Background of the Invention
[0001] This present invention relates to an auxiliary flue to vent harmful pollutants and
contaminants during secondary operations in furnaces. The invention is described in
the preferred atmosphere of furnace with bi-directional regenerative burners.
[0002] Furnaces have been utilized for centuries for heating objects. The stereotype furnace
is an enclosure directly heated by the products of combustion from a burner before
discharge of such products through a stack. This furnace serviceably heats anything
in the enclosure. This type of furnace is acceptable to persons who do not particularly
concern themselves with economies of operation, temperature stabilities or with governmental
pollution regulations. However, persons with concerns in these areas cannot tolerate
the operating characteristics of stereotype furnaces. With increasing foreign competition
it is important that furnaces operate efficiently - and this calls for regenerative
or recuperative burners. With ever tightening manufacturing tolerances it is important
that the temperature of the furnaces be tightly controlled - and this calls for burners
performing as designed. With governmental pollution regulations it is important that
furnaces operate reliably and consistently - and this calls for furnaces uniformly
meeting of all operating parameters. The stereotype furnace is unable to always meet
these requirements due to many factors - one of which is the build-up of pollution
and contaminants within the burners, furnace, pollution control equipment and stacks
due to secondary treatment manufacturing operations on the material within the furnace.
These contaminants also limit the in-service life of furnaces by plugging up the regenerative
beds and other parts of the furnace.
Summary of the Invention
[0003] The invention of this present application is directed towards alleviating the build-up
of pollution and contaminants from secondary manufacturing operations by venting them
separately of the ordinary production discharge of the products of combustion of the
furnace burner.
[0004] It is an object of this invention to avoid the problems associated with contaminants
from secondary operations on furnace parts.
[0005] It is an object of this invention to increase the service life of regenerative burners
by reducing the plugging of the regenerative beds of such burners.
[0006] It is an object of this invention to increase the usability and reliability of regenerative
furnaces.
[0007] It is an object of this invention to increase the efficiency of regenerative burners.
[0008] Other objects and a more complete understanding of the invention may be had by referring
to the following specification and drawings in which:
Brief Description of the Drawings
[0009]
FIGURE 1 is a block diagram representation of the flow chart operation of a regenerative
furnace incorporating the alternate flue of the invention.
FIGURE 2 is a conceptual block diagram of a regenerative furnace incorporating the
alternate flue of the invention.
FIGURES 3 - 5 are representations of the conceptual block diagram of FIGURE 2 showing
the furnace under varying operating conditions.
FIGURE 6 is a block diagram representation of a typical regenerative furnace, and
FIGURE 7 is a graph of the operational characteristics of the alternate flue furnace
of FIGURE 2 in contrast with the operational characteristics of a typical regenerative
furnace.
Detailed Description
[0010] The regenerative furnace 10 of the figures includes a furnace chamber 11, two regenerative
burners 12, 13 and an auxiliary flue 14.
[0011] The furnace chamber 11 is designed to hold the material to be heated. The furnace
chamber 11 shown in the preferred embodiment is designed to process aluminum and as
such is a refractory chamber approximately fourteen feet long, nine feet wide and
seven feet high having a volume of about 900 cubic feet. The melt rate for the furnace
is some twenty-thousand pounds an hour with a charge rate (for aluminum) of some one-hundred
and sixty-thousand pounds for every twenty-four hour period.
[0012] In a typical installation this furnace chamber may be heated by a pair of regenerative
burners 112, 113 such as shown in FIGURE 6. These two regenerative burners 112, 113
are selectively alternatively connected to an air blower 115 and exhaust fan 116 through
the four way valve 117. The burner 112, 113 connected to the air blower 115 is fired
with the products of combustion thereof as well as any pollution and contaminants
produced during the particular manufacturing operation discharging through the inactive
opposing burner 112, 113, the exhaust fan 116 and the stack 118. This type of operation
- 100% of everything discharged at all times through the opposing inactive burner
112, 113 and stack 118 - is plagued with problems such as plugging (due to the contaminants
from secondary operations building up during discharge), inefficient operation (due
to the use of a single sized discharge passage) and shortened service life (due to
heat mal-distribution attributable to contaminant buildup). These problems are undesirable.
The invention of this present application is directed towards alleviating these problems.
[0013] The preferred embodiment of the invention of this present application is described
in the atmosphere of a furnace for melting aluminum. If all an aluminum furnace did
was melt scrap, the typical regenerative furnace of FIGURE 6 would be satisfactory;
it is possible to optimize a furnace for a particular single operation, especially
when that operation is providing heat (i.e. avoid the problems from secondary operation's
contaminants by never doing the secondary operations in the first place). However,
unfortunately for the typical furnace, there are multiple operations involved in most
furnaces including the example aluminum furnace. One operation (in an aluminum furnace),
fluxing, is particularly damaging to regenerative furnaces. In this fluxing operation
the operator adds a substance to the melt to facilitate the fusing of the metals in
the furnace. In our example aluminum furnace some eleven-thousand two-hundred pounds
of flux is used in two periods over the twenty-four hour furnace cycle. The flux itself
consists of five-thousand three-hundred seventy-six pounds of sodium chloride, an
equal amount of potash and four-hundred forty-eight pounds of aluminum fluoride. This
fluxing operation produces contaminants that quickly plug up the beds of the regenerative
burners in the furnace. (The sodium chloride makes magnesium chloride, sodium chloride
and aluminum chloride. The aluminum fluoride removes magnesium from aluminum and makes
magnesium chloride.) With this fluxing operation, a typical furnace could be operated
for only a few charging cycles before the regenerative beds would plug up from the
contaminants produced during this secondary operation. The graph of FIGURE 7 plots
the increase in pressure across a particular bed against the number of charging cycles.
In this furnace the pressure increases from an initial six inches of water to twelve
inches in only two or three charging cycles (line 140). As twelve inches is the plugging
limit 41 for the particular bed charted, the beds have to be removed for cleaning
after this same number of cycles (at 142). Removal entails shutting down the furnace
for a cool-down and start-up period in addition for the actual time of cleaning. This
time, about two hours per removal, is forever lost to manufacture - compromising the
efficiency of a typical furnace severely. This inefficiency is directly related to
the contaminant build-up in the beds that occurs during the secondary operation. Industry
puts up with this inefficiency due to the lack of alternatives.
[0014] The alternate flue of this present invention provides a preferable alternative to
this typical installation.
[0015] The furnace chamber 11 of the present invention is provided with an auxiliary vent
14. This vent 14 allows the pollution and contaminants from secondary operations to
be vented from the furnace chamber 11 otherwise than through the regenerative burners
12, 13 and association components. This venting is selectively operated to optimize
the operation of the furnace. (FIGURE 1)
[0016] Sometime during the normal operation of a furnace an operator conducts a secondary
operation on a material in a furnace chamber 11 (50). At the time of the secondary
operation, the operator should have a pretty good idea of whether or not the secondary
operation should or should not produce contaminants (based upon past experience, manufacturing
guidelines and other sources). The operator should therefor know whether contaminants
are likely or unlikely from the secondary operation.
[0017] If contaminants are likely (51) (as for example in the fluxing operation in the example
aluminum furnace), the operator opens the auxiliary vent 14 (52) and operates the
burner controls to fire both burners 12, 13 simultaneously (53). (The firing of both
burners is preferred due to its optimization of burn-off of the contaminants and in
the inherent elimination of the need to valve or otherwise protect the inactive burner
and its regenerative bed from the contaminants. The same effect, albeit at a slower
rate, would also occur if only one burner was used with the vent 14.) If the secondary
operation produces contaminants (as expected in a fluxing operation - 54) the operator
continues firing the burners 12, 13 until the auxiliary flue 14 vents all contaminants
from the secondary operation (55). At this point, or if the firing of both burners
produces an unexpected result of no contaminants (56) (totally unexpected in a fluxing
operation but possible with other secondary operations), the operator closes the auxiliary
vent 14 (57) and operates the burner controls again in the normal production manner
(60) - (in this instance alternating single burner operation).
[0018] If contaminants are unlikely (61) (as for example in a purging of an aluminum furnace),
the operator insures that the vent 14 is closed (62) and continues the normal operation
of the furnace (63). If the continued normal operation of the furnace produces an
unacceptable (and unexpected) level of contaminants (64) (i.e. a pocket of flux arises
to the surface of the melt of aluminum) the operation immediately opens the auxiliary
vent 14 (52) and proceeds as if contaminants were originally expected. If the firing
of the burner produces no contaminants (65), the operator continues the normal furnace
operation (60).
[0019] During the normal operation of the furnace it is possible that a fluxing or other
secondary operation will again take place in the furnace. If so the operator treats
the furnace immediately after this new secondary operation as if it was the first,
making again the decision of whether or not contaminants are likely (from the new
secondary operation) and proceeding accordingly (i.e. returning to choice 51, 61).
[0020] With a furnace operation including the auxiliary venting of contaminants from secondary
operations, the pressure drop across the regenerative burners 12, 13 remains relatively
constant even through repeated charging cycles (line 40 in FIGURE 7). In a furnace
equivalent to that of our previous example but utilizing the auxiliary flue 14 of
the invention for venting contaminants from a secondary fluxing operation, the furnace
can be operated for many times the number of charging cycles (14 instead of 2 in the
graph) before the plugging limit of twelve inches of water is realized and the regenerative
bed must be removed for cleaning (at 42). This increase in number of charging cycles
is directly reflected in the overall operating efficiency of the furnace.
[0021] The operation of this furnace leaves a large measure of discretion with and responsibility
on the operator of the furnace. However even the most conscious operator cannot produce
a perfect operation, if only because some contaminants from secondary operations are
invisible to human senses. The operation of the furnace can be facilitated to virtual
perfection by the use of sensors to measure the various levels of contaminants and
by the use of automatic controls dependent on such sensors to operate the furnace.
In this regard the only decision the operator would have to make would be whether
or not contaminants are likely (51, 61) from the secondary operation (and even this
decision can be made by a carefully programmed computer). A preferred system designed
with this in mind is shown in FIGURE 2. The preferred furnace is fourteen feet long,
nine feet wide and seven feet deep (900 cubic feet total). The furnace is made of
refractory brick. The burners for this furnace are 13.5 million BTU (at 6˝ wc) regenerative
burners. The burner intake blower is a 20 horsepower 12 ounce per square inch guage
(O.S.I.G.) blower while the exhaust blower is a slightly large 25 horsepower 20 O.S.I.G.
blower.
[0022] The automatic control system of FIGURE 2 incorporates a microprocessor control 20
with the preferred furnace 10. In this automatic system, the operator's main control
over the furnace is via the operational parameters and the sensor limits the programs
into the microprocessor (via the keyboard 21).
[0023] In the preferred embodiment the operator's primary input would be to program in the
limits for the contaminant sensors 22, 23 and 24.
[0024] After initiation of the secondary operation and upon contaminant sensors 22, 23 at
the openings of the regenerative burners 12, 13 sensing contaminants at or above this
programmed level, the microprocessor 20 would automatically manipulate the intake
30-31, discharge 32-33, vent 34 and burner operation valves 35-36 to vent the contaminants
from the secondary operation otherwise than through the regenerative burners 12, 13.
Ordinarily this would mean closing the exhaust valves 32-33, opening the intake 30-31
and burner valves 35-36 and opening the vent valve 34 (as shown in FIGURE 2). Both
burners 12, 13 would then operate with all products of combustion and contaminants
being discharged through the vent 14. Note that since the blower 15 is preferably
sized to match normal production operating parameters - i.e. meeting 100% of the operating
needs of a single burner at one time and then with the exhaust blower 16 also in operation
- this simultaneous burner 12-13 operation may tax the capabilities of the blower
15: the burners 12, 13 would have a restricted and inefficient operation. As our concern
is more with damage due to contaminants from a secondary operation than efficient
production-type operation, this restricted operation is acceptable during the limited
period of the secondary operation. If appropriate this restricted operation could
be avoided by reducing the level of burner operation, through the use of an auxiliary
supplementary means such as a high speed capability to the blower 15, via the use
of but a single burner (still venting via vent 14) or otherwise adapting the system
to meet the needs of the system during the venting operation. The venting of contaminants
from the secondary operation would continue until the level of contaminants being
discharged through the vent 14 is at an acceptable level (as determined by the sensor
24 later described). During this period of discharge through the vent 14, the contaminants
are preferably treated by a pollution control system (electrostatic participator for
example) before discharge into the air. A separate pollution control system 18 is
preferred in that it can be designed especially for the vented contaminants from the
secondary operation (instead of the normally different range of operational pollutants).
(The existing pollution system 17 for the furnace could also be used instead of/in
addition to the separate system 18).
[0025] The vent 14 remains open and the furnace 10 in its venting mode until the venting
sensor 24 determines that the level of contaminants being vented from the secondary
operation has reached the level the operator has programmed as acceptable. At this
time the microprocessor 20 would automatically manipulate the intake 30-31, discharge
32-33, vent 34 and burner operation valves 35-36 to control the operation of the furnace
10 in its typical manner (i.e. alternating operation of the regenerative burners 12,
13 with the inactive burner 12, 13 used as a discharge as shown in FIGURES 3 and 4).
[0026] The microprocessor 20 is quick enough to alter the settings of the controls of the
furnace 10 virtually immediately in response to the sensors 22, 23, 24. This type
of immediate operation could disturb the functional efficiency of the furnace during
the secondary operation (by changing its mode on even transitory contaminant levels
within the furnace) and its longevity (by operating the controls repeatedly at frequent
intervals). To avoid the problems that may be associated with the instantaneous response
of the microprocessor 20, it is preferred that some sort of a delay be incorporated,
ideally limiting the operation of the controls until the level of contaminants has
been above (or below) the programmed level for a certain period of time or until the
expected contaminants from the secondary operations have had a sufficient opportunity
to appear. The period of time would be chosen as a compromise between the physical
damage caused by the contaminants vs. the potential loss of the operational production
efficiency of the furnace (i.e. damage to the discharge passage through the burners
12, 13 against the cost of the loss of efficiency regeneration). Therefor, although
the invention has been described in its preferred form with a certain degree of particularity,
it is to be understood that numerous changes may be made without deviating from the
invention as hereinafter claimed:
1. In a furnace with a burner heating a furnace chamber having an operational discharge
and the operation of the furnace occasionally including a secondary operation producing
physical contaminants harmful to part of the operational discharge, an improvement
comprising an auxiliary vent and means to selectively operate said auxiliary vent
to allow the physical contaminants from the secondary operation to depart the furnace
chamber independently of the part of the operational discharge of the furnace that
would be harmed by the physical contaminants.
2. The improved furnace of claim 1 wherein the furnace utilizes regenerative burners
and the part of the operational discharge is through an inactive regenerative burner.
3. The improved furnace of claim 1 wherein the contaminants are customarily produced
in an externally controlled secondary operation in the furnace and characterized in
that said auxiliary vent is open on initiation of the externally controlled secondary
operation in the furnace.
4. The improved furnace of claim 3 wherein there are two regenerative burners heating
a furnace chamber with the burner alternatively firing into and discharging products
of combustion from the furnace chamber and characterized in that the two burners are
both fired during the period of open operation of said auxiliary vent.
5. In a furnace with two regenerative burners alternately heating a furnace chamber
with products of combustion discharged thereinto, the products of combustion operationally
discharged form the furnace chamber through an inactive burner, and the secondary
operation in the furnace producing physical contaminants harmful to the operational
products of combustion discharge through the inactive burner, the improvement of an
auxiliary vent, means to selectively operate said auxiliary vent to allow the physical
contaminants from the secondary operation to depart the furnace chamber independently
of the inactive burner and means to selectively limit the operational discharge of
the products of combustion through the inactive burner such that the contaminants
from the secondary operation and products of combustion are discharged fro the furnace
chamber through said auxiliary vent during the period of the secondary operation.
6. The improved furnace of claim 5 characterized in that said means to selectively
limit the operational discharge of the products of combustion through the inactive
burner comprises the firing of such inactive burner.
7. The improved furnace of claim 5 wherein the contaminants are customarily produced
in an externally controlled secondary operation in the furnace and characterized in
that said auxiliary vent is open on initiation of the externally controlled secondary
operation in the furnace.
8. The improved furnace of claim 5 characterized by the addition of a sensor means
to sense the level of contaminants in the furnace chamber during the secondary operation
and said means to selectively operate said auxiliary vent is responsive to said sensor
means.
9. The improved furnace of claim 5 wherein the operational discharge from the furnace
chamber through an inactive burner includes an exhaust blower and characterized by
the addition of means to deactivate the exhaust blower during the operation of said
auxiliary vent.
10. An improved method for operating a furnace having a burner and an operational
discharge, the operation of the furnace occasionally including a secondary operation
producing physical contaminants, the method comprising the steps of firing the burner
with the operational discharge limited and an auxiliary flue open during the period
of production of the physical contaminants in the secondary operation.
11. The improved method of claim 10 wherein the operational discharge is through an
inactive burner and characterized in that the operational discharge is limited by
the firing of the burner the operational discharge is through.
12. The improved method of claim 10 wherein there is an exhaust blower that pulls
air through operational discharge and characterized in that said exhaust blower does
not pull air through the operational discharge substantially during the time the auxiliary
flue is open.
13. An improved method of operating a furnace having two regenerative burners alternately
firing into and discharging products of combustion from a furnace chamber, the operation
of the furnace occasionally including a secondary operation producing physical contaminants
harmful to the discharge passage through the inactive burner, the method comprising
the step of firing one burner while limiting the discharge through the other burner
and opening an auxiliary flue during the period of production of the physical contaminants
in the secondary operation with the result that the harmful physical contaminants
from the secondary operation are discharged from the furnace chamber through the auxiliary
flue instead of the inactive burner.
14. The method of claim 13 characterized in that the discharge through the inactive
burner is limited by the firing of such burner.
15. The improved method of claim 13 wherein there is an exhaust blower that pulls
air through operational discharge and characterized in that said exhaust blower does
not pull air through the operational discharge substantially during the time the auxiliary
flue is open.
16. The method of claim 13 characterized in that the operation of the auxiliary vent
is under the control of a sensor that determines the level of physical contaminants
in the furnace chamber during the secondary operation.