Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Technica~ Field
The present invention relates to the liquid purging of plate surfaces
in the back-pass of steam generatingboilersupon which sintering fly ash collects.
The invention further relates to directing purging liquid over the surfaces upon
which the fly ash collects to force the ash to a single collection position where
the si~e of the ash may be mechanically reduced prior to ultimate disposal.
Background Art
Various fuels burned in the utility boiler produce residue. This
residue collects on the walls of the chamber in which the combustion takes place.
There is an ongoing problem of removing this solid residue of combustion. The
burning of pulverized coal as a fuel leaves the largest amounts of solid residue
behind for disposal.
In addition to the problem of removing solid residue from the bottom
of the combustion chamber, there is the problem of the fly ash carried over into
the back-pass to which the combustion chamber discharges. The temperature of
the combustion gases is reduced as they flow into heat exchange contact with
structures mounted in the back-pass. The temperature of the combustion gases,
typically within the 1000 to 1200F range, may reduce to the range including
800~ after initial contact with the economizer mounted in the back-pass. The
fly ash sinters within this temperature range and gravitates into impact upon
surfaces of the back-pass which change the directlon of the combustion gas flow.
As the fly ash sinters into an enlarging ~ody) it may actually become an
obstruction to the flow of combustion gases in the back-pass.
The problem addressed by the present invention is continuous removal
of the collected fly ash from the 800F environment. A mechanism must be applied
to continuously~quench the fly ash and periodically remove the collected fly ash.
Preferably, liquid is to be applied as an agent to purge the plate surface upon
which the fly ash collects~
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Disclosure of the Invention
In a broad aspect, the invention resides in a back~pass section of a
furnace burning solid uel which produces fly ash carried into the back-pass by
entraining heating gases as products of the combustion~ including,
a section of back-pass from a furnace including a first downwardly directed
portion and a second portion connected to the first portion at substantially a
right angle,
a receptacle positioned below the gas descending in the first portion of
the back-pass,
a body of liquid impounded by the receptacle having a surface receiving fly
ash from combustion gases flowing from the first back-pass portion into the
second back-pass portion as the entraining gases are diverted in their downward
path from the first portion into a second path within the second portion,
a series of step surfaces beneath the surface of the body of liquid
receiving fly ash gravitated through the body of liquid,
an exit from the receptacle located at the lowest o the step surfaces,
a nozzle for each step surface arranged to direct liquid supplied to the
nozzle over its step surface in removing ash from the step surface to the exit
at the lowest of the step surfaces,
a supply of li~uid for each o~ the nozzles,
and a conduit connected to the exit through which fly ash is continuously~
removed.
Other objects, advantages and features of the invention will become
apparent to one skilled in the art upon consi~eration of the written specifica-
tions, appended claims and accompanying drawings.
Brief Description of Drawings
Fig. 1 is a perspective of the section of the ~ack-pass of a steam
generator in which an impingement surface is arranged fGr fly ash and having a
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system of fluid purging embodied in the present invention.
~ig. 2 is an enlargement of the lower portion of Fig. 1.
Fig. 3 is an alternate arrangement of purging structure similar to
that of Figs. 1 and 2.
Fig. ~ is an alternate arrangement to those arrangements disclosed in
Figs. 1, 2 and 3.
Best Mode for Carrying Out the Invention
The present invention was brought into existence by the problem of ash
disposal from the products of combustion discharged from furnaces. The term
"furance" is used in a broad sense. A steam generator is a particular form of
furnace. The common denominator of all forms of furnaces is found in a com-
bustion chamber where coal, oil or gas is burned as a source of heat. The heat~
whether in the form of radiation and/or convection, is passed through the walls
of pipes to elevate the temperature of fluids 10wing through the pipes.
The solid residue of the combustion process may largely collect upon
the walls of the combustion chamber and present a problem of removal. Addition-
ally, solid particulate from the combustion process is ca~ried aiong with the
combustion gasesA
The solid particulate entrained by t'he hot gases flowed from the
furnace will be referred to as ~ly ash. The conduit from the furance, carry~ing
this mixture of combustion gases and fly ash, will be termed ~he "back-pass".
hs the back-pass changes direction, the fly ash will collect
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or drop out at the bottom of the direction change. The ash ~ay sinter,
due to the high temperature, and eventually obstruct the back-pass to
the flow of combustion gases therethrough.
In Fig. 1, the back-pass from the furnace is disclosed at 10.
This back-pass is seen as being square or rectangular in cross-section.
This conduit is depicted to extend vertically downward. The combustion
gases are indicated as flowing downwardly in the direction indicated by
arrows 11.
As is customary, an economizer section of pipes 12 spans the cross- _
sectional area of the conduit. So positioned9 the economizer 12 is heated
by the convective heat of the combustion gases flowing downwardly through
the conduit. As a matter of interest, the temperature of these gases is
in the order of 1200F prior to their contact with economizer 12. Their
temperature will reduce to the order of 800F after passing through the
econom;zer 12. The fly ash entrained in the combustion gases passes
through the economizer structure and readily collects upon those surfaces
immediately following the economizer structure 12 which effects the change
of the direction of the flow of gases.
Some of the fly ash may collect upon and adhere to tubes of the
economizer 12. The surfaces of these tubes present a problem not con-
sidered by this disclosure, but solved by soot blowing. Whatever solid
particulate or fly ash passes through the economizer structure presents
the problem addressed by the present ;nvenl;ion.
Below the economizer structure 12, back-pass 10 usually changes
direction sharply. This sharp change in direction o~ the combustion
gases is indicated by the arrows 13 which are continuations of the
arrows 11. It has been customary to ~rovide a dry receptacle7 or hopper,
at this bend in the back-pass for the collection of the fly ash thrown
by centrifugal force as the combustion gases are caused to deviate from
their vertical downward direction. It has been a continual problem to
remove the collection of fly ash which tends to sinter into large masses
upon this surface of conduit 10. This fly ash may accumulate to form
such a large body ofsint~ed material that its obstruc~ion to following
oombustion gases becomes a serious problem.
The present invention substitutes a structure for the dry collection
surface of the prior art. The substituted structure is indicated to a
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large extent in Fig. 1 and in durther detail in Fig. 2.
Essentially, the present invention provides a receptacle 15 in
which a body of liquid 16, preferably water, is impounded to present a
surface 17 which will collect the fly ash. It can be readily discerned
from the drawings that the fly ash is thrown into the body of fluid 16.
Fly ash has its temperature reduced by the liquid-water and as a solid
material settles through the water to the bottom of receptacle 15.
Surface 17 of the body of water 16 can be regarded as the impingement
surface for the ~fly'ash. ~'On the other hand, the water body 16 can be
regarded as receiving the fly ash as solid material thrown into the body
of water. In both events, the solid particulate is expected to gravitate
to the bottom of receptacle 15.
In Figs. 1 and 2, the bottom of' the recep~acle 15 is Formed into a
series of steps 18, 19 and 20. The bottom is not limited to the three
steps disclosed. The three steps 18, 1~ and 20 simply represent a
plurality of such structures leading down to a position 21 from which the
fly ash is allowed to exit the receptacle.-
Presumably, the fly ash thrown in~o the body of water 16 will
gravitate to all the steps comprising the bottom of the receptacle 15.
A set of nozzles is mounted above each step to direct purging jets of
water over the surface'of the steps. Nozzle set 22 directs water over
the horizontal surface of step 18; nozzle set 23 directs water over step 19;
and nozzle set 2~ directs water over step 20. No speciFic size, pattern,
or number of nozzles limits the invention. The invention is embodied in
the arrangement whereby these nozzles flush, scour, or purge the solid
material on the steps toward position 21 which is the lowest position on
the floor of structure 15.
Rather than attempting to convey the fluid across a single floor
surface of receptacle 159 the floor is broken up into steps or stages in
order to make separate purging of each step possible within the capabilities
of moving the 'liquid a horizontal distance with the pressure available. A
single exit could be provided at position 21 through which the mixture of
water and particulate would be directed to an ultimate disposal point;
To provide for the requirement of reducing the size of this particular
material, a mechanical grinder 25 is provided into which all the fly ash
particulate is carried from position 21. In grinder 25, the Fly ash is
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ground to a desired size and the mixture of yround ash and water is taken
by conduit 26 to an ultimate disposal destination.
Figs. 3 and 4 disclose arrangements alternate to that of Figs. 1
and 2 and also embody the present invention. In Fig. 3, receptacle 30
is sized and arranged to substitute for receptacle 15 of Figs. 1 and 2.
Receptacle 30 impounds water body 31 with surface 32 upon which the fly
ash collects as entrained combustion gases are diverted in their direction
of flow.
A bottom, or floor, for receptacle 30 has a series of steps 33, 34,
35. However, step 35 is centralized between steps 33 and 34 to Form the
final, lower, position to which the fly ash is forced. Nozzles 36 are
disc~osed as directing water jets across surface 33 while nozzles 37
direct similar jets of water across surface 34. Other nozzles may be
positioned, as required, to force the fly ash on all the surfaces toward
central opening 38.
The fly ash and water flowing through opening 38 may be passed to
an ultimate disposal point. Additionally, grinder 39 may be provided to
receive the fly ash forced to this position. The grinder 39 can then
reduce the size of the fly ash to that required for reach movement through
a pipe to an ulti~ate disposal point.
Fig. 4 discloses still another arrangement for ready disposal of fly
ash under the concepts of this invention. In Fig. 4, receptacle 40
impounds water body 41 to provide a surface 42. The bottom of receptacle 40
is disclosed as a plurality of hoppers 43, 44, 45. As disclosed, the
conical sides of these hoppers may readily guide the fly ash received into
the fluid body 41 toward grinders 4~, 47~ 48. ThereFore, i-F the plurality
of grinders and hoppers can be accepted, it may be possible to eliminate
~he need for water nozzles to additionally provide force for promoting the
movement of fly ash into the grinders. Of course, the use of additional
water-jetting nozzles is not precluded from this embodirnent. Any and all
forces provided by the invention can be used to move the fly ash to its
ultimate disposal.
