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INERGY, HEADQUARTERED in Kansas City, Mo., is a major provider of propane and services to 600,000 customers. While most of its operations are in the Southern, Midwestern and Northeastern states, the company operates a natural gas liquids site in Bakersfield, Calif., that includes processing, storage and terminal services.
Propane manufactured at the facility is stored in bullet tanks, each of which holds 10,000 to 15,000 gallons of propane. It is critical for the company to monitor levels and temperatures in each of the containers, since propane expands as temperatures rise. If pressure increases too much, the company must vent gas into the atmosphere and risk violating stringent California environmental regulations.
Ken Clifton, instrumentation and electrical supervisor at the plant, says personnel used to rely on sight glasses and “spinner” gauges mounted in the tanks to visually judge levels. “Our people would have to actually go out there and look at the tanks to determine the levels,” he says, adding that it was inefficient.
To improve the situation, Inergy decided three years ago to install field instruments in each tank that would send readings on temperature and level back to Inergy’s control system. “We could have put separate temperature and level transmitters into each of 40 tanks, but that involved quite a bit of instrumentation and wiring. Instead, we purchased instruments from K-Tek, each of which was able to monitor both of those variables,” says Clifton.
The transmitters send 4-20 mA level readings back to the plant’s programmable logic controller equipped with a HART gateway and use a HART digital signal to communicate temperature and level information. Using the two readings, the system is able to calculate the level in each tank accurately and display it on the system’s HMI.
“With this system, we’re able to get two readings for the price of one, and it’s worked well for us,” says Clifton. “We’ve had a few minor problems, but none involving use of the HART protocol.”
“In fact,” adds Clifton, “all the instrumentation we put in this plant has the HART protocol, because it makes troubleshooting easy for our instrumentation techs.”
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