Compressor Control for Cranberry Processor
When Clement Pappas decided to upgrade the facility, company officials turned to Devault Refrigeration, a design-build contractor from Colmar, Pa. The plant, a pre-World War II vegetable processing facility, was converted into a cranberry juice and sauce processing facility and cold storage warehouse.
Until recently, an ammonia system with three reciprocating compressors and cooled salt brine solution removed heat from the plant. There were three heat exchanges between the product and the refrigerant: R-717 to a salt-brine solution, salt-brine solution to propylene glycol, and the propylene glycol to the product. The brine solution was piped underground to the processing plant. The evaporators were located in the processing and storage rooms.
This was not an optimum control strategy for several reasons, officials said: 5,500 pounds of ammonia were used to cool 30,000 gallons of brine, which cooled the glycol; the glycol then cooled the cranberry juice. Company officials said they wanted to replace the old system to reduce inefficiencies (it was consuming approximately 250,000 kWh per month) and eliminate the use of ammonia. The plant is in a residential area.
EFFICIENT SOLUTIONBill Sauer, sales engineer and project manager at Devault, worked with Tom DeThomas, director of engineering for Clement Pappas, and his staff to design a replacement system with a new propylene glycol/R-22 process chiller.
Devault designed and built a customized package chiller on a skid that contained a Frick screw compressor and a Vilter reciprocating compressor. An evaporative condenser was located remotely, and a plate-frame heat exchanger was used to chill the cranberry juice to precise temperatures via propylene glycol. By eliminating the brine and its associated heat exchanger, the system has reduced its pumping losses and decreased its leak potential. In general, less energy is consumed.
“This system is basically a mini engine room on a skid. It can be moved relatively easily if the customer expands his operation or moves its location,” Sauer said.
“We had some very interesting challenges with this project,” he continued. “Juice plants are unique because of shelf-life considerations, design changes, and the variability of many of the parameters.”
The customer runs three lines, Sauer said. In eight hours it can produce 50 different labels and 15 different formulas of juice or cranberry sauce. Accurate temperature control is paramount in processing juices, he said. The juice must be held at 34°F.
The product is batched, pasteurized, and bottled. Pasteurization is a critical control point where the product needs to be heated, filled, and cooled immediately. The bottle temperature must be brought down from 182° to 100° very quickly in order to preserve juice quality. Because it is batch processing, the raw juice plant can be idle or it can be producing at a rate of 35 gallons per minute.
UNDER CONTROL“We essentially used two different manufacturers’ compressors to handle the load,” explained Sauer. In order to design the system within the budget specifications, a screw and a reciprocating compressor were both used on the package.
The screw is the lead compressor. When the glycol pump turns on, it activates the screw compressor. If it’s in anti-recycle delay mode and unavailable to turn on, or if additional cooling capacity is required to achieve the target temperature, a Danfoss EKC331T electronic controller signals the reciprocating compressor to turn on. The controller then loads and unloads the reciprocating compressor in steps of 100 percent, 75 percent, 50 percent, and 25 percent.
A Danfoss AKC21W temperature sensor monitors the glycol’s leaving temperature to determine when the compressors need to run. “The system was designed with no flywheel effect, which means the entire volume of glycol is turned over in eight minutes,” said Sauer. “There is very little reserve glycol in the system, so tight refrigerant control is crucial. There was only one other compressor sequencing with the screw, and it was a reciprocating unit; a microprocessor sequencing panel did not fit within our project’s budget, so the solution we came up with was ideal. For a fraction of the cost, we were able to achieve the same result.”
According to Brian Davis, vice president of Danfoss Industrial Refrigeration, “We were able to provide the link between the screw and the reciprocating compressors to achieve stable control and system efficiency.” The controller works harmoniously with the other Danfoss valves and sensors that were also installed on the package.
SMOOTH STARTUPThe mobile skid package system was delivered to the Clement Pappas facility on the back of a flatbed trailer. The system was started up in March of 2005.
According to DeThomas, once the package was started up, Clement Pappas noticed efficiency improvements immediately. “We are using 25 percent less energy in the processing than with the old reciprocating units that had been in place. The energy cost of cooling the juice was reduced to approximately one cent per gallon.”
Significant energy reduction is a benefit to both Clement Pappas and the environment. But the ecological impact goes beyond energy consumption.
Eliminating the external water-cooled condenser means Clement Pappas was able to reduce water consumption by approximately 20 percent as a result of the new skid package design. Along with the savings in water consumption is the reduction in wastewater purging. “Our disposal of wastewater is reduced by approximately 300 gallons per minute,” said DeThomas.
“We always strive to stay current on the latest technology so we can help solve our customers’ unique challenges,” said Sauer.
DeThomas was also pleased with results of the project. “Devault was able to design a system that met my budget and our specific needs. I was able to save money with the reciprocating compressor and the controller, but I didn’t sacrifice anything in the control processing side.”
Publication date: 04/02/2007