'The Total Cost of Ownership of Automated Valves'

摘要

Control valves, are one of the most neglected part of process loops in the chemical industry, from the perspective of "opportunity". While process measurement can be redundant and also often replaceable "on the fly", this is rarely the case with control valves. This is why their "Total Cost of Ownership" [TCO] can have significant impact on the profitability of chemical processes. From design to installation, startup commissioning and maintenance, there are few process control devices that contribute more to process controllability than control valves. This paper will address the details that impact control valve total cost, including design, capacity sizing, automation sizing, installation, startup commissioning and maintenance. Historically, plant design has focused more on moving the process from point A to point B, and monitoring process conditions to maintain them within certain parameters. The maintenance of the conditions is accomplished through both passive and active elements. Passive elements, like heat tracing and insulation, require minimal design while active elements such as control valves, automated louvers, and variable speed pumps, require significantly more. Design is done, often overlooking the need for adequate attention being given to the efficiency of the active elements. Energy loss, control precision and undesired variables such as vibration and noise, are dealt with "after the fact", in a remedial fashion, if they are addressed at all. Many problems are left to be corrected in the field after the plant goes into operation. Specifically, not a lot of effort is put into plant design to match the process and control needs to the control valves that are selected for use. Other factors, such as automation sizing can greatly influence control quality and represent, in many cases, over 60% of the initial cost of the control valve assembly. Installation and commissioning of control valves are crucial steps to ensure that interruptions during plant startup are minimized and that troubleshooting can be better focused on the real problems rather than a "hit and miss" process. Proper installation generally means following the "Original Equipment Manufacturer's" [OEM] recommendations. How closely these installation procedures are followed varies greatly. Control valve installation and operational problems are difficult to identify, using process measurements, particularly in new facilities, and specifying additional instrumentation on control valves to facilitate troubleshooting is often cost-prohibitive. Without commissioning the control valves properly, how can it be certain this extra instrumentation is working properly? Insuring that the correct valves, that match the plant engineering design, functioning as intended and are installed correctly, in the right locations, is important to the successful startup and operation of a new facility.