Anti-Leak Valve Flushing System for Thermal Regeneration Apparatus

A. Field of the Invention

This invention relates to thermal regeneration systems for anti-pollution purposes and in particular to apparatus and a method for reducing the flow of unpurified industrial or commercial effluent into the atmosphere.

B. Prior Art

Thermal regeneration apparatus is known such as shown in the U.S. Pat. No. 3,895,918 issued to James H. Mueller on July 22, 1975. In that system, a number of heat-exchange sections are arranged about and in communication with a central, high temperature chamber. Each heat-exchange section includes a heat-exchange bed with a large number of refractory elements or "stones" confined within a heat-exchange bed by inward and outward perforated retaining walls. An industrial effluent to be purified is applied to an inlet duct ring which has branch ducts that distribute the effluent to selected ones of the heat-exchange sections whenever its associated inlet valve is open. In such a case, the effluent traverses the heat-exchange bed which has a temperature gradient from the front inner retaining wall to the rear outer retaining wall. The front inner wall and region are hotter than the regions located more toward the outside since the front is closer to the very high temperature central combustion or incineration chamber.

All of the heat-exchange sections are also coupled by branch conduits to an exhaust duct ring, the ring itself being connected to an exhaust fan that draws the gaseous contents of the exhaust ring out and applies them to an exhaust stack or equivalent.

The effluent initially traverses a first heat-exchange bed in one of the inlet heat exchange sections after passing through an open inlet valve (the outlet valve of that section being kept closed) and then is drawn through the central combustion chamber where it is purified by high temperature oxidation. It is then drawn through at least a second heat-exchange bed to whose stones the purified combustion products lose their very high heat. In the second heat exchange section, the inlet valve remains closed whereas the outlet valve is open.

When the next cycle begins, however, a second heat-exchange section may be caused to operate as an inlet heat exchanger, whereas the first inlet heat-exchange section may have its role reversed to function as an outlet heat exchanger. Thus, in the next cycle, the first heat exchange section will have its outlet valve turned off and its inlet valve opened whereas the second inlet heat exchange section will have just the opposite valve condition. Before the next cycle begins, however, there is an intermediate period in which both valves of the first section will be turned off so that any residual effluent in that section may be drawn off by the suction generated by the exhaust fan. Otherwise, when the next cycle begins and the condition of the valves in the first section are reversed, this residual unpurified effluent might be drawn directly into the outlet exhaust ring without having traversed the heat-exchange bed in the first section, the central combustion chamber and the heat-exchange bed in the second heat-exchange section. This would result in the emission of noxious or dangerous gases into the atmosphere.

The valves used at the inlet and outlet of the respective heat-exchange sections are often metal-to-metal because of the temperatures involved. Even if the valves are nominally closed, imperfections in manufacture of the valves or defects in them induced by heat or by other operating causes may result in leaks of the effluent through the inlet and outlet valves, especially when there is a changeover of a heat-exchange section from an inlet to an outlet mode so that the effluent flows directly in the outlet exhaust ring thereby bypassing the thermal oxidation process.

Although there is a problem with valves such as these insofar as leakage is concerned, there is no practical way to measure such leakage once it has been installed in the apparatus as shown. While an individual valve can have its leakage measured on a test stand using ambient air, the latter is so much lower than actual operating gas temperatures that such tests are not too valid. To simulate actual operating temperatures would require elaborate heat exchange equipment and other expensive equipment. Furthermore, because of shop machining practices and allowable tolerances, no two valves which are supposed to be the same have the same leakage rate. While it may be that the leakage is less than 1%, even that small amount may be intolerable in certain areas where antipollution measures are stringently enforced.

Several ways of combating this leakage have been proposed among which is a plan whereby double valves in series are used at the inlet and outlet valves so as to reduce the pressure differential across each valve and thereby the rate and volume of leakage. This proposal is made in the co-pending application Ser. No. 052,670, filed June 27, 1979 entitled "Double Valve Anti-Leak System for Thermal Regeneration Incinerators." This method may be further improved, as explained in that application, by applying some of the purified exhaust gas under pressure to the space between each pair of series valves. While this is an effective method to prevent leakage, it does require the use of a double number of valves and appurtenant controls.

It is therefore among the objects of the present invention to:

(1) provide a system for preventing leakage of effluent across valves in incineration systems.

(2) provide an anti-leak system for incineration apparatus which does not require the use of double valves and the concomitant instrumentation for them.

Purified effluent in the exhaust of a thermal regeneration apparatus is fed back to blanket at least one side of valves located in the inlet and/or outlet duct which communicates with each heat-exchange section of the apparatus to prevent unpurified effluent from leaking through the valve(s) when nominally closed thereby avoiding passage through the main incineration chamber of the apparatus.

FIg. 1 is a plan view of apparatus constructed in accordance with the present invention.

FIG. 2 is a fragmentary, and sectional view of the apparatus shown in FIG. 1 taken along section line 2--2 in the direction indicated.

A thermal regeneration system is shown in the figures in which there are a number of heat-exchange sections 16 arranged equiangularly around, and in communication with, a central combustion zone 18 having a burner 31 therein. Each of the heat-exchange sections 16 has a bed of heat-exchanging ceramic elements 16d retained by vertical perforated walls 16b and 16c. An industrial effluent to be incinerated is applied via an inlet duct (shown at 5) to an upper duct ring 14 to which vertical ducts 15 are coupled that convey the effluent to each of the sections 16 into flue chambers 16a outwardly of the retaining wall 16b. There is a corresponding outlet or exhaust ring 20 located below the upper ring 14, the exhaust ring being coupled to an exhaust fan (shown at 7). The negative pressure produced within the ring 20 causes the effluent to be sucked in from ring 14 through one or more of the heat-exchange sections 16, through the associated heat-exchange elements 16d into the high-heat combustion chamber 18 and then out through a different one of the sections 16 to the exhaust 20 via duct 19. Of course, in order to follow the trajectory described above, it is necessary to operate certain valves on the inlet and outlet of the various sections 16. Thus, when it is desired to have the effluent pass through the section 16 illustrated in FIG. 2, the valve 22 is opened whereas the valve 26 is closed. At the same time, in another section 16, the inlet valve is closed and the outlet valve is open. The stack 6 is coupled to the exhaust fan for discharge into the ambient air.

As explained above, the system thus far is of conventional construction and in general accordance with the teachings of the aforementioned Mueller patent. In accordance with the present invention, there is another duct ring 10 provided outwardly of the sections 16 having pipes 12 communicating with it and with the downward ducts 15 as shown so that its free end is just above each of the inlet valves 22. This ring may be considerably smaller than the inlet duct 14 and communicates by way of duct 8 with the exhaust stack 6. Ordinarily, because of the action of the exhaust fan throughout the system, there will be a negative pressure just above the inlet valves 22 say, on the order of -2.5 inches (water). This suction will be sufficient to draw from the stack 6 a certain portion of the purified exhaust air which applies it in blanketing fashion above the valve 22 when it is closed. Thus, this purified and warm air constantly occupies the space just above the valve 22 so that if the negative pressure induced in the vertical duct 15 by the exhaust system is able to pull gases through the valve 22 even when closed, it is the purified exhaust air which will enter the section 16 outwardly of the wall 16b, not the unpurified effluent in ring 14. Therefore, when the inlet valve is supposed to be closed, no effluent will proceed from the inlet ring to the sections 16 and down into the exhaust ring 20 past the nominally closed outlet valve 26 which is located in the vertical connecting duct 19.

A similar arrangement can be used to flush the outlet valves 26. For this, there is another duct ring 28 supported by bracket 29 which, through vertical ducts 32, is coupled to a fan 34 whose input communicates by way of horizontal branch duct 33 with the stack 6. Fan 34 operates to draw out relatively hot purified air from the stack 6 and apply it via elbow 35 to the region just above the outlet valve 26. This fan is required because of the large difference in the pressure existing just above the inlet valve 22 and just above the outlet valve 26. In the former region, the pressure may be -2.5 inches whereas in the other region it may be -5 inches or -11 inches for example. When both the inlet and outlet valves for a particular heat-exchange section 16 are closed, there may be some residual effluent in the space outwardly of the retaining wall 16b. By having the region just above valve 26 blanketed with hot purified exhaust, it is this exhaust rather than the effluent which it supplants, which may be drawn through a nominally closed outlet valve 26 into the exhaust ring 20.

Therefore, by using the system described, the bad effects of effluent leaking past inlet valves 22 or outlet valves 26 when nominally closed are considerably mitigated and thus there is considerably less chance that unpurified effluent can get into the exhaust ring 20. To the extent that the hot exhaust air does get pulled down past closed valve 22 or to the extent that the hot air supplied by the elbow 35 does not all leak through nominally closed valve 26, this hot air will pass through the heat-exchange beds into the central combustion chamber. Since it is recycling whatever imperfectly combusted compounds that may exist in the exhaust, those residual compounds will be subjected to a further incineration and purification step. For example, purification might be increased by 1% if approximately 5% of the total flow to the unit is recycled in this valve-blanketing fashion. The recycling of part of the exhaust also helps the thermal efficiency since the purified exhaust is considerably hotter than the usual effluent applied to the apparatus.

As pointed out in the Mueller patent previously alluded to, additional amounts of purified exhaust may be used to purge or flush the spaces in the section 16 outwardly of the retaining wall 16b when the inlet and outlet valves 22 and 26 are both supposed to be closed at the same time. Whatever residual effluent may happen to be in that area can be effectively flushed by recycling some of the exhaust into a third duct ring 21 which communicates with stack 6 by way of horizontal duct 25 and with the section 16 by elbows 23 in which valves 24 may be located.

While the invention has been explained in terms of a thermal regeneration system in which there are three or more heat-exchange sections, it could also be applied to other incineration systems for gaseous effluents wherein it is possible for the incoming effluent to by-pass a heat-exchange or combustion chamber through which it normally should pass. In such case, the upstream side of the inlet valve may be blanketed with purified effluent as previously explained.

Still other applications and embodiments of the invention will be apparent to one skilled in the art upon perusal of the specification and drawings herein.