WO2001007804A1

WO2001007804A1 - Packing gland assembly for sootblowers

Info

Publication number: WO2001007804A1
Application number: PCT/AU2000/000868
Authority: WO
Inventors: Rodney Ivory
Original assignee: Loy Yang Power Management Pty Ltd
Priority date: 1999-07-23
Filing date: 2000-07-20
Publication date: 2001-02-01
Also published as: AUPQ180599A0

Abstract

A packing gland assembly for a sootblower, the packing gland assembly comprising: a packing material for providing a seal between a lance tube and a feed tube of a sootblower; a gland follower fixedly mounted relative to the non-discharge end of the lance tube; and a spring which is compressively mounted relative to the packing material to supply a compressive force to the packing material, wherein the compressive force of the spring acts on the packing material to urge the packing material towards the gland follower to effect the seal between the lance tube and the feed tube.

Description

PACKING GLAND ASSEMBLY FOR SOOTBLOWERS

The present invention relates to a packing gland assembly for a sootblower, such as those employed for the periodical removal of ash and slag deposited on boiler heating surfaces on combustion of coal. More particularly, the invention relates to a packing gland assembly which includes a spring which acts against packing of the gland to ensure sealing between the feed tube and the lance tube of the sootblower.

Sootblowers and packing gland assemblies therefor are known. Conventionally, sootblowers include a lance tube through which cleaning fluid, which may be for example water, steam, detergent or mixtures thereof, is passed and discharged through one or more nozzles in the forward most end thereof. The discharged fluid is directed at internal heating surface of boilers to remove ash and slag deposits, and possibly also rust, corrosion or the like. The fluid is generally supplied to the lance tube through a feed tube which is coaxially aligned with the lance tube. The lance tube is mounted about the feed tube to facilitate insertion and retraction of the lance tube into and out of the boiler respectively. These means for imparting movement to the lance tube are discussed throughout the prior art and will be readily ascertained by those in the art. As such, they will not be discussed in any detail herein.

The invention relates to the packing gland assembly which forms a sealing assembly between the lance tube and the feed tube of the sootblower.

Conventionally, the lance tube and feed tube are concentrically mounted. The feed tube is connected to a source of fluid under suitable pressure to be used as the cleaning medium. The lance tube is mounted at its rearmost end on the feed tube by means of a carriage. The seal between the lance tube and feed tube is generally provided by a stuffing box within the carriage which contains a deformable packing material which, under compression and deformation by a gland follower, provides a fluid tight seal between the outer surface of the feed tube and the inner surface of the lance tube.

Various means have been suggested for maintaining sufficient compression and deformation of the packing material to ensure that an effective seal between the lance tube and feed tube is provided. Conventionally, the packing material is contained in a stuffing box between the outer surface of the feed tube and the inner surface of the lance tube and is compressed by a gland follower. The gland follower is generally manually operable to compress the packing material as desired by external gland nuts which are fixedly threaded relative to the lance tube. As such, on tightening of the gland nuts, the packing material is compressed and deformed by the gland follower. In this conventional embodiment, the timing of adjustment and tightening of the gland nuts is generally determined by leakage of fluid from between the lance tube and feed tube. That is, the gland nuts are tightened when leakage, and therefore an ineffective seal, is detected. The gland nuts are tightened only enough to prevent leakage of fluid from between the lance tube and the feed tube as excessive tightening will shorten the life of the packing material and increase the load on the drive motor of the sootblower assembly. Further, tightening of the gland nuts should be conducted when the feed tube is at its hottest condition to ensure that tightening due to thermal expansion is prevented. If the tightening operation does not stop the detected leak, then the packing material must be renewed.

Alternatives to this conventional arrangement have been proposed. These alternatives in some instances provide a similar arrangement to that described above, but rather than tightening of the gland nuts on detected leakage, the gland follower is supplied with a constant force which is applied to the packing material to ensure sufficient compression and deformation of the packing material to provide a seal between the lance tube and the feed tube. Generally, such arrangement include an external spring which is mounted relative to the gland follower to provide the constant force to the packing material. For example, the gland follower may have mounted relative thereto a number of mountings, each of which includes a reciprocating flange which engages the gland follower and a fixed flange which is fixedly mounted relative to the lance tube. Between each pair of reciprocating and fixed flanges of each mounting is a spring which acts to force the reciprocating flange, and therefore the gland follower, toward the packing material causing a substantially constant compression and deformation of the packing material.

In another alternative, a similar arrangement is seen with the packing material being compressed by a gland follower which is supplied with compressive force by a single external spring which is coaxially mounted between the lance tube and the feed tube such that the feed tube passes through the spring, and which engages the gland follower indirectly through a mounting arrangement.

In each of the above alternatives where a spring is used to impart compression to the packing material, the spring acts to compress the packing material towards the discharge end of the lance tube. That is, against the force of the cleaning fluid which is being fed to the lance tube from the feed tube and which is trying to escape from between the lance tube and feed tube. According to the present invention, an alternative packing gland assembly is provided which advantageously forgoes the need for periodical adjustment and tightening to prevent leakage of cleaning fluid from between the lance tube and feed tube of a sootblower and which provides advantages over known sealing arrangements between the lance tube and feed tube of a sootblower.

According to the present invention there is provided a packing gland assembly for a sootblower, the packing gland assembly comprising: a packing material for providing a seal between a lance tube and a feed tube of a sootblower; a gland follower fixedly mounted relative to the non-discharge end of the lance tube; and a spring which is compressively mounted relative to the packing material to supply a compressive force to the packing material, wherein the compressive force of the spring acts on the packing material to urge the packing material towards the gland follower to effect the seal between the lance tube and the feed tube. The packing gland assembly according to the invention advantageously provides a compressive force, supplied by the spring, which acts against the packing material to urge the packing material towards the gland follower mounted relative to the non-discharge end of the lance tube. That is, the compressive force is applied to the packing material in the same direction as pressure which is being applied to the packing material due to fluid pressure within the sootblower assembly when the assembly is in use. As such, the fluid pressure within the system enhances the seal between the lance tube and the feed tube, higher fluid pressures resulting in higher compressive forces being applied on the packing material by the spring.

The spring may be mounted relative to the packing material in any suitable fashion provided that the compressive force supplied by the spring to the packing material acts in the same direction as pressure which is applied to the packing material as a result of fluid pressure within the assembly. Further, the assembly may include more than one spring arranged such that each spring meets the compressive force requirement above. Preferably, the spring is a single spring which is coaxially mounted between the lance tube and the feed tube such that the packing material is located between the spring and an abutment surface of the gland follower. In a particularly preferred embodiment, the spring is mounted between a first mount, for example a throat bush, which is part of or which is fixedly mounted on the lance tube and a second mount, for example a washer, which abuts the packing material. Preferably, the second mount also acts to protect the packing material from damage by the spring.

In order to install the spring between the lance tube and the feed tube on the process side of the sootblower, an amount of packing material corresponding to approximately half of that conventionally used is employed. This is necessary as the spring takes up space in the recess between the lance tube and the feed tube which would conventionally contain the packing material. However, it has been found that the effectiveness of the packing material in providing a seal between the lance tube and the feed tube is not reduced due to the lesser amount of packing material present. Rather, as is recognised, most of the sealing work is achieved by only a small portion of the packing material. For example, when the packing material is a plurality of packing rings, such as chevron packing rings, the majority of the sealing work is done by the first two packing rings. Further, wiping rings which are generally employed to abut either end of the packing material in conventional assemblies are advantageously removed from the assembly according to the invention. This, in combination with the reduced amount of packing material which is employed, advantageously represents a substantial reduction in the production costs for the packing gland assemblies of the invention compared with conventional assemblies.

The gland follower may be directly or indirectly mounted relative to the non-discharge end of the lance tube. In a preferred embodiment, the gland follower is mounted directly onto the non-discharge end of the lance tube. More preferably, the gland follower directly abuts the packing material at the non-discharge end of the lance tube. The spring which is internally mounted in the packing gland assembly, is advantageously formed from a corrosion resistant material, such as carbon steel and more preferably stainless steel. This is desirable, even though the fluid to which the spring is subjected is generally non- corrosive, for example demineralised water. Furthermore, stainless steel is desirable given the temperatures of use of the assembly to which the spring will be exposed and also due to some exposure to more corrosive conditions. These temperatures are generally in the order of about 350 °C at a maximum. The exposure of the spring to more corrosive conditions is relatively limited, with "Fire and General Service Water" being employed during off-line cleaning of the assembly. Such cleaning time would total to approximately 100 hours per year.

In a similar fashion, the mounts used as spring supports for an internally mounted spring are advantageously manufactured from a material, such as carbon steel or brass, so as to ensure that degradation and corrosion of the mounts is minimal.

The packing material may be formed from any of the materials conventionally used for this purpose. In a preferred embodiment the packing material is Teflon based chevron rings. The rings may have, for example an internal diameter of 60mm, and outer diameter of 79mm and be 77mm wide as supplied by Garlock. Reference will now be made to the accompanying drawings which illustrate a preferred embodiment of the invention and in which:

Figure 1 is a perspective view of a sootblower which illustrates the relative positioning of the packing gland assembly;

Figure 2 is a sectional view of a conventional packing gland assembly; and Figure 3 is a sectional view of the packing gland assembly according to the invention incorporating a coaxially mounted internal spring.

Referring to Figure 1, a sootblower 10 cleans boiler heating surfaces by impacting steam from two nozzles 11 located at a discharge end of a translational-rotational lance tube 12 which receives a blowing medium from a feed tube 13. The operating cycle begins with the unit in a retracted position. When power is applied to a drive motor, a carriage 14 moves along guide channels located on each side of a beam 15 which forms the backbone of the sootblower 10, to project the lance tube 12 into the boiler.

When the nozzles 11 are inside the boiler, the carriage 14 opens a poppet valve 16 to begin the cleaning cycle. The carriage 14 then continues to project the rotating lance tube 12 into the boiler until it reaches a maximum forward position. At this point, the carriage 14 reverses its direction and at the same time indexes the lance tube 12 to return on a different nozzle path (spiral). The lance tube 12 rotates on a 100mm helix and, as such, the opposing nozzles 11 provide cleaning at 50mm intervals. A 25mm shift in blowing pattern for the reverse travel of the carriage 14 bisects the blowing pattern for forward travel, thus producing a cleaning helix every 25mm.

The carriage 14 continues to retract until the nozzles 11 are near the boiler wall, at which the poppet valve 16 is shut. The operating cycle is completed when the carriage 14 returns to its original fully retracted position.

The blowing pressure of the sootblower 10 may be varied by an adjustable orifice inside the poppet valve 16. The carriage 14, as described above, drives the lance tube 12 into and out of the boiler.

The carriage 14 consists of an assembly which includes a drive motor, a gearbox and a packing gland 17. The packing gland 17 confines the blowing medium, such as steam, within the lance tube 12 and the feed tube 13. This advantageously prevents leakage of the blowing medium from the connection between the lance tube 12 and the feed tube 13. The carriage 14 is completely sealed to facilitate protection against dirt and corrosive atmospheric conditions.

The feed tube 13 supplies the blowing medium, generally steam, from the poppet valve

16 to the lance tube 12. The rear end of the feed tube 13 is inserted in an outlet of the poppet valve 16 and is keyed to a valve mounting plate which is bolted to a valve mounting bracket 18.

A feed tube gasket is compressed in the poppet valve outlet to seal the connection between the poppet valve outlet and feed tube to prevent leakage of the blowing medium.

At the front end, the feed tube 13 is telescoped into the lance tube 12. The connection between the lance tube 12 and feed tube 13 is sealed by a packing material in the packing gland 17. The feed tube is generally made of highly polished stainless steel to ensure an adequate sealing surface for the packing material. The lance tube 12 is flange mounted to a lance hub on the carriage 14 and is projected through a sootblower wall box and sleeve 19 into the boiler when the sootblower 10 is in operation. The lance tube 12 is designed to withstand the high temperature encountered under operating conditions and is generally formed from a low chromium stainless steel.

The blowing medium is blown from two opposed nozzles 11 in a nozzle block welded onto the end of the lance tube 12. The nozzles 11 are positioned in the lance tube 12 to be perpendicular, either leading or lagging, depending on the cleaning application. The nozzles 11 have a venturi type profile for maximum efficiency.

Referring to Figure 2, a conventional packing gland assembly 20 is shown in which a lance tube 21 is telescopically mounted about a feed tube 22 in accordance with the conventional sootblower described above, and in which a packing material 23, in the form of chevron ring packing, is located between the lance tube 21 and feed tube 22 to provide a seal. The packing material 23 is mounted between two wiping rings 24, the innermost of which abuts a throat bush 25 mounted on the lance tube 21 , and the other of which abuts a gland follower 26. The gland follower 26 is adapted to compress the packing material 23 by "nipping up". This procedure is carried out when leakage of blowing medium from between the lance tube 21 and feed tube 22 is detected and involves tightening of nuts 27 which forces the gland follower 26 into the recess which houses the packing material 23.

Referring to Figure 3, a packing gland assembly 30 according to the invention again includes a packing material 33 which is disposed between the lance tube 31 and feed tube 32 of a sootblower to provide a seal there between. However, in the gland assembly 30 of the invention, the amount of packing material 33 is reduced, relative to the conventional gland assembly 20, to facilitate housing of a spring 34 which is coaxially mounted between the lance tube 31 and the feed tube 32 to provide a compressive force to the packing material 33. The wiping rings 24 seen in the conventional assembly 20 are also removed to facilitate housing of the spring 34. The innermost portion of the spring 34 rests in abutment with a mount 35a which is mounted on, or which is part of the lance tube 31. The other end of the spring 34 abuts a washer 35b which advantageously acts to protect the packing material 33 from damage by the spring 34. The washer 35b is similar in construction to the mount 35a.

As was the case in the conventional assembly 20, the packing gland assembly 30 of the invention includes a gland follower 36 which abuts the outermost end of the packing material 33. The gland follower may be tightened by nuts 37, and acts to maintain the packing material within the recess 38 between the lance tube 31 and feed tube 32.

When the sootblower is in use, blowing medium which is under pressure is fed through the feed tube 32 along the path as indicated into the lance tube 31. Blowing medium which is fed into the lance tube 32 is discharged through nozzles 11 (as shown in Figure 1), but also passes between the feed tube 32 and the lance tube 31 into the recess 38. The packing material 33 acts to prevent the leakage of the blowing medium from the recess 38 between the lance tube 31 and feed tube 32. As the blowing medium enters the recess 38 the pressure of the medium acts in the same direction as the compressive force of the spring 34 acting on the packing material 33. This advantageously causes expansion of the spring 34 and, as a result, compression of the packing material 33 to ensure a satisfactory seal between the lance tube 31 and the feed tube 32. Furthermore, the compression of the packing material 33 will be greater at higher blowing medium pressures, and lesser at lower blowing medium pressures. Thus, a variable compressive force is applied to the packing material 33 depending on the conditions and parameters of use of the sootblower.

The present invention provides an alternative packing gland assembly to those conventionally employed in sootblowers which may advantageously have reduced manufacturing costs and maintenance requirements compared with conventional gland assemblies. The packing gland assembly according to the invention advantageously does not require "nipping up" as do conventional gland assemblies, and provides enhanced sealing between the lance tube and feed tube of a sootblower compared with that provided by conventional arrangements.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and substrates referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of said steps or features.

Claims

1. A packing gland assembly for a sootblower, the packing gland assembly comprising: a packing material for providing a seal between a lance tube and a feed tube of a sootblower; a gland follower fixedly mounted relative to the non-discharge end of the lance tube; and a spring which is compressively mounted relative to the packing material to supply a compressive force to the packing material, wherein the compressive force of the spring acts on the packing material to urge the packing material towards the gland follower to effect the seal between the lance tube and the feed tube.

2. An assembly according to claim 1 , wherein compressive force, supplied by the spring, acts against the packing material to urge the packing material towards the gland follower mounted relative to the non-discharge end of the lance tube.

3. An assembly according to claim 1, wherein the spring comprises a single spring which is coaxially mounted between the lance tube and the feed tube such that the packing material is located between the spring and an abutment surface of the gland follower.

4. An assembly according to claim 1 , wherein the spring is mounted between a first mount which is part of or which is fixedly mounted on the lance tube and a second mount which abuts the packing material.

5. An assembly according to claim 1 , wherein the second mount acts to protect the packing material from damage by the spring.

6. An assembly according to claim 4, wherein the first mount is a throat bush and the second mount is a washer.

7. An assembly according to claim 1 , wherein the gland follower is mounted directly onto the non-discharge end of the lance tube.

8. An assembly according to claim 7, wherein the gland follower directly abuts the packing material at the non-discharge end of the lance tube.

9. An assembly according to claim 1, wherein the spring is formed from a corrosion resistant material.

10. An assembly according to claim 9, wherein the corrosion resistant material is carbon steel or stainless steel.

11. An assembly according to claim 1 , wherein the packing material is formed from Teflon based chevron rings.