Project Proposal and Feasibility Study
Team 14: GRE-cycle
Hannah Albers, Ben Guilfoyle, Melanie Thelen, and Cole Walker
ENGR 339--Senior Design Project
November 10, 2014
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Executive Summary
The Senior Design team is designing a biodiesel production plant that uses triglyceride-containing
waste vegetable oil as its feed source. The proposed plant will use waste vegetable oil collected from
local restaurants in Miami, FL and convert it to biodiesel. The main chemical reaction in this process is
called transesterification. This reaction converts triglycerides in the feed to methyl esters (biodiesel) in the
presence of an alcohol and a basic catalyst. The biodiesel produced will be compatible with current diesel
engines. The demand for alternative energy sources is increasing as the demand for energy increases and
global supply of fossil fuels decreases. Furthermore, restaurant grease is a waste product with no further
applications, which makes it an ideal feedstock for biodiesel production.
This design process prioritizes stewardship by recycling a waste product, caring by focusing on
safety, and transparency by adhering to all government regulations on product quality. Many variables
will be considered when designing this plant including: acid catalyst type, alcohol type, alkaline catalyst
type and reactor type. For the purpose of this preliminary feasibility study, the sulfuric acid, methanol,
sodium hydroxide, and a batch reactor will be used. There are three main process sections: pre-treatment,
post treatment and settling, with waste product distillation in between each.
With these variables chosen, the project was found to be economically feasible. The upfront
construction costs were estimated to be $14.8 million. It was determined that a 10% rate of return is
obtained when the selling price for biodiesel is $3.41. This falls in line with current biodiesel plant
pricing. A yearly profit of $1.8 million will occur at this selling price, with a plant lifespan of 20
years. The customer will be fuel distributors with existing infrastructure to provide the public with
blended biodiesel. Infinite demand will be assumed with potential competition coming from the
diesel market.
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Table of Contents
Executive Summary ...................................................................................................................................... 2
Table of Contents .......................................................................................................................................... 3
Table of Figures ............................................................................................................................................ 5
Table of Tables ............................................................................................................................................. 6
1. Introduction ............................................................................................................................................... 7
1.1 Background Information ..................................................................................................................... 7
1.2 Objective ............................................................................................................................................. 8
1.3 Scope ................................................................................................................................................... 8
1.4 Past Project Teams .............................................................................................................................. 9
1.5 Feasibility............................................................................................................................................ 9
2. Design Norms ......................................................................................................................................... 10
2.1 Stewardship ....................................................................................................................................... 10
2.2 Caring................................................................................................................................................ 11
2.3 Transparency ..................................................................................................................................... 11
3. Team Organization.................................................................................................................................. 11
Team Responsibilities ......................................................................................................................... 12
Hannah Albers .................................................................................................................................... 12
Ben Guilfoyle ...................................................................................................................................... 13
Melanie Thelen ................................................................................................................................... 13
Cole Walker ........................................................................................................................................ 13
4. Process Overview.................................................................................................................................... 14
4.1 Process Research ............................................................................................................................... 14
4.1.1 Block Flow Diagram .................................................................................................................. 14
4.1.2 Key Variables............................................................................................................................. 14
4.1.3 Design Alternatives .................................................................................................................... 17
4.2 Material Research ............................................................................................................................. 18
4.2.1 Feed Sources .............................................................................................................................. 18
4.2.2 Product ....................................................................................................................................... 19
5. Preliminary Design ................................................................................................................................. 19
5.1 Transesterification Reactor ............................................................................................................... 19
5.1.1 Design Alternatives .................................................................................................................... 20
5.1.2 Catalyst ...................................................................................................................................... 22
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5.2 Pre-Treatment Section ...................................................................................................................... 24
5.2.1 Filter ........................................................................................................................................... 24
5.2.2 Acid Treatment .......................................................................................................................... 26
5.3 Post-Treatment Section ..................................................................................................................... 28
5.3.1 Glycerin Separation.................................................................................................................... 29
5.3.2 Methanol Recovery .................................................................................................................... 29
6. Safety Considerations ............................................................................................................................. 31
6.1 Chemicals.......................................................................................................................................... 31
6.2 Operating........................................................................................................................................... 31
7. Business Plan .......................................................................................................................................... 33
7.1 Market Study..................................................................................................................................... 33
7.1.1 Customer .................................................................................................................................... 34
7.1.2 Competition................................................................................................................................ 34
7.2 Tax Information ................................................................................................................................ 35
7.3 Costs.................................................................................................................................................. 36
7.3.1 Capital Costs .............................................................................................................................. 36
7.3.2 Operating Costs .......................................................................................................................... 36
7.4 Profitability ....................................................................................................................................... 37
8. Conclusion .............................................................................................................................................. 40
References ................................................................................................................................................... 41
Appendix ..................................................................................................................................................... 44
1. Overall Process Mass Balance ............................................................................................................ 44
2. Filter Calculations ............................................................................................................................... 45
3. Competing Biodiesel Plants in Florida ............................................................................................... 45
4. Material Safety Data Sheets (MSDS) ................................................................................................. 45
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Table of Figures
Figure 1: Work breakdown schedule organized as critically linked tasks .................................................. 12
Figure 2:Overall Process Block Flow Diagram .......................................................................................... 14
Figure 3: Reaction mechanism for transesterification of triglycerides following an acid pre-treatment: ... 14
Figure 4: Saponification of Free Fatty Acids to form soap ......................................................................... 16
Figure 5: Water formation in an acid catalyst reaction to convert Fatty acids to biodiesel ........................ 16
Figure 6: Transesterification of triglycerides to form biodiesel (methyl esters) ......................................... 20
Figure 7: Levenspiel plot of the pre-treatment reaction. ............................................................................. 28
Figure 8: Million barrels of biodiesel produced in the United States from January 2012 to May 2014 ..... 33
Figure 9: Cash flow diagram for the plant lifespan..................................................................................... 39
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Table of Tables
Table 1: EPA Biodiesel Specifications ....................................................................................................... 19
Table 2: Relative densities of effluent stream components ........................................................................ 29
Table 3: Current market value for process materials .................................................................................. 37
Table 4: Cost of input materials per year .................................................................................................... 38
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1. Introduction
1.1 Background Information
Fossil fuels account for approximately 82% of the United States’ energy consumption.
Though geologists estimate that less than half the total volume of crude in below-ground reserves
will be depleted by 2030 (http://instituteforenergyresearch.org/topics/encyclopedia/fossil-fuels/),
it remains a fact that the supply of crude oil continues to decrease as the energy demand
necessary to support the rapidly advancing lifestyles around the world increases. Oil has done
well to advance human technology to the point where it is today, but the drawbacks of crude oil
cast a shadow across the benefits. The demand for crude oil has caused wars, damaged the
atmosphere, and eventually must be replaced by more sustainable energy sources.
Used restaurant grease was recently found to contain high levels of triglycerides, which
store large amounts of energy. According to USA Today, approximately 3 billion pounds of
grease are produced in the United States each year. The average fast food restaurant produces
about 150 - 200 pounds of grease every week, says the New York Times. The disposal of waste
grease has been a large burden on restaurants, since grease cannot be processed in a waste water
treatment plant. It must be collected in a grease trap and disposed of in alternative ways.
Restaurants have been selling their used grease in recent days to recycling companies that
convert the used grease into fresh cooking oil. Rather than recycling the grease for consumption,
the burden of grease waste disposal can be alleviated by instead converting this grease to fuel.
Also, in contrast to fossil fuels, biofuels are produced from renewable plant and animal
material such as vegetable oils, grease, or animal fats (Institute for Energy Research). Over the
past decade, interest in producing biodiesel from oils and grease has grown into a marginally
successful industry as the future availability of fossil fuels became uncertain. Additionally,
burning biodiesel produces 56-87% less greenhouse gas emissions than conventional diesel,
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according to the EPA, which makes it a viable and promising option as an alternative to crude
oil.
1.2 Objective
The main objective of this project is to design a biodiesel production plant that will
provide a clean alternative to diesel. Obtaining feedstock for the plant will require the
participation of restaurants who have to pay an outside source to dispose of the grease they
generate on a daily basis. By establishing the plant in a populous area with a lot of restaurants, a
significant amount of biodiesel will be able to be produced. As stated previously, current fuel
production is unsustainable whereas the supply of restaurant grease is readily available.
Secondly, the team purposes to make the plant profitable. Biodiesel production will not
increase unless there is money to be made in the industry. Despite its environmental
implications, production will be limited if it continues to be more profitable to use fossil fuels to
run our vehicles. By designing a profitable biodiesel plant, the team hopes to prove that biodiesel
production is part of the answer for a more sustainable future.
1.3 Scope
The team is attempting to design a production plant in the Miami area that will buy used
grease from surrounding restaurants and convert it into a usable biodiesel. The size of the Miami
area will allow significant grease collection for the production of a substantial amount of
biodiesel. Currently, based on the number of restaurants in the area and understanding that grease
will not be obtained from every one of these sources, the production of biodiesel is anticipated to
be in the hundreds of barrels per day range.
Biodiesel is commonly blended with conventional diesel in 50:1, 20:1, and 5:1 diesel to
biodiesel ratios. The team assessed the possibility of blending the produced biodiesel at the plant
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but determined that this was outside the scope of the project. The plant will be used exclusively
to produce purified biodiesel that can be blended elsewhere.
1.4 Past Project Teams
Several senior design teams have completed projects pertaining to biodiesel production.
In 2008, Team Rinnova designed a small scale biodiesel reactor for home users and using
feedstock from Calvin College Dining Services. Rinnova met their project goals but included
recommendations for a second prototype. Suggested changes included adding a completely
electronic control system, using better materials for piping, and installing a coarser filter. The
Diesel Crew took these recommendations in 2013-2014 and designed a second prototype for
home users. Their design utilized a microwave reactor, unlike the batch reactor designed by
Rinnova. Microreactors are used for continuous processes.
Though the scope of this report is full scale plant design, references to these project
groups are found scattered throughout this report, particularly in the design alternatives for each
plant section. The team will not be building off of other team projects by scaling up the past
designs. but will take into consideration their design decisions when making decisions this year.
1.5 Feasibility
The use of biodiesel compared to currently available diesel has both advantages and
disadvantages. For one, restaurant grease can be obtained inexpensively, which makes the plant
more economically feasible by lowering operating costs. Additionally, biodiesel has positive
environmental implications as it produces less hydrocarbons and carbon monoxide than regular
diesel when burned. The proposed process is more sustainable, helping the environment while
eliminating waste. The traditional diesel process requires a depletion of Earth’s natural resources
to produce the fuel, while biodiesel uses otherwise useless waste.
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Despite these advantages, the use of biodiesel instead of traditional diesel does pose some
challenges, most notably gelling. In colder weather, some biodiesels gel making them unusable.
This is one reason the plant will be placed in Florida. Considering the warm climate in the state,
gelling should not be a concern. Though biodiesel significantly decreases carbon emissions, it is
less efficient than normal diesel. It has been found that fuel efficiency is reduced by 10%
compared to regular diesel. Despite these cons, the team feels that the economic and
environmental considerations make the proposed process a valuable and feasible project to
pursue.
2. Design Norms
Crucial to the sustainability of the proposed plant is the promotion and prioritization of
certain design norms, three of which are detailed in this report. These norms should be integrated
into early planning stages of the plant as well as during the more detailed design work,
construction, and daily operation to ensure the health, well-being, and integrity of employees and
customers alike.
2.1 Stewardship
From its conception the biodiesel plant proposal is centered on the importance of
environmental stewardship. It becomes increasingly vital in a world of unlimited demand and
limited resources to think forward to a time when the nonrenewable resources currently used for
energy generation are no longer a feasible option. Additionally, exercising stewardship requires
examining the consequences of energy consumption and making every effort to mitigate the
problems (greenhouse gas emissions or high volumes of dangerous waste material) faced by the
energy industry. The proposed biodiesel plant would lower total emissions, generate less
hazardous waste, and draw from a readily available and constant feed source of grease and turn
something originally considered waste into a desirable product.
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2.2 Caring
Once built, the proposed plant would require employees to operate the plant equipment.
Caring, one of the design norms, becomes an important attribute of the design engineers for the
safety of all employees. From the reactor catalyst selection to the layout of the plant units, caring
must be exercised to ensure employees aren’t required to put themselves in harm’s way as part of
their job description and to ensure safety procedures are established for routine and nonroutine
tasks. This design norm will be reflected when designing the controls used in the plant and by
not introducing dangerous chemicals into the design without proper safety measures.
2.3 Transparency
The potential for dangerous situations that could extend beyond the plant property are
necessary to communicate to local government and local citizens who could be negatively
affected by the plant. Transparent business practices require full disclosure to employees and
citizens about potential hazards, Furthermore, since the final product must meet certain
governmental standards to be used in diesel engines, it is important to the team to ensure that the
plant meet or even go beyond these standards. No shortcuts or half-measures will be taken in the
design process in an attempt to promote the profitability of the design over the quality.
3. Team Organization
In order to meet the team goal of designing a profitable plant, it was necessary to plan
ahead. Task deadlines were assigned based on both class and team-specific deadlines. Professor
Jeremy VanAntwerp was assigned to the team as a project advisor, and he met with the team
every other week to discuss progress and design challenges. Professor VanAntwerp connected
the team with Randy Elenbaas, who served as an industrial consultant. Randy Elenbaas is a
chemical engineer employed at Vertellus Specialties, Inc. in Zeeland, Michigan with valuable
knowledge of process design.
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As seen in Figure 1, the project could be divided into three sections with research
interlaced throughout the process: the main reaction with pretreatment, the main reaction without
pretreatment, and post-treatment.
Figure 1: Work breakdown schedule organized as critically linked tasks
Team Responsibilities
In addition to the tasks specified below, each team member was responsible for ongoing
research about their section of the design and biodiesel production in general. This approach
enabled all members to be familiar with all aspects of the project in order to validate and
constructively critique each other’s work. Deliverables for class deadlines such as the team
poster and executive summary were compiled collectively to ensure all team members were
aligned on the objectives and scope of the project as these elements became more specific.
Additionally, each team member was responsible for communicating their section of the design
verbally and in writing relevant documents.
Hannah Albers
Hannah was tasked with the preliminary transesterification reactor design which includes
catalyst aspects such as catalyst selection, reactor type, and preliminary sizing. She was also
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responsible for post-treatment research and recording the team’s weekly progress to be reported
to Professor VanAntwerp during regular meetings.
Ben Guilfoyle
Ben was tasked with preliminary pretreatment design including esterification reaction
kinetics, sizing, and design alternatives, and he was also responsible for feedstock research in the
Miami area. Ben also worked in cost estimation and proving the plant’s profitability. He is the
team’s webmaster and will keep the team’s website up to date throughout the year.
Melanie Thelen
Melanie was also tasked with preliminary transesterification reactor design including
reaction kinetics, sizing, and design alternatives. She headed research pertaining to
governmental biodiesel standards and regulations, safety, and kept the team organized by
ensuring all class deadlines were met and deliverables were submitted on time.
Cole Walker
Cole was also tasked with the preliminary pretreatment design including filter selection
and design alternatives. He was also responsible for financial research pertaining to market
trends and plant profitability. Melanie and Cole are also working in the lab with grease samples
to help the team better understand typical compositions of restaurant grease for the design.
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4. Process Overview
4.1 Process Research
4.1.1 Block Flow Diagram
Figure 2:Overall Process Block Flow Diagram
4.1.2 Key Variables
The overall chemistry for the reaction of grease to biodiesel can be seen below in Figure
3.
Figure 3: Reaction mechanism for transesterification of triglycerides following an acid pre-treatment:
Where the triglycerides are grease and methyl esters are biodiesel.
The feedstock to be used in the process will be trap grease—that is food waste grease that
is unable to be processed as wastewater. The oil portion of the grease may or may not be solid at
room temperature but it will contain solid food particles that need to be filtered out. Within trap
grease, there are two main types of grease: brown grease and yellow grease. Brown grease is
essentially rotten food oil while yellow grease is rendered animal fat and used vegetable frying
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oil. The most significant difference in regard to biodiesel production is the free fatty acid (FFA)
content of the grease. Brown grease contains more than 15% FFA while yellow grease has less
than 15%. An increased amount of FFA is undesirable since it decreases the amount of
triglycerides that can be turned into biodiesel. However, there are methods of turning FFAs into
esters, which will be discussed later. Yellow and brown grease can either be processed
simultaneously or separated beforehand. The rest of the grease is composed of triglycerides
which can be directly converted to biodiesel, as seen in Figure BLANK.
The most promising process involves a pre-treatment of feedstock with high FFA with an
acid catalyst. An acid catalyst like sulfuric acid or hydrochloric acid will convert the FFAs to
esters, increasing the overall conversion and product quality. It has been found that feedstocks
need to have approximately 1% FFAs or less to provide acceptable product quality. One problem
with this pre-treatment is that water forms as a byproduct of the FFA to ester reaction. This water
needs to be removed using a separation technique since it would contaminates the final product.
Another issue with the acid pre-treatment is potential damage to vessels—so an appropriate
material needs to be selected for the vessels. This acid pretreatment can be repeated to lower the
FFA level to less than 1%.
However, the acid pre-treatment is necessary to lower the FFA content. A lower FFA
content indicates a higher overall process conversion to biodiesel. Also, FFAs can cause
undesirable side reactions in the reactor, the main being saponification which causes soap
formation, as seen in Figure 4.
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1
Figure 4: Saponification of Free Fatty Acids to form soap
The FFA needs to be removed or converted before contacting with NaOH base to prevent the
soap formation. The saponification reaction needs to occur in the presence of water, so the water
formed in the acid catalyst reaction, seen in Figure BLANK, needs to be removed.
Figure 5: Water formation in an acid catalyst reaction to convert Fatty acids to biodiesel 2
Some soap formation is inevitable though and separation will be discussed later.
Once the feedstock has been pre-treated, it is transferred to the main reactor where it is
heated to between 50C and 60C. The temperature must remain below the boiling point of the
chosen alcohol so it remains in the liquid phase without pressurizing the reactor. A solution of
alcohol and alkaline catalyst is prepared separately and added to the reactor. The alkaline catalyst
is present to speed the reaction of triglycerides to methyl esters and convert any remaining FFA
to soap. An agitator is used for up to one hour to ensure proper mixing, and the new solution
settles. After proper separation, there will be a layer of biodiesel at the top of the reactor and any
1
2
http://domainbiotech.blogspot.com/2013/02/the-mechanism-that-ill-be-presenting.html
http://www.intechopen.com/source/html/17584/media/image4.jpg
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soap formed will settle at the bottom. These layers are separated and the biodiesel is ready for
use. The variables to be manipulated in this process are:
·
·
·
·
·
·
·
·
·
Number of pre-treatment cycles (0, 1, or 2)
Acid catalyst used in pre-treatment (sulfuric , hydrochloric , or other)
Alcohol used in pre-treatment (methanol or ethanol)
Ratio of acid catalyst to alcohol
Temperature
Alkaline catalyst (NaOH, KOH, NaOCH3, metallic Na, or other)
Ratio of alkaline catalyst to alcohol
Agitator time
Settling Time
This assumes a given feedstock where the initial composition cannot be predicted or
manipulated with accuracy.
4.1.3 Design Alternatives
There are many alternative processes under development, which turn used grease to
biodiesel. One option is using a supercritical reactor for processing grease with a high FFA
composition. This process operates at high temperature (275C to 325C), high pressure, and and
therefore must take place in heavy-duty reaction vessels. This reactor does not require a catalyst
because of the high temperature and pressure used, so separation steps can be taken out to purify
the product downstream. Also, side-reactions are less of a concern with no catalyst present. The
process is also less affected by initial FFA content, water formation and glycerol formation, due
to the high operating conditions. However, the capital and operating costs are astronomical. This
is not a feasible option for a start-up plant of this scope, and would be better implemented as part
of a revamp for a current facility.
Another process is glycerolysis, which is able to handle feedstocks with greater than 10%
FFA. Glycerin is heated to 400F and reacted with the FFAs in the feed to form monoglycerides.
These monoglycerides can be processed as normal with the triglycerides by using an alkaline
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catalyst to form biodiesel. Problems with this process include high operating costs due to the
high heat, a high-pressure boiler to keep the process in liquid phase, and a vacuum to remove any
formed water. Glycerolysis is similar to the process mentioned earlier because the glycerin must
be separated at the end, but there is much more glycerin produced in glycerolysis.
Finally, the use of solid acid catalyst is an emerging option for processing grease. Solid
acid catalyst is packed into a packed bed reactor and the mixture of grease and alcohol flows
through the reactor. Water is still formed during the reaction though, so the alcohol/water
solution separated the end must be distilled to recycle the alcohol. Also, contaminants in the oil
like phosphorus and water can foul the catalyst.
4.2 Material Research
4.2.1 Feed Sources
The feed grease will be collected from restaurants in the Miami area. In the Miami
greater area, it was found that there are approximately 10,750 restaurants. It was also found that
an average restaurant produces about 35 lbs of grease per day. This means that about 375,000 lbs
of waste restaurant grease is used per day in the Miami area. The greater Miami area is 6,137
square miles, which is well within reason to expect the plant’s trucks to be able to collect from
the entire area. At the same time, It is not feasible to expect every restaurant to contribute to the
plant’s feed stock, so it was estimated that the plant could collect approximately 75% of this
waste grease. This leads to the estimation the plant will operate with a feed of 130,000 kg of
waste restaurant grease per day.
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4.2.2 Product
Table 1 features the federal EPA specifications for 100% biodiesel stock fuel which will be met
Table 1: EPA Biodiesel Specifications
All of these specifications will be met via separation techniques.
5. Preliminary Design
5.1 Transesterification Reactor
For the main reactor, three parts methanol and one part triglycerides are sent to a reactor
for the transesterification of triglycerides to methyl esters according to the reaction presented
below:
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Figure 6: Transesterification of triglycerides to form biodiesel (methyl esters)
The catalyst in the reaction is a salt (typically sodium hydroxide or potassium hydoxide),
which assumes that the waste vegetable oil has been pretreated to decrease the amount of FFAs
by a processed described below.
5.1.1 Design Alternatives
Selecting a reactor for optimal biodiesel production requires tradeoffs between high
capital costs, reaction times, energy requirements, and conversion. Batch, semi continuous, and
continuous reactors are most commonly used to produce methyl esters.[1]
Batch Reactors:
Batch reactors are most commonly used by individuals who independently make biodiesel
for personal use. They are easy to build on a small, garage operation scale and have a low
capital cost for plant use. Batch reactors can convert a wide variety of feedstocks into methyl
esters, which is favorable when restaurant grease that by nature has a variable composition is
used.
The downsides to batch reactors are low conversion, high energy requirements, and long
total reaction time.[2] Batch reactions typically take place with either sodium or potassium
hydroxide as a catalyst for transesterification, which is inefficient and leads to low yields.
However, research shows that adding an agitator or series of agitators increases conversion up to
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99% while decreasing reaction time.[3] Agitator speeds typically range from 200-900 rpm, with
higher speeds promoting greater conversion.
Despite lowering reaction time, the combined time of heating, reacting, cooling, and
preparing for subsequent runs makes the batch reactor time inefficient. Waste cooking oil must
pass through a pretreatment step to lower FFA content in order to decrease the amount of
glycerol formed as a side reaction during transesterification. This side reaction lowers methyl
ester selectivity, and glycerol must be later separated from the methyl esters in order to meet
production standards.
Continuous Reactors:
Continuous reactors may be favored over batch reactors for several reasons. The alcohol
catalysts utilized for batch operations form glycerol soaps as a side product that have to be
separated from the methyl esters in a pretreatment process. This pretreatment requires an acid
such as sulfuric acid that can be corrosive or difficult to dispose of in an environmentally
friendly way. Continuous reactors do not require this pretreatment step since they use solid
catalysts such as ion-exchange resin catalysts, clays, or solid bases such as sodium and potassium
hydroxide on activated carbon. These catalysts do not react with FFAs to form soaps. Clays are
particularly suitable because they are low cost, have low environmental impact, promote high
selectivity, and are reusable.[4] The primary drawback to solid catalysts is deactivation. The
catalysts used can absorb some of the reactants and increasingly render catalytic sites useless.
When this happens, the catalyst must either be regenerated or replaced with fresh catalyst, and
both of these alternatives require time and added expenses.
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Microreactors:
Microreactors that consist of many small, parallel micro-channels have also been used in
biodiesel production. A liquid catalyst such as sodium hydroxide is used to drive the
transesterification that takes place simultaneously in all the channels. The reaction take place as
low as room temperature, which decreases energy requirements. Corrosion issues are avoided by
constructing microreactors out of plastic resins such as polysulfone and polytetrafluoroethylene.
Use of microreactors drastically decreases reaction time in comparison to batch reactions and
other continuous reactors, but the pretreatment step cannot be avoided. High FFA content can
cause plugging in the micro-channels.[microreactor article]
Preliminary Design Decision
Currently, a batch reactor is the most attractive because the reaction rates are high,
catalysts are inexpensive, and any conversion deficiencies can be mitigated with agitation.
Several batch reactors would be required in parallel to simulate a continuous process and
accommodate the feedstock volumes. The team will continue to research other reactor types to
ensure that the best type is selected for our objectives.
5.1.2 Catalyst
Design Criteria
The catalyst selected to promote transesterification must meet certain criteria, and one of
the most important factors is cost. If, from the beginning, biodiesel is less profitable than diesel,
lowering the cost of materials used will help increase profit margins and make the plant a
worthwhile venture. Furthermore, the faster the transesterification proceeds, the more grease can
be processed and sold. The catalyst should minimize undesirable side reactions, and a significant
portion must be recycled in an energy efficient manner to further cut costs.
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Design Alternatives
Catalysts used for transesterification include acids, bases, clays, and enzymes. Bases are
most commonly used largely because they are less expensive than clays and enzymes, and they
promote faster reaction rates than acids.
Homogeneous Bases (key paper info)
Homogeneous bases such as NaOH, KOH, and methoxides (reacting alkali bases with an
alcohol such as methanol) are the most commonly used catalysts because they are inexpensive,
promote high reaction rates, and are not accompanied by high energy requirements. However,
these bases also react with FFAs to produce soaps, which decreases overall methyl ester yields
and create emulsions that make product purification difficult. Alkali catalysts are also known to
form soaps with water.
Heterogeneous Bases
Heterogeneous catalysts such as MgO, CaO, and NaOH on AlCl3 are easily separated
from products. While homogeneous catalysts must either be disposed of or recycled after
separation, a solid catalyst like CaO can be regenerated and reused easily. FFAs still react with
heterogeneous catalysts to form soaps, and catalyst leaching becomes a further issue. Most
heterogeneous bases are rendered ineffective when used at room temperature, so higher energy
costs are necessary to protect the catalysts from degenerating.
Recent studies indicate that strontium oxide (SrO), or SrO doped SiO2, as a catalyst
promotes yields over 90% in approximately 10 minutes and has a FFA tolerance above the
typical 3 wt%. SrO catalysts can tolerate between 3 and 3.5 wt% FFAs. However, SrO is more
expensive than typical alcohol catalysts.
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Past Design Teams
Team Rinnova’s design utilized KOH over NaOH for transesterification because it mixes
well with methanol. Once mixed with methanol, NaOH required a full day to dissolve, whereas
KOH dissolves much faster. Liquid catalysts are ideal for batch reactions because the amount of
catalyst needed is essentially the amount necessary for one batch.
The Diesel Crew used CaO, a solid commonly sold by cement supply companies. One of
their objectives was to design a continuous process, and solid catalysts lend themselves to this
type of system.
Design Decision
The team is leaning towards using NaOH because it is inexpensive, readily available, and
most compatible with a batch reaction system. The cost difference between KOH and NaOH is
marginal since the catalyst is already one of the least costly aspects of the design. The catalyst
choice may be revisited in the future.
5.2 Pre-Treatment Section
5.2.1 Filter
The waste vegetable oil (WVO) contains food debris and particulates that must be
removed to prevent waste build up in the pumps and pipes and to control the quality of the feed
entering the acid treatment. The pre-treatment filter must be able to remove the roughly 3%
solids from the feed.
Leaf Filter:
Vertical Pressure Leaf Filters are applied for liquids with low solid content (roughly 1%
to 7%). The vessel of the leaf filter can be suited with a steam jacket to control the temperature in
the filter for liquids that require higher operating temperatures. Vertical pressure leaf filters can
be used, rather than horizontal filters, in cases where light/fine particles are removed to minimize
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floor space. Vertical Pressure Leaf Filters have applications in the fuel and biofuel industry to
filter crude oil and fatty acids. The fact that these filters have been used in the industry
previously ensures they would be a good choice for the plant. Also, the maximum filter area in a
vertical leaf filter is approximately 100 m2. This should be noted as multiple vertical leaf filters
would be needed in this process to achieve the necessary filtration. The steam jacket capability of
the vertical pressure leaf filter is essential to maintain a low viscosity of grease, meaning if this
filter is chosen the steam jacket will most likely be necessary.
Centrifuge:
Centrifuges are commonly used to separate solids from liquids. It uses centripetal
acceleration to separate a mixture based on density; the denser substance moving farther from the
axis of rotation, while the lesser dense substance is being pushed toward the axis. Large
industrial centrifuges are used to separate waste grease into white, yellow, and brown grease
based on fatty acid concentration. It is also used in the biofuel industry for fuel purification.
Using a centrifuge for the pretreatment would not only separate the solids from the
grease, but also separate the grease into a heterogeneous mixture; yellow and brown grease. The
centrifuge would most likely result in four separate phases: solids, brown grease, yellow grease,
and water. The separation of the liquid phase would complicate the system. The different phases
would have to be treated separately and the system would have to include two processes; a
process to treat the yellow grease and a separate process to treat the brown grease. This would
involve multiple pretreatments stages and reactors.
To simplify the system and reduce capital costs, the team wishes to have a single
homogeneous liquid phase for the grease feed. Therefore, the centrifuge would not be a desirable
filtering method for the system.
25
Preliminary Design:
It has been decided that preliminarily vertical leaf filters will be used to separate out the
solids from the waste grease feed. This comes from the fact that the leaf filters are able to handle
the expected solid content of the feed (3 wt %) as well as its wide use in filtering fatty acid
mixtures. The vertical leaf filter can also be fitted with a steam jacket which is necessary to
maintain high temperature in the filter vessel and minimize grease viscosity. In order to size the
filters needed the following equation was employed.
LA(1-𝜀 )𝜌p = cs(V+𝜀 LA)
In the above equation, L is the cake thickness, epsilon is the porosity of the cake, rho is
the density of the solid particles in the cake, cs is the weight of solids per volume of filtrate, and
V is the volume of filtrate. These are used to solve for A, or the filter area needed in the process.
A complete calculation and the values used for the above properties can be found in Appendix 2.
From this, it was determined that 225 m2 of filter area would be needed for the process. As the
maximum filter area of a vertical leaf filter is 100 m2, it was decided that with equal sized filters
3-75 m2 vertical leaf filters will be used in the process.
5.2.2 Acid Treatment
If a batch or microreactor is chosen to produce biodiesel, an acid treatment must proceed
the transesterification reaction to lower the FFA content in the feed to less than 1%. However,
this is not true if the catalyst used for transesterification is not an alcohol and thus will not form
glycerol soaps in an undesirable side reaction. The design for this pre-treatment reactor will be
covered, but, as stated above, will not be needed in some scenarios.
In the treatment reactor, sulfuric acid is used as an acid catalyst. Methanol, in the
presence of this acid, esterifies the FFAs . This not only increases the overall conversion in the
26
main reactor, but also improves the quality of the biodiesel product by removing impurities. If
the FFA content is above the 1% mark mentioned previously, the quality of the product will not
be sufficient to meet regulations.
It was determined that this acid treatment will take place in an isothermal PFR. This was
selected by analyzing results from an experiment found in the Iraqi Journal of Chemical
Engineering. The isothermal PFR provides higher ester formation than an isothermal CSTR of
the same volume. It is also is more efficient than any reactors run adiabatically. An isothermal
batch system could provide the needed conversion will similar efficiency, however the
drawbacks of a long set up and cleaning time leads to the selection of the PFR.
Knowing the intended flow rates of each component in the plant through the process flow
diagram, a preliminary volume of the pretreatment reactor was able to be calculated. First a rate
law was developed to model the reaction. For the preliminary design, it was assumed that the
reaction follows an elementary rate law. This was modeled as follows;
-rFFA = kCFFACMeOH.
Further modifications were made to this rate law in order to express it in terms of
conversion. The derivation led to the rate law being expressed as,
-rFFA = kC2FFA,0(1-X)(𝜃-X).
Here, theta refers to the ratio of methanol concentration to free fatty acid concentration
entering the reactor. These initial concentrations were found by using molar masses and densities
with initial molar flow rates. From this, it was found that the initial concentration of FFAs is
1.046 mol/L and the initial concentration of methanol is 24.71 mol/L. Through research it was
found that typical k values in these types of reactions averaged about 0.0833 L/(mol*hr).
27
Using the values and equations outlined above, a Levenspiel plot was made which plotted
conversion on the x-axis and the value of FFA molar flow rate divided by the reaction rate on the
y-axis. This plot can be seen below:
Figure 7: Levenspiel plot of the pre-treatment reaction.
Using the process flow diagram it was determined that a conversion of 97% in the pretreatment is needed to keep the FFA content entering the main reactor under 1%. The volume of
the PFR needed is then equal to the area under the curve in Figure 7 from a conversion of 0 to
0.97. This area was calculated by first fitting a polynomial equation to the Levenspiel plot. This
polynomial was then integrated and solved using the above limits to find the necessary volume
of 460 L. The preliminary recommendation is then to use a 460 liter PFR to produce the needed
FFA concentration entering the main reaction.
5.3 Post-Treatment Section
The products leaving the main reactor are primarily methyl esters, excess methanol, and glycerin. The
objective of the post-treatment section is two-fold: the methyl esters must be purified to meet government
specifications, and the excess methanol must be recovered and fed back to the main reactors.
28
5.3.1 Glycerin Separation
The EPA specifies that up to 0.24 wt% glycerin can be present in biodiesel product. Even with a rigorous
pretreatment process to mitigate soap generation, glycerin in the reactor effluent must be separated from
the biodiesel, and one way to accomplish this is adding a large settling tank downstream of the reactor.
The glycerin will enter the tank with the liquid products, and settle to the bottom. A settling tank would
be simple and effective because other components in the effluent stream are much less dense, as shown in
Table 2, and the product flowing out of the tank would have only trace amounts of glycerin.
Table 2: Relative densities of effluent stream components
Effluent Stream
Density (g/L)
Glycerin
1.26
Methanol
0.792
Methyl Esters
<1
Triglycerides (unreacted)
<1
The team was advised to avoid a solid-liquid separation. Solids are usually avoided in industry as
they are harder to work with than liquids. The glycerin is a liquid when leaving the reactors, but has a
melting point near room temperature (64 F). As this is still a lower temperature, the team finds it wise to
add some form of heat exchange to ensure glycerin remains a liquid. The most obvious alternative is to
heat the stream entering the settling tank. This could take the form of a heat exchanger immediately after
the reactors, or reactors operating at elevated temperatures. Keeping this heating precaution in mind, a
large tank is the most likely settling device used to remove glycerin.
5.3.2 Methanol Recovery
Design Criteria
The EPA specification for methanol is less than 0.2 vol% in the finished biodiesel product. The
team is currently researching different methods of separating methanol and methyl esters, which include
29
distillation, centrifugation, and pervaporation. Discussion of centrifuge use is described in the
pretreatment section of this report and therefore will not be described in detail here.
Design Alternatives
Distillation
Methanol and water are commonly separated by distillation. The Diesel Crew utilized Team
Rinnova’s vacuum distillation design, which requires an operating pressure below 1 atm, and found it
effective for their purposes. There is over a 60 F difference between the boiling points of water and
methanol, which makes distillation an attractive and effective choice. However, distillation is the
generally the most energy intensive separation technique, and the added energy costs of operating a
vacuum tower in a plant may make a different separation technique more feasible.
Pervaporation
Pervaporation is a technology that is commonly used to separate water from organic solvents.
The process takes advantage of differences in polarity and molecular size to pass a smaller and more polar
molecule through a selective membrane that is aided by a vacuum. The membrane used is inert, and the
only energy requirements are heating the incoming stream (the process is more effective at high
temperature) and running the vacuum. Since methanol and water are similar in their polarity, the
membrane selection would be particularly important. One downside to pervaporation is that it is usually
precedes a distillation column and may not be effective as the only method of separation. If distillation or
a centrifuge will be required following pervaporation, it may be more worthwhile to use the budget for
one very effective column or centrifuge.
Design Status
The team has not determined which alternatives to incorporate in the design, but will continue
exploring alternatives and quantifying the pertinent differences between each option.
30
6. Safety Considerations
6.1 Chemicals
The main chemicals used in this process that present safety concerns are the acid catalyst, the
base catalyst and the alcohol. For this preliminary design and safety evaluation sulfuric acid, sodium
hydroxide and methanol will be used. The Material Safety Data Sheets for these chemicals can be found
in Appendix 4.
Sulfuric Acid is a colorless, odorless, highly-corrosive material. The main acute exposure hazard
is severe burns to skin and eyes. It is more harmful than other strong acids due to the dehydrating nature
of the chemical, which releases extra heat, causing secondary burns. It will cause temporary or permanent
blindness if contacted with eyes in either liquid or vapor form. Long term exposure also causes lung
damage, vitamin deficiency and potentially cancer.
Sodium Hydroxide is a caustic base that is white solid, typically available in flakes or pellets. It is
a highly corrosive alkali that will decompose living tissue on contact. It also causes secondary burns, as
the decomposition reaction is highly exothermic. Aqueous sodium hydroxide is more dangerous than
solid, although solid NaOH will also exhibit some corrosive behavior if there is any water present
(including sweat or humid air). There are no known long-term exposure effects of NaOH; all of the health
effects are acute effects due to corrosivity.
Methanol is a colorless, flammable liquid with a distinct odor. If ingested, methanol will be
metabolized to formic acid which damages the central nervous system and causes blindness, coma or
death. The adverse health effects associated with methanol all occur internally. While contact with skin
will not cause external damage, it may provide a route for the chemical to enter one’s central nervous
system. Methanol is highly flammable and easily ignites.
6.2 Operating
Sulfuric acid must be stored in a vessel made of a non-reactive reactive material, such as glass.
Great care should be taken that the acid does not contact the operator’s skin. Proper personal protective
31
equipment (PPE) for handling sulfuric acid includes: safety goggles, face shield, boots, gloves and aprons
made from a suitable material (see MSDS for more information). Sulfuric acid will be pumped directly
from the storage vessel to the pre-treatment vessel, limiting the amount of operator contact needed. If
sulfuric acid does contact the skin though, any contaminated clothing must be removed and the affected
person must wash the acid off under a safety shower for at least 15 minutes. Then seek medical attention
immediately. Also, when diluting the sulfuric acid the acid must be added to the water instead of water
added to the acid. This way, the high heat capacity of water will absorb the heat released as the two
chemicals mix.
Sodium hydroxide must also be stored in a non-reactive vessel, preferably the container in which
it was delivered. Keep sealed tightly in a cool, dry, well-ventilated area. When handling sodium
hydroxide, the same PPE should be worn as for sulfuric acid. If an operator needs to create the sodium
hydroxide solution, a respirator should also be worn. The same procedure as for the sulfuric acid should
also be followed if sodium hydroxide contacts skin.
Methanol must be stored in a cool, dry, well-ventilated area away from any potential sparks. If
the methanol does ignite, water will not extinguish the fire. A fire extinguisher will be necessary.
Methanol will be pumped directly from a storage container to the various vessels, so operator contact with
methanol is limited. If an operator must come into contact with the methanol, the same PPE as for sulfuric
acid must be worn. If the area is not well ventilated, a respirator must also be worn. If methanol is
ingested, drink two glasses of water and seek medical attention immediately. If methanol contacts any
part of the body, follow the same procedure as for sulfuric acid.
All three chemicals are considered hazardous waste and need to be properly disposed of
according to OSHA standards.
32
7. Business Plan
7.1 Market Study
Despite being a relatively new energy source with oldest plants dating back to the mid2000s, biodiesel is a growing market in the United States. According to the US Energy
Information Administration, approximately 100 million gallons of biodiesel per month are
produced in 96 US plants that have a combined capacity of 2 billion barrels every year. Biofuels
provide nearly 6% of the energy supplied annually, and as of 2009 the United States produces
the second largest volume of biofuels. Figure 8 depicts the amount of biofuel produced monthly.
It can be see that the volume steadily increases overall as more biodiesel plants are built every
year.
Figure 8: Million barrels of biodiesel produced in the United States from January 2012 to May 2014
Producing biodiesel is profitable due to a $1 per barrel tax credit for blenders. Without
this incentive, expensive feed and raw materials prevent biodiesel from competing with
33
conventional diesel prices. Some states provide further benefits to biodiesel producers, as
detailed in a following report section.
7.1.1 Customer
The final product will be marketed and sold to blenders who have the capacity to blend
large volumes of purified product and who will ultimately supply the blended fuel to consumers
with diesel engines. These customers would potentially be community leaders, retail gas station
owners, who value sustainability and desire to promote alternative energy sources. In keeping
with the project objective of introducing a competitive product into the market, the target
customer is one who would benefit from cheaper diesel.
The plant will be designed to operate for 20 years. At the end of the period the team will
decide, depending on the market, to either sell the plant or specific pieces of equipment at
salvage value for further profits or refurbish the equipment to continue biodiesel production for
an extended period. In the scenario of retiring the plant, future customers would include those
who have interest in producing biodiesel themselves or interest in a similar process.
7.1.2 Competition
The competition in the biodiesel market comes from inside the biodiesel industry and the
alternate fuel industries.
The competition from the biodiesel industry comes from similar biodiesel production plants in the
area. For the team, this competition pertains to the biodiesel production plants in Florida, who will
compete for the business of the diesel blenders. According to the plants listing section of biodiesel.org,
there are currently five companies in Florida that produce biodiesel. These business will need to sell their
product to blenders who will then blend the biodiesel with diesel made from crude oil. The blended
product is what will be sold to the public as biodiesel at the pump.
34
There is also competition from the industries creating fuel other than biodiesel. The most
comparative competition comes from the diesel industry because, biodiesel is compatible with diesel
engines. If there is a large discrepancy between the price of biodiesel and diesel, the environmental
benefits of biodiesel will not be enough to overcome the financial burden. This would result in the public
being unwilling to buy biodiesel versus regular diesel at the pump and consequently blenders will lose
interest in purchasing biodiesel from the production businesses. This is unlikely because crude oil is a
limited resource and trends show the price of diesel only increasing in the future. Therefore, the cost
difference of biodiesel and diesel will continue to decrease until biodiesel becomes more cost effective
than diesel.
A more likely source of competition comes from the alternative fuel industry. There is a large
effort to find alternative fuels such as electricity, wind, water, etc. Today vehicles either run on
combustion engines, electric engines, or a combination of both. The biodiesel industry depends on the
continual use of combustion engines. However, as electric motors become more efficient, combustion
engines might eventually become obsolete. With so much research invested into alternative fuels, it is
difficult to tell how the market will change in the future which is a main reason why the expected plant
life is only 20 years.
7.2 Tax Information
Under federal law, a $1 per-gallon tax credit will be applied for the production of
biodiesel that complies with fuel standards and Clean Air Act requirements. This credit will be
increased to $1.10 for the first 15 million gallons produced (approximately BLANK years of
production). It is estimated that the production facility will receive tax credit for 100% of taxes
with the 75% state rebate and $1.10/gallon rebate from the federal government. This credit is
valid through 2017 and is expected to be renewed further.
35
A major factor in determining the location of the plant was the tax credits available in
certain states beyond the standard $1-per-barrel credit. Overall, Florida is the most helpful for
renewable fuel plant start-ups and provides the proposed plant with the greatest chance of being
competitive with diesel providers.
“An income tax credit is available for 75% of all capital, operation, maintenance, and
research and development costs incurred in connection with an investment in the production,
storage, and distribution of biodiesel (B10-B100), ethanol (E10-E100), or other renewable fuel in
the state, up to $1 million annually per taxpayer and $10 million annually for all taxpayers
combined.”
This tax credit makes biodiesel production possible, since the process is not efficient
enough to make a profit on its own. This credit is good through December 31, 2018. The credit
may only be applied toward taxes; no rebates will be issued.
7.3 Costs
7.3.1 Capital Costs
An efficient way to estimate the capital cost of the plant this early into the design process
was put forward by Don Hofstrand of Iowa State University. The cost, plus working capital, is
estimated by $1.57 of the nameplate capacity, or the gallons per year output of the plant. From
the process flow diagram, it was found that an estimated 9.5 million gallons per year of biodiesel
will be produced. After multiplying by the above cost factor, it can be preliminarily estimated
that the total upfront cost of building the plant will be $14.8 million.
7.3.2 Operating Costs
In a similar fashion to estimating capital costs, a rough estimate for operating costs can be
made. Fixed costs can be estimated as $0.25 of the nameplate capacity and variable costs can be
estimated as $0.26 of the nameplate capacity. Using the yearly production of 9.5 gallons per year
36
as detailed previously it was calculated that the overall operating costs are preliminarily
estimated at $4.8 million per year.
7.4 Profitability
In order to determine the profitability of the proposed plant, a selling price for the
biodiesel product to produce a rate of return of 10% was calculated. At a 10% return rate, the
project becomes economically feasible.
The first step in doing this was to calculate the costs of the needed chemical inputs. The
costs for each of the process materials used can be found in the table below. It was determined,
preliminarily, that sodium hydroxide will be used instead of potassium hydroxide due to ease of
availability. A very small percentage of hydroxide is used compared to the feed stock, so the
price difference becomes insignificant.
Table 3: Current market value for process materials
Material
$/lb
Methanol
0.28
Sodium Hydroxide
0.23
Potassium Hydroxide
0.185
Sulfuric Acid (95%)
0.18
In addition to the above prices, it was found that currently the restaurant grease needed can be
purchased for approximately $0.25 per gallon. Using these prices along with the flow rates in the PFD,
the following input costs were calculated.
37
Table 4: Cost of input materials per year
Input Costs ($/yr)
waste grease
$
23,595,000.00
MeOH
$
2,490,850.25
H2SO4
$
94,285.71
NaOH
$
90,447.50
The totals costs per year then, including operating costs calculated previously, are $31.1
million. The total revenue of the plant comes from the sale of biodiesel and the side product
glycerin. The glycerin can be sold for $0.10 per pound, or a total of $0.74 million. The revenue
of the biodiesel is not known at this point until the cash flow diagram is created. This process
will described next and allows for a biodiesel selling price to be calculated.
The cash flow diagram was created assuming a construction time of one year. For this
reason the entire capital cost was placed in year -1 of the diagram. As stated above a 20 year life
span was assumed as this is a typical plant life. So, the salvage price of the plant, 10% of the
capital costs, and the working capital was added to year 20 of the cash flow diagram. Using this
knowledge equations were used to bring all costs back to present value. For the plant
construction cost using the necessary 10% return, the equivalent cost was found with,
$14.8E6(1+0.10)1.
Similarly the salvage and working capital were brought to present value using the 10%
rate of return and the equation,
$2.8E6(1+0.10)-20.
38
The yearly profit was then solved for using the equation,
Yearly Profit*((1+0.10)20-1)/(0.10(1+0.10)20) = $2.8E6(1+0.10)-20 - $14.8E6(1+0.10)1.
Using the above equation it was found that the plant would need a yearly profit of $1.9
million in order to achieve the needed rate of return. This value was used with the prices of the
other materials in the system detailed above to find a needed yearly biodiesel revenue of $32.2
million. Knowing the yearly output of biodiesel (9.5 million gallons), this can be converted to a
selling price per gallon. In order for the plant to be economically feasible, then, the biodiesel will
need to be sold for $3.41 per gallon. According to research this falls well within the reasonable
selling price for biodiesel plants, meaning that the proposed process will be profitable. The
complete cash flow diagram that had been described previously can be seen below.
Figure 9: Cash flow diagram for the plant lifespan
39
8. Conclusion
In conclusion, it is feasible to open a 9.5 million gallon per year biodiesel production plant. While
this plant alone will not solve the energy crisis, it can be used to demonstrate profitability for others
looking to open biodiesel production plants. With preliminary estimates, the plant will produce a 10% rate
of return over a 20 year lifespan. Many specific decisions still need to be made, such as the reactor type
and catalyst, but this report clearly outlines the main design criteria and options. Decision matrices will
need to be formed to determine the best variable choices for this plant. These decisions should be made to
further increase the overall rate of return while not infringing on any of the selected design norms. As
these specific decisions are made, the project will become more technical and design focused.
40
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43
Appendix
1. Overall Process Mass Balance
44
2. Filter Calculations
LA(1 - ε)ρp = cs (V + εLA)
Cake thickness (L): estimated to 1cm
Porosity (ε): estimated at 0.5
Volume of filtrate (V): used PFD and molar flows/density to find a volumetric flow of 145 m^3/day
Weight of solids per volume of filtrate (cs): weight of solids = (3 wt %)(130,000 kg/day)
cs=26.85 kg/m^3
Density of Solid Particles in Cake: used an average cake density of 3500 kg/m^3
Used in above equation to find Area of Filtration Needed per Day: 225 m^2
3. Competing Biodiesel Plants in Florida
4. Material Safety Data Sheets (MSDS)
See attached
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