Patent Abstract:
A reaction vessel which includes internally placed temperature controlling mixing baffles in which liquid is boiled, resulting in an isothermal heat sink. The energy of vaporization is supplied by the reaction vessel contents. The vapor produced by the boiling is directed to channel coils which surround the outside of the reaction vessel wall. The channel coils contact the outside wall of the reaction vessel perpendicularly, and provide mechanical support for the reaction vessel. The mechanical support from the channel coils allows for a decrease in the thickness of the reaction vessel wall and corresponding increased heat transfer efficiency between the channel coil contents and the reaction vessel contents. The entire above described apparatus is enclosed within an evacuated shell to provide additional insulation. The apparatus includes a gravitationally powered device that ensures that saturated or sub-cooled liquid enters the isothermal mixing baffles, thus guaranteeing that isothermal phase change will occur therein.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. application Ser. No. 08/878,372 filed Jun. 18, 1997 now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to chemical or biological reactors generally, and in particular to an apparatus for controlling the temperature within a chemical reactor. 
     BACKGROUND OF THE INVENTION 
     Temperature control of a chemical reaction is often the key to obtaining desired products. Where the temperature is controlled, generally the reaction kinetics are controlled. Where the reaction kinetics are controlled, undesired intermediates and byproducts can be diminished or avoided. Traditional temperature control of industrial reactors is generally attained in one of two ways. One method is to control the temperature of the reactants as they enter the reactor. This method fails to address the heat of reaction, which is often responsible for the majority of heat produced or absorbed in a reaction. The heat of reaction can then alter the temperature of the reactants to produce undesirable products. This is especially true for tank reactors. 
     Conversely, endothermic reactions require the addition of heat during the reaction to maintain the temperature of the reactants. Again, pre-adjustment of the temperature of reactants fails to adequately address this situation. Further, complicated production processes may have exothermic and endothermic reactions taking place (usually at different times) as reactants are added or products withdrawn. Pre-adjustment of reactant temperature is clearly totally inadequate in such situations. 
     A second method of temperature control of industrial reactors involves the placement of a jacket around the outside of the reaction vessel. In such a case, a fluid of desired temperature is passed through the jacket, thereby cooling or heating the reaction medium. The effectiveness of the jacket is limited by heat transfer properties which are in turn limited by mechanical design characteristics and geometry, including specifically vessel diameter and length. Material of construction, wall thickness, vessel diameter and length are critical design parameters for both strength and heat transfer. Unfortunately, however, heat transfer and mechanical strength are competing values in reactor design. For a given vessel diameter and length, the reactor wall may be thick enough to meet pressure and strength requirements, but too thick for optimal heat transfer between the jacket fluid and the reaction medium, as heat transfer is decreased with increased wall thickness. Where the reactor wall is thinned to improve heat transfer, the structural integrity of the vessel is diminished. This trade-off has historically been the source of design efforts seeking to gain maximum heat transfer efficiency while meeting mechanical strength requirements. If there is an increase in vessel diameter for a given length, the wall becomes weaker under internal pressure and weaker (to a higher order) under external pressure. Increasing vessel diameter, for a given length, also decreases (heat-transfer) surface to reacting medium volume, further inhibiting heat transfer mechanisms. 
     In the design of reactor cooling systems, two additional concerns arise when low temperatures are needed and cryogenic fluids are being contemplated for use as refrigerants. First, the temperature of the jacket fluid is calculated based on heat transfer requirements for a given reaction medium and reactor design. The required jacket fluid temperature is often below the freezing point of the reactor medium. As a consequence, the reactor contents can freeze along the inside of the reactor wall. The formation of “ice” results in a thicker wall overall and decreased heat transfer efficiency, as well as potentially inconsistent reactor medium composition, and in some cases, destruction of some reactants or products through freezing. Second, when a cryogenic fluid changes phase the vapor generated could occupy as much as 100 times the same volume as the liquid from which it originated. This large increase in specific volume can lead to erratic heat transfer mechanisms and, consequently, poor reactor medium temperature control. 
     Thus, there is a need for an improved apparatus for controlling the temperature of a reactor during operation that would allow for a (1) thin wall and resultant increased heat transfer to the contents and (2) increase of reactor size (diameter and length) without sacrificing the required mechanical properties of the reactor. Additionally, such an apparatus which prevents the build-up of frozen reactor contents would maintain high heat transfer efficiency and constant reactor medium temperature gradients, resulting in homogeneous and uniform reaction kinetics. The desired reactor would maximize the desired properties of high mechanical strength and high heat transfer efficiency, two qualities which have historically competed, regardless of size (i.e. diameter and length). 
     SUMMARY OF THE INVENTION 
     The present invention is an insulated chemical or biological reactor (such as a fermenter) system comprising a reaction vessel, an evacuated insulation shell, a plurality of temperature controlling mixing baffles immersed in the reactor contents and a temperature controlling helical channel coil outside of the reactor but inside the evacuated shell. A device designed to control the separation of phases of the working fluid chosen is required and may be external to the reactor. This device is referred to as the phase separator and has two outlets, one for each phase of the working fluid. The temperature controlling mixing baffles are designed to accept the working fluid in a single phase proceeding from one outlet of the phase separator and to, in turn, cause this fluid to change phase therein without carryover of any of the inlet fluid in the evolved phase. The changing of phase of the working fluid in the temperature controlling mixing baffles takes place at a uniform temperature, the level of which is dictated by the thermodynamic properties of the working fluid selected. The temperature controlling mixing baffles are referred to as isothermal mixing baffles. The channel coil is adapted to accept a circulating fluid, specifically of a single phase evolved by the mixing baffles and the other outlet of the phase separator. The particular working fluid selected depends on the intended temperature control purposes, that is whether heating or cooling is desired and the degree of heating or cooling needed. The channel coil is affixed to the outside wall of the reactor in a helical configuration and adapted to receive the single phase of the working fluid evolved by the mixing baffles and the other outlet of the phase separator which flows spirally upward or downward around the outside of the reactor. The channel coil is shaped to have two straight, parallel sides of the coil in contact with the reactor, normal to the surface of the outside wall of the reactor. This right angle contact between the channel coil and reactor wall increases the section modulus of the vessel wall, and thereby increases the mechanical strength of the reactor wall under external pressure. The wall can thus be made thinner to promote better heat transfer across the wall. The reactor, including the mixing baffles and the affixed coil, are together enclosed within an evacuated jacket. 
     The separation of the phases of the working fluid is very important for the optimal and predictable operation of the present invention, particularly when cooling of the reactor contents is anticipated. In the cooling mode the isothermal cooling baffles are intended to boil the working fluids which enter as a liquid and evolve only a saturated vapor with no liquid carryover in the form of droplets or mist. The isothermal mixing baffles, therefore, operate in the boiling heat transfer regime exchanging the latent energy of vaporization (at constant temperature) with the reactor contents. The vapor evolved from the isothermal mixing baffles, as well as the vapor evolved from the phase separator upstream therefrom is commingled and directed to enter the helical channel coil that serves as the reactor external jacket, wherein it exchanges sensible thermal energy with the reactor contents, gaining temperature to approach that of the reactor contents as it travels further along the inside of the coil. 
     The present invention thus controls heat transfer regimes by assuring that distinct single phases will exist in the isothermal mixing baffles (boiling liquid for cooling mode; condensing vapor for heating mode) and helical channel coil (vapor increasing in temperature for cooling mode; liquid decreasing in temperature for the heating mode). 
     The isothermal mixing baffles, of which there are typically at least two, are vertically oriented, elongated, generally cylindrical devices with an inlet and an outlet. As with the jacket, the isothermal mixing baffles may be used for heating or cooling the contents of the reaction vessel. Where heating is desired, a hot liquid or gas can be introduced into the isothermal mixing baffles through the inlet. The resultant cooler liquid or condensed vapor or liquid can be removed via the outlet. Where cooling is desired, upstream of the isothermal mixing baffles inlet there is provided a phase separator to insure only a liquid stream enters the isothermal mixing baffles. The inlet to the isothermal mixing baffles is typically placed into the top of the reactor and a liquid of desired boiling point is allowed to enter the isothermal mixing baffles while the reactor is in use. Where cooling is desired, the liquid selected would have a boiling point at or below the desired reaction temperature. The heating and boiling of the liquid introduced into the isothermal mixing baffles provides for the removal of heat from the reactor contents. For additional temperature control, the vapor produced from the boiling of the isothermal mixing baffles contents may be taken from the top of the isothermal mixing baffles, coming led with gas emanating from the phase separator and passed through the channel coil surrounding the outside of the reaction vessel. 
     The isothermal mixing baffles are designed and arranged so that their combined cross-sectional area will be such that the velocity of the vapor evolved from the liquid phase boiling therein will be below a critical value, Uc, above which droplets or slugs of the liquid phase will be entrained in the evolved gas and expelled from the isothermal mixing baffles. To accomplish this requirement, the inlets and outlets of the isothermal mixing baffles will be piped in parallel. 
     Thus in one aspect the present invention is an insulated chemical reactor comprising; a reaction vessel having a wall with inner and outer surfaces, an evacuated insulation shell spaced apart from and surrounding the reaction vessel, at least one isothermal mixing baffle disposed within the reaction vessel, a phase separator in fluid communication with the baffle so that only one saturated or sub-cooled liquid phase of a heat transfer working fluid enters the isothermal mixing baffle, a temperature controlling helical channel coil fixed to the outer surface of the wall of the reaction vessel, the helical channel coil having at least two walls disposed normal to the outer surface of the wall of the vessel, thus defining an open helical channel coil fixed to the wall of the vessel, the helical channel coil having a winding pitch so that successive coils of the channel coil are spaced apart from each other, thus defining a closed path to receive a fluid to contact the wall of the reaction vessel, the wall of the reaction vessel being of a thickness less than that required for use under a given temperature and pressure regime, the channel coil serving to add structural strength to the wall of the reaction vessel, so that the reaction vessel with the channel coil fixed thereto can be operated under the temperature and pressure regime; the helical channel coil fixed to the outer surface to enhance conductive heat transfer and transfer of convective energy flow inside the helical channel coil through the wall of the vessel; and means to combine vapor from the phase separator and vapor from the isothermal mixing baffle and introduce the vapor into the helical channel coil. 
     Thus in another aspect the present invention is an apparatus for isothermally cooling contents of a reaction vessel having a top and bottom, by allowing a saturated or subcooled liquid to boil inside an isothermal mixing baffle immersed in the reactor contents, to produce gas inside the isothermal mixing baffle, comprising; a vertically oriented, elongated generally cylindrical isothermal mixing baffle having a top and a bottom, the isothermal mixing baffle immersed in the contents in the reaction vessel, means for introducing the liquid into the top of the isothermal mixing baffle to a predetermined level, means for removing gas from the isothermal mixing baffle, and, means for controlling the level of liquid in the isothermal mixing baffle. 
     In yet another aspect the present invention is an apparatus for supplying saturated or superheated gas to a temperature controlling helical channel coil disposed helically around a reaction vessel, comprising; an isothermal mixing baffle, immersed in contents contained in the reactor, as mixing baffle containing a saturated or subcooled liquid, means for supplying vapor discharged from the isothermal mixing baffle to the helical channel coil, means for monitoring flow of the vapor into the helical channel coil, and, means for controlling flow of vapor into the helical channel coil. 
     In still another aspect the present invention is a method for controlling the temperature in a reaction vessel comprising the steps of; disposing a helical channel temperature control coil around an outside surface of the reaction vessel, introducing a heat transfer working fluid into a phase separator, withdrawing a liquid portion of the working fluid from the phase separator and introducing the liquid portion into an isothermal mixing baffle disposed in contents contained in the reaction vessel, withdrawing a vapor portion of the working fluid from the phase separator and mixing it with a vapor phase working fluid withdrawn from the isothermal mixing baffle to produce a mixed heat exchange fluid; and introducing the mixed heat exchange fluid into said helical channel coil. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1A  is a flow diagram that depicts the flow scheme of the present invention in a cooling mode for the phase separator and the reaction vessel, which contains internal isothermal mixing baffles and an external helical channel coil. 
         FIG. 1B  is a flow diagram that depicts the flow scheme of the present invention in a heating mode for the phase separator and the reaction vessel, which contains internal isothermal mixing baffles and an external helical channel coil. 
         FIG. 2A  is a side view of a reaction vessel having a cylindrical cross-sectional shape with an external channel coil according to the present invention. 
         FIG. 2B  is a side view of reaction vessel with an external channel coil according to an alternate embodiment of the present invention. 
         FIG. 3A  is a cross-sectional view of the generally cylindrical reaction vessel of  FIG. 2A  with an external helical channel coil, and integral isothermal mixing baffle entering the reactor vessel from the top in accordance with the present invention. 
         FIG. 3B  is a cross-sectional view of the reaction vessel of  FIG. 2B  with an external helical channel coil, and integral isothermal mixing baffle entering the reactor vessel from the top. 
         FIG. 4  is a cross-sectional view of a reaction vessel with an external channel coil, integral isothermal mixing baffle entering the reactor vessel from the top and evacuated jacket, in accordance with the present invention. 
         FIG. 5A  is a partial cross-sectional view of an isothermal mixing baffle according to the present invention with circular cross-section the isothermal mixing baffle shown entering the reactor vessel from the top. 
         FIG. 5B  is a partial cross-sectional view of an isothermal mixing baffle according to the present invention with circular cross-section, the isothermal mixing baffle shown entering the reactor vessel from the bottom. 
         FIG. 5C  is an alternate embodiment of the device of  FIG. 5A  showing the use of an internal snubber made to be removable from outside the reactor vessel without disturbing the reactor vessel contents or evacuated shell. 
         FIG. 5D  is an alternate embodiment of the device of  FIG. 5B  showing the use of an internal snubber made to be removable from outside the reactor vessel without distributing the reactor vessel contents or evacuated skill. 
         FIG. 5E  is a horizontal cross-sectional view of an alternate embodiment of the cross-sectional shape of the device of  FIG. 5A . 
         FIG. 5F  is a horizontal cross-sectional view of an alternate embodiment of the cross-sectional shape of the device of  FIG. 5B . 
         FIG. 6A  is a cross-sectional view of the reaction vessel with external channel coil, evacuated jacket, and integral isothermal mixing baffle according to the present invention showing the integral isothermal mixing baffle entering the reactor vessel from the top. 
         FIG. 6B  is a cross-sectional view of the reaction vessel with affixed channel coil, evacuated jacket, and integral isothermal mixing baffle according to the present invention, showing the integral isothermal mixing baffle entering the reactor vessel from the bottom. 
         FIG. 7A  is a partial cross-sectional view of the reaction vessel with external channel coil, evacuated jacket, two isothermal mixing baffles, and a mixing apparatus, according to the present invention, with the integral isothermal mixing baffles entering the reactor vessel from the top. 
         FIG. 7B  is a partial cross-sectional view of the reaction vessel with affixed channel coil, evacuated jacket, two isothermal mixing baffles, and a mixing apparatus, according to the present invention, with the integral isothermal mixing baffles entering the reactor vessel from the bottom. 
         FIG. 8A  is a fragmentary cross-sectional view of one embodiment of the channel coil according to the present invention. 
         FIG. 8B  is a fragmentary cross-sectional view of an alternate embodiment of a channel coil according to the present invention. 
         FIG. 8C  shows a comparison of a conventional half-pipe jacket cross-section to that of the present invention. 
         FIG. 8D  is a fragmentary cross-sectional view of another alternate embodiment of the channel coil wherein the full reaction vessel wall can be exposed to the fluid in the channel coil. 
         FIG. 9A  is a partial cross-sectional view of an alternate embodiment of the isothermal mixing baffle of the present invention. 
         FIG. 9B  is a partial cross-sectional view of another embodiment of the isothermal mixing baffle of the present invention. 
         FIG. 10  is a cross-sectional view of a preferred embodiment of the phase separator of the present invention for use in cooling or heating according to the present invention. 
         FIG. 11  is a partial cross-sectional view of an alternative embodiment of the phase separator of the present invention for use in cooling or heating according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the prior art, increasing reactor size (diameter and length) affects heat transfer to the reactor contents as the distance from the reactor external jacket to the centerline of the reactor increases (this is the radius). The present invention eliminates this problem as the insertion of isothermal mixing baffles in the reactor contents brings heat sinks (cooling) or sources (heating) to the contents as required to achieve temperature uniformity. 
     Since most reactors are basically cylindrical, there is a circular interface region between the highest level of the content and the empty (head) space above it. The ratio of this content/head space cross-sectional area to the volume of the content increases with increasing level of content. 
     With good mixing and temperature uniformity, the reactions in the content occur homogeneously in the bulk of the liquid content. Evolved gases, however, must pass through the circular content/head space interface. Therefore, as the reactor content level is increased the surface to volume ratio decreases and the potential for the flux of evolved gases increases. In this instance, foaming of contents can occur. 
     Foaming occurs because the evolved gas flux across the content/head space interface increases above a critical point. The gas flux in question is defined as velocity/cross-sectional area. Once foaming occurs, some of the contents are out of solution and remain un-reacted, thus affecting the uniformity and extent of the desired reactions. 
     Consider a simple experiment where a pint of beer is poured into a regular 1 pint glass with diameter D and height h where h/D≈4. Then pour an equivalent amount in a shallow pan with h/D≈1. The beer in the pint glass will require three to four times more “breathing” time than the beer in the shallow pan. 
     This problem is exacerbated by the use of an agitator (for mixing reactor content) which, consistent with the First law of Thermodynamics, delivers shaft energy to the content as kinetic energy and can locally exceed the latent heat of vaporization at the blade edges. This is known as cavitation amongst mariners. 
     The careful placement of the isothermal mixing baffles and the engineering of the geometry thereof can mitigate or eliminate the foaming problem. 
     The last performance characteristic of note is the requirement that the reactor content must be able to be placed under a vacuum for the purpose of crystallization, evaporation of solvent or vacuum distillation. In typical commercial-size reactors, typically 300 gallons and larger, the vessel wall must be thicker to withstand the external pressure due to vacuum on the inside, than otherwise required for internal pressure alone; external pressure is said to be the controlling wall thickness criteria. The present invention addresses this issue by configuring the jacket coil in such a unique way that allows for smaller wall thickness under internal content vacuum conditions, thus internal pressure becomes the controlling wall thickness criteria for the operating range of the reactor. 
       FIG. 1A  is a flow diagram that depicts the flow scheme of the present invention in a cooling mode for the phase separator  50  and the reaction vessel  110 , which contains isothermal mixing baffles  400  and the helical channel coil  100  fixed to the outer surface of reaction vessel  110 . For the purposes of illustration only one baffle is shown. In a preferred embodiment the helical channel coil  100  may also extend to cover the upper head  112  and lower head  113  of reaction vessel  110 . Low “quality” (low vapor content) working fluid shown by arrow  10  enters the phase separator  50  and is split into a vapor phase shown by line  13  and a liquid phase shown by line  11 , the separation effected by gravitational means. The liquid phase  11  from the phase separator is piped to the isothermal mixing baffle(s)  400 , wherein it changes into a vapor shown by line  12  by boiling and absorbing thermal energy from the contents inside the reaction vessel  110 . The vapor  13  emanating from the phase separator  50  is commingled with the vapor  12  generated in the isothermal mixing baffles  400  in a mixing chamber  60 . The now combined vapor streams shown by line  14  are fed into the helical channel coil  100 , wherein the vapor absorbs sensible thermal energy from the content inside the reaction vessel  110  until it exits the channel coil via line  15  at a temperature very close to that of the average temperature of the reactor content. 
       FIG. 1B  is a flow diagram that depicts the flow scheme of the present invention in a heating mode for the phase separator  50  and the reaction vessel  110 , which contains the isothermal mixing baffle(s)  400  and the helical channel coil  100  fixed to the outer surface of reaction vessel  110 . In a preferred embodiment the helical channel coil  100  may also extend to cover the upper head  112  and lower head  113  of reaction vessel  110 . High “quality” (mostly vapor content) working fluid shown in line  30  enters the phase separator  50  and is split into a vapor phase shown by line  13  and a liquid phase shown by line  11 , the separation effected by gravitational means. The vapor phase  13  from the phase separator  50  is piped to the isothermal mixing baffle(s)  400 , wherein it changes into a liquid by condensing and delivering thermal energy to the content inside the reaction vessel  110 . The liquid  11  emanating from the phase separator  50  is commingled with the condensate in line  32  generated in the isothermal mixing baffle(s)  400  in a separate mixing chamber  34 . The now combined liquid streams in line  36  are fed into the channel coil  100 , wherein the liquid delivers sensible thermal energy to the content inside the reaction vessel  110  until it exits the channel coil in line  15  at a temperature very close to that of the average temperature of the reactor content. 
       FIG. 2A  is a cross-sectional view of a reaction vessel  110  with a channel coil  100  fixed to the outer surface in a helical wound arrangement. In a preferred embodiment, the reaction vessel  110  consists of a cylindrical section  120  and two “dished” heads, an upper head  112  and a lower head  113 . The inside wall of channel coil  100  is the outside surface of wall  120  of reaction vessel  110  and will be disposed along the axial length of the cylindrical section  120  of reaction vessel  110 . The channel coil  100  may also cover part of the upper head  112  and/or the lower head  113 . The channel coil  100 , before it is fixed to the reaction vessel  110 , has only three outer sides,  121 ,  122 , and  123 . A fourth side of the channel coil  100  is formed by the outer surface of the wall of cylindrical section  120  of the reaction vessel  110 . A closed channel is only achieved when the channel coil  100  is fixed to the outer surface of reaction vessel  110 . The channel coil  100  surrounds the reaction vessel  110  in a helical configuration. The configuration allows for helical and corresponding downward or upward flow, with respect to the central vertical axis of the reaction vessel  110 . The channel coil  100  may be constructed from any suitable material, the most likely for industrial use being carbon steel, stainless steel, Inconel (trademark for an alloy of nickel and chromium available from the Huntington Alloy Products Division of International Nickel Co. Inc. of Huntington, W. Va.), and any number of Hastelloy alloys, including Hastelloy C-276 and Hastelloy B-2. Hastelloy is a trademark for nickel-based corrosion-resistant alloys obtained from Union Carbide Corp. of New York, N.Y. Hastelloy C-276 is a nickel-based alloy containing nickel, chromium, molybdenum, tungsten, iron, carbon and silicon. Hastelloy B-2 differs from Hastelloy C-276 in that it does not contain tungsten and the other components appear in different concentrations. 
     As shown in  FIG. 2B , in an alternate embodiment, the cylindrical section  120  of reaction vessel  110  of  FIGS. 1A and 1B  can be fabricated as a conical reactor  114  having a tapered wall  125  and two “dished” heads, a larger upper head  115  and a smaller lower head  116 . This alternate embodiment allows for better mixing of the contents and is advantageous in applications where gaseous reaction by-products are generated in the reaction vessel content. 
       FIG. 3A  is a cross-sectional view of the cylindrical reaction vessel  110  of with integral channel coil  100  and integral isothermal mixing baffle  400  (one only shown for simplicity).  FIG. 3B  is a cross-sectional view of a conical reactor  114  with integral channel coil  100  and integral isothermal mixing baffle  400  (one only shown for simplicity).  FIG. 2A ,  FIG. 2B ,  FIG. 3A  and  FIG. 3B  show two characteristics of channel coil  100 , which combine to add mechanical strength to reaction vessel  110 . The first is that the point of contact  130 ,  131  is a right angle to the reaction vessel wall  120 ,  125  respectively in the vertical section of the reaction vessel  110  or the tapered wall section of conical reactor  114 , as well in the upper heads  112 ,  115  and lower heads  113 ,  116  respectively. That is, walls  121  and  123  form a right angle with walls  120  and  125 . In the preferred embodiment shown in  FIGS. 1A and 3A , walls  121  and  123  must form a right angle with the axis of the cylinder reaction vessel  110  having a vertical cylindrical section where the channel coil is fixed to the wall  120 . In the upper  112  and lower  113  head sections of the reaction vessel  110 , walls  121  and  123  are perpendicular to the line tangent to the convex (external) surface of the head,  112  or  113 , where the tangent point is at the bisector between  121  and  123 . The channel coil  100  surrounding wall  120  of vessel  110  and wall  125  of vessel  114  can be covered with insulation  700 . 
     The same effect is achieved for the reaction vessels of  FIGS. 2B and 3B  where the vertical section has a cone shaped wall  125  by fixing portions  121  and  123  perpendicular to wall  125 . The perpendicularity of portions  121  and  123  of channel coil  100  to wall  120  or wall  125  of the reaction vessel  110  or  114  is required in order to meet the criteria established by section UG-28 of the ASME Boiler And Pressure Vessel Code Section VIII Division 1 so that elements  121 ,  122  and  123  can be considered as adding strength to the wall  120  under external pressure. The second characteristic adding strength to reaction vessel  110  concerns the pitch at which the helical channel coil  100  is affixed to the reaction vessel wall  120 . For the vertical portion (cylindrical or tapered wall) of the reaction vessel  110  or  114 , the pitch is the slope of the coil  100 , with respect to a horizontal radial plane which is perpendicular to the vertical axis of the reactor. A larger slope is considered a higher pitch. The channel coil  100  is affixed at a pitch less than or equal to a maximum pitch, which is that pitch beyond which the desired improvements in the reaction vessel wall  120 ,  125  section modulus are no longer achieved, as dictated by the rules of pressure vessel design codes such as ASME Section VIII, Division 1, sections UG-27 and UG-28 thereof. Section UG-27 explains how to calculate “Thickness of Shells Under Internal Pressure”, and section UG-28 describes how to calculate “Thickness of Shells and Tubes Under External Pressure”. Exactly what this pitch is will depend on many factors. As to reaction vessel  110  or  114  these include the diameter of reaction vessel  110 , the average diameter of vessel  114 , the material of construction of the reaction vessel and the operating parameters for which the reactor is designed. As the pitch (or slope) of the coil increases, the distance between successive coils increases. The coil is made of elements  121  and  123  that are perpendicular to the vessel wall,  120 ,  125  which allows for the vessel, under the rules of pressure vessel design codes such as ASME Section VIII, Division 1 to take credit for the reinforcement to reaction vessel wall  120 ,  125 . As the distance between successive coils increases the degree of reinforcement decreases. At some point, the degree of reinforcement becomes too low and reaction vessel wall  120 ,  125  becomes too weak for the desired function. The reinforcement required will depend upon the differential pressure between the inside and outside of reaction vessel wall  120 ,  125 . This is a design parameter easily calculated by one skilled in the art. Thus, the maximum pitch of channel coil  100  will depend on the designed maximum operating pressure for reaction vessel  110 ,  114  among other factors. For example for the head sections  112 ,  113  of the reaction vessel  110 , the pitch is the distance of each helical 360° course of the coil  100 , with respect to the previous and/or subsequent helical 360° course. A greater separation is considered a higher pitch. The channel coil  100  is fixed at a pitch less than or equal to a maximum pitch, which is that pitch beyond which the desired improvements in the reaction vessel wall  120  section modulus are no longer achieved, as dictated by the rules of pressure vessel design codes such as ASME Section VIII, Division 1, sections UG-27 and UG-28 thereof. Section UG-27 explains how to calculate “Thickness of Shells Under Internal Pressure”, and section UG-28 describes how to calculate “Thickness of Shells and Tubes Under External Pressure”. Exactly what this pitch is will depend on many factors including the diameter of reaction vessel  110 , the material of construction of the reaction vessel  110  and the operating parameters for which the reactor is designed. As the pitch (separation) of the coil  100  fixed to the upper or lower heads  112  and  113  of reaction vessel  110  increases, the distance between successive coils increases. 
     The points of contact  130  and  131  between reactor vessel wall  120  and channel coil  100  of reaction vessel  110  and between reactor vessel wall  125  and channel coil  100  of reactor vessel  114  ( FIGS. 2A ,  3 A and  FIGS. 2B ,  3 B respectively) is a right angle, and the pitch of the channel coil  100  is less than or equal to the maximum pitch. These two factors combine to increase the section modulus of the reaction vessel  110 . Under the rules of pressure vessel design codes such as ASME Section VIII, Division 1, section UG-28 thereof this resultant increase in the section modulus, due to the channel coil  100 , allows the reaction vessel wall  120  be thinner than that which would otherwise be required when the channel coil  100  is not fixed according to the present invention in order to achieve desire maximum allowable pressure for reaction vessel working conditions. Because the reaction vessel wall  120  may be thinner than that which would be required without channel coil  100 , improved heat transfer efficiency is achieved. A thinner reaction vessel wall increases the overall heat transfer coefficient across the reaction vessel wall because the thermal resistance resulting from the thermal conductivity of the reaction vessel wall is reduced. Under the rules of pressure vessel design codes such as ASME Section VIII, Division 1, the greatest advantage of the present invention is realized in larger diameter reaction vessels that operate at relatively low pressures, e.g., up to 10 bar and at full vacuum (FV). Under these conditions, the FV condition inside the reaction vessel dictates the use of thicker wall  120 ,  125  than otherwise be required to withstand positive internal pressure only. By using the present invention, the thickness of wall  120 ,  125  is controlled by positive internal pressure in the reaction vessel and will be thinner. 
     One additional advantage of the present invention is evident by examining  FIG. 8C , which depicts a comparison of a conventional half-pipe jacket cross-section R to that of the present invention with proportional dimensions. The cross-sectional area of a jacket coil  100  in accordance with the present invention, compared to that of a conventional half-pipe jacket coil R of proportional dimensions, is 4/π or 27% greater. This allows for higher fluid flow for the same unit pressure drop, and thus greater heat transfer. 
     The channel coil  100  may be additionally insulated with insulation  700  attached directly to the three outer sides,  121 ,  122 , and  123 , of the coil  100  as shown in  FIG. 8C . Alternatively, insulation  700  may be wrapped around channel coil  100  and reaction vessel  110  or reaction vessel  114  as shown in  FIG. 3A  and  FIG. 3B , before placement in an evacuation shell.  FIG. 4  shows vessel  110  placed inside evacuation shell  300 . Insulation  700  may be any suitable material which does not out-gas when it is evacuated and/or heated. Reflective multi-layer insulation, made of alternating layers of fiberglass cloth, cured of any residues, which would otherwise out-gas when evacuated and/or heated, and aluminum foil are preferred. The alternate layer method of application may be varied, e.g. two layers of cloth and one layer of aluminum foil, etc. The “no out-gassing” requirement is essential for the evacuated multi-layer reflective insulation of the preferred embodiment to be successful. 
     An alternative insulation method for the reaction vessel entails the use of evacuated dry perlite powder in the annular space between the reaction vessel, which comprises the jacket coil  100  and vessel wall  120 , and the evacuated shell  300 , ( FIG. 4 ). In this alternative embodiment, the physical space between the jacket coil  100  and the evacuated shell  300  must be at least six (6) inches, but typically eight (8) to twelve (12) inches in order for evacuated dry perlite powder to serve as a suitable insulation medium. 
       FIG. 4  is a sectional view of reaction vessel  110  with the channel coil  100  fixed to the outer surface of reaction vessel  110 , integral isothermal mixing baffle  400  (one only shown for simplicity) and an evacuated shell  300 . The evacuated shell  300  completely encloses reaction vessel  110  and channel coil  100 , with the exception of related piping and utilities, which penetrate the evacuated shell  300 . The placement of the evacuated shell  300  around the apparatus as described above allows for additional insulation of reaction vessel  110  and channel coil  100  from the ambient air. Insulation from the ambient air results in decreased heat transfer through both the reaction vessel wall  120  and the channel coil walls  121 ,  122 , and  123 , as some of the energy is parasitically lost outwardly to the environment through the insulation  700 . The utilization of evacuated shell  300  results in greater temperature control of the reaction vessel contents, making the insulation  700  more thermally efficient. The evacuated shell may be constructed from any suitable material, including carbon steel, stainless steel, Inconel, or Hastelloy C. Further, evacuated shell  300  can also include reflective material on the inner or outer surface thereof to reduce radiant heat transfer. 
       FIG. 5A  is a partial cross-sectional view of an isothermal mixing baffle of uniform circular cross-section (a cylinder) in accordance with the present invention. In the exemplary embodiment, an isothermal mixing baffle  400  is used where there exists a need to cool the reaction vessel contents. However, such isothermal mixing baffles can also be used where heating of the contents of the reaction vessel, e.g. reaction vessel  110  of  FIG. 4  is needed. The isothermal mixing baffle  400  is inserted into the reaction vessel contents through the top head  112  and evacuated shell  300  as shown in  FIG. 6A . For cooling, a saturated or subcooled liquid is introduced into the isothermal mixing baffle  400  through an inlet pipe  410 . As previously discussed, the liquid is selected primarily because of its boiling point, providing, of course, other factors do not prevent its use, such as availability, cost, reactivity, toxicity, etc. A liquid having a boiling point lower than that of the reaction vessel contents will boil when heat is absorbed from the reaction vessel contents. Fluids which may be used for cooling or heating in the present invention include, but are not limited to nitrogen, brine, steam, chilled water, carbon dioxide, ammonia, CF 4 , ethane, ethylene and hot water. Other fluids may also be used depending on the particular needs of the reaction for which the reactor is designed. 
     The ideal temperature (or range of temperatures) of the reaction vessel contents can be determined from the chemistry of the reaction. This temperature, along with the physical characteristics of the isothermal mixing baffle (dimensions, material of construction, number of baffles, etc.) and relevant heat transfer equations, are combined to give rise to a required amount of heat transfer which must occur across the wall  448  ( FIGS. 5A ,  5 B,  5 C, and  5 D) of the isothermal mixing baffle  400  in order to maintain the reactor contents at the desired temperature. From this required value of heat transfer, a fluid is selected such that the latent heat of vaporization plus any sensible heat transfer occurring from any rise in temperature of the fluid to its boiling point, will give the desired total heat transfer. It should be noted that a fluid with precisely the right characteristics does not have to exist for accurate control of the temperature. Controlling the flow rate of the fluid into the isothermal mixing baffle  400  or the liquid level thereof will allow for fine tuning the heat transfer and corresponding temperature of the reactor contents. Further, controlling the pressure of the liquid could help alter its boiling point and fine tune the cooling power and range of the liquid. The selected fluid need only fall within a range of necessary heat transfer requirements. Where heating is desired, as shown in  FIG. 1B , a hot gas, such as gaseous ammonia, is introduced via line  13  into isothermal mixing baffle  400 , the condensed ammonia in line  32  is then combined with other condensed ammonia in line  11  emanating from the phase separator  50  and introduced via line  36  into the channel coil  100 . This condensate then heats the contents of reaction vessel  110 . 
     For instance, if a higher rate of cooling is desired, then fluid flow into the isothermal mixing baffle  400  can be increased. This will raise the level of boiling liquid  450  to a level shown as  451  in  FIG. 5A  in the isothermal mixing baffle  400 . This in turn will expose a greater surface area of boiling liquid  450  to wall  448  of isothermal mixing baffle  400 , thus allowing greater heat transfer from the reaction vessel contents through wall  448  of baffle  400  into boiling liquid  450 . 
     Alternatively, the isothermal mixing baffles  400  can be used in one of several different heating and cooling schemes. The isothermal mixing baffles  400  may be used to gain only sensible heat, in which case they will serve as sensible energy mixing baffles. The isothermal mixing baffles  400  can also be utilized with a liquid having a boiling point higher than the desired temperature of the reactor contents. Cooling or warming liquid could be passed through the isothermal (or sensible energy) mixing baffles. Additionally, a gas may be passed through the isothermal (or sensible energy) mixing baffles  400 . Any fluid that provides the necessary heat transfer properties can be used in the isothermal (or sensible energy) mixing baffles for effective temperature control of the reaction vessel contents. In these cases, the isothermal (or sensible energy) mixing baffles  400  act as simple heat exchangers. 
     Isothermal mixing baffles  400  can be inserted from the top of the reactor, as shown in  FIG. 5A  and  FIG. 6A  or from the bottom of the reactor, as shown in  FIG. 5B  and  FIG. 6B . In the preferred embodiment, isothermal mixing baffles  400  have been inserted from the top of the reactor as a matter of convenience and tradition. 
     In cooling applications, the isothermal mixing baffles  400  are designed and arranged in so that their combined cross-sectional area will be such that the velocity of the vapor evolved from the liquid phase boiling therein will be below a critical value, Uc, above which droplets or slugs of the liquid phase will be entrained in the evolved gas and expelled from the isothermal mixing baffles. As shown in  FIGS. 5A ,  5 B,  5 C, and  5 D in order to accomplish this requirement, the saturated or sub-cooled inlets  410  and vapor outlets  430  of the isothermal mixing baffles  400  will be piped in parallel. Discrete cooling control can be accomplished by isolating individual isothermal mixing baffles from the plurality of isothermal mixing baffles piped in parallel. 
       FIG. 5A  shows a sintered, porous metal phase separator or “snubber”  411  placed at the end of inlet pipe  410 . The snubber  411  curtails the flow of the liquid into or out of the isothermal mixing baffle, just as a kitchen faucet nozzle controls the water flow into a sink, thereby minimizing splashing. Snubber  411  also serves to disengage and allow the phases to separate inside the isothermal mixing baffle. 
       FIG. 5A  and  FIG. 5B  also show a means for the gas formed from the boiling liquid inside the inside the isothermal mixing baffle  400  to escape. An annular space  420  surrounds the inlet pipe  410 . Annular space  420  comprises the same atmosphere as that above the liquid level in the isothermal mixing baffle  400 . As liquid flows into the isothermal mixing baffle  400  through inlet pipe  410 , resultant vapor or gas is pushed upward and out of the isothermal mixing baffle  400  through exit  430 . The exiting gas may then be utilized in various ways. If environmentally safe gas is used, it may be exhausted to the atmosphere by venting it, although this is likely not cost effective. The gas may be recovered by piping it to a condenser, or used at another site where the particular vapor or gas is needed. Finally, the exiting gas may be transported, through vacuum jacketed or otherwise insulated pipe, to the channel coil  100  for further cooling of the reactor contents, as dictated by the preferred embodiment of this invention and depicted in  FIG. 1A . 
       FIG. 5A  shows means for detecting the level of liquid in the isothermal mixing baffle  400 . A dual leg dip tube  440  is inserted into the isothermal mixing baffle  400 . The top opening  445  of the dip tube  440  is near the top of the isothermal mixing baffle  400 , and the bottom opening  447  of the dip tube  440  is near the bottom of the isothermal mixing baffle  400 . The level of liquid  450  in the isothermal mixing baffle  400  is maintained below the top opening  445  and above the bottom opening  447  of the dip tube. The pressure differential is detected as the pressure of the head of liquid in the dip tube. The pressure at the top opening  445  is the pressure of the gas above the liquid  450 . The pressure at the bottom opening  447  is the pressure of the gas above the liquid  450  plus the pressure caused by the weight of the liquid  450  which is above the bottom opening  447 . The pressure created by the weight of liquid  450  above the bottom opening  447  can be found by subtracting the value of the pressure at the top opening  445  from the value of the pressure at the bottom opening  447 . This pressure can be used (in conjunction with the density of the liquid) to calculate the height of liquid above the bottom opening  447 .  FIG. 5B  shows the mixing baffle  400  inserted through the bottom of the reactor vessel. In this instance the top opening is  446  and the bottom opening  449  of dip tube  440 . 
       FIGS. 5C and 5D  are alternative embodiments of  FIGS. 5A and 5B , respectively, wherein the internal sintered, porous metal phase separator or “snubber”  411  is made to be removable from outside the reactor vessel, without disturbing the reactor vessel contents or evacuated shell  300 . 
       FIGS. 5E and 5F  are alternative embodiments  470  of the isothermal mixing baffles  400  which employ non-circular cross-sectional geometries, such as ellipsoids and airfoils  448 . These alternative embodiments may be prescribed to augment surface area and/or direct the flow of reactor contents to enhance mixing. 
       FIG. 6A  shows the present invention including reaction vessel  110 , channel coil  100 , and one isothermal mixing baffle  400  inserted from the top of the reactor, which penetrates the upper head  112  and evacuated shell  300 . It would be apparent to one of ordinary skill in the art that multiple isothermal mixing baffles  400  could be used to increase the overall rate of heat transfer between the reactor contents and isothermal mixing baffle contents. An additional advantage to utilizing multiple isothermal mixing baffles  400  is seen where the reactor contents are agitated with a mixing blade apparatus. 
       FIG. 7A  shows an embodiment where multiple isothermal mixing baffles  400  are used in conjunction with an agitator  460 . In such a case, the isothermal mixing baffles  400  must be arranged outside the radius of mixing blades  490  of agitator  460 . In such a configuration, the isothermal mixing baffles  400  also act as mixing baffles, thus our use of the term isothermal mixing baffles. 
       FIG. 6B  shows an alternative embodiment of the present invention including reaction vessel  110 , channel coil  100 , and one isothermal mixing baffle  400  inserted from the bottom of the reactor, which penetrates the lower head  113  and evacuated shell  300 . 
     Where the reactor is agitated as shown in  FIG. 7A  and  FIG. 7B , formation of frozen reactor contents on the outside surface of the isothermal mixing baffle  400  is prevented by placing the isothermal mixing baffle  400  in or near the streamlines corresponding to maximum free stream velocity. By placing the isothermal mixing baffle  400  in these high velocity streamlines, turbulent flow around the isothermal mixing baffle  400  is maximized. By maximizing turbulent flow immediately adjacent to the isothermal mixing baffle  400 , the thickness of the laminar thin film at the surface of the isothermal mixing baffle  400  is minimized. Minimizing the thickness of this film is important in preventing material from solidifying on the surface of the isothermal mixing baffle  400 . Formation of ice on the surface of the isothermal mixing baffles  400  is detrimental as the temperature of the ice will be at the freezing point of the reactor content fluids, not the much lower boiling liquid  450  inside the isothermal mixing baffles  400 . 
     The correlation between high turbulence and avoidance of ice (or solid) formation is due to the fact that heat transfer through a laminar layer is largely conduction controlled, but heat transfer through a turbulent fluid is largely convection controlled. Convective heat transfer takes place because a fluid is in motion and eddies within the fluid effectively carry heat throughout the fluid. This is very efficient heat transfer. Conductive heat transfer, however, is due to interaction (molecular) between the molecules comprising the medium through which the heat passes. This type of heat transfer is much less efficient than convective heat transfer. Where heat transfer is convection controlled, it occurs much more quickly than for the same fluid, not moving, where conduction is the only source of heat transfer. Moreover, when a fluid has turbulent flow characteristics, heat transfer is much quicker than where the same fluid is not moving (and other pertinent factors are the same). So where the laminar, non-moving, fluid film thickness is minimized, more heat is transferred through it in a given time period and the formation of ice is subsequently slowed or prevented. Where the laminar layer is thick, heat transfer is limited, and the layer freezes more quickly than where the layer is thinner. The above mentioned probe placement provides for an overall heat transfer coefficient that is largely convection-controlled, corresponding to fully developed turbulent flow. This maximizes overall heat transfer and prevents formation and build-up of frozen reactor contents on the probe surface. A further requirement to prevent the formation of ice on the external surface of the isothermal mixing baffles  400  is that the convective film heat transfer coefficient, on the outside of the isothermal mixing baffles  400  (in contact with the reactor contents), be greater than the convective film heat transfer coefficient on the inside of the isothermal mixing baffles  400  (in contact with the boiling liquid  450 ). This outcome can be achieved through a programmable control device available through Arencibia Associates Inc., Center Valley, Pa. 
       FIGS. 7A and 7B  show alternative embodiments of the isothermal mixing baffles  400 , wherein the cross-sectional area of the isothermal mixing baffles is increased at axial locations where there will not be interference with reaction blades  490  of agitator  460 . This alternative embodiment results in increased heat transfer area. 
       FIGS. 8A and 8B  show additional embodiments of the cross-sectional shape of channel coil  100 . The outside walls  121 ,  123  of the channel coil  100  may be of nearly any shape. It is critical, however, that the portion of outside walls  121 ,  123  adjacent wall  120  of vessel  110  shown as walls  701 ,  702  ( FIG. 8A) and 703 ,  704  ( FIG. 8B ) are both normal to the outside reaction vessel wall  120 . In this configuration, channel coil  100  supports and strengthens reaction vessel wall  120 , allowing use of a thinner wall and greater heat transfer. 
       FIG. 8D  shows a particular embodiment wherein the cross-sectional area of channel coil  100  available for flow of heat transfer working fluid can be increased by joining adjacent coils with wall  124 , which may be flat, as shown, or nearly any shape. If flat, like wall  122 , wall  124  will also ad strength to the reaction vessel and further allow for the reduction of the thickness of the reaction vessel wall  120 , if external pressure is controlling. The channel defined by wall  124  and adjacent walls of the helical channel coil can be used to introduce additional fluid to contact wall  120  to thus further improve the heat transfer. The fluid in this channel can be different than the fluid in the helical channel coil. 
       FIGS. 9A and 9B  are alternative embodiments of  FIGS. 5A and 5B , respectively, wherein the wall  449   a  comprises cylindrical sections of different diameters so that the smaller diameter accommodates the trajectory of agitator blades and the larger diameter allows for greater heat transfer area. 
       FIG. 10  is a cross-sectional view of a preferred embodiment of phase separator  50  having an internal vessel  57  and an evacuated shell  59  of the present invention for use in a cooling or heating mode application. The evacuated shell  59  completely encloses internal vessel  57 , with the exception of related piping and utilities, which penetrate the evacuated shell  59 . The placement of the evacuated shell  59  around the apparatus as described above allows for additional insulation of internal vessel from the ambient air. Insulation from the ambient air results in decreased heat transfer through the internal vessel  57 , as some of the energy is parasitically lost outwardly to the environment through the insulation  58 . The utilization of evacuated shell  59  results in greater temperature control of the reaction vessel contents, making the insulation  58  more thermally efficient. The evacuated shell  59  may be constructed from any suitable material, including carbon steel, stainless steel, Inconel, or Hastelloy C. Further, evacuated shell  59  can also include reflective material on the inner or outer surface thereof to reduce radiant heat transfer. 
     Working heat transfer fluid which may be sub-cooled, saturated or contain both phases enters the phase separator at the inlet nozzle  10  and is ducted vertically through an internal coaxial pipe  51  to a porous membrane diffuser  52  through which it enters the internal phase separator vessel  57 . 
     In order for the liquid and vapor phases of the working heat transfer fluid to separate by gravity, the cross-sectional area of the internal vessel  57  of phase separator  50  will be such that the velocity of the vapor separated from the liquid phase entrained therein will be below a critical value, Uc, above which droplets or slugs of the liquid phase will be entrained in the evolved gas and expelled from the phase separator. 
     The liquid phase of the working heat transfer fluid enters the annulus between the external coaxial pipe  55  and the internal coaxial pipe  51  through apertures  56  on the external coaxial pipe  55  located at the lower end of the internal vessel  57 . The liquid phase of the working heat transfer fluid then exits the phase separator at the outlet liquid nozzle  11 . The vapor phase of the working heat transfer fluid then exits the phase separator at the outlet vapor nozzle  13 . 
       FIG. 11  is a cross-sectional view of alternate embodiment of the phase separator of the present invention for use in a cooling or heating mode application. In this alternative embodiment the working heat transfer fluid inlet nozzle is located on top along with the outlet vapor nozzle  13 . The outlet liquid nozzle  11  is located in the bottom. 
     Upper sensing line  53  in  FIG. 10  and  FIG. 11  and lower sensing line  54  in  FIG. 10  and  FIG. 11  detect liquid inventory of working heat transfer fluid in the phase separator  50 , by the same mechanism described for determining liquid level in the isothermal mixing baffles  400 , in connection with  FIG. 5A . Upper sensing line  53  in  FIG. 10  and  FIG. 11  is analogous to  445  in  FIG. 5A . Lower sensing line  54  in  FIG. 10  and  FIG. 11  is analogous to  447  in  FIG. 5A . 
     Although the present invention has been described with reference to exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed to include other variants and embodiments of the invention, which may be made by those of ordinary skill in the art without departing from the true spirit and scope of the present invention.

Technology Classification (CPC): 1