Fuel Analysis and Burning Characteristics

Transcription

1 Fuel Analysis and Burning Characteristics

2 Fuel Analysis and Burning Characteristics - Terms and Concepts Particle burning stages: drying - devolatilization char Proximate & ultimate analysis Heating value Biofuels vs coals H and O in Fuels: H/C vs O/C diagram

3 Single Particle Burning of Polish Coal mg 800 ºC 21% O 2 (air) Burning in open furnace and the sample on a hook

4 Polish Coal Particle 271 mg

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6 Polish Coal Particle Residue after Burning

7 Single Particle Burning of Wood 92.6 mg 800 ºC 21 % O 2 (air)

8 Wood Sample Before Burning

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10 Combustion of Solid Fuel Particles Stages of Burning H 2 O CO, CO 2, H 2 O Fuel particle Drying C x H y O 2 Air CO, CO 2 O 2 Pyrolysis/ devolatilisation and gas combustion Char combustion Ash

11 N 2 O 2 CO 2 pump Vent. pump SO 2 CO/CO 2 Filter NO Vent. Single Particle Burning System (Source: Åbo Akademi)

12 CO 2 formation Single Particle Burning 4 % On-line CO2 Analysis 3 % Pyrolysis 2 % 1 % Char combustion 0 % time (seconds)

13 CO 2 (ppm) Single Particle Burning Volatile vs. Char Carbon Volatile carbon Char carbon time

14 (CO+CO 2 ) formed (ppm) SO 2 formed (ppm) NO formed (ppm) magazine paper 70 Rec-Mod g N / 100 g Magazine Paper Waste 40 Rec-Mod g S / 100 g Standard fuel analysis Rec-Mod g C / 100 g time (seconds) C 32,1 % H 4,5 % N 0,1 % S 0,2 %

15 Burning Stages

16 Combustion of Solid Fuel Particles Stages of Burning H 2 O CO, CO 2, H 2 O Fuel particle Drying C x H y O 2 Air CO, CO 2 O 2 Pyrolysis/ devolatilisation and gas combustion Char combustion Ash

17 H 2 O Drying Heat from surrounding atmosphere leads to vaporization of water in fuel Rate determined by heat transfer

18 CO, CO 2, H 2 O C x H y O 2 Devolatilization/Pyrolysis Terms which can be used interchangeably Thermal break-down of fuel during heating Results in release of volatile organic gases Volatile gases: CH 4, CO, H 2, C x H y, tars, Burns with visible flame (soot)

19 At a given T & P Fuel dependent INCREASES WITH: Volatile Yield Increasing H/C ratio of fuel (example. wood vs. coal) Increasing Temperature DECREASES WITH: Increasing Particle/Droplet Size Increasing Pressure

20 CO, CO 2 Char combustion O 2 Heterogeneous reaction (gas-solid) Rate deependent on po2 and T Usually slower than pyrolysis No visible flame

21 Solid Fuels: Proximate Analysis Water Volatile Matter Char (Fixed Carbon) Ash

22 Proximate Analysis 1. MOISTURE/WATER: Dry a weighed sample of fuel at o C & 1 atm. 2. VOLATILES: Heat up the dried fuel to a defined temperature and pressure ( o C, 1-10 bar) in an inert gas atmosphere (N 2, Ar). Weigh sample after thermal treatment 3. ASH: Combust the remaining fixed carbon (CHAR) structure and weigh the residue (=ash).

23 Abbreviations/Terms d = dry: all water is removed dm = dry matter ad = air dry: the amount of water in fuel is in balance with water content of surrounding gas (air) atmosphere ar = as received: principally equal to as fired condition of fuel daf = dry and ash free: the combustible fraction of fuel Fuel ratio: X FC /X VOL Xi: Wt. fraction of i FC: Fixed Carbon VOL: Volatiles

24 Summary of terms and concepts for analysis of solid fuels Fuel Drying Combustion Pyrolysis/ devolatilization Char combustion Moisture air dry (ad) Or Dry matter (dm) Volatiles as received (ar) dry (d) Char Fixed carbon Ash Ash Moisture + Volatiles + Fixed carbon + Ash = Proximate Analysis

25 Ultimate/elemental Analysis Ultimate analysis: Fuel elemental composition C, H, S, N (& O) Elemental analysis: Ash forming matter (AFM) elements as such: Si, Ca, Mg, K... or as their typical oxides: SiO2, CaO, MgO, K2O...

26 Summary of terms and concepts for analysis of solid fuels Fuel Drying Combustion Pyrolysis/ devolatilization Char combustion air dry (ad) Or as received (ar) Moisture Dry matter (dm) dry (d) Volatiles Char Fixed carbon Ash Ash Combustible matter (daf) Volatiles Fixed carbon (AFM ash) Ultimate/elemental Analysis Moisture + Volatiles + Fixed carbon + Ash = Proximate Analysis

27 Exercises 1) Identify which information in given fuel analysis is from: a) Proximate analysis? b) Ultimate/elemental analysis? 2) What is the amount of fixed carbon for respective fuel as (% (d)) 3) What is the difference in (% (d)) between ash and AFM?

28 van Krevelen diagram

29 Coalification Process Decaying vegetation Peat Lignite/Brown Coal Bituminous Coal Peatification: Bacterial and fungal decay in a water saturated anaerobic environment Lignification: Air oxidation followed by decarboxylation (-COOH CO 2 (g)) and dehydration (H 2 O split off) Bituminisation: Continued decarboxylation Anthracite Coal Anthracitisation: Condensation of small aromatic ring systems to larger ones and Dehydrogenation (H 2 split off) (Graphite)

30 Mean Age (x10 6 yrs) Cannel coals of Artic 380 Anthracite 300 Bituminous Sub-bituminous 120 Lignite Peat <1 *It takes an ~100m deep pile of decaying plant material to make a 1m deep seam of coal

31 Heating Values

32 Storage for Solar Energy hv CO H O hv CH O O

33 Energy release during combustion In combustion energy is first put into the fuel/oxidizer mixture to initiate the reaction by breaking the first bonds and forming the first radicals During combustion, new/stronger bonds are formed, releasing energy This released energy/unit of fuel combusted is called the Heating Value (HV) *can also be called calorific value or energy value

34 Heating value can be approximated for fuels with well defined structure The structure of most solid fuels is not well known In practical cases: Heating value determined experimentally Calorimetric determination of HHV 1) Known heat capacity C (Joule/Kelvin) for system 2) Combust known amount of fuel (m fuel ) 3) Register temperature rise (ΔT) of system 4) HHV = (C ΔT)/m fuel

35 Lower Heating Value (LHV): C,H,S -> CO2, H2O, SO2 Water assumed to be as vapor in flue gas (like in many real cases) Also called the net heating value Commonly used in Europe Higher Heating Value (HHV): Includes the energy from condensed water vapor and fully oxidized components of fuel Also called gross heating value Commonly used in North-America

36 Lower vs Higher Heating Value LHV = HHV Heat to vaporise H 2 O H 2 O: fuel moisture + H 2 O formed from H in fuel HHV is obtained from fuel analysis (calorimeter) HHV determined for dry fuel (MJ/kg dry fuel) HHV converted to LHV

37 Lower vs Higher Heating Value LHV = HHV Heat to vaporise H 2 O H 2 O: fuel moisture + H 2 O formed from H in fuel LHV/kg dry fuel HHV/kg dry fuel H 2 O formed from fuel H 2.26 MJ/kg H 2 O LHV/kg wet fuel HHV/kg wet fuel Moisture H 2 O formed from H 2.26 MJ/kg H 2 O

38 Higher Heating Value, MJ/kg (d) Comparison of fuel properties Coal Brown coal Peat Wood H is hydrogen content wt-%(daf) C is carbon content wt-%(daf) Volatile matter, %(d) Ekman, E., Kiinteiden polttoaineiden koostumus ja muut ominaisuudet, VTT

39 Exercises 1) Identify which information in given fuel analysis is from: a) Proximate analysis? b) Ultimate/elemental analysis? 2) What is the amount of fixed carbon for respective fuel as (% (d)) 3) What is the difference in (% (d)) between ash and AFM? 4) Use the graph showing comparison of fuel properties to determine the type (wood, peat, brown coal, coal) of respective fuel (1 and 2).

40 K2O Na2O MgO CaO clorine sulphur nitrogen oxygen hydrogen carbon Ash (dry) % Volatile matter (dry)% Fixed carbon (dry) % EXAMPLES OF FUEL COMPOSITION P2O5 SO3 Fe2O2 TiO2 AlzO3 SiO2 Bituminous coal % on dry and ash free % on ash Red oak sawdust Alder/fir sawdust Forest residuals Pine sawdust Bagasse Switch grass, average Miscantus Straw (DK) Rice hulls Almond < shells Olive pits Dry sewage sludge RDF

41 THE FUEL PROPERTIES ARE DECISIVE FOR THE DESIGN OF EQUIPMENT Proximate and elemental analyses amounts of air and combustion products Energy content (moisture) and volatiles heat balance and combustion behaviour Precursors to gaseous emissions (N,S,Cl) Ash-forming elements (K,Na,Ca,Mg,Al,Si,P) Trace elements (Cd,Tl; Hg; Sb,As,Pb,Cr,Co,Cu, Mn,Ni,V;...)

42 HEATING VALUE, MJ/kg Fluidized Bed Characterization of Solid Fuels 35 PETROLEUM COKE POLYOLEFIN COLORED COLORED PLASTICS OR PRINTED OR PRINTED (PE, PP, PC...) PLASTICS, MIXED CLEAN PLASTICS 20 BITUMINOUS COAL REF PELLETS CONSUMER REF REF MIXED PLASTICS PVC BROWN COAL, LIGNITE CHIP- BOARD PLY- WOOD REF COMMERCIAL & INDUSTRIAL WOOD & PLASTICS PVC RDF 10 PEAT WOOD BIOMASS DEMOLITION WOOD PAPER & WOOD MSW CHICKEN LITTER COW MANURE BARK 5 BIO & FIBER SLUDGE DEINKING SLUDGE SEWAGE SLUDGE POK\class.ds4/0299/ams STANDARD DESIGN SOME CHALLENGES MULTIPLE CHALLENGES 10 N/A FOR FLUIDIZED BED

43 Fuel Analysis and Burning Characteristics - Terms and Concepts Particle burning stages: drying - devolatilization char Proximate & ultimate analysis Heating value Biofuels vs coals H and O in Fuels: H/C vs O/C diagram