Sample handling and integration back ground information
Abstract Sample handling is often forgotten to be one of the most important aspects for process analysis. While in laboratory environment the sample handling is a well addressed issue (3) in process analysis the focus is commonly on the analysis itself. A number of developments in the area of process analysis sampling will be addressed here.
First, a conventional process sample handling system consists of a sample take-off and preconditioning system, sample transport and sample conditioning and calibration system. These are basic blocks needed to built a sample handling system.
The particular parameters that need to be controlled are pressure, flow and temperature, clean-up of the sample by filtration, liquid separation and calibration. For example when a system is build to analyse environmental samples the pressure is normally atmospheric and a pump is needed to pull the sample through the system, then liquids are taken out of the system using a cooler in combination with a peristaltic pump, after which temperature is slightly elevated above the dew point to prevent any gasses to condense during transport and further treatment. One important aspect here is not to drop-out any of the components of interest during the liquids drop-out step.
Sampling from a process at a high pressure
Another example where the sample is taken from a process at a high pressure. Normally the pressures at the process pipe, particular in natural gas transport, are relative high (50-100 barg). To be able to analyse the sample with an analyser, which is generally done at a few bar gauge, the sample first needs to be reduced in pressure. Doing that a pressure drop will result in a temperature drop due to the Joule Thompson effect (also called a throttling process). This results in unwanted effects like freezing at the sample take-off point. The sample handling device to neutralize this effect is a vaporizing regulator. This device is often installed at the sample take-off point as close as possible to the sample probe.
A new development is a probe which uses the process fluid energy in conjunction with an internal heat transfer device to heat the pressure regulator installed at the bottom in the probe to neutralize the temperature drop effect (see Figure 3 on the left)
Figure 3 Genie Retractable Probe Regulator Model GPR with integrated membrane (courtesy of Genie inc.).
Further developments in sample handling (NeSSI™)
A new development in sample handling is the NeSSI platform (Ref 4) which reduces conventional sample handling systems to a standardized miniaturized platform. The NeSSI initiative was begun to simplify the tasks, and reduce the overall costs, associated with engineering, installing and maintaining chemical process analytical systems. NeSSI is an acronym for New Sampling/Sensor Initiative. The specific objectives of NeSSI are:
- to increase process analytical system reliability,
- through the use of increased automation,
- shrink the physical size, sample and energy use by means of miniaturization,
- decrease sample flush times by analyser and sample handling integration,
- promote the creation and use of industry standards for process analytical systems,
- and help create the infrastructure needed to support the use of the emerging class of robust and selective micro-Analytical sensors.
Figure 4: standardized building block for the NeSSI platform (courtesy of Circor Tech)
The sample handling building blocks are standardized resulting in simplified engineering and construction of the sample handling system. The components are interchangeable which reduces the cost and maintainability.
Figure 5: a sample handling system on the NeSSI platform (courtesy Circor Tech)
The sample volume Vsample in is reduced to a minimum on this platform.
A number of other analytical devices/sensors are available on this platform; e.g. a photometer, a moisture sensor, a viscosity meter and an oxygen sensor. An interesting development from EIF is the Astute 3D Probe. Here the integration reaches an ultimate level, the sample take-off probe, sample preconditioning, and sample analysis are all integrated in one device.
Figure 6: all steps from sample take-off to analysis integrated in one 3D probe (courtesy of EIF)
Integration of equipment in process plants a slim analyser package (aSAP) (5)
Another new development of further integration of equipment with its sample handling in a process plant and the increase of sampling speed has been developed by ASaP BV the Netherlands. It consists of a flexible cabinet called a Slim Analyser Package (aSAP) with integrated sample handling.
For the analyser(s) and maintenance personnel a weather protective enclosure is provided. The construction of the enclosure is such that by opening both enclosure doors are at an angle of 90°, a weather protective area is created for maintenance personnel. Both doors will be fixed at 90° by special plastic breaking rods. In case of an emergency maintenance personnel can walk/fall through the doors which will open to 180°. This concept called will enclose the requested analyser(s) and its sample handling system and utilities.
Figure 7: on pipeline installation including side platform
Figure 8: a Slim Analyser Package (aSAP), )(the back wall is transparent for illustration)
Direct on top of the pipeline installation is possible with this setup. It will also reduce overall installation and engineering costs. Below example shows the integration steps of a µGC into a Process (ATEX) certified µPGC and an aSAP analyser package.
Figure 9 a µGC integrated into a Process (ATEX) certified µPGC and an aSAP analyser package