Category Archive: Metrics

Jan
16

Centrifugal Compressor Efficiency – Part 2

As addressed in Part 1 of the centrifugal compressor efficiency series, the enthalpy of the gas stream at the compressor suction and discharge must be known to determine the compressor efficiency. Also, the isentropic enthalpy must be determined based on the gas stream entropy at the compressor suction and the compressor discharge pressure. These properties …

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Jan
09

Centrifugal Compressor Efficiency – Part 1

Centrifugal compressors play an important role within the process industry. In some cases compressor capacity may determine the throughput of a plant. If a compressor is used for refrigeration then any variation in compressor operation may directly impact the temperature control in key unit operations such as flash vessels and exothermic reactors. Also, the compressor …

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Nov
28

Improving Continuous Process Operation Using Data Analytics

At Emerson Exchange, 2011, I had the pleasure of working with Frank Seibert, Technical Manager and Eric Chen, Associate Researcher, Pickle Research Center, University of Texas at Austin SRP and John Caldwell, Advanced Control Marketing Manage, and Willy Wojsznis, Senior Technologist, Emerson Process Management, to host a workshop that addresses how data analytics may be …

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Nov
04

Secondary Flow Loops Offer a Primary Advantage

A secondary flow loop offers opportunities for feedforward control, identification of valve stick-slip and backlash, online metrics, diagnostics, rejection of pressure disturbances, linearization, and modeling. However,  a secondary flow loop can be detrimental when the primary loop has a 63% response time less than 10 seconds. If the 63% response time is greater than 5 seconds, an exceptionally …

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Aug
11

Effect of Mechanical Design – UA

The product of the overall heat transfer coefficient and area (UA) determines the controllability of temperature processes. The deterioration of the UA is a particular concern for crystallization and polymerization processes. Frosting and fouling can decrease process efficiency and production rate even if the controllers are retuned. For exothermic reactors, a decrease in the UA …

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Jul
28

Effect of Mechanical Design – Mixing

Mixing changes the game. Mixing has a broad impact on disturbances, interactions, and noise. Mixing breaks paradigms on tuning, control, and performance. Mixing is at play in key unit operations offering incredible tightness of control and forgiveness of mistakes enabling exceptional product quality. I became sensitized to the role of mixing early in my career …

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Jun
23

Top Ten Limitations – Value Analysis

Automation engineers don’t get anywhere near the credit they deserve for increases in process performance. The value would be obvious if the automation system could be turned off but no one would allow this capture of the “before” and “after”. We need to do a better job of documenting where we are and could be. …

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Jun
17

Top Ten Limitations – Missing Measurements

The greatest limitation I experienced as a user for process control improvement (PCI) was unmeasured process variables. If we had a high degree of instrumentation, so that only a configuration change was needed we could let our creativity roam free and quickly implement various improvements including new loops and feedforward control. Also, from trend charts …

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Jun
09

Top Ten Limitations – Tuning

Money spent to reduce deadtime (e.g. greater agitation, faster valves, faster measurements) will be wasted if the controller is not tuned faster. You may have wonderful process dynamics but loop performance will be lousy if the PID is not tuned to be commensurate with the opportunity. A loop with excessively slow tuning and low deadtime …

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Jun
02

Top Ten Limitations – Deadtime

Deadtime sets the ultimate limit to loop performance. Deadtime is any delay in the action needed to exceed the threshold for the start of error correction. The loop deadtime is the sum of pure actuation, correction, or recognition delays and the equivalent deadtime from lags smaller than the largest time constant in the loop. For …

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