Tank gauge system and the application of it to oil lease tanks is not new. The historical problem has been finding a tank gauge system that provides all the necessary features to be able to fully control the tank and with most oil lease tanks this needs to be accomplished through a single opening. There are many technologies used for tank gauge system such as radar, guided wave radar, ultrasonic, servo, reed switch, and magnetostrictive.
When comparing the technologies, make sure to look at the needed features/specifications and compare the overall installed costs of the tank gauge system and not just the level transmitter. To adequately report inventory, you will need to monitor two liquid levels, temperature, and calculate volume. The first liquid level is the product level in the tank and, for oil lease tanks, this is the desired product of crude oil or condensate. The second liquid level is to detect or monitor the water level in the tank. The water level is needed to distinguish how much product is in the tank versus the overall level. A temperature measurement is needed for the volume calculation to be able to determine the net volume instead of the gross volume in the tank. Net volume calculations are used to remove the influence of physical expansion and contraction with temperature fluctuations. Without product level, water level, temperature, and volume, the tank gauge system is not able to fully monitor the tank.
Each tank gauge system is different as each uses a different technology and requires different equipment. The differences can add up to a large difference in the installed costs of the system. The installed cost includes any and all costs to install the system and receive the information in the control room. A partial list would include level transmitter, cable, conduit, secondary devices, auxiliary equipment, and/or specialty tools. Even if the level transmitters are comparable in costs, the installed costs of the system can vary by thousands of dollars. Be particular and research the details of each system and each technology.
Most of the level measurement technologies (radar, guided wave radar, ultrasonic, and servo) do not offer the ability to measure the temperature of the liquid without a secondary device. A secondary device could require a second opening and typically oil lease tanks do not have spare openings. The cost of tank modifications would eliminate the cost competitiveness of that system. For some of the technologies, the secondary device is a combination temperature sensors and water level/detection sensor, as the primary device can only measure one liquid level and this reduces the need for a third opening. The installed cost of these technologies is typically higher due to the extra equipment that is needed to complete the overall tank gauge system.
Out of all of the technologies only two, reed switch and magnetostrictive, can provide a product level, interface level for water detection, and temperature measurement from a single opening. These two technologies are going to offer a better installed cost as they do not require secondary devices or tank modifications. The difference between magnetostrictive and reed switch comes down to performance, as magnetostrictive level transmitters are more accurate, field repairable, and offer additional features such as volume measurement from the level transmitter and integral HI level switch.
This article comes from oilmanmagazine edit released
