Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~47793
; This invention relates to apparatus for automati-
cally determining the smoke density, that is solids contents,
of waste gas being released to the atmosphere.
In order to determine the smoke density of waste gases
- from combustion processes, in particular flue gases from the
combustion of fuel gas, to determine whether the content of
solid particles exceeds a permitted value, it is usual to draw a
portion of the waste gas through a filter device by means of a
suction pump and to separate out solid unburnt matter from the
waste gas. The separated matter, usually on a filter paper, is
evaluated by a visual comparison method. For example the
deposited soot spot is compared with a scale of spots of
increasing grey tonality running from white to black and
determined under identical conditions with gas flows of known
smoke content.
Disadvantages of apparatus hitherto used have been
the subjectiveness of sampling and reading, if determinations
were carried out visually, the variations in sampling volumes
due to various factors, including the temperature of the gases,
the suction speed thereof, the duration of the time gaps between
subsequent strokes of the pump, the atmospheric pressure which
is different from place to place and from time to time, and the -
impossibility of measuring very high smoke densities.
According to the present invention, there is provided
apparatus for automatically determining the smoke density of
waste gas from a combustion process, which comprises a programmer
for controlling operation of other component parts of the appara-
tus, a pump for withdrawing waste gas from a conduit through which
it passes, in use, and comprising a piston having an associated
motor means for effecting linear reciprocating travel of the
piston, an electrically operated valve associated with said
programmer for automatic operation thereby to achieve discharge
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of said gas from the pump, a filter holder having an associated
geared motor for automatically feeding a filter paper across
the path of travel of waste gas through the apparatus and means
for automatically scanning filter paper from the apparatus and
providing a record of the smoke density of the waste gas passed
therethrough.
For a better understanding of the invention and to
show how the same can be carried into effect, reference will now
be made, by way of example only, to the accompanying drawings,
showing a preferred embodiment, in which:
Figure 1 is a photograph showing, in elevation, one
form of apparatus embodying the present invention; ~-
Figure 2 shows in longitudinal section a filter holder
: device for use in automatic apparatus embodying the present
invention;
Figure 3 shows a transverse cross-section through the
filter holder of Figure 2, and
Figure 4 shows diagrammatically an automatic device
for controlling the piston which forms part of apparatus
embodying this invention.
Referring to Figure 1, a preferred form of apparatus
~mbodying this invention comprises a programmer 1 and geared
motor 2 for operating a sampling pump 3, a servomotor 4 for the
automatic control of the stroke of an electric valve 5 automati-
cally operated by the programmer 1 for discharging the gases
from pump 3, a holder 6 for filter paper, a geared motor 7 for
:- the automatic feeding of filter paper into the holder 6 and an
automatically operating beta-rays reading device 8. Pressure
gauges (not shown) are provided upstream and downstream of the
filter holder 6, in the region of the travel path of the filter
paper.
device 9 contains elements for detecting temperature
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and pressure and electxonic circuits for correlating variations
of temperature and pressure with the total sampling volume, in
order to enable measurements to be obtained automatically.
Hence, with an apparatus according to this invention, it is
possible to carry out one or more analyses by inserting in the
programmer the number of piston strokes, the time period between
subsequent samplings and the number of the required samples.
Referring next to Figure 2, there is shown a preferred
form of filter holder for use in the apparatus embodying this
invention. The filter hGlder comprises a casing 10 formed of a
non-magnetisable material, a fixed part 11 closing one end of the
holder, a mobile part consisting of two concentric elements 12
and 13, a spring 14 for connecting the elements 12 and 13, guide
elements 15 preventing mobile parts 12 and 13 from rotating, a
system for producing a magnetic field comprising a fixed part 16
and a mobile part 17, and a spring 18 for opening an electrical
circuit which causes the magnetic field to be set up. The
, arrangement and configuration of the parts of the holder are such
as to provide clamping of filter paper travelling along path 19
(Figure 3) under constant pressure. The clamping acts uniformly
on a sealing annular zone and does not cause any tensile or slip-
Fing stress in the filter paper, unlike with filter holders in
hitherto described apparatus. The electromagnetic control of the
clamping enables clamping to be maintained automatically. The
fixed part 11 and the element 12 each has axial bores at the
intersection of which lies, in use, the filter paper and through
which waste gas is passed in use.
Referring finally to Figure 4, suction pump 21 for
drawing waste gas through the filter holder 6 of Figure 1 and
discharging the gases from the interior of the pump comprises
a three way electrically operated-valve 20 constructed to prevent
return of gases to the filter paper and a piston 22 having a
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piston rod 23 and a rod head 24 by which the piston is dis-
placed between a fixed stroke end position 25 and a stroke end
position 26 which can be altered automatically to compensate for
pressure and temperature variations by achieving a corresponding
variation in the pump capacity.
Although not shown in the drawings, the filter holder 6
will comprise further elements which can be of conventional type
for detecting variations in pressure in the gas impinging in the
filter paper and affecting blackening of the filter paper and so
enabling variation in the pump capacity to be achieved. The
additional elements also provide a stop time for the apparatus,
that is the time required for the pressure drop, caused by the
filter, to reach zero.
It is clear from the foregoing that automatic regula-
- tion of the stop time allows volumes of sampling gas to be
obtained having a high degree of constancy. It is further clear,
that completely automatic carrying out of a series of operations
can be achieved with a single manual operation that is the
operation required for inserting the number of measurements in
the programmer. The logic sequence and the various compensations
occur automatically by operation of the programmer. The reading
of the filter paper from the filter holder by means of ~-rays
obviates the need for the subjective intervention of an operator
and allows an exact evaluation of spots having a high density;
evaluation is impossible optically in such a case.
The automatic apparatus forming the subject of this
invention can be employed with recording equipment or
digital calculators having print--out means for constantly
recording smoke density, in the form of a direct numerical
record.
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