FIELD OF THE INVENTION
The invention relates to ceramic honeycombs with multiple channels for passage
of hot gas/fluid with wall material having high temperature resistance properties
including heat transfer and heat storage characteristics for thermal energy
storage and heat regeneration applications. More particularly the invention
relates to a ceramic honeycomb device for storage of high temperature thermal
energy. The invention further relates to an extrusion process for manufacturing
ceramic honeycomb devices for storage of high temperature thermal energy.
BACKGROUND OF THE INVENTION
Thermal energy storage (TES) at high temperature is one of the upcoming areas
in energy storage field which attracted major players in this field and new
applications are coming up both in traditional energy-intensive industry sector as
well as in solar thermal energy sector. High temperature air combustion
technology developed in Japan is being used in Gas fired furnaces which saves
about 30% energy. In this system, the ceramic honeycombs are used as a high
temperature thermal energy storage device because of its high surface area,
high thermal capacity and high temperature thermal shock withstanding
capability. These multi- channel honeycombs enable flow of hot air/gas/fluid
(upto 1600oC) through the channels during which heat is transferred and stored
in the bulk ceramic. The stored thermal energy is extracted from the ceramic
blocks when the cold air/gas/fluid is passed through its channels and the
temperature of incoming air can be heated up as high as 1000oC.

Important design parameters of the honeycomb are cell density (CPSI),wall
thickness, geometrical surface area (GSA) and open frontal area (OFA) whereas
the key material properties of the honeycomb are thermal expansion, thermal
shock resistance, refractoriness, thermal conductivity, specific heat and density;
all are critical for heat regeneration applications.
US 5,848,885 discloses a regenerative burner where regenerative heat exchange
system performs heat exchanger by alternatively passing combustion exhaust
gas as high-temperature fluid and combustion air as low-temperature fluid
through a fixed regenerator. US 6, 926,516 relates to an improvement in a
burner apparatus and a combustion method thereof.
US 5,876,197 and US 6,250,917 describe methods for heating a fuel-fired
industrial furnace, particularly a metal smelting furnace, upon employment of
regenerators and burners through which hot exhaust gas and cold combustion
air flow in alteration.
JP 2000297320 discloses a batch type annealing furnace body, and consists of
fast switching type regenerative combustion burner, the fast switchable
regenerative combustion burner, a plurality of combustors comprising a burner
and a ceramic honeycomb made of regenerator.
US 4,215,553 and US 4,405,010 disclose a sensible heat storage method for
solar thermal system energy using ceramic honeycombs.

US 7,159,643 describes a heat storing element and method for manufacturing
heat storage apparatus using the element. WO 2004113816 relates to a
honeycomb body for thermally treating waste gas, particularly for regenerative
heat storage.
EP 0472605 B1 teaches that ceramic masses can be used in regenerators for
exhaust gas treatment as heat storage.
CN 102515775 discloses a preparation method for an energy-saving honeycomb
ceramic, wherein the method is suitable for solar energy high temperature
thermal power generation, industrial kiln and hot blast stove heat storage
honeycomb ceramic processing. Here, waste high aluminum ceramic or the
refractory material is adopted as the main raw material (70-85% by wt).
CN 102875128 discloses a fly ash-based (45-82%), heat storage honeycomb
ceramic. CN 201858920 discloses a honeycomb ceramic body where the specific
surface area and the porosity of the honeycomb ceramic body are greatly
improved, therefore the thermal storage performance of the honeycomb ceramic
body is improved.
CN 10142014 describes a composite thermal storage material produced from
waste chromium hydroxide the use temperature is above 1250oC; the thermal
storage density is 2 to 3 times of that of mullite and cordierite honeycomb
ceramic thermal storage bodies.

JPH 0293297 discloses material to improve the thermal shock durability as well
as the heat exchanging efficiency by selecting specific coefficient of thermal
expansion apparatus and Young’s modulus for the matrix segment and the
adhesive for a heat transfer and storage type ceramic heat exchanger.
CN 1412518 relates o a high-temperature cellular ceramic heat-storing body and
its preparation technology. Said heat-storing body is made up by using A1203,
MgO, ZrO2.
CN 101628823 discloses a preparation method of corundum honeycomb ceramic
with enhanced slag resistance using bauxite, kaolin, soapstone and feldspar as
starting raw materials. An aluminum-chromium phosphate compound protective
layer is coated on the surface of the inner wall of the honeycomb ceramic hole.
US 8,206,787 describes process for producing honeycomb bodies for thermal
regenerators where channels are glazed.
All the above prior art describe methods of preparing ceramic honeycomb and its
uses as heat storage elements in regenerative burners, etc. However, for
efficient heat storage and heat transfer properties, two key design properties
which are competing each other i.e. the geometric surface are and honeycomb
density ratio have to be maximized. Hence, a new approach to increase
honeycomb density without reducing surface area is required where both
honeycomb design and material of construction are to be considered.

Another practical requirement for catering to thermal energy storage application
is to use abundantly available materials. This is because for high temperature
heat storage applications, the economic materials available are suitable for
sensitive heat delivery, means large quantity of such materials are required.
Hence the construction materials for Thermal Energy Storage Blocks should be
abundant, easily available and inexpensive.
Further to minimize the large requirement of space for installations, the Thermal
Energy Storage Elements should have high thermal mass which can be achieved
by developing material composition having high density and capable of
fabricating into desired shapes with the desired thermal properties.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a ceramic
honeycomb device for storage of high temperature thermal energy.
Another object of the present invention is to propose an extrusion process for
manufacturing ceramic honeycomb devices for storage of high temperature
thermal energy.
A still another object of the present invention is to propose a ceramic honeycomb
device for storage of high temperature thermal energy in which the honeycomb
having multiple channels of polygon shapes which gives higher geometric surface
area and mass density for better heat transfer and heat storage applications.

Yet another object of the present invention is to propose a ceramic honeycomb
device for storage of high temperature thermal energy wherein the honeycombs
are formed of raw materials abundantly available and inexpensive and having
high thermal mass which can be shaped easily into desired configuration to
produce the desired thermal properties.
A further object of the present invention is to propose an extrusion process for
manufacturing ceramic honeycomb devices for storage of high temperature
thermal energy, which uses refractory grains and powders to manufacture the
honeycomb body.
SUMMARY OF THE INVENTION
Accordingly, there is provided in a first aspect to a ceramic honeycomb device
for storage of temperature thermal energy.
In a second aspect, the invention provides an extrusion process for
manufacturing ceramic honeycomb devices for storage of high temperature
thermal energy.
In gist, the present invention relates to an improvement in a known burner
apparatus for performing non-oxidizing combustion or reduction combustion
wherein a ceramic honeycomb is included as regeneration medium.

The ceramic honeycomb of the present invention having multiple channels of
polygon shapes which give higher geometric surface area and mass density for
better heat transfer and heat storage application. Further, the ceramic
honeycombs are manufactured with higher mass density from a mixture of
ceramic raw materials containing inert refractory grains selected to give higher
mass density and fine powders to give ceramic bonding phases during the heat
treatment. The honeycomb thus manufactured has high thermal shock
resistance, refractoriness, and other mechanical and thermal properties suitable
for the regenerative burners of reheat furnace in a steel plant and for thermal
storage in the regenerative burners of reheat furnace in a steel plant and for the
thermal storage in solar thermal system or similar applications.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention, at least two configurations of honeycombs i.e triangular
and hexagonal channels are designed and their key physical properties are given in
Table 1 (see Examples 1 and 2). Open frontal area (OFA) defined by percentage of
cross section area of opening to total cross section area for hexagonal and
triangular honeycombs are 39.4 % and 41 % indicating similar flow behavior of hot
gas or air though the channels. Geometrical surface area (GSA) defined by total
surface area provided all the channels. The per unit volume for the hexagonal and
triangular honeycombs are 0.77 mm2/mm3 and 0.99 mm2/mm3 respectively. Higher
the GSA higher is the heat transfer properties. However, honeycomb density ratio
(i.e ratio of bulk density of product to bulk density of wall material) of hexagonal

channeled honeycomb is 0.57 which is higher than that of the triangular
honeycombs (0.54). Higher density ratio of the honeycomb product gives higher
heat capacity values.
Moreover, according to the present invention, there is provided a method of
manufacturing ceramic a method of producing ceramic honeycombs to provide
higher material density and thermal storage properties for thermal storage and
regenerative burner applications. The ceramic material is prepared from batch
containing two parts: the first part of more than 50 %of batch weight containing
inert refractory grains or powders; the 2nd part of below 50% of total batch weight
containing fine powder which are reactive and will form required phases such as
cordierite, mullite, corundum, etc. during subsequent heat treatment of produced
ceramic honeycombs. First part is selected from either of the inert refractory
powder such as fused mullite, sintered mullite, fused alumina, Zircon, calcined
Chromite, SiC, calcined magnesite etc or combination of these refractory powders.
Second part is prepared from fine ceramic raw materials such as calcined alumina,
clay, talc, etc. The particle size of these raw materials is very important to get the
required properties after firing. First part is selected from larger particle size than
that of that of First part but preferably below 200 microns more preferably below
75 microns. Second part is selected from lower particle size than that of that of
First part for better sintering behavior in the chosen firing temperature preferably
of particle size below 10 microns more preferably below 5 microns. True Density of
material is important criteria to get product with higher density. First of part is
selected from material having density more than 3.0 gm/cc.

Moreover, according to the present invention, there is provided a method of
manufacturing of ceramic honeycombs for thermal storage applications and
related applications where the production method involves the mixing of two
parts of ceramic raw material in a high intensive or similar mixer with organic
binders and water. The paste is extruded though a die to provide ceramic
honeycombs having multiple channels of polygon shapes which gives higher
geometric surface area and mass density. The dried products are fired in the
kilns at 1300-1600 Deg C, more preferably 14000 to 1550 Deg.
These ceramic honeycombs have thermal mechanical properties suitable for high
temperature regenerative burners of reheat furnace in a steel plant and for thermal
storage in solar thermal system.
Examples


Example 3 to 4.
Raw material used for first part is mullite. Raw material used for second part is
calcined alumina and clay in Example 3. Cordierite forming raw material such
as clay, talc and alumina is used in Example 4. Ratio of first part and second
part was maintained equally. Honeycombs as per Examples 1 and Examples 2
were produced by extrusion and firing at 1550 Deg C for Example3 and 1400
Deg C for Example 4.

Example 5 to 6. Raw material used for first part is Chromite. Raw material used
for second part is Clay. Chromite content is 50 % in Example 5 and 80% in

Example 6. Honeycombs as per Examples 1 were produced by extrusion and
firing at 1400 C. Properties of ceramic sample are produced are shown in Table
3.

Example 7:
Honeycombs prepared as per Example 3 and Example 6 are tested for thermal
storage capacity in a test rig
An experimental setup to evaluate the heat regenerative capacity of the ceramic
honeycomb in the temperature range of 500 Deg C – 1000 Deg C was designed
to study the storing and discharging characteristics in a cyclic mode. The cycling
was done such that the sample was heated to near steady state by passing air at
800 deg C and then discharged with inlet air at 27 Deg C to give outlet air at >
500 Deg C there after charging was resumed. Ceramic honeycombs prepared as
per Example 3 showed cycle time of 28 min and heat storage 490 MJ/m3
Ceramic honeycombs prepared as per Example 6 showed cycle time of 33 min
and heat storage 613 MJ/m3 when discharged to give outlet air at > 500 Deg C.

WE CLAIM :
1. A ceramic honeycomb device for storage of high temperature thermal
energy, wherein the honeycombs having multiple channels of polygon
shapes to provide higher geometric surface area including mass density,
characterized in that the ratio of bulk density of product to bulk density
of wall materials is more than 0.5.
2. An extrusion process for manufacturing ceramic honeycomb devices for
storage of high temperature thermal energy, the process comprising the
steps of :
- mixing ceramic raw materials containing inert refractory powders and
fine powders selected to provide higher mass density including ceramic
bonding phases respectively;
- mixing the raw materials with binder and water to make an extrudable
paste;
- forming honeycomb body in an extrusion process with the paste; and
- firing the said honeycombs at a temperature between 1300oC, wherein
the amount of inert refractory powder used to form the extrudable
paste , more than 50 % of total weight is preferably more than 60%
of the total weight.

3. The method as claimed in claim 2, wherein the inert refractory
powders are selected from a group of refractory powders consisting
of fused mullite, sintered mullite, fused alumina, Zircon, calcined
Chromite, SiC, calcined magnesite etc or combination of these
refractory powders.
4. The honeycomb device as claimed in claim 1, wherein when an inlet
air at 800 Deg is passed through the device, the temperature of the
outlet hot air is reduced to 500°C.
5. The honeycomb device as claimed in claim 1, wherein the ceramic
honeycombs exhibit a heat capacity of more than 400 MJ/m3.