Claims:1. A radial seal arrangement (1) for rotary air preheater (RAPH), comprising:
a) a seal stiffener (10) that runs along the radial length of diaphragm plate (8) with radial seals (2) being attached to it;
b) middle flat bars (11) placed between said seal stiffener (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) side supports (12) placed at regular intervals on said diaphragm plate (8); and
d) a guide angle arrangement (13) placed at said outboard end (8b) of said diaphragm plate (8), comprising top guide angle (13a) and bottom guide angle (13b),
wherein said seal stiffener (10) is bolted with said middle flat bar (11) and said diaphragm plate (8) only at in-board end (8a) and remaining portion of said seal stiffener (10) is allowed to slide freely between said middle flat bar (11) and said side support (12).

2. The radial seal arrangement (1) as claimed in claim 1, wherein said seal stiffener (10) is used either separately or in combination with at least one component selected from middle flat bars (11), side supports (12) and guide angles (13) to reduce the radial leakage.

3. The radial seal arrangement (1) as claimed in claim 1, wherein said seal stiffener (10) is not limited to an inverted L cross-section.

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

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

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

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

8. The radial seal arrangement (1) as claimed in claim 1, wherein said side supports (12) restrict lateral movement of said seal stiffener (10).

9. 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 guide angle (13a) and said bottom guide angle (13b).
, Description:FIELD OF THE INVENTION:

The present invention relates generally 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 of the thermal power plant.

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 cavities between the diaphragm plates. The rotor post axis is the center axis of RAPH about which it rotates.

Generally RAPH is classified into bi-sector, tri-sector and quad-sector based on the sector plate divisions / arrangement. In bi-sector RAPH, the static sector plates are placed on either side of the rotating cylindrical drum and divides the RAPH into two halves, as air side and gas side. In tri-sector RAPH, further the air side is divided into high pressure primary air side and secondary air side in addition to flue gas side. In quad-sector RAPH, in addition to the flue gas side, the air side is divided into three divisions with high pressure primary air side in the middle and secondary air side on either side of primary air (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 is a static component of 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 factor 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 with respect to RAPH size. In-general, reducing the leakage has major advantages like reduction in auxiliary (Induced Draft, Primary Air & Forced Draft - fan) power consumption, increase in thermal efficiency of RAPH and enhancement in boiler combustion efficiency.

In the existing design, radial seals are attached directly with diaphragm plate. As a result during rotor turn-down, these seals will follow the diaphragm plate turn-down path (curved profile), which 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 perform the same function as that of Automatic Leakage Control System (ALCS) but must be cost effective. In-addition to that, it must function seamlessly even in harsh environment (highly erosive environment).

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 the improved 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 thermal performance of the RAPH / boiler by reducing the radial leakage.

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 will function 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.

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 radial seal arrangement that includes, radial seals, seal stiffener, middle flat bars, side support and guide angles. The beam type radial seal arrangement is bolted suitably with the diaphragm plate at only one end, contributing to cantilever effect of the radial seals. During the RAPH operation, though the rotor turn-down occurs, this radial seal arrangement remains almost in its original position set during installation due to its cantilever effect. This cantilever effect of the radial seal arrangement significantly reduces the gap between the sector plate and the diaphragm plate as compared to the existing design, thereby reducing the radial leakage.

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 radial seal components;

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

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

FIG. 9 illustrates schematic representation of side support arrangement of improved radial seals;

FIG. 10 illustrates schematic representation of guide angle arrangement of improved radial seals; and

FIG. 11 illustrates schematic representation of guide angle bolt nut arrangement of improved 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 stiffener
11 - Middle flat bars
12 - Side support
13 - Guide angle arrangement
13a - Top guide angle
13b - Bottom guide angle
14 - Bolt & nut arrangement
14a - Preset clearance
15 - Housing

DETAILED DESCRIPTION OF THE INVENTION:

The present invention relates to a 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) taken into the boiler system for combustion process. Thus the RAPH, eliminates the loss of huge amount of heat energy being 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 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, the static sector plates (3) are placed on either side of the rotating cylindrical drum (9) and divides the RAPH into two halves, as air side (5,6) and gas side (4). In tri-sector RAPH, further the air side is divided into high pressure primary air side (5) and secondary air side (6) in addition to flue gas side (4). In quad-sector RAPH, in addition to the flue gas side (4), the air side is divided into three divisions with high pressure primary air side (5) in the middle and secondary air side (6) on either side of primary air (5). 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 are of flat, or formed, pressed-steel sheets with corrugated, notched, or undulated rib-bing. These heat exchange elements are used in combination, which form passages for the smooth 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 through the gas and 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 an air preheater. 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 a seal stiffener (10) to which the radial seals (2) are attached. Radial leakage leads to mixing of air into the flue gas side (4) which increases the 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) path 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 stiffener (10), middle flat bars (11), side support (12) and guide angles (13). These components are assembled over the diaphragm plate (8) as shown in FIGS. 6 & 7.

FIG. 6 illustrates front view of improved radial seal components in which the radial seals (2) in the improved radial seal arrangement (1) are firmly attached with the seal stiffener (10) instead of diaphragm plate (8) as in conventional design. In between the seal stiffener (10) and diaphragm plate (8), middle flat bars (11) are introduced which are firmly attached with the diaphragm plate (8), from in-board end (8a) to out-board end (8b). The function of the middle flat bars (11) is to offer a smooth surface for the seal stiffener (10) to slide over it during the RAPH operation. Seal stiffener (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 stiffener (10) at the out-board end (8b) is allowed to slide freely over the middle-flat bar (11).

In accordance with the present invention the radial seals (2) are attached with a single seal stiffener (10) which is bolted with the diaphragm plate (8) only at the in-board end (8a) contributing to the cantilever effect of the seal stiffener (10). The clamping distance of the seal stiffener (10) at the in-board end (8a) plays a pivotal role in the effective sealing of radial leakage and the clamping distance of the seal stiffener (10) for each air preheater is determined using Finite Element Analysis. The clamping distance is optimized in such a way that there is no significant rubbing 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 radial seal arrangement (1) remains almost in its original position set during installation, due to its cantilever effect. This cantilever effect of seal stiffener (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 radial seal arrangement (1) below sector plate. Referring to FIGS. 7 & 9, the purpose of the side supports (12) are to restrict the lateral movement of the seal stiffeners (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 guide angles (13) are placed at the outboard end (8b) of the diaphragm plate (8). The top guide angle (13a) is attached with the seal stiffener (10) and the bottom guide angle (13b) is attached with the middle flat bar (11) located at the out-board end (8b). As shown in FIG. 11, there is a preset clearance (14a) between the two guide angles (13) controlled by the bolt & nut arrangement (14). This guide angle (13) arrangement prevents the heavy rubbing of radial seals (2) with the sector plate (3) at extreme operating conditions, by pulling down the hanging part of the seal stiffener (10) along with the diaphragm plate (8).

In one embodiment, the seal stiffener (10) is used either separately or in combination with at least one component such as middle flat bars (11), side supports (12) and guide angles (13) to reduce the radial leakage.

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

In yet another embodiment, the seal stiffener (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 stiffener (10) 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 stiffener (10) is not limited to a structure that is simply supported, over hanging, continuous and fixed. The clamping distance of the seal stiffener (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 drastically reduces the clearance between the sector plate (3) and diaphragm plate (8) due to its cantilever effect thereby reducing the direct leakage of air into flue gas side (4) of RAPH. Apart from leakage reduction, 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.