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BIODIESEL PLANT DESIGN FOR RURAL APPLICATION
Article · September 2013
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ZENITH International Journal of Multidisciplinary Research _______________ISSN 2231-5780
Vol.3 (9), September (2013)
Online available at zenithresearch.org.in
BIODIESEL PLANT DESIGN FOR RURAL APPLICATION
O P CHATURVEDI*; SANJAY MANDE*;
P RAJAN**; K KUNDU**
*TERI UNIVERSITY, NEW DELHI;
**MERADO, LUDHIANA
ABSTRACT
The biodiesel production process in reality is much more than just a chemical reaction. The
practical aspects of how to convert a locally available bio-oil resource into a modern biodiesel
fuel in a rural-scale biodiesel plant is of utmost importance for enhancing its techno-socioeconomic viability. It has been proven, under Indian conditions that the industrial-scale biodiesel
plant application had failed due to variety of feedstock problems and its management. This paper
gives details of work carried out in developing assembly of a prototype semi-continuous batch
biodiesel production plant that is not only portable but also suitable to support rural population
that wish to become self manufacturer of biodiesel. The batch biodiesel plant has a daily
production capacity of approximately 100 liters when working on two shifts of 10 hour each. It
can be set up for virgin vegetable oil (edible or non-edible), waste cooking oil as well as high
free fatty acid (FFA) oil. It can support esterification reaction as well as transesterification
process that uses a non-pressurized reaction vessel and elevated reaction temperatures. Another
key advantage of the proposed plant design is that it has methanol recovery unit, without adding
much extra cost. With the initial total capital investment of about ` 2 lacs the proposed 100LPD
biodiesel plant (annual production capacity of 30 tons of biodiesel) can earn a profit to the tune
of ` 70 thousand giving about 35% Return on Investment (ROI) and break even in merely less
than 3 years.
KEYWORDS: Biodiesel, biodiesel plant, transesterification, esterification
______________________________________________________________________________
1.0 INTRODUCTION
Biodiesel, an alternative to fossil petroleum diesel fuel, is made from renewable biological
sources such as vegetable oils and animal fats. It is biodegradable, nontoxic and has low
emission profiles making it environmentally benign (Michael et al, 1996). Under Indian
conditions to avoid conflict with scarcity of cultiviable land for growing demand of food crops,
an emphasis by the Government has always been to explore the possibility of using non-edible
oils for biodiesel production (Planning Commission Report, 2003). There are number of ways to
make the vegetable oil equivalent to diesel fuel. These methods include; transesterification,
pyrolysis, micro-emulsion, blending and thermal depolymerization (Srivastava and Prasad,
2000). One of the most common methods used to reduce oil viscosity in the biodiesel industry is
called transesterification. The major objective during these interventions then was to develop a
simplified method for extracting glycerol during soap production which was much needed for
war-time explosives production (Gerpen, 2005).
46
ZENITH International Journal of Multidisciplinary Research _______________ISSN 2231-5780
Vol.3 (9), September (2013)
Online available at zenithresearch.org.in
There is an urgent need to develop and demonstrate technologies to potential plant operators and
fuel consumers, and to develop new technologies for reducing the input costs to enhance
economic viability of biodiesel production. Hence, an effort was made to design an assembly of
a 100 LPD semi-continuous biodiesel pilot plant suitable for rural application. The work was
carried out at the Mechanical Engineering Research and Development Organization (MERADO)
Ludhiana (India) an extension centre of Central Mechanical Engineering Research Institute,
Durgapur (India). The AUTODESK INVENTOR 10.0 software was used for design.
2.0 Material and Methods
2.1 Choice of reaction
Transesterification is one of the reactions that are used to prepare esters. Transesterification of
vegetable oil is the process of reacting triglycerides with methanol in order to obtain fatty acid
methyl esters and glycerol and the process is important for preparation of biodiesel.
2.2 Process flow diagram
The biodiesel production plant is separated into five sections as follows. Section A: Reactant
Preparation, Section B: Pre-treatment section, Section C: Transesterification Reaction, Section
D: Purification and Solvent Recovery and Section D: Product Storage. The corresponding
Process Flow Diagrams (PFD’s) are presented in Figure 3. The section A is concerned with the
storage and distribution of chemical required for the other sections of the plant and consists of
four storage tanks and two mixing vessel. Tank A1 and A2 are used for vegetable oil and alcohol
storage purpose and tank A4 and A5 are for storage of sulfuric acid and KOH catalyst. The two
mixing vessel AM1 and AM2 are used to prepare the mixture of alcohol and catalyst.
The pre-treatment section (B) is the part of the process used for pre -treatment of the vegetable
oil, if required. Generally for transesterification to be successful, the free fatty acid content
should be less than 1.0%. The section B is consisting with reactor (BR1), one separating vessel
(BS1), waste (during esterification) storage tank (BW1) and mixing vessel AM1 used for
preparation of sulfuric and alcohol mixture. The section C is the main unit operation in the plant
where the treated vegetable oil from the section B (if FFA>1.0%, otherwise from tank A1) along
with methanol and catalyst react to form the main product, biodiesel, and by-product glycerol, by
means of transesterification process. This section has the main reaction vessel (CR1) and two
separation tanks CS1 and CS2. The treated vegetable oil from the tank BS1 was pumped into the
reactor and the mixture of alcohol and catalyst from tank AM2.
Section D is the part of the biodiesel plant where the purification of biodiesel was carried out.
The
transestrified
biodiesel
from
the
vessels
CS1
and
CS2
contain
biodiesel/methanol/soap/catalyst mixture. Therefore the water washing is an essential part in
biodiesel production unit. Before the water washing, it is also essential to recover the excess
methanol from the biodiesel phase. Section E in the storage system network is to store
impurities, wastewater
47
ZENITH International Journal of Multidisciplinary Research _______________ISSN 2231-5780
Vol.3 (9), September (2013)
Online available at zenithresearch.org.in
Figure 3 Process flow diagram for biodiesel production plant
and the purified biodiesel product. This section consists of four storage tanks, E1 and E2. The
purified biodiesel from the reactor BR1 was pumped into biodiesel storage tank E2 and glycerol
in tank E1 and the recovered methanol into tank A3. Tank BW1 is for the storage of waste from
pre-treatment step.
2.3 Floor plan
The biodiesel production plant requires about 16 square meter floor area with dimensions length,
height and width of 4x3x4 meters, respectively. The production unit comprises the equipment
required for the five stages of the process, pump and pipe work for easiness of fluid transfer from
stage to stage. The equipment is arranged such that the reactant and product tanks are located in
the either side of biodiesel plant for ease of filling/emptying.
3.0 RESULTS AND DISCUSSION
3.1 Reactors and mixture
In order to design the reactor and mixture for this process, the volumes were first determined
using the mass balance. The volume of all the components entering the reactor were added
together to give the total liquid volume of the reactor (equivalent of one batch). For preventing
the chances of any overflow, reactors were designed to 75% fill capacity; therefore, the reactor
sizes were 1.43 times greater than the liquid volume. The diameters and heights of various
reactors can be determined using following equation:
D  4V / R
Where,
D = Reactor diameter (m)
V = Reactor volume (m3)
R = Reactor H/D factor
The reactor height H is given by:
H  D R
48
ZENITH International Journal of Multidisciplinary Research _______________ISSN 2231-5780
Vol.3 (9), September (2013)
Online available at zenithresearch.org.in
Since the pre-treatment reactors (BR1) contain corrosive sulfuric acid, stainless steel was chosen
as the material of construction. Stainless was also chosen for the transesterification reactor CR1,
because of the corrosive caustic being used as a catalyst.
3.2 Separating vessel
The volume of the separating vessel was determined on the basis of mass balance and batch
requirement. As the material handled by separating vessel is the mixture of biodiesel, soap,
methanol, glycerol and catalyst, hence, stainless steel material was chosen for its construction.
Separating vessel is equipped with special type layer indicator device to see the biodiesel and
glycerol layer.
3.3 Frame
The frame for the biodiesel plant was designed to fix the reactors, separating vessel, mixing tank,
pumps and transmission system on it. The total frame height was 2.12 meters. Both of mixing
vessel were placed such that, there was gravitational flow methoxide into reactor. The frame was
built with 60x60x60 mm square hollow pipe of carbon steel material.
4.0 MASS BALANCE
Initially the reactor BR1 was charged with 50.4 kg/batch and 11.09 kg/batch of oil and methanol,
respectively. After effective pre-treatment the yield of treated oil was 48.99 kg/batch. In the
transesterification stage, the reactor CR1 was charged with 24.5, 5.55 and 0.38 kg/batch treated
oil, methanol and KOH, respectively. After, this stage of treatment, a product yield of 22.03
kg/batch biodiesel is produced and an equivalent total formation of 5.62 kg/batch glycerol byproduct is realized. The detailed mass flow rate per batch in different reactors are presented in
Table 1.
5.0 ECONOMICS ASSESSMENT
An estimate of the implementation cost was obtained by calculating the sum of all materials and
labour expenses. The total material cost was found to be around ` ninety thousand.
Manufacturing/machining cost was assumed conservatively to be 35% of the material cost and
piping cost to be around 10% of the capital cost as this is a very small plant and pipe length
would be minimal as compared to industrial sized plant. The instrumentation cost was estimated
to be approximately 10% of the material cost as there was very simple requirement of
temperature indicator and its controller. Hence, total equipment capital cost works out to be `
1.33 lacs. The installation cost of the biodiesel plant was assumed to be 25% of the equipment
capital cost. The total capital investment (TCI) was estimated ` 1.91 lacs, which is the start-up
cost of the biodiesel production plant. This amount includes all proper over-run cost, such as the
5% contingency fund and a 10% working capital.
49
ZENITH International Journal of Multidisciplinary Research _______________ISSN 2231-5780
Vol.3 (9), September (2013)
Online available at zenithresearch.org.in
Table 1 : Mass balance of biodiesel plant
Reaction
Component
Mass (Kg)
Volume (l)
Oil
50.40
54.78
1st
reaction Methanol
11.09
14.02
(Esterification)
Sulfuric Acid
1.01
0.55
Total in reactor BR1
62.50
69.35
Oil / Biodiesel
47.88
54.41
1st Separation Top
Methanol in top layer
1.11
1.40
layer
Total in top Layer
48.99
55.81
Methanol in bottom layer
4.44
5.61
Bottom layer
Water / Glycerol / Acid
9.07
10.89
Total in bottom layer
13.51
16.49
Top layer mixture (from 1st
24.50
27.91
separation)
2nd
reaction
Methanol
5.55
7.01
(Transesterification)
KOH
0.38
0.38
Total in reactor CR1
30.42
34.92
Biodiesel
22.03
25.03
2nd Separation Top
Methanol in top layer
0.56
0.70
layer
Top Layer
22.58
25.73
Methanol in bottom layer
2.22
2.81
Bottom layer
Water / Glycerol / Base
5.62
5.62
Bottom Layer
7.84
8.43
The raw materials used in the production stage include: methanol, sulfuric acid and potassium
hydroxide, with methanol being the primary reactant. Although the purification stage does
extract and return a major portion of used methanol, some methanol is lost. The average
transesterification reaction consuming rate of methanol was found to be 22% by weight of
feedstock, which equates to 22.2 kg per batch. With additional methanol lost in the glycerol and
waste streams, an additional 11% by weight is adjusted. This equates 44.38 kg of methanol per
batch or 155.54 kg of methanol per week. 14.14 kg of sulfuric acid and 10.16 kg of KOH are
required per week, therefore, the average weekly cost of raw materials used was approximately `
3000 only. It is assumed to that, the oil cost is ` 27 per kg.
Daily electricity consumption was estimated to be 82.5 kWh which results in a weekly power
consumption of 577.5 kWh. At the current electricity rate of ` 3/kWh, the total cost of power
works out to about ` 1,700 per week. The water cost is assumed to ` 0.5 per liters and weekly
requirement of water is 700 liters, hence, the total utilities cost is ` 2.1 thousand per week. Any
additional heating of the working environment that might be required in cold weather has not
been taken into account due to prevailing hot climate in India.
The labour cost to process a single batch of feedstock oil is not representative of economic
operation because of the large amount of ‘idle time’. It is therefore sensible to consider the
labour cost on per day basis. Also the assumption is made that cold weather difficulties do not
apply. Normally there are two shift operation of 10 hrs is required to run the biodiesel plant.
Assuming the labour cost of ` 200 per day and there is requirement of two labour per day. Hence,
the total cost for weekly operation works out to is ` 2800.
50
ZENITH International Journal of Multidisciplinary Research _______________ISSN 2231-5780
Vol.3 (9), September (2013)
Online available at zenithresearch.org.in
The production rate of biodiesel is 700 liters per week, and according to the current diesel price
of ` 39 per liter, weekly revenue of ` 27300 could be realized. This provides the net profit of
` 1624 per week and is estimated to be a profit of ` 2.32 per liter of biodiesel produced without
including the revenue from the selling of by-product (glycerol). In the whole biodiesel
production cost calculation, the revenue from the glycerol sell is taken to be negligible. With the
process consuming just over one kg of methanol for every 4.5 liters of biodiesel produced, the
cost of methanol per liter of biodiesel is 6.67 paise. With the production rate of 30 tons of
biodiesel annually, a profit of ` 70 thousand each year is realized. By considering the initial Total
Capital Investment of 1.91 lacs, this equates to a Return on Investment (ROI) of 35%, and the
biodiesel production plant will break even at approximately 2.74 years.
6.0 ENVIRONMENTAL ASSESSMENT
The biodiesel production process creates two waste streams, viz. glycerol and wastewater
(containing large quantities of methanol, soap, potassium sulphate and trace amount of potassium
hydroxide). The compositions of these waste streams were examined at laboratory level with one
liters per batch biodiesel production unit and compared to environmental regulations to
determine the appropriate actions required for safe disposal. The composition of the wastewater
is summarized in Table 2.
Table 2: Waste water composition
Component
Water
Methanol
Potassium hydroxide
Potassium Sulfate
Soap
Total
Mass (kg)
547.61
102.69
1.4
21
27.3
700
Mass Fraction
0.7823
0.1467
0.002
0.03
0.039
1
In order to discharge the wastewater, the sulphate, soap and methanol concentration must be
reduced, along with pH. To reduce sulphate concentrations, it may be treated by either
precipitating with barium ions (at low pH), or through anaerobic digestion. The pH can be
reduced through the addition of an acid, such as HCl. Glycerol is produced as a by-product in the
main transesterification reactions. Approximately 220 kg of glycerol is produced in one week,
which will contain amounts of biodiesel, un-reacted methanol, KOH and soap. Due, to
complexity in the purification of glycerol, it is decided that the glycerol by-product will not be
purified in this rural facility, instead, the glycerol will be sent to specialty waste facility for
proper purification.
7.0 CONCLUSION
The designed biodiesel plant is capable to handle both esterification reactions as well as
transesterification process in a non-pressurized reaction vessel, thus can be handled by a semiskilled labour in remote areas. The biodiesel plant has a production capacity of approximately 30
tons per annum (100 LPD) when working in two shift of 10 hour working. It is set up for virgin
vegetable oil (edible or non-edible), waste cooking oil as well as high free fatty acid (FFA) oil.
The key advantage of this plant design is that it has a methanol recovery unit, without adding
51
ZENITH International Journal of Multidisciplinary Research _______________ISSN 2231-5780
Vol.3 (9), September (2013)
Online available at zenithresearch.org.in
much extra cost, hence lot of saving on working capital from the use of recovered methanol
resulting in reduced biodiesel production cost. With the production rate of 30 tons of biodiesel
annually, a profit of ` 70 thousand each year can be realized with pay back period of
approximately 2.74 years.
REFERENCES
Gerpen, J.V., 2005. Biodiesel processing and production. Fuel processing Technology, vol. 86,
1097-1107.
Michael, S. G. and Robert, L.M., 1998. Combustion of fat and vegetable oil derived fuels in
diesel engines. Prog. Energy combust. Sci., Vol,24, pp125-164.
Planning Commission Report, 2003. National mission on biofuels. Published by Ministry of
planning commission, Govt of India.
Srivastava, A, Prasad R. 2000. Triglycerides-based diesel fuel. Renewable and Sustainable
Energy Reviews. Vol 4, 111-133.
http://www.dfwbiodiesel.com/technology.html (access on 15/07/2007)
52
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