INVESTIGATION OF THE BEHAVIOUR OF LAFIA-OBI COAL IN A FLUIDIZED BED COMBUSTION CHAMBER

1. INVESTIGATION OF THE BEHAVIOUR OF LAFIA-OBI COAL IN A FLUIDIZED BED COMBUSTION CHAMBER O.T. POPOOLA and A. A. ASERE Department of Mechanical Engineering,Faculty of Technology,Obafemi Awolowo University,Ile-Ife, Nigeria. OAUTekCONF 2011 Faculty Of Technology Conference

2. INTRODUCTION

3. General Background • There is a large deposit of coal in the middle belt and eastern part of the Nigeria which remains underexploited. • The coal reserves in Nigeria are estimated to be in excess of 2.5 billion tonnes. • Available data show that Nigerian coals are mainly sub-bituminous steam except for the Lafia-Obi bituminous coal • Coal is a major source of energy. Coal has played this important role for centuries – not only providing electricity, but also as an essential fuel for steel and cement production, and other industrial activities. • The value of coal is partially offset by the environmental impacts of coal combustion.

4. Geological Map of Nigeria indicating Lafia Obi coal area

5. General Background cont. • Fluidized Bed Combustion is a Clean Coal Technologies that: • effectively and inexpensively combust low-grade coals with high content of moisture (≤60%), ash (≤ 70%) and Sulphur (≤ 10%), • achieve high combustion efficiency (>99%); • achieve boiler flexibility with type and quality of coal; • provide effective environmental protection from SO2, NOx and solid particles (SO2 < 400mg/m3, N0x< 200 mg/m3, solid particles < 50 mg/m3); • achieve a wide range of load turndown ratio (20-100%); and

6. Pressurized fluidized Bed combined cycle for electricical power generation using coal (Sambo,2009)

7. OBJECTIVES • The objectives of this study are to : • investigate the effect of Lafia-Obi coal particle sizes on combustion bed temperature; • determine the effects of the coal particle sizes and combustion temperature on emission characteristics; and • evaluate the coal ash content at various operating conditions.

8. SCOPE • This study covers the combustion of Lafia-Obi coal in a fluidized bed with the view to generate electricity. • Emphasis will be on variation of coal combustion feed size at varying coal combustion feed rate and • The resultant effects on combustion bed temperature, NOx , CO and rate of ash generation will be measured and analyzed.

9. METHODOLOGY

10. PRELIMINARY LABORATORY STUDIES • Raw Material Acquisition and Handling • Sample Preparation • Determination of Physical Characteristics

11. PROXIMATE ANALYSIS • Volatile Matter • Moisture Content • Fixed Carbon • Ash Content

12. ULTIMATE ANALYSIS • Hydrogen Content • Carbon Content • Nitrogen Content • Sulfur Content • Oxygen Content

13. FUEL PREPARATION • Sun Drying • Separation • Crushing (using hammer mill) • Sieving (using ISO standard sieve set)

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15. Summary of ASTM international standards used in investigation

16. Summary of ASTM international standards used in investigation cont.

17. COMBUSTION Fig. 1 Experimental Setup

18. COMBUSTION

19. DATA COLLECTION • Temperature- 6 Chromel-Alumel Thermocouples and 6-channel digital readout were used to measure the variations in the combustion bed and freeboard temperatures. • The temperature along the height of the atmospheric reactor was taken at distances of 2, 10, 40, 60 and 80 cm above the gas distributor • The composition of the flue gas at the various conditions was determined using a gas analyzer. • The ash and fragmented coal particles content of the extracts after quenching at different operation conditions were tested and classified. • A U-tube manometer was used to measure the pressure drop through the bed. • Air was supplied by a 4hp centrifugal blower and the air flow rate was measured by means of a rotameter.

20. EXPERIMENTAL CONDITIONS Table 1: Summary of Experimental conditions

21. RESULTS

22. Proximate & Ultimate Analysis Table 4.1: Analysis of Lafia-Obi Coal

23. Effect of on Lafia-Obi Coal Feed Size on Combustion Bed Temperature Sudden temperature drops due to release of volatiles Sudden temperature rise due to ignition of volatileFluctuations in temperature is coal particle size dependent As the coal particle size increases, char combustion rate and in consequence, bed temperature decreases Figure 4.2: Effects of coal particle size on temperature at a coal feed rate of 0.2kg/min

24. Effect of on Lafia-Obi Coal Feed Size on Combustion Bed Temperature cont. Figure 4.4 Summary of the effects of coal particle size and feed rate on temperature

25. Effects of Coal Particle Size on CO Emission Increased CO concentration with increased feed sizeabrupt changes in CO concentration as a result of repeated char particle fragmentation, Reduced CO concentration with increase in average bed temperature Figure 4.6: Effects of coal particle size on CO emission at a coal feed rate of 0.3kg/min

26. Effects of Coal Particle Size on CO Emission cont. Fig. 7 Effect of bed temperature on NOx emissions

27. NOX formation increased with increasing carbon conversion, attributed to a decrease in NOX reduction in the pores of char particles as they shrank. Tullin, et al., (1993) NOX concentration decreases with increasing particle size. This investigation was carried out above the critical average diameter of the Lafia-Obi coal Jing et al., (2007), Effects of Coal Particle Size on NOx Emission Figure 4.13 Effect of coal particle size on NOx emission at a coal feed rate of 0.3kg/min

28. Effects of Coal Particle Size on NOx Emission cont. Fig. 9 Graph of flue gas temperature against NOx emissions

29. Effect of Temperature on CO emission Theoretically, as the bed temperature increase, there is an increase in the rate of char combustion and an increase in the CO oxidation rate; this situation causes lower CO concentration in the flue gases. The level of the scatter for the lines is an indication of the level of variation exhibited by spontaneously varying rates of reaction which has been attributed to the fragmentation of the coal articles in the fluidized bed combustor. Figure 4.8: Effect of combustion bed temperature on CO emission at a coal feed rate of 0.2kg/min

30. Effect of Temperature on NOx Emission Coal properties that affect NOX emissions include nitrogen content of the coal, coal reactivity, and mineral makeup of the coal. Because this experimental procedure occurred at a temperature lower than 10000C, the NOx measured during this experiment will be thermal NOx. Lohuiset al., (1992) and Kilpinen & Hupa (1991) Figure 4.10: Effect of temperature on NOX emission at a coal feed rate of 0.2kg/min

31. Figure 4.16: Effect of feed rate on NOx emission at a coal FED of 10mm Figure 4.17: Effect of feed rate on CO emission at a coal FED of 10mm Effect of Fuel Feed Rate On Emission

33. CONCLUSION

34. CONCLUSION The bench-scale fluidized bed combustor methods Modified in this program has provided relevant information for assessing the behaviour of Lafia-Obi coal in Fluidized Bed Combustion.

35. CONCLUSION The studies conducted revealed that Lafia-Obi coal has low moisture, high volatile matter and very high fixed carbon content. The volatile matter content, places Lafia-Obi in the medium-volatile bituminous rank.

36. CONCLUSION • This study has provided useful empirical projection of emissions of greenhouse gases from FBC combustion of Lafia-Obi Coal • This data obtained is useful in application of fluidized bed combustion for energy production using Lafia-Obi Coal

37. ThAnKyOu