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7/28/2019 ABE 482 Lecture 10
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ABE 482Environmental
Engineering in Biosystems
September 26
Lecture 10
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Today
Wrap up anaerobic digestion
Experimental design
Lab 2
Question for next class
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Questions so far
Explain why anaerobic digestion is a neutral
GHG method of generating energy Why are anaerobic digesters not good for
disposing of wood waste?
Name a few factors that affect biogasproduction in anaerobic digesters (ratio orquantity)
What are the 3 anaerobic digester outputs
we must consider when doing a massbalance?
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Digester Heat Balance
Balance between energy producedfrom biogas and energy required tomaintain mesophilic temperatures
Other energy requirements of
anaerobic digester? Stirring, pumping, etc.
Energy produced depends on OMR, so
for feedstocks with lower ODM,energy produced will be lower
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Example 5Digester heat balance
If the 7,500 m3 per day of biogas is used to
produce hot water only, what percentage ofthis hot water energy is required fordigester heating?
What percentage of the hot water energyfrom a CHP unit is required for digesterheating?
What percentage of energy produced (hotwater only) is required for digester heatingduring a Saskatchewan winter?
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12 weeks3 weeks digestion, plus
5 weeks composting
Process time required to produce
mature compost
Nil100 150 m3
/MgBiogas production
Energy demandEnergy surplusEnergy balance
100%20%Odours
100%50%Space requirement (footprint)
CompostingAnaerobic Digestion
Comparison Table From: Introduction to Anaerobic Digestion,Wolfgang Muller and Axel Huttner, ORA -Organic Resource Agency Ltd., Malvern Hills Science Park, Geraldine Road, Malvern, Worcestershire WR143SZ, and IGW Ingenieurgemeinschaft Witzenhausen Fricke & Turk, and GmbH, Bischhuser Aue 12, D-37213 Witzenhausen, Germany. Presented at the Biowaste: Digesting the Alternatives Seminar, April 2005,UK.
A Comparison of Anaerobic Digestion and Composting
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References
Wikipedia, 2007. Anaerobic Digestion. Online:
http://en.wikipedia.org/wiki/Anaerobic_digestionAccessed: October 25, 2007.
Class notes for ChEng 882. 2006. University ofSaskatchewan.
Kiely, G. 1997. Environmental Engineering. McGrawHill:USA.
Chesshire, M. 2005. Process Calculations for Full-Scale Digesters. Biogas from Energy Crops andAgrowastes. 15th Jyvskyl Summer School:Cropgen.
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Experimental Design
You have been asked to determinethe biogas production potential ofseveral types of feedstock
How do you do it?
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Feedstock biogas production
0.952.11.5
Feedstock 3Feedstock 2Feedstock 1
L of biogas/L of feedstock per day
2.33.61.9
0.81.41.4
1.90.81.7
2.13.41.8
1.70.81.2
1.83.91.1
0.952.11.5
Feedstock3
Feedstock2
Feedstock1
L of biogas/L of feedstock per day
0.571.340.30stdev
1.652.291.51average
Replication allows the degree of
variability in the data to be
assessed
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Feedstock biogas production
Biogas production from various feedstocks
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Biogas production (L of biogas/L of feedstock per day)
Feedstock 1Feedstock 2
Feedstock 3
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Experimental Design
You have been asked to optimize theoperating parameters to improvebiogas production from a specificfeedstock
How do you do it?
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Biogas production by varyingparameters
4.4955
3.67401.1435Feedstock 3
2.41855
2.41245
2.4730Feedstock 2
0.71550
2.11040
1.8535Feedstock 1L of biogas/L of feedstock per dayDM ContentTemperature
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Factorial Experimental Design
When several factors are of interest in an experiment,
a factorial experiment should be used In each complete replicate of the experiment, all
possible combinations of the levels of the factors areinvestigated
Each feedstock should be digested at each
temperature and each DM content for validcomparisons 3 feedstocks x 3 DM contents x 3 temperatures equals
27 experiments
The effect of each factor can then be separatelyassessed
Can also investigate the interaction of effects (butonly with a factorial experimental design)
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1.7104012.35401
1.93401
0.7510301
2.153012.13301
1.510251
2.15251
1.83251L of biogas/L of feedstock per dayDM ContentTemperatureFeedstock
Biogas production by varyingparameters
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Factorial Experimental Design
Effect of new treatments or factorsshould always be compared to acontrol
Treatment = new coating for o-rings
Effect = increase tensile strength of o-rings at lower temperatures
Experimental design
Measure the tensile strength of untreatedand treated o-rings at 3 temperatures
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Factorial Experimental Design
Are the results significant?
Cannot make that assessment without a measure ofthe variability of data
1.810% DM
2.65% DM
2.33% DM
2.440 degrees
2.430 degrees
2.025 degrees
2.1Feedstock 3
2.9Feedstock 2
1.8Feedstock 1
Average
0.85
0.62
0.69
0.75
1.00
0.49
0.79
0.62
0.47
StdDev
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Factorial Experimental Design
How many replicates?
Depends on how powerful you want yourexperiment to be
Are the results significant?
Can crunch the numbers by hand, butstatistical software is very useful
SPSS in computer labs
Minitab more user friendly
Excel will work in a pinch (if you know whatyoure doing)
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Lab 2 Experimental Design
We have 12 reactors to play with
Lets go with 2 replicates so we have6 treatment combinations to work
with 3 feedstocks, 2 DM contents?
1 feedstock, 2 DM contents, 3 pHs?
? What will you measure?
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Question for next class
Calculate the $ value of the electricity produced if all theMSW waste and manure waste produced in Canada eachyear was anaerobically digested. 25 million wet tonnes of MSW/year 132 million wet tonnes of manure/year
30% dairy cow 30% beef cow
20% pig 20% other
Assume digester runs 365 days a year, 24 hours a day Assume you can sell electrical energy for 14 cents/kW-hr Assume you can convert methane to electricity with an
efficiency of 32%
How many Canadians will this serve?
Use: Table 1 from lecture, ASABE standards for manurecomposition, internet for electricity consumption of Canadians.
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Next Day
Waste to energy calculation anddiscussion