Heat can be recovered indirectly from a fryer’s fat-laden exhaust gases via a heat exchange system and used for pre-heating air and water for use in other facility processes. Conditioning of the exhaust gas is required, however, to remove fats and to reduce fouling of the heat exchange system. McCain Foods, a global manufacturer of frozen potato products, installed a special system for recovering heat from exhaust gases on the potato frying line at its Scarborough, England, facility in 1995. Fryer exhaust gases were first saturated with water vapor using turbine washers, then routed to a two-pass shell and tube vapor condensing heat exchanger. The heat exchanger shells were oriented vertically, which allowed condensate, fat, and fatty acids to drain freely into a sump below the heat exchangers. The heat exchanger was used to pre-heat air for the facility’s potato chip dryers, to heat water used in potato blanchers, and to provide facility hot water. Exhaust gases exiting the vapor condenser passed through a scrubbing tower and were discharged to the atmosphere. Heat recovery from the fryer exhaust gases saved the company a reported £77,060 per year in natural gas costs .It is also possible to recover additional heat from a fryer’s fat-laden exhaust gases using direct combustion.

Commercially-available fryer gas combustion systems exist that can recover useful heat in a two-stage process. In the first stage, dutch buckets system heat is recovered from exhaust gases exiting the fryer using economizers that that pre-heat facility and process water. In the second stage, exhaust gases are combusted in a small natural gas-fired furnace. Exhaust gases exit the furnace at around 700° C to 800° C and are passed through a second heat exchanger, which is used to heat fryer oil .Kitchen Range Foods, a UK based manufacturer of frozen fried potato products and frozen vegetables, installed a fryer gas combustion heat recovery unit on its frying line in 2002. The heat recovery system reportedly supplies 10% of the energy needed to heat the fryers, eliminates exhaust odor problems, and produces no effluent . Heat recovery via adsorption cooling. As discussed in Chapter 12, adsorption cooling systems can use waste heat instead of electricity to produce chilled water for use in facility air conditioning and process cooling applications. In 2004, the California Energy Commission financed a demonstration project to evaluate the use of adsorption cooling technology to generate chilled water from fryer exhaust gas heat. A 300 ton adsorption chiller was installed on a potato chip frying line that fried about 20,000 pounds of potato chips per hour and produced about 15,000 pounds of exhaust water vapor per hour. Formerly, the exhaust was discharged to the atmosphere.

The project was estimated to save about 1.5 million kWh per year in facility air conditioning energy, amounting to about $123,000 in annual energy cost savings . According to Flex Your Power , the simple payback period associated with adsorption chillers generally ranges from one to three years . Using spent fryer oil as fuel. The frying process can generate significant amounts of spent oil, which can be a costly solid waste problem for many companies. However, spent fryer oil can be used as a diesel engine fuel in lieu of disposal at facilities that have diesel cogeneration units or diesel backup power generators. Most diesel engines can run on vegetable oils if the oils are properly filtered to remove contaminants and if special modifications are made to the fuel injection system. Using spent oil as a bio-diesel fuel reduces solid waste while at the same time reducing a company’s necessary purchases of diesel fuels. The Mayno Food Company, a Japanese firm that manufactures tempura , decided to install a diesel co-generation system in 1997 that burns a mixture of spent vegetable oil and marine gas oil. The system features a fuel mixer to blend vegetable oil with marine gas oil, a line heater to adjust the viscosity of the fuel, a filter and sedimentation tank to remove contaminants from the spent vegetable oil, and a specially designed fuel injection system. The system runs on a 70:30 fuel ratio of spent vegetable oil and marine gas oil and burns 32 to 42 tons of spent vegetable oil per month. As of 2002, the system was running with no major problems and was able to run with fuel and maintenance costs that were 50% less than a co-generation system running on marine gas oil alone .

The system was also reported to reduce both emissions of sulfur oxides and the smoke density of the exhaust.Sterilizer insulation. All exposed surfaces of sterilizers should be properly insulated to minimize heat losses. Furthermore, insulation should be checked regularly for damage or decay and repaired promptly when needed. The typical payback for insulating sterilizers where the temperatures of exposed surfaces are greater than 75° C is two to three years . Heat recovery from pasteurization. While most modern pasteurizers use some form of internal heat regeneration, the heat contained in rejected water can also be recovered using heat pumps or a heat exchanger and used to pre-heat air or water in other facility applications. Compact immersion tube heat exchangers. Compact immersion tube heat exchangers consist of a combustion chamber and a heat exchange tube that is coiled inside a reservoir of water. Exhaust from the combustion chamber, which is fired by natural gas, is circulated directly through the immersed tubes, which transmit heat to the water in the reservoir. The hot water is then circulated to another heat exchanger for use in pasteurization and sterilization processes. Compact immersion tube heat exchangers reportedly use up to 35% less energy than centralized water heating systems . The A. Lassonde Company pasteurizes around 30 million liters of apple juice per year at its Rougement, Quebec, facility. To help reduce its energy bills, the company replaced its old electric water heating system used for pasteurization with a pair of 880 kW natural gas-fired compact immersion tube water heating units. The company reported energy cost savings of $18,100 per year , maintenance cost savings of $13,000 per year , and a payback period of less than two years . Helical heat exchangers. Helical heat exchangers can reportedly offer increased heat transfer rates, reduced fouling, and reduced maintenance costs compared to traditional shell and-tube heat exchangers. These heat exchangers might therefore offer an energy-efficient heat exchange option for continuous pasteurization and sterilization processes . Induction heating of liquids. An induction heater works by dissipating the energy generated when the secondary winding of a transformer is short-circuited, which instantly imparts heat to liquid circulating in a coil around the transformer core. Applications in the fruit and vegetable processing industry include continuous liquid sterilization and pasteurization processes. Energy savings compared to boiler-based methods of liquid heating have been estimated at up to 17% . The Laiterie Chalifoux dairy in Sorel, Quebec, installed induction heaters for milk pasteurization and realized a simple payback period of 3.3 years .Heat recovery from discharge steam. Ideally, residual steam from steam-based peelers should be harnessed for heat recovery rather than being discharged directly to the atmosphere. Heat can be recovered from the discharge steam using condensing heat exchange systems and used to heat facility or process water. The Frites specialist company in Arcen, the Netherlands, dutch buckets manufactures both fresh and frozen potato products. In the late 1990s. the company installed a condensing heat exchange system to recover energy from its steam-based potato peeling process for use as a heating medium for pasteurizing potato pre-heating water. Previously, the company released steam directly to the atmosphere, which was perceived as a nuisance in the surrounding neighborhood. The system works by discharging steam from the peeler into a blow down vessel, in which a spray of recirculated process water condenses the steam into hot water.

The hot water collected at the bottom of the vessel is fed through a heat exchanger to pasteurize process water. The company reportedly saved 852,000 m3 of natural gas per year with a simple payback period of 3.4 years . Multi-stage abrasive peeling. In general, abrasive peeling methods consume less energy than steam-based peeling methods . However, a major drawback of traditional abrasive peeling methods is that along with the removal of peels, a significant amount of usable product is usually lost during the process. Multi-stage abrasive peelers can reduce the amount of usable product that is lost—and thereby increase product yields—by routing the product through a series of progressively milder abrasive drums. While no energy efficiency data on multi-stage abrasive peeling are yet available, the process is expected to save energy in upstream processes, because increased yields mean that less product must be processed prior to peeling to maintain a given production rate. Utz Quality Foods of Hannover, Pennsylvania, has used a multi-stage abrasive peeler on its potato chip processing line since 2001. The new peeling process was estimated to reduce potato usage by 354,000 pounds per year while maintaining the same production rate . The savings in reduced potato costs were estimated at $31,860 per year. Additional reported benefits included less potato waste for disposal as well as fewer quality problems with downstream processes such as slicing and frying. Dry caustic peeling. Caustic peeling methods are generally less energy- and water-intensive options than steam-based peeling methods . However, wet caustic peeling methods can generate wastewater with a very high pH and organic load, which leads to high wastewater treatment costs. In contrast, dry caustic peeling methods use less water and less caustic solution than wet caustic peeling methods and thus generate less wastewater. The wastewater generated by dry caustic peeling also has lower pH and organic loading than wet caustic peeling methods, which reduces wastewater treatment costs . The dry caustic peeling process subjects products to a heated caustic solution to soften the skin, which is then removed by dry rubber discs or rollers. Chapters 6 through 13 discussed a wide range of energy efficiency measures and practices that are based on proven, commercially available technologies. In addition to these opportunities, there are also a number of emerging technologies that hold promise for improving energy efficiency in the U.S. fruit and vegetable processing industry. New and improved technologies for food processing are being developed and evaluated continuously, many of which can provide not only energy savings, but also water savings, increased reliability, reduced emissions, higher product quality, and improved productivity. In this chapter, several promising emerging technologies for fruit and vegetable processing are briefly discussed. Where possible, information on potential energy savings compared to existing technologies and other technology benefits are provided. However, for many emerging technologies, such information is scarce or non existent in the published literature. Thus, the energy savings and other benefits discussed here are preliminary estimates. Actual technology performance will depend on the facility, the application of the technology, and the existing production equipment with which the new technology is integrated.Heat pump drying. Heat pumps are a class of active heat recovery equipment that allows low temperature waste heat to be increased to a higher, more useful temperature for other process heating applications. The use of heat pumps allows for the recovery of waste heat where traditional heat recovery methods are not practical. As an active heat recovery method, heat pumps require the input of energy to convert low temperature waste heat into high temperature process heat. However, in general it is still less energy intensive to use a heat pump to transform low temperature waste heat into useful process heat than it is to supply that process heat via traditional energy sources . Perera and Rahman have reported that heat pump dehumidifying dryers offer several advantages over conventional hot-air dryers for the drying of food products, including higher energy efficiency, better product quality, and the ability to operate regardless of ambient weather conditions. Heat pump dehumidifying dryers consist of a condenser, a compressor, an evaporator, and a fan to provide air movement, while the heat pump is located along with the product in an enclosed chamber. Dry, heated air is passed continuously over the product, and, as it picks up moisture, it condenses on the heat pump, giving up its latent heat of vaporization, which is taken up by the refrigerant in the evaporator. This heat is used to reheat the cool dry air passing over the hot condenser of the heat pump.