Valves Provide Safety, Reliability
EP Editorial Staff | July 20, 2020
Fifteen years running, solenoid valves make a difference.
For many years the products of Bayer Division Crop Science have contributed to good yields and bigger harvests in more than 120 countries. The R&D process for a new crop-protection product takes 10 to 15 years. To enable fast and individual production, Bayer created a multi-purpose system that places huge demands on safety and reliability.
The multi-purpose system, at Bayer’s site in Dormagen, Germany, houses everything under a single roof, from the development and manufacture of new active ingredients for crop protection to laboratory processing, sampling, and piloting. All of those steps lead to final production processes. The system is designed so subsystems and equipment such as dryers, centrifuges, distillers, stirrer tanks, and other reactors can be flexibly connected and operated. An in-house pipeline, with adaptable piping, is used for material flow, while the decentralized process-control system is distributed throughout 67 automation systems, enabling controls to be flexibly adjusted.
Since the process development requires the use of flammable operating fluids, frequent process changeovers, and numerous interfaces and intervention points, the entire system has been classified as potentially explosive zone 1 and zone 2.
Minimizing safety risks
The probability of an incident occurring at a chemical plant depends largely on the reliability of the system components and the individual processes. This includes, for example, the availability of coolant water, emergency-stop devices, electricity, stress-relief devices, pumps, mixers, and process valves.
Processes can be reliably controlled when all important elements operate correctly, from system operation to the safety functions for instrumentation and control technology. Safeguarding process facilities in the chemical and petrochemical industry using instrumentation and control technology is very important. Not only does this prevent dangerous plant conditions, but also detects future trends at an early stage and initiates, in part automatically, suitable measures.
The system uses numerous instrumentation and control devices to switch dosing, exhaust, steam, and additional valves to failsafe positions. The solenoid valves that activate the actuators must, at a very minimum, have the same SIL (safety integrity level) classification as the entire safety loop (with single-channel architecture). A solenoid valve in a safety loop is generally placed between the positioner and the actuator and is used to quickly exhaust the actuator and close the process valve in case of an emergency.
Solenoid valves VOFC and VOFD, from Festo (Islandia, NY, festo.com), can be supplied with TÜV certification to SIL 3. These valves, in accordance with the latest SIL classification from TÜV Rheinland, guarantee a failure probability rate of 2.41 E-4 and a safe failure fraction of 75%. If used properly, a maximum of one faulty operation will occur in 2,410 switching cycles.
Assuming that such safety loops undergo a failsafe inspection once a year, this means that a faulty operation will occur once in 2,410 years, so it is virtually impossible for a valve not to switch when it should. The solenoid valves are available with ignition protection types Ex em and Ex ia.
The ability to use Festo solenoid valves universally and their adherence to strict safety requirements were convincing arguments for the decision makers at Bayer. More than 1,500 solenoid valves VOFC were installed in safety-related and non-safety-related circuits in the system. A large number are used to actuate ball-valve units at tank systems, media-supply systems, reactors, and other applications. The company also wanted a solenoid valve that could be used across the board and would be suitable for several applications. Everything needed to be covered by a single valve, regardless of whether they would be used in indoor or outdoor applications and whether large or small actuators needed to be controlled. They also had to be compatible with the requirements for actuation in intrinsically safe circuits (Exi) in zone 1.
The VOFC range was developed specifically to meet these requirements—a solenoid valve with piston poppet valve technology and no dynamic seals that can be switched by a diaphragm without any friction. By avoiding dynamic sealing elements, the switching operations were free of friction force, which might otherwise have a negative impact on switching performance.
Using this technology had other advantages. With a comparably low solenoid coil power rating of 1.8 W (or less than 200 mW with the intrinsically safe variant), the solenoid valve has excellent flow characteristics, which in turn has a positive effect on the safety valve’s closing time.
The system’s harsh ambient conditions were taken into account, and the solenoid valves have Ematal corrosion protection. As the valves are designed primarily for use outdoors, they don’t have venting holes and the exhaust ports are equipped with special non-return devices. This prevents rainwater and outdoor air from penetrating the valves and the downstream actuators.
Thus far none of the approximately 1,500 solenoid valves with TÜV certification up to SIL 3 installed in Bayer’s multi-purpose system has malfunctioned during 15 years of operation. EP
For more information, go to festo.com.