PLCs, HMIs and drives deliver flexibility and transparency

In process engineering, programmable logic controllers (PLCs) are usually only deployed in sub-processes, with higher-level tasks handled by a central process control computer. However, engineers at Follmann & Co have taken a different approach, installing a highly flexible cooling, storage and filling plant (for adhesives) that be reconfigured, expanded and relocated at any time. Instead of an expensive centralised process control system, Follmann has used compact modular controllers and HMI control terminals from Mitsubishi Electric, combining outstanding flexibility with full transparency.

The Follmann Group manufactures chemical products for paper and textile finishing. Its product range includes printing inks for paper napkins and wallpaper, PVC pastes for technical textiles, micro-encapsulated perfume and aroma oils for advertising, adhesives, construction sealing systems and other specialised chemicals. It also makes adhesives for the wood and furniture industries.

Sales growth meant the existing cooling and storage tanks and the filling plant had reached the limits of their capacity, so the company decided to expand the existing facility and to take the opportunity to automate processes that had previously been manual.

The market for adhesives is so competitive that the company simply could not afford to shut down production. This meant that the expansion and conversion project had to be completed while the plant remained in operation, and while maintaining a 24hr delivery service.

Flexible and transparent

Control technology had to be expandable, flexible and failure-resistant, easy to operate and provide transparent visualisation of the processes. The management also wanted to have fast and reliable access to key process and production data.

After considering these specifications, the project team opted for an automation system controlled via a fieldbus for the product process paths, which run from the reaction tanks to the cooling and storage tanks and the bottling plant.

The key question was, could the demanding control and process visualisation tasks required by this plant be performed without a conventional centralised process control system? Follmann believed they could, and selected a combination of compact PLCs and HMI control panels from Mitsubishi Electric to control the entire upgraded plant. Frequency inverter drives from the same manufacturer were also chosen to operate all the pumps at the optimum speeds.

Compact controller

Follmann's plant is divided into several control zones: A MELSEC FX2N compact controller fitted with a full set of 256 inputs and outputs controls the reactor, the raw materials metering, the cooling system with the pigging line, the storage tanks and the filling plant. This controller is one of the world's fastest PLCs, with a program cycle period of just 0.08 microseconds per logical instruction.

Detailed information on the open- and closed-loop control processes in the automated plant are provided by graphical HMI control panels of the E series – MAC E900T and MAC E910T models – installed at the individual stations. These high-end process visualisation systems from Mitsubishi Electric are just one step below industrial personal computers (IPCs) in terms of performance and are fitted with high-resolution displays and a choice of either physical function keys or touch screens.

Inverter drives

Frequency inverter drives of the compact FR S 500 series control the adhesive reactor's metering pumps, and the transport pumps for the storage tanks are controlled by powerful inverters from the FR A 500 range. The objective here is to transport the products at maximum speed, making use of the full available capacity of the pumps to guarantee rapid delivery. This is no easy task, because the viscosity and the percentage of solid constituents in the different adhesives vary considerably, requiring both a precisely-variable inverter drive and an experienced operator. The throughput of the pump – which can fill buckets, containers or entire tanker trucks – is set manually at the control terminal.

With 600-1000 signals being processed, it was clear that a single compact controller was not going to be able to handle this task on its own, hence the distributed design of the control system. This helped with another key requirement: that every system be quickly reconfigurable and expandable to cater to customer requirements.

Automation

PLC expansion and special function modules have been used to automate valve head selection at the container filling station. The local PLC uses an incremental rotary transducer to position a pneumatic cylinder. This cylinder moves between the valves, which are arranged in two rows, selects the correct filling head for the current product and then transports it and positions it over the filler pipe of the container.

The reactor controller has an Ethernet communications module that connects the PLC network to the company's office computer network. This makes it easy to exchange data with the system and perform diagnostics and programming from any computer in the network. Follmann uses MX Sheet software to feed the process data from the PLCs directly into the existing office software.

Follman is continuing its expansion, with more components and function constantly being added to the control system, including an automated tanker truck filling system.