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Pump rapidly pulls down vacuum in reactor vessel

Edited by the Engineeringtalk editorial team Oct 17, 2000

In developing a new high-performance, chlorine-free, lubricating oil dispersant at its Bromborough plant, Lubrizol needed a reliable vacuum solution and turned to Rietschle

In developing a new high-performance, chlorine-free, lubricating oil dispersant at its Bromborough (Merseyside) plant, Lubrizol Limited needed a vacuum solution that was robust, reliable and technically capable of meeting very demanding process specifications.

Rietschle's 'Twister' single stage vacuum pump satisfied all of the process requirements, and thanks to its dry running design, it has given Lubrizol a zero environmental load.

With revenues of $1.75 billion in 1999, the Lubrizol Corporation is the world's largest independent supplier of additives.

Its engineered chemicals are essential components in lubricants and fuels, contributing to the smooth and dependable operation of cars, trucks, tractors and industrial machinery.

Although base mineral oils have altered little over the years, the lubricants in today's car engines allow them to run for thousands of miles without maintenance.

Additives are behind the enormous improvement in lubricants, as readers old enough to remember constant oil changes and sumps full of sludge will testify.

A key challenge facing Lubrizol in developing a high performance, chlorine-free dispersant, was finding the right vacuum system.

It had to be robust enough to cope with process temperatures above 200C, and be capable of rapidly pulling down vacuum in the reactor vessel to 70 mbar (abs).

Chemical feed stocks are always demanding products to handle, but the reactant material used in the process is Maleic Anhydride (MAA), which is particularly tricky.

It sets solid if it comes into contact with water at any stage, or if the process temperature drops below 53C.

MAA is also a Class A volatile organic compound (VOC).

Lubrizol looked at various vacuum solutions, including the use of a liquid ring pump.

However this was ruled out, partly on environmental grounds and partly because of the reaction of MAA to contact with water.

Reliability was also a major consideration for process engineer, Chris Smith.

"The last thing you want to be doing is shutting down an MAA process and having to strip out the material by hand - either from a health and safety or a cost viewpoint." Lubrizol's choice was the VSA 800 from Rietschle's Twister range dry-running, twin screw, single stage vacuum pumps.

Highly tolerant of process by-products, Twister vacuum pumps are ideal for solvent recovery and high vacuum duties.

The VSA 800 supplied to Lubrizol had all process-wetted parts nickel coated, and was designed with special clearances to run at elevated temperatures.

Lubrizol considered a number of alternative solutions, but many dry-running vacuum pumps are over-complicated for arduous duties.

Only the Twister was sufficiently robust, and technically capable of handling the full range of specification, particularly the need for rapid pull-down in the dehydration phase.

Its dry-running design has given Lubrizol a zero environmental load, which means that there is no contaminated oil or other waste to dispose of.

Exhaust vacuum from the pump goes straight into a thermal oxidiser, which eliminates VOCs and any other entrained organic compounds.