Biodiesel from Microalgae Report IV
Week 12
Group Delta
Kevin Jackson
Xin Qin
Joshua Jones
Dan Detro
Valerie Delligatti
Table of Contents
I. Abstract………………………………………...
II. Executive Summary……………………………
III. Introduction……………………………………
IV. Previous Work………………………………..
V. Discussion…………………………………….
VI. Design Proposal……………………………….
VII. Conclusion/Recommendations………………
VIII. Acknowledgements…………………………
IX. References……………………………………
Appendices:
1: Process Flow Diagram......
2: Material and Energy Balance......
3: Data Sheet......
4: Calculations......
5: Economic Evaluation Factored from Equipment Costs......
6: Utilities......
7: Conceptual Control Scheme......
8: General Arrangement – Major Equipment Layout......
9: Distribution and End-Use Issues Review......
10: Constraints Review......
11: Applicable Standards......
12: Design Basis......
13: Project Communications File......
14: Information Sources and References......
I. Abstract
II. Executive Summary
Group delta presents an alternative choice to fossil fuels by harvesting algae and converting it into biodiesel. The current political climate is very sensitive to the use of foreign oil and is concerned over the pollution produced from burning fossil fuels. A solution to depleting nonrenewable resources exists that requires little to no modification of hardware and also improves, rather than destroys the environment. Biodiesel can be produced from triglycerides that originate from sources such as soybeans and vegetable oils, but our group has a novel choice: chlorella algae. The advantage of using this aquatic species is that precious farmland is not wasted for the creation of fuel. Chlorella can be grown in wastewater streams thereby nearly eliminating the need for specialty sites. Algae require carbon dioxide to survive, and thrive when more is fed into their habitat. Our group proposes the use of the waste carbon dioxide effluent from a power plant to improve algae growth, as well as reducing the carbon footprint from the atmosphere. In an era where carbon dioxide emissions are going to be taxed, it is advantageous to have a process where carbon dioxide is used rather than produced.
Our clients are concerned individuals and businesses that wish to offset the use of fossil fuels for power output and choose a more environmental friendly product.
Introduction
This report is a compilation of details concerning the progress of the design of a facility to mass produce microalgae which is sequentially turned into transport fuel (biodiesel). The specific objectives of this report are as follows:
1.) Present the amounts of triglycerides and algae needed to produce enough biodiesel to replace 10,000 barrels a day of gasoline and justification for these calculations.
2.) Display the types of unit operations that will be used to mass produce algae.
3.) Discuss the strain of algae that would be used for this process.
4.) Present a detailed process flow diagram.
5.) Complete material and energy balances on the process.
6.) Analyze the steps of the process, starting with separation of algae from water.
7.) Present progress made in making contact with specialists in the industry.
Previous Work
All information obtained by Group Delta has been made possible by previous work on this subject. These works, as well as industrial contacts, are listed in the references section.
Discussion
10,000 BPD of Gasoline Biodiesel Equivalence Calculations:
To the determine the amount of oil, in the form of triglycerides, necessary to produce enough biodiesel to match and replace 10,000 barrels per day (BPD) of gasoline, material and energy analysis was necessary. First, the energy content of 10,000 BPD of gasoline was determined and used to find the amount of biodiesel needed to produce the same energy content. The methanol transesterification reaction stoichiometry was used to convert the amount of biodiesel needed to the amount of triglycerides that must be fed into the reaction to form the needed amount of biodiesel.
Once the amount of triglycerides needed is found, the amount of algae needed to be processed per day can be determined by assuming 99% oil extraction process efficiency along with the oil content data of the algal species being harvested. It has been determined that 6,500 tons of algae per day are need for this process. For complete analysis, see the appendix.
2.) Operations Used to Mass Produce Algae:
There are two main types of bioreactors used to produce algae, photobioreactors and raceway ponds. Photobioreactors are essentially closed systems consisting of a degassing column and lengths of relatively thin, clear piping. The algae and water mixture is continuously circulated through this system, gaining solar energy as it traverses through the clear tubes and being fed with CO2 and degassed of O2 in the degassing column. Temperature control can be attained via cooling or heating coils in the degassing column. This type of bioreactor is more expensive to construct than a raceway pond. A raceway pond essentially looks like a winding river and can be an open system if it is not covered. Contamination of the algae in the raceway pond is an issue since the raceway pond design is usually open to the environment. Evaporative water loss is also an issue with raceway ponds. This type of bioreactor uses a paddlewheel to create flow of water and algae. A steady stream of water and algae is extracted from this reactor and that is the product stream.
The Four Corners Power Plant has recently done a three month study on using a scrubbed flue gas waste stream from the coal-fired power plant as a CO2 feed for an algae bioreactor. This method was an inspiration to Group Delta and this design will be implemented into the overall microalgae to biodiesel process. Engineering Supervisor Bruce Salisbury was contacted and the notes taken on this telephone call was a valuable resource to the project. Mr. Salisbury has offered some of his time for another telephone conference, in which case Group Delta will ask a detailed list of questions on how this Power Plant used that flue gas stream.
It seems to be that raceway ponds are used for large scale production of algae while photobioreactors are used for laboratory scale studies or small scale algae production. This was verified by Bruce Salisbury, Engineering Supervisor of the Four Corners Power Plant. The decision has been made to use a combination of photobioreactors and raceway ponds for our facility. The number of photobioreactors used will be much smaller than the raceway ponds. The photobioreactors will serve two functions: to initially grow the algae and to ensure a constant species composition. The photobioreactors will feed into the raceway ponds. If the raceway ponds become contaminated, the pond will be cleaned and the photobioreactors will feed chlorella algae into the pond. At startup, the algae will need to grow to fill the raceway ponds before harvesting can begin. The photobioreactors will be used for the grow up process to prevent competing species from reducing yields.
3.) Type of Algae:
The type of algae chosen for this process is Chlorella sp, more commonly known as green microalgae. The reason this strain of algae was chosen was because it is a widely known, widely researched type of algae that can grow in either fresh or saltwater. It is generally comprised of 45% protein, 20% fat, 20% carbohydrate, 5% fiber, and 10% minerals and vitamin9. The Chlorella oil content has been shown to be around 20-32% by mass. The concentration of carbon dioxide and mineral nutrients such as salts and phosphate has been shown to affect the oil content of the algae.
Chlorella algae has been successfully grown and harvested for use in the health food industry. Typically, the algae is grown in a batch process and dried for use as a food and supplement. Our process is a continuous process, however, requiring the use of the raceway pond to constantly circulate and harvest the algae.
For the amount of algae living in the raceway ponds and photobioreactions, it has been determined that nutrient requirements are as follows:
Nutrient / Requirement (short ton/day)Calcium / 14.35
Iodine / 0.03
Iron / 8.44
Magnesium / 20.45
Phosphorus / 58.11
Zinc / 4.61
Nitrogen / 29.06
To feed the nutrients to the algae, a CSTR will be utilized to initially mix the compounds with water. This is because compounds such as calcium chloride produce heat when mixed with water, which could harm the algae. The nutrients will then be fed into the raceway ponds via pipelines.
4.) Process Flow Diagram with more detail:
As progress is made another “unknown unknown”, as Professor Perl would say, is identified. When the original PFD was made very little was known about the entire process. There were steps of the process that were not identified yet and unit operations were needed in places not previously known. As these steps are identified, they usually result in the addition of another box to the process flow diagram, resulting in a more detailed and representative PFD. An updated PFD is included in Appendix A that shows a better representation of the entire process.
The water will be removed from the algae with French drain sand filters. These units are better suited to our scale of production, and can be built cheaply to harvest the algae. The units are capable of accepting a flow rate of 1000 gal/min, and have a size of 180 feet by 60 feet. These are shallow pits that are simply excavated from the earth, then vertical pipes made out of PVC are placed in the ground. A base layer of ash from the power plant is then placed over the pipes, and then the filter is filled with sand. The solvent extraction unit has been detailed with flow streams, as well as information regarding steam, cooling water, air, and hexane requirements according the sales representative from Crown Iron Works.
5.) Process steps (unit operations):
A.) Photobioreactor and Raceway Ponds
There will be 25,290 raceway ponds that are 978.5 m2, with a small photobioreactor for each pond. This total area is ten square miles, which is slightly larger than the UIC campus, about from Halsted to Western.
The side walls of the ponds will be filled with concrete, and the bottom is covered with asphalt. There will be a plastic liner that covers the ponds. The liner is UV resistant and has a life span of twenty years. The walls of the ponds are six inches wide, and the depth is 0.3 meters, with an additional six inches for the concrete liner at the bottom. The total cost of the raceway ponds is $891,514,495. This is about 80% of the total costs.
B.) Flue Gas Scrubber and Demoisturizing Column from Power Plant
Algae to Biodiesel: Scrubbing the Flue
This process relies on utilizing a flue gas stream from a coal fired power plant to supply CO2 to the algae producing raceway ponds and photobioreactors. This part of the process will use the Four Corners Power Plant as a basis in our model. This 2,040 megawatt facility supplies power to approximately 300,000 households and produces about 2X 1010 kg (20,000,000 metric tons) of CO2 per year.
The flue gas from the power plant will be assumed to have regulatory levels of all pollutants on its way out of the flue stack. This flue will be assumed to have 200 parts per million of SO2 in it. The algae can only tolerate an SO2 concentration of about 20 ppm, so this flue must be sent through an additional scrubbing process to remove that pollutant to tolerable levels.
An Excel Spreadsheet is attached to this page. It includes the mass balance on the scrubbing unit. The scrubber will be a modeled as a wet scrubber. An average installed cost for a FGD (flue gas desulfurization) scrubbing unit is around $350/kW (2007) for a 300 megawatt and above power plant (powermag.com). Most wet FGD systems use alkaline slurries of limestone or slaked lime as sorbents, preferred for their availability and relatively low cost. Sulfur oxides react with the sorbent to form calcium sulfite and calcium sulfate.
SO2 + CaCO3 = CaSO3 + CO2
The product is a wet and solid material that may require additional treatment or can be oxidized to gypsum, which can be sold as an insulating material. This reaction will be used in the scrubber mass balance. Waste water treatment is required in wet scrubbing systems. In disposal of the solid waste, 53% of respondents to the power plant survey sourced are using an old or new landfill; slightly fewer (35%) are recycling at wallboard plants (powermag.com source). The material balance on the flue gas scrubber can be found in Appendix F.
There is a lot of water vapor in the effluent that must be removed as it can harm the algae if it is not clean. To remove the water, a column packed with gravel will have the effluent passed through it. The surface area of the packing and the length of the column will allow the water to condense and be removed from the effluent. This water will be stored in a tank and tested. If it is clean, then it can be used as makeup water for the raceway ponds or sold to the municipality. If the water is dirty, then it can be sent to the power plant’s waste treatment area.
C.) French Drain Sand Filters and Algae Toasters:
The algae coming from the bioreactor will be soaking in water that needs to be separated from the algal biomass before the algae is sent to the oil extraction unit. One way to do this is with centrifuges. Centrifuges are a reliable yet costly route to separating the water from the algae. Centrifuge Specs are as follows: 150 horsepower motor, 350 Gallon per Minute Capacity, and the cost is approximately 500,000 dollars per centrifuge. The density of the water/algae stream needs to be known in order to do the calculation of the number of centrifuges needed to do this process. No data could be found online so Group Delta decided to contact the Four Corners power plant on 2/11/09 to try to get some rough answers. Mr. Salisbury was incredibly educated on the subject and the first piece of information that will be used from that conversation is that the specific gravity of an algae/water mixture is nearly identical to that of water (1.0) since algae are largely composed of water. If the algae are a saltwater species this specific gravity will be approximately equal to that of brine (1.03). As a basis, we will assume the algae are in fresh water. It is important to note that the mass percent of algae in a typical product stream from a bioreactor is not yet known, yet needs to be in order to accurately do these calculations. Group Delta is working on getting that number, but until then hypothetical numbers were used. With a product stream of 50% algae by weight, 7 whole centrifuges are needed, costing 3.5 million dollars. With a product stream of 1% algae by weight, 31 whole centrifuges are needed, costing 15 and a half million dollars. The calculations are detailed in the appendices.