Method for using ethylene process wastewater as electro-desalting injection water

Abstract

The invention relates to a method for using ethylene process wastewater as injection water for electro-desalting, which comprises the following steps: using process wastewater generated by an ethylene device instead of demineralized water as injection water for an electro-desalting device for washing crude oil, and arranging a process wastewater pipeline to convey the ethylene process wastewater from the ethylene device to a water injection tank, the water in the water injection tank is conveyed to the salt-containing sewage-injected water heat exchanger through a water injection pump, and the water conveyed by the water injection pump is subjected to heat exchange and then is conveyed into an electric desalting tank for crude oil electric desalting. According to the invention, the existing ethylene cracking electro-desalting water injection heat exchange process is changed, and the ethylene process wastewater is used for replacing demineralized water as electro-desalting water injection, so that on one hand, the consumption of the demineralized water can be reduced, precious demineralized water resources are saved, the energy consumption of the device is reduced, on the other hand, the sewage discharge capacity of the ethylene device can be reduced, and good social benefits are achieved.

Description

Technical Field

[0001] This invention belongs to the field of petrochemical technology, and specifically relates to a method for using ethylene process wastewater as electro-desalination water injection. Background Technology

[0002] Crude oil containing salt and water easily causes scaling on equipment, reducing processing capacity, increasing furnace load, and wasting fuel. In severe cases, it can even block equipment, leading to shutdowns and posing a significant threat to petroleum processing equipment. Crude oil hydrolysis produces highly corrosive HCl, which corrodes equipment, shortens its lifespan, causes scaling, affects heat transfer, and can even block equipment. Furthermore, after distillation, most of the salts in crude oil remain in the heavy fractions and residue, increasing the heavy metal content in secondary processing feedstocks and exacerbating catalyst contamination and poisoning. Therefore, electrostatic desalting is essential for the safe operation of refining units.

[0003] Electro-desalting involves injecting demineralized water into crude oil to dissolve the salts. Then, a demulsifier is injected to break down the adsorption film at the oil-water interface and on the surface of solid salt particles in the oil. A high-voltage electric field induces polarization in the water droplets, causing them to become charged. Under the influence of this variable electric field, the differently charged droplets attract each other and merge into larger droplets. The difference in specific gravity between the oil and water causes stratification, and the salts in the oil are removed along with the water. Electro-desalting controls the salt content of the desalted crude oil to be ≤3 mg NaCl / L and the water content to ≤0.3%.

[0004] Refinery desalting units typically use purified water from the wastewater stripping unit as the desalting injection water. The purified water from the wastewater stripping unit has the following characteristics: sulfide: ≤15 mg / L; NH3-N: ≤100 mg / L; pH: 6.5–9.5.

[0005] Ethylene plants typically use products from oil refining units as feedstock. However, in recent years, ethylene plants directly integrated with atmospheric distillation units have become a new and mature high-efficiency conversion process. During normal production, ethylene plants generate wastewater, which is called process wastewater within the plant. This process wastewater originates from the dilution steam of the ethylene cracking furnace and enters a process wastewater stripping tower to remove hydrocarbon components, forming purified process wastewater that is then sent to a wastewater treatment plant. The indicators for purified process wastewater are: sulfides: ≤15 mg / L; NH3-N: ≤100 mg / L; pH value: 6–9.5.

[0006] The ethylene plant is located far from the oil refinery and cannot use the purified water from the refinery's wastewater stripping unit. Therefore, demineralized water must be used as injection water for the electro-desalting process. The demineralized water is of high quality and requires 1.3-1.5 times the amount of fresh water to obtain, leading to an increase in the company's water consumption. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for using ethylene process wastewater as electro-desalting injection water. This method changes the type of water used for electro-desalting in existing ethylene cracking processes, and uses ethylene process wastewater instead of clean demineralized water as electro-desalting injection water. On the one hand, it can reduce the amount of demineralized water used, save valuable demineralized water resources, and reduce the energy consumption of the equipment. On the other hand, it can also reduce the amount of wastewater discharged from the ethylene plant, which has good social benefits.

[0008] This invention provides a method for using ethylene process wastewater as injection water for electro-desalination, comprising the following steps:

[0009] The process wastewater generated by the ethylene unit is used instead of demineralized water as the injection water for electro-desalting. A process wastewater pipeline is set up to transport the ethylene process wastewater from the ethylene unit to the injection tank. The water in the injection tank is then transported to the saline wastewater-injection heat exchanger by the injection pump. After heat exchange, the water transported by the injection pump is sent to the electro-desalting tank for crude oil electro-desalting.

[0010] Furthermore, it also includes setting up demineralized water as an auxiliary water injection for electro-desalting, used to replenish the water supply or water quality when there are fluctuations in the ethylene plant.

[0011] Furthermore, the demineralized water is transported to the water injection tank via a demineralized water pipeline.

[0012] Furthermore, the demineralized water pipeline is equipped with a flow meter and / or a regulating valve.

[0013] Furthermore, the process wastewater pipeline is equipped with a flow meter and / or a regulating valve.

[0014] This invention utilizes the process wastewater produced by the ethylene plant as the injection water for electro-desalting. The auxiliary process involves setting up a demineralized water pipeline. When the flow rate or quality of the process wastewater cannot meet the requirements, demineralized water can be used to meet the quality requirements of crude oil electro-desalting.

[0015] Beneficial effects

[0016] This invention changes the existing ethylene cracking electro-desalination water injection heat exchange process by using ethylene process wastewater instead of demineralized water as the electro-desalination water injection. On the one hand, it can reduce the amount of demineralized water used, save valuable demineralized water resources, and reduce the energy consumption of the unit. On the other hand, it can also reduce the amount of wastewater discharged from the ethylene unit, which has good social benefits. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the process flow of the present invention; wherein, 1-electric desalination tank; 2-salt wastewater-water injection heat exchanger; 3-water injection tank; 4-water injection pump; 5-demineralized water pipeline; 6-process wastewater pipeline. Detailed Implementation

[0018] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0019] Example 1

[0020] As Figure 1 shown, this embodiment provides a method for using ethylene process wastewater as electro - desalting injection water, which includes the following steps: replacing desalted water with the process wastewater generated by the ethylene plant as electro - desalting injection water, setting up a process wastewater pipeline to transport the ethylene process wastewater from the ethylene plant to the injection water tank, and sending the water in the injection water tank to the salt - containing sewage - injection water heat exchanger through an injection water pump. After heat - exchanging the water transported by the injection water pump, it is sent to the electro - desalting tank for crude oil electro - desalting. That's all. This process also includes using desalted water as auxiliary electro - desalting injection water. The desalted water is transported to the injection water tank through a desalted water pipeline. The desalted water pipeline is provided with a flowmeter and / or a regulating valve. The process wastewater pipeline is provided with a flowmeter and / or a regulating valve.

[0021] Taking the injection water volume of 15 t / h of a 2 - million - ton - per - year crude oil electro - desalting unit supporting a 1 - million - ton - per - year ethylene plant as an example, when using desalted water as injection water, the dosage is 15 t / h, and 15 t / h of salt - containing sewage is generated after passing through the electro - desalting unit and sent to the sewage treatment device. The flow rate of the ethylene process wastewater sent to the sewage treatment device is 20 t / h.

[0022] Using 15 t / h of ethylene process wastewater as electro - desalting injection water to replace desalted water reduces the desalted water usage by 15 t / h and reduces the ethylene process wastewater sent to the sewage treatment device by 15 t / h.

[0023] Optimization effect: It can replace 15 t / h of desalted water and reduce the external discharge of ethylene process wastewater by 15 t / h. Calculated based on the desalted water price of 12 yuan / t, sewage treatment cost of 3 yuan / t, annual working hours of 8400 h, the benefit is 1.89 million yuan / year, the energy saving is 126 tons of standard oil / year, and the carbon emission reduction is 499 tons / year.

Claims

1. A method for using ethylene process wastewater as electro-desalination injection water, characterized in that, Includes the following steps: The process wastewater generated by the ethylene plant is used instead of demineralized water as the injection water for the electro-desalting unit to wash crude oil. A process wastewater pipeline is set up to transport the ethylene process wastewater from the ethylene plant to the injection tank. Then, the water in the injection tank is transported to the saline wastewater-injection heat exchanger by the injection pump. After heat exchange, the water transported by the injection pump is sent to the electro-desalting tank for crude oil electro-desalting.

2. The method according to claim 1, characterized in that, It also includes setting up demineralized water as an auxiliary water injection for electro-desalting.

3. The method according to claim 2, characterized in that, The demineralized water is transported to the water injection tank via a demineralized water pipeline.

4. The method according to claim 3, characterized in that, The demineralized water pipeline is equipped with a flow meter and / or a regulating valve.

5. The method according to claim 1, characterized in that, The process wastewater pipeline is equipped with a flow meter and / or a regulating valve.

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