US3714719A

US3714719A - Apparatus for desolventizing solvent extracted milled rice and rice bran

Info

Publication number: US3714719A
Application number: US00111632A
Authority: US
Inventors: T Wayne
Original assignee: Wayne T & Ass
Current assignee: Wayne T & Ass; Wayne T & Ass us
Priority date: 1971-02-01
Filing date: 1971-02-01
Publication date: 1973-02-06
Anticipated expiration: 1990-02-06

Abstract

A method and apparatus of desolventizing previously solvent extracted milled rice and, in certain embodiments of the invention, desolventizing of the bran removed from the rice. The method and apparatus contemplates using a desolventizing gaseous medium comprising inert gas as the major component thereof wherein the gaseous medium is contacted with the rice when at a temperature in the range from about 100* F. to about 150* F., whereby the solvent is vaporized from the rice at a relatively low temperature, thereby preserving the quality of the rice. The gaseous medium with the vaporized solvent entrained therein is subsequently condensed to remove the solvent therefrom and the medium is subsequently heated and recycled.

Description

United States Patent 11 1 m1 3,714,719 Wayne Feb. 6, 1973 [54] APPARATUS FOR DESOLVENTIZING 2,571,143 10 1951 Leslie ..34 37 x SOLVENT EXTRACTED MILLED RICE 2,618,560 1 l/1952 Leslie D C BRAN 2,81 1,539 10/1957 Komofsky ..260/412.4

[76] Inventor: Truman B. Wayne, c/o Truman B. Primary Examiner xenneth Sprague Wayne & Assc" Box Assistant Examiner-James C. Yeung- Houston Attorney-Delmar L. Sroufe et al.

[22] Filed: Feb. 1, 1971 [21] Appl. No.2 111,632

Related US. Application Data [57] ABSTRACT A method and apparatus of desolventizing previously solvent extracted milled rice and, in certain embodiments of the invention, desolventizing of the bran removed from the rice. The method and apparatus contemplates using a desolventizing gaseous medium comprising inert gas as the major component thereof wherein the gaseous medium is contacted with the rice when at a temperature in the range fromabout 100 F. to about 150 F., whereby the solvent is vaporized from the rice at a relatively low temperature, thereby preserving the quality of the rice. Thegaseous medium with the vaporized solvent entrained therein is subsequently condensed to remove' the solvent therefrom and the medium is subsequently heated and recycled.

4 Claims, 7 Drawing Figures PATENTEUFEB 6 I973 3,714 719 SHEET 2 BF 5 APPARATUS FOR DESOLVENTIZING SOLVENT EXTRACTED MILLED RICE AND RICE BRAN This application is a division of application Ser. No. 695,632, filed Jan. 4, 1968 which was a continuationin-part of copending application Ser. No. 529,81 1 filed Feb. 21, 1966, by the same inventor.

This invention relates to a method and apparatus for desolventizing previously solvent extracted milled rice. More particularly, it relates to a method of desolventizing solvent extracted milled rice with a gaseous medium comprising inert gas as the major component thereof, wherein the gaseous medium is contacted with the rice at a relatively low temperature andon the order of from about 100 F. to about 150 F., whereby the quality of the rice is preserved during the desolventizing thereof.

There has recently come into use various apparatus and methods for milling and solvent extracting brown rice. Examples of such apparatus and methods are taught in the following U.S. Pat., for example: No. 3,165,131,; No. 3,217,769; No. 3,261,690 and No. 3,330,666.

In the milling of rice, it is desirable to maintain as many whole milled kernels as possible with the smallest amount of checking or breaking as possible. However, rice kernels, particularly milled rice, are very sensitive to changes in not only temperature, but water and sol-' vent content. During the process of removing the solvent from solvent extracted milled rice, unless great care -is exercised, the rice kernels have a great tendency to check or crack or break and in some instances, to assume an undesirable rather chalky white appearance.

Many apparatus and methods have been developed for the purpose of desolventizing various solvent extracted particles. Patents which are representative of .the prior art include the following U.S. Pat.: No.

2,571,143; No. 2,618,560; No. 2,691,830 and No. 2,811,539.

However, it has been found that none of the prior art apparatus and methods are completely successful with respect to the desolventization of solvent extracted milled rice for various reasons, including excessive breakage of kernels by the violet agitation of the particles, excessive heat and the like.

It is therefore an object of this invention to provide an improved method and apparatus for desolventizing previously solvent extracted milled rice, and in some instances, desolventizing the bran removed from the rice, which apparatus and method overcome the aforesaid shortcomings of the prior art.

It is still another object of this invention to provide an improved apparatus and method for desolventizing solvent extracted milled rice which preserves the integrity of the rice-kernels during the operation. 1

Another object is to provide an improved extractive milling process wherein difficulties in the vapor handling and recovery systems are eliminated by feeding clean kernels of rice substantially free of loose polish to the desolventizing operation.

Still another object is to provide an improved desolventizing procedure in an extractive milling process which minimizes chalking and development of fissures in kernels of the rice and removes residual solvent to the desired limits.

Another object is to provide an improved extractive milling process wherein hazards due to vapor and dust explosions are minimized.

Other objects and advantages will become apparent to those skilled in the art from the following description and the attached drawings.

An improved desolventizing procedure for the clean rice is-contemplated which effects substantial savings in equipment costs, and produces a desolventized clean rice of improved appearance and free from residual solvent. The present process also avoids problems in processing due to a large quantity of fine bran and polish residues remaining on the finished rice.

Briefly stated, the method of this invention contemplates passing solvent extracted milled rice through a first chamber. A desolventizing gaseous medium comprising inert gas as the major component thereof is passed through the first chamber to thereby vaporize solvent contained in the rice. The medium is at a temperature in the range from about to 150 F. upon introduction into the first chamber. Thereafter, the medium is withdrawn from the first chamber with the vaporized solvent contained therein and with the medium being at a temperature within the range of about 95 F. to about F. A major portion of the vaporized solvent is then condensed from the withdrawn medium, with the medium subsequently being heated and recycled through the first chamber.

It is preferred that the medium be substantially oxygen free and that the inert gas portion of the medium be a combustion gas resulting from a substantially perfect combustion of a hydrocarbon fuel. The medium will preferably be substantially water-saturated upon withdrawal from the first chamber. In certain embodiments of the invention, additional inert gas is added to the medium to make up losses of gas therefrom. 1n certain embodiments of the invention, the rice may pass to a second chamber containing a gaseous medium comprising inert gas as the major component thereof to further desolventize the rice. in still further embodiments of the invention, the bran which has previously been removed from the rice and solvent extracted may also be desolventized with a gaseous medium comprising inert gas supplied from a common source or that used to desolventize the rice.

Briefly stated, the apparatus of this invention for desolventizing solvent extracted milled rice includes a housing arranged for passage of the rice therethrough in a semi-fluidized state, with the housing having inlet and outlet means for passing a desolventizing gaseous medium comprising inert gas as a major component therethroughand in intimate contact with the rice therein to therebyvaporize solvent from the rice. The apparatusalso includes a system for generating and recycling the medium through the housing, which system comprises a gas generator for generating inert gas to make up the medium, a heater for heating the medium to a temperature in the range of from about 100 F. to about F. upon introduction into the housing. It also includes first conduit means for conducting the heated medium from the heater to the inlet of the housing, a compressor connected to receive the medium from the outlet of the housing and to deliver the medium under pressure to thereby provide a driving force for the medium through the housing; and a second conduit means arranged to receive the pressurized medium from the compressor. It also includes condenser means connected to receive the said medium transmitted by the second conduit means for condensing solid vapors from the medium third conduit means for conducting said mediums from the condenser to the heater, and valve means connected to be responsive to the pressure differential between the medium in the first and second conduit means and arrangedfor delivering additional inert gas generated by the generator to said medium when the pressure differential exceeds a predetermined limit. Certain embodiments of the apparatus may also include means for circulating a gaseous medium through another housing through which the bran is passed, and in certain instances, the desolventizing medium may be the same for both housings, as will be explained hereinafter.

Preferably the last washing of the rice fraction is conducted with fresh solvent on a vibrating screen so that any residual particles of bran and polish are completely removed from the rice which is again shaken on a vibrating screen to free it of adhering solvent before introdu'ction of the rice into a desolventizer. Elimination of bran and polish particles from the rice fraction prior to introducing the rice into a desolventizing step eliminates difficulties due to accumulation of these materials in recovery steps subsequent to desolventizing wherein the solvent is recovered from the recirculated gas stream.

The desolventizing step preferably is conducted by passing the rice. through a housing containing warm inert gas, preferably combustion gases, for vaporizing solvent from the rice. Preferably warm inert gas containing solvent vapor from the desolventizer passes through a recycling system in which the gas is cooled, evaporated solvent contained therein is condensed and separated from the gas, and the gas is reheated and returned to the desolventizer. Such recycle of desolventizer gas prevents build-up of solvent vapor in the desolventizing gas to an explosive level, and assists in a very high rate of recovery of solvent from the used gas.

For some reason, at present unknown, a mixture of gases resulting from substantially perfect combustion of a hydrocarbon material, such as natural gas in air and containing as its principal components nitrogen, carbon dioxide and water vapor, decreases chalking of the rice during desolventizing and gives the rice a better appearance. It is believed that this effect is due to theprevention'of water loss from the outer layers of the milled kernel by. the moisture content of the inert gas mixture. 1

Reference to the drawings will further explain the invention wherein like numerals refer to like partsandin which;

FIG. 1 is a simplified and highly schematic drawing showing the arrangement of the system for generating and recycling the gaseous medium as taught and explained in greater detail in FIGS. 3-5.

FIG. 2 is a simplified and high schematic alternative embodiment of another system for generating and recyclingagaseousmedium.

FIG. 3 shows a portion of the apparatus for desolventizing the'bran fraction obtained from a solvent extraction milling process.

FIG. 4 shows a portion of the system which is considered to be an extension of FIG. 3 and particularly shows one means for condensing the gaseous medium.

FIG. 5 is considered an extension of FIGS. 3 and 4 and shows in particular one means for generating the inert gas and one means for contacting the gaseous medium with the rice.

FIG. 6 is a generally side elevation view in schematic form showing an alternate housing for contacting the rice with the gaseous medium.

FIG. 7 is a cross-sectional view taken generally along line 7-7 of FIG. 6.

Referring now to the drawings, the bran cake, which has been solvent extracted, is discharged directly into bran desolventizer U which comprisestwo or more steam-jacketed cylindrical sections 44 in each of which a cutflight screw conveyor 45 receives the bran cake at the head end of each section and discharges it at the opposite end into the succeeding cylindrical section. Steam or a hot liquid is circulated in the jackets of the two or more cylindrical sections to heat the bran meal which quickly forms from the bran cake received into the first section, and causes evaporation of the solvent.

This bran meal is treated in countercurrent manner with superheated inert gas, or a mixture of superheated inert gas and solvent vapor, which has been heated to an elevated temperature, usually within the range of 150 330 F., in recycle gas heater V (FIG. 4) and delivered through duct 46 into bran'holder 47 and is circulated through the dried bran meal and escapes through duct 48 into'the lower cylindrical section of bran desolventizer U and continues countercurrently upward through the upper dryer sections and escapes through duct 49 from which it is drawn into recycle gas blower W and is delivered by means of duct 49a to recycle gas condenser X (FIG. 4) wherein the evaporated solvent vapor is condensed and removed as liquid solvent in the knockout drum section 50 of recycle gas heater V, and is collected in solvent separator Y where the solvent is settled from its water content and is returned to the extraction plant by means of solvent pump Z and pipe 63.

The residual gas which comprises a mixture of inert gas and solvent vapor is then reheated to a temperature of 150 330 F. and is recycled through duct 46 to the bran holder 47, and the cycle is repeated. Any decrease in pressure within the recycle gas system due to gas losses or condensation of solvent vapors by condensor X is regained by supplying inert gas from duct 51 (FIG. 5) through differential pressure control valve 52 (FIG. 3) which maintains a constant differential pressure within the range of S to 10 feet WP. between ducts 16 and 49a, with the pressure always higher in duct 49a.

The fully desolventized, deodorized rice bran is discharged from bran desolventizer U through vapor lock 53 into bran holder 47 and is then recovered sequent handling of the bran are conventional and do not comprise part of this invention.

The washed rice from the solvent extractive milling process, which still contains small amounts of dilute, oil-containing solvent and some polish fines, is elevated system can be supplied by readily available commercial generators to have an analysis substantially as follows when burning gulf coastal natural gas:

Dry Gas Basis Carbon dioxide 12.0 per cent Unburned combustibles 0.5 per cent Oxygen 0.5 per cent Nitrogen (by difference) 87.0 per cent EEMPERATURE OF sa'rum'rnn oxsi F. F. 100 F. 105 F. 110 F.

Saturation humidity, (lbs.

\vatcr/lb.(1ry gas) 0.03115 0.03688 0.04312 0.06061 0.05032 Saturation moisture, (lbs.

water/cu. it. sat. gas) 0.00214 0.00248 0.00286 0.00320 0.00877 1 Pressure, 20.021 Hg.

Although the amount of moisture in the saturated inert gas is small, it is nevertheless important in the prevention of moisture loss from the milled rice during desolventizing which causes brittleness and a chalkywhite appearance in the kernels. its presence also reduces the partial pressure of the hexane and allows its removal at lower temperatures, a function which is also common in various degrees to the other inert gas constituents. As may be seen from the preceding table, if the inert gas is delivered from generator NN at 105 F. and enters a recycle gas stream in pipe 74 from heater KK which has been heated to above 105 F. there will be no condensation in the gas stream along its path to desolventizer 60. However, assuming that the entering inert gas is only slightly superheated above its saturation temperature and the gas is exhausted from nozzle 68 at 95 F., there will have been a moisture loss equal to 0.05061 minus 0.03668 lbs. water/lb. dry gas from the entering inert gas stream to the rice and evaporated hexane.

Assuming that approximately 1.25 to 1.5 lbs. of this slightly superheated (above its saturation temperature) inert gas stream is used perpound of solvent-wet rice per hour, the maximum quantity of moisture that could be absorbed by the rice, assuming that all moisture condensed between the saturation temperatures of 120 and 95 F. was thus absorbed and none was absorbed in the increased volume of gases due to the evaporated hexane vaporsin the gas stream discharged from exhaust duct 68, would be I 1.5 (0.05061 0.03668) 0.0290 lbs. moisture per lb. of rice or 2.09 percent of the weight of the rice.

However, the solvent retention by the drained and vibrated rice received from desolventizing screen EE should not exceed 6 percent of the weight of the rice. Since solvent penetration into the rice kernel does not exceed a few hundredths of an inch, most of it exists as interstitial liquid solvent which together with the small amount of solvent to be removed from the kernels is readily vaporized and removed by the substantially moisture saturated recycled gas. Thus, there is at most only inconsequential absorption of moisture from the recycled gas by the rice which occurs temporarily during the volatilization of the solvent which has only slightly penetrated its outer surface.

Rice, due to its crystalline or vitreous structure, is very sensitive to temperature changes, and particularly those that affect its normal moisture content which ranges between 10 and 13 percent when ready for milling. Once the bran layers and germ are removed, the moisture content will decrease slightly. However, the milled rice is even more sensitive to changes in temperature and in its moisture content. An advantage of desolventizing at a low temperature with nearly water saturated combustion products within a relatively narrow gas temperature range of between about 100 and 150 F. (and preferably between 1 10 and 130 F.), and

' withdrawal ,of the discharged gas-hexane vapor mixture within the range of 90 to 120 F. (and preferably within the range of 90 to 110 F.), is the effective removal of the solvent without the necessity for raising the temperature of the rice.

The mean molar heat capacities of the combustion gas mixture of carbon dioxide, nitrogen, trace constituents and water vapor between the entering and discharge temperature ranges above given, when used in the proportion of 1.25 to 1.50 lbs./lb. ofrice/hn, are ample to effect substantially complete desolventizing in section 66 of apparatus GG, but the use of additional combustion gas in the lower deodorizing section :at temperatures ranging between and F. andin the proportion of from 0.125 to 0.200 lbs/lb. rice/hr. is

' sufficient to guarantee the continuous production of an cooling, but in addition retains the sensible heat of the rice to assist in desolventizing it in section 66 in contact with the inert gas recycle stream which completes the solvent removal. The latter occurs without raising the temperature of the rice and further insures against checking of the kernels.

Thus, in addition to protecting the rice from moisture losses, the introduction of an inert gas which is only slightly superheated above its saturation point reduces the partial pressure of the solvent and effects its removal at lower temperatures than is possible with superheated, substantially anhydrous solvent vapors which withdraw moisture from the outer surfaces of the kernels during the volatilization of the solvent therefrom. The latter accounts for the chalky whiteness observed in rice desolventized by the superheated hexane recycle gas method.

The rice kernels then cool slowly in the 90 to F. atmosphere in the lower deodorizing section 75 and should be discharged from vapor lock 80 into a room atmosphere which has its temperature within the range of 70 to 80 F. to gradually reduce its temperature before it enters storage.

As stated above, FIG. 1 .is a simplified schematic drawing of the system for generating and recycling the gaseous medium as previously taught in greater detail in reference to FIGS. 3 5. The same numerals are used to denote the same parts and the operation thereof is the same unless stated otherwise. Hence, emphasis is here placed upon describing the system for handling to vibratory washer DD by means of elevator FF where it is successively washed with pure solvent obtained from solvent pipe 63 (FIG. 5). The solvent is preferably metered through rotameter 64 and is forced through' the two spray headers at the termini of solvent pipe 63. The washings drain through pipe 61 to surge tank 65 which supplies pump CC. The washed rice, now substantially free of oil-containing solvent and polish fines, but still wet with fresh rinse solvent, passes to vibratory desolventizer EE where most of the remaining surface and interstitial solvent is shaken off and drains through pipe 61a to pipe 61 and thence to surge tank 65.

The cleanly milled rice, which still contains some absorbed and surface solvent on the order of about 6 percent by weight or less is then discharged at a temperature preferably in the range of about 105 to about I l5 F. to rice desolventizer GG (FIG. 5) which, in the embodiment shown, comprises a vertical column having an upper section 66 with internal staggered baffles, op-

positely placed recycle

gas manifolds

67 and 67a, an exhaust stack 68 and a hoppered bottom 69 which is equipped with a slide gate. The column is filled and recycle gas blower l-II-I is started to establish desolventizing gas circulation into this blower from recycle gas stack 68 into exhaust duct 70 and thence into recycle gas condenser 11 where all or any desired part of the solvent in the recycle gas may be condensed and drained to pipe 71 which delivers to solvent separator Y (FIG. 4). The remaining gas, now saturated with respect to the solvent vapor and moisture, passes through duct 72 to the knockout section 73 of recycle gas heater KK and thence into the tubular heater section where it is superheated to a temperature sufficient to'have evaporative ability when recycled to upper section 66 of the rice desolventizer through duct 74 which supplies the

recycle gas manifolds

67 and 67a. To prevent cracking of the rice, the entering gas temperature is preferably within the range of 100 150 F. The solvent-saturated gas leaving the desolventizer to be recycled usually is at a temperature of 95 l20 F.

During startup, when the rice in upper section 66 is sufficiently desolventized, the slide gate in hopper bot tom 69 is opened and circulation into lower deodorizer section 75 of the apparatus is established. As desolventized rice enters section 75, additional solvent-wet rice enters the upper section 66. When both column sections are full, inert gas is admitted from pipe 76a through

flow control valves

77 and 77a. The inert gas is forced upwards through the rice to remove the last traces of solvent, and is exhausted throughstack 78 into main vent header 79 which collects solvent vapors from the high point of all apparatus in which they occur. The main vent header terminates to vent condenser LL (FIG. 4) which condenses most'of the sol vent vapors and delivers the liquid solvent to solvent Inert gas generator NN comprises a conventional apparatus for the exact combustion of a fuel, preferably natural gas, so that the combustion produces are primarily nitrogen, carbon dioxide, water vapor and traces of oxygen, unburned hydrocarbons and carbon monoxide which are delivered at a pressure of from 5 to 10 psi. The main inert gas ducts 51 and 51a originate from water knockout pot 51b, and through several branches supply both the bran desolventizer U and the rice desolventizer and deodorizer GG with a substantially oxygen-free inert atmosphere which will prevent explosions of solvent vapor in all apparatus throughout the process. When drawn from branch

inert gas pipes

76, 76a, 76b and 760 it is preferably under a moderate pressure of 2 to 3 psi. It will, therefore, flow freely through the deodorizer section 75 of apparatus GG and into other apparatus and vessels in which atmospheric pressure or a slight negative pressure exists due to vent connections from them to the main vent header which in turn connects to the vent condenser LL and from thence to the vapor recovery system MM in which there is a final vent. A pressure of 5 to 6 psi in the main inert gas ducts 51 and 51a is sufficient to deliver inert gas through differential

pressure control valves

52 and 81 intothe return recycle gas ducts 46'and 74, respectively, to maintain a constant pressure differential between them and the recycle blowers discharge lines 49a and 70', respectively. Thus, a constant driving force is provided through both desolventizing systems, regardless of the pressure drop through their respective recycle condensing and gas heating apparatus due to condensation of solvent vapor.

Referring to the flow diagram of the recycled gas system in FIG. 5, pipe 51a and its regulating valve 81 maintain the PV relationship in the recycled gas required to provide the proper pressure differential between

lines

70 and 74. The blower HH withdraws through duct 68 the full volume of the recycled desolventizing gas which enters section. 66, plus the evaporated solvent vapor from section 66 of vessel GG, and propels this volume of gas mixture through condenser JJ, knockout 73, heater KK and pipe 74. The decrease in gas volume and the pressure drop which occur in condenser J], the losses of incondensibles from a vent header connection from knockout section 73, require an inert gas makeup into pipe 74 from pipe 51a through control valve 81 which is governed by the unnumbered differential pressure controller. The latter is set to maintain a selected pressure differential between

pipes

70 and 74 with the pressure always higher in pipe'70.

A further purpose of this pressure differential control system is to provide stabilization of the system once an operational equilibrium is established, and, of course, to initially establish the proper pressure balance and gas' flow rates before solvent evaporation has been fully established and the operational equilibrium has been reached. To take care of sudden pressure surges in the system due to faulty operation of pressure control valve 81 and its differential controller, a pressure control valve from the knockout section 73 apparatus KK is provided.

The inert gas delivered to the rice desolventizing system from inert gas generator NN, water knockout 51b and pipe 51a; and also that similarly delivered through pipe header 51 to the bran desolventizing the gaseous medium and reference should be made to FIGS. 3-5 for specific details, particularly concerning the handling of the rice and bran fractions in relation to the gaseous medium. In summary then, 'inert gas generator NN supplies a continuing source of inert gas to the desolventizing system associated with rice desolventizer 60 through differential pressure control valve 81. The medium is withdrawn from desolventizer 06 by blower HH and transmitted to condenser JJ and thence to water knockout section 73 of heater KK where it is heated for recycle back to desolventizer 66.

Similarly, additional makeup inert gas is supplied from generator NN through differential pressure control valve 52 to line 46 which transmits the medium to bran desolventizer U from which it is drawn by blower W and transmitted to condenser X and thence to knockout section 50 of heater V where it is heated for recycling to desolventizer U. Hence, it may be said that the desolventizing mediums for both the rice desolventizing apparatus and the bran desolventizing apparatus are separately condensed to remove the solvent vapors therefrom heated and recycled.

An alternate embodiment of the system for handling the gaseous medium is shown in FIG. 2 which is somewhat simplified with respect to that shown in FIGS. 1 and 3 to 5, and which has certain advantages blower HH removes the gaseous medium from ricedesolventizer 66 through vapor scrubber 70a, which is of conventional type and is provided with nozzles connected to a source of liquid solvent and arranged such that the gaseous medium is passed through afine spray which removes the bran dust therefrom. The liquid discharge from scrubber 70a may be collected in conventional manner. The gaseous medium is then transmitted by conduit 70 to heater V (which has knockout section 50 removed) where it is heated and transmitted to bran desolventizer U through

ducts

46 and 48, after passage upwardly through desolventizer U. At the same time, additional inert gas is passed through bran holder 47 via line 51c which is connected to duct 51 as shown.

it is conducted to the desolventizer unit 60 through conduit 74.

Makeup inert gas from generator NN is supplied to the system through differential

pressure control valves

52 and 81 in the same manner as in the embodiment shown in FIGS. 1 and 3.t0 5.

The heavily loaded solvent vapor-inert gas stream leaves bran desolventizer U through pipe 49, and is through knockout section 73 as described above.

The advantages of this modification are several:

1. The two recycled gas streams from the rice and bran desolventizers are merged into one .stream which has initially the size of the rice stream alone. Starting with inert gas from generator NN which enters pipe 74, the recycle system for desolventizer G6 is eliminated. The volume of desolventizing gas required in GG is relatively large because of the small enthalpy of the 120 F. gas which enters it. Therefore, it may be sent directly to heater V and is recycled at a much higher temperature (240 300 F.) to the bran desolventizer U. The spent gas from U is then condensed in condenser X where its temperature and solvent content are both drastically reduced, from which it is returned to the rice desolventizing system heater KK and thence to the rice desolventizer G6.

2. 22,000 lbs/hr. of rice at 5 percent hexane contains 1,100 lbs/hr. of hexane to be evaporated without heating the rice kernels to above 120 F. By concurrent evaporation, higher recycle gas temperatures can be used without substantially raising the temperature of the rice kernels. 3,000 lbs/hr. of wet bran will not contain over 1,200 lbs/hr. of hexane, which is about the same quantity that is in the milled rice. The hexane in the bran may be evaporated at much higher temperatures in a very small equipment system, especially if the modified Schneckens apparatus illustrated as desolventizer U in FIG. 3 is used. Thetemperature increase from 100-120 F. to 240-300 reactivates the gas as a desolventizing medium.

3. Better heat economy results. Also, besides eliminating some equipment and considerable piping, the entire installation is more compact. A very great improvement in plant layout is possible.

4. The condenser water requirements of the system are reduced.

5. A better opportunity is afforded to properly trap the polish dust from desolventizers GG and U where it actually belongs; i.e., in the bran rather than in condensers, heaters, etc.

6. The recycle gases fromcondenser X tothe knockout section 73 of heater KK can be supplied to desolventizer GO in cleanly washed condition due to the heavy solvent condensation which occurs in condensor X and the elimination of solids-contaminated solvent mist in knockout section 73.

7. The desolventizing effect of a gas stream comprising a major proportion of inert gas is high. For instance, each 1,000 cu. ft. of the mixed gas stream from desolventizer G6 at 0 psig and 100 F. will contain 655 cu.

.ft. of inert gas and 335 cu. ft. of hexane vapor which,

' from the rice desolventizing step, per se. This is due, of

course, to the greater solvent capacity of the hotter recycle gas stream.

The solvent used to extract the rice and bran may be any suitable commercially available type such as hexane, heptane, trichloroethylene, ethylene dichloride,.

substantially anhydrous isopropanol, or the like, which are commonly used insolvent extraction processes. I

Constant boiling azeotropes comprising one or more solvents with small proportions of water are also contemplated. l-lexane is the preferred extractive solvent because of its ready availability and low cost, and its ready recovery by evaporation and stream stripping.

.. The desolventizing the clean rice may be accomplished in any of several types of apparatus. However, since rice is a special case requiring careful handling to preserve it as whole grains to the greatest possibleextent, it is preferred that it'be desolventized in a housing wherein the rice is placed in a semi-fluidized condition, as does a baffled vertical column type desolventizer similar to that illustrated in FIG. 5, wherein the fully washed, solvent-wet, clean rice enters at the upper part of the desolventizer and is contacted by a pressurized stream of inert combustion gas, or mixture of an inert gas and solvent and vapor which has been superheated to allow rapid vaporization and removal of the solvent from the rice mass as it moves downward in a slightly expanded bed in a state of incipient fluidization to promote rapid circulation of a desolventizing vapor within the moving bed of rice. The gases from the operation are sent in part or entirely through a recycled gas condenser and thence to a recycled gas heater before being retumed-as superheated recycled gas'to the desolventizer. Since 90 to 95 percent of the total solids entering as brown riceare received and desolventized in this apparatus, it must be of high capacity to permit fast throughput in which the rice is not subjected to temperatures exceeding 140 F.-, as temperatures above this value result in heat checking and breakage of the rice.

The total bran and polish solids represent only about 5 to 10 percent of the weight of brownrice entering the process. Therefore, in a plant which processes 25,000 pounds of brown rice per hour, the hourly bran polish production does not necessarily exceed 2,500 pounds on the dry basis. The solvent content of the bran and polish solids entering the byproduct solids desolventizer doesnot exceed about 50'percent by weight of these solids. While any of several type of desolventizers inclusive of desolventizentbasters, flash desolventizer systems, and steam jacketed dryers commonly known as Schneckens apparatus, may be used in desolventizing the solids at temperatures up to 330 F., the applicant prefers to use a modified Schneckens apparatus similar to that illustrated at U (FIG. 3) which is equipped with a holding tank at its discharge end to which may be introduced either saturated or superheated gas, with or without added steam, which sweeps countercurrently through the solids and evaporates the solvent with the aid of indirect steam heat provided by a surrounding steam jacketor within hollow flights of the screw flights within the apparatus. The solvent containing inert gas is exhausted from the apparatus by a recycle gas blower and sent wholly or in part to a recycle gas condenser before being sent to the recycle gas heater from which the super-heated gas is returned to the bran holding tank and the cycle is repeated.

It is to be understood that the present invention is not limited to either a vertical cascading tower or to countercurrent flow of rice and gases in order to be carried out properly. For example, a series of vapor-type vibrating screen conveyors equipped for either concurrent or countercurrent flow may be used, which conveyors may be arranged end to end or in superposing relationship. Referring now to to FIGS. 6 and 7, an alternate desolventizing apparatus for the rice will be explained, which alternate embodiment may be described as a vibrating, spring-mounted drying conveyor which a may be connected to receive the gaseous medium of this invention and arranged to convey the rice in a semi-fluidized state so as to contact the gaseous medium with the rice. I

More specifically, FIG. 6 shows three such units generally designated bythe

numerals

201, 202 and 203, connected in series, and each having a vibrating screen surface 204 which is arranged to advance the rice from left to right therealong, and a plurality of side inlets 205 which are arranged to receive the gaseous medium therethrough and to direct it upwardly through the screens 204. lnlets 205 to units 201and 202, may for example, be connected to conduit 74 of the'previous embodiment so as to receive the desolventizing gaseous medium thereinto.

Each of

theunits

201, 202 and 203 has outlets 207 in the top thereof through which the gaseous medium is discharged, and in the case of units 201 and 202, the outlets 207 may be connected to conduit of the previous embodiment.

The inlets 205 to unit 203 may be connected to conduit 76 of the prior embodiment thereby making unit 203 a deodorizing section, with the outlets 207 thereof being arranged to recycle through unit 202 as shown by small blowers or the like.

The sections or

units

201, 202 and 203 may be arranged in horizontal sequence as shown above, or in vertical stacked alignment. In concurrent flow, the gaseous medium enters the inlets 205 as described and rice enters through vapor lock A. The desolventizing medium leaves at the upper outlets 207, as described above, and the partially desolventized rice then travels to unit 202 where it is contacted with additional gaseous medium, which may be made up from recycled gas and fresh inert gas from unit 203. The desolventized, deodorized rice leaves unit 203 through a vapor lockB.

When

units

201, 202 and 203 are stacked vertically,

the sequence is the same. Intermediate vapor locks between the sections are not required when the first unit, i.e., 201 is fed concurrently. The same applies to unit 202. There may also be small countercurrent recycle blowers between subsections of each

unit

201, 202 and 203.

' It is to be understood that other types of desolventizingapparatus could be used, including non-vibrating conveyors of the fluidized bed typ'e, rotating cylinders fitted with lifters, or moving belts in vapor locked horizontal or vertical enclosures'or the like.

Further modifications may be made in the invention as particularly described without departing from the scope thereof. Accordingly, the foregoing description is to be construed as illustratively only and not as a limitation upon the invention as defined in the following claims.

What is claimed is:

1. ln apparatus for desolventizing solvent extracted milled rice, the combination comprising:

.a housing arranged for passage of said rice therethrough in a semi-fluidized state, said housing having inlet and outlet means for passing a desolventizing gaseous medium comprising inert gas as the major component therethrough and in intimate contact with said rice therein to thereby vaporize solvent from said rice; and a system for generating and recycling said medium through said housing, said system comprising;

a gas generator for generating said inert gas;

a heater for heating said medium to a temperature in-the range of from about 100 F. to about 150 F. 'upon introduction into said housing;

first conduit means for conducting said medium from said heater to said inlet means of said housa compressor connected to receive said medium from said outlet means of said housing, and to deliver said medium under pressure to thereby provide a driving force for said medium through said housing;

second conduit means arranged to receive said pressurized medium from said compressor;

condenser meansconnected to receive said medium transmitted by said second conduit means for condensing solvent vapors from said medium;

third conduit means for conducting said medium from said condenser to said heater; and

valve means connected to be responsive to the pressure differential between said medium in said first and second conduit means and arranged for delivering additional inert gas generated by said generator to said medium when said pressure differential exceeds a predetermined limit.

2. The invention as claimed in claim 1 including:

a second housing arranged for passage therethrough of solvent extracted bran previously removed from said rice, said housing having an inlet and outlet;

means for heating and passing a desolventizing gaseous medium comprising inert gas as the major component through said second housing in intimate contact with said bran therein at a desolventizing temperature to thereby vaporize solvent from said bran; and

second valve means connected for supplying inert gas from said generator to said medium circulated through said second housing.

3. The invention as claimed in claim 2 including:

a second condenser connected to receive the medium passed through said second housing, whereby said medium used to d'esolventize said bran is separated from that medium used to desolventize said rice and is separately recycled.

4. The invention as claimed in claim 2 wherein: sald second conduit means lS connected to said means for heating and passing a medium through said second housing; and the outlet means of said second housing is connected to deliver said medium to said condenser; whereby said medium is successively recycled through said first and second housings.

Claims

1. In apparatus for desolventizing solvent extracted milled rice, the combination comprising: a housing arranged for passage of said rice therethrough in a semi-fluidized state, said housing having inlet and outlet means for passing a desolventizing gaseous medium comprising inert gas as the major component therethrough and in intimate contact with said rice therein to thereby vaporize solvent from said rice; and a system for generating and recycling said medium through said housing, said system comprising; a gas generator for generating said inert gas; a heater for heating said medium to a temperature in the range of from about 100* F. to about 150* F. upon introduction into said hOusing; first conduit means for conducting said medium from said heater to said inlet means of said housing; a compressor connected to receive said medium from said outlet means of said housing, and to deliver said medium under pressure to thereby provide a driving force for said medium through said housing; second conduit means arranged to receive said pressurized medium from said compressor; condenser means connected to receive said medium transmitted by said second conduit means for condensing solvent vapors from said medium; third conduit means for conducting said medium from said condenser to said heater; and valve means connected to be responsive to the pressure differential between said medium in said first and second conduit means and arranged for delivering additional inert gas generated by said generator to said medium when said pressure differential exceeds a predetermined limit.

2. The invention as claimed in claim 1 including: a second housing arranged for passage therethrough of solvent extracted bran previously removed from said rice, said housing having an inlet and outlet; means for heating and passing a desolventizing gaseous medium comprising inert gas as the major component through said second housing in intimate contact with said bran therein at a desolventizing temperature to thereby vaporize solvent from said bran; and second valve means connected for supplying inert gas from said generator to said medium circulated through said second housing.

3. The invention as claimed in claim 2 including: a second condenser connected to receive the medium passed through said second housing, whereby said medium used to desolventize said bran is separated from that medium used to desolventize said rice and is separately recycled.