Patent Publication Number: US-5293827-A

Title: Regenerative thermal oxidizer with gate manifolds including purges

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to an improved method and apparatus for regenerative thermal oxidation. More specifically, it is a method and a thermal oxidizer for purifying gases by incineration while providing regenerative heat exchange between inleting and outleting gases and providing for purging of gases in individual thermal chambers. Such systems are used in commercial and industrial operations for removal of air pollutants from gases which would otherwise be released to the atmosphere. By thermal oxidation, these gases are raised to their auto ignition temperature, creating safer, and more simple exhaust gas compounds. By using proper heat exchange techniques, as described herein, the efficiency in the cost of operation is enhanced. By purging therein, exhaust gases are recycled to replace dirty or partially processed air to enhance efficiency. Thus, the present invention, a regenerative thermal oxidizer apparatus and process, utilizes a unique gate manifolding system for the control of airflow into and out of the thermal oxidizer. 
     2. Information Disclosure Statement 
     Regenerative thermal oxidizers such as in the present invention, utilize a back flow of gases through the heat exchanger to maximize the recapture of heat which might otherwise be lost to the atmosphere. These systems include minimally a combustion chamber which receives the preheated gas, and recovery chamber which cools the gas exiting so as to reclaim most of the heat to be applied to the inleting process gas before entering the combustion chamber. A burner is used to maintain temperature in the combustion chamber. Typically the system operates dynamically holding inlet and outlet conditions for a predetermined period of time before continuing on to the next inlet/outlet condition. In this manner, the regenerator could become one of a heating regenerator rather than an exhaust regenerator and the portion or unit which constituted the heating regenerator could become the cooling regenerator. 
     Early regenerator systems involved the use of, for example, two chambers wherein the gases to be purified entered into the bottom of one chamber, rose up therethrough for oxidation, and back down through and out a second chamber unit for capture of the heat. Operated in this manner, for a period of time, the process was reversed so that the inlet gas is now moved first into what was the exhaust chamber utilizing the energy for preheat. One of the problems which existed during the flow reversal involved large pressure swings which create back pressure effecting manufacturing systems which require equilibrium within the system. Oxidizers with three or more chambers can make use of an idle chamber which transitions with one or more of the other chambers to maintain an even flow across the systems during changes in airflow direction through the equipment. Difficulties arose with respect to the manifolding of these gases because, historically, flap valves which rotated were utilized to provide the inleting and outleting of the process exhaust gases. This caused inefficiencies, improper sealing problems, mechanical wear and tear due to the rotational aspects, thermal expansion problems, and pockets of process air which would not be treated after the flap valves transitioned from inlet to outlet positions. In addition, flap valves require a complicated array of control to insure each valve is opening and closing properly. In fact prior art makes no provision for allowing both inlet and outlet flap valves from opening and closing simultaneously, allowing contaminated air to bypass the oxidation chamber and be exhausted, unprocessed, to the atmosphere. 
     Various solutions have been developed to address problems incurred in regenerative heat chambers, although the prior art does not teach or suggest the present invention described herein. The following patents are representative of the state of the art: 
     U.S. Pat. No. 3,741,286 issued to Wolf Muhlrad described a regenerative heat exchanger and method for purging its flow passages. The invention described involves double chambers with gases passing up one side and down the other and then reversing. This is accomplished by rotation of a series of dampers which do not eliminate the above mentioned problems with rotational valves. 
     U.S. Pat. No. 4,470,806 issued to Richard Greco described regenerative incinerators utilizing a series of heat exchanger chambers with perforated horizontal support grates with combustion chambers located above heat exchangers and utilizes openings and closing of various lines to achieve reversals for heat exchange. However, as in the other prior art, this patent utilizes valves which rotate to open and close the inlet and outlet manifolds. 
     U.S. Pat. No. 3,225,819 issued to E. S. Stevens describes an apparatus and method for air-to-air heat exchange, but again, utilizes rotational valving. 
     U.S. Pat. No. 4,754,806 describes a reciprocating heat exchanger and utilizes a porous metal element for absorbing heat for the exhaust air stream and also describes movement of this porous metal element from one side to another so as to effectively exchange heat by receiving heat from exiting gases and moving it over to inlet gas lines. However, this patent does not describe valving or manifolding and takes a totally different approach by never reversing the flow of gases but only reciprocally relocating heat absorbing elements. 
     U.S. Pat. No. 4,966,228 and U.S. Pat. No. 5,026,277, describe some recent developments of the art in this field. The latter patent to James York describes a regenerative thermal incinerator apparatus utilizing a system of valved duct work to direct gases to various combustion chambers and to idle a third regenerator for purging of partially treated gas so as to recycle it back through the system and so as to, thereby, reduce or eliminate lost gases which have not been properly purified. 
     U.S. Pat. No. 4,280,416 issued to Phillip Edgerton, describes a rotary valve for regenerative thermal reactors. While this patent describes valves which rotate instead of swing or rotate about an axis parallel to the valve surface, it still requires rotation of a valve about an axis at right angles to its surface and rotational friction and mechanical drive is necessitated. 
     U.S. Pat. No. 4,966,228 issued to Sherwood Fawcett describes a regenerative gas-to-gas heat exchanger requiring a special geometry for a chamber and utilizing gate valves to direct or redirect gases through different chambers. Unlike the present invention, however, Fawcett does not reverse gas flow and Fawcett does not rely upon the use of sliding gates having an orifice which is moved from an inlet to dead space or closed off space to an outlet and recycled back and forth so as to control the flow of gases in one direction and then in the exact opposite direction within a specific chamber unit. 
     U.S. Pat. No. 5,134,945 to the present inventors herein describes the present state of the art in the field. The thermal oxidizers described therein utilize at least three regenerative thermal chamber units and these have on a single surface both inlet and outlet openings with slidable, controlled and timed gates to set opened or closed each of the inlet and outlet openings to shift regeneration inlet and outlet from chamber unit to chamber unit. This prior art patent does disclose overall oxidizer purging based on inleting purge gases through the top of the entire set of units for purging, but neither suggests nor teaches individual purging of separate chamber units through the inlet/outlet gate area of each separate chamber unit, as set forth in the present invention. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved regenerative thermal oxidizer and a method of purifying gases by raising gases to their auto ignition temperature and by exchanging heat by inleting and outleting gases. The reactor has at least three regenerative thermal chamber units and these units have on a single surface at least three openings, a purge opening, an inlet opening and an outlet opening, which are connected to recycled inlet or outlet gases for purging, and to inlet and outlet gases respectively. Set against the purge, inlet and outlet openings is a slidable gate which has a single opening which moves through cycles so that its single opening coincides with the inlet opening of its chamber unit, or coincides with one or more spaces which are closed between the inlet and outlet opening, or with the purge opening, or coincide with the outlet opening. In other words, the gate cycles between inleting gases, no gas movement, purge position, no gas movement and outleting gases. There are means provided for moving the gate through the aforesaid cycle and, inlet ducts, purge ducts and outlet ducts are connected to their respective openings. The method involves utilizing the aforesaid apparatus so as to purify gases by thermal oxidation and to cause heat exchange by first running inlet gases through a given chamber unit and outlet gases through another chamber unit and reversing the flow between units as well as switching units for inlet and outlet purposes, and as well as purging used process gases as needed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more fully understood when the specification herein is taken in conjunction with the appended drawings. These drawings illustrate the following: 
     FIG. 1 is a cut top view of a single chamber unit of a regenerative thermal oxidizer of the present invention; 
     FIG. 2 shows a cut end view of a portion of the chamber unit shown in FIG. 1; 
     FIG. 3 shows a top view of three chamber units utilized in the present invention including the FIG. 1 chamber unit but without the gates shown and the drive gear ports shown so as to simplify the view to illustrate the various openings of a typical oxidizer of the present invention; and, 
     FIG. 4, and FIG. 5 show a side cut diagrammatic view of a simplified arrangement for three chamber units of a present invention thermal oxidizer utilizing horizontal gates, using exhaust gases for purging in FIG. 4 and using input gases for purging in FIG. 5. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to eliminating rotation or revolution of valve mechanisms in regenerative thermal oxidation units. Thus, it is an objective of the present invention to provide gates which neither rotate nor revolve but merely slide back and forth. This can be accomplished with vertical or horizontal or otherwise positioned gates without exceeding the scope of the present invention. 
     It is also an object of the present invention to eliminate or substantially reduce problems typical of the rotational valves, sealing problems and heat loss problems resulting from such inefficiencies, thereby substantially increasing the efficiencies of the system. 
     It is also an object of the present invention to provide for purging of each chamber unit in a regenerative oxidizer, either on an as needed basis or as in preferred embodiments, automatically for each individual chamber unit following a preselected segment of the otherwise open inlet, rest, open outlet cycling. 
     It is an object of the present invention to also provide a new, reliable, different and more cost effective mechanism for reversing gas flow in chamber units for regenerative thermal oxidation systems with selective purging included. 
     It is also an object of the present invention to permit chambers to be idle for purposes of purging or otherwise and to operate on a cycle with continual switching and reversing of chambers and gas flow direction which includes automatic purging. 
     FIG. 1 shows a top cut view of a single regenerative thermal chamber unit 1 of a present invention multi-unit reactor apparatus. This unit 1, has a lower receiving chamber and an upper combustion chamber such as is discussed in conjunction with FIG. 4 below. 
     Unit 1 has walls 3, 4, 6 and 8 and a base surface 5. In this embodiment, the base surface 5 is a bottom surface, but it could be otherwise, e.g. a side surface. Base surface 5 includes a gas inlet opening 7 a purge gas opening 8, and a gas outlet opening 9. Here, opening 7, 8, and 9 are rectangular, but they could be of any configuration, such as a square or a round orifice. They are separated or spaced apart by a distance, which is at least equal to the width of a gate orifice 13. Gate 11 movably rests atop and against base surface 5 and contains gate orifice 13, as shown. 
     Gate 11 moves through cycles with at least four critical positions for advanced manifolding of unit 1. One critical position occurs when gate orifice 13 seats against gas inlet opening 7. In this position, gas outlet opening 9 is closed and only inlet gases enter chamber unit 1. A second critical chamber position is when gate orifice 13 rests against base surface 5 at an area between openings 7 and 8 or between openings 8 and 9, respectively shown as areas 10 and 12. 
     This is as shown in FIG. 1 and in this position, inlet opening 7, purge gas opening 8, and outlet opening 9 are closed. In a third critical position, gate orifice 13 is seated against purge gas opening 8 and exhaust gases may be controllably, selectively or automatically recycled, or other clean (e.g. pre-heated) gases, may be fed into chamber unit 1 via gate orifice 13 and opening 8. In a fourth critical position, gate orifice 13 is seated against outlet opening 9 and gases only exit the chamber unit 1. 
     FIG. 2 shows an end cut view of the chamber unit 1 of FIG. 1 along line AB. 
     Referring now to both FIGS. 1 and 2 taken together, and in which identical components are identically numbered, gate 11 includes roller wheels 15, 17, 31 and 33 (typical). Guide brackets 19 and 25 are also shown and include ends 21, 23, 27 and 29. While guide brackets and wheels are shown in this embodiment, other guide means could be used or none could be employed if the gate where sized or seated or if the gate relied upon gravity, e.g. was on pulleys on a side wall. In fact, any known arrangement for maintaining a slide plate or gate in position for opening and closing may be used. 
     Gate 11 has cut outs 51 and 53 on its underside and these mesh with gears 53 and 57, which pass through gear openings 71 and 73 in base surface 5. Gears 53 and 57 are connected to axle 59, which is driven by motor 67 and controlled by computer 72. The control involves movement of gate 11 from one end of the brackets 19 and 25 to the other end and back again, completing a cycle. The gate 11 may be stopped for a preset time at each of its critical positions mentioned above or continuously move during the cycle. The controls may be by electric timers, mechanical cycling wheels, hydraulics, pneumatics, computer, a combination of these or otherwise. 
     The chamber unit 1 is employed in a present invention thermal oxidizer having at least two other chamber units. The controls are employed so that respective gates are out of phase with one another in their respective critical positions. In one preferred embodiment, the respective gates are 120° out of phase. In cases where, for example, four chambers are utilized, and two are typically closed at any one time, they may be 90° out of phase or multiple of 90° out of phase, or 225° out of phase or otherwise, as may now be within the purview of the artisan. 
     A typical three unit reactor will have cycles in which the gates will move sequentially so that when in critical positions, will always have two inlets closed, two outlets closed, one outlet from a chamber open, one inlet from another chamber open and one purge inlet or outlet from another chamber open. (These would double in number for a six chamber reactor.) 
     As can be appreciated, the sequences stated above could readily be altered, reversed, etc., and yet still achieve the advantageous manifolding of the present invention. 
     FIG. 3 shows a top opened view of a three chamber unit oxidizer of the present invention. Oxidizer 100 includes chamber unit 1 shown in FIGS. 1 and 2 but the chamber units here have the gates, rollers, guides, etc. removed to illustrate inlet and outlet connections. With respect to chamber unit 1, components identical to those of FIGS. 1 and 2 are identically numbered. Chamber units 80 and 90 have walls 73, 78, 83 and 88 as shown, and common wall 76 and end wall 86. The common walls 6 and 76 do not extend completely to the top of the reactor and an open flow area (shown in conjunction with other embodiments below) is not shown. Unit 80 includes inlet opening 77, purge opening 58, and outlet opening 79, located on base surface 75. Unit 90 includes inlet opening 87, purge opening 68, and outlet opening 89 on base surface 85. 
     Main gas inlet conduit 101 is connected to inlet openings 7, 77 and 87, purge gas conduit 102 is connected to purge gas openings 8, 58 and 68, and purified gas outlet conduit 103 is connected to outlet openings 9, 79 and 89. Incoming gases containing undesirable components to be thermally oxidized enter one or two chambers via main inlet conduit 101 and exit through one or two chambers (where the inlet openings are not open) and then go through outlet conduit 103 or purge gases exit through conduit 102 and are reintroduced into conduit 101 to be processed at the beginning of an inlet cycle. Purge gases enter through conduit 102 into whatever chambers have the purge gas opening in the open position and exit via open outlet openings and then via outlet conduit 103. The gates (not shown) may be 120° out of cycle and operate consistent with the sequences mentioned above. By this method, the same volumetric flow of inlet and outlet gases continuously pass through the chamber units for an efficient operation. In fact, when one gate opens and another gate closes an inlet or outlet, they may be precisely timed so that the total open area of the one opening and the other closing equals a single, fully opened inlet orifice. 
     FIG. 4 and FIG. 5 show front schematic diagrams of an alternative thermal oxidizer embodiments of the present invention. FIG. 4 uses exhaust or output gases for purging and FIG. 5 uses input gases for purging. Identical parts are identically numbered in both Figures. Here, oxidizer 111 includes chamber units 102, 103 and 104 as shown. A common flow path at the top of these chambers is shown as connecting section 105. Additionally, each of the chamber units has combustion chamber sections 106, 107 and 108 respectively and recovery chambers 109, 110 and 171, respectively. These are shown as being divided by dotted lines in this schematic. However, these chambers may contain conventional heat exchange devices such as rakes or grids, heat exchange saddles, or any other known heat exchange materials which are utilized in the thermal oxidation systems. Additionally, any conventional firing mechanisms may be used and are not points of criticality with respect to this invention. Burners 151 and 161 are located as shown, for example. 
     At the bottom surface 118 of chamber unit 102 is inlet opening 112, outlet opening 115 and purge gas opening 153. Likewise, in chamber units 103 and 104 respectively there are base surfaces 119 and 120 with inlet openings 113 and 114, outlet openings 116 and 117 and purge gas openings 155 and 157. Gases to be purified flow in general through main duct 124 and may flow into chamber units 102, 103 or 104 via inlet lines 121, 122 and 123 as shown. Likewise, purified gases which have been thermally oxidized may exit through exit lines 125, 126 or 127 for chamber units 102, 103 and 104. These join at main outlet line 128 and are exhausted to exhaust line 130 via impeller 129. Purified gases in exhaust line 130 may be recycled via purge gas line 141, (or line 141&#39; in FIG. 5, utilizing inlet gases in place of exhaust gases) and fed into the separate chamber units 102, 103, 104, respectively, sequentially by the opening of purge gas openings 153, 155 and 157, e.g. after their respective inlet openings have been opened and closed. In FIG. 5, the flow is reversed, using the inlet gases, as shown. Optional valves 161 (FIG. 4) and 161&#39; (FIG. 5) provide additional purge control, as needed. 
     Chamber unit 102 includes a gate 131 with gate orifice 132 as shown. Not shown in this schematic with respect to any of the chamber units is a mechanism for moving the gate left to right. However, such a mechanism may be that which is shown in FIGS. 1 and 2, or it may be by pulley or chain or push-rod or other mechanism such as is described herein. In any event, chamber units 103 and 104 includes gates 133 and 135 with gate orifices 134 and 136. In FIG. 4, the gates 131, 133 and 135 are cycling at 120° out of phase. Therefore, in this &#34;freeze frame&#34; schematic diagram, gate 131 is left most with gate orifice 132 being superimposed over inlet opening 112. In chamber unit 103, gate 133 is centrally located and gate orifice 134 is over gas purge opening 155 for purging this unit. Had it been positioned so as to have its orifice 134 located in the dead space between openings 113 and 155, for example, there would be no gas movement into or out of chamber unit 103. Chamber unit 104 has its gate 135 in a right most position with gate orifice 136 superimposed over gas outlet opening 117. Thus, as shown by the arrows, inlet gases enter through chamber unit 102 and are combusted through section 105 and down through chamber unit 104 where heat is recovered and the gases exit via line 128 and exhaust 130. 
     Taking into consideration FIGS. 1, 2, 4 and 5 it can be seen that the dynamics of reactor 111 are similar to that described in conjunction with the above drawings, and, for example, as gate 131 shifts to the right, gate 133 and chamber unit 103 would shift to the left so that the combined volume of gases entering chamber unit 102 and chamber unit 103 would be a constant. Eventually, gate 133 which shifts to the left and gate 131 would be moving across the middle, either purging or shutting off any flow in either direction in chamber unit 102. The sequence would continue to complete full cycles of inleting, closing, purging, closing, outleting, closing, purging, closing and back to inleting. Purging could be shortened or eliminated in either or both directions by, for example, automatic control of shut off valve 161. 
     As mentioned, the present invention includes three or more chamber units and it can be seen that rather than just one chamber unit being shut off at a given time, a plurality of chamber units could be shut off at a single time. Likewise, it is possible to work with five chambers whereby two chambers are inleting gases and two chambers outleting gases with a shifting of one chamber at a time. Further, with six chamber units, two could be open, for example, with inlet gases flowing in, two could be closed and two could be open for outlet gases flowing out and the sequences would be identical to the system just described except that double the number of chambers would be in use at any given time. 
     Other variations should now be seen obvious to the artisan in view of the detailed description and the appended drawings. For example, the gates could be in a non-horizontal plane, e.g. slanted or vertical plane. Also, the base surface of the present invention reactor and gate need not be flat. The base surface and the gate could be arcuated and operate without exceeding the scope of the invention. This would be the case utilizing a vertical gate within a circular chamber unit. Also, the purge gas opening need not be between the inlet and outlet openings but could be on the outside of one or the other, i.e. at the end of the gate movement so as to have a single purge rather than two purges for each complete cycle. Further, the above representations are presented to be merely illustrative and the scope of the present invention should not be construed to be strictly limited to the particular examples set forth above. 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.