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Oil production by entrained flow pyrolysis of biomass
Biomass 6 (1984) 69-76
Oil Production by Entrained Flow Pyrolysis of Biomass J. A. Knight, C. W. Gorton and R. J. Kovac Engineering Experiment Station and School of Chemical Engineering, Georgia Institute of Technology, A Unit of the University System of Georgia, Atlanta, Georgia 30332, USA (Received: 27 May, 1984)
ABSTRACT The objective o f this investigation was to optimize the production o f oil from biomass using entrained flow pyrolysis. Recent small-scale research efforts at Georgia Institute o f Technology and other laboratories have indicated that high oil yields can be obtained in entrained flow pyrolysis o f wood. A process research unit (PR U) has been designed and constructed with a nominal operating feed rate o f 56.7 kg h -1. The PRU has been operated satisfactorily with oak feedstock. A mass balance enclosure o f 96.8% was obtained in one experimental run in which the mass oil yield was 36.4%, which corresponds to a thermal yield o f 40. 7% based on the heating value o f wood feed. A mass oil yield o f 41.3% was obtained in a subsequent experiment. The research is ongoing with emphasis on determining the conditions for optimum oil production in entrained flow pyrolysis o f biomass. Key words: Pyrolysis, entrained reactor, liquefaction, maximum oil yield.
INTRODUCTION Pyrolysis of biomass is one of the most energy efficient of all the conversion processes currently under investigation and produces oil, char, gases and water. Wood pyrolysis oil, produced in a vertical-bed pyrolysis reactor, has been used successfully as a fuel for commercial kiln operation and in the operation of a power boiler. ~ The oil has been blended and test burned successfully with pulverized char and/or other 69 Biomass 0144-4565/84/$03.30-© Elsevier Applied Science Publishers Ltd, England, 1984. Printed in Great Britain
70
J. A. Knight, C. W. Gorton, R. J. Kovac
fuel oils. 1,2 Wood pyrolysis oil has been tested as an alternative fuel for gas turbines, and the results indicate that the process is technically viable with high combustion efficiency.3 Wood pyrolysis oil also has potential as a chemical feedstock. Properties of wood pyrolysis oil obtained from a 50.8 dry tonne per day field development unit with a vertical packed bed have been reported. 4 . Because of the need for liquid fuels and the demonstrated utilization of wood pyrolysis oil as a fuel, the current research effort at Georgia Institute of Technology is seeking to determine the conditions for optimum oil production by entrained flow pyrolysis of wood. Recent research work with rotating tube furnace produced oil yields of 28% by weight of original dry feed, 5 contrasted to 17% for the stationary tube furnace yield. 6 A recent publication 7 based on experimental data indicated that pyrolysis of sawdust in a fluidized bed gives oil yields as high as 36%. A mathematical model of the process, which predicts the data trends well, was based on postulated kinetics which includes oil formation and subsequent decomposition of the oil to char and gases so that a maximum is exhibited in the oil production rate. 7 Recently, Scott and Piskorz 8 reported yields of 61% wood oil and 4% organics by weight of moisture-free wood by pyrolysis in a fluidized bed of sand.
EXPERIMENTAL APPROACH The objectives of the research effort were to construct an entrained pyrolysis process research unit (PRU) and to conduct an experimental program to obtain basic engineering data for maximum oil productions. The design and construction of the PRU have been completed and the details have been reported.9 Flow diagram A flow diagram of the PRU is given in Fig. 1, and its operation is described in the following. Propane gas (1) and air (2) supplied by an air compressor are burned stoichiometrically in an inert gas generator, and the combustion products are cooled with a water spray (3) so that the gases leave saturated with water vapor. The exit stream from the inert gas generator is split into two streams. One of these (4) provides
71
Oil production by entrained flow pyrolysis of biomass
PYROLYZER i \ / I REACTOR ~ L .___._
j
cR.
I COn[RSER[1
) h j® I!!l.,,,,s,.,0,
II,"I~E"ERA'ORI ' ilIWATER ®
~ ~RURRER "~ 1,_,i
g ®
®l® v Jl--I
FLARE Fig. 1.
Entrained flow pyrolysis process research unit.
moderating gas for the burner and the other (5) provides conveying gas for the feed particles (6). Propane (7) also fuels the burner which also operates stoichiometrically with air (8) supplied by a blower. The mixture consisting of moderating gas, conveying gas, burner combustion products and wood particles moves vertically upwards through the reactor tube in which the entrained pyrolysis takes place; the resulting mixture (9) consists of noncondensable gases, water vapor (entering moisture plus combustion and pyrolysis products), noncondensable gases and pyrolysis oil vapors. In the cyclone, almost all of the char particles (10) are removed, and the stream (11) leaving the cyclone consists of noncondensable gases, water vapor, pyrolysis oil vapor and some char fines. This mixture enters the condenser, and the pyrolysis vapors (and some water vapor) are condensed in the aircooled condenser. The condensed phases (12) are removed via sumps and collection receivers, and the exiting mixture (13), consisting of noncondensable gases, water vapor, light oil vapors, an aerosol of oil, and possibly some fines, enters the demister. In the demister most of the aerosol and fines are removed (14). The resulting mixture (15) consisting mainly of noncondensable gases, water vapor with some aerosol and fines enters the flare where air is introduced, the mixture
72
J. A. Knight, C. W. Gorton, R. J. Kovac
is burned, and the products of combustion (16) are exhausted to the atmosphere. Instrumentation and control The P R U is instrumented so that appropriate temperatures, pressures and pressure drops can be obtained. All temperatures are measured with thermocouples and recorded on strip-chart recorders. Pressures and pressure drops are determined with manometers, gages and transducers. All input and output gaseous stream flow rates of the unit are determined with orifices. The amounts of solid and liquid products are determined by weighing. The input feed rate is determined with a lossin-weight feeder, which automatically controls the feed rate at a specified rate. Stoichiometric conditions are maintained in the burner by a proportional control system. Chemical analysis The chemical analyses that are performed on the input gas streams, feed and o u t p u t products and off-gas stream are given in Table 1.
TABLE 1
Chemical Analyses of Feed, Carrier Gas, and Solid, Liouid and Gaseous Products Material
Feed Inert gas Air Propane Char Oil Noncondensed gas stream
Analytical determinations
Moisture, ash, higher heating value Composition determined by gas chromatography Composition determined by gas chromatography Composition determined by gas chromatography Moisture, ash, higher heating value Water (Karl-Fisher technique), higher heating value Composition determined by gas chromatography and data from condensation train. Higher heating value calculated from composition
Oil production by entrained flow pyrolysis of biomass
73
RESULTS AND DISCUSSION A material balance and heating values are presented for a selected experimental run. The input feed weight is determined with the loss-inweight feeder. The mass flow rates of the inert moderating and conveying gases are determined with orifice plates. The mass flow rates of the air and propane gas for the hot gas burner are also determined with orifice plates. During a data test run, the inert gas, air and propane are sampled and analyzed by gas chromatography (GC). The char and liquid products are weighed. The noncondensed gaseous stream is sampled continuously during a pyrolysis run downstream of the demister cyclone. This sample is passed through a condensation train for recovery of the condensable components and periodic sampling of the noncondensed gases, which are analyzed by GC. These data are used to calculate the mass flow of the off-gas stream by a nitrogen balance. The mass balance results for an experimental run are presented in Table 2 with a closure of 96.8%. A limited number of runs has been made to date so that a statistically meaningful determination of the variability between runs is not possible at this time. However, a detailed error analysis indicates a maximum error in the total inlet flow rate of -+2.5%. The estimated maximum error in the total exit flow rate was -+6%. Higher heating values for the feed and pyrolysis products are presented in Table 3. All values given were determined experimentally, except the value for the noncondensable gases. The value given for the oil is a weighted average of values for oil collected in the six condenser sumps, the demister and oil leaving in the off-gas stream. The values varied from a low of 19.68 to a high of 24.57 MJ kg -1. The oil yield (dry) for the run reported here was 36.4% based on a moisture- and ash-free w o o d feed. The corresponding thermal yield (total heating value of oil divided by total heating value of the wood feed) was 40.7%. It is worth noting that oil yield on a mass basis is not such an important criteria as oil yield on a thermal basis. There is evidence in the literature that indicates that very high oil yields on a mass basis (60% or so) are accompanied by a correspondingly lower heating value. In order to determine the composition of the pyrolysis gases, a calculational procedure was developed. For the particular run reported
74
J. A. Knight, C. W. Gorton, R. J. Kovac TABLE 2
Mass Balance for an Entrained Flow Pyrolysis Experiment Flow rate (kg h -1) Entering stream s Wood with moisture Inert gas Propane (burner) Air (burner)
50.62 31.03 3-63 47.63
Entering flow rate (A)
132.91
Leaving streams Char (as produced) Condensates (includes water) Condenser Demister Off-gases (included water and aerosol)
Leaving flow rate (B)
5.26 8-03 11-11 104.28 128-68
B
% Closure = - - x 100 A % Closure = 96.8
TABLE 3
Higher Heating Values (HHV) of Feed and Pyrolytic Products Stream
Wood (dry basis) Char (dry basis) Oil (dry basis) Noncondensable gases (calculated from composition which includes nitrogen)
H H V (MJ kg -l) 19.45
26.08 22.17 2.86
Oil production by entrained flow pyrolysis of biomass
75
TABLE 4
Calculated Nitrogen-Free Noncondensable Pyrolysis Gas Composition in Off-Gas Stream Gas component
Ar 02 CO CO2 H2 Cl~ C2H2 C2H4 C2H6 C3H6
CsHs C4Hlo
Mole fraction x 100a
3.9 1.9 41.4 16.7 24.1 6.9 0 2-9 0-4 1-5 0.3 0
100.0 a For ideal-gas mixtures this is also the volume percent.
here, the amount of propane was slightly greater than the stoichiometric amount. The assumptions were made that all of the hydrogen in the propane formed water and that the remaining oxygen produced a mixture of carbon monoxide and carbon dioxide with no free oxygen. These calculated values were subtracted from the measured values in the off-gases. The calculated results on a nitrogen- and moisture-free basis are given in Table 4. The research efforts are being continued to determine the conditions for maximum oil production in entrained flow pyrolysis of biomass. ACKNOWLEDGMENTS This program is supported by DOE through Battelle Pacific Northwest Laboratories (subcontract B-C5863-A-Q). This support is gratefully acknowledged.
76
J. A. Knight, C. W. Gorton, R. J. Kovac
REFERENCES 1. Bowen, M. D., Smyly, E. D., Knight, J. A. & Purdy, K. R. (1978). A vertical-bed pyrolysis system, Solid wastes and residues, ACS Symposium Series, No. 76, 94-125. 2. Demeter, J. J., McCann, C. R., Ekmann, J. M. & Bienstock, D. (1977). Combustion o f char from pyrolyzed wood waste, Pittsburgh Energy Research Center, PERC/RI-77/9. 3. Jasas, G. & Kasper, J. (1982). Gas turbine demonstration of pyrolysis-derived fuels, Proceedings o f the 14th Biomass Thermochemical Conversion Con~actors' Meeting, Arlington, Virginia, CONF-820685, PNL-SA-10646. 4. Knight, J. A., Hurst, D. R. & Elston, L. W. (1977). Wood oil from pyrolysis of pine bark-sawdust mixtures, Fuels and energy from renewable resources, eds D. A. Tillman et al., New York, Academic Press, pp. 169-95. 5. Knight, J. A., Gorton, C. W., Elston, L. W., Kovac, R. J. & Hurst, D. R. (1981). Thermochemical conversion of biomass via the Georgia Tech entrained pyrolysis/ gasification process, Second Quarterly Report, DOE. 6. Knight, J. A. (1976). Pyrolysis of pine sawdust, eds F. Shafizadeh et al., Thermal uses and properties o f carbohydrates and lignins, Academic Press, New York, pp. 159-73. 7. Kosstrin, H. (1980). Direct formation of pyrolysis oil from biomass,Proceedings, Specialists' Workshop on Fast Pyrolysis o f Biomass, SERI/CP-622-1096. 8. Scott, D. S. & Piskorz, J. (1981) Continuous flash pyrolysis of hybrid biomass Fuels from biomass and wastes, eds D. L. Klass and G. H. Emert, Ann Arbor, Ann Arbor Science Publishers, pp. 421-34. 9. Knight, J. A., Gorton, C. W. & Kovac, R. J. (1983). Entrained flow pyrolysis of biomass, Proceedings of the 15th Biomass Thermochemical Conversion Contractors'Meeting, Atlanta, Georgia, CONF-830323, PML-SA-11306.
Oil Production by Entrained Flow Pyrolysis of Biomass J. A. Knight, C. W. Gorton and R. J. Kovac Engineering Experiment Station and School of Chemical Engineering, Georgia Institute of Technology, A Unit of the University System of Georgia, Atlanta, Georgia 30332, USA (Received: 27 May, 1984)
ABSTRACT The objective o f this investigation was to optimize the production o f oil from biomass using entrained flow pyrolysis. Recent small-scale research efforts at Georgia Institute o f Technology and other laboratories have indicated that high oil yields can be obtained in entrained flow pyrolysis o f wood. A process research unit (PR U) has been designed and constructed with a nominal operating feed rate o f 56.7 kg h -1. The PRU has been operated satisfactorily with oak feedstock. A mass balance enclosure o f 96.8% was obtained in one experimental run in which the mass oil yield was 36.4%, which corresponds to a thermal yield o f 40. 7% based on the heating value o f wood feed. A mass oil yield o f 41.3% was obtained in a subsequent experiment. The research is ongoing with emphasis on determining the conditions for optimum oil production in entrained flow pyrolysis o f biomass. Key words: Pyrolysis, entrained reactor, liquefaction, maximum oil yield.
INTRODUCTION Pyrolysis of biomass is one of the most energy efficient of all the conversion processes currently under investigation and produces oil, char, gases and water. Wood pyrolysis oil, produced in a vertical-bed pyrolysis reactor, has been used successfully as a fuel for commercial kiln operation and in the operation of a power boiler. ~ The oil has been blended and test burned successfully with pulverized char and/or other 69 Biomass 0144-4565/84/$03.30-© Elsevier Applied Science Publishers Ltd, England, 1984. Printed in Great Britain
70
J. A. Knight, C. W. Gorton, R. J. Kovac
fuel oils. 1,2 Wood pyrolysis oil has been tested as an alternative fuel for gas turbines, and the results indicate that the process is technically viable with high combustion efficiency.3 Wood pyrolysis oil also has potential as a chemical feedstock. Properties of wood pyrolysis oil obtained from a 50.8 dry tonne per day field development unit with a vertical packed bed have been reported. 4 . Because of the need for liquid fuels and the demonstrated utilization of wood pyrolysis oil as a fuel, the current research effort at Georgia Institute of Technology is seeking to determine the conditions for optimum oil production by entrained flow pyrolysis of wood. Recent research work with rotating tube furnace produced oil yields of 28% by weight of original dry feed, 5 contrasted to 17% for the stationary tube furnace yield. 6 A recent publication 7 based on experimental data indicated that pyrolysis of sawdust in a fluidized bed gives oil yields as high as 36%. A mathematical model of the process, which predicts the data trends well, was based on postulated kinetics which includes oil formation and subsequent decomposition of the oil to char and gases so that a maximum is exhibited in the oil production rate. 7 Recently, Scott and Piskorz 8 reported yields of 61% wood oil and 4% organics by weight of moisture-free wood by pyrolysis in a fluidized bed of sand.
EXPERIMENTAL APPROACH The objectives of the research effort were to construct an entrained pyrolysis process research unit (PRU) and to conduct an experimental program to obtain basic engineering data for maximum oil productions. The design and construction of the PRU have been completed and the details have been reported.9 Flow diagram A flow diagram of the PRU is given in Fig. 1, and its operation is described in the following. Propane gas (1) and air (2) supplied by an air compressor are burned stoichiometrically in an inert gas generator, and the combustion products are cooled with a water spray (3) so that the gases leave saturated with water vapor. The exit stream from the inert gas generator is split into two streams. One of these (4) provides
71
Oil production by entrained flow pyrolysis of biomass
PYROLYZER i \ / I REACTOR ~ L .___._
j
cR.
I COn[RSER[1
) h j® I!!l.,,,,s,.,0,
II,"I~E"ERA'ORI ' ilIWATER ®
~ ~RURRER "~ 1,_,i
g ®
®l® v Jl--I
FLARE Fig. 1.
Entrained flow pyrolysis process research unit.
moderating gas for the burner and the other (5) provides conveying gas for the feed particles (6). Propane (7) also fuels the burner which also operates stoichiometrically with air (8) supplied by a blower. The mixture consisting of moderating gas, conveying gas, burner combustion products and wood particles moves vertically upwards through the reactor tube in which the entrained pyrolysis takes place; the resulting mixture (9) consists of noncondensable gases, water vapor (entering moisture plus combustion and pyrolysis products), noncondensable gases and pyrolysis oil vapors. In the cyclone, almost all of the char particles (10) are removed, and the stream (11) leaving the cyclone consists of noncondensable gases, water vapor, pyrolysis oil vapor and some char fines. This mixture enters the condenser, and the pyrolysis vapors (and some water vapor) are condensed in the aircooled condenser. The condensed phases (12) are removed via sumps and collection receivers, and the exiting mixture (13), consisting of noncondensable gases, water vapor, light oil vapors, an aerosol of oil, and possibly some fines, enters the demister. In the demister most of the aerosol and fines are removed (14). The resulting mixture (15) consisting mainly of noncondensable gases, water vapor with some aerosol and fines enters the flare where air is introduced, the mixture
72
J. A. Knight, C. W. Gorton, R. J. Kovac
is burned, and the products of combustion (16) are exhausted to the atmosphere. Instrumentation and control The P R U is instrumented so that appropriate temperatures, pressures and pressure drops can be obtained. All temperatures are measured with thermocouples and recorded on strip-chart recorders. Pressures and pressure drops are determined with manometers, gages and transducers. All input and output gaseous stream flow rates of the unit are determined with orifices. The amounts of solid and liquid products are determined by weighing. The input feed rate is determined with a lossin-weight feeder, which automatically controls the feed rate at a specified rate. Stoichiometric conditions are maintained in the burner by a proportional control system. Chemical analysis The chemical analyses that are performed on the input gas streams, feed and o u t p u t products and off-gas stream are given in Table 1.
TABLE 1
Chemical Analyses of Feed, Carrier Gas, and Solid, Liouid and Gaseous Products Material
Feed Inert gas Air Propane Char Oil Noncondensed gas stream
Analytical determinations
Moisture, ash, higher heating value Composition determined by gas chromatography Composition determined by gas chromatography Composition determined by gas chromatography Moisture, ash, higher heating value Water (Karl-Fisher technique), higher heating value Composition determined by gas chromatography and data from condensation train. Higher heating value calculated from composition
Oil production by entrained flow pyrolysis of biomass
73
RESULTS AND DISCUSSION A material balance and heating values are presented for a selected experimental run. The input feed weight is determined with the loss-inweight feeder. The mass flow rates of the inert moderating and conveying gases are determined with orifice plates. The mass flow rates of the air and propane gas for the hot gas burner are also determined with orifice plates. During a data test run, the inert gas, air and propane are sampled and analyzed by gas chromatography (GC). The char and liquid products are weighed. The noncondensed gaseous stream is sampled continuously during a pyrolysis run downstream of the demister cyclone. This sample is passed through a condensation train for recovery of the condensable components and periodic sampling of the noncondensed gases, which are analyzed by GC. These data are used to calculate the mass flow of the off-gas stream by a nitrogen balance. The mass balance results for an experimental run are presented in Table 2 with a closure of 96.8%. A limited number of runs has been made to date so that a statistically meaningful determination of the variability between runs is not possible at this time. However, a detailed error analysis indicates a maximum error in the total inlet flow rate of -+2.5%. The estimated maximum error in the total exit flow rate was -+6%. Higher heating values for the feed and pyrolysis products are presented in Table 3. All values given were determined experimentally, except the value for the noncondensable gases. The value given for the oil is a weighted average of values for oil collected in the six condenser sumps, the demister and oil leaving in the off-gas stream. The values varied from a low of 19.68 to a high of 24.57 MJ kg -1. The oil yield (dry) for the run reported here was 36.4% based on a moisture- and ash-free w o o d feed. The corresponding thermal yield (total heating value of oil divided by total heating value of the wood feed) was 40.7%. It is worth noting that oil yield on a mass basis is not such an important criteria as oil yield on a thermal basis. There is evidence in the literature that indicates that very high oil yields on a mass basis (60% or so) are accompanied by a correspondingly lower heating value. In order to determine the composition of the pyrolysis gases, a calculational procedure was developed. For the particular run reported
74
J. A. Knight, C. W. Gorton, R. J. Kovac TABLE 2
Mass Balance for an Entrained Flow Pyrolysis Experiment Flow rate (kg h -1) Entering stream s Wood with moisture Inert gas Propane (burner) Air (burner)
50.62 31.03 3-63 47.63
Entering flow rate (A)
132.91
Leaving streams Char (as produced) Condensates (includes water) Condenser Demister Off-gases (included water and aerosol)
Leaving flow rate (B)
5.26 8-03 11-11 104.28 128-68
B
% Closure = - - x 100 A % Closure = 96.8
TABLE 3
Higher Heating Values (HHV) of Feed and Pyrolytic Products Stream
Wood (dry basis) Char (dry basis) Oil (dry basis) Noncondensable gases (calculated from composition which includes nitrogen)
H H V (MJ kg -l) 19.45
26.08 22.17 2.86
Oil production by entrained flow pyrolysis of biomass
75
TABLE 4
Calculated Nitrogen-Free Noncondensable Pyrolysis Gas Composition in Off-Gas Stream Gas component
Ar 02 CO CO2 H2 Cl~ C2H2 C2H4 C2H6 C3H6
CsHs C4Hlo
Mole fraction x 100a
3.9 1.9 41.4 16.7 24.1 6.9 0 2-9 0-4 1-5 0.3 0
100.0 a For ideal-gas mixtures this is also the volume percent.
here, the amount of propane was slightly greater than the stoichiometric amount. The assumptions were made that all of the hydrogen in the propane formed water and that the remaining oxygen produced a mixture of carbon monoxide and carbon dioxide with no free oxygen. These calculated values were subtracted from the measured values in the off-gases. The calculated results on a nitrogen- and moisture-free basis are given in Table 4. The research efforts are being continued to determine the conditions for maximum oil production in entrained flow pyrolysis of biomass. ACKNOWLEDGMENTS This program is supported by DOE through Battelle Pacific Northwest Laboratories (subcontract B-C5863-A-Q). This support is gratefully acknowledged.
76
J. A. Knight, C. W. Gorton, R. J. Kovac
REFERENCES 1. Bowen, M. D., Smyly, E. D., Knight, J. A. & Purdy, K. R. (1978). A vertical-bed pyrolysis system, Solid wastes and residues, ACS Symposium Series, No. 76, 94-125. 2. Demeter, J. J., McCann, C. R., Ekmann, J. M. & Bienstock, D. (1977). Combustion o f char from pyrolyzed wood waste, Pittsburgh Energy Research Center, PERC/RI-77/9. 3. Jasas, G. & Kasper, J. (1982). Gas turbine demonstration of pyrolysis-derived fuels, Proceedings o f the 14th Biomass Thermochemical Conversion Con~actors' Meeting, Arlington, Virginia, CONF-820685, PNL-SA-10646. 4. Knight, J. A., Hurst, D. R. & Elston, L. W. (1977). Wood oil from pyrolysis of pine bark-sawdust mixtures, Fuels and energy from renewable resources, eds D. A. Tillman et al., New York, Academic Press, pp. 169-95. 5. Knight, J. A., Gorton, C. W., Elston, L. W., Kovac, R. J. & Hurst, D. R. (1981). Thermochemical conversion of biomass via the Georgia Tech entrained pyrolysis/ gasification process, Second Quarterly Report, DOE. 6. Knight, J. A. (1976). Pyrolysis of pine sawdust, eds F. Shafizadeh et al., Thermal uses and properties o f carbohydrates and lignins, Academic Press, New York, pp. 159-73. 7. Kosstrin, H. (1980). Direct formation of pyrolysis oil from biomass,Proceedings, Specialists' Workshop on Fast Pyrolysis o f Biomass, SERI/CP-622-1096. 8. Scott, D. S. & Piskorz, J. (1981) Continuous flash pyrolysis of hybrid biomass Fuels from biomass and wastes, eds D. L. Klass and G. H. Emert, Ann Arbor, Ann Arbor Science Publishers, pp. 421-34. 9. Knight, J. A., Gorton, C. W. & Kovac, R. J. (1983). Entrained flow pyrolysis of biomass, Proceedings of the 15th Biomass Thermochemical Conversion Contractors'Meeting, Atlanta, Georgia, CONF-830323, PML-SA-11306.