Heavy oil pretreatment method
Technical Field
The invention relates to a heavy oil pretreatment method, in particular to a pretreatment method before fixed bed hydrogenation treatment of inferior heavy oil.
Background
Crude oil resources tend to be heavy and inferior gradually in the world, the reserves of heavy crude oil are estimated to be about 50% of the reserves of the globally recoverable crude oil after 2020, and the efficient processing and utilization of heavy oil are major challenges faced by the oil refining industry. According to different technological processes, the existing heavy oil processing technologies in the world can be classified into three types: (1) a process taking a coking process as a pilot; (2) a flow taking solvent deasphalting as a pilot; (3) the hydrogenation treatment is taken as a leading flow.
The coking process is the most thorough decarburization process and is also the technology capable of directly processing all inferior heavy oil at present, but the coking process can generate about 30 percent of low-value coke, namely, oil is partially converted into coke, and the coked light fuel also needs to be further refined to become a qualified product. Therefore, not only the economic benefit of the refinery is influenced, but also a great amount of precious petroleum resources are wasted. The solvent deasphalting process belongs to the physical process, and mainly provides raw materials for catalytic cracking, hydrocracking and other processes, or is a necessary link for processing lubricating oil. The solvent deasphalting process does not directly produce light fuel, and the process operation is complex and the energy consumption is high, so that the solvent deasphalting process is not developed on a large scale as a heavy oil processing means, and the main application field is limited to producing lubricating oil raw materials. The heavy oil hydrotreating is an important means for heavy oil modification and lightening, has the advantages of good product quality, higher light oil yield and the like, and can deeply crack heavy oil into light fuel by combining with a catalytic cracking process. In recent years, the technology is developed rapidly and becomes a heavy oil deep processing method which is compatible with catalytic cracking.
Whatever the technology, the heavy oil is expected to be lightened to the maximum extent, and the technically mature fixed bed hydrogenation technology is the best choice at present. However, the application of this technique is restricted by the properties of the feedstock oil, and heavy feedstocks with high metal and carbon residue contents cannot be processed. Taking the fixed bed heavy oil hydrogenation technology as an example, only heavy oil with metal content less than 150 mug/g and carbon residue less than 15% can be processed. In fact, when the metal content is higher than 150. mu.g/g, the service life of the catalyst is seriously affected. In order to process more inferior heavy oil by the fixed bed hydrogenation technology, two approaches are generally adopted: firstly, a brand new catalyst is developed, the metal capacity of the catalyst is greatly improved, and the service life of the catalyst is prolonged; and secondly, the inferior heavy oil is pretreated, so that the property of the inferior heavy oil is improved, and the inferior heavy oil meets the feeding requirement of a fixed bed hydrogenation technology.
With the continuous and intensive research on the inferior heavy oil, people gradually find that the distribution of heteroatoms such as metal, sulfur, nitrogen, oxygen and the like which seriously affect the quality of the inferior heavy oil has a certain rule, namely most of the sulfur, nitrogen, oxygen and most of the metal are concentrated in the asphaltene of the vacuum residue oil. Therefore, the inferior residual oil can be separated into raw materials meeting the fixed bed hydrogenation technology by adopting a proper means. Solvent deasphalting is one of the technical means utilizing the principle, but the solvent deasphalting process is complex, the energy consumption is high, the realization is difficult, the deasphalted oil has high viscosity, and light oil needs to be doped to reduce the viscosity, so the efficiency of a fixed bed device is reduced.
CN 103102934a discloses a pretreatment method of inferior heavy oil, wherein inferior heavy oil raw material enters a visbreaking device for moderate visbreaking, then is mixed with light solvent to reduce viscosity, and then enters a centrifugal separation device, oil generated by visbreaking is separated into overflow component and underflow component by means of centrifugal force, and the overflow component is mixed as the feed of a fixed bed hydrogenation device. The method can effectively pretreat the inferior heavy hydrocarbon raw material to obtain the qualified raw material of the fixed bed hydrogenation device. However, the method needs to add a large amount of light solvent for dilution, the viscosity-reduced residual oil is still in relatively stable phase balance, the separation efficiency is low, and multiple stages of series connection are needed to achieve relatively high separation rate, so that the equipment investment and energy consumption are increased.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a heavy oil pretreatment method. The method is particularly suitable for the pretreatment method of inferior heavy oil, has the advantages of low equipment operation cost, high separation efficiency and the like, can improve the yield of overflow materials, and is favorable for weakening the influence on the activity stability of the catalyst in the subsequent fixed bed hydrogenation treatment process.
The heavy oil pretreatment method comprises the following steps:
a) Feeding the heavy oil raw material into a visbreaking device for visbreaking to obtain visbroken residual oil;
b) Adding a composite modifier into the viscosity-reduced residual oil obtained in the step a), and then continuously settling the mixture to obtain an overflow material at the upper part and a bottom flow material at the lower part;
wherein, the composite modifier comprises the following components: polyacrylamide (CPAM), polyaluminum chloride (PAC), 2, 6-di-tert-butyl-4-methylphenol (BHT) and N, N' -disalicylidene propylene diamine in a weight ratio of (10-40): (30-70): (10-100): (0.5 to 3).
The addition amount of the composite modifier in the step b) accounts for 0.01-0.2% of the weight of the heavy oil raw material in the step a), and preferably 0.05-0.1%.
The heavy oil raw material in the step a) comprises one or more of atmospheric residue, vacuum residue, deasphalted oil, oil sand asphalt, thick crude oil, coal tar and coal liquefaction heavy oil.
The heavy oil feedstock of step a) has a metal content greater than 150 μ g/g based on the weight of Ni and V, and a combined gum and asphaltene content greater than 50 wt%.
The visbreaking in the step a) adopts a shallow thermal cracking process, and the process operating conditions are as follows: the reaction temperature is 350-450 ℃, the reaction pressure is 0.1-1.5 MPa, and the weight conversion rate of visbreaking is 1-40%; preferred operating conditions are: the reaction temperature is 400-450 ℃, the reaction pressure is 0.5-1.5 MPa, and the weight conversion rate of visbreaking is 10-20%. Wherein the conversion is in weight percent of light components (fractions boiling below the heavy oil feedstock) obtained by visbreaking as a percentage of the weight of the heavy oil feedstock.
The composite modifier in the step b) comprises the following components: polyacrylamide (CPAM), polyaluminum chloride (PAC), 2, 6-di-tert-butyl-4-methylphenol (BHT) and N, N' -disalicylidene propylene diamine, preferably in the weight ratio of (15-35): (35-65): (55-85): (1-2).
The continuous sedimentation in the step b) adopts a gravity separation principle, and the continuous sedimentation device adopts a high-efficiency thickener or a cone deep thickener and operates according to the solid-liquid separation condition, wherein overflow materials are materials discharged from an overflow outlet of the continuous sedimentation device, and underflow materials are materials discharged from an underflow outlet of the continuous sedimentation device. The operating temperature of the continuous settling device is 0-100 ℃, and preferably 70-80 ℃. The operating pressure of the continuous settling device is the pressure for keeping the added composite modifier as a liquid phase at the operating temperature.
And c) obtaining overflow materials and underflow materials by the continuous settling device in the step b), wherein the volume yield of the overflow materials is 60-90% of the volume yield of the feed materials of the continuous settling device, and is preferably 65-90%. The impurities such as metal in the overflow material are obviously reduced, and the overflow material can be used as the feed of a fixed bed hydrogenation device after passing through a filtering device. Heavy components with larger asphaltene isopycnic density in the underflow material enrich most of metal and other impurities in the heavy oil and can be used as the feed of a delayed coking device.
Compared with the prior art, the heavy oil pretreatment method has the following advantages:
(1) in the step a) of the method, the heavy oil raw material enters a visbreaking device for visbreaking, the reaction depth is controlled, coking is prevented, and the asphaltene in the visbroken residual oil reaches a higher content;
(2) in the step b) of the method, the viscosity-reduced residual oil is continuously settled by adopting the composite modifier, the characteristics of poor stability and unstable colloidal phase balance of the viscosity-reduced residual oil generated in the step a) are utilized, the composite modifier is added, the balance of a continuous phase and a disperse phase is further destroyed by the coordination and synergistic action among polyacrylamide (CPAM), polyaluminum chloride (PAC), 2, 6-di-tert-butyl-4-methylphenol (BHT) and N, N' -disalicylidene propane diamine, most of asphaltenes cannot be stably peptized in a system and are aggregated and separated, the original single homogeneous phase is changed into two phases, so that the asphaltenes are settled, the separation speed and the separation efficiency are greatly improved, the asphaltene components rich in impurities such as metal, sulfur, nitrogen, oxygen and the like in the inferior heavy oil are effectively removed, and simultaneously, the synergistic effect of the composite modifier can also inhibit the activity of active metal ions in oil products, prevent excessive oxidation of colloid into asphaltene in the sedimentation process, thereby improving the yield of overflow materials, being beneficial to easier removal of metal impurities (such as nickel, vanadium, copper and the like) contained in the overflow materials in the subsequent residual oil hydrotreating process and reducing the influence on the activity stability of the catalyst.
Drawings
FIG. 1 is a schematic flow diagram of a combined heavy oil pretreatment and hydrogenation process of the present invention;
in the figure: 1-heavy oil raw material, 2-visbreaking device, 3-composite modifier, 4-continuous settling device, 5-delayed coking device and 6-fixed bed hydrogenation device.
Detailed Description
To further illustrate the technical solution of the present invention, the following detailed description is made with reference to fig. 1.
As shown in fig. 1, a process of the present invention is: and (3) feeding the heavy oil raw material 1 into a visbreaking device 2 for visbreaking to obtain visbroken residual oil. The viscosity-reducing residual oil and the composite modifier 3 are mixed and enter a continuous settling device 4 for separation to obtain an overflow material and a bottom flow material. The overflow material is filtered to meet the feeding requirement of fixed bed hydrogenation treatment, and can be used as the feeding of the fixed bed hydrogenation device 6. The underflow material can enter a delayed coking unit 5 for coking reaction.
The technical solutions and effects of the present invention are further described below with reference to the following examples, but the present invention is not limited to the following examples. The operation period of the present invention refers to the time taken for the shutdown from the start of the timing of the raw material feeding to the time when the pressure drop reaches the design value.
Example 1
This example is one embodiment of a process for the pretreatment of a vacuum residuum feedstock. And feeding the vacuum residue raw material into a visbreaking device for visbreaking. After proper visbreaking, visbreaking residual oil is obtained. Adding a composite modifier into the viscosity-reduced residual oil, wherein the added composite modifier is formed by mixing polyacrylamide (CPAM), polyaluminum chloride (PAC), 2, 6-di-tert-butyl-4-methylphenol (BHT) and N, N' -disalicylidene propylene diamine in a weight ratio of 20: 40: 60: 1, the addition amount of the composite modifier is 0.05 percent of the weight of the vacuum residue raw material. The mixture enters a continuous settling device for continuous settling, and the operating conditions are as follows: the temperature is 80 ℃, and the operation pressure is the pressure for keeping the liquid phase of the composite modifier added at the operation temperature. And obtaining overflow materials at an overflow outlet of the continuous settling device, wherein the volume yield of the overflow materials is 70%, and obtaining underflow materials at an underflow outlet of the continuous settling device.
The properties of the vacuum resid feedstock used in the tests are listed in table 1. It can be seen from table 1 that the residual oil feedstock is very high in viscosity, carbon residue, and metal content, and is a poor quality feedstock that is difficult to process using conventional residual oil hydrogenation units. The visbreaking test conditions and test results are shown in table 2, the visbreaking residue (> 350 ℃ cut) properties are shown in table 3, and the overflow material properties are shown in table 4.
The fixed bed residue hydrogenation was carried out on the overflow material of example 1, and the reaction conditions and test results of 500 hours of operation are shown in table 5.
Example 2
The same as example 1 except that polyacrylamide (CPAM), polyaluminum chloride (PAC), 2, 6-di-tert-butyl-4-methylphenol (BHT) and N, N' -disalicylidene propylene diamine were added in a mixed ratio of 30: 60: 60: 1. the volume yield of the overflow material was 68%, and the properties of the overflow material are shown in Table 4.
Example 3
The same as example 1 except that polyacrylamide (CPAM), polyaluminum chloride (PAC), 2, 6-di-tert-butyl-4-methylphenol (BHT) and N, N' -disalicylidene propylene diamine were added in a mixed ratio of 20: 40: 80: 2. wherein the volume yield of the obtained overflow material is 72 percent.
Example 4
The same as example 1, except that the amount of the composite modifier added was 0.02% by weight based on the weight of the vacuum residue feedstock. Wherein the volume yield of the obtained overflow material is 63%.
Example 5
The same as example 1, except that the amount of the composite modifier added is 0.1% of the weight of the vacuum residue feedstock. Wherein the volume yield of the obtained overflow material is 78%.
Comparative example 1
As in example 1, except that only polyacrylamide (CPAM) and polyaluminum chloride (PAC) were added in a weight ratio of 1: 2. wherein, the volume yield of the overflow material is 59 percent.
The fixed bed residue hydrogenation was carried out on the overflow material of comparative example 1, and the reaction conditions and test results of 500 hours of operation are shown in Table 5.
Comparative example 2
The fixed bed residual oil hydrogenation is carried out by using the mixed oil of the conventional residual oil blended with wax oil as a raw material, the properties of the raw material are shown in table 4, and the reaction conditions and results are shown in table 5.
From the results in tables 3 and 4, it can be seen that the overflow material obtained after the high carbon residue and high metal content inferior heavy oil which cannot be treated by fixed bed hydrogenation is subjected to moderate viscosity reduction and continuous sedimentation by using the composite modifier can be used as a raw material for fixed bed hydrogenation, thereby widening the raw material range of the fixed bed hydrogenation.
It can be seen from the results of example 1 and comparative example 1 that the addition of the composite modifier prevents the oxidation of the colloid to asphaltene during the settling process, improves the yield of the overflow component, and reduces the coking of the catalyst bed and prolongs the operation period due to the reduction of the colloid asphaltene in the residual oil during the subsequent hydrogenation of the residual oil in the fixed bed.
Compared with the conventional raw materials, the viscosity of the product treated by the continuous sedimentation combined process of the visbreaking and composite modifier for the visbreaking residual oil is greatly reduced, the colloid asphaltene is reduced to a certain extent, and the added composite modifier can inhibit the poison of metal impurities to the catalyst, so that the coking of a catalyst bed layer is reduced, the running period is prolonged, and the product quality is improved.
TABLE 1 vacuum residuum Properties
Item
|
Data of
|
Density (20 ℃ C.), g/cm3 |
1.0052
|
Viscosity (100 ℃ C.), mm2/s
|
578.4
|
Carbon residue in wt%
|
17.28
|
Metal content Ni + V, wppm
|
178
|
Four components, wt%
|
|
Saturation fraction
|
21
|
Aromatic component
|
30
|
Glue
|
44
|
Asphaltenes
|
5 |
TABLE 2 conditions and results of visbreaking tests
Item
|
Data of
|
Test conditions
|
|
Temperature, C
|
400
|
Pressure, MPa
|
1
|
Residence time, min
|
120
|
Yield (mass fraction) of the product%
|
|
Cracked gas
|
3.3
|
<200℃
|
7.8
|
200~350℃
|
11.1
|
>350℃
|
77.8 |
TABLE 3 Properties of the visbroken residue obtained in example 1
Item
|
Data of
|
Density (20 ℃ C.), g/cm3 |
0.9868
|
Viscosity (100 ℃ C.), mm2/s
|
70.7
|
Carbon residue in wt%
|
20.14
|
Metal content Ni + V, wppm
|
222.6
|
Four components, wt%
|
|
Saturation fraction
|
29
|
Aromatic component
|
26
|
Glue
|
33
|
Asphaltenes
|
12 |
TABLE 4 Overflow Material Properties
Item
|
Example 1
|
Example 2
|
Example 3
|
Example 4
|
Example 5
|
Comparative example 1
|
Comparative example 2
|
Density (20 ℃ C.), g/cm3 |
0.9624
|
0.9586
|
0.9636
|
0.9756
|
0.9542
|
0.9658
|
0.9846
|
Viscosity (100 ℃ C.), mm2/s
|
68.7
|
66.9
|
69.2
|
69.8
|
66.4
|
68.9
|
112.0
|
Carbon residue in wt%
|
11.42
|
11.03
|
11.65
|
12.21
|
10.98
|
12.6
|
12.62
|
Metal Ni + V, wppm
|
89.6
|
88.7
|
89.9
|
90.2
|
86.1
|
91.5
|
82.0
|
Four components, wt%
|
|
|
|
|
|
|
|
Saturation fraction
|
44.3
|
44.0
|
43.9
|
43.3
|
44.4
|
44.3
|
37.8
|
Aromatic component
|
39.7
|
40.3
|
38.6
|
39.5
|
38.9
|
40.2
|
40.7
|
Glue
|
13.2
|
12.6
|
14.1
|
13.7
|
14.6
|
11.9
|
17.1
|
Asphaltenes
|
2.8
|
3.1
|
3.4
|
3.5
|
2.1
|
3.6
|
4.4 |
TABLE 5 fixed bed residuum hydrogenation test conditions and reaction results
Item
|
Example 1
|
Comparative example 1
|
Comparative example 2
|
Test conditions
|
|
|
|
Temperature, C
|
380
|
380
|
380
|
Pressure, MPa
|
15
|
15
|
15
|
Volume ratio of hydrogen to oil
|
650
|
650
|
650
|
Liquid hourly volume space velocity, h-1 |
0.23
|
0.23
|
0.23
|
Results of the experiment
|
|
|
|
Density (20 ℃ C.), g/cm3 |
0.9312
|
0.9343
|
0.9350
|
Carbon residue in wt%
|
5.14
|
5.50
|
5.87
|
Metal Ni + V, wppm
|
14.0
|
15
|
15
|
Operating cycle, h
|
9200
|
8600
|
8100 |