Electrodesalination of Tahe crude oil

It’s indeed a big challenge! We use a blending method to refine it together with other oils. The problem that arises is that the temperature after the replacement is low, which affects the processing volume ； The desalination effect is extremely poor, with values not exceeding 35 before and after; it is practically ineffective compared to the total salt content ； The slag softening point is too high, affecting transportation. Salts cannot be removed, which has a significant impact on subsequent processes, leading to salt buildup and blockages in furnace tubes and distillation trays, as well as catalyst poisoning.

The electrodeposition effect for Tahe oil is also poor; the value remains below 50 before and after deposition. Just like the one upstairs, it’s very poor. Which sea friend has a better solution? Share it! :handshake

Sinopec’s Tahe plant processes high-acid, high-sulfur Tahe oil with a density of 0.94. For direct processing via atmospheric and vacuum distillation, 3-stage electrodesalination is employed due to the high density. The effect is good; the salt content after desalination is less than 7. It was designed by LPEC. Everyone can use this as a reference.

The oil-electric desulfurization method in Tahe doesn’t work; it seems better to avoid pressure reduction and simply remove the normal residue directly.

The Tahe oil has a high metal content; would the addition of a demetallizing agent improve the desalination effect?

We process the crude oil from Tahe. The quality of this crude oil is quite poor, with a viscosity level around 947. We use three-stage electrodesalination, and the overall desalination effect is fairly good, with the viscosity remaining at around 4. The operating conditions are as follows: demulsifier FJT-1 at a concentration of 25 PPM, water injection at around 7% (three-stage re-injection process), and a voltage of 19 KV to 25 KV. Some time ago, during technical tests conducted by the company, when the voltage was 13 KV, the current was 120 A; however, after adjusting the voltage back to 19 KV, the current dropped to 40 A. In my opinion, this is due to an enhanced weak electric field in the electrodesalination process, which leads to a reduction in metal ions and water content, thereby increasing the resistance. I’m not sure if this is correct, but I’d like everyone to discuss it together: handshake :handshake

We once worked with Tahe oil, which has a high metal content. A plan was developed for its centralized processing; the processing took 3 days in total. The desalination effect was extremely poor, with a high salt content remaining after desalination, which caused significant problems for the subsequent units, especially the catalytic systems. Heavy metal poisoning of the catalysts was a major issue; at that time, the catalyst consumption was 1.8, and there was a tendency for salt accumulation in the distillation towers. It is necessary to quickly change the plan and blend it with other oils at a 10% concentration; this will have a lesser impact on the subsequent processing units. However, the problem of heavy metals remains serious, and the reagent consumption is 1.4, requiring a large amount of balancing agents, which makes it not worth it.

1. Basic properties of Tarim crude oil: The basic properties of Tarim crude oil are shown in Table 1. As can be seen from the data in Table 1, the density of Tarim crude oil at 20°C is 853.8 kg/m3 ； The dynamic viscosity at 50°C is 7.92 mm2/S ； The freezing point is -9°C. The sulfur and nitrogen contents are 0.70‰ and 0.11‰ respectively, while the salt content and acid value are 64.04 mg NaCl/l and 0.21 mg KOH/g respectively ； Residual carbon is 4.65%m%, and ash content is 0.012%m% ； The contents of iron, nickel, and copper in the crude oil are 3.12 ppm, 5.13 ppm, and 0.52 ppm respectively, while the vanadium content is relatively high at 42 ppm. In terms of the crude oil’s distillation range, the fraction distilled before 300°C accounts for 45.00% (V%). Table 1: Basic properties of Tarim crude oil
1. Sample name: Tarim crude oil
Iron: 3.12
2. Sampling date: 10/9/2001, 18:00
Metal content: Nickel: 5.13
3. Sampling location: Truck; ppm
Copper: 0.52
4. Density: kg/m³ at 20°C: 853.8; Vanadium: 42
5. Specific gravity index API0: 33.5
Boiling range (V%):
6. Dynamic viscosity: mm²/s at 50°C: 7.92
Initial boiling point: °C: 57
7. Water content: m%; trace amount at 100°C: 5.00
8. Residue content: m%: 4.65 at 120°C; 8.75
9. Ash content: m%: 0.012 at 140°C; 12.50
10. Acid value: mgKOH/g: 0.21 at 160°C; 17.50
11. Salt content: mgNaCl/L: 64.04 at 180°C; 22.50
12. Sulfur content: m%: 0.70 at 200°C; 26.25
13. Nitrogen content: m%: 0.11 at 220°C; 30.00
14. Freezing point: °C: -9 at 240°C; 32.50
15. Asphaltenes content: m%: 2.09 at 260°C; 36.25
16. Resins content: m%: 5.71 at 280°C; 41.25
17. Wax content: m%: 2.69 at 300°C; 45.00

As can be seen from Table 2, based on key components and sulfur content, Tarim crude oil belongs to the category of sulfur-containing – intermediate base crude oil. The actual boiling point distillation cut data for Tarim crude oil are shown in Table 3. Table 2: Properties of key fractions of Tarim crude oil
Key Fractions, °C: First key fraction, Second key fraction
250–275 °C, 395–425 °C
Density, kg/m³ at 20°C: 832.8, 883.4
Specific gravity index (API): 37.6, 28.0
Sulfur content in crude oil, m%: 0.70
Nature of crude oil: Sulfur-containing – intermediate grade

Table 3: Distillation yields of Tarim crude oil based on actual boiling points
Boiling range, °C; Yield, m%; Total yield, m%
HK–100: 8.26, 8.26, 100%
100–120: 2.60, 10.85%
120–145: 4.44, 15.29%
145–160: 2.61, 17.90%
160–180: 3.38, 21.28%
180–200: 3.93, 25.21%
200–220: 3.00, 28.20%
220–240: 3.74, 31.95%
240–250: 1.70, 33.65%
250–275: 4.58, 38.23%
275–300: 4.23, 42.46%
300–320: 3.73, 46.18%
320–350: 5.53, 51.71%
350–500: 20.96, 72.67%
>500: 26.85, 99.52%

2. Properties of the straight-run products of Tarim crude oil:
Residue yield at 350°C: 47.81 m%; Char content: 8.63 m%; Saturated hydrocarbon content: 50.98%; Resin + asphaltenes content: 14.67%; Sulfur and nitrogen contents: 1.27 m% and 0.24 m% respectively; Vanadium content: 74 ppm. This residue can be blended in appropriate amounts as a feedstock for catalytic cracking. 3.3 >500℃ residue yield is 26.85%, with a high char content of 17.21%. The sulfur and nitrogen contents are 1.82 m% and 0.35 m% respectively, while the vanadium content is as high as 119 ppm. Table 7 Properties of the diesel fractions from Tarim crude oil
Boiling range, °C: 240–350
Yield (as a percentage of crude oil): 19.76%
Density at 20°C: 845.9 kg/m³
Freezing point, °C: –12
Dynamic viscosity at 20°C: 5.69 mm²/s
Corrosivity (on copper sheets): 1a
Acidity, mgKOH/100ml: 6.86
Sulfur content, %: 0.32
Nitrogen content, ppm: 50.6
Flash point (closed cup), °C: 128
Relevant index: 29.54
Characteristic factor: 11.91
Initial boiling point: 256°C
Boiling points for different percentages:
10%: 273°C; 30%: 281°C; 50%: 291°C; 70%: 302°C; 90%: 319°C; 95%: 324°C
Dry point: 330°C

Table 8 Properties of the feedstock for catalytic cracking and the residue from Tarim crude oil
Boiling range, °C: 350–500; >350; >500
Yield (as a percentage of crude oil): 20.96%; 47.81%; 26.85%
Density at 20°C, kg/m³: 897.8; 953.2
Dynamic viscosity, mm²/s: 22.62 (at 50°C); 57.40 (at 100°C)
Sulfur content, %: 0.74%; 1.27%; 1.82%
Nitrogen content, ppm: 0.06%; 0.24%; 0.35%
Residue content, %: 8.63%; 17.21%
Saturated hydrocarbons, %: 88.08%; 50.98%
Aromatic hydrocarbons, %: 9.49%; 30.02%
Resin content, %: 1.28%; 10.08%
Asphaltene content, %: 0.07%; 4.59%
Relevant index: 38.17
Characteristic factor: 12.01
Metal contents:
Iron: –; 4.58; 10.03
Nickel: 0.05; 9.06; 22.02 ppm
Copper: 0.05; 0.61; 0.64
Vanadium: 74; 119 ppm

4. Summary:
4.1 The Tarim crude oil evaluated in this study is of medium quality, with a sulfur content of 0.70%. Its vanadium content is relatively high, at 42 ppm. This crude oil belongs to the category of sulfur-containing, intermediate-grade crude oils. 4.2 For this crude oil, the total distillation yield before 500°C of its actual boiling point was 72.67%, and the yield of light oil before 350°C was 51.71%. 4.3 At temperatures above 350℃, the yield of residue is 47.81%, the carbon residue content is 8.63%, and the vanadium content is 74 ppm. This residue can be used as a feedstock in catalytic cracking processes in appropriate amounts; however, the high vanadium content hinders the progress of catalytic cracking reactions, so the proportion of this crude oil used in processing should be controlled appropriately.

What distillation column is meant by salt deposition and blockage in the distillation column trays? How can we tell?

Salt deposition in distillation columns occurs in both catalytic and coking processes, and in severe cases it can also occur at the atmospheric pressure column top. The main manifestations are a decrease in the separation precision of the product, frequent non-conformity of the product at the tower top, cavitation in the top circulation pump, and an increase in the pressure drop at the tower top.

Our electrodialysis performance is also poor, mainly due to large fluctuations; the current control method involves regulating the proportion of river oil in the blending tower

The high salt content in the Tahe crude oil primarily leads to a reduced heat transfer efficiency in the pre-desulfurization heat exchanger (high asphaltenes deposition causing coking in the heat exchanger), as well as excessive salt levels in the product after desulfurization. We use a high proportion of blending, up to 40%, but the salt content after desalination is simply not up to standard; it’s usually around 20. Think about how much such a salt content affects the downstream equipment Moreover, when blending Taer River crude oil, in order to control the softening point of the residue, overflow must be arranged for lines 3 and 4; otherwise, the softening point could rise to around 80. Recommendation: If large-scale processing of Tahe crude oil is to be carried out over the long term, the original process flow must be redesigned; otherwise, electrodialysis will not meet the required standards!

Is the Tahe oil high in acids? To process crude oil with a high acid content, an oil deacidification unit can be used; this unit enables both acid removal and the recovery of naphthenic acid, which is a very valuable substance... This is a project of CNPC, and our company has expert professionals in this field working on it, with full commercialization upcoming

For Tahe oil, electrodeposition can also be used. . . The series requires three stages; the settlement rate should be less than 80% of the value typically used in design. The desalination temperature must then be maintained between 135 and 145 degrees, and an emulsifier suitable for the process should be selected to ensure clear phase separation. . . :Lol, after removal, it can generally reach 5–7 milligrams. . . :lol Last edited by chengkang on 2009-2-26 12:34 ]

Watermelon, are you a staff member from Tahe? How do you know so much about our electrodesalination processes and the chemicals used in them? We process crude oil from Tahe, and its quality is quite poor, usually around 947. We use a three-stage electrodesalination process, and the overall desalination efficiency is fairly good, with the salt content remaining at around 4. The operating conditions are as follows: demulsifier FJT-1 at 25PPM, water injection at around 7% (three-stage re-injection, first stage), and voltage between 19KV and 25KV. Some time ago, during technical tests conducted by the company, when the voltage was 13KV, the current was 120A; but after adjusting the voltage back to 19KV, the current dropped to 40A. I think this is due to an enhanced weak electric field in the electrodesalination process, which leads to a reduction in metal ions and water content, thereby increasing resistance. I’m not sure if this is correct, but let’s discuss it together. In fact, in 2008, for almost half a year, the salt content after desalination remained below 4mg/l. But as extraction of crude oil from Tahe continues, the quality of that oil has become increasingly poor. Although the electrical desalination level is higher than the 3mg/l limit set by the group company, I think the current performance is quite good. Our facility has been in operation for 8 years, during which it has undergone 2 major overhauls. According to the latest maintenance records, the unit has been in continuous operation for nearly 4 years, during which corrosion has been quite severe. In particular, the welds at several flanges located before the outlet valve of the feed pump P-109AB in the vacuum distillation furnace, as well as the welds around the feed control valve of the same furnace, have suffered severe corrosion. There have been 3 or 4 instances of corrosion-related leaks, but all were resolved. However, there is an objective reason for this: during the construction of the unit, the material used for the flanges was installed incorrectly. Post-analysis, the flange installed was made of 20# carbon steel. Naphthenic acid causes the most severe corrosion of carbon steel, reaching up to 20 mm/year.

May I ask how effective is the oil and electricity desalination process you use in Tahe?