A tube type recuperator is provided with a top manifold having a plurality of openings slidably receiving a plurality of ceramic tubes, a retainer ring fixed to each of said tubes within the top manifold and a flexible expansion compensator seal member sealingly engaging the top ends of the tubes within the retainer ring. Preferably the ceramic tubes are made up of inner and outer coaxial ceramic tubes each connecting to a separate top manifold.

This invention relates to ceramic tube recuperators and particularly to 
ceramic tube type recuperators in a top supported configuration using 
inner and outer tubes. 
Recuperators have been used in furnace systems for recovery of heat from 
the furnace for many years. Typical of such recuperators is that shown in 
U.S. Pat. No. 3,602,296 and the references cited therein. These 
recuperators have been based on the use of metal tubes for recuperating 
transfer of heat. With the present energy crisis and the accompanying 
increase in fuel costs, the tendency has been to increase the air preheat 
temperature and thus to recuperate as much energy from the hot waste gas 
as possible. Unfortunately, however, as the air temperature increases, 
difficulties arise in selecting a satisfactory metallic material for use 
in such applications. 
The present invention provides a solution to this problem of increased 
temperatures and to the problem of finding materials to withstand these 
higher temperatures and the erosion which occurs with them. 
We have developed a tube type recuperator having at least one top manifold 
having a plurality of openings slidably receiving a plurality of ceramic 
tubes, a retainer ring fixed to each of said tubes within the top manifold 
and a flexible expansion compensator seal member sealingly engaging the 
top ends of the tube within the retainer ring. Preferably the ceramic 
tubes are made up of inner and outer coaxial ceramic tubes each connecting 
to a separate top manifold. In order to achieve maximum efficiency and 
heat recovery along with most economy in design, the double ceramic tube 
recuperator can be used in parallel or series with conventional metallic 
recuperators.

Referring to the drawings we have illustrated an outer ceramic tube 10 
closed at one end and open at the other end into plenum 11. An inner 
ceramic tube 12 open at both ends extends axially within the outer tube 10 
from a second plenum 13 to a point adjacent the closed end of outer tube 
10. The surface of outer tube 10 is exposed to the hot gas stream from the 
furnace and receives heat from this hot gas stream by convection and 
radiation. The gas to be heated entering from second plenum 13, flows 
through the inside of the inner tube 12, then out of the bottom open end 
12 to the annulus 14 between inner tube 12 and outer tube 10. The heated 
gas then rises through this annulus to first plenum 11 from which it is 
withdrawn. 
The details of the preferred method of setting and sealing the ceramic 
tubes 10 and 12 to this metal sheet bottom of the respective plenums is 
illustrated in FIG. 2. A tube holder 17 is welded to the tube sheet 16 
forming the base of plenum 11 or plenum 13, and is lined with ceramic 
fiber 18. The ceramic tube 10 or 12, having a slightly enlarged head 10a 
or 12a is placed in holder 17. A tube fastener 19, in the form of a 
donut-shaped ring is threaded into the end of holder 17 to force the head 
10a or 12a as the case may be into tight sealing contact with the holder 
17 and ceramic fiber sealant 18. For the case of plenum l3, a layer of 
suitable castable 15 is added to protect the metal sheet from direct 
exposure to the hot gas. 
In FIGS. 3 and 4 we have illustrated another modification of the invention 
again based on the use of double axial ceramic tubes. In this embodiment 
we have illustrated a recuperator assembly within a supporting housing 30 
of usual construction. Each recuperator assembly is made up of a pair of 
top superimposed plenums or manifolds 31 and 32 supported on housing 30 by 
support channels 32a. Depending from the upper manifold 31 are inner 
ceramic tube 33 which extend coaxially within outer ceramic tubes 34 
depending from lower manifold 32 and terminate short of the outer ceramic 
tube 34. The air to be heated passes from manifold 31 down through inner 
ceramic tube 33 and up through the annulus 35 between inner ceramic tube 
33 and outer ceramic tube 34 to lower manifold 32 from which it is carried 
to the point of use. The hot flue gases pass through housing 30 around 
ceramic outer tubes 34 in the usual manner of recuperators. 
Preferably the manifolds 31 and 32 are insulated over their surfaces with a 
layer of rigid insulant 40 to retain the maximum heat efficiency. 
In the foregoing specification, we have set out certain preferred practices 
and embodiments of our invention, however, it will be understood that this 
invention may be otherwise embodied within the scope of the following 
claims.