MXPA99009705A - Apparatus and method for oxidizing undigested wastewater sludges - Google Patents

Abstract

A hydrothermal process (10) is integrated into a wastewater treatment facility (12) to fully oxidize an undigested wastewater sludge produced by the treatment facility. A thickened and conditioned feed mixture comprising sludge from the treatment facility is first pressurized to a critical pressure and then heated to a reaction initiating temperature below the critical temperature. An oxidant is injected into the feed mixture at the reaction initiating temperature to initiate an oxidation reaction in low light-off temperature constituents of the feed mixture to produce a partially reacted mixture and raise the temperature of the partially reacted mixture to at least the critical temperature for water in a supercritical water oxidation reactor (52). Heat from the supercritical water oxidation reaction is used to heat the feed mixture and also to condition the sludge from the wastewater treatment plant preferably by thickening and heating the sludge. The effluent from the supercritical water oxidation reactor (52) may also be used to produce a standard, high quality steam which may be used to drive a steam turbine (72). Solids laden effluent from the supercritical water oxidation reactor (52) is reduced in a pressure reducing arrangement (90).

Description

APPARATUS AND METHOD FOR THE OXIDATION OF UNDIGESTED WASTEWATER SLUDGES Field of the Invention The present invention relates to the treatment of wastewater and, more particularly, to the treatment of undigested wastewater sludge. The invention includes both an apparatus and the method for economically oxidizing sludge to obtain products that can be discharged into the environment or that can be easily disposed of. Municipal wastewater treatment plants and other types use several processes to decompose raw sewage effluents and produce sewage sludge. The mud obtained as a final product includes water, organic matter and small amounts of inorganic and inert materials. A typical wastewater treatment plant first produces a sludge collected from a primary clarification or sedimentation unit. A secondary sludge is collected from a containment pile after a process is applied to the material that remains after the removal of the primary sludge. The water separated from the secondary sludge is usually treated with a disinfecting agent such as chlorine and subsequently discharged from the plant. The process used to produce the second sludge can be a biological process such as an activated sludge process, a drip filtration system, an aeration lagoon or a rotating biological contactor. The process can also be a physical-chemical process. The combined primary and secondary sludge are drip-dried and subsequently digested to further decompose the organic material. Finally the digested sludge is removed from the water to produce a material that can be eliminated in some way. There are a large number of problems associated with these common wastewater treatment plants. First, the facilities are expensive and difficult to operate, and generally do not provide useful products. The sludge from some wastewater treatment facilities can be composted to produce a material suitable for use as a soil improver or fertilizer, however, this byproduct is manufactured only at a considerable cost. The sludge that is not used to produce a compost has the problem of its elimination. A hydrothermal process known as superical water oxidation has been suggested to completely oxidize digested sludge from wastewater and other organic waste. Another hydrothermal process commonly referred to as wet air oxidation has been employed for the oxidation of various organic materials. As used herein, the term "wet air oxidation" refers to a hydrothermal oxidation process conducted at a lower temperature than the ical temperature for water, while "superical water oxidation" refers to a process of hydrothermal oxidation that is carried out at superical conditions for water, that is, at or above the ical temperature and ical pressure. The ical temperature for pure water is approximately 705 ° F (374 ° C), while the ical pressure is 3.199 psia (220.4bar). The objective of any of these processes is to destroy the organic material in the sludge by oxidation. While oxidation with moist air can not achieve complete oxidation of a particular feed, the superical water oxidation can oxidize substantially all organic material in the reaction mixture, leaving water, CO2, N2, and inorganic materials such as metals, salts , sand and clay. The amount of organic material to be destroyed in a waste such as a sewage sludge can be desed in terms of the chemical oxygen demand or COD of the material. Generally, the COD of a given material is the amount of oxygen required to completely oxidize the material. As wellboth oxidation with moist air and oxidation with supercritical water are exothermic reactions and the feedstocks for the reactions can be described in terms of their calorific value, commonly expressed in Btu / pound of feedstock. The sewage sludge can additionally be described in terms of suspended volatile solids or VSS in percent by weight. VSS can be defined as the relative organic material content of the entire mixture. The patent of the U.S.A. No. 4,338,199, granted to Modell (the "patent '199") suggests that sewage sludge can be reacted with an oxidant at temperatures and pressures in supercritical conditions to remove all of the COD from the sludge. The '199' patent teaches the initiation of the oxidation reaction to supercritical conditions to achieve the desired destruction of the organic material. The described system requires a feed having a low concentration of organic material or COD in order to maintain the reaction temperature at acceptable levels in the supercritical water oxidation reactor. Temperatures above about 1100 ° F to 1200 ° F can weaken reactor materials to a point where the material is not able to withstand the force from the pressure of the reaction mixture. In addition, reaction temperatures above 1400 ° F can cause NO2 formation. The patent of the U.S.A. No. 5,240,619, issued to Copa (the "patent '619") describes a two-stage oxidation reaction for high strength wastewater. In the process shown in the '619 patent, most of the COD is removed in an oxidation reaction with moist air carried out in a separate reactor. Any remaining COD is removed in a supercritical water oxidation reactor. Neither the '199 patent nor the' 619 patent is directed to the treatment of undigested sewage sludge. The '199 patent results in an oxidation of undigested, high strength blackwater sludge and is based on sludge digestion or dilution to produce a feed mix that has a low COD and calorific value. The system described in the '619 patent requires a separate reactor for subcritical oxidation or wet air to maintain the material under subcritical conditions for a sufficient time to remove the bulk of the COD. Thus, the '619 patent process requires additional equipment and relatively long residence times to give rise to the separate subcritical oxidation process of relatively slowness. The patent of the U.S.A. No. 5,433,868, granted to Fassbender (the "patent '868") is specifically directed to the treatment of dried sewage sludge and mainly to the problem of the removal of nitrogen compounds from the discharge stream in the treatment plant. The process described in the '868 patent preferably includes the liquefaction of sewage sludge in an alkaline digestion process to produce a stream with a low ammonia content and a stream with a high ammonia content. This stream with high ammonia content is subjected to a hydrothermal process to destroy most of the ammonia in the stream. In another embodiment, the '868 patent suggests that a sewage sludge, dried and undigested, can be treated with a hydrothermal process to remove nitrogen. However, where the hydrothermal process is applied to the undigested, dried and complete sludge, the removal efficiency of the nitrogen compounds is reduced. In any case, the effluent from the hydrothermal process is not a clean product and must be returned to the treatment plant in front of the primary clarifier.

Objectives of the Invention It is an object of the invention to provide an apparatus and method for the treatment of wastewater, which overcome the deficiencies described above and others associated with the previous wastewater treatment systems. More particularly, it is an object of the invention to provide an apparatus and method for the rapid and cost-effective treatment and oxidation of an undigested sewage sludge. For the purpose of achieving these objects, an installation for the treatment of waste water, in accordance with the invention, includes a hydrothermal processing component integrated with the treatment plant in order to maximize the use of energy from the hydrothermal reaction. According to the invention, heat energy from the hydrothermal reaction can be used to condition and preheat the feed matepal to produce a feed mix with relatively high COD or VSS. The hydrothermal process can also be integrated to recover in an economical way mechanical energy that can be used to produce electricity or to recover useful steam. Also, the invention includes a robust arrangement for reducing the pressure of the effluent from the hydrothermal process. The arrangement of the hydrothermal process, according to the invention, is particularly adapted to use a feed comprising undigested sewage sludge. The invention takes advantage of the high calorific value and composition of an undigested sludge and eliminates the digestion and water removal stages that are commonly carried out in a wastewater treatment plant. The elimination of these stages of digestion and reduction of water saves important costs and improves the overall economy of the system. The invention is not limited to undigested sewage sludge, but may also be useful in the economical processing of any feedstock that includes a sufficient concentration of constituents with low volatilization temperature and having a total calorific value within a certain range. The preferred embodiment of the invention takes an undigested and thick sewage sludge from a wastewater treatment plant to form a feed mix having a VSS level of about 1.0% to 14.4% by weight. This equates to a calorific value of the feed mix from 100 Btu to 1400 Btu per pound. After the conditioning of the sludge to produce the feed mixture comprising organic matter, inorganic and inert materials and water, the feed mixture is pressurized to a supercritical pressure using a high pressure pump. The pressurized feed mixture is then heated in a primary heat exchanger by heat exchange with hot effluent from an oxidation reactor with supercritical water. According to the invention, the temperature of the feed mixture is increased above a volatilization initiation or reaction temperature by some of the constituent organic material. An oxidant is injected into the feed mixture at a point or points in the process where the feed mixture is at a critical pressure and at a subcritical temperature, for example, 250 ° F to 450 ° F, to initiate a reaction of oxidation. The initiation of the oxidation reaction at this subcritical reaction initiation temperature produces heat to raise the temperature of the remainder of the feed mixture to a supercritical temperature either before the mixture penetrates the oxidation reactor with supercritical water or while the mixture is in the reactor. The benefit of initiating oxidation reactions at a subcritical temperature is twofold. First, the heat of the reaction provides a significant amount of the sensible heat required to raise the feed mixture to a supercritical temperature. The capture of the calorific value of the sludge together with the heating of the feed mixture by heat exchange with the effluent of the reactor produces a significant saving of energy. Second, by initiating the reactions at subcritical temperatures, a larger increase in temperature may occur before reaching the maximum operating temperature, 1400 ° F for example, and in this way, higher concentrations of sludge can be fed to the unit. If, however, the oxidant addition was delayed until after the sludge had been heated to a supercritical temperature, then the allowable temperature rises because the heat of the reaction would be much smaller and the COD or VSS of the mixture of power would be limited to a lower value. In another aspect of the invention, a solids separator receives the effluent from the oxidation with supercritical water to form two effluent streams, a clean fluid effluent and an effluent of solid-charged fluid. The effluent of clean fluid is directed to a pressure reducing arrangement to reduce the pressure and produce a standard quality steam, such as a steam of 600 psig for example. While this standard quality steam can be used for any suitable purpose, the steam is preferably expanded through a steam turbine that can be connected to drive an electrical generator. In this way, the system according to the invention can economically recover electrical energy from the energy of the oxidation reaction with supercritical water and any additional energy required to reach the subcritical temperature of initiation of the desired reaction. The invention also preferably includes an arrangement for using heat from the supercritical water oxidation effluent to condition the sludge from the wastewater treatment plant. Conditioning may include reducing the water content of the sludge, preheating to provide some of the initial energy required in the entire process, or preheating to reduce the viscosity and improve the overall flow characteristics of the sludge, or any combination thereof. stages. In the preferred form of the invention, heat from the oxidation reaction with supercritical water is further recovered from the fluid loaded with solids after separation of solids. This fluid charged with solids is preferably passed through a secondary heat exchanger to heat the feed mixture before the point at which the feed mixture enters the primary heat exchanger. The invention further includes an arrangement for reducing the pressure of the charged portion of solids from the oxidation effluent with supercritical water. The arrangement combines the robustness and reliability of a static pressure reducing device with the flexibility and control of a pressure regulating valve. In accordance with the present invention, a static pressure reduction mechanism first reduces the pressure of the solid-charged effluent to a gas-phase pressure to allow both the gas phase and the liquid phase to exist. The mixture is then allowed to separate by gravity in a pressure vessel. A loose gas release conduit is positioned in the upper part of the pressure vessel and includes a back pressure regulating valve operated to maintain the pressure of the gas phase in the pressure vessel. A liquid conduit draws liquid loaded with solids from the bottom of the container and includes a liquid removal valve. The liquid removal valve is periodically opened under the control of a mechanism adapted to maintain a desired level of liquid in the container. The liquid removal valve, in a manner different from that of a standard pressure regulating valve, works either in a fully open position or in a fully closed position. Therefore, said valve is not subject to wear severe caused by solid particles that could occur in a pressure regulating valve where the flow area is much smaller and the flow velocities are much higher. Pressure transients that occur within the separation vessel and that may be caused by the opening or closing of the liquid removal valve are effectively damped by expanding or compressing the volume of gas above the liquid . The changes over time in the pressure drop through the static pressure reducing device and that are due to erosion, they are automatically compensated by the backup pressure regulating valve located in the loose gas release line. In this way, the pressure of the effluent stream loaded with solids is economically and safely reduced to atmospheric pressure or near atmospheric pressure, without the problems normally associated with the pressure drop from a high pressure steam and that is loaded with solids. These and other objects, advantages and features of the invention will be clear from the following description of the preferred embodiments, considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagrammatic representation of an integrated wastewater treatment facility and hydrothermal treatment process embodying the principles of the invention. Figure 2 is a diagrammatic representation of a preferred hydrothermal process according to the invention. Figure 3 is a diagrammatic representation of a sludge conditioning arrangement, which embodies the principles of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in Figure 1, the invention incorporates a hydrothermal processing unit 10 into a wastewater treatment plant. According to the invention, the hydrothermal processing unit 10 receives and treats all the solids from the plant other than the material withdrawn from the initial screening units 14. The hydrothermal unit 10 works to substantially oxidize all of the organic material in the undigested sludge that comes from the treatment plant and produces an inorganic or inert material, without gas and water. The loose gas comprises mainly CO2 with relatively small amounts of N2, O2 and water vapor, and may also include some rather smaller amounts of volatile organic compounds, CO and NOx. The loose gas can be released into the atmosphere or recovered for some use. The water from the hydrothermal processing unit 10 is sufficiently clean to be returned to any point of the installation, preferably either to the discharge plant 16 or to a pool or chamber 18 for contact with chlorine. Inorganic or inert solids may comprise sand, clay, salts and metals, and may be disposed of in any way desired and consistent with applicable regulations. The wastewater treatment plant 12 receives a raw sewage effluent in the preliminary units 14 which classify materials such as coarse solids, grains of sand and grease. After the preliminary units 14, raw sewage is directed to a primary settling basin or a clarifier 19 that allows a primary sludge to settle for removal 0 through line 20. After the primary sludge is removed , the remaining material is subjected to an appropriate treatment process 22. The treatment process can be a biological based process such as an activated sludge process, a drip filtration system, an aerated lagoon process or a biological contactor. Rotary The process can alternatively comprise a physical-chemical process. Regardless of the particular process employed, the processed material is again contained in a settling tank 24 to allow a secondary sludge to settle. This secondary sludge is removed from the settlement tank through line 26 and the water is removed from the settlement tank and treated with chlorine in a chamber or pool 18 of contact with chlorine. The chlorine or chlorine-containing compound, such as sodium hypochlorite, is injected from the injection unit 28. The primary and secondary sludge is combined and thickened by one or more thickening units 30 to produce a thick sewage sludge and undigested The water removed from the thickening process is recycled through the plant 12 and commonly returned to the primary sedimentation basin 19. The undigested and thick sludge commonly has a total concentration of suspended solids in the range of 2% to 10% in weight, while the undensified sludge may have a total suspended solids content of about 0.5% to 7% by weight. Solids in the undigested sludge include organic solids such as cellulosic materials and other biological materials, inorganic materials such as sand, clay, metals and salts, nitrogen compounds and phosphorus compounds, for example. Those skilled in the art will appreciate that some wastewater treatment facilities do not include a primary clarifier such as unit 19 of Figure 1. At these facilities, only one sludge is collected after the application of the particular treatment process such as process 22. This single sludge will be considered as equivalent for the combined primary and secondary sludge, for the purposes of this description. Referring to Figure 2, the hydrothermal processing unit 10 collects sludge from wastewater, conditioning and thickened, or feed mixture in a feed tank 40. A pump 42 preferably comprising a crusher pump, feeds a high pressure pump 44 to through a suitable check valve 45. A feed pressure control device 46 maintains a desired inlet pressure towards the high pressure pump 44 and returns the excess feed mixture back to the feed tank 40. The device 46 may comprise capillarity tubes, an orifice, or a control valve. The high pressure pump 44 may comprise a variable speed pump or other suitable pump and works to pressurize the feed mixture to a supercritical pressure, that is, a pressure above the critical pressure for water, approximately 3200 psia. Preferably the pressure applied by the pump 44 is in the range of from 3600 psia to 4500 psia. The pressurized feed mixture is directed to one or more heat exchangers and preferably to a primary heat exchanger 48 and a secondary heat exchanger 50. The primary heat exchanger 48 can be any suitable arrangement for transferring heat from the effluent from the the oxidation reaction with supercritical water 52 to the feed mixture. The heat exchanger 48 is referred to as the primary heat exchanger because it is the primary mechanism for raising the temperature of the feed mixture to a desired reaction start temperature as described below. Where the secondary heat exchanger 50 is used, it is placed in front of the primary heat exchanger 48. The secondary heat exchanger 50 transfers heat from a portion of the oxidation effluent with supercritical water to the feed mixture to recover additional energy from the source. of the supercritical oxidation reaction and provide preheating. Similar to the primary heat exchanger 48, the secondary heat exchanger 50 can comprise any suitable heat exchange arrangement including a tube heat exchanger in tube or pipe and shell, for example. The preferred form of the invention includes a bypass arrangement of heat exchanger or means 47 to selectively allow a portion of the feed mixture to be derived from the heat exchanger. The bypass means 47 of the heat exchanger includes a bypass conduit 49 and a control valve 51. The control valve 51 is controlled by the temperature sensed by an appropriate sensing device (not shown) at a point after the arrangement of the exchanger Heat and conduit 49. The heat exchanger bypass means compensate for variations in the heat exchange rate due to fouling in the heat exchanger or for variations in the flow velocity. When the temperature detected by the detector is higher than a target temperature, the detector causes an actuator (not shown) associated with the valve 51 to open the valve, allowing a portion of the feed mixture to deviate from the heat exchangers and the temperature of the mixture downstream of the heat exchangers is reduced. The feed mixture is heated to or near a reaction initiation temperature with the arrangement of the heat exchanger. The reaction initiation temperature depends on the constituent organic material in the reaction mixture. According to the invention, the reaction initiation temperature is below the critical temperature for water, that is, below 705 ° F, but at or above a temperature at which constituents of low volatilization temperature (light-off) in the feed mixture they begin at least to partially oxidize in the presence of an oxidant. This reaction initiation temperature can vary from about 200 ° F to 675 ° F and will depend on the nature and concentration of the constituents with low volatilization temperature. These constituents typically include carbon-sulfur, carbon-nitrogen, carbon-chlorine, carbon-carbon, and simple carbon-oxygen bonds. The constituents with low volatilization temperature begin to oxidize at the reaction initiation temperature to release heat. Because the mixture is sufficiently pressurized to prevent the formation of steam, the heat from the initial oxidation increases the temperature and the total enthalpy of the now partially oxidized mixture. It is important to note that the constituents with low volatilization temperature of the feed mixture may not be completely oxidized at the reaction initiation temperature. Rather, the initial oxidation reaction can form intermediate organic compounds with higher or more stable volatilization temperature. As the temperature increases from the reaction initiation temperature in the presence of sufficient oxidant, more and more of the constituents with low volatilization temperature are removed from the mixture and the intermediates begin to oxidize further, releasing more heat to reach the temperature supercritical of water. The hydrothermal unit 10 also includes means for adjusting the temperature of the feed mixture which preferably comprises a heater / cooler 54. The heater / cooler 54 is operated by a control arrangement (not shown) to adjust the temperature of the mixture of feed entering the reactor to obtain a specified temperature value within the reactor 52. Typically, the temperature of the reactor effluent is used to control the heater / cooler 54, although none of the various temperatures measured along the length of the reactor It can be used for this purpose. The heating or cooling applied by the heater / cooler 54 depends on the COD (calorific value) of the feed mixture and the amount of heat recovered in the primary and secondary heat exchangers. Specifically, the COD of the feed mix determines the final effect of the sensible heat of the complete oxidation of the sludge. The heat exchanger and bypass arrangement 49 are the main variables that determine the amount of heating of the feed obtained because the initial temperature of the feed mixture and the exit temperature of the reactor 52 are kept constant. In the preferred form of the invention, the bypass arrangement and the COD of the feed mixture are controlled to minimize the heat that must be added or removed through the heater / cooler 54. An oxidant is injected into the feed mix at through an appropriate mechanism before the point at which the feed mixture reaches the critical temperature for water. The injection point may be before or after the primary heat exchanger 48 and preferably after the heater / cooler 54. The oxidant is supplied from an oxidant supply 56 and pressurized to an injection pressure by the compressor 58. The preferred form of the invention also includes a vaporizer 60 to ensure that the oxidant is injected in the gas phase. Appropriate valve means may be employed in the oxidant injection lines 61a, 61b or 61c to control the point at which the oxidant is introduced into the feed mixture. The oxidant may comprise air or pure oxygen. Alternatively, a liquid such as hydrogen, peroxide, nitric acid or solutions of nitrate salts can be used as the oxidant. The temperature of the feed mixture and the feed mixture itself are controlled to partially react the feed mixture and boost the temperature of the partially reacted feed mixture to a supercritical temperature in or before the oxidation reactor with supercritical water. The initiation of the reaction in the system conduit such as in lines 62, 63 or 64 before the oxidation reactor with supercritical water 52 produces several benefits. First, the early oxidation reaction results in a larger temperature rise (due to the heat of the reaction) before reaching the maximum operating temperature for reactor 52, approximately 950 ° F to 1400 ° F. Thus, the feed mix may contain higher concentrations of sludge. Second, the initiation of the reaction under subcritical conditions allows the heat generated in the subcritical reaction to heat the feed mixture to near the critical temperature for the water and significantly reduces the amount of heat that would otherwise be required to add to the water. through the heater. The oxidation reactor with supercritical water 52 can be any type of appropriate reactor that is made of materials that can withstand the temperatures and pressures produced in the oxidation reaction with supercritical water. For example, the supercritical water oxidation reactor 52 may comprise an elongated tube or a small diameter winding tube. The inside diameter of the pipe will depend on the capacity and speed of the system and the nature of the feed mix, but it can vary from 1.25 inches to 6 inches to achieve system flow rates between approximately 2 feet to 14 feet per second. . The primary requirement for the supercritical water oxidation reactor 52 is that the reactor provides sufficient residence time under supercritical conditions to completely and substantially oxidize all of the organic material in the feed mixture. Since the oxidation reaction with supercritical water proceeds very fast, residence times in the reactor can be as low as 10 seconds. However, the preferred reactor 52 is arranged to have a residence time of about one minute to ensure that the reaction is complete. Although not shown in the drawing, the reactor 52 may also include one or more orifices through which cold water may be injected if necessary to control the temperature of the mixture being reacted. The heat load of the heater / cooler 54 will be controlled by the maximum temperature detected by any of the various temperature detectors located in the reactor 52. The preferred control method would also include input signals from temperature detectors located before and after the primary heat exchanger 48, which would cause the heater / cooler 54 to stop the discharge in the case of an unusually high temperature in these locations. For example, a large sudden increase in the calorific value of the feed mixture could cause a temperature excursion in the primary heat exchanger 48 (considering addition of oxidant before heat exchanger 48) which would cause the heater / cooler 54 stop the discharge, passing over the temperature signals coming from the reactor. An additional safety feature of temperature control would be a mitigation pump that injects cold water into the process conduit before or after the heater / cooler 54 cools the reaction mixture in the event that a reactor temperature exceeds a predetermined set point, typically 1200 ° F. The effluent of the oxidation reactor with supercritical water 52, which may be at a temperature of between 950 ° F and 1400 ° F, and preferably of about 100 ° F, is used as the heat exchange fluid in the primary heat exchanger 48. This heat exchange reduces the temperature of the supercritical effluent at a temperature in the range between 450 ° F and 1000 ° F. In the preferred form of the invention that was illustrated, which uses a portion of the reactor effluent to produce electricity, the temperature of the reactor effluent will generally be 900 ° F or better still dependent mainly on the requirements of the device used to produce electricity . Thus, in this preferred form of the invention, the effluent remains above the critical conditions and this reduced temperature, the supercritical effluent is directed towards a solids separator 66. The solids separator 66 works to divide the reactor effluent into two. components. The first component comprises an effluent of clean supercritical fluid, while the second component comprises an effluent of supercritical fluid which contains or which is charged with inorganic or inert solids. The solids contained in this second component will include inorganic materials such as sand. Clay and precipitated salts having low solubility in water at supercritical conditions. The solids separator 62 may comprise a hydrocyclone device or a centrifuge, or any other suitable solids separating device that is capable of working under supercritical conditions. Those skilled in the art will appreciate that the solids separator 66 can receive a subcritical effluent in which two outlet streams would also include subcritical fluids. The preferred clean supercritical fluid effluent is removed from the solids separator through a pressure regulating valve 70. The pressure regulating valve 70 reduces the pressure of the clean supercritical fluid effluent to an adequate pressure for a standard quality steam, together with gases produced in the oxidation process, mainly CO2, N2 and excess oxygen. For example, the pressure may be reduced to produce a 600 psig vapor at a temperature between about 650 ° F and 750 ° F. This standard quality steam is used to drive a turbine 72. The turbine 72 can be connected to drive an electrical generator (not shown) to produce electricity. In the preferred form of the invention, heat from the clean supercritical fluid effluent is used to condition the sludge from the wastewater treatment plant. In the illustrated form of the invention, the low pressure exhaust from the turbine 72 is directed towards an arrangement or sludge conditioning means 74. The sludge conditioning means 74 serve to thicken the sludge additionally and preferably heat the sludge to reduce its viscosity and improve in some way the ease of pumping the sludge. The heat added to the sludge at this point also helps to increase the temperature of the sludge towards the initiation temperature of the reaction. Alternatively to the use of a turbine exhaust to condition the sludge, the high pressure steam can be used directly by the sludge conditioning means 74. For example, standard quality high pressure steam can be directed from the regulator 70 to a heat exchanger (not shown) to heat the sludge and evaporate water to increase the VSS of the feed mixture. Referring to Figure 3, the preferred sludge conditioning means 74 includes a heat exchanger / condenser 80 and a blower 82. The heat exchanger / condenser is adapted to receive the steam from the turbine exhaust in an exchange ratio of heat with the mud or other residue. The vapor will include CO2, N2 and any other gas from the reactor effluent and may be below atmospheric pressure and at a temperature of 135 ° F to 150 ° F, for example. The heat exchange with the steam increases the temperature of the sludge, while the blower 82 forces air over the surface of the sludge to help remove the water that evaporates from the sludge. The steam condenses in the heat exchanger / condenser 80 and is pumped back to atmospheric pressure by the condensate pump 84. In the preferred form, the heat exchanger / condenser 80 comprises a "U" shaped gutter having a jacket (not shown) to receive the steam. The heat is exchanged between the steam in the jacket and the mud in the gutter. A probe or other suitable agitator in the gutter continuously moves the sludge and can still scrape the surface of the bottom and sides of the gutter to provide even more heating, improve evaporation and prevent the sludge from cooking on the gutter surface. An area above the gutter is left open to allow air from the blower 82 to pass over the surface of the sludge in the gutter. In an alternative sludge conditioning arrangement, not shown in the drawings, a blower can be used to force air over a cold air condenser that accepts the steam from the turbine outlet. The air from the blower is heated by the condenser and this stream of hot air can be directed over the sludge to help evaporate water from the sludge and to somehow heat the sludge. Referring again to Figure 2, the supercritical fluid loaded with solids coming from the solids separator is preferably used as a heat exchange fluid for the secondary heat exchanger 50. This additional heat exchange with the effluent from the reaction of Oxidation with supercritical water makes maximum use of the energy of the reaction. However, those skilled in the art will readily appreciate that the supercritical fluid loaded with solids, after it has been cooled, can be passed directly to a pressure abatement arrangement. The arrangement or pressure reducing or pressure reducing means 90 which are preferred work to reduce the pressure in the solid-charged effluent to approximately atmospheric pressure without relying on an orifice or capillarity for complete reduction of pressure. The pressure release means 90 includes a pressure reducing device 92, a separation device 94, a backup pressure regulating valve 96 and a liquid removal valve 98. The pressure reducing device 92 may comprise an orifice or another suitable device and reduces the pressure from a critical pressure to a gas phase pressure which may be from about 500 psia to 3000 psia. This gas phase pressure allows a separate gaseous phase to be separated towards the upper part of the container 94 with the liquid phase charged with solids collecting in the lower part of the separation vessel. The backup pressure valve 96 is connected to maintain the pressure of the gas phase in the vessel 94 and releases gas to maintain the pressure in the vessel. The solid-charged liquid that is collected in the lower part of the container 94 is withdrawn through the liquid removal valve 98 which is connected to the vessel by an appropriate conduit and which preferably works either in a fully open or fully closed. An appropriate level control arrangement LEV 100 associated with the container 94 controls the position of the liquid removal valve 98. When the level control mechanism 100 detects the level of liquid rising above the particular point in the separation vessel 94, the control causes the liquid removal valve 98 to open momentarily and allow the liquid charged with solids to flow out of the vessel to atmospheric or near-atmospheric pressure. The level control 100 may include any suitable level detection arrangement such as a float associated with the container 94. Although the liquid removal valve 98 abruptly opens and closes abruptly, the gas in the container 94 expands or compresses to dampen pressure transients in the container 94. By having a large flow area and by working in the fully open or fully closed position, the removal of the liquid does not subject to a severe Erosion to the valve components due to solid particles that are in the liquid effluent and also less subject to plugging. In addition, the change in pressure drop through the pressure reducing device 92, which may occur in time due to erosion in the device 92, is automatically compensated by the back pressure regulating valve 94. The liquid withdrawn from the container 94 contains water and mainly inorganic or inert solids, although some very small amounts of organic matter, of the order of 5 ppm, can remain. The liquid may also include smaller amounts of salts in solution. The inert / inorganic solids comprise sand, silt, clay, and typically form from 10% to 25% by weight of the liquid stream. Water can be added to the container if there is insufficient water condensing from the effluent stream. The solids in this liquid can be allowed to settle by gravity or by other means of separation and then removed in any permissible manner. The water can be discharged or sent to the chlorine contact container 18 of the treatment facility (Figure 1). The composition of the loose gas removed from the container 94 will vary with the operating pressure of the container, that is, the pressure of the gas phase. The loose gas will mainly contain CO2 with lower amounts of excess oxygen, nitrogen and water vapor. The method for the treatment of wastewater sludge, according to the invention, can be described with particular reference to Figure 2. The method first includes the production of a feed mix having a total VSS content of 1.0% at 14.4%, a calorific value of 100 Btu at 1400 Btu / lb and a COD of 17,000 to 235,000 ppm, including approximately 50% material with low volatilization temperature. In the preferred form of the invention, the feed mixture is produced from a sludge of sewage, thickened and undigested, which comes from a wastewater treatment facility 12 (Figure 1). The method immediately includes pressurizing the feed mixture with a high pressure pump 44 to a supercritical pressure, that is, a pressure above the critical pressure for water, approximately 3200 psia, and preferably, 3600 psia to 4500 psia. . The feed mixture is then heated by the heat exchanger with an effluent from the supercritical oxidation reactor using heat exchangers 48 and 50 and the temperature is further adjusted with the heater / cooler 54 to bring the feed mixture to an initiation temperature. of reaction. An oxidant is then injected at the reaction initiation temperature from the oxidant compressor 58 through the injection line or lines 61a, 61b or 61c. The reaction initiation temperature is a temperature below the critical temperature for water, but at or above the volatilization temperature for the constituents with low volatilization temperature which are in the feed mixture. The reaction initiation temperature can vary from 200 ° F to 675 ° F.

The method immediately includes reacting the feed mixture and, particularly, the low volatilization temperature components found in the feed mixture, starting at the reaction initiation temperature to raise the temperature of the then partially reacted mixture to at least the critical temperature for water either before or in the oxidation reactor with supercritical water 52. In reactor 52, the partially reacted feed mixture is subjected to oxidation with supercritical water below 1400 ° F for a sufficient time to ensure Complete oxidation of all volatile solids suspended in the mixture. The residence time in the reactor can vary from 10 seconds to 3 minutes. By subjecting the feed mixture to oxidation with supercritical water in the reactor 52 an oxidation effluent with supercritical water is produced comprising a mixture of supercritical fluid and inert and inorganic solids, including precipitated salts. The method immediately includes separating the effluent from reactor 52 to produce a clean supercritical fluid effluent and a supercritical fluid effluent loaded with solids. The method of the invention may further include reducing the supercritical fluid effluent pressure loaded with solids to produce a process vapor and reducing the pressure of the effluent of solid-charged fluid at atmospheric pressure or other lower pressure as desired. The preferred step of reducing the effluent pressure of the supercritical fluid loaded with solids comprises reducing the temperature of the mixture below the critical temperature of the water and reducing the pressure of the mixture with the reduction device 92 to allow a gas phase to separate from the liquid phase in the separator vessel 94. The method also includes maintaining the pressure of the gas phase in the vessel 94 by releasing gas through the backup pressure valve 96, and removing the charged liquid of container solids through the liquid removal valve 98 under the liquid level detection device associated with the separation vessel 94. The method further includes recovering energy from the oxidation reactor effluent with supercritical water. For example, the method may include the step of driving a turbine 72 with the process steam produced from the clean supercritical fluid effluent from the reactor 52. Additionally, the method may include the use of the energy from the supercritical fluid effluent. to thicken and condition the sludge to produce the desired feed mix. The step of using the heat from the reactor effluent may comprise the production of a stream of hot air and the passage of this over the sludge to evaporate water from the sludge or, alternatively, heat the sludge with heat from the effluent of the oxidation reactor. with supercritical water to evaporate water from the mud. The above-described preferred embodiments are intended to illustrate the principles of the invention, and not to limit the scope of the invention. Various other modalities and modifications to these preferred embodiments may be made by those skilled in the art without departing from the scope of the following claims. For example, where it is desirable to produce a standard quality steam for driving a turbine or for other uses, the solid separator 66 and the secondary heat exchanger 50 can be omitted from the system. The effluent from the reactor 52 may in this case be sent directly to the pressure reducing means 90, or to the pressure reducing means after transferring heat from the effluent for the conditioning of the sludge to produce the desired feed mixture and to cool the effluent. In addition, since it is not necessary to separate the solids from the supercritical fluid stream to produce vapor susceptible to use, the temperature of the effluent can be lowered below the critical temperature in the primary heat exchanger. Where standard quality steam is not desired, heat exchanger 48 can be sized to heat the feed mixture without the need for separate heater / cooler 54. In this case, the bypass means 47 can be used to adjust the temperature of the feed mixture to the reaction initiation temperature. Thus, the bypass means 47 may comprise the temperature adjustment means.

Another arrangement for the temperature adjusting means may include a heat exchanger to remove heat from the reaction mixture after the point at which the oxidant is injected. This arrangement can result in even higher COD feed mixes and can recover more useful heat from the reaction. All those skilled in the art will readily appreciate that the components of the hydrothermal unit must be heated to near operating conditions in a start-up process prior to the operation. The components are preferably heated by circulation of clean water through the system. This clean water can be heated using the heater / cooler 54 where said heater is included in the system, or in a separate heater. The conduit and the valve means required for the introduction of clean, start-up water have been omitted in the drawings for purposes of simplification of the figures.

Claims (21)

1. Novelty of the Invention 1. An effluent handling apparatus that is used in a supercritical water oxidation treatment system, the effluent handling apparatus comprising: a) a pressure reducing device to receive an effluent loaded with solids from a supercritical process and reducing the pressure of the effluent loaded with solids at a gas phase pressure at which there is a significant gas phase with a liquid phase loaded with solids; b) a vessel connected to receive the liquid phase charged with solids and gas at the pressure of the gas phase; c) a pressure regulating valve associated with the container for maintaining the pressure of the gas phase in the container and allowing gas to exit the container to maintain the pressure of the gas phase; d) a fluid removal conduit connected below a liquid level in the container and possessing a two-position liquid removal valve; and e) control means for moving the liquid removal valve to a fully open position in response to a value of the highest liquid volume in the container, and for moving the liquid removal valve to a fully closed position in response to a value of the lowest liquid volume in the container. The apparatus of claim 1, wherein the control means for controlling the position of the liquid removal valve comprise: a) a float mechanism associated with the container to indicate the volume of liquid in the container. The apparatus of claim 1, further comprising: a) a solids separator for receiving an effluent from an oxidation treatment system with supercritical water and for separating the effluent laden with solids from an effluent of clean liquid, the effluent loaded with solids comprising solids in a fluid. The apparatus of claim 3, further comprising: a) sludge conditioning means for the application of heat from a clean liquid effluent or from solid-loaded effluent to thicken a sludge to be treated in the oxidation treatment system with supercritical water. The apparatus of claim 4, wherein the sludge conditioning means includes: a) a heat exchanger / condenser having a gutter to receive a sludge to be thickened and a jacket to receive a subcritical fluid in a ratio of heat exchange with the sludge in the gutter, the subcritical fluid being produced from the clean effluent or the effluent loaded with solids; and b) a blower to force air over the surface of the sludge in the gutter to improve the evaporation of the sludge. The apparatus of claim 3, further comprising: a) a clean fluid pressure reducing arrangement for reducing the pressure of the clean fluid effluent to produce a process vapor; and b) a steam turbine adapted to produce mechanical energy from the process steam. The apparatus of claim 3, wherein the supercritical water oxidation treatment system includes: a) a secondary heat exchanger connected to transmit a feed mixture to be treated from a pump to a primary heat exchanger, and further connected to receive the effluent loaded with solids from the solids separator in a heat exchange relationship with the feed mixture to preheat the feed mixture. 8. An apparatus for depressurizing a high pressure fluid containing solids, the apparatus comprising: a) a pressure reducing device for reducing the pressure of a fluid charged with solids and at high pressure to a gas phase pressure at which there is an important gaseous phase with a liquid phase loaded with solids; b) a vessel connected to receive the liquid phase loaded with solids and gas at the pressure of the gas phase; c) a pressure regulating valve associated with the container for maintaining the pressure of the gas phase in the container and allowing gas to exit the container to maintain the pressure of the gas phase; d) a fluid removal conduit connected below a liquid level in the container and possessing a two-position liquid removal valve; and e) control means for moving the liquid removal valve to a fully open position in response to a value of the highest liquid volume in the container, and for moving the liquid removal valve to a fully closed position in response to a value of the lowest liquid volume in the container. The apparatus of claim 8, wherein the control means for controlling the position of the liquid removal valve comprises: a) a float mechanism associated with the container to indicate the volume of liquid in the container. 10. An apparatus for the management of effluents, which is used in an oxidation treatment system with supercritical water, the apparatus for handling effluents comprising: a) sludge conditioning means for the application of heat from at least a part of the effluent from the oxidation treatment system with supercritical water to thicken a sludge to be treated by the oxidation treatment system with supercritical water. The apparatus of claim 10, further comprising: a) a solids separator for receiving an effluent from an oxidation treatment system with supercritical water and for separating a solid-charged effluent from a clean fluid effluent, the effluent loaded with solids comprising solids in a fluid; and b) wherein the sludge conditioning means uses heat from either the effluent of clean fluid or the effluent charged with solids, to thicken the sludge. 12. A method for the management of effluents, to be used in an oxidation treatment system with supercritical water, the method for the management of effluents comprising the steps of: a) receiving an effluent loaded with solids from a waste treatment system. oxidation with supercritical water and reducing the pressure of the effluent loaded with solids at a gas phase pressure at which there is an important gas phase with a liquid phase loaded with solids; b) contain the liquid phase loaded with solids and gas in a container at the pressure of the gas phase; c) maintaining the pressure of the gas phase in the container and allowing gas to exit the container to maintain the pressure of the gas phase; d) moving a liquid removal valve to a fully open position in response to a value of the highest liquid volume in the container, and to move the liquid removal valve to a fully closed position in response to a volume value of lower liquid in the container, the liquid removal valve being connected in a liquid removal conduit located below a lower liquid level in the container. The method of claim 12, further comprising the step of: a) controlling the movement of the liquid removal valve with a float mechanism associated with the container, the flotation mechanism responding to the volume of liquid in the container. The method of claim 12, further comprising the step of: a) receiving an effluent from the oxidation treatment system with supercritical water and separating the effluent laden with solids from a clean fluid effluent, the effluent laden with solids comprising solids in a fluid. The method of claim 14, further comprising the step of: a) applying heat from either the effluent of clean fluid or the effluent charged with solids to thicken the sludge. The method of claim 14, further comprising the steps of: a) reducing the pressure of the clean fluid effluent to produce a process vapor; and b) produce mechanical energy from the process steam. The method of claim 14, further comprising the step of: a) placing the effluent charged with solids in a heat exchange relationship with a feed mixture to be treated in an oxidation treatment system with supercritical water to preheat the feeding mixture. 18. A method for depressurizing a high pressure fluid containing solids, the method comprising the steps of: a) reducing the pressure of a fluid charged with solids and at high pressure to a gas phase pressure at which there is an important gas phase with a liquid phase loaded with solids; b) contain the liquid phase loaded with solids and gas in a container at the pressure of the gas phase; c) maintaining the pressure of the gas phase in the container and allowing gas to exit the container to maintain the pressure of the gas phase; and d) moving a liquid removal valve to a fully open position in response to a value of the highest liquid volume in the container, and moving the liquid removal valve to a fully closed position in response to a volume value of lower liquid in the vessel, the liquid removal valve being connected in a liquid removal conduit that is connected to the vessel at a level below a lower liquid level in the vessel. The method of claim 18, further comprising the step of: a) controlling the movement of the liquid removal valve with a float mechanism associated with the container, the float mechanism responding to the volume of liquid in the container. 20. A method for the management of effluents, which is used in an oxidation treatment system with supercritical water, the method for the management of effluents comprising: a) the application of heat from at least a part of the effluent from the system of Oxidation treatment with supercritical water to thicken a sludge to be treated by the system. The method of claim 20, further comprising the step of: a) receiving an oxidation effluent with supercritical water, from an oxidation treatment system with supercritical water and separating a solid-charged effluent from a clean fluid effluent , the effluent loaded with solids comprising solids in a fluid; and b) wherein the step of applying heat from at least a portion of an effluent from the oxidation treatment system with supercritical water comprises the application of heat from either the effluent of clean fluid or the effluent charged with solids.