| 1. |
- Boman, Christoffer, et al.
(författare)
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Stove performance and emission characteristics in residential wood log and pellet combustion : Part 1: Pellet stoves
- 2011
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 25:1, s. 307-314
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Tidskriftsartikel (refereegranskat)abstract
- Stove performance, characteristics and quantities of gaseous and particulate emissions were determined for two different pellet stoves, varying fuel load, pellet diameter and chimney draught. This approach aimed at covering variations in emissions from stoves in use today. The extensive measurement campaign included CO, NOx, organic gaseous carbon, volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), total particulate matter (PMtot) as well as particle mass and number concentrations, size distributions and inorganic composition. At high load, most emissions were similar. For stove B, operating at high residual oxygen and solely with primary air, the emissions of PMtot and particle numbers were higher while the particles were smaller. Lowering the fuel load, the emissions of CO and hydrocarbons increased dramatically for stove A, which operated continuously also at lower fuel loads. On the other hand for stove B, which had intermittent operation at lower fuel loads, the emissions of hydrocarbons increased only slightly lowering the fuel load, while CO emissions increased sharply, due to high emissions at the end of the combustion cycle. Beside methane, dominating VOCs were ethene, acetylene and benzene and the emissions of VOC varied in the range 1.1-47 mg/MJfuel. PAH emissions (2-340 µg/MJfuel) were generally dominated by phenantrene, fluoranthene and pyrene. PMtot (15-45 mg/MJfuel) were in all cases dominated by fine particles with mass median diameters in the range 100-200 nm, peak mobility diameters of 50-85 nm and number concentrations in the range 4×1013- 3×1014 particles/MJfuel. During high load conditions the particulate matter was totally dominated by inorganic particles at 15-25 mg/MJfuel consisting of potassium, sodium, sulfur and chlorine, in the form of K2SO4, K3Na(SO4)2 and KCl. The study shows that differences in operation and modulation principles for the tested pellet stoves, relevant for appliances in use today, will affect the performance and emissions significantly, although with lower scattering in the present study compared to compiled literature data.
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| 2. |
- Brus, Elisabet, et al.
(författare)
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Bed agglomeration characteristics of biomass fuels using blast-furnace slag as bed material
- 2004
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Ingår i: Energy & Fuels. - Washington, D.C. : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 18:4, s. 1187-1193
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Tidskriftsartikel (refereegranskat)abstract
- Agglomeration of bed material may cause severe operating problems during fluidized bed combustion. The attack or coating layers that are formed on the bed particles during combustion play an important role in the agglomeration process. To reduce bed agglomeration tendencies, alternative bed materials may be used. In this paper, bed agglomeration characteristics during the combustion of biomass fuels using a relatively new bed material (iron blast-furnace slag) as well as ordinary quartz sand were determined. Controlled agglomeration tests lasting 40 h, using five representative biomass fuels (bark, olive residue, peat, straw, and reed canary grass) were conducted in a bench-scale fluidized bed. The bed materials and agglomerates were analyzed using SEM/EDS and X-ray diffraction. Chemical equilibrium calculations were performed to interpret the experimental findings. The results showed that blast-furnace slag had a lower tendency to agglomerate than quartz sand for most of the fuels. The quartz particles showed an inner attack layer more often than did the blast-furnace slag. The blast-furnace slag had a lower tendency to react with elements from the fuel. The outer coating layer had similar characteristics and thickness for both bed materials when the same fuel was combusted. However, the inner attack layer thickness was larger for quartz particles. SEM/EDS analyses of the agglomerates showed that the inner Ca-K-silicate-rich attack layer was responsible for the agglomeration of quartz sand. The composition of blast-furnace slag agglomerate was similar to the outer coating layer. Chemical equilibrium calculations showed that the original composition of the blast-furnace slag was close to the equilibrium composition, and hence there was no major driving force for reactions between that bed material and K and Ca from the fuel. The homogeneous silica-rich attack layer (with a low melting temperature) was not formed to the same extent for blast-furnace slag, thus explaining the lower bed agglomeration tendency.
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| 3. |
- Eriksson, Gunnar, et al.
(författare)
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Combustion characterization of rapeseed meal and possible combustion applications
- 2009
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 23:8, s. 3930-3939
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Tidskriftsartikel (refereegranskat)abstract
- A future shortage of biomass fuel can be foreseen. The production of rapeseed oil for a number of purposes is increasing, among others, for biodiesel production. A byproduct from the oil extraction process is rapeseed meal (RM), presently used as animal feed. Further increases in supply will make fuel use an option. Several energy companies have shown interest but have been cautious because of the scarcity of data on fuel properties, which led to the present study. Combustion-relevant properties of RM from several producers have been determined. The volatile fraction (74 ± 0.06%wtds) is comparable to wood; the moisture content (6.2−11.8%wt) is low; and the ash content (7.41 ± 0.286%wtds) is high compared to most other biomass fuels. The lower heating value is 18.2 ± 0.3 MJ/kg (dry basis). In comparison to other biomass fuels, the chlorine content is low (0.02−0.05%wtds) and the sulfur content is high (0.67−0.74%wtds). RM has high contents of nitrogen (5.0−6.4%wtds), phosphorus (1.12−1.23%wtds), and potassium (1.2−1.4%wtds). Fuel-specific combustion properties of typical RM were determined through combustion tests, with an emphasis on gas emissions, ash formation, and potential ash-related operational problems. Softwood bark was chosen as a suitable and representative co-combustion (woody) fuel. RM was added to the bark at two levels: 10 and 30%wtds. These mixtures were pelletized, and so was RM without bark (for durability mixed with cutter shavings, contributing 1%wt of the ash). Each of these fuels was combusted in a 5 kW fluidized bed and an underfed pellet burner (to simulate grate combustion). Pure RM was combusted in a powder burner. Emissions of NO and SO2 were high for all combustion tests, requiring applications with flue gas cleaning, economically viable only at large scale. Emissions of HCl were relatively low. Temperatures for initial bed agglomeration in the fluidized-bed tests were high for RM compared to many other agricultural fuels, thereby indicating that RM could be an attractive fuel from a bed agglomeration point of view. The results of grate combustion suggest that slagging is not likely to be severe for RM, pure or mixed with other fuels. Fine-mode particles from fluidized-bed combustion and grate combustion mainly contained sulfates of potassium, suggesting that the risk of problems caused by deposit formation should be moderate. The chlorine concentration of the particles was reduced when RM was added to bark, potentially lowering the risk of high-temperature corrosion. Particle emissions from powder combustion of RM were 17 times higher than for wood powder, and the fine-mode fraction contained mainly K-phosphates known to cause deposits, suggesting that powder combustion of RM should be used with caution. A possible use of RM is as a sulfur-containing additive to biomass fuels rich in Cl and K for avoiding ash-related operational problems in fluidized beds and grate combustors originated from high KCl concentrations in the flue gases.
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| 4. |
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| 5. |
- Jonsson, Carrie, et al.
(författare)
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Deposit formation in a grate-kiln plant for iron-ore pellet production. : Part 1: Characterization of process gas particles
- 2013
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 27:10, s. 6159-6170
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Tidskriftsartikel (refereegranskat)abstract
- Slag formation in the grate-kiln process is a major problem for iron-ore pellet producers. It is therefore important to understand the slag formation mechanism in the grate-kiln production plant. This study initiated the investigation by in situ sampling and identifying particles in the flue gas from a full-scale 40 MW grate-kiln production plant for iron-ore pelletizing. Particles were sampled from two cases of combustion with pulverized coal and heavy fuel oil. The sampling location was at the transfer chute that was situated between the traveling grate and the rotary kiln. The particle-sampling system was set up with a water-cooled particle probe equipped with nitrogen gas dilution, cyclone, and low-pressure impactor. Sub-micrometer and fine particles were size-segregated in the impactor, while coarse particles (>6 μm) were separated with a cyclone before the impactor. Characterization of these particles was carried out with environmental scanning electron microscopy (ESEM), and the morphology of sub-micrometer particles was studied with transmission electron microscopy (TEM). The results showed that particles in the flue gas consisted principally of fragments from iron-ore pellets and secondarily of ashes from pulverized coal and heavy fuel oil combustions. Three categories of particle modes were identified: (1) sub-micrometer mode, (2) first fragmentation mode, and (3) second fragmentation mode. The sub-micrometer mode consisted of vaporized and condensed species; relatively high concentrations of Na and K were observed for both combustion cases, with higher concentrations of Cl and S from heavy fuel oil combustion but higher concentrations of Si and Fe and minor P, Ca, and Al from coal combustion. The first fragmentation mode consisted of both iron-ore pellet fines and fly ash particles; a significant increment of Fe (>65 wt %) was observed, with higher concentrations of Ca and Si during heavy fuel oil combustion but higher concentrations of Si and Al during coal combustion. The second fragmentation mode consisted almost entirely of coarse iron-ore pellet fines, predominantly of Fe (∼90 wt %). The particles in the flue gas were dominantly iron-ore fines because the second fragmentation mode contributed >96 wt % of the total mass of collected particles.
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| 6. |
- Lindström, Erica, et al.
(författare)
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Slagging characteristics during combustion of cereal grains rich in phosphorus
- 2007
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 21:2, s. 710-717
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Tidskriftsartikel (refereegranskat)abstract
- A residential cereal burner (20 kW) was used study the slagging characteristics of cereal grains with and without lime addition. The deposited bottom ash and slag were analyzed using X-ray diffraction (XRD), to identify the crystalline phases, and environmental scanning electron microscopy, coupled with energy-dispersive X-ray spectroscopy (ESEM/EDS), to study the morphology and elemental composition. Phase-diagram information was utilized to extract qualitative information about the behavior of cereal grain ashes under combustion conditions. Chemical equilibrium model calculations were used to interpret the experimental results. In addition, investigations of the melting behavior of the produced slags were conducted. The results showed significant differences in slagging characteristics between the fuels that were used. The slags consisted of high-temperature melting crystalline phases (calcium/magnesium potassium phosphates) and a potassium-rich phosphate melt for all cereal grains. For oat and barley, cristobalite was also identified in the slag. Furthermore, in these cases, the slags most probably contained a potassium-rich silica melt. The differences in the melting behaviors of the slags had a considerable effect on the performance of the burner. The addition of lime reduced the formation of slag for barley and totally eliminated it for rye and wheat. This occurs because lime contributes to the formation of high-temperature melting calcium potassium phosphates
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| 7. |
- Ma, Charlie, et al.
(författare)
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Characterization of reactor ash deposits from pilot-scale pressurized entrained-flow gasification of woody biomass
- 2013
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 27:11, s. 6801-6814
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Tidskriftsartikel (refereegranskat)abstract
- Pressurized entrained-flow gasification of renewable forest residues has the potential to produce high-quality syngas suitable for the synthesis of transport fuels and chemicals. The ash transformation behavior during gasification is critical to the overall production process and necessitates a level of understanding to implement appropriate control measures. Toward this end, ash deposits were collected from inside the reactor of a pilot-scale O 2-blown pressurized entrained-flow gasifier firing stem wood, bark, and pulp mill debarking residue (PMDR) in separate campaigns. These deposits were characterized with environmental scanning electron microscopy equipped with energy-dispersive X-ray spectrometry and X-ray diffractometry. The stem wood deposit contained high levels of calcium and was comparatively insubstantial. The bark and PMDR fuels contained contaminant sand and feldspar particles that were subsequently evident in each respective deposit. The bark deposit consisted of lightly sintered ash aggregates comprising presumably a silicate melt that enveloped particles of quartz and, to a lesser degree, feldspars. Discontinuous layers likely to be composed of alkaline-earth metal silicates were found upon the aggregate peripheries. The PMDR deposit consisted of a continuous slag that contained quartz and feldspar particles dispersed within a silicate melt. Significant levels of alkaline-earth and alkali metals constituted the silicate melts of both the bark and PMDR deposits. Overall, the results suggest that fuel contaminants (i.e., quartz and feldspars) play a significant role in the slag formation process during pressurized entrained-flow gasification of these woody biomasses.
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| 8. |
- Nordgren, Daniel, et al.
(författare)
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Ash transformations in pulverised fuel co-combustion of straw and woody biomass
- 2013
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Ingår i: Fuel processing technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 105, s. 52-58
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Tidskriftsartikel (refereegranskat)abstract
- Ash transformation processes have been studied during co-firing of wheat straw and pine stem wood and softwood bark. Pilot-scale trials in a 150kW pulverised-fuel-fired burner were performed. Thermodynamic equilibrium calculations were made to support the interpretation of the results. The results show that reactions involving condensed phases are kinetically limited compared to reactions between gaseous ash compounds. Accordingly, the conditions promote gas phase reactions resulting in the formation of chlorides, sulphates and carbonates whereas reactions involving condensed reactants are suppressed. Both the slagging and fouling propensities of all co-firing mixes were reduced compared to that for pure straw. For the wood/straw mixes this was mainly due to a dilution of the ash forming elements of straw whereas for straw/bark, an additional effect from interaction between the fuel ash components was observed to reduce slagging. In general it can be concluded that under powder combustion conditions equilibrium is approached selectively and that the ash matter is strongly fractionated. The general results in this paper are useful for straw-fired power stations looking for alternative co-firing fuels.
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| 9. |
- Näzelius, Ida-Linn, et al.
(författare)
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Influence of peat addition to woody biomass pellets on slagging characteristics during combustion
- 2013
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 27:7, s. 3997-4006
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Tidskriftsartikel (refereegranskat)abstract
- Upgraded biofuels such as pellets, briquettes, and powder are today commonly used in small as well as large scale appliances. In order to cover an increasing fuel demand new materials such as bark, whole tree assortments, and peat are introduced. These materials have higher ash content which is why they are potentially more problematic compared with stem wood. In general, few studies can be found regarding cocombustion of peat and biomass and in particular where the slagging tendencies are discussed. The overall objective of this study was therefore to determine the influence of peat addition to woody biomass pellets on slagging characteristics. Two different peat assortments (peat A and B) were copelletized separately in four different dry matter levels (0-5-15-30 wt %) into stem wood and energy wood, respectively. Peat A was a traditional Scandinavian fuel peat, with a high ash and Si content (carex), and peat B had a low ash content and relatively high Ca/Si ratio (sphagnum) chosen for its special characteristics. The produced pellets were combusted in a commercial underfed pellet burner (15 kW) installed in a reference boiler. The collected deposits (bottom ash and slag) from the combustion experiments were chemically characterized by scanning electron microscopy (SEM) combined with energy-dispersive X-ray analysis (EDS) and X-ray diffraction (XRD) regarding the elemental distribution and morphology and phase composition, respectively. In addition, the bottom ashes were characterized according to inductively coupled plasma atomic emission spectroscopy (ICP-AES). To interpret the experimental findings chemical equilibrium model calculations were performed. The slagging tendency increased when adding peat into the woody biomasses. Especially sawdust with its relatively low ash and Ca content was generally more sensitive for the different peat assortments. Cofiring with the relatively Si and ash rich peat A resulted in the most severe slagging tendency. A significant increment of the Si, Al, and Fe content and a significant decrement of the Ca content in the slag could be seen when increasing the content of peat A in both woody biomasses. The slagging tendency increased when adding peat A because high temperature melting Ca-Mg oxides react to form more low temperature melting Ca/Mg-Al-K silicates. The slagging tendency was significantly lower when adding the more ash poor peat B, with relatively high Ca/Si ratio, into the woody biomass fuels compared with the peat A mixtures. The slag from the peat B mixings had a slightly higher Ca content compared with the Si content and a clearly higher content of Ca compared with the peat A mixtures. There were still Ca-Mg oxides left in the bottom ash i.e. a less amount of sticky low temperature melting K-silicate rich melt was formed when peat B was added to the woody biomasses.
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| 10. |
- Olwa, Joseph, et al.
(författare)
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Potassium retention in updraft gasification of wood
- 2013
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 27:11, s. 6718-6724
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Tidskriftsartikel (refereegranskat)abstract
- The release of compounds of K with producer gas during biomass gasification is known to play significant roles in fouling and high-temperature corrosion in boilers and high-temperature heat exchangers as well as blades in gas turbines that use producer gas as fuel. These phenomena are a major setback in the application of biomass fuel in combination with advanced process conditions. Updraft gasification provides gas filtering by the fuel bed with a gas cooling effect, conditions anticipated to create an avenue for K retention in the gasifier. The objective of this study was to determine the K retention potential of such gasifiers during wood gasification. Samples for the determination of the fate of K compounds included in the feedstock were collected from the generated producer gas using Teflon filters and gas wash bottles and also from wall deposits and ash residues. Analyses of samples were carried out using inductively coupled plasma-atomic emission spectrometry/mass spectrometry and X-ray diffraction methods. The finding was that about 99% of K was retained in the gasifier. K was found in the ash samples as a crystalline phase of K 2Ca(CO3)2(s) (fairchildite). A possible reaction mechanism leading to the formation of K2Ca(CO 3)2 is discussed in the paper. The 1% K understood as released, equivalent to 1200 ppbw content of K entrained in the producer gas stream, exceeds a known limit for application of the gas in conventional gas turbines. This would suggest application of the gas in an externally fired gas turbine system, where some limited K and other depositions in the heat exchanger can be relatively easy to handle.
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