Citrus Waste Disposal
In was in the 1930's that citrus canneries first addressed the problem of disposing of waste. This waste consists mostly of peel, along with other elements such as seed, rag, core, pulp, and others. As early as 1931 Dan Vincent was operating a peel dryer in order to produce a feed for dairy cows.
The investment required for a modern citrus feedmill is in the millions of dollars. And, at today's low grain prices, it is a poor investment. As a result the citrus processors in small countries cannot justify erecting a feedmill.
At the same time environmental laws are coming into play that limit the options for disposing of citrus waste. Basically, there are the following alternatives to consider:
- In Sicily, Spain, Mexico and California the small plants give the peel to nearby farmers for livestock feed. The animals eat it fresh, within a couple days. No energy is required. The peel must be eaten before it starts to ferment.
- There are medium sized processors in Belize, Sicily and Mexico that have too much peel to give away, even for free. Their options are to either landspread or landfill the waste. This practice is being challenged on the basis of groundwater contamination.
- Many medium sized processors in Mexico have gone one step further. They react the peel with lime and then dry it in rotating drum dryers. The dry peel is then sold either as bulk dry feed or it is pelleted. About 1,500 BTU per pound of water evaporated are required to evaporate the moisture in the peel, so the fuel cost is apt to exceed the value of the livestock feed produced.
- In California some medium sized plants react the peel with lime and press it into press liquor and press cake. They concentrate the press liquor into citrus molasses (in steam evaporators) which is sold, either to distilleries or as a liquid animal feed. The press cake is sold as livestock feed which has a shelf life of a couple weeks. Some farmers store the peel press cake in gigantic plastic bags (10' diameter, up to 300' long) for extended storage. The only energy required is the steam for the molasses evaporator. This system is quite economic, but it is practical only in California where immense dairies and feedlots are located near citrus processors.
- In Florida and Brazil the citrus feedmills all have waste heat evaporators (WHE) in use. These greatly improve the thermal efficiency of the feedmill by driving the evaporator with the flue gasses from the dryer. The process is to react the peel with lime and press the peel into press liquor and press cake. The press liquor is made into molasses in the WHE, and this molasses is added back to the peel, usually in the reaction conveyor. The press cake is dried in a rotary drum dryer and subsequently pelleted. The process requires about 500 BTU per pound of water evaporated.
- The new option is to burn the peel as fuel. The heat value of the solids in the peel is excellent. The heat released by combustion is used to dry the peel and to generate steam. The steam can be run through a generator in order to supply more than enough electrical energy to run the entire citrus processing plant. In addition, the steam can be extracted from the turbine at 35 psi so as to supply the steam required by the juice evaporators.
Vincent Corporation gave a presentation at the recent 1998 Citrus Processing Short Course. This paper details the process of burning citrus waste in order to make the processing plant energy self-sufficient. A summary will be released in a future issue of Pressing News.