Underground salt caverns are frequently used for crude oil storage. One customer pumps oil from barges into the storage caverns. An ultrasonic flowmeter records the total flow. To
get the oil out of the caverns, a brine solution is pumped into the cavern through a magnetic flowmeter. Brine and crude oil flowing in both directions are measured and reported to the DCS using the HART communication protocol for accuracy. The DCS tracks flow rate and total quantity to maintain a certain pressure inside the caverns (Figure 21).
Figure 21: Underground
Petroleum Storage
A Texas wastewater treatment plant replaced stand-alone flowmeters and chart recorder outstations that required daily visits for totalization with a HART system. HART-based magnetic flowmeters were multidropped into HART RTUs to create a cost-effective SCADA network. The use of HART technology
reduced system and cable costs,
enhanced measurement accuracy, and eliminated time-consuming analog calibration procedures.
A system of 11 HART multidrop networks was used to connect 45 magnetic flowmeters from different plant areas. Each flowmeter communicated flow rate and a totalized value over the HART network. Multidrop networks eliminated the need for additional hardware and PLC programming while providing a more accurate totalized value. Complex and costly system integration issues were also avoided—for example, there was no need for synchronization of totals between the host and field PLCs.
Multidrop networking further reduced the installation cost by reducing the required number of input cards from the traditional 45 (for point-to-point installations) to 11. Maintenance was simplified because of access to instrument diagnostic and status data.
