March 31, 2009 ISSUE 209
One of the by-products of a citrus processing plant is known as "pectin peel". Production of pectin peel involves washing the sugars and oils from the peel and then drying the peel at low temperature. The dried peel is shipped to companies which use an acid-alcohol precipitation process to extract the pectin. The pectin produced in this manner is sold world-wide as a food ingredient.
This processing of pectin peel is an area of technical expertise of Vincent Corporation. For many years we designed the plants and manufactured the machinery that is required. Today we offer free technical assistance and only our applicable specialty machines, screw presses and shredders.
Pectin peel is generally made from lime or lemon peel, although it can also be made from grapefruit and orange peel.
The dried peel is sold to firms such as CP Kelco in Denmark and Brazil, Danisco in Mexico, Cargill in Germany, and ICHI (Pectine Industria) in Italy. These firms, in turn, extract pectin from the peel, for sale as a food additive.
Pectin peel generally sells in the range of US$ 300 to $600 per short ton. [April, 2011: It is now around $1,000 a ton!] This can be compared to selling pelletized citrus peel, for animal feed, where the market is in the range of US$ 50 to $100 per ton (in the United States).
The process of producing pectin peel revolves around washing the peel in water so as to diffuse out the soluble sugars. Normally about 3 kilos of fresh water are required to wash one kilo of peel. In advanced systems, only 1.25 kilo of water is used per kilo of peel.
This contrasts to drying citrus waste to make animal feed, in which the first step is to react the peel with lime. Hydrated lime degrades the pectin, releases the bound juices, and thus permits efficient pressing and dehydrating. In contrast to this, the production of pectin peel must preserve the pectin; therefore it can not be limed.
As a consequence of the washing process, the peel is a lot more slippery and a lot more difficult to press (dehydrate). Accordingly we de-rate the capacity of our screw presses by 50%, or more, in pectin peel applications.
Further, pectin peel must be dried very carefully at low temperatures and with carefully controlled humidity. The Vincent-design rotating drum drier was the norm for the industry; however, we withdrew from the dryer business in 2007. That dryer permitted recirculating some of the partially dried peel and mixing it with the material coming from the screw press. The design was a triple pass dryer with a stationary outer shell, which contrasts to the single pass rotating drum dryer most commonly used in the production of animal feed.
Processing plants where Vincent, over 40 years, installed pectin operations include Ci Pro Sicilia and Cesap in Italy; Laconia, Paco Hellas, Nikopolis (ex-Esperis) and Greek Juice Processing in Greece; Citrex and San Miguel in Argentina; Quimica Hercules, Productos Esenciales, Industrial Citricola, and Industriales Limonera in Mexico; Jn-Jacques and Moscoso in Haiti; Priman Canning and Yahkin in Israel; Avante in Brazil; and Unipectin in Morocco.
Currently there are no processors producing pectin peel in the United States: Ventura Coastal and Sunkist in California and Parman Kendall in Florida have all discontinued their peel washing operations. Environmental considerations, especially disposal of the sugar laden, used wash water, were driving factors.
Typically we look at peel coming from juice extraction in the range of four tons of peel per hour on the low side and sixteen on the high side. More recently flows of 26 MTPH have been of interest.
The following equipment is key to the process:
Vincent VS-180 Shredder. This machine slices the peel in order to permit proper washing and pressing without creating excessive fines. It is of the thin, rigid blade design, as contrasted to the hammer mill concept.
Pulp Wash Conveyors or Tanks. These are used for diffusing the sugar from the peel. We recommend either three or four counterflow wash stages, in either vertical or horizontal configuration.
Pulp Wash Sumps. Stainless steel sump tanks, possibly with progressive cavity peel transfer pumps.
Dewatering Between Stages. We recommend the use of either static screens or rotary drum screens for dewatering between wash stages. Water usage is reduced by pressing the solids from these screens with Vincent Series KP "soft squeeze" presses,
Vincent Screw Press. Traditionally the Series VP presses have been used to remove moisture from the peel prior to further dehydration in the dryer. Oversize, low speed KP presses are proving to be a more economical alternative. The Series TSP Twin Screw presses have also proven successful.
The press is a horizontal, all stainless machine featuring an interrupted flight design. The unit is equipped with an air cushioned cone, complete with pneumatic controls. Rotating cones are used on the single screw machines.
The pectin peel is made from the cake, which usually comes out in the range of 84% to 86% moisture, depending if we are talking about lemon peel, or Persian, Limon Mexicano, Tahitian, and Key limes.
Furnace. The dryer comes with its burner and refractory lined furnace for burning natural gas, light weight fuel oil, or a combination of these fuels. A very low gas temperature, in the neighborhood of 1200º F or less, must enter the dryer. A low wet bulb temperature is important in the production of high quality pectin peel, whereas a feedmill dryer must produce high wet bulb temperature in order to drive the Waste Heat Evaporator.
Dryer Feeder. This is a stainless steel screw conveyor and feeder with a companion flange matched to the dryer throat. It has a variable speed drive.
Dryer Drum. A triple pass dehydration unit with a stationary outer drum works best. The unit is equipped with recycle extractor conveyors so that partially dried material is extracted at the end of the second pass and mixed with the incoming press cake. Also important is a 180º elbow between the furnace and the inlet to the drum. The selection of this dryer must be made using the appropriate de-rating associated with (low temperature) pectin peel production.
Exhaust System. This separation system features a low level entry cyclone separator that has been proven in producing pectin peel. The expansion chamber is complete with an air lock screw conveyor product discharge.
Exhaust Fan. A radial blade fan complete with inlet elbow and exhaust stack.
Standard Instruments. A solid state programmable controller modulates combustion through a sensor mounted at the inlet to the third pass of the dryer. This is required for precise control of product quality.
Cooling Reel. The cooling reel uses ambient air for final drying. It is complete with a fan, dust collector, ductwork, supports, and electric motors. This type of cooler is not used in modern feedmills because of the need for a pellet cooler (which is not used in pectin peel production).
Product Elevating Screw and Surge Hopper. A carbon steel conveyor and hopper, leading to the bagging or baling equipment, are used.
Sewing Head and Bagging Scale. Most pectin peel is baled, so that a maximum amount can be loaded into a cargo container. If bagging is used, a Fischbein sewing head and conveyor with a bagging scale are typically included.
Despite the length of this letter, there are a great many details that have been left out. We would be glad to work with your specific requirements.
Robert B. Johnston, P.E.
PS The purchasing contacts are as follows:
Paul van Wagernen
011-52-332-40940 or 42155
Wayzata MN 55391 USA
Tel 1 952 742 0291
HERBSTREITH & FOX
Tel +49 7082 7913 400