Combustion of Difficult Biomass Fuels: from Particle Ignition to Large-Scale Studies. Mário Costa Instituto Superior Técnico, Lisboa, Portugal

Transcription

1 Combustion of Difficult Biomass Fuels: from Particle Ignition to Large-Scale Studies Mário Costa Instituto Superior Técnico, Lisboa, Portugal

2 Structure of the presentation Overview (facts, projections, resources, potentials) Difficult biomass fuels (what do I mean?, biomass properties) Single particle studies (early combustion stages: ignition & devolatilization) Drop tube studies (soot and char yields, particulate matter & particle fragmentation) Large-scale studies (ash deposition & role of potassium) Concluding remarks (includes research needs) 2

3 Overview 3

4 World energy markets by fuel type World energy consumption by country grouping, (quadrillion Btu) Total world energy consumption by energy source, (quadrillion Btu) Renewables: world s fastest-growing energy source (increase 2.6%/year from 2012 to 2040) Nuclear: world s second fastest-growing energy source (increase 2.3%/year from 2012 to 2040) Coal: world s slowest-growing energy source (increase 0.6%/year from 2012 to 2040) Fossil fuels: still account for 78% of energy use in 2040 Dotted lines for coal and renewables show projected effects of the U.S. Clean Power Plan Source: International Energy Outlook,

5 World delivered energy use by sector World net electricity generation by energy source, (trillion kilowatthours) buildings, industrial, and transportation sectors Buildings: projected an increase of 2.1%/year from 2012 to 2040 for non- OECD countries (in OECD countries: increase of 0.6%/year) Industrial: accounts for more than half of total energy use through 2040, but is the slowest-growing sector (increase of 1.2%/year in non- OECD countries: 1.5%/year, in OECD countries: 0.5%/year) Transportation: liquid fuels remain dominant source, but share declines from 96% in 2012 to 88% in Source: International Energy Outlook,

6 Renewable resources World net electricity generation from renewable power by fuel, (trillion kwh) Solar is the world s fastest-growing form of renewable energy, with net solar generation increasing 8.3%/year Other includes biomass, waste, and tide/wave/ocean Of the around 6 trillion kwh of new renewable generation added over the projection period: hydroelectric account for 33% wind account for 33% solar for 15% biomass and waste for 14% Source: International Energy Outlook,

7 World carbon dioxide emissions World energy-related carbon dioxide emissions by fuel type, (billion metric tons) Liquid fuels: accounted for largest share (43%) of total CO 2 emissions in 1990, 36% in 2012, and projected to remain at that level through 2040 Coal: accounted for 39% of total emissions in 1990, 43% in 2012, but projected to decline to 38% in 2040 Natural gas: share of CO 2 emissions (19% in 1990) increases to 26% of total fossil fuel emissions in 2040 Source: International Energy Outlook,

8 Energy crops Woody crops Agricultural crops Waste products Wood residues Temperate crop wastes Tropical crop wastes Animal wastes Municipal solid waste Commercial and industrial wastes Biomass resources 8

9 Biomass potentials (1/2) Forest production (million tonnes) Technical potential of agricultural residues (million tonnes) Source: Bentsen & Felby (2010). Technical potentials of biomass for energy services from current agriculture and forestry in selected countries in Europe, The Americas and Asia. University of Copenhagen 9

10 Biomass potentials (2/2) Energy potential from agricultural residues and current forest production Source: Bentsen & Felby (2010). Technical potentials of biomass for energy services from current agriculture and forestry in selected countries in Europe, The Americas and Asia. University of Copenhagen 10

11 Difficult biomass fuels 11

12 Difficult biomass fuels Biomass fuels with difficult physical properties Wet sludges, straw... Very wet biomass fuels Wet sludges, wet chips... Biomass fuels with difficult ashes Animal and poultry wastes 12

13 Biomass fuels with difficult physical properties Cereal straws for biomass are harvested, transported, stored and handled as large bales This requires special equipment, which is expensive and not very flexible Straw is difficult to pulverize down to sizes < 300 mm due to its fibrous structure torrefaction is a useful pre-treatment because makes the milling process easier Temperature: ºC Atmospheric pressure No oxygen Residence time: min Heating rate: < 50 ºC/min 13

14 Very wet biomass fuels Green wood materials generally have total moisture contents up to around 55%-60% which may have a significant impact on the heat balance across the mill... 14

15 Biomass fuels with difficult ashes Levels of Ca, K and P in biomass residues can be extremely high, which can increase the ash deposition on boiler surfaces Risk of high temperature corrosion of boiler components because of the high Cl content of (some) biomass materials Risks of low ash fusion temperatures and, thus, increased slag formation, depending on the ash content and ash chemistry of the biomass Risks of increased deposition and other ash-related impacts associated with biomass firing leads to restrictions in the range of biomass materials that can be used 15

16 Biomass fuels properties 16

17 Context of the presentation In last decades, the environmental pressure on power production industry focused on the replacement of coal by neutral CO 2 fuels like biomass Currently, there is an increasing interest on a new generation of low cost biomass fuels such as agricultural residues and refuse derived fuels (RDF) Research on the various aspects of the combustion of these renewable fuels is going on at three scales: single particle studies drop tube studies large-scale studies 17

18 Single particle studies Sandia National Laboratories USA Tsinghua University China Probe High-speed camera Particle feeder Optical McKenna flat flame burner (1) (2) Rotameter (1) - Water in (2) - Water out Flowmeters Northeastern University USA Technische Universita t Darmstadt Germany CH 4 N 2 /O 2 Instituto Superior Técnico Portugal 18

19 Topics covered in this lecture on single particle studies Early combustion stages of single biomass particles in air (ignition delay time, ignition mode) Combustion of single biomass particles in air and simulated oxy-fuel conditions Investigation of ignition and volatile combustion of single particles using advanced optical techniques 19

20 Early combustion stages of single biomass particles in air (1/3) Probe High-speed camera Particle feeder Optical McKenna flat flame burner (1) (2) Rotameter (1) - Water in (2) - Water out Flowmeters Pine (homogeneous ignition) Straw (heterogeneous ignition) Coal (homogeneous ignition) CH 4 N 2 /O 2 pine bark, sycamore branches, vine branches, kiwi branches, wheat straw, almonds shells, olive residues, grape pomace doped with K and Ca, Soma lignite, Tunçbilek lignite, bituminous coal mm, mm, mm, mm Temperature: K; oxygen: 3.5%-7.6% Source: Simões, Magalhães, Rabaçal, Costa, PROCI, 2017; Magalhães, Kazanc, Ferreira, Rabaçal, Costa, submitted to FUEL,

21 Typical statistical convergence of t ig and t vol for a biomass residue Early combustion stages of single biomass particles in air (2/3) t ig : minimum of 50 events for each biomass to have statistical convergence t vol : minimum of 30 events for each biomass to have statistical convergence t ig tends to decrease with increase of atmosphere temperature regardless of the solid fuel t ig of solid fuels with the same particle size converge as temperature increases Source: Simões, Magalhães, Rabaçal, Costa, PROCI, 2017; Magalhães, Kazanc, Ferreira, Rabaçal, Costa, submitted to FUEL,

22 Early combustion stages of single biomass particles in air (3/3) Both t ig and t vol increase with the demineralization process t ig decreases as K increases, but for Ca, t ig first increases and then decreases as Ca increases t vol decreases as K and Ca increase (more evident in case of Ca impregnation) Impact of K and Ca more significant on t vol than on t ig Source: Carvalho, Rabaçal, Costa, Alzueta, Abián, submitted to FUEL,

23 Combustion of single biomass particles in air and simulated oxy-fuel conditions (1/2) olive residue, sugar cane bagasse, pine sawdust, torrefied sawdust mm temperature: 1400 K; oxygen: 21%-50% Source: Riaza, Khatami, Levendis, Álvarez, Gil, Pevida, Rubiera, Pis, B&B,

24 Combustion of single biomass particles in air and simulated oxy-fuel conditions (2/2) Source: Riaza, Khatami, Levendis, Álvarez, Gil, Pevida, Rubiera, Pis, B&B,

25 Investigation of ignition and volatile combustion of single coal particles using high-speed OH-PLIF Mean gas temperature (CARS) OH-PLIF images at z = 14 mm Radial OH-profiles high volatile (36 wt.%) bituminous coal mm four oxygen-enriched exhaust gas environments different transport gas Temporal information obtained from the high-speed OH-LIF measurements allowed to determine the onset of ignition (sheet-imaging versus chemiluminescence imaging) Source: Ko ser, Becker, Goßmann, Bo hm, Dreizler, PROCI,

26 Early combustion stages of single particles: collaboration with Lund University, Sweden Probe High-speed camera Particle feeder (1) - Water in (2) - Water out Optical McKenna flat flame burner (1) (2) Flowmeters Rotameter Images of spontaneous emissions from burning wheat straw particles with different filters (size: 3x3 cm; time delay: 40 ms) CH 4 N 2 /O 2 Distribution of excimer-laser induced photo-fragmentation fluorescence Source: Weng, Rabaçal, Costa, Li, Aldén, work-in-progress 26

27 Drop tube studies Curtin University Australia Instituto Superior Técnico Portugal Lulea University of Technology Sweden Université Catholique de Louvain Belgium Université de Haute-Alsace France 27

28 Topics covered in this lecture on drop tube studies Relationship between biomass pyrolysis conditions and gas composition, soot and char yields Particulate matter emissions from combustion of biomass Particle fragmentation during last stages of combustion of biomass 28

29 Relationship between biomass pyrolysis conditions and gas composition, soot and char yields (1/2) pinewood, beechwood, Danish wheat straw, alfalfa straw, leached wheat straw mm 1000, 1250, 1400 ºC Soot and char yields Gas composition For all straws char yield significantly decrease as temp increases Soot yields of wood higher than those from straw above 1250 C Leached wheat straw forms less soot than the other two straws Source: Trubetskaya, Peter Jensen, Anker Jensen, Llamas, Umeki, Glarborg, FPT,

30 Relationship between biomass pyrolysis conditions and gas composition, soot and char yields (2/2) Wheat straw char contains Si, K, Ca and alfalfa straw char Ca, K, S, Si, P Original alfalfa straw contains much K and Ca, and therefore forms mainly K and Ca rich compounds in char Ash elemental retention of original alfalfa and wheat straw and their chars at 1000, 1250 and 1400 ºC Inorganic elements in alfalfa and wheat straw soot consist mostly of K, Cl, S High levels of K and Cl in soot caused by KCl release under the fast heating rate in DTF Ash elemental retention of alfalfa and wheat straw soot and char at 1400 ºC Source: Trubetskaya, Peter Jensen, Anker Jensen, Llamas, Umeki, Glarborg, FPT,

31 Particulate matter emissions from combustion of biomass (1/2) Biomass components have different contents of inorganic species (especially Na, K, Mg, Ca and Cl) PM emission from the combustion of individual biomass components versus whole-tree biomass dry biomass basis useful energy basis ash input basis components of mallee trees (bark, leaf, wood), mixture of these components (15% bark, 35% leaf, 50% wood) mm 1400 ºC Source: Gao, Rahim, Chen, Wu, PROCI, 2017 Mass-based PSDs of PM10 and yields of PM0.1, PM0.1-1, PM1, PM1-10, PM2.5, and PM10 from the combustion of bark, leaf and wood 31

32 Particulate matter emissions from combustion of biomass (2/2) Measured and calculated mass-based PSDs of PM10 and yields of PM0.1, PM0.1-1, PM1, PM1-10, PM2.5, and PM10 from the combustion of the whole-tree biomass Source: Gao, Rahim, Chen, Wu, PROCI,

33 Particle fragmentation during last stages of combustion of biomass wheat straw, µm wheat straw, rice husk < 1000 mm, µm, µm, µm 1100 ºC straw rice husk Source: Branco & Costa, ECM,

34 Large-scale studies Clausthal University of Technology Germany Xi an Jiaotong University China University of Leeds, UK Universität Stuttgart Germany Instituto Superior Técnico Portugal 34

35 Topics covered in this lecture on large-scale studies Ash deposition during biomass (co-)combustion Potassium behavior during biomass combustion 35

36 Ash deposition during biomass co-combustion (1/3) sawdust, pine branches, wheat straw, olive stones, peach stones, bituminous coal biomass fuels: < 1000 mm; coal: < 300 mm; air-cooled stainless steel deposition probes and uncooled ceramic deposition probes C Data logger T g Test Section T s Probe Deposit Layer Cooling Air T out T in 50 Dimensions in mm Source: Abreu, Casaca, Costa, FUEL, 2010; Wang, Pinto, Costa, FUEL,

37 Deposition rate (g/m 2 h) Ash deposition during biomass co-combustion (2/3) Sawdust Olive stones Coal Solid fuel in the blend (thermal fraction %) Source: Abreu, Casaca, Costa, FUEL, 2010; Wang, Pinto, Costa, FUEL,

38 Concentration (% wt) Concentration (% wt) Ash deposition during biomass co-combustion (3/3) a) Coal 10% sawdust 20% sawdust 30% sawdust 50% sawdust coal + sawdust co-firing high content of Si and Al SiO 2 e Al 2 O 3 high melting temperatures Si Al Fe K Cu Ca Mg Ti S Na Element b) Coal 10% olive stones 20% olive stones 30% olive stones 50% olive stones coal + olive stones co-firing high content of K K 2 O and K 2 SO 4 have low melting temperatures high content of S Formation of sulfates Si Al Fe K Cu Ca Mg Ti S Na P Element Source: Abreu, Casaca, Costa, FUEL, 2010; Wang, Pinto, Costa, FUEL,

39 Ash deposition during combustion of biomass Three times more deposit formed for biomass fuels than for coal Deposition rate correlates with particle temperature for biomass fuels mixed wood, sawdust, fermentation-process residues, grain residues, South African coal biomass fuels: 40 wt.% < 300 mm; coal: 75 wt.% < 75 mm uncooled ceramic probes C Sticking efficiency of impacting particles at 970 C and 0.4 at 1170 C Source: Weber, Poyraz, Beckmann, Brinker, PROCI,

40 Potassium behavior during biomass combustion Condensation of K species is the origin of the slag layer formation on superheater surfaces during biomass combustion Condensation mechanisms of K species wheat straw, corn stalk two K salts (KCl, K 2 SO 4 ), mixture of both (1:1) biomass fuels and K salts: μm stainless steel condensation probe 1000 C Source: Jin, Ye, Deng, Che, E&F, nucleation 2. heterogenous condensation; 3. thermophoresis and diffusion 4. Inertial impaction Initial slagging layer is formed by heterogeneous condensation of KCl vapor, and thermophoresis and diffusion of KCl and K 2 SO 4 fine particles 40

41 Concluding remarks The intense use of wood derived fuels in domestic and industrial combustion processes is putting an enormous pressure on the forest To meet the existing scenarios, we must increase the use of alternative biomass fuels, in particular herbaceous materials and agricultural residues... but such residues can cause a number of problems because of the presence of alkali metals and chlorine and other ash related impacts as well as corrosion on the metallic surfaces and particulate matter emissions which may limit the variety of biomass fuels that can actually be used in combustion processes 41

42 Research needs Ignition and combustion of single (and streams) biomass particles Influence of ash composition, particularly of K and Ca elements, on all aspects of biomass combustion Particle/char fragmentation during biomass combustion Characteristics of pure biomass flames in large-scale combustors 42

43 Acknowledgements This work was supported by Fundação para a Ciência e a Tecnologia (FCT), through IDMEC, under LAETA, project UID/EMS/50022/

44 IST research team