Milklink Kirkcudbright Upgrade of the Gasti Control System

As the existing process-control system based on a Siemens S5-135U became difficult to support, the decision was made to upgrade to a state-of-the-art system.

Due to the age of the obsolete control system the client had some reliability issues, and often, no indication of what had caused the machine to stop was given, this resulted in long periods of unnecessary downtime while the engineers tried to debug the code to ascertain what had caused the problem.

S5-135U prior to conversion	S7-400 post installation

Following consultation with the plant engineers iTech put forward a solution based on a Siemens S7-400. The PLC program was converted from S5 to S7 and then examined to extract all the possible causes of alarms and errors which could affect the machine. Set point / configuration values relating to the machine setup were also extracted from the original code. All these configured alarms and values were then configured on a Siemens Touch Panel TP277B HMI, allowing the process operators to visualise what was actually happening on the machine for the first time.

A simulation program was produced for the machine so that the process operators and plant engineers could run / test the program to ensure correct functionality. The changeover from the old system to the new control system was made during a scheduled machine outage with no production losses during a busy period. When required the machine started up and ran as normal with no problems.

The strong partnership that was forged between the two companies ensured that the plant control was changed with no disruption to production during a busy schedule. The system now offers a comprehensive range of control features enabling the process team to easily identify faults and modify production parameters.

Services supplied:

• Detailed engineering and design
• PLC & HMI software
• PLC & HMI hardware
• Installation Mechanical / Electrical
• Re-engineering control panels
• FAT, SAT and commissioning

Kemira Chemicals (Reactor Chemical Manufacturing)

In an increasingly competitive marketplace, no company can afford to run at anything less than maximum capacity. However, it’s a fact that mature, obsolete equipment can become troublesome, require attention and even in the worst circumstances fail. The ability to both acquire spare parts and receive qualified technical support can be a real business benefit when it comes to maintaining optimum production capacity as well as delivering competitive advantage.

Kemira Chemicals were faced with such challenges when it came to considering how best to meet the challenges raised by its busy manufacturing schedule. Kemira 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 current system consisted of three mixing vessels each of which are capable of running 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 done by weigh cells on the first two vessels. 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.

After the completion of Phase one, all three mixing vessels were now able to run in full automatic mode for any of the four specified recipes. All the associated interlocking was now handled automatically mixes. Recipes are selectable from the central WinCC visualisation, with the appropriate chemical components, to provide the most economic process. Three term temperature (PID) control ensured reliable and predictable reaction times. The routing to silos were also addressed, unacceptable conflicts were resolved such as; products in wrong silos, silos overburdened and running out of product. 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 would only deliver 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.

Scottish Water (Partick WWPS)

In the case of Partick WWPS, we were initially contacted as the existing system had faulted and Scottish Water required our assistance to get the PLC up and running. As suitable parts and more critical no copy of the PLC program was available, a retrofit was offered to Scottish Water. The PLC Scottish Water previously had installed was an OMRON, that particular series had been obsolete for some time. Rather than spend resources repairing the faulty unit, iTech advised that it may be more economic to upgrade to a current Siemens model.

Original OMRON PLC	New S7 300 PLC
On agreement iTech began to start writing the software from scratch as no drawing or original program were available at that time. The existing PLC had to be removed and appropriately disconnected. A new control panel was fitted containing the new S7 300 PLC, which was suitably interconnected with the other control panels. The entirety of the project was completed in just over one week.