FIELD OF INVENTION
The present invention relates to a catalytic combustor unit capable of connecting
to the exhaust of any fuel cell or battery for combustion of excess hydrogen gas in the
exhaust to eliminate safety hazards. More particularly the invention relates to the design
and development of a catalytic combustor assembly which houses catalyzed honeycomb
monoliths which can be connected to any excess hydrogen fuel source such as stack of
fuel cell or battery. The invention further relates to a process of using catalysed
honeycombs inside the converter assembly unit to utilize the Hydrogen coming out of the
exhaust of fuel cells or battery pack since unutilized hydrogen presents a safety hazard
due to its inflammability.
BACKGROUND OF THE INVENTION
A fuel cell is an electrochemical cell that converts a source fuel into an electrical
current. They are made up of three segments which are sandwiched together: the anode,
the electrolyte, and the cathode. There are many types of fuel cells and the electrolyte
substance usually defines the type of fuel cell. Most common fuel used is hydrogen. For
operation of a fuel cell stack, a certain amount of excess fuel is always supplied. Most of
the fuel cell systems, being developed worldwide, work on ~ 80-85% fuel utilization, i.e.
approximately 15- 20% extra fuel is usually supplied. In systems where only fuel cell

stacks are used, there is no alternative but to vent the excess Hydrogen coming out at
the Anode exhaust. This, however, limits the application of Fuel Cell based power packs
either to only well ventilated areas, or, where vent pipes may be erected.
Therefore, to overcome this problem, a suitable catalytic combustor has to be
developed which includes development of a combustor unit assembly which houses the
suitably catalysed honey-combs and finally encapsulating the catalysed honeycombs into
a suitable container which can be connected to the Anode exhaust of any fuel cell stack.
US 20040081871 Al discloses a catalytic combustor used with a solid oxide
fuel cell. The combustion of hydrocarbons is usually incomplete and releases both non-
combustibles that contribute to smog and other pollutants in varying amounts. A fuel cell
preferably includes a fuel cell stack for receiving reactants and conducting a reaction to
produce an electrical current, a catalytic combustor for combusting reactants that pass
un-reacted through the fuel cell stack, and a heat exchanger for exchanging heat from an
exhaust of the catalytic combustor to the reactants received by the fuel cell stack.
WO 2005034269 Al relates to an integrated fuel cell stack and catalytic
combustor apparatus, assembly, and method of use. An integrated fuel cell stack and
catalytic combustor apparatus includes a fuel cell stack assembly having multiple fuel cell
stacks between which is defined a cavity, each of said fuel cell stacks including a plurality
of individual fuel cells; and a catalytic combustor disposed at least partially within the

cavity, the catalytic combustor having a catalytic bed and a catalytic igniter. An
integrated fuel cell stack and catalytic combustor generally includes a catalytic combustor
disposed within a tubular fuel cell assembly that is, in turn, surrounded by a cathode air
profiling shell that creates a cathode air plenum over the tubular fuel cell.
US 7858255 B2 discloses a rapid light-off catalytic combustor for fuel cell
vehicle. A catalytic combustion unit for a fuel cell system is provided. The catalytic
combustion unit includes a reactor having a porous medium with a catalyst deposited
thereon. The reactor is disposed adjacent a heat exchanger and adapted to receive an air
stream and a hydrogen stream. The reactor is further adapted to promote an exothermic
reaction and modulate a temperature of a fuel cell stack. A fuel cell system and method
employing the catalytic combustion unit are also provided.
WO/2013/100490 relates to a fuel cell hybrid system. The fuel cell hybrid
system includes: a heat engine including a compression unit compressing an oxidizing
agent supply gas containing air and an expansion unit expanding the oxidizing agent
supply gas to generate mechanical energy; a fuel cell including an anode receiving a fuel
gas, a cathode receiving the oxidizing agent supply gas, and a catalyst combustor
combusting the non-reaction fuel gas of an anode exhaust gas exhausted from the anode
to heat the oxidizing agent supply gas; a first heat exchanger exchanging heat between
the oxidizing agent supply gas discharged from the compression unit and the cathode

exhaust gas exhausted from the cathode; and a second heat exchanger exchanging heat
between the oxidizing agent supply gas discharged from the first heat exchanger and the
oxidizing agent supply gas discharged from the catalyst combustor. Here, the oxidizing
agent supply gas discharged from the second heat exchanger is supplied into the catalyst
combustor via the expansion unit, and the oxidizing agent supply gas discharged from
the catalyst combustor is supplied into the cathode via the second heat exchanger.
IMECE2008-67040 discloses integration of catalytic combustion and heat
recovery with meso scale solid oxide fuel cell system. To facilitate high-power density
operation of a meso-scale solid oxide fuel cell (SOFC) system, fuel processing and anode
exhaust catalytic combustor with waste heat recovery are critical components. An
integrated modeling study of a catalytic combustor with a solid oxide fuel cell and a
catalytic partial oxidation (cpox) reactor indicates critical aspects of the butane-fueled
system design in order to ensure stable operation of the SOFC as well as the combustor
and cpox reactor. The modeled system consists of: 1) a Rh-coated ceramic foam catalytic
partial oxidation reactor, 2) a SOFC with a Ni/YSZ structural anode, a dense YSZ
electrolyte, and a LSM/YSZ cathode layer, and 3) a Pt-coated anode exhaust combustor
with waste heat recovery. Model results for a system designed to produce < 30 W electric
power from n-butane show how the design of the inlet-air cooled catalytic combustor can
maximize combustion efficiency of the anode exhaust and heat recovery to the system

inlet air flow. There is a strong sensitivity of the system operation to the SOFC operating
voltage as well as the overall air to fuel ratio, and these sensitivities place important
bounds on the range of operating conditions.
US 6077620 A discloses a Fuel cell system with combustor-heated reformer. The
invention relates to a fuel cell system having a combustor for heating a fuel reformer. A
fuel cell system including a fuel reformer heated by a catalytic combustor fired by anode
effluent and/or fuel from a liquid fuel supply providing fuel for the fuel cell. The
combustor includes a vaporizer section heated by the combustor exhaust gases for
vaporizing the fuel before feeding it into the combustor. Cathode effluent is used as the
principle oxidant for the combustor.
Ramesh Koripella, Rajnish Changrani et.al., disclose an integrated Miniature
Catalytic Combustor for Fuel Processor Applications. A miniature methanol steam
reformer is being developed to generate on-board hydrogen gas to run small fuel cells for
portable power applications. Steam reforming is an endothermic reaction and heat must
be supplied to sustain the reaction. Development of an efficient and compact combustor
is needed to provide and regulate the heat required for carrying out the steam reforming
reaction. This paper describes the design and development of a miniature catalytic
combustor that can be integrated with a miniature methanol steam reformer for portable
fuel cell applications in the range of 1 - 20W. The catalytic combustor was designed to fit

the footprint (35mm x 15mm x 5mm) of a miniature steam reformer, and fabricated
using multi-layer ceramic technology. The multi-layer technology enables a 3D integration
of the catalytic combustor with the miniature steam-reforming reactor.
Maxey, Christopher (University of Maryland, College Park, Md.) disclose in
their Thesis the Thermal integration of tubular solid oxide fuel cell with catalytic partial
oxidation reactor and anode exhaust combustor for small power application. In the
current study, a system configuration of a tubular SOFC with a catalytic partial oxidation
(CPOx) reactor and an anode exhaust catalytic combustor is explored to test the
feasibility of such a system. A system level model was developed to more fully assess
system design and operability issues. For the SOFC, a detailed 1-D SOFC determines local
current production and is combined with down-the-channel flow models for the SOFC as
well as the catalytic combustor/heat exchanger, and CPOx reactor. System model results
showed that variations in fuel flow and air to fuel ratio have large impacts on
temperature distribution and power out, with lower fuel flows and air-to-fuel ratios
providing higher SOFC power densities (~0.64 W/cm2) at high efficiencies (~45%). The
system model also shows that external heat loss greatly reduces system power and
efficiency but lower air-to-fuel ratios can offset associated temperature and associate
performance losses.
Sangmin Lee, Jaeyoung Han, Seokyeon Im, Sangseok Yu, Kook Young
Ahn and Young Duk Lee describe Flow Uniformity of Catalytic Burner for Off-Gas

Combustion of Molten Carbonate Fuel Cell. A catalytic combustor is a device to burn off
fuel by surface combustion that is used for the combustion of anode off-gas of molten
carbonate fuel cells by employing the catalytic combustor. Purified exhaust gas can be
recirculated into the cathode channel for C02 supply to improve thermal efficiency. In
this study, flow uniformity of the catalytic combustor was investigated in two steps: a
preliminary step with a model combustor and a main analysis step with a practical 250
kW catalytic combustor. Models of the 0.5 and 5 kW class combustors were used in the
preliminary step. In the preliminary step the model combustors were used to determine
supporting matters for flow uniformity. The inlet direction of the mixing chamber below
the catalytic combustor was also examined in the preliminary step. In the main analysis
step the flow uniformity of the scale-up combustor was examined with selected
supporting matter and inlet direction into the mixing chamber. Geometric and operating
parameters were investigated. In particular, the flow rate under off-design operating
conditions was examined. All the above disclosures are specific to certain type of fuel
cells and the processes involved. The focus of available literature is on the combustion
process and the catalysts used therefore. The present invention relates to the design and
development of a simple and separate catalytic combustor unit using certain catalysed
surface which can be connected to anode exhaust of any fuel cell or to any excess
hydrogen fuel source with an arrangement for preheating the whole assembly so as the
exothermic reaction can start.

OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a catalytic combustor unit
capable of connecting to the exhaust of any fuel cell or battery for combustion of excess
hydrogen gas in the exhaust to eliminate safety hazards particularly in closed spaces
which is capable of housing the catalysed ceramic or metallic honeycomb monoliths and
of being connected to the Anode exhaust of any fuel cell stack.
Another object of the invention is to propose a catalytic combustor unit capable of
connecting to the exhaust of any fuel cell or battery for the combustion of excess
hydrogen gas in the exhaust and thereby eliminate safety hazards. Further object is to be
able to design the catalytic combustor as a separate module in a way so as to be capable
of augmenting the capacity by adding additional catalyzed honeycombs units to meet the
various fuel cell or battery pack, depending on volume of excess.
A still another object of the invention is to propose a catalytic combustor unit
separately placed but capable of easily connecting to the exhaust of any fuel cell or
battery for combustion of excess hydrogen gas in the exhaust to eliminate safety hazards
which has the catalysed honeycombs in a suitable container with safe initial preheating
arrangement which are safe by isolating electrical contacts away from the enclosed
vulnerable space.

A further object of the invention is to propose a portable catalytic combustor unit
connected to the exhaust of any fuel cell or battery for combustion of excess hydrogen
gas in the exhaust to eliminate safety hazards without altering or compromising function
of any parts of the main fuel cell and battery unit.
SUMMARY OF THE INVENTION
One of the safety issues of fuel cell and battery pack is the Hydrogen gas
exhausted from the system, which poses a serious hazard of the possibility of explosion
inside the vulnerable space and need to be safely vented out.
A simplified catalytic combustor unit is designed by using a simple metal tube to
assemble the required number of honeycombs with compressible materials such as fibre
blanket or sheet to avoid gas leakage and integrity of the assembly. The tubes can be
arranged in a circular or rectangular manner covered by a shell or uncovered with a
suitable tie rod arrangement. The flanges are held together and suitably tightened with
the help of multiple nuts and bolts to avoid any gas leakage. Hydrogen and air inlet ports
have been provided in the top dome and an outlet port in the bottom flange. For mixing
of the two gases, a tubular structure with small holes has been provided in the top dome.
The modules can be designed with or without an outer shell.
In the current invention a suitable catalytic combustor unit is developed which
encapsulates the catalysed honeycombs into a suitable container with safe initial

preheating arrangements which can be connected to the exhaust of a standard fuel cell
stack.
The combustor has to be pre-heated typically between 50-60 deg C. various
arrangements can be used for the initial pre-heating. In one of the designs, electrical
band heaters were used to surround the bundle of tubes individually with all electrical
connections completely outside the combustor unit.
In another pre-heater design, a water jacket was created around the tubes. An
enclosure was created around the bundle of tubes by welding a steel sheet along the
periphery of the top & bottom flanges. Hot water could be used in such an arrangement
for heating the tubes directly. Moreover, at higher Hydrogen flow rates, when the
honeycombs are expected to get overheated, tepid water may be made to flow through
the same arrangement to effect cooling of the honeycombs or to even extract some
useful heat from the catalytic combustion.
A hot air blower can also be used to heat the tube assembly from outside for initial
pre-heating.
The power generated from fuel cell can be used to provide the initial electrical pre-
heating. External heating is needed only for initial heating and once the catalytic

combustion starts converting at typical 50-60°C, the exothermic heat of the reaction
alone is enough to maintain the combustor at the desired temperature.
Also, a temperature sensor can be used inside the catalytic combustor assembly so
as to cut off the initial heat requirement once the exothermic reaction is sufficient to
maintain the temperature on its own. The temperature requirement of the presently
available catalysed honeycombs as known in the art for catalyzing hydrogen into water is
about 50 to 60°C. The sensor employed in this invention cut the heat supply at this
temperature and need not be active till the exothermic reaction proceeds keeping the
temperature above this temperature.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 : Shows a closed catalytic combustor unit according to the invention.
Fig. 2 : Shows a cross-sectional view of a metal tube assembly according to
the invention.
Fig.3 : Shows the top view of the top and bottom flanges.
Fig.4 : Shows a tubular structure for gas mixing.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
The present invention relates to the design and development of a simple
independent catalytic combustor unit using certain catalysed surface which can be
connected to anode exhaust of any fuel cell or to any excess hydrogen fuel source with
an arrangement for safe preheating of whole assembly so as the exothermic reaction can

start. The unit encapsulates the catalysed monoliths for combustion of unutilized
hydrogen in the exhaust of a fuel cell or battery and its capacity can easily be augmented
by adding additional catalyzed honeycomb units to meet the need for various fuel cell or
battery pack. This unit is independent of the source of such exhaust.
The catalytic converter consists of
1. Metal shell(C) with flanges (7,8)
2. Upper (13) and lower (15) domes with inlet (11,12) and outlet (14) ports and
flanges
3. Tubes (1) containing catalysed honeycombs (2)
4. Sealing rings (10) and insulation materials (17)
5. O-ring (10)
Fig 1 shows design of a closed catalytic combustor unit. As shown in Fig 2, a metal
tube (1) with external diameter more than that of a honeycomb monolith been used to
assemble the honeycombs (2). A metal ring (3) with internal diameter (dl) less than the
outer diameter(d2) of honeycomb monolith as spacer to separate the honeycombs placed
inside the tube to avoid any displacement. The honeycombs have been wrapped with thin
compressible blanket (4) which is completely covered at the tube ends by metal rings so
that the honeycomb surface is exposed completely. The thickness of blanket is adjusted
to enable the honeycomb assembly to fit into the metal tubes. The tubes can be arranged
in a circular or rectangular tubular manner with an open design or a cylinder (6)
depending on the type of heating method used. Both top (7) and bottom flanges (8) have
been tightened with multiple nut and bolts (9) or several tie rods depending on module

design to avoid any gas leakage. A thin insulation material (17) is placed between both
flanges. As shown in fig 3, a silicone O-ring (10) was used between the two flanges to
provide a tight seal. Two ports for air (11) and hydrogen inlet (12) have been provided in
the top dome (13) and an outlet port (14) in the bottom dome (15). As shown in fig 4,
for mixing of the two gases, a tubular structure with small holes (16) has been provided
in the top dome.
In one of the modules, 9 tubes were assembled, 8 tubes were placed in the
circular arrangement and one tube was placed at the centre of the flange. The whole
assembly was covered by a metal shell welded to the top and bottom domes.
EXPERIMENTAL DATA
The catalysed honeycombs were canned in the metal tubes first. Assembled unit
was heated at 50 Deg C in an external drier for 2 hours. After that 1.5 LPM Air and 0.15
LPM of H2 was allowed in the inlet through in-built mixer inside the converter. Mild water
accumulations were observed when the Converter outlet exhaust is flown over a cold
glass beaker, temperature of the Converter inside was between 48-50 Deg C. However,
no moisture accumulations noticed when the temperature of the converter drops below
48 Deg C. In another trial, the Air and H2 were passed through a pre heater to the cold
converter, but moisture was not generated. Mild water accumulation seen on cold beaker
surface indicates that the 'combustor exhaust' contained traces of 'product' water,

indicating that Hydrogen had indeed got combusted inside the combustor. No moisture
was generated when the combustor was cold as no reaction may have taken place when
the Combustor is cold.
One such sealed module containing 27 Numbers of catalysed honeycombs was
designed, fabricated and totally assembled and connected to the anode exhaust of a
PEMFC (proton exchange membrane fuel cell) for further evaluation.
In a typical PEMFC stack of 1 kW capacity requiring about 15 Ipm of Hydrogen,
even with a lower fuel utilization factor of about 75%, the quantity of Hydrogen at Anode
exhaust was around {15x(l-0.75) = 3 75 Ipm}, thus, one standard module containing 27
catalyzed honeycombs was connected to the exhaust. Calculations made on the basis of
the initial test data suggest that above about 50 deg C, > 90% Hydrogen is easily
combusted. Higher capacity combustors could be made using a number of such modules
together.
ADVANTAGES
1. A simplified catalytic combustion unit which can be used with any fuel cell or
battery pack for converting un-burnt hydrogen in its exhaust.
2. A catalytic combustor which is separate and independent unit such that the use of
which does not depend on any specific design features of fuel cell or battery.

3. A catalytic combustor having safe initial pre-heating arrangements avoiding
electrical operations near to the exhaust containing un-burnt hydrogen gas.
4. A catalytic combustor, the capacity of which can easily be augmented by adding
additional catalyzed honeycomb units to meet the need for various fuel cell or battery
pack.

WE CLAIM
1. A catalytic combustor unit capable of connecting to the exhaust of any fuel cell or
battery for combustion of excess hydrogen gas in the exhaust to eliminate safety
hazards, the said catalytic combustor comprising;
a metal shell (C) comprising top dome (13) and lower dome (15) and a cylinder
(6) connected to said domes (13, 15) by top (7) and bottom (8) flanges, the said flanges
being tightened with plurality of nuts and bolts (9) for avoiding any gas leakage;
a silicon O-ring (10) disposed between the said flanges (7,8) for providing a tight
seal;
thin insulation material (17) disposed between both flanges (7,8) and the cylinder
(6), respectively;
at least two ports (11,12) disposed on the top domain (13), one port (11) for air,
other port (12) for connecting to fuel cell or battery exhaust which may contain
hydrogen;
a third port (14) disposed on the bottom dome (15) for outlet;
a tubular structure (16) with small holes;
a metal tube (1) with external diameter (D) more than that of a honeycomb (2)
disposed for housing the said honeycomb (2);
a metal ring (3) disposed inside the said tube (1), with internal diameter (d1), less
than the outer diameter of honeycomb monolith (d2) for restricting the honeycomb
monolith (2) for any displacement inside the tube (1); wherein

the honeycomb monoliths (2) are wrapped with thin compressible blanket (4) and
covered completely at the tube ends by metal rings (3) making the honeycomb surface
exposed completely wherein the catalytic combustor houses the metal tube (1) having
the catalysed honeycomb monoliths (2) for getting connected to anode exhaust of any
fuel cell stack.
2. The catalytic combustor as claimed in claim 1, wherein the tubular structure (16)
with small holes is disposed in the top dome (13) for mixing of two gases.