Seal-less pumps

Circulate vessel contents via external, seal-less pump... 

It should be noted that shaft- and plunger-seal problems can be avoided by using hermetic (seal-less) pump types. 

The VOC emissions occur from leaks around from valve stems, pump shafts, worn packings, and pipe joints. Fugitive VOC emissions can be minimized with proper design and specifying seal-less pumps and valves, and with good preventive maintenance. 

A wide variety of excellent pumps is available in the chemical industry. It is sometimes a problem to choose the best from the large number available. This discussion will be limited to centrifugal pumps. Assuming that one has sized the pump, decided on a centrifugal pump, and chosen a suitable list of vendors, the main choices involve (1) metallurgy, (2) seal-less pumps versus conventional centrifugal pumps, and (3) the type of seals for conventional pumps. 

Properly installed and maintained, seal-less pumps, especially magnetic drive pumps,... 

Seal-less pumps are becoming very popular and are widely used in the chemical industry. Mechanical seal problems account for most of the pump repairs in a chemical plant, with bearing failures a distant second. The absence of an external motor and a seal is appealing to those experienced with mechanical seal pumps. However, do not assume that just because there is no seal, seal-less pumps are always safer than pumps with seals, even with the advanced technology now available in seal-less pumps. Use seal-less pumps with considerable caution when handling hazardous or flammable liquids. 

A monitor to detect bearing wear is available on some seal-less pumps but they generally don t offer complete monitoring of all internal bearings for axial and radial wear. Seal-less pumps typically run so smoothly and quietly that it is usually not possible to determine by vibration or noise if a bearing is badly worn. 

However, the best approach of all is to continue moving left along the equation and remove the hazard itself. One of Trevor Kletz s mottos was, If a tank s not there, it can t leak. So, in the case of the leaking pump seal the smart safety professional asks questions such as, Can we use a canned/seal-less pump or Can we replace the pump with a gravity feed system (These new concepts introduce a new set of risks that also must be analyzed and deemed to be acceptable before they are implemented.)... 

This seal-less pump has the motor and all rotating components inside a pressure vessel. The pressure vessel components are designed for full reactor coolant system pressure. The pressure boundary integrity is verified for normal, anticipated transients and postulated accident conditions. The pressme boundary components meet the requirements of the ASME Boiler and Pressure Vessel Code, Section III, as described in Section 6.3.2.1.3. 

Unlike shaft seal pumps, seal-less pumps cannot be repaired in situ, requiring a design to be developed for quick removal and replacement of entire pumps. 

Design work is currently ongoing to upscale the canned motor reactor coolant pumps of the AP600 to the more powerful seal-less pumps required by the APIOOO. 

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