Improved Process Valve Control Techniques & Enhanced Monitoring Are Vital To Energy & Waste Reduction In Food & Beverage Plants

2nd June 2009
Posted By : ES Admin
Improved Process Valve Control Techniques & Enhanced Monitoring Are Vital To Energy & Waste Reduction In Food & Beverage Plants
The cost-down pressures inherent in all process industries mean that plant operators are consistently required to improve efficiency, at the same time as ensuring repeatable product quality. Moreover, these objectives have to be achieved within the required environment of high hygiene standards, where reliable assurance of clean and cleanable pipework and equipment is paramount.
In pursuit of efficiency goals, companies are prepared to invest heavily in new plant and equipment. However, in many cases, real savings and improvements in efficiency can be achieved relatively simply and at relatively low cost by focussing on cutting energy usage, and by reducing product wastage.

With valves, pumps and fans used widely in food and beverage production, the possibilities for energy savings are considerable. Take compressed air, for example; its generation is equivalent to about 10% of industry’s total electricity usage, rising to 30% in some sectors. This highlights why companies have compelling reasons to pursue energy saving initiatives in this area. However, one area of pneumatic energy saving potential is still largely unexploited: improved process valve control techniques. These can lead to reduced compressed air use through the adoption of on-actuator or in-actuator pneumatic solenoid valves.

At present, the majority of pneumatically piloted valves on production and process lines centralise pneumatic control around valve islands in a control cabinet or enclosure. This arrangement means that the pipework carrying the pilot pressure to the actual valve from the valve island can travel for many metres before it reaches the valve head. As a result, the venting cycle of the valve’s operation will exhaust proportionately more air than is necessary.

The solution to this problem is from within Burkert’s types 1066, 8631 and 8692 valve control heads ranges. Developed for use in the food, beverage and pharmaceutical industries, these units provide a decentralised method of opening and closing of process valves automatically, eliminating the need for the wasteful venting of control air normally associated with pneumatic tubing between the process valve and its related control solenoid valve.

The control heads integrate electrical and pneumatic control components as well as position feedback units and, optionally, an ATEX-approved version or field bus interfaces for AS-Interface or DeviceNet. They are mounted directly above the valve body, and, because there is little or no distance between the actuator and the valve that it is piloting, there is no air bleed: it is sealed. With this system the pressure feed goes directly into the valve head and the control signal is supplied either from a local closed loop control sensor or switch; or from a PLC / machine controller via a control bus - AS-Interface or DeviceNet – or multipole (parallel) directly into the valve.

Similarly, adopting digital positioners with integral solenoid valve control heads for regulating modulating process control valves will automatically lead to air savings, as these will normally ensure zero-air use in their stable state. The traditional technique of process valve positioners incorporating pneumatic flapper-nozzle systems means that air is being bled constantly, even when the valve is at rest. This can average the equivalent of a 0.75kW (or one-horsepower) in compressed air for every ten to twenty valves in operation; a large process site can therefore be using a vast amount of energy – unnecessarily.

Choosing the option of an embedded PID process controller, working in conjunction with the positioner, provides a fast-acting, decentralised control loop in combination with the associated process sensor. This arrangement also reduces complexity and saves unnecessary components and wiring.

Where the problem is wastage rather than energy reduction, this can be improved greatly by accurate monitoring of process fluids, using new, innovative techniques of pH and conductivity measurement, as provided by Burkert’s new 8201 and 8221 units. With probes made to the highest standards of surface finish, and with the use of glass-free, food quality materials, the opportunity now exists for measuring and controlling process lines during all phases of production and cleaning. An example of this is the robust, enamel-based pH electrode on the 8201pH sensor, which is able to stay in process, even during CIP purification. The ‘fit-and-forget’ design of the 8201 pH measuring system saves users both time and cost, by removing the requirement for sensor withdrawal, cleaning and recalibration. The non-breakable sensor also obviates the problems of fracture with glass sensors; while its enamelled stainless steel finish provides the highest levels of non-stick performance for maximised hygiene whilst pH values are measured.

In common with the 8201, Burkert’s 8221 conductivity sensor is also designed for CIP, even during steam sterilisation. This feature allows the sensor to provide the time and cost saving benefits of phase detection across all transmitted mediums, including aggressive cleaning agents. It also guarantees transparency of the process at all times, and protections for the user against expensive errors in respect of what fluids are being conveyed.

The ability of both the 8201 and 8221 units to stay in place over long periods means that requirements for recalibration become infrequent, decreasing manual intervention and downtime. Moreover, there is the extra assurance that wastage through process uncertainty or incorrect operator actions may become a thing of the past. Additionally, combining these types of sensors with a transmitter incorporating data-logging hardware and software delivers the optimum in performance and product assurance.

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