The suitability of energy plants as fuel for power boilers

1. The suitability of energy plants as fuel for power boilers Aadu Paist Tallinn University of Technology Thermal Engineering Department 2005

2. Content • Introduction • Energy plants as fuel • Typical combustion characteristics of energy plants • Firing facilities • Potential of biofuels and peat long-run

3. Introduction • In Estonia the role of renewables (biomass, biogas, hydro, wind) is not considerable in electricity production (about 1%) • The main fuel in electricity production is oil shale • In heat generation the role wood fuels and biogas 17 % and peat 4% Estonia has declared to increase the share of renewables in electricity production up to 5,1 % by the year 2012

4. Forest resources in Estonia Data from Estonian Agricultural University • According to last taxation data of Estonian forests we have 2,25 Mha (51,5 % from country area) forest land with growing stock of 462 mln s.m3. By ownership these are divided : • Forest district of State - 830 000 ha (37%), • Private forests - 680 000 ha (30%), • Forests under land reform - 710 000 ha (31%), • Other State forests - 15 000 ha (1%), • Other forests - 15 000 ha (1%). Relation between State and private forests in counties vary substantially.

5. Energy plants as fuel • Using energy plants as fuel in boiler, furnaces of the dryers and in other combustion equipment assumes that we have sufficient knowledge of the combustion characteristics • Heterogeneous, non-prognosticated and seasonally different quality of the energy plants as fuels presumes that before we start to use energy plants we thoroughly analyse the environmental aspects, efficiency and lifetime of the combustion equipment. • Essential characteristics which we must take into consideration in the design and operation of combustion equipment are: moisture, ash content, ash-fusibility temperatures, ash composition, density and so etc.

6. Reed and cattail characteristics

7. Moisture • Moisture content of reed and cattail is lower in April and May and at the same time heating value and energy content is higher (table 1, Fig 1). • The best time for storing their energy plants is late winter – early spring, to reduce energy consumption for drying. • Moisture content of cattail (table 1, Fig 2) is higher than for read, because the stalk cattail is spongy from inside, which help to keep moisture also in early spring

8. Seasonal changes in moisture content(read)

9. Seasonal changes in moisture content (cattail)

10. Fig 1. Cattail: Wr =30-40 %, Qrl=9-10 MJ/kg, Er=2,5-3,0 MWh/t, Ad=5-6 %

11. Combustion characteristics of read, cattail and flax.

12. Ultimate analysis and chlorine content in read, cattail and flax

13. Read-, Cattail- and Flax-Ash Chemical Composition

14. Read and Cattail Ash-fusibility Temperatures

15. Combustion Characteristics. Conclusions • Combustion characteristics, structure and look of read is rather similar to straw, which is in use as fuel for energy production in many countries. • Analysis show that read as fuel is higher quality than straw, because fusibility temperatures are over 1 400 °C, for example for oats straw fluid temperature only  900 °C (high content of K2O) In winter thanks for low moisture content ,up to 15 %, heating value of the read ca 15 MJ/kg (4,2 kWh/kg) . Ash content is also similar to straw, 4 %. • Using cattail as fuel is needful additional drying or mixing with dry bio fuels. • In spring read and cattail moisture content is lowest and plants are suitable for direct burning or granulating.

16. Data of bio fuels and peat boilers

17. Boilers for pellets Technology transfer Pellet–fed plants are usually intended for domestic heating and consist of a boiler and a closed storage for pellets. A screw feeder feeds the fuel into the hearth located in the boiler furnace see fig.Combustion air is supplied by a blower.

18. Fully automated combustion equipment for pellets

19. Boilers for big bales (Batch-fired boilers) Technology transfer The boiler is fired with 1 bale a time. A tractor fitted the bale through a feeding grate at the front of the boiler. Capacity of the boiler smaller than 1 MW, an efficiency 75 % and CO content below 0,5 %. In Estonia has three such type of boilers

20. Burning bales of straw and energy plants in “cigar burner” Technology transfer Bales of straw and energy plants possible to use for energy production in heating plants (cogeneration plants) where the bales through a feeding grate pushed to “cigar burner”. Capacity of the boilers 4 – 6 MW

21. Facility for burning scarified straw or energy plants Technology transfer • Pales of straw or energy plants is copped/scarified and transported to the furnace by screw conveyors or blowers. Burning of copped plants take place on the hearth, mechanical grate or in the fluidized bed. Copped/scarified energy plants possible to burn together with fossil fuels, wood chips and peat. Adequate combustion tests made on the experimental equipment in TED of TUT and Ldt Kuressaare Soojus.

22. Fluidized bed boiler for burning crushed fuelTechnology transfer • Kolle • Tsüklon • Ülekuumendi • Ökonomaiser • Katalüsaator • Õhueelsoojendi • Kütuse punker • Liiva punker

23. Stocker burner elaborated in TED of TUT

24. Forecast of wood fuel supply for coming 30 yearsEstonian Agricultural University

25. Potential of biofuels and peat today and long-run • * These biofuels are available for cogeneration of heat and power,if needful equipment is installed.