Energy Balance for Piedmont Biofuels in the Production of Biodiesel
Using Rendered Chicken Fat for 2008
Collaborative research of: North Carolina State University, Masters of Microbial
Biotechnology Program; R. Burton et al. Piedmont Biofuels Industrial. And NC State
University: Dr.S.D. Terry (Mechanical and Aerospace Engineering Department), Dr. A.
Hobbs (NCSU Solar House), & Dr. M. Flickinger (BTEC).
23 April 2009
Abstract: Piedmont Biofuels, a North Carolina based biodiesel production plant,
produced 1,046,389 gallons of biodiesel in 2008 through the transesterification process
of chicken fat. Piedmont Biofuels was interested in looking at their energy balance for
2008 in order to improve the efficiency of their biodiesel production process. This study
found that in 2008, Piedmont Biofuels had a net energy ratio (NER) of 2.54. The energy
balance model used in this study was compared to other energy balance models such as
the NREL and GREET. In this paper, we have presented the results of these energy
balance analyses and offered suggestions to Piedmont Biofuels on possible ways to
improve their overall net energy ratio.
Increasing concerns about global warming and energy consumption has
stimulated efforts for the production of cleaner, eco-friendly, renewable energy fuels.
Piedmont Biofuels, a worker and member owned cooperative located in Pittsboro, North
Carolina, promotes, produces, and sells biodiesel fuel and was established with this goal
in mind. In 2008, Piedmont Biofuels used 1,268,241 gallons of rendered chicken fat to
produce 1,046,389 gallons of biodiesel. To produce biodiesel, Piedmont Biofuels uses a
transesterification process, in which methanol reacts with the triglyceride oils contained
in rendered chicken fats to form fatty acid methyl esters (biodiesel) and glycerin. In
addition, heat and a strong base catalyst such as sodium hydroxide or potassium
hydroxide are required for this reaction. However, Piedmont Biofuels uses potassium
methylate (methanol + potassium hydroxide) as the catalyst for this reaction. Since
economic viability is a major concern in biodiesel production, it is important to adopt a
biorefinery model to improve the production process. This mainly calls for the recovery
and purification of the process waste to minimize the loss of recyclable materials. In early
2009, Piedmont Biofuels began implementing changes in their production process to
include a biorefinery model in their plant [See Figures: 1 & 2], which includes methanol
and biodiesel recovery from process waste and glycerin refining. In addition, Piedmont
Biofuels added wash water acidulation and biodiesel refining to their process.
The energy balance for a biofuel production system can be defined as the relation
between the energy produced (output/ kg biodiesel) and the energy consumed (input/kg
biodiesel) for each unit product, thus making it an important index for the economic and
environmental feasibility of a biofuel project (da Costa, 2006). In order to improve and
access the biodiesel production with biorefinery model, Piedmont Biofuels wanted to
know their energy balance for 2008, thus allowing them to compare it with 2009, when
they began implementing changes to their process.
The following four groups of graduate students from North Carolina State
Universitys Masters in Microbial Biotechnology worked with Piedmont Biofuels: the
Energy Balance Group worked on an energy balance study on the Piedmont Biofuels
Industrial plant for all of its processes relating to biodiesel production, the Sidestreams
Group conducted feasibility studies for alternative techniques for dealing with
sidestreams including wash water and glycerin, the Enzymatic Lab Group tested the
effectiveness of Novozymes (a Denmark based biotechnology company with a plant
located in Franklinton, NC which is a major producer of enzymes) enzymes for the
production of biodiesel from triglycerides and free fatty acids under various conditions,
while the SBIR Grant Group wrote a SBIR grant to fund enzymatic biodiesel production
research/pilot plant. Our group, the Energy Balance Group, was given the task of
performing an energy balance study for Piedmont Biofuels production process.
For the basis of our energy balance model, we used a customized version of the
NREL model, which was expanded to include human labor and the biorefinery process.
We compared our model to the NREL model, the GREET model, and a modified GREET
model which included human labor. According to the model of Sheehan et al. (1998),
also known as the National Renewable Energy Laboratory (NREL) study, the energy
ratio should be defined as: RNREL = Eb/E.f2, where Eb is the total input energy for the
biodiesel and E.f2 is the fraction of the input energy associated with biodiesel. The
GREET model calculates fossil fuel energy requirements on a per-mile basis for the
major alternative fuels and vehicle systems (Andress, 2002). Both the NREL and GREET
models assigned the energy in proportion to the mass fraction of output (Pradhan, 2007).
The purpose of this study was to write an energy balance study on the Piedmont
Biofuels Industrial plant for all of its processes relating to biodiesel production. This
would allow Piedmont Biofuels to make a comparison of the energy balance for 2008 to
the energy balance for 2009. Piedmont Biofuels introduced different methods in 2009 to
their production process in an attempt to improve the energy balance.
The study included all upstream energy consumption, energy used in transporting
and processing the process ingredients, and the energy used in biodiesel production. To
calculate the energy balance we included both primary and secondary process energy.
Primary energy is the energy content of the feedstock, methanol, and methoxide (Table
1). Secondary energy input for the biodiesel production was the total energy used in the
transportation of methanol, potassium methylate, wash water, and feedstock. This mainly
included the fuel type used and distance traveled during transportation. Electricity
consumption was also included in secondary energy (Table 3 & Figure 3). Electricity
consumption of the entire plant was monitored to check the efficiency of the pumps and
motors used in the processes from raw materials to biodiesel production. Also, Piedmont
Biofuels used solar panels to provide energy for methanol recovery and feedstock heating
(Table 4). Solar energy is a renewable source of energy, thus it was not included in the
energy balance calculation as an energy input. In addition, labor was included as
secondary energy input. A typical energy input per worker is 100 W; we calculated labor
input based on 360kJ/ hour (Energy input labeling standards, 2008). All the calculations
were done by converting the energy consumptions into BTUs. Mass energy balance was
calculated to determine the mass losses during the production stages (Table 4).
A Net Energy Ratio (NER) was calculated for the process to provide a measure
for how much fossil fuel equivalents were used to produce the fuel, compared to the total
energy value of the biodiesel. This yields a measure for the renewability of the process.
The definition for the NER, NER=Eb/ (E1*f1+E2*f2+E3*f3), was adopted from the 1998
NREL study (Sheehan et al. 1998). For this definition, Eb is the energy value of the
biodiesel. E1 equals the energy input required to grow the raw feedstock, with f1 being the
fraction of that energy allocated to biodiesel. E2 is the energy used in processing the raw
materials before they are fed to chickens as chicken feed, with f2 being the fraction of that
energy allocated to the feedstock. E3 equals the energy used in the transesterification
process; and f3 again being the fraction allocated to biodiesel.
A feed conversion ratio (FCR) was used to convert the energy allocated to initial
raw materials used as chicken feed to the energy in the fat. The FCR was assumed to be
1.88 lb feed per 1 lb chicken meat for a young chicken (<40 days) (J. Petitte, personal
correspondence). In other words, if total energy required to produce 1 lb of chicken feed
was x BTUs, 1 lb of chicken fat created from that feed would require 1.88x BTUs of
The presented data corresponds to the data provided by Piedmont Biofuels, and
information that was gathered during the evaluation of Piedmont Biofuels process. The
study found the energy balance for Piedmont Biofuels to be 2.54, using the previously
described, customized version of the NREL model. Other models such as the GREET +
labor, GREET, and NREL models calculated a NER of 2.87, 3.00 and 3.38, respectively
Figure 1: 2008 Biodiesel Production Process
In Figure 1, above, the 2008 biodiesel production process is given in a simplified
form. Methanol and methoxide are mixed together, and are then combined with chicken
fat in the reaction vessel. After approximately 4 hours the reaction is complete and is
allowed to settle for separation of the biodiesel and glycerin phases. Next, the biodiesel is
washed to remove methanol and other contaminants, and the glycerin is disposed of
together with the wash water. Solar heating provided about 5% of the power used in the
This process differs from the 2009 process in the following ways: in 2009 a
biorefinery module was added that is able to remove most of the excess methanol from
the biodiesel and glycerin phases and can therefore recycle this energy-rich component.
After removal of the methanol present in the glycerin phase it is more concentrated (65%
glycerol instead of 35%) and can potentially be used for other purposes. This process is
presented in graphical form in Figure 2.
Figure 2: 2009 Biodiesel Production Process
In Figure 3, below, the electricity use is presented in graphical form. As can be
seen from the figure, the largest energy users are the various resistance heaters present in
the process to heat the large reaction and wash vessels. Potentially this could be an area
where Piedmont Biofuels could save energy. Furthermore, the large pumps, e.g., the
vacuum pump and the air compressor in biorefinery process use a fair amount of
Figure 3: Electricity Consumption: This chart lists the main electricity utilizations in the process.
Farming inputs Btu/Gal
Chicken fat 17968.8 11622.7 15813.8
Soybean oil 12529.6 4666.9 9621.0
Model Our Model NREL GREET
Table 1: Energy input in Feedstocks. This table compares the energy inputs from farming and
processing the feedstock between the authors model and other commonly cited studies such as
NREL and GREET.
Table 1, above, lists the different farm and feedstock processing energy inputs for
both soybeans and chicken fat. Depending on the model and assumptions used, the
energy inputs are vastly different. This is due to significant differences in the various
energy inputs for each step in the study, as well as, different inclusion criteria. These
differences are analyzed in greater detail in Pradhan, et al., 2007. The fertilizer energy
input used in this model is broken down in Table 2 for each of the elements that make up
Fertilizer Fertilizer Energy for Soybeans
Nitrogen 2822.64 BTU/bushel
Phosphate 2473.80 BTU/bushel
Potassium 2736.50 BTU/bushel
Total 8032.94 BTU/bushel
Table 2: Energy for Fertilizer processes to Produce Soybeans. This table shows the approximate
energy required to produce the fertilizer used in growing 1 bushel of soybeans.
A more detailed analysis of the electricity usages in the biodiesel production plant
is given in Table 3. This is a condensed table that only shows the major energy draws in
the system, as there are dozens of total appliances in the system. As can be seen in the
table, the wash tank heaters, feedstock tank heater and reactor heaters use a majority of
the total electricity. Other large draws in the system are the air compressors and the
vacuum pump used in the biorefinery process.
Table 3: Electricity Consumption. Table 3 shows the largest electrical energy usages in the process.
The main energy expenditures in this area can be found in the heating elements and the larger
Table 4: Energy Balance of Various Models. This table shows the composition of the NER for
different starting assumptions, and provides the total value of the NER for each scenario. Solar
heating values are not included in the NER and are only shown to illustrate how much electrical
energy is saved.
Table 4 shows the result of the energy balance for this study. It uses the total
energy inputs for 2008, together with the total amount of biodiesel produced in that year,
to derive a relative NER based on a gallon of biodiesel. Besides the model used in this
study, several other models are given to illustrate some of the assumptions made about
the input energies. The GREET model is fairly close to the modified model in terms of
farming and processing inputs. The main difference is that it does not include the waste
disposal energy costs associated with disposing of glycerin and wash water.
GREET GREET w/ Labor
E1f1 15814 15814
E2f2 6842 6842
E3f3 24382 24399
Eb 125100 125100
NER 2.66 2.66
Table 5: Energy in farming processes. This table shows the energy required to produce biodiesel
from chicken fat if the assumed energy inputs from the GREET model were converted to chicken fat
Table 5: Legend for Energy in farming processes
The purpose of Table 5 is to illustrate the difference inclusion of labor energy
inputs makes on the NER. As can be seen from the final values, it is a minor amount in
comparison to several other inputs and does not change the ratio at all. The energy used
in processing soybeans was calculated based on data from Argonne National Laboratories
(2007), as shown, below, in Table 6.
Energy for Soybean Processing
Soybean oil 1143.7 BTU/lb
Soybean meal 1143.7 BTU/lb
Table 6: Energy used to process soybeans fed to chickens. This energy input corresponds to the
energy used to crush and process the raw soybeans and turn them into soybean meal and oil.
The converted energy inputs for farming and soybean processing are shown
below, Table 7, for both the 1998 NREL study and the 2006 GREET study.
E1f1: Energy in farming
E2f2: Energy in Processing Feedstocks
E3f3: Energy in Transesterification Process
Eb: Energy in biodiesel
NER: Net Energy Ratio
Table 7: Comparison of Energy in Soybeans fed to Chickens
Based on the findings, there are numerous ways for Piedmont Biofuels to improve
their energy balance ratio. From the production of biodiesel, Piedmont Biofuels generates
various types of wastes. Two that constitutes for the bulk of waste produced are crude
glycerin and wash water. The Sidestreams Group looked at alternative techniques for
dealing with these wastes. Possibly the best option for disposing of the glycerin is to burn
it in a CHP diesel engine modified to burn the glycerin. The CHP engine will save
Piedmont Biofuels money by cutting their energy costs, which will also help improve
their net energy ratio, thus their energy balance. Also, the Sidestreams Group explored
the option of using an anaerobic digester. Since glycerin and the wash water are good
sources of carbon, they could both be utilized by anaerobic bacteria to produce methane.
Theoretically the methane could be converted into methanol and then used back into the
biodiesel production process.
Another option would be to use the biogas generated by an anaerobic fermenter as
heat energy throughout the production process and sell the compost to local farmers.
This option has the potential to save Piedmont Biofuels money on storage cost and on the
disposal of the two sidestreams. Both elimination options are still in the experimental
stage of development. Currently, there are no amounts determined on methanol or biogas
yields from crude glycerin and wash water. Also, the anaerobic organism used in the
process will impact the yields. Research will have to be conducted to determine a
suitable organism in order to reach optimal yields. A feasibility analysis will also have to
be completed to determine if the disposal cost savings and profits made from selling the
compost will out-weigh the cost of setting up the anaerobic digester in the long run.
While these waste elimination options are excellent suggestions that should be explored
further, currently there is no supporting evidence that adopting these practices will have a
positive effect on the energy balance.
For the biodiesel production process, excess methanol is required to force the
reaction to completion, generally 20-100% more methanol than actually required for
reaction. Piedmont Biofuels currently uses more than 100% methanol, half of which goes
into the wash water. A study to access the optimal amount of excess methanol that is
required for the reaction may help reduce the energy input of methanol. This would not
only reduce the energy input from methanol, but also energy consumed in recovering
methanol from waste water and glycerol.
Our study revealed that the feedstock, chicken fat, is the major contributor of
energy input. Using different feedstock may be helpful in reducing the energy input and
the net energy ratio in the long run. A study of different feedstocks and their energy
content would be helpful to see which source of feedstock would be optimal for Piedmont
Biofuels. While exploring different feedstock may help bringing up the energy balance,
its availability and cost could be a possible constraint.
Farming + processing energy
8043.7 3901.8 MJ/ha
1300.1 630.7 BTU/lb
After studying the electricity consumption of the plant, we found that most of the
plants total electricity is consumed by reactor heater and wash water tank heater, about
31% and 21%, respectively. Piedmont Biofuels can improve the energy balance by
reducing the electricity consumption in these two heaters, possibly by using more
efficient pumps and motors. Electricity consumption can also be reduced by using
cavitation technology combined with enzymatic biodiesel production, as suggested by the
Also, transesterification requires a large amount of heat, elevated temperatures,
excess methanol, and high grade feedstock. Low grade feedstock have high free fatty acid
(FFA) content which must be removed, before transesterification, using acid to avoid
soap formation that interfere in the transesterification reaction. The energy balance can be
improved by using biological catalyst, an enzyme, for the biodiesel production. The
Enzymatic Group studied the use of lipase in biodiesel production. The group suggested
that using lipase would reduce the amount of heat and electricity required for the
transesterification process. Also, the use of low grade feedstock would not pose a
problem because of absence of alkali in the reaction and hence, no soap formation. This
would indeed increase the yield as enzyme can convert FFAs to methylesters without
producing soap. Also, enzymes do not require water removal from feedstock which
otherwise leads to the production of soap. Using enzymes would reduce the amount of
methanol needed for the process and would allow the use of low-grade cost effective
feedstock. Enzymatic biodiesel production has several advantages but the cost and
feasibility of using enzymes would need to be determined for use in an industrial scale.
Also, use of enzymes is still in the research phase and there is no evidence of enzymatic
biodiesel production in commercial scale.
In conclusion, Piedmont Biofuels 2009 process clearly indicates an improved
production process in terms of cost and energy due to implementation of biorefinery
model. However, Piedmont Biofuels could improve the biodiesel production by exploring
other feedstocks, improving electricity and methanol consumption, and considering
burning the glycerin wash product in a CHP engine. Even though use of glycerol and
wash water for production of methanol or biogas is still under research, this option could
prove to be very effective in improving Piedmont Biofuel’s energy balance. Finally, the
use of enzymes may seem optimistic but enzymatic biodiesel production could improve
the process, making it more energy favorable and less harsh to the environment.
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Acknowledgments: The authors would like to thank the following people in their guidance
for the production of this research: From Piedmont Biofuels: Rachel Burton, Lyle Estill,
Amanda Egdorf-Sand, Leif Forer, Russell Harper, Greg Austic, from Southern Energy
Management: Scott Hoover; and finally from NC State University: Dr.Steven D Terry
(Mechanical and Aerospace Engineering Department), Dr. Alex Hobbs (NCSU Solar
House), & Dr. Michael Flickinger (BTEC).