Claims:1. A self adjusting radial seal arrangement (1) for rotary air preheater (RAPH), encompassing the following:
a) seal mount (10) comprising the bi-metallic strip (16) as an integral part and runs along the radial length of diaphragm plate (8) with radial seals (2) being attached to the top of the seal mount (10);
b) middle flat plates (11) placed between said seal mount (10) and said diaphragm plate (8) and firmly attached with said diaphragm plate (8) from in-board end (8a) to out-board end (8b);
c) lateral guides (12) placed at regular intervals on said diaphragm plate (8); and
d) a protector angle arrangement (13) placed at said outboard end (8b) of said diaphragm plate (8), comprising top protector angle (13a) and bottom protector angle (13b),
wherein said seal mount (10) is bolted with said middle flat plates (11) and said diaphragm plate (8) only at in-board end (8a) and remaining portion of said seal mount (10) is allowed to slide freely between said middle flat plate (11) and said lateral guide (12).

2. The radial seal arrangement (1) as claimed in claim 1, wherein said seal mount (10) comprising the bi-metallic strip (16) is used either separately or in combination with at least one component selected from middle flat plates (11), lateral guide (12) and protector angles (13) to reduce the radial leakage.

3. The radial seal arrangement (1) as claimed in claim 1, wherein said bi-metallic strip (16) is used either separately or in combination with any other mechanism to reduce the radial leakage.

4. The radial seal arrangement (1) as claimed in claim 1, wherein said seal mount (10) and bi-metallic strip (16) is not limited to an inverted L cross-section.

5. The radial seal arrangement (1) as claimed in claim 1, wherein said seal mount (10) is of any type including but not limited to simply supported, over hanging, continuous and fixed.

6. The radial seal arrangement (1) as claimed in claim 1, wherein said seal mount (10) is attached by any means with said diaphragm plate (8) or rotor.

7. The radial seal arrangement (1) as claimed in claim 1, wherein said seal mount (10) is clamped with said diaphragm plate (8) from in-board end (8a) until 2/3 of diaphragm plate's (8) radial length.

8. The radial seal arrangement (1) as claimed in claim 1, wherein said seal mount (10) slides over said middle flat plates (11) during air preheater operation.

9. The radial seal arrangement (1) as claimed in claim 1, wherein said lateral guides (12) restrict lateral movement of said seal mount (10).

10. The radial seal arrangement (1) as claimed in claim 1, comprising a preset clearance (14a) which is controlled by bolt and nut arrangement (14) between said top protector angle (13a) and said bottom protector angle (13b).

, Description:This application is a Patent of Addition to Indian Patent Application No. 201841020380 filed on 31st May, 2018, the entire content of which are specifically incorporated herein by reference.

FIELD OF THE INVENTION:

The present invention relates to air preheaters used in power plants. More particularly, it relates to an improved radial seal arrangement for effective sealing between air side and flue gas side of a rotary air preheater.

BACKGROUND OF THE INVENTION:

In power plants, rotary air preheater (hereinafter referred as RAPH) is an important boiler auxiliary which is used to pre-heat the atmospheric air used for the combustion process thereby increasing the combustion efficiency and boiler efficiency.

The RAPH contains a cylindrical drum (also called as rotor) attached to the rotor post by means of diaphragm plates. Matrix of heat exchange elements are tightly packed in the pockets between the diaphragm plates. The rotor rotates about its axis carrying the heating elements.

Generally, RAPH is classified into bi-sector, tri-sector and quad-sector based on the sector plate divisions / arrangement. In bi-sector RAPH, two static sector plates are located over the rotor to create two passages, Viz. gas and air. Similarly, in tri-sector RAPH, there are three sector plates to accommodate gas, primary air and secondary air passages. In quad-sector RAPH, one is for flue gas passage, two for secondary air passages and the primary passage is sandwiched between the two secondary air passages. (Pulverized coal fired boiler normally utilizes air for drying, classification and transport of coal to the pulverizer. The air to the pulverizer is referred to as primary air while the remaining combustion air is referred to as secondary air). The cylindrical drum is surrounded by housing which serves as casing for RAPH.

During RAPH operation, heat exchange elements gains the heat from hot flue gas entering the RAPH from one side. These heat exchange elements at hot condition rotates further into the air side to pre-heat the atmospheric air entering the RAPH system from the other side. Thus, the air preheater continuously pre-heat the atmospheric air used in the boiler for combustion.

At working condition, RAPH rotor is subjected to thermal gradient between its hot and cold ends. This thermal gradient leads to differential expansion between the hot and cold ends of the rotor which alters the clearance between the rotor and corresponding sealing surfaces at various locations of an RAPH. This structural deformation of rotor increases the clearance between the sector plate and diaphragm plate at hot-end and this effect is also termed as rotor “turn-down”. In an effort to reduce the leakage due to the structural deformation of rotor, various seals such as radial seals, circumferential seals / by-pass seals, axial seals and post seals are installed at different locations of an RAPH.

Air-to-gas leakage occurring due to differential pressure between the air and the flue gas side, is inherent in all air preheaters and is one of the important factors which contributes to major portion of the total leakage. This leakage is also termed as “direct leakage”. The direct leakage percentage varies with RAPH size, heating element profile & height, in addition to operating conditions of an RAPH. The other type of leakage called as entrained leakage, occurs due to entrainment of air between the heating elements and this air escapes into the flue gas side during the rotary action of RAPH and similarly flue gas that gets trapped between the heating elements, escapes in to the air side due to rotary action of RAPH.

In order to reduce the direct leakage occurring at radial ends of the rotor, radial seals are attached at either end of the diaphragm plates that are intended to pass closely with the sector plate. These radial seals are segmented and attached with the diaphragm plate suitably. In-general, reducing the leakage has major advantages like reduction in auxiliary power consumption (Induced Draft, Primary Air & Forced Draft - fan), increase in efficiency of RAPH and enhancement in boiler combustion efficiency.

In conventional RAPH design, radial seals are attached directly with diaphragm plate, along its entire length. During RAPH operation, the conventional radial seals attached with diaphragm plate will follow the turn-down pattern same as that of the diaphragm plate. This increases the clearance between the radial seals and the sector plate. This gap leads to increased leakage and reduced performance of RAPH.

A few systems for reducing radial leakage are known in the existing art.

Chinese patent no. 205481102 to YANG JING entitled “Air heater and sealing device thereof” discloses a sliding type radial sealing arrangement between sector plate and diaphragm plate of rotary air preheater to reduce radial leakage. This seal arrangement is such that the upper mounting plate and central laminated separator are detached from each other. In this design, radial seals are attached with the upper mounting plate and the upper mounting plate is clamped to one end of the diaphragm plate using the end clamp mounting. Lower mounting jaw inter-connects the central laminated separator and the diaphragm plate. As the rotor turn-down occurs during RAPH operation, the upper mounting plate is able to slide over the central laminated separator and compensates the mushroom shaped deformation of the rotor and reduces the radial leakage.

Chinese patent no. 102997275 to BAI JIANGZHAO et al., entitled “Rotary air preheater 'h-type' sealing jacket” discloses a cantilever radial seal (i.e. Jacket) arrangement between the sector plate and diaphragm plate of rotary air preheater, to reduce radial leakage. The stiffener is placed between jacket and conventional radial seals to ensure the rigidity of the upper part of the jacket in-addition to the metal strip placed between two plates of “h-type” jacket. A shockproof bolt is attached with diaphragm and jacket to prevent the jacket from abnormal deformation. A tab plate is placed at outer end of diaphragm to prevent air leakage.

Though the existing prior art discloses a radial seal arrangement between sector plate and the diaphragm plate of rotary air preheater to reduce radial leakage, it has many drawbacks like increased entrained leakage due to height of radial seal arrangement, jamming of rotor due to ash accumulation between “h-type” arrangement and rotor partition. More importantly, the existing art cannot be retrofitted.

Hence, there is a need for an improved radial seal arrangement that overcomes the above-mentioned drawbacks and minimize the gap between the sector plate and diaphragm plate created by the rotor turn-down, providing an effective sealing for direct air leakage. The improved radial seal arrangement must be robust in design but cost effective. In-addition to that, it must function seamlessly for a longer duration even in harsh environment (highly erosive environment) with almost nil manual intervention during operation. The seal design should be such that it can be retrofitted to existing RAPH of any size and configuration.

Our co-pending patent application number 201841020380 discloses a radial seal arrangement which includes a seal stiffener bolted with the diaphragm plate at the in-board end contributing to the cantilever effect. The clamping distance of the seal stiffener provides effective sealing of radial leakage. During the RAPH operation, the improved radial seal arrangement remains almost in its original position set during installation, due to its cantilever effect and thereby reducing the direct leakage of air into flue gas side of RAPH.

SUMMARY OF THE INVENTION:

An objective of the present invention is to minimize the gap between the sector plate and the diaphragm plate created by the rotor turn-down, providing an effective sealing for direct air leakage by means of improved self adjusting radial seal arrangement.

It is yet an objective of the invention to reduce the auxiliary power consumption (Induced Draft, Primary Air & Forced Draft - fan power consumption) by reducing the radial leakage.

It is also an objective of the invention to increase the performance of the RAPH / boiler by reducing the radial leakage and thereby reducing the heat losses.

It is still another objective of the invention to replace the radial seals in existing RAPH, with an adaptive seal arrangement which can be retrofitted to any existing RAPH.

It is also an objective of the invention to facilitate speedy and cost-effective seal replacement of the damaged seals.

It is yet another objective of the invention to provide an RAPH sealing system which can be used in any operating environment (coal or any other fuel firing system).

It is still another objective of the invention to provide an RAPH sealing system which eliminates the use of proximity sensor or any other sophisticated sensor mechanism required for its operation, which generally fails or become inoperative.

It is also an objective of the invention to increase the life and robustness of the radial seals at extreme operating conditions.

For achieving the above-mentioned objectives, the present invention provides a self adjusting radial seal arrangement that includes radial seals, middle flat plates, seal mount, bi-metallic strip, lateral guides and protector angles. The beam type “seal mount” is bolted suitably with the diaphragm plate only at in-board end, contributing to cantilever effect of the complete radial seal arrangement. A “bi-metallic strip” with higher thermal expansion coefficient as compared to the seal mount material, is attached to the lower portion of the seal mount at in-board end. The bi-metallic strip is positioned such that, it lifts the seal mount at hot operating condition, to a designed value in the out-board end. This lift ensures that the “radial seals” will always remain close to the sector plate (in other words, the radial seals remains in its original position) in-spite of the rotor turn-down. This in-turn reduces the leakage gap significantly as compared to the existing design, thereby reducing the direct leakage of air into the flue gas side.

Other objects, advantages and features of the present invention will become more apparent from the following detailed description and claims, taken in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed for the purpose of illustration only and are not intended as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS:

The objective of the present invention will now be described in more detail with reference to the accompanying drawings, in which:

FIG. 1 illustrates a general arrangement of rotary air preheater;

FIG. 2 illustrates a schematic view of air preheater drum along with rotor post and sector plate;

FIG. 3 illustrates exploded view of air preheater drum, diaphragm plate, rotor post and sector plate;

FIG. 4 illustrates exploded front view of existing radial seal components;

FIG. 5 illustrates schematic representation of existing radial seal assembly over diaphragm plate;

FIG. 6 illustrates exploded front view of improved self adjusting radial seal components;

FIG. 7 illustrates schematic representation of improved self adjusting radial seal assembly over diaphragm plate;

FIG. 8 illustrates schematic representation of improved self adjusting radial seal arrangement below sector plate;

FIG. 9 illustrates schematic representation of lateral guide arrangement of improved self adjusting radial seals;

FIG. 10 illustrates schematic representation of protector angle arrangement of improved self adjusting radial seals; and

FIG. 11 illustrates schematic representation of protector angle bolt nut arrangement of improved self adjusting radial seals.

REFERENCE NUMERALS:

1 - Improved radial seal arrangement
2 - Radial seal
3 - Static sector plates
4 - Flue gas side
5, 6 - Air side
7 - Rotor post
8 - Diaphragm plates
8a - In-board end
8b - Out-board end
9 - Cylindrical drum
10 - Seal mount
11 - Middle flat plate
12 - Lateral guide
13 - Protector angle arrangement
13a - Top protector angle
13b - Bottom protector angle
14 - Bolt & nut arrangement
14a - Preset clearance
15 - Housing
16 - Bi-metallic strip

DETAILED DESCRIPTION OF THE INVENTION:

The present invention relates to a self adjusting radial seal arrangement which minimizes the gap between the sector plate and diaphragm plate created by the rotor turn-down, providing an effective sealing for radial leakage.

Referring now in detail to the appended drawings, FIG. 1 shows a general arrangement of a rotary air preheater (hereinafter referred as RAPH). The primary function of the air preheater is to recover the waste heat from the flue gas (4) before being let into the atmosphere and transfer the recovered heat to the primary air (5) and secondary air (6) supplied into the boiler system for combustion process. Thus the RAPH, eliminates the loss of huge amount of heat energy, otherwise directly let into the atmosphere, thereby increasing the thermal efficiency of power plants.

The main components of the air preheater are described below. A cylindrical drum (9) or rotor comprising radially extending diaphragm plates (8) attached with the centrally located rotor post (7). The diaphragm plates (8) divides the cylindrical drum (9) into number of radial sectors depending on the RAPH size. Each diaphragm plate (8) additionally has vertically extended seal plates (2) at either end (hot-end at one side and cold-end at other side of the diaphragm plate (8)) to seal the gap between the diaphragm plate (8) and the sector plate (3) as shown in Fig. 2. Maintaining this gap to a minimum during the RAPH operation, reduces the radial leakage occurring due to pressure differential between the air (5, 6) and flue gas side (4).

Generally, RAPH is classified into bi-sector, tri-sector and quad-sector based on the sector plate divisions / arrangement. In bi-sector RAPH, two static sector plates (3) are located over the rotating cylindrical drum (9) to create two passages, Viz. Gas (4) and Air (5,6) passage. Similarly, in tri-sector RAPH, there are three sector plates (3) to accommodate gas (4), primary air (5) and secondary air passages (6). In quad-sector RAPH, one passage is for gas (4), two for secondary air (6) and the primary air passage (5) is sandwiched between the two-secondary air (6) passages. The cylindrical drum (9) is surrounded by housing (15) which is a static component of RAPH.

Bundles of metallic heat exchange elements / sheets are stuffed inside the baskets to facilitate the air or flue gas to pass through it. Generally, the shape of heat exchange elements is of flat, or formed, pressed-steel sheets with corrugated, notched, or undulated ribbing. These heat exchange elements are used in combination, which form passages for flow of air and gas through it. Each of these baskets are arranged closely inside each sector of the cylindrical drum (9). These regenerative heat transfer surface inside the cylindrical drum (9) rotates continuously and alternatively through the gas & air streams during an RAPH operation.

In-general counter flow is observed in RAPH, where the heat exchange elements gains the heat from hot flue gas entering the RAPH from one side and these heat exchange elements at hot condition rotates further into the air side (5, 6), to pre-heat the atmospheric air entering the RAPH system from the other side. Thus, the air preheater continuously pre-heat the atmospheric air used in the boiler for combustion.

The continuous process of heat exchange between hot flue gas and air during an RAPH operation results in a significant metal temperature gradient between the hot-end and cold-end of air preheater rotor. Due to this temperature gradient, the hot-end of rotor expands in radial direction becoming larger in diameter, while the cold end at the bottom remains smaller in diameter which leads to a predictable deformation in the shape of the total air preheater. This effect due to the thermal gradient is termed as turn-down which increases the clearance between the radial sealing surfaces of diaphragm plate (8) and sector plate (3). This turn-down effect also alters the clearance between the circumferential sealing surfaces of an RAPH between housing (15) and cylindrical drum (9).

FIG. 3 illustrates exploded view of air preheater drum, diaphragm plate, rotor post and sector plate

The present invention focuses on the control of radial leakage with the use of seal mount (10), wherein a bi-metallic strip (16) is attached to its lower portion and radial seals (2) are attached to its top. Radial leakage leads to mixing of air into the flue gas side (4) which increases the mass flow through Induced Draft Fan thereby increasing the Induced Draft Fan power consumption. Similarly, more air needs to be pumped into the air side (5, 6) to make up for the leakage which leads to increase in Forced Draft and Primary Air Fan power consumption. In-general the RAPH leakage leads to increase in auxiliary power consumption.

FIG. 4 illustrates exploded front view of existing radial seal components. The limitations with existing radial seal (2) arrangement is that, when the rotor turn-down occurs, the radial seals (2) follows the diaphragm plate (8) turn-down pattern as it is firmly attached with the diaphragm plate (8) from in-board end (8a) to out-board end (8b) as shown in FIG. 5. It increases the gap between sector plate (3) and radial seals (2) which leads to increase in direct leakage.

In order to overcome the current design limitations and to minimize the direct leakage, an improved radial seal arrangement (1) is provided. The improved radial seal arrangement (1) includes, radial seals (2), seal mount (10), middle flat plate (11), lateral guide (12), protector angles (13) and bi-metallic strip (16). These components are assembled over the diaphragm plate (8) as shown in FIGS. 6 & 7.

FIG. 6 illustrates front view of improved self adjusting radial seal arrangement (1) in which the radial seals (2) are firmly attached with the seal mount (10), instead of diaphragm plate (8) as in conventional design. In between the seal mount (10) and diaphragm plate (8), middle flat plates (11) are introduced which are attached to the diaphragm plate (8), from in-board end (8a) to out-board end (8b). The function of the middle flat plate (11) is to offer a smooth surface for the seal mount (10) to slide over it during the RAPH operation. Seal mount (10) is firmly attached with the diaphragm plate (8) & middle flat bar (11) only at the in-board end (8a), whereas the remaining portion of the seal mount (10) at the out-board end (8b) is allowed to slide freely over the middle-flat plate (11) (otherwise we can say it is hanging). A bi-metallic strip (16) is attached to the lower portion of the seal mount (10) at the in-board end (8a).

In accordance with the present invention the radial seals (2) are attached with a single seal mount (10) which is bolted with the diaphragm plate (8) only at the in-board end (8a) contributing to the cantilever effect of the seal mount (10). A bi-metallic strip (16) for a calculated length is attached to the lower portion of the seal mount (10) at in-board end (8a) and the bi-metallic strip (16) is positioned such that during APH operation, it lifts the seal mount (10) at out-board end (8b) to a designed value. This lift ensures that the radial seals (2) will always remain close to the sector plate (3) in-spite of the rotor turn-down. This in-turn reduces the leakage gap significantly as compared to the existing design, thereby reducing the direct leakage of air into the flue gas side (4). The bolt configuration of seal mount (10) at in-board end (8a) is determined using Finite Element Analysis (FEA) and plays a pivotal role in the effective working of the radial seals. The clamping distance of the seal mount (10) is different for each air preheater and is determined using FEA. The clamping distance is optimized in such a way that there is no significant interference of radial seals (2) with sector plate (3). This helps to increase the life of radial seals (2) and sector plate (3). During the RAPH operation, in-spite of the rotor turn-down, the improved self adjusting radial seal arrangement (1) remains always close to the sector plate (3), due to its bi-metallic effect. This bi-metallic effect of seal mount (10) significantly reduces the gap between the sector plate (3) and the diaphragm plate (8) as compared to the existing design thereby reducing the direct leakage of air into flue gas side (4) of RAPH.

FIG. 8 illustrates schematic representation of improved self adjusting radial seal arrangement (1) below sector plate. Referring to FIGS. 7 & 9, the purpose of the lateral guide (12) is to restrict the lateral movement of the seal mount (10) that are likely to occur at its non-clamped area, due to pressure difference between the flue gas side (4) and air (5, 6) side. As shown in FIG. 10, the protector angles (13) are placed at the outboard end (8b) of the diaphragm plate (8). The top protector angle (13a) is attached with the seal mount (10) and the bottom protector angle (13b) is attached with the middle flat plate (11) located at the out-board end (8b). As shown in FIG. 11, there is a preset clearance (14a) between the two protector angles (13) controlled by the bolt & nut arrangement (14). This protector angle (13) arrangement allows the upward movement of seal mount (10) to only a preset value (14a) and thus prevents interference of radial seals (2) with the sector plate (3) at extreme operating conditions.

Our co-pending patent application number 201841020380 discloses a radial seal arrangement which includes a seal stiffener bolted with the diaphragm plate at the in-board end contributing to the cantilever effect. During the RAPH operation, the improved radial seal arrangement remains almost in its original position set during installation, due to its cantilever effect and thereby reducing the direct leakage of air into flue gas side of RAPH. The seal mount provides shorter clamping distance in order to provide the cantilever effect to the diaphragm plate. If the diaphragm plate is having larger diameter, only a portion is sealed with the seal mount, it causes the sagging of diaphragm plate due to higher thermal expansion. The present invention disclosed herein focused on aforesaid problem to avoid the sagging effect of diaphragm plate by providing a “bi-metallic strip” with higher thermal expansion coefficient to the lower portion of the seal mount at in-board end. The bi-metallic strip is positioned such way that, it lifts the seal mount at hot operating condition. This lift ensures that the “radial seals” always remain close to the sector plate (in other words, the radial seals remains in its original position) in-spite of the rotor turn-down. This in-turn reduces the leakage gap significantly, thereby reducing the direct leakage of air into the flue gas side.

In one embodiment, the seal mount (10) comprising the bi-metallic strip (16) is used either separately or in combination with at least one component such as middle flat plates (11), lateral guide (12) and protector angles (13) to reduce the radial leakage.

In another embodiment, the seal mount (10) is attached either directly or in-directly with the diaphragm plate (8) or rotor.

In yet another embodiment, the seal mount (10) is attached with the diaphragm plate (8) from in-board end (8a) until 2/3 of diaphragm plate's (8) radial length.

It is further understood that the cross-sectional shape of the seal mount (10) and bi-metallic strip (16) as presented herein is not limited to that of an inverted L cross-section and can be embodied in any alternative cross-section in accordance with the appended claims. The type or structure of the seal mount (10) is not limited to a structure that is simply supported, over hanging, continuous and fixed. The clamping distance of the seal mount (10) at the in-board end (8a) and its corresponding cross-section plays a pivotal role in the effective sealing of radial leakage and it is determined for each air preheater, using Finite Element Analysis.

The advantage of the improved radial seal arrangement (1) is that it significantly reduces the clearance between the sector plate (3) and diaphragm plate (8) due to its bi-metallic effect, thereby reducing the direct leakage of air into flue gas side (4) of RAPH. Other advantage is that it can be retrofitted to any type of RAPH without making any modifications to the other RAPH components except for replacing the existing radial seals (2).

While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope of the invention as claimed.