Method and system for robotic algae harvest   

Abstract: A Robotic Algae Harvester (RAH) of the present invention works by providing a CO2 collection mechanism that is installed in power plants or vehicles. These systems are available using current technology and have been proven to be scalable. CO2 is then transported to RAH using ships. The RAH will feed and re-circulate algae broth through the photobioreactors (PBRs). The PBRs float in the ocean while the algae through photosynthesis will transform the CO2 into biomass in a continuous process. The extracted algae will processed into a stable mix of oil and bi-product and transferred to the ship that brought the CO2. The algae is then processed onshore in some of the following manners: converted to biodiesel via transesterification; converted to bio-ethanol via fermentation; burned for electricity generation; and/or used as protein for animal feed or food products.

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This application claims priority from and is a Continuation of U.S. patent application Ser. No. 12/341,990, entitled “Method and system for robotic algae harvest”, filed on Dec. 22, 2008, which is incorporated by reference in its entirety for all purposes as if fully set forth herein.

FIELD OF THE INVENTION

The present invention relates generally to a method and system for growing and harvesting algae for use in bio-fuels. More specifically, the present invention relates to a method and system for robotic algae harvest for use in bio-fuels and other applications.

BACKGROUND OF THE INVENTION

There are two challenges facing our society that could menace our standards of living and way of life. The first is carbon emissions from our cars and power plants are contributing to global warming and could in the long term threaten landmasses by raising water levels. The second is fuel prices are forcing many industries out of business, as well as putting pressure on the average citizens on their daily work. Current fuel prices produce a drag on the U.S. economy and create large cash surpluses in sometimes questionable oil rich countries.

In 2007, the International Monetary Fund (IMF), warned that higher biofuel demand in the United States and the European Union (EU) has not only led to higher corn and soybean prices, it has also resulted in price increases on substitution crops and increased the cost of livestock feed by providing incentives to switch away from other crops. Researches have found that converting rainforests, peatlands, savannas, or grasslands to produce food-based biofuels in Brazil, Southeast Asia, and the United States creates a ‘biofuel carbon debt’ by releasing 17 to 420 times more CO2 than the annual greenhouse gas (GHG) reductions these biofuels provide by displacing fossil fuels. Other researches have found that corn-based ethanol increased emissions by 100% and biofuels from switchgrass, if grown on U.S. corn lands, increase emissions by 50%.

Many alternative energy solutions attack one problem, at the danger of worsening the other. For example, the there has been much effort in processing fuels from oil-rich sands. Even though this approach has the potential of reducing the price of fuel, in turn, it could increase the fuel consumption and increase carbon emissions. Other technologies such as windmills, or hybrid vehicles could increase water pollution by increasing the usage of batteries with heavy metals. Other approaches would cause huge infrastructure investments that even if the U.S. and other developed countries would be willing to undertake, other large polluters like China and India would be less inclined to invest.

Many attempts have been made at growing algae for bio-fuels; most of them on land. One of the most notorious has been GreenFuel Technologies. The main reason that some of those systems failed to this day to be profitable is that they assumed algae growth that although possible under laboratory conditions, it cannot be sustained outdoors. The foundations for these systems were all derived from these algae growth rates, then propagated through their cost estimates and engineering designs. The GreenFuel claims cannot be substantiated following simple conservation of energy equations given the amount of energy received from the sun.

SUMMARY

The present invention teaches a novel robotic Algae harvester for the production of bio-fuels from algae that overcomes the shortcomings of prior art solutions.

The major hurdles with microalgae harvesting include: Algae varieties rich in oils do not survive well in open ponds because the have a hard time competing with naturally occurring algae; Optimal algae grows is dependent on the temperature of the water; Algae cultures require large amounts of water; and Dissolving sufficient amounts of CO2 from the air require large air-water surfaces.

The present invention teaches a sustainable process for growing algae for the production of biofuels. The recent interest in the use of agriculture products as replacements for petrochemical products (biodegradable plastics, ethanol for transportation, etc) has had unintended consequences (rise in food prices) and unseen environmental impact (carbon emissions). The proposed project may enable a bio-fuel that does not impact critical food prices while having a more environmentally friendly carbon implant. In fact, this project is expected to make use of sequestered carbon in the growth of the algae.

World demand for biofuels will expand at a nearly 20 percent annual pace to 92 million metric tons in 2011, despite recent concerns about the impact of biofuels on the environment and food supplies. Market expansion will come from a more than doubling of the world market for bioethanol, and even faster increases in global biodiesel demand. Despite the growing size of the world\'s largest producers, the proliferation of new companies and rapid expansion of the biofuel industry overall combined to limit the top nine producers to just a 30 percent share of the market in 2006. This lack of dominant companies will enable Robotic research to compete in this rabidly growing market.

The proposed system referred to herein as the Robotic Algae Harvester (also referred to as “RAH”) is composed of an ocean floating robotic system that provides a set of enclosed volume photobioreactions (PBR) for algae growth. Some of the advantages of the proposed system include: Absorption of CO2 with the production of biodiesel; the sea provides ample heat dissipation maintaining the water at optimal growth temperatures; an abundant water supply; enclosed growth environment that allows growth of oil rich algae varieties; enclosed growth environment that provides advantages for high rates of CO2 enrichment; no real estate costs as the robotic platform will be floating in the ocean; maximum photosynthetically active radiation (PAR) by strategically locating the systems in areas where the 400-700 nm part of the spectrum is the strongest and has the least to no environmental impact as RAH will be floating far away from coastal areas; and high endurance to storms as RAH will sink below surface to avoid rough weather.

The system and method taught by the present invention produces multiple products and generates multiple sources of income from: biodiesel; ethanol; carbon credits; tax subsidies; and dry algae briquettes. The present invention does not require significant changes to the current infrastructure, does not require large landmasses, and each individual technology is currently available.

It is therefore an objective of the present invention to teach an economically and environmentally sustainable system and method for the production of algae for bio-fuel use. The present invention is responsive to the USDA\'s call for economically and environmentally sustainable production of biomass material to be used as fuel, including but not limited to, ethanol.

It is also therefore an objective of the present invention to teach the use of algae that will not have adverse effects on food prices, nor result in a ‘bio-fuel carbon debt’ unlike bio-fuels products based on food products.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.

FIG. 1 illustrates the method of the Robotic Algae Harvester (RAH);

FIG. 2 is a list of microalgae being considered for biofuels and their typical percentage of dry weight oil;

FIG. 3 illustrates the results achieved on land utilizing open raceway ponds and land based PBRs;

FIG. 4 illustrates a simple functional schematic of the Robotic Algae Harvester (RAH) of the present invention;

FIG. 5 illustrates the basic PBR design of the present invention;

FIGS. 6 and 7 illustrate visual simulation results of RAHs stability using seastates; and

FIG. 8 illustrates a preliminary model of several hexagons subjected to a seastate level 5.

DETAILED DESCRIPTION

In the following detailed description of the invention of exemplary embodiments of the invention, reference is made to the accompanying drawings (where like numbers represent like elements), which form a part hereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, but other embodiments may be utilized and logical, mechanical, electrical, and other changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.

In the following description, numerous specific details are set forth to provide a thorough understanding of the invention. However, it is understood that the invention may be practiced without these specific details. In other instances, well-known structures and techniques known to one of ordinary skill in the art have not been shown in detail in order not to obscure the invention.

Referring to the Figures, it is possible to see the various major elements constituting the apparatus of the present invention. The present invention is a method for generating, producing, and distributing advertising materials. The present invention is a method and system for robotic algae harvest.

Now referring to FIG. 1, the method of the Robotic Algae Harvester (RAH) is illustrated. The Robotic Algae Harvester (RAH) 100 of the present invention works by providing a CO2 collection mechanisms 101 that is installed in power plants 102 and vehicles 103. These systems are available using current technology and have been proven to be scalable. CO2 111 is then transported to the RAH 100 using ships 104. The RAH 100 will continuously feed and re-circulate the algae broth 105 through the photobioreactors (PBRs) 106. The PBRs 106 float in the ocean 107 while the algae 108, through photosynthesis, transforms the CO2 into biomass in a continuous process. The extracted algae 109 will be transferred and preprocessed into a stable mix of oil and bi-product 110 to the ship 104 that brought the CO2 111. The extracted algae 109 is then processed onshore 112 in some of the following manners: converted to biodiesel via transesterification 113; converted to bio-ethanol via fermentation 114; burned for electricity generation 115; and/or used as protein for animal feed 116.

The method of the present invention will be an around the year continuous process. RAH will autonomously control the location of the platform slowly shifting it to zones with high PAR. RAH will also submerge the PBRs in cases where the weather could damage the system (i.e. hurricanes).

Photosynthesis transforms CO2 into carbohydrates (CH2O)n. it can be represented as:

CO2+2H2O---->O2+[CH2O}+H2O

These carbohydrates have a heating value of 468 kJ per mole, and a mole of PAR photons is 217.4 kJ. Therefore the eight protons that photosynthesis needs to capture one molecule of CO2 will yield a maximum conversion efficiency of:

Q photo = 477   kJ 8 × 208   kl = 28.7  %

This could only be achieved if the organism did nothing except transforming CO2 into (CH2O)n. However, algae perform other bodily functions not directly related to the conversion, and due to the pathway taken by the sun to arrive to the cell as well as the processing of the final product. Therefore, the actual conversion numbers are lower than the above 28.7%. Now referring to these other parameters that affect the efficiency of the cell as Qs. These include: Ql is the efficiency loss due to other algal function not directly related with oil generation Qpp is the efficiency loss due to photosaturation and photoinhibition Qo is the efficiency loss due to the optical path taken by the sun Qpris the efficiency loss due to the processing of the fuels The efficiency Q of the proposed system will be:

Q=Qphoto*Ql*Qpp*Qo*Qp

In the following subsections it is estimated that each of the efficiency parameters shown above will have the following impact.

The overall efficiency therefore is:

Q=Qphoto*Ql*Qp*Qo*Qp

Q=28.7*0.875*0.9*0.715*0.921=14.88%

The energy in the form of biomass generated by RAH, can be computed as: E=PAR*Q. Where PAR in the equatorial regions where RAH would be floating is 130-140 w/m2. It is assumed the lower bounds on this estimate. Therefore, E=130*14.88%=19.34.

Now, although this is the total biomass, the question is what is the oil content. FIG. 2 is a list of microalgae being considered for biofuels and their typical percentage of dry weight oil 200.

At this point any particular culture may be used, so, for exemplary purposes only, the value used is the conservative 40% . The enclosed PBRs allow the flexibility to cultivate monocultures or mix and match varieties to improve the need or costs. In comparison, other prior art systems use a 30% lower bound and a 70% upper bound for the algal varieties suitable for biodiesel generation. Therefore, the amount of biodiesel that RAH would be able to produce would be:

Vbdiesel=19.34*0.4*0.264172052=2.04 gallons/m2/year

In comparison, the table 300 shown in FIG. 3 illustrated the results achieved on land utilizing open raceway ponds and land based PBRs. The typical productivity is in gallons of dried biomass. The results presented for efficiency and biomass are comparable to the computed values above. Please note that the values shown in the table 300 are for biomass and not lipid content. This is a very important difference as the percent of diesel generated from this biomass can drastically change depending on the variety of algae used. In particular, open ponds will only generate lipids in the order of 2-4% and therefore only suitable as feed or fermentation (with much lower cost-reward curves).

Now referring to FIG. 4, a simple, functional Robotic Algae Harvester (RAH) ocean going platform 400 is composed of a set of floating interconnecting photobioreactors (PBRs) 401 and 402, Processing and Control Modules (PCM) 403, and loading and unloading stations (LUS) 404. The RAH is built modularly so that when different parts need to be taken offline, new modules can be exchanged. The exact shape of the physical configuration of RAH will be determined as part of the proposed research effort to minimize overall cost.

The RAH consumes energy to perform some of its functions: Station keeping to optimize PAR; Algae broth pumping (to minimize photo-saturation, de-oxygenation and pipe cleaning); and Submersion for storm survival. The RAH will make use of the energy generated by the waves to perform the two first functions while using the amount of CO2 available in the PBR to change its buoyancy.

Water needs to be circulated through the PBR to prevent photosaturation, to enrich the broth with CO2, to reduce the amount of oxygen and to clean the surfaces. To approximate the amount of energy necessary to provide circulate this water. It is assumed that a 0.05m diameter pipe, and a 40m length. There are two mechanisms that can be used to generate the pumping action: using the wave energy to directly pump the algal broth; and using the waves as a generator and use a conventional pump to pump the broth.

Using the wave energy to directly pump the broth is a more appealing idea because it provides higher efficiencies. On the other hand, since the direct pumping does not provide a storage capability, the pumping speed will be highly dependent on the waves that RAH will be subject to. No studies are currently available that provide the effects on the algal culture given these constraints. The effort will fund a trade study to compare both methodologies.

The algae growth can be thwarted by the amount of CO2 diluted in the broth. Thus it is not possible to sustain algal growth without aiding the dilution of CO2 in the water. Since the amount of CO2 in the atmosphere is relatively small (approximately 387 ppm) a large surface area is needed to dissolve sufficient CO2 in the broth to maintain the algae growing at optimal rates. The surface area of the air-to-water interface is one of the limiting factors for algal growth, and by recycling CO2 this limit can be lifted. The ideal Gas Law is: PV=nRT. Therefore, the number of moles in 1 Cubic meter of water at 1 atm and 27 deg C. can computed as follows:

n = 1   atm * 1000   l 0.082 * 300   k = 41   mols

And therefore, the concentration of CO2

C=41 mol*0.000387=0.016 mol CO2/m3 or 0.7 g of CO2 per m3.

Assuming that, at best, the carbon dioxide concentration in the water is zero, the maximum gas phase carbon dioxide mass transport flux, N, is:

N=CK=0.7 g/m3*5 cm/h*1m/100 cm*20 h/1d=0.84 g

Where C is the carbon dioxide concentration at the surface and K is mass transport rate. Therefore these 0.84 g of CO2 per m{circumflex over (0)}2/day will provide an algal growth support flux of:

P=0.85 g*1 g/4 g*2 g*365=153.3 g

These is algae g/m2/year, which is equivalent to 0.04 gallons/m2/year, which is significantly lower than the 2.04 gallons/m2/year that the algae is capable of achieving given the above calculations. These findings supports the proposed technique of utilizing recaptured CO2 to feed the algae at a rate that can keep up with its growth.

Now in comparison, using CO2 to feed the algal broth:

C=41 mol CO2/m3*44 g CO2/mol CO2=1.8 Kg CO2/m3

N=C*K=1.8 kg CO2/m3*1 g Carbon /4 g CO2*2 g Algae/1 g Carbon*365 days=329 kg Algae/m

Or 87 gallons/m2/year, which far exceeds the growth that the algae would be capable of producing. In other words, the amount of area necessary to dissolve CO2 is 2.04 gallons/87 gallons=2.3%. Given this result, it is required that one design the broth-gas exchange chamber to meet these ratios.

Given the previous results it is clear that feeding the algal broth from the air will require much larger surface areas that are cost effective from the proposed platforms. Therefore, it would be necessary to provide CO2 sources other than air. The process of CO2 sequestration has made some significant advances in the past few years. CO2 scrubbing from power plants is currently being utilized, and there are several initiatives to make carbon scrubbers for vehicles. The main reason that these methods for sequestration have not been thoroughly adopted is that there is no good alternative for getting rid of the CO2. Some initiatives have been made to pump the CO2 into oil wells, or to pump in underground reservoirs. In other words, there is ample supply of CO2 that could be used to feed RAH. The cost of collecting and delivering CO2 needs to be taken under consideration as operation costs, however we believe that the political changes currently being proposed will “cap and trade” the emissions of CO2 producers. Under these new rules, producers will have to bear the cost of capturing the CO2 producing a large surplus of CO2, without having any cost efficient way of getting rid of it. RAH will consume this CO2 providing yet another source of income from CO2 credits.

Now referring to FIG. 5, the design is composed on triangular shaped PBRs 500 organized into hexagons. Each triangle 500 will be composed of water inflatable tubes 502 in its periphery for compression support and tensioned wire frame core 503 for rigidity and to hold the algae tubing 501.

A preliminary model of RAH based on the triangular design, and the hexagonal design has been generated. These simulated platforms 600 and 700 are shown in FIGS. 6 and 7 and are subjected to a sea-state level two. The round/oval compartments are air pockets used to provide buoyancy control. Phase I of the research topic will concentrate on refining this model and subjecting larger platforms to the wave actions.

FIG. 8 shows the preliminary model of several hexagons 800 subject to a seastate level five. The model used for generating these simulations assumes that the triangular structure is rigid, and therefore they should only be used as preliminary results. That being said, the forces created by the sea-state level five are within the design parameters of the proposed architecture. A model that takes under consideration the fluid dynamics of the forces excerpted to the different parts of the design will be used to improve and/or verify the design.

Further objectives and advantages of the invention will become apparent from a consideration of the drawings and ensuing description. Furthermore, other areas of art may benefit from this method and adjustments to the design are anticipated. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.