P rocess Description Figure 2: Flow Diagram for Alba Field Oil and Gas Processing and Corresponding Abbreviations of units

Table 1. The principal objective of First Stage Separators is to keep heavy hydrocarbons ( ) while getting rid of lighter portions. To reduce pressure at each stage to avoid flash vaporization, etc. choke valves are employed. Furthermore, with the purpose of monitoring the separation of compounds in the mixture, at the exit of various process vessels pressure and liquid level control valves are positioned.

Once the separation process of oil at FSSs is completed, the separated oil is being transmitted via the streams O-5 and O-6 to the DUs which function at 6 bar and ( ). However, before entering DUs, by virtue of HE-4 and HE-5, the corresponding streams are cooled down. The working principle of Degassing Unit is based on the utilization of the vacuum to release dissolved and free gas in the liquid which enters the unit and by means of automated exhaust valves to expel it. It is crucial to note that the decrease in pressure reduces the solubility of gas. To define the most suitable and effective operational conditions of the DUs based on the pressure and vaporization temperature of heavy compounds within the crude oil mixture, once again Table 1 is being used as a reference. The subsequent stage involves the passage of the separated oil via the streams O-7 and O-8 to the ECs which operate at 3 bar and ( ), the main purpose of which is to eliminate the remaining water droplets. Electrostatic coalescers function through the creation of an electric field by virtue of internal electrodes. Based on the concept that water is electrical conductor, whereas oil is insulator, when the electric field is created, the surface bonds that exist between the molecules break up; consequently, water is being separated and discharged into WTU through the lines W-6 and W-7. Based on the corresponding publications and research, it was found out that by using electrostatic coalescers, it is feasible to decrease the water content of the existing mixture up to 0.05%, so that the purchaser’s specifications are met. After the processed oil have passed through all the above-mentioned stages where the large potion of all available water and gas content has been withdrawn, the resulting composition is likely to have high viscosity and lower mobility. Thus, to ensure that the butane remains in liquid state and to provide an easy form of transportation, by means of HE-6 and HE-7 the mixture is being heated and then is being pumped into the FSU which operating conditions are 5 bar and ( ).

As for gas lines coming from FSSs through lines G-2 and G-3, from TS via the line G-1 and from DUs through the streams G-4 and G-5, they merge in the stream G-9 and enter KOD which operates at 4 bar and ( ). When it comes to the working principle of the Knockout Drum, by applying the centrifugal force, all the remaining liquid droplets are taken to the outer side of equipment for the withdrawal, whereas the fluids which are in gaseous state are transferred through the above and the center. There is a certain spinning gating screen positioned inside of a knockout drum and in the moment when any liquid droplet gets in contact with this screen, the collision between the droplet and the screen takes place which leads to the acceleration of the tiny droplet towards the base of the vessel owing to gravity. Consequently, the accumulated liquid at the bottom part of the KOD is transmitted to the EC through the line O-9 for further treatment. The composition of the initial crude oil had certain amounts of toxic gases, namely , , and ; these gases are extremely hazardous and may lead to adverse consequences for consumers if not removed from the crude oil during processing operations. Therefore, the gas mixture leaving the KOD is being sent directly to sweetener (S) via the line G-11, the main function of which is to get rid of all these toxic components by using a range of various chemical substances. The next step in the processing of purified gas is the adiabatic compression inside of the compressor unit (C). Due to high pressure conditions, the gas molecules experience strong vibrations which in turn cause an immediate increase in temperature inside of the compressor to about ( ). As a result, before such gas can be employed as fuel, its temperature should be lowered by means of HE-9 located at the outlet of the compressor unit. To ensure safe transportation of gas through pipelines without any further issues such as overheating or pipeline corrosion, this step of colling gas once it exits the compressor is crucial to evade extra cost especially in offshore.

When it comes to water streams which are leaving FSSs through the lines W-2 and W-3, and TS via the line W-1, and, finally, ECs through the lines W-6 and W-7, they all come together at the stream W-10 which is entering WTU working at 5 bar and ( ). In the water treatment unit, leftover oil droplets which are taken out of the water are being further recycled via the line O-18 to the RF-3 stream which comes from the manifold. As for the processes taking place inside of the water treatment unit, heavy water particles settle down to the base of the WTU unit through the precipitation process and then get removed via the line W-11. Moreover, some extra amount of saltwater from the sea (wavy illustration in