1. Pellet Stove Efficiency Alliance for Green Heat BNL Workshop (Gael Ulrich 7 April 2016)

2. Heat Exchanger combustion products T af = adiabatic flame temper ature Q flue gases T = ? Black Box Combustor/Reactor ash T = ? fuel 25 o C air 25 o C Q Efficiency = Fuel Energy useful heat Black box model of a biomass combustor showing quantities that define and determine efficiency

3. Heat Exchanger combustion products Q flue gases Black Box Combustor/Reactor ash fuel air 2 1 3 4 25 T af = ? useful heat T fg 5 T ash Preliminary process flow sketch for a biomass combustor.

4. CH 1.4 O 0.6 N 0.005 S 0.007 + (1+ e) x [O 2 + 3.76 N 2 + 0.03 H 2 O] CO 2 + [0.7 + (1 + e)(0.03 x)] H 2 O + 0.005 NO + 0.007 SO 2 + x [eO 2 + (1+ e) 3.76 N 2 ] CH 1.4 O 0.6 N 0.005 S 0.007 + 1.06 (1+ e)[O 2 + 3.76 N 2 + 0.03 H 2 O] CO 2 + [0.7 + (1 + e)(0.03)] H 2 O + 0.005 NO + 0.007 SO 2 + 1.06 [e O 2 + (1+ e) 3.76 N 2 ] Biomass Composition CH 1.4 O 0.6 N 0.005 S 0.007

5. Wood Pellets (4.5% water in fuel, 50% excess air for combustion) Stream Chart/Mass Balance (g/s) Componentm.w.FuelAirCombustion Products Flue Gases Ash Stream 1Stream 2Stream 3Stream 4Stream 5 C120.515 H1.00.060 O2O2 320.4122.180.73 S320.010 Ash300.005 H2OH2O180.0470.0380.625 N2N2 280.0037.18 CO 2 441.89 SO 2 640.019 Total 1.0529.4110.45 0.005

6. combustion products T af = adiabatic flame temperat ure fuel 25 o C air 25 o C a b c d H 2 O(liquid) 25 o C H 2 O(gas) 25 o C Reaction CO 2, H 2 O( l ), O 2, N 2 1 g/s x HHV = - 20,000 J/s +1440 J/s Enthalpy path chosen to migrate from reagents to products in a biomass/air flame.

7. 18,560 J/s 1460 deg-C 150 deg-C 1340 J/s

8. combustion products T af = adiabatic flame temper ature fuel 25 o C air 25 o C a b c d H 2 O(liquid) 25 o C H 2 O(gas) 25 o C Reaction CO 2, H 2 O( l ), O 2, N 2 1 g/s x HHV = - 20,000 J/s +1440 J/s e T fg = flue gas exit temperature Q Enthalpy path including heat exchange step d to e.

9. 18,560 J/s 1460 deg-C 150 deg-C 1340 J/s Δ h de = Q = 18,560 J/s – 1340 J/s = 17,220 J/s

10. Q 17,220 J/s e = -------------- = ------------ = 86% Fuel Energy 20,000 J/s Adiabatic Flame Temperatures and efficiencies for burning wood pellets at various percentages of excess air with flue gases exiting at 150 o C. Air % X's Air T af, ( o C) Efficiency at T fg = 150 o C 30 1640 87.5% 50 1460 86% 100 1180 84% 200 860 80.5% 400 500 69% 700 300 53% 1000 230 41%

11. Flue gas oxygen and CO 2 concentrations in combustion calculated for the burning of 4.5% moisture wood pellets at various percentages of excess air. [1] % Excess Air CO 2 Concentration Oxygen Concentration Wet Basis Dry Basis Wet Basis Dry Basis 0 17.3% 18.9% 0.0% 0.0% 30 13.7% 15.4% 4.4% 4.9% 50 11.9% 12.7% 6.3% 6.7% 100 9.2% 9.6% 9.7% 10.2% 200 6.3% 6.5% 13.3% 13.8% 300 4.8% 5.0% 15.2% 15.8% 400 3.8% 3.9% 16.3% 16.7% 500 3.2% 3.3% 17.1% 17.5% [1]Volumetric or molal concentration, the standard convention for gases.

12. Calculated efficiencies for firewood burners (30% moisture) [top figure] and wood pellet burners [bottom figure] shown as a function of excess air rate and flue gas temperature.

13. Calculated efficiencies for pellet stoves. (Alliance for Green Heat, September 2015[Medium firing rate]; St. Croix and Pleasant Hearth data added March 2016) Stove Flue Gas (dry) % X's Air Flue Gas Efficiency e Brand O 2 CO 2 Temp. ( o C) (Figure 9b) Enviro 18.7% 2.2% 840% 148 48 % Ravelli 16.6% 4.2% 390% 197 62 % Englander 16.0% 4.7% 315% 223 63 % Quad 17.7% 3.3% 520% 162 61 % Harman 13.8% 6.9% 190% 204 74 % Piazzetta 12.9% 7.8% 160% 204 76 % St. Croix 18.1% 2.7% 620% 91 76 % Pleasant Hearth 16.0% 4.8% 320% 161 71 %

14. Calculated CO emissions of pellet stoves studied in the September 2015 Alliance for Green Heat test series. CO emissions Stove (As measured) (mg/kJ of Normalized Brand % X's Air Efficiency e (ppm) (Rank) heat deliv'd) (Rank) Ratio* (ppm)** Enviro 840% 48% 474 (5) 2.97 (8) 5.1 1724 Ravelli 390% 62% 407 (3) 1.05 (5) 1.8 757 Englander 315% 63% 465 (4) 1.00 (2) 1.7 759 Quad 520% 61% 347 (2) 1.14 (6) 2.0 868 Harman 190% 74% 959 (8) 1.25 (7) 2.2 1081 Piazzetta 160% 76% 506 (6) 0.58 (1) 1.0 506 St. Croix 620% 76% 331 (1) 1.01 (3) 1.7 946 Pleasant Hearth 320% 71% 532 (7) 1.03 (4) 1.8 869 *Normalized to Piazzetta as the reference. **Rationalized with Piazzetta as reference using Wikipedia formula.