As part of a project to upgrade their manufacturing facilities at the Boksburg factory, Unifoods contracted Rockwell Automation and BeST SA who successfully implemented and commissioned Phase 1 of a four-phase batching control system project.
Project overview
As part of the project, Unifoods had to decide on a strategy for the control system. The project would result in an increase in I/O of about 65%, as well as a significant increase in the number and complexity of products produced. The processes included batch and semicontinuous.
Evaluation
The existing control system consisted of a DCS system that was about eight years old. BeST were appointed to assist with evaluation of the various options. The following were considered:
* Expand with existing or updated DCS technology.
* Expand with updated DCS technology and S88-compliant batch package.
* Replace with a hybrid system and S88-compliant batch package.
* Replace with a PLC/scada system and S88-compliant batch package.
The options were evaluated on a number of criteria, including the capital cost of the project, system maintenance costs, costs of future projects, local support, and the possibility of making good use of the strategic relationship with one of the Unilever preferred equipment vendors - Rockwell Automation.
It was decided that the optimal solution for the project was to use Allen-Bradley ControlLogix PLCs with RSView scada and RSBatch. One of the key deciding factors was that with PLC/scada technology now being acceptable to control a plant of this type, Unifoods Boksburg have a site-wide control strategy where one type of PLC, the Allen-Bradley ControlLogix, and one scada, RSView, covers an estimated 90% of all automation applications. This facilitates significant savings for Unifoods in terms of training, spares holding and the number of skilled people required.
The use of RSBatch for the batch sections of the plant
On the DCS a bespoke batch solution was used that enabled a process engineer to easily combine various software phases into a recipe that performed the required actions. This was replaced with RSBatch, an S88-compliant batch package. Some of the main motivating forces for using RSBatch were:
* It gave very good flexibility for processing any number of different products through the batch vessels, using different processes where required.
* It facilitated the easy incorporation of new equipment into the system without extensive software changes.
* It gave a very good framework for recipe management and reporting.
* There are a number of similar vessels, so much of the code for each of the vessels is identical.
Using RSBatch has given the process engineer the facility to modify his process by manipulating the control of pre-defined phases through the RSBatch standard recipe editor without the need to modify PLC code.
Information management and reporting
The nature of the process at Unifoods requires very careful tracking of product around the factory. This was previously done in a semi-automated fashion. Using Rockwell's RSSQL product every transfer of product is recorded in an MS-SQL Server database. This information is used for both reporting via a web-based reporting system developed by BeST and interfacing to an in-house package that does a material mass balance on each section of the plant. The web based user interface for reporting makes reports available to everyone in the company on the company Intranet, as required.
Recipe management
Product formulations are managed using an application developed by BeST. These formulations are stored in an MS-SQL server database. They contain all the ingredients and parameters required by the RSBatch recipe. The data that is to be passed to RSBatch is created from the data stored in SQL server. This allows multiple recipes to exist for a particular product. When a recipe is released it is available to the operator for download to RSBatch. This allows multiple revisions of a particular recipe to exist, and to be used as the need arises providing the operator with the flexibility required for reordering, deleting and prioritising recipes as production demands. Another benefit of the application is that the batchID can be set automatically. The operator is normally prompted for this when a recipe is scheduled.
A full log of the history of each blend formulation is kept and a new copy is created each time the record is revised. This allows the user to go back to see which ingredients and parameters were used to create a particular batch, and to make that particular revision of the recipe active again if he so desires.
All possible recipes are displayed to the operator using an ActiveX control embedded in an RSView page. The operator selects the appropriate recipe and the required parameters and then places the recipe in a proposed queue to be transferred to RSBatch. The priority of recipes can be changed while they are in this proposed queue.
Architecture
The control system consists of 2 Mb ControlLogix controllers connected on a ControlNet network. The supervisory system consists of two RSBatch Servers in a cold redundant configuration, that form the heart of the system, and two RSView Servers in a hot standby redundancy configuration, both of these systems communicate with the ControlLogix PLC by means of RSLinx, an Ethernet connection. Five operator stations running RAD RSView and Batch View will be used to monitor and control the plant. Also connected to the control system is a MS_SQL Server database, which receives batch transactions details directly from the PLCs utilising Rockwell Automation's RS-SQL software.
Project implementation
A key factor to the success of the project was the ability to change over the existing control system to the new control system on the existing plant in as short a time as possible. Unifoods were responsible for the hardware changeover. Unifoods implemented a solution that required only 4 h to change the plant over from the old control system to the new control system. In addition it was possible to change back to the old control system in only 4 h as well. This was used to commission the plant in two stages. During the first changeover three sections of the plant were commissioned during a one-week period. The plant was then changed back to the old control system. The system was then changed over a second time one month later for the final commissioning. The fact that it was possible to change back to the old control system at any stage took most of the risk out of the operation.
Key aspects of the project were the use of RSBatch for the batch sections of the plant, and the quality of information management and reporting.
Future
Phase 2, 3 and 4 of the project, currently in the development phase, will expand the current capacity of the refinery. The control batching functionality will be enhanced in these phases with the development of a custom batch scheduler connected to the MS-SQL Server database and RSBatch. This batch scheduler will allow for the easy development of batch recipes and the facility for the plant operator to queue batches to RSBatch.
BeST SA
(011) 884 0510
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