TECHNICAL FIELD OF THE INVENTION
The present invention relates to a methanation reactor for reacting hydrogen
with a carbon-based compound and producing methane. It applies in particular to
industrial methanation and the co-generation of thermal energy and meth<:)ne.
STATE OF THE ART
Methanation is an industrial process that catalytically converts hydrogen and
carbon monoxide or carbon dioxide into methane.
The formula for the methanation reaction varies according to the nature of the
10 carbon~Based-compound. Depending on the case, this formula 1s:
CO + 3 H2 -+ CH4 + H20
In order to optimize the yields of this reaction, a catalyst bed is placed in a
reactor in which the reaction occurs. This bed can be fixed or fluidized. As the
15 methanation reaction is highly exothermic, it gives rise to significant requirements to
remove heat, and therefore to cool the reactor. A fluidized catalyst bed allows the
temperature of the reactive area to be homogenized. Lastly, the kinetics of this
reaction at the temperatures normally utilized are high, requiring as a consequence a
small amount of catalyst.
20 In current fixed-bed systems, known as "Throughwall Cooled Reactors", a heat
transfer is produced by reactor walls cooled by a coolant fluid. However, significant
surface areas are required to produce the heat transfer and the costs of
manufacturing the reactor are high.
In current fluidized-bed systems, one or more heat exchangers are immersed
25 in the fluidized bed inside the reactor. Then, for example, water, water vapor or a
thermal oil are circulated in these exchangers. The thermal exchange coefficients
between the wall of the exchanger and the fluidized bed are very high, of the order of
2
thermal exchange coefficients between a liquid and a wall. However, the use of
thermal oils is only possible up to reaction temperatures of the order of 380oc to
400°C. In addition, in these systems the size of the reactor depends upon the size
occupied by each exchanger to be immersed in the fluidized bed. These systems
5 lead to manufacturing costs and a non-optimized use of space for the reactor. In
addition, the efficiency of the heat exchanges between the bed and the coolant fluid
are highly dependent upon the fluidization conditions.
In current fixed-bed or fluidized-bed systems, the injection of vapor mixed with
hydrogen and the carbon-based compound makes it possible to limit the formation of
10 a carbon deposit in the form of coke on the catalyst, one of the consequences of
which is the premature deactivation of the catalyst. Lastly, as methanation catalysts
are preferably made at least in part of nickel, the methanation reaction risks leading
to the formation of carbonyl, a highly toxic compound, on contact with walls brought
to a temperature of less than 260°C, which makes the cooling system more complex.
15 Documents W02012/035881, US4312741 and DE2506199 are known. The
teachings of these documents do not make it possible to achieve cooling of a
methanation reactor while limiting the formation of coke or carbonyl in the reactor.
In particular, document W02012/035881 describes a reactor with inlets and
outlets that can implement a methanation reaction. However, this reactor does not
20 comprise an inlet for injecting water into the reactor to cool down the chemical
reaction.
Document US4312741 describes a methanation reactor. However, this reactor
does not comprise a liquid-phase water inlet into the reactor.
Document DE2506199 describes a methanation reactor with a water inlet
25 above a catalyst bed contained in the reactor. This system has the drawback of not
limiting the formation of coke or carbonyl in the reactor during the injection of water.
SUBJECT OF THE INVENTION
The present invention aims to remedy all or part of these drawbacks.
30 To this end the present invention envisages, according to a first aspect, a
methanation reactor for reacting dihydrogen with at least one carbon-based
compound and producing methane, comprising:
3
a hollow body configured to receive a fluidized bed of catalytic particles and
comprising an inlet for each carbon-based compound and for dihydrogen and
an outlet for methane and water,
and which also comprises an inlet for the injection of liquid-phase cooling water into
5 the fluidized bed.
Although introducing a product of the reaction, in addition to reagents, into the
fluidized bed of the reactor is, in principle, the opposite of what the person skilled in
the art does to obtain a good yield from the reaction, the inventors have determined
that this introduction is favorable in terms of controlling the temperature inside the
10 reactor, the reactor's dimensions, the reactor's complexity, and the manufacturing
and maintenance costs of the reactor, insofar as the reagent is introduced in liquid
phase. This introduction also makes it possible to reduce, even eliminate, the
production of carbonyl. Lastly, this introduction allows the formation of coke on the
surface of the catalyst surface to be limited; the injected water is vaporized on
15 contact with the hot bed.
Thanks to the charaCteristics of the reacfor that is the subject of the present
invention, the reactor's size can be defined as a function of the quantity of catalytic
bed to be contained to convert the hydrogen and the carbon-based compound. In
addition, the water introduced is used by the methanation reaction through the
20 "Water Gas Shift" reaction, in which carbon monoxide and water produce carbon
dioxide and dihydrogen. Lastly, these provisions make it possible to obtain, on output
from the reactor, a water molar composition of the water vapor and methane mixture
that is higher than 50%.
In certain embodiments, the input of each carbon-based compound and the
25 dihydrogen is realized in the bed.
These embodiments make it possible to increase the yields of the reaction
between each carbon-based compound and the dihydrogen in the catalyst. The input
of water in the bed means it can be cooled without risk of carbonyls forming on
contact with the walls.
30 In certain embodiments, the water inlet is closer to the base of the hollow body
than the inlets of each carbon-based compound and of the dihydrogen.
These embodiments make it possible to prevent the deposit of coke on the
catalyst.
4
... In certain embodiments, each carbon-based compound is a gas, the reactor
comprising at least one water-injection nozzle and at least one injection nozzle for a
gas comprising the carbon-based gas and dihydrogen, at least one water-injection
nozzle being positioned below at least one gas-injection nozzle.
5 These embodiments allow an optimized injection of gas and water into the
hollow body of the reactor.
In certain embodiments, the reactor that is the subject of the present invention
comprises a means of condensing water vapor present downstream of the outlet for
methane and water.
10 These embodiments allow the water to be separated, by condensation, from
the methane downstream of the methane outlet In addition, these embodiments
allow the condensed water to be recovered.
In certain embodiments, the reactor that is the subject of the present invention
comprises a circuit for transporting condensed water to the inlet for injecting cooling
15 water.
These. embodiments make it possible to recycle the water created by the
methanation reaction for cooling this reaction.
In certain embodiments, the reactor that is the subject of the present invention
comprises, downstream of the outlet for methane and water, a gas-solid separation
20 means.
These embodiments make it possible to ensure that the methane and water
output from the device are in gas phase and to prevent the presence of solids on
output from the device such as, for example, particles from the catalyst bed.
In certain embodiments, the reactor that is the subject of the present invention
25 comprises a temperature sensor in the reactor and a means of regulating the flow
rate of the water introduced into the hollow body as a function of the temperature
measured by the temperature sensor.
These embodiments allow the reaction temperature to be optimized so as to
obtain an optimum yield of methane according to the carbon-based compound
30 introduced into the reactor.
In certain embodiments, the reactor that is the subject of the present invention
comprises a heat exchanger, downstream of the outlet for methane and water,
5
. configured to cool the methane and water and to co-generate thermal energy during
the heat exchange realized.
These embodiments make it possible to co-generate thermal energy and
methane, from the water vapor and methane mixture on output from the hollow body.
5 In certain embodiments, the amount of water introduced into the hollow body
by the water injection inlet is more than 75% of the amount of water output from the
hollow body. The water introduced therefore results in an especially high level of
cooling.
According to a second aspect. the present invention envisages a methanation
10 method for reacting dihydrogen with at least one carbon-based compound and
producing methane, comprising:
a step of inputting each carbon-based compound and dihydrogen into a hollow
body configured to receive a fluidized bed of catalytic particles,
a step of methanation reaction between the hydrogen and each carbon-based
15 compound, and
a step of outputting -methane and water;
and which also comprises a step of injecting liquid-phase cooling water into the
fluidized bed during the methanation reaction step.
As the particular features, advantages and aims of this method are similar to
20 those of the methanation reactor that is the subject of the present invention, they are
not repeated here.
BRIEF DESCRIPTION OF THE FIGURES
Other particular advantages, aims and features of the invention will become
25 apparent from "the non-limiting description that follows of at least one particular
embodiment of the methanation reactor and the methanation method that are the
subjects of the present invention, with reference to drawings included in an appendix,
wherein:
figure 1 represents, schematically, a particular embodiment of the methanation
30 reactor that is the subject of this invention; and
- figure 2 represents, in the form of a logical diagram, steps in a particular
embodiment of the methanation method that is the subject of the present
invention.
6
DESCRIPTION OF EXAMPLES OF REALIZATION OF THE INVENTION
The present description is given a~> a non-limiting example.
It is now noted that figures 1 is not to scale.
Figure 1 shows a first particular embodiment of the reactor 10 that is the
5 subject of the present invention. This reactor 10 comprises:
a hollow body 105 configured to receive a fluidized bed of catalytic particles
106 and which comprises at least one nozzle 110 for injecting a carbon-based
compound and dihydrogen, and at least one nozzle 120 for injecting water;
an outlet 115 for methane and water;
10 a means of gas-solid separation 135 for the methane produced by the
methanation reaction;
a heat exchanger 145 configured to cool the methane and water and to cogenerate
thermal energy during the heat exchange realized;
a means of condensing 125 water vapor present downstream of the methane·
15 outlet 115;
a circuit 130-foflransporting condensed water to a nozzle for injecting cooling
water 120; and
a means of regulating 140 the flow rate of the water introduced into the hollow
body 105 as a function of the temperature measured in the reactor 10 by a
20 temperature sensor 107.
The hollow body 105 is, for example, a metallic cylinder of revolution closed at
its extremities. This hollow body 105 is partially filled with a fluidized catalyst bed.
Through the action of gravity, this catalyst is located near the base of the hollow body
105. This hollow body 105 comprises at least one carbon-based compound and
25 dihydrogen injection nozzle 110, allowing the carbon-based compound and
dihydrogen to be introduced into the fluidized bed. Preferably, the carbon-based
compound is carbon monoxide or carbon dioxide in gaseous form.
In addition, the hollow body 105 comprises at least one nozzle 120 for
injecting cooling water. The outlet of each nozzle 120 for injecting cooling water is
30 preferably closer to the base of the hollow body 105 than the outlet of each nozzle
110 for injecting the carbon-based compound. In this way, the injected water is very
quickly brought to the vapor state on contact with the fluidized bed, absorbing phasechange
latent heat. As most of the heat exchange between the injected water and
7
the fluidized bed occurs in the vicinity of the cooling water injection nozzle 120, the
temperature of the fluidized bed at the location of the carbon-based compound
injection nozzle 110 is higher than 260°C, which reduces or even eliminates the
formation of carbonyl.
5 Preferably, the amount of water introduced by the water injection nozzles 120
is more than 75% of the amount of water output from the hollow body, more
preferably more than 80% and, even more preferably, more than 85%. The injection
of water, by the injection nozzles 120, is preferably realized directly into the fluidized
bed contained in the hollow body 105.
10 This hollow body 105 comprises, lastly, a methane and water vapor outlet 115
that emerges onto a duct 116. This duct takes the methane and water vapor to a
means of gas-solid separation 135 for the methane output. This gas-solid separation
means 135 is, for example, a filter configured to hold the fine catalyst particles that
may be transported by the methane and/or the water vapor.
15 This reactor 10 also comprises, downstream of the gas-solid separation
means 135;-alleat exchanger 145 configured to cool the methaneand water-and to
co-generate thermal energy during the heat exchange realized. This exchanger 145
is, for example, a U-shaped tube heat exchanger. In some variants, this exchanger
145 is an exchanger from amongst the following:
20 horizontal tube bundle heat exchanger;
vertical tube bundle heat exchanger;
spiral heat exchanger;
plate heat exchanger;
block heat exchanger; or
25 finned heat exchanger.
rhis reactor 10 also comprises, downstream of the heat exchanger 145, a
means of condensing 125 water vapor. This condensation means 125 is, for
example, a condenser with separated fluids. In some variants, this condensation
means 125 is a condenser with direct contact between a coolant fluid and the vapor
30 to be condensed. In other variants, this condensation means 125 is a shell-and-tube
or tube bundle heat exchanger. In these variants, the heat exchanger 145 and the
condensation means 125 are combined into a single device. The methane, not
condensed, exits via a duct 117.
8
In some variants, downstream of the condensation means 125, the reactor 10
comprises the circuit 130 for transporting condensed water, one part of which is
evacuated by an output duct 118 and one part of which is transported to the nozzles
120 for injecting cooling water by utilizing a pump 132. The proportion of water
5 recycled in this way is of the same order of magnitude as the condensate flow-rate,
i.e. of the order of 85% to 95% depending on the temperature of the condensation
means.
The reactor 10 also comprises a means of regulating 140 the flow rate of the
water introduced into the hollow body 105 as a function of the temperature measured
10 in the bed in the reactor 10 by a temperature sensor 107. The regulation means 140
is, for example, a valve controlled pneumatically or electronically by an electronic
circuit (not shown). This electronic circuit receives information representative of the
temperature inside the hollow body 105 and actuates the valve as a function of the
information received so that the flow-rate of water introduced into the hollow body is
15 an increasing function of the temperature measured. In this way a control loop is
realized -for the interior temperature in the fluidized catalyst bed of the hollow body
105.
Figure 2 shows logical diagram of steps in a particular embodiment of the
methanation method 20 that is the subject of the present invention. The method 20
20 comprises:
a step 205 of injecting liquid-phase cooling water into a fluidized bed contained
in a hollow body during a methanation reaction step 215;
a step 210 of inputting the carbon-based compound and hydrogen into the
hollow body configured to receive a fluidized bed of catalytic particles;
25 a step 215 of methanation reaction between the hydrogen and the carbonbased
compound to produce methane and water;
- a step 225 of measuring the temperature inside the hollow body; and
- a step 220 of outputting methane and water.
The step 205 of injecting cooling water into the hollow body is realized, for
30 example, by utilizing cooling water injection nozzles that inject the water at the
location of a fluidized catalyst bed contained in the hollow body.
The step 210 of inputting the carbon-based compound and hydrogen into the
hollow body is realized, for example, by utilizing cooling water injection nozzles for
9
injecting carbon monoxide. or dioxide and dihydrogen. These injection nozzles inject
the gas above at least one, and preferable all, of the cooling water injection nozzles.
The step 220 of outputting methane and water is realized, for example, by
utilizing a duct, one inlet of which is located on an upper portion of the hollow body.
5 The measurement of the temperature inside the hollow body carried out during
the step 225 is used to slave the flow-rate of the water introduced into the hollow
body during the step 205, this flow-rate being an increasing function of the
temperature inside the hollow body.
The various steps shown in figure 2 are performed continuously and
10 simultaneously during the nominal operation of the reactor. Preferably, the water
introduced into the hollow body during the step 205 is the water from the reaction
cooled by a condenser and, possibly, a heat exchanger, or a device combining the
functions of a condenser and a heat exchanger.
As can be seen by reading the description above, the present invention
15 enables the size of a methanation reactor to be reduced. In effect the injection of
Water directly into the reaction medium means thatone does not have to use a heat
exchanger wherein the exchange surfaces to be used are large. In addition, the
injected water is used within the reactor through the gas to water reaction formula so
as to ensure the presence of dihydrogen in the methanation reaction. In addition, the
20 presence of a water condensation means downstream of the methane and water
outlet allows the water produced naturally by the methanation reaction to be recycled
for subsequently cooling the reaction. Lastly, the temperature inside the reactor is
slaved by introducing water according to an increasing function of the temperature
measured in the reactor, and the production of carbonyl can be minimized.

CLAIMS
1. Methanation reactor (10) for reacting dihydrogen with at least one carbon-based
compound and producing methane, comprising:
a hollow body (1 05) configured to receive a fluidized bed of catalytic particles
(1 06) and comprising an inlet (11 0) for each carbon-based compound and for
s dihydrogen and
an outlet (115) for methane and water,
the reactor further comprising an inlet (120) for the injection of liquid-phase cooling
water into the fluidized bed.
10 2. Methanation reactor (1 0) according to claim 1, wherein the inlet (11 0) of each
carbon-based compound and the dihydrogen is positioned in the bed (106).
15
3. Methanation reactor (10) according to claim 2, wherein the water inlet (120) is
closer to the base of the hollow body (1 05) than the inlets of each carbon-based
compound and of the dihydrogen (11 0).
4. Methanation reactor (10) according to one of claims 2 or 3, wherein each carbonbased
compound is a gas, the reactor comprising at least one water-injection nozzle
(120) and at least one injection nozzle for a gas comprising the carbon-based gas
20 and dihydrogen (11 0), at least one water-injection nozzle being positioned below at
least one gas-injection nozzle.
5. Methanation reactor (10) according to one of claims 1 to 4, further comprising a
means (125) of condensing water vapor present downstream of the outlet (115) for
25 methane and water.
6. Methanation reactor (1 0) according to claim 5, further comprising a circuit (130) for
transporting condensed water to the inlet (120) for injecting cooling water.
11
7. Methanation reactor (1 0) according to one of claims 1 to 6, further comprising,
downstream of the outlet for methane and water (115), a gas-solid separation means
(135).
5 8. Methanation reactor (10) according to one of claims 1 to 7, further comprising a
temperature sensor (1 07) in the reactor and a means (140) of regulating the flow rate
of the water introduced into the hollow body as a function of the temperature
measured by the temperature sensor.
10 9. Methanation reactor (1 0) according to one of claims 1 to 8, further comprising a
heat exchanger (145), downstream of the outlet for methane and water (115),
configured to cool the methane and water and to co-generate thermal energy during
the heat exchange.
15 10. Methanation reactor (1 0) according to one of claims 1 to 9, wherein the amount of
water introduced into the hollow body (105) by the water injection inlet (120) is more
than 75% of the amount of water output from the hollow body.
11. Methanation method (20) for reacting dihydrogen with at least one carbon-based
20 compound and producing methane, comprising:
a step (210) of inputting each carbon,based compound and d}hydrogen into a
hollow body configured to receive a fluidized bed of catalytic particles,
a step (215) of methanation reaction between the hydrogen and each carbonbased
compound, and
25 a step (220) of outputting methane and water;
the method further comprising a gtep (205) of injecting liquid-phase cooling water into
the fluidized bed during the methanation reaction step.