There is an inherent irony at the root of many industrial manufacturing processes: oftentimes, “bad” things are needed to produce “good” things. Or, to be a little more specific, hazardous things are needed to manufacture useful things. Manufacturers who produce chemical-based compounds such as caustics, acids, solvents and polymers should be well aware of this dichotomy.
Hazardous substances like toluene, xylene and ethylene oxide—along with hundreds of others—that can be harmful to humans and the environment if mishandled are nevertheless indispensable components that must be used in a large number of industries and end products. A tip-of-the-iceberg list of such industries and products includes, but is hardly limited to, petrochemicals, paints and coatings, soap and detergents, biofuels, adhesives, pulp and paper, food processing and herbicides and pesticides.
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 through the loss of raw materials, as well as for cleanup and potential environmental remediation. These factors combine to make the full containment of dangerous chemicals a front-of-mind concern for facility operators.
Pumps are critical pieces of equipment used in the manufacture and handling of dangerous chemicals. They are commonly used to introduce raw materials into the production process or to transfer end products for packaging, storage or shipping to end users. Mechanically sealed pumps have become the accepted technology of choice for these transfer activities. However, this article will attempt to illustrate how sealless pump technologies may be a more effective choice when full containment of dangerous and valuable chemicals is an absolute must.
Challenges
When handling dangerous chemicals, there are four main areas of concern that manufacturers must identify and satisfy:
Safety: Ensuring that site personnel, surrounding communities and the environment are not harmed
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
Maintenance: Mechanical shaft-seal failures are the number one cause of pump downtime in chemical processing activities. Excessive maintenance costs generally are accumulated in two ways—the need to constantly repair, rebuild or replace underperforming pumps or components, and in the downtime that brings production runs to a halt for several hours or days
Operating costs: An overlooked strain on the bottom line can be found 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 when creating a budget
The most common pump technologies used in the manufacture and handling of dangerous chemicals include diaphragm, sliding vane, lobe, progressive cavity, centrifugal and gear. All these traditional pump technologies have one thing in common: they rely on various types of mechanical seals or packing rings to prevent shaft leakage.
Mechanical seals and packing rings are present in most of the pumps used in hazardous chemical processing applications, but both have their own potential operational shortcomings.
Packing rings: This method utilizes braided packing material that includes a set of formed rings wrapped around the pump shaft and held in place by an adjustable gland that has been designed to control shaft leakage. To that end, a small amount of leakage is needed for lubrication and cooling, which can become problematic when handling hazardous chemicals. Therefore, while packing has been widely used in a variety of industries (such as in resin and paint and coatings), it should not be generally considered a best practice for transferring hazardous chemicals.
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, maintain and replace.
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 and may result in downtime that can slow the production process.
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 a chemical cleanup process. 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 raises liability issues, while a major leak that can cause damage to the environment can have far-reaching negative effects.
Solutions
While sealed pumps can perform admirably in the manufacture, transfer and handling of dangerous chemicals and other hazardous materials, the shortcomings inherent in their sealed design can make them insufficient for the job. An alternative technology that can help eliminate some of the major concerns associated with achieving full containment: sealless
sliding vane, internal gear and eccentric disc pumps.
Let’s take a look at 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 with 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 can help contribute to an estimated 50% reduction in maintenance costs. .
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, high suction lift 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 usable raw materials and saleable end products.
Sealed pumps have been performing sufficiently in chemical manufacturing operations for many years. However, operators who are looking for an alternative are now able to upgrade their facilities with sealless pumps.
