Horizontal regenerative thermal oxidizer unit

A regenerative thermal oxidizer unit comprising two heat regenerator units in which a gas to be purified from VOCs passes through the units in an essentially horizontal direction.

BACKGROUND OF THE INVENTION 
This invention relates to thermal regenerator units and specifically to 
units designed for efficient use of recycled heat in thermal oxidizer 
units where a horizontal layout allows very efficient utilization of 
space. 
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. 
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. 
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. 
GENERAL DESCRIPTION OF THE INVENTION 
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 compartment and then subsequently in the 
reverse direction through the second compartment. 
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 with access means to 
permit such ready installation and removal of such monoliths and hence 
permit easy maintenance.

DETAILED DESCRIPTION OF THE INVENTION 
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 FIG. 1, process gas containing VOCs enters through pipe, 1, and feeds a 
first distributor passage, 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 FIG. 2 the valve on the left is closed 
whereas in FIG. 3, it is the valve on the right that is closed. From the 
distributor passage the gas enters a first heat exchanger 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 thermal 
regenerator oxidizer unit, 4', through an upper level compartment, 7', and 
then, reversing direction, enters a lower compartment, 5'. Both upper and 
lower compartments house ceramic honeycomb monoliths, 6'. From the lower 
compartment the gas enters a second distributor tube, 8, which has valves, 
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 FIGS. 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. FIG. 2 shows the flow in one direction and 
FIG. 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 the units of the invention are used 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 is 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 mediathen would also include removal of trapped 
particulates.