O - Mechanical Engineering

Energy from biomassCourse outline1. Biomass macro systems Global warming and resources‣ Biomass properties and characterization‣ Conversion processes2. Biomass micro systems3. Practical work/ Mechanical Engineering 18-11-2011 PAGE 2

Characteristics of biomass fuels• Wide range of fuel types• Important for• Conversion technology• Plant design• Homogeneity• Economy of scales• Standardization• CEN, ISO, DIN, ASTM/ Mechanical Engineering 18-11-2011 PAGE 4

Biomass properties• Internet databases• ECN www.ecn.nl/phyllis• DoE Biomass program• Wood (untreated, treated)• Grass• Manure• Waste• Sludge• Straw• Husk/shell/pit• Organic residue• Algae• Vegetable oil/ Mechanical Engineering 18-11-2011 PAGE 5

Physical characteristics (1)Moisture contentStorage, dry-matter lossesVolatile content/compositionAsh contentThermal decomposition,combustion technologyDust emission, ash manipulationFixed carbonCombustion technologyCalorific/HeatingValueFuel utilization, plant design/ Mechanical Engineering 18-11-2011 PAGE 6

Physical characteristics (2)Ash meltingSafety, process controlFungiHealth risksBulk densityLogisticsParticle density, heatcapacity, conductivityDimension, shape,distributionThermal decompositionConveying, drying, bridging,combustion technology/ Mechanical Engineering 18-11-2011 PAGE 7

Chemical properties / elements (1)Carbon CHydrogen HOxygen ONitrogen NChlorine ClSulphur SFluor FHeating ValueHeating ValueHeating ValueNO x , N 2 O emissionsHCl, PCDD/F emissions, corrosionSO x emissions, corrosionHF emissions, corrosion/ Mechanical Engineering 18-11-2011 PAGE 8

Chemical properties / elements (2)Potassium KSodium NaMagnesium MgCalcium CaPhosphor PHeavy metalsCorrosion, ash meltingCorrosion, ash meltingAsh melting, utilizationAsh melting, utilizationAsh utilisationEmission, ash melting/ Mechanical Engineering 18-11-2011 PAGE 9

Structure of woodSoftwoodHardwood/ Mechanical Engineering 18-11-2011 PAGE 10

Composition of woody biomassTracheids/ Mechanical Engineering 18-11-2011 PAGE 11

Composition of woody biomassCombination of three CHO components1. Cellulose2. Hemicellulose3. Lignin/ Mechanical Engineering 18-11-2011 PAGE 12

Composition of woody biomass1. Cellulose (C 6 H 10 O 5 ) n• Structure, fibre walls• Carbohydrate (sugar)• Polymer of glucose C 6 H 10 O 6/ Mechanical Engineering 18-11-2011 PAGE 13

Composition of woody biomass2. Hemicellulose (C 5 H 8 O 4 ) n• Encasing of cellulose fibre• Carbohydrate• Other than glucose• Dissolvable/ Mechanical Engineering 18-11-2011 PAGE 14

Composition of woody biomass3. Lignin (C 40 H 44 O 6 )• Binding agent / strength• Non-sugar polymer• Aromatic structure/ Mechanical Engineering 18-11-2011 PAGE 15

Composition of woody biomassCellulose Hemicellulose LigninBeech 45.2 32.7 22.1Birch 44.5 36.6 18.9Pine 45.0 26.4 28.6Spruce 48.5 21.4 27.1/ Mechanical Engineering 18-11-2011 PAGE 16

Characterization methods• Proximate analysis• Moisture content• Volatile matter• Fixed carbon• Ash content• Ultimate analysis• C, H, O, N, S, …• Bomb calorimeter• Calorific/Heating value/ Mechanical Engineering 18-11-2011 PAGE 17

Proximate analysis• Place biomass sample on a scale in an oven filled with inert gas• Heat up to 110˚C → moisture evaporates• Measure weight loss → moisture content• Wet basis:• w = (wet weight-dry weight)/wet weight• Dry basis:• u = (wet weight-dry weight)/dry weight• Conversion:• w = u/(1+u) u = w/(1-w) u > w/ Mechanical Engineering 18-11-2011 PAGE 18

Moisture contentMoisture content may vary a lot/ Mechanical Engineering 18-11-2011 PAGE 19

Proximate analysis continued• Sample is heated (carbonized) to 950˚C• Volatile matter (VM) is released from sample• Tar: monomers of (hemi)cellulose, lignin polymers• Gas: CO, H 2 , CH 4 , CO 2 , H 2 O…• Weight loss gives VM contentY VM = weight loss / dry weight(wt % d.b.)/ Mechanical Engineering 18-11-2011 PAGE 20

Proximate analysis continued• Air is allowed to enter the system• The sample burns and ash remains• Ash contentY Ash = weight ash / dry weight(wt % d.b.)• Fixed carbon content determined by differenceY FC = 1 - Y VM - Y Ash(wt % d.b.)/ Mechanical Engineering 18-11-2011 PAGE 21

Proximate analysesVM FC Ash VM FC Ash/ Mechanical Engineering 18-11-2011 PAGE 22

Thermo-Gravimetric Analysis (TGA)• Put sample in inert atmosphere• Pure nitrogen N 2• Slowly heat up sample• Heating rate ~20 °C/min• Measure weight loss as function of time• Typical result…/ Mechanical Engineering 18-11-2011 PAGE 23

Weight (%)Temperature (°C)TGA of pine barkSample: Bark 90 micronSize: 4.8961 mgMethod: BiomassComment: first test120DSC-TGAFile: C:\TA\Data\TGA\Bark90micron.002Operator: AdrianRun Date: 5-Nov-03 13:5860010010.47% moisture(0.5128mg)8040049.41% Volatiles(2.419mg)604020037.96% F.C.(1.858mg)200Residue:2.037% Ash(0.09972mg)00 20 40 60 80 100 120Time (min)Universal V3.0G TA Instruments/ Mechanical Engineering 18-11-2011 PAGE 24

Results of pine bark% Wet % Dry % DAFMoisture 10.5 - -Ash 2.1 2.3 -Volatile Matter 49.4 55.2 56.5LowFixed Carbon 38.0 42.4 43.4/ Mechanical Engineering 18-11-2011 PAGE 25

Derivative TGA curveCelluloseHemicelluloseLignin/ Mechanical Engineering 18-11-2011 PAGE 26

TGA and DTG for softwood biomass/ Mechanical Engineering 18-11-2011 PAGE 27

TGA and DTG for hardwood/ Mechanical Engineering 18-11-2011 PAGE 28

Fitting a devolatilization model/ Mechanical Engineering 18-11-2011 PAGE 29

Exam questionSample is put in N 2 filledfurnace. After 45 min. thetemperature is increased to110 ℃. After 30 min. it isslowly increased to 600 ℃.Finally, air is supplied.a) Explain the curve.b) Determine compositionon wet basis, and dryand-ash-freebasis./ Mechanical Engineering 18-11-2011 PAGE 30

Answer/ Mechanical Engineering 18-11-2011 PAGE 31

Ultimate analysis• Sample is burned in O 2 atmosphere with He ascarrier gas• Combustion gases are CO 2 , H 2 O, NO, NO 2 , SO 2 , SO 3and N 2• SO 3 , NO and NO 2 are reduced at copper contact toSO 2 and N 2• H 2 O, SO 2 and CO 2 are captured in differentadsorption columns/ Mechanical Engineering 18-11-2011 PAGE 32

Ultimate analysis continued• N 2 is not captured and is detected by a thermalconductivity detector (TCD)• N 2 → N• Consecutively, H 2 O, SO 2 and CO 2 will be sent to TCD• H 2 O → H• SO 2 → S• CO 2 → C• Mass percentage is determined integrally• O is found by difference/ Mechanical Engineering 18-11-2011 PAGE 33

Ultimate analyses/ Mechanical Engineering 18-11-2011 PAGE 34

Coalification (Van Krevelen) diagram/ Mechanical Engineering 18-11-2011 PAGE 35

Gross calorific / Higher heating value• Empirical relation for biomassGCV = 34.91 Y C + 117.83 Y H + 10.05 Y S– 1.51 Y N – 10.34 Y O – 2.11 Y ash [MJ/kg d.b.]Y i is content in wt% d.b.Calculation exercise for CH 1.0 O 0.4375/ Mechanical Engineering 18-11-2011 PAGE 36

Bomb calorimeterDevice to measureheating value/ Mechanical Engineering 18-11-2011 PAGE 37

Effect of moisture on heating value• Gross Calorific Value (GCV) Higher Heating Value (HHV)• Heat released during combustion per mass unit fuel• Final temperature same as initial temperature• Water is formed in liquid phase• Net Calorific Value (NCV)• Water is formed in gaseous phaseLower Heating Value (LHV)• Latent heat + sensible heat (100-25℃)/ Mechanical Engineering 18-11-2011 PAGE 38

Net calorific valueDerived from GCV18NCV ( GCV 2.442 h)*(1 w) 2.442w2[MJ/kg d.b.]w = water content wt% w.b.h = hydrogen concentration wt% d.b. (~6%)Calculation exercise for dry CH 1.0 O 0.4375/ Mechanical Engineering 18-11-2011 PAGE 39

Ash• Inherent ash versus entrained ash• Bottom ash versus fly ash• Constituents• Plant nutrients: CaO, MgO, K 2 O,P 2 O 5 , Na 2 O• Other oxides: SiO, Al 2 O 3 , Fe 2 O 3• Heavy metals: Cu, Zn, Cr• Organic contaminants: PCDD/Fand PAH/ Mechanical Engineering 18-11-2011 PAGE 40

Ash melting behavior• Sintering: agglutination of particles• Softening temperature: change of surface, rounding,shrinking.• Hemisphere temperature: spherically shaped• Melting temperature: size reduced to 1/3• Ca and Mg increase• K and Na decrease/ Mechanical Engineering 18-11-2011 PAGE 41

Improving biomass quality• Growing phase• Harvesting date (moisture)• Fertiliser (Cl in straw)• Rainfall during storage on the field• Supply phase: Upgrading• Increase energy density• More homogeneous− Chunking, chipping, grinding− Drying− Compressing (pellets and briquettes)/ Mechanical Engineering 18-11-2011 PAGE 42

Leaching of barley straw by rainfall/ Mechanical Engineering 18-11-2011 PAGE 43

Conversion processes/ Mechanical Engineering 18-11-2011 PAGE 44

Biomass conversion routes/ Mechanical Engineering 18-11-2011 PAGE 45

Thermochemical conversion• Advantage: High throughput• Three main processes• Pyrolysis Air ratio = 0• Gasification Air ratio = 0.25 – 0.50• CombustionAir ratio = 1 – inf.• Difference: the amount of oxidizer (air) availableAir ratio =Actual air fuel ratioAir fuel ratio for stoichiometric combustion/ Mechanical Engineering 18-11-2011 PAGE 46

Questions/ Mechanical Engineering 18-11-2011 PAGE 47