December - 20199MANUFACTURING TECHNOLOGY INSIGHTSHow and Why Energy Models Work:With thousands of instruments, failure of one or multiple instruments is probable. Many times, failures are not detected because control systems can compensate and hide them. Fortunately, the laws of physics and thermodynamics are well understood and consistently hold true. For example, when a steam valve opens, there are multiple responses in the system defined by scientific laws:1. The process will respond by absorbing the energy supplied by the steam2. The steam generating system will respond to added demand3. The cooling system will respond as needed to the additional heat (e.g. condense process vapors). When the responses of these systems do not follow the laws of nature, there is a defect in the system: a failed meter, valve, trap, or exchanger. For example, when a valve feeding a steam jet opens from 0 percent to 100 percent, the plant steam generation should on average increase by the designed amount and the heat load on the cooling tower should increase by a similar amount. When the response is not consistent with expectations, there is an indication that equipment is malfunctioning and not fulfilling its purpose. There are many more operations in a site occurring simultaneously. The beauty of a comprehensive model is that it can factor out all of the other operations and isolate the impact of the valve alone. Only a handful of energy models are needed to monitor thousands of instruments on a site. When the process deviates from a model, an instrument has failed and an investigation is required.The technique of energy modeling has been a tool for improvement for quite some time. Their use has allowed for continuous, low to no capital improvement for years. Unfortunately, until the existence of operational analytical packages, models were very difficult to develop, quite simplistic, rarely updated and would eventually become obsolete. Today's analytical packages resolve all of those previous modeling issues. Current energy models are now very easy to develop and update, have multi-variate complexity, and consistently identify energy reduction opportunities. They were the cornerstone of the improving trends below. It is expected that the early findings of operational analytics packages will increase the slope of improvement and extend it for quite some time. Graph 1: Example of steam jet model on SeeqGraph 2: Purchased energy consumption per ton of resin produced, 2010-2018 (allnex)
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