The Problem

To decaffeinate green coffee beans economically, a relatively large capacity vessel was required. The vessel had to be operated at pressures of up to 5,000 psi to maintain the carbon dioxide in its liquid form.

For the process to be effective, the beans had to proceed through the vessel in a uniform mass flow pattern. The resulting first-in first-out flow pattern would achieve uniform residence times for each batch of material in the vessel. A minimum residence time was critical for proper decaffeination of the beans.

Jenike & Johanson's Solution

An insert was designed to be placed inside the conical hopper to ensure mass flow. This allowed the walls to be less steep and therefore minimize the overall height of the vessel – which reduced its capital cost.

Jenike and Johanson determined the proper outlet dimensions by using our proprietary two-phase flow computer program. In order to minimize the size of the outlet valve and its associated costs, we concluded that fluid flow had to be in the same direction as that of the discharged beans, and at a specified rate. By providing another exit for the fluid displaced from the lower lock hopper, this fluid could be injected into the larger vessel through a distributor located just above its outlet, thereby providing a flow co-current with that of the beans.

The Result

The laboratory testing, modeling work, and innovative solution by Jenike & Johanson provided a sound basis for the design of the pressure vessel. The equipment was installed and operated as expected. Initial costs were minimized, and no modifications were necessary. The design was unique and a patent was awarded.

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