Troubleshooting Seals
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PHILLIPS KILN SERVICES LTD.
TROUBLESHOOTING SEALS
Any discussion of drum end seal maintenance can be lengthy because of the wide variety of seal designs used over the years by various rotary equipment manufacturers. The designs are as simple as a piece of rubber belting or ceramic fiber blanket, or as elaborate as utilizing counterweights, pulleys and air cylinders in an attempt to create a more positive seal. The primary purpose of any seal is to keep “tramp” air out of the unit to allow better control of the process. A secondary but important function is to help control dust and hot gases from escaping from the kiln or dryer if there is some sort of “upset” condition. To be successful, the seal for a rotary kiln or dryer must accommodate both axial and radial movement. The major downfall of most seals is too many moving parts susceptible to “sticking” or failure from dust contamination or heat distortion. The three main causes for seal failure are abrasion from product contamination, excessive shell run out in the seal area, and expansion and contraction of the unit during operation. For the purpose of this discussion maintenance issues of four common types of seals will be reviewed. The four types are the graphite block seal, face plate type seals, the outward facing leaf seal and the inverted leaf seal. Troubleshooting Seals
Page 1
In attempting to accommodate these conditions, the major downfall of most seals is too many moving parts!
Page 2
Troubleshooting Seals
The graphite block seal has been around for many years with several variations. The basic components of the seal are two rows of graphite blocks with one end of each block contoured to fit the radius of the shell. The blocks are positioned radially in slide holders that are spring loaded to keep them in contact with the shell. The graphite blocks are staggered in the two rows with every other block overlapping. Many of these installations have now been converted to some style of leaf seal.
Troubleshooting Seals
Page 3
The typical problems encountered with the graphite block seal are heat distortion of the block holders, and dust accumulation causing the blocks to “bind” so they can’t move freely in their respective slides. The result is that the springs can’t keep the blocks in contact with the shell. Another problem is spring failure. Various spring designs have been tried with little success.
Page 4
Troubleshooting Seals
The face plate type of seal has many variations, but the operating principle of most of them is the same and therefore the maintenance issues are similar. We will use the arrangement shown in this illustration as an example for general discussion. The main sealing components are a floating seal plate mounted on the face of the hood, and a fixed seal plate that rotates with the shell. The floating plate has some type of flexible section attached to it which allows the seal to move with the shell. The fixed and floating plates have a wear plate of brass or phenolic material sandwiched between them and held in place with springs, counterweights or air cylinders. Contamination can cause this type of seal to stick. Typically the floating half gets stuck and the sealing rings will disengage with any axial movement of the shell. Product may also build up to the point that it deforms the flexible section of the pressure assembly and causes failure.
Troubleshooting Seals
Page 5
COMMON PROBLEMS causing the face plate seal to leak and become ineffective: 1.
Failure of the device applying pressure to the seal plates. The device should be inspected regularly.
2.
The wear plate can become too thin or “scratched” and “gouged” from contamination; the seal will leak.
3.
Excessive run-out in the shell. These types of seals are particularly susceptible to failure if the shell run-out causes the fixed seal plate to “wobble”. The flexible assembly will allow longitudinal movement but cannot compensate for “wobble” of the rotating fixed ring.
Page 6
Troubleshooting Seals
Another common type of seal is the overlapping leaf seal. The two basic designs are outward-facing and inward-facing (inverted) leaves. The principle of these seals is the same, the major difference being the direction in which the leaves face. The drawback of the outward facing leaves is that they are susceptible to damage from dust accumulation. Most direct-fired units will operate with a slight negative pressure in the hood on which the seal is mounted. An outward-facing seal acts to seat itself tighter against the shell with that prevailing negative pressure. Hence, it creates a positive seal against infiltration of ambient air which is the seal’s intended purpose. However, most combustion is not altogether “smooth” and flame turbulence, even on the best burners, will cause bumps and puffs of positive pressure. The outward-facing seal has an inherent disadvantage because the positive puffs blow the seal open allowing hot air and dust to blow out.
Troubleshooting Seals
Page 7
DAMAGE TO NON-INVERTED SEALS The leaves should be made of a material that can withstand the temperature extremes to which they will be subjected, and still maintain spring pressure without taking a permanent set. The leaf spring should also exhibit some abrasion resistance to provide an adequate service life. The major drawback of the outwardfacing leaf design is their susceptibility to damage from dust accumulation.
Page 8
Troubleshooting Seals
INVERTED SEAL The spring action of the individual spring plates is strong enough to hold against the negative operating pressure in the firing hood. The first advantage of the inverted seal is that a positive puff will act to tighten up the seal, preventing blow-back. With no blow-back there is no hot air flow, no dust can be conveyed through the seal, and dust accumulation is significantly reduced. Secondly the seal leaves run on the riding band instead of directly touching the kiln shell. This provides a sacrificial member if wear occurs. The riding band is mounted in such a way to negate shell run-out at the time of installation. Since the shell run-out has been all but eliminated the flexing of the seal leaves is minimized thereby extending their service life.
Troubleshooting Seals
Page 9
The seal is equipped with a “stub” hopper. The seal is an air seal not a material seal. Nevertheless occasional spillage is expected so a means of removing spillage must be provided. The stub hopper, which is supplied with the seal, is a transition between the open bottom of the seal and some type of conveyor (supplied by others) to remove the the spillage. The conveyor can be a simple material chute, provided enough headroom is available to use gravity or can be as elaborate as an enclosed drag chain in case of limited head room as shown here. The installation shown at the right was installed on a 17’ (5 meter) diameter kiln with only 30” (76cm) clearance from the shell to a concrete floor.
Page 10
Troubleshooting Seals
A “worm’s” eye view inside the hopper reveals the third advantage of the inverted seal. The seal plates are above the hopper, which carries away product spillage. Unlike the non-inverted seal, which “catches” product spillage, the inverted seal does not create a shelf on which product can accumulate. Phillips recommends spraying a graphite powder onto the riding band under the leaves to lubricate them whenever possible. This will help extend their service life.
Troubleshooting Seals
Page 11
PHILLIPS ENVIRO SEAL The inverted leaf seal does have a space requirement but the real plus of the inverted seal is its simplicity of design. There are no moving parts to “stick”. The design incorporates a method to keep the dust buildup away from the sealing components and it is very forgiving of shell run-out.
Page 12
Troubleshooting Seals
Operating a kiln or dryer with ineffective seals or no seal costs money in wasted fuel due to inefficient burning. Also, during an upset condition, puffs of hot gases and product can become a major safety issue as well as an environmental problem.
Troubleshooting Seals
Page 13
CASE STUDY In Unit I of M/s Maihar Cement, two kilns (3 pier each) of 4.35M diameter x 64M length are in operation. Both kilns were equipped with pneumatic plate-to-plate seals at the feed end. The rotating wear plate was mounted on the kiln flange. Pneumatic cylinders were mounted on the stationary plate. Pressure was applied against the smoke chamber plate to force the stationary plate to move in an axial direction to come in contact with the rotating plate. To reduce wear on both plates, a grease pump provided grease lubrication, The seals demanded high maintenance and operational costs. Phillips’ Enviro Seals replaced the pneumatic seals, installed in November 1997 and August 1998. Operational efficiency of the kilns was improved; air ingress was reduced and out-going dust was captured. There has been no maintenance cost on the seal to date (1997 - 1998). The life of the leaf plates has yet to be established. Plant operators have calculated that they have saved $22,000 in fuel costs in one year.
Page 14
Troubleshooting Seals
TROUBLESHOOTING SEALS
Any discussion of drum end seal maintenance can be lengthy because of the wide variety of seal designs used over the years by various rotary equipment manufacturers. The designs are as simple as a piece of rubber belting or ceramic fiber blanket, or as elaborate as utilizing counterweights, pulleys and air cylinders in an attempt to create a more positive seal. The primary purpose of any seal is to keep “tramp” air out of the unit to allow better control of the process. A secondary but important function is to help control dust and hot gases from escaping from the kiln or dryer if there is some sort of “upset” condition. To be successful, the seal for a rotary kiln or dryer must accommodate both axial and radial movement. The major downfall of most seals is too many moving parts susceptible to “sticking” or failure from dust contamination or heat distortion. The three main causes for seal failure are abrasion from product contamination, excessive shell run out in the seal area, and expansion and contraction of the unit during operation. For the purpose of this discussion maintenance issues of four common types of seals will be reviewed. The four types are the graphite block seal, face plate type seals, the outward facing leaf seal and the inverted leaf seal. Troubleshooting Seals
Page 1
In attempting to accommodate these conditions, the major downfall of most seals is too many moving parts!
Page 2
Troubleshooting Seals
The graphite block seal has been around for many years with several variations. The basic components of the seal are two rows of graphite blocks with one end of each block contoured to fit the radius of the shell. The blocks are positioned radially in slide holders that are spring loaded to keep them in contact with the shell. The graphite blocks are staggered in the two rows with every other block overlapping. Many of these installations have now been converted to some style of leaf seal.
Troubleshooting Seals
Page 3
The typical problems encountered with the graphite block seal are heat distortion of the block holders, and dust accumulation causing the blocks to “bind” so they can’t move freely in their respective slides. The result is that the springs can’t keep the blocks in contact with the shell. Another problem is spring failure. Various spring designs have been tried with little success.
Page 4
Troubleshooting Seals
The face plate type of seal has many variations, but the operating principle of most of them is the same and therefore the maintenance issues are similar. We will use the arrangement shown in this illustration as an example for general discussion. The main sealing components are a floating seal plate mounted on the face of the hood, and a fixed seal plate that rotates with the shell. The floating plate has some type of flexible section attached to it which allows the seal to move with the shell. The fixed and floating plates have a wear plate of brass or phenolic material sandwiched between them and held in place with springs, counterweights or air cylinders. Contamination can cause this type of seal to stick. Typically the floating half gets stuck and the sealing rings will disengage with any axial movement of the shell. Product may also build up to the point that it deforms the flexible section of the pressure assembly and causes failure.
Troubleshooting Seals
Page 5
COMMON PROBLEMS causing the face plate seal to leak and become ineffective: 1.
Failure of the device applying pressure to the seal plates. The device should be inspected regularly.
2.
The wear plate can become too thin or “scratched” and “gouged” from contamination; the seal will leak.
3.
Excessive run-out in the shell. These types of seals are particularly susceptible to failure if the shell run-out causes the fixed seal plate to “wobble”. The flexible assembly will allow longitudinal movement but cannot compensate for “wobble” of the rotating fixed ring.
Page 6
Troubleshooting Seals
Another common type of seal is the overlapping leaf seal. The two basic designs are outward-facing and inward-facing (inverted) leaves. The principle of these seals is the same, the major difference being the direction in which the leaves face. The drawback of the outward facing leaves is that they are susceptible to damage from dust accumulation. Most direct-fired units will operate with a slight negative pressure in the hood on which the seal is mounted. An outward-facing seal acts to seat itself tighter against the shell with that prevailing negative pressure. Hence, it creates a positive seal against infiltration of ambient air which is the seal’s intended purpose. However, most combustion is not altogether “smooth” and flame turbulence, even on the best burners, will cause bumps and puffs of positive pressure. The outward-facing seal has an inherent disadvantage because the positive puffs blow the seal open allowing hot air and dust to blow out.
Troubleshooting Seals
Page 7
DAMAGE TO NON-INVERTED SEALS The leaves should be made of a material that can withstand the temperature extremes to which they will be subjected, and still maintain spring pressure without taking a permanent set. The leaf spring should also exhibit some abrasion resistance to provide an adequate service life. The major drawback of the outwardfacing leaf design is their susceptibility to damage from dust accumulation.
Page 8
Troubleshooting Seals
INVERTED SEAL The spring action of the individual spring plates is strong enough to hold against the negative operating pressure in the firing hood. The first advantage of the inverted seal is that a positive puff will act to tighten up the seal, preventing blow-back. With no blow-back there is no hot air flow, no dust can be conveyed through the seal, and dust accumulation is significantly reduced. Secondly the seal leaves run on the riding band instead of directly touching the kiln shell. This provides a sacrificial member if wear occurs. The riding band is mounted in such a way to negate shell run-out at the time of installation. Since the shell run-out has been all but eliminated the flexing of the seal leaves is minimized thereby extending their service life.
Troubleshooting Seals
Page 9
The seal is equipped with a “stub” hopper. The seal is an air seal not a material seal. Nevertheless occasional spillage is expected so a means of removing spillage must be provided. The stub hopper, which is supplied with the seal, is a transition between the open bottom of the seal and some type of conveyor (supplied by others) to remove the the spillage. The conveyor can be a simple material chute, provided enough headroom is available to use gravity or can be as elaborate as an enclosed drag chain in case of limited head room as shown here. The installation shown at the right was installed on a 17’ (5 meter) diameter kiln with only 30” (76cm) clearance from the shell to a concrete floor.
Page 10
Troubleshooting Seals
A “worm’s” eye view inside the hopper reveals the third advantage of the inverted seal. The seal plates are above the hopper, which carries away product spillage. Unlike the non-inverted seal, which “catches” product spillage, the inverted seal does not create a shelf on which product can accumulate. Phillips recommends spraying a graphite powder onto the riding band under the leaves to lubricate them whenever possible. This will help extend their service life.
Troubleshooting Seals
Page 11
PHILLIPS ENVIRO SEAL The inverted leaf seal does have a space requirement but the real plus of the inverted seal is its simplicity of design. There are no moving parts to “stick”. The design incorporates a method to keep the dust buildup away from the sealing components and it is very forgiving of shell run-out.
Page 12
Troubleshooting Seals
Operating a kiln or dryer with ineffective seals or no seal costs money in wasted fuel due to inefficient burning. Also, during an upset condition, puffs of hot gases and product can become a major safety issue as well as an environmental problem.
Troubleshooting Seals
Page 13
CASE STUDY In Unit I of M/s Maihar Cement, two kilns (3 pier each) of 4.35M diameter x 64M length are in operation. Both kilns were equipped with pneumatic plate-to-plate seals at the feed end. The rotating wear plate was mounted on the kiln flange. Pneumatic cylinders were mounted on the stationary plate. Pressure was applied against the smoke chamber plate to force the stationary plate to move in an axial direction to come in contact with the rotating plate. To reduce wear on both plates, a grease pump provided grease lubrication, The seals demanded high maintenance and operational costs. Phillips’ Enviro Seals replaced the pneumatic seals, installed in November 1997 and August 1998. Operational efficiency of the kilns was improved; air ingress was reduced and out-going dust was captured. There has been no maintenance cost on the seal to date (1997 - 1998). The life of the leaf plates has yet to be established. Plant operators have calculated that they have saved $22,000 in fuel costs in one year.
Page 14
Troubleshooting Seals
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