23rd European Biomass Conference and Exhibition, 1-4 June 2015, Vienna, Austria, pp

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1 MITIGATION ASH-RELATED PROBLEMS BY COFIRING COAL WITH WOODY BIOMASS IN CASE OF KAKANJ THERMAL POWER PLANT EXPERIMENTAL AND TRIAL RUN Nihad Hodžić 1), Izet Smajević 1,2), Anes Kazagić 2) 1) University of Sarajevo, Faculty of Mechanical Engineering Vilsonovo šetalište 9, BiH Sarajevo 2) Elektroprivreda BiH dd Sarajevo, Vilsonovo šetalište 15, BiH Sarajevo ABSTRACT: Thermal power plant Kakanj (2x118 MW e, 1x230 MW e ) uses blend of brown coals of Middle Bosnia from a coal basin with huge coal reserves. Principally it is low grade brown coal with very high percentage of ash - over 40%, high sulphur content and inconvenient ash composition, exhibiting a strong tendency to slagging and fouling. The very high percentage of ash particularly makes clear certain differences between this coal type compared with some other world coal types, providing a strong argument for investigating the specific ash-related problems as well as ways to improve combustion behavior. Co-firing with woody biomass is one of the possible solution for the improvement and that is the subject of investigation in this study. Two groups of experimental tests were performed in this study: laboratory testing of co-firing and trial run on a large-scale plant based on the laboratory research results. A laboratory experiment was carried out in an electrically heated entrained pulverized-fuel flow furnace. Coal-woody biomass blends of 93:7% by weight and 80:20% by weight were tested. Biomass used in this case is spruce sawdust. Co-firing trials were conducted over a range of the following process variables: process temperature, excess air ratio and air distribution. Neither of the two coal-sawdust blends used produced any significant ash-related problems provided that the process temperature did not exceed 1250 o C. Based on and following the laboratory research findings, a trial run was carried out in a large-scale utility - the Kakanj power station Unit 5 (118 MW e ), using two mixtures; one in which 5%/w and another in which 7%/wt of brown coal was replaced with the woody sawdust. Compared to a reference firing process with 100% coal, these co-firing trials produced a more intensive redistribution of the alkaline components in the slag in the melting chamber, with a consequential beneficial effect on the deposition of ash on the superheater surfaces of the boiler. The outcome of the tests confirms the feasibility of using 7%w of woody sawdust in combination with the coal without risk to the efficiency of the unit, its combustion process and with the benefits of emissions reductions as well as reducing ash deposits problems. Furthermore, they show that no modification to the existing coal transport system and boiler equipment is necessary to achieve this outcome. Keywords: biomass, coal, ash, furnace, boiler. 1 INTRODUCTION As set out in the European Commission s White Paper on Energy for the Future: Renewable sources of energy [1], in the short-to-medium term, the cocombustion of biomass and bio-waste in coal-fired power plants is one of the most straightforward biomass applications. The main reasons for using biomass as cofuel is its dual role in greenhouse gas mitigation, as a substitute for fossil fuels (bio-energy) and as a carbon sink, [2]. Fuels derived from biomass also contain less sulfur or trace elements. Current research on cocombustion is focused on controlling combustion behaviour, emissions, corrosion, agglomeration, and fouling-related problems. Biomass for combustion in industrial-scale furnaces must meet a number of criteria, including availability throughout the year to ensure security of supply, high density to minimize transportation costs, sufficiently high heating value, and acceptable price, [2]. Wood residue meets these requirements, [2-4]. In the last decade, significant progress has been made in the utilisation of biomass in coal-fired power stations. Over 250 units in the world have either tested or demonstrated co-firing of biomass or are currently co-firing on a commercial basis, [5]. Coal is often replaced with up to 30% by weight of biomass in pulverised coal plants, as in Belgium, Canada, Denmark, Finland, The Netherlands, Sweden, United Kingdom, Germany, Poland and The United States. Most of these projects are related to co-firing with biomass of highranked coal (both bituminous and anthracite), while cofiring of low-ranked sub-bituminous coal and lignite with biomass is more limited, e.g. those projects involving Greek lignite reported in [6]. Bosnian coal types - lignite and brown coal, mainly fired into Bosnian coal-based power plants, are generally low rank, with high propensity to the slagging and fouling, high content of ash and sulphur and low net calorific value. Due to some specific benefits and synergy effects, co-firing of coal with woody biomass in existing coal-fired power plants is supposed to be one of the perspective combustion technologies for Bosnian case, [7-10]. Ongoing research activities is focused on controlling combustion behaviours, emissions, as well as slagging and fouling-related problems the issue which is of vital importance for the boiler operators. Primary goal of the research presented here is to investigate how the fuel type and the process temperature influence to the slag formation during co-firing of pulverised Bosnian coals with pulverised woody biomass. The work is a part of continuous research on slagging/fouling and emissions in co-firing of coal and biomass being carried out by Faculty of Mechanical Engineering of University in Sarajevo, supported by EPBiH power utility of Bosnia and Herzegovina. 2 FUEL TEST MATRIX Two groups of experimental tests were performed in this study: lab-scale tests of the co-firing and trial run on a large-scale power plant followed on the lab-scale research results. The co-firing fuel test matrix is shown in Table 1, with proximate and ultimate analyses of the fuel tested given. The ash-reach Kakanj brown coal (K) has been chosen as basic coal for the lab-scale tests. This coal is mainly used in the boilers with slag tap furnaces in the

2 Kakanj power station (2x118 MWe, 1x230 MWe), with a share of %w in the coal blend. Biomass used in this case is spruce sawdust (S). Blends of coal Kakanj with woody biomass at 93:7%w and 80:20%w proportions were tested. The basic coal blend (U), consisting of the coals Kakanj:Breza:Zenica at approximate mass ratio of 70:20:10 was used in co-firing trial run on Kakanj TPP unit 5 (118 MWe) with a mix of different waste woody biomass in form of sawdust (B) at 5%w and 7%w of the biomass portion in fuel blend. Principally, tested coals are low grade brown coals with very high percentage of ash 40%, high sulphur content and inconvenient ash composition, exhibiting a strong tendency to slagging and fouling, see Table I. Comparison of the results in Table 1 for the coals and biomass, suggest that the main difference between them relates to the ash content, as the coal types tested have very high ash content compared to the sawdust. This has a significant influence on the combustible content and calorific value of the fuels. On the other hand, the biomass sample has a very high volatile content, which may be expected to accelerate the combustion process, while the coal types have a much higher fixed carbon concentration. Finally, the wood sample has significantly lower sulfur content. Table I: Proximate and ultimate analyses of the fuels tested Fuel K100 U100 S100 B100 K93S7 K80S20 U95B5 U93B7 No Proximate analysis, %, as-received Moisture Ash Volatiles Fixed C Combustible Ultimate analysis, %, as-received Carbon Hydrogen Sulphur Nitrogen Oxygen Heating value, kj/kg, as-received Gross Net In Table II, the ash chemical analyses of the coals and the biomass tested, in their oxides, are given. Compared to the coal types tested, the spruce sawdust has very high potassium content in its ash and mix of sawdust high percantage of sodium, which could cause serious ash deposition problems. Distribution of alkali metals and lower content of silica and alumina compounds are anticipated to reduce the ash fusion temperatures of the sawdust samples. Table II: Ash chemical composition of the fuels tested Fuel K100 U100 S100 B100 K93S7 K80S20 U95B5 U93B7 No SiO Fe 2 O Al 2 O CaO MgO SO < TiO < Na 2 O K 2 O EXPERIMENTAL CONFIGURATIONS Two groups of experimental tests were performed in this study: - Lab-scale tests, and - Trial runs on a large-scale power plant. 3.1 Lab-scale tests Lab-scale furnace configuration: Laboratory tests have been carried out by an electrically heated entrained pulverized-fuel flow furnace, installed at Faculty of Mechanical Engineering of Univerity in Sarajevo, in Laboratory for combustion of coal and biomass, see Figure 1. The main feature of the experimental furnace is ability to change the process temperature at desire in the range from the ambient to 1560 ºC. It is provided by SiCtype electric heaters controlled by a central PLC and thiristor units connected at PLC digital outputs for each heating zones of the furnace, [7-10].

3 Figure 1: Schematic layout of the lab-scale furnace used for the co-firing tests Various types of coal and biomass can be used, processed to appropriate particle size by a laboratory hammer mill. The pulverized fuel particles were fed into the reactor by means of a volumetric-type feeder, equipped with a speed controller, allowing mass flow in the range of kg/h. The air for combustion from the blower was split into carrier or primary air, secondary air, tertiary air, and over fire air (OFA), see Figure 1. The first three air portions were fed into the reactor over a burner placed at the top of the reactor, so that the air-fuel particle mixture flowed downward. The final air portion or OFA is ised for burning out, i.e. to investigate the air stage combustion, simulating the OFA system used in large boilers. It was fed directly into the reaction tube at two pozitions, see Figure 1. The excess air ratio was adjusted by controlling the air flow in each air line at a constant fuel flow. Lab-scale test demonstration: In each co-firing run in the laboratory, sawdust was mixed with coal, the fuel mixture was pre-dried at approximately w = 0%, milled to the specific particle size range and then supplied into the feeder tank of the furnace. Particle size distribution for the fuels tested rest on the sieve in %w, is shown in Table III. Table III: Particle size distribution for the fuels tested rest on the sieve in %wt Total passed Fuel % µm µm µm µm µm µm µm K S K93S K80S Fuel thermal load was kept at approximately 5 kw th in all runs. Process temperature varied from 880 to 1550 C and excess air ratio from 0.95 to 1.4. Depending on the kind of fuel used and excess air amount, the total airflow rate was between 4.29 and 6.60 m n 3 /h. The primary (carrier) air flow rate was set at 1.50 m n 3 /h for all runs, with the rest of the air divided into secondary and tertiary portions, at a ratio of 2.6:1. During the tests, ceramic probes were set at 2 m off the top of the burner, see Figure 1. After 90 minutes of ash collecting, the ceramic probes with ash deposits are carefully taken out from the reactor for analyses. There was sufficient combustion efficiency for such a type of laboratory furnace in all co-firing regimes, with burning out in fly ash and slag deposits at 96.5 to 99.5% for brown coal sawdust co-firing, see Table IV. Methodology of ash deposition investigation: The lab-scale furnace is operated at varying electric power rates to vary the gas temperature, and so vary the nature of deposits formed at different process temperatures on the probes inside the furnace: two non-cooled ceramic probes, and a water-cooled metal surface of the lance head. The temperature ranges for different types of deposits are then determined from the data points obtaining during the tests. Slagging and fouling indicators are based on 6-criteria evaluation of the ash deposits, as described in detail in [9]. Basically, shape, state and structure of the ash deposit sample are determined on the base of visual observation (photographically) and optical observation by a microscope. Rate of adhesion and cohesion of the ash deposit are determined by physical acting to the ash sample. Finally, deposition rate is defined as a mass of the deposit collected at the probe, divided by the deposition area, as a function of time, [9]. Additionally, chemical composition analysis and Ash Fusion Test (AFT) of the deposits were also done to provide information on alkali metals distribution as function of the type of fuel and the process temperature. After analyses considering above mentioned criteria, those single evaluations are aggregated into final evaluation on propensity to the slagging/fouling for the given fuel and process conditions, [10]. The final evaluation on slagging/fouling propensity is expressed linguistically by the following terms: - Low slagging/fouling - Moderate slagging/fouling - Strong slagging/fouling - Very strong slagging/fouling The data points are then plotted against various coal/biomass property based indices, to estimate their range limits and general usefulness for Bosnian coal types and biomass, as described in [10]. 3.2 Trial run on a large boiler Large-scale boiler design: Based on the laboratory research findings, a trial co-firing run was carried out at the Kakanj power station unit 5 (118 MW e ), equipped with PF boiler with slag tap furnace, hammer mills and low NOx swirl burners, Figure 2, and which is fuelled with brown coal from the nearby coal mines of Middle Bosnia. The unit was fully reconstructed in 2003, when a new combustion system with low NOx swirl burners and OFA system was installed, and boiler efficiency increased up to 91%. Temperature in the slag chamber of the furnace

4 has been reduced following the reconstruction from its previous level of 1550 º C to 1450 º C at maximal load. Consequently, NO x emissions have been reduced from 1400 mg/m n 3 to approximately 700 mg/m n 6% O 2 dry, supported by the low NOx swirl burners and the Over Fire Air system installed. Seven types of brown coal are used in an appropriate coal blend, prepared and homogenized on the coal depot. The coal is transported from the coal depot to the boiler bunkers by belt conveyers. Then it is pulverized in the hammer mills, and dried by the hot air before introducing into the boiler over the coal burners. Thus, temperature of PF coal-air mixture obtained in the duct prior to the coal burners is approximately 150 º C (the coal was low-volatile), [11]. mixture at the exit from the mill was at the lower limit of the allowable range of temperatures (75 o C), possibly due to the higher moisture content in the fuel (the sawdust was wintered at the coal depot because the trial run was delayed in time), but this had no negative impact on the stability of combustion process and boiler operation. At the lower boiler loads, as well as in the process with 5% of sawdust, temperatures of fuel-air mixture were common. Figure 3: Temperatures at outlet cross section of melting chamber (points 1-4) and at furnace outlet (point 5) of Kakanj power plant Boiler unit 5 Figure 2: Boiler of TPP Kakanj unit 5 (118 MWe) Trial run demonstration: The trial run was adapted to the brown coal - spruce sawdust blends with the sawdust weight ratio of 0%, 5% and 7% (fuel blends U100, U95B5 and U93B7, respectively). Proximate and ultimate analyses of the fuels used in the trial run are given in Table 1. Spruce sawdust was supplied from the nearby sources by a contracted supplier. The blend of coal and sawdust is prepared at the coal depot, where the fuels are mixed by coal excavators before being transported to the boiler. The fuel mixture was fed into the furnace over the hammer mills and the coal burners. The thermal load was varied between 70 and 100% of maximal load, operating the unit at a gross electric power output of 75, 90 and 105 MWe. All measurements on the boiler used in this analysis (measurement of temperatures, flue gas compositions, emissions etc.) are operational measurements obtained from the existing modern SIEMENS-XP TELEPERM system installed on the Unit, which has been maintained, checked and revised according to the relevant standards and procedures. The boiler (block) operation during co-firing was stable for both of the co-firing mixtures, with 5 and 7%w ratio of the sawdust, in the complete range of the load, from a minimum (75 MW) to the maximum load (105 MW). At maximum load (105 MW) in the process with 7%w of spruce sawdust, the temperature of the fuel-air Temperatures of flue gases along the boiler, starting from the combustion chamber of the furnace up to the outlet of the boiler, have not experienced any adverse changes in co-firing of mixtures with 5 and 7%w of sawdust compared to temperatures recorded in the process with reference coal, in the entire range of boiler loads. The results of the temperature of flue gases in the melting chamber of the furnaces (measured by 4 optical pyrometers arranged evenly over the cross section at the outlet of the melting chamber), for various fuel mixtures in the trial run for a maximum load of the boiler are given in Figure 3, points 1-4. The temperature at the end of the furnace (measured by Pt-Rd-Pt thermocouples) that is relevant to the process of ash slugging/fouling in the flame zone threshold and superheaters surfaces in the boiler, is even more favorable (lower) in co-firing mixtures compared to the test with the reference coal, see Figure 3, point 5. So, not only has a negative impact been observed in terms of the temperature field in the boiler in co-firing trials, which could adversely affect the slagging/fouling and the efficiency of the boiler, but the temperature field in the boiler is even more favourable in the co-firing regimes tested. 4 TESTS RESULTS 4.1 Lab-scale tests results As aforementioned, evaluation of ash deposit types collected in the lab-scale furnace was supported by visual (photographically) and by microscope observation of the deposits. Figure 3 shows photos of the ash deposits collected on the non-cooled ceramic probes after 90 minutes for the Kakanj coal - spruce sawdust blends tested. This has shown that combustion of the coalsawdust blends tested yields no significant increasing of ash deposition compared to the Kakanj brown coal alone at temperatures up to 1250 o C. Above this temperature, ash deposition is accentuated for the coal-sawdust blend K80S20 and ash deposits melt and then harden, Figure 4.

5 Ash chemical composition, AFT and the unburnt of the ash deposits from the Kakanj coal-spruce sawdust cofiring are given in Table 6, to investigate influence of the fuel type and process temperature to the process efficiency and chemical compounds distribution. It can be noticed very high efficiency for the Kakanj coal alone in all regimes (burning out at 99%), as well as for blend K93S7 at 1140 ºC (burning out at 99.7%) and K80S20 in regime 1140 ºC (burning out at 99%). For remained the brown coal sawdust co-firing regimes efficiency is also high enough, with a value of burning out at 96.5%, see Table IV. Figure 4: Photos of the ash deposits for the Kakanj coal - spruce sawdust blends Table IV: Chemical composition and AFT of the ash deposits for the Kakanj brown coal-sawdust co-firing Ash deposit sample K 1140 K 1250 K 1400 K93S K93S K93S K80S K80S K80S Ash chemical composition, % unburnt SiO Al 2 O Fe 2 O CaO MgO K 2 O Na 2 O TiO SO AFT (temperature, o C) Sintering Softening Hemispherical Molten It can be noticed from Table IV that CaO content in ash deposits was increased when the process temperature has risen for all fuels tested. Furthermore, when temperature has risen, SO 3 content in the ash deposits was decreased for all the fuels tested. The reason is wellknown phenomenon of better bonding of SO 2 to the CaO and other alkali metal particles at lower temperatures, as reported by Rask, [12]. When temperature rises, CaSO 4 formed at lower temperatures becomes chemically unstable and sulphur oxides are released. This contributes to the higher SO 2 emission and consequently to a decreasing of sulphur oxides content is the ash when temperature rises, that is confirmed by this tests. In regard to AFT of the deposits, it can be noticed that fusion temperatures are principally decreased when biomass is added to the coal. This fact must be seriously taken into account for PF combustion in large boilers. It must be highlighted also that the decreasing for some fusion temperatures does not follow always proportionally the share of biomass in the fuel blend, see AFT in Table IV. The similar correlations were reported in [13, 14], According to the procedure of aggregation of single criteria evaluations into final evaluation of ash deposits, given in [10], in Table V evaluation of slagging behaviors, based on the lab-scale furnace tests, is provided for the Kakanj-spruce sywdust combinations tested. Table V: Final evaluation of slagging propensity at different process temperatures for the Kakanj/Spruce combinations tested ºC K100 K93S7 K80S Low Low 1140 Moderate Moderate Moderate 1250 Moderate Strong Strong 1400 Strong Strong Very strong 1550 Very strong - Very strong For the further analysis, the test points, reflecting above-mentioned final evaluations on propensity to slagging/fouling, are plotted against the appropriate coal/biomass indices onto graphic diagrams, see Figure 5. On the base of such a diagram, the limit values for certain slagging/fouling indicators may be set as function of combustion temperature. This presents an improvement of the use of traditional slagging/fouling indices, which use so far was based on the chemical ash composition only. This methodology makes analysis of slagging/fouling propensity to be more reliable.

6 consequently a beneficial effect on the characteristics of ash deposition formed on the superheater surfaces of boiler TPP Kakanj unit 5. Figure 5: Correlation between base-acid ratio and gas temperature from the lab-scale co-firing tests of the Kakanj brown coal-spruce sawdust, below line 1: low slagging/fouling, above line 2: strong slagging/fouling, between line 1 and line 2: moderate slagging/fouling 4.2 Trial run tests results In the planned pauses between the fuel trials during the trial run, a detailed inspection of the state of boiler heating surfaces was carried out in terms of identification of slagging/fouling of the boiler surfaces. Sampling of ash deposits was done in order to complete chemical analysis and to examine the detailed distribution of alkaline components in the composition of deposits. Deposits taken from the melting chamber and the superheater in zone of the furnace outlet are compared for different kinds of fueling, and analyzed for their chemical composition. A comparison of deposits taken from the superheater PP2A placed at the furnace outlet is given in Figure 6. There was no deterioration in the form of deposits in the co-firing trials compared to the trial of reference coal. On the contrary, deposits from the cofiring trials are more brittle. Specifically, the form of ash deposits in this zone of the boiler (the furnace outlet) is normal and acceptable; they are more brittle and easy-toremove. They do not represent a threat to the stability of operation or the boiler efficiency. This correlates with the findings of the laboratory tests and a suggestion that deposits will not be a problem if 7%w sawdust is blended with the coal used in large power stations. Figure 6: Ash depozits taken from superheater PP2A, fuel trials U100, U95B5 and U93B7 The base-acid ratio for the ash deposits is given in Figure 7. The results confirm the findings of the condition of the ash deposits in the region of the furnace outlet (Superheater PP2A), which is better in the cofiring trials than the deposits from the trial of reference coal. This corresponds to a lower (more favorable) base/acid ratio for deposits taken from superheater PP2A after the co-firing process. The results in Figure 7, and the findings on the deposits condition described above, indicate that co-firing regimes U95B5 and U93B7 produce a more intensive redistribution of alkaline components in the slag in the melting chamber, having Figure 7: Base/acid ratio for the ash depozits taken from the Boiler TPP Kakanj unit 5 5 CONCLUSIONS Two groups of experimental tests were performed in this study: laboratory testing of co-firing and trial run on a large-scale plant based on the laboratory research results. A laboratory experiment was carried out in an electrically heated entrained pulverized-fuel flow furnace. Coal-woody biomass blends of 93:7% by weight and 80:20% by weight were tested. Biomass used in this case is spruce sawdust. Co-firing trials were conducted over a range of the following process variables: process temperature, excess air ratio and air distribution. Neither of the two coal-spruce sawdust blends used produced any significant ash-related problems provided that the process temperature did not exceed 1250 o C. Based on and following the laboratory research findings, a trial run was carried out in a large-scale utility - the Kakanj power station Unit 5 (118 MW e ), using two mixtures; one in which 5%/w and another in which 7%/wt of brown coal was replaced with a mix of woody sawdust. Compared to a reference firing process with 100% coal, these co-firing trials produced a more intensive redistribution of the alkaline components in the slag in the melting chamber, with a consequential beneficial effect on the deposition of ash on the superheater surfaces of the boiler. The outcome of the tests confirms the feasibility of using 7%w of woody sawdust in combination with the coal without risk to the stability and efficiency of the large bolier. 6 REFERENCES [1] European Commission, Energy for the Future: Renewable sources of energy, White paper for a community strategy and action plan. See also: [2] Wischnewski R, Werther J, Heidenhof N. Synergy Effects of the Co-combustion of Biomass and Sewage Sludge with Coal in the CFB Combustor of Stadtwerke Duisburg AG, VGB PowerTech 2006;12: [3] Baxter, L. L., Rumminger M., Lind T., Tillman D. And Hughes E. Cofiring Biomass in Coal Boilers: Pilot- and Utility-scale Experiences. Biomass for

7 Energy and Industry: 1st World Conference and Technology Exhibition, Seville, Spain, [4] Koppejan J., 2004: Overview of experiences with cofiring biomass in coal power plants, IEA Bioenergy Task 32: Biomass Combustion and Cofiring, [5] KEMA, IEA Bioenergy Task 32, Report, August, [6] Kakaras E. Low emission co-combustion of different waste wood species and lignite derived products in industrial power plants. In: XXXII Krafwerkstechnisches colloquium Nutzung schwieriger brennstoffe in kraftwerken. Dresden 2000., p [7] Kazagić A., Smajević I., Experimental investigation of ash behavior and emissions during combustion of Bosnian coal and biomass, Energy (Elsevier), Volume 32, Issue 10 (October 2007), p [8] Kazagić A., Smajević I., Synergy Effects of Co-firing of Woody Biomass with Bosnian Coal, Energy (Elsevier), Volume 34 (May 2009), p [9] Kazagić A., Smajević I., Evaluation of Ash Deposits During Experimental Investigation of Co-firing of Bosnian Coal with Woody Biomass, Tagungsband, Kunftiges Brennstoff- und Technologieportfolio in der Kraftwerkstechnik, 40. Kraftwerkstechnisches Kolloquium, Dresden, October 2008., Band 2, p [10]Kazagić A., Smajević I., Duić N., Selection of sustainable technologies for combustion of Bosnian coals, International scientific journal Thermal Science, Volume 14, No. 3 (Year 2010), pg [11]Smajević I., Kazagić A., Musić M., Becic K., Hasanbegović I., Sokolović S., Delihasanovic N., Skopljak A., Hodzic N., Co-firing Bosnian Coals with woody biomass: experimental studies on a laboratoryscale furnace and 110 MWe power unit, THERMAL SCIENCE, volume 16, issue 3, year 2012., p [12]Raask E., Mineral Impurities in Coal Combustion, Central Electricity Generating Board Technical Planning and Research Division, Leatherhead, England, U.K., [13]Kupka T., Zajac K., Weber R., Influence of fuel type and deposition surface temperature on the growth and chemical and physical structure of ash deposit sampled during co-firing of coal with sewage sludge and saw dust, 8. International INFUB Conference, Vilamoura, Portugal, March [14]Kupka T., Mancini M., Irmer M., Weber, R., Investigation of ash deposit formation during co-firing of coal with sewage sludge, saw-dust and refuse derived fuel, Fuel (2008), doi: /j.fuel at the end of the paper. 7 ACKNOWLEDGEMENTS We thank you for successfully following these instructions. This will make the Delivery easier and avoid queues at the Desk! The Authors are grateful to the students of our Faculty for their helpful cooperation The President of. 10 LOGO SPACE If you wish, you may add your logos (e.g. Organisations, Project Partners, Supporters, Brands etc)