The present disclosure generally relates to furnace and furnace components, and more particularly to an apparatus for regulating air flow through a port introducing air to a boiler.
The chemical recovery boiler is a part of the pulp production process. Specifically, the chemical recovery boiler helps recover and regenerate cooking liquors. The furnace of a chemical recovery boiler for burning black liquor has a front wall, a rear wall and sidewalls. Black liquor spraying devices are disposed on said walls on one or several levels. A plurality of air ports are arranged on several horizontal levels on said walls for introducing air into the furnace from an air supply. Flue gas generated in black liquor combustion is led into contact with various heat transfer devices, superheaters, the boiler bank and water preheaters (economizers) of the boiler, whereby the heat present in the gas is recovered in water, steam or mixture thereof flowing in the heat transfer devices.
Air is introduced into the boiler usually at three different levels: primary air into the bottom part of the furnace, secondary air above the primary air level, but below the liquor nozzles, and tertiary air above the liquor nozzles for ensuring complete combustion. Air is usually fed in via several air ports either from all four walls of the boiler or from two opposites walls only. More than three air levels for introducing air into the furnace may be arranged in the boiler.
In one aspect, a velocity type damper is provided for use for controlling airflow into a furnace. As will be described herein, it has been determined that in prior damper designs, the velocity of the air being introduced to the furnace diminishes at the exit of the damper, which is the result of a change in volume for the air passage from the damper to the inlet to the furnace. The damper provided by the present disclosure avoids this reduction in air velocity by reducing the change in volume between the damper exit and the inlet to the furnace. In some embodiments, the damper designs described herein can provide for increased control of the airflow and increased control of the velocity of the air being introduced to the furnace through the damper by aligning the damper blade edges, i.e., an edge of the air control surface for the damper, to the furnace wall at the inlet. As will be described herein, the damper blades, i.e., air control surfaces, may be hinged velocity plates and/or deformable diagram plates. Without being bounded by theory, it is believed that aligning the damper blade edges to the furnace wall ensures that the air flow passage between the damper and the inlet to the furnace does not include a pronounced increase in volume relative to the air flow passage through the damper.
The velocity type damper may include at least one velocity plate that is rotated about a hinged end to provide the air control surface of the damper. In one example of this embodiment, the velocity type damper includes an air port damper body for engagement to an air port opening of a furnace. The velocity type damper may include at least one velocity plate in hinged engagement to the air port damper body so that the air controlling end surface of the velocity plate is substantially aligned to a wall of the furnace at the air port opening when the velocity plate is in a fully opened position.
The velocity type damper may also have at least one deformable diaphragm to provide the air control surface of the damper. In one example of this embodiment, the velocity type damper includes an air port damper body for engagement to an air port opening of a furnace. The velocity type damper may also include at least one diaphragm damper in engagement to the air port damper body so that when deformed, the at least one diaphragm reduces the cross sectional area of the air port damper body. The at least one diaphragm is engaged to the air port damper body so that an end of the at least one diaphragm is substantially aligned to a wall of the furnace at the air port opening.
In another aspect, a method is provided for controlling airflow into a furnace that employs a velocity type damper. In one embodiment, the method for controlling airflow may include engaging a velocity type damper to an air port opening of a furnace, in which the velocity type damper includes at least one air controlling surface that is positioned proximate to a wall of the furnace at the air port opening so that air velocity exiting the at least one air controlling surface is substantially equal to the air velocity entering the air port opening to the furnace. The method may further include adjusting a cross-sectional area through the velocity type damper to control air velocity into the furnace through the air port opening.
These and other features and advantages will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.
The following description will provide details of embodiments with reference to the following figures wherein:
Reference in the specification to “one embodiment” or “an embodiment” of the present invention, as well as other variations thereof, means that a particular feature, structure, characteristic, and so forth described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrase “in one embodiment” or “in an embodiment”, as well any other variations, appearing in various places throughout the specification are not necessarily all referring to the same embodiment,
Wood pulp for papermaking is usually manufactured according to the sulfate process wherein wood chips are treated with a cooking liquor including sodium sulfide and sodium hydroxide. The wood chips and the cooking liquor, called “white liquor,” are cooked in a digester under predetermined heat and temperature conditions. After cooking, the used liquor, termed “black liquor,” containing spent cooking chemicals and soluble residue from the cook, is washed out of the pulp and treated in a recovery unit where the cooking chemicals are reclaimed. Without reclamation and reuse of the cooking chemicals, the cost of the papermaking process can be prohibitive.
In the recovery process, the black liquor is first concentrated by evaporation to a low water solution, which solution is then sprayed into the firebox of a black liquor recovery boiler, a type of chemical reduction furnace. The chemical reduction furnace is a reactor wherein the processes of evaporation, gasification, pyrolysis, oxidation and reduction all occur interdependently during recovery of the cooking chemicals. The organic materials in the black liquor, lignin and other wood extracts, maintain combustion in the firebox, and the heat produced dries and melts the spent cooking chemicals as they fall to the floor of the firebox, where they build a mound of material called a char bed. The char bed is further heated to further liquefy the chemicals into a molten smelt that flows Out of the furnace through a smelt spout to a collection tank. Concurrently, combustion heat is employed to generate steam in water walls of the boiler for use as process steam and for generating electricity.
The combustion process requires the introduction of large volumes of air into the firebox. The combustion air is distributed by means of wind boxes or ducts disposed at several levels in surrounding relation to the firebox and outside the walls of the furnace. The air is forced into the firebox from the wind boxes through a plurality of passages or air ports in the walls of the furnace, viz.: primary, secondary and tertiary air ports. The primary air ports, through which about 30 to 40 percent of the air enters the furnace, are disposed on all the walls of the firebox near the bottom of the furnace and close to the char bed. The air supplied to the primary air ports is at a comparatively low pressure in order to promote a reducing atmosphere in the burning mass of char. The secondary air ports, which are fewer in number than the primary air ports and through which about 45 percent of the air enters the furnace, are disposed around the walls of the firebox, higher than the primary air ports, and usually below the level of the entry conduits through which the black liquor is sprayed into the firebox. Air supplied through the secondary air ports is at a slightly higher pressure in order to promote burning of combustible gasses rising from the glowing mass of the char bed. While the primary air ports provide a relatively large volume of air with considerable turbulence for maintaining a fireball in the char bed, the secondary air ports are intended to provide a finer control and distribution of air above the char bed and distribute the air evenly in the black liquor spray to support the combustion thereof. Air is supplied through the tertiary air ports at a still higher pressure to promote combustion of gases rising through the firebox, the tertiary air ports being higher on the wall of the furnace than the secondary air ports.
The volume and distribution of combustion air supplied to the furnace will also vary depending on the load of the furnace and the moisture content of the liquor being reduced. The distribution and volume of air entering a furnace is conveniently adjusted by regulating means such as dampers provided in supply conduits (also referred to as “air port damper bodies”) of the wind boxes. Dampers may also be provided at various locations in the wind boxes, and individual air ports may furthermore be provided with a damper, thus making possible a selective distribution of air within each wind box, or in each wind-box passage or each air port, respectively, thereby maintaining the desired air supply in all parts of the furnace.
The present disclosure provides velocity type dampers for use fur controlling airflow into a furnace through at least one of the air ports described above. The velocity type dampers 100a, 100b, 100c, 100d, 100e of the present disclosure are depicted in
In some embodiments, the black liquor sprayed into the firebox, swirls, burns and falls toward the bottom of the firebox in the form of combustion products comprising char material and smelt. The smelt and char material contact and flow down the outer walls of the firebox and, cooled by the inflowing air, form excrescent deposits around edges of the air ports, particularly along the top edges of the air ports where the excrescent material builds up and outward under influence of air rushing through the air port. Such buildup of char material can block air flow through a port by as much as fifty percent. In addition to controlling airflow into the furnace for general operations, the velocity type dampers 100a, 100b, 100c, 100d, 100e can also adjust airflow to account for the change of air flow capacity that results from the aforementioned buildup of char material.
Air flow adjustment through the dampers 100a, 100b, 100c, 100d, 100e can be achieved by manipulating the air control surfaces of the dampers 100a, 100b, 100c, 100d, 100e to increase or decrease the cross sectional area of the pathway of the airflow through the damper. In the embodiments depicted in
In the embodiments depicted in
It has been determined that in prior damper designs that the decrease in the velocity of at the exit of the damper prior to the air being introduced to the furnace results from a change, i.e., increase, in volume of the air passage between the damper and the inlet to the furnace. More specifically, a high volume region is present from the end leaving the final air control surface of the damper. This means that although the adjustment of the damper can control air flow through the damper, control of the velocity of the jet of air through the damper is diminished by the presence of the high volume region, which limits the operational control of the damper.
Referring to
Referring to
In some embodiments, the dampers 100a, 100b, 100c, 100d, 100e can be integrated into a wind box (not shown) that is also mounted to the exterior surface of the boiler outer wall. The wind box can be a sheet metal structure that is fastened to the boiler wall and can provide support for the components of the dampers 100a, 100b, 100c, 100d, 100e such as the air port damper body 55, and the air control surfaces, such as the velocity plates 50 and the diaphragm plate 60. The wind box may also have provisions for supporting a port redder that is compatible with the dampers 100a, 100b, 100c, 100d, 100e that are described herein. The wind box encloses the air ports 70 and includes an opening to allow air to enter the wind box.
The damper 100a that is depicted in
The velocity plate 50 may he formed from a metal, such as steel, stainless steel or other alloys. The velocity plate 50 may be rigid and substantially planar in geometry. In other examples, the velocity plate 50 may include at least one curvature, which can aid in the control of air through the air port damper body 55. The edge of the velocity plate 50 opposite the edge of the velocity plate 50 that is directly connected to the hinge 51 is the end of the air control surface for the damper. Adjustment, e.g., the angle α produced by rotation, of the velocity plate 50 can be provided using hydraulic actuators, electrical actuators, pneumatic actuators and combinations thereof.
The velocity plate 50 may be positioned as close as possible to the wall of the furnace 80 near the inlet 70. In the embodiment depicted in
Although
Without a force applied to the pressure applied surface S1, the deformable air control surface 65 is positioned along a sidewall of the air port damper body 55 in an open position (OPEN). Applying a force, such as compressed air, pressurized hydraulic fluid, or a mechanical force, to the pressure applied surface Si deforms the deformable air control surface 65 to extend from the sidewall of the air port damper body 55 towards the center of the air pathway through the damper 100d. The deformable air control surface 65 extended towards the center of the air pathway to a position (REDUCED PORT) that reduces the cross-sectional area for the air pathway through the damper 100d. Removing the force, or applying an opposing force, such as a vacuum, to the pressure applied surface S1 can return the deformable air control diaphragm 65 back to an entirely open position (OPEN) for the damper, which provides the greatest cross sectional area through the air port damper body 55. It is noted that when the deformable air control diaphragm 65 is in the substantially closed (REDUCED PORT) position, the cross sectional area through the air port damper body 55 may be reduced up to 70%. In another example, when the deformable air control diaphragm 65 is in the substantially closed (REDUCED PORT) position, the cross sectional area through the air port damper body 55 may be reduced up to 50% in an even further example, when the deformable air control diaphragm 65 is in the substantially closed (REDUCED PORT) position, the cross sectional area through the air port damper body 55 may be equal to 25% or less. By controlling the cross-sectional area through the air port damper body 55, the deformable air control diaphragm 65 controls the air flow through the damper 100d.
The diaphragm plate 60 may be positioned as close as possible to the sidewall of the furnace 80 near the inlet 70. The deformable air control diaphragm 65 of the diaphragm plate 60 may be formed from a deformable sheet metal, such as steel, stainless steel or an alloy. In other embodiments, the deformable air control diaphragm may be composed of a composite material. In one embodiment, the diaphragm plate 60 is connected to the sidewall of the air port damper body 55 on at least two opposing ends of the deformable sheet metal 65.
Although
The dampers 100a, 100b, 100c, 100d, 100e that are described herein may be used in a method for controlling airflow into a furnace 80. The method may include engaging a velocity type damper to an air port opening 70 of a furnace 80, as depicted in
The method for controlling airflow into a furnace 80 further includes adjusting a cross-sectional area through the velocity type damper 100a, 100b, 100c, 100d, 100e to control air velocity into the furnace 80 through the air port opening 70.
In some embodiments, the method employs a velocity type damper 100a, 100b, 100c. that includes an air port damper body 55 is engaged to the air port opening 70 of the furnace 80, and the at least one velocity plate 50 in hinged engagement to the air port damper body 55 so that an end of the air controlling surface of the at least one velocity plate 50 is substantially aligned to the sidewall of the furnace 80 at the air port opening 70 when the at least one velocity plate 50 is in a fully opened position (OPEN), as depicted in
In some embodiments, the method employs a velocity type damper 100d, 100e that includes an air port damper body 55 and at least one diaphragm plate 60, as depicted in
It is further noted that the damper designs 100a, 100b, 100c, 100d, 100e may be integrated with a port rodder. Port rodders are provided on recovery boilers to clean the air ports or openings, keeping them free from combustion by-products and other deposits commonly referred to as char. By frequently cleaning the port openings, air flow is uniform from all ports into the boiler thus facilitating a high rate of heat transfer and optimum operation.
A rodder generally includes a tip or cutter mounted on the end of a ram which is in turn connected to an actuator which causes the ram to be extended or retracted, e.g., into the air port 70. One such actuator would be a pneumatic cylinder. Extension and retraction of the cylinder causes the cutter to move in and out of the port, e.g., air port 70. When extended into the air port 70, the cutter contacts and dislodges the char by cutting and/or pushing it through the port and into the boiler 80.
It will also be understood that when an element is referred to as being “on” or “over” another element, it can be directly on the other element or intervening elements can also be present. In contrast, when an element is referred to as being “directly on” or “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements can be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.
It is to be appreciated that the use of any of the following “/”, “and/or”, and “at least one of”, for example, in the cases of “A/B”, “A and/or B” and “at least one of A and B”, is intended to encompass the selection of the first listed option (A) only, or the selection of the second listed option (B) only, or the selection of both options (A and B). As a further example, in the cases of “A, B, and/or C” and “at least one of A, B, and C”, such phrasing is intended to encompass the selection of the first listed option (A) only, or the selection of the second listed option (B) only, or the selection of the third listed option (C) only, or the selection of the first and the second listed options (A and B) only, or the selection of the first and third listed options (A and C) only, or the selection of the second and third listed options (B and C) only, or the selection of all three options (A and B and C). This can be extended, as readily apparent by one of ordinary skill in this and related arts, for as many items listed.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly, indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” and the like, can be used herein for ease of description to describe one element's or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the term “below” can encompass both an orientation of above and below. The device can be otherwise oriented (rotated 9( )degrees or at other orientations), and the spatially relative descriptors used herein can be interpreted accordingly. In addition, it will also be understood that when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or one or more intervening layers can also be present.
It will be understood that, although the terms first, second, etc., can be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. Thus, a first element discussed below could be termed a second element without departing from the scope of the present concept.
Having described preferred embodiments of a method, structures and systems for velocity dampers for a recovery boiler, it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments disclosed which are within the scope of the invention as outlined by the appended claims. Having thus described aspects of the invention, with the details and particularity required by the patent laws, what is claimed and desired protected by Letters Patent is set forth in the appended claims.
This application is a divisional application of U.S. application Ser. No. 16/747,174, entitled “VELOCITY DAMPER FOR A RECOVERY BOILER,” filed on Jan. 20, 2020, which claims the benefit of U.S. Provisional Patent Application No. 62/797,522 filed on Jan. 28, 2019, the disclosures of which are incorporated herein in their entireties by reference.
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Number | Date | Country | |
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20220065447 A1 | Mar 2022 | US |
Number | Date | Country | |
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62797522 | Jan 2019 | US |
Number | Date | Country | |
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Parent | 16747174 | Jan 2020 | US |
Child | 17524296 | US |