By Jim Riggs1 In the first article of this series, Jim discussed control relevant issues associated with distillation columns. The second article presented the major disturbances affecting composition control and the importance of properly functioning regulatory controls. The third article discussed the use of product composition measurements in distillation column control and explored single composition […]
By Fred Thomasson1 In the Control Magazine article entitled Envelope Optimization by Bela Liptak (www.controlglobal.com; 1998), a multivariable control strategy is described whereby a process is “herded” to stay within a safe operating envelope while the optimization proceeds. Building on that work, a method to implement Envelope Optimization using fuzzy logic is described in this […]
By Peter Nachtwey1 Since most of us don’t have our own heat exchanger to test on, I thought it would be good to show how one can be simulated. This would allow us to test the equations that calculate the PI tuning values over the range from a conservative to aggressive response. In addition, the […]
By Jim Riggs1 In the first article of this series, Jim discussed control relevant issues associated with distillation columns. The second article presented the major disturbances affecting composition control and the importance of properly functioning regulatory controls. In this article, Jim discusses the use of product composition measurements in distillation column control. He also explores […]
By Jim Riggs1 In the first article of this series, Jim discussed the importance and challenges associated with distillation control and the control relevant issues of distillation operations. Here he continues the discussion by presenting the major disturbances affecting composition control and the importance of properly functioning regulatory controls. Please refer to the previous article […]
By Jim Riggs1 Background Approximately 40,000 distillation columns are operated in the U.S. chemical process industries and they comprise 95% of the separation processes for these industries. Because distillation operation directly affects product quality, process production rates and utility usage, the economic importance of distillation control is clear. Distillation control is a challenging problem because […]
By Allen D. Houtz 1 My objective is to continue the discussion we began in the article Cascade, Feed Forward and Boiler Level Control. Here we explore the causes and cures of the dynamic shrink/swell phenomena in boilers.
By Allen D. Houtz 1 One common application of cascade control combined with feed forward control is in level control systems for boiler steam drums. The control strategies now used in modern industrial boiler systems had their beginnings on shipboard steam propulsion boilers. When boilers operated at low pressure, it was reasonably inexpensive to make […]
By Allen Houtz1 and Doug Cooper We explored override control using select elements in a previous article and learned that environmental and energy efficiency concerns for metered-air combustion processes can be partially addressed with a single select override element. Examples illustrated how a select override can either prevent having too much fuel or too much […]
By Allen Houtz1 and Doug Cooper A select element receives two input signals and forwards one of them onward in the signal path. A low select, shown below to the left, passes the lowest of the two signals, while ahigh select, shown to the right, passes the larger value onward.