(110d) Radioisotope Methods for Obtaining Process Information

In all chemical plants and refineries there generally is not enough instrumentation in the right places in our processes.  During the design phase, decisions were made between knowing more about the process, which means buying more instruments, and saving capital funds.  When a problem appears with the operation of a vessel, there are always gaps in the knowledge of what is happening due to a lack of instruments in the places where knowledge is not routinely required.  Process engineers and operations personnel need to know what is happening so they can take corrective action. When knowledge is missing, they often take actions that make matters worse.

 For distillation and separation processes Chemical Engineers have historically relied upon plant process measurements such as flow rates, temperatures, and pressures and model or simulation results for data with which to solve troubleshooting or re-design problems.  An array of on-line diagnostic services are available that can provide additional data offering real-time information on how pieces of process equipment are actually operating. 

 The most common application is Gamma Scanning.  This test is primarily applied, but not necessarily limited to, distillation or separation columns.  Gamma scans provide a density profile of the internal process of operating distillation columns and other process vessels.  The density profile can be used to diagnose the hydraulic operating conditions of mass transfer devices such as damage to internals, flooding, degree of entrainment or weeping, liquid levels on trays and distributors, liquid distribution through packed beds, etc.  The presenter will show case studies where scanning revealed vital process information that helped solve an operating problem, or helped make a revamp/re-design successful.

Additional derivatives from gamma scanning of detecting flow distribution patterns will be demonstrated.  The CAT-Scan technique is a specialized horizontal gamma scan used to generate a topographic profile of the internal cross-sectional density of process equipment.  This profile is useful for the detailed study of liquid flow distribution through packed columns as well as having applications beyond distillation columns.  A hybrid application involving tracers and scanning on fixed bed catalytic reactors will also be discussed.

 Another technique involving radioactive materials is the Tracer Test, in which a radioactive tracer is introduced into the process for investigating the process flows. External radiation detectors are placed at strategically chosen locations outside vessels and piping to monitor the tracer flow through the process. Either liquid, gas or a solid tracer can be utilized depending on process conditions and the fluid to be studied. This tracer technique can identify liquid or gas maldistribution in fixed or fluidized bed reactors. The residence time through a tank or reactor can be measured and compared with the calculated residence time.  Observed differences can relate directly to the degree of mixing or channeling inside the reactor. These tracer techniques have also been used in identifying leakage of heat exchangers and valves.