On-line Calculation of Critical Characteristics for Cryogenic Storage Vessels

Cryogenic products, such as Oxygen, Nitrogen or Argon, are commonly delivered to customers by the supplier. To do so, the supplier is responsible for managing the inventory of product at the customer site, in most cases. It is important to have access to an accurate estimation of the quantity of product stored at any time in cryogenic vessels to avoid run-outs for the customer and to optimize the product deliveries, which means saving money and reducing pollution due to trucks fuel consumption. Former studies showed that an accurate mass estimation can be made from differential pressure measures between the bottom and the top of the vessel, the pressure on top, and required vessel characteristics. Differential pressure measurements are installed on cryogenic tanks and the data is available remotely through a remote telemetry unit (RTU). Often, the tank characteristics are unknown or only roughly estimated limiting the accuracy of the mass estimation in the tank. This paper presents an on-line method to estimate the critical required tank characteristics: radius, total height (for vertical tanks), total length (for horizontal tanks), bottom height, and maximum liquid height. This method relies on a physical model describing the vessel during a filling and providing a relationship between the delivered mass of product, the pressure measures and the vessel characteristics.