February 17, 2016
Over a period of fifteen years Vincent participated in tests with spent pectin peel at four citrus pectin production facilities. The goal was to reduce the moisture content of the residue (spent pectin peel) which remains after pectin is extracted using the normal acid and alcohol precipitation process. Until 2013 none of these tests showed much promise.
Trials have shown that successful dewatering of spent pectin peel with a screw press requires two elements: (1) press aid (cellulose fiber) must be blended into the material, and (2) hydrated lime [calcium hydroxide, Ca(OH)2] must be mixed into the spent peel for a chemical reaction. Meeting these requirements involves quite a bit of equipment besides a screw press.
Alternatively, a belt press can be used to dewater spent pectin peel. Starting with 10% to 12% solids, this press removes free water, and a cake with about 16% solids can be produced.
In contrast, with the proper mix of lime and press aid, a screw press can increase the solids into the range of 30% to even 40%.
The advantage of dewatering the spent peel is that it becomes a saleable animal feed. Since large amounts of water no longer need to be transported, the geographic range in which the material can be sold is greatly expanded. One pectin producer has done very well by assigning a trade name to their spent pectin peel, giving it market identification.
An important consideration is that a large amount of wastewater is produced when the spent peel is dewatered. Since the flow of press liquor can be four times greater than that of the press cake, most of the dissolved solids go out with the press liquor. Although it can vary quite a bit, typically the press liquor has 5% solids, which translates into high BOD effluent. To overcome this, some pectin producers are considering the use of multiple effect evaporators to concentrate their wastewater into a molasses.
It is notable that, because of the dissolved solids, the solids capture rate in the press cake is only about 70% of the total solids entering the screw press. The rest go out with the press liquor.
Typically from 1% to 2.5% hydrated lime is added to the spent pectin peel. The lime is mixed with about ten parts water prior to blending with the spent peel.
We have tested a variety of press aids. By far the most successful is ground wood, sold commercially in both Europe and America. Suppliers include SCM in Sweden, International Fiber Corp. in North Tonawanda, NY, and Mat, Inc. in Floodwood, MN. The primary market for these press aids are factories engaged in the production of fruit juices such as apple juice. Typically 2.0% to 2.5% press aid works with spent pectin peel.
The main piece of equipment needed to blend press aid with spent pectin peel is a mixing tank commonly known as a hydrapulper. Bales of press aid are mixed with liquid in the hydrapulper. This fiber is pumped to be blended with the spent peel and the hydrated lime. This mixing can be done in a blender such as a Lodige or Khal. More economically, the mixing can be performed in a mixing paddle conveyor (known as a reaction conveyor in the citrus industry). The mixed and chemically reacted material is what is fed into the screw press.
APPLE PECTIN
Recently we tested dewatering the spent material after the pectin has been removed from apple pomace. We found that there was an excellent reaction with hydrated lime. The addition of press aid was not required. Once reacted with the lime, the material shows great promise in being dewatered with a screw press.