The Background.
Our client wanted to upgrade the existing SATT PLC and SCADA system to proactively give them the opportunity to acquire the pertinent support to keep their plant running at the maximum capacity.
The first phase of the retrofit was to specify which products will best suit the needs and requirement of the task. Working closely with Siemens, a S7-400 PLC and WinCC SCADA were selected to provide the hardware & software solution.
The existing system consisted of three mixing vessels, each of which could run four recipes. Only two of the vessels could run in semi-automatic mode, with the bulk raw material required to be fed into the machine by belt feeders and various liquids by pump valves etc. All interlocking and other safety aspects were handled manually by the staff and metering of these components was carried out by weigh cells on the first two vessels.
The Client: Kemira Chemicals
Our client works within the water intensive industries, operating in over 40 countries.
The Solution.
Following the specification and correlation of plant requirements the project was split into two phases.
Phase one was to effectively replace and replicate what the previous system performed with various enhancements to the functionality. Phase two confronted a new problem with the availability of the raw materials becoming scarcer and uneconomic to produce, therefore research had to be done to investigate what new material could be used to contest this.
The final stage of Phase one was the introduction of two completely new HMI’s (Siemens TP170B’s) at the tanker filling stations. These stations, which are linked via Profibus DP, involve the tanker drivers inputting their request slip number and the automated system would then meter out the exact amount their order had requested. Additionally, it only delivers the requested product, erasing the danger of cross-product pollution.
During the research period it was decided to realise Phase two, a new material was to be used under a new process. This new process included cooking the new material under pressure in the reactor. This can be achieved in a far quicker time and the new product would be delivered to the three existing tanks for final mixing, followed by distribution of the existing silos as previously. The reaction is far more demanding as a larger quantity of product is mixed and heated at around 5-6 bar pressure. In view of this reduced reaction time the product throughput is considerably higher. Owing to the process being more critical it was decided to utilise Profibus PA for the instrumentation thus easing the hardship of wiring and cost of analogue PLC modules.
The Benefits.
All three mixing vessels are now able to run in fully automatic mode for any of the four specified recipes, therefore increasing the rate of production.
Recipes are now selected from the central WinCC visualisation, with the appropriate chemical components, to ensure the most economic process is provided
Three term temperature (PID) control ensures reliable and predictable reaction times.
The routing to silos were also addressed, with unacceptable conflicts resolved such as products in wrong silos, silos overburdened and running out of product.