Electrical Process Tomography
What is Electrical Process Tomography?
Electrical Tomography is a measurement technique for obtaining
information about the contents of process vessels and pipelines. Multiple
electrodes are arranged around the boundary of the vessel at fixed locations in
such a way that they do not affect the flow or movement of materials. Tomographic measurement techniques differ
from point measurement techniques, because they sample a substantial proportion
of the process volume rather than at a single point. Circular pipeline-based
sensors measure an entire cross-sectional volume.
The technology can be used for liquid/liquid, solid/ liquid,
gas/liquid, gas/solid/liquid systems. The spatial resolution of the imaging
method and the sensitivity of the method depend specifically on the electrical
properties of the system being measured and upon the dimensions of the process.
Typically, a sensor consists of 16 electrodes and for research
applications up to 8 x 16 electrodes may be arranged within a process vessel.
The technique can be used with a wide range of research and
development applications demonstrated, including:
ü
interrogation of mixing processes
ü
investigating a solid-liquid filtration process
ü monitoring the performance of a hydro cyclone
ü measurement and control of bubble columns
ü measurement of multiphase flow
One of the main application areas of electrical tomography is
the measurement of multiphase flow regimes.
Flow processes may involve a variety of phases or components in
the gas, liquid or solid phase and are complex in their nature. Electrical tomography
techniques provide the capability for flow visualization, regardless of
material opacity, to enhance the understanding of such complex flow processes.
Measuring
Solid-Liquid Flow Using Electrical Resistance Tomography
Electrical Resistance Tomography (ERT) met the criteria due to
the robust and simple nature of the equipment and the absence of any
radioactive, cryogens or dangerous components means the equipment can be
readily employed at mine sites both above and below ground. Measurements were
performed on a 100 mm diameter flow loop with closely graded 2 mm silica sand
suspended in clear shear thinning polymer suspensions. These ‘model'
suspensions mimic the behaviour of bimodal suspensions of particles containing
a large fraction of fine rheologically active particles that would form a
non-Newtonian carrier in which would be suspended the coarser fractions such as
those found on mining co-disposal lines.
Figure 1 shows a comparison between a photograph of the actual
pipe flow and ERT derived concentration maps using on-line single step Linear
Back Projection (LBP) algorithm and off-line iterative Sensitivity Conjugate
Gradients (SCG) algorithm. The LBP algorithm has the advantage that images are produced
on-line at rates of multiple images per second. However, it can be seen that
there is some blurring of the solid-liquid interface. The SCG algorithm is in
substantial agreement with actual pipe flow conditions.
Fig 1
No comments:
Post a Comment