Grey box fault detection of hear exchangers

A grey-box model-based method for fault diagnosis is proposed in this paper . The method is based on a first principle model of the process unit, i.e. a heat exchanger, and on a grey-box model of the fault, i.e, the deteriorat ion of the heat transfer surface by aging. During normal operating conditio ns the heat transfer coefficient is constant or slowly decreasing due to ma terial settling on the heat transfer surface. In old heat exchangers big pi eces of settled material can break off causing damage. When this happens, t he heat transfer coefficients will rise sharply. In the proposed method a r ecursive least-squares estimator with forgetting factor is used to track th e heat transfer coefficients. The settled material breakage fault is detect ed via detection of abrupt positive jump in the estimated heat transfer coe fficients using a cumulative sum (CUSUM) test. The capability to detect fau lts in any industrial equipment is heavily dependent on the availability of suitable measurements, For heat exchangers the variables related to the in - and outflows of the equipment (flowrates and temperatures) are usually me asured, but measurements along the equipment length are rarely available. T herefore, the possibilities of fault location in space are rather limited. However, simplified models can be used for fault detection in this case. Mo reover, a fault detection method is proposed with the possibility of spatia l fault location when measurements along the cold side are available. The p roposed method is illustrated on simulated examples with different measurem ent situations. (C) 2000 Elsevier Science Ltd. All rights reserved.