Abstract:
A system and method for oxidizing a feed material includes a reactor vessel that forms an enclosed chamber. The vessel includes a port for introducing the feed material into the chamber where it can be oxidized to create salts and particulates, together with a fluid effluent. After their creation, the salts and particulates flow into a brine pool maintained within the chamber. Thereafter, brine, including salts and particulates, can be removed from the chamber through a vessel outlet. Further, the vessel includes a fluid effluent discharge pipe extending from outside the vessel, through the brine pool, into the chamber. As a result of this structure, the fluid effluent can be separated from the salts and particulates and discharged from the chamber through the pipe, passing through the brine pool.

Description:
[0001]    The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Contract No. F08630-02-C-0083 awarded by the Air Force Armament Center. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention pertains generally to methods and systems for water oxidization of material for the purposes of waste destruction, energy generation, or production of chemicals. More specifically, the present invention pertains to methods and systems for water oxidization of organics that contain or generate inorganic compounds such as salts or oxides, or other particulates. The present invention is particularly, but not exclusively, useful as a method and system for separating the salts and particulates from the fluid effluent generated during oxidization to facilitate energy recovery from the fluid effluent. 
       BACKGROUND OF THE INVENTION 
       [0003]    As set forth in U.S. Pat. No. 6,054,057, which is herein incorporated by reference, the process of wet oxidization involves the addition of an oxidizing agent, typically air or oxygen, to an aqueous stream including feed materials at elevated temperatures and pressures. The resultant “combustion” of organic or inorganic oxidizable feed materials occurs directly within the aqueous phase. 
         [0004]    For supercritical water oxidization (“SCWO”), oxidization occurs essentially entirely at conditions which are supercritical in both temperature (&gt;374° C.) and pressure (&gt;about 3,200 psi or 220 bar). Importantly, SCWO has been shown to give rapid and complete oxidization of virtually any organic compound in a matter of seconds at five hundred degrees Celsius to six hundred fifty degrees Celsius (500° C.-650° C.) and 250 bar. During this oxidization, carbon and hydrogen in the oxidized material form the conventional combustion products carbon dioxide (“CO 2 ”) and water. When chlorinated hydrocarbons are involved, they give rise to hydrochloric acid (“HCl”), which will react with available cations to form chloride salts. Due to the adverse effects of HCl, alkali may be intentionally added to the reactor to avoid high, corrosive concentrations of hydrochloric acid in the reactor and especially in the cooldown equipment following the reactor. When sulfur oxidization is involved, the final product in SCWO is a sulfate anion. This is in contrast to normal combustion, which forms gaseous sulfur dioxide (“SO 2 ”). As in the case of chloride, alkali may be intentionally added to avoid high concentrations of sulfuric acid. Similarly, the product of phosphorus oxidization is phosphate anion. 
         [0005]    At typical SCWO reactor conditions, densities are in the range of 0.1 g/cc, so water molecules are considerably farther apart than they are in ambient liquid water. Hydrogen bonding, a short-range phenomenon, is almost entirely disrupted, and the water molecules lose the ordering responsible for many of liquid water&#39;s characteristic properties. In particular, solubility behavior is closer to that of high pressure steam than to liquid water. Smaller polar and nonpolar organic compounds, with relatively high volatility, will exist as vapors at typical SCWO conditions, and hence will be completely miscible with supercritical water. Gases such as N 2 , O 2 , and CO 2  show similar complete miscibility. Larger organic compounds and polymers will hydrolyze to smaller molecules at typical SCWO conditions, thus resulting in solubilization via chemical reaction. The loss of bulk polarity by the water phase has striking effects on normally water-soluble salts, as well. In particular, because they are no longer readily solvated by water molecules, salts frequently precipitate out as solids that can deposit on process surfaces and cause fouling of heat transfer surfaces or blockage of the process flow. 
         [0006]    This precipitation of solids presents a significant problem in industrial uses of SCWO applications. Specifically, one of the key issues that must be addressed in SCWO applications is the energy cost of compressing air for use in the feed material. In order to reduce energy costs, efforts have been made to recover energy from the reactor stream. However, the large quantities of salts and particulates in the reactor stream interfere with the energy recovery devices. Various systems have been proposed to overcome such interference. For instance, some systems have utilized a filter or cyclone device downstream of the reactor to separate the salts and particulates from the stream before energy recovery. However, the salts and particulates often plug the flow of the stream at the reactor. Therefore, the flow must first be quenched to a low enough temperature to form an aqueous phase. Quenching the reactor stream lowers its temperature and reduces the net energy that can be recovered therefrom. 
         [0007]    In order to avoid the reduction of recoverable energy, a reversing flow reactor was developed. In such a reactor the flow enters and exits at the top, while a brine pool is maintained at the reactor bottom. While this design addresses the energy recovery issue, it limits the reaction zone to 3-4 L/D before the fluid reverses. Further, it limits the conditions in the reaction zone to a back-mixed zone. As a result, achieving high destruction efficiency in such a reactor requires a large diameter vessel with a high capital cost. 
         [0008]    In light of the above, it is an object of the present invention to provide a system and method that provides for separation of the fluid effluent from the salts and particulates resulting from oxidization. Another object of the present invention is to provide a system and method that provides a fluid effluent substantially free of salts and particulates while retaining a high destruction efficiency. Still another object of the present invention is to provide a system and method which allows recovery of energy from the high temperature, high pressure fluid effluent. Yet another object of the present invention is to provide a system and method which is easy to implement, simple to use, and cost effective. 
       SUMMARY OF THE INVENTION 
       [0009]    In accordance with the present invention, a system oxidizes a feed material under conditions wherein the temperature is within a range from above approximately 374° C. to approximately 800° C. and the pressure is above approximately 25 bar. Structurally, the system includes a hollow, generally cylindrical-shaped reactor vessel that creates an enclosed chamber. At its top end, the vessel includes a port to allow the feed material to be introduced into the chamber. In the chamber, the feed material is oxidized to create a fluid effluent together with salts and particulates. The vessel further includes a brine pool at its bottom end for collecting salts and particulates that result from the reaction of the feed material. 
         [0010]    For the present invention, the vessel includes an inlet in fluid communication with the brine pool for maintenance thereof. Specifically, the inlet provides for the introduction of a quench fluid to the chamber to maintain the brine pool. Further, the bottom end of the vessel includes an outlet in fluid communication with the brine pool to allow selective removal of salts and particulates from the chamber. Likewise, a discharge pipe is provided for removal of the fluid effluent from the chamber. Structurally, the discharge pipe is affixed to the bottom end of the vessel and is oriented to extend through and beyond the brine pool. As a result, the internal end of the discharge pipe is positioned inside the chamber and above the brine pool while the external end of the discharge pipe is positioned outside the chamber. 
         [0011]    During the operation of the system of the present invention, the feed material is introduced into the chamber through the port. Preferably, the feed material, including at least one reactant and water, is forced into the chamber by a jet assembly. The jet assembly jet mixes the feed material in the section of the chamber proximate the top end of the vessel, i.e., the back-mixing section. Due to the jet mixing, reaction of the feed material is initiated. As the feed material moves downward, additional reaction occurs in the section positioned between the back-mixing section and the brine pool, i.e., the plug flow section. 
         [0012]    As a result of the reaction of the feed material, high temperature, high pressure fluid effluent is formed in the chamber along with salts and particulates. Due to gravitational forces, the salts and particulates flow downward into the brine pool. In order to maintain the brine pool as it accumulates salts and particulates, a quench fluid is selectively introduced into the pool through the inlet. Further, brine, and the salts and particulates it holds, is removed from the chamber through the outlet at the bottom of the vessel. In this manner, the salts and particulates are separated and removed from the fluid effluent. The relatively clean fluid effluent can be removed from the chamber through the discharge pipe passing through the brine pool. Because the fluid effluent exits the chamber through the brine pool, the system is able to facilitate reactions through the back-mixing and plug flow sections. After removal of the fluid effluent from the vessel, heat and/or energy can be removed therefrom by appropriate recovery units without complications due to salts and particulates. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
           [0014]      FIG. 1  is a schematic diagram of the components of a system in accordance with the present invention; and 
           [0015]      FIG. 2  is a schematic cross-sectional representation of a reactor for the present invention, showing flow characteristics within the reactor. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    Referring initially to  FIG. 1 , a system in accordance with the present invention is shown schematically and is generally designated  10 . As shown, the system  10  includes a hollow, generally cylindrical-shaped reactor vessel  12  that encloses a reactor chamber  14  with side walls  16 . It is also shown that the reactor vessel  12  has ends  18  and  20 . Preferably, the reactor vessel  12  is substantially vertically oriented with the top end  18  directly above the bottom end  20  so that gravitational forces will act to draw the combustible material through the reactor chamber  14 . It is to be appreciated, however, that the vessel  12  can be oriented other than vertically, as long as an exit section  22  is below the reaction zone to avoid density instabilities. Further, it should be ensured that excessive solids do not fall onto and accumulate on the side walls  16 . Regardless of the particular orientation, the important factor, which is more fully set forth below, is that there be a substantially unidirectional flow of material through the vessel  12 . 
         [0017]    The feed material to reactor vessel  12  of the system  10  can, in certain embodiments, include four separate identifiable constituents. These are: (1) the reactant to be processed; (2) an auxiliary fuel, if necessary to sustain reaction in the reactor chamber  14 ; (3) water; and (4) a pressurized oxidant. More specifically,  FIG. 1  shows that the reactant  24  which is to be processed is initially held in a holding tank  26 . As contemplated for the present invention, the reactant  24  can consist of organic material, inorganics, particulates, sludge, soil, neutralizing agents, salt-forming agents, minerals, and/or combustible material. As indicated in  FIG. 1 , it may be necessary to combine this reactant  24  with an auxiliary fuel  28 , such as ethanol, which can be initially held in a holding tank  30 . 
         [0018]      FIG. 1  also shows that both the reactant  24  and the auxiliary fuel  28 , if used, are pressurized before being introduced into the reactor chamber  14 . Specifically, a transfer pump  32  and high pressure pump  34  are used to pressurize the reactant  24 . Similarly, a transfer pump  36  and a high pressure pump  38  are used to pressurize the auxiliary fuel  28 . As shown for the schematic of system  10  in  FIG. 1 , the pressurized reactant  24  and auxiliary fuel  28  are combined in line  40  and transferred to the top end  18  of the reactor chamber  14 . It is to be noted that while the reactant  24  and auxiliary fuel  28  are respectively pressurized by high pressure pumps  34  and  38  to pressures above about 220 bar, they are not necessarily raised in temperature prior to being introduced into the reactor chamber  14 . Thus, as intended for the system  10 , the reactant  24  can be introduced into the reactor chamber  14  at ambient temperatures. 
         [0019]    In addition to the reactant  24  and auxiliary fuel  28 , the feed material to reactor chamber  14  can also include pressurized water  42  and a pressurized oxidant. As shown in  FIG. 1 , water  42  is drawn from holding tank  44  by transfer pump  46  and is thereafter pressurized by high pressure pump  48  before it is passed into line  50 . At the same time, air, or some other oxidant, is pressurized by a compressor  52  and is passed into the line  50 . For purposes of the present invention, the oxidant to be used, as an alternative to air, can be pure liquid or gaseous oxygen, enriched air, hydrogen peroxide, nitric acid, nitrous acid, nitrate, and nitrite. Alternatively, a substoichiometric oxidant can be used for applications in which partial oxidization of the reactant  24  is desired. In any event, at this point the pressurized water  42  and compressed air (oxidant) are mixed and introduced into a preheater  54 . As contemplated by the present invention, the heating of the pressurized water/air mixture in preheater  54  can be accomplished in several ways. For example, a regenerative heat exchange with hot effluent from reactor chamber  14  can be used. Alternatively, an external source, such as electricity, or a fired heater, or a combination of these, can be used. For a cold startup of the system  10 , external heat sources must be used. When using a reactant  24  that has sufficient inherent heating value by itself, the preheater  54  may be shut down once a steady state operation of the system  10  has been achieved. 
         [0020]    As the air/water mixture leaves the preheater  54 , it is mixed with the reactant  24  and auxiliary fuel  28  from the line  40 . This mixing occurs at the junction  56 , and the feed material, including the combination of reactant  24 , auxiliary fuel  28 , water  42 , and compressed air (oxidant) is then introduced into the reactor chamber  14  via a port  58 . As will be appreciated by the skilled artisan, an alternative for the system  10  is to use separate feed lines for introducing one or more of the streams which make up the feed material into the reactor chamber  14  through the port  58 . If so, one feed line could be used for the introduction of the reactant  24  and auxiliary fuel  28 , and another feed line would be used for the introduction of water  42  and oxidant. Similarly, a separate feed line could be used for the reactant  24 , the auxiliary fuel  28 , the water  42 , and the oxidant. Further, depending upon the particular reactant  24 , it may be important to use a high shear mixer at the junction  56  to mix the feed/fuel stream from line  40  with the water/oxidant stream from the preheater  54 . For example, if the reactant  24  is largely water insoluble, high shear mixing is desirable to ensure sufficient mixing of combustible materials and high pressure oxidant. 
         [0021]    Referring now to  FIG. 2 , it will be seen that the vessel  12  and chamber  14  generally define a longitudinal axis  60 . For purposes of the present invention, it is preferable that this longitudinal axis  60  of the vessel  12  be vertically oriented with the top end  18  directly above the bottom end  20  so that gravitational forces act generally downwardly along the axis  60  on the feed material. With this orientation, all of the feed material that is to be introduced into the reactor chamber  14  through the port  58  is passed through a jet assembly including a nozzle  62 . Importantly, the nozzle  62  introduces a stream of material  64  into the reactor chamber  14  of the vessel  12  in a direction which is substantially along the axis  60 . In one embodiment, the nozzle  62  can introduce a straight single jet of the stream  64  at a velocity of about fifty feet per second (50 fps). In another embodiment, the nozzle  62  can consist of a plurality of nozzles  62  with their respective streams  64  introduced as jets which are inclined toward the axis  60 . With this inclination, the streams  64  are directed slightly toward each other for collision with each other. 
         [0022]    Importantly, the feed material from nozzle  62  should be directed so as not to directly impinge on the walls  16  of the reactor chamber  14 . In this way, build up of solid materials on the walls  16  of the reactor chamber  14  can be minimized. As shown in  FIG. 2 , the reaction stream  64  is introduced into the upper portion of the reactor chamber  14  where it is subjected to vigorous back-mixing. Specifically, fluid flow in this back-mixing section  66  is characterized by a turbulence in the reaction stream  64  that results from entraining shear forces and eddies  68  which are set up as the feed material enters into the reactor chamber  14 . The feed material is thus rapidly brought above the supercritical temperature of three hundred seventy-four degrees Celsius (374° C.) and rapid reaction commences. Further, while the present system  10  avoids direct impingement of the reaction stream  64  onto the walls  16 , heat transfer from the walls  16  in the back-mixing section  66  can assist in the propagation of the reaction within the vessel  12 . 
         [0023]    Below the back-mixing section  66  in reactor chamber  14  is a plug flow section  70 . This plug flow section  70  is characterized by the fact that there is no large scale back-mixing of the reaction stream  64  in this lower portion of the reactor chamber  14 . The flow of the reaction stream  64  in the plug flow section  70 , however, does exhibit local turbulent mixing. 
         [0024]    The present system  10  also includes a pool of brine  72  having a surface level  74  below the plug flow section  70 . The brine  72  captures the salts and particulates  76  that tend to flow down the side walls  16  of the chamber  14 . As is known, the salts and particulates  76  may flow down the side walls  16  as a result of scraping of the walls. As the salts and particulates  76  are received by the brine  72 , the composition of the brine  72  changes. In order to maintain the temperature and water content of the brine  72 , the vessel  12  is provided with a quench inlet  78 . Specifically, the quench inlet  78  is positioned below the surface level  74  of the brine  72  to allow the introduction of quench fluid  80  (shown in  FIG. 1 ) to the pool of brine  72 . As seen in  FIG. 1 , the quench fluid  80  is stored in a holding tank  82  that is in fluid communication with the quench inlet  78  via line  84 . Also connected to line  84  is a neutralizing agent  86  stored in a holding tank  88 . The neutralizing agent  86  may be added to the quench fluid  80  in order to control and manipulate the content of the pool of brine  72 . It may be desirable to quench the brine  72  for a number of reasons, including to dissolve the salts and particulates  76 , to adjust the pH of the brine  72 , and/or to allow the use of the brine  72  outside the reactor vessel  12 . If desired, the quench fluid  80  may be water  42  from holding tank  44 . In such cases, line  84  may be connected to holding tank  44 . Preferably a high pressure pump (not shown) is utilized to draw the water  42  from the holding tank  44  to the quench inlet  78 . 
         [0025]    It will be appreciated that water from an external source, or relatively dirty water (e.g., sea water), or cool, recycled brine can be used as a quenching medium. These options would help to reduce the system&#39;s need for clean quench water. Additionally, it should be appreciated that the cooling fluid should be relatively cool when compared to the brine to provide the quenching medium. Stated another way, the cooling fluid need only be cooler than the brine to cool the brine. 
         [0026]    Referring back to  FIG. 2 , the vessel  12  is shown having a brine outlet  90 . Brine outlet  90  allows the brine  72 , and the salts and particulates  76  therein, to be selectively removed from the vessel  12 . Also shown in  FIG. 2  is a fluid effluent discharge pipe  92  which is formed with a lumen  94 . Although in  FIG. 2 , the discharge pipe  92  is shown affixed to the end  20  of the vessel  12  and oriented to extend through the brine  72 , the discharge pipe  92  need not be so designed. Specifically, the discharge pipe  92  may pass through the side wall  16  of the vessel  12 , either above or below the surface level  74  of the brine  72 . Regardless of the specific design of the discharge pipe  92 , the internal end  96  of the discharge pipe  92  is positioned inside the chamber  14 , below the port  58 , and above the surface level  74  of the brine  72 , preferably in the plug flow section  70 . The external end  98  is positioned outside the chamber  14 . With this cooperation of structure, the discharge pipe  92  provides for removal of relatively clean, high temperature, high pressure fluid effluent  100  from the chamber  14  through the lumen  94 . As further shown in  FIG. 2 , the internal end  96  of the discharge pipe  92  may include a structure  102  that forces the fluid effluent to change direction prior to entering the discharge pipe  92  as indicated by arrows  104 . Also shown are baffles  106  for reducing entrainment of salts and particulates at the internal end  96  of the discharge pipe  92 . 
         [0027]    Referring now to  FIG. 1 , it is seen that line  108  is in fluid communication with the external end  98  of the discharge pipe  92  (shown in  FIG. 2 ). As shown, line  108  leads to an energy recovery unit  110 , such as an engine or a turbine. The energy recovery unit  110  is able to recover energy from the 3400 psia, 1200° F. fluid effluent  100  without encountering the salts and precipitates  76  created during oxidization. The recovered energy can be used to power the air compressor  52  or other components in the system  10 . In some embodiments, the heat of the fluid effluent  100  may be recovered by a heat recovery unit  112  which is also connected to line  108 . As further shown in  FIG. 1 , brine outlet  90  is connected to a line  114  which leads to a heat recovery unit  116 . With this arrangement, heat may be recovered from the brine  72  after it is discharged through the brine outlet  90 . 
         [0028]    While the particular system and method as herein shown and described in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.