JPS5816959B2 - Wastewater treatment method when cleaning oil tanks - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering and treating waste liquid during cleaning of large petroleum tanks such as heavy oil and crude oil.

Due to the revision of the Fire Service Act enforced on June 1, 1975, crude oil,
As a measure to prevent accidents that occur due to the deterioration of large oil tanks that store heavy oil, etc., especially oil spill accidents, 1.
1 in 1,000 or more oil tanks once every 5 years, 1 in 1,000 or more 1
Oil tanks with a capacity of less than 1 in 10,000 are now required to be inspected once every 10 years.

To do this, it is necessary to empty and clean this type of oil tank, and to conduct non-destructive inspections such as extremely high wave method and magnetic particle testing method to check for cracks and corrosion in the oil tank. be.

The present invention addresses the various problems encountered when cleaning oil tanks, specifically the recovery of residual oil before cleaning, and the recovery of resinous substances that lack fluidity, are sticky, and accumulate at the bottom of the tank. After that, the tank is steam-washed and the oil-containing wastewater that dissolves and floats is quickly separated into oil and water. Among these, the separated water is reused, and the oil-containing wastewater that is discharged after cleaning is filtered to keep it below the regulated concentration. In order to achieve smooth and quick discharge of water, we have systematized this, and since we are targeting large oil tanks that are installed individually in tank yards, we have simplified the transportation and relocation work to the respective tank yards. The purpose of this system was to make it convenient not only for assembly but also for assembly and disassembly on-site, and for the effective use of existing equipment in the oil tank.

Below is an overview of the process for cleaning oil tanks according to the present invention.
This will be explained based on the flow sheet shown in FIG.

1 is a floating tank that is closed with a floating lid 2 or a fixed ceiling lid 2 and stores crude oil, heavy oil, etc., and is installed in a tank yard 4 surrounded by an oil spill prevention wall 3 as shown in FIG. Fixed.

A steam pipe 5 is drawn into the bottom of the tank 1 to enable heating and circulation of crude oil, heavy oil, etc. in the tank 1.

Therefore, when performing a periodic inspection of the oil tank 1 as described above that has been used for many years, the residual oil remaining at the bottom of the tank 1 is first collected.

This opens the drain valve 6 at the bottom of the tank 1, and the residual oil recovery line L1 consisting of a strainer 7 and a feed pump 8.
The oil is separately transferred to the oil tank 9 via the oil tank 9.

As recovery of the residual oil progresses and the pump 8 gradually ceases to transfer the residual oil, as the highly sticky resinous substance (sludge) that has been deposited at the bottom of the tank 1 for many years begins to be fed.

Therefore, it is necessary to process and recover the resin-like substances deposited in large quantities at the bottom of the tank 1.

This resinous material is composed of asphaltene, ash, and mud water, and has a high pour point and is deposited in a strong and stable state, but in order to process and recover it, more than twice the amount of the same kind of oil as the resinous material is required. The tank 1 is filled with oil and separately filled with nitrogen, and heated and circulated to the steam pipe 5 using steam as a heat source to dissolve the resinous substance in the oil.

This dissolved oil is transferred to the reservoir tank 11 via the line L2 branched from the switching valve 10 behind the pump 8 in the line L1, further heated and adjusted in the reservoir tank 11, and then transferred again from the line L2 of the feed pump 12. The oil is collected in another oil tank 9.

After transferring the dissolved oil in this manner, the tank 1 is gas freed, and after checking the gas concentration and oxygen concentration, hot water is injected into the tank 1 from the water supply source 13 via the line L3, and the steam pipe 5 The tank 1 is heated and circulated using the steam as a heat source.

Next, steam is forced into the tank 1 from a steam source 14 instead of the water supply source 13 via a line L3, and steam is fed into the tank 1 from an injection port 15 that is movably provided in the tank 1 and operates like a butterfly with steam pressure. Backworthing cleaning, in which high-pressure steam is injected onto the wall surface, dissolves adhering substances such as oil and dirt that are stuck to the wall surface or have entered and solidified in cracks.

The oil-containing wastewater containing dissolved oil that has floated on top of the hot water by this steam cleaning is caused to flow into the storage tank 17 via the line L4 from the floating suction member 16 supported floating on its surface layer.

Next, the waste liquid that has flowed into the storage tank 17 is forced to be sent by the feed pump 18 from the valve 19 of the pumping line L5 to the horizontal oil-water separation treatment column 20.

The column 20 is provided with an appropriate number of compartments, and the inflowing waste liquid is pressurized, heated, and stagnation treated, and in particular, the stagnation and heat treatment increase the specific gravity difference between the dissolved oil and hot water. However, the water contained in the dissolved oil is separated.

The separated oil and water are further pressurized within the column 20, and the oil therein is collected and reused in another oil tank 9 via the line L6 and line L2 from the valve 21 to the reservoir tank 11. served.

Further, the coarsely separated water is returned from the valve 22 to the line L3 via the line L6, and is reused as circulating hot water within the tank 1.

In this way, the tank 1, the storage tank 17, and the oil/water separation column 20
By repeatedly purifying the oil-containing wastewater that has been steam-washed between the tanks, the entire inner wall surface of the tank 1 is cleaned, and the wastewater is separated from oil and water.

The drained liquid after steam cleaning of tank 1 is drained from drain valve 23.
The oil and water are finally separated in the oil-water separation treatment column 20 through the switching valve 24 of the line L1 and the line L5 of the pump 18, and the separated oil is transferred to the line L6.
, L2 and is collected in another oil tank 9.

In addition, the wastewater that has been roughly separated by removing free carbon, free paraffin, and floating oil from the wastewater in the column 20 is pumped from the valve 22 through the discharge side line L6, and then from the valve 24 to the polypropylene It flows into a horizontal column 25 filled with crimped fibers.

The crimped fibers filled in this column 25 have a characteristic that they have a much larger surface area than normal fibers and can easily capture oil droplets of fine particle size, and are also lipophilic and have the property of adsorbing oil. It also has

On the other hand, oil droplets with a fine particle size generally carry a negative charge in waste water, and an index caused by electricity acts between the crimped fibers and the oil droplets with a fine particle size.

Therefore, the waste water containing fine oil droplets flowing into the column 25 captures the oil droplets through collision contact with the crimped fibers filled in the column 25, and is caused by the electric charge acting between the fibers and the oil droplets. Due to the traction force and physical collision action, fine oil droplets gather on the surface of the filter medium, the adsorption action progresses, and eventually the filtration process in the column 25 is completed.

The waste water flows into the adjustment tank 26 from line L7.

After periodically measuring and inspecting the oil concentration in this adjustment tank 26, the wastewater with a certain concentration is sent to the line L by the feed pump 21.
8 into a horizontal column 28 filled with activated carbon.

The column 28 is filled with activated carbon in the form of crushed Colebes particles on a supporting bed covered with a wire mesh.

This activated carbon for wastewater treatment has the property of adsorbing specific substances from the liquid, so the wastewater that flows into the column 28 is further adsorbed and filtered by the action of the activated carbon, and the wastewater flows out of the column 28 at a concentration below the specified value. It is discharged 29 via line L9.

In addition, 30 and 31 in the figure are steam pipes, of which 30 carries the recovered oil in the reservoir tank 11, and 31 carries the oil/water separation column 20.
Each of the waste liquids is heated by steam, and both are supplied from the heating steam source of the oil tank 1 and the cleaning steam source 14 in the same way.

14′. 30' and 31' are the steam supply valves.The waste liquid washed in the tank in the above equipment and process is separated into oil and water after the steam washing in the final process.
The oil concentration, chemical oxygen demand COD, suspended solids (SS), and pH in each treatment process are treated as follows: They were compatible as shown in the table.

Since the present invention is configured as described above, it effectively solves various problems when cleaning large tanks for crude oil, heavy oil, etc., and contributes to rapid and efficient purification of large volumes of waste liquid.

[Brief explanation of the drawing]

Fig. 1 is an overall schematic diagram of tank cleaning, and Fig. 2 is a schematic diagram of the tank yard. 1...Tank, 2...Floating lid, 3...Wall, 4...
Tank yard, 5...Steam pipe, 6...Drain valve, T...Stracer, 8...Pump, 9...Tank, 10...Switching valve, 11...Storage tank, 12...・
・Pump, 13... Water supply source, 14... Steam source, 15
...Injection port, 16...Suction, 17...Storage tank, 18...Pump, 19...Valve, 20...Column, 21...Valve, 22...Valve, 23...・
・Drain valve, 24...Switching valve, 24'...Valve, 25...Column, 26...Adjustment tank, 27...
・Pump, 28...Column, 29...Discharge, L1~
L9...Line, 30.31...Steam pipe.

Claims (1)

[Claims] 1. After recovering residual oil and resinous substances remaining at the bottom of the tank, hot water is poured into the tank for steam cleaning. In other words, the oil-containing waste water that has been dissolved and floated by steam cleaning of the tank is fed to an oil-water separation treatment column by heating and circulating, and in the treatment column, the waste liquid is pressurized, heated, and accumulated while being separated from oil and water to remove one oil. The oil-containing wastewater that has been collected and circulated back to the tank is further separated from oil and water in the oil-water separation treatment column, and the separated wastewater is filtered through a column filled with crimped polypropylene fibers and flows into the adjustment tank. A method for collecting and treating waste liquid during oil tank cleaning, characterized in that the adjusted waste liquid is filtered through a column filled with activated carbon and discharged. 2 After collecting the residual oil at the bottom of the tank, more than twice the amount of the same type of oil is poured into the resinous substance deposited at the bottom of the tank, and nitrogen is sealed in and heated and circulated to dissolve and recover the resinous substance. A method for collecting and treating waste liquid during cleaning of an oil tank according to claim 1, characterized in that: