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Production of Biodiesel from Waste Vegetable Oil

Bachelorarbeit 2010 125 Seiten

Ingenieurwissenschaften - Chemieingenieurwesen

Leseprobe

Table of Contents

1 INTRODUCTION
1.1 Problem Statement
1.2 Scope and Limitation of the Study
1.3 Definition of Terms
1.3.1 Alcohol
1.3.2 Aromaticity
1.3.3 Biodiesel
1.3.4 Cetane number
1.3.5 Diesel or diesel fuel
1.3.6 Distillation
1.3.7 Esters
1.3.8 Flash point
1.3.9 Glycerol
1.3.10 Methanol
1.3.11 Transesterification
1.3.12 Vegetable fats and oils
1.3.13 Viscosity
1.4 Densities of different compounds
1.5 Specific heats of different compounds

2 LITERATURE REVIEW
2.1 Introduction
2.2 Historical Background

3 PROCESS SELECTION

4 PROCESS DESCRIPTION
4.1 Raw materials Used in Bio diesel Production
4.1.1 Vegetable oils, animal fats, and recycled greases
4.1.2 Alcohol
4.1.3 Catalyst Selection
4.1.4 Neutralizers
4.2 Production Process
4.2.1 Mixing of alcohol and catalyst
4.2.2 Continuous Process Systems
4.2.3 Separation
4.2.4 Alcohol Removal
4.2.5 Glycerin Neutralization
4.2.6 Methyl Ester Wash
4.2.7 Product Quality
4.3 Operating Parameters Table

5 MATERIAL AND ENERGY BALANCE
5.1 Material Balance
5.1.1 Mixer
5.1.2 Reactor 1
5.1.3 Centrifuge 1
5.1.4 Reactor 2
5.1.5 Centrifuge 2
5.1.6 Washing Tank
5.1.7 Centrifuge 3
5.1.8 Distillation Column
5.2 Energy Balance
5.2.1 Mixer
5.2.2 Centrifuge 1
5.2.3 Centrifuge 2
5.2.4 Washing Unit
5.2.5 Centrifuge 3
5.2.6 Distillation Column

6 EQUIPMENT SELECTION AND DESIGNING
6.1 Equipment Selection
6.1.1 Reactor
6.1.2 Pumps :
6.1.3 Centrifuges
6.1.4 Distillation Column
6.1.5 Material of Construction
6.2 Equipment Design
6.2.1 Mixer design
6.2.2 Heat Exchanger
6.2.3 Reactor Design (CSTR)
6.2.4 Gravity Settling Tank
6.2.5 Distillation Column (Biodiesel Purification)
6.2.6 Pump Designing

7 PROCESS INSTRUMENTATION AND CONTROL
7.1 Objective of Instrumentation and Control System
7.2 Components of the Control System
7.2.1 Process
7.2.2 Measurement Mean
7.2.3 Process Variables
7.2.4 Temperature Measurement
7.2.5 Pressure Measurement Control
7.2.6 Flow Measurement and Control
7.3 Instrumentation & Control on Reactor
7.4 Components of Feedback Control Loop
7.5 Auto / Manual Switch
7.6 Process Requirements
7.7 Justification of Proposed System
7.7.1 Thermocouple
7.7.2 Resistance Thermometer
7.7.3 Bimetallic Strip Thermometer
7.7.4 Radiation Pyrometry
7.8 Controller & Pneumatic Control Valve
7.9 P & I Diagram of CSTR

8 COST ESTIMATION
8.1 Purchase Cost of Equipment (PCE)
8.2 Total Physical Plant Cost (PPC)
8.3 Fixed capital
8.4 Working Capital
8.5 Annual operating cost
8.6 Variable cost
8.7 Utilities
8.8 Fixed Cost
8.9 Direct Production Cost

9 SUMMARY

10 REFERENCES

11 APPENDIX
11.1 Appendix A Physical Properties Data
11.2 Appendix B Properties Charts
11.3 Appendix C Sample Calculations for Equipment Design

LIST OF TABLES

Table 1 Densities of different compounds

Table 2 Specific heats of different compounds

Table 3 Operating Parameters for Biodiesel Production

Table 4 Measuring instruments

1 Introduction

Biodiesel is one of the available alternative fuels in the market. It is derived from biomass, which is one of the sources of renewable energy. Waste Vegetable oil is one of the sources of biodiesel and of all the other sources, it would be best in tropical countries.

The blending of Biodiesel in diesel fuel became mandatory when the Biofuels Act of 2006 (also known as Republic Act 9367) was signed into law by President Gloria Macapagal-Arroyo on January 2007. The said act was initiated by Senator Mirriam Defensor-Santiago, who also authored and sponsored the Biofuels Law. The said law requires bioethanol content of all gasoline sold in the country to be increased to at least ten percent (10%) by the fourth year of the law’s effectivity. On the other hand, diesel fuels sold in the country will be required to have at least one percent (1%) blend of biofuel upon the effectivity of the law, which will be later increased up to two percent (2%) after the second year.

1.1 Problem Statement

The study of BioDiesel fuel is very timely because of arising problems such as the rising cost of fuel in the market, global warming phenomenon, and health problems such as respiratory diseases caused by the harmful byproducts of burning petroleum-based fuels. Another problem concerning the use of diesel is the deteriorating effects of the increased amount of Greenhouse Gases in the atmosphere. This is due to the high emission of carbon dioxide coming from incomplete combustion of diesel fuel in vehicles. Last of all, the emission of pollutants such as nitrogen oxide caused also by incomplete combustion of diesel fuel is one of the leading contributors of smog and can trigger serious respiratory problems.

1.2 Scope and Limitation of the Study

This study will use data and will generate a design of a process with a particular capacity and using a flow sheet of this process from an authentic source.. No new experiments have been conducted to prove any theory or hypothesis regarding the said topic.

1.3 Definition of Terms

1.3.1 Alcohol

Alcohol is any organic compound in which a hydroxyl group (-OH) is bound to a carbon atom of an alkyl or substituted alkyl group.

1.3.2 Aromaticity

Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. It can also be considered a manifestation of cyclic delocalization and of resonance.

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Figure 1 Molecular Structure of Aromatics

1.3.3 Biodiesel

Biodiesel refers to a diesel-equivalent, processed fuel derived from biological sources (such as vegetable oils), which can be used in unmodified diesel-engined vehicles. It is thus distinguished from the straight vegetable oils (SVO) or waste vegetable oils (WVO) used as fuels in some modified diesel vehicles.

1.3.4 Cetane number

Cetane number or CN is a measure of the combustion quality of diesel fuel via the compression ignition process. Cetane number is a significant expression of diesel fuel quality among a number of other measurements that determine overall diesel fuel quality. Cetane number is actually a measure of a fuel's ignition delay; the time period between the start of injection and start of combustion (ignition) of the fuel.

1.3.5 Diesel or diesel fuel

Diesel or diesel fuel is a specific fractional distillate of fuel oil (mostly petroleum) that is used as fuel in a diesel engine invented by German engineer Rudolf Diesel. The term typically refers to fuel that has been processed from petroleum, but increasingly, alternatives such as biodiesel or biomass to liquid (BTL) or gas to liquid (GTL) diesel that are not derived from petroleum are being developed and adopted.

1.3.6 Distillation

Distillation is a method of separating chemical substances based on differences in their volatilities. Distillation usually forms part of a larger chemical process, and is thus referred to as a unit operation.

1.3.7 Esters

Esters are organic compounds in which an organic group (symbolized by R' in this article) replaces a hydrogen atom (or more than one) in a hydroxyl group. An oxygen acid is an acid whose molecule has an -OH group from which the hydrogen (H) can dissociate as an H+ ion.

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Figure 2 Molecular Structure of Ester

1.3.8 Flash point

Flash point of a flammable liquid is the lowest temperature at which it can form an ignitable mixture in air. At this temperature the vapor may cease to burn when the source of ignition is removed. A slightly higher temperature, the fire point, is defined as the temperature at which the vapor continues to burn after being ignited.

1.3.9 Glycerol

Glycerol, also well known as glycerin and glycerine, and less commonly as propane-1,2,3-triol, 1,2,3-propanetriol, 1,2,3-trihydroxypropane, glyceritol, and glycyl alcohol is a colorless, odorless, hygroscopic, and sweet-tasting viscous liquid. Glycerol is a sugar alcohol and has three hydrophilic alcoholic hydroxyl groups (OH-) that are responsible for its solubility in water. Glycerol has a wide range of applications. Glycerol has a prochiral spatial arrangement of atoms.

1.3.10 Methanol

Methanol, also known as methyl alcohol, carbinol, wood alcohol or wood spirits, is a chemical compound with chemical formula CH3OH. It is the simplest alcohol, and is a light, volatile, colorless, flammable, poisonous liquid with a distinctive odor that is somewhat milder and sweeter than ethanol (ethyl alcohol). It is used as an antifreeze, solvent, fuel, and as a denaturant for ethyl alcohol.

1.3.11 Transesterification

Transesterification is the process of exchanging the alkoxy group of an ester compound by another alcohol. These reactions are often catalyzed by the addition of an acid or base.

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Equation 1 Molecular Formula Showing the Chemical Reaction of Transesterification

1.3.12 Vegetable fats and oils

Vegetable fats and oils are substances derived from plants that are composed of triglycerides. Nominally, oils are liquid at room temperature, and fats are solid; a dense brittle fat is called a wax. Although many different parts of plants may yield oil, in actual commercial practice oil is extracted primarily from the seeds of oilseed plants.

1.3.13 Viscosity

Viscosity is a measure of the resistance of a fluid to deform under shear stress. It is commonly perceived as "thickness", or resistance to flow. Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction.

1.4 Densities of different compounds

Table 1 Densities of different compounds

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1.5 Specific heats of different compounds

Table 2 Specific heats of different compounds

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2 Literature Review

In relation to the problem statement whereas, the rising cost of diesel fuels in the world market, the negative result of greenhouse gasses emissions in the environment and the bad effects to our health - this report provide information with better understanding of what biodiesel is, the process of how it is produces as well as the equipments used; the public policy currently approved; the importance of using biodiesel as an alternative; the advantage and disadvantages of using biodiesel, the economic benefits.

2.1 Introduction

By 2030, the world’s population is expected to reach 8 billion (Newsweek, dec. 06-07) and as the population grows, more energy is required to produce the basic needs of people. An energy that is more practical to use in the same way that it is safer, renewable, available and of course - affordable. Biodiesel is one of the candidates of this needed energy because of its abundance and potential source in the country. Biodiesel is a clean-burning diesel replacement fuel that can be used in compression-ignition (CI) engines, and which is manufactured from the following renewable, non-petroleum-based sources:

Virgin vegetable oils such as soy, mustard, canola, rapeseed and palm oils; Animal fats such as poultry offal, tallow, and fish oils; and Used cooking oils and trap grease from restaurants.

Biodiesel is produced in pure form (100% biodiesel or B100), but is usually blended with petrodiesel at low levels, between 2% (B2) to 20% (B20) in the U.S., but at higher levels in other parts of the world, particularly in Europe, where higher-level blends up to B100 are used. Blends of biodiesel higher than B5 require special handling and fuel management as well as vehicle equipment modifications such as the use of heaters and changing seals/gaskets that come in contact with fuel. The level of care needed depends on the engine and vehicle manufacturer.

Biodiesel is generally made when fats and oils are chemically reacted with an alcohol, typically methanol, and a catalyst, typically sodium or potassium hydroxide (i.e., lye), to produce an ester, or biodiesel.

2.2 Historical Background

Rudolf Diesel, the inventor of the first compression-ignition (CI) engine, once said that "the use of vegetable oils for engine fuels may seem insignificant today but such oils may become, in the course of time, as important as petroleum and the coal-tar products of the present time." He was indeed right because nowadays biodiesel is one of the greatest alternative sources of renewable fuel. The discovery of transesterification of vegetable oil in 1853 by scientists E. Duffy and J. Patrick gave way to the invention of biodiesel fuel.

Rudolf Diesel's prime model, a single 10 ft (3 m) iron cylinder with a flywheel at its base, ran on its own power for the first time in Augsburg, Germany on August 10, 1893. In remembrance of this event, August 10 has been declared "International Biodiesel Day". This engine stood as an example of Diesel's vision because it was powered by peanut oil — a biofuel, though not biodiesel, since it was not transesterified. He believed that the utilization of biomass fuel was the real future of his engine.

In 1979, more than a century later after the discovery of the first transesterification of vegetable oil, South Africa initiated the use of trans- esterified sunflower oil, and refined it to diesel fuel standards, By 1983 the process for producing fuel-quality, engine-tested biodiesel was completed and published internationally. An Austrian company, Gaskoks, obtained the technology from the South African Agricultural Engineers; the company erected the first biodiesel pilot plant in November 1987, and the first industrial-scale plant in April 1989 (with a capacity of 30,000 tons of rapeseed per annum).

Throughout the 1990s, plants were opened in many European countries, including the Czech Republic, Germany and Sweden. France launched local production of biodiesel fuel (referred to as diester) from rapeseed oil, which is mixed into regular diesel fuel at a level of 5%, and into the diesel fuel used by some captive fleets (e.g. public transportation) at a level of 30%. During the same period, nations in other parts of world also saw local production of biodiesel starting up: by 1998 the Austrian Biofuels Institute had identified 21 countries with commercial biodiesel projects.

In September of 2005 Minnesota became the first U.S. state to mandate that all diesel fuel sold in the state contain part biodiesel, requiring a content of at least 2% biodiesel. In Asia, Chemrez Technologies Inc. is the the biggest and most modern biodiesel facility, which started its operation on May 2006. Chemrez Technolologies Inc. produces 60, 000 metric tons of Bio-Active (the brand name of their BioDiesel) premium biodiesel per annum.

3 Process Selection

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4 Process Description

Biodiesel can be produced from straight vegetable oil, animal oil/fats, tallow and waste cooking oil. The process used to convert these oils to Biodiesel is called transesterification.

Bio diesel can be produced from straight vegetable oil, animal oil/fats, tallow and waste oils. There are two basic routes to biodiesel production from oils and fats:

- Base catalyzed transesterification of the oil.
- Direct acid catalyzed transesterification of the oil.

Most of the biodiesel produced today is done with the base catalyzed reaction for several reasons:

1. It is low temperature and pressure.
2. It yields high conversion (98%) with minimal side reactions and reaction time.
3. It is a direct conversion to biodiesel with no intermediate compounds.
4. No exotic materials of construction are needed.

Almost all biodiesel is produced using base catalyzed transesterification as it is the most economical process requiring only low temperatures and pressures and producing a 98% conversion yield. For this reason only this process will be described.

The Transesterification process is the reaction of a triglyceride (fat/oil) with an alcohol to form esters and glycerol. A triglyceride has a glycerine molecule as its base with three long chain fatty acids attached. During the esterification process, the triglyceride is reacted with alcohol in the presence of a catalyst, usually a strong alkaline like sodium hydroxide. The alcohol reacts with the fatty acids to form the mono-alkyl ester, or biodiesel and crude glycerol. In most production methanol or ethanol is the alcohol used (methanol produces methyl esters, ethanol produces ethyl esters) and is base catalyzed by either potassium or sodium hydroxide.

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Equation 2

4.1 Raw materials Used in Bio diesel Production

The primary raw materials used in the production of biodiesel are

4.1.1 Vegetable oils, animal fats, and recycled greases

Vegetable oils, animal fats, and recycled greases. These materials contain triglycerides, free fatty acids, and other contaminants depending on the degree of pretreatment they have received prior to delivery.

4.1.2 Alcohol

The most commonly used primary alcohol used in biodiesel production is methanol, although other alcohols, such as ethanol can also be used. A key quality factor for the primary alcohol is the water content. Water interferes with transesterification reactions and can result in poor yields and high levels of soap, free fatty acids, and triglycerides in the final fuel. Ethanol is 3.4 times more expensive than methyl alcohol.

In addition, a base catalyzed process typically uses an operating mole ratio of 6:1 mole of Alcohol rather than the 3:1 ratio required by the reaction. The reason for using extra alcohol is that it “drives” the reaction closer to the 99.7% yield we need to meet the total glycerol standard for fuel grade biodiesel. The unused alcohol must be recovered and recycled back into the process to minimize operating costs and environmental impacts. Methanol is considerably easier to recover than the ethanol. Ethanol forms an azeotrope with water so it is expensive to purify the ethanol during recovery. If the water is not removed it will interfere with the reactions. Methanol recycles easier because it doesn’t form an azeotrope.

4.1.3 Catalyst Selection

Most processes for making biodiesel use a catalyst to initiate the esterification reaction. The catalyst is required because the alcohol is sparingly soluble in the oil phase. The catalyst promotes an increase in solubility to allow the reaction to proceed at a reasonable rate. Base catalysts are used for essentially all vegetable oil processing plants essentially all of the current commercial biodiesel producers use base catalyzed reactions. Base catalyzed reactions are relatively fast, with residence times from about 5 minutes to about 1 hour, depending on temperature, concentration, mixing and alcohol:triglyceride ratio. Most use NaOH or KOH as catalysts, although glycerol refiners prefer NaOH.

4.1.4 Neutralizers

Neutralizers are used to remove the base or acid catalyst from the product biodiesel and glycerol. If you are using a base catalyst, the neutralizer is typically an acid, and visa versa. If the biodiesel is being washed, the neutralizer can be added to the wash water. While hydrochloric acid is a common choice to neutralize base catalyst.

4.2 Production Process

In general, vegetable oil contains 97% of triglycerides and3% i- and monoglycerides and fatty acids. The process of removal f all glycerol and the fatty acids from the vegetable oil in the presence of a catalyst is called transesterification The vegetable oil reacts with methanol and forms esterified vegetable oil in the presence of sodium/potassium hydroxide as catalyst.

4.2.1 Mixing of alcohol and catalyst

The catalyst is typically sodium hydroxide (caustic soda. It is dissolved in the methyl alcohol using a standard agitator or mixer.

4.2.2 Continuous Process Systems

The alcohol/catalyst mix is then charged into a closed reaction vessel and the oil or fat is added. The system from here on is totally closed to the atmosphere to prevent the loss of alcohol. The reaction mix is kept just above the boiling point of the methyl alcohol (around 60 °C) to speed up the reaction and the reaction takes place. Excess alcohol is normally used to ensure total conversion of the fat or oil to its esters. Approximately 90-98% oil conversion to methyl esters was observed within 90 min. Care must be taken to monitor the amount of water and free fatty acids in the incoming oil or fat. If the free fatty acid level or water level is too high it may cause problems with soap formation and the separation of the glycerin by-product downstream.

A popular variation of the batch process is the use of continuous stirred tank reactors (CSTRs) in series. The CSTRs can be varied in volume to allow for a longer residence time in CSTR 1 to achieve a greater extent of reaction. After the initial product glycerol is decanted, the reaction in CSTR 2 is rather rapid, with 98+ completions takes place. An essential element in the design of a CSTR is sufficient mixing input to ensure that the composition throughout the reactor is essentially constant.

The reactor is the only place in the process where chemical conversion occurs. Continuous reactors have a steady flow of reactants into the reactor and products out of the reactor. Once a continuous flow reactor reaches steady state operation, the product composition leaving the reactor becomes constant. For CSTRs, the reactants are fed into a well-mixed reactor. The composition of the product stream is identical to the composition within the reactor. Hold-up time in a CSTR is given by a residence time distribution. The residence time is defined by the length of time required for molecules to travel through the reactor.

The most important considerations within a reactor are the extent of reaction of the reactants, which is known as conversion key reactor variables that dictate conversion are temperature, pressure, reaction time (residence time), and degree of mixing. In general, increasing the reaction temperature increases the reaction rate and, hence, the conversion for a given reaction time.

4.2.3 Separation

Once the reaction is complete, two major products exist: glycerin and biodiesel. Each has a substantial amount of the excess methanol that was used in the reaction. The reacted mixture is sometimes neutralized at this step if needed. The glycerin phase is much denser than biodiesel phase and the two can be gravity separated with glycerin simply drawn off the bottom of the settling vessel. In some cases, a centrifuge is used to separate the two materials faster. Centrifuges are most typically used to separate solids and liquids, but they can also be used to separate immiscible liquids of different densities. This type of separation can also be achieved using a settling tank. While a settling tank may be cheaper, a centrifuge can be used to increase the rate of separation relative to a settling tank. In a centrifuge the separation is accomplished by exposing the mixture to a centrifugal force. The denser phase will be preferentially to the outer surface of the centrifuge. A centrifuge generally consists of

1. A bowl containing the mixture,
2. A drive shaft and drive-shaft bearings,
3. A drive mechanism,
4. A casing to segregate the separated products.

Centrifuges are very amenable to continuous operation. A range of different centrifuge configurations are available with a common form being disc centrifuges.

4.2.4 Alcohol Removal

Once the glycerin and biodiesel phases have been separated, the excess alcohol in each phase is removed with a flash evaporation process or by distillation. In others systems, the alcohol is removed and the mixture neutralized before the glycerin and esters have been separated. In either case, the alcohol is recovered using distillation equipment and is re-used. Care must be taken to ensure no water accumulates in the recovered alcohol stream. An important separation device for miscible fluids with similar boiling points (e.g., methanol and water) is the distillation column. Separation in a distillation column is predicated on the difference in volatilities (boiling points) between chemicals in a liquid mixture. In a distillation column the concentrations of the more volatile species are enriched above the feed point and the less volatile species are enriched below the feed point. The vaporization in the column is driven by heat supplied in the reboiler, which is subsequently removed in the overhead condenser. The temperature in the distillation column is the highest at the bottom and decreases moving up the column. Distillation columns can use either trays or packing.

4.2.5 Glycerin Neutralization

The glycerin by-product contains unused catalyst and soaps that are neutralized with an acid and sent to storage as crude glycerin. In some cases the salt formed during this phase is recovered for use as fertilizer. In most cases the salt is left in the glycerin. Water and alcohol are removed to produce 80-88% pure glycerin that is ready to be sold as crude glycerin. In more sophisticated operations, the glycerin is distilled to 99% or higher purity and sold into the cosmetic and pharmaceutical markets.

4.2.6 Methyl Ester Wash

Once separated from the glycerin, the biodiesel is sometimes purified by washing gently with warm water to remove residual catalyst or soaps, dried, and sent to storage. This is normally the end of the production process resulting in a clear amber-yellow liquid with a viscosity similar to petro diesel. In some systems the biodiesel is distilled in an additional step to remove small amounts of color bodies to produce a colorless biodiesel. It means of separating chemicals in a fluid mixture is by exploiting the differences in boiling points between the chemicals. If the boiling points are sufficiently different for the chemicals to be separated, such as with water and biodiesel, an evaporator or flash vaporizer can be used for the separation. In the evaporator, the liquid is heated to a temperature in which only the more volatile chemical species will vaporize. As such the vapor stream leaving the evaporator will be enriched in the more volatile species and the liquid stream from the evaporator will be enriched in the less volatile species. In an evaporator, the separation is accomplished by supplying heat while the mixture is held at a fixed pressure. In contrast, a flash vaporizer first heats the liquid, at an elevated pressure. Then, the heated liquid is sent through a flash valve that decreases the pressure. The decrease in pressure causes the more volatile portion of the liquid mixture to vaporize.

4.2.7 Product Quality

Prior to use as a commercial fuel, the finished biodiesel must be analyzed using sophisticated analytical equipment to ensure it meets any required specifications. The most important aspects of biodiesel production to ensure trouble free operation in diesel engines are:

- Complete Reaction
- Removal of Glycerin
- Removal of Catalyst
- Removal of Alcohol
- Absence of Free Fatty Acids

4.3 Operating Parameters Table

Table 3 Operating Parameters for Biodiesel Production

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5 Material and Energy Balance

5.1 Material Balance

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5.1.1 Mixer

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5.1.2 Reactor 1

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5.1.3 Centrifuge 1

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5.1.4 Reactor 2

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5.1.5 Centrifuge 2

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5.1.6 Washing Tank

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[...]

Details

Seiten
125
Jahr
2010
ISBN (eBook)
9783656008170
ISBN (Buch)
9783656008361
Dateigröße
10.9 MB
Sprache
Englisch
Katalognummer
v178353
Institution / Hochschule
University of Engineering & Technology, Lahore
Note
A+
Schlagworte
production biodiesel waste vegetable

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Titel: Production of Biodiesel from Waste Vegetable Oil