Equipment Reliability Improvements in the Pulp and Paper Industry: Part 3 of 3 – Energy Savings Using Technology

Part 3 – Energy Savings Using Technology

Following on from Part 1 in this series, where we reviewed issues and solutions surrounding effective bearing lubrication, and Part 2, which discussed uncontrolled water leakage from the stuffing box – we now look at ways to reduce energy consumption of common sealing methods used within the pulp and paper industry.

Mechanically Packed or Gland Packed Equipment

Historically, swapping the packing for a mechanical seal has been the answer to reducing energy consumption in gland or mechanically packed equipment. But does this still hold true today?

Traditional packing was manufactured using raw fibres that were beneficial for temperature absorption, pressure stability and the ability to withstand chemical attacks. These were “stitched” together, forming tight bundles that create a tortuous path for pressurised liquids to pass through – making it a good sealant. The bundles of fibres are often dipped into agents that block the path of pressurised liquids and reduce the friction caused by compression along the moving shaft.

The effectiveness of the seal was determined by the method of manufacture, materials and the quality of the installation. The latter particularly affects how the packing seals against stationary stuffing box walls, as well as rotating or reciprocating equipment shafts.

However, tightening the gland follower nuts to prevent leakage is not the answer. It increases friction onto the shaft, leading to premature shaft and shaft sleeve wear and, eventually, excessive leakage and the resulting downtime to replace.

Furthermore, upping the friction levels increases the power demand necessary to move the shaft.

Today’s advanced material technology and improved installation techniques overcome many of these issues in the following ways:

• Heat-resistant fibres, such as premium carbon yarns, have high resistance to pressure and temperature conditions, sealing well with gentle compression.
• In turn, this reduces the friction on the shaft and the power needed to move the shaft.
• Combining this with a high-resilience aramid fibre that’s inter-braided in a particular way results in a high-performance DualPac packing, requiring significantly fewer gland adjustments, a simplified inventory, minimises shaft/shaft sleeve scoring and provides lower power consumption than traditional packing.

These tables compare lab testing over various traditional design packing compared to the latest technology.

Removing human error that’s often associated with overtightening is key. Automated gland adjustment systems use air pressure control to provide only the necessary compression required. This removes excessive drag on the shaft and the resulting wasted power.

Packing installation also plays a key role in reducing power consumption. Many stuffing boxes use lantern rings to aid lubrication. These are often mislocated within the stuffing box, as older packing rings shrink and harden over time and then over-compress onto shafts. Again, this increases friction and energy needs. This anomaly is covered in greater depth in Part 2.

The key takeaway is that selecting the latest packing technology and installation methods equals immediate power consumption savings.

Bearing Isolation – Lip Seals

Part 1 covered the functionality of lip seals as bearing isolators/protectors and how traditional designs can fret shafts. These older designs can also create drag on the shaft, thus draining more power to overcome it.

The latest design profiles and materials effectively reduce friction along the shaft and reduce power consumption accordingly. Advanced heat and friction-resistant materials are now used in many applications, substantially lowering power usage.

Moving to a labyrinth seal removes shaft friction entirely. Labyrinths create a convoluted surface, making it difficult for lubricating oils and greases to escape. It’s also hugely effective against the ingress of water and dirt into the bearing housing. Removing all friction and drag dramatically reduces energy needs, and being wholly contactless, the technology has a virtually infinite lifespan.

Mechanical Seals

Mechanical seal use in rotating equipment is increasing in popularity. The design uses less power – however, users should ensure the following to minimise energy usage and effective operation.

1. A balanced mechanical seal face

• Has lower closing force applied, thus requiring less turning power to overcome closing friction
• Hard face in-line configuration can be used with slurry applications with a balance feature

2. Run one softer face material against a harder face material

• A softer face is self-lubricating, therefore, creates less friction.
• It can be used in slurry applications in combination with a good environmental controller.

3. Mechanical seal environment control

• Seal support systems can waste power in the following ways:
• Flushing a single mechanical seal (or compression packing) involves injecting external cold fluid into the sealing cavity to provide cooling.
• Cooling systems used with single mechanical seals affect the thermal efficiency of pumping systems.
• Dual mechanical seal cooling requirements lose thermal energy due to the design.

The following examples look at the energy involved in two scenarios of a condensate pump:

Scenario 1

Pump sealed with mechanical seal that uses cooled recirculation (Plan 23).

This system moves liquid into a heat exchanger and then re-flushes it back to the seal chamber. This fluid becomes isolated by the close clearance neck or throat bush. This leads to a mismatch of the amount of stuffing box liquid and that which needs to be reheated, resulting in a loss of energy that equates to US$819 per annum.

Scenario 2

Pump sealed with a single mechanical seal with special design.

The seal faces use a unique geometry that doesn’t require external cooled recirculation to function. This system is the most efficient pump operation method without compromising on reliability.

Modern technology, advancements in materials and design experience drive many new innovations that reduce energy demands. Small changes to both lip seals, packing and mechanical seals can equal large savings in power consumption.

This 3-part series has been designed to show multiple methods of improving plant equipment efficiency, output and reliability within the pulp and paper industry.

Chesterton can provide bespoke solutions to overcome many of your plant challenges. To explore these efficiency and money-saving options, contact one of our experts today.