Abstract:
A system for processing oil from algae is disclosed. Specifically, the system recycles byproducts of the process for use as nutrients during algae growth and oil production. The system includes a conduit for growing algae and an algae separator that removes the algae from the conduit. Also, the system includes a device for lysing the algae and an oil separator to remove the oil from the lysed matter. Further, the system includes a biofuel reactor that receives oil from the oil separator and synthesizes biofuel and glycerin. Moreover, the algae separator, oil separator and biofuel reactor all recycle byproducts back to the conduit to support further algae growth.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention pertains generally to processes for harvesting oil from algae. More particularly, the present invention pertains to a cost efficient supply of nutrients to support the growth of algae cells having a high oil content. The present invention is particularly, but not exclusively, useful as a system and method for recycling byproducts of an algae oil harvesting process for use in supporting algae cell growth and oil production. 
       BACKGROUND OF THE INVENTION 
       [0002]    As worldwide petroleum deposits decrease, there is rising concern over shortages and the costs that are associated with the production of hydrocarbon products. As a result, alternatives to products that are currently processed from petroleum are being investigated. In this effort, biofuels such as biodiesel have been identified as a possible alternative to petroleum-based transportation fuels. In general, biodiesel is a fuel comprised of mono-alkyl esters of long chain fatty acids derived from plant oils or animal fats. In industrial practice, biodiesel is created when plant oils or animal fats are reacted with an alcohol, such as methanol. 
         [0003]    For plant-derived biofuel, solar energy is first transformed into chemical energy through photosynthesis. The chemical energy is then refined into a usable fuel. Currently, the process involved in creating biofuel from plant oils is expensive relative to the process of extracting and refining petroleum. It is possible, however, that the cost of processing a plant-derived biofuel could be reduced by maximizing the rate of growth of the plant source. Because algae is known to be one of the most efficient plants for converting solar energy into cell growth, it is of particular interest as a biofuel source. However, current algae processing methods have failed to result in a cost effective algae-derived biofuel. 
         [0004]    In overview, the biochemical process of photosynthesis provides algae with the ability to convert solar energy into chemical energy. During cell growth, this chemical energy is used to drive synthetic reactions, such as the formation of sugars or the fixation of nitrogen into amino acids for protein synthesis. Excess chemical energy is stored in the form of fats and oils as triglycerides. Thus, the creation of oil in algae only requires sunlight, carbon dioxide and the nutrients necessary for formation of triglycerides. Nevertheless, with the volume requirements for a fuel source, the costs associated with the inputs are high. 
         [0005]    In light of the above, it is an object of the present invention to provide a system and method for processing oil from algae which reduces input costs. For this purpose, a number of systems have been developed, such as those disclosed in co-pending U.S. patent application Ser. No. ______ for an invention entitled “Photosynthetic Oil Production in a Two-Stage Reactor,” co-pending U.S. patent application Ser. No. ______for an invention entitled “Photosynthetic Carbon Dioxide Sequestration and Pollution Abatement” and co-pending U.S. patent application Ser. No. ______ for an invention entitled “High Photoefficiency Microalgae Bioreactors,” which are filed concurrently herewith and assigned to the same assignee as the present invention, and are hereby incorporated by reference. Another object of the present invention is to provide a recycling system for feeding oil harvesting byproducts back to the conduit where high oil content algae is grown. Still another object of the present invention is to provide a system for supplying nutrients to algae cells in the form of processed algae cell matter. Another object of the present invention is to provide a system for recycling the glycerin byproduct from the creation of biofuel as a source of carbon to foster further oil production in algae cells. Another object of the present invention is to provide a system for processing oil from algae that defines a flow path for continuous movement of the algae and its processed derivatives. Yet another object of the present invention is to provide a system and method for processing algae with high oil content that is simple to implement, easy to use, and comparatively cost effective. 
       SUMMARY OF THE INVENTION 
       [0006]    In accordance with the present invention, a system is provided for efficiently processing oil from algae. For this purpose, the system recycles byproducts of the process for use as nutrients to support algae cell growth and the cellular production of oil. Structurally, the system includes a chemostat that defines a conduit for growing algae cells. The chemostat&#39;s conduit includes input ports for feeding material into the conduit as well as an output port. Further, the system includes a plug flow reactor that defines a conduit for fostering oil production within the algae cells. For the present invention, the plug flow reactor has an input port that is positioned to receive material from the output port of the chemostat. 
         [0007]    In addition to the chemostat and plug flow reactor, the system includes an algae separator. Specifically, the algae separator is positioned in fluid communication with the plug flow reactor to remove the algae cells from the plug flow reactor&#39;s conduit. Structurally, the algae separator includes an outlet for the remaining effluence which is in fluid communication with the input port of the chemostat. Further, the system includes a device for lysing algae cells to unbind oil from the algae cells. For purposes of the present invention, the lysing device is positioned to receive algae cells from the algae separator. 
         [0008]    Downstream of the lysing device, the system includes an oil separator that receives the lysed cells and withdraws the oil from remaining cell matter. For purposes of the present invention, the oil separator has an outlet for the remaining cell matter which is in fluid communication with the input port of the chemostat. Further, the system may include a hydrolyzing device interconnected between the oil separator and the chemostat. In addition to the cell matter outlet, the oil separator includes an outlet for the oil. For the present invention, the system includes a biofuel reactor that is in fluid communication with the outlet for oil. In a known process, the biofuel reactor reacts an alcohol with the oil to synthesize biofuel and, as a byproduct, glycerin. Structurally, the biofuel reactor includes an exit for the glycerin that is in fluid communication with the input port of the plug flow reactor. 
         [0009]    In operation, algae cells are grown in the chemostat and are continuously transferred to the plug flow reactor. In the plug flow reactor, the algae cells increase the rate of intracellular oil production. Thereafter, the algae separator removes the algae cells from the remaining effluence in the plug flow reactor. The remaining effluence is diverted back to the chemostat to serve as a source of nutrition for the algae cells growing therein while the algae cells are delivered to the cell lysis device. At the cell lysis device, the cells are lysed to unbind the oil from the remaining cell matter. This unbound cell material is received by the oil separator from the cell lysis device. Next, the oil separator withdraws the oil from the remaining cell matter and effectively forms two streams of material. The stream of remaining cell matter is transferred to the hydrolysis device where the cell matter is broken into small units which are more easily absorbed by algae cells during cell growth. Thereafter, the hydrolyzed cell matter is delivered to the chemostat to serve as a source of nutrition for the algae cells growing therein. At the same time, the stream of oil is transmitted from the oil separator to the biofuel reactor. In the biofuel reactor, the oil is reacted with an alcohol to form biofuel and a glycerin byproduct. The glycerin byproduct is fed back into the plug flow reactor to serve as a source of carbon for the algae cells therein during the production of intracellular oil. 
       BRIEF DESCRIPTION OF THE DRAWINGS 
       [0010]    The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawing, taken in conjunction with the accompanying description, in which the Figure is a schematic view of the system for processing oil from algae in accordance with the present invention. 
     
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0011]    Referring to the Figure, a system for processing oil from algae in accordance with the present invention is shown and generally designated  10 . Specifically, in the system  10  byproducts of the processing method are recycled to foster growth of algae cells having high oil content. As shown, the system  10  includes a conduit  12  for growing algae cells with high oil content (exemplary cells depicted at  14 ). As further shown, the conduit  12  includes an upstream conduit section  16  that is defined by a continuously stirred first stage reactor or chemostat  18 . Also, the conduit  12  includes a downstream conduit section  20  that is defined by a plug flow second stage reactor  22 . As shown, each conduit section  16 ,  20  includes input ports  24   a - e.  Further, the upstream conduit section  16  includes an output port  26 . As shown, the output port  26  of the upstream conduit section  16  and the input port  24   c  of the plug flow reactor  22  are in fluid communication. In this manner, the conduit  12  passes through the chemostat  18  and the plug flow reactor  22 . 
         [0012]    As further shown in the Figure, the system  10  includes an algae separator  28  that is in fluid communication with the downstream conduit section  20  in the plug flow reactor  22 . For purposes of the present invention, the algae separator  28  removes algae cells  14  from the downstream conduit section  20 . As shown, the algae separator includes outlets  29   a  and  29   b.  Also, the system  10  includes a cell lysis device  30  that receives algae cells  14  from the outlet  29 a of the algae separator  28  via pipe  32 . As shown, the cell lysis device  30  is in fluid communication with an oil separator  34 . Specifically, a pipe  36  interconnects the cell lysis device  30  and the oil separator  34 . For purposes of the present invention, the oil separator  34  is provided with two outlets  38   a - b.  As shown, the outlet  38   a  is connected to a hydrolysis device  40  by a pipe  42 . Further, the hydrolysis device  40  is connected to the input port  24   b  in the upstream conduit section  16  of the chemostat  18  by a pipe  44 . 
         [0013]    Referring back to the oil separator  34 , it can be seen that the outlet  38   b  is connected to a biofuel reactor  46  by a pipe  48 . It is further shown that the biofuel reactor  46  includes two exits  50   a - b.  For purposes of the present invention, the exit  50   a  is connected to the input port  24   e  in the downstream conduit section  20  of the plug flow reactor  22  by a pipe  52 . Additionally or alternatively, the exit  50   a  may be connected to the input port  24   b  in the upstream conduit section  16  of the chemostat  18  by a pipe  54  (shown in phantom). As further shown, the exit  50   b  is connected to a pipe  56  which may connect to a tank or reservoir (not shown) for purposes of the present invention. 
         [0014]    Referring now to the algae separator  28 , it can be seen that the outlet  29   b  is in fluid communication with the input port  24   a  of the chemostat  18 . Further, a blowdown  57  is shown to be interconnected between the algae separator  28  and the input port  24   a.  Specifically, a pipe  59  connects the outlet  29   b  and the blowdown  57 , and a pipe  61  connects the blowdown  57  and the input port  24   a.    
         [0015]    In operation of the present invention, algae cells  14  are initially grown in the upstream conduit section  16  in the chemostat  18 . Specifically, a medium with a nutrient mix is continuously fed through input port  24   a  into the upstream conduit section  16  at a selected rate. Further, the conditions in the upstream conduit section  16  are maintained for maximum algal growth. For instance, in order to maintain the desired conditions, the medium and the algae cells  14  are moved around the upstream conduit section  16  at a fluid flow velocity in the range of approximately ten to two hundred centimeters per second, and preferably at fifty centimeters per second. Further, the amount of algae cells  14  in the upstream conduit section  16  is kept substantially constant. Specifically, the medium with nutrient mix is continuously fed into the input port  24   a  and an effluence  58  containing algae cells  14  is continuously removed through the output port  26  of the upstream conduit section  16  as overflow. Under preferred conditions, approximately ten grams of algae per liter of fluid circulate in the upstream conduit section  16 . Preferably, the residence time for algae cells  14  in the upstream conduit section  16  is about one to ten days. 
         [0016]    After entering the input port  24   c,  the effluence  58  containing algae cells  14  moves through the downstream conduit section  20  in the direction of arrows  60  in a plug flow regime. Preferably, the effluence  58  moves through the downstream conduit section  20  of the plug flow reactor  22  at a rate of between ten and two hundred centimeters per second. Further, as the effluence  58  moves downstream, a modified nutrient mix may be added to the downstream conduit section  20  through the input port  24   d.  This modified nutrient mix may contain a limited amount of a selected constituent, such as nitrogen or phosphorous. The absence or small amount of the selected constituent causes the algae cells  14  to focus on energy storage rather than growth. As a result, the algae cells  14  form triglycerides. 
         [0017]    At the end of the downstream conduit section  20 , the algae separator  28  removes the algae cells  14  from the effluence  58 . To facilitate this process, the depth of the downstream conduit section  20  may be increased near the algae separator  28 . The corresponding increase in the fluid flow cross-sectional area, and decrease in fluid flow rate, allows the algae cells  14  to settle to the bottom or float to the top of the conduit section  20 , depending on the oil content of the algae cells  14 . In certain embodiments, the modified nutrient mix may include a limited amount of a predetermined constituent to trigger flocculation of the algae cells  14  in the downstream conduit section  20 . The predetermined constituent may be the same as the selected constituent such that a shortage of nitrogen, for example, causes both the production of triglycerides and the flocculation of the algae cells  14 . 
         [0018]    After the algae cells  14  are removed from the conduit  12  by the algae separator  28 , the remaining effluence (indicated by arrow  63 ) is discharged from the algae separator  28  through the outlet  29   b.  As shown, the remaining effluence  63  passes through the blowdown  57  where impurities, such as salt, are removed. Then, additional nutrients (indicated by arrow  65 ) may be added to the remaining effluence  63  for replenishment to support further cell growth in the chemostat  18 . After being replenished, the remaining effluence  63  is fed back into the chemostat  18  through the input port  24   a.    
         [0019]    While the remaining effluence  63  is discharged through outlet  29   b,  the algae cells  14  removed by the algae separator  28  are delivered to the cell lysis device  30 . Specifically, the algae cells  14  pass through the outlet  29   a  and the pipe  32  to the cell lysis device  30  as indicated by arrow  60 . For purposes of the present invention, the cell lysis device  30  lyses the algae cells  14  to unbind the oil therein from the remaining cell matter. After the lysing process occurs, the unbound oil and remaining cell matter, collectively identified by arrow  62 , are passed through pipe  36  to the oil separator  34 . Thereafter, the oil separator  34  withdraws the oil from the remaining cell matter as is known in the art. After this separation is performed, the oil separator  34  discharges the remaining cell matter (identified by arrow  64 ) out of the outlet  38   a  and through the pipe  42  to the input port  24   b  of the chemostat  18 . 
         [0020]    In the chemostat  18 , the remaining cell matter  64  is utilized as a source of nutrients and energy for the growth of algae cells  14 . Because small units of the remaining cell matter  64  are more easily absorbed or otherwise processed by the growing algae cells  14 , the remaining cell matter  64  may first be broken down before being fed into the input port  24   b  of the chemostat  18 . To this end, the hydrolysis device  40  is interconnected between the oil separator  34  and the chemostat  18 . Accordingly, the hydrolysis device  40  receives the remaining cell matter  64  from the oil separator  34 , hydrolyzes the received cell matter  64 , and then passes hydrolyzed cell matter (identified by arrow  66 ) to the chemostat  18  through pipe  44 . 
         [0021]    Referring back to the oil separator  34 , it is recalled that the remaining cell matter  64  was discharged through the outlet  38   a.  At the same time, the oil withdrawn by the oil separator  34  is discharged through the outlet  38   b.  Specifically, the oil (identified by arrow  68 ) is delivered to the biofuel reactor  46  through the pipe  48 . In the biofuel reactor  46 , the oil  68  is reacted with alcohol, such as methanol, to create mono-alkyl esters, i.e., biofuel fuel. This biofuel fuel (identified by arrow  70 ) is released from the exit  50   b  of the biofuel reactor  46  through the pipe  56  to a tank, reservoir, or pipeline (not shown) for use as fuel. In addition to the biofuel fuel  70 , the reaction between the oil  68  and the alcohol produces glycerin as a byproduct. For purposes of the present invention, the glycerin (identified by arrow  72 ) is pumped out of the exit  50   a  of the biofuel reactor  46  through the pipe  52  to the input port  24   e  of the plug flow reactor  22 . 
         [0022]    In the plug flow reactor  22 , the glycerin  72  is utilized as a source of carbon by the algae cells  14 . Importantly, the glycerin  72  does not provide any nutrients that may be limited to induce oil production by the algae cells  14  or to trigger flocculation. The glycerin  72  may be added to the plug flow reactor  22  at night to aid in night-time oil production. Further, because glycerin  72  would otherwise provide bacteria and/or other non-photosynthetic organisms with an energy source, limiting the addition of glycerin  72  to the plug flow reactor  22  only at night allows the algae cells  14  to utilize the glycerin  72  without facilitating the growth of foreign organisms. As shown in the Figure, the exit  50   a  of the biofuel reactor  46  may also be in fluid communication with the input port  24   b  of the chemostat  18  via the pipe  54  (shown in phantom). This arrangement allows the glycerin  72  to be provided to the chemostat  18  as a carbon source. 
         [0023]    While the particular Photosynthetic Oil Production with High Carbon Dioxide Utilization as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.