Note: Descriptions are shown in the official language in which they were submitted.
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95/0101
Method of monitoring the operation of a device for
feeding an abrasive medium by mean~ of a fluid.
The invention relates to a method of monitoring the
operation of a device for feeding an abrasive medium,
especially of a dust-recycling system, into a melting
gasifier, the dust extracted from a melting gasifier or
reduction shaft furnace being introduced by means of a
fluid via a dust conveyor tube through at least one
dust burner into the melting gasifier as an additional
carbon carrier. The method can also, however, be used
for the feeding of abrasive media by means of fluid
injection into other melting or incineration plants,
such as e.g. fluid bed reactors.
From DE 40 41 936 C1 is known a way of feeding the
gases, of deposited hot dusts, streaming out of melting
gasifiers or reduction shaft furnaces, back into the
process of a melting gasifier. In this process, an
injector is used in order to pass the dust which is to
be recycled via a dust conveyor tube and via at least
one dust burner back into the melting gasifier.
During operation, under the known severe conditions for
melting gasifiers, hot gases or unburned oxygen can
flow back into the dust recycling system. In such a
case, there exists the very great danger that plant
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components can be damaged or destroyed as a result of
an explosion.
It is therefore the purpose of the invention to detect
such a state as soon as possible and reliably to
prevent any threat being caused by gases flowing back
into the dust recycling system.
According to the invention, this purpose is fulfilled
by the features contained in claim 1. Advantageous
embodiments and developments of the invention arise
with the exploitation of the features mentioned in the
subordinate claims.
Through detecting the flow direction in the conveyor
tube of a dust recycling system, the returned dust
being the abrasive medium and being used as an
additional carbon carrier in the melting gasifier, it
is possible in a simple and reliable way to determine
whether any undesired backflow of gases is occurring
and a corresponding scenario can be initiated which
reliably prevents a threat such as already mentioned
(explosion) from occurring.
A favourable possibility for this consists in
monitoring simultaneously the pressure in the melting
gasifier and in the dust conveyor tube. If a rise in
pressure in the dust conveyor tube is detected, in the
case where there is no corresponding rise in pressure
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in the melting gasifier, it can be clearly inferred
than an undesired operating situation has been reached
which can pose a threat to the system. With such a
measuring result, in this case it can be inferred that
hot gas or oxygen has penetrated into the dust
conveying system of the dust-recycling system and this
must be reacted to appropriately in order to overcome a
state of danger.
A particularly advantageous way of determining the flow
direction in the dust conveyor tube consists in the
fact that at least two measuring channels are led
through the wall of the dust conveyor tube, the angles
of inclination of these measuring channels being
different in relation to the longitudinal axis of the
dust conveyor tube in the measuring plane. A measuring
channel can here be inclined orthogonally to the
longitudinal axis of the dust conveyor tube and the
second measuring channel can be inclined at an acute
angle to this axis.
As is also the case with other measuring methods which
are based on the principle of fluid dynamics, it has an
advantageous effect, in order to prevent blocking of
the measuring channel apertures, if a fluid is led
through said apertures into the conveying flow.
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Nitrogen suggests itself in particular as such a
measurement fluid since nitrogen, as a known inert gas,
cannot lead to any threat in the dust-recycling system.
As a result of the differing inclination of the
measuring channels in relation to the longitudinal axis
of the dust conveyor tube, the pressures in both
measuring channels - with the exception of the
operating point which is defined by the zero crossing
or null balance - always differ, the pressure
difference being - under otherwise identical conditions
- a measurement for the flow velocity in the conveyor
tube. If expediently a null balance is carried out for
the current-free state, a reversal of the flow
direction can be directly inferred from a change of
sign of the pressure difference, which reversal is a
pre-requisite for the feared case of a backflow of hot
flame gases or oxygen into a dust conveyor tube. The
proposed arrangement of the measuring channels can,
however, be adapted to different conditions by other
variants, especially different selected angles of
incllnation, of the measuring channels whose pressure
values are to be compared with one another.
A further possible way of monitoring the backflow of
oxygen into the dust-recycling system consists in the
fact that a flame guard is led through the wall of the
dust conveyor tube. In this process, problems must be
taken into account which can occur through possible
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blockages caused by dust. Negative effects which occur
from harmful components (e.g. H2S) in the conveyor flow
must likewise be taken into account. The flame guard
has a fuel-gas supply and an ignition device which can
for example be configured as a heat plug or a spark
generator. If oxygen penetrates via the aperture of
the dust burner into the dust conveyor tube and reaches
the flame guard, the ignition of the combustible gas
mixture occurs and this can be detected via optical or
acoustic sensors or via a measurement of temperature.
The invention is to be described in more detail below
with the aid of embodiments, given by way of example.
Here the figures show:
Fig. 1 a block diagram of the application of a fluid
dynamic measurement principle with two measuring
channels;
Fig. 2 variants for possible measuring channel
arrangements and
Fig. 3 the monitoring of a dust conveyor tube by means
of a flame guard.
In the principle of a pressure difference measurement
shown in Fig. 1, this measurement is carried out in two
measuring channels 1 and 2. The measuring channels 1
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and 2 are here configured as bores which are led
through the wall of the dust conveyor tube 3. The
measuring channel 1 is here inclined orthogonally to
the longitudinal axis of the dust conveyor tube 3 and
the measuring channel 2 is inclined at an acute angle
to same. The arrow Vc drawn in Fig. 1 indicates the
direction in which a danger situation can occur, i.e.
hot gases or oxygen flow back into the system. In
principle, a reverse arrangement of the probes in
relation to the flow direction can also be used.
Nitrogen is fed into the measuring channels 1 and 2 via
a supply line 4. The volume flow of the nitrogen which
is led into the measuring channels 1 and 2 is kept
constant by means of a control system. For this
purpose, volume flow sensors 5 and 6 with control
valves 7 and 8 are present. For the supply of the
measurement fluid (nitrogen), a further valve 9 is
present in conjunction with a pressure sensor 10.
As well as the measurement of the pressure difference
in the measuring channels 1 and 2, the absolute
pressure in the dust conveyor tube 3 is monitored by
means of a further pressure sensor 11.
The pressure difference in the measuring channels 1 and
2 is measured by means of pressure sensor 12. The
pressure difference detected is a measurement for the
flow velocity in the conveyor tube. If a null balance
... . .
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is carried out for the current-free state, it is
possible with the aid of a change of sign of the
pressure difference to detect that backflow into the
dust conveyor tube 3 has taken place and a
corresponding signal can be generated in order to shut
off the supply of oxygen. The suitable shut-off
mechanism for this purpose is not shown in this
illustration.
Through the fact that the absolute setting values for
the two measurement fluid flows through the measuring
channels 1 and 2 can be favourably chosen with regard
to the required measuring sensitivity and the measuring
range for the measurement of the pressure difference,
an optimum region suitable for monitoring can be set
without problem. Via the setting of the ratio of the
measurement fluid flows, a null balance of the pressure
difference can be carried out moreover.
Through the parallel injection of the measurement fluid
via the two measuring channels 1 and 2 and the
measurement of the difference in pressure between these
two measuring channels, the measured value is
practically independent of the static pressure and is
only affected directly by the static pressure (namely
via the density) of the gas used. Through the slight
inclination of the measuring channels transversely to
the flow direction (bore in the wall of the dust
conveyor tube 3), the ideal Bernouilli measurement
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principle Pd~ = Ptotal ~ Pstat cannot be realised and a
corresponding measurement arrangement must be
calibrated.
From Fig. 2 can be taken altogether six different
possible arrangements of respectively two measuring
channels. Here the arrangements shown in the upper row
are so chosen that the corresponding apertures of the
respective measuring channels are disposed at one point
in the dust conveyor tube 3.
However, there also exists the possibility of arranging
the measuring apertures of the measuring channels in
different places, as can be seen from the lower row of
Fig. 2. If the latter arrangement is chosen, what must
be considered is that an increased time constant, which
is determined by the spacing of the measurement
apertures, must be taken into account when the
difference in pressure between the measuring channels 1
and 2 is measured directly.
Moreover, when the version which has the measuring
channels in one point is used, under certain
circumstances a significantly higher measuring
sensitivity can be achieved than with the version with
separate measuring points.
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From Fig. 3 can be taken a further example of an
embodiment of a monitoring system configured according
to the invention in which a flame guard 13 is used.
The flame guard 13 is here led at least partially
through the wall of the dust conveyor tube 3, and in
the case of backflow out of the melting gasifier via
the dust burner, which likewise cannot be recognised in
this representation, oxygen can reach the region of the
flame guard 13. Through a supply line 14, combustible
gas passes via an aperture through the flame guard 13
and can be led into the dust conveyor tube 3, the flow
direction of the fuel-gas being discernible from the
arrows.
In addition, an ignition device 15 is present which can
be configured for example as a heat plug or a spark
generator. If oxygen now reaches the region of the
flame guard 13, the fuel-gas is ignited with the aid of
the ignition device 15 and, in this example by means of
an optical monitoring system 16, it is determined
whether oxygen is located in the dust conveyor tube 3
or not. To protect the optlcal monitoring system 16, a
protective glass 17 in front of a lens system 18, which
focuses the light which may be detected during ignition
onto a photocell 19, can be arranged in front of the
latter.
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As well as the optical monitoring of the flame guard
13, there is also the possibility of using a
corresponding acoustic sensor or a temperature sensor.
.
