Advanced Control Methodology for Biomass Combustion Stefan Bjornsson A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering University of Washington 2014 Committee: Igor V. Novosselov, Chair Philip C. Malte John C. Kramlich Program Authorized to Offer Degree: Department of Mechanical Engineering Table of Contents List of Figures .................................................................................................................................................iii List of Tables ................................................................................................................................................... vi Chapter 1 Introduction ................................................................................................................................ 2 1.1 Motivation ............................................................................................................................................. 2 1.2 Objectives .............................................................................................................................................. 3 Chapter 2 Literature Review & Fundamental Concepts ................................................................. 5 2.1 Biomass .................................................................................................................................................. 5 2.2 Biomass Combustion ......................................................................................................................... 8 2.2.1 Heating & Drying ........................................................................................................................ 9 2.2.2 Solid Particle Pyrolysis ............................................................................................................. 9 2.2.3 Gas Phase Pyrolysis & Volatile Combustion ................................................................. 13 2.2.4 Char oxidation .......................................................................................................................... 13 2.3 Chemical Kinetics ............................................................................................................................ 14 2.4 Chemical Reactor Network Models .......................................................................................... 17 2.5 Pollutant Formation ....................................................................................................................... 19 2.5.1 Carbon Monoxide .................................................................................................................... 19 2.5.2 Particulate Matter ................................................................................................................... 20 Chapter 3 Experimental Data Collection & Results ....................................................................... 25 3.1 Furnace Description ....................................................................................................................... 25 3.2 Experimental Setup ........................................................................................................................ 27 3.3 Experimental Results ..................................................................................................................... 28 3.3.1 Dec. 12th 2013 Burn ................................................................................................................ 28 i 3.3.2 Air Staging Effects ................................................................................................................... 32 3.4 Conclusions ........................................................................................................................................ 34 Chapter 4 Chemical Reactor Network Development .................................................................... 35 4.1 Chemical Composition of Wood & Kinetics ........................................................................... 35 4.2 CRN Configuration .......................................................................................................................... 37 4.2.1 PFT1 ............................................................................................................................................. 38 4.2.2 PSR2.............................................................................................................................................. 40 4.2.3 PSR3.............................................................................................................................................. 40 4.2.4 PFR4 ............................................................................................................................................. 40 4.3 Conclusions ........................................................................................................................................ 41 Chapter 5 CRN Model Validation .......................................................................................................... 42 5.1 Dec. 12th 2013 Burn ........................................................................................................................ 42 5.2 Effects of Air Staging on CO Concentration ........................................................................... 46 5.3 Conclusions ........................................................................................................................................ 49 Chapter 6 Conclusions............................................................................................................................... 50 Chapter 7 Future Work ............................................................................................................................. 52 7.1 CRN Based on CFD Simulations ................................................................................................. 52 7.2 Chemical Species and Reaction Rates ...................................................................................... 54 7.3 Model Temperature Input ............................................................................................................ 56 Low-Cost Sensors, Heat Transfer Model & CRN Info. ........................................... 57 Bibliography ................................................................................................................................................ 111 ii List of Figures Figure 1.1: Overview of factors influencing biomass combustion [3]. ............................................. 3 Figure 2.1: Left: Lignocellulose – a matrix of cellulose and hemicellulose held together by lignin [5]. .................................................................................................................................................................. 6 Figure 2.2: Lignin fragment [7]. ....................................................................................................................... 6 Figure 2.3: Sequential stages of wood combustion Figure from [10]. .............................................. 8 Figure 2.4: TGA and DTG results of four wood samples. Figure taken from Van Loo [3]. ..... 11 Figure 2.5: TGA and DTG analysis of white oak [12]. ........................................................................... 12 Figure 2.6: Major stages in combustion of a solid biomass particle [3]. ....................................... 14 Figure 2.7: Left: PSR is a steady-state, steady-flow, perfectly mixed reactor. Right: PFR is a steady-state, steady-flow reactor and has no axial mixing. ............................................................... 17 Figure 2.8: Gas turbine combustor modeled with a CRN consisting of two PSR elements and a PFR [14]. WSR stands for well stirred reactor and is practically equivalent to a PSR for the purpose of this figure. ...................................................................................................................................... 18 Figure 2.9: CO emissions from a) a simple, manually charged wood boiler b) a down-draught wood log boiler c) an automatic furnace with combustion technology as of 1990; d) an automatic furnace with enhanced combustion technology as of 1995 [20]. .............................. 20 Figure 2.10: Graphical overview of soot formation from fuel species [7]. .................................. 21 Figure 2.11: Evolution of CO and PAH with combustion temperature [3]. ................................. 22 Figure 2.12: Particle size distribution of PM from residential wood furnaces on a mass basis [24] . ........................................................................................................................................................................ 24 Figure 2.13: Number concentration of particles from residential wood furnaces [24]. ........ 24 Figure 3.1: Experimental biomass furnace .............................................................................................. 25 Figure 3.2: White Oak burning in the biomass furnace. ...................................................................... 26 Figure 3.3: Experimental furnace and data acquisition system. ...................................................... 28 Figure 3.4: White oak fuel used in one of the experiments. .............................................................. 29 Figure 3.5: Fuel weight and temperatures in