Minimizing Safety Risk and Improving Batch Performance

Articles such as Oil & Gas iQ’s Five Deadliest Onshore Oil & Gas Blasts remind us of the critical importance and focus that is required for process and personnel safety. I lived in New Orleans at the time of one of the five mentioned. The accident occurred during the night and the shock waves from the blast were like someone repeatedly slapping on the windows with open hands.

For some facilities, the distance to tank locations from the main control room has made it difficult to instrument the tanks to give the operators a clear view into these areas. Operator rounds to manually inspect the tanks and tank levels have been standard operating procedure.

Emerson's Brian Lux

Emerson’s Brian Lux shared a story where a Rosemount 2160 wireless level switch that not only eliminated the risk of operators performing manual inspections in these hazardous locations around the tanks, but also help to improve the performance of the operation.

The chemical manufacturer needed to detect the level and interface of acid/water in the acid decant tank. There is a layer of water on the top of the acid in the tank for stability purposes, but when the acid is decanted into containers, any water included in the acid could result in a scrapped batch.

The emptying had to be stopped before the water was introduced into the container. For this application, top down radar was unsuitable because the microwave signal could not pass through the water layer on top of the acid. Other options such as magnetostrictive devices were considered, but these were complex to configure and their flexibility in different fluids was not good.

Established practice was for the operators to perform visual inspection of the phase change/interface through a site glass in a pipe spool piece. After observing the interface, they radioed the control room to turn off a valve to stop decanting into the container.

Unfortunately, this manual approach resulted in huge batch-to-batch variations given the proficiency of the various operator performing these inspections. This chemical manufacturer needed to reduce variability to improve batch consistency and accurately measure the layer of water on top of the acid.

Since the site had an existing wireless network for their WirelessHART devices, using a wireless level switch was the best approach. With the 2160 wireless vibrating fork level switch, the frequency of the forks changes depending on whether the forks were in the acid or water and this frequency change gives a reliable indication of the phase change from acid to water. The C-276 wetted material option for this level switch was suitable to avoid acid corrosion.

In addition to minimizing operator time in this hazardous location, product quality improved and throughput is more consistent throughout.

Cost savings were also made due to the elimination of scrapped batches, and because the Rosemount 2160 is a wireless device, the installation was straightforward.

Based on the success of the project, the chemical manufacturer is equipping a second tank with this solution.

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