8 Chapter 2 Biomass Conversion Processes Problems and Discussion Issues Heat Energy Conversion Efficiency 2.1 One tonne [1.1 tons] of dried manure is converted into heat energy. Determine the efficiency if this biomass is converted into heat. The total amount of heat produced during the process is 15,000 MJ. The heating value of the manure was reported at 19.7 MJ/kg [8,500 Btu/lb]. Solution: a. Efficiency equation as presented in Equation 2.1 is given as follows: 100 (%) x input output Efficiency b. Substituting for the variables with correct units to estimate efficiency as follows: % 1 . 76 100 1000 1 1 1 / 7 . 19 0000 , 15 (%) x kg ton metric x ton metric x kg MJ MJ Efficiency Energy of Feedstock and Biofuel Product 2.2 One hundred kg [220 lbs] of soybean oil was converted into biodiesel. Assuming 100% conversion efficiency, compare the energy of the biodiesel with that of the vegetable oil if the energy content of refined soybean oil was found to be 27.87 MJ/L [100,000 Btu/gallon]. How much energy in units of Joules with appropriate prefixes (or in million Btu or MMBtu) was in the biodiesel that was produced if the resulting energy content of the ester was 32.94 MJ/L [118,170 Btu/gal]. The density of bodiesel product was 888.7 kg/m 3 [7.4 lb/gal] and the density of refined soybean oil was 912.7 kg/m 3 [7.6 lb/gal].
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Chapter 2 Biomass Conversion Processes · Chapter 2 Biomass Conversion Processes Problems and Discussion Issues Heat Energy Conversion Efficiency 2.1 One tonne [1.1 tons] of dried
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8
Chapter 2
Biomass Conversion Processes
Problems and Discussion Issues
Heat Energy Conversion Efficiency
2.1 One tonne [1.1 tons] of dried manure is converted into heat energy. Determine the efficiency
if this biomass is converted into heat. The total amount of heat produced during the process is
15,000 MJ. The heating value of the manure was reported at 19.7 MJ/kg [8,500 Btu/lb].
Solution:
a. Efficiency equation as presented in Equation 2.1 is given as follows:
100(%) xinput
outputEfficiency
b. Substituting for the variables with correct units to estimate efficiency as follows:
%1.761001000
1
1
1
/7.19
0000,15(%) x
kg
tonmetricx
tonmetricx
kgMJ
MJEfficiency
Energy of Feedstock and Biofuel Product
2.2 One hundred kg [220 lbs] of soybean oil was converted into biodiesel. Assuming 100%
conversion efficiency, compare the energy of the biodiesel with that of the vegetable oil if the
energy content of refined soybean oil was found to be 27.87 MJ/L [100,000 Btu/gallon].
How much energy in units of Joules with appropriate prefixes (or in million Btu or MMBtu)
was in the biodiesel that was produced if the resulting energy content of the ester was 32.94
MJ/L [118,170 Btu/gal]. The density of bodiesel product was 888.7 kg/m3 [7.4 lb/gal] and the
density of refined soybean oil was 912.7 kg/m3 [7.6 lb/gal].
9
Solution.
a. Energy content of refined oil
MJm
L
kg
m
L
MJoilkgMJEnergy 054.3
1000
7.912
87.27100)(
3
3
GJMJ
GJMJGJEnergy 1.3
1000054,3)(
MMBtuBtu
MMBtu
lbs
gal
gal
BtuoillbsMMBtuEnergy 97.2
000,000,1
1
4.7
000,100220)(
b. Energy content of the ester of oil is calculated from
GJMJ
GJ
m
L
kg
m
L
MJoilkgGJEnergy 17.3
000,1
1000
7.888
94.32100)(
3
3
MMBtuBtu
MMBtu
lbs
gal
gal
BtuoillbsMMBtuEnergy 42.3
000,000,1
1
6.7
170,118220)(
Note that there is more energy contained in the ester product than the refined oil.
Methanol was also added as a reactant containing additional amounts of energy. This
calculation does not imply that more energy is produced than the energy in the refined
vegetable oil. The yield of biodiesel may also be less than 100%.
Ethanol Yield Per Unit of Area
2.3 A certain variety of sweet sorghum has a sugar content 15.9% by weight and the biomass
yield is 57.8 tonnes/hectare [25.74 tons/acre] and a stalk sugar yield of around 9.2 tonnes/ha
b. Equation 2.8 may then be used to calculate the efficiency of the steam generator as
follows:
%3.61%100/000,660
/640,404(%)
hrMJ
hrMJgeneratorsteam
c. Equation 2.9 will be used to estimate the overall thermal efficiency of the system as
follows (or simply output divided by the biomass input fuel)
%8.21%1006.3
000,3022000,40(%)
kWh
MJ
kg
hr
MJ
kgkWth
Biomass Energy Conversions Homework #2 Biomass Energy Conversions Overview
1. Determine the efficiency of converting granulated sugar into ethanol. The energy content of granulated sugar was found to be 6,850 Btu/lb [15.9 MJ/kg]. A gallon of ethanol with an energy content of 84,000 Btu was produced from 15 lbs of sugar.
2. How much glycerin was produced (in lbs) from converting a million lbs of biodiesel from canola oil in a year? Note that since the governing equation is in units of mass, to convert to units on a volume basis, one needs the density of the material. Report the glycerin yield in gallons if the density of glycerin is 10.5 lbs/gal.
3. How many lbs of pure sugar (i.e. glucose) is needed to produce 1 million gallons of ethanol? Assume the density of ethanol to be 6.66 lbs/gal.
4. Determine the amount of manure needed each day (in lbs) to generate 1MW of electrical power for 24 hrs using an engine. Assume that the amount of biogas produced per lb of manure was 3 ft3 and the overall engine conversion efficiency was 20% (both thermal and mechanical). The heating value of biogas was assumed to be 550 Btu/ft3.
5. Determine the estimated chemical formula for the following biomass material with the ultimate analysis as follows by weight: C= 75.5%; H=5.0%; O=4.9%; N=1.2%; S=3.1%. Determine also the air to fuel ratio for a stoichiometric combustion of this material in air.
Biomass Energy Conversions Homework #2 Biomass Energy Conversions Overview
1. Determine the efficiency of converting granulated sugar into ethanol. The energy content
of granulated sugar was found to be 6,850 Btu/lb [15.9 MJ/kg]. A gallon of ethanol with an energy content of 84,000 Btu was produced from 15 lbs of sugar. Solution: a. The input energy is first calculated
Btulbslb
BtuBtuEnergyInput 5.757,10215
5.850,6)(
b. Then the conversion efficiency is calculated next.
2. How much glycerin was produced (in lbs) from converting a million lbs of biodiesel from canola oil in a year? Note that since the governing equation is in units of mass, to convert to units on a volume basis, one needs the density of the material. Report the glycerin yield in gallons if the density of glycerin is 10.5 lbs/gal. Solution: a. From the governing ideal equation, about 100,000 lbs of glycerin may be produced b. To convert the units in gallons the given density is used as follows:
gallonslbs
gallonslbsgallonsGlycerin 524,9
5.10000,100)(
3. How many lbs of pure sugar (i.e. glucose) is needed to produce 1 million gallons of
ethanol? Assume the density of ethanol to be 6.66 lbs/gal. Solution: a. Using the ideal governing equation, the amount of sugar is easily calculated as
follows:
b. Thus, it would take about at least 13 million lbs of pure sugar to achieve this goal.
4. Determine the amount of manure needed each day (in lbs) to generate 1MW of electrical power for 24 hrs using an engine. Assume that the amount of biogas produced per lb of manure was 3 ft3 and the overall engine conversion efficiency was 20% (both thermal and mechanical). The heating value of biogas was assumed to be 550 Btu/ft3. Solution: a. The amount of biogas needed is first calculated
sugarlbsmillionethanolgallonsgal
lbs
ethanollbs
sugarlbslbsSugar 13101
66.6
92
180)( 6
%75.81%1005.757,102
000,84(%)
Btu
BtuEfficiencyConversionEnergy
b. Then the amount of manure is estimated.
5. Determine the estimated chemical formula for the following biomass material with the following ultimate analysis by weight: C= 75.5%; H=5.0%; O=4.9%; N=1.2%; S=3.1%. Determine also the air to fuel ratio for a stoichiometric combustion of this material in air. Solution: a. The molar ratios are first calculated using the MS of each element: C = 75.5/12 g/mol
= 6.3; H = 5.0/1 = 5.0; O = 4.90/16 = 0.31; N = 1.2/14 = .086; S = 3.1/32= 0.1
b. Then, the estimated chemical formula will be the subscript of each element as follows:
c. The stoichiometric combustion equation may be set-up to determine the air-to-fuel ratio as follows:
FIGURE 2.10The MixAlco process to convert biomass into higher alcohols and hydrocarbon fuels.
002x010.eps
Courtesy of CRC Press/Taylor & Francis Group
Biomassfeed tank
Cycloneseparators
Gascompression
systemFluidizedbedor
downdraftgasifier Syngas scrubber system
Syngas storage tanks
Biostat D-75 fermentor
FIGURE 2.11Schematic of OSU pilot syngas fermentation system. (Adapted from Kundiyana, D. K., R. L. Hunke and M. R. Wilkins, Journal of Bioscience and Bioengineering 109, 492, 2010.)
002x011.eps
Lecture 2Biomass Energy Conversion
Processes
Sergio C. CaparedaBEAN, TAMU
Learning Objectives• Describe the overview of the various biomass conversion processes
• Differentiate between chemical, biological and thermal conversion processes
• Recognize the various units and terminologies used for estimating efficiencies of different biomass energy conversion processes
• Compare new and advanced biomass conversion processes including combinations and hybrids
• Enumerate all applications of various conversion processes and list important products and co‐products produced
Biomass Energy Conversion Efficiency• Energy Conversion Efficiency
• Energy Input (example animal manure)– One metric tonne of animal manure at 15 MJ/kg– Energy contained in manure = 15,000 MJ
• Energy Output (example biogas)– 150 m3 of biogas with energy content of 20.5 MJ/m3
Biodiesel Production• Schematic of the biodiesel conversion process
• One of the simplest biomass conversion processes (physico‐chemical conversion)
• Complications arise from generating RBD oil (i.e. refined, bleached and deododized oil) from oil seeds prior to conversion process
• Transesterification – the process of converting oils into esters of oil (i.e. soybean oil to soybean oil methyl ester, SME)
How Big is a 1MGY Biodiesel Plant?
• A 1 million gallon per year biodiesel facility needs to produce about 3,000 gallons of biodiesel each day for 333 days to satisfy this requirement as shown in calculations below
• A 3,000 gallon tank may have a diameter of 10 feet and a height of only 5.1 feet (or 401 cubic feet since a cubic feet is 7.48 gallons).
• Thus, a million gallon facility is rather small.
daygallons
daysyear
yeargallons
daygaloductionPrDaily 003,3
3331101 6
US Biodiesel Production
High Price of Crude Vegetable
Oil
Bioethanol Production• Various pathways for the conversion of biomass into ethanol
• The use of microorganisms to convert sugars into ethanol, a biological conversion process
• Understand the nature of microorganisms
Most Popular Microbes for Ethanol Production
• Fermentation of sugar to ethanol– Saccharomyces cerevisiae – common yeast– Ethanol Red – most popular commercial brand in US
• Saccharification of starch to sugars– Aspergillus niger – common mold – Aspergillus awamori – another strain of molds
• Hydrolysis of cellulose into simple sugars followed by fermentation of sugars produced– Trichoderma reesei – a Genencor enzyme producer
US Bioethanol Production • Over 1,620 million gallons in the year 2000• Over 13,230 million gallons in 2010• US is still the world’s top ethanol producer representing more than half (57.5%) of the world’s production in 2010
• Brazil is second with about 6,920 million gallons in 2010.
Biogas Production• Conversion pathway to break down complex organics into methane and carbon dioxide
• Biogas = methane or CH4 (65%) + CO2 (35%) + other gases such as H2S
Utilization of Biogas• Heating value = 500‐600 Btu/ft3 [18.6‐22.3 MJ/m3]
• Direct source of heat• Use in internal combustion engines to generate mechanical energy and electrical power
• The H2S must be scrubbed to prolong the life of engines.
• CO2 must also be separated to improve the conversion efficiency since it has no heating value
• Newer engines that runs of low Btu gas are now available commercially
Thermochemical Conversion of BiomassRelationships among thermal conversion processes on the amounts of air
used as well as relative temperatures of reaction.
Torrefaction
• Torrefaction ‐ a mild thermal treatment of biomass to improve its properties prior to conversion
• Properties enhanced– Improve energy density– Reduced moisture– Improve bulk density for ease of transport– Improve biomass composition
Torrefaction Facilities
3.17.09.0
MassEnergyionDensificatEnergy
Energy Densification in Torrefaction Process
‐ 90% of the energy is retained (or 0.90)‐ 70% of the mass is conserved (or 0.70)
Pyrolysis• Irreversible thermal conversion process in complete absence of oxidant (also called “destructive distillation”)
• Products are condensible liquids (biooil), combustible synthesis gas and recyclable biochar
• Temperature is between 200‐600oC• Products are as follows:
Products Estimated Percentages
Biochar 30‐35%
Organic Liquids 18‐20%
Synthesis Gas 20%
Slow Pyrolysis Set‐up
The pyrolysis setup used for biomass. (A) Purge gas (N2), (B) Gas flow meter 1, (C) Digitally‐controlled furnace, (D) tar/moisture trap, (E) Condenser, (F) Thermocouple reader, (G) Liquid collector, (H) moisture trap, (I) Gas flow meter 2, (J) Sampling/exhaust port, and (K) Gas analyzer.
Pyrolyzer/ReactorB
CA DE
G
H
IJ
K
F
Hood
A
B
C
D
E
F
G
The pyrolysis set‐up used in the experiment showing the following parts: (A) steel container, (B) horizontal tube reactor, (C) horizontal tube furnace, (D) condenser, (E) thermocouple reader, (F) liquid collector/ cold
trap, and (G) displacement tanks.
SimpleSlow
PyrolysisSet‐up
Products of Slow Pyrolysis
Solids/CharLiquid Products: Bio‐oil
Gaseous Product
Gasification• Gasification – use of deficient amount of oxygen to produce combustible synthesis gas (CO+H2)
• A simple updraft gasifier for synthesis gas production from biomass
• HV syngas = 100‐250 Btu/ft3
• Air used is less thanstoichiometric amounts
• Synthesis gas is also calledsyngas or producer gas
Energy and Mass Balances in A Gasification System
About 20‐25%
biochar by weight
Heat content of syngas about 150
Btu/ft3 [5.5 MJ/m3]
Carbon Conversion Efficiency in Gasification
• Carbon Conversion Efficiency (CCE) Equation
• Thus, if carbon in synthesis gas is 50% (by adding all carbon content of all gases) and carbon in original biomass is 70% (from ultimate analysis), the CCE is calculated as follows:
%100biomassoriginalinCarbon
gassynthesisinCarbonEfficiencyConversionCarbon
%4.71%10070.050.0
EfficiencyConversionCarbon
Effect of Steam on the Gasification of Biomass
% Steam 10% 20% 30% 40%Blast Temp (o C) 47 60 70 76Reaction Temp (o C) 795 699 646 601
• Combustion – conversion of biomass into heat, carbon dioxide (CO2) and water (H2O)
• Total heat produced is the heating value of the biomass being combusted
• Wood fuel combustion is still the most predominant use of biomass in developing countries
• Other countries like India, animal (cow) manure is still popular biomass used for cooking and heating purposes
Most Popular Biomass Combustion System: The Spreader Stoker System
1‐ Refuse charging hopper2‐ Refuse charging throat3‐ Charging ram4‐ Grates5‐ Roller bearings6‐ Hydraulic power cylinders and control valves7‐ Vertical drop off8‐ Overfire air jets9‐ Combustion air10‐ Automatic sifting removal system
Other Unique Biomass Conversion Processes
• The MixAlco TM Process Developed at Texas A&M University by Dr. Mark Holtzapple– Organic acids are produced and further converted into organic salts, thermally converted into ketones and catalytically converted into gasoline
• The Syngas Fermentation System to Produce Ethanol– Syngas is used by microorganisms that produce ethanol
The MixAlcoTM Process• A process that converts biomass into organic acids (methane production is inhibited) and salts. These salts are thermally converted into ketones and hydrogenated into alcohols and further oligomerized into hydrocarbon fuels such as gasoline using suitable catalysts.
The Syngas Fermentation Process• Biomass is gasified to generate synthesis gas. The synthesis gas is used by microorganisms to convert this into ethanol.
Applications of Biomass Conversion Products
• Heat Energy– Use of fuel wood for cooking is still predominant in developing
countries• Electrical Energy and Power
– Use of biomass in steam cycles for power generation • Combined Heat and Power (CHP)• Mechanical Energy
– Use of biogas or synthesis gas in commercial engines • Liquid Biofuels or Biofuels Production
– Biodiesel and bioethanol production• Synthesis Gas Production and Use
– Use of synthesis gas for liquid fuel production• Biochar Production
– Use of biomass conversion co‐products for biochar soil amendment
Concluding Remarks
• Maintain a good balance between biomass usage and sustainability of agricultural land for food production
• Improvement of efficiencies of conversions• Understanding the logistics of biomass conversion processes
• Diversification of biomass resources from non‐food sources as well as lignocellulosic types
• Development of infrastructures for biorefineries(pretreatment, processing, storage and transport)