Abstract:
Disclosed is an apparatus for heating a viscuous liquid slurry by direct steam injection in small scale installations. A process tube, through which the slurry flows, is surrounded by a pressure vessel. The pressure vessel acts as a high pressure steam boiler tank, heating the process tube. The process tube, having a length to accommodate mixing of the slurry within, act as a reaction chamber, into which steam is injected via a direct steam injection assembly. The integration of the injector, reactor, and boiler avoids the need for an external boiler and associated plumbing.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to a direct steam injection apparatus for gas and liquid contact, and more particularly to a direct steam injection apparatus having an integrated reactor and boiler for starch liquefaction. 
     DESCRIPTION OF RELATED ART 
     U.S. Pat. No. 3,197,337, issued to N. F. Schink, teaches a starch heater apparatus that includes a diffusing steam distributor and a T-tube design for heating viscuous process liquid by directly mixing the liquid with steam. The steam is introduced to the device from a remote location. 
     U.S. Pat. No. 3,424,613, issued to K. J. Huber, et al., teaches an apparatus for the continuous production of starch pastes. It outlines an apparatus having a reaction tube downstream from a steam injection heater wherein a process slurry continues to be affected by heating while heat loss is retarded by insulation. The &#39;613 apparatus teaches a component approach to process system integration, using a long pipe path and remote heating sources. 
     BACKGROUND OF THE INVENTION 
     During the process of preparing ethanol from starches, such as those found in corn grain, the carbohydrates comprising the starches must undergo a number of process stages so as to prepare a saccharide, such as glucose, for final fermentation. These stages include “extraction,” “cooking,” “conversion,” and “sterilization,” followed by cooling and fermentation. The extraction, cooking, conversion, and sterilization stages can be efficiently accomplished on a continuous basis using a steam injection device known as a “jet cooker” for the “cooking” stage. The “jet cooker” was adopted from the paper pulp processing industry. 
     Approximately 150 psi of steam is necessary for starch cooking. Steam boilers capable of producing the 150 psi of steam are expensive, heavy, and dangerous. Proper operation of these steam boilers often requires advanced knowledge or certification of proper construction, operation, and installation procedures. Further, given the high amount of pressure necessary for cooking, including for jet cooking, the technique of continuous jet cooking for small or portable fermentation process installations has been unavailable. Accordingly, the benefits of continuous direct stream injection cookers has been solely the privilege of large processing plants where the cookers have capacities characterized by pipe diameters of larger than two-and-one-half inches. There is a need for a jet cooker apparatus that is available for small or portable fermentation process installations, and, particularly, to have a jet cooker apparatus available for smaller, remote processors working in a scale as small as one-and-one-fourth inch pipe diameters. 
     Further, prior art steam heaters for transporting and converting vegetable starch do not teach an integrated system containing the three necessary components for jet cooking, i.e., an injector, a reactor, and a boiler. Rather, the prior art apparatuses use a non-integrated boiler to generate the steam to be injected into a process tube, that acts as a reactor in which the process fluid cooks. There is a need for a heater that is an integrated system of the three necessary components so as to accommodate small-scale processes. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present direct steam injection heater apparatus provide a low cost, portable, safe, simple, and more efficient, integrated solution to heating a viscuous liquid slurry. 
     The direct steam injection heater accomplishes heat transfer to a process fluid traveling through the heater in the heater&#39;s process tube. The heat transfer is accomplished by two methods. First, the process fluid is heated upon contact with steam that is directly injected into the process fluid. Upon injection, the steam mixes with the process fluid. Second, the process fluid is heated by heat conducted through the process tube from the exterior of the process tube, which is affected by the condensation of steam and the liberated heat absorbed by the process material within the process tube. 
     During the heating steps, the process tube acts as a heated reaction tube. In one embodiment, the process tube contains a static mixer insert. In a particular configuration of this embodiment, the static mixer insert is composed of static banks of trapezoidal mixing elements. 
     In other embodiments, the process fluid may also be heated by multiple external heating methods, such as by use of an electric tape heater, direct firing, oil bath submersion, or radiation, to name a few. 
     Embodiments of the present direct steam injection heater also extend retention time of the process fluid in the externally and internally heated process tube. By externally heating the process tube and extending retention time, a lower steam temperature is required than would be required to achieve the same heating effect by direct steam injection heating in an unheated process tube of an extended heat exchanger. Extending the retention time further reduces the thermal degradation of delicate process material in the process fluid, which is a risk when process fluid travels from high temperatures in a mixing zone to the cooler temperatures of an unheated process tube. Further, heating the process tube reduces the unwanted gelling often associated with an unheated process tube. 
     Embodiments of the present direct steam injection heater also integrate the three components of jet cooking, i.e., the injector, reactor, and boiler, by enclosing the process tube in a high pressure steam boiler tank. The boiler tank encases the process tube, which functions as the reactor, and the injector, thus integrating the three components of the jet cooker. By wrapping the boiler around the process tube, the external surface of the process tube and the injection mechanism are exposed to condensing steam. This configuration reduces the need for potentially-dangerous, expensive, and complicated connecting plumbing that would accompany live steam and condensate trapping, as well as eliminating the need for turbine pumping. 
     The purpose of the foregoing Summary is to enable the public, and especially the scientists, engineers, and practitioners in the art who are not familiar with patent or legal terms or phraseology, to determine quickly from a cursory inspection, the nature and essence of the technical disclosure of the application. The Summary is neither intended to define the invention of the application, which is measured by the claims, nor is it intended to be limiting as to the scope of the invention in any way. 
     Still other features and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description describing preferred embodiments of the invention, simply by way of illustration of the best mode contemplated by carrying out my invention. As will be realized, the invention is capable of modification in various obvious respects all without departing from the invention. Accordingly, the drawings and description of the preferred embodiments are to be regarded as illustrative in nature, and not as restrictive in nature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a right-side elevation view of a direct steam injection heater with integrated reactor and boiler according to an embodiment of the invention. 
         FIG. 2  is a right-side elevation view of a component of the direct steam injection heater with integrated reactor and boiler according to the embodiment in  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While the invention is susceptible of various modifications and alternative constructions, certain illustrated embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific form disclosed, but, on the contrary, the invention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention as defined in the claims. 
     As shown in the figures for purposes of illustration, the apparatus is embodied in a novel direct steam injection heater with integrated reactor and boiler that allows for smaller-scale process use in a safe, simple, portable, and efficient integrated system. 
     In the following description and in the figures, like elements are identified with like reference numerals. The use of “or” indicates a non-exclusive alternative without limitation unless otherwise noted. The use of “including” means “including, but not limited to,” unless otherwise noted. 
     An embodiment of a direct steam injection heater with integrated reactor and boiler  20  is shown in  FIGS. 1 and 2 . The heater  20  comprises two coaxial tubes of a process tube  8  and a pressure vessel  9 , preferably positioned longitudinally horizontal so that heating liquid condensate  17  contained within the pressure vessel  9  are able to collect within the pressure vessel  9 . It is preferred that the process tube  8  be of the minimum wall thickness necessary to adequately resist collapse due to external steam pressure acting upon it while minimizing the conductive heat path through the tubing wall. Further, the process tube  8  should be of a minimum diameter to allow adequate transportation of process mass flow while accommodating the expansion of steam injected into process liquid with consideration given to the displacement of a direct steam injector assembly  22 , located partially within the process tube  8 . Still further, the process tube  8  should be of a length necessary to adequately retain the process fluid for a period of time for continuous heat absorption and mixing, during which the process tube  8  acts as an absorbing heat exchanger. Still further, the process tube  8  should be composed of a material strong enough to accommodate the heat and force of pressurized steam, with properties resistant to corrosion and softening from steam and the contained process fluid, thermal conduction properties adequate to transfer heat of condensing steam through the material to the process fluid, thermal expansion properties adequate to withstand temperature differentials between the process fluid and high pressure steam, and capable of being formed and joined to additional material into an assembly of adequate strength to contain high steam pressure. Accordingly, it is preferred that the process tube  8  be constructed from welded stainless steel. 
     The process tube  8  has a process fluid inlet  5 , through which process fluid to be heated and mixed enters the process tube  8 , and a process fluid outlet  19 , through which process fluid that has been heated and mixed exits the process tube  8 . In the embodiment shown in  FIG. 1 , a static mixing element  18  is enclosed within the process tube  8 . 
     The process tube  8  is surrounded by the pressure vessel  9 , which is sealed upon the process tube  8  thereby creating an envelope  24  between the process tube  8  and the pressure vessel  9 . The envelope  24  acts as both a steam heating jacket and a steam boiler. External heat sources  13  are concentrated on the exterior of the pressure vessel  19 . 
     It is preferred that the pressure vessel  9  be constructed of a similar material to the material used to construct the process tube  8  and be welded to the process tube at the extreme ends of the pressure vessel so as to form a seal capable of withstanding the resulting high pressure in the envelope  24  between the pressure vessel  9  and the process tube  8 . The diameter of the pressure vessel  9  should be minimized to minimize the wall thickness necessary for containing the high pressure steam contained within the envelope  24  but of a diameter large enough to create an envelope of adequate configuration and volume to accommodate the accumulation of sufficient heating liquid condensate  17  within the pressure vessel  9  so as to allow the pressure vessel  9  to act as a boiler tank. 
     Attached to the pressure vessel  9  are a first external connection fitting  3 , a second external connection fitting  7 , and a third external connection fitting  11 . The first external connection fitting  3  is located at the highest point of the pressure vessel  9  and is configured to allow venting, sensing, and measurement of live steam. It is preferred that the first external connection fitting  3  is configured to be of a size adequate for venting steam at a rate appropriate for the applied heat input. In some embodiments, the first external connection fitting  3  may be configured to allow attachment of a suitable pressure relief device (not shown). 
     The second external connection fitting  7  and the third external connection fitting  11  are configured to accommodate the function of an external water level control unit (not shown). Further, the second external connection fitting  7  is configured to allow for sensing of the level of the heating fluid condensate  17 , and the third external connection fitting  11  is configured to allow for sensing of the steam pressure. 
     The embodiment of the direct steam injection heater with integrated reactor and boiler, as shown in  FIGS. 1 and 2 , also includes a direct steam injector assembly  22 , comprising a vertically-arranged injector tube  4  that passes vertically from the interior of the process tube  8 , through the envelope  24 , through the pressure vessel  9 , to the exterior of the pressure vessel. 
     The injector tube  4  defines a port  2  located in the section of the injector tube  4  that is between the process tube  8  and the pressure vessel  9 . The port  2  is configured to accommodate the flow of steam through port  2  into the injector tube  4 . 
     A steam flow rate throttle  1  is attached to the injector tube  4  at a section of the injector tube  4  located exterior to the pressure vessel  9 . The steam flow rate throttle  1  is configured to accommodate adjustment of a throttling interference element  12 , which is configured to accommodate control of the flow of steam through port  2  into the injector tube  4 . A seal  16  is located inside the injector tube  4 , between the steam flow rate throttle  1  and the throttling interference element  12 . The seal  16  is configured to discourage leakage of steam to the exterior of the pressure vessel  9 . 
     A steam diffuser  10  is attached to the injector tube  4  at the section of the injector tube  4  located within the process tube  8 . The steam diffuser  10  is configured to accommodate passage of steam from the injector tube  4  to the interior of the process tube  8 . It is preferred that the steam diffuser  10  be configured to accommodate down-stream flow of the steam passing from the injector tube  4  into the interior of the process tube  8 . 
     In some embodiments the direct steam injector assembly  22  is configured so that the steam diffuser  10  is located center to the process tube  8 , so as to allow steam to radially disperse from the center of the process tube  8 . 
     While there is shown and described the present preferred embodiment of the invention, it is to be distinctly understood that this invention is not limited thereto but may be variously embodied to practice within the scope of the following claims. From the foregoing description, it will be apparent that various changes may be made without departing from the spirit and scope of the invention as defined by the following claims.