH) was 13 µg/m 3. The relevant values for SO2 were 55 µg/m 3 and 19 µg/m 3, respectively. As for Kozani the average smoke concentration in the air during January of 1988 was 62 µg/m 3, while in January 1995 it was 22 µg/m 3 [5]. The relevant values for SO 2 were 170 µg/m 3 and 15 µg/m 3. µg/m^ Smoke (before DH) Smoke SO2 (before DH) SO2 Figure 6: Average smoke and sulphur oxides air concentration, before and after the operation of the DH system in the city of Kozani The sulphur contained in heating oil and also the deficient combustion conditions in small central heating boilers in towns are to a large extent the factors responsible for the concentration of sulphur oxides, nitrogen oxides and particulate matter in the towns atmosphere which have adverse effects on public health and also at the environment. In addition, when there is no wind the atmosphere id divide into layers which comprise relative smooth isothermal surfaces. When the temperature of the layers of air increases form the earth s surface towards the upper layers we have the greenhouse effect. As a result of this, the pollutant emissions from low level central heating chimneys in towns are not diffused and therefore they appear as pollution, which makes the environments in towns much worse. On the other hand the concentrated emissions of pollutants from tall chimneys are usually diffused in the higher atmosphere layers not causing serious problems. 6. Conclusions Since the district heating system was set in operation in 1993, the following benefits to the city of Kozani, its residents as well as the national economy, have been reported: The operation of the DH system has contributed significantly to the reduction of gas and dust emissions and especially in a city which is greatly affected by the 60-years old neighboring lignite industry To date, every year the operation of the DH system substitutes more than 20,000 ton oil equivalents, with an obvious benefit for the national economy

9 For every resident there is an annual saving of 70 from the use of DH system instead of oil. Consequently, the city of Kozani provides disposable income 2,900,000 per year The operation of the DH system provides potential for further development of the area in the primary and secondary sectors of the economy (e.g greenhouses or special plantations) 7. References 1. Ministry of Development Integrated Information System 2. Greek National Statistic Service 3. District Heating Applications in Greece and the optimized exploitation of domestic fuel sources CERTH / Institute for Solid Fuels Technology & Applications, May Greek Electricity market in Greece - Energy Regulation Authority, Annual activities Report 2002 of Municipal District Heating Company of KOZANI