Mobile applications in hazardous areas
Inline dispersing machine on multiple stories
A leading pharmaceutical company wanted to use a mobile inline dispersing machine on multiple storeys of a building, in different locations of Zone 1 hazardous areas. With R. STAHL's assistance, machine builder Ystral was able to develop a successful solution for this requirement, which also involved connections to the existing distributed control system.
The operator's explosion protection requirement was for a whole system that could be operated in Zone 1 hazardous areas, with an explosive atmosphere that falls into explosion group IIB and temperature class T3. The non-electrical system components fullfil the requirements of equipment category 2
(Zone 1) with constructional safety c type of protection.
R. STAHL's control system combines multiple protection concepts to create the optimal explosion protection solution. The electronic devices, such as frequency converters, motor protection devices, contactors, fuses and relays, as well as PLCs for controlling machinery and isolators for intrinsically safe electric circuits, are housed in a switch cabinet with pressurised enclosure p type of protection. The thermal release contactor also features a flameproof enclosure because it conducts voltage, even when the pressurised enclosure is not in operation. The intrinsically safe operating and monitoring terminal and the Ex d main switch are built into the cabinet door.
The cabinet volume and the design of the Ex p system are tailored essentially to the consumers installed in the switchgear and to the environmental conditions where this equipment is installed. Potential critical interactions resulting from the combination of different system components were analysed and reliably identified in the course of the risk assessments and analyses of ignition hazards conducted as stipulated in the relevant standards.
System control system
The equipment had to be able to be operated locally as a standalone system, anywhere the customer required; it also had to be able to be operated via the distributed control system at any of up to 64 different locations. This requirement forms the basis for the system control system concept. The ready-to-use system control system installed on the system base frame has just two connection cables. Besides the power supply (mains electrical connection), the control system features a second, intrinsically safe, plug connection with multipolar binary encoding to identify the location and an intrinsically safe Ethernet connection. To identify the location, the multipolar plug connection where the equipment is located is encoded by contact bridges.
The operating data for the Ystral inline dispersing machine's drive is transmitted via PROFIBUS from the 15 kW frequency converter to a Siemens S7-300 programmable logic controller, which then processes this data. The measurement data that has been collected is sent on to the master distributed control system via Ethernet along with other operating data for the system. In the control system, it can then be monitored and documented.
An R. STAHL operating and monitoring terminal was provided to allow the system to be operated locally as a standalone system and to allow operating data to be displayed. In addition to in situ operation, the Ethernet connection allows the system to be controlled at any of the intended locations via the control system. The system operator can monitor the process data on the text display on the local operator terminal.
The mobile inline dispersing machine solution succeeded in fulfilling the operator's various explosion protection, process, technical and chemical requirements, whilst also allowing maximum system mobility.