01 January 2003
Automation to the rescue for milling, sugar, and brewing
By Ellen Fussell and John Yunger
Flour, sugar, and beer might not be the best recipe for cake, but they do have something in common: a production process that benefits from control systems automation. Manufacturers across the globe are looking for ways to improve their quality, costs, and production processes. Whether it's trying out a new technology or following advice on a new concept, it's all about better processes and improved productivity.
Flour milling is one process that could definitely benefit from automation, as Washington Quality Foods' director of information, Tony Murray, pointed out. He described how the small Baltimore-based company went from a manually operated mill to one of total automation, improving quality and saving time and money.
"In our old facility, before automation, we brought over 300 ingredients to the mixer manually," Murray said. "We had storage bins for flour, sugar, salt, and scales in the mix room that were movable on overhead tracks so we'd roll the scale down to the sugar silo, weigh out 1,200 pounds of sugar, and roll it back to the mixer and discharge over the mixer. Then the scale would go back to the salt silo and roll back to the mixer-the same with flour."
Murray said the other ingredients-leavening agents, coloring, or special flavors-had to be put in the mixer by hand: 50-pound bags of baking soda, soy flour, and cornmeal. "If the recipe called for 400 pounds, a guy would have to cut and dump bags all manually," he said. "This left a tremendous window for error. And it caused tremendous labor overhead," he said.
The process required two men per mixer just to charge the mixer. "Most of our batches hover around 5,000 pounds. If half was flour, we'd still have 2,500 pounds to put in manually. Plus, recipes were in Excel and printed out on sheets going to the mix room for someone to check off the ingredients as they dumped them into the mixer. If there was a change in the recipe, it might not always get to the mix room, so that was a quality control issue," Murray said.
To fix the problem, Murray's team gutted the entire facility and constructed a tank farm of 18 silos housing six different grades of flour, salt, sugar, and dextrose (corn sugar) and 12 other food grade chemicals and baking soda. "We'd gone through an analysis of the ingredients we used in the highest volume," he said.
All these conveyed to the mixer using a software program called InBatch. (InBatch is a member of the Invensys FactorySuite family of products that can work in conjunction or independently.) "You load the recipe into InBatch, and in that recipe you can associate the ingredients with the container that holds it," he said.
"Say salt is in silo No. 10. Once we've built a recipe in InBatch, we schedule a batch to be executed and tell InBatch to run it," Murray said. "The software program records the ingredients and the process-how long it should be blended, if we need tanks from the tank farm-through InBatch and its connection to an I/O server. Those ingredients are automatically moved using air through pipes to the mixer. So all our ingredients come to the mixer automatically when we need them. The software program knows when it's time, how much, and where it needs to get it," he said.
Murray said the company now has a complete product genealogy. InBatch tracks lots and quantities because it knows which lot is in which batch. "So if we have to do a recall, it's easy. We go into the historical database, as opposed to what we used to dothrough a bunch of papers to find which batch is affected."
At ISA 2002 in Chicago, Dindo Nicolas presented his paper, "The Impact of Control System Upgrade in the Efficient Operation of Con tinuous Vacuum Pan of CADP," which gave a detailed view of how Central Azucarera Don Pedro (CADP), a sugar refinery in Nasugbu, Batangas, in the Philippines, simplified its installed system to operate its sugar boiling process more efficiently.
Initially, the company used a continuous vacuum pan from FCB, a developer of sugar manufacturing products in Brisbane, Queensland, Australia. The system had modern complex control loops, "when simple loops would have served the same purpose," Nicolas said in his paper. "Control systems should be based on the basic functions needed rather than installing a system that requires extensive and costly maintenance in the future," he said.
But it doesn't have to be that way if manufacturers follow the lead of CADP and change some processes. With the old system, the company suffered through frequent breakdowns of massecuite and seed pumps; clogging of low-grade centrifugal feed chutes due to hardened, carbonized massecuite; and expensive chemical tube cleanings.
For optimum operations, companies should consider proven field sensors and instruments, reliable sugar applications, robust design, low initial investment, and flexible operations with little human intervention, Nicolas said. In operating a continuous vacuum pan, manufacturers should be able to rely on the stability of massecuite brix, purity, and crystal content to every pan compartment.
To alter its processes and save money, CADP made just a few changes. The company kept its electronic transmitter of absolute pressure and connected it in the high position at the condenser to avoid calibrating the transmitter with a differential setting for zero. It replaced the differential pressure level measurement with the ultrasonic type.
"Inaccuracies usually occur because of temperature, pressure, or composition changes that cause variations in the fluid density," Nicolas said. To control sediment flow-one of the most important loops in the system because it determines the pan capacitycompany decided a magnetic flowmeter would be more appropriate than a more expensive mass flowmeter.
One of the most important changes, though, was in the brix control. The Brix scale is a specific gravity scale used almost exclusively in sugar refining; degrees brix represents the weight percent of pure sucrose in water solution at 17.5°C.
"The measurement and control of brix is very important in the system because it gives the direct feedback and the algorithm that will calculate the flow of liquor to be regulated at the input of every pan compartment," Nicolas said. Thus the brix analytical instrument needs to be accurate to measure the actual liquor's real dry matter content.
CADP used a transducer set designed by the Sugar Research Institute in Australia to monitor the water content of sugar solutions. This process control sensor is also suitable for high purity materials, Nicolas said. Sugar Research Institute also recommended in stalling the brix sensors in areas where little boiling actions take place: below calandria, away from feed inlet pipes and regions with vapor bubbles.
The results? Operations realized a significant break in maintenance costs, more flexibility in one operation, readily available instrument spare parts, and uniformity of C massecuite grains, brix, and purity. It also maintained an average of 97.38 C massecuite brix constant and eliminated carbonized, hardened massecuite.
In converting the control system, the company spent Php 3.5 million ($65,700) in design and implementation and realized a savings of Php 5.5 million ($103,300), Nicolas said.
Briess Malting Co. is another process trendsetter with its switch to a new system that controls its extraction process from end to end for the new brew house, evaporator, and packaging line. Briess produces specialty malts for the brewing and food industries.
Control Concepts Corp. in Appleton, Wis., designed the new system based on a totally integrated automation architecture from Siemens. The process of producing malt from various grains means converting starches into sugars and relies on simple variables of moisture, temperature, and time. Briess's Chilton, Wis., facility included an 18,000-square-foot malt extract plant that went online in early 2002. The company used highly automated batch equipment at other facilities but decided to use a fully integrated control system to tie vessels and instrumentation together into a continuous process.
The new system included programmable logic controllers (PLCs), drives, and other motor controls and a Profibus communications network for greater product consistency and yield. "We wanted the same kind of trouble-free operation that our stand-alone equipment gave us," said Chuck Kleinhans, Briess's Chilton plant manager.
The critical link is a redundant human-machine interface/supervisory control and data acquisition (HMI/SCADA) package, Simatic WinCC, built on a client/server platform. The redundancy option has two parallel WinCC server PCs monitoring each other. If one server fails, the second server assumes control of the entire system. When the failed server resumes operation, the contents of all message and process value archives are copied back to the restored server.
Control Concepts integrated PC servers and Briess-built, touch panel thin clients with the Simatic PLCs via Ethernet. The configuration is automatic through WinCC. Each server has its own process connection and its own data archives.
Redundancy guarantees automatic archive matching for system and user-specific archive data. If either of the WinCC stations fails, the other one takes over archiving messages and process data to guarantee constant data integrity. In client/server operation, the system automatically switches clients from the failed server to the redundant machines. When the failed server starts up again, the system automatically matches in the background all the process values and messages for the down period without influencing online operation. This means two stations are available again and contain the same data.
The HMI/SCADA package performs all batch processing using ISA SP88 standards conventions. It needs no special batch software (see Standards story on new SP88 standard, page 20).
A Siemens motor control center contains a series of drives and a Simocode module that basically operates as a separate PLC running with or without a supervisory PLC. Operations can see the number of starts, trips, trip current, hours of operation, and other diagnostic functions at the control stations. Simocode also allows the Siemens motor control center to talk to an existing Square D motor control center in the same room.
Throughout the process, there are hardly any manual controls or pilot devices. Any monitoring or manual intervention takes place through the main control console or the touch screens on the thin clients. The new process assures Kleinhans "that if a batch is supposed to take eight hours, it will take eight hours. Now we can process two truckloads of malt in one day, as opposed to one truckload over two days," he said. IT
Behind the byline
John Yunger is a systems engineer at Controls Concepts Corp. in Appleton, Wis.