Sample Points for Bottom Product Analyzer Control

12 Sample Points for Bottom Product Analyzer Control 

The general comments at the opening of the discussion on locating sample points for top product analyzer control also apply here and will not be repeated. The following sampling locations are used for controlling bottom product composition. 

Unless the dynamics of the system are well known, and the lags in the system are acceptable, sampling from the top of the next column should be avoided. The sample flashpot technique (Fig. 18.106) can be used to exclude the heavies from the sample before it enters the sample conditioning system. 

On a bottom section tray. This is analogous to locating the top product sample point on a top section tray. The considerations are identical to that case. Successful experiences in this location have been reported (13, 422). 

Fourroux et al. (122) found the same oscillation period when comparing the response of an analyzer/temperature control to that of an analyzer only control. This can be expected if the temperature controller is tuned for slow response, because the analyzer will adjust the temperature controller set point faster than the temperature controller can react. In the imusual case of slow temperature control, an analyzer/temperature control is therefore best avoided (406). The analyzer/temperature control relies on fast temperature control for its success. 

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