library_technicalarticles_21_pic1In October of 1980, Lever Brothers Co. dedicated a bar soap plant which more than doubled its soap processing and packing capacity at Hammond, Ind. Built on the same site as Lever’s original, 1930-vintage manufacturing plant, the facility is one of the most advanced in the world. Its continuous soap processing technology reduces a 10-day batch operation to a matter of hours.

In conjunction with the new plant, Lever initiated a soap improvement project designed to optimize deodorization of the soap making oils. The project was aimed at achieving product improvement and cost reduction as well by increasing the effectiveness of the perfume agents needed for the soap. Chosen to accomplish this goal was a three-stage “Evactor” (stream jet ejector) system complete with surface intercondensers and sophisticated energy saving arrangements designed and manufactured by Croll Reynolds, Westfield, N.J.

At Lever Brothers, soap making basically involves saponification of tallow and vegetable oils. The vacuum deodorization process is designed to vaporize and remove the lighter fractions of the oil that contain the odoriferous products. The heat of a normal boiling process would damage the oil. However, under high vacuum, the oil vaporizes at low ambient temperature. This is essentially a steam distilling process, with steam sparged through the oil at low pressure. The steam carries away the lighter fractions, which are collected to be used in industrial soaps or sold.

The vacuum deodorization system is designed for energy efficiency. The primer, used in conjunction with the first-stage booster, handles the product vapor while reducing the pressure to 100 mm Hg abs. The main system is capable of further reducing the pressure to 4.5 mm Hb abs. – when supplied with 200 psi steam and 75 degree F cooling water.

For energy efficiency, intercondensers are used between stages. They are made of carbon steel and are surface (shell and tube) type. The first intercondenser has a 36 inch diameter shell and 1420 feet of surface area; the second an eight-inch diameter shell and 35 square feet of surface area.

The Hammond plant is located on Lake Michigan and uses its water for cooling in this vacuum deodorization system. Surface type condensers were specified to prevent any possible contact of product with condensing water from the lake.

Depending on the weather, lake water temperature varies throughout the year, from a summer high of 75 degrees F, down to 32 degrees F, in winter. Designed for the high temperature water, the system works at higher efficiency when water is cooler. To take advantage of the cooler water when available, Croll Reynolds provided a ratio control which reduces steam pressure when cooling water is below the design temperature of 75 degrees F. This reduces steam consumption and also ensures that the system will operate at the exact vacuum required, regardless of variables. When lake water reaches 60 degrees F., for example, total steam consumption drops from 4,270 pounds to 3,500 pounds per hour. At lower temperatures, the ratios are even more favorable.

In planning the soap improvement project, Lever explored the possibility of using vacuum pumps for the preliminary stages, although it realized that only a steam ejector could reach the high vacuum needed. Investigating mechanical vacuum pumps, the company found that the fatty acids present in the oils would require the pump to be custom made of costly exotic materials. The presence of fatty acids also ruled out the use of liquid ring pumps for the initial stages, because of contamination of the cooling water.

Lever has had very good success with the operation of the Croll Reynolds “Evactor” system. Its steam consumption has been found to be reasonable for the reliable high vacuum it produces, and the system is even more favorable during that part of the year when lake temperatures are lower than design.

By: William Neuner, Project Engineering Manager – Bar Soaps, Lever Brothers Co. New York.