Abstract:
A system and method for performing hydrothermal treatment includes a reactor vessel having a pressure bearing wall. The surface of the pressure bearing wall that faces the reactor chamber is covered by a liner to protect the wall from exposure to temperature extremes, corrosives and salt deposits. The liner is formed with a porous layer and a non-porous, corrosion resistant layer. The corrosion resistant layer is positioned adjacent to the porous layer to seal the porous layer between the corrosion resistant layer and the wall of the vessel. Connectors extend through the wall of the reactor vessel to allow for fluid communication between the porous layer and an externally located pump. A heat transfer fluid can be selectively passed through the porous layer to maintain the temperature of the liner.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention pertains generally to methods and systems for hydrothermal treatment to destruct waste, recovery heat, or produce beneficial chemicals. More specifically, the present invention pertains to methods and systems for the hydrothermal treatment of organics which contain inorganic compounds such as salts or oxides or which will generate these inorganic compounds. The present invention is particularly, but not exclusively, useful as a method and system for the hydrothermal treatment of organics under supercritical temperature and pressure conditions, or at supercritical temperatures and elevated, yet subcritical pressures.  
         BACKGROUND OF THE INVENTION  
         [0002]    The process of wet oxidation has been used for the treatment of aqueous streams for over thirty (b  30 ) years. In general, a wet oxidation process involves the addition of an oxidizing agent, typically air or oxygen, to an aqueous stream at elevated temperatures and pressures. The resultant “combustion” of organic or inorganic oxidizable materials occurs directly within the aqueous phase.  
           [0003]    A wet oxidation process is typically characterized by operating pressures in the range of 30 bar to 250 bar (440 psia-3,630psia) and operating temperatures in a range of one hundred fifty degrees Celsius to three hundred seventy degrees Celsius (150° C.-370° C.). Under these conditions, liquid and gas phases coexist for aqueous media. Since gas phase oxidation is quite slow at these temperatures, the reaction is primarily carried out in the liquid phase. To do this, the reactor operating pressure is typically maintained at or above the saturated water vapor pressure. This causes at least part of the water to be present in a liquid form. Even in the liquid phase, however, reaction times for substantial oxidation are on the order of one (1) hour. In many applications, reaction times of this length are unacceptable.  
           [0004]    In addition to unacceptably long reaction times, the utility of conventional wet oxidation is limited by several factors. These include: the degree of oxidation attainable; an inability to adequately oxidize refractory compounds; and the lack of usefulness for power recovery due to the low temperature of the process. For these reasons, there has been considerable interest in extending wet oxidation to higher temperatures and pressures. For example, U.S. Pat. No. 2,944,396, which issued Jul. 12, 1960 to Barton et al., discloses a process wherein an additional second oxidation stage is accomplished after wet oxidation. In the Barton process, unoxidized volatile combustibles which accumulate in the vapor phase of the first stage wet oxidation reactor are sent to complete their oxidation in the second stage. This second stage is operated at temperatures above the critical temperature of water, about three hundred seventy four degrees Celsius (374° C.).  
           [0005]    A significant development in the field occurred with the issuance of U.S. Pat. No.4,338,199, to Modell on Jul. 6 , 1982. Specifically, the Modell &#39;199 patent discloses a wet oxidation process which has now come to be widely known as supercritical water oxidation (“SCWO”). As the acronym SCWO implies, in some implementations of the SCWO process, oxidation 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 oxidation of virtually any organic compound in a matter of seconds at temperatures between five hundred degrees and six hundred fifty degrees Celsius (500° C.-650° C.) and at pressures around 250 bar. During this oxidation, carbon and hydrogen in the oxidized material form the conventional combustion products, namely carbon dioxide (“CO 2 ”) and water. When chlorinated hydrocarbons are involved, however, they give rise to hydrochloric acid (“HCl”), which will react with available cations to form chloride salts. Due to the corrosive effect of HCl, it may be necessary to intentionally add alkali to the reactor to avoid high concentrations of hydrochloric acid in the reactor. This is especially important in the cooldown equipment following the reactor. In a different reaction, when sulfur oxidation is involved, the final product in SCWO is a sulfate anion. This is in contrast to standard, dry combustion, in which gaseous sulfur dioxide (“SO 2 ”) is formed and must generally be treated before released into the atmosphere. As in the case of chloride, alkali may be intentionally added to avoid high concentrations of corrosive sulfuric acid. Similarly, the product of phosphorus oxidation is a phosphate anion.  
           [0006]    At typical SCWO reactor conditions, densities are around 0.1 g/cc. Thus, water molecules are considerably farther apart than they are in water at standard temperatures and pressures (STP). Also, hydrogen bonding, a short-range phenomenon, is almost entirely disrupted, and the water molecules lose the ordering that is responsible for many of the characteristic properties of water at STP. In particular, the solubility behavior of water under SCWO conditions is closer to that of high pressure steam than to water at STP. Further, at typical SCWO conditions, smaller polar and nonpolar organic compounds, having relatively high volatility, will exist as vapors and are completely miscible with supercritical water. It also happens that gasses such as nitrogen (N 2 ) oxygen (O 2 ) and carbon dioxide (CO 2 ) show similar complete miscibility in supercritical water. The loss of bulk polarity in supercritical water also significantly decreases the solubility of salts. The lack of solubility of salts in supercritical water causes the salts to precipitate as solids and deposit on process surfaces causing fouling of heat transfer surfaces and blockage of the process flow.  
           [0007]    A process related to SCWO known as supercritical temperature water oxidation (“STWO”) can provide similar oxidation effectiveness for certain feedstocks but at lower pressure. This process has been described in U.S. Pat. No. 5,106,513, issued Apr. 21, 1992 to Hong, and utilizes temperatures in the range of six hundred degrees Celsius (600° C.) and pressures between 25 bar to 220 bar. On the other hand, for the treatment of some feedstocks, the combination of temperatures in the range of four hundred degrees Celsius to five hundred degrees Celsius (400° C.-500° C.) and pressures of up to 1,000 bar (15,000 psi) have proven useful to keep certain inorganic materials from precipitating out of solution (Buelow, S. J., “Reduction of Nitrate Salts Under Hydrothermal Conditions,” Proceedings of the 12 th  International Conference on the Properties of Water and Steam, ASME, Orlando, Fla., September 1994).  
           [0008]    The various processes for oxidation in an aqueous matrix (e.g. SCWO and STWO) are referred to collectively as hydrothermal oxidation, if carried out at temperatures between about three hundred seventy-four degrees Celsius to eight hundred degrees Celsius (374° C.-800° C.), and pressures between about 25 bar to 1,000 bar. Similar considerations of reaction rate, solids handling, and corrosion also apply to the related process of hydrothermal reforming, in which an oxidant is largely or entirely excluded from the system in order to form products which are not fully oxidized. The processes of hydrothermal oxidation and hydrothermal reforming will hereinafter be jointly referred to as “hydrothermal treatment.” 
           [0009]    A key issue pertaining to hydrothermal treatment processes is the means by which feed streams containing or generating sticky solids are handled. It is well-known that such feed streams can result in the accumulation of solids that will eventually plug the process equipment. Sticky solids are generally comprised of salts, such as halides, sulfates, carbonates, and phosphates. One of the earliest designs for handling such solids on a continuous basis is disclosed in U.S. Pat. No. 4,822,497. In general, and in line with the disclosure of the &#39;457 patent, the reaction is a hydrothermal treatment process carried out in a vertically oriented vessel reactor. Solids form in the reactor as the reaction proceeds and these solids are projected to fall into a cooler brine zone that is maintained at the bottom of the reactor. In the brine zone, the sticky solids re-dissolve and may be continually drawn off in the brine from the reactor. Solids separation from the process stream is achieved because only the fraction of the process stream that is necessary for solids dissolution and transport is withdrawn as brine. The balance of the process stream, which is frequently the largest portion, is caused to reverse flow in an upward direction within the reactor. The process stream, less the solids, is then withdrawn from the top section of the reactor. By this means, it becomes possible to recover a hot, nearly solids-free stream from the process. To minimize entrainment of solid particles in the upward flow within the reactor, the velocity is kept to a low value by using a large cross-section reactor vessel. Experience has shown that while a large fraction of the sticky solids is transferred into the brine zone, a certain portion also adheres to the vessel walls, eventually necessitating an online or off-line cleaning procedure.  
           [0010]    The extreme temperatures, pressures, corrosives and insoluble salts present in the hydrothermal reactor vessel present what can only be characterized as a harsh environment to the pressure bearing wall of the reactor vessel. To alleviate the effects of this environment on the pressure bearing wall, liners have been heretofore suggested to separate the reactor chamber from the pressure bearing wall. For example, U.S. Pat. No. 5,591,415 which issued to Dassel et al. entitled “Reactor for Supercritical Water Oxidation of Waste” discloses a reactor enclosed in a pressure vessel in a manner that the walls of the pressure vessel are thermally insulated and chemically isolated from the harsh environment of the reaction zone. Unfortunately, the liner disclosed by Dassel et al. fails to adequately address the problem associated with insoluble salt buildup and reactor plugging. Similarly, U.S. Pat. No. 3,472,632 which issued on Oct. 14, 1969 to Hervert et al. entitled “Internally Lined Reactor for High Temperatures and Pressures and Leakage Monitoring Means Therefore” discloses a liner that is not sealed to the vessel wall and that has a porous layer for a high temperature reactor. Hervert et al., however, does not disclose the use of the liner for hydrothermal treatment environments, and consequently, the disclosed liner lacks at least one very important feature necessary for using a liner in hydrothermal treatment, namely, a suitable mechanism for relieving the effects of insoluble salt buildup and reactor plugging.  
           [0011]    In light of the above, it is an object of the present invention to provide a liner to protect the pressure bearing wall of a hydrothermal treatment reactor incorporating a mechanism to control the liner temperature and thereby prevent the buildup of insoluble salts on the liner. Another object of the present invention is to provide a liner to protect the pressure bearing wall of a hydrothermal treatment reactor wherein the liner incorporates a mechanism for pre-heating the reaction chamber before steady state treatment conditions are achieved. Yet another object of the present invention is to provide a liner to protect the pressure bearing wall of a hydrothermal treatment reactor wherein the liner incorporates a mechanism for passing a heat exchange fluid by the reactor chamber to allow heat to be recovered from the reaction. Still another object of the present invention is to provide a liner to protect the pressure bearing wall of a hydrothermal treatment reactor wherein the liner incorporates a mechanism for altering the liner temperature, and consequently the liner dimensions, to allow for easy installation and removal of the liner. Still another object of the present invention is to provide a liner to protect the pressure bearing wall of a hydrothermal treatment reactor wherein the liner includes a system for leak detection that is operable during the hydrothermal reaction which allows for reactor shutdown before a severe attack on the pressure bearing wall occurs. Yet another object of the present invention is to provide a system and method for accomplishing hydrothermal treatment which is easy to implement, simple to use, and cost effective.  
         SUMMARY OF THE PREFERRED EMBODIMENTS  
         [0012]    In accordance with the present invention, a system for performing hydrothermal treatment at temperatures above three hundred seventy-four degrees Celsius (374° C.) and pressures above about 25 bars, includes a reactor vessel that is formed with a pressure bearing wall which surrounds a reactor chamber. Generally, the feed material is introduced into the reactor chamber from one end of the reactor vessel and the reaction products are withdrawn from the other end of the reactor vessel.  
           [0013]    The surface of the pressure bearing wall that faces the reactor chamber is covered by a liner to protect the wall from exposure to temperature extremes, corrosives and salt deposits. The liner is formed with a porous layer and a non-porous, corrosion resistant layer. The corrosion resistant layer is positioned adjacent to the porous layer to interpose the porous layer between the corrosion resistant layer and the wall of the vessel. Seals extend from the ends of the corrosion resistant layer to the wall of the reactor vessel to further encapsulate the porous layer between the wall and the corrosion resistant layer.  
           [0014]    A connector extending through the pressure bearing wall of the reactor vessel is provided to allow fluid communication between the porous layer and an externally located pump. When activated, the pump allows a heat transfer fluid to be pumped into the porous layer for circulation within the porous layer. A second connector in the wall provides an exit for heat transfer fluid circulating within the porous layer. The discharged heat transfer fluid that is flowing through the second connector can be piped back to the pump or to a storage reservoir for recirculation.  
           [0015]    In addition to the connectors used for pumping of the heat transfer fluid, one of the heat transfer fluid connectors, or another connector may be provided in the wall of the reactor vessel to allow for sampling of the fluid within the porous layer. Specifically, the purpose of this sampling will be to determine whether a leak has developed in the corrosive layer of the liner. To do this, the physical or chemical properties of a sample may be measured by a sensor. Physical and chemical properties that may be useful for this purpose include: fluid pressure; fluid flow; fluid temperature; and detection of the presence of a particular chemical species in the fluid. For the present invention, the leak detection connector can function in at least two different ways. In one configuration, a sensor can be positioned within the porous layer allowing the connector to function as a conduit to relay a signal from the sensor to a recorder/display. Alternatively, the connector can function as a fluid passageway allowing the fluid from the porous layer to flow through the connector to an externally located sensor. In either case, the connectors allow for leak detection measurements to be performed during the hydrothermal treatment of the reactants thereby ensuring the continuous integrity of the corrosion resistant layer of the liner.  
           [0016]    For the present invention, partitions can be positioned within the porous layer, with each partition extending from the corrosion resistant layer to the pressure bearing wall. Thus, the partitions divide the porous layer into sections and isolate the sections from each other. If partitions are used, separate connectors can be provided for each section to thereby allow each section to be independently heated, cooled and monitored for leaks. Also, an optional layer of insulation can be selectively interposed between the porous layer of the liner and the wall of the reactor vessel to insulate the pressure bearing wall of the reactor vessel.  
           [0017]    In operation, a warming fluid can be selectively passed through the porous layer to pre-heat the reactor chamber during periods preceding steady state treatment conditions. Additionally, a coolant can be selectively passed through the porous layer of the liner during the hydrothermal treatment of the reactants to cool the pressure bearing wall and the corrosion resistant layer of the liner. By maintaining the temperature of the corrosion resistant layer of the liner at sub-critical temperatures, corrosion rates can be reduced and the accumulation of insoluble salts on the liner can be prevented. Also in accordance with the present invention, the connectors can be utilized to perform leak detection measurements during the hydrothermal treatment of the reactants to ensure the continuous integrity of the corrosion resistant layer of the liner. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    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:  
         [0019]    [0019]FIG. 1 is a schematic diagram of the components of a system in accordance with the present invention;  
         [0020]    [0020]FIG. 2 is a schematic cross-sectional representation of an exemplary downflow reactor including a two layer liner in accordance with the present invention; and  
         [0021]    [0021]FIG. 3 is a schematic cross-sectional representation for an embodiment of the present invention having a layer of insulation positioned between the reactor vessel wall and the two layer liner. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    Referring initially to FIG. 1, a hydrothermal treatment system in accordance with the present invention is shown schematically and is generally designated  10 . As shown, the system  10  includes a reactor vessel  12  formed with a pressure bearing wall  15  that surrounds a reactor chamber  14 . It is also shown that the reactor vessel  12  has an end  16  and an end  18 . It is to be appreciated that the vessel  12  can be oriented vertically, horizontally or at an orientation somewhere therebetween.  
         [0023]    The feed material to reactor vessel  12  of the system  10  can, in certain embodiments, include several separate identifiable constituents. These are: (i) the reactant to be processed; (ii) an auxiliary fuel, if necessary to sustain reaction in the reactor chamber  14 ; (iii) water; and (iv) oxidizer(s). More specifically, FIG. 1 shows that the reactant  20  which is to be processed is initially held in a holding tank  22 . As contemplated for the present invention, the reactant  20  can consist of organic material, inorganics, sludge, soil, neutralizing agents, salt-forming agents, minerals, and/or combustible material. Further, particulates capable of entering and exiting the reactor vessel  12  can be added to the reactant  20  to remove salt from the reactor vessel  12 . These particulates can be inert materials such as sand, silica, soil, titanium dioxide, clay, metal, or ceramic. Also, catalyzing materials such as zeolites, heavy metal oxides or noble metals may be used. In either case, the particulates can be added to the reactor vessel  12  to thereby allow insoluble salts to adhere to the surface of the particulate. The coated particulate may then be removed from the reactor vessel  12 . As indicated in FIG. 1, it may be necessary to combine this reactant  20  with an auxiliary fuel  24 , such as ethanol, which can be initially held in a holding tank  26 .  
         [0024]    [0024]FIG. 1 shows that both the reactant  20  and the auxiliary fuel  24 , if used, are pressurized before being introduced into the reactor chamber  14 . Specifically, a transfer pump  28  and high pressure pump  30  are used to pressurize the reactant  20 . Similarly, a transfer pump  32  and a high pressure pump  34  are used to pressurize the auxiliary fuel  24 . As shown in the schematic of system  10  in FIG. 1, the pressurized reactant  20  and auxiliary fuel  24  are combined in line  36  and transferred to the end  16  of the reactor vessel  12 . It is to be noted that while the reactant  20  and auxiliary fuel  24  are respectively pressurized by high pressure pumps  30  and  34  to pressures above about 25 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  20  can be introduced into the reactor chamber  14  at ambient temperatures.  
         [0025]    In addition to the reactant  20  and auxiliary fuel  24 , the feed material to reactor chamber  14  can also include pressurized water  38  and a pressurized oxidizer  39 . Specifically, water  38  is drawn from holding tank  40  by transfer pump  42  and is thereafter pressurized by high pressure pump  44  before it is passed into line  46 . At the same time, oxidizer  39 , is drawn from holding tank  41  and pressurized by a compressor  48  and is passed into the line  46 . For purposes of the present invention, the oxidizer  39  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 amount of oxidizer  39  can be used for applications in which partial oxidation of the reactant  20  is desired. In any event, at this point the pressurized water  38  and compressed air (oxidizer  39 ) are mixed and introduced into a preheater  50 . As contemplated by the present invention, the heating of the pressurized water/air mixture in preheater  50  can be accomplished in several ways. For example, this preheat may be accomplished by a regenerative heat exchange with a hot reaction stream from reactor chamber  14 . The preheat can also be accomplished by an external source, such as electricity, or a fired heater, or a combination of these. External heat sources must be used for preheater  50  when a cold startup of the system  10  is required. On the other hand, it should also be noted that for reactant  20  which has sufficient inherent heating value by itself, the preheater  50  may be shut down once a steady state operation of the system  10  has been achieved.  
         [0026]    As the air/water mixture leaves the preheater  50 , it is mixed with the reactant  20  and auxiliary fuel  24  from the line  36 . This mixing occurs at the junction  52 , and the feed material, including the combination of reactant  20 , auxiliary fuel  24 , water  38 , and compressed air (oxidizer  39 ) is then introduced into the reactor chamber  14  via a duct  54 . As will be appreciated by the skilled artisan, an alternative for the system  10  is to use separate ducts for introducing one or more of the streams which make up the feed material into the reactor chamber  14 . If so, one duct could be used for the introduction of the reactant  20  and auxiliary fuel  24 , and another duct would be used for the introduction of water  38  and an oxidizer  39 . Similarly, a separate duct could be used for the reactant  20 , the auxiliary fuel  24 , the water  38 , and the oxidizer  39 . Further, depending upon the particular reactant  20 , it may be important to use a high shear mixer (not shown) at the junction  52  to mix the feed/fuel stream from line  36  with the water/oxidizer stream from the preheater  50 . For example, if the reactant  20  is largely water insoluble, high shear mixing is desirable to ensure sufficient mixing of combustible materials and high pressure oxidizer  39 .  
         [0027]    Referring now to FIG. 2, a representative vessel  12  incorporating the features of the present invention is shown. Specifically, the vessel  12  shown in FIG. 2 is representative of a downflow reactor as disclosed in U.S. Pat. No. 6,054,057 entitled “Downflow Hydrothermal Treatment” which issued to Hazlebeck and is assigned to the same assignee as the present invention. It is to be appreciated that other reactor vessel configurations known in the pertinent art, such as a reversible reactor, can be used with the present invention. As shown in FIG. 2, the vessel  12  generally defines a longitudinal axis  56  and is formed with a wall  15 . For the case of a downflow vessel, the longitudinal axis  56  of vessel  12  is vertically oriented with the end  16  directly above the end  18 . With this orientation, all of the material that is to be introduced into the reactor chamber  14  through the duct  54  is passed through a nozzle  58 . For the exemplary downflow vessel, the nozzle  58  introduces a stream of material  60  into the reactor chamber  14  of the vessel  12  in a direction which is substantially along the axis  56 . The nozzle  58  can introduce a straight single jet of the stream  60  or the nozzle  58  can consist of a plurality of nozzles  58  with their respective streams  60  introduced as jets which are inclined toward the axis  56 . With this inclination, the streams  60  are directed slightly toward each other for collision with each other.  
         [0028]    For the representative downflow reactor vessel, the reaction stream  60  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  62  is characterized by a turbulence in the reaction stream  60  that results from entraining shear forces and eddies  64  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.  
         [0029]    For the representative downflow vessel  12  shown in FIG. 2, a plug flow section  66  is located below a back-mixing section  62  in reactor chamber  14 . This plug flow section  66  is characterized by the fact that there is no large scale back-mixing of the reaction stream  60  in this lower portion of the reactor chamber  14 . The flow of the reaction stream  60  in the plug flow section  66 , however, does exhibit local turbulent mixing. In certain applications, it may be advantageous to provide a filtering device (not shown) below the plug flow section  66 . Such a device is useful for trapping low levels of sticky solids or for retaining particulates within the reactor until they have been completely reacted.  
         [0030]    The representative downflow vessel  12  can also include a quenching section  67  as shown in FIG. 2 to cool the effluent stream. It may be desirable to quench the effluent stream for a number of reasons, including to re-dissolve any solids that may have developed during the reaction and/or to adjust the pH of the effluent stream. Returning to FIG. 1, for the moment, it can be seen that a high pressure pump  68  is positioned to take water  38  from holding tank  40  and pass it along via line  70  to an input duct  72  (See FIG. 2) near the end  18  of the reactor chamber  14 . The water  38  injected through duct  72  is used for quenching the reaction stream  60  in the quenching section  67 . Specifically, the quenching fluid that is introduced through duct  72  mixes with the reaction stream  60  and re-dissolves any sticky solids which developed during reaction in the reactor chamber  14 . This quenching occurs below the quench fluid level  74 , but above the exit port  76 , so that the reaction stream  60  can pass through exit port  76  and into the line  77  without causing plugging or fouling of the exit port  76 .  
         [0031]    It will be appreciated by the skilled artisan that fluids such as high pressure gas, rather than water, can be used as a quenching medium. Also, it will be appreciated that water from an external source, or relatively dirty water (e.g., sea water), or cool, recycled reaction stream  60  can be used as a quenching medium. These options would help to reduce the amount of clean quench water needed by the system  10 . Additionally, it should be appreciated that the quenching fluid be maintained at temperatures low enough to allow salts to dissolve in the quenching fluid.  
         [0032]    Importantly, as seen in FIG. 2, a liner  82  is disposed within the reactor chamber  14 , covering a portion of the inner surface  84  of the vessel  12 . As shown, the liner includes a porous layer  86  and a non-porous, corrosion resistant layer  88 . For the present invention, the corrosion resistant layer  88  is positioned adjacent to the porous layer  86  to interpose the porous layer  86  between the corrosion resistant layer  88  and the inner surface  84  of the vessel  12 . As such, the corrosion resistant layer  88  is positioned for contact with the reactants  20  in the reactor chamber  14 . For purposes of the present invention, the corrosion resistant layer  88  can be made from suitable corrosion resistant materials known in the pertinent art including titanium, platinum, iridium, titania, and zirconia. The corrosion resistant layer  88  is preferably solid or of a suitable construction to prevent fluid from passing from the reactor chamber  14  to the porous layer  86 . For this purpose, seals  90  are located at the ends  92 ,  94  of the porous layer  86 , to attach the corrosion resistant layer  88  to the vessel  12  to thereby encapsulate the porous layer  86  between the corrosion resistant layer  88  and the inner surface  84  of the vessel  12 .  
         [0033]    The porous layer  86  can be a powder such as a metallic powder (sintered or unsintered), a metal or other suitable material having machined pores, a porous ceramic (sintered or unsintered), an expanded metal or metallic foam, or any other material known in the pertinent art that is sufficiently porous to allow fluid to flow through the porous layer  86 . Further, for purposes of the present invention, the porosity of the porous layer  86  can be substantially uniform or a porosity gradient may be established in the porous layer  86  to selectively channel fluid flow. In the preferred embodiment of the present invention, the porous layer  86  does not need to be pressurized, and consequently, the liner  82  is capable of transmitting the pressure generated in the reactor chamber  14  from the reactor chamber  14  to the walls  15  of the vessel  12 . Alternatively, the porous layer  86  can be pressurized during operation to levels that are equal or greater than the pressures experienced in the reactor chamber  14 , thereby allowing the use of liner materials that would be otherwise incapable of transmitting the pressure from the reactor chamber  14  to the wall  15  of the reactor vessel  12  without collapsing.  
         [0034]    As will be appreciated from the detailed discussion below, in accordance with the present invention, the porous layer  86  can be used to perform several functions including: detecting leaks in the corrosion resistant layer  88 ; cooling the corrosion resistant layer  88  to prevent the accumulation of insoluble salts on the liner  82 ; lowering the service temperature of the walls  15  of the vessel  12 ; withdrawing heat from the reactor chamber  14  for heat recovery; and contracting the liner  82  to detach the liner  82  from the wall  15  during removal of the liner  82  from the vessel  12 . To accomplish these functions, connectors  96  are provided that extend through the wall  15  of the vessel  12  to the porous layer  86 . Each connector  96  allows a passageway  98  to the porous layer  86  from outside the vessel  12 .  
         [0035]    With combined reference to FIGS. 1 and 2, it can be seen that a pump  100  can be placed in fluid communication with the porous layer  86  to thereby allow a heat transfer fluid  102  to be pumped into and through the porous layer  86 . Specifically, as shown, a heat transfer fluid  102  can be pumped from reservoir  104  through line  106  to a connector  96 . For use in the present invention, the heat transfer fluid  102  can be water, ethylene or propylene glycol, an inert gas or any other fluid suitable for use as a heat transfer fluid at the temperatures contemplated and described above.  
         [0036]    Referring now to FIG. 2, it can be seen that the heat transfer fluid  102  is pumped from line  106  through connector  96   a  via passageway  98   a  and into porous layer  86 . After circulation within porous layer  86 , heat transfer fluid  102  exits the porous layer  86  through connector  96   b  via passageway  98   b  and flows into line  108 . As described below, a heat transfer fluid  102  can be pumped through the porous layer  86  for several purposes. For example, a heat transfer fluid  102  can be pumped though the porous layer  86  to pre-heat the reactor chamber  14 . Referring now to FIG. 1, a preheater  110  is shown positioned along line  106  to preheat heat transfer fluid  102  prior to entering the porous layer  86 . Specifically, the reactor chamber  14  can be preheated during periods preceding steady state reactor conditions. As discussed above, combustion of the reactants  20  in the reactor chamber  14  produces heat, and this heat can be used to obtain and maintain the temperatures and pressures required for the hydrothermal treatment. Once the desired temperature and pressure within the reactor chamber  14  is obtained, the feed rates of the reactants  20 , auxiliary fuel  24 , water  38  and oxidizer  39  can be adjusted to maintain steady state reactor temperatures and pressures. Prior to obtaining the steady state reactor temperature, the chamber  14  can be preheated by passing a preheated heat transfer fluid through the porous layer  86 . It is to be appreciated that for applications that do not require a preheated heat transfer fluid  102 , the preheater  110  can be bypassed or turned off.  
         [0037]    During hydrothermal treatment, a heat transfer fluid  102  can be passed through the porous layer  86  to cool the corrosion resistant layer  88  of the liner  82  and a thin layer of fluid in the reactor chamber  14  that is immediately adjacent to the liner  82 . It is known that below certain temperatures (solubility inversion temperature), inorganic salts become highly soluble in water. As explained above, during normal hydrothermal treatment conditions, most inorganic salts are insoluble due to the high temperatures and pressures in the reactor chamber  14 . In the absence of specific precautions, these inorganic salts are free to deposit and accumulate on exposed surfaces, often plugging the reactor vessel. By maintaining the temperature of the corrosion resistant layer  88  and a thin layer of fluid in the reactor chamber  14  that is immediately adjacent to the liner  82  below the solubility inversion temperature, solids near the corrosion resistant layer are forced to dissolve rather than deposit on the surface of the corrosion resistant layer  88 . Also explained above, corrosion rates generally increase with increasing temperature. Consequently, reducing the temperature of the corrosion resistant layer  88  can effectively decrease the rate of corrosion when liner  82  is exposed to corrosives in the reaction stream  60 .  
         [0038]    Also in accordance with the present invention, during hydrothermal treatment, a heat transfer fluid  102  can be passed through the porous layer  86  to cool the pressure bearing wall  15  of the reactor vessel  12 . It is to be appreciated that by lowering the service temperature of the pressure bearing wall  15 , thinner wall sections and/or less exotic materials can be used in constructing the vessel  12 . In an alternative embodiment shown in FIG. 3, a layer of insulation  112  can be positioned between the porous layer  86  of the liner  82  and the wall  15  to lower the service temperature of the pressure bearing wall  15 . In the embodiment of the present invention shown in FIG. 3, a heat transfer fluid  102  can still be passed through the porous layer  86  to cool the corrosion resistant layer  88 , to preheat the reactor chamber  14 , or as discussed below, to recover heat from the hydrothermal treatment.  
         [0039]    With combined reference to FIGS. 1 and 2, it will be seen that a heat transfer fluid  102  can also be pumped through the porous layer  86  to recover heat generated during hydrothermal treatment. As shown in FIG. 1, heat transfer fluid  102  exiting the vessel  12  through line  108  can be sent to a heat exchanger  114  for heat recovery and then routed to a reservoir  116 .  
         [0040]    Referring now to FIG. 2, a partition  118  can be used to divide the porous layer into sections  120 ,  122 , isolating section  120  from section  122 . Although only one partition  118  is shown in FIG. 2, it is to be appreciated that more that one partition  118  may be used in accordance with the present invention. As shown in FIG. 2, separate connectors  96  can be provided for each section  120 ,  122 , allowing for independent pumping of heat transfer fluid  102  through each section  120 ,  122 . Specifically, heat transfer fluid  102  can be pumped from line  106  into section  120  of porous layer  86 , entering through connector  96   a  and exiting through connector  96   b . Similarly, heat transfer fluid  102  can be pumped from line  106 ′ into section  122  of porous layer  86 , entering through connector  96   a  and exiting through connector  96   b . Although the additional line  106 ′ is not shown in FIG. 1, it is to be appreciated that an additional line, pump and reservoir can be provided to accommodate each additional section  120 ,  122 .  
         [0041]    Also in accordance with the present invention, as shown in FIG. 2, each section  120 ,  122  of the porous layer  86  can be monitored to ensure that the high pressure reaction stream  60  is not leaking through the corrosion resistant layer  88  of the liner  82 . Specifically, connectors  96 , such as connector  96   c  shown in FIG. 2, can be provided that extend through the pressure bearing wall  15  of the vessel  12  allowing access to the porous layer  86  for monitoring. Although not shown in the Figures, it is to be appreciated that a single connector  96  could function both as a passageway  98  for pumping a heat transfer fluid  102  into the porous layer  86  and to provide access for leak detection. In one embodiment of the present invention, an external sensor  124  can be positioned outside the vessel  12  as shown in FIG. 2. Fluid communication between the external sensor  124  and section  120  of the porous layer  86  is provided by the connector  96   c . Specifically, fluid from section  120  is allowed to flow through the passageway  98   c  to the external sensor  124  and preferably, back to the porous layer  86 . For the present invention, the external sensor  124  can be a device capable of measuring flow rate, pressure, pH, temperature, the presence of any chemical species known to be in the reactor chamber  14 , or any other property known in the pertinent art which will indicate that a leak has developed in the corrosion resistant layer  88  of the liner  82 . It is to be appreciated that each section  120 ,  122  can be monitored by a separate external sensor  124  (for example, FIG. 2 shows section  122  being monitored by external sensor  124 ′) or each section  120 ,  122  can be piped together for monitoring by a single external sensor  124 .  
         [0042]    In another embodiment of the present invention, as shown in FIG. 3, internal sensors  126  can be provided to monitor each section  120 ,  122  of the porous layer  86  to ensure that the corrosion resistant layer  88  of the liner  82  is not leaking. In this embodiment, connectors  96 , such as connector  96   d  shown in FIG. 3, can be provided that extend through the pressure bearing wall  15  of the vessel  12  allowing a signal from the internal sensor  126  to be sent through the passageway  98   d  over wire(s)  128  to a display/recorder  130  located outside the vessel  12 . It is to be appreciated that the signal from the internal sensor  126  could also be sent to a controller having a processor (not shown). For the present invention, the internal sensor  126  can be a device capable of measuring flow rate, pressure, pH, temperature, the presence of any chemical species known to be in the reactor chamber  14 , or any other property known in the pertinent art which will indicate that a leak has developed in the corrosion resistant layer  88  of the liner  82 . It is to be appreciated that each section  120 ,  122  can be monitored by a separate internal sensor  126  (for example, FIG. 3 shows section  122  being monitored by external sensor  126 ′).  
         [0043]    Returning now to FIG. 1, it will be seen that as the reaction stream  60  is removed from the vessel  12  it is passed through the line  77  to a cooler  132 . As contemplated for system  10 , the cooler  132  may use regenerative heat exchange with cool reactor stream, or heat exchange with ambient or pressurized air, or a separate water supply, such as from a steam generator (not shown). Once cooled by the cooler  132 , the high pressure reactor stream is then depressurized. Preferably, depressurization is accomplished using a capillary  134 . It will be appreciated, however, that a pressure control valve or orifice (not shown) can be used in lieu of, or in addition to, the capillary  134 .  
         [0044]    After the effluent  78  from the reactor chamber  14  has been both cooled by the cooler  132  and depressurized by capillary  134 , it can be sampled through the line  136 . Otherwise, the effluent  78  is passed through the line  138  and into the liquid-gas separator  140 . To allow accumulation of a representative sample in separator  140 , it can be diverted to either tank  142  during startup of the system  10 , or to tank  144  during the shutdown of system  10 . During normal operation of the system  10 , the line  146  and valve  148  can be used to draw off liquid  150  from the collected effluent. Additionally, gas  152  from the headspace of separator  140  can be withdrawn through the line  154  and sampled, if desired, from the line  156 . Alternatively, the gas  152  can be passed through the filter  158  and valve  160  for release as a nontoxic gas  162  into the atmosphere. As will be appreciated by the person of ordinary skill in the pertinent art, a supply tank  164  filled with an alkali agent  166  can be used and the agent  166  introduced into the separator  140  via line  168  to counteract any acids that may be present.  
         [0045]    While the particular systems and methods for hydrothermal treatment as herein shown and disclosed in detail are fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that they are 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.