Abstract:
A system and method for processing algae cells to create biofuel are disclosed. Specifically, the system and method utilize steam to rupture algae cells in order to utilize intracellular oil therein. The system includes a conduit for growing algae cells and a generator for creating steam. Further, the system includes a lysing device that mixes the algae cells and the steam to rupture the algae cells. In order to maximize the efficiency of the lysing process, the system may further include a heat exchanger for preheating the algae cells with the lysed cells. In addition, the system includes a bioreactor to synthesize biofuel from the unbound oil.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention pertains generally to processes for separating intracellular materials from one another. More particularly, the present invention pertains to a lysing system and method for rupturing cells to unbind intracellular material. The present invention is particularly, but not exclusively, useful as a system and method for separating intracellular oil from other cell matter in algae for use in the creation of biofuel from the intracellular oil. 
       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, biofuel such as biodiesel has been identified as a possible alternative to petroleum-based transportation fuels. In general, a 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 minimizing the costs associated with extracting plant oils. 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. However, the extraction of triglycerides from algae is typically not efficient and the associated costs 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 processing 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 “Transportable Algae Biodiesel System,” which is filed concurrently herewith, co-pending U.S. patent application Ser. No. 11/549,532 for an invention entitled “Photosynthetic Oil Production in a Two-Stage Reactor” filed Oct. 13, 2006, co-pending U.S. patent application Ser. No. 11/549,541 for an invention entitled “Photosynthetic Carbon Dioxide Sequestration and Pollution Abatement” filed Oct. 13, 2006, co-pending U.S. patent application Ser. No. 11/549,552 for an invention entitled “High Photoefficiency Microalgae Bioreactors” filed Oct. 13, 2006, and co-pending U.S. patent application Ser. No. 11/549,561 for an invention entitled “Photosynthetic Oil Production with High Carbon Dioxide Utilization” filed Oct. 13, 2006. All aforementioned co-pending U.S. patent applications are 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 system for efficiently separating intracellular materials in algae cells. Still another object of the present invention is to provide a system for harvesting oil from algae. Another object of the present invention is to provide a system for lysing algae cells to unbind intracellular oil. Another object of the present invention is to provide a system for processing oil from algae that utilizes live steam to rupture algae cells. 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 and method are provided for the creation of biofuel from oil in algae. In the system and method, algae cells are lysed to efficiently process the cells&#39; intracellular oil. For this purpose, the system utilizes steam to rupture algae cells and to unbind the intracellular oil. Structurally, the system includes a chemostat that defines a conduit for growing algae cells. 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 is positioned to receive material from 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. Further, the system includes a generator for creating steam. Also, the system includes a device for lysing algae cells to unbind oil from the algae cells. Specifically, the lysing device mixes live steam from the generator with the algae cells to rupture the cells. For this purpose, the lysing device is positioned to receive algae cells from the algae separator. 
         [0008]    For purposes of the present invention, the system also includes a heat exchanger for transferring heat between the heated outputs and the non-heated inputs of the lysis device. Specifically, the heat exchanger transfers heat from lysed cell material to algae cells that have not yet entered the lysis device. In this manner, heating costs are reduced. Also, the system includes a bioreactor for synthesizing biofuel from the unbound oil. 
         [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 rate of intracellular oil production in the algae cells is increased. After the algae cells have attained a high oil content, the algae separator concentrates the algae cells for removal from the plug flow reactor and delivers them to the cell lysis device through a pipe that passes through the heat exchanger. Then, the cell lysis device mixes live steam with the cells to rupture the cells and unbind the intracellular oil from the remaining cell matter. This unbound cell material is passed through the heat exchanger in order to preheat the incoming algae cells. Thereafter, the unbound intracellular oil is synthesized into biofuel by the bioreactor. 
     
    
     
       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 lysing algae cells in accordance with the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0011]    Referring to the FIGURE, a system for lysing algae cells in accordance with the present invention is shown and generally designated  10 . Specifically, in the system  10 , steam is used to efficiently lyse algae cells to facilitate the use of intracellular oil. As shown, the system  10  includes a conduit  12  for growing algae cells  14  with high oil content. 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 . In this manner, the conduit  12  passes through the chemostat  18  and the plug flow reactor  22 . For purposes of the present invention, the conduit  12  is provided with ports  23   a  and  23   b  for receiving input materials into the upstream conduit section  16  and the downstream conduit section  20 , respectively. 
         [0012]    As further shown in the FIGURE, the system  10  includes an algae separator  24  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 cells  14  are concentrated in the downstream conduit section  20  to form an algae cell concentrate  25 . Further, the algae separator  24  removes the algae cell concentrate  25  from the downstream conduit section  20 . Also, the system  10  includes a cell lysis device  26  that receives algae cell concentrate  25  from the algae separator  24  via pipe  28 . In the present invention, the pipe  28  passes through a heat exchanger  29  for preheating as is more fully explained below. 
         [0013]    As shown, the cell lysis device  26  is connected in fluid communication with a steam generator  30  via a pipe  32 . Also, the cell lysis device  26  is shown to be in fluid communication with an oil separator  34 . Specifically, a pipe  36  interconnects the cell lysis device  26  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  that passes through a filter  44 . Also, the pipe  42  passes through the heat exchanger  29  to transfer heat to the pipe  28 . For the present invention, the filter  44  is connected directly to the downstream conduit section  20  by a pipe  46 . Further, the hydrolysis device  40  is connected to the upstream conduit section  16  of the chemostat  18  by a pipe  48 . 
         [0014]    Referring back to the oil separator  34 , it can be seen that the outlet  38   b  is connected to a biofuel reactor  50  by a pipe  52  that passes through the heat exchanger  29  to transfer heat to the pipe  28 . It is further shown that the biofuel reactor  50  includes two exits  54   a - b.  For purposes of the present invention, the exit  54   a  is connected to the downstream conduit section  20  of the plug flow reactor  22  by a pipe  56 . Additionally or alternatively, the exit  54   a  may be connected to the upstream conduit section  16  of the chemostat  18  by a pipe  58 . As further shown, the exit  54   b  is connected to a pipe  60  which may connect to a tank or reservoir (not shown) for purposes of the present invention. 
         [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  62   a  is continuously fed into the upstream conduit section  16  through the port  23   a  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  62   a  and the algae cells  14  are moved around the upstream conduit section  16  at a preferred fluid flow velocity of approximately 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  62   a  is continuously fed into the upstream conduit section  16  through the port  23   a  and an effluence  64  containing algae cells  14  is continuously removed from the upstream conduit section  16  as overflow. Under preferred conditions, approximately one to 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 five days. 
         [0016]    After entering the downstream conduit section  20 , the effluence  64  containing algae cells  14  moves in a plug flow regime. Preferably, the effluence  64  moves through the downstream conduit section  20  of the plug flow reactor  22  at a rate of between ten and one hundred centimeters per second. Further, as the effluence  64  moves downstream, a modified nutrient mix  62   b  may be added to the downstream conduit section  20  through the port  23   b . This modified nutrient mix  62   b  may contain a limited amount of a selected constituent, such as nitrogen or phosphorous. Alternatively, no further material may be added through the port  23   b  and selected constituents in the effluence  64  may be exhausted. 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 cells  14  form the algae cell concentrate  25  that the algae separator  24  removes from the effluence  64 . To facilitate this process, the depth of the downstream conduit section  20  may be increased near the algae separator  24 . 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 of the conduit section  20  forming the algae cell concentrate  25 . In certain embodiments, the modified nutrient mix  62   b  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  to form the concentrate  25 . 
         [0018]    After the algae cell concentrate  25  is removed from the conduit  12  by the algae separator  24 , it is delivered to the cell lysis device  26 . As shown, the algae cell concentrate  25  passes through the pipe  28  (and through the heat exchanger  29 ) to the cell lysis device  26  as indicated by arrows  66 . For purposes of the present invention, the cell lysis device  26  lyses the algae cells  14  in the algae cell concentrate  25  to unbind the oil therein from the remaining cell matter. Specifically, steam (identified by arrow  68 ) created by the steam generator  30  is delivered to the lysis device  26  through pipe  32 . Inside the lysis device  26 , the live steam  68  is directly mixed with the algae cell concentrate  25  causing cell lysis and an increase in temperature and water content of the (now ruptured) algae cells  14  within the concentrate  25 . Preferably, the amount of steam utilized is between about 2-20% of the mass of the incoming algae cell concentrate  25 , and most preferably about 5%. In other words, the mass flow rate of the steam M S  is approximately 2-20%, and more preferably approximately 2-5% of the mass flow rate of the algae cell concentrate M A . Further, the steam  68  preferably is at a pressure of about 3-5 bar. 
         [0019]    After the lysing process occurs, the unbound oil and remaining cell matter, collectively identified by arrow  70 , 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  72 ) out of the outlet  38   a  and through the pipe  42 , with the remaining cell matter  72  eventually reaching the chemostat  18 . As shown, the remaining cell matter  72  passes through the heat exchanger  29  in order to transfer heat to the algae cell concentrate  66  in the pipe  28 . 
         [0020]    In the chemostat  18 , the remaining cell matter  72  is utilized as a source of nutrients and energy for the growth of algae cells  14 . Because small units of the remaining cell matter  72  are more easily absorbed or otherwise processed by the growing algae cells  14 , the remaining cell matter  72  may first be broken down before being fed into 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  72  from the oil separator  34 , hydrolyzes the received cell matter  72 , and then passes hydrolyzed cell matter (identified by arrow  74 ) to the chemostat  18  through the pipe  48 . Alternatively, large units  76  of the remaining cell matter  72  may be removed from the pipe  42  by the filter  44 . These large units  76  of cell matter  72  are delivered to the downstream conduit section  20  through the pipe  46  to be used as a flocculation aid. 
         [0021]    Referring back to the oil separator  34 , it is recalled that the remaining cell matter  72  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  78 ) is delivered to the biofuel reactor  50  through the pipe  52 . In order to efficiently utilize the energy contained in the heated oil  78 , the oil  78  passes through the heat exchanger  29  and transfers heat to the algae cells  66  in the pipe  28 . In the biofuel reactor  50 , the oil  78  is reacted with alcohol, such as methanol, to create mono-alkyl esters, i.e., biodiesel. This biodiesel (identified by arrow  80 ) is released from the exit  54   b  of the biofuel reactor  50  through the pipe  60  to a tank, reservoir, or pipeline (not shown) for use as fuel. In addition to the biodiesel  80 , the reaction between the oil  78  and the alcohol produces glycerin as a byproduct. For purposes of the present invention, the glycerin (identified by arrow  82 ) is pumped out of the exit  54   a  of the biofuel reactor  50  through the pipe  56  to the plug flow reactor  22 . 
         [0022]    In the plug flow reactor  22 , the glycerin  82  is utilized as a source of carbon by the algae cells  14 . Importantly, the glycerin  82  does not provide any nutrients that are otherwise being kept at a limited amount to induce oil production by the algae cells  14  or to trigger flocculation. Preferably, the glycerin  82  is added to the plug flow reactor  22  at night to aid in night-time oil production. Further, because glycerin  82  would otherwise provide bacteria and/or other non-photosynthetic organisms with an energy source, limiting the addition of glycerin  82  to the plug flow reactor  22  only at night allows the algae cells  14  to utilize the glycerin  82  without facilitating the growth of foreign organisms. As shown in the FIGURE, the exit  54   a  of the biofuel reactor  50  may also be in fluid communication with the chemostat  18  via the pipe  58  (shown in phantom). This arrangement allows the glycerin  82  to be provided to the chemostat  18  as a carbon source. 
         [0023]    As discussed above, the heat exchanger  29  provides for the transfer of heat between the heated outputs and the non-heated inputs of the lysis device  26 . As shown, the algae cell concentrate  25  flows from the algae separator  24  to the lysis device  26  through the pipe  28  which passes through the heat exchanger  29 . Typically, the algae cell concentrate  25  enters the heat exchanger  29  at a temperature of about 20° C. At the same time, lysed cells in the form of unbound oil and remaining cell matter  70  flow through the heat exchanger  29 . Specifically, the remaining cell matter  72  and the oil  78  flow through the heat exchanger  29  in pipes  42  and  52 , respectively. Preferably, the remaining cell matter  72  and oil  78  have a temperature of about 100° C. upon entering the heat exchanger  29 . After heat is transferred between the pipes  42  and  52  and the pipe  28 , the algae cell concentrate  25  exits the heat exchanger  29  at a temperature of about 80° C., while the remaining cell matter  72  and oil  78  exit the heat exchanger  29  at a temperature of about 40° C. While the FIGURE illustrates a system  10  in which the remaining cell matter  72  and oil  78  are separated before passing through the heat exchanger  29 , it is contemplated that the heat exchange could be performed before the oil separation process. However, it is noted that separation before cooling can reduce the tendency for the formation of an emulsion in the unbound oil and remaining cell matter  70 . 
         [0024]    While the particular High Efficiency Separations to Recover Oil From Microalgae 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.