Combustion – Process of combustion or burner operation – Controlling or proportioning feed
Reexamination Certificate
1999-11-09
2001-04-10
Lazarus, Ira S. (Department: 3743)
Combustion
Process of combustion or burner operation
Controlling or proportioning feed
C431S019000, C431S089000
Reexamination Certificate
active
06213758
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to burners, and more particularly to a method and apparatus for regulating the ratio of air to fuel in the burner to optimize the burner performance.
BACKGROUND OF THE INVENTION
In drying a moving web of material, such as paper, film or other sheet material, it is often desirable that the web be contactlessly supported during the drying operation, in order to avoid damage to the web itself or to any ink or coating on the web surface. A conventional arrangement for contactlessly supporting and drying a moving web includes upper and lower sets of air bars extending along a substantially horizontal stretch of the web. Heated air issuing from the air bars floatingly supports the web and expedites web drying. The air bar array is typically inside a dryer housing which can be maintained at a slightly sub-atmospheric pressure by an exhaust blower that draws off the volatiles emanating from the web as a result of the drying of the ink thereon, for example.
One example of such a dryer can be found in U.S. Pat. No. 5,207,008, the disclosure of which is hereby incorporated by reference. That patent discloses an air flotation dryer with a built-in afterburner, in which a plurality of air bars are positioned above and below the traveling web for the contactless drying of the coating on the web. In particular, the air bars are in air-receiving communication with an elaborate header system, and blow air heated by the burner towards the web so as to support and dry the web as it travels through the dryer enclosure.
Regenerative thermal apparatus is generally used to incinerate contaminated process gas. To that end, a gas such as contaminated air is first passed through a hot heat-exchange bed and into a communicating high temperature oxidation (combustion) chamber, and then through a relatively cool second heat exchange bed. The apparatus includes a number of internally insulated, heat recovery columns containing heat exchange media, the columns being in communication with an internally insulated combustion chamber. Process gas is fed into the oxidizer through an inlet manifold containing a number of hydraulically or pneumatically operated flow control valves (such as poppet valves). The process gas is then directed into the heat exchange media which contains “stored” heat from the previous recovery cycle. As a result, the process gas is heated to near oxidation temperatures by the media. Oxidation is completed as the flow passes through the combustion chamber, where one or more burners are located (preferably only to provide heat for the initial start-up of the operation in order to bring the combustion chamber temperature to the appropriate predetermined operating temperature). The process gas is maintained at the operating temperature for an amount of time sufficient for completing destruction of the volatile components in the process gas. Heat released during the oxidation process acts as a fuel to reduce the required burner output. From the combustion chamber, the process gas flows through another column containing heat exchange media, thereby cooling the process gas and storing heat therefrom in the media for use in a subsequent inlet cycle when the flow control valves reverse. The resulting clean process gas is directed via an outlet valve through an outlet manifold and released to atmosphere, generally at a slightly higher temperature than inlet, or is recirculated back to the oxidizer inlet.
According to conventional combustion science, each type of burner flame (e.g., premix flame, diffusion flame, swirl flame, etc.) burns with a different optimal burner pressure ratio of fuel to combustion air, by which optimal stoichiometric low emission concentrations in the burner flue gas appear. It is therefore important to control or maintain the desired optimal burner fuel/air pressure ratios of the burner. Failure to closely regulate the burner air/fuel ratio over the range of burner output can lead to poor flame quality and stability (flameout, yellow flames, etc.) or excessive pollution (high NO
x
, CO).
To that end, U.S. Pat. No. 4,645,450 discloses a flow control system for controlling the flow of air and fuel to a burner. Differential pressure sensors are positioned in the air flow and gas flow conduits feeding the burner. Optimal differential pressures of the air and fuel flow are determined through experimentation and flue gas analysis and stored in a microprocessor. These optimal values are compared to measured values during operation, and the flow of air and/or fuel to the burner is regulated based upon that comparison by opening or closing respective valving. This system does not sense the back pressure on the burner. It also generates a fuel flow “signal” indicative of the rate of fuel into the burner rather than through the burner.
Mechanical valves used in conventional systems are connected by adjustable cams and linkages to control the volumetric flow rates of the air and fuel. However, if the air density changes due to atmospheric pressure and/or temperature variations, the air fuel ratio is upset. In addition, mechanical valves are subject to wear and binding of the cams and linkages over time, and considerable skill is required to adjust the device. Systems which use mass flow measuring devices are cost prohibitive.
It is therefore an object of the present invention to optimize the mix of fuel and air in a burner.
It is a further object of the present invention to provide a control system for a burner and thereby increase the efficiency of the burner.
It is another object of the present invention to reduce the flue gas emissions of a burner.
SUMMARY OF THE INVENTION
The problems of the prior art have been overcome by the present invention, which provides a control system and method for regulating the air/fuel mix of a burner for a web dryer or a regenerative or recuperative oxidizer, for example. Differential air pressure is monitored between the air chamber of the burner and the enclosure into which the burner fires (such as a flotation dryer or the combustion chamber of a regenerative thermal oxidizer). Fuel flow is monitored by a differential pressure measurement between the fuel chamber of the burner and the enclosure into which the burner fires. These measurements are compared to predetermined values, and the fuel flow and/or air flow to the burner is regulated accordingly. Regulation of the air flow is achieved with a combustion blower with a variable speed drive controlled motor which has both acceleration and deceleration control, rather than with a damper to achieve faster and more accurate burner modulation and to use less electrical energy. In addition, the preferred drive should incorporate dynamic braking technology for tighter control. Dynamic braking is desired for rapid dissipation of high DC bus voltages that are generated when the motor is rapidly slowed down. The excess voltage is applied to the braking resistors, allowing the motor to slow down faster. The present invention uses the burner housing itself to provide a direct measurement of the air and fuel flow rates, thereby eliminating expensive flow measuring devices.
REFERENCES:
patent: 1174003 (1916-02-01), Gibson
patent: 1620240 (1927-03-01), Smoot
patent: 1736752 (1929-11-01), Smith
patent: 1736753 (1929-11-01), Smith
patent: 2197171 (1940-04-01), Annin
patent: 2220837 (1940-11-01), Donaldson, Jr.
patent: 2777289 (1957-01-01), Boucher et al.
patent: 2963082 (1960-12-01), Binford et al.
patent: 3070149 (1962-12-01), Irwin
patent: 3164201 (1965-01-01), Irwin
patent: 3269448 (1966-08-01), Martin
patent: 3373007 (1968-03-01), Ticknor
patent: 3602487 (1971-08-01), Johnson
patent: 3694137 (1972-09-01), Fichter et al.
patent: 3792330 (1974-02-01), Ottoson
patent: 3815002 (1974-06-01), Clemente et al.
patent: 3916276 (1975-10-01), Ottoson
patent: 3968489 (1976-07-01), Richards et al.
patent: 4033505 (1977-07-01), Lutes et al.
patent: 4067684 (1978-01-01), McInerney
patent: 4097218 (1978-06-01), Womack
patent: 4252300 (1981-02-01), Herder
patent: 42603
Bria Michael P.
Tesar Michael G.
Bittman Mitchell D.
Lazarus Ira S.
Lee David
Lemack Kevin S.
Megtec Systems Inc.
LandOfFree
Burner air/fuel ratio regulation method and apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Burner air/fuel ratio regulation method and apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Burner air/fuel ratio regulation method and apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2468251