Citrus Feedmills 101

October 4th, 2005

Last month Vincent Corporation gave a presentation at the Citrus Short Course (now called the International Citrus & Beverage Conference). Entitled "Citrus Feedmills 101", the presentation reviewed the efficiencies and economics of various feedmill concepts. The important points were as follows:

1. Feedmill efficiency is measured by the therms of energy required to produce a ton of citrus animal feed. This was presented as the gallons of fuel oil required per ton of pellets. It was seen that a very efficient feedmill requires 29 gallons of fuel oil per ton of feed.

2. With the selling price of pellets being around $55 a ton, delivered to the port of Tampa, it is evident that feedmill operators face a serious cost problem. Thus variations of the California Feedmill #4 option, which does not use a dryer, are of particular interest.

3. The "dryer" ceases to be a dryer once a waste heat evaporator (WHE) is installed. Instead, it is a generator of nearly saturated, high wet bulb temperature, gasses. This point is overlooked by dryer companies, attempting to enter the market, without familiarity with the fundamentals of citrus feedmills and the WHE technology.

4. It was shown that the screw presses account for only 7% of the capital cost of a feedmill, and the dryer, 13%. The WHE accounts for 33% of the capital cost.

5. The WHE does wonders for feedmill thermal efficiency because it works under a vacuum. This allows it to evaporate water with very low heat input. Furthermore, the WHE makes its own vacuum by condensing the moisture in the gasses.

6. The Vincent presentation included a statistical industry report. It showed that the typical feedmill has an overall energy consumption of about 600 BTU's per pound of water evaporated. This is contrasted to the typical stand-alone dryer, which requires at least double that much. (A British Thermal Unit (BTU) was defined as an energy unit, 1000 of which are required to evaporate a pound of water at sea level atmospheric pressure.)

7. It was shown that it is of little use to press citrus waste to where it has less than 63% moisture. There are presses available that can do this. However it is of little value because the resulting volume of press liquor will be beyond the capability of the WHE.

8. Material balances were presented, although they are upper classman, not freshman, technology. These are expressed in simple "in equals out" equations and the concept of Brix. Reiteration of simultaneous equations in a spreadsheet gives the material balance.

9. Brix is a measurement of the amount of solids (usually sugar) dissolved in water, much like a percent. If the water in material going into a screw press has 10° Bx, then the amount of dissolved solids in the press liquor will also be 10° Bx. Similarly, if you squeeze a drop of water out of the press cake, it, too, will be 10° Bx. You cannot concentrate dissolved solids in a liquid by squeezing the liquid. This relationship is important to the calculation of the material balance.

Issue 165