WO1990001367A1

WO1990001367A1 - Thermolytic detoxification reactor system

Info

Publication number: WO1990001367A1
Application number: PCT/US1989/003387
Authority: WO
Inventors: Terry Randolph Galloway
Original assignee: Thermolytica Corporation
Priority date: 1988-08-08
Filing date: 1989-08-07
Publication date: 1990-02-22
Also published as: JPH04501677A; AU4305889A; KR900701388A

Abstract

A thermolytic detoxification reactor system (19) is described for reacting hazardous toxic compounds. A detoxification reactor having a central high temperature core region (22) and a lower temperature annulus (25) coaxially disposed with respect to the core region (22) is utilized in the system. Gaseous toxic compounds are circulated into the core region (22) for reaction therein and from thence into the annulus (25). Water in excess of stoichiometry is introduced (59) to the stream of gaseous toxic compounds prior to entry thereof into the core region. Heat is exchanged (17) between the stream of gaseous toxic compounds (39) immediately prior to entry thereof into the core region (22), and the stream of effluent gas leaving the annulus.

Description

_!_

THERMOLYTIC DETOXIFICATION REACTOR SYSTEM This invention relates to thermolytic detoxification reactor systems. More particularly, the invention relates to an improved reactor system and method for operating same for reacting hazardous and toxic compounds with water to achieve very high destruction levels of such compounds.

The destruction of hazardous toxic compounds to extremely high levels is a goal of many types of technologies. Hazardous and toxic compounds are those compounds which represent a potential health hazard to humans or animals when released to the environment in even very low levels. Hazardous wastes typically contain such hazardous and toxic compounds. Most of these prior art systems are basically incinerators, relying upon high temperature burning of the toxic compounds to effect destruction. Such oxidation reactions normally result in formation of other compounds which are as toxic or even more toxic than the compounds which are destroyed. Moreover, such reactions evolve heat, are frequently unstable, are often difficult to control, and operate at pressures which often exceed ambient, creating danger of discharge of toxics into the environment in the event of explosion, reaction run-a-way, leak or failure. So called Thermolytica detoxification avoids most of the problems inherent in incineration processes by utilizing a reaction which is endothermic and which avoids the presence of free oxygen. Such a process has been described in co-pending United States Patent Application Serial No. 089,573. In this process, hazardous and toxic compounds are gasified and reacted in a suitable reactor at high temperature with water in excess of stoichiometry and without the presence of free oxygen. The thermolytic detoxification process results in very high destruction levels, in excess of 99.99%, while producing an effluent gas flow comprising carbon monoxide, carbon dioxide, hydrogen, and water. The reaction is more easily controlled than exothermic reactions, and may be operated with no risk of explosion and at substantially atmospheric pressure or below, resulting in increased safety.

Thermolytic detoxification reactor systems represent a relatively new-technology. The present invention constitutes an improvement on such technology wherein high destruction levels can be achieved in an efficient way with relatively low maintenance and high throughput. The full significance of the invention will become apparent to those skilled in the art from the following description, taken in connection with the accompanying drawings wherein: FIGURE 1 is a schematic flow diagram of a thermolytic detoxification reactor system constructed in accordance with the invention; and

FIGURE 2 is a cross-sectional schematic view of a thermolytic detoxification reactor incorporated in the system of the invention.

Very generally, the thermolytic detoxification reactor system of the invention reacts hazardous toxic compounds with water to achieve high destruction levels. The system includes a detoxification reactor having a central high temperature core region and a lower temperature annulus coaxially disposed with respect to the core region. Means are provided for heating the core region. Means are provided for circulating a stream of gaseous toxic compounds into the core region for reaction therein and then into- the surrounding annulus. Water in excess of stoichiometry is introduced to the stream of gaseous toxic compounds prior to entry thereof into the core region for reaction with the toxic compounds in the core region. Heat exchange takes place between the stream of gaseous toxic compounds immediately prior to entry thereof into the core region, and the stream of effluent gas leaving the annulus.

Referring now more particularly to FIGURE 1, the reactor system of the invention is shown schematically. The system operates to process gaseous toxic compounds which originate from a feed system 11.

The feed system 11 may be ofany suitable construction to gasify toxic compounds. However, a preferred form of feed system 11 is an autoclave as shown and described in co-pending U.S. Application Serial No. 092,041. In that system, drums of toxic waste are heated by hot gaseous effluent from the thermolytic detoxification reactor circulating outside the drum and inside the autoclave. The hot gaseous effluent is then circulated into the drum itself, containing the toxic waste in liquid form. Heating of the drum, together with the circulation through of the hot gaseous effluent, results in vaporization and some gasification of the liquid toxic waste contained in the drum. This gas is then used as the feed system source for return to the detoxification reactor.

In FIGURE 1, the feed system 11 is shown connected via a conduit 13 having a valve 15 to a primary heat exchanger 17. This primary heat exchanger 17 serves to raise the toxic gas stream to a high temperature at which it is inserted through the bottom of the detoxification reactor 19. The detoxification reactor 19 includes an inner cylindrical wall 21 which defines a high temperature reaction chamber or core region 22. Spaced from and coaxial with the cylindrical wall 21 is a second cylindrical wall 23. The space between the walls 21 and 23 form a lower temperature annulus 25 coaxially disposed with respect to the core region 22.

Means are provided for heating the high temperature core region 22. In the illustrated embodiment, these means are a plurality of elongated resistance heating elements 27. The elements 27 extend downwardly from a supporting disc 29 which may be a suitable ceramic structure such as fibrous aluminum oxide. The disc 29 is thermally insulated from the reactor core 22 by a dense structurally supporting disc 31 of insulating material. Suitable electrical connections, not shown in FIGURE 1, are made to the resistance heating elements for raising the temperature of the core 22 to a high enough level.

In the event of excess pressure within the cylindrical wall 23, a burst disc 33 will rupture to relieve the pressure through a vent tube 35.

The incoming flow of gaseous toxic compounds passes into the central reactor core region via an inlet duct 37 which is suitably connected as will be described below. After passing upwardly through the core region

22, the gases return via the annulus 25 to the bottom of the reactor 19 where they are carried back to the heat exchanger 17 via a conduit 39. The conduit 39 includes a suitable solids trap 41 for discharging accumulated solids, which may be disposed of as is known in the art.

Effluent gas from the conduit 39 passes through the heat exchanger 17 and then passes .via a conduit 43 to a further heat exchanger 45. This heat exchanger is connected in series with two additional heat exchangers 47 and 49 in which heat exchange takes place as described below. The heat exchanger 45 is connected to the heat exchanger 47 via a conduit 51, and the heat exchanger 47 is connected to the heat exchanger 49 via a conduit 53. A turbine 55 is provided to which reactor effluent is passed from the heat exchanger 49 via a conduit 57. The turbine 55 provides the driving force for the system and the output of the turbine 55 is optionally connected via a conduit 59 to a -suitable scrubber 61 or directed straight through to sorber tower 85. A bypass loop 56 having a valve 58 is provided for the flow control of the turbine 55. Construction of the optional scrubber 61 may be in accordance with techniques well know to those skilled in the art. The scrubber is normally added as an option when the hazardous and toxic compounds involve halogens in significant capacity. After the turbine 55 and, if present, after passing through the optional scrubber 61, effluent is passed via a conduit 63 to a sorber tower 65. The sorber tower may be of any suitable construction. However, in the illustrated embodiment, the sorber tower 65 includes a pair of activated carbon beds 67 and a pair of activated alumina beds 69 of suitable material such as SELEXSORB (trademark) available from Alcoa and Coastal Chemical. Gases passing through the sorber tower 65 are collected in a plenum 71. The outlet of the plenum 71 is connected to a T connection 73 from whence flow may continue upwardly through a conduit 75 back to the heat exchanger 49. Flow from the conduit 75 is continued from the heat exchanger 49 to the heat exchanger 47 via a conduit 77 and from the heat exchanger 47 to the heat exchanger 45 via a conduit 79. Thus, heat exchange takes place in the heat exchangers 45, 47 and 49 between the higher temperature effluent emanating from the heat exchanger 17 via the conduit 43 and the lower temperature effluent leaving the sorber tower 65 via the conduit 75. To maintain suitable control flow rates, the conduit 75 is provided with a venturi flow meter section 81.

After leaving the heat exchanger 45, the cooler effluent passes via a conduit 83 to a T section 85. The T section 85 is connected via a valve 87 to a further T section 89 in the conduit 13 between the valve 15 and the heat exchanger 1*7. The other leg of the T section 85 is connected via a valve 91 through a conduit 93 having a venturi flow meter section 95 to a catalytic converter 97.

The catalytic converter 97 may be of any construction suitable for converting the carbon monoxide, hydrogen, methane, etc. in the effluent to less harmful carbon dioxide and water. The preferred embodiment involves an outer annulus section 160 containing an automotive-type two-way catalyst 161. An air inlet vent 99 is provided to the catalytic converter 97 via a valve 101. Inlet to the outer annular catalytic section 160 is provided from the T section 73 via a conduit 103 and valve 105 to remove carbon monoxide, hydrogen, methane, etc. from vent gases before they are released. A vent 107 is provided for the release of finished gases from the catalytic converter 97 via a venturi section 109. Outflow from the catalytic converter 97 is heated by the evolved heat from the air-driven oxidation reaction therein and is provided through a conduit 111 to the feed system 111 for returning the heated effluent gas to the feed system. The purpose of running hot gases from conduit 93 through the catalytic converter 97 is to maintain the catalyst 161 above its "light-off¹* temperature of 400°C (650°F) . As previously mentioned, the effluent gas may then be used to volatilize liquid toxic compounds contained in the feed system at a faster rate using the heat recovered from the catalytic converter 97. As previously mentioned the thermolytic detoxification reactor system of the invention employs water in excess of stoichiometry in the reactor for the thermolytic detoxification reaction. To this end, two alternate means of providing water injection to the system are provided. The first is a water inlet conduit 153 having a valve 155 which is positioned in the conduit 59 between the turbine 55 and the scrubber 61. A second inlet position for adding water to the system is provided via an inlet conduit 157 and a valve 159. In operation of the system illustrated in

FIGURE 1, gaseous toxic compounds entrained with hot effluent gases from the reactor 19 are produced by the feed system 11 and conveyed via the conduit 13 and valve 15 to the primary heat exchanger 17. There, the gas flow is further heated by heat exchange with hot gaseous effluent from the reactor 19. The gas stream is then conveyed to the reactor 19 via the conduit 37. Water is introduced to the gas stream via the conduit 153 (or 157) through the valve 155 (or 159) . Typically, this water will be in the form of highly superheated steam. Superheated steam may be produced by introducing water to cooling coils (now shown) in the turbine 55, then to cooling coils in the reactor turret (FIGURE 2) described below, and then to the conduit 153 (or 157) .

Upon entry into the high temperature core region 22, the toxic compounds are destroyed as is described below. The effluent from the high temperature core region 22 then flows into the annulus 25 over the upper edge of the cylinder 21 in the space below the insulation disc 31. Flow through the annulus 25 is downward where it is collected and circulated via the conduit 39 to the heat exchanger 17. The effluent then passes through ,τ_e three secondary heat exchangers 45, 47 and 49 via the conduits 43, 51 and 53 to the conduit 57 where it is circulated through the turbine 55 and thence through the conduit 59 to the optional scrubber 61. Upon leaving the optional scrubber 61, the effluent gas is circulated through the conduit 63 to the sorber tower 65 for further removal of any remaining molecules of toxic compounds. Upon leaving the sorber tower 65 via the plenum

71 and T connection 73, the effluent gas is returned via the conduit 75, through the heat exchangers 49, 47 and 45 to increase the temperature of the effluent gas from the conduit 75 to the conduit 83. In typical operation, the valve 87 is closed and the valve 91 is open, permitting the effluent to flow through the conduit 93 and through the central heat exchange pipe of the catalytic converter 97. In the catalytic converter, the gas is converted to carbon dioxide and water (steam) and heat is evolved which further heats the gas in conduit 111. Any excess heat is vented through the vent 107. The heated gas in conduit 111 is then returned to the feed system 11 via the conduit 111 for further heating and gasifying toxic compounds in the feed system, typically in liquid form. The valves 87 and 15 permit recirculation of the effluent directly from the heat exchanger 45 to the heat exchanger 17, bypassing the feed system 11. This configuration is utilized during start-up and shutdown conditions. The valve 105, when opened, permits venting of a portion of the clean, detoxified effluent from the sorber tower 65 directly to the outside.

Although operating temperatures in the system may vary depending upon the destruction levels desired and the type of products being processed, typical operating temperatures will be as follows: Conduit 39 - 1850°F

Conduit 37 - 1275°F

Pressures in the system are maintained generally at close to or slightly below atmospheric, particularly in the reactor 19 itself. Pressure in the conduit 37 typically will be at -15 inches of water (-0.5 psi) whereas pressure in the conduit 39 will typically be at -30 inches of water (1.0 psi). Pressure drop across the turbine 55 typically is from +38 inches to -56 inches of water. Referring now more particularly to FIGURE 2, the specific construction of a thermolytic detoxification reactor is illustrated. As described in connection with FIGURE 1, the reactor 19 includes inner and outer coaxial cylinders 21 and 23, respectively, arranged to define the high temperature core region 22 and the lower temperature annular plenum 25. Heating of the core region 22 is provided by the elongated heating elements 27. The upper end of the reactor is closed by a ceramic fiber insulating plate 29 protected against flow scouring by a dense insulating disc 31, both available from Zircar. The heating elements 27 are supported by a plurality of electrical mounts 113 of suitable construction mounted above the plate 29. The upper portion of the reactor is enclosed by a "turret top" enclosure 115 capped by a top plate 117. Copper cooling coils 119 are arranged on the inside of the turret top walls and top plate for superheating of steam made from circulation of water from turbine 55 cooling coils (not shown) . Woven electrical cable 121 for the heating elements is fed through the turret top 115 by a suitable electrical pass through 123.

The reactor is enclosed in a 316-L stainless steel (or any other suitable alloy) outer vessel 125 which is coaxial with the cylinders 21 and 23. The lower end of the vessel is closed by a 321 stainless steel (or any other suitable alloy) plate 127 having a central opening 129 and a plurality of peripheral, openings 131 exiting the annulus 25. Supported on the top surface of the plate 127 is a castable alumina base 133. This base has openings therein aligned with the ports 129 and 131. The opening aligned with the port 129 is flared at 134 to provide for improved flow dispersion of the entering gases. The port 129 is connected to the conduit 37 (FIGURE 1) whereas the ports 131 are manifolded to the conduit 39 (FIGURE 1) . Typically there will be four exit ports 131. The stainless steel vessel 125 is optionally surrounded by a wall of suitable insulation, such as KAOWOOL (trademark) 137 available from Babcock and Wilcox. In-between the ceramic tube 23 and the stainless steel wall 125 is disposed a light-weight bulk alumina fiber in the layer 139. The inner surface of the ceramic tube 21 is protected by a tube 141 of impervious Mullite (trademark)available from Bolt in Germany. The high temperature core region 21 is filled with a plurality of reticulated foam, high porosity ceramic discs 143 available from Zircar. - These discs are stacked in the region above the base 133 and are provided with passages therein for accommodating the heating elements while at the same time providing support thereto. Further passages may be provided in the ceramic discs 143 as desired in order to provide suitable gas flow mixing and residence time in the high temperature core region 22. For monitoring the temperature in the high temperature core region 22, a thermocouple tube 149 extends downwardly centrally thereof. A suitable thermocouple 151, typically a dual-junction platinum-rhodium thermocouple within an alumina sheath,is mounted within the alumina tube 149 passing through the plates 29 and 31. Inlet gases circulating to the reactor 19 from the conduit 37 enter through the port 129 and flow upwardly through the ceramic discs. In the high temperature core region 22, the gases are mixed and heated such that they react (the toxic compounds with the superheated steam) to form substantially carbon monoxide and hydrogen. These gases exit the high temperature core region over the upper edge of the cylinder 21.below the plate 31. The effluent gas then circulates downwardly through the annular plenum 25 where some further reaction may take place. The effluent gases then exit through the ports 131 and are conveyed to the conduit 39 as earlier described.

A particular advantage of the reactor system of the invention as described above is that the effluent gas stream from the reactor is very hot and thus capable of providing substantial heat delivery to the feed system 11. Any carbonaceous deposits in the gases passing through the conduit 13 from the feed system 11 will steam gasify as a result of the high temperatures reached in the heat exchanger 17. Also, the use of the heat exchanger 17 to heat exchange the reactor feed and exit gases helps to relieve any problems of ash or carbonaceous deposits within the reactor. Such deposits may be removed easily through the trap 41, avoiding the necessity of frequent cleaning of internal baffles in the reactor vessel.

Another advantage of the system of the invention is the elimination of any need for ceramic caulking or rashig rings, ceramic spheres or other similar material to produce adequate mixing of the gases. The required preheating and mixing is performed within the heat exchanger 17 and is further provided by the ceramic discs in the high temperature core region itself.

It may be seen, therefore, that the invention provides an improved thermolytic detoxification reactor system for reacting hazardous toxic compounds. The system is efficient, compact, and easy to operate. Other advantages of the invention will become apparent from the foregoing description to those skilled in the art. Various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from a reading of the foregoing specification and accompanying drawings. Such modifications are intended to fall within the scope of the appended claims.

Claims

WHAT IS CLAIMED:

1. A thermolytic detoxification reactor system for reacting hazardous and toxic compounds, comprising, a detoxification reactor having a central high temperature core region and a lower temperature annulus coaxially disposed with respect to said core region, means for heating said core region, means for circulating a stream of gaseous toxic compounds into said core region for reaction therein and then into said annulus, means for introducing water in excess of stoichiometry into the stream of gaseous toxic compounds prior to entry thereof into said core region for reaction with the toxic compounds in said core region, and primary heat exchange means for exchanging heat between the stream of gaseous toxic compounds immediately prior to entry thereof into said core region and the stream of effluent gas leaving said annulus.

2. A reactor system according to Claim 1 wherein said means for introducing water is positioned in the system to introduce the water between said primary heat exchange means and said core region.

3. A reactor system according to Claim 1 wherein said means for introducing water is positioned in the system to introduce the water to the stream of gaseous toxic compounds prior to said primary heat exchange means.

4. A reactor system according to Claim 1 including a feed system wherein at least some of the effluent gas from said reactor is circulated thereto for mixing with gaseous toxic compounds for circulation to said reactor.

5. A reactor system according to Claim 4 including secondary heat exchange means for exchanging heat between the stream of effluent gas immediately after leaving said primary heat exchange means and the stream of effluent gas prior to circulation to said feed system.

6. A reactor system according to Claim 5 including catalytic converter means between said secondary heat exchange means and said feed system.

7. A reactor system according to Claim 1 including means for maintaining the pressure inside said reactor substantially at or below atmospheric pressure.

8. A reactor system according to Claim 1 wherein said reactor includes ceramic means within said core region for providing a dispersed flow of gas therein sufficient to cause substantial micro-mixing of gases in said core region.

9. A reactor system according to Claim 8 wherein said means for heating said core region include a plurality of elongated resistance heaters extending axially within said core region, and wherein said ceramic means are configured to support said heaters therein.

10. A reactor system according to Claim 1 wherein said primary heat exchange means are positioned within said annulus.

11. A method for operating a thermolytic detoxification reactor system having a detoxification reactor having a central high temperature core region and a lower temperature annulus coaxially disposed with respect to said core region, said method comprising, heating said core region to a temperature sufficient for the decomposition of toxic compounds therein, circulating a stream of gaseous toxic compounds into said core region for reaction therein and then into said annulus, introducing water in excess of stoichiometry into the stream of gaseous toxic compounds prior to entry thereof into said core region for reaction with the toxic compounds in said core region, and exchanging heat between the stream of gaseous toxic compounds immediately prior to entry thereof into said core region and the stream of effluent gas leaving said annulus.

12. A method according to Claim 11 wherein the water is introduced to the system between the core region and the position at which said heat exchange step takes place.

13. A method according to Claim 11 wherein the water is introduced to the system to the stream of gaseous toxic waste prior to the position at which said heat exchange step takes place.

14. A method according to Claim 11 wherein at least some of the effluent gas from said reactor is circulated back to the source of gaseous toxic compounds for circulation to said reactor.

15. A method according to Claim 11 wherein the pressure inside the reactor is maintained substantially at or below atmospheric pressure.