TECHNICAL FIELD

The invention relates to primary oil refining procedure to obtain straight-run fractions and can be used in Refining industry.

PREVIOUS TECHNICAL KNOWLEDGE

There is a method of successive oil refining in atmospheric and vacuum columns to produce the distillate fractions and the distillation residue. One of the important distillation efficiency indices is the increase of extraction depth of these fractions, achieved at the stage of vacuum distillation by vacuum deepening, temperature increasing and the use of volatile agent (M. L. Krejmer "Refiner Reference Manual", L., Khimiya, 1986, p. 68-69; S. A. Akhmetov "Technology of Advanced Oil and Gas Refining" Ufa, Gilem, 2002, p. 222-224). All these examples have the following limitations: vacuum deepening is limited by the increase of energy costs and the existing level of vacuum technology, temperature increasing is limited by insufficient thermal stability of distillation residue, increasing of evaporating agent amount is limited by residue temperature decreasing, resulting the decrease of partial pressure of hydrocarbon vapors and the corresponding reduction of stripping efficiency. In this regard, there are different ways to improve the efficiency of the distillation process as a whole.

There is oil distillation method to produce the straight-run fractions and the distillate residue, whereby diesel fraction and residue (fuel oil) obtained in the atmospheric column are sent to the vacuum column, at that, diesel fraction is supplied as a volatile agent to the stripping section, and fuel oil is supplied to the feed area (patent for invention RU N° 2043387, C 10G7/06, declared 02.12.1992, published 10.09.1995). Straight-run diesel and gasoil fractions as well as final distillation residue (tar), supplied to additional vacuum evaporator to remove volatile agent hydrocarbons, are withdrawn from the vacuum column. The use of diesel fraction as a volatile agent increases the cost of oil refining in general, since the transformation of this fraction into the product flow, i.e. commercial diesel fuel, is carried out twice - first in the atmospheric column, and then in the vacuum column. Besides, the disadvantage of this method is the need of tar secondary evaporation.

There is also a method to distillate oil successively in atmospheric and vacuum columns, wherein the distillate fraction (diesel fraction) and the residue (fuel oil) obtained in the atmospheric column are sent to the vacuum column, at that, fuel oil is supplied to the feed area, and the distillate fraction is separated to vapor and liquid parts, after that vapor part is supplied to the stripping section to be used as a volatile agent, and the liquid part is used as one of the target products (patent for invention SU Λ¾ 1685974 A l , C 1 0G7/06. declared 1 1 .07. 1989, published 23. 1 0. 1 99 1 ). Distillate fractions and the final distillation residue (tar) are withdrawn from the vacuum column. The volatile agent (the light part of the diesel fraction) with hydrocarbons stripped from the tar is obtained from the top of the vacuum column. At that, the presence of such volatile agent within common vapor stream at the top part of the column results the corresponding increase of the costs for vapor stream condensing, which is a disadvantage of the procedure in general.

There is another known method of oil distillation, which is the most similar to the claimed invention. It includes the recuperative oil heating, its partial topping in the first atmospheric column to extract light naphtha from the top of the column, the heating of the residue of the first atmospheric column in the furnace to supply it to the second atmospheric column feed area to separate the topped oil to heavy naphtha, kerosene, diesel fuel and fuel oil, to be sent further as raw material to the vacuum column, preliminarily heating in the furnace, extracting from the first atmospheric column the side draw, which is taken from the bottom half-blind tray of column reinforcing section, extracting from the second atmospheric column heavy straight-run fraction side draw, which is taken from the bottom half-blind tray of the reinforcing section (patent for invention RU JVS 2484 122, C 10G7/02, B01 D3/14, declared 20.03.20 1 2, published 1 0.06.2013). The disadvantages of this invention are the need for more energy to process heavy straight-run fraction, withdrawn from the second atmospheric column by the side draw from the bottom half-blind tray of the reinforcing section in the secondary processes of catalytic or thermal cracking, and probable partial penetration of side draw components from bottom half-blind tray of the reinforcing section of the first atmospheric column.

There is also primary oil refining unit, which realizes the standard procedure, comprising the first and the second atmospheric distillation columns, vacuum distillation column, strippers, furnaces, boilers, coolers, tanks and pumps interconnected by the pipelines, pipelines of feedstock input and oil distillate output (patent for invention RU .\ ^o 2063999, C 1 0G7/06, C 1 0G7/00, B0 1 D3/14, declared 1 2. 1 0. 1 993 , published 20.07. 1996). The main disadvantage of the unit is low sharpness of the separation of oil hydrocarbons to fractions required, which reduces the completeness of the extraction of light oil products in comparison with their potential content in the feed oil.

There is also primary oil refining unit, which is the most similar to the claimed invention, comprising the first and the second atmospheric distillation columns, strippers, furnaces, boilers, coolers, tanks and pumps interconnected by the pipelines, pipelines of feedstock input and oil distillate output. At that, the atmospheric distillation columns are equipped with half-blind trays. The half-blind tray of the first atmospheric distillation column is piped to the half-blind tray of the second atmospheric distillation column, from which the atmospheric gasoil is withdrawn, at that, the bottom of the second atmospheric distillation column is connected to the vacuum column (patent RU J a 2484122, C 10G7/02, B01 D3/14, declared 20.03.2012, published 10.06.2013). The disadvantages of this invention are the need for more energy to process the atmospheric gasoil and the potential penetration of unevaporated hydrocarbons, coming to the half-blind tray of the second atmospheric distillation column from the half-blind tray of the first atmospheric distillation column, involving them in recycling, which requires the additional capital and operating costs.

DISCLOSURE OF INVENTION

The purpose of the claimed invention is to reduce the energy costs for the process and the rational use of heavy oil fraction obtained from the second half-blind tray of the second atmospheric column.

The problem is solved due to the primary oil distillation method comprising the recuperative oil heating, its partial topping in the first atmospheric column to extract light naphtha from the top of the column, heating the residue of the first atmospheric column in the furnace supplying it to feed area of the second atmospheric column to separate the topped oil to heavy naphtha, kerosene, diesel fuel and fuel oil, provided further as raw material for vacuum column, preheating it in the furnace and extracting heavy naphtha side draw from the first atmospheric column, obtained from the bottom half-blind tray of column reinforcing section, extracting from the second atmospheric column gasoil side draw, taken from the bottom half- blind tray of the reinforcing section, characterized in that the side draw, which is heavy naphtha and is extracted from the bottom half-blind tray of the reinforcing section of the first atmospheric column, is supplied to the trays, located above bottom half-blind tray of the reinforcing section of the second atmospheric column. The fuel oil of the second atmospheric column in vacuum column is separated to gas, diesel fuel, light vacuum gasoil, heavy vacuum gasoil and tar. The side draw of heavy straight-run fraction, taken from bottom half-blind tray of the reinforcing section of the second atmospheric column, is supplied as a reflux of bottom layer of vacuum column concentration part packing located above the area of feed by the residue of the second atmospheric column. The proposed transfer of the part of low-grade product of the half-blind trays from the first atmospheric column to the second atmospheric column and from the second atmospheric column to the vacuum column allows in both cases the same improvement of fractionation principle due to the following factors:

• transfer of the low-grade product as liquid equilibrium phase of half-blind trays from higher pressure column to lower pressure column allows vaporizing at least of a part of the low-grade product without heating in the furnace, which reduces fuel consumption in the furnace comparing with the joint heating of this low-grade product with column residue, from which the side draw is not taken;

• input of evaporating low-grade product to lower pressure distillation column results an increase, respectively, of the steam reflux in the package of trays above the input of evaporating low-grade product and an increase, respectively, of the liquid reflux in the package of trays below the input of evaporating low-grade product, which will increase the efficiency factor of these trays and the separation sharpness of oil product on these trays.

The problem is solved the same way as in the unit comprising recuperative oil heating system, the first and the second atmospheric distillation columns, strippers, furnaces, boilers, coolers, tanks and pumps interconnected by pipelines, pipelines of feedstock input and oil distillate output, wherein the atmospheric distillation columns are equipped with half-blind trays. The half-blind tray of the first atmospheric distillation column is piped to the half-blind tray of the second atmospheric distillation column, providing atmospheric gasoil. At that, the bottom of the second atmospheric distillation column is connected with the vacuum column, characterized in that the bottom part of the reinforcing section of the first atmospheric column in the area of half-blind tray is connected by the output pipeline of heavy naphtha side draw with the concentration part of the second atmospheric column above column half-blind tray, and the bottom part of the reinforcing section of the second atmospheric column in the area of half-blind tray is connected by atmospheric gasoil output pipeline with the concentration part of vacuum column above vacuum column input of fuel oil heated in the furnace.

It is efficient to use the cross-flow packing as the contact devices in the vacuum column.

LIST OF DRAWINGS

The claimed invention is illustrated by the drawing, where Figure 1 shows a diagram of the proposed primary oil distillation unit using the proposed primary oil distillation method. The diagram of primary oil distillation unit comprises the following positions:

10, 20 - the first and the second atmospheric columns, respectively,

30 - the vacuum column. 40, 50 - stripper,

60, 70, 80 - furnace,

90, 100 - heat exchanger,

1 10, 120 - condenser-cooler,

130 - boiler,

140, 150, 160, 170 - circulating reflux,

1 -9, 1 1-19, 21 -29, 31 -37 - pipelines.

BRIEF DESCRIPTION OF DRAWINGS

The proposed method of primary oil distillation comprises the following. The oil heated in the atmospheric furnace and heat exchangers is supplied to the first atmospheric column 10, from where naphtha, liquid side draw and the residue (topped oil) are withdrawn, at that, naphtha is sent for further processing, and the liquid side draw, which is heavy naphtha, and the residue of the first atmospheric column are sent to the second atmospheric column 20: the liquid side draw by gravity due to the difference of pressures in columns 10 and 20 is supplied to trays located above the bottom half-blind tray of the reinforcing section of the second atmospheric column 20, and the residue after heating in the furnace is also supplied to the second atmospheric column 20, from the top of which naphtha vapors, condensed in condenser-cooler 120, are withdrawn. A part of the condensate is returned to column 20 for the reflux, and the net part of the condensate is taken for further processing. The uncondensed vapors are removed from the unit. From the reinforcing section of the second atmospheric column side draws of kerosene fractions and diesel fuel are supplied to the strippers, from where kerosene and diesel fuel are withdrawn, and stripped light fractions are returned from the strippers to atmospheric column 20. Kerosene stripping is performed using the boiler at its bottom part, and diesel fuel stripping is provided by water steam supply. From the bottom half-blind tray of the reinforcing section of the second atmospheric column 20 liquid side draw (atmospheric gasoil) is taken as a reflux for the bottom layer of the packing of the concentration part of vacuum column 30, located above the area of feed by the residue of the second atmospheric column 20, from where fuel oil is withdrawn from the bottom to the furnace and further to vacuum column 30, to the bottom part of which water stream is supplied for fuel oil stripping. Diesel fuel, light and heavy vacuum gasoil and tar are withdrawn from vacuum column 30.

Primary oil distillation unit operates as follows: desalted and dehydrated oil flowing through pipeline 1 is preheated in recuperative heat exchanger 90, then being heated up to predetermined temperature the desalted and dehydrated oil comes to the first atmospheric column (preliminary evaporation column) 10 via pipeline 2. From the top of the column the vapors of naphtha, water and gas are sent via pipel ine 3 to air condenser-cooler 1 10, then to the separator (is not shown in Fig. I ), from where gas is withdrawn via pipeline 4, and condensed liquid (light naphtha) - via pipeline 5, the part of it returns via pipeline 6 to the first atmospheric column 10 as live reflux, and the remaining part is withdrawn as light naphtha via pipeline 7 for further processing. The first atmospheric column 10 is equipped with half-blind tray in the reinforcing section and is connected via pipeline 8 to the second atmospheric column 20. From the bottom part of the first atmospheric column 10 pipeline 9 is connected to furnace coil 60, the output of which by pipeline 1 1 is connected to the first atmospheric column 10 and to the input of heat exchanger 100, the outlet of which is connected to furnace coil 70, the output of which is connected via pipeline 13 to the bottom part of the second atmospheric column 20, to the bottom part of which water steam is supplied via pipeline 28. From the top of the second atmospheric column 20 through pipeline 14 naphtha vapors are withdrawn, which are cooled and condensed in condenser-cooler 120, then are sent to the separator (is not shown in Fig. 1 ), after that, gases are withdrawn via pipeline 15 and condensed naphtha - via pipeline 16, the part of condensed naphtha is returned through pipeline 17 to the top tray of the second atmospheric column 20, and the net amount of naphtha is removed from the process via line pipe 1 8. The middle part of the reinforcing section of the second atmospheric column 20 via kerosene and diesel fraction output pipelines 19 and 23 is connected to the strippers, respectively, 40 and 50, from the top of which vapors through pipelines 21 and 24, respectively, are returned to the second atmospheric column 20. Kerosene fraction stripping is performed using boiler 130, located in the bottom part of stripper 40, and diesel fraction stripping is followed by water steam supply to the bottom part of stripper 50. The bottom of strippers 40 and 50 is equipped with kerosene and diesel fuel outlet pipelines, respectively, 22 and 25. The second atmospheric column 20 is equipped with two circulating refluxes 140 and 150 along height of the column, i.e. the stream is withdrawn from the column, is cooled in heat exchangers and is returned under output trays of side draws, and in the bottom part of the reinforcing section of the second atmospheric column 20 it is equipped with half-blind tray, connected via pipeline 27 to vacuum column 30. Pipeline 29 connects the bottom part of the second atmospheric column 20 to furnace coil 80, the output of which is connected via pipeline 31 to the bottom part of vacuum column 30. From the top of vacuum column 30 the uncondensed gases and the water steam arc withdrawn via pipeline 32. the tar is pumped out from the bottom via pipeline 37. Two circulating refluxes 160 and 1 70 are provided along height of the reinforcing section of vacuum column 30. Diesel fuel, light and heavy vacuum gasoils are taken as side draws from vacuum column 30 via pipelines 33, 34 and 35, respectively.

A comparison of the proposed method of primary oil distillation with the prototype has been carried out using mathematical modeling of primary oil distillation process as applied to West Siberian oil distillation. The oil amount of 440 t/h, partially stripped in the first distillation column and heated to the temperature of 352 °C. is sent to the second atmospheric column - as per the prototype and the proposed method as well. Water steam amount of 1 .0 t/h is supplied to the bottom of the second atmospheric column. The temperature at the top of the second atmospheric column is 164 °C, and the pressure 0.17 MPa, the temperature at the bottom is 336 °C. From the top of the second atmospheric column naphtha with the boiling point of 180 °C is withdrawn, diesel fuel and heavy straight-run fraction are taken as side draws, from the bottom of the second atmospheric column the fuel oil is withdrawn, which shall be heated in the vacuum furnace up to 390 °C and supplied to the vacuum column. To provide the reliable comparison of columns operation as per the prototype and the proposed method, the mode of vacuum column operation is selected so that to obtain a uniform quality of all products, while the corresponding parameters are given in Tables 1 and 2. According to data given in Table 1 , as per the proposed method, it is possible to increase the generation of diesel fuel from 13.4 to 33.4 t h, i.e. by 149 %, vacuum gasoil - from 50 to 80 t/h, i.e. by 60 % in the vacuum column, by supplying the atmospheric gasoil, withdrawn from the bottom half-blind tray of the reinforcing section of the second atmospheric column, wherein 50 t/h are used for the reflux of bottom layer of vacuum column concentration part packing. The total output of diesel fuel in the unit in comparison with the prototype has increased from 142.7 to 162.7 t/h, i.e. by 14.8 %, the fractional composition of total diesel fuel according to the claimed invention is almost identical to the protitype (Table 2). At that, the additional equipment for atmospheric gasoil processing is not required.

Vacuum column is equipped with circulating refluxes against overheating: in the top part of the column and in the middle of the reinforcing part at the level of vacuum gasoil output. The pressure in the top part of vacuum column is 6.5 kPa, the top temperature is 198 °C and column bottom temperature is 369 °C. The vapors from the top of the column are condensed at 40 °C, the condensed part is withdrawn as vacuum diesel fuel, and the uncondensed vapors are sucked out using vacuum generating system. The corresponding energy costs given in Table 3 are required to perform such operation mode as per the prototype and the proposed method as well. The comparison of given performance parameters of the vacuum column as per the prototype and the proposed method shows that to obtain uniform quality products the energy costs, such as the additional heat removal in the condenser and using the circulating reflux in the claimed invention are higher, than in the prototype, however, considering the low cost of the reversible cooling agent in the condenser and the possibility of recuperative use of the heat obtained thanks to the circulating reflux, as well as the increase of diesel fuel output in the vacuum column by 149 % and of vacuum gasoil by 60 % without the use of additional process equipment, the proposed solution is efficient.

The proposed method is applicable, as it is based on the use of existing equipment and known technological procedures, while providing the increase of desired product output without further processing of semi-finished products.

Flow rate, t/h

Stream name

Prototype Proposed method

Topped oil 440,0 440,0

Heavy naphtha 76,4 76,4

Diesel fraction from atmospheric 129,3 129,3 column

Diesel fraction from vacuum column 13,4 33,4

Total diesel fraction 142,7 162,3

Atmospheric gasoil 50,0 50,0

Fuel oil 184,3 184,3

Vacuum gasoil 50,0 80,0

Tar 121 , 1 121 , 1

Water steam into the second 1 ,0 1 ,0 atmospheric column

Water steam into vacuum column 0.3 0,3

Uncondensed gases 0,3 0,3

Table 1

Index name Measur. unit Prototype Proposed method

Flow rate of top circulating

t/h 83,00 100,00 reflux

Top circulating reflux

GJ/h 7,50 8,90 against overheating

Lower circulating reflux

GJ/h 3,20 3,00 against overheating

Heat removal in condenser GJ/h 0,49 1 , 19

Table 3