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

INTRODUCTION 5/25/20162

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. 5/25/20163

Geological Map of Nigeria indicating Lafia Obi coal area 5/25/20164

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 SO 2, NO x and solid particles (SO2 < 400mg/m 3, N0 x < 200 mg/m 3, solid particles < 50 mg/m 3 ); achieve a wide range of load turndown ratio (20-100%); and 5/25/20165

Pressurized fluidized Bed combined cycle for electricical power generation using coal (Sambo,2009) 5/25/20166

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. 5/25/20167

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, NO x, CO and rate of ash generation will be measured and analyzed. 5/25/20168

METHODOLOGY 5/25/20169

PRELIMINARY LABORATORY STUDIES Raw Material Acquisition and Handling Sample Preparation Determination of Physical Characteristics 5/25/201610

PROXIMATE ANALYSIS Volatile Matter Moisture Content Fixed Carbon Ash Content 5/25/201611

ULTIMATE ANALYSIS Hydrogen Content Carbon Content Nitrogen Content Sulfur Content Oxygen Content 5/25/201612

FUEL PREPARATION Sun Drying Separation Crushing(using hammer mill) Sieving (using ISO standard sieve set) 5/25/201613

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Summary of ASTM international standards used in investigation S/NDesignationTitle 1D5192 – 09Standard Practice for Collection of Coal Samples 2D2013/D2013M – 09Standard Practice for Preparing Coal Samples for Analysis 4D3172 – 07aStandard Practice for Proximate Analysis of Coal and Coke 5D3302/D3302M – 10Standard Test Method for Total Moisture in Coal 6D3175 – 07Standard Test Method for Volatile Matter in the Analysis Sample of Coal and Coke 7D3174 – 04Standard Test Method for Ash in the Analysis Sample of Coal and Coke from Coal 5/25/201615

Summary of ASTM international standards used in investigation cont. 8D5373 – 08Standard Test Methods for Instrumental Determination of Carbon, Hydrogen, and Nitrogen in Laboratory Samples of Coal 9D 3179 – 02Standard Test Methods for Nitrogen in the Analysis Sample of Coal and Coke 10D 3178 – 89 (Reapproved 2002) Standard Test Methods for Carbon and Hydrogen in the Analysis Sample of Coal and Coke 11Designation: D3177 – 02 (Reapproved 2007) Standard Test Methods for Total Sulfur in the Analysis Sample of Coal and Coke 5/25/201616

COMBUSTION 5/25/ Fig. 1 Experimental Setup

COMBUSTION 5/25/201618

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. 5/25/201619

EXPERIMENTAL CONDITIONS 5/25/ Table 1: Summary of Experimental conditions Design parametersMaterial/value Type of fuel/ feed sizeLafia-Obi/(5-25mm) Bed material / size (µm)Sandstone/ Bed temperature ( o C ) Static bed height (m)0.1 Fuel feed rate (kg/min)0.2 & 0.3 Bed diameter (mm)150 Fluidization Velocity(l/min) Pressure drop across distributor plate (mmH 2 O)43 Pressure drop across bed (mmH 2 O)428.8 Distributor plate No. of holes311 Diameter of holes (mm)1.5 Thickness (mm)4

RESULTS 5/25/201621

Proximate & Ultimate Analysis 5/25/ AnalysisValue Proximate Analysis Moisture (wt %)2.91 Volatile matter (% 1 )27.19 Ash (% db)18.62 Fixed carbon (%) TOTAL100.00% Colour of ashLight grey Ultimate Analysis (wt% 1 ) C59.29 H40.61 N2.10 S1.81 Gross calorific (KJ kg -1 )23, Table 4.1:Analysis of Lafia-Obi Coal

Sudden temperature drops due to release of volatiles Sudden temperature rise due to ignition of volatile Fluctuations 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 5/25/ Effect of on Lafia-Obi Coal Feed Size on Combustion Bed Temperature

Figure 4.4 Summary of the effects of coal particle size and feed rate on temperature 5/25/ Effect of on Lafia-Obi Coal Feed Size on Combustion Bed Temperature cont.

Increased CO concentration with increased feed size abrupt changes in CO concentration as a result of repeated char particle fragmentation, Reduced CO concentration with increase in average bed temperature 5/25/ Figure 4.6: Effects of coal particle size on CO emission at a coal feed rate of 0.3kg/min Effects of Coal Particle Size on CO Emission

5/25/ Effects of Coal Particle Size on CO Emission cont. Fig. 7 Effect of bed temperature on NOx emissions

NO X formation increased with increasing carbon conversion, attributed to a decrease in NO X reduction in the pores of char particles as they shrank. Tullin, et al., (1993) NO X 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), 5/25/ Figure 4.13 Effect of coal particle size on NO x emission at a coal feed rate of 0.3kg/min Effects of Coal Particle Size on NOx Emission

5/25/ Fig. 9 Graph of flue gas temperature against NOx emissions Effects of Coal Particle Size on NOx Emission cont.

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. 5/25/ Effect of Temperature on CO emission Figure 4.8: Effect of combustion bed temperature on CO emission at a coal feed rate of 0.2kg/min

Coal properties that affect NO X 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 C, the NO x measured during this experiment will be thermal NO x. Lohuis et al., (1992) and Kilpinen & Hupa (1991) 5/25/ Figure 4.10: Effect of temperature on NOX emission at a coal feed rate of 0.2kg/min Effect of Temperature on NOx Emission

Effect of Fuel Feed Rate On Emission 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 5/25/201631

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CONCLUSION 5/25/201633

5/25/ 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.

5/25/ 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.

5/25/ 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

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