Horizontal regenerative thermal oxidizer unit

Abstract: A regenerative thermal oxidizer unit comprising two heat regenerator unite (4,4') in which a gas to be purified from VOCs passes through the units in an essentially horizontal direction.

Description: This invention relates to thermal regenerator units. Many chemical and petrochemical processes result in an emission of off-gases containing volatile organic components, (referred to in the industry as "VOC"s), many of which are believed to be environmentally harmful. There has as a consequence been a concerted effort to clean up such emissions by removal of VOCs prior to venting the off-gases to the atmosphere. One such approach is to pass the gases through combustion chambers where they are mixed with fuel and burned. To make this process more efficient the heat generated is typically used to pre-heat the incoming VOC-containing gases. This is done in a thermal regenerator unit. In such a unit the gases exhausted from the combustion chamber pass through a container holding a heat sink media which absorb the heat of combustion. When the heat sink media have reached the desired temperature, the flow is reversed and the incoming gases pass over the heated media and the exhausted gases pass through a second container of heat sink media. This process continues with the flow being reversed as the heat extracted from the exhaust gases reaches the desired level. WO 97/44119 discloses a regenerative thermal oxidizer comprising first and second heat exchange columns, each column containing heat exchange media and having a gas inlet, a gas outlet, and being in communication with a combustion chamber. DE-610173 describes a horizontal regenerator, especially for coke-ovens, which comprises several superimposed regenerator chambers comprising channels, wherein the regenerator chambers are connected by reversal chambers. The reversal chambers are divided in such a manner that the upper channels of the first regenerator chamber are connected to the lower channels of the second regenerator chamber and vice versa. WO90/14560 discloses an installation for thermal oxidation of organic compounds in waste gas or exhaust gas steams with regenerative heat recovery. The waste gas or exhaust gas stream is alternatively heated and cooled in at least two regenerators containing heat accumulator materials. The heat accumulator material consists essentially of at least one essentially prismatic, the main prism axis of which is arranged essentially in the direction of gas flow and comprising regularly disposed, essentially rectilinear channels. A further document DE 2 301 445 discloses a thermal regenerative oxidizer unit according to the preamble of claim 1 in a vertical arrangement. Such processes are quite economical and reduce the costs of operating such regenerative units. However since the units are typically added to existing equipment as it is modernized to meet new environmental standards, they must often fit into existing available space rather than be designed as part of the installation before it is constructed. As was indicated above, space must be allocated for twin passages through which the exhaust gases can reach the combustion chamber and this is not easy to accommodate except by installation of vertical towers for the heat exchange. However since the heat sink material has to be changed from time to time, maintenance of such towers is a major problem. It is therefore the object of the present invention to overcome the drawbacks and disadvantages of the prior art. This object is solved by the thermal regenerative oxidizer unit according to independent claim 1. Further advantageous features, aspects and details of the invention are evident from the dependent claims. A horizontal thermal regenerative oxidizer unit has now been developed which occupies comparatively little space and is easily maintained being adapted to use modular heat sink units that are readily installed and removed. The invention relates specifically to units designed for efficient use of recycled heat in thermal oxidizer units where a horizontal layout allows very efficient utilization of space. The present invention provides a horizontal thermal regenerative oxidizer unit comprising a combustion chamber connected to two heat regenerator units housing heat sink media wherein each unit comprises at least first and second compartments in vertically stacked relationship with connecting passageways such that gases passing therethrough pass horizontally in a first direction through the first unit and then subsequently in the reverse direction through the second unit. The heat regenerator units can if desired comprise more than two compartments stacked one above the other with the exhaust gases passing horizontally in alternating directions as they move up, (or down), the stack. Generally however two per unit is preferred. The compartments preferably are adapted to house heat sink media in the form of porous ceramic blocks with a plurality of obligatory passages. These are sometimes referred to as "honeycomb monoliths". Such monoliths are easily installed and removed as modules and the compartments of the thermal regenerator units are preferably designed to receive such monoliths and hence permit easy maintenance. The above-mentioned features of this invention are illustrated by the following drawings: Figure 1 is perspective view, partly in cut-away section showing an embodiment of the Invention. Figure 2 is a plan diagram of the equipment illustrated in Figure 1 with the arrows indicating the direction of gas passage in a first mode of operation. Figure 3 is similar to Figure 2 except that the gas flow is reversed to illustrate a second mode of operation. The invention is now described in more detail with specific reference to the Drawings. These illustrate a preferred configuration for the horizontal thermal regenerator oxidizer unit according to the invention but should not be taken as inferring any limitation on the essential scope of the invention claimed herein. In Figure 1, process gas containing VOCs enters through inlet, 1, and feeds a first distributor tube, 2, equipped with valves, 3, permitting flow in one direction but not the opposite direction, depending on which of the valves is in the open position. In Figure 2 the valve on the left is closed whereas in Figure 3, it is the valve on the right that is closed. From the distributor tube the gas enters a first heat regenerator unit, 4, through a lower level compartment, 5, which contains a honeycomb monolith, 6. From this compartment the gas reverses direction and enters an upper level compartment of the unit, 7, which likewise contains a honeycomb monolith. The gas passes directly from the upper level compartment to a combustion chamber, 8, where it is subjected to temperatures that result in the combustion of the VOCs. Gas exhausted from the combustion chamber enters a second heat regenerator unit, 4', through an upper level compartment, 7', and then, reversing direction,- enters a lower level compartment, 5'. Both upper and lower compartments house ceramic honeycomb monoliths, 6'. From the lower compartment the gas enters a second distributor tube, 13, which has valves, 9, 9', allowing gas entering the second distributor tube to exit only through an exhaust port, 10, from which it is drawn by a pump, 11, and vented through a stack, 12. In Figures 2 and 3 the movement of the gas through the system is shown by numbered arrows which indicate the sequence of passage through the indicated portions of the unit. Figure 2 shows the flow in one direction and Figure 3 shows the flow in the reverse direction. It will be noted that, by operation of the valves in the first and second distribution tubes, the direction of flow can be instantly reversed with no required down time. Replacement of a ceramic honeycomb monolith in the upper or lower compartment of the first and second thermal regenerator oxidizer units can readily be accomplished by removal of the end portion of the unit connecting upper and lower compartments, (which is conveniently hung on hinges which are not shown), and then sliding out the monolith to be replaced. While the heat sink media have been shown as ceramic honeycombs, this is by no means necessary. The monoliths can be substituted by modular units of individual heat sink media or even by dumped heat sink media though this does not afford all the advantages of easy servicing described above. The heat sink media are preferably ceramic but it is possible to use other suitable materials where the composition or temperatures of the gases make this advisable. Where the media are not monoliths they can have any convenient shape such as wheels, tubes, "bow-ties", saddles, cylindrical pellets and balls. The unit has been described with upper and lower compartments only but this is by no means a limitation on the scope of the invention since each thermal regenerator oxidizer units can also comprise three, four or even more stacked compartments. Generally however two stacked compartments are sufficient. The units of the invention can be used wherever off-gases from a process comprise VOCs. Typical processes where the unit can be used include removal of traces of organic solvents from the air flow surrounding various coating operations in which the material coated is carried in an organic solvent. Generally it used be applied after recovery of as much solvent as is practicable by other means since thermal regenerative oxidizer units are primarily intended for removal of relatively minor amounts of VOCs. The unit according to the invention are also extremely useful when the gases to be treated are contaminated with particulate matter. Any such particulate matter will usually be trapped in the heat exchange media, and the pore diameters can be selected with this consideration in mind. Periodic cleaning of the media then would also include removal of trapped particulates.

Claims: A thermal regenerative oxidizer unit comprising a combustion chamber (8) connected to two heat regenerator units (4,4') housing heat sink media (6,6'), said heat regenerator units (4,4') being connected by a first and a second distributor tube, said first distributor tube (2) comprising an inlet (1) for process gases containing VOCs and valves (3,3') for directing said process gases alternatively into the first or the second heat regenerator unit (4,4'), said second distributor tube (13) comprising an exhaust port (10) and valves (9,9') for directing the gas flow alternatively from the first or the second heat regenerator unit (4,4') to the exhaust port (10), wherein the gas flow direction through the heat regenerator units (4,4') can be reversed by operation of said valves (3,3', 9,9'), and wherein each heat regenerator unit (4,4') comprises at least first and second compartments (5,5', 7,7') in vertically stacked relationship with connecting passageways characterized in that the thermal regenerative oxidizer is arranged horizontally and that the gases passing through said heat regenerator units (4, 4') pass horizontally in a first direction through the first compartment (5,5') and then subsequently in the reverse direction through the second compartment (7,7'). A horizontal thermal regenerative oxidizer unit according to claim 1 or 2 in which each compartment (5,5' 7,7') of each heat regenerator unit (4,4') comprises a ceramic honeycomb monolith heat sink media (6,6'). A horizontal thermal regenerative oxidizer unit according to any of the preceding claims in which each compartment is provided with access means adapted to permit ready removal of the heat exchange media therein.

Inventors: NIKNAFS HASSAN S, NIKNAFS, HASSAN S.
Applicants: NORTON CHEM PROCESS PROD, NORTON CHEMICAL PROCESS PRODUCTS CORPORATION
Application year: 1997
Main classification: F23G7
IPC codes: F23G7, F28D17