Note: Descriptions are shown in the official language in which they were submitted.
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Crude gas bleeder/flare of a variable opening cross-section for bleeding
off/flaring
combustible gases and process for the combustion of crude gases
[0001] The invention relates to a contrivance designed as crude gas
bleeder/flare
with variable bleeder/flare crude gas outlet consisting of several tubes
nested inwardly
which form a bleeder/flare for bleeding off/flaring crude gases, this
arrangement contain-
ing a nozzle of a variable cross-section, said nozzle controlling the feed of
crude gas in
such a manner that an almost constant velocity can be adjusted at the
bleeder/flare outlet
side and an almost constant pressure be adjusted on the bleeder/flare inlet
side. In this
way undesired extinction and straying of the bleeder/flare flame can be
avoided during
operation. The invention also relates to a process for the combustion of coke
oven crude
gases, in which a constant flow velocity is achieved at the discharge side of
the bleed-
er/flare by the use of a nozzle of a variable cross-section and the use of
tubes of a specif-
ic cross-section ratio.
[0002] Many industrial processes produce gases which are not used for further
applications because this is not desired for economical or technical reasons.
Examples of
such processes are the production of coke oven gas or the production of
refinery prod-
ucts, with waste gases being obtained which are destroyed by combustion or
burning.
This process is also called bleeding-off/flaring because the combustion
process is nor-
mally run at the outlet end of an open tube and is not used for the generation
of energy.
The gases to be bled off/flared are typically obtained at too high or varying
pressure dur-
ing a malfunction in the gas-treating or gas-purifying plant section. and can
therefore not
be used for further applications.
[0003] It is also possible that the gases intended for combustion are of a
chemical
composition which results in a lower calorific value and, therefore, the gases
can only be
used to a limited extent for further applications. Due to these reasons the
intended bleed-
ing-off/flaring of the gases also encounters further technical problems. For
bleeding-
off/flaring, the gas to be bled off/flared must be supplied at a sufficient
and constant pres-
sure to ensure adequate combustion. Because the combustion gases are normally
dis-
charged into the surrounding atmosphere the gas to be bled off/flared must be
combusted
as completely as possible and without any interruption. This means that not
only the
pressure of the gas to be bled off/flared must be controlled but also the air
supply for
combustion. In addition, it must also be ensured that the escaping gas can
immediately
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be re-ignited at the discharge end of the bleeder tube when the flame goes
out, this re-
quiring the availability of a reliable ignition device.
[0004] Finally, efforts are made to avoid so-called "straying" of the flame or
at
least to reduce it significantly. This process denotes the uncontrolled
flickering of the
flame at the outlet end of the tube, in particular under the influence of
wind. This straying
causes a shift of the point of maximum heat flux intensity of the flame in
such a way that
the bleeder/flare facilities or even adjacent plant sections may be damaged.
[0005] Contrivances, suitable for bleeding off/flaring a gas to be combusted
and
designed for avoiding such problems, are known in prior art. US 5472340 A
describes a
contrivance which claims a flare igniter and a crude gas flare intended for
this purpose.
The contrivance includes at least two conduits which are of different length
and share a
common longitudinal axis, the conduits being arranged as an outer and inner
conduit at
least in sections in such a manner that air for combustion can pass into the
area disposed
between both conduits, and in which one end of the inner conduit allows the
entry of
combustion gas in such a way that the contrivance forms a flare. At least two
points of the
flare also comprise fins for the deflection of the gas and air flows during
combustion. Op-
tionally the ignition device can also be operated using a solar powered
source.
[0006] The said invention particularly solves the task of providing a reliable
flare
igniter. However, the contrivance mentioned can only be operated without any
interrup-
tion at a relatively constant pressure of the gas to be cornbusted. No process
step is men-
tioned which allows bleeding off/flaring the gas also at a low pressure. Also,
no process
step is mentioned for lessening the influence of wind and ensuring atmosphere-
independent, undisturbed combustion. Finally, when combusting high-carbon
gases ef-
forts are made to minimise the formation of soot in order to exclude
detrimental impact on
the surrounding atmosphere. Again, for this measure no process step is
mentioned in the
said patent application. Finally, the contrivance can also be damaged by an
excessive
thermal load as taking place, for example, in a straying flame direction.
[0007] Therefore, the objective is to provide a contrivance which
allows/obtains an
as complete as possible and soot-free combustion of the gas to be bled
off/flared, with
the lowest possible emission of soot and nitrogen oxides. The combustion
should also
take place in an undisturbed and uninterrupted manner at varying inlet
pressures of the
gas to be bled off/flared. The flame direction should be as constant as
possible to main-
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tam n a low thermal load of the bleeder/flare material. The impact of wind on
the flame
should have no disturbing influence. Finally, the contrivance should also
provide a reliable
ignition of the gas to be bled off/flared.
[0008] The invention achieves the objective by a contrivance of a variable
opening
cross-section for bleeding off/flaring combustible gases, the said contrivance
consisting of
three different tubes arranged around a common longitudinal axis, and the
tubes being
arranged at least in sections at a common cross-section level, and the inner
tube being
designed as a gas feed tube, and this tube being equipped with a baffle of
variable cross-
section at the opening that ends upwards in vertical direction, said baffle
being used to
close or control the gas flow and being equipped with an automatable mechanism
for ad-
justing the opening cross-section. The contrivance typically also consists of
at least one
air guide plate and shaped sections at the outer tube which allow a directed
supply of air
and an undisturbed burning of the gas to be bled off/flared.
[0009] The contrivance also includes an ignition device which allows the undis-
turbed ignition of the gas as well as feed devices for an inert fluid which is
preferably wa-
ter vapour in order to minimise the formation of soot and carbon monoxide,
i.e. to corn-
bust the hydrocarbonaceous gas as completely as possible. The inlet pressure
of the es-
caping gas and its discharge velocity can be controlled in a wide range or
kept constant
by the baffle of variable cross-section. As a result, combustion and flame
formation can
be maximally controlled and optimised.
[0010] In particular, the invention claims a contrivance of a variable opening
cross-section for bleeding off/flaring combustible gases, consisting of
= a gas feed tube provided with an opening that ends upwards in vertical di-
rection,
= a mixing tube of a larger inner cross-section than the largest outer cross-
section of the gas feed tube such that an area is left free between these
tubes, the mixing tube consisting of a concentric tube, a diffuser with a
cross-section increasing upwards and a confuser with a cross-section in-
creasing downwards,
= an inner tube which is arranged around the gas feed tube and is of a larger
inner cross-section than the largest outer cross-section of the gas feed
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tube, and of a smaller outer cross-section than the smallest inner cross-
section of the mixing tube,
= at least one air guide plate located between the inner tube and the mixing
tube,
and which is characterised in that
= a baffle of variable cross-section is arranged at the opening that ends up-
wards in vertical direction, said baffle being used to close or control the
gas flow and being equipped with an automatable mechanism for adjusting
the opening cross-section.
[0011] The embodiment of the tubes can also be of any type. Typically, the
outer
tube, also called mixing tubeõ is provided at the top with an extension that
enlarges up-
wards. It is also called diffuser. Said upper part is used for directing the
flame. The lower
part of the mixing tube is primarily used for supplying air. This part of the
mixing tube is
also called confuser and enlarges into a downward opening. Said part can also
be pro-
vided with baffle plates or air guide plates for the directed supply of
combustion air. In
principle, baffle plates or air guide plate can be provided at each tube and
in any ar-
rangement. Embodiments for the design of the tubes are known in prior art.
[0012] The combustion air enters the mixing tube through the confuser and is
routed both into the area between the mixing tube and the inner tube as well
as between
the inner tube and the gas feed tube. This results in a two-stage combustion
which coun-
teracts the formation of nitric oxides.
[0013] The baffle, which adjusts or closes the cross-section of the inner
tube, can
be of any type, provided it reliably controls or closes the cross-section of
the inner bleed-
er/flare tube. The diaphragm is preferably made of a heat-resistant material
in order to be
resistant to the temperatures of the flame forming at the bleeder/flare
outlet. The baffle
material must also be resistant to any corrosive constituents contained in the
gas to be
bled off/flared. This material is preferably heat and corrosion resistant
steel.
[0014] In an exemplary embodiment, the baffle consists of plates which are
closa-
ble concentrically, tangentially and circularly towards the gas feed tube
centre. This cor-
responds to an embodiment as it comparatively exists in a photographic
diaphragm. For
opening and closing these plates are moved in horizontal direction towards the
centre of
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the tube. The number and size of the plates can be optional. It is important
that the mate-
rial of the baffle is resistant to the prevailing temperatures and to the gas
or liquid constit-
uents. An embodiment of baffles which close tangentially and circularly
towards a tube
centre ("iris shutters") is known from US 4094492 A. However, this patent
specification
does not teach any control of bleeders/flares for the combustion of gases,
including the
resulting special requirements, such as high temperatures and resistance to
corrosive
gases.
[0015] In a further exemplary embodiment, the baffle consists of plates which
are
closable concentrically, secantially and directly horizontally towards the gas
feed tube
centre.
[0016] In a further embodiment, the plates can be tilted upwards or downwards
in
vertical direction for opening. In this case, the plates are designed as
blades which are
preferably drawn upwards in flow direction by an actuator. This corresponds to
an embod-
iment as it comparatively exists in an iris diaphragm. The more the blades are
pulled up-
wards, the more the diaphragm opens. The number of blades, their size and
material can
also be optional. An embodiment of baffles which are drawn upwards or
downwards in
the tube in vertical direction for opening ("iris nozzles") are known from DE
10002529 Al.
This patent specification neither teaches any control of bleeders/flares for
the combustion
of gases, including the resulting special requirements, such as high
temperatures and re-
sistance to corrosive gases.
[0017] In an exemplary mode, the diaphragm can be adjusted by an electric actu-
ator. However, a pneumatic actuator can also be selected. The selection of the
actuator
type is left to the executing person skilled in the art. The arrangement of
the baffles can
temporarily or permanently be selected in such a manner that there is an
aperture in the
centre of the baffle arrangement.
[0018] In an embodiment of the invention, at at least one point inside the gas
feed
tube, the inner tube or the mixing tube a nozzle is located for feeding an
inert gas . Typi-
cally, this is water vapour. Depending on the combustion conditions the
feeding of water
vapour as driving gas enables continuous flame control and a considerable
reduction in
the formation of soot and carbon monoxide at almost complete to complete
combustion of
the hydrocarbons contained in the gas. This contrivance can be a nozzle or a
simple inlet
tube. Nozzles for feeding water vapour into gases to be bled off/flared are
known in prior
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art. An exemplary embodiment of feed nozzles is taught in DE 69917073 T2.
These noz-
zles can in turn be provided with a controlling device of any type. The latter
can also con-
sist of baffles like the inventive contrivance.
[0019] In a further embodiment of the invention, the inventive contrivance is
pro-
vided with a device for igniting the gas. For example, it is thus possible to
arrange ignition
lances inside the cross-section of the inner tube or the mixing tube. In an
advantageous
embodiment these are at least two ignition lances which are arranged at an
angle of 80
to 100 and with the aid of which an electric arc or ignition spark can be
generated by
electric voltage. The electric voltage can be generated by any means. It can
be freely se-
lected to ensure reliable ignition. An example of a prior-art ignitor rod
arrangement is giv-
en in US 4147498 A.
[0020] The gas inlet/gas feeder to the bleeder/flare can also be of any type.
In a
simple embodiment this is a simple tube leading into the gas inlet of the
inner tube in
such a way that the pressure of the escaping gas is controlled by the
inventive baffle only.
In a further and preferred embodiment a bleeder/flare valve, which can be shut
off, is lo-
cated below the inner tube and the mixing tube. This bleeder/flare valve can
be of any
type. For example, it can consist of a float cup with water supply so that the
pressure of
the gas fed into the float cup can already be controlled to some extent or
shut off at the
gas inlet to the bleeder/flare. An embodiment of a pressure-controlling float
cup is de-
scribed in EP 1390440 B1.
[0021] In a further embodiment, the bleeder/flare valve comprises at least a
float
cup consisting of two compartments, with said compartments to be opened,
controlled
and closed independently of each other. In this way the bleeder/flare valve is
of redun-
dant configuration as a result of which the bleeder/flare valve is still
operable even in the
case of a failure of one compartment and the gas to be bled off is prevented
from being
discharged into the atmosphere in an unburned state. Gas feeding bleeder/flare
valves
provided with float cups are sufficiently known in prior art. Preferably, the
bleeder/flare
valves are opened, controlled or closed pneumatically with the aid of a
pneumatic cylin-
der. For the embodiment of the present invention it is possible to actuate
each compart-
ment individually. As two pneumatic cylinders are available, the float cup is
still operable
even in the case of a failure of one cylinder.
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[0022] The invention also claims a process for the combustion of coke oven
crude
gas using the inventive contrivance. It typically feeds the gas to be bled
off/flared into the
gas feed tube and controls the setting of the discharge velocity of the gas to
be bled
off/flared by means of the baffle of variable cross-section. Typically, the
velocity of the es-
caping gas to be bled off/flared is controlled during bleeding off/flaring in
such a manner
that the velocity remains constant and an undisturbed flame control is
ensured. This pro-
cedure also prevents the undesired straying or extinction of the flame.
[0023] In an embodiment of the invention, a two-stage combustion leads to a re-
duced flame temperature. This two-stage combustion is achieved by selecting
the ratios
of the cross-sections of gas feed tube and inner tube as well as of inner tube
and mixing
tube in such a way that a reduced air feed rate to the inner tube leads to a
substoichio-
metric combustion air ratio (first combustion stage) and the proportionately
increased air
feed rate via the annular gap between the mixing tube and the inner tube to
the upper
part of the mixing tube leads to a hyperstoichiometric combustion air ratio in
the mixing
tube above the inner tube (second combustion stage). This two-stage combustion
coun-
teracts the formation of nitrogen oxides.
[0024] In a further embodiment of the invention, an inert gas is fed into the
gas
feed tube, the inner tube or the mixing tube. Preferably, this inert gas is
water vapour.
However, additional crude gas, intended for bleeding off/flaring, can be
supplied. Finally,
in a further embodiment of the invention, a mixture of water vapour and gas to
be bled
off/flared can also be supplied. This mixture is preferably supplied at a
pressure of 7 to 15
bar.
[0025] Suited for bleeding off/flaring are all gases of a sufficiently high
calorific
value.. Typically, these gases are coke oven crude gases or refinery gases.
[0026] The feeding of the gas to be bled off/flared into the inventive
bleeder/flare
can be performed as desired. In a simple embodiment, this can be performed by
a simple
tube in an uncontrolled manner. In a preferred embodiment, an upstream
bleeder/flare
valve comprising at least a float cup is arranged below the bleeder tubes.
[0027] As described, this valve is preferably made of two float cups which may
al-
so be designed as two compartments to be operated independently. In a
preferred em-
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bodiment, each of the two compartments of the float cup of the upstream
bleeder/flare
valve can synchronously be opened, controlled or closed by a pneumatic
cylinder.
[0028] However, each compartment of the entire float cup can be operated indi-
vidually. In this way, an undesired blockage of the valve can be counteracted
in the case
of a failure of a controlling device to prevent the gas from being discharged
into the at-
mosphere in unburned state. According to the invention, a gas collecting
vessel/receiver
serving as a buffer vessel can be allocated to the bleeder/flare in order to
counteract a
pressure build-up when closing the baffle or the upstream bleeder/flare valve.
[0029] Finally, the use of the inventive process allows a considerable
reduction of
the number of crude gas bleeders/flares since the heat development of the
bleed-
ers/flares is lower and the reliability higher. Half the normal number of
bleeders/flares is
frequently sufficient. The bleeders/flares can also be of lower height design
since heat ra-
diation is lower and the emission of unburned gas does not have to be taken
into account.
[0030] The invention has the following advantages: The bleeder/flare can be op-
erated at a constant discharge velocity of the gas to be bled off/flared,
resulting in contin-
uous flame control accompanied by a high bleeding-off/flaring reliability.
Straying flames
accompanied by an undesired shift of the point of maximum heat flux intensity
are avoid-
ed in order to prevent any damage to the bleeder/flare and impairment of the
environ-
ment. The impact of wind results in a considerably lower disturbing influence
on the
bleeding-off/flaring process than in prior-art devices. The possibility of
installing a reliable
ignition device ensures continuous combustion in such a way that the undesired
emission
of non-burned gas is practically suppressed. The formation of soot when
bleeding
off/flaring high-carbon gas can practically be excluded by feeding inert gas
and the for-
mation of nitrogen oxides can successfully be counteracted by two-stage
combustion.
[0031] The invention is illustrated in more detail by means of four drawings
show-
ing exemplary embodiments, the invention not being limited to these
embodiments.
[0032] FIG. 1 shows the lateral view of an inventive crude gas bleeder/flare
with-
out upstream bleeder/flare valve and the baffle in open position. FIG. 2 shows
an in-
ventive crude gas bleeder/flare with upstream bleeder/flare valve and the
baffle in open
position. FIG. 3 shows an inventive crude gas bleeder/flare with upstream
bleeder/flare
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valve and the baffle in closed position. FIG. 4 shows the inventive crude gas
bleeder/flare
seen from above.
[0033] FIG. 1 shows the lateral view of an inventive crude gas bleeder/flare
(1).
The crude gas (2) escapes through the gas feed tube (3) to the top. The gas
feed tube (3)
is surrounded by the so-called inner tube (4). This, in turn, is surrounded by
the mixing
tube (5) consisting of a centre part (5a), a confuser (5h) and a diffuser
(5c). The upper
discharge end (3a) of the gas feed tube (3) is provided with a baffle (6)
which opens by
lifting upwards in vertical direction. Shown is the actuator (7) which opens,
controls and
closes the baffle (6). A flame (8) forms at the upper discharge end of the
bleeder/flare.
[0034] FIG. 2 shows the lateral view of an inventive crude gas bleeder/flare
(1)
with upstream bleeder/flare valve (9). The crude gas (2) escapes through the
gas feed
tube (3) to the top. The upper discharge end (3a) of the gas feed tube (3) is
provided with
a baffle (6) which opens by lifting upwards in vertical direction. Here it is
shown in open
position (6a). Also actuator (7) is to be seen which opens, controls and
closes the baffle
(6). Above this baffle (6) there is an ignition mechanism (10) consisting of
two ignition
lances (10a,10b) staggered by 900. By means of these ignition lances (10a,10b)
an igni-
tion spark or an electric arc (10c) can be generated by applying electric
voltage which is
supplied by two poles (10d,10e, not shown here). Also shown here are air guide
plates
(11) which are arranged in the inner tube (4) or the mixing tube (5). The
bleeder/flare (1)
is also provided with a feed device (12) for an inert gas (12a) which is
preferably water
vapour. An upstream bleeder/flare valve (9) is provided below the
bleeder/flare (1) and
comprises a float cup consisting of two compartments (9a,9b). Each of the two
compart-
ments is provided with a cover which can be lifted by a pneumatic actuator.
[0035] FIG. 3 shows the lateral view of an inventive crude gas bleeder/flare
(1)
with upstream bleeder/flare valve (9). The crude gas (2) escapes through the
gas feed
tube (3) to the top. The upper discharge end (3a) of the gas feed tube (3) is
provided with
a baffle (6) which opens by lifting upwards in vertical direction. It is shown
here in closed
position (6b) so that the gas flow is completely or almost completely shut
off.
[0036] FIG. 4 shows the top view an inventive crude gas bleeder/flare (1).
Shown
are the cross-section of the bent mixing tube (5), the inner tube (4) and the
gas feed tube
(3). The baffles (6) are arranged tangentially and can be opened by lateral
tilting. Shown
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here are the actuator (7) and the ignition lances (10a,10b). Also shown here
are the feed
nozzles (12) for the inert gas (12a) which is preferably water vapour.
[0037] List of references used
1 Crude gas bleeder/flare
2 Crude gas
3 Gas feed tube
3a Discharge end of the gas feed tube
4 Inner tube
Mixing tube
5a Central part of the mixing tube
5b Confuser
Sc Diffuser
6 Baffle
6a Opened baffle
6b Closed baffle
7 Actuator
8 Flame
9 Bleeder/flare valve
9a Float cup compartment
9b Float cup compartment
Ignition mechanism
10a Inner ignition lance
10b Outer ignition lance
10c Electric arc
10d Power supply
10e Power supply
11 Air guide plates
12 Feed nozzles
12a Inert gas
