RU2802186C1 - Method for delayed coking of oil residues - Google Patents

Abstract

FIELD: coke production.

SUBSTANCE: invention is related to technologies for production of petroleum cokes and coke additives with a simultaneous increase in the yield of light petroleum products and can be used in the oil refining industry. The method includes supplying secondary raw materials from the evaporation column through a reaction-heating furnace to the coking chamber, accumulating coke, separating distillate coking products in a distillation column into vapor products - water vapor and coking naphtha, light gas oil, heavy gas oil and heavy bottoms residue. Moreover, heavy distillation residue mixed with light gas oil in a ratio of 1:2 to 1:8 parts is used as a recirculate in the formation of secondary raw materials.

EFFECT: increase of selection of light oil products with a simultaneous increase in the selection of gasoline and diesel fractions and increase of stability of the plant as a whole by increasing the uniformity of the resulting coke due to smoothing its quality fluctuations throughout the volume of the coking chamber.

4 cl, 2 dwg, 2 tbl, 4 ex

Description

The invention relates to technologies for the production of petroleum cokes and coke additives with a simultaneous increase in the yield of light petroleum products and can be used in the oil refining industry.

Processing of petroleum residues to obtain petroleum coke refers to large-scale secondary processes of oil refining and is designed to produce petroleum coke with a simultaneous increase in the yield of light petroleum products.

The industrial coking process is carried out in three types of plants: periodic coking in coke cubes, delayed coking in chambers, and continuous coking in a fluidized bed of coke carrier. Delayed (semi-continuous) coking is the most widespread in world practice.

The need for petroleum coke and coke additives is very significant, so the capacity of delayed coking units reaches 6 million tons per year for processed raw materials. Petroleum coke is used for the manufacture of electrodes and corrosion-resistant equipment, for the production of carbides (calcium, silicon), which are used in the production of acetylene, as well as a reducing agent in the production of ferroalloys, in the production of grinding materials, in the manufacture of refractories and in other industries. The main consumer of coke is the aluminum industry: coke serves as a reducing agent (anode mass) in the smelting of aluminum from aluminum ores (bauxites). The specific consumption of coke is quite high - 550-600 kg/t of aluminium. Coke is also used to make electrodes used in steelmaking furnaces.

The content of volatile substances in coke and its mechanical strength depend on the physicochemical characteristics of the coking feedstock.

The origin of the coking feedstock significantly affects the thermal regime of the coking chambers, since different chemical and hydrocarbon compositions of the feedstock cause different total thermal coking process.

The determining influence on the content of volatile substances in petroleum cokes is exerted by the technological parameters of the coking process. The decrease in the content of volatile substances in coke is facilitated by an increase in the temperature at the inlet and outlet of the coking chamber, an increase in the duration of filling the chamber and the recirculation coefficient.

However, such a change in these parameters is not always favorable for the process. Thus, an increase in the heating temperature of the raw material at the outlet of the furnace leads to a reduction in the duration of its operation before the operation of cleaning the coil from coke deposits. An increase in the duration of filling the coking chamber leads to a decrease in the productivity of the plant in terms of feedstock. The use of heavy gas oil and distillation column bottoms as recirculation leads, with an increase in the recirculation ratio, to a significant increase in the yield of coke and a decrease in the yield of distillates, which is not always justified.

The content of volatile substances in coke and its mechanical strength depend on the physicochemical characteristics of the coking feedstock. The origin of the coking feedstock significantly affects the thermal regime of the coking chambers, since different chemical and hydrocarbon compositions of the feedstock cause different total thermal coking process.

The determining influence on the content of volatile substances in petroleum cokes is exerted by the technological parameters of the coking process. The decrease in the content of volatile substances in coke is facilitated by an increase in the temperature at the inlet and outlet of the coking chamber, an increase in the duration of filling the chamber and the recirculation coefficient.

However, such a change in these parameters is not always favorable for the process. Thus, an increase in the heating temperature of the raw material at the outlet of the furnace leads to a reduction in the duration of its operation before the operation of cleaning the coil from coke deposits. An increase in the duration of filling the coking chamber leads to a decrease in the productivity of the plant in terms of feedstock. The use of heavy gas oil and distillation column bottoms as recirculation leads, with an increase in the recirculation ratio, to a significant increase in the yield of coke and a decrease in the yield of distillates, which is not always justified.

Depending on the direction of further use and on the technology of the process, ordinary, isotropic and needle (anisotropic) coke is obtained with the production of a wide range of coke grades. Therefore, despite the formal similarity of the hardware design of the principal technological schemes for delayed coking of oil residues, this process is implemented using various technological methods.

A known method for producing petroleum coke, including heating the feedstock, separating it into light fractions and a heavy residue, heating the latter and its subsequent coking with the removal of vapor-liquid products and obtaining coke, wherein the separation of the feedstock into light fractions and a heavy residue is carried out in an evaporator, while light fractions are subjected to fractionation in a distillation column together with vapor-liquid coking products (patent for invention RU 2075495, IPC C10B 55/00, filed on 04/17/1995, published on 03/20/1997). The disadvantages of the method are:

• tight relationship between the quality of the produced coke and the heavy residue produced from the feedstock;

• the selection of light oil products is strictly determined by the heating of the feedstock;

• low selection of light oil products due to increased coke formation, which increases the yield of coke;

• coke along the height of the coking chamber turns out to be significantly inhomogeneous in quality.

A known method for producing a coking additive by delayed coking of oil residues, which consists in the fact that the feedstock after heating is fed into the evaporator for mixing with recirculation and the formation of secondary raw materials, which are heated in a reaction furnace and fed into the coking chamber, where a coking additive and vapor-liquid coking products are formed , fractionation of the latter in a distillation column with the formation of gas, gasoline, light and heavy gas oils and bottom coking residue, and the bottom residue is mixed with calcium and / or magnesium oxide and fed into the coking chamber simultaneously with the supply of heated secondary raw materials, while the feedstock is heated to temperature 250-390°C, secondary - up to a temperature of 450-480°C, and the recirculation ratio is not more than 1.2 ., published on December 10, 2012). The disadvantages of the method are:

• low total yield of light oil products, amounting to 58.05-45.7% for raw materials;

• low content of naphtha in light oil products - 6.0-6.4%, which is only 10.8-10.07% of the selection of light oil products;

• high instability of work on obtaining light oil products;

• coke along the height of the coking chamber turns out to be significantly inhomogeneous in quality.

Also known is the method of delayed coking closest to the claimed invention, including heating the feedstock, supplying the heated feedstock to the evaporator for mixing with the recycle with the formation of secondary raw materials and removing light fractions from the evaporator to the distillation column, heating the secondary feedstock to the coking temperature and then feeding it into coking chamber with production of coke and removal of distillate products to the lower part of the distillation column, fractionation in the distillation column of distillate coking products together with light fractions from the evaporator to form gas, gasoline, light and heavy coking gas oils and bottom residue, heated secondary gas before being fed into the coking chamber the raw material is mixed with a part of the distillation residue, while the quantity and quality of the heavy coking gas oil and the distillation residue are regulated by changing the amount of heavy gas oil supplied as circulating reflux to the trays of the lower part of the distillation column, and the remaining part of the distillation residue is supplied for mixing with the feedstock before it is heated , while VAT residue is used as a recirculation (patent for invention RU 2562999, IPC C10B 55/00, B01D 3/14, Appl. 06/25/2014, publ. September 10, 2015). The disadvantages of the method are:

• low total yield of light oil products, amounting to 56.8-55.0% for raw materials;

• low content of naphtha in light oil products - 6.8-6.2%, which is 11.9-11.3% of the selection of light oil products;

• Significant instability in the production of light oil products;

• coke along the height of the coking chamber turns out to be significantly inhomogeneous in quality.

A common disadvantage of the considered methods of delayed coking is the significant heterogeneity of the quality of the resulting coke along the height of the coking chamber. In addition, the use of heavy coking gas oil or distillation residue or mixtures thereof as a recirculation agent predetermines an increase in the yield of coke and a decrease in the amount of produced distillate fractions and, accordingly, a decrease in the yield of light oil products.

When creating the invention, the task was to develop a method for delayed coking of oil residues, providing an increase in the selection of light oil products with a simultaneous increase in the selection of gasoline and diesel fractions and increasing the stability of the plant as a whole by increasing the uniformity of the obtained coke due to smoothing its quality fluctuations throughout the volume of the coking chamber.

The solution to this problem is provided by the fact that in the method of delayed coking of oil residues, including the supply of secondary raw materials from the evaporation column through the reaction-heating furnace into the coking chamber, the accumulation of coke, the separation of distillate coking products in the distillation column into vapor products - water vapor and coking naphtha, light gas oil, heavy gas oil and heavy distillation residue, characterized in that heavy distillation residue mixed with light gas oil in a ratio of 1:2 to 1:8 parts is used as a recirculation in the formation of secondary raw materials.

Due to the introduction of light gas oil into secondary raw materials, a number of the following technological effects are achieved, other things being equal, the technological parameters of the prototype and the claimed invention:

1) the introduction of light gas oil into secondary raw materials increases the flow rate of secondary raw materials in the tubes of the tube furnace coil, which heats this flow, which reduces the time spent by the flow in the zone of the highest temperatures, which forms the formation of nucleating coke microstructures, reduces the number of nuclei formed in the furnace and indirectly reduces the yield coke in the coking chamber;

2) the introduction of light gas oil into the secondary feedstock reduces the viscosity of the reaction medium in combination with an increase in the flow rate, due to which the time of passage of the reaction medium through the channels in the conglomerate of the resulting coke is reduced, but remains sufficient for easy cracking of the feedstock and heavy bottoms with the formation of a large amount of light , especially light, hydrocarbons, but not enough to form a large amount of coke;

3) the introduction of light gas oil into the secondary feedstock reduces the partial pressure of hydrocarbons in the heavy bottoms residue and the feedstock, which, according to the Le Chatelier principle, shifts the set of equilibrium reactions of the delayed coking process towards decomposition reactions and prevents the compaction reactions from occurring;

4) the introduction of light gas oil into the coking feedstock makes it possible to provide additional heat to the coking chamber without changing the process temperature, which makes it possible to increase the homogeneity of coke as it accumulates along the height of the coking chamber and without increasing the amount of coke formed and at the same time increasing the yield of gasoline and light gas oil;

5) when coking heavy residues, when the amount of heavy VAT residue is small and amounts to 4-5% of the raw material, the ratio of heavy VAT residue in the mixture with light gas oil should be increased to the maximum value corresponding to the complete involvement of light gas oil in the mixture with heavy VAT residue, which corresponds to ratios 1: (7-8);

6) when coking light residues, when the amount of heavy VAT residue increases significantly and amounts to 10-15% of the raw material, the ratio of heavy VAT residue in the mixture with light gas oil should be increased to the maximum value corresponding to the complete involvement of light gas oil in the mixture with heavy VAT residue, which corresponds to relations 1: (2-3).

It is advisable to feed the heavy distillation residue into the primary feed line at the inlet to the evaporation column, since this ensures high-quality mixing of the two streams due to the turbulent mode of flow in the supply line pipeline.

It is recommended to supply light gas oil for the formation of secondary raw materials to the line of secondary raw materials after the evaporation column, which excludes the creation of an additional circulation circuit of a part of light gas oil in the system evaporation column - distillation column during the formation of recirculation.

It is rational to supply a part of the heavy VAT residue to the transfer line after the reaction-heating furnace, depending on the required quality of the resulting coke in an amount from 0 to 50%, while this part of the heavy VAT residue bypasses the reaction zone of the reaction-heating furnace, which reduces the formation of coke nucleation microstructures and mediated by the output of coke on the raw material.

The figure 1 shows one of the possible schematic diagrams of the installation for the implementation of the claimed invention using the following notation:

100 - heat exchangers;

200 - evaporation column;

300 - reaction heating furnace;

400 - coking chamber;

500 - distillation column;

1-11 - pipelines.

Installation according to figure 1 operates as follows.

The coking feedstock enters through pipeline 1 and, after heating in heat exchangers 100, is sent to the evaporation column 200 via pipeline 2, where the raw material is mixed with the bottoms, which enters through pipeline 7 from the bottom of the distillation column 500. At the outlet of the evaporation column 200, into the feedstock mixture light coking gas oil is supplied with the VAT residue from the distillation column 500 through pipeline 11. The resulting secondary feedstock is fed into the reaction-heating furnace 300 through pipeline 3, where partial cracking of secondary raw materials occurs, then the reaction mixture enters the coking chamber 400 through pipeline 5, where formation and accumulation of coke, at the same time thermal destruction of heavy hydrocarbons. The distillate products of the coking process from the coking chamber 400 and the steam-gas products from the evaporation column 200 enter the distillation column 500, respectively, through pipelines 6 and 4 for separation into vapor products: gas and gasoline are removed from the top of the column through pipeline 8 for further use, light gas oil through pipeline 10 is sent for subsequent consumption, part of the light gas oil is fed through pipeline 11 into the mixture of feedstock, heavy gas oil is discharged through pipeline 9.

The method of delayed coking of oil residues is illustrated by the following calculation examples of mathematical modeling of the operation of a delayed coking unit with an assessment of the uneven quality of coke as a coefficient equal to the ratio of the amount of volatile hydrocarbons in the lower quality coke in the upper part and in the higher quality coke in the lower part of the coking chamber.

Example 1. The implementation of the method of delayed coking of oil residues according to the prototype - patent RU 2562999. The tar, the quality of which is shown in table 1, was heated in heat exchangers to a temperature of 275°C and fed into the evaporation column, where it was mixed as recirculation with the distillation residue of the distillation column with formation of secondary raw materials. Recirculation ratio 1.3. Heated in the reaction-heating furnace up to 500°C, the secondary raw material was fed into the coking chamber to produce coke. Distillate coking products from the coking chamber and gas-vapor products from the evaporation column were sent to a distillation column for separation into vapor products (gas and gasoline), light and heavy gas oils and distillation residue. In accordance with the material balance of the process, 12.0% of gasoline, 37.7% of light gas oil (the sum of light oil products was 49.7%) and 23.5%) of coke were obtained with a coke quality unevenness coefficient of 1.6.

Then, calculation examples 2-4 were performed according to the proposed method, in which the feedstock and the technological regime were maintained at parameters equal to example 1, but at the same time, light gas oil was introduced into the secondary feedstock in different ratios of VAT residue and light gas oil.

Example 2 (according to the proposed method). The tar, the quality of which is shown in Table 1, was heated in heat exchangers to a temperature of 275°C and fed into the evaporation column, where it was mixed as recirculation with the bottoms of the distillation column, and at the outlet of the evaporation column, the mixture of feedstock with the bottoms was mixed as recirculation with light coking gas oil from the distillation column to obtain secondary raw materials. The ratio of distillation residue and light gas oil in the recycle was 1:2. Recirculation ratio 1.3. The secondary raw material was sent to the reaction-heating furnace and after heating to 500°C was fed into the coking chamber to produce coke. Distillate coking products from the coking chamber and gas-vapor products from the evaporation column are sent to a distillation column for separation into vapor products (gas and gasoline), light and heavy gas oils and distillation residue. In accordance with the material balance of the process, 12.1% of gasoline, 38.1% of light gas oil (the sum of light oil products was 50.2%) and 23.1% of coke were obtained with a coke quality unevenness coefficient of 1.51.

Example 3 (according to the proposed method). The tar, the quality of which is shown in Table 1, was heated in heat exchangers to a temperature of 275°C and fed into the evaporation column, where it was mixed as recirculation with the bottoms of the distillation column, and at the outlet of the evaporation column, the mixture of feedstock with the bottoms was mixed as recirculation with light coking gas oil from the distillation column to obtain secondary raw materials. The ratio of distillation residue and light gas oil in the recycle was 1:5. Recirculation ratio 1.3. The secondary raw material was sent to the reaction-heating furnace and after heating to 500°C was fed into the coking chamber to produce coke. Distillate coking products from the coking chamber and gas-vapor products from the evaporation column are sent to a distillation column for separation into vapor products (gas and gasoline), light and heavy gas oils and distillation residue. In accordance with the material balance of the process, 12.3% of gasoline, 39.1% of light gas oil (the sum of light oil products was 51.4%) and 22.2% of coke were obtained with a coke quality unevenness coefficient of 1.38.

Example 4 (according to the proposed method). The tar, the quality of which is shown in Table 1, was heated in heat exchangers to a temperature of 275°C and fed into the evaporation column, where it was mixed as recirculation with the bottoms of the distillation column, and at the outlet of the evaporation column, the mixture of feedstock with the bottoms was mixed as recirculation with light coking gas oil from the distillation column to obtain secondary raw materials. The ratio of distillation residue and light gas oil in the recycle was 1:8. Recirculation ratio 1.3. The secondary raw material was sent to the reaction-heating furnace and after heating to 500°C was fed into the coking chamber to produce coke. Distillate coking products from the coking chamber and gas-vapor products from the evaporation column are sent to a distillation column for separation into vapor products (gas and gasoline), light and heavy gas oils and distillation residue. In accordance with the material balance of the process, 12.5% of gasoline, 39.3% of light gas oil (the sum of light oil products was 51.8%) and 21.2% of coke were obtained with a coke quality unevenness coefficient of 1.32.

The results of calculations and the values of technological parameters for examples 1-4 are shown in table 2.

An analysis of table 2 shows that the use of the proposed method of delayed coking will, in comparison with the prototype method, increase the uniformity of the obtained coke along the height of the chamber (the coefficient of coke quality unevenness decreased from 1.6 to 1.32) and, in addition, increase the yield of the most valuable distillate fractions (gasoline and light gas oil) by 0.5-2.1%. As shown in figure 2, an increase in the content of light gas oil in a mixture with a VAT residue most effectively affects the coefficient of uneven quality of coke at a consumption of light gas oil relative to heavy residue from 0 to 5 kg/kg (with completely the same quality of coke along the height of the reaction chamber, the coefficient of uneven quality coke is equal to one). In the entire range of recommended ratios of distillation residue to light gas oil in the recirculation, a proportional change in the technological and quality parameters of the plant operation is ensured, which simplifies the regulation of the plant operation and increases its stability. With the capacity of the delayed coking unit for processed tar of 1 million tons/year and the average profit from the sale of additional light oil products of 10 rubles/kg, the expected economic effect from the use of the claimed invention will be from 50 to 210 million rubles/year without taking into account the improvement in the quality of the produced coke.

Thus, the claimed invention solves the problem of increasing the selection of light oil products with a simultaneous increase in the selection of gasoline and diesel fuel and increasing the stability of the installation as a whole by increasing the uniformity of the obtained coke due to smoothing its quality fluctuations throughout the volume of the coking chamber.

Claims (4)

1. The method of delayed coking of oil residues, including the supply of secondary raw materials from the evaporation column through the reaction-heating furnace into the coking chamber, the accumulation of coke, the separation of distillate coking products in the distillation column into vapor products - water vapor and coking naphtha, light gas oil, heavy gas oil and heavy distillation residue, characterized in that heavy distillation residue mixed with light gas oil in a ratio of 1:2 to 1:8 parts is used as a recirculate in the formation of secondary raw materials. 2. The method according to p. 1, characterized in that the heavy VAT residue is fed into the primary feed line at the inlet to the evaporation column. 3. The method according to claim 1, characterized in that the light gas oil for the formation of secondary feedstock is fed into the secondary feedline after the flash column. 4. The method according to p. 1, characterized in that part of the heavy VAT residue is fed into the transfer line after the reaction-heating furnace, depending on the required quality of the resulting coke in an amount of 0 to 50%.