TORREFIED BIOMASS PELLETS AS COAL SUBTITUTE IN GASIFICATION PLANTS 5th International Freiberg Conference on IGCC and XtL Technologies, 21-24 May 2011, Leipzig, Germany Gobierno de Navarra Ministerio de Ciencia e Innovación Ciemat Ministerio de Industria, Turismo y Comercio
TORREFACTION ADVANTAGES Torrefied biomass has a higher cost than the original, however, it has in turn a number of clear advantages for logistics and some applications: A higher energy density reducing significantly transport costs A less fibrous structure that requires less power consumption for milling Greater stability in prolonged storage because it is more resistant to biological degradation A very low moisture content regardless of the environmental conditions of storage (hydrophobic behaviour) A more homogeneous fuel with constant characteristics These advantages may offset the cost of processing in the following applications: Large consumption of biomass that require long distance transport and / or long term storage Applications that require fine pulverisation of biomass 2
TORREFACTION PRODUCT CHARACTERISTICS Example: torrefied beech wood pellet (low-medium torrefaction degree) Elemental analysis C (%daf) : 54,3 H (%daf): 6,0 N (%daf): 0,18 Moisture content (% wet basis): 3,8% Ash content (% dry basis): 1,8% LHV (Mj/kg dry basis): 19,8 Bulk density (kg/m 3 ar): 680 Energy density (Gj/m 3 ): 13,5 Fines content (%): 2,0% Pellet durability (%): 97,2% Hardgrove Grindability Index (HGI): 26 Source: CENER (cod. 09/004/PE01; sample 11_477) 3
TORREFACTION PRODUCT CHARACTERISTICS Torrefied wood pellet water resistance: Water immersion test Comparison: torrefied beech wood pellet vs normal beech wood pellets Initial 10 seconds 1 minute 10 minutes 1 hour 24 hours 4
TORREFACTION PRODUCT Milling properties Samples supplied by CENER Cod. 2011-247 10.006-S001-4 Cod. 2011-260 10.006/T05; Cod. 2011-257 10.006/T04; Torrefaction degree (daf basis) 9% 18% 5
TORREFACTION PRODUCT Co-milling Properties Hardgrove Grindability Index: : Milling and co-millig properties of torrefied biomass tests carried out at Source: Torrefied and hydrothermal carbonised Biomass Products: Co-milling, Combustion and Emission Properties Gregory Dunnu, Jörg Maier, Günter Scheffknecht gregory.dunnu@ifk.uni-stuttgart.de 6
TORREFACTION PROCESS CONCEPT Indirectly heated reactor using thermal fluid at temperatures between 250 and 300ºC The process is heat integrated: The combustible vapors are burned to heat up the thermal fluid. Flue gases from the boiler at temperatures higher than 300ºC are used in the drier. Previous biomass drying down to 5-10% moisture content Additional fuel could be necessary for content and target torrefaction degree. raw biomass drying, depending on biomass moisture Particle size reduction below 20-40 mm for biomass feedstock is required to increase reactor throughput, improve heat transfer rate and guarantee homogeneous product characteristics. 7
TORREFACTION REACTOR The core of the process equipment is the torrefaction reactor of special design manufactured by LIST AG (www.list.ch): It is a cylindrical horizontal reactor with an agitator shaft and attached elements of special design procuring axial transport characteristic for all kind of biomass, radial product homogenisation inside the reactor and excellent heat transfer conditions. Reactor heating is carried out indirectly through the hot reactor walls, the actively heated shaft tube and the actively heated internal shaft elements using thermal oil as heat transfer fluid. 8
TORREFACTION REACTOR Main advantages of this Torrefaction reactor are: The technology is very flexible being able to process a very wide range of very different biomasses (particle size distributions, bulk densities and compositions, products requiring different transport mechanisms) It can process biomass with high fines content Excellent ratio of heat transfer surface to volume of reactor allowing shorter residence times and procuring high performance Continuous and very effective product renewal / product mixing from the internal heating surface, generating higher heat transfer rates and avoiding radial temperature profiles inside the reactor The design of the shaft elements provide an axial conveying quite close to plug flow, assuring a good product residence time control (narrow residence time distribution), and at the same time an excellent mixing of the product in each section of the reactor, assuring a good product temperature control over the whole length of the reactor (avoiding temperatures differences in the product and minimizing the risk of smouldering) Large free gas and vapour space allows the flow of the torrefaction gas with minimal pressure drop keeping biomass feeding and product discharge at low pressure reducing inert gas consumption Large vapour dome cross section minimize dust entrainment with the gas Using thermal oil as heat transfer medium facilitate energy integration and process control. At the same time plant operation is more flexible and safer. 9
TORREFACTION REACTOR Feedstock flexibility Torrefaction reactor acept a wide range of values of feedstock properties Parameter Reactor Dimension /nominal size, mm < 40 mm Bulk density, kg/m >50 (1) Moisture, % 5-10% Amount of fines, % ( 3,15 mm) < 20% (1) Dust content (250 < microns) <2% (1) (1) Provisional values under revision Example of feedstock: Sample code: 2011-479 Chipped < 30 mm ; Average particle size 8,6 mm % w/w 45 40 35 30 25 20 15 10 5 0 < 3,15 3,15-8 8-16 16-31,5 31,5-45 45-63 > 63 dp (mm) 10
TORREFACTION REACTOR product homogenity Wood mixing, homogeneous temperature and residence time control : homogeneity for all size fractions to warranty product Sample code Sample origin Moisture Ash Heating value HHV (MJ/kg) LHV (MJ/kg) Elemental analysis %C %H %N % w/w-"ar" % d.b. d.a.f. d.a.f. 2011-257 1,5 1,4 22,2 21,0 55,5 5,9 0,17 257 (<8mm) 1,5 1,4 22,3 21,1 55,6 5,9 0,17 257 (16-8mm) 10.006/T04; 1,5 1,4 22,3 21,1 55,5 5,9 0,16 257 (>16mm) 1,5 1,4 22,2 21,0 55,5 5,9 0,16 Difference 0% 0% <0.1 MJ <0.1 MJ <0.1% 0% <0.1% 2011-260 1,0 1,3 20,7 19,4 52,0 6,1 0,16 260 (<8mm) 1,0 1,3 20,8 19,5 51,9 6,1 0,16 260 (16-8mm) 10.006/T05; 1,0 1,3 20.7 19.5 51,7 6,1 0,13 260 (>16mm) 1,0 1,3 20,7 19,5 51,6 6,1 0,13 Difference 0% 0% <0.1 MJ <0.1 MJ <0.4% 0% <0.3% Analysis acceptance <0.2% <0.3% <0,12 MJ <1% <0.5% <0.1% repeatability criteria 11
TORREFACTION REACTOR temperature control Modeling temperature profile in the reactor and product conversion: Considerations of the model: A number of perfectly mixed reactors in series. The products output from one stage will be the input of the next. The torrefaction process is according the kinetic model from Di Blasi Lanzetta. Kinetic parameters are obtained by thermogravimetric analysis of studied biomasses. Biomass particles are considered as isothermal. Intraparticle temperature profiles are neglected. Heat of reaction is considered constant For each stage mass balance and energy balance equations are solved Calculates conversion, temperature profile, gas temperature and heat demand of the reactor Model validation. Biomass conversion in good agreement with experimental results in terms of product conversion Torrefaction degree simulated - - - - - - - - - - - - - - - - - - Torrefaction degree real Beech Pine 12
TORREFACTION REACTOR temperature control Being a indirectly heating reactor with high heating surface to volume ratio could help to control product temperature at high heating temperatures and conversion rates with an exothermal reaction. Heat transfer medium absorbs part of reaction heat limiting the possibilities of a run away. Modeling torrefaction reactor for 35% volatiles release (daf basis) using different values for reaction enthalpy Testing results at pilot plant up to 35 % torrefaction degree for beech wood no over heating problems detected 13
TORREFACTION PROCESS CONCEPT Mass and energy balance: Preliminary balance: optimization studies ongoing 40.000 t/year production plant; 30% weight loss (daf basis) 14
PRODUCTION COST Production cost breakdown: 40.000 t/year production plant Preliminary results: optimization studies ongoing Example for beech and 30% weight loss (daf): results depends very much on biomass and product specification In this case: Production cost 24% higher than conventional pellets in the same conditions 15
BIOMASS PRETREATMENT UNIT Chipping and chopping area Drier Milling area Torrefaction system Pellet mill Pelletizing area 16
TORREFACTION PILOT PLANT Cooling screw Torrefactor Biomass feeding 17
TORREFACTION PILOT PLANT Torrefaction reactor Capacity 300-500 kg / h input (wood chips) Working temperature <300 C Working pressure <2 mbarg Rotary type reactor, with internal elements designed specifically for this application. Heating of the reactor is carried out indirectly through the wall, the shaft and the reactor internals using thermal fluid. 18
TORREFACTION PILOT PLANT Auxiliaries Thermal fluid circuit: Cooling screw Thermal oxidizer 19
PRETREATMENT UNIT - OBJECTIVES The target of the pilot plant is the development of advanced processes for production of solid biofuels from a wide range of biomass, allowing the combination of conventional physical processes with torrefaction. Thus, this experimental setup allows: Development of the processes of torrefaction and pelletizing Definition of process layout, equipment specifications and operational conditions Optimization of operating conditions, depending on the target product characteristics and mass and energy balances Development of torrefied products Production tests with different biomasses Characterization of torrefied product as function of operating conditions. Production of torrefied product batches for end use application tests 20
Thank so much for your attention The construction of the plant has been financed by the Government of Navarre (Navarre Plan 2012) and by the Spanish Ministry of Science and Innovation (National Programme for Scientific-Technological Infrastructures). 21
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