Valves in action -
Bleeding and venting valve EB 1.12
Ventilation of pipelines for the loading of oil on ships
Transporting crude oil through pipelines sometimes is neither economically viable nor technically feasible. Therefore, the oil is often transported in large tank ships to its place of destination. Oil tankers have as advantages that they can transport oil as well as further processed crude oil products. This allows the petrochemical industry to settle directly at the oil excavation site, where the first production steps of the processing chain can be accomplished.
A lading port for petrochemical products or crude oil consists of tank installations for the storage of the product and of pipelines, whose length varies between 2 and 5 kilometres. The product is then pumped into the ship’s cargo hold through these pipelines. Once the pipe connection has been established, the pumping process starts. It is initially relatively slow because the entire pipeline is still completely filled with nitrogen. During the previous filling process, the pipeline was pigged clean and nitrogen gas was fed in to drain the residual medium.
In the beginning, the flow velocity of the filling process is at 0.5 m/s to ensure that no pressure surges will be generated. Once the major part of the nitrogen gas has escaped, the pressure within the pipeline slowly rises until economical flow velocities of more than 3 m/s have been achieved – depending on the product being laden.
Mankenberg’s bleeding and venting valves are used to discharge the nitrogen gas from the pipelines. Startup bleeding valves are installed at the pipeline endpoints whilst pipeline high points are furnished with continuous bleeding valves of the EB 1.12 type, which safely discharge gas bubbles. The pipeline sections suitable for the bleeding process have been chosen in close cooperation with the plant engineer. The valve is adjusted in such a manner that it discharges nitrogen gas during normal operation, but remains closed during the pigging process that is normally performed at a pressure higher by abt. 3 - 4 bar. The valves have been designed to suit the lower density of petrochemical products and equipped with the corresponding seals. Effective venting with the EB 1.12 valve considerably cuts the operational costs of the tank installations because the entire pipeline is available for transport without any trapped air thus reducing the loading time of the ships.
