Experiences from operation of CFB Boilers for Combustion of Local Lignite of Low Heating Value in Turkey, comparison of Turkish and Serbian lignites

Transcription

1 Experiences from operation of CFB Boilers for Combustion of Local Lignite of Low Heating Value in Turkey, comparison of Turkish and Serbian lignites Karol Zuzčák, Miloš Teleky SES Tlmače a.s., Slovakia

2 1. Abstract Recently, there has occurred a demand on Turkish market to increase capacities of electric power generation based on coal combustion. It is concerning combustion of local lignite as there are large reserves of lignite in various places across the country as well as coal imported to Turkey and combusted in power plants situated alongshore. Lignite mined in Turkey is of different quality depending on location. Its calorific value ranges from 900 kcal/kg to 2500 kcal/kg. Its water content reaches up to 55%. The fuel is often of high surface humidity that causes problems with its transporting and storing. Imported fuels are bituminous coal. Two circulating fluidized bed boilers were commissioned by SES Tlmače on Turkish market. It was the fluidized bed boiler of 120 t/h steam output for combustion of local lignite in the heating and power plant of the aluminium smelter in Seydisehir. In the second boiler of 460 t/h steam output it is combusted the imported fuel bituminous coal from the Ukraine. The boiler is in the power plant near Zonguldak city on the north coast of Turkey. Currently, SES Tlmače a.s. works on two projects of thermal power plants in Turkey for combustion of local lignite of total output of 535 MWe. There are four fluidized bed boilers, of 370 t/h steam output each. 2. Electrical Power Market in Turkey The Turkish energy market is witnessing rapid growth and liberalization process with the recent privatizations, licensing tenders and strategic partnerships. The sector has been remarkably active recently and offers major opportunities to investors. Energy consumption in Turkey is low when compared with Western European countries. However, the large, young and increasing urban population together with expected industrial development potential in Turkey represents a significant growth potential. Currently, GDP of Turkey Source: World Bank Diagram No.1 GDP of Turkey

3 Turkey is a major energy importer, as the increase in its energy consumption has outpaced domestic production. Substantial investment in the energy sector will be required in the near future in order to meet the increasing demand in Turkey. The Turkish electricity market is one of the fastest growing in the world. Installed capacity has continued to rise regularly between 1998 and 2009 from 23,354 MW to 44,766 MW. In line with the increase in the number of natural gas fired power plants and hydroelectric plants, both constitute the highest share in energy resources with 34 percent each, followed by hard coal and lignite forming 24 percent together. Coal is mainly used for power generation in Turkey. 30 percent of the total primary energy consumption in Turkey is derived from coal. Only one-half of the coal used is produced domestically in Turkey, which makes Turkey's coal market dependent on imports. The Turkish electricity market is currently going through a liberalization process and rapid growth. The market is experiencing a transition into a competitive electricity market in order to attract private sector investments and maximize efficiency. Electricity demand in 2008 equalled 198 TWh, representing a 4.3 percent annual growth from Electricity demand has been growing in parallel with the urbanization and industrialization level and economic development. Also supported by the increase in population, electricity demand in Turkey holds great potential for further growth. Diagram No.2 Electricity Generation and Demand The current energy supply including the existing power plants, the licensed plants and those under construction was expected to be insufficient to cover the base energy demand. On the other hand, the decline in economic activity, which has affected electricity demand, has also delayed the electricity imbalance. After a recovery in electricity demand, there will be a requirement for further capacity to balance supply and demand. The estimated investment required for the period of is between USD billion, which comprises USD billion for generation, USD 6-7 billion for transmission and USD 7-8 billion for distribution.

4 3. Coal Mining in Turkey and Serbian and Turkish Lignite comparison According to studies there are 181 well- explored lignite deposits and 98 lignite deposits, which require further investigation. Generally, large lignite deposits are mined by TKI (Turkish Coal Enterprises ) and low reserve lignite deposits are mined by private enterprises. Hard coals are produced only by TTK (Turkish Hard Coal Enterprise) in Zonguldak. Picture No.1 Turkish Lignite and Hard coal deposits 3.1 Hard Coal Resources in Turkey The most important hard coal reserves of Turkey are located only around Zonguldak province in the northwest of Anatolia (Picture No.1). The hard coal reserves of 1.1 billion tonnes have been proved according to the results of the studies in the Zonguldak basin. The average net calorific value is kcal/kg (25,12 MJ/kg). Zonguldak hard coals are mainly consumed by the Catalagzi thermal power plant and heavy industry plants. Partly Zonguldak hard coal is used by new 160 MWe unit with CFB boiler supplied by SES.

5 3.2 Lignite Resources in Turkey The majority of lignite deposits in Turkey are used as open-pit mines. Total lignite coal reserve is estimated to be around 8.25 billion tonnes. Investigations and privatizing lignite mining are going on in Turkey. Regional reserve distributions and average chemical properties of Turkish lignite are given in Table No.1. The lignite has generally calorific values between kcal/kg ( kj/kg), water content between %, ash content between %, and total sulphur content between %. Almost 80% of the total reserves have calorific values below 2500 kcal/kg ( kj/kg), 13% are in the range kcal/kg, while only 7% are over kcal/kg ( kj/kg). The lignite having low heating value is generally burned in power plants while the lignite having relatively high calorific value is utilized for domestic and industrial use. Table No.1 Properties of Turkish Lignite 3.3 Serbian Turkish Lignite comparison Serbia has own Lignite reserves, maily concentrated in two coal basins. It is Kostolac coal basin and Kolubara coal basin. To compare Turkish and Serbian Lignite we have used available data of coal composition of main Serbian coal basins. Coal composition of Kostolac and Kolubara coal basins are mentioned in table below No.2 Serbian Lignite composition.

6 Kostolac coal basin Kolubara coal basin Total moisture % 39,22 43,6-55 Ash % 17,8 9-18,5 Sulphur % 1,18 0,35-1,0 Calorific value MJ/kg 10,02 7,1-8,9 Calorific value kcal/kg Table No.2 Serbian Lignite composition Verified balance and non-balance coal reserves in OM Drmno calculated in 2007 are 870 mil.tons. Verified balance and non-balance coal reserves in Kolubara cola basin calculated in 2009 are mil.tons. Comparison of Serbian and Turkish Lignites shows that range of heating value of Serbian lignites 7,1 10 MJ/kg is within Turkish range 5 14,6 MJ/kg. Ash content in the Lignite is less in Serbian Lignite in comparison to Turkish and vice-versa moisture content in Turkish Lignite is less in comparison to Serbian one. 4. Turkish Lignite Firing CFB Boiler In the heating plant of ETI Aluminium in the city Seydisehir, SES Tlmače built CFB boiler for local low grade Lignite burning with capacity 120 t/h. The first contact with the client launched in April The customer is an owner and an operator of the aluminium works. The aluminium works included heating plant with several decades old oil boilers. The customer decided to reconstruct its heating plant by replacing old oil boilers to new CFB boiler burning of lignite from the Picture No.2 Bayavsar Lignite mine nearby coal mine. In 2006 the customer bought the Lignite mine Bayavsar a few kilometres distant from the heating plant. Opencast coal-mining is used in Bayavsar coal mine. For this reason, the customer thought tooperate

7 the mine just during the warmer season of the year. During the winter season, the customer presumed to use coal from stock yard close to the heating plant. In November 2006 SES Tlmače a.s. signed a contract for CFB boiler for ETI Aluminium Seydisehir. CFB boiler steam parameters are: 120 t/h, 438 C, 4,6 MPa Contractual parameters of burned Lignite are as follows: Moisture content 20-48,2% Heating value kcal/kg Ash content 16,7 31,5 % Based on available information and concerns regarding degradation of fuel quality mainly during raining season we decided to use the safest configuration of the boiler refractory lined combustor. The only heating surface in circulating circuit is an evaporator bundle in FBHE (fluid bed heat exchanger). Combustor, cyclone, seal pot and all ducts were made of steel plates internally refractory lined. FBHE is a key element of CFB boiler, that allows to operate boiler with the wide Picture No.3 CFB boiler Seydisehir range of fuels (in this case the wide range of heating value and water content) and the wide range of boiler loads. Due to the wide range of produced flue gas amount, the boiler is equipped with flue gas recirculation. Recirculation operation is considered in case of burning fuel of heating value at the top of the contracted heating value range with a low moisture content and subsequently a low generated flue gas amount. In the reality, the coal heating value is usually at bottom of the heating value range and during a certain period it is less than the minimal contracted heating value. In the diagram No.3 you can see the main properties of Lignite burned in CFB boiler Seydisehir from January to April 2009.

8 Diagram No.3 Lignite properties During May 2009 performance tests were performed at the nominal and the minimal boiler load with Lignite of heating value 1305 kcal/kg. The performance tests confirmed the contracted guarantee values. The results are in the Table No.3. Measured Measured Value Unit Guaranteed value value at Nominal value at Minimal Result load load Steam flow (nom./min.) t/h 120 / ,6 47,6 Fulfilled Steam parameters MPa / C 4,6 / 438 4,6 / 442 4,6 / 441 Fulfilled SO 2 mg/nm Fulfilled No x mg/nm Fulfilled

9 CO mg/nm Fulfilled Dust mg/nm Fulfilled Table No. 3 Seydisehir CFB boiler Performance tests results During commissioning the boiler was running very well and even with fuel out of the contracted range of burning, desulphurization processes were running good and the performance values were reached. The main problem regarding low calorific lignite burning was moisture of delivered fuel. The total moisture was not an issue, but surface moisture was a real problem that we had to solve before successful handing over the plant to the client. Fuel was delivered from the opencast coal mine Bayavsar. During long-term rains coal was mined from the mine full of water. Even after a certain storage time at the stock yard near the heating plant, coal was wet and made problems on all way from the stock yard up to the boiler inlet. The critical points were coal bunkers, coal crushers and spills. Wet coal was very sticky and many outages of individual coal lines due to blockages happened. Together with the client we agreed on measures to minimize the problems arising from high surface moisture of fuel: - roofed coal stock yard were built - air nozzles were used to ensure coal flow in critical coal transport places Picture No.4 New roofed coal stock yard

10 Picture No.5 Air nozzles installed on coal bunker During the boiler operation within the guarantee period, the boiler was operated with lignite of the heating value close to the lower limit, in some cases below it. As the guaranteed operating range of the coal heating value was wide, client asked us to make test with fuel with heating value at the upper limit of the heating value range. Coal suitable for such test was the coal from mine Ilgin, which is relatively near Seydisehir. Ilgin coal used for test had the following characteristics: Coal heating value 2254 kcal/kg Moisture content 40,1 % Ash content 18,8 % The test lasted 2 days. Various mixtures of Bayavsar coal and Ilgin coal were tested and finally just Ilgin coal was burned.

11 Ilgin coal portion vs. heating value Heating value of coals mixture kcal/kg Ilgin coal portion % Diagram No.4 Ilgin coal proportion vs. heating value coal Tests confirmed that the boiler was able to operate at nominal load with the above mentioned coals mixture, or with coal of the heating value at the upper limit of the guaranteed heating value range. Operation of the boiler with recirculation fan was demonstrated to the client. Influence of the recirculation rate on the combustor temperature was evaluated. 5. Hard Coal Firing CFB Boiler in Turkey In Zonguldak province, SES built CFB boiler for hard coal burning. The main parameters of the boiler are as follows: Electric power of the unit 160 MWe Live steam flow 465 t/h Live steam temperature and pressure 563/165 C/bar Reheated steam temperature and pressure 563/41 C/bar The boiler was designed for burning of hard coal with following properties: Coal heating value 4,48 6,49 kcal/kg Moisture content 7 15 % Ash content %

12 Actually, in the boiler there are burned coals of different origin. There is supplied coal from the Ukraine, Russia, Columbia and South Africa. At the time of lack of imported coal, local hard coal from Zonguldak province had been burned. The boiler nominal load was achieved will all supplied coals. The boiler has been operated since summer 2010 and most of the time it has been operated at the nominal load. At the time of writing this paper, the preparation of performance tests was under progress. Picture No.6 CFB boiler in Zonguldak for hard coal burning 6. New Local Coal Firing CFB Boilers New projects with CFB boilers for local Lignite burning are in preparation in Turkey. Picture No.5 CFB boiler in Zonguldak for hard coal burning In two of them SES had signed the contracts. The projects are in the stage of engineering and finalising of financing. The projects are in different locations. One of them is in Bolu province and the other one in Cankiri province. The boilers are designed for local lignite with following properties: Bolu Goynuk Yildizlar Lignite heating value 2,43 2,29 kcal/kg Moisture content 30 26,5 % Ash content 26 34,1 %

13 Bolu Goynuk 2x 373 tph Yildizlar 3x 369 tph Picture No.7 Lignite burning CFB boilers in Turkey ready for construction 7. Conclusion Turkey economy rapidly grew in the last decade and it has high potential to economy growth in the near future but it is connected with increase of power demand. The main local source of energy are large lignite reserves that are relatively easy accessible by opencast mining. The reason why these reserves were not widely used up to now is poor quality of most of lignite. This makes harder to use these reserves with PC boilers. CFB technology gives an opportunity to use local lignite in different size of boilers with possibility to operate boilers in a wide range of load without supplementary fuel and with good economy. Experiences with our CFB boiler in Seydisehir proved that lignite of the heating value of about 1000 kcal/kg is possible to burn if a boiler is designed accordingly. Design and operating experiences gained with boilers for Turkish Lignites can be fully reflected in design of CFB boilers for Serbian power plants which will burn Serbian Lignites.