Recent advances in Gland Packing (Part-1)

  • A dyestuffs manufacturing unit was facing difficulty in sealing stuffing box of glass lined reactor used for hydrogenation at 120°C &3KG pressure. Packing rings of imported graphite /PTFE hardened within 1 month; with continuous leakage of acidic fumes causing pollution and corrosion to surrounding steel structure.
  • A chemical manufacturing plant had a problem of sealing stuffing box of rotary vacuum dryer. The equipment contained a powder to be dried; which, if comes in contact with moisture in air would be useless and a waste. Conventional packing like asbestos impregnated with PTFE resin as well as PTFE / Kevlar were tried with little success. Vaccum loss , Ingestion of moisture, scoring of the shafts /sleeve were reported.
  • A chemical manufacturer had a problem in the smooth operation of chemical pumps handling concentrated nitric acid. The pumps shaft were fitted with Teflon Bellow Mechanical Seats and rotated at speed of 2800 rpm. The mechanical seals failed and had leakage rate of 70 to 80 drops per minute. The plant had a total of eight pumps. This resulted not only loss of chemicals but also created pollution problem.
  • A pesticide manufacturing unit reported leakage of pesticide from the stuffing boxes of screw pumps. They also reported loss of vacuum, leakage of obnoxious fumes from stuffing boxes of agitator reactor vessel and glass lined reactor vessel. In all the equipments the shaft / sleeve were badly scored. To seal these leaky stuffing boxes various packings like PTFE / Graphite. Kevlar, and asbestos were used but failed to give desired sealing.

Most process engineers have a nightmarish experience of leaking stuffing boxes in pumps, agitators reactors, glass lined reactors, autoclaves, agitator nutche filters, rotary vacuum dryers, high temperature steam valves and other equipment having rotating shafts. Some of the problems encountered are mentioned below :

 

Loss of expensive chemicals.

Excessive man-hours lost to continuously adjust leaking stuffing boxes.

Frequent plant downtimes due to premature packing failures.

Frequent bearing failures du to contamination of bearings lubricants by the process fluid.

Continuous escape of dangerous chemicals & fumes through stuffing box can result in plant shut down by the pollution control board.

 

Loss of recovered gases / liquid Lowering of yield / purity

In unit operations carried under vaccum, air ingestion through stuffing box results in loss of vacuum thus increasing batch time, reducing plant productivity and poor product quality.

Leaking stuffing boxes can jeopardize the functioning of the entire chemical plant.

 

Conventional Compression Packings You can visualize Leakage.

Conventional gland packing including asbestos, pure PTFE yarn, pure Graphite yarn PTFE Graphite yarn and Kevlar/aramid are categorized as compression gland packings. These packing constantly need to be tightened to grab the shaft to control leakage. Now if you tighten these gland packing you get scored shaft /sleeve and increase load on motor, leading to more leakage as leakage path way is already made. If gland follower is not tightened leakage is not controlled. These compression packing when tightened frequently becomes hard/glaze and eventually fail to provide proper sealing. During this frequent tightening process, only gland packing rings near gland followers get compressed to control the leakage causing 70% wear and tear of shaft sleeve; whereas remaining packing ring so not participate in sealing, due to absence of glad pressure transfer to the inner most ring. (as illustrated in the diagram) The inherent drawback associated with compression packing i.e. “COMPRESSION SET” takes place, resulting in hardening and glazing of packing rings. Hence it is a practice to replace the gland packing rings near the gland follower with new rings.

*********DIAGRAM 01
Sealing by conventional Compression Gland packing

 

Reinforced Synthetic Yarn Packings

In the early nineties Stoplik introduced patented Reinforced Synthetic Yarn Packings composed of PTFE/Graphite Yarn reinforced with synthetic fibre. The synthetic fibre imparts the property the recuperation, there by exerting a back pressure on the gland follower. Gland load transfer is to the innermost ring and sealing is by the entire packing set. This enables the packing to work effectively with minimum gland load. The packing does not grab the shaft and does not solidify. The packing rings remain soft for prolonged operations. The packing materials are self lubricating, have extremely low coefficient of friction and exhibit excellent heat transfer characteristics. This results in excellent sealing.

****DIAGRAM 02

Behaviour Pattern of Reinforced Yarn Packing

 

In-Situ Mold

Sealing stuffing box with scored shaft /sleeve is a nightmare for process engineer as the packing gets cut into pieces in no time. Stoplik have developed patented In-situ Mold for sealing even if shaft /sleeve is scored. As the name suggests the packing mold it self in the stuffing box and seals the undulations /scorings. This mold fills up the deformities & scorings in the shaft and provides an even surface for glad packings. It is an excellent packing material for forming. Unlike pure carbon fibre packing and flexible graphite tape die formed ring which require minimum 32 RMS finish of Shaft / Stem to function effectively. In-situ mold have been used successful on pitted /scored shafts. The patented design and composition of inter lock fibre allows it to be used most effectively for these critical application without extrusion.

More details on Stoplik In-situ Mold will be published in Part 2 the following week.

 

Case Studies

  • The hydrogenation plant of a leading manufacturer of flavouring chemicals reported of a very poor yields. The hydrogenator consisted of a pressure vessel with a rotating shaft at 1440 rpm & 40 mm diameter. Hydrogenations was carried under pressure of 2.5 bar and temperature 80°C. The stuffing box packed with conventional PTFE/Graphite was ineffective as there was continuous leakage of hydrogen, resulting in pressure loss & there was a possibility of explosion due to hydrogen leakage and low yields. Nine hydrogen gas cylinders were required per batch. The stuffing box was repacked with patented “Stoplik“ Reinforced Yarn Packing. After installation there was no leakages of hydrogen resulting in excellent yields & improved product quality. Only six hydrogen gas cylinder were required per batch. Plant productivity increased substantially.
  • A leading detergent manufacturing company was finding a difficulty in sealing leakaging stuffing box of LABSA gear pump. The pump was having shaft die of 32mm and rotating at 1440 RPM. Conventional asbestos impregnated with PTFE resin as well as PTFE /PTFE Graphite combination (panther/zebra) packing used could not serve purpose as LABASA was continuously leaking. The pump was repacked with patented Stoplik reinforced yarn packing and in-situ mold. This combination performed successfully for mote than four months without leakage of LABSA. Pollution from the stuffing from the stuffing box was totally eliminated leading to better working conditions.

A reputed petrochemical plant reported leakages super heated steam from valves of various sizes and designs. Conventional Packings including flexible graphite, asbestos with Iconel wire and carbon fibre packings were tried without success. The valves stems were repacked with Stoplik In-situ High Temperature Mold sandwiched between the exiting packings. Leakages of steam from the valves were stop resulting in substantial energy savings, reduced down times and reduced maintenance cost.

 

M/S. STOPLIK SERVICES (I)PVT.LTD.
Kirit Kumar Nanani-Director,
Plot no A /465, Road no.28, Wagle Industrial Estate, Thane -400604.,(Mah.), India.
Ph.: 022-61597100 / 101 / 102
Fax : 022-25822564
Website : www.stoplikpackings.com

 

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