TRACERCO Diagnostics™ - Leak Study
A TRACERCO Diagnostics™ Leak Study was employed to look for evidence of any process gas by-passing through the Intermediate Shift Reactor (ISR), or gas leaking through the ISR by-pass valve and to identify a cause for this effect on a chemical plant in India. A variety of process measurements and analysis had indicated that the ISR was performing at a reduced efficiency. The most likely cause of this effect was a mechanism for the process gases to by-pass this system. Two possible scenarios had emerged for the cause of this gas bypassing effect.
The TRACERCO Diagnostics™ Leak Study is based on the principle that if a pulse of a gamma-ray emitting radiotracer is injected into the process stream feed to a particular process component (in this case the ISR), then any leakage or by-passing within the system will be seen as a ‘double peak’, by sensitive radiation detectors positioned externally at a strategic position on the gas exit line.
This ‘double peak’ is caused by a detector response firstly to the ‘bypassing or the channelling’ radiotracer then a secondary response due to the tracer which has followed the normal route through the system.
In addition to these detectors, additional ones were placed at various locations to monitor the progress of the tracer in the system. Detectors were placed downstream of the gas bypass valve and their response to the radiotracer would provide indications of any leakage through this valve.
Also rings of detectors were placed circumferentially at two elevations on the reactor itself. The timing, comparative magnitude and shape of their response would provide additional information to the passage of the radiotracer through the reactor.
The responses from these detectors were relayed via co-axial cables to a data processing unit. A computer connected to the processing unit is used to log the data on a dedicated software package, which was also used to analyse the response data. The test was performed utilising a suitable radioactive gas tracer, injected via a ¼” instrument nozzle, into the reactor gas feed line approximately two metres upstream of the by pass valve T-piece. The radiotracer pulse was then monitored using externally mounted radiation detectors as it passed through the system. Results from the TRACERCO Diagnostics™ Leak Study showed that as bypassing was detected during four separate tracer injections and was calculated to be of the order of approximately 15-18% of the total gas flowrate through the reactor.
The mean bypassing residence time through the reactor was measured at approximately 5.6 seconds. The bulk gas residence time through the reactor was approximately 20.2 seconds. There was no indication of any leakage detected across the ISR bypass valve. Some signal variations were apparent from the circumferentially mounted rings of detectors, on the vessel, which were at two different elevations. However, there is not sufficient evidence at this time to conclude that any of the gas is bypassing down the outer vessel shroud. Critically, a very small response from the North East detector mounted in the lower ring of detectors arrived at the same time as the bypassing had been detected on the first exit detector. Therefore, some degree of bypassing cannot be ruled out for the North East quadrant of the reactor. No similar effect was observed from the top ring of detectors. Channelling of gas through catalyst bed appears unlikely.