destillation tower in detail describing each part in the tower .ppt
- 1. Modem refinery operations can "be divided, into three main operations known as separation, Treatment and conversion. 1- The separation of different petroleum products from crude oil is known as distillation 2- The Treatment of different petroleum products obtained by distillation to remove the undesired impurities either by chemical or physical means is known as treatment. the treatment helps in a gaining the desired specification. 1
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- 3. 3- The conversion of surplus amounts of petroleum fractions such. as Gasoline into other type of fractions in which there is a shortage is known as conversion 3
- 4. The most important operation in a petroleum refinery is known as distillation. The different type of distillation units are. a-Atmospheric distillation units b- Reduced pressure distillation (Vacuum Distillation). c- High pressure distillation units. 4
- 5. The first type units are needed when there is a wide range between the boiling range of the top and bottom products as in the case of distillation of crude oil producing Gasoline as a top product and Fuel oil as a bottom product 5
- 6. The second type units are needed when the boiling rang of the feed. is very high to prevent crack . The feed to this un its is generally fuel oil. Vacuum reduces the boiling point and the desired products are obtained without, cracking. 6
- 7. The third type is done when. the boiling range 'between the top and the bottom product is very narrow as in the case of stab ilization of Gasoline to produce stabilized gasoline as bottom products and gases (C3C4) as top product. Another example is the separation of propane from butane under high pressure. 7
- 8. The most important conditions of distillation are 1- Presence of liquid phase vapor phase. 2- Counter current flow of liquid and vapour phase (Fig.3). 3- Equilibrium between liquid and vapour phase. 4-Temperature of vapour must be higher than temperature of liquid at the same plate. 8
- 9. 5- Through such contact between the vapor and liquid mas transfers is obtained between the two parts phases through the slots of the bubble caps* The effect is the enriching of the more volatile constituents in the vapor phase and enriching the liquid phase with the less volatile constituents. Fig. 10 shows the conditions of distillation diagrammatically indicating the bubble cap, liquid, slots, weir and down crammer. 9
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- 20. Atmospheric distillation units can be classified into three main types ';-. 1- Distillation using one fractionating column.. 2- Vaporization using a preflash tower and main fractionating tower. 3- Vaporization using a preflash vessel and main fractionating tower 20
- 21. The Purpose Of Reflux(Function Of Reflux) 1-Removes heat from the towers (preflasher or main tower) . 2-Control the temperature of the hot plate. 3-Control the required specification of the top product (i.e. it control the quality and quantity of gasoline’s with drum from the top of the preflash or main fractionating tower), 21
- 22. 4-Reflux initiates liquid flow in the towers. This is very imp ortant for the conditions of distillation mentioned previously (Vapour- liquid contact), I,e, evaporation & Condensation. 5- final point .of gasoline are deter mined by the reflux. 6-Reflux ratios differs from one distillation to the other. 22
- 23. The main types of reflux are :- 1- Cold reflux. 2- Hot reflux. T C R (top circulating reflux). 3-Intermediate Circulating reflux (I.C.R). 4-Internal Reflux Reflux ratio : the reflux ratio is usually defined as the ratio between the amount of reflux (R) and the amount of top product (D) R/D = Reflux Ratio The reflux ratio varies according to the type of distillation in case of atmospheric distillation it is 4:1 or 3:1 in case of pressure distillation 5:1 or 8:1 23
- 24. A. Cold Reflux Cold reflux is defined as reflux that is supplied at temperature a little below that at the top of the tower. Each pound of this reflux removes a quantity of heat equal to the sum of its latent and sensible heat required to raise its temperature from reflux drum temperature to the temperature at the top of the tower. 24
- 25. B. Hot Reflux It is the reflux that is admitted to the tower at the same temperature as that maintained at the top of the tower. It is capable of removing the latent heat because no difference in temperature is involved. 25
- 26. D. Circulating Reflux It is also able to remove only the sensible heat which is represented by its change in temperature as it circulates. The reflux is withdrawn and is returned to the tower after having been cooled. 26
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- 30. The feed point at the fractionating tower divides the tower into two main parts Rectifying section (upper one) and Stripping section (Lowe: one). Rectification can be defined at the end by the separation of heavier components from light components. In ordinary distillation the lower part of the fractionating column is used as a means of further fractionation such the bottom product will reach the required composition. 30
- 31. The fractionation of this liquid (in stripping section)is very difficult because of the following factors:- 1-High viscosity of the F.O minimize the efficiency of the bubble cap-action. 2-Low volatility of the F.O reduce the amount of vapour produced. 3-Solid particles plug the slots openings of the bubble caps. 4-The corrosive sulfur compounds specially at the highest tempe rature section of the tower destroy and cause rapid deteriora tion of the bubble caps 31
- 32. To solve this problem baffle -plates or perforated plates are used in this section of the tower instead of the bubble cap plates 32
- 33. trays Bubble cap trays Baffle plates Vapuour load good Very good Liquid Load good good Efficiency good Very good Elasticity exellent good Press- Drop good less Design Price Very easy good Very easy exellent 33
- 34. The liquid falling to the lower section contains some entrained vapor which has not been separated at the feed zone. This, vapor must be separated and sent upwards to the top of tower in the rectifying section. Some of the lighter components of the feed still in the liquid phase at the feed zone 34
- 35. . This is due to the imperfect fractionation while heating the feed. Such components should therefore, be evaporated back to the upper section of the tower. The vapors rising to the upper section of the tower might also contain some heavy components due to imperfect fractionation. 35
- 36. Such components are separated by means of the bubble cap tray the section, and are counteracted at the Lowerest tray of the rectifying section. The liquid overflow from this tray goes down to the lower section of the tower in order to produce the heavier components which the bottom products. 36
- 37. 1.Separation of the entrained vapor from the liquid entering this section. This done by using baffle plates in this section The effect of baffle plate is to spread the liquid surface and hence separate the vapor. 2.To evaporate and remove any lighter components in the liquid flowing to this section whether it is coming from the feed or from the liquid overflow from the Lowers' tray of the rectifying section.. 37
- 38. Such evaporation is carried by heating and using a stripping agent such as superheated. Steam 350° and 2.5 Kg/Cm2 pressure 38
- 39. Superheated steam (high temperature 350°C, low pressure 2.5Kg/Cm2 is injected at the bottom of the tower . The stripping effect of steam is due to the fact that when it mixes with hydrocarbon vapors, it will have a particle pressure proportional to its molar fraction,? Since the total pressure of the vapor mixture is constant, it follows that the hydrocarbon partial pressure will be reduced. 39
- 40. The hydrocarbons will be evaporated under a partial vacuum and consequently will require a lower temperature for their evaporation. The fuel oil leaving the bottom of the tower having the highest temperature in the column has been primarily cooled by heat exchangers wˉ the crude oil. It is further cooled by cooling H2O after which it is sent to storage tanks. 40
- 41. The Viscosity of fuel oil is controlled by: A- the transfer line temperature press. B-Stream amount of middle distillates withdrawn from the tower C- and control the temperature for the middle of the tower by the circulating reflux. Higher viscosities is necessary in summer season. 2000 red-1-sec and lower viscosity about 1500 sec.red-1 in winter. 41
- 42. The more fouling liquid (crude) flows normally inside the tube of heat exchangers and the less fouling liquid (F.O) flows outside the tube (Shell side). Fuel oil is directed into commercial marketing or to vacuum distillation for production of Lube cut and asphalt. Fig. 15 shows combination of preflasher, main fractionating tower and vacuum distillation tower. 42
- 43. The temperature gradient in the fractionating tower can be simplified that: the flash zone temperature at which the main fractionators receives the crude oil feed at a temperature of 310-330°C accordingly to the kind of crude oil, it produces the more volatile components (gas + heavy gasoline) at a temperature of 100-110°C which is known as the top temperature 43
- 44. , two side streams or three side streams are known as kerosene, gas oil and diesel oil at a tem perature of 170-180°C, 230-250ºC and 250-290°C i.e. for the kerosene, gas oil and diesel oil cut are withdrawn at the previous mentioned temperature. The higher temperature is the temperature of bottom product known as fuel oil which reduces about 300ºC-310ºC 44
- 45. The temperature of the feed is choosen to be exactly = F.B.P on E.F.V.C of the heaviest side product (solar or diesel if present). This temperature is regulated automatically "by the amount of fuel oil burned in the crude oil heater. It is controlled by the so called. TEC = temperature recorder controller) . 45
- 46. The temperature of the trans fer line is the temperature of the crude oil leaving the heater to the inlet point feed at the main fractionating towers The temperature of the top product which leaves the top of the tower in form of vapor. The temperature of the top plate correspond to the F.B.P of the top product on the F.V.C, 46
- 47. If the temperature is law, some of the top product will be produced with the first side stream (Kerosine}» If the top temperature is high some of the sides stream will be evaporated wˉ the top product and it will leave with it. The temperature of the top plate will be automatically controlled. wˉ reflux In order to control the F.B.P of the top product. 47
- 48. Law temp erature will give law F.B.P and high temperature will produce gaso line wˉ higher boiling point i.e., F.B.P. This depends essentially upon the variation of the amount of reflux (top reflux) or its temperatures. The side products kerosene gas oil are withdrawn in form of liquid from the fractionating tower. 48
- 49. T he temperature of kerosene, gas oil zones or plates correspond to the I.B.P of the desired products on E.F.V.C. At higher temperature part of the side product will evaporated and produced with the upward product, at law temperature part of the higher product will be obtained in the liquid will be produced wˉ the desired product. 49
- 50. In order to get the correct specification, the side draw plate temperature should be exactly the I.B.P of the side product (Kero sene , Solar) on the F.V.C It is common in practice to take the side product from a plate having a temperature BELOW the I.B.P on the F.V.C of the desired product, and as close to it as can as possible. 50
- 51. Generally in industry the liquids obtained as side streams will contain part of the higher component. This is corrected by intro ducing the liquid In a "STRIPPER" or SECONDARY COLUMNS”. The str ipper is a small tower wˉ 4 or 5 bubble cap trays, steam in the form of superheated steam is injected at the bottom. 51
- 52. The I.B.P of the side steams Kerosene, Gasoil are controlled by both the amount and tempe rature of steam at the 'bottom of the stripper Flash points of the side streamed are corrected by steam in order to be meet the required specification not less than 100°F for kerosene and not LESS 130-150°F for gasoil and not less than 160ºF diesel oil. 52
- 53. The lighter vapors, mixed wˉ leave the top of the stripper and returns back to the main fractionating , it is known as strip up, the strip up products are produced wˉ the next upward product All the strippers are usually combined together in one structure to economies cost of foundation. 53
- 54. The temperature of the bottom depends upon the temperature of transfer line high temperature produce high viscosity fuel oil and law temperature produce law viscosity fuel oil. The fixation of the temperature gradient by controlling the top temperature of the main fractionator control the temperature of the side streams automatically control the composition of the "botom products. 54
- 55. Temperature of the bottom may be calculated by making a heat balance for the stripping section of the tower. The importance of calculating this temperature) is to help in the design of the heat exchangers and coolers which will be used for this product. Fig. 1 shows the temperature gradient in fractionating tower, side streams and strippers. 55
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- 57. Distillation which are usually done in chemical laboratory for testing petroleum fractions is known as A.S.T.M distillation. The two other types of distillation which are very important are known as flash vaporization distillation or equilibrium flash vaporization E.F.V.D and true boiling point distillation (T.B.P.)
- 58. In the A.S.T.M distillation a known volume of the sample is heated vapors are condensed immediately and collected in a reservoir(known volume) The A.S.T.M curve is plotted as % distilled and the temperature recorded for the known volumes
- 59. In the true boiling point (T.B.P) distillation; actual separation of the individual constituents is desired at a high degree of accuracy. This requires multi-stage fractional distillation using a sufficiently large number of theoretical plates and a high reflux ratio as possible. For that purpose a packed tower is used in laboratory which is connected to the top of a still. A reflux condenser is plated at the top having a suitable device for controlling the reflux ratio.
- 60. A . ST . M . D T . B . P . D E . F . V . D 1 - Rough Distillation 2 - No Reflux . 3 - Laboratory Dist 4 - No equilibrium 5 - Individual Components not required 6 - Noramal distillation 7 - High I.B.P 8 - Law F.B.P 9 - Vapour are immediately removed after heating 10 - Constant pressure 1 - Accurate Distillation 2 - Reflux 3 - Laboratory Dist 4 - Equilibrium bet .VAP.phase &liq phase 5 - Individual Components required 6 - Packed Tower 7 - Law I.B.P 8 - High F.B.P 9 - Vapoure are condensed and recycle as reflux 10 - Constant Pressure 1 - Accurate Distilla 2 - Reflux 3 - Industry Dist 4 - Equilibrium between Vap. phase &lig phase 5 - Higher I.B.P.than A.S.T.M&T.B.P . 6 - Law F.B.P.than A.S.T.M& T.B.P 7 - the liquid is heated gradually and the vapors allowed to remain for a period wˉ liquid to attain equilibrium . 8 - Constant pressure .
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