Note: Descriptions are shown in the official language in which they were submitted.
13~ o
The invention involves an apparatus for the dehydrogenation
of liquid hydrides with a chemical reactor, designed as a heat
exchanger, for the dehydrogenation of heated vaporous hydride,
a heat exchanger fluid to heat the hydride, at least one combus-
tion chamber to heat the heat exchanger fluid by burning hydrogen,
at least one heat exchanger to heat the hydride fed to the reac~
tor using the heat exchanger fluid or -the dehydrogenation products
leaving the reactor, at least one heat exchanger to cool down the
dehydrogenation products leaving the reactor and at least one
storage container for the cooled dehydrogenation products leaving
the reactor.
In particular, the invention refers to an apparatus for the
dehydrogenation of liquid hydrides suitable to drive hydrogen-
powered vehicles.
A fundamental problem in the development of practical vehic-
les driven by means of hydrogen-powered combwstion engines is
how to store the hydrogen suitably in the vehicles. In this
regard, it has proven useful from various points of view to make
use of the organic-chemical storage of hydrogen in liquid hydrides.
Methyl cyclohexane, which is a liquid that can be stored in
simple tanks under normal pressure and at a normal temperature,
is especially suited as a liquid hydride. The hydrogen is stored
by hydrogenation of toluene in methyl cyclohexane.
Methyl cyclohexane is pumped into the vehilce as a liquid
hydride carrier. The vehicle contains a dehydrogenation system in
which the methyl cyclohexane (MCH) is split into toluene and
hydrogen in a chemical reactor usiny the application of heat and
a suitable catalyst. The hydrogen recovered in this way is stored
'
2 --
temporarily and used mainly to drive the hydrogen-powered combus-
tion engine, but in part also to generate the heat in the reactor
required for dehydrogenation. The liquid toluene produced during
dehydrogenation is also stored and returned to the pump the next
time the vehicle is filled up. The toluene can then be hydro-
genated once again to MCH in suitable hydrogenation plants,
closing the cycle.
Appropriate test set-ups were developed which showed that
the aforesaid process can definite:ly be realized in practice.
However, in the case of these test set-ups the dehdrogenation
system, including the necessary auxiliary equipment and measuring
equipment, was of such a volume that it took up the space of the
loading area of a truck or of a trailer. This is one of the basic
reasons why this technology is not yet realizable in practice at
present.
The objective of the invention, therefore, is to create an
apparatus for the dehydrogenation of liquid hydrides of the type
mentioned at the beginning. These hydrides are especially dis-
tinguished by the fact that they are compact, lightweight and
inexpensive to produce.
As claimed, this objective is essentially solved by the fact
that the chemical reactor and the heat exchangers are all plate-
shaped, that the plate-shaped heat exchangers are stacked side by
side, that a storage container is placed on each front end of the
heat exchanger stack and the two storage containers enclose the
heat exchanger stack between them, that plates acting as tie rods
are placed on both sides of the stack (these plates being attach-
ed to opposite end sections of the storage containers and at a
distance from the heat exchanger stack) and that at least one
combustion chamber as well as baffle and connecting channels, via
- :
.
~ ?
-~ ' '
.
. .
,
. ;,. . .
3B~
-- 3
which the various heat exchangers are linked together, are placed
in the space between the side plates and the opposi-te sides of
the heat exchanger stack.
The plate-shaped design of the heat exchangers and their
stack-shaped arrangement creates an ex-tremely space-saving con-
figuration. As the reaction medium is under a pressure of 10 to
20 bar, the apparatus must be very stable. This high stability is
attained through the especially simple structural method of
placing the heat exchanger packet between the storage containers
located at the ends, which can be made of sufficiently strong
material, and through the side plates, which function as tie rods
and which are linked to the storage containers, absorbing the
forces acting on the storage containers in a simple way. There-
fore, it is possible to make the plate-shaped heat exchangers, in
which an operating pressure of approximately 20 bar prevails, of
thin material while reducing costs and material expenditures,
since the pressure forces are absorbed by the clamp-shaped stor-
age container/side plate arrangement surrounding the heat ex-
changer packet.
~ particularly space and material-saving arrangement also
results from the fact that the combustion chamber used to heat
the heat exchanger fluid by burning hydrogen as well as the
baffle or rather connecting channels linking the various heat
exchangers together are placed in the space between the side
plates and the opposite sides to them of the heat exchanger
stack. In addition, this also results in the various fluids
having to travel especially short distances, which also contri-
butes to the apparatus being highly efficlent.
In the ideal design of the invention, the storage containers
are partially cylindrical, the cylinder axis running parallel to
the plate-shaped heat exchangers, the diamater of the partial
~L3~
-- 4
cylinder being greater than the width of the heat exchanger stack
and the partial cylinder extending more than 180 in the radial
direction. Accordingly, the partially cylindrical storage con-
tainers extend beyond the heat exchanger stack on both sides, the
side plates of the apparatus being located almost tangentially to
the partially cylindrical walls of the storage containers and
welded to them at this point~ The partially cylindrical shape of
the storage containers gives them high mechanical stability with,
at the same time, comparatively thin wall strengths. In an appro-
priate subsequent development of the invention, it is planned to
arrange the heat exchangers in such a way -that -the chemical
reactor is located in the middle of the heat exchanger stack and
-that the less hot heat exchangers are connected to it in an
outward direction. If several heat exchangers are used, the mean
temperature, in particular, of the individual heat exchangers may
decrease from the interior towards the exterior. This keeps heat
losses low and also reduces insulation problems.
In accordance with an especially ideal feature of the inven-
tion, the apparatus is designed symmetrically in such a way that
identical heat exchanger stages are attached to both sides of the
reactor located in the middle. Consequently, all of the other
heat exchanger stages, with the exception of the reactor, are
provided twice in an identical fashion and -the process runs twice
in both directions in an identical fashion between the central
reactor and the two storage containers on the sides. More speci-
fically, a heat exchanger serving as a superheating stage can be
placed on each side of the reactor, then on both sides of these
heat exchangers serving as a vaporization stage, then on both
sides of these heat exchangers serving as a pre-heating stage and
on both sides of these heat exchangers serving as a cooling stage
or condenser. The fluids circulate in such a way that the hydride
passes through the pre-heating stages, the vaporization stages,
the superheating stages and the reactor one after the other, in
such a way that, after the dehydrogenation of the
.......
. . . ~.
'~
136~ 38~
-- 5
hydride, the dehydrogenation products (H2 and toluene and non-
reactive MCH) pass through the superheating stages, the pre-
heating stages and the cooling stages and in such a way that the
heat exchanger fluid used to heat the hydride in the reactor and
in the vaporization stages - where it is used with H2 combustion
engines, the engine exhaust air - passes through the vaporization
stages after passing through the reactor.
In accordance with an especially ideal feature of the inven-
tion, an extremely compact, very highly efficient apparatus
results if the plate-shaped heat exchangers are designed as a
hybrid heat exchanger of a type which is basically known, con-
sisting in each case of a number of stamped profiled sheets which
are welded together and which define between them alternately a
large number of parallel tube-shaped flow medium channels and a
number of slot-shaped, wave-like channels vertical to the former.
Such hybrid heat exchangers combine the resistance to heat and
pressure of a tube exchanger with the compact and material-saving
design of a plate exchanger, heating surfaces densities of up to
250 m2 exchange surface per cubic meter of structural volume
being realizable. The wave-shaped course of the transverse -flow
channels produces great turbulences and, thus, excellent heat
transmission conditions. For example, suitable hybrid heat ex-
changers are offered by IPG Bavaria, Industrieplanungsgesell-
schaft mbH fur thermische Verfahrenstechnik /Industrial Planning
Private Limited Company for Thermal Process Engineering/, Munich,
under the name IPEX-Hybrid.
Further advantageous features of the invention result from
the other sub-claims and from the description below in which an
ideal example of the invention is described in more detail using
the drawing. The drawing contains:
., . .. -
., ~ . .. ~, , - -~
-- 6
Fig. 1 a diagrammatic representation of the dehydrogenation
process of the claimed apparatus,
Fig. 2 a side view of the claimed apparatus in a half-diagram-
matic representation,
Fig. 3 a top view of the claimed apparatus in a half-diagram-
matic representation,
Fig. 4 a sectional view of the individual heat exchanger stages
of the apparatus in accordance with Fig. 2 viewed in the
direction of arrow IV, the individual heat exchanger
stages being shown side by side in a lateral view with
only half of the apparatus being illustrated, and
Fig. 5 a section through a hybrid heat exchanger of the claimed
apparatus.
Reference is first made to the basic diagram in Fig. 1.
It should be noted that, in contrast to the illustrations in
Figs. 2 and 3, a single heat exchanger stage is illustrated in
the basic diagram in Fig. 1, whereas in the case of the example
shown in Figs. 2 to 4 two identical heat exchanger stages are
provided. However in the interests of clarity the second set of
heat exchanger stages was not illustrated in Fig. 1.
In Fig. 1, reference number 2 designates a dehydrogenation
apparatus used to dehydrogenate the liquid hydride, specifically
methyl cyclohexane (MCH), stored in a vehicle tank 4. MCH, which
represents an organic carrier of hydrogen, is fed from the tank 2
of the dehydrogenation apparatus 2 under a pressure of approxi-
mately 20 bar into the dehydrogenation apparatus 2 where it is
.
:
.
.
.. : ..:
split catalytically and wi-th the application of heat into hydro-
gen and toluene. The hydrogen recovered through this process
is stored temporarily in a storage container 6 and used to power
the hydrogen engine 8 driving the vehicle, for example a truck.
The hot exhaust air of the hydrogen engine 8 is fed to the de-
hydrogenation apparatus 2 in order to heat the reactor. Since the
heat transferred from the engine exhaust gases to the dehydrogen-
ation apparatus 2 is not sufficient to meet the heat require-
ments of the dehydrogenation unit, the heat deficit in the de-
hydrogenation apparatus is covered by burning part of the hydro-
gen produced.
The cycles illustrated in Fig. 1 are discussed in more
detail below.
The dehydrogenation apparatus 2 is made up of a condensation
stage 10, a pre-heating stage 12, a vaporization stage 14, a
superheating stage 16 and a chemical reactor 18. The MCH in the
tank 4 is fed to the dehydrogenation apparatus 2 via the pump 20
under a pressure of approximately 20 bar, where it first passes
through the pre-heating stage 12 designed as heat exchangers in
which it is pre-heated to a temperature o~ approximately 235C.
Then the pre-heated MCH passes through the vaporization stage 14,
which is also designed as heat exchangers, in which the MCH,
which has been liquid up to this point, is heated further and
vaporized. The MCH vapor is then passed through the superheating
stage 16 designed as heat exchangers in which the vapor is super-
heated to approximately 390C, just under the reaction temper-
ature. The superheated vapor then enters the reactor 1~3 in which
it is dehydrogenated catalytically with the application of fur-
ther heat, hydrogen and vaporous toluene being produced as the
main dehydrogenation products.
., ,, . ~
~3~l~8~3
_ 8 _
The hydrogen-toluene mixture exhausted from the reactor 18
now has a temperature of approximately 420C and is once again
fed into the superheating stage 16 where it transfers part of its
heat to the MCH to be superheated. ~fter leaving the superheating
stage 16, the hydrogen-toluene mixture has a temperature of
approximately 250C and is then fed to the pre-heating stage 12
in which it pre-heats the liquid MCH coming from the tank 4.
Finally, the hydrogen-toluene mixture which has been cooled down
passes through the condensation stage 10 in which the toluene is
further cooled and condensed. Air is provided as the cooling
medium for the condensation stage 10 in the example described
here. This air is fed to the heat exchanger 10 via a fan 22.
Obviously, cooling water, for example, could also be used as an
alternative cooling medium.
The dehydrogenation products cooled to approximately 30C,
specifically hydrogen and toluene in the main, are finally stored
or stored temporarily in storage container 6, the toluene being
in liquid form, the hydrogen in vaporous form. In addition, if
desired, the toluene can be separated from the hydrogen in a
manner not described in more detail.
In order to heat the reactor 18, hot exhaust air from the
hydrogen engine is fed to it. Because, as already mentioned, the
temperature of the exhaust air from the hydrogen engine is not
sufficient to meet the heat requirement of the reactor 18, addi-
tional hydrogen is burned in suitable combustion chambers 24, 26
and 28 of the reactor 18 in order to raise the temperature of the
exhaust air from the hydrogen engine to approximately 650C. In
order to assure a uniform distribution of the heat over the
entire reactor, the latter is designed in three stages in total.
Each stage has a combustion chamber 24, 26 or 28 respectively in
which the exhaust air which has been cooled down to approximately
420C is heated again to 650C.
'
.
,
'. . : ' :
- ~36~
After passing through the reactor 18, the exhaust air from
the hydrogen engine ~lows through the vaporizer 14 in which it
is cooled down to approximately 330C while transferring heat to
the MCH. Then the exhaust air is exitted into the atmosphere.
Reference is made below to Figs. 2 to 5.
As can be seen from Figs. 2 and 3, the dehydrogenation
apparatus 2 consists of one unified block. It is made up of the
centrally located reactor 18 and, attached to each side of it,
a superheating stage 16a, 16b, a vaporization stage 14a, 14b, a
pre-heating stage 12a, 12b, a condensation stage 1Oa, 1Ob and a
storage container 6a, 6b. Each of the stages 10a, 10b, 12a, 12b,
14a, 14b, 16a and 16b as well as the reactor 18 are designed as
p]ate-shaped heat exchangers and have in the direction of arrow
IV in Fig. 2 essentially the same dimensions. The individual
plate-shaped heat exchangers are stacked side by side so that
they form a unified block, as can be seen clearly from Figs. 2
and 3. A storage container 6a, 6b is placed at both ends of the
heat exchanger block. Each storage container is partially cylind-
rical and its axis extends parallel to the longitudinal side of
the individual heat exchanger plates. The diameter of the part-
ially cylindrical storage containers 6a, 6b is, as can be clearly
seen in Fig. 3, greater than the depth of the heat exchanger
packet so that the storage containers 6a, 6b project laterally
beyond the heat exchanger packet. Side plates 30, 32 are provided
which run parallel to the lateral surfaces of the heat exchanger
packet and which are welded firmly to the storage containers on
both edges facing the storage containers 6a, 6b in such a way
that the side plates 30, 32 run almost tangentially to the part-
ially cylindrical storage containers 6a, 6b. As can be seen in
Fig. 2, the head pieces allocated to the individual heat exchang-
ers close the heat exchangers at the top. A lower closing plate
34 is welded to the storage containers 6a, 6b by its front end
': ' , ~ :
.
_ 10 _
and to the side plates 30, 32 along its longitudinal side, clos-
ing the heat exchanger packet at the bottom.
AS is explained below in more detail, the individual heat
exchangers 1Oa to 16b and the reactor 18 consist of individual,
comparatively -thin plates which are not capable of containing the
high operating pressure prevailing in the heat exchanger packet
without additional reinforcement. In the case of the claimed
arrangement, the pressure is absorbed by the two storage contain-
ers 6a, 6b at the ends. These storage containers are made of
sufficiently strong material and, in any case, exhibit a high
inherent stability based on their cylindrical configuration. The
side plates 30, 32 linking the two storage containers 6a, 6b
serve as tie rods between the two storage containers 6a, 6b, so
that the heat exchanger packet is bracketed by the two side
plates and, as a result, the pressures occurring are absorbed by
the dehydrogenation apparatus in the simplest way.
The guide and baffle channels for the fluids flowing through
the individual heat exchangers and the combustions chambers 24 to
28 are located in the spaces 36 and 38 between the side plates
30, 32 and the opposite side walls of the heat exchanger packet.
The individual heat exchangers 1Oa to 16b and 18 each con-
sist of hybrid heat exchangers as illustrated in cross-section in
Fig. 5. Each heat exchanger conists of several plate elements 40
welded together which exhibit stampings of such a kind that a
welded plate packet has tube-like flow medium channels in the one
direction - in the case of the sectional view in Fig. 5, vertical
to the drawing plane - and slot-shaped flow medium channels
extending wave-like from one side to the other of the plate
packet in a transverse direction - in the case of the illustra-
tion in Fig. 5, horizontally. The tube-like flow medium channels
42 are called tubes below, the slot-shaped, wave-like flow medium
channels slots.
:; :
. ~
.
: ~ '
_ 11. --
Reference will be made below to the illustration in Fig. 4.
Only half of the arrangement illustrated in Figs. 2 and 3 is
illustrated in Fig. 4. However the other half is completely
identical so that explanation of the one half is sufficient to
understand the invention.
The MCH fed from the tank 4 (compare Fig. 1) to the dehydro-
genation apparatus 2 enters the pre-heating stage 12 from below
and passes through the vertical running slots of the heat ex-
changer. The heat exchanger of the pre-heating stage 12 consists
of six compartments 12.1, 12.2, 12.3, 12.4, 12.5 and 12.6 stacked
on top of one another whose slots are linked together. The tubes
are arranged horizontally and the dehydrogenation products coming
from the superheating stage 16 flow through each compartment one
after the other, starting with the upper compartment 12.6 and
ending with the lower compartment 12.1. As illustrated by the
arrows, the dehydrogenation products mainly flow serpentine-like
in the pre-heating stage 12 from the top to the bottom, so that
the two components flow through the pre-heating stage 12 on a
counter-current basis. Suitable guide plates are placed* in the
lateral spaces 36, 38 in order to bring about the serpentine-like
flow through the individual compartments 12.1 to 12.6.
The pre-heated MCH leaves the pre-heating stage 12 at its
upper side and is then fed to the upper side of the vaporization
stage 14. The slots of the heat exchanger also run vertically and
the tubes transversely to them, horizontally, in this vaporiza-
tion stage. The MCH first flows through the vaporization stage 14
from the top to the bottom and then on the opposite side of the
. .
* and stampings are provided on the appropriate places on the
plate elements.
.:
,
fi~
_ 12 _
heat exchanger from the bottom to the top. The starnpings in the
middle of the plate elements ensure that the left section of
the heat exchanger is separa-ted from the righ. in Fig. 4.
The heated exhaust air coming from the reactor 18 flows from
above via the space 38 into the vaporization stage 14 and reaches,
after flowing through the tubes of the heat exchanger, the space
36, from which it exits into the atmosphere.
The now vaporous MCH leaving the vapori~ation stage 14 is
fed to the superheating stage 16 from above and leaves it from
the lower end. The design of the superheating stage 16 corres-
ponds to that of the pre-heating stage 12, in particular, the
superheating stage 16 is also composed of six compartments 16.1
to 16.6 which are stacked on top of one another and which the
dehydrogenation products leaving the reactor 18 flow through from
the top to the bottom, meander-like. The two components flow
through the superheating stage 16 on a counter-current base as
well.
The vaporous MCH exitting at the bottom of the superheating
stage 16 is then fed from the top to the reactor 18 in which the
slots of the heat exchanger once again run vertically, so that
the MCH passes through the reactor wave-like from the top to the
bottom. The reactor 18 is constructed of three stages 18.1, 18.2
and 18.3 stack~d on top of one another, the exhaust air from the
hydrogen engine passing through each stage 18.1 to 18.3 one after
the other. By means of baffle plates in the spaces 36, 38, the
exhaust air is directed through successive stages in alternately
opposing directions. The baffle plates 46, 43 in the spaces 36,
38 define chambers 24, 26, 28 into which hydrogen feed pipes 50,
52, 54 open, in each case into the lower section. Additional
hydrogen is burned in these combustion chambers 24, 26 and 28 in
order, as described above, to heat the exhaust air from the
hydrogen engine to the required reachtion temperature.
. .
. .
,
.. . ., . ~ :
.. . . :
, : .
_ 13 -
As is clear from Fig. 4, on the whole the reactor 18 is also
operated on counter-current basis.
The dehydrogenation products leaving the lower end of the
pre-heating stage 12, specifically hydrogen and toluene in the
main, are fed to the upper side of the condensation stage 10
whose heat exchanger has vertical continuous slots and horizontal
tubes. In order to cool down the hydrogen-toluene mixture, fresh
air is fed to the tubes of the heat exchanger 10 ~rom below via
space 38 by means of a fan. This fresh air passes through the
heat exchanger from right to left, is collected in space 36 and
exitted upwards into the atmosphere.
Finally, the cooled hydrogen-toluene mixture is exitted to
the bottom of the condensation stage 10 and then fed to the
storage container, in which the hydrogen is stored temporarily
for further use.
,
.
,
' ' , : ' '
.:
8~
1~
REFERENCE N~MBER LIST
.
2 Dehydrogenation apparatus
4 Tank
6 Storage container
8 Hydrogen engine
Condensation stage
12 P~e-heating stage
14 Vaporization stage
16 Superheating stage
18 Reactor
Pump
22 Fan
24 Combustion chamber
26 Combustion chamber
28 Combustion chamber
Side plate
32 Side plate
34 Closing plate
36 Space
38 Space
Plate element
42 Tubes
44 Slots
46 Baffle plate
48 Baffle plate
,. ,",. i ,, . ~ - . , ` ,
' ' . :' ; ` ` ' ' ~
.
`' : ` '. ` ~ ' . " :
