INTEGRATED SAMPLING SYSTEM

As it is well known, the accuracy and reliability of process analyzers are directly linked to the quality of the valves, manifolds, fittings and various hardware used in the sampling system. The best trace gas analyzer can’t have better performance than the sampling system it is connected to. In short, an analyzer is only as good as it’s sample system. By many order of magnitude, today’s trace gas analyzers outperform the analyzers designed 20 or 30 years ago and yet, it is not uncommon to find the same sampling system design philosophy found 30 years ago. For example, the quick connectors are still in use in many Air Separation plants even with gas analyzers having ppb sensitivity.

As a trace gas manufacturer, Contrôle Analytique reports that, more than 90% of its service calls are problems related to the sampling system. It is obvious that there is a need for a new approach concerning sample stream selection systems and that this need is highly addressed to the industrial gas industries.

The Target

ü Compact design: - reduces enclosure and housing costs;

ü Leak proof, Air diffusion resistant;

ü No sample stream cross contamination;

ü Small gas volume;

ü No dead or unswepted dead volume:
- eliminates virtual leaks
- reduces dry-down and purge time

ü Ease of operation; micro processor, intelligent support

ü Easy integration to an automatic process as remote control or automatic sample selection, calibration or truck loading operations;

ü Possibility of serial communication with remote computer, PLC or DCS.

The Solution

The Conventional Way

The conventional way requires the implication of many people from the engineering department, the purchasing and third party contractors. It is very expensive and prones to communication errors. This type of system is bulky and the performances are variable.

Ø Replaces complete sample panel, discrete valving system with one small 5 inch high rack mounted cabinet.

In figure 1, the SV valves are miniature, low internal volume, manifold mounted two way sample selection valves. The FV valves and associated FT flow transducers are used as bypass “electronic rotometers”. Each inlet has its own 2 micron particle filter. The FT-V flow transducer, monitors the outlet backpurge flow.

In figure 1, sample #1 is selected, so SV-1 is open and SV-2 to SV-n are closed. On each respective sample inlet, there is a bypass flow that is maintained by the microprocessor at the entered bypass flow set point. So each FV bypass flow control valve maintains the bypass flow at their respective set point. The unselected sample stream valves have their discharge side backpurged with the gas coming from the selected stream. The backpurge flow is limited by its respective flow restrictor “R”. This eliminates any unswept dead volume and speeds up upset recovery.

The output stabilisation loop allows a smooth, equilibrated flow and no dead volume. Finally, an optional electronic back pressure regulator may be installed to maintain outlet pressure constant.

Practically all SV valves are mounted on a stainless steel manifold. All gas inlets and outlets are welded on the manifold’s body. Finally the manifold, holding the selection SV valves, is mounted in a box that can be purged or maintained under vacuum, based on application. This eliminates completely the possibility of air diffusion into the system. All other parts of the system like the inlet bypass flow control valves and associated flow transducers are mounted outside of the purged box. These parts are not critical for the sample contamination.

Each system may be tailor made to fit the final application. The number of sample inlets or outlets, the number of systems in a cabinet, etc…

The software controls all the system operations. The user interface is done through 4x4 keypad and 4x40 LCD display. Upon power up, the user is prompted for inlet stream bypass flow set point. Optionally, the user enters back pressure set point if the system is equipped with an electronic back pressure regulator.

The user also enters identification tags for sample inlet. The stream (or tag) to be sampled is selected by pressing the associate number on the keypad. Automatic sample stream sequencing can be configured. The back purge flow is also displayed. The software will issue an alarm when there is not enough flow (pressure) from a sample stream inlet. An appropriate digital dry contact output will be activated. The software makes sure to close a valve before opening a newly selected one to avoid cross flow. The system has an isolated RS-232C communication port for interface with PLC, DCS, computer, etc…


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INTEGRATED SAMPLING SYSTEM

The Solution The Conventional Way

The Solution

The Conventional Way