SEE 2006: Bangkok, Thailand Least-cost NO x Emissions Control in a Fluidized-bed Combustor Fired with Rice Husk Kasama Janvijitsakul and Vladimir I. Kuprianov School of Manufacturing Systems and Mechanical Engineering, Sirindhorn International Institute of Technology, Thammasat University, Thailand 1
Production of Rice Husk 2
Objectives 1. To study the effectiveness of two least-cost techniques aimed at minimizing NO x emissions from a fluidized-bed combustor firing rice husk: - air-staged combustion - adding water to as-received fuel. 2. To study the effects of operating conditions (through variation of the secondary-to-total air ratio) and fuel properties (through variation of the fuel-moisture content) on combustion and emission characteristics of the reactor. 3
Materials and Methods 4
Experimental Set-up with a 400 kw th Conical Fluidized Bed Combustor Flue gas G T Probe G T Insulation Ash Flue gas analyzer G T Fuel Invertor Motor Air distributor primary air Air G G G G T T secondary air T Burner T Sand LPG Tank Flow meter F Flow meter F Data acquisition PC Secondary Blower Primary Blower Note: F - Flow meter T - Thermocouple G - Gas Sampling Point - Control Valve - Butterfly valve 5
Measurement of Gas Concentrations NO, CO and O 2 concentrations were measured in flue gas at different locations in the conical FBC and at the cyclone exit using a Testo-350 gas analyzer. 6
Experimental Planning: Independent Variables Air-staged combustion: Secondary-to-total air ratio (S/T): 0, 0.2 and 0.4; Fuel feed rate (FR): about 80 kg/h; Total excess air (EA): about 60%. Conventional combustion of rice husk for variable fuel-moisture content: Moisture content (MC): 7.3, 18.4, 28.0 and 38.2%; Fuel feed rate: about 80 kg/h; Excess air: about 65%. 7
Properties of Rice Husk Used in the Combustion Tests with Air-staging Property Proximate analysis (wt.%, as-received basis): Moisture Ash Ultimate analysis (wt.%, as-received basis): Carbon Hydrogen Oxygen Nitrogen Sulfur LHV (MJ/kg) Sample 1 7.30 15.7 42.82 4.45 29.38 0.37 0.02 15.71 8
Properties of Rice Husk Used in the Combustion Tests with Variable Fuel-Moisture Content Property Sample 2 Sample 3 Sample 4 Proximate analysis (wt.%, as-fired basis): Moisture 18.4 28.0 38.2 Ash 13.8 12.2 10.4 Ultimate analysis (wt.%, as-fired basis): Carbon 37.69 33.26 28.55 Hydrogen 3.92 3.46 2.97 Oxygen 25.86 22.82 19.59 Nitrogen 0.33 0.29 0.25 Sulfur 0.02 0.01 0.01 LHV (MJ/kg) 13.53 11.64 9.64
Results and Discussion 10
Effects of Air-staging on the Axial Temperature Profiles in the Conical FBC Firing 80 kg/hr of Rice Husk at (Total) EA 57% Temperature ( o C) 1200 1000 800 600 400 200 0 Secondary air EA = 55.4 %, S/T = 0.4 EA = 56.5 %, S/T = 0.2 EA = 59.0 %, S/T = 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Height above air distributor (m ) 11
Effects of Air-staging on the Axial O 2 Concentration Profiles in the Conical FBC Firing 80 kg/hr of Rice Husk at EA 57% 25 O 2 concentration (vol.%) 20 15 10 5 Secondary air EA = 55.4%, S/T = 0.4 EA = 56.5%, S/T = 0.2 EA = 59.0%, S/T = 0 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Height above air distributor (m) 12
Effects of Air-staging on the Axial CO Concentration Profiles in the Conical FBC Firing 80 kg/hr of Rice Husk at EA 57% CO concentration (vol.%) 6 5 4 3 2 1 EA = 55.4%, S/T = 0.4 EA = 56.5%, S/T = 0.2 EA = 59.0%, S/T = 0 Secondary air 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Height above air distributor (m) 13
Effects of Air-staging on the Axial NO x Concentration Profiles in the Conical FBC Firing 80 kg/hr of Rice Husk at EA 57% NO x concentration (ppm) 500 400 300 200 100 EA = 55.4%, S/T = 0.4 EA = 56.5%, S/T = 0.2 EA = 59.0%, S/T = 0 Secondary air 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Height above air distributor (m) 14
Effects of Air-staging on the NO x and CO Emissions from the Conical FBC Firing 80 kg/hr of Rice Husk at EA 57% 200 500 NOx emissions (ppm, 7% O2) 160 120 80 40 NOx emissions CO emission 400 300 200 100 CO emission (ppm, 7% O2) 0 0 0.2 0.4 Secondary to total air ratio 0 15
Effects of the Fuel-Moisture Content on the Axial Temperature Profiles in the Conical FBC Firing 80 kg/hr of Rice Husk at EA 65% Temperature ( o C) 1200 1000 800 600 400 200 EA = 59.0%, MC = 7.3% EA = 66.6%, MC = 18.4% EA = 62.7%, MC = 28.0% EA = 66.5%, MC = 38.2% 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Height above air distributor (m) 16
Effects of the Fuel-Moisture Content on the Axial O 2 Concentration Profiles in the Conical FBC Firing 80 kg/hr of Rice Husk at EA 65% O 2 concentration (vol.%) 25 20 15 10 5 EA = 59.0%, MC = 7.3% EA = 66.6%, MC = 18.4% EA = 62.7%, MC = 28.0% EA = 66.5%, MC = 38.2% 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Height above air distributor (m) 17
Effects of the Fuel-Moisture Content on the Axial CO Concentration Profiles in the Conical FBC Firing 80 kg/hr of Rice Husk at EA 65% CO concentration (vol.%) 6 5 4 3 2 1 EA = 59.0%, MC = 7.3% EA = 66.6%, MC = 18.4% EA = 62.7%, MC = 28.0% EA = 66.5%, MC = 38.2% 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Height above air distributor (m) 18
Effects of the Fuel-Moisture Content on the Axial CO Concentration Profiles in the Conical FBC Firing 80 kg/hr of Rice Husk at EA 65% NO x concentration (ppm) 500 400 300 200 100 EA = 59.0%, MC = 7.3% EA = 66.6%, MC = 18.4% EA = 62.7%, MC = 28.0% EA = 66.5%, MC = 38.2% 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Height above air distributor (m) 19
Effects of the Fuel-Moisture Content on the NO x and CO Emissions from the Conical FBC Firing 80 kg/hr of Rice Husk at EA 65% 200 400 NO x emissions (ppm, 7%O 2) 150 100 50 NOx emissions CO emission 300 200 100 CO emission (ppm, 7% O 2) 0 0 0 10 20 30 40 Fuel-moisture content (%) 20
Conclusions Both air-staging and variation in the fuel quality results in substantial effects on the axial CO and NO x concentration profiles in the conical FBC firing rice husk. With implementation of air-staged combustion, NO x emissions from the conical FBC can be reduced by 15% (at S/T = 0.4); however, the CO emission is expected to increase by 67%. By increasing the fuel-moisture content from 7.3 to 38.2%, NO x emissions from the conical FBC can be reduced by 15%; however, the CO emission is expected to increase by about 40%. 21
Acknowledgements The Authors would like to acknowledge sincerely the financial support from the Royal Golden Jubilee Ph.D. Program, The Thailand Research Fund. 22
THANK YOU! 23
Chemical Reactions Related to CO Formation/Reduction in the Conical FBC for Conventional Combustion of Biomass Fuel CO concentration (vol.%) Formation Reduction Quasi-equilibrium Height above air distributor (m) CO formation: C + CO 2 2CO C + H 2 O CO + H 2 2C + O 2 2CO CO reduction: CO + O 2 CO 2 CO + H 2 O CO 2 + H 2
Chemical Reactions Related to NO x Formation/Reduction in the Conical FBC for Conventional Combustion of Biomass Fuel NOx concentration (ppm) Formation Reduction Quasi-equilibium NO formation (homogeneous): HCN+1/2O 2 CNO CNO + 1/2O 2 NO + CO NH 3 + 5/4O 2 NO+3/2H 2 O NO formation (ash-catalysed): HCN + 7/4O 2 NO + CO 2 + H 2 O NO reduction: Height above air distributor (m) NO + CO 1/2N 2 + CO 2 NO + NH 3 N 2 + 3/2H 2 O