Continuous flow method and apparatus for making biodiesel fuel

Abstract

In an economical and efficient process and apparatus for producing biofuel from waste oil, such as vegetable oils and animal fats, waste oil is esterified with alcohols to produce alcohol esters and the by-products of the transesterification reaction are recovered. Static pressure may be used as well as continuous flow-through reaction vessels and separation tanks without the need for additional pumps. There may also be specialized reaction tanks that have vertical rotating feed tubes having separators and inlet and outlet openings. The method and device achieves efficient production of biofuel while employing reaction and mixing tanks having a limited size, which in turn permits a smaller plant layout or “footprint”. For example, the largest tank may be in a size of about 36/100,000 times the desired plant output in gallons per year. The benefits of the process and apparatus include minimal space for a plant; minimal on-site feedstock needed therefore minimal on-site storage is needed; minimal capital costs to build a plant e.g., reduction by about fifty to sixty five percent (50 to 65%); reduction in construction time from typically over one year to under three months in many plants; minimal energy usage, e.g., reduction by about sixty percent (60%); minimal labor costs due to the automatic continuous flow; minimal pumps needed thereby reducing pump operation and maintenance costs; environmentally friendlier and safer plant design; and due to smaller plant footprint, lower capital cost and minimal construction time enables site selection much nearer to the raw material supplies, thereby minimizing or even eliminating transportation costs for yellow grease or vegetable oil.

Description

CROSS-REFERENCE

This application claims the priority of previously filed U.S. provisional patent application Ser. No. 60/317,090 filed Sep. 4, 2001, incorporated by reference herein.

BACKGROUND OF THE INVENTION

1 . Field of the Invention

The present invention is directed to a process and apparatus for producing “biofuel” from oil or waste oil such as “yellow grease” (also known as tallow or used oil from food).

2. Description of the Related Art

A number of approaches have been taken to produce “biofuels” from waste oils or “yellow grease” (also known as tallow or used oil from food). These greases include fat grease, chicken fat, and vegetable oils. Generally, the method involves obtaining a fatty acid alkyl ester by transesterification of monoglycerides, diglycerides and triglycerides with alkyl alcohol. For example, the yellow grease may be heated and then mixed with sulfuric acid and methanol in a large tank or reaction vessel. The acid and methanol break down long chain molecules (“fatty acid reduction”). That is, the methanol reacts with the fatty acid in the oil and produces a methyl ester material. After mixing in the reaction vessel, the mixture is pumped into a large settling tank. The methanol and sulfuric acid settle to the bottom, and the treated yellow grease is at the top. The bottom material is recycled.

The oil is then pumped to an unloading tank, reheated, and then mixed with potassium hydroxide and more methanol in a second reaction vessel. The material is mixed for a period of time, e.g., one hour and undergoes “esterification.” A slight excess of caustic alcohol may be added. The mixture is then pumped into a second settling tank. Again, the treated oil, now “ester,” is separated from the top, and glycerol and more fatty acid soap are settled at the bottom of the tank. This process uses extremely large tanks, e.g., thousands of gallons. It takes a very long time, e.g., ten (10) to twelve (12) hours or more to empty a 10,000 to 12,000 gallon tank. Further, the footprint of a plant that is sized for a million gallons of biodiesel fuel per year is about one to one and a half acres (40,000 to 60,000 sq ft) to accommodate large reactors and multiple settling tanks, collectively totaling 60,000 to 100,000 gallons in capacity. The plant runs twenty four (24) hours and requires a lot of labor, pumps and heating equipment. Because of the need for settlement in the multiple settlement tanks, the industry does not consider a continuous flow process. Due to such large tanks and handling time, it is difficult to control the temperature of the tank's contents. The tank's contents cool during lengthy unloading and settling processes, and the temperature of the contents vary in such large tanks. A number of approaches have thus been taken to optimize the reaction and process.

U.S. Pat. No. 5,972,057 (Hayafuji et al.), for example, incorporates an initial pre-mixing step wherein the alkaline catalyst is completely dissolved in the alcohol before adding the alcohol and catalyst to the oil rather than mixing the catalyst, alcohol and oil together in the same tank simultaneously. According to the '057 patent, the pre-mixing step accelerates the reaction such that the oil reaches an equilibrium conversion rate of 99% in 1.0 minute or less at a reaction temperature of 60° C., and at a stirring speed of 300 rpm. As noted in the '057 patent, conventional methods would produce an equilibrium conversion rate of 96% in thirty minutes or more under the same conditions.

The method disclosed in the '057 patent, however, requires that the heat of dissociation generated at the time of dissolving the catalyst in the alcohol be removed by heat exchange between cooling water and the catalyst-containing alcohol solution. This is accomplished by placing a cooling water jacket on the outside of the dissolving and stirring tank. Further, the supply speed of the catalyst to the dissolving and stirring tank is controlled so that the temperature of the catalyst solution does not exceed 64° C. If the supply speed of the catalyst is too high, the generated heat of dissolution is not removed in time and creates a hazard.

U.S. Pat. No. 5,424,467 (Bam et al.) discloses a method for producing purified alcohol esters and a method for recovering the by-products of transesterification. In general terms, the process involves reacting an alcohol and a triglyceride in the presence of a catalyst and separating out a first phase, which includes the alcohol ester, unreacted alcohol and catalyst, from a second heavier phase comprising a by-product such as glycerin, un-reacted alcohol and catalyst. The second heavier phase is then treated to separate glycerin from un-reacted alcohol and catalyst, and the first phase is treated to separate out glycerin and catalyst from the alcohol ester. The transesterification reaction is catalyzed by bases such as sodium hydroxide, or by acids such as sulfuric acid, which are mixed with the alcohol prior to reaching the reaction vessel.

According to the invention disclosed in the '467 patent, an excess of alcohol in the transesterification reaction is used to effect separation of the resulting ester phase from the alcohol phase without further treatment of the reaction mixture. In one embodiment, for example, the alcohol is introduced in a ratio ranging from 7% to 40% by weight based upon the amount of oil used. The catalyst is added in an amount ranging from about 0. 1% to 2.0% by weight based upon the amount of oil used. If sufficient excess alcohol is not employed, it may be necessary to add more alcohol to initiate the phase separation, which would result in larger equipment sizes being required to handle the increased volume.

U.S. Pat. No. 6,015,440 (Noureddini et al.) recognizes that the use of biodiesel fuel is limited in practice due to adverse cold temperature properties such as viscosity, ‘pour point’ and ‘cloud point’, and discloses a method for producing a biodiesel fuel with reduced viscosity and a cloud point below 32° F. The process utilizes potassium hydroxide and methanol to transesterify triglycerides from animal or vegetable origin. Once transesterification occurs, the mixture of crude glycerol and biodiesel fuel esters are subjected to an etherification process, which produces a mixture of ethers of glycerol and biodiesel esters. This mixture is then recombined with pure biodiesel fuel to form an ‘oxygenated’ biodiesel fuel with a cloud point reduced to approximately 20° F.

SUMMARY OF THE INVENTION

In one embodiment, the present invention achieves continuous flow through all the reaction vessels and separation tanks without the need for additional pumps. The invention preferably employs preferably closed tanks (though preferably not sealed) to provide for methanol recovery, and may include vertical rotating feed tubes having separators and inlet and outlet openings. These features permit production of a larger quantity of biodiesel fuel while employing reaction and mixing tanks having a limited size, which in turn permits a dramatically smaller plant layout or “footprint”. Further, the process preferably pre-mixes the catalyst and methanol, but does not require pre-mixing prior to adding the catalyst to the oil or a means for actively removing heat from the system.

In one embodiment, the process comprises the steps of providing waste oil at a starting temperature of about 50° F. to 150° F., mixing it with a catalyst and alcohol, such as sulfuric acid and methanol, and passing the mixture through a heating means to promote the reaction of methanol and sulfuric acid with the oil to produce methyl ester material. The methanol and sulfuric acid may be fed back to the pump for re-use.

The oil or “yellow grease” is preferably provided to the system using a means for controlling the flow rate of the grease. For example, a chemical mixing pump may be employed to pump at a desired flow rate, e.g. 2 gpm, through a heat exchanger to reach a temperature of about 160° F. The mixture is then directed to a first reaction vessel (“RV1”), preferably through a rotating central pipe. The pipe may be rotated by a motor, chain and sprocket configuration and comprises blades and upper and lower perforations that permit the reaction mixture to flow into and out of separate chambers within RV1. It is desireable to maintain a temperature of 140 to 155° F. homogeniously. This is very difficult to do in large tanks without incorporating very expensive heating and cooling units.

The reaction mixture flows next to a first separation tank (“ST1”). Flow through the tanks and reaction vessels is preferably set up to be continuous due to level differentials, thus the flow coming to ST1 from RV1 is relatively hot (e.g. 140° F.), and RV1 and ST1 may be insulated to help maintain the heat. Sulfuric acid and methanol are heavier than the oil and flow out of the bottom of ST1, while the oil flows out near the top of ST1 and to a second reaction vessel (“RV2”). The oil may be passed through a heating means after it exits ST1 so that it is close to 150° F. to 180° F. when it enters RV2.

Potassium hydroxide and additional methanol are added to the oil in RV2. RV2 may be identical to RV1, but is preferably shorter to maintain static pressure continuous flow and since the reaction time in reactor RV2 is approximately half of the reaction time required for RV1, the plant design lends itself to a smaller RV2 which may thus be shorter in height than RV1 to perfectly accommodate the difference in height needed for static flow through-processing. Likewise, ST2 may be identical to ST1, but is preferably shorter and has an input level lower than the liquid level in RV2. In ST2, oil and glycerol separate, and the ester is sent to a means for removing additional methanol and glycerol, such a water centrifuge.

In at least one embodiment, the present invention is to provide an economical process and apparatus for obtaining biofuel from waste oil or oil byproducts.

In at least some embodiments, the present invention produces biofuel using as continuous flow process.

The present invention may also provide an efficient method and apparatus for producing biofuel in large quantities while simultaneously permitting reduced tank size and plant footprint in comparison to prior plants for producing the same quantity.

In at least some embodiments, static pressure is used to move the flow from one tank or vessel to successive tanks or vessels in a continuous flow manner.

According to another aspect of the invention, a novel mixing tank is formed by a housing, multiple vertical chambers, mixing blades and a rotating input pipe passing through all of the chambers.

In a further embodiment, a novel input pipe has inlet and outlet openings, mixing blades and structure to rotate the blades.

In another embodiment of the invention, a plant for the production of biofuel has a first and a second reaction vessel and a first and a second separation tank located in a two by two layout.

In another embodiment of the present invention, a method and an apparatus are provided for the production of biofuel wherein the apparatus and method produce about one million or more gallons per year from four tanks, with the largest tank having a capacity of about 360 gallons.

These and other objects and advantages of the present invention will be apparent from a review of the following specification and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of the steps, using schematic views of a preferred plant structure, for producing biofuel according to a preferred embodiment.

FIG. 2 is a cross sectional view of a tank RV1 and its input pipe used in a plant and process of FIG. 1.

FIG. 3 is a cross sectional view of a tank ST1 used in a plant and process of FIG. 1.

FIG. 4 is a side view schematic of the height differentials and configuration of the tanks and vessels used in a plant and process of FIG. 1.

FIG. 5 is a cross sectional view of the input pipe for RV1 or RV2 of FIG. 1.

FIG. 6 is a top view of the plant layout and flow direction used in a plant and process of FIG. 1.

FIG. 7 is a plane view of an exemplary biofuel plant of a first floor of a two story plant in accordance with a second embodiment of the invention.

FIG. 8 is a plane view of a second floor in the exemplary biofuel plant of FIG. 7.

FIG. 9 is a sectional view taken along a line A-A of the first and second stories of the plant of FIG. 7.

FIG. 10 is a sectional view taken along a line B-B of the first and second stories of the plant of FIG. 7.

FIG. 11 is a schematic flow diagram of a biodiesel plant in accordance with a third embodiment of the invention.

FIG. 12 is a schematic side elevation view of a stage A mixing vessel.

FIG. 13 is a schematic partial top view of the mixing vessel of FIG. 12 showing a cover thereof.

FIG. 14 is a schematic top view and sectional view of the mixing vessel of FIG. 12 showing a stand and details of a water jacket for the mixing vessel.

FIG. 15 is a schematic side elevation view of a stage A settling tank.

FIG. 16 is a schematic partial top view of the settling tank of FIG. 15 showing a cover thereof.

FIG. 17 is a schematic top view and sectional view of the settling tank of FIG. 16 showing a stand and details of a water jacket for the mixing vessel.

FIG. 18 is a schematic side elevation view of a stage B mixing vessel.

FIG. 19 is a schematic partial top view of the mixing vessel of FIG. 18 showing a cover thereof.

FIG. 20 is a schematic top view and sectional view of the mixing vessel of FIG. 18 showing a stand and details of a water jacket for the mixing vessel.

FIG. 21 is a schematic side elevation view of a stage B settling tank.

FIG. 22 is a schematic partial top view of the settling tank of FIG. 21 showing a cover thereof.

FIG. 23 is a schematic top view and sectional view of the settling tank of FIG. 21 showing a stand and details of a water jacket for the mixing vessel.

FIG. 24 is a schematic view of a variation of a separator in the reaction vessel RV1 (or RV2) of FIG. 2.

FIG. 25 is a schematic view of another embodiment of a reaction vessel and settling tank, with a hot water jacket and a pressure maintaining apparatus.

FIG. 26 is a schematic view of another embodiment of a reaction vessel.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The detailed description set forth below in connection with the appended drawings is intended as a description of presently-preferred embodiments of the invention and is not intended to represent the only forms in which the present invention may be constructed and/or utilized. The description sets forth the functions and the sequence of steps for constructing and operating the invention in connection with the illustrated embodiments. However, it is to be understood that the same or equivalent functions and sequences may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention.

In one embodiment, the invention comprises a continuous flow process for extracting oil from yellow grease, e.g., for making biodiesel fuel, and an apparatus for such process. The invention may be described, with reference to FIGS. 1-5, as follows:

Yellow grease, preferably at a starting temperature of about 50° F. to 150° F., is mixed with an alcohol and catalyst, such as sulfuric acid and methanol. The yellow grease is preferably provided to the system using a means for controlling the flow rate of the grease. For example, a chemical mixing pump may be employed to pump at a desired flow rate, e.g. 2 gpm, through a heat exchanger to reach a temperature of about 160° F., which promotes the reaction of the H₂S and methanol with the yellow grease to produce the methyl ester material. The sulfuric acid and methanol may be fed back and reused at the pump.

In the first reaction vessel, RV1, the H₂S and methanol enter through a centrally located pipe. The pipe is preferably rotated, e.g. by a motor using a chain and sprocket, and has blades on it, e.g., two or more. Where there are two blades, e.g., the pipe may be turned at approximately 120 RPMs, while four blades would preferably be turned slower. The blades may be flat or curved. It is preferable to keep the liquid in the tank as long as possible, so a blade tending to send liquid out and/or up is preferable. The blade may have a scoop on the end to help lift liquid away from the wall. The pipe is preferably 2½″ to 3″ in diameter and has perforations, as shown in FIG. 2. The upper perforation in each chamber (shown with a dot inside in FIG. 2) is an inlet of liquid into the chamber, preferably above the blades. The pipe is blocked off at or just above the blade. There is also a perforation (shown with an “x” in FIG. 2) below the blades for output flow from the chamber to the next one. Preferably, these holes are on opposite sides of the pipe. The pipe in tanks RV1 and RV2 may be formed by tack welding four 2½″ pipe sections, each with one closed end inside the larger 3″ pipe. The holes for inlet and outlet may then be drilled in the two pipes where needed.

RV1 is divided into chambers, e.g., four chambers using separators. The separators preferably attach to the central pipe in a liquid tight manner, and are angled slightly up. At the outer periphery, the separators preferably meet a rubber ring to help prevent fluid flow downward between the tank wall and the separators. The mixture eventually flows out the lower hole (with the “x” as shown in FIG. 2), into the pipe, then out the upper hole in the next lower chamber (chamber 2), and so on. Flow reaching the bottom of RV1 and the bottom of the pipe flows through an elbow and up to the inlet at the top of the first separating tank ST1. The flow is continuous due to the pump continuously sending liquid at the flow rate into RV1, and the static pressure from the liquid level of RV1 being sufficiently higher than the highest level of the input to ST1, by a distance A. See FIG. 4. Flow through remaining tanks ST1, RV2 and ST2 is also set up to be continuous due to level differentials B, C and D, respectively, as shown in FIG. 4.

The volume of RV1 is preferably 360 gallons, for a flow rate of 2 gpm. In such a system, it would take liquid going into tank RV1 three hours to pass through the tank. Since the reaction time in RV1 is preferably about two hours, and since the chambers are designed to keep liquid swirling upward, it is expected that it is very likely that only an insignificant amount of liquid will pass through the system in less than two hours. It should also be noted that much of any such liquid will still be reacted roughly to a percentage equal to the percentage of two hours that the liquid was in the tank, i.e.: $\text{Percent Reacted Liquid}=\frac{\mathrm{Actual}\mathrm{Time}\mathrm{In}\mathrm{RV}}{\mathrm{Two}\mathrm{Hours}}$

Because there are four separate chambers in the reactor, the liquid must pass from one chamber to the other in equal amounts depending on the feed rate at the top. Liquid can not pass from one chamber to the next and commingle. In other words, new liquid entering a tank will not mix with liquid that has been in the tank for a long time thus ensuring a reaction time of at least two hours for at least 90 to 95% of all liquid. The balance of the liquid with less than two hours reaction time will still be partially reacted. Therefore, there is only a small amount of unreacted liquid that will pass through the system. Any such unreacted biofuel is liquid will end up in the glycerin, which may also be sold. This is a relatively small loss, and is insignificant compared to the many benefits of the continuous flow process.

The reaction mixture next flows to a first settling tank, ST1. Sulfuric acid and methanol, which are heavier than oil, eventually separate from the oil and flow out the bottom of ST1. ST1 preferably includes a deflector located just below the outlet hole of the inlet pipe to help the liquid disperse and also to help prevent liquid from flowing out of the tank before the sulfuric acid and methanol and oil separate. Because the invention uses a continuous flow process, the liquid flowing from RV1 is relatively hot, e.g., 140° F. RV1 and ST1 may be insulated tanks, to help maintain the heat. At temperatures of about 110° F. and up, the oil and sulfuric acid and methanol in tank 1 and glycerol in tank ST2 separation will occur almost immediately. Moreover, the first tank may also have a hot water jacket, preferably of about 1½″ to 2″, and a hot water heater may supply the water jacket. This however, is generally not necessary, since at about 140° F., the input is sufficiently above 110° F. such that the separation is fast. Where a water jacket is employed, the water out from the bottom of the jacket may be returned to the heater and then back to the top of the jacket at about 160° F. A conventional standard water heater may be used, such as a 50-gallon water heater with a recovery rate of about 75 gallons per hour. The tanks may be insulated instead of or in addition to the use of the heater, and insulating may also be provided around a water jacket.

Next, the oil flows out near the top of ST1 and goes to RV2. It may be returned to the heat exchanger (or the flow may be directed through a second heat exchanger) before entering tank RV2 so that it is preferably at or close to 160° F., or is preferably at least about 150° F. This is a good temperature for the reactions in RV1 and RV2. In RV2, potassium hydroxide and additional methanol is added to the oil. RV2 may be identical to RV1, but is preferably shorter to maintain the static pressure continuous flow (See FIG. 4.) Likewise, ST2 may be identical to ST1, but is preferably shorter and has its input level disposed at a position lower than the liquid level in RV2. A sufficient drop between the liquid level of one tank and the input level of the next tank is expected to be about two feet. (A, B, C and D equal two feet in FIG. 4.) The flow is next directed to a second separation tank, ST2. Glycerol and oil (ester) separation in ST2 is fast at over 110° F., especially since glycerol has an sg of about 1.05 and biofuel has an sg of about 0.85. After ST2, the oil (ester) is sent to a water centrifuge, as is conventional in the art, to remove more methanol and glycerol.

Settling times in ST2 must be considered depending on crude oil feed to the plant. In practice, soybean oil and three different types of yellow grease feed have exhibited settling times of less than one hour at temperatures between 120 and 140° F. However, other feed stocks, such as heavier greases and tallow may require longer settling times. To provide for greater settling times without changing the flow rate through the system, the continuous flow settling tank for stage B can be significantly increased by simply increasing the diameter of the tank only a relatively small amount. For example, a diameter increase of six (6) inches from twenty four (24) inches to thirty (30) inches increases settling time by over fifty percent (50%) and has little or no impact on the plant's overall design. If the biodiesel still contains a significant amount of glycerin, the glycerin may be centrifuged as is well known in the art. Or, an additional settling tank or additional settling tanks may be added, preferably in parallel. In addition, a coalescing agent may be used as is well known in the art.

All four tanks RV1, ST1, RV2, ST2 may be about 2′ in diameter, and may comprise a 1½″ to 2″ water jacket and 1½″ to 2″ of insulation. Each of the four tanks may be supported on a four foot by four foot stand, four feet high, to provide a footprint of 8′×8′ (See FIG. 6). If desired or necessary, an additional reaction vessel may be plumbed in series with RV1 and/or RV2 to ensure complete reactions, especially if the flow rate is increased. The tanks preferably are not sealed, and are preferably vented. All of the tanks preferably have level indicators. It is expected that at 2 gpm, over one million gallons a year can be produced from a set of four tanks, with the largest tank being about 360 gallons instead of 17,000 gallons.

An example of a plant designed for a two story building is shown in FIGS. 7-10. It uses the process and apparatus described with reference to FIGS. 1-6, or it may use the process as shown in FIG. 11, or as shown and described with respect to FIGS. 12 et seq. Three sets of four tanks are provided in FIG. 7. In the first rectangular group of six tanks shown, the first set of four tanks is shown in a two by two arrangement plumbed in series going clockwise, starting from the top left of the rectangle, i.e., A1 mixer, A2 settlor, B1 mixer, B2 settlor. The next group of four tanks is also plumbed in series clockwise, but is split somewhat due to the existing building structure, i.e., C1 mixer, C2 settlor, D1 mixer, D2 settlor. The last group of four tanks is shown as the four tanks in a two by two array at the right side of the second rectangle, i.e., E1 mixer, E2 settlor, F1 mixer, and F2 settlor. In the plant, it is envisioned that preferably the methanol and sulfuric acid will be pumped from separate sources into mixing tanks (in the explosion proof rooms), and the contents of the mixing tanks will simultaneously be pumped into the A stage reactors (A1, C1 and E1, respectively), achieving continuous flow of the methanol and acid mixture too. This is distinct from the concept of batch mixing of the catalyst.

The plant of FIG. 7 has three sets of four tanks. Using just one set of tanks, with the 2 gpm flow rate and the tank corresponding to the first reaction vessel RV1, i.e., tank A1, having a 360 gallon capacity, the annual output of biofuel is expected to be about 1.3 million gallons. If two sets of tanks are used, the output is expected to be about 2.6 million gallons. If three sets of tanks are used, the output is expected to be about 3.9 million gallons.

The plant is divided into the following areas:

• 1. Feedstock storage
• 2. Alcohol/acid catalyst mixing
• 3. Alcohol/basic catalyst mixing
• 4. Stage A
• 5. Stage B
• 6. Heating
• 7. Washing
• 8. Product Storage
• 9. Systems controller (PLC or PC based)
• 10. Vapor Recovery System
  Theory of Operation

Crude oils, typically vegetable oils or grease, specifically yellow grease, are reacted in an esterification/transesterification reaction to produce methyl and ethyl esters suitable for combustion in a diesel engine. This product is generically referred to as biodiesel, having similar boiling points and density as conventional diesel. The National Biodiesel Board currently defines specifications for this product. The primary reaction for biodiesel is the conversion of triglycerides into an ester having the desired characteristics as mentioned above. This is accomplished via a transesterification reaction where the raw oils are reacted with a C₁ to C₄ alcohol, e.g. methanol, in the presence of a basic catalyst, e.g. potassium or sodium hydroxide. The base catalyst and the alcohol produce a sodium or potassium methoxide, which in turn is reacted with the raw oils and allowed to settle. Glycerin forms on the bottom, while the methyl esters float to the top. This reaction is generally carried out with an amount of alcohol in excess of stochiometric conditions so that the bias of the reaction is directed towards the production of esters and glycerin.

In the case of greases, the presence of free fatty acids (FFA) in the grease inhibits the reaction and form undesirable side chain reactions. This requires that the FFA content be reduced prior to transesterification reaction. This is generally achieved by an esterification reaction where a strong acid such as sulfuric acid is used as a catalyst and is added to a C₁ to C₄ alcohol, which in turn is reacted with the raw oils. As is the case with the transesterification reaction, an excess of alcohol is used to forward the bias of the reaction towards the production of methyl esters.

After the production of glycerin and methyl esters, the esters must be washed to separate them from any residual glycerin not separated, the catalyst, any water, particulates, etc. prior to the esters being suitable for a certified biodiesel product.

Conventional methodology calls for a batch operation to carry out each phase of the production. As will be described in greater detail below, the design of this plant is to carry out the reactions in a continuous operation, eliminating necessary downtime while allowing the slowest portion of the batch operation to conclude, reduces wear and tear of the equipment in startup/shutdown procedures, allows for a downsizing of required vessels, and allows for the correction of production problems without having to discard of a failed batch.

The size of the plant described is for an 5.5-gpm throughput, resulting in approximately 2.8 million gallons per year throughput.

Feedstock Storage

Crude Oil: The capacity of crude oil on hand at any given time should be of sufficient volume so as not to impede production, should delays in delivery be incurred. For a 5.5 gpm throughput, a desired tank size would be 25,000 gallons, thereby providing a three day supply of feedstock. A suitable alternative would be to feed the oil or grease directly from its production to the plant, thereby capturing for use any residual temperature as a result of initial processing. The tradeoff for this energy saving approach would be that a loss of production of the oils or grease would halt the production of biodiesel. The crude oil tank would also consist of the following peripheral equipment:

• • One level indicator. An electronic transducer and a mechanical level indicator are desired.
  • One Positive Displacement (PD) pump capable of the nominal throughput of 5.5 gpm. Note: It is believed that the continuous operation may allow for a greater throughput than is initially designed. In addition, it may be desirable to decrease throughput without having to shut the plant down. Therefore it would be desirable to be able to turn down the throughput of a 12 gpm PD pump through the use of a variable speed AC motor.
  • One flow meter capable of handling a fluid with the viscosity of yellow grease in a slightly acidic environment (FFA content anticipated to be in the 15-20% range). For PLC control, a transducer output is desired.

Methanol: In the esterification reaction (Stage A), the methanol content is typically 15% of the volume of the raw oil or grease feedstock. As a result, approximately 5% of the total volume is defined as bottoms and is removed from the processing sequence. Therefore, approximately 95% of the initial feedstock, including catalyst and surplus alcohol is available for the transesterification reaction (Stage B). For this reaction, approximately 20% by volume of methanol is added to the feed material of Stage B, or approximately 19% by volume additional alcohol is required (95%×20%). This necessitates that the methanol demand is 34% of the volume of raw oil feedstock, the bulk of which will be consumed as part of the reaction. A three-day supply of the methanol would require that the tank have the capacity for storage of at least 8500 gallons (34%×25,000 gallons). The methanol tank would also consist of the following peripheral equipment:

• • One level indicator. An electronic transducer and a mechanical level indicator are desired.
  • One Positive Displacement (PD) pump capable of the nominal throughput of 0.8 gpm (15 v %×5.5 gpm) for Stage A. The pump must be compatible with methanol. Note: It is believed that the continuous operation may allow for a greater throughput than is initially designed. In addition, it may be desirable to decrease throughput without having to shut the plant down. Therefore it would be desirable to be able to turn down the throughput of a 2 gpm PD pump through the use of a variable speed AC motor.
  • One flow meter capable of handling methanol. For PLC control, a transducer output is desired.
  • One PD pump capable of the nominal throughput of 1 gpm for Stage B (20 v %×5.5 gpm×95 v %). The pump must be compatible with methanol. Note: It would be desirable to be able to turn down the throughput of a 2 gpm PD pump through the use of a variable speed AC motor.

The presence of water in the reaction is considered detrimental. Depending upon the purity of the commercial alcohol, it may be necessary to add a dryer stage and a bulk methanol/dry methanol tanking system. If so, an additional level indicator and two transfer pumps will be required (bulk methanol to dryer stage; dryer stage to dry methanol storage). Sulfuric Acid: For Stage A, the amount of sulfuric acid is 4.62 v % of the amount of methanol or 0.693 v % the volume of the raw oil or grease. For a three-day supply, the size of the sulfuric acid holding tank would need to be a minimum of 175 gallons (25,000 gal×0.693 v %). The sulfuric acid tank would also consist of the following peripheral equipment:

• • One level indicator. An electronic transducer and a mechanical level indicator are desired.
  • One Positive Displacement (PD) pump capable of the nominal throughput of 0.04 gpm (0.693 v %×5.5 gpm) compatible with sulfuric acid handling. Note: It is believed that the continuous operation may allow for a greater throughput than is initially designed.

In addition, it may be desirable to decrease throughput without having to shut the plant down. Therefore it would be desirable to be able to turn down the throughput of a 0.08 gpm PD pump through the use of a variable speed AC motor.

• • One flow meter capable of handling sulfuric acid. For PLC control, a transducer output is desired.
  • Piping adequate to handle sulfuric acid.

Potassium Hydroxide: Potassium hydroxide may be obtained in 50 lb bags. Storage requirements would be in a dry enclosed area away from ambient moisture. Requirements are for 1.2 g per liter of product, or 250 lb for a three-day supply (5.5 gal/min×3.785 l/gal×60 min/hr×72 hrs/3-days×1.2 g/l×l/453.5924 g/lb=237.9 lb/3-days). It is anticipated that the potassium hydroxide would be added manually, therefore no transfer pumps or level indicators would be required.

Alcohol/Acid Catalyst Mixing

Theory of Operation: Through the PLC or PC based controller system, the quantities of both methanol and sulfuric acid are regulated to remain proportionally in sync with the throughput of raw feedstock oil. Both of the quantities are metered into the MeOH/H₂SO₄ mixing tank. This tank must be of such construction as to be able to withstand the low pH as imparted by the sulfuric acid. A level indicator will be monitored by the PLC for 4 states: High-High, High-Low, Low-High, and Low-Low. In the event that either flow from the methanol or the sulfuric acid triggers a High-Low alarm or a Low-High alarm, a timer will be activated to give the operator sufficient time to make corrections without forcing a plant shutdown. In the event that a High-High or Low-Low alarm is triggered, the feed pump from the feed oil to the Stage A reactor will be shut down, as will downstream agitators and pumps. Either an HH or LL alarm will force a full plant shutdown. In order to avoid this situation, the mixing tank size must be of sufficient capacity to allow the operator time to make corrections. However, it should be noted that in the invention, because the reaction vessel is relatively low capacity in comparison with the conventional plant designs, the catalyst may be mixed relatively slowly and thus relatively safely.

Design Capacity: If a 45 minute interval is deemed sufficient and the HL and LH levels are set at 80 v % and 20 v % with the HH and LL levels set at 98 v % and 2 v %, and the targeted flow rate of the methanol and the sulfuric acid is 0.84 gpm, then the capacity of the tank will need to be a minimum of 200 gallons. (98%−80%=18%. 0.84 gpm×45 min=37.8 gal. If 18% =37.8 gal, then 100% =210 gallons). If the capability to increase production were doubled, then the tank would need to be a minimum of 400 gal.

Safety Protocol: The design capacity allows 45 minutes for the extreme condition of a downstream blockage. The same would be true if the methanol and sulfuric acid feed tanks went empty. A loss of flow from either the methanol or the sulfuric acid would also constitute a likewise potential shutdown. As a secondary safety backup to the flow meters, a temperature gauge would monitor the temperature inside the vessel. The mixing of sulfuric acid and methanol is exothermic and therefore releases heat as the two are mixed. If the ratio of acid to methanol is reduced, the temperature will decrease. If the ratio of acid to methanol is increased, then the temperature will increase. Should either of the flow meters become stuck, the operator would not know that a potential alarm condition existed. The temperature monitoring would give an independent alarm status monitoring as a redundant safety backup. Temperature monitoring also consists of 4 alarm states: HH, HL, LH, and LL. The triggering of HL or LH would alert the operator that the reaction has exceeded nominal conditions, allowing for the capability of correcting the problem without disrupting production. In the case of variable speed AC pumps, the output could be limited iteratively until the condition is rectified. A HL alarm would shut down or decrease the speed of the pump supplying the acid (P05) to limit the exothermic reaction. A LH alarm would shut down or decrease the output of the methanol pump (P04) until the temperature is brought back into tolerance. In the case of a pump shut down, the pump could restart once the HL or LH alarm had been deactivated below 10% of the triggering event. In the case of a persistent problem, the operator has the option of locking out a restart until an examination of the problem has been made. Safety protocol and lockout procedures against accidental restart are to be followed. In the event that a HH or LL alarm is triggered, a plant shutdown procedure is initiated, including a sequential shutdown of all downstream pumps.

Initialization: Flow must be detected at the crude oil tank flow meter before the mixing tank is allowed to engage.

The MeOH/H₂SO₄ mixing tank will also consist of the following peripheral equipment:

• • One flow meter downstream from the dry methanol feed tank capable of a scale reading 0-2 gpm. The flow meter must be compatible with methanol.
  • One flow meter downstream from the sulfuric acid storage tank capable of a scale reading of 0-0.1 gpm. The flow meter must be compatible with sulfuric acid.
  • One level indicator
  • One temperature gauge capable of reading 0-160° F. with signal output
  • One PD pump capable of 1 gpm (0.8 gpm-Methanol+0.04 gpm-Sulfuric acid) Note: If the design throughput is increased to 12 gpm, then the PD pump must be capable of 2 gpm with a variable speed AC motor capable of turndown.
  • One one-way valve downstream of the MeOH/H₂SO₄ PD pump, so that the crude oil pump can not back flush into the MeOH/H₂SO₄ mixing tank. Alcohol/Basic Catalyst Mixer

Theory of Operation: This step requires the mixing of a liquid (methanol) with a solid (potassium hydroxide. As such, the potential for errors is greater in an automated system than is found in the liquid-liquid mixture of methanol and sulfuric acid found in Stage A. The most common errors induced are interaction of the KOH with ambient moisture, forming clumps, which may in turn form bridging in an automated feed hopper. For his reason, the mixing stage is a manual operation. Commercial quantities of KOH are typically obtained in 50 lb. bags. Through the use of a feed pump (P07), a predetermined amount of methanol is measured into the mixing tank. The operator then manually starts the mixer and adds the correct volume of KOH at a rate slow enough to provide for adequate mixing, ensuring that all KOH is dissolved into the methanol and no clumps are left at the bottom. Once the KOH is adequately dissolved, the MeOH/KOH solution is transferred to a feed tank, which is now ready for use in the operation. A level indicator in the MeOH/KOH feed tank alerts the operator when the volume is sufficiently low enough to require a new batch of MeOH/KOH to be mixed.

Through the use of a transfer PD pump (P08) and flow meter, a predetermined amount of the alcohol/basic catalyst is added to the feed stream from Stage A Settler to the Stage B Reactor.

Design Capacity: 95 v % of the initial raw oil is transferred over for processing from the Stage A settler, with the remaining 5 v % settling out of the bottom. Therefore, the quantity of raw oil is 5.225 gpm (5.5 gpm×95%). The reaction requires 20 v % of methanol or 1.045 gpm, and 1.2 g/l of KOH. If the assumption is to have the feed tank empty to 20% of its volume once every 9 hours, then the design capacity is 1000 gallons (1.045 gpm×60 min/hr×9 hrs×1/80%=705 gallons. 150% design capacity=1058 gallons). An alternative method to sizing the feed tank is to examine the practical nature of a manual mix. The conventional size of KOH is in 50 lb bags. Assuming 1.2 g of KOH and 200 ml of MeOH is added to a liter of oil, then a 50 lb bag will treat 1000 gallons of methanol (50 lb×453.5924 g/lb×200 ml MeOH/1.2 g KOH×1/3785 ml/gal=998 gallons). Therefore, one 50 lb bag will treat 1000 gallons of methanol, which is 150% of the design capacity of a 9 hr/mixing interval, or in other words, at 5.5 gpm throughput of raw oil into the plant, a 50 lb treatment of KOH will last approximately 12.5 hrs.

If the plant is to be designed for the capability of twice the throughput, then either the interval between mixes is 6 hours or the requisite volume of the feed tank is 2000 gallons. The mixing tank is designed to mix 80% of the volume of the feed tank, therefore the volume of the mixing tank is 800 gallons, or 1600 gallons for a plant turn up of 100 percent.

Safety Protocol: The reaction between KOH and methanol is mildly exothermic, therefore for a manual operation, the operator will need to be trained to slowly add the bag of KOH to the methanol. This is consistent with a desire for a well-mixed batch. No temperature gauges are necessary since there will be an operator overseeing the mixing operation. A level indicator on the feed tank will alert the operator when the level gets below 20%, providing 3 hours of warning (20%×1000 gal=200 gal. 200 gal×1/1.045 gpm=191 minutes)

Initialization: Pump 08 will require a positive flow signal from the flow meter from Stage A settler in order to initiate flow.

The MeOH/KOH mixing tank and feed tank will also consist of the following peripheral equipment:

• • One flow meter downstream from the dry methanol feed tank with an accumulative total (totalizer) capable of a scale reading of 0-1000 gal. The flow meter must be compatible with methanol and a high pH.
  • One flow meter downstream from the MeOH/KOH feed tank capable of a scale reading of 0-2.5 gpm. The flow meter must be compatible with a slightly basic methanol.
  • One level indicator
  • One PD pump capable of 1 gpm. Note: If the design throughput is increased to 12 gpm, then the PD pump must be capable of 2.5 gpm with a variable speed AC motor capable of turndown.
  • One transfer pump from the methanol tank to the MeOH/KOH mixer tank. Delivery schedule is not critical for a manual mix, however a 100-gpm capability allows the operator to fill the mixer tank in 10 minutes.
  • One one-way valve downstream of the MeOH/KOH PD pump, so that the raw oil can not back flush into the MeOH/KOH feed tank.
    Stage A

Theory of Operation: The crude oil, having been mixed with the appropriate amounts of sulfuric acid and methanol are heated via Heat Exchanger HE01 to a nominal temperature of 140 to 145° F., where it is then introduced into the Stage A reactor from the top. Agitators of a proprietary design maintain the solution as a homogenous mixture with a relative residence time of between one to two hours before exiting from the bottom. The Stage A reactor is stainless steel and jacketed, with the jacket containing 145 to 150° F. water. The purpose is to maintain the optimal temperature profile across the reactor. Once the product leaves the Stage A reactor, it is directed to the center of the Stage A Settler from the top. The Stage A Settler is also jacketed to maintain a nominal temperature profile. Once the level reaches a take-off pipe, the oil is directed to the Stage B Reactor for further treatment. The acid catalyst and any salts are dropped to the bottom of the Stage B Settler, where they are periodically drained off of the tank. The salt is separated from the acid and the acid is returned to the sulfuric acid holding tank for reuse.

Design Capacity: The Stage A reactor is a vertical cylinder with a tapered bottom and a ratio of an internal diameter to height of 1:6.15. The exact dimensions and ratio of the reactor is not critical, however in general terms a slender cylinder has a smaller footprint than one with a lower diameter to height ratio. The Stage B Settler is also of a slender vertical cylinder, with the intent not only to have a smaller footprint for compactness of design, but also provides for better separation of the reacted oil from the acid and salts. The premise is that a greater height to diameter ratio allows for better separation of the oil, which tends to rise to the top versus the heavier acid and salts, which tend to settle to the bottom. For a two hour residency time, the capacity of both the Stage A Reactor and Settler should be a minimum of 1000 gallons ([5.5 gpm oil+0.8 gpm methanol+0.04 gpm acid]×60 min/hr×2 hr=760.8 gallons. 760.8/80%=951 gallons). The reduction of FFA's is a time sensitive reaction, meaning that too little of a residency time and low yields are obtained, while too long of a residency time results in an unusable product without additional treatment. For this reason, the maximum capacity design should not deviate significantly from the target residency. To insure that the majority of the oil receives the proper residency time, the reactor utilizes a proprietary staged design integral to the agitators.

Safety Protocol: A temperature gauge at both the entrance and the exit of the reactor keep the operator informed of the temperature inside the reactor. Should the temperature exceed 150° F., an excessive amount of alcohol may evaporate. Allowing for this contingency, the reactor is covered with a removable stainless steel top with a 1½″ vent pipe. The vent pipe is connected to a collection tank where evaporating methanol is captured for reuse. The collection tank also serves as an overflow secondary protection device. A level indicator on the reactor with alarms notifies the operator if the reactor becomes too full or too low. The Stage A Settler has an isolation valve at the bottom which normally remains closed. The valve is periodically opened and drained of excess salts and acid. The opening of the bottom of the Stage A Settler is noted in the operators log.

Initialization: The agitators in the Stage A reactor are not engaged until the level is sufficient to cover the agitators. A bottom drain valve is not opened for downstream treatment until the level is within a nominal operating range. This valve is manually opened and is part of the start up and shut down procedures. The Stage A Settler bottom valve is checked to make sure it is closed, where it remains during the processing until manually drained by the operator. An alternative is to have an automatic dump, based on the volume of bottoms accumulating. For the size of the 5.5 gpm unit described, the additional cost of automation for an automatic dump does not appear warranted.

Stage B

Theory of Operation: Once the FFA content of the crude oil is reduced in Stage A, the product is directed towards the Stage B Reactor. The appropriate quantities of KOH and methanol are injected into the stream. The mixture passes through the trimmer heat exchanger HE02 to maintain 140 to 145° F. Like the Stage A Reactor, the feed stream is introduced into the top of the Stage B Reactor and is kept as a homogenous mixture through the use of agitators. Stage B is also jacketed and hot water is passed through the jacket to maintain a consistent temperature profile. As in Stage A, the use of the water through the jacket is to maintain the appropriate temperature profile. In general, any heat transfer medium may be used, e.g. steam, thermoil, heater coils, etc. In the example of the 5.5 gpm design, water is used due to its low cost, availability, most oil production plants have steam readily available as part of its processing, and steam has the potential risk of allowing the reaction temperature to exceed practical thermal limits. Once reacted, the oil passes out the bottom of the Stage B reactor into the Stage B Settler. The piping from the bottom of the Stage B Settler is height adjusted to insure that only crude glycerin is removed from the bottom. Near the top of the Stage B Settler is a take-off pipe that removes the biodiesel, which is now separated from the glycerin.

Design Capacity: In general terms, the reaction time of the esterification stage is one hour, being one half that of the first stage to remove FFA's. This reaction is not time sensitive specifically however. Therefore, the dimensions of the Stage B reactor is smaller than Stage A reactor. For consistency, the internal diameter may be kept the same as the Stage A reactor, reducing only the height, although this is not a requisite. As in Stage A, the Stage B Settler is of a slender cylindrical design, allowing for greater separation of the biodiesel from the crude glycerin. For a 5.5 gpm throughput with a one-hour residency time, the capacity of both the Stage B Reactor and Stage B Settler should be a minimum of 500 gallons ([5.225 gpm oil+1.045 gpm methanol]×60 minutes/hr=376.2. 376.2/80%=470 gallons)

Safety Protocol: The amount of KOH added in the transesterification is greater than the acid added at Stage A, therefore any residual acid that is carried across to Stage B is neutralized. As in the Stage A Reactor, the bottom is protected by an isolation valve which maintains fluid in the reactor until the height is of a level sufficient to cover the agitators. So as not to entrain air in the mixture, the agitators are not engaged until they are completely covered. Notification to the operator is via a level indicator in the reactor. The top of the Stage B Reactor has a removable stainless steel cover with a 1½″ vent pipe which serves a dual role of collecting any methanol vapors and condensing them into a collection tank and also as an overflow secondary safety device. Any excess methanol is returned to the methanol storage tank for reuse.

Initialization: No action is taken to engage the Stage B reactor agitators until sufficient feedstock is introduced to cover the agitators. The purpose of not initiating the agitators until they are covered is to minimize entrainment of air into the mixture. The operator is notified of the proper level by the use of a level indicator in the Stage B reactor.

Heating

Theory of Operation: In the case of HE01, the purpose is to raise the temperature of the crude, raw oil to the nominal operating temperature. In the case of HE02 and the water jackets, the purpose is to trim, or maintain the desired temperature profile. HE02 trims the temperature back up to the desired temperature range, being 140 to 145° F., making up the losses from the pipe from the Stage A Settler to the Stage B Reactor. The water jackets of both Stage A and B Reactors, as well as Stage A and B Settlers maintains an even temperature profile. Given that the reaction in both of the reactors is mildly exothermic, the jacket serves to carry any excess heat, if any, away from the reactors.

Design Capacity: The size of HE01 is dependent upon the application. For example, if the raw, crude oil is coming directly off of a production stream, in all likelihood the oil is already at an elevated temperature, therefore the size of HE01 need not be excessively large. If, on the other hand, the oil is stored outdoors in a storage tank where it is allowed to cool, HE01 will need to have a greater heating capacity.

Safety Protocol: Steam from the boiler or steam lines at the location heat the water to the 140 to 145° F. range. This insures that the heat applied to the reactors does not become excessive, as could possibly occur if the steam supplied the heat demand directly. The temperature of the water is regulated by the use of a thermocouple. Because the temperature of the water is not excessive, the water continues to flow through the heat exchangers and jackets to maintain equilibrium, even during a plant shut down.

Initialization: Water is heated and circulated through the heat exchangers and reactors prior to start up of the plant. The process is not started until the temperature in each of the jackets is stable.

Washing

Theory of Operation: Once the product leaves the Stage B Settler, the product must be washed with water to remove any excess glycerin and KOH not separated in the Stage B Settler. Once it has been washed, the water is removed from the biodiesel in a commercial dryer. Depending upon the application and size of the plant, this may be accomplished by any of the standard industrial methods, e.g. centrifuge, molecular sieves, etc. The number of wash and dry sequences is dependent upon the initial feedstock and the resistance of separation of the final product. The glycerin is separated from the wash water in the conventional method, with the glycerin directed to the glycerin storage tank and the recovered water recycled for the next wash sequence. Industrial wash and drying stages are available from various manufacturers and are incorporated into the plant design, based upon the recommendations of the manufacturer.

Product Storage

Theory of Operation: In the completion of the process, there are essentially four products produced: biodiesel, crude glycerin, wash water, and recovered alcohol. The biodiesel is typically stored in a rundown tank, where the lab on location can verify basic properties prior to its being released into the final biodiesel storage tank. Depending upon the application, the biodiesel can be either stored in a biodiesel storage tank, or loaded directly from the rundown tank into tankers or rail cars. For a 5.5 gpm throughput as described herein, this represents approximately 8500 gallons per day, for a 24 hour period ([5.5 gpm oil+0.8 gpm Stage A methanol+0.04 gpm sulfuric acid+1 gpm Stage B methanol)×80 v % recovery×60 min/hr×24 hrs/day=8455). The crude glycerin may be sold as such, or further refined for sale at a premium. The excess methanol may be recovered from the crude glycerin and stored in the bulk methanol storage tank for reuse. The recovered water from the wash stage may be used in subsequent wash sequences.

Systems Controller

Theory of Operation: The primary purposes of the systems controller is to maintain the appropriate nominal operating conditions, i.e. temperature, throughput, blend ratios, etc., and to serve as an alarm and safety device, should any condition arise that forces a shutdown of the plant. The systems controller serves as a diagnostic tool to aid the operators in producing a consistent product safely. Conventionally, the task is performed by either a PLC (programmable logic controller) or a PC-based system, which integrates the information supplied by the I/O devices monitoring temperature, flow, pump speeds, and tank levels. Depending upon the size of the plant, bottom valves may be closed or opened in a similar fashion. Such PLC or PC based systems are readily available by various manufacturers and can be programmed for each of the specific demands as described above.

Safety Protocol: As with all good operating practices, the systems controller is backed up with standard gauges for the operator to monitor periodically. Servicing the plant requires that the operator manually lock out any valves or controls that might adversely affect the safety of the system or the operator during any shut down. This entails standard “tag and lock” safety protocols.

Many variations of the above embodiments are possible. For example, to enhance settling and speed up throughput, two settling tanks may be used for one mixing tank. Therefore, instead of doubling the size of the settling tank, a second tank is provided to yield about twice as much settlement time without reducing the throughput of the system. The settlement tanks would be identical, other than the second tank preferably having a lower liquid level than the first settlement tank in order to facilitate the use of static pressure, where static pressure is used. One can also use multiple reaction vessels in each stage.

It is also possible to modify the reaction vessels such as RV1 and RV2. For example, the central pipe may simple be a rotatable axis, but not have pipe sections and inlets and outlets for the liquid being mixed. Instead, the separators can have an upward slanted shape having a small pipe section, e.g., one and a half inches (1½″) in diameter and two to two and a half inches (2 to 2½″) tall at a predetermined distance on the separator from the central axis, extending upward from the separator, and communicating with a hole in the separator leading to the chamber below. The liquid will drip through due to the pressure. The height and diameter of the through pipe and its radial position on the separator may be selected to help ensure sufficient mixing of the liquid in the chamber. Of course, multiple pipes could be used too.

This variation of the separators is shown in FIG. 24. The edges of the separators may sit on or against bearings, formed e.g., by polyurethane riveted to the tank walls. In this embodiment, there may be no need for a bearing at the bottom center of the vessel.

Another variation of the invention may involve use of a semi-continuous flow process. For example, if the mixing in the first tank is preferably performed without using continuous flow, a 360 gallon first reaction vessel can be filled in about 9 minutes using a 40 gpm pumping rate. After 2 hours, the reaction vessel is unloaded at 40 gpm into the settling tank. This settling tank may be made 360 gallons also, or may be split into two tanks totalling 360 gallons. For the stage A settling, separation occurs quickly, i.e., typically in about ten minutes with the lighter or thinner sources of biofuel. Even for heavier biofuel sources, settling in stage A should be well within the two hour reaction time of the mixing tank. The remainder of the tanks could also be semi-continuous flow, i.e., using a high speed, e.g., 40 gpm pump for the B stage mixing tank and for the B stage settling tank(s). Because the tanks are small and because the reactions and/or settling are accelerated by heating, the through put of the system is still quite fast. In the above example, the filling and unloading time of the first tank totals 18 minutes, which only adds about 15% to the processing time of the system with continuous flow (2 hours). Therefore, the plant throughput will be as much as the continuous flow will 15% more time. Heretofore, such higher speed pumping was thought to mix up the separator tanks to much and be adverse to the settlement process. However, even in the B stage settlement process, which takes longer than the A stage settlement, and even with a relatively heavy feed source of grease, tallow or the like, the B stage can be conducted over a longer time than two hours by using larger tanks or preferably multiple tanks filled in parallel.

It should also be noted that the reactor and settlor tanks may be built to be interchangeable, by removing the separators and spinning mechanisms from the reactor, if plant output needs or operational parameters change necessitating modifications to the number and/or placement of tanks.

FIG. 25 shows a variation of a reaction vessel RVx and settlor tank STx combination, and shows additional aspects of the invention, to form a hot water control system. In this variation, a head tank HT is connected by a pipe line HTx to a line Lx between the hot water jacket on the reaction vessel RVx and settlor tank STx. The head tank maintains a constant pressure, e.g., 6 psi, on the reaction vessel and/or settlor tank from the water in the water jacket. This structure enables the tank and vessel walls to be made of a strength less than otherwise needed to avoid implosion, buckling or the like if no head tank or other constant tank pressure mechanism were used. For example, the tank well may be made of sixteen (16) gauge stainless steel, rather than a heavier gauge, thereby reducing the cost of construction materials and construction in general.

Head tank HT may be a fifty five (55) gallon drum. If pressure drops in line Lx, e.g., due to head loss, water will tend to flow down in line HTx to make up for lost pressure. A water pump, WPx is preferably a high volume, low pressure pump. Preferably, a constant low pressure such as six (6) psi is desireable. The pumped water enters heat exchanger HEx which it is heated, as previously explained, e.g., to at or about 155° F. The hot water passes along pipe line Lxi, enters a hot water jacket on reaction vessel RVx, and exists the vessel via line Lx, e.g., at about 152° F. Hot water then enters a water jacket around settlor tank STx, and exits at about 149° F. through a pipe line Lxo. High volume flow is preferred for better control of tank temperatures, especially since the boiling point of methanol is 160° F. The control helps avoid boiling the methanol.

FIG. 26 shows a variation of a reaction vessel RVy generally similar to that of FIG. 2, using a center shaft, separators, and mixing blades (not shown) as in FIG. 2. Such a vessel also has a vacuum vent V, a pipe coupling, e.g., a standard 2″ pipe coupling PC, a shaft S connected to a chain, gear and motor (e.g., as in FIG. 2), a hot water jacket having an inlet and outlet, as may be provided for all vessels and tanks, and an inlet and outlet for reaction fluid. As in the other reaction vessels, preferably the outlet is located at the bottom of the tank, where the lower end of the center shaft fits into a standard pipe coupling PC′, such as a 2″ coupling, preferably with a threaded surface and a machined surface, for fitting into a plug PG such as a 4″ plug with bearings for the machined surface of the pipe coupling PC′. The pipe coupling PC′ and bottom of the center shaft CS are located in a T-fitting, such as a 4″ tee.

While the present invention has been described with regards to particular embodiments, it is recognized that additional variations of the present invention may be devised without departing from the inventive concept.

Claims

1. A process of obtaining biofuel oil from oil byproducts, wherein the process uses a continuous flow of the oil byproducts through a series of mixing tanks and separation tanks.

2. The process of claim 1 wherein the process mixes sulfuric acid and methanol with the oil byproducts at a temperature of about 180° F.

3. The process of claim 1 wherein the flow rate through each of the mixing tanks is about two gpm and the flow rate to each of the separation tanks is about the same.

4. The process of claim 1 wherein the mixing tank is heated.

5. The process if claim 1 wherein the separation tank is heated.

6. A process of continuously flowing liquid from one tank to a successive tank by pumping liquid into the first tank and using static pressure to propel liquid to the next tank.

7. The process of claim 6 wherein the tanks are open.

8. A mixing tank comprising:

a housing;

multiple vertical chambers defined by separators;

a mixing blade in each chamber;

an input pipe passing through all of the chambers;

wherein each mixing blade is attached to the input pipe and the input pipe is rotated.

9. The tank of claim 8 wherein the separators are attached to the input pipe, and slant upward and outward.

10. The tank of claim 8, wherein the pipe has an inlet opening in each chamber above the mixing blade, and an outlet opening below the blade, and being plugged between the inlet and outlet.

11. A plant for production of biofuel, wherein a first and second reaction vessel and a first and second separation tank are located in a two by two layout.

12. A plant for production of biofuel, wherein the plant can produce about one million or more gallons per year from four tanks, and largest tank having a capacity of about 360 gallons, for the fatty acid reduction and esterification reactions.

13. The plant of claim 12, wherein each tank is supported on a stand of about four feet by four feet.

14. The plant of claim 12, wherein the four tanks have a footprint of less than or equal to sixty four square feet.

15. The plant of claim 12 wherein feedstock is supplied to the reaction vessel at about two gallons per minute.

16. The process of claim 1 further comprising a step of heating at least one of the separation tanks.

17. The process of claim 16 further comprising a step of heating using a water jacket on each tank.

18. The process of claim 17 wherein there is a step of maintaining constant pressure from the water jacket on at least one tank.

19. The process of claim 1 further comprising the steps of mixing sulfuric acid with methanol in a first tank, flowing the sulfuric acid and methanol into a second tank and allowing them to settle out, and oil to settle on top thereof, allowing the oil to flow to a third tank and mixing it with potassium hydroxide and methanol, and allowing them to settle out in a fourth tank.