Heating – Processes of heating or heater operation – Including passing – treating or conveying gas into or through...
Reexamination Certificate
2000-04-20
2002-09-24
Lu, Jiping (Department: 3749)
Heating
Processes of heating or heater operation
Including passing, treating or conveying gas into or through...
C432S019000, C432S036000, C432S037000, C432S047000, C432S146000, C432S149000, C432S159000, C065S029210, C065S162000, C065SDIG001
Reexamination Certificate
active
06454562
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to furnaces, and in particular to control of furnace temperatures.
2. Brief Description of the Related Art
An increased demand for flat glass (produced in float furnaces) all over the world is expected to become the major driving force for oxidant-fuel (“oxy”) boosting technology. Joshi, M. L., et al, “Oxygen-fuel boosting as applied to float glass furnaces”, Presented at the American Flame Research Committee, 1996, AFRC Spring Members Technical Meeting, Orlando, Fla., May 6-7, 1996. Due to relatively long engineering and construction phases for green field float plants, an effective on-the-fly oxy-boosting solution to meet immediate market needs is considered to be both a cost-effective and low-risk option by those in industry.
Typical float furnaces are side-fired regenerative types with five to eight ports per side.
FIG. 1
illustrates a typical float glass tank
10
with six ports
22
. The furnace
10
includes a sidewall
12
, an interior chamber or space
14
, and an entrance or doghouse
16
. A waist section
18
receives the glass flow downstream of the interior chamber
14
, from which the glass moves to a conditioning end
20
of the furnace. Due to the large dimensions of the tank, only cross firing is possible.
FIG. 1
illustrates a six-port furnace with one regenerator chamber
24
assigned for each port. The regenerator chambers are used for preheating combustion air to between about 2200° F. (1204° C.) and about 2400° F. (1316 °C.). A 20 to 30 minute cyclic process for heat recovery is typically applied using the exhaust gases. Air-fuel burners (not illustrated) are installed on each port with 2 to 3 burners per port. The burners are fired “under port,” “through port,” or using “side of port” firing configuration.
The furnace is also provided with oxy-boost burners
26
. The common oxy-boost system is “port
0
” boosting, meaning that the oxy-boost burners
26
are positioned between the charging wall at doghouse
16
and the first port
22
. Typically, standard oxy burners or high performance staged oxy burners are installed at the port
0
location. The oxy-boost firing capacity can be as much as 5% to 20% of the total melter firing capacity. The oxy-boost process is used to attempt to increase the furnace pull rate, increase glass quality (e.g., reduced number of seeds, stones, etc., per ton of glass) at the same pull rate or at higher pull rate, decrease or maintain furnace peak refractory temperatures at the same or higher pull rate, decrease or maintain regenerator chamber temperatures at the same or higher pull rate, avoid plugging problems in the regenerator, as well as overcoming other difficulties which can not be achieved by the air-fuel firing of the port burners alone.
The challenge to successful use of oxy-boost technology is optimum firing of oxy burners at port
0
(or other strategic locations), coupled with specific (measured) changes in the air-fuel firing rate of the port burners. Thus, prior systems have attempted to optimize the overall heat-input profile to yield the above benefits.
The furnace operators at flat glass plants have attempted this optimization process by trial and error methods. For example, a human operator may reduce the air-fuel firing rate incrementally for each port, and subsequently increase the oxy-boost firing rate until the desired furnace refractory temperatures and profile, desired glass bottom temperatures and profile, required pull rate, and target glass quality numbers are obtained.
The difficulty in prior furnace operations is compounded due to the fact that oxy-boost control systems are not the same as, integrated with, or communicate with the air-fuel combustion control. Thus, retrofit oxy-boost systems are generally a stand-alone type and must be operated separately to manage the overall furnace operation. In many instances, the changes in oxyboost firing and air-fuel firing are not complementary and can upset the furnace operation. This can result in poor product quality or possible overheating of critical furnace refractory during this period.
The set point adjustments to achieve the desired furnace crown temperatures and glass bottom temperatures during oxy-boosting can take several weeks to several months, depending on the furnace and expertise level of the operator. A longer furnace settling time means greater loss in furnace productivity, poor product quality, and higher operating costs. Furthermore, if the furnace pull rate is changed for some reasons (say, due to changes in market demand), the whole adjustment procedure has to be repeated and new set points have to be determined for both oxy-boosting and air-fuel firing.
SUMMARY OF THE INVENTION
According to a first exemplary embodiment, a system useful for heating a product comprises a furnace having a sidewall and an interior space, at least one oxy-fuel burner positioned to direct a flame into the furnace interior space, a source of an oxidant in fluid communication with the at least one oxy-fuel burner, a source of fuel in fluid communication with the at least one oxy-fuel burner, a first valve set interposed between the oxy-fuel burner and the sources of fuel and oxidant, the first valve set operable to control the flow of oxidant and fuel to the at least one oxy-fuel burner, at least one air-fuel burner positioned to direct a flame into the furnace interior space, a source of air in fluid communication with the at least one air-fuel burner, a source of fuel in fluid communication with the at least one air-fuel burner, a second valve set interposed between the air-fuel burner and the sources of fuel and air, the second valve set operable to control the flow of air and fuel to the at least one air-fuel burner, at least one furnace condition input device generating at least one output signal, and a controller in communication with the at least one furnace condition input device to receive the at least one furnace condition input device output signal, the controller having a setpoint value for the at least one furnace value, the controller generating at least one control signal based on a comparison of the output signal and the setpoint, the controller being in communication with the first valve set to communicate the at least one control signal to the first valve set to set the flow rates of oxidant and fuel through the first valve set and to the oxy-fuel burner.
According to a second exemplary embodiment, a process of operating a furnace comprises the steps of firing an oxy-fuel burner into the furnace to heat a load, firing an air-fuel burner into the furnace to heat the load, measuring a furnace process parameter, inputting the measured process parameter into a controller, the controller having at least one setpoint for the measured process parameter, and controlling both the firing of the oxy-burner and the firing of the air-fuel burner with the controller based on a comparison of the measured process parameter and the at least one setpoint value.
Still other objects, features, and attendant advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description of embodiments constructed in accordance therewith, taken in conjunction with the accompanying drawings.
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patent: 4368034 (1983-01-01), Wakamiya
patent: 4473388 (1984-09-01), Lauwers
patent: 4480992 (1984-11-01), Okamoto
patent: 4577278 (1986-03-01), Shannon
patent: 4657507 (1987-04-01), Kohama et al.
patent: 5335164 (1994-08-01), Gough, Jr. et al.
patent: 5513098 (1996-04-01), Spall et al.
patent: 5687077 (1997-11-01), Gouch, Jr.
patent: 5954498 (1999-09-01), Joshi et al.
patent: 6055524 (2000-04-01), Cheng
patent: 90/12760 (1990-11-01), None
patent: WO 00/23856 (2000-04-01), None
Gough, B., et al., “Predicitive-Adaptive Temperature Control of Molten Glass”, Mar. 29, 2000, Brainwave Bulletin, Universal Dynamics Technologies, Inc., pp. 1-10.
Gough, B
Joshi Mahendra L.
Marin Ovidiu
L'Air Liquide-Societe' Anonyme a' Directoire et C
Lu Jiping
Russell Linda K.
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