Note: Descriptions are shown in the official language in which they were submitted.
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Method for carryine out chemical reactions
The present invention relates to a method for effecting a chemical reaction
between components in two fluids. It is particularly concerned with a method
in
which the two fluids are of different phases.
Conventional. systems for effecting chemical reactions employ columns
which may be packed columns, plate columns or bubble-cap columns, or columns
with some other form of contact medium. In these systems, the gas and liquid
streams flow countercurrently.
l0 These prior art systems suffer the disadvantage that in order to achieve a
significant degree of gas/liquid contact, the columns have to be large and
their
operation is hampered by excessive foaming. In addition, any subsequent
stripping
section which might be required to remove the gas from solution must also be
large,
to handle the large volume of solvent or reagent used. Since the operation may
well
be carned out under high pressure and since the fluids involved may be highly
corrosive, the capital costs of the large columns and subsequent stripping
section are
high. Furthermore, operating costs and maintenance costs are high. Finally,
these
systems tend to be inefficient.
It is an object of the present invention to provide a system for effecting a
2 o chemical reaction between components in two fluids of different phases,
which does
not suffer from the disadvantages of the prior art.
More generally, it is an object of the invention to provide a method of
effecting a chemical reaction transfer between components in fluids of
different
phases with a high degree of efficiency and more economically than in existing
2 5 methods.
According to one aspect of the invention, there is provided a method of for
effecting a chemical reaction between at least one component in a first fluid
and at
least one component in a second fluid of a different phase, the method
comprising:
subjecting the two fluids to turbulent mixing, and allowing the selected
components
3 0 to react.
In this application, fluids in different phases are any two fluids which are
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immiscible or are only partly miscible. Examples of such systems include
gas/Iiquid,
oil/water, fluidised solid/gas etc.
The invention also extends to the apparatus for carrying out this method.
The turbulent mixing is very intense and results in extremely efficient
contact
between the two fluids. The mixing regime is preferably turbulent shear layer
mixing. The efficient mixing means that reaction can take place very rapidly
and in a
relatively small reactor volume compared to that required in conventional
columns.
This in tum means that any liquid duty in the equipment is dramatically
reduced
resulting in a consequential reduction in the size of any downstream
regeneration
section. At the same time, the mixing system used is simple and inexpensive
compared to prior art systems, leading to reduced costs. Finally, an
efficiency of
approaching 100% can be achieved for certain applications.
In addition, conventional methods often involve the evolution of heat which
must then be removed from the system. While the method of the invention is
capable
of operation with a relatively low pressure drop across the mixing means, when
greater pressure drop is employed, a cooling effect is achieved and this may
render
the need for additional cooling unnecessary.
The high mass and heat transfer coegicients of the method of the present
invention make the system suitable for use in gas absorption processes. In
particular,
2 0 the present invention has the advantage that any adiabatic expansion of a
gas passing
through a contactor reduces the contact temperature between a gas and a
liquid,
thereby increasing the quantity of gas which can be taken up by the liquid.
Additionally, in systems where the heat of condensation and heat of solution
of a gas
in a liquid is significant, and normally causes the liquid temperature to rise
and thus
2 5 the absorption capacity of the liquid to fall, the adiabatic cooling can
offset this
undesirable effect.
The present method is also suitable for chemisorption reactions. In processes
of adsorption with chemical reaction, the reactions are usually exothermic,
and the
heat of reaction causes the liquid temperature to rise. This reduces the
adsorption
3 0 capacity of the liquid phase. Using the present method, the adiabatic
cooling of the
gas can offset the heating effect of the reaction, thereby maintaining the
adsorption
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capacity of the liquid. Careful design of the apparatus may eliminate the need
for
external cooling which is required in many chemisorption processes.
The short contact time needed for reaction means that short contact lines can
be achieved with high interphase transport fluxes. This property makes the
apparatus
of this invention suitable for treating heat sensitive or chemically unstable
fluids or
fluid mixtures.
Optionally a plurality of components are involved in the reaction. In one
possible regime, the f rst fluid is a gas mixture and the second fluid is in
the liquid
phase. In another regime, the first fluid is a liquid mixture or a liquid
solution and
the second fluid in the liquid phase. In a third regime, the first fluid is a
liquid
mixture or a liquid solution and the second fluid is in the gas phase.
Preferably, the method is carried out as a continuous process with the two
fluids flowing co-currently. The co-current flow eliminates any problems that
might
be associated with foaming and flooding, since separation can easily be
effected
downstream of the mixer.
The turbulent shear layer mixing may be achieved by any convenient means.
Preferably the mixing is conducted in a turbulent contactor including a first
fluid
inlet, a second fluid inlet, an outlet leading to a venturi passage, and a
tube extending
from the outlet back upstream, the tube being perforated and/or being spaced
from
2 o the periphery of the outlet. Preferably, the tube is located in a vessel,
the vessel
including the first fluid inlet, the second fluid inlet and the outlet. In one
arrangement, the first fluid is supplied to the tube, optionally directly, and
the second
fluid is supplied to the vessel, and so the first fluid draws the second fluid
into the
venturi and the two fluids are mixed. In another arrangement, the first fluid
is
2 5 supplied to the vessel and the second fluid is supplied to the tube,
optionally directly,
whereby the first fluid is drawn into the venturi by the second fluid and the
two fluids
are mixed. In a further possible arrangement, one of the fluids is in the gas
phase and
one of the fluids is in the liquid phase, and both fluids are supplied to the
vessel, the
liquid being supplied to a level above the level of the outlet, whereby the
gas is
3 0 forced out through the outlet via the tube, thereby drawing the liquid
into the venturi
so that the two phases are mixed.
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One suitable contactor is a mixer supplied by Framo Engineering A/S and is
described in EP-B-379319. Alternatively, the contactor may be an ejector. such
as a
jet pump.
It will be appreciated that the invention is broadly applicable to any
chemical
reactions between components in two different fluid phases and is particularly
applicable to any application where the reaction kinetics are rapid.
The following are possible areas of application of this method although this
list is not to be regarded as exhaustive. (i) The refining of fuel gas and
feedstock gas
purification using various solvents for the contaminating gases (including
H,S, HCI,
l0 RHS, COS, S02). (ii) The stabilisation of petroleum oils and/or distillates
by the
removal of dissolved gas from the oils andlor distillates, and controlling the
vapour
pressure by depressurising the liquid across the contactor and recycling the
gas phase,
or by using an inert carrier gas (e.g. N~, steam). (iii) The removal of
dissolved
hydrocarbon gases or acid gases and odorous components from refining waste
water.
(iv) Oxygenation/aeration of refinery waste water in aerobic biochemical
treatment
processes. (v) Absorption recovery of components from "waste" gases, both
reaction
and combustion gases. (vi) Gas-liquid reactions where the products) is/are a
liquid,
where the gas absorbs into the liquid phase and then undergoes a chemical
reaction.
(vii) Gas liquid reactions where the gas phase is recycled and part is vented
to control
2 o the concentration of inert components which may reduce the reaction
conversion, or
of components which may poison the catalyst(s).
Thus, the invention therefore also extends to a method for effecting a
chemical reaction between two or more components in different fluid phases
which
comprises: forming a homogeneous mixture of the fluid phases, the homogeneous
2 5 mixture being formed by subjecting the fluid phases to turbulent mixing
conditions,
preferably turbulent shear layer mixing conditions, separating a first fluid
phase and a
second fluid phase; and optionally treating the relevant phases) to remove the
reaction product(s).
The fluid mixture may be a mixture of gases or may be in the liquid phase.
3 o The components to be reacted may be a finely divided solid disperse phase,
a
dissolved solid, a liquid or a gas.
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The invention also extends to the apparatus for canrying out this method.
According to a more specific aspect of the invention, there is provided a
method for effecting a chemical reaction between two or more components in
different fluid phases which comprises: supplying the fluids to a mixer or
turbulent
5 contactor; subjecting the fluids to turbulent shear layer mixing in the
contactor to
form a homogeneous mixture; allowing the selected components to react;
optionally
cooling the homogeneous mixture; separating the cooled homogeneous mixture
into
separate phases; treating the separated phases to remove the reaction
product{s); and,
if appropriate, recycling either of the fluid phases containing unreacted
reactants.
The separation of the homogeneous mixture into separate phases may take
place in any suitable separator. For example, a gas-Liquid mixture may be
separated
in a hydrocyclone. Preferably any cooling and/or heating of either the
reagents or
products is achieved, at least in part, by mutual heat exchange.
Preferably, in instances where the first fluid is a gas mixture at a low
pressure,
and the second fluid is a liquid, the liquid is pumped to the contactor and
thereby
draws the gas mixture with it through the contactor. Preferably, when the
first fluid
is a gas mixture at a high pressure, and the second fluid is a liquid, the gas
is
conveyed to the contactor at a high pressure and thereby draws the liquid with
it
through the contactor.
2 0 The invention also extends to apparatus for carrying out such a method.
Preferably, the contactor is a turbulent contactor as described above, or
alternatively
an ejector or a jet pump.
The invention rnay be considered to extend to the use of a turbulent contactor
to effect a chemical reaction between at Least one component in a first fluid
phase and
2 5 at least one component in a second fluid of a different phase.
The preferred features of any'of the various aspects of the invention
described
above may be equally applicable to the other aspects of the invention.
The reaction systems described are single operations, however it will be
appreciated that mufti-reactions may be performed. These may be carried out
3 0 simultaneously or sequentially and may also be carried out in series or in
parallel.
The present invention is applicable in wide variety of applications. For
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example it can be used in petroleum and gas production in a number of ways -
sweetening, removal of CO,, removal of NOX gases, stabilisation of liquid
feedstocks
and products, waste water treatment, in deodorising, removal of acid gas,
removal of
NH3 etc. It can also be used in wastewater treatment, in particular
denitrification of
wastewater and run off water from landfills. In petrochemical and fine
chemicals
manufacture, the contactor may be used on vent lines to recover reactants from
vent
gas or as a tail gas scrubber to recover products or remove toxic/noxious
compounds.
In gas phase chemical reactions, the contactor may be used to selectively
recover
reaction products from reactor discharge gases. In the food and consumer
products
1 o industries, the contactor may be used to prepare emulsions, the device
affording a
method of control of emulsion form by pressure control in phase continuity
drop size
distribution. As stated previously, this list is not to be regarded as
exhaustive, but
merely illustrative of the scope of use of the method of this invention.
The invention may be put into practice in various ways and two specific
embodiments will be described by way of example to illustrate the invention
with
reference to the accompanying drawings, in which:
Figure 1 is a flow diagram of the process for use when the first fluid is a
gas
under low pressure;
Figure 2 is a flow diagram of the process for use when the first fluid is a
gas
2 0 under high pressure;
Figure 3a is a view of a turbulent contactor suitable for use in the method of
this invention;
Figure 3b is a view of a contactor similar to that in Figure 3a, but with the
tube connected to a fluid inlet;
2 5 Figure 4a is a variant of the contactor shown in Figure 3a;
Figure 4b is a view of a contactor similar to that in Figure 4a, but with the
tube connected to a fluid inlet;
Figure 5 is a view of a contactor similar to that shown in figure 3a but with
the perforated tube arranged so that all the fluid which passes through the
outlet does
3 0 so by way of the tube;
Figure 6 is a variant of the contactor shown in figure 5; and
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Figure 7 is a view of a jet pump which can be used as ari alternative to the
contactor.
In one embodiment of the invention, a continuous process operation for a
chemical reaction between a component in a gas phase and a second component in
a
liquid phase is shown in figure 1. A liquid stream 1 including the second
selected
component is conducted by a pump 2 to a contactor 3 (though this could be an
ejector) capable of inducing turbulent mixing. A gas stream 4, including the
first
selected component is drawn into the contactor 3 by the low pressure generated
in the
venturi by the liquid stream after it has passed through the pump (stream la).
This
arrangement provides an automatic means of self regulation as the gas mixture
to
liquid ratio can be maintained for varying flow rates. At the outlet of the
contactor 3
the liquid and the gas stream are in the form of a homogeneous mixture (stream
5)
and the chemical reaction between the selected components may occur very
rapidly.
The mixed two phase stream 5 may then be conveyed to a cooler 6 and on
into a hydrocyclone 7 or other suitable separator device. A gas stream 8,
which may
or may not contain a reaction product, may be taken off and the liquid stream
9,
which may or may not contain a reaction product, may pass on to a regeneration
system. The reaction products) will be separated from the appropriate streams)
by
any suitable means, and any unreacted reagents may be recycled for reuse. For
2 o example if the reaction product is a liquid, this may be separated from
the unreacted
liquid phase by means of heating (10) and then condensing of the product
stream (11)
in a condenser (not shown). Alternatively, if the reaction product is a solid,
the
product may be removed by filtration.
It will be clear to a person skilled in the art that the cooler 6 and the
heater 10
2 5 if they are present may be combined to form a heat exchange unit.
An alternative system for a chemical reaction between two or more
components, one or more in a high-pressure gas stream, and the rest in a
liquid
stream, is shown in figure 2. A high-pressure gas stream 20 containing a first
selected
component is conveyed to a contactor 21 similar to that shown in figure 3a.
The high
3 o pressure of the gas draws a controlled amount of the liquid stream from
the recycle
stream 22 and from a reservoir 23 into the contactor 21.
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At the outlet of the contactor 21 the two phases are in the form of a
homogeneous mixture (stream 24) and the chemical reaction between the selected
components takes place.
The two-phase mixture (stream 24} may pass through a cooler 25 to a
5 hydrocyclone unit 26 or other suitable separation device. The gas stream is
taken off
in stream 27 and the liquid stream 28 may pass to a regeneration system. Again
the
reaction products) may be solid, liquid or gas and will be separated from the
appropriate stream using any suitable apparatus. As before, either or both of
the gas
and liquid streams containing unreacted reagents may be recycled. As before, a
liquid
1 o product may be separated from the liquid stream 28 by means of heating 29
and then
condensing the product stream 30.
As in the first embodiment, the heater 29 and the cooler 25 if present may be
combined to form a heat exchange unit.
The contactor used in both the above embodiments may be that shown in
15 figure 3a. The turbulent contactor 100 comprises a vessel 101 having a
first fluid inlet
102, a second fluid inlet 103 and an outlet 104 leading to a venturi passage
105.
There is a tube 106 (which may or may not be perforated) extending from the
outlet
104 back into the vessel 101. The tube 106 may be open ended into the vessel
101 as
shown in figure 3a, or it may be connected to the fluid inlet 103, as shown in
figure
20 3b.
In a first arrangement, the first fluid (e.g. a gas mixture) is supplied to
the
vessel 101 and the second fluid (e.g. a liquid) is supplied to the tube 106
whereby the
first fluid is drawn into the venturi by the second fluid and the two phases
are mixed.
In a second arrangement, the second fluid (e.g. a liquid) is supplied to the
2 5 vessel 1 O1 and the first fluid (e.g. a gas mixture) is supplied to the
tube 106, whereby
the second fluid is drawn into the venturi by the first fluid and the two
phases are
mixed.
In a third arrangement, the second fluid (e.g. a liquid) and the first fluid
(e.g. a
gas mixture) are supplied to the vessel 101, the second fluid being supplied
to a level
3 o above the Ievel of the outlet 104, whereby the first fluid is forced out
through the
outlet 104 via the tube 106, thereby drawing the second fluid into the venturi
so that
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the two phases are mixed.
A fourth variant is shown in figure 4a. This embodiment is similar to that
shown in figure 3a, but the contactor 110 is inverted and is suitable only for
use with
gas-liquid reactions. It comprises a vessel 111 with a liquid inlet 112, a gas
inlet 113
and an outlet 114 leading to a venturi passage 115. There is a tube 116 (which
may
or may not be perforated) extending from the outlet 114 back into the vessel
111.
The tube 116 may be connected directly to the gas inlet 113.
In this embodiment the liquid is forced up the tube 116 and the gas is drawn
into the venturi passage 115 by the liquid and the two phases are mixed. When
the
tube 116 is perforated, the gas may be drawn into the tube 116 through the
perforations.
A fifth arrangement is shown in figure 4b. This embodiment is similar to that
shown in figure 4a, but the first fluid inlet 113 is connected to the tube 116
and is not
open ended as in figure 4a. The arrangement comprises a vessel 111 with a
second
fluid inlet 112, an outlet 114 leading to a venturi passage 115. The fluid
inlets 112
and 113 may be fed by gas as well as liquid.
A further example of a contactor which may be used in both the above
embodiments is that shown in figure 5. The turbulent contactor 200 comprises a
vessel 201 having a first fluid inlet 202, a second fluid inlet 203 and an
outlet 204
2 0 leading to a venturi passage 205. There is a perforated tube 206 extending
from the
outlet 204 back into the vessel 201. The perforated tube 206 is arranged such
that
there is no gap at the outlet 204 of the vessel 201 for the fluids to pass
through. The
result of this arrangement is that all the fluid exits the vessel 201 via the
perforated
tube 206.
In a first arrangement, the first fluid (e.g. a gas mixture) is supplied to
the
vessel 201 and the second fluid (e.g. a liquid) is supplied to the tube 206
whereby the
first fluid is drawn into the venturi by the second fluid and the two phases
are mixed.
In a second arrangement, the second fluid (e.g. a liquid) is supplied to the
vessel 201 and the first fluid (e.g. a gas mixture) is supplied to the tube
206 whereby
3 0 the second fluid is drawn into the venturi by the first fluid and the two
phases are
mixed.
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In a third arrangement, the second fluid (e.g. a liquid) and the first fluid
(e.g. a
gas mixture) are supplied to the vessel 201, the second fluid being supplied
to a level
above the level of the outlet 204, whereby the first fluid is forced out
through the
outlet 204 via the tube 206, thereby drawing the second fluid into the venturi
so that
5 the two phases are mixed.
A fourth variant is shown in figure 6. This embodiment is v similar to that
shown in figure 5, but the contactor 210 is inverted. It comprises a vessel
211 with a
liquid inlet 212, a gas inlet 213 and an outlet 214 leading to a venturi
passage 215.
There is a perforated tube 216 extending from the outlet 214 back into the
vessel 211.
10 As for the embodiment shown in figure 5, the perforated tube 216 is
arranged such
that there is no gap at the outlet 214 of the vessel 211 for the gas mixture
to pass
through. All the fluids must pass through the perforated tube 216 to the
venturi
passage 215.
In this embodiment the liquid is forced up the tube 216 and the gas is drawn
into the venturi passage 215 by the liquid and the two phases are mixed. Since
the
tube 216 is perforated, the gas is drawn into the tube 216 through the
perforations.
The contactors referred to in the above embodiments may be replaced by jet
pump arrangements which are capable of inducing turbulent mixing. Figure 7
shows
a jet pump 120 comprising a ~ first fluid inlet I2I for the high-pressure
fluid and a
2 0 second fluid inlet 122 for the low-pressure fluid. The high-pressure fluid
draws the
low-pressure fluid along the length of the jet pump 120 to the outlet 123. The
fluids
are well mixed into a homogenised mixture in the region 124 at the outlet of
the high-
pressure inlet 121.
