Influence of Feedstock on the Release of Potassium, Sodium

Article pubs.acs.org/EF

Influence of Feedstock on the Release of Potassium, Sodium, Chlorine, Sulfur, and Phosphorus Species during Gasification of Wood and Biomass Shells Marc Blas̈ ing,* Mostafa Zini, and Michael Müller Institute for Energy and Climate Research (IEK-2), Forschungszentrum Jülich GmbH, Leo-Brandt-Straße 1, 52425 Jülich, Germany ABSTRACT: The objective of this work was to investigate the influence of feedstock on the release of trace elements during gasification. Therefore, different types of woody biomass and biomass residues (shells) were thermochemically converted in an atmospheric flow channel reactor furnace at different temperatures (900, 1200, and 1400 °C) under gasification-like conditions. For the determination of the composition of the hot gas, the flow channel reactor was coupled to a molecular beam mass spectrometer. The focus was set on the release of alkali metals (K and Na) and non-metals (S, Cl, and P), which are known for their high volatility and influence on the solid- and gas-phase chemistries, as well as the volatility of the other elements. The main gaseous species were 36HCl+, 58NaCl+, 74KCl+, 64SO2+, 60COS+, and 63PO2+. After quantification, the data set was correlated with the elemental composition of the biomass and likely release mechanisms are discussed. were screened for a particle size of ≤0.54 mm. The powder was stored under dry conditions at room temperature. The analysis of the biomass samples under investigation was performed by standard analytical methods by ENEA7 and the central division of analytical chemistry of Forschungszentrum Jülich GmbH. The results of the analysis of the biomass are given in Table 1. 2.2. Gasification of Biomass and Characterization of Inorganic Trace Species in the Product Gas. A schematic of the experimental setup is given in Figure 1a. The experimental setup has already been described in detail elsewhere.8 Therefore, only sufficient detail to allow the work to be reproduced is provided, and only relevant modifications are described. The thermochemical conversion of the biomass was carried out in an electrical-heated high-temperature tube furnace. Vapor alkali metal, phosphorus, sulfur, and chlorine species in the high-temperature product gas were detected online by molecular beam mass spectrometry (MBMS). The reactor consisted of a 21 mm diameter alumina tube reactor, placed in a furnace working through five heating zones, independently adjustable of each other. The reactor was made of alumina to prevent reactions between conversion products and the reactor walls and to allow for thermal cracking of hydrocarbons at high temperatures (1500 °C, as shown in Figure 1a). The end of the reactor was coupled to the sampling orifice of the MBMS device, to sample the high-temperature gasification products. The orifice protruded into the furnace, to maintain an elevated temperature to prevent condensation of gasphase species on the tip of the orifice. The gas and sample inlet consisted of a brass flange sealed to the cold zone of the reactor. A platinum sample boat containing the biomass was attached to the end of a 6 mm diameter alumina rod. The furnace was maintained at a constant temperature of 900, 1200, and 1400 °C in the reaction zone, as shown in Figure 1a. The experiments were performed at atmospheric pressure. The atmosphere consisted of He/0.2% O2. The low oxygen content was necessary to simulate gasification-like conditions during the thermochemical conversion of biomass, as shown by Porbatzki et al.9,10 The overall flow rate was 3.0 L/min [standard temperature and pressure (STP)]. The residence time of

1. INTRODUCTION The role of renewable energies in the energy supply is increasing worldwide; e.g., for Germany, the whole energy supply can be produced by renewables in the year 2050, as shown by a study of the Federal Environment Agency.1 There is no doubt that the use of biomass as an energy source will play an important role within the renewable energy supplying sector. However, the use of biomass in energy conversion should not be in competition with other types of use, especially food production. Therefore, the focus of the investigation was set on woody biomass as well as biomass residues. Biomass can be used for efficient power generation by thermochemical conversion. This is typically achieved using combustion, gasification, or pyrolysis techniques. Despite the fact that these techniques have been established for decades, several problems are still not satisfactorily solved. The release of inorganic species can give rise to several problems in power plants. Phosphorus and sulfur species can cause catalyst deactivation.2−4 Alkali metal and chlorine species can cause several problems in downstream parts of the gasifier, e.g., fouling, slagging, and corrosion.5,6 Secondary reactions of the released species with unburned fuel or ash can have significant influence on the release. Therefore, it is important to clearly understand the mechanisms by which the releases take place. The objective of this work was to study the influence of the composition of the biomass on the release of different trace elements during gasification of biomass. 2. EXPERIMENTAL SECTION 2.1. Biomass Samples. A first criterion for the use of biomass in energy production is the availability on a significant scale. Therefore, woody biomass has been chosen in the first order.7 Then, biomass shells have been considered for use, because they are not in competition with food production.7 In summary, six biomass and biomass residue samples were used in the experiments (Table 1). Some biomasses were delivered pelletized or in the form of chips. Powder with a particle size of ≤0.54 mm was obtained using an IKA laboratory mill to chop the samples into pieces. Afterward, the samples © 2013 American Chemical Society

Received: December 17, 2012 Revised: February 10, 2013 Published: February 21, 2013 1439

dx.doi.org/10.1021/ef302093r | Energy Fuels 2013, 27, 1439−1445

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Article

Table 1. Results of the Analysis of Biomass (wt %) willow

poplar

HHV (MJ/kgdry) ash (dry) humidity (as received) C H O N S Cl P Al Si Fe Ca Mg Na K

19.38 0.81 7.8 47.9 6.3 44.5 0.44 0.0430 0.0170 0.0190 0.0032 0.0196 0.0033 0.3649 0.0315 0.0007 0.0962

19.6 0.88 5.0 49.3 6.41 43.2 0.14 0.0800 0.0150 0.0167 0.0147 0.1041 0.0126 0.2864 0.0327 0.0041 0.0960

K/Cl S/Cl K/(Si + Al) P/S Ca/S

5.1 2.8 3.0 0.5 6.8

5.8 5.9 0.6 0.2 2.9

oak

pine seed shells

19.02 21.4 2.13 1.12 10.5 13.8 48.5 51.3 6.3 6.4 42.8 40.7 0.25 0.48 0.0300 0.0130 0.0400 0.0190 0.0231 0.0058 0.0114 0.0016 0.0357 0.1602 0.0104 0.0043 0.1764 0.0278 0.0854 0.0297 0.0043 0.0043 0.1248 0.0617 Elemental Ratio (Molar Basis) 2.8 2.9 0.8 0.8 1.9 0.3 0.8 0.5 4.7 1.7

conversion products in the reactor before reaching MBMS was in the range of 0.1−0.2 s. A typical experimental run consisted of the following steps. At the start of the experiment, a platinum boat loaded with 140 mg of biomass was inserted into the air-cooled end of the heated flow channel. The gas mixture was fed into the reactor, and the background signal was detected by MBMS. After about 20 s, the sample boat was placed in the hot reaction zone by a horizontally displaceable alumina rod. The heating of the biomass particles occurred with about 300 K/s. The devolatilization temperature was reached shortly after sample insertion. The hot gaseous products flowed to the end of the reactor. All parts downstream of the reaction zone were kept over the condensation point of the alkali metal, phosphorus, sulfur, and chlorine species of interest. For online analysis of the hot product gas, the reactor was coupled to MBMS. A schematic of MBMS is given in Figure 1b. A more detailed description of MBMS can be found elsewhere.11,12 The reaction products entered MBMS through a nozzle with 0.3 mm in diameter. MBMS consists of three differentially pumped chambers. Because of immediately supersonic free jet expansion of the hot gas into the first high vacuum chamber (10−2 mbar), the species are cooled far below room temperature in microseconds, attain free molecular flow, and therefore form a molecular beam. The core of the free jet expansion is extracted by a conical skimmer of 1 mm in diameter and directed into the third chamber. There, a hot filament emits electrons with an electron energy of 50 eV and an emission current of 1 mA. Every 10−4−10−3 molecule is ionized by electron impact. After passing the deflector, the ions are filtered in a quadrupole mass analyzer and detected by an off-axis electron multiplier. The amplified signal is recorded by a computer and software package as a function of the time and mass-to-charge ratio. To be able to monitor the gasification process with sufficient temporal resolution, 10 scans per second were acquired. To ensure reproducibility, six samples of each biomass were measured. In preliminary measurements, mass spectra from 10 to 150 atomic mass units (amu) were scanned. Because of the high temperature of the cracking zone of 1500 °C, most of the volatile organic matter was effectively cracked, despite the short residence time of 0.1−0.2 s.13,14

hazel nut shells

almond shells

20.4 0.86 12.8 51 6.1 41.5 0.45 0.0220 0.0260 0.0093 0.0058 0.0277 0.0058 0.1746 0.0274 0.0013 0.2480

20.22 1.65 11.2 47.8 6.38 43.6 0.44 0.0260 0.0290 0.0439 0.0202 0.1090 0.0169 0.1779 0.0394 0.0167 0.5779

8.7 0.9 5.3 0.4 6.4

18.1 1.0 3.2 1.7 5.5

3. RESULTS AND DISCUSSION The experiments simulate the gasification of the biomass samples from initial heating to devolatilization and conversion of the char. Exemplary intensity versus time profiles sampled during the experiments with oak and hazel nut shells at 900, 1200, and 1400 °C in He/0.2% O2 are shown in panels a and b of Figure 2. Species of interest with a significant high signal-tonoise ratio were 60COS+ (m/z 60), 64SO2+ (m/z 64), 36HCl+ (m/z 36), 74KCl+ (m/z 74), 58NaCl+ (m/z 58), and 63PO2+ (m/ z 63). The occurrence of the S species 60COS+ indicated clearly that the experimental conditions during the devolatilization phase represent gasification-like conditions. The bulk of the release of the species under investigation occurred during the devolatilization phase. Therefore, quantification of the spectra was performed only for this phase. Quantification was performed by normalization of the peak area during the devolatilization phase to the 34O2+ signal of the first 20 s of the experimental run, during which time, the steady oxygen concentration led to a steady signal. The averaged, normalized peak areas of 60COS+, 64SO2+, 36HCl+, 74KCl+, 58NaCl+, and 63 PO2+ are depicted in panels a−f of Figure 3. The bars of the charts are the averaged, normalized peak areas and belong to the left y axis. The error bars stand for the variance of the measurements and belong to the left y axis. The symbols represent the content of inorganic elements, which play an important role for the release of the species of interest in the figure. The data of the element content belongs to the right y axis. The detailed description and further discussion of the spectra are given in the following. Shortly after sample insertion, the sample reached the required temperature for devolatilization. During devolatilization, volatile organic matter and inorganic matter were released and reacted immediately with oxygen. This caused a lack of oxygen, as shown by the sharp drop off of the 34O2+ signal intensity (panels a and b of Figure 2). However, the changeover from devolatilization to char reaction 1440


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seed shells with 4.34 × 10−3 at 900 °C, 5.73 × 10−3 at 1200 °C, and 3.62e−3 at 1400 °C, despite the fact that it has the lowest S content of the six biomasses, as shown in panels a and b of Figure 3. A likely explanation has to include the mode of occurrence of sulfur and calcium, because easily available Ca is well-known for its ability to capture S. In general, the amount of Ca was much higher than the amount of S for the biomass under investigation, despite the pine seed shells, as shown by the molar ratio Ca/S in Table 1. For the latter, the amount of Ca is only slightly higher than the amount of S. Furthermore, the release of 64SO2+ and 60COS+ was in good correlation with ratio Ca/S on a molar basis. A likely explanation is that the fuel Ca is an active suppressor for the release of the S species 64SO2+ and 60COS+. The increasing amount of 64SO2+ with an increasing temperature could be likely explained by the formation of Ca−silicates and Ca−aluminosilicates, as shown exemplarily by eq 1, which is becoming favored at 1200−1400 °C. An indication for the correctness of this assumption is the high increase from 900 to 1200 °C and the low increase from 1200 to 1400 °C, which can be explained by the state of the ash-forming minerals, which changed from solid to molten with an increasing temperature in the temperature range of investigation. The negative correlation of the release of 64 SO2+ with the ratio alkaline earth metal/sulfur and alkaline earth metal/phosphorus and phosphorus/sulfur is the formation of stable, non-volatile alkaline earth metal sulfides, sulfates, and phosphates and competing reactions.9,10 The latter is expressed by way of the example in eq 2, which results in the release of H2S. H2S can undergo further reaction in the gas phase and form COS (eq 3).

Figure 1. Schematic of the (a) tube reactor and (b) molecular beam mass spectrometer.

CaO + x AlSi yOz ⇄ Ca−aluminosilicate

(1)

3CaS + 3H 2O + P2O5 ⇄ Ca3(PO4 )2 + 3H 2S

(2)

H 2S + CO2 ⇄ H 2O + COS

(3)

36

+

The bulk of the chlorine species HCl was released during the devolatilization phase at 900, 1200, and 1400 °C (spectra in panels a and b of Figure 2). The averaged, normalized peak areas are depicted in Figure 3c. The release decreased significantly with an increasing temperature. The pine seed shells showed the highest release with an averaged, normalized peak area of 9.28 × 10−2 at 900 °C, 6.77 × 10−2 at 1200 °C, and 3.86 × 10−2 at 1400 °C. In general, the woody biomasses showed a lower release than the biomass shells. The released amount of the woody biomass was about 27−39% of the amount of the pine seed shells at 900 °C, about 26−36% of the amount of the pine seed shells at 1200 °C, and about 30−44% of the amount of the pine seed shells at 1400 °C. The correlation analysis showed no direct correlation of the Cl content of the biomasses and the released amount of 36HCl+, as shown in Figure 3c. This is obviously significant for oak, which has the highest Cl content but showed one of the lowest released amounts of 36HCl+. On the opposite, pine seed shells have a comparatively low Cl content but showed the highest released amount of 36HCl+. A likely explanation of the observed release behavior can be found in the good negative correlation of the ratio alkaline metals/chlorine and alkaline earth metals/ chlorine and the amount of 36HCl+. The mentioned metals form thermodynamically stable chloride species. The equilibrium of metal chloride and hydrogen chlorine, as shown by eqs 4 and 5, is changed to the metal chlorides with a decreasing temperature, which can additionally cause changes of the

phase is gradual and not as sharp as marked in the panels. The length of the devolatilization phase decreased with an increasing temperature from 900 to 1200 to 1400 °C (phase I in panels a and b of Figure 2); e.g., the devolatilization phase was 14.3 s at 900 °C, 11.4 s at 1200 °C, and 11.4 s at 1400 °C for the hazel nut shells and 15.7 s at 900 °C, 13.4 s at 1200 °C, and 12.9 s at 1400 °C for the oak. The bulk of the sulfur species 60COS+ was released within the devolatilization phase with low to moderate intensity. Another detected S species was 64SO2+, which was released with high intensity during the devolatilization phase and low intensity during the char reaction phase (phase II in panels a and b of Figure 2). The averaged, normalized peak areas of 60COS+ and 64 SO2+ are depicted in panels a and b of Figure 3, respectively. In general, the amount of 64SO2+ was about 1 order of magnitude higher than the amount of 60COS+. The amount 64 SO2+ strongly increased with an increasing temperature from 900 to 1200 to 1400 °C. The amount of 60COS+ showed no significant temperature dependence. The latter was mainly caused by the high variance of the released amount, as expressed by the error bars of the normalized peak areas. In general, pine seed shells showed the highest release of 64SO2+, with an averaged, normalized peak area of 3.84 × 10−2 at 900 °C, 8.18 × 10−2 at 1200 °C, and 1.38 × 10−1 at 1400 °C. Also, the averaged, normalized peak area of 60COS+ was high for pine 1441


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Figure 2. Intensity−time profiles of 34O2+/34H2S+ (m/z 34), 60COS+ (m/z 60), 36HCl+ (m/z 36), 74KCl+ (m/z 74), 58NaCl+ (m/z 58), and 63PO2+ (m/z 63) gained during the gasification of (a) oak and (b) hazel nut shells (I, devolatilization phase; II, char reaction phase).

reactions are strongly effected by the residence time. This explanation is supported by Knudsen et al.15 They found a significant recapture of released HCl during combustion experiments of wheat straw in the temperature range of 400− 950 °C. Their spectroscopic and chemical analyses revealed that HCl was mainly captured by the inherent metal species. Furthermore, Björgman and Strömberg16 suggested that the release of Cl may occur when KCl reacts in an ion-exchange reaction with chain-bound carboxylic groups, yielding an alkaline carboxylate and HCl. This reaction is likely favored

amount of metal chloride and hydrogen chloride. However, this is only a thermodynamic point of view, and the kinetics seems to have a significant effect on the release. Therefore, a likely explanation is given in the following. According to Jensen et al.,3 much of the original organic straw matrix is destructed during pyrolysis (straw) and Cl and K are probably released from the original binding sites and transferred to a liquid tar phase. Cl can be further released to the gas phase as HCl or combine with K to KCl or with basic functionalities on the char surface. Further, Jensen et al.3 observed that secondary 1442


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Figure 3. Averaged, normalized peak area of (a) gasification experiments.

Article

60

COS+, (b)

SO2+, (c)

64

at temperatures below 700 °C, because the alkaline carboxylate is degraded at higher temperatures. In summary, it seems that there is a narrow temperature window for the effective recombination of K and Cl to KCl. At lower temperatures, less alkaline and alkaline earth metals are available for the formation of chloride. At least parts of Cl have already left the biomass and formed HCl before a recombination with the mentioned metals could lead to the formation of chloride. Therefore, Cl can mainly form HCl. At higher temperatures (1200−1400 °C), K, Na, Ca, and Mg become available more easily, because of faster thermal degradation of carboxylates and carbonates. This can cause decreasing of the release of 36HCl+ with an increasing temperature. However, the underlying reactions are very complex and competitive, as shown in eq 4 by way of an example. An increasing temperature shifts the

36

HCl+, (d)

63

PO2+, (e)

58

NaCl+, and (f)

74

KCl+ gained during the

reaction to the side of Ca(OH)2 and HCl. Therefore, an overall satisfying release mechanism of HCl could not been proposed. CaCl 2 + H 2O ⇄ Ca(OH)2 + 2HCl

(4)

KCl + H 2O ⇄ KOH + HCl

(5)

The phosphorus species 63PO2+ was detected with a low signalto-noise ratio (panels a and b of Figure 2) and high variance (Figure 3d). In general, the released amount of 63PO2+ was low for both the woody biomass and the biomass shell samples; e.g., the pine seed shells showed the lowest released amount, with an averaged, normalized peak area of 1.24 × 10−3 at 1200 °C. There was no significant correlation of the released amount and amount of P of the biomass, as expressed in Figure 3d. Furthermore, there was no significant correlation of the 1443


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released amount of 63PO2+ and the temperature. However, this was most likely caused by the high variance of the results, because of the low signal-to-noise ratio, which indicated that the measurement was performed close to the detection limit. The bulk of the alkali metal species 74KCl+ and 58NaCl+ was released during the devolatilization phase (panels a and b of Figure 2). This can be explained by the mode of occurrence of alkali metals in biomass. Main forms are alkali chloride and organic-bond alkali metal ions. Commonly, alkali metals form highly volatile species, e.g., KCl, KOH, NaCl, and NaOH. The release of 58NaCl+ showed a high variance of the normalized peak areas of 58NaCl+, and further interpretation must be taken with care. However, there is one significant observation. The released amount of 58NaCl+ was relatively high in comparison to the amount of 74KCl+ (panels e and f of Figure 3), despite the fact that the amount of K of the biomass under investigation is about 1 order of magnitude higher than its amount of Na. A likely explanation is the formation of K− aluminosilicates, as shown in eq 6, and the ion exchange, as shown in eq 7. K−Aluminosilicates are thermodynamically more stable than Na−aluminosilicates, and therefore, the formation of K−aluminosilicates as well as the ion exchange is favored from a thermodynamic point of view. The released amount of 74KCl+ decreased with an increasing temperature; e.g., willow showed an averaged, normalized peak area of 4.89 × 10−3 at 900 °C, 2.57 × 10−3 at 1200 °C, and 1.63 × 10−3 at 1400 °C. Part of an explanation could be the shift of the equilibrium between KCl and HCl, as shown in eq 5, which has been mentioned above. However, this should cause an increase of HCl with an increasing temperature, which was not observed. Therefore, the formation of K−aluminosilicates seems to be a major part of the explanation of the observed temperature dependency. More information about the alkali metal fate came from recently performed X-ray diffraction (XRD), scanning electron microscopy (SEM), and energydispersive spectrometry (EDS) analysis of straw, wood, and Miscanthus ash (at 550 °C and gasification-like conditions).17 The analysis revealed that the composition was mainly formed of SiO 2 , K− and Ca−aluminosilicates, CaS, different phosphates, and very small amounts of Cl species. Additionally, the negative, high correlation of the release of 74KCl+ with the ratio (Si + Al)/K (as shown in Table 1) can be explained by the formation of K−aluminosilicates and is therefore an additional indicator of the correctness of the explanation.

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AUTHOR INFORMATION

Corresponding Author

*Telephone: +49-2461-61-1574. Fax: +49-2461-61-3699. Email: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The work described in this paper has been performed in the framework of the UNIQUE project, funded by the European Community (EC) in the seventh framework program (Contract 211517). Part of the biomass analysis results were kindly supplied by ENEA Biomass Laboratory, Rotondella, Italy.

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REFERENCES

(1) Klaus, T.; Vollmer, C.; Werner, K.; Lehmann, H.; Müschen, K. Energy Target 2050: 100% Renewable Electricity Supply; Federal Environment Agency: Dessau, Germany, 2010. (2) Baxter, L. L.; Miles, T. R.; Jenkins, B. M.; Milne, T.; Dayton, D.; Bryers, R. W.; Oden, L. L. The behavior of inorganic material in biomass-fired power boilers: Field and laboratory experiences. Fuel Process. Technol. 1998, 54, 47−78. (3) Jensen, P. A.; Frandsen, F. J.; Dam-Johansen, K.; Sander, B. Experimental investigation of the transformation and release to gas phase of potassium and chlorine during straw pyrolysis. Energy Fuels 2000, 14, 1280−1285. (4) Jensen, P. A.; Frandsen, F. J.; Hansen, J.; Dam-Johansen, K.; Henriksen, N.; Horlyck, S. SEM investigation of superheater deposits from biomass-fired boilers. Energy Fuels 2004, 18, 378−384. (5) Nielsen, H. P.; Frandsen, F. J.; Dam-Johansen, K.; Baxter, L. L. The implications of chlorine-associated corrosion on the operation of biomass-fired boilers. Prog. Energy Combust. Sci. 2000, 26, 283−298. (6) Hupa, M. Ash-related issues in fluidized-bed combustion of biomasses: Recent research highlights. Energy Fuels 2012, 26, 4−14. (7) Valerio, V.; Villone, A.; Nanna, F.; Barisano, D. Biomass selection for the test campaign at the UNIQUE pilot plant. Proceedings of the International Conference on Polygeneration Strategies; Vienna, Austria, Sept 1−4, 2009. (8) Wolf, K. J.; Smeda, A.; Müller, M.; Hilpert, K. Investigations on the influence of additives for SO2 reduction during high alkaline biomass combustion. Energy Fuels 2005, 19, 820−824. (9) Porbatzki, D.; Florjan, M.; Smeda, A.; Müller, M. Influence of mineral phases on the release of inorganic constituents from biomass ashes under combustion and gasification conditions. Proceedings of the 14th European Biomass Conference and Exhibition; Paris, France, Oct 17−21, 2005. (10) Porbatzki, D.; Müller, M. Release of phosphorus during combustion and gasification of herbaceous biomass. Proceedings of the 15th European Biomass Conference and Exhibition; Berlin, Germany, May 7−11, 2007. (11) Dayton, D. C.; Frederick, W. J. Direct observation of alkali vapor release during biomass combustion and gasification. 2. Black liquor combustion at 1100 °C. Energy Fuels 1996, 10, 284−292. (12) Dayton, D. C.; French, R. J.; Milne, T. A. Direct observation of alkali vapor release during biomass combustion and gasification. 1. Application of molecular beam mass spectrometry to switchgrass combustion. Energy Fuels 1995, 9, 855−865. (13) Bläsing, M. Release of Inorganic Trace Elements from HighTemperature Gasification of Coal; Forschungszentrum Jülich GmbH: Jülich, Germany, 2012; ISBN: 978-3-89336-772-6.2. (14) Porbatzki, D.; Stemmler, M.; Müller, M. Release of inorganic trace elements during gasification of wood, straw, and miscanthus. Biomass Bioenergy 2011, 35, 79−86. (15) Knudsen, J. N.; Jensen, P. A.; Lin, W.; Dam-Johansen, K. Secondary capture of chlorine and sulfur during thermal conversion of biomass. Energy Fuels 2005, 19, 606−617.

KCl + H 2O + x AlSi yOz ⇄ K−aluminosilicate + HCl (6)

KCl + Na−aluminosilicate ⇄ K−aluminosilicate + NaCl (7)

4. CONCLUSION In this work, the influence of feedstock and temperature on the release of alkali metal, chlorine, sulfur, and phosphorus species during gasification of different types of biomass at 900, 1200, and 1400 °C was investigated by MBMS. The bulk of the release of 60COS+, 64SO2+, 36HCl+, 74KCl+, 58NaCl+, and 63PO2+ occurred during the devolatilization phase. The length of the devolatilization phase decreased significantly with an increasing temperature. Shifts of reaction equilibrium caused by temperature change as well as secondary reactions with ash-forming material (e.g., aluminosilicates) have significantly changed the released amount of the species under investigation. 1444


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(16) Björgman, E.; Strömberg, B. Release of chlorine from biomass at gasification conditions. Energy Fuels 1997, 11, 1026−1032. (17) Porbatzki, D. Freisetzung anorganischer spezies bei der thermochemischen umwandlung biogener festbrennstoffe. Ph.D. Thesis, Jülich, Germany, 2008.

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Influence of Feedstock on the Release of Potassium, Sodium

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