Energy efficiency is a significant focus area in many sustainability-related initiatives. Compressed air consumption is one important area to investigate. When considering technologies to reduce air consumption, looking beyond smart device air consumption data based on static analysis is essential. As an analogy, it would be like measuring fuel consumption while idling instead of when the engine is under load.
I caught up with Emerson’s Riyaz Ali for his thoughts on this topic. For air-operated control valves, the pneumatic power at a constant supply pressure is proportional to the mass flow rate of instrument air. The pneumatic/electro-pneumatic/microprocessor-based digital valve controller is used on most control valves operated in closed-loop control, where the input signal is continuously changing.
Energy consumption of the control system and associated instrumentation is part of the operating cost of manufacturing and production processes. However, when attempting to minimize energy consumption by restricting energy flow to final control elements, such as control valves, this practice may compromise the controllability of the process.
Zero consumption is not a realistic design goal for pneumatically actuated control valves. This final control element must consume energy if it moves in response to the controller output changes, which occur after any disturbance or operating change to a closed-loop control system. In many applications, the instrument air is bled into actuator enclosures to help keep corrosive surrounding air out.
Digital valve controllers, such as the Fisher FIELDVUE DVC6200 Series, have provided low-bleed options for control and on/off service since their release in 2009. For the DVC6200 with a low-bleed relay, here are the steady-state air consumption specifications:
- At 1.4 bar (20 psig) supply pressure: Less than 0.056 Nm3/hr (0.035 scfm) for single-acting actuators
- At 5.5 bar (80 psig) supply pressure: Less than 0.184 Nm3/hr (0.115 scfm) for double-acting actuators
The fully encapsulated electronics in the FIELDVUE DVC6200 series resist the effects of vibration, temperature, and corrosive atmospheres. The self-diagnostic capability provides valve performance and health evaluation.
Here’s a good description from a Chemical Engineering Progress (CEP) article, Leveraging Smart Valve Positioners, on how these diagnostics help optimize air consumption.
Typical in-service diagnostics include monitoring, friction analysis, troubleshooting, and air consumption tests. Monitoring diagnostics indicate important parameters such as air pressure, input setpoint, valve travel, and other values critical to operation. A friction analysis can be done while the valve is in operation to determine the amount of friction present in the valve assembly; excess friction can make the valve more difficult to control. Air consumption tests can be conducted to determine whether the valve assembly is using an excessive amount of air. Excessive air usage can be caused by wear or damage to the pressure-retaining portions of the actuator assembly and/or to the instrument tubing.
When optimizing air consumption, advanced diagnostics and low-bleed digital valve controllers are essential components in your sustainability-related initiatives. Visit the Digital Valve Controllers section on Emerson.com to learn more.
