Note: Descriptions are shown in the official language in which they were submitted.
4~3
UNDERGRATE AIR BLASI' . ON G~.S PRODUCE_
THIS invention relates to gas producers and more
particularly it relates to the undergrate air
bla~t arrangement of coal gas producers.
Conventional gas producers are normally of the
type comprising an elongated cylindrical structure
of refractory material having at the upper region
thereof coal feed arrangement and gas take-off
arrange~ent and having at the lower end thexeof
a metal seal skirt which extends into an annular
trough which is filled with water. ~his trough
acts as a seal to prevent producer gas from escaping
from the producer and it also acts as an ash
collecting zone. ~ grate structure, usually
conical in shape is mounted over the area defined
by the anDular inner ~lall of the trough. Below
the grate a conduit asssmbly, ofte~ called the grate
air blast is located through which steam saturated
air is fed into the producer ~ia the grate.
To ensure proper removal of ash fro~ the producer the
trough and grate assembly is rotated and accordingly
a seal is required between the grate assembly and
the grate air blast as the matter is stationary.
Various disadvantages exist in known arrangements
~ for delivering air to the producer and some of
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these will hecome apparent from the discuss.ion ~elow.
It is an o~ject of the invention at least to minimi:se
some of these dis-advanta~es-.
The existing meth.od of introducing the ~lhole of the air
for combustion of the coal th.rough the grate is extremely
poor as the area of the grate ïs normally only in the region
of 40~ of the total cross s-ectîonal area of the firebed.
~ecause of this the volume o.f air per unit area of
firebed be.comes increasingly les:s towards the outside
of the firebed and the highest concentration of air is
in the centxe which has the smallest unit firebed area.
Thi:s not only results in un.even f;rebed conditions with
consequent une~en treatment o the coal in the producer,
but also results in the highest firebed temperatures
being in the centre and the formation of clinker at this
point.
For perfect operation of a gas producer, the flow of air
should be constant over the whole of the firebed, thus
reducing the temperature at the centre and permitting
constant conditions for gasification to the whole of
the coal a~ove the firebed.
According to th.e invention a gas producer is provided
in which coal is oxidized in the presence of air and
steam to produce gas. The producer comprises a side
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wall for containing the burnlng coal at the upper portion
of the producer and ash at its lower portion. An undergrate
is positioned substantially in the center of the lower portion,
and a main air feed flows a mixture of air and steam toward
the producer. An undergrate feed is connected between the
main air feed and the producer for flowing air and steam to
the undergrate. An ash zone feed is connected between the main
air feed and the producer for flowing air and steam from the
main air feed to the producer. An undergrate damper control
is located in the undergrate feed, and an ash zone damper
control is in the ash zone feed. A plurality of apertures in
the side wall at substantially the same level as the under-
grate communicates directly with the lower porti.on of the
gas producer at the periphery thereof and is connected with
the ash zone feed, so that air and steam from the main air
feed can be allocated between the undergrate feed and the ash
zone feed by the dampers. The air and steam flowing through
the undergrate feed enter the gas producer in the lower zone
-thereof, which during the operation is filled with ash, and
the air and steam flowing through the ash zone feed all enter
the producer in the lower zone adjacent to the side wall and
flow upwardly to assure that the air and steam will all enter
the producer through the ash zone substantially uniformally
over the cross section of the producer.
This invention thus provides for the injection of air
around the outside of the firebed into the area
known as the ash space which is the larger area
in the firebed. The total volume of
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air remai~s the s!a~e a~ the conYentional undergrate ai.r
b`last, ~ut the volume of aLr delivered to the undergrate
i.s decreased~ Therefore th.e temperat~re in the centre. of
the ~irehed i.s consi`derably reauced thus permi`tting thR use
of a larger range of fuels than has been previously possible
especi:ally wh.ere ash. fusion temperatures have to he taken
i`nto account~ Also the quality of the gas produced will
improve due to the eyen treatment of the coal being
gas.ifi.ed., and control of the operat;on of the producer
wi.ll be. simplIfied.
In addition the even burning of the firebed will reduce
or eli`mi`nate the quantity of unburnt fuel which is
invariably removed with the ash. from the producer.
To achieve hetter distrib.ution of air in and through the
grate an air diYerter i.s located inside the grate carrier
adjacent t-he i.nlet to the grate assembly. The air diverter
may comprIse a conical element arranged to have its apex
pointïng upstream.
It is necessary in a gas producer to have a rotating seal
between the grate which revolves and the undergrate air
blast tube ~hIch is stationaryO The conventional method
of doing this is with a water seal of sufficient depth to
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seal the air pressure ïn the undergrate from the. atmosphere~
Mechanical seals are not sat;$~actory due to the tolerances
required for out-of~line movement o~ the grateO
The depth of water seal must of course be greater than
the air pres.s:ure of the undergrate air blast and
this: creates prob.lems due to the neces~sity of forming
a pit under the producer to accommodate the seal or
raisin~ the producer by the s~me height~ This problem
becomes more $ï.gni.ficant with generati.ng gas at
lQ hi:gher pressures. as the depth of water seal h.as to be
increased proportionately~ For instance when the
pressure at the outlet of the producer is 30" water
gauge this requires an undergrate pressure of 6Q"
water gauge necessitatïng a water seal of about 66"
în depth.
~ccording to another a~pect of the present invention
the seal between th.e grate and the undergrate air
blast tub.e. comprises a depending cylindrical skirt
secured about the ;nlet to the grate carrier and
extending into a mercury filled annular trough carried
on th.e upper extremity of th.e undergrate air blast
tube.
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To a~oid oxidation of the. mercur~ a la~er of oil is floated
on the mercury~.
Another pro~lem often encountered wlth.gas producers
results~ from i`nterrupti.ons due to mechanical or
eIectrical fai.lures. Sucfi.i`nterruptions necessitate
purging the equipment ~efore placing the producer
back on li`ne, ~ producer sh.ould alwaYs be .under a
positi~e pressure to prevent ingress of air at any
point, and during shutdown it will come under a
negative pressure thus necessitating purging.
The purging is particularly necessary where electro-
static precipi.tators are installed such as on hot
detarred and cold cleaned gas plants. Pur~ing is
both a long and arduous. procedure but the danger
of an explosion occurring after the producer has
come under a negati.ve pressure, makes it a very
necessary procedure.
According to a further aspect of the present
inven-tion the undergrate air feed is fitted with
an emergency fan activated by an independent power
source and arranged to come into operation automatic-
ally upon the pressure in the producer dropping to
below a predetermined minimum positive pressure,
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the fan beïng adapted to mainta1~n. a ~osi`ti~e press:u.re
in the producer~
Th.us a small engi`ne dr$ven fan with.an electrï.c
starter operated by storage batteries which.~ill
start up immedi`.ately the mai`n air blast fans cease
to operate is: fi`tted to the main air b.last conduit.
The alternative to the engine driven fan is a small
D.C~ motor dri.ven fan operated by storage batteries
maintained by a trickle charger to operate the fan
for any~predetermined time.
The effect of this fan wi.11 be that the whole of
the gas producing equlpment will be maintained at
a small positive pressure should the main fans
stop ~or any reason whatsoever and the production
of gas can b.e continued immediately any fault or
electrical failure has been recti.fied without the
delays and work required to purge the system.
~ithout limi.ting the scope of the present invention a
preferred embodiment will now be described with reference
to the accompanying drawing which is a partly sectioned
elevation of a gas producer incorporating the various
features of the present invention.
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Referri~ng to t~e accompanying drawIng a gas producer
comprises a side ~all primaxily of refractory material
(not shown~ the bo-ttom sectIon of whi`ch side wall
con~titutes a water ~ac~et 1 and a seal skirt 2. The
seal skirt 2 depends into an annular trough 3 which
is filled witEI water. ~ platform 4 extends over
the space defïned bAy~ the inner wall 3a of the trough
and a grate carri`er 5 is mounted on the platform 4.
In turn the conical grate 6 is mounted on the grate
carrier 5. A number of the apertures through the
grate 6 is schematically shown at 6a. The traugh 3
and grate assembly 5 and 6 are rotated on bearings 7
in any known manner.
Steam saturated air is fed into the producer in
t~o ways. The main air feed 8 is branched into an
undergrate feed 9 and an ash zone feed 10. In the
undergrate feed an air diverter 11 is located for even
distribution of the air which passes through the grate.
The diverter comprises two cones which are secured
2Q together at their bases.
The seal b~etween the rotating grid assembly and the
stationary undergrate aïr blast pipe is constituted
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by a depending skirt 12 which is located about an
inlet opening through the platform 4 and which depends
into a trough 13 which is filled with mercury (Dot
shown) on top of which a layer of oil is floated.
The undergrate feed system described above has the
advantage of better air distribution through the grate
and a seal which is effective and which permits a
certain degree of out of iine movement of the rotating
asse~bly. As mercury is used as a sealing medium the
seal may be relatively small in dimensions.
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~he ash zone feed conduit 10 discharges air into
a manifold structure 14 comprising an annular
pipe 15 extending about the producer aDd having
a plurality of d1scharge~tubes 16 through which air
is delivered through the side wall of the producer
via apertures 16a in-to the so-called ash zone. It
will be notGd that the apertures 16a are substantially
on the same level as the lower apsrtures 6a of the
~rat^ 6.
The feed conduits 9 and 10 are each provided with a
damper control 17 which in use are adausted to e~sure
even distribution of ~ir through the firebed.
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As pointed out above a mercury seal (12 and 13~ is
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carried on top of the stationary undergrate air
blast tube 18. ~he tube 18 is open at both ends
and the undergrate air blast delivers its load into
tube 18 intermediate its ends.
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Air is removed fro~ the tube 18 by ~eans of a screw
conveyor which is described in greater detail in our
co-pendiDg application e~titled "Urldergrate air blas-t
ash removal system".
An emergency ~aD as discussed in the general
description above is also provided but not shown
iD the drawings. This fan would be arranged to
discharge before the branching of conduits 9 and 10.
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Many variations of detail may be thought of without
departing from the spirit of the inverltion and it
is not the intention to limit the scope of the
invention -to the pzrticular e~bodiment described
hereln.
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