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Innovations in continuous drum processing of pasta, rice and vegetables

Overflow water heat energy captured; mid-process quench cycle introduced prior to chilling

February 01, 2013
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By Jim McMahon

Lyco_Heat-RecoveryAmidst efforts to reduce costs while improving sustainability, one critical objective for food processors is less energy and water consumption. Implementing energy- and water-efficient practices and technologies should be a senior management priority in food manufacturing plants.      

The U.S. Department of Energy’s Energy Star and Industrial Technologies programs address process functions in manufacturing plants that use steam, compressed air, process heat, electric and other systems. These programs put particular emphasis on the importance of new technology in achieving energy sustainability.   

The continuous-process cooking and cooling of pasta, rice and vegetables has over the course of the last four decades been considerably improved. Some recent advances in continuous-drum processing, including the capture and reuse of the heat energy in overflow water and the introduction of an energy-efficient mid-process quench cycle, contribute to those efforts.    

From batch to continuous

Batch processing was for a long time the standard cooking and cooling method, and continuous-process cooking and cooling evolved from it. Batching has drawbacks. It is difficult to maintain precise temperatures and dwell times in cooking and cooling food products. A batch process is also limited in the extent to which the load can be agitated to keep products separate, which otherwise facilitates consistent product temperatures.

The first generation of continuous-process systems used conveyors to move product through the process in series. Conveyor-based systems, however, are prone to variable production rates, which introduces product-temperature variations, resulting in inconsistent product quality.

These systems have been superseded by rotary drum continuous-process cooker/coolers, which use an auger to move product through an enclosed, water-filled drum. Considered an industry standard for continuous-process cook and chill, rotary drum cooker/coolers have improved pasta, rice and vegetable processing.   

These improvements ensure uniform processes and higher throughputs. Step-blanching, for example, enables incremental temperature increases to be made throughout the process. Gentle mechanical agitation is imparted to food product as it progresses through cook and chill. A combination of air and water injection buoyantly supports heavier loads and more evenly distributes product in the cooker or cooler.    

As is well known, automation has made these and other improvements possible. Recipe management and other production functions are managed using PC-based software. Programmable logic controllers (PLCs) automate process functions. Control systems minimize time required to perform complex tasks and increase operations efficiency, reduce operator error and process cycle times, enable improvement in product quality and consistency, increase production throughput and ensure equipment ROI.   

The latest improvements in rotary drum continuous-process cooker/coolers enable processing the same volume of pasta, rice or vegetables in less time, using significantly less energy to heat the water needed.

Recapturing cooker overflow

With conventional rotary-drum continuous-process cooking, the cooker is filled with ambient-temperature water of about 65 F and heated to the range of 200 F to 205 F. Water must be continually heated to compensate for the constant addition of ambient-temperature product. Additionally, because water is absorbed into the product during cooking, ambient-temperature make-up water needs to be continually added into the rotary drum. This adds to the cooker’s heat load requirements.   

During a process run of pasta, rice or starchy vegetables, which may continue 20 continuous hours, as much as 10 gallons of water can be overflowed per minute to reduce the buildup of starch in the water. This means an equal amount of make-up water needs to be added. The volume of overflow and make-up water varies depending on cooker size and product type and volume.

Overflow water is discarded as wastewater, and takes all the heat energy absorbed along with it. For every gallon that comes out of the cooker at 200 F to 205 F as overflow, a gallon of make-up tap water at approximately 65 F need be added. The cooker, then, has to heat that water back up to 200 F to 205 F to continue the cook process. Not only is overflow heat energy from the cooker wasted, but new energy now has to be added to reheat the water in the cooker to 200 F to 205 F.

An innovation in continuous-process rotary-drum cooking allows capture and reuse of heat from the overflow water. Overflow water leaving the cooker, instead of going down the drain, is moved to a storage tank where it is pumped through a heat exchanger. Heat is transferred from the hot overflow water to a reservoir of ambient-temperature make-up water before it is put into the cooker.   

In this way, make-up water can reach 125 F, considerably higher than the approximately 65 F tap-originated make-up water used in all prior continuous-process cooker systems. This significantly reduces the heating load requirements of the cooker, as considerable energy savings can be realized when heating water to 200 F from a starting point of 125 F, rather than from 65 F.   

Additionally, the starch-laden overflow water, which had previously been discarded, is then screened to remove particulates and reused as make-up water to compensate for product absorption, providing significant water savings.

This system was developed by Lyco Manufacturing, a leader in the manufacture of commercial rotary drum continuous-process cooking and cooling equipment. The new technology can be integrated into existing rotary drum continuous-process cooking lines. The upgrade can pay for itself, in energy savings alone, within a six-month timeframe.

Quench system energy recuperation

In rotary drum cooking and cooling, the pasta, rice or vegetables come out of the cooker at 200 F to 205 F. Product immediately goes into a chiller where it is cooled in water at 35 F to 40 F. Initially, the water put into the chiller is tap water with a temperature of about 65 F. To bring the chiller’s water temperature down to the 35 F to 40 F range needed for cooling product, energy has to be expended.   

As hot food products are released into the chiller, water has to be continually cooled to take heat out of the product and bring its temperature down to a safe 40 F range quickly, to reduce potential for bacterial growth.   

Bacteria predominantly grow in an environment that is between 40 F and 140 F. During cooking, raw ingredients are brought up past 140 F as quickly as possible to the final cooking temperature, minimizing the time period for food products to be influenced by bacterial growth. The same is true with the cooling of the product — reducing its temperature as quickly as possible to below 40 F is essential.

Energy usage in this cook-and-cool process is improved upon with the addition of a mid-process quench step, done by adding a small reservoir between the cooker and the cooler. Instead of moving the product directly from the 200 F to 205 F water temperature of the cooker and into the 35 F to 40 F chiller water, a mid-process quench cycle with unheated ambient-temperature tap water can capture much product heat before it enters the primary chill cycle. Since the quench tap water is not preheated, it requires no energy input.   

Quenching reduces the temperature of the pasta, rice or vegetables down to 110 F to 120 F, capturing 45% to 50% of the cooked product’s heat energy in the quench water. The 110 F to 120 F water in the quench can then be used in the cooker for make-up water to re-hydrate the product, instead of bringing in the usual 65 F tap water to reach the 200 F to 205 F temperature cooking range. This sizably reduces the energy draw normally needed to heat the cooker water.

The quench then releases the product into the chiller, which now only has to bring the product temperature down 70 F to 80 F to reach the targeted 40 F, instead of needing to bring the temperature down 160 F to 165 F if the quench cycle was not in place. The energy savings in the chiller from the reduced refrigeration load is significant.

The quench system, called Easy-Flow, also developed by Lyco Manufacturing, maintains 100% uniform product cooling with less than 1 percent product damage. Rice, most varieties of pasta and select vegetables can be cooled in the quench to 110 F to 120 F before entering the chilled water cooler.

Easy-Flow uses a patented plenum technology to achieve its high-speed cooling without damaging product. Pasta, rice or vegetables are pulled through the cooling plenum at the bottom of the tank by Venturi effect, which increases the velocity of the fluid without pump impeller contact. The Venturi effect creates a pressure differential that pulls water and product through the plenum at up to 300 gallons of water and product per minute.

Reduced consumption

Compared to conventional rotary drum continuous-process cooking, recapturing heat and water from cooker overflow and quench systems can result in considerable savings. When recapturing heat and water from cooker overflow, British thermal units (BTUs) can be reduced by 60%, kilowatt hours (kWh) can be reduced by 72% and water usage can be reduced by 25%. With the quench system in place, for a continuous-process rotary tank cooker, BTUs and kilowatt hours can be reduced by 35% compared to an identical rotary tank cooker without the quench system. For the chiller under the same conditions, with the quench system in place, BTUs, tons of cooling required per hour, and kilowatt hours can be reduced by 41%.   

These advances in continuous-process cooking and cooling can allow food processors to significantly reduce energy and water consumption, while achieving improved equipment and process ROI.

About Lyco Manufacturing

Lyco Manufacturing, a world-leading manufacturer of commercial cooking and cooling equipment for food processors, is focused on improving its customer’s return on investment through innovative design. Founded in 1980 by the owner and Chairman of the Board, David R. Zittel, Lyco Manufacturing is housed in a state of the art 80,000 square-foot facility located in Columbus, WI, 30 miles northeast of Madison, WI, USA. For more information contact Randy Unterseher, VP of Marketing, Lyco Manufacturing, Inc.; Phone 920-623-4152; randy.unterseher@lycomfg.com;  115 Commercial Drive, Columbus, Wisconsin 53925; www.lycomfg.com.

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