Wireless pressure gauges prevent toxic gas releases

Toray Fine Chemicals (TFC) in Chiba, part of Toray Industries, is the only plant to produce DMSO (dimethyl sulfoxide) and polysulfide polymer in Japan, and also produces acrylic polymer.

Wastewater discharged from the plant’s manufacturing processes is biologically treated at the plant’s wastewater treatment plant before being released to public water bodies. A typical blower used in a wastewater treatment process is an aeration blower that sends oxygen into the aeration tank. At TFC there are also six blowers that are used for biological treatment equipment other than general aeration tanks.

The operation state of the six non-aeration blowers was monitored continuously by using the on/off signal from the control circuit as a signal to the monitoring system. Like aeration blowers, if these blowers are stopped, the supply of oxygen is stopped. Once the supply of oxygen is stopped, the processing of waste liquid sludge becomes anaerobic and toxic hydrogen sulfide and phosphorous is generated. Therefore, when the blower stops abnormally due to some fault, it is critical to restore oxygen supply immediately to avoid toxic releases.

In the case of an aeration blower, early detection of a malfunction of the blower is possible by the monitoring of pump operation and trend monitoring of the dissolved oxygen in the aeration tank. However, for the six blowers in the biological treatment facility, it was difficult to detect a malfunction as the blowers could only be monitored through manual rounds.

Three continuous monitoring methods can help to detect blower malfunction due to breakage or detachment of a drive belt: monitoring load current (power), monitoring of the blower discharge flow rate and monitoring of the blower discharge output pressure.

The monitoring of load current required significant rework — such as adding new measurement equipment into the existing control panel and other related installations — to send output back to the operator station. Monitoring of blower discharge flow rate would have required large-scale construction work to install a flowmeter for the discharge piping with a large diameter. On the other hand, continuous monitoring of the discharge pressure of the blowers using the existing process connection pressure gauge was seen as a more viable option.

Choosing the third option, TFC installed Rosemount wireless pressure gauges — replacing the existing mechanical pressure gauges — to measure the discharge pressure of the blowers. Previously, it was difficult to detect malfunctions, as there was only the on/off status monitoring of the blower or periodic manual rounds in which visual inspection was necessary to detect any detached or broken belt. With WPG, the discharge pressure was continuously monitored at the operator station with minimal manual rounds and the early detection of blower malfunctioning is now possible.

With continuous monitoring and trending of blower discharge pressure, TFC is now able to prevent the generation of toxic gas by early detection of blower malfunctions, which would impact the supply of oxygen to the biological treatment facility. Blower discharge pressure trending can also be used to detect and confirm membrane clogging issues. The Rosemount wireless pressure gauge utilises piezoresistive sensor technology to deliver reliable pressure readings, and the large 4.5″ gauge face also provides easy field visibility.

Using wireless gauges meant that the total instrument and installation costs were reduced by approximately 50% when compared to wired instrumentation. There was no additional mechanical gauge needed for field checks, and there were no more mechanical gauge failures due to high vibration of the blower, hence the measurement was reliable and maintenance-free.

“With the Rosemount wireless pressure gauges, we were able to prevent the wastewater treatment capacity from decreasing by 13% for every blower failure, and therefore avoid the loss of about 450,000 yen per day,” said Takashi Kuroda, of Toray Fine Chemicals.