To the average person, many of the raw materials that are commonly used in the manufacture of chemicals can resemble either a steaming bowl of alphabet soup – KOH, NaOH, HCl and HF, for example – or a bad Scrabble rack – toluene and xylene, monomers and polymers, for instance. However, those who make a living manufacturing such chemical-based compounds as caustics, acids, solvents and polymers know that valuable chemicals are pivotal to the production process, but can also be extremely dangerous and harmful to site personnel and the environment if not handled properly.
Chemical processors who require full product containment would be wise to consider the benefits of sealless pumps when compared to traditional pumps that feature packing glands or mechanical seals.
This is a constant concern for manufacturers, as hazardous chemical compounds are used in a large number of industries and products, such as: adhesives, biofuels, petroleum additives, polyurethane foam, molten sulfur, pulp and paper, food processing, resins, soap and detergents, paint and coatings, lube oils and greases, petrochemicals, herbicides and pesticides, and silicates.
In addition to being widely used and potentially dangerous or hazardous if mishandled, many chemical compounds are also extremely expensive. If a leak were to occur during the handling or transfer of these products, large costs would be incurred by the operator due not only to the loss of raw materials, but also for cleanup and potential environmental remediation. All of these factors combine to make the full containment of dangerous chemicals a front-of-mind concern for facility operators.
Crucial pieces of equipment that are utilized during the manufacture and handling of dangerous chemicals are the pumps that either introduce raw materials into the production process or transfer end products for packaging, storage or shipping to end users. Mechanically sealed pumps are commonly used for these transfer activities, but this article illustrates how sealless pump technologies can often be the more effective choice when full containment of dangerous and valuable chemicals is an absolute must.
Sealless sliding vane pumps feature a magnetic coupling consisting of samarium-cobalt magnets and a unique bearing and head design that allows a small quantity of pumpage to circulate through the containment can, which minimizes temperature rise and maximizes bearing life.
The challenge
When handling dangerous chemicals, there are four main areas of concern for manufacturers:
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- Safety: Ensuring that site personnel, surrounding communities and the environment are not harmed
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- Product containment: When dangerous or hazardous products are fully contained and not allowed to leak, valuable raw materials and products are not lost to the environment, improving safety overall
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- Maintenance: Mechanical shaft-seal failures are the number one cause of pump downtime. Excessive maintenance costs generally are accumulated in two forms—the need to constantly repair, rebuild or replace underperforming pumps or components, and in the downtime that brings production runs to a grinding halt
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- Operating costs: An overlooked drag on the bottom line can be in the form of seal-flush water with the impact of the seal water on the process and the cost of the flush water needing to be taken into account
The most common pump technologies that are used in the manufacture and handling of dangerous chemicals include diaphragm, sliding vane, lobe, progressive cavity, centrifugal and gear. All of the traditional pump technologies have one thing in common: they rely on various types of seals to prevent shaft leakage. The two most common types of seals, packing and mechanical, are used in many hazardous-chemical applications, but they both have their own potential shortcomings:
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- Packing rings: This method utilizes braided packing material that includes a set of formed rings that are wrapped around the pump shaft and held in place by an adjustable gland that has been designed to control shaft leakage. A small amount of leakage is needed for lubrication and cooling. Packing has been widely used in a variety of industries (such as in resin and paint and coatings), but should not be generally considered a best practice for hazardous chemicals.
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- Mechanical seals: These seals come in two general variations: single and double. Single mechanical seals can usually adequately address the problem of fluid leakage, but when used with liquids of higher viscosity, the product drag can distort the seal or cause it to break away from the shaft completely. Single mechanical seals also are incapable of containing potentially hazardous vapors. Double mechanical seals can prevent the escape of vapors and are more reliable when handling viscous liquids, but they can be prohibitively expensive to acquire, repair, clean and maintain.
While any of the various types of seals can perform admirably for long periods of time, they will eventually need maintenance or need to be replaced before major shaft leakage can occur. Replacing the seals, not only after they fail but also as a form of preventative maintenance, is costly.
The cost of a leak to a manufacturer includes the loss of valuable raw materials or finished products, downtime in production, and the costs and potential penalties associated with the chemical cleanup. Leaks of hazardous materials that reach the outside environment can be subject to fines and remediation costs from the U.S. Environmental Protection Agency (EPA), as well as other local and state regulatory agencies. Additionally, other countries have their own sets of regulations, which can often be more stringent than those in the U.S. Spilled hazardous materials also pose safety risks for site personnel and cleanup crews, which raise liability issues.
Next-generation sealless internal gear pumps feature only one fluid chamber, which not only enhances product containment, but eliminates product entrapment, especially when transferring high-viscosity liquids.
Sealless eccentric disc pumps feature no seals, packing, couplings or magnets, which translates to full product containment coupled with the added benefit of optimized product-recovery rates.
The solution
While sealed pumps can perform admirably in the manufacture, transfer and handling of dangerous chemicals and other hazardous materials, the sealed design can sometimes make them insufficient for the job. For the operators of chemical-manufacturing facilities, sealless pumping technologies can help eliminate some of the major concerns associated with achieving full containment: sealless sliding vane, internal gear and eccentric disc pumps.
Here are some of the advantages of a few specific sealless pumping technologies:
- Sliding vane: Sealless sliding vane pumps constructed of corrosion-resistant stainless steel generally feature a magnetic coupling consisting of samarium-cobalt magnets and a unique bearing and head design that allows a small quantity of the pumpage to circulate through the containment can and onto the bearing surfaces. This positive flow of fluid minimizes temperature rise during operation, which helps maximize bearing life. Replaceable 316 stainless-steel end discs allow easy rebuilding of the pumping chamber to like-new condition without having to remove the pump from the piping. Additionally, carbon-graphite sleeve bearings help ensure no metal-to-metal contact during operation. Operationally, sealless sliding vane pumps offer the same advantages as their sealed cousins: volumetric consistency, self-priming and limited dry-run capability, drain plugs that allow easy draining and easy replacement of worn vanes.
- Internal gear: Technological advancements in internal gear pump design and operation now offer to the market models that have only one fluid chamber. This method of construction removes the adapter plate that is a staple of traditional two-chamber magnetically coupled internal gear pumps, which eliminates product entrapment concerns, especially when transferring high-viscosity liquids. One-chamber operation is achieved through a between-the-bearings design that places the magnets directly on the pump rotor, resulting in a simpler flow path and full leak-free product containment. Some sealless internal gear pump models are also constructed of as few as seven parts, which helps contribute to an estimated 50% reduction in maintenance costs when compared to sealed pumps. There are also sealless internal gear pump brands and models that are interchangeable with 95% of competitive sealed or packed-gear pump brands, making time-saving drop-in replacement a reality.
- Eccentric disc: Sealless eccentric disc pump models feature no mechanical seals, packing, couplings—or even magnets, with the shaft sealed instead by a unique double stainless-steel bellows. Operationally, sealless eccentric disc pumps can still offer self-priming, dry-run and low-shear operation, very high suction and discharge pressures, the ability to pump both low- and high-viscosity liquids and clean-in-place/sanitize-in-place (CIP/SIP) capability. Additionally, by virtue of the unique eccentric disc operating principle that allows them to pump air, sealless eccentric disc pumps can achieve product-recovery rates of 90% or more on the suction side and 60% to 80% on the discharge side of transfer lines. This enhanced product-recovery capability can result in thousands of dollars in cost savings annually from the retrieval of still useable raw materials and saleable end products.
These varying types of sealless pump technologies can help overcome the four major challenges in handling dangerous chemicals or hazardous materials: optimized safety; full product containment; reduced maintenance; and streamlined operating costs.
Conclusion
Sealed pumps have been performing sufficiently in chemical-manufacturing operations for many years. However, operators who are looking for an alternative should look to upgrade their facilities with sealless pumps. These types of pumps will reduce leakage events and improve containment of dangerous or hazardous materials. Maintenance costs can also be lowered to such a level that the lifetime cost to operate the sealless pump may be half that of a sealed model. Most important to the operator, the use of sealless pumps can increase the peace of mind that comes with knowing that not only is personal and environmental safety being optimized, but that the bottom line is receiving a boost, as well.
