Study of Clear Liquid Height and Dry Pressure Drop Models for Valve Trays
Wang, Chao
Mccarley, Ken
Cai, Tony
Vennavelli, Anand
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Wang C., Mccarley K., Cai T., Vennavelli A., 2018, Study of Clear Liquid Height and Dry Pressure Drop Models for Valve Trays, Chemical Engineering Transactions, 69, 409-414.
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In this work, literature correlations developed for tray clear liquid height and dry pressure drop are analysed and compared with FRI published data. Four valve trays measured and published by FRI are used in the data analysis. For clear liquid height models, the fundamental Colwell (1979) correlation based on Francis’s equation was analysed. The Bennett (1983) model based on air-water data, the Hofhuis and Zuiderweg (1979) model based on spray regime and mixed-froth regime, the Dhulesia (1984) model based on V1 valve and air-water data, the Brambilla (1969) model based on air-water data, and the Glitsch (2013) from Koch-Glitsch Bulletin 4900 were also analysed and compared with each other.
The dry tray pressure drop can be modelled by two ways. For the fixed valve tray and the sieve tray, an orifice type equation is used. The major difference between different researchers is the correlation for orifice constant. For the movable valve/float valve tray, the pressure drop curve is divided into three regions by the valve positions: fully closed region, partially open region, and fully open region. These three regions are determined by the closed balance point (CBP) and the open balance point (OBP). In this work, five literature models were analysed and compared with FRI data. Two of them are based on fixed valve tray or sieve tray (Smith and Van Winkle, Stichlmair), while the other three are based on movable valve tray (Glitsch, Klein, Bolles).
In conclusion, this work studied the two hydraulic parameters for valve trays by analysing literature correlations with FRI measured data. Results show that most of the literature correlations under-predict the clear liquid height for the above four trays. Except for the models based on Francis’s theory, the literature correlations cannot predict the trend of the clear liquid height with the bubbling velocity. For the dry tray pressure drop, the three-region models give better prediction than orifice type models for the four valves in FRI database. This work provided a new thought and pathway for future model development.
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