Case Study: Repurposing a Tank Farm
A large US food manufacturing company planned to repurpose a tank farm, originally used in the manufacture of ice cream. The repurposing of the tank farm could be considered a greenfield installation, providing various oils to a new fryer system. The new designs would allow the storage and transfer of (1) newly delivered oil, (2) flavored oil to be reused and (3) waste oil to be discarded.
ECS Solutions was hired to help evaluate the existing system which was controlled by five Allen-Bradley SLC 5/03 PLCs. The ECS engineers determined the IO was sufficient for the planned changes as well as many of the existing valves. ECS redesigned the controls incorporating one new Allen Bradley CompactLogix controller to control the system and an Ethernet network to connect each of the existing SLC racks, which would be repurposed as remote IO racks. In addition, we provided new PowerFlex variable frequency drives to control the pumps that would move the oil from place to place. An existing Inductive Automation Ignition operator interface application was expanded to incorporate the oil storage system. In effect, the scope of the project was to evaluate the control systems available and to incorporate new controls where required.
As our Engineers developed the project, we found that communications between the Oil Storage System and the GEA manufactured fryers would be a challenge. At the time, there was no good way to connect the systems via Ethernet communications. Working with the customer and GEA, we developed a hardwired communication scheme that allowed the GEA fryer to call for and send oil to and from the oil storage system on demand.
The functionality of the new PLC program included provisions for the following procedures:
- The unloading of tanker trucks of oil into clean storage tanks
- The filling of a clean day tank with oil from one of the storage tanks
- The filling of a day tank with used oil selecting the proper flavor as the source (chicken, beef, pork, fish, or spare)
- Transfer oil to the fryer
- Flavor changes requiring the system to be flushed with clean oil
- Transfer used oil which is determined to be waste, to the waste area.
A significant improvement resulting from the installation of the new controls was the ability to reliably track the amount of oil being used in the manufacturing process. Furthermore, it was now possible to establish an inventory of the oil onsite. Since oil is very expensive, knowing exactly how much oil was on hand and the amount used from week to week was clearly a major advantage to the company.
Another significant improvement was the ability to store and reprocess oils that were still good. The cooking oil used in the fryers becomes flavored with the taste of the product being processed and may also attain a color profile inappropriate for other products. The new tank farm arrangement allows used oil to be stored and available for reuse when required rather than pumped to a waste tank in which it is held until a tanker truck can haul it away. The new system also allows the company to store used oil at the end of a flavor profile, again ready to be reused rather than wasted.