September 22, 2009 ISSUE #215
In 1975 Vincent Corporation sold equipment for a feedmill that would process pineapple waste. The project, sold by FMC Corporation, was for Dole Pineapple in Mindanao, in the Philippine islands. Now long abandoned, the project involved dewatering waste from pineapple juicing so that it could be sold as animal feed. Because of the current high value of animal feed, several inquiries have been received recently about the process.
Dave Kalashian's trip report from Mindanao mentions that the cake was coming out of the press at no more than 78% moisture content, that being acceptable. We also found a material balance prepared by FMC in which they worked with 76% press cake moisture.
This leaves too much water to be evaporated in a dryer. The cost of the fuel required would exceed the value of the animal feed produced. Therefore recently tests were undertaken in Tampa.
Pineapples were shredded and pressed to remove the juice. The waste from this process was tested with three different press aids. We tried varying percentages of hydrated lime, gypsum, and alum. The gypsum and alum had no effect. However, an excellent reaction with lime was achieved.
The waste with lime pressed to much lower values, in the range of 60% to 70% moisture content. A relatively high amount of lime was required, 1% to 3% by weight. This is similar to what we have found with other wastes such as potato peel, onion peel, and tomato waste. It compares to 0.5% which is typically used on orange peel.
Pressing material with this much lime is a high torque operation. The cake becomes very hard and dry. Lime mixed with water makes cement, as used for concrete. It is likely that to some extent this reaction is occurring in the press. Nevertheless, the pressing operation is within the range of normal screw presses.
We were not able to test with steam injection, due to the small scale of our trials. However, we know that direct injection of steam into the pineapple waste will reduce the moisture content of the final press cake. In the case of orange peel, moisture content is reduced by up to four percentage points with steam injection (Pressing News #129 of July, 2002).
In the pineapple waste feedmill, the press cake would be dried to 10% moisture in a rotary drum dryer. This would be pelleted and sold. Reportedly the value is higher than that of dried citrus waste because the nutritional value is greater.
Pineapple waste has a little more Brix than citrus waste. This means that it is practical to use a conventional Waste Heat Evaporator (WHE) to make pineapple molasses out of the press liquor. Unfortunately, most likely candidates for a pineapple feedmill are too small to afford the investment required for a WHE. (The use of a WHE would reduce fuel consumption per ton of finished product by as much as two thirds.)
This means that the press liquor will be sent to the wastewater treatment plant (WWTP). This will present a severe load on the WWTP as about two thirds of the solids in the pineapple waste, in the form of dissolved sugars, will be lost with the press liquor. If a lagoon system is used, odor problems are likely.
One alternative under consideration is to use the press liquor as a feed to an anaerobic digester. The biogas produced therein would be an excellent boiler fuel. And the odor problem would be addressed.