Using Wireless Throttling Valves in Column Control

Emerson’s Kurtis Jensen and Terry Blevins teamed up with the University of Texas at Austin’s Stephen Briggs to control a column with wireless valves. Their abstract:

The control performance that may be achieved using wireless throttling valves has been evaluated through tests conducted at the UT Pickle Research Center on an 6″ distillation column. The test results indicate that the control achieved using a wireless throttling valve is comparable to that achieved using a wired valve for a variety of flow control applications. Information on control implementation and results achieved with the WirelessHART throttling valve are shown where both wired and WirelessHART transmitters were used to access the control measurement.

Kurtis opened describing the application of PIDPlus and the new HART command in wireless control. Emerson recently donated the PIDPlus algorithm to the FieldComm Group—the new name for the soon to be combined HART Communications Foundation and Fieldbus Foundation.

For this application wireless throttling valves are being used in flow control on a 6″ divided wall distillation column. The challenge of using wireless devices in a PID control loop is the slow update rate, typically 8 seconds for a 5-7 year batter life, and non-periodic update rates. A new HART command helps the analog output (AO) block required for the control valve so it knows when the valve changes.

The valve receives the signal to change position and sends an acknowledgement back that it has received the command. The feedback from the valve position provides feedback that the command was executed.

Wireless-PID-Output

Here’s the flow lab in Marshalltown where the testing on this throttling valve was performed.

Marshalltown-Flow-Lab

Terry noted that industrial size pumps and valves were used in the wireless control test. A Micro Motion Coriolis meter was used for the flow measurement. Unmeasured disturbances were introduced using a load valve downstream of the control valve. Both wired and wireless valves were used to benchmark performance against one another. The same PID tuning parameters were applied to both loops.

Another test was performed with a wireless device for the measurement instrument—so the control loop included a wireless sensing device, wireless control valve, and a DeltaV controller running the PIDplus algorithm. Other than a slight delay in response, the control performance was comparable to a wired equivalent.

Steve presented the next step where field trials would be performed at the field trial site at UT’s Separations Research Program. This program is cooperative industry/university program performs fundamental research of interest to chemical, biotechnological, petroleum refining, gas processing, pharmaceutical, and food companies.

For the field trial, six flow control loops are designed to use wired or wireless input, wired or wireless throttling valves. The tests are being conducted to compare control performance using wired vs wireless field devices. This process will be commissioned this month and information will be inserted at this point in the final presentation that shows the flow loop control performance for wired and wireless measurement and wired and wireless valve.

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