Connections for Sampling

With sampling connections, it is important to ensure that the fluid arrives at the analyzer inlet at the desired phase. This is most important for vapor samples. Vapor samples must contain no liquid droplets when leaving the column, because on vaporization they become a significant part of the sample volume and can prompt a misleading analysis. Another important consideration (particularly in packed columns) is to obtain a representative sample. An excellent extensive discussion on column-sampling techniques is available elsewhere (2). A valuable discussion on the best locations for sample connections is also available (268). An excellent technique for obtaining representative samples in packed columns was described by Silvey and Keller (366). 

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Figure 1. Vacuum line and transfer system for the determination of single stage fractionation factors and composition of the phases (1) storage hulb for purified NO (2) manometer (3) silica gel tube for further purification of NO (4) gas burette containing mercury covered with a layer of a-bromonaphthalene (5) manometer (6) equilibrium vessel (7) connection for mechanical pump (8) connection for sample tube (9) stainless steel Helicoid gage (10) connection to mercury diffusion pump...

Other nozzles can be manhole, overflow pipe, emptying pipe, connections for sample taking etc. 

A conventional controller whose set, point and measurement are both accessible as electrical or pneumatic signals can be readily connected for sampling service. One timer is neeessary to set the control interval, and another to set the sampling interval, if no sampling analyzer is used. Figure 4.25 shows how a pneumatie eontroller would be connected. 

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