Note: Descriptions are shown in the official language in which they were submitted.
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COAL ~IEATER TEMPERATURE CONTROL
Back~round of the Invention
This invention relates to industrial processes which
call for the heating of coal, or the heating and drying of coal,
to temperatures above 100C~ or 212F. More particularly, this
invention relates to a method for maintaining heating equipment
for coal in standby operating condition, at a desired operating
temperature in the heating equipment, during routine interrup-
tions in the supply of coal.
As an example, this invention has been adapted for use
in a system ~nown as the "Pipeline Charging System". The Pipeline
Charging System relates to heating (also known as "preheating")
granular coal and conveyance of the coal (also known as "pre-
heated coal"), as particles, through a pipeline to coke ovens for
the conversion o the coal partiales into coke, rather than
conveying the coal to the coke ovens by means of a coal charging
car or larry car. In this example, the heating equipment for the
coal is known as a "coal preheater" or as "preheating equipment".
Patents which relate generally to the Pipeline Charging System
or various aspects of the ~ystem include the following U.S.
Patents: 3,512,723 to J. A. Geoffroy; and 3,523,065 and 3,457,141;
both to L. D. Schmidt.
In the example of a Pipeline Charging System, large
quantities of heat are supplied to preheating equipment for the
purpose of heating the coal, thereby producing preheated coal,
prior to conveying the coal through the pipeline. It is de~ir-
able to provide a method for maintaining ~he temperature of the
various parts of the preheating equi~pment at a desired level of
temperature at times when the supply of coal being fed to the
preheating equipment is interrupted.
The supply of coal being fed to the preheating equipment
may be interrupted for any one of the number of reasons during
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operation of a coke plant. For example, any plant breakdown
that delays the removal of the coke from the coke ovens may
require interruption of the coal being fed ~o the preheating
equipment. A malfunction in the preheating equipment or pipeline
charging equipment may require interruption of the coal being
supplied to the heating equipment. The normal effects of changes
in personnel between the various shifts in the 2~ hour operation
of a coke plant may require interruption of the coal supply.
It is desirable to avoid the necessity of stopping the
supply of heat to the preheating equipment or of greatly reducing
the supply of heat, which would cool the preheating equipment to
a temperature below the normal range of operating temperatures
o the heating equipment and probably cause the oxygen content
in the atmosphere in the heating equipment to rise. Such cooling
is undesirable because when operation is resumed, the preheating
equipment will then have to be brought up to the desired tempera-
ture again and-down to the desired oxygen content. Instead, it
is desirable to have a method of maintaining the heating e~uip-
ment at the desired temperature during interruptions of coal feed
and maintaining the heat source in a standby operating condition
which keeps it in its normal range of operation with reference to
heat output and combustion characteristics during interruptions
of coal feed.
An emergency system is already known and used for pre-
venting the temperature of the preheating equipment from rising
to a dangerously high level during such interruptions of the
coal feed in order to avoid damage to the equipment and possible
formation of explosive mixtures. This prior art emergency system
includes the injection of water automatically into the preheating
equipment to absorb the heat. However, this emergency system -
causes substantially complete shutdown of the preheating equipment
and does not maintain the heat output from a heat source in the
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heating equipment at a heat output level during interruption of
coal feed which is within its normal range of heat output when
coal feed is being supplied. Thus, this emexgency syetem does
not provide an~ method by which the temperature in the preheating
equipment may be controlled in order to maintain the preheating
equipment in standby operating condition, that i5, at the desired
level of temperature, during routine interruption of the coal
feed.
Summary of the Invention
The invention is a method for maintaining heating equip-
ment for coal in standby condition at a desired level of tempera-
ture in the preheating equipment, during routine interruption of
the coal feed. The method includes: monitoring the temperature
in the preheating equipment; providing an artificial heat load to
the preheating equipment; causing the artificial heat load ~o
absorb substantially all of the heat, normally absorbed by the
coal feed, from a heat source to cause the heat source to operate
in its normal range of operation during routine interruption of
the coal feed; maintaining the heat output from the heat source
at a heat output level during interruption of coal feed which is
within its normal range of heat output when coal feed is being
supplied; and controlling the amount of the artificial heat load
being provided at a level which wlll ab~orb sufficient heat in
the heating equipment to maintain the temperature in the heating
equipment at a desixed level.
The method further includes: adjusting the heat output
from the heat source to a heat~level which is in the lower portion ^
of the normal range of heat output from the heat source. The
method further includes: selecting a location in the heating
equipment at which the artificial heat load is provided. The
step of selecting such a location includes: selecting a point in
the heating equipment between the source of heat and the equipment
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which the coal feed normally contacts.
The step of providing an artificial heat load includes;
injecting a supply of a fluid, pre~erably a liquid, such as
water, as the artificial load into the heating equipment.
The step of injecting a supply of fluid includes pro-
viding a pipeline through which the liquid is supplied to the
heating equipment. The step of controlling the amount of arti-
ficial heat load includes: providing a standby control valve
for controlling the supply of artificial heat load -to the heating
equipment. The step of controlling the amount of artificial heat
load may further include adjusting the flow of liquid to the `
heating equipment to a flow rate which is based upon the normal
heat output of the heat source supplying heat to the heating
equipment.
The step of monitoring the temperature includes: posi-
tioning a temperature sensing element in the heating equipment
downstream of the location at which the artificial heat load is
provided.
This invention provides a number of significant advan-
tages which include the following: First, this invention pro-
vides a method for maintaining standby operation o the heating
equipment for heating coal without cobling the heating equipment
below its normal OPerating temperature. Second, this invention
provides a method for testing the heating equipment and asso-
ciated equipment, at operating temperatures without supplying
coal to the heating equipment. Third, this invention provides
for additional safety in the operation of heating equipment and
pipeline charging equipment by providing a method for cooling
the heating equipment and pipeline charging equipment, in addi-
tion to presently available emergency methods. Fourth, this
invention provides a method for adjusting the burner of heating
equipment to desired combustion conditions without overheating
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part of the equipment when the burner heat output is within its
normal range of operation. Fifth, this invention provides a
method for improving safety conditions in coal heating equipment
and reducing the possibility of explosions by establishing
conditions under which any required amount of time may be used
in adjusting the heat source, such as a burner, and in ad~usting
the oxygen content in the heating equipment to any desired per-
centage before coal is introduced in the heating equipment.
Description of the Drawings
Fig. 1 i9 a schematic illustration of typical heating
equipment as used with pipeline charging equipment in a coke
plant, indicating a first embodiment of this invention.
Fig. 2 is a partial schematic illustration of the same
heating equipment shown in Fig. 1, but indicating a second embo-
diment of this invention.
Fig. 3 is a cros3-sectionaL view of a small portion of
the heating equipment shown in Fig. 1. Fig. 3 shows typical
apparatus used to provide an artificial heat load to the venturi
throat of Fig. l.
Fig. 4 is a block diagram of apparatus used in one
embodiment of this invention for controlling the flow of artifi-
cial heat load.
Detailed Description
This invention relates to a method for maintaining
heating equipment for coal in a standby condition at a desired
level of temperature in the heating equipment. The heating
equipment is intended to heat the coal, or heat and dry the coal,
to temperatures above 100C. or 212F. The method will be
described in reference to a Pipeline Charging System in which
the heating equipment is hereinafter called "preheating equipmentl'.
The coal is heated (hereinafter called "preheated coal") and then
conveyed by pipeline charging to coke ovens. However, the method
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of this invention may be used with other heating equipment for
coal, other than the Pipeline Charging System.
Referring to Figs. l and 2, partially crushed, wet
coal is supplied to a feed hopper 2, then to twin screw feeders
4, then to a flash drying chamber 6 above a ventuxi throat 8. A
fuel (such as a coke oven gas) and air are supplied to a burner
10 of a combustion chamber 12 for combustion therein, producing
hot flue gases. A temperature sensing unit 3 signals a tempera-
ture control unit S to adjust the flow of fuel through valve 7
to burner lO to that required to maintain the temperature at the
temperature sensing unit 3 at a preselected level which normally
is within the range o temperakures from 500F. to 575F. (260C.
to 300C.). A graup of sensing units (not shown) and controls
(not shown) automatically adju~t the air input to burner 10
proportionately to the ~uel input to burner lO. Thus, the heat
output of burner lO is adjusted to produce the desired temperature
in the preheating equipment, as sensed by temperature sensing
unit 3. The flue gases from the combustion chamber 12 travel up
through the venturi throat 8 and contact the coal in the flash
drying chamber 6. The hot flue gases heat the coal and evaporate
a substantial part of the surface moisture on the coal, thereby
producing partially dried, preheated coal. The partially dried
coal moves up through a crush-disperser 14, rotating in a dilute
fluid bed in which the coal is further dried and heated, then
through an elutriation zone 16 and then through a coal duct 18
which leads to a set of cyclones 20. The coal then moves through
a rotary feeder 22 and/or feeder pipes 23 to a distribution hopper
25, then to charge bin~ 26, then to pipelines 28 which c~nvey
the coal, mixed with superheated steam, to coke ovens.
The method of this invention relates to the preheating
equipment, referred to generally by the numeral 29. The pre-
heating equipment 29 includes: the combustion chamber 12, burner
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l, venturi throat 8, flash drying chamber 6, crusher-disperser
14, elutriation zone 16, coal duct 18, and cyclones 20, among
other equipment. More particularly, the method of this invention ..
relates to maintenance of the preheating equipment in standby
operating condition, at a desired operating temperature in the
preheating equipment, during routine interruptions in the supply
of coal through screw feeders 4.
The method includes: monitoring the temperature in the
preheating equipment 29; providing an artificial heat load to the
preheating equipment 29; causing the artifical heat load to
absorb substantially all of the heat from the heat source, such
as burner 10, normally absorbed by the coal prior to interruption
of the coal feed, to cause the heat source to operate in its
normal range o~ operation; maintaining the heat output from the
heat source at a heat output level during interruption of coal
feed which is within its normal range of heat output when coal
feed is being supplied; and controlling the amount of the artifi-
cial heat load being provided at a level which will absorb suffi- ;~
cient heat in the preheating equipment 29 to maintain the tempera-
ture in the preheating equipment at a desired level. In the
embodiments of Figs. 1 and 2, the heat source is a burner 10
which is part of combustion chamber 12.
The method further includes adjusting the heat output
from the heat source to a heat output level which is in the lower
portion of the normal range of heat output from the heat source
when the coal is being supplied to the preheating e~uipment,
prior to interruption of the coal feed. In this embodiment, the
heat output from the heat source is in the range of from 20
million BTU's per hour to 125 million BTU's per hour. As a first
example, for a unit rated at a nominal input of about ~0 U.S. tons
of coal per hour, the heat source may have a heat output capacity
of about 20 million BTU's per hour. As a second example) for a
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unit rated at a nominal input of about 100 ~.S. tons of coal per
hour, the heat source may have a heat output capacity of about
75 million BTU's per hour. As a third example, for a unit rated
at a nominal input of about 150 U.S. tons of coal per hour, the
heat source may have a heat output capacity of about 125 million
BTU's per hour. Preferably, in the first example for a 40 U.S.
ton per hour unit, the artificial heat load is adjusted to require
a heat output level fxom the heat source of approximately 5
million BTU's per hour during interruption oE coal feed. Prefer-
ably, in the second example for a 100 U.S. ton per hour unit, the
artificial heat load is adjusted to require a heat ou~put level
from the heat source of approximately 20 million BTU's per hour
during interruption of coal feed. Preferably, in the third
example for a 150 U.S. ton per hour unit, the artificial heat load
is adjusted to require a heat output level from the heat source
of approximately 30 million BTU's per hour during interruption of
the coal feed. Since the heat source is still fully in operation
within its normal range of heat output during interruption of
coal feed, operation of the preheating equipment can easily and
conveniently be resumed, without delay in bringing the heat source
back into operation.
The method ~urther includes selectiny a location in the
preheating equipment 29 at which the artificial heat load is
provided. The step o selecting such a location in the preheating
equipment 29 includes selecting any convenient location in the
preheating equipment 29 between the source of heat and the equip-
ment which the coal feed normally contacts prior to interruption.
For example, the artificial heat load may be provided at the
venturi throat 8 in a first embodiment of this invention as illus-
trated in Fig. 1. In the alternative, the artificial heat load
may be provided at the flash drying chamber 6 in a second embodi-
ment of this invention as illustrated in Fig. 2. In the alternative,
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the artificial heat load may be provided at a location immediately
under, that is, upstream of the crusher-disperser 14.
The step of providing an artificial load includes
injecting a supply of a fluid, preferably a liquid, such as water,
as the artificial load, into the preheating equipment. The step
of injecting a supply of water includes providing a pipeline 30
through which a flow of water is supplied to the preheating
equipment 29. The step of monitoring the temperature includes
positioning a temperature sensing element 24 in the prehelting
equipment 29 downstream of the location selected for providing
the artificial heat load. In a first embodiment, the temperature
sensing element 24 may be positioned in the preheating equipmeht
29 downstream of the crusher-disperser 14, such as in the elutria-
tion zone 16, as illustrated in Fig. 1. In the alternative, in a
second embodiment the temperature sensing element 2~ may be posi-
tioned in the coal duct 18 of the preheating equipment 29 down-
stream from the elutriation zone 16 of the preheating equipment,
as illustrated in Fig. 2. The elutriation zone 16 is located
above the crusher-disperser 14. The function of the elutriation
zone 16 is to separate larger particles in the coal stream.
An emergency system is already known and used or pre-
venting the temperature of the preheating equipment 29 from
rising to a dangerously high level during interruptions of the
coal feed. This emergency system operates automatically and uses
a water supply pipeline 30. The same water supply pipeline may
also be used for the method of this invention. The emergency
system uses a valve 32 positioned in the water supply pipeline
and the same valve may also be used for the method of this inven-
tion. An additional flow control valve 32, not presently used
for the emergency system, may be provided for controlling the
flow of water through the valve during non-emergency conditions.
The emergency system also uses a temperature sensing element or
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a series of temperature sensing elements. Preferably/ a separate,
additional temperature sensing element 24 may be used for the
- method of this invention.
In the embodiment illustrated in Fig. 1, where the
location selected for providing the artificial load is the venturi
throat 8, Fig. 3 illustrates a typical apparatus which may be
used for injecting the artificial heat load, such a~ water into
the venturi throat 8. A plurality of conduits 36, such as pipes,
are provided to conduct the artificial heat load into the venturi
~10 throat 8. In this example, four such conduits 36 are provided.
In other embodiments, a greater or lesser number of conduits may
be used. Preferably, each conduit 36 is arranged at an angle 38
with the horizontal of approximately 45. Preferably, a nozzle
40 is provided at the interior end of each conduit 36 within the
venturi throat 8 for the purpose of projecting the artificial
heat load across the high velocity flow of hot flue gases passing
through the venturi throat 8. Spray nozzles 40 forming a cone
pattern of approximately 45 are preferred. In the alternative,
the artificial heat load may be projected through conduits 36
without the use of a nozzle, if a sufficient number of conduits
are used ~uch that the maximum injection rate is no more than
five gallons per minute per conduit 36.
Apparatus similar to that illustrated in Fig. 3 may be
used to inject the artificial heat load into the flash drying
chamber 6, according to the embodiment illustrated in Fig. 2, or
into other parts of preheating equipment. Water pipes of 1/2
inch diameter have been found to work well in supplying water to
the preheating equipment. Referring to Fig. 3, each of the
conduits 36 may preferably be provided with a purging means 42
for purging the conduits 36 of dust, such as by use of air~when
the conduits 36 are not in use. Optionally, each of the conduits
36 may also be provided with a convenience valve 46.
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The step of providing a supply of artificial heat load,
such as water, may be accomplished in two ways: a simplified
arrangement; or a more sophisticated arrangement. Referring to
Figs. 1 and 2, in the simplified arrangement, a si~ple, on-off,
flow valve 32 is used. A predetermined flow of artificial heat
load is provided from a supply of artificial heat load 44 which
provides fixed, metered flow at a predetermined flow rate. A
temperature switch (TS~ 35 operates a flow control 34 to turn
the supply of water on and off by means of flow valve 32 automa-
tically according to the temperature in the preheating equipment 29
or manually at the discretion of the operator.
Referring to Fig. 4, the more sophisticated arrangement
permits an operator to adjust the flow of artificial heat load
to the preheating equipment based upon the heat output o the heat
source supplying heat to the preheating equipment 29. For example,
; the more sophisticated arrangement permits an operator to use a
reduced flow of artificial heat load during warm-up of the
equipment. It also permits an operator to adjust the artificial
heat load over the entire operating range of heat source capacity
should this be desired for any reason, such as for checking uni-
formity of combustion at various operating rates. The more
sophisticated method uses the temperature sensing element 24, a
temperature indicating and control unit 48, a flow rate indicating
and control unit 50, an adjustable flow control valve 52, and
a flow rate sensing unit 54. The flow rate sensing unit 54
senses the flow of artificial heat load. The flow of artificial
heat load is adjustable by means of the adjustable flow control
valve 52. The flow rate sensing unit 54 transmits a si~nal to
the flow rate indicating and control unit 50. As a result, the
flow rate indicating and control unit 50 adjusts the flow control
valve 52 to the desired flow rate of artificial heat load. The
temperature sensing element 24 senses the temperature in the
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~ os~ z~reheating equipment and the temperature condition is registered
in the temperature indicating and control unit 48.
In both the simplified method and the more sophisti-
cated method, the temperature sensing element may be a thermo-
couple means. In general, the flow rate should be in the range
of 5 to 100 gallons per minute.
Preferably, the flow rate of the artificial heat load
should provide a heat load of about 20~ to 50~ of the normal heat
output capacity of the heat source, such as the burner 10, of the
preheating equipment 29. The desired flow rate may be established
as follows. Assume that the capacity of the heat source is
60 million BTU/hr, for example. The desired flow rate is one
which will use 20 to 30 million BTU's/hour, preferably 25 million
BT~'s/hour. In the example where the artificial heat load is
water, the water is evaporated and the resultant steam is super-
heated to about 500F. at about atmospheric pressure. (Coal
drying and preheating equipment usually is operated at about at-
mospheric pressure.~ For such conditions, each pound of water
requires about 1250 BTU, and the water requirement is, therefore:
25~250 = 20,000 lbs/hr (+20%) which is about 40 gallons per
minute (+20~).
Most of the water injected into the preheating equipment
29 evaporates before it reaches the elutriation zone 16. By
keeping the heat source, such as burner 10, within its normal
range of operation, the atmosphere within the preheating equip-
:.
ment 29 will be main~ained in a safe, non-explosive condition.
Controlling the atmosphere in the preheating equipment
` 29 also prevents detrimental oxidation of the coal being preheated
by maintaining a low oxygen concentration. Keeping the oxygen
content below 5% eliminates the possibility of explosions from
all possible sources. The oxygen content is normally held below
1~ to minimize possible damage to the coking properties of the
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