Seal-less gear pumps

Paul Boughton

When transporting toxic and environmentally hazardous liquids, the use of magnetically coupled pumps can be a very good alternative to traditional mechanical seal construction, as only minimal maintenance is necessary.

Since the mid-1990s, the Desmi Rotan type ED pump (Environmental Duty) has become increasingly popular within a wide range of sectors. Major application areas include chemical raw and refined material transfer, liquid tar, pitch for making electrodes to the aluminium industry, liquid sulphur among many others. Rotan pumps are available in many different materials with or without heating jackets.

Rotan magnetically driven pumps have two design features which gives maximum performance during liquid transfer: The patented cooling system, which is an internal pumping system, eliminates the need for external cooling, and the dynamic axial balancing system which minimises axial loads, energy use, and ultimately increases lifespan. ED pumps are used in many industries to pump a great variety of chemical raw material and finished products. Just two examples, which have often caused problems with sealed or packed pumps:

- Isocyanate (Toluene di-isocyanate and MD), prevents serious implications for health, safety and environment. At the same time life cycle costs are significantly reduced compared with traditionally sealed pumps.

Rotan's magnetically coupled pump is the ultimate solution to one of the most hazardous problems of all pumps, namely the leakage problem. The Rotan ED pump offers a leakage free option and environmentally friendly transfer of liquids with viscosities up to 10000cSt. Isocyanate is one of the components in almost all foam products. There are various types of isocyanate, but common to all of them is that they react to the humidity of the air, thus forming very hard crystals which wear out the pumps and mechanical shaft seals. There are different methods to avoid this problem of humid air getting into storage tanks:

Using inert gas in the storage tank (nitrogen), fitting a silica gel filter on top of the tank or having ultra dry air as an 'inert gas', prevents the isocyanate from forming hard crystals.

Systems pumping isocyanate should be provided with a filter or a strainer to avoid crystals, if any, to circulate in the system constantly. All isocyanates are hazardous and the vapour should not be inhaled. Contact with the skin leads to discoloration and prolonged contact may result in allergic reactions. Rotan always recommend the use of magnetically-coupled pumps for isocyanate.

Bearings in tungsten carbide is the preferred bearing material. Rotan ED pumps are recognised by leading international and domestic manufacturers such as Bayer, BASF and Huntsman. The ED pumps effectively reduce the life cycle costs and downtime in the factories.

ED pumps hold a major future in the petrochemical, paint and coating business as well as the liquid pitch and tar industry, and magnetically driven Rotan pumps are often a very economic solution compared to traditionally sealed pumps.

- Liquid sulphur. Although molten sulphur is commonly delivered using packed style pumps, the product that seeps through the packing creates significant problems. Several years ago a Rotan magnetically driven pump was offered where zero leakage was required in the soap industry. For the first time a Rotan ED series pump was offered.

Sulphur temperature must be controlled within a 120°-155°C temperature range. Outside this temperature range sulphur solidifies. Rotan model MD33EFDK-1U33 jacketed pump including carbon graphite bushings and high temperature magnets proved successful.

Following our initial success the process engineer agreed to serve as a reference where Rotan pumps were being considered in a more aggressive service where sulphur is delivered to a burner in the production of mercaptan. Mercaptan is used as an odorant within natural gas and used in the production of plastics.

The initial success in the soap industry lead to a nice order within Arkema Corporation and included five Rotan model MD51EFDK-3U88 units complete with gear reduction. In this case stainless steel construction was required where contaminates caused corrosion to cast iron materials. Due to higher continuous duty operating pressures, tungsten carbide bearings and thrust washers were selected. Following several years of success, a sister plant followed with another significant order in 2009.

Molten Sulphur is burned to produce S02 in a process that conditions flue gas in coal burning power plants. A Rotan model MD101EFDK-1U33 is used as a transfer pump and another order followed in the same service.


Rotan magnetic driven pumps are proven in molten sulphur service where typical flows range from 2-150gpm. Care should be taken since some sulphur products are corrosive and some include abrasive contaminants. In these cases stainless steel materials and tungsten carbide should be considered.

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Dan Roldgaard is with DESMI A/S, Norresundby, Denmark.

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