GAMMA SCANNING
OF INDUSTRIAL PROCESS COLUMNS
Gursharan
Singh*
In chemical, petro-chemical
and petroleum refining industries, proper working of process columns
such as distillation, extraction and stripper is very important
as it affects the production efficiency and product quality. This
results in huge revenue losses in case of any mal-functioning.
During the operational life of these columns, many problems can
develop, which can lead to mechanical damage to the column internals
or the problem in the process itself. The malfunctioning of columns
may also lead to fire hazards and atmospheric pollution. To determine
why a column does not perform up to the desired design expectations
is challenging. This is because many problems in the column can
produce similar symptoms.
The conventional
techniques used to identify troubles in the column are: on-line
tests like pressure drop, density and viscosity measurements and
simulation studies based on mathematical models and hydraulic
correlations. The validity of
these depends upon the availability of accurate operating data
on stream composition or vapour- liquid distribution data.
These studies are
useful to identify the problem areas but they cannot pinpoint
the exact location of the problem. Gamma
scanning is a non-invasive technique used frequently for troubleshooting
of distillation columns. The technique is frequently used even
for predictive maintenance of column hardwares. The technique
uses absorption of gamma ray emitted from radioisotopes by process
fluids consisting of vapour and liquid. The technique is gradually
being used to solve more and more complex problems like maldistribution
in packed bed and entrainment from tray columns. In the international
scenario this technique is exploited on a routine basis and offered
as specialized service. Gamma scanning technique has also emerged
as a reliable research tool to generate valuable performance data.
Gamma scanning of
trayed or packed bed column is based on the absorption of gamma
radiation by the process fluids and the column components. For
investigating a column, a source of penetrating radiation, usually
a gamma ray emitting radioisotope, is placed on one side of the
vessel and a suitable detector on the other. The scans are made
by simultaneously moving the source and detector up or down the
opposite sides of the tower. The wall thickness and column diameter
are taken into account when specifying the energy and intensity
of the source, so that the radiation not only penetrates the walls
but is also sufficiently absorbed within the in-process material.
The source is usually Cobalt – 60 which is heavily shielded and
its radiation beam is collimated, so that it represents minimal
risk to personnel. The radiation detector is generally a thallium-activated
sodium iodide crystal that produces fluorescent light when struck
by radiation.
In India, gamma
scanning was introduced about 7 years ago, under an MOU between
the Bhabha Atomic Research Centre (BARC) and Engineers Indian
Limited (EIL) as a technique to see inside of an operating distillation
column. The technique has since been developed to a high degree
of precision and adaptability and has been successfully applied
in column troubleshooting process optimization and predictive
maintenance for almost all the major chemical process industries
in the country. BARC alone has successfully diagnosed over 150
different types of columns so far. BARC’s expertise in gamma scanning
is being used by several public and private sector undertakings
within India and Sri Lanka. These include Bharat Petroleum Corporation
Ltd., Indian Oil Corporation Ltd., Gas Authority Of India Ltd.,
Alkyl Amines Chemicals Ltd., Patalganga, Maharashtra, National
Organic Chemicals Ltd(NOCIL), Thane, Reliance Industries Ltd.,
Hazira,Gujarat, Reliance Petroleum Ltd., Jamnagar, Gujarat, Hindustan
Petroleum Corporation Ltd., Indian Petrochemical Corporation Ltd.,
Gujarat Narmada Valley Fertilizers (GNFC), Bharuch, Herdillia
Chemicals Ltd., Navi Mumbai, Mangalore Refineries and Petrochemicals
Limited, Mangalore, Heavy Water Plant, Department of Atomic Energy
and Ceylon Petroleum Corporation Ltd., Sri Lanka.(PIB Features)
*Head,
Isotope Applications Division, BARC, Mumbai
