Coating Calcium Carbonate

CONTINUOUS COATING OF CALCIUM CARBONATE WITH STEARIC ACID

The mixing and coating technologies represent major activities within the powder processing division of Bepex. Over the years Bepex has developed several processes which lend themselves to very efficient utilization of certain standard product lines. This paper is intended to describe one such specific process. The Bepex Turbulizer™ isused to continuously heat and coat calcium carbonate with stearic acid. The purpose of heating the mixture is to melt the stearic acid whereby it can be added in powder or flake form. Within the Turbulizer™ the melted stearic acid homogeneously coats the calcium carbonate. Stearate treatment levels range from .5 to 2% by weight. The material residence time inside the Turbulizer™ is approximately5 seconds. The incoming feed materials enter the Turbulizer™ at ambient temperatures and discharge at temperatures ranging from 200-300°F. Turbulizer™ jacket temperatures range from 350-500°F. Hot oil is the most common heat transfer media for this application, however steam at 150 psi is also used in some plants. The energy required for heating and coating the materials in this application isapproximately 50 kilowatt hours/ton. Ten cents/kilowatt hour amounts to 5 dollars/ton of processed material. This price does not include the 20 pounds/ton of stearic acid consumed.

Bepex International LLC
333 Taft Street NE Minneapolis,
MN 55413 USA
Phone: +1 612 331-4370 Fax: +1 612 627-1444
www.bepex.com

HISTORY The Turbulizer was first invented in 1958 by the Strong-ScottManufacturing Company which later became Bepex Corporation, and is now called Bepex. Its intended usage, at that time, was for dispersing shortening into flour mixes for the bakery industry. A few years later, the first jacketed unit was developed for both heating and mixing of ingredients. The Turbulizer’s heat transfer efficiency was discovered to be extremely high due to the intimate contact betweenthe material and the heated inside surface. With the maximum tip speeds in the 8-10 thousand feet/minute range, the Turbulizer is very effective at dispersing the materials in the short time that they spend in the mixing chamber. Typical residence times range from one to ten seconds. With this type of flexibility the Turbulizer has been used in a wide range of applications, from simple mixing ofpowders to continuous reacting of powders with gases. Several hundred units have been sold over the years in the food, chemical, plastics, mineral and pharmaceutical industries. Turbulizers come in sizes ranging from 8” diameter to 48” diameter and in throughput rates from 200 pounds/hour to 200 tons/hour. With the compact design, a very minimal amount of floor space and head room is required.Turbulizers have been constructed in a variety of materials ranging from carbon steels and stainless steels, to exotic materials such as Hastalloy and Inconel. Turbulizers are currently being used in the following applications: Mixing of dry ingredients Mixing of dry ingredients with liquids De-agglomerating/delumping Homogenizing Dispersing Reacting Heating Agglomerating Coating

BATCH VS.CONTINUOUS
Batch mixing and coating is characterized by a time sequence of three stages: components weighing, blending/coating and discharge. Weighing of components can be done in or outside the mixer or a combination of both, as is frequently applied in the case of one major component and a number of small ingredients. Unloading may take a considerable part of the cycle time. The mixer is then usedas a live hopper. With badly flowing blends which are heat sensitive, or fragile, speed reduction of the rotating internals may be necessary. Continuous mixing is the simultaneous metering, blending/coating and discharge of material. There is a great interaction between the feeders and the mixing device. The feeding accuracy required is determined by the ability of the mixer to compensate for...