Solvay in Rheinberg, Germany
Conversion and modernization of soda and glycerin production systems
Uninterrupted exchange with compact INTERFACE Ex technology
INTERFACE modules ensure a safe and uninterrupted signal transfer between the field level and the control level. Precise and error-free transmission of measured values is an important prerequisite for optimum process control.
To ensure safety and proper functioning of systems in an explosive atmosphere, signal circuits are designed with the "Intrinsic Safety" protection type.
The system modernization at Solvay in Rheinberg shows the other demands made on modern INTERFACE technology.
Modification and modernization of the soda and glycerin production systems
The Solvay group in Germany is a part of the international chemical and pharmaceutical
company Solvay S.A. and has its head office in Brussels. In 2001, with about 31600 employees across 50 countries, the annual turnover of this company reached 8.7 billion euros. Solvay manufactures chemical substances such as soda and glycerin as well as plastics with the PVC, special polymer and polyolefine main products at the Rheinberg plant.
The corporate strategy is to facilitate sustained growth by way of extensive investments in production systems among other things. A PCP-capable modern and more efficient process control technology plays a vital role in increasing the productivity and optimizing the quality of process control systems.
system (Ex) are thus being completely renovated in continuous expansion stages from 2002 to 2006. The existing field instruments are retained. Systems are expanded with HART-capable, analog (0/4…20 mA) field devices using the same technology.
The control system has to process the 1500 AI, 600 AO, 1000 DI and 500 DO signals in the soda system alone. The field signals in both systems are directed to the respective jumpering and device space using a 60-wire master cable and provided to the jumpering honeycomb in the distributor field. From there, the signals are routed to the control system cabinets in the same space. So far, no modifications have been made to the system structure during the modernization.
The old control system in both systems has a 19-inch design where the
input/output cards are electrically isolated from each other and have intrinsically safe inputs or outputs.
This control system is now replaced with a high-performance process control system with DIN rail technology. This control system communicates with the visualization and archiving level and other control levels via bus systems. The signals of a system area are now assigned to a control system cabinet.
Modifications are made during system operation without system downtime, where one by one, the signals are transferred to the new cabinets during the migration.
Electrical isolation of analog signals
Safe and uninterrupted transmission of state variables such as temperature, pressure, flow or pH value, that have been converted to analog electrical signals, is an important prerequisite for optimum process control.
Electrical isolation, i.e. the decoupling of electrical circuits plays a vital role in eliminating disturbance variables such as ground loops and coupling of inductance or capacitance especially in complex systems. That is why the persons in charge in the automation department included a channel by channel electrical three-way isolation of analog signals in the specifications of the new control technology.
The design width is not the only important criterion
The design width was an essential criterion for the selection of the INTERFACE technology so that all analog inputs and outputs could be electrically isolated.
In order to reduce the variability of types and to minimize storage costs, the selected INTERFACE technology should be used for the non-Ex soda production system as well as for the glycerin system with potentially explosive atmospheres of zone 1 in the production process.
Moreover, this INTERFACE level should be used in the motherboard technology so that it can be connected to the I/O stations using pre-assembled system cables.
Independent wiring
The PI-Ex-MB 16 and PI-MB 16 motherboards used here have a length of 224 mm, so that exactly three of these 16-channel motherboards can be installed on every DIN rail at the rear of the swing frame. Comparable INTERFACE solutions take up around 30 % more space and would not have made this solution possible.
The design of the PI motherboards offers further advantages to the user: the carrier board is securely integrated in a DIN-rail mountable panel mounting base, thus facilitating mounting. A redundant diode-coupled power supply with fault message contact provides additional safety. Independent wiring as the basic principle of process interfaces has additional advantages since the terminal points for field cabling are positioned directly on the motherboard.
It is easy for the external control cabinet designer to mount the empty motherboards and the cabling is then connected directly to the rugged motherboard
terminals. The modules are plugged in (immediately or subsequently), at which point they are automatically encoded and make vibration-free contact with the motherboard by means of a snap-in mechanism (gold-plated contacts).
Functional adaptations are easily possible during the startup phase; reserves are simple to retain. In this application, 15% of the slots are kept empty for subsequent expansions. Costs for isolators are incurred even during system expansion. Ex parameters, which have the maximum possible width, make PI isolators compatible to all the commonly used field devices.
Therefore, three module types are sufficient for the conditioning of all analog field signals present in both systems: The PI-Ex-RPSS measuring transducer repeater power supply for two-conductor transmitters by different manufacturers, for flow, density of gas, temperature and Ph value. The PI-Ex- AIS input isolator is used for inductive flow transmitters that are Ex-e supplied from the field side: All analog control valves are controlled via the PI-Ex-IDS output isolator.
Thanks to the innovative circuit technology, the 12.4 mm thin Ex isolators distinguish themselves with their accurate signal processing (linearity deviation < 0.1 %) and low power dissipation (repeater power supply: max: 1.3 Watt). Inputs, outputs and power supply units are electrically isolated from each other.
All used isolators transmit the Hart protocol bidirectionally. Here, Hart is used for parameterization and device diagnostics. PI Ex isolators have been approved as intrinsically safe associated equipment for Zone 0 as per Atex.
Summary
At Solvay, process interfaces from Phoenix Contact help in increasing the productivity of the systems efficiently using a modern process control technology .