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2 2- Crude Sweetening : A process of cleaning crude oil from hydrosulphide (H2S ) and other sulfur compounds General sweetening processes at production facilities: 1- Stage vaporization with stripping gas. 2- Trayed stabilization with stripping gas. 3- Reboiled trayed stabilization

3 1- Stage vaporizer with stripping gas

4 2- Trayed Stabilizer with Stripping gas

5 3- Reboiled Trayed stabilizer

6 8- Vapour Recovery 1 ) Vapour Loss Sources : 1- Breathing loss 2- Standing Storage losses 3- Filling loss 4- Emptying loss 5- Boiling Loss 2) Liquid Vapour Pressure 1- Vapour pressure affects the loss rate 2- Increases with temperature 3- Its effect depends on the oil composition 3) Temperature Changes in Tanks 1- day time 2- night time

7 9 – Vapour Recovery Systems Methods of recovery 1- Absorption :- under pressure – liquid of higher molecular weight 2- Condensation by compressing 3- Condensation by simple cooling 4- Hydrocarbon vapour + air, Heat or depressurization 10 – Vapour Recovery System Economics

8 Maximum BS&W per cent Maximum Salt Concentration lb/1000 BBL Maximum Hydrogen Sulfide ppm Basic Specifications of Crude Oil 11- Crude oil specifications

9 o API = (141.5 / SGo) – where: o API – API Gravity in degrees; SGo – Specific Gravity of the crude, equals to the ratio of martial density to the waters density at Temperature = 60 o F (15.6 o C).

10 Crude Class o API GravityExamples 1.Extra Light o API > 45 o Some Crudes of Saudi Arabia 2.Light35 o < o API < 45 o Crudes of Algeria & Libya 3.Medium25 o < o API < 35 o Crudes of Saudi Arabia, UAE, & Kuwait 4.Heavy o API < 25 o Crudes of Egypt & Syria

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13 1- Crude Stabilization The transportation of liquids from the oil field to the user is more economic than gas transporting. The liquid phase consists of various components such as oil, lighter hydrocarbons, water and dissolved salt. The purpose of stabilization is to keep as much as possible hydrocarbons in the crude in liquid phase, and remove the light ends that cannot be kept in it. For crude stabilization two process are used: 1. Stage Separation and 2. Trayed stabilization

14 Simple Three Stage Separation 1- Stage separation Series of separators with sequentially reducing pressure.

15 Determination of the number of stages : By field tests or process calculations Calculations need complex thermodynamic correlations General rules of thumb for determining the absolute pressure ratio, R, per stage of separation: R < 5for gas condensate production R < 7for crude oil separation where the stock tank oil gravity is greater than 50 API. R < 9for crude oil reparation where the stock tank oil gravity is less than 40 API. Assuming that R is equal b/n stages. The liquid recovery increased with the increasing of the stage number

16 2-Stage Separation Bbl/mmcf 4-Stage Separation Bbl/mmcf Increase in Stock Tank Liquid Recovery 4-Stage vs 2-Stage (Per Cent) Stock-Tank Liquid Recovery * Separator Temperature = 85F

17 3- Trayed Stabilization Stabilization a fractioning of the first stage separator liquids to maximize the volume of stable hydrocarbon liquids under stock tanks conditions Stabilizer – a fractioning column. 1- Self contained 2- Safe operation 3- Simple control system 4- Easy dismantling and reassembly

18 4- Basic Types of Stabilizers 1- Re flux type P = 150 – 300 Psi Coolers or loop refrigeration systems _ in large central gas processing plants. 2- Non Re-flux Type P = 55 – 85 Psi Feed temperature as low as possible to prevent pentanes and heavier loss. 5- Stabilizer Operation : - Fixed overhead and bottom temp. - The T as low as possible to maximize recovery

19 Stabilizer Operation: 1.Cool liquid from separator inters at the top of the column 2.Falling cold liquid contacts with hot vapors rising from the bottom. 3.Rising vapors strip lighter ends from liquid 4.Liquid absorbs and dissolves some of heavier ends from vapors 5.Equilibrium cannot take place on the first tray, because of the large ΔT and short contact time. 6.So light ends vaporize lower 7.Some light end may be recondenced while rising up. 8.Stabilizers can operate at any pressure

20 Non-refluxed stabilizer (Diagram )

21 Stabilizer Design : Stabilizers with P > 200 Psi have 20 bubble trays. Stabilizers with P < 200 Psi have bubble trays Temperature gradient b/n top and bottom_ High with high P. General role of thumb: 1 sq ft of tower area will handle 100 BBL / D of stock tank liquid.

22 Stabilizer Applications Has significant advantages over simple stage in the following cases: 1. First stage separation temperature between 0 and 40F. 2. First stage separation pressures greater than 1200 PSI. 3. Stock tank liquid gravity greater than 45 API. 4. Oils containing significant quantities of pentanes plus even though their gravity is less than 45 API. 5. Rigid product composition specifications that require minimum light ends.