One of the world’s largest steam generating plants is located on an island in a major U.S. metro area. The plant distributes steam for heating and air conditioning throughout its local service area, but has to pull fuel for its oil-fired boilers from a tank farm approximately two miles away. To complicate mattersCONTROL ENGINEERING China版权所有, 85% of that distance is through a tunnel under a heavily traveled river. Given local environmental concerns, that fuel delivery system has to be closely monitored to make sure no oil is being lost in between.

Comparing the schematics of the three systems, it is possible to see how the technology evolved over 40+ years of operation

        The plant purchases No. 6 fuel oil from a tank farm across the river, so oil has to be pumped through a pressure-Controlled pipeline that runs through a tunnel under the river, at a maximum flow rate of 300 gpm. Stringent requirements for the leak detection systems on the pipeline require that the system be able to detect any leak in excess of 60 gallons in 20 minutes, which effectively amounts to 1% of maximum flow.
        Oil in = oil out?
        The material balance method of leak detection is simple: quantity in – quantity out = size of leak. Simple控制工程网版权所有, yeswww.cechina.cn, but implementation is more complicated. The system must manage temperature and pressure differentials and time lag. If the system is based on volume控制工程网版权所有, temperature compensation is especially challenging when different segments of the pipeline run at different temperatures. The oil temperature can change as it passes from the tank to underground to under water. Because multiple measurement devices are involved, measurement error accumulates, with negative consequences for overall accuracy.
        In the early 1990s控制工程网版权所有, the utility company assessed its leak-detecti