JPS5821548B2 - How to recover residual oil - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering residual oil in a floating roof tank on which pyrophoric substances, particularly iron sulfide, etc. have formed and adhered.

When a storage tank for oil containing hydrogen sulfide, such as slop oil, is used for a long period of time, the side walls and ceiling walls inside the tank react with the hydrogen sulfide, producing iron sulfide.

This iron sulfide is extremely active and can easily ignite in the presence of oxygen, causing a fire.

In addition, sludge etc. accumulates at the bottom of such tanks,
Since the internal volume of the tank decreases and the function of ancillary equipment in the tank, such as an agitator, decreases, it is necessary to periodically open the tank for cleaning, repair, etc.

Although various methods have been proposed for recovering and cleaning residual oil in tanks, a method for safely and quickly opening tanks contaminated with pyrophoric substances such as sulfides has not yet been established.

The present invention provides an effective method for recovering residual oil in a tank to safely and quickly open and clean this type of tank.

In other words, the present invention removes oil in a floating roof tank with naturally combustible substances attached to the inner wall until the roof support reaches the bottom of the tank, and then removes the oil so that the oil reaches the level of the roof support of the tank. This method of recovering residual oil in the tank is characterized by introducing water into the tank and extracting the residual oil through a nozzle installed in advance at the height of the roof support or higher.

The present invention will be explained in detail below.

First, extract as much oil from the tank as possible until the floating roof lowers, that is, until the roof support attached to the floating roof touches the bottom plate of the oil tank.

If the roof support attached to the floating roof reaches the bottom of the oil tank and oil is still extracted, air will flow into the tank from the Atmos valve attached to the floating roof and ignite the iron sulfide attached to the inner wall of the tank. This is dangerous as it may ignite the combustible gas in the gas phase in the upper part of the tank.

For this reason, it is extremely important to never allow air to be sucked between the oil layer and the floating roof.

Next, water is poured into the tank from which the oil was extracted, causing the remaining oil in the tank to float to the surface of the water.

This floating residual oil is extracted and recovered through a nozzle installed in advance at the height of the roof support attached to the floating roof of the tank or at a higher height.

In this extraction method, water can be pumped in at a time to the nozzle position or above to draw out the residual oil (or, the water can be pumped in and drawn out several times in order to finally reach the nozzle position). Water may be pumped up to a height to completely remove residual oil.

In order to recover this residual oil more completely and to further clean the inner wall of the tank, it is necessary to repeat the supply and withdrawal of water several times and to heat the water being supplied or after being supplied. ,effective.

In addition, if there is no nozzle that can be installed at an appropriate location on the tank, i.e. at or above the height of the roof support, the hot tapping method, i.e., the piping with a valve attached to the outside of the tank, may be installed by welding. For safety reasons, it is preferable to install the nozzle by drilling a hole in the side plate of the tank.

Furthermore, the nozzle is preferably installed at a position as low as possible so that air will not be sucked between the floating roof and the oil layer even if residual oil is extracted.

The method of implementing the present invention will be specifically described below with reference to FIGS. 1 and 2.

In FIG. 1, oil in a floating roof tank 1 is extracted through an oil feed pipe 2.

At this time, the process is continued until just before the roof support 4 attached to the floating roof 3 reaches the tank bottom 5.

If sludge or the like is present at the bottom of the tank, the extraction ends just before the roof support 4 reaches the sludge layer.

Even if the roof support 4 reaches the tank bottom 5 (or the roof support does not go down), it is still necessary to drain the oil and be careful not to create negative pressure inside the tank.

Next, water is fed into the tank from the oil feed pipe 2.

As shown in Figure 2, residual oil 6 floats on top of water 7.
is finally fed to the nozzle 8, and the residual oil 6 is extracted from the nozzle 8.

Note that, if necessary, water is added from the oil feed pipe 2 and extracted from the oil extraction pipe 8 several times (repeated) as necessary.

The process up to cleaning inside the tank will be described below.

After most of the residual oil has been collected, the water in the tank is heated and stirred using an attached heating coil and a stirrer (not shown) to transfer the oil adhering to the tank inner wall and bottom plate to the surface of the water layer.
Drain the aqueous layer.

When discharging this water, it is preferable for safety to replace the lid of the roof manhole 9 with a lid equipped with a nozzle for nitrogen sealing and to discharge the water under a nitrogen seal.

It is better to repeat this heating and stirring several times by replacing the water.

Next, after confirming that there is no combustible material in the tank, release the nitrogen seal.

Next, leaving a small amount of water at the bottom of the tank, the shell manhole 10 is opened and the iron sulfide on the side walls, attic, bottom plate, etc. of the tank is scraped off and cleaned.

At this time, it is preferable that the iron sulfide be in a second state so that it is completely soaked into the water at the bottom of the tank.

As described above, the method of the present invention is economically advantageous because it does not require a large amount of nitrogen, and the tank can be cleaned extremely safely.

Examples will be described below.

Example 5000U' floating roof tank (roof support 1.8m)
The opening and cleaning were carried out using the following procedure.

■ The oil layer in the tank is 2m high (residual oil amount is 700kl)
It was transferred to another tank until

■ Sending 880 tons of main fishing to the tank, the total liquid height was 4.5 m,
The height of the water layer was 2.5 m.

■ The extraction piping was installed at a height of 2 m using the hot tapping method.

■ After stirring with a stirrer attached to the tank and allowing it to stand still, residual oil and water were extracted through an extraction pipe and the residual oil was recovered.

■ Approximately 180 tons of water was then pumped in, and residual oil and water were extracted from the extraction pipe with a liquid height of 2.5 m.

This operation was repeated twice.

■ Water was pumped in until the water layer height reached 15 m.

(Water volume: 4,500 tons) ■ The roof manhole cover was replaced with a cover equipped with a nozzle for sealing N2 while sprinkling water.

(2) Water was drained to a water layer height of 2 TrL, and then the water was drained completely while N2 gas was fed into the tank.

A 700 ton C-line fishing rod was heated and stirred using a heating coil and a stirrer attached to the tank to bring the water temperature to about 30° C., and the water was drained under an N2 seal.

This operation was repeated twice. When draining the final water,
Water was left to about 0.5 m.

[Phase] After releasing the N2 seal, we opened all the manholes and scraped off the iron sulfide on the attic, side walls, and bottom plate of the tank by inputting information while wearing an airline mask.

■ Finally, we drained and cleaned the water.

[Brief explanation of drawings]

Figures 1 and 2 show cross-sectional views of floating roof tanks.゛Among these, Figure 2 shows the state in which the extraction piping is installed by the hot tapping method of the method of the present invention. 1...Floating roof tank, 2...Oil pipe, 3...Floating roof, 4...Roof support, 8... Extraction piping, 11...Atmos, Kurub.

Claims (1)

[Claims] 1. Remove the oil in a floating roof tank with naturally combustible substances attached to the inner wall until the roof support reaches the bottom of the tank, then pour water into the tank to a level that is at least the height of the tank's roof support. A method for recovering residual oil in the tank, characterized in that the residual oil is extracted from a nozzle installed in advance at the height of the roof support or higher.