JPS6014788B2 - Crude oil vapor recovery method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering crude oil vapor generated from a crude oil storage tank.

Recently, large-scale stockpiling of oil has been discussed.
Crude oil storage methods include onshore tank storage, underground storage,
Various methods are currently in use or under development, including offshore stockpiling.

At this time, due to operations such as receiving crude oil and changes in temperature, the hydrocarbons in the crude oil evaporate and are released into the atmosphere in the form of gas as so-called crude oil vapor, resulting in the loss of valuable resources and the atmosphere. causing pollution. The methods for recovering hydrocarbons released into the atmosphere are generally absorption methods,
Possible methods include adsorption method, cooling condensation method, etc.

Another possible countermeasure is to make the tank itself have a floating roof structure to fundamentally prevent the release of hydrocarbon vapor, but this is not the case for large tanks such as oil storage tanks for crude oil storage or oil storage tank ships. It is difficult to apply. In addition, in the case of 5 million yen storage, approximately 0.1%, or 50,002', is expected to evaporate upon receipt, so the evaporation rate is extremely small, but since the amount stored is extremely large, the amount of loss will be large. The significance of collecting it is great. The present invention selectively and efficiently absorbs and dissolves only hydrocarbon vapor into crude oil from crude oil vapor generated from a tank or the like, that is, a mixed gas of light hydrocarbons and inert gas. This is a method of recovering hydrocarbons, and since normal pressure absorption has a small absorption capacity, it is absorbed under pressure, and then the crude oil in the absorbent is returned to the original oil storage tank.

That is, the invention of the present application pressurizes the crude oil vapor generated from the oil storage tank 12 as shown in FIG.
/ sphere G or more, preferably 7k9/bulb G or more, and introduce the crude oil vapor into the absorption tower 1 so that the gas-liquid ratio between the crude oil vapor and the absorbent is 2 mol/mol or more, preferably 5 mol/mol or more. Crude oil is introduced into the absorption tower 1, and the liquid taken out from the absorption tower is led to the flash drum 5 at a pressure of 2 kg/G or more, preferably 2.5 kg/G or more, and the ratio to the taken out liquid is 20 mol or more. This crude oil vapor recovery method is characterized by introducing an amount of fresh crude oil into the flash drum 5 and guiding the liquid taken out from the flash drum 5 to the oil storage tank 12.

Note that the gas at the outlet of the absorption tower 1 can be subjected to detoxification treatment, such as by burning it.

In addition, when the concentration of hydrocarbons in the gas generated from the oil storage tank is 8% or more, it is treated by the method of the present invention, and the gas at the outlet of the absorption tower is detoxified by combustion, so that the concentration of hydrocarbons in the gas is 8% or more.
In the following cases, it is possible to achieve a hydrocarbon recovery rate of 90% or more and an absorption tower outlet concentration of 8% or less by bypassing the equipment for the recovery method of the present invention and using it properly for combustion abatement. I can do it.

As a crude oil vapor recovery method, in addition to the absorption method applied to the present invention, for example, a cooling condensation method can be considered, but the relationship between absorption pressure or condensation pressure and hydrocarbon (HC) recovery rate is shown below. As is clear from FIG. 2, absorption method A is superior to condensation method B at 5° C. in terms of recovery.

Also, as is clear from Figure 2, the absorption pressure is 4k9/
A high HC recovery rate is obtained when the ratio is G or more, and the recovery rate reaches 90% when it is 7k9/Cuna G or more.

FIG. 3 illustrates the relationship with the re-evaporation rate in the flash drum.

The parameters in Figure 3 are absorption pressure (kg/G)
). However, the re-evaporation rate (molnomole) in the flash drum is (amount of vapor leaving the flash drum,
It is defined as line 20) in Fig. 1/vapor amount from the oil storage tank, line 19) in Fig. 1. As can be seen from Figure 3, the lower the flash pressure, the higher the reevaporation rate.
The load on the compressor increases accordingly, resulting in a disadvantage in terms of power.

Therefore, in order to reduce the load on the compressor, it is desirable to increase the flash pressure. However, if the flash pressure is set too high, the problem of re-evaporation will occur in the piping after the flash drum, as described below.

FIG. 4 is a graph showing the relationship between re-evaporation in the piping from the flash drum to the downstream and the mixing ratio of fresh crude oil in the flash drum.

FIG. 4 shows the case where the absorption pressure is 10k9/mass G, and the parameters indicate a flush pressure of 4 [9/mass G]. The re-evaporation rate (molar) in the piping is (amount of vapor generated in the piping after the flash drum)/(amount of vapor generated from the oil storage tank) Vapor on line 19 in Figure 1 amount). The mixing ratio of the flash drum is (amount of flash crude oil supplied to the flash drum, amount of fresh crude oil on line 17 in Figure 1)/(amount of vapor generated from the oil storage tank, amount of fresh crude oil on line 19 in Figure 1). vapor amount).

As can be seen from FIG. 4, if the flash pressure is high, there is a danger that re-evaporation will occur in the unloading pipe, causing vibration in the pipe.

At a flash pressure of 2.5k9/G or higher and a mixing ratio of 20 to 30 mol with fresh crude oil, re-evaporation within the pipe can be completely prevented.

FIG. 1 shows a specific flowchart of an embodiment of the method of the present invention.

The structure of an apparatus for implementing the present invention will be explained below with reference to FIG.

This is an absorption tower that allows dissolved components in crude oil vapor to be absorbed into crude oil under a predetermined pressure.

2 compresses crude oil vapor to a predetermined pressure and transfers it to line 1.
3 to the absorption tower 1.

3 is a floating roof type crude oil buffer tank. It is installed to absorb and dilute the crude oil vapor generated from the oil storage tank 12 after unloading from the tanker 11, and is also used when offloading a small amount from the tanker 11 (pumping up the bottom of the ship).

4 transfers the crude oil 10 in the crude oil buffer tank 3 to the line 14
This is a crude oil pump that sends crude oil to the absorption tower 1.

5 is a flash drum, in which the absorbed crude oil that has absorbed crude oil vapor in the absorption tower 1 enters the flash drum 5 through a line 15, is bypassed from an unloading pipe 16, and is mixed with diluent crude oil sent through a line 17 into the flash drum 5. is thoroughly mixed.

The crude oil pump 6 is provided to take out the mixed absorbed crude oil from the flash drum 5 and introduce it again into the unloading pipe 16 via a line 18. 7 is a suction vapor gas-liquid separator.

The crude oil vapor generated in the oil storage tank 12 enters the suction vapor gas-liquid separator 7 through a line 19, and the light components reevaporated in the flash drum 5 enter the suction vapor gas-liquid separator through a line 201. They enter the container 7 and are sent together to the compressor 2 via a line 21. The mist in the vapor is separated by the absorption vapor gas-liquid separator 7, and the liquid accumulated at the bottom is returned to the oil storage tank 12 via a line 22. 8 is a shield ram, and 9 is a combustion furnace unit.

The gas remaining after absorption in the absorption tower 1 enters the shield ram 8 via a line 23, and then is sent via a line 24 to the combustion furnace unit 9 where it is burned and detoxified. Next, the operation when the present invention is implemented in the above flowchart will be described.

When unloading crude oil from the tanker 1 to the oil storage tank 12 via the unloading pipe 16, a gas mixture of vertical hydrocarbons and inert gas containing mist generated in the oil storage tank 12 is sucked into the vapor gas-liquid separator 7. The liquid is separated and returned to the oil storage tank 12, and the crude oil vapor is compressed by the compressor 2 to more than 7k9/g of crucian carp and sent to the absorption tower 1.

The oil storage tank is filled with inert gas in advance to ensure safety. On the other hand, the crude oil 10 stored in the crude oil buffer tank 3 is pressurized to 7k9/lump G or more by the crude oil pump 4 and sent to the absorption tower 1.

The absorbed and dissolved components of the crude oil vapor efficiently come into contact with the crude oil in the absorption tower and are absorbed, and the remaining gas passes through the shield drum 8 and is sent to the combustion furnace unit 9 where it is burned and decontaminated. The absorbed crude oil discharged from the absorption tower 1 is sent to the flash drum 5 where it is
The crude oil is reduced in pressure to 45 kg/G and is efficiently mixed in the flash drum 5 with the crude oil bypassed from the unloading pipe 16, and sent to the unloading pipe 16 by the crude oil pump 6.

At this time, the crude oil vapor reevaporated in the flash drum 5 enters the suction vapor gas-liquid separator 7 and is sent to the compressor 2 together with the crude oil vapor sent from the oil storage tank 12.
Although 12 has been described above as an oil storage tank, the same applies to other oil storage means such as an oil storage tank ship on the sea.

As for the type of absorption tower, a sieve tray type is preferable from the viewpoint of anti-fouling measures, operation and maintenance, as packed towers are difficult to use due to the risk of clogging problems due to the presence of sludge etc. in the crude oil.

The features and effects of the present invention are as follows.

'1} A recovery rate of 90% or more can be achieved by setting the operating conditions of the absorption tower to an absorption pressure of 7k9/lump G or higher and a gas-liquid ratio (L/G) of 5 mol or more. '21 The absorbed crude oil discharged from the bottom of the absorption tower is kept under reduced pressure in a flash drum and reevaporated.

'3' Flash drum operating conditions at flush pressure 2
．． Dilution ratio with fresh crude oil of 5k9/G or higher is 20~
A scale of 30 mol/mol prevents evaporation in the piping.

(2) This method can be said to be the most economical and safe method by operating according to the above {1} to '3}.

[Brief explanation of drawings]

FIG. 1 is a flow diagram of one embodiment of the present invention. FIG. 2 is a graph showing the relationship between absorption pressure and HC recovery rate,
FIG. 3 is a graph showing the relationship between the flash pressure and the reevaporation rate in the flash drum, and FIG. 4 is a graph showing the relationship between the reevaporation rate in the pipe and the mixing ratio in the flash drum. 1... Absorption tower, 3... Crude oil buffer tank, 5. ．．・．． ．．・Flash drum, 7...
... Gas-liquid separator, 9... Combustion furnace unit, 12.
...Oil storage tank. Volume 'Kanikuzu Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. Vapor generated from crude oil (hereinafter referred to as crude oil vapor) is pressurized and introduced into an absorption tower with a pressure of 4 kg/cm^2G or more, and the gas-liquid ratio of the crude oil vapor and absorbent is determined. Crude oil is introduced into the absorption tower as an absorbent so that the ratio is 2 mol/mol or more, and the liquid extracted from the absorption tower is led to a flash drum with a pressure of 2 kg/cm^2G or more, and the ratio to the extracted liquid is 20 A method for recovering crude oil vapor, comprising introducing fresh crude oil in an amount of mole/mole or more into the flash drum, and recovering liquid taken out from the flash drum as crude oil.