WO1995034464A1

WO1995034464A1 - Apparatus and method for continuous evacuation of tanks filled with fluids

Info

Publication number: WO1995034464A1
Application number: PCT/NO1995/000100
Authority: WO
Inventors: Preben Rasmussen
Original assignee: Preben Rasmussen
Priority date: 1994-06-13
Filing date: 1995-06-13
Publication date: 1995-12-21
Also published as: NO179317B; NO942217L; NO942217D0; NO179317C

Abstract

Apparatus and methods for continuous draining or 'stripping' of a fluid tank (1) by use of a unique apparatus comprising at least two pilot tanks (2) connected through pipelines (7, 8, 16) with a pressure medium source (10, 13) for intermittent suction in the pilot tanks of fluid from the fluid tank and expelling of the fluid intermittently from the pilot tanks through the drain pipeline (6) and the fluid outlet (15).

Description

Apparatus and method for continous evacuation of tanks fi 1 led with fluids.

The invention relates to apparatus and method for continuous evacuation of tanks filled with for instance chemicals, petroleum products or other fluids.

In tanks where pipes through the bottom of the tanks cannot be used, evacuation of the tank usually takes place by the help of pumps submerged in the tank. This method is used for instance when draiijing tanks on board ships or floating installations in connection with oil exploration, and when draining tanks in industry or other sectors, both under normal operations, and in connection with damages, accidents and other incidents. Evacuation of tanks where for instance chemicals or petroleum products are stored, is often hazardous with respect to fires and explosion, and the equipment used is therefor subject to strict specifications in terms of explosion safety. When using submerged pumps, which is most common, strict requirements are specified with regard to the pumps' quality, construction and state. When using submerged pumps, there is risk of overheating, stoppage, explosion when loading/unloading the pump and its pipelines. The consequences of fires or explosions due to faults in the pump equipment or its use may have catastrophic consequences. If there is need for overhaul or maintenance of a submerged pυmp when it is located in a tank, it will often be impossible or very difficult to undertake this work in the tank, due to the considerable risk of fire and explosion which is at hand.

According to the invention, use of submerged pumps is avoided, which increases the operational safety when draining tanks filled with fluids. In addition, the risk of fires and explosion are reduced; and the method according to the invention also offers substantial cost effectiveness, since the pump equipment that is used according to the invention is less expensive than previously known techniques.

According to the invention, this is achieved by mounting of two or more pilot tanks 2 inside, outside or at the tank 1 which is to be drained. The size, design and volume of the pilot tanks 2 are adapted to the desired rate of drain for the tank to be emptied. In the bottom of the pilot tanks 2 are arranged inlets 3 for the fluids which are to be filled into the pilot tank. The bottom of the inlet 3 is equipped with a one-way flap valve 4. Near the bottom of the pilot tank 2 is fitted an additional flow line for draining of the pilot tank. Said flow line is connected to one or several flow lines 5 from other pilot tanks 2 where this is desirable, and these are again connected to a drain pipe 6 via one or more valves 7, for selection of pilot tank 2 from which draining will take place. The valve 7 also prevents transfer of drain fluid from one pilot tank 2 to one or other pilot tanks 2.

Pilot tank 2 is further equipped with inspection hatch 9, which is fitted with a quick closing device, through which maintenance, cleaning and inspection may take place.

At the top of the pilot tank 2; valve 8 is fitted for connection to gas- or vacuum pump 10, for adjustment of pressure or vacuum, for control of draining or filling of fluid into the pilot tank 2.

In order to control pressure, and accordingly fluid level in the pilot tanks 2, vacuum pump 10 or ejector, connected to the pilot tanks via pipelines 8, are fitted. Each pilot tank 2 may either be equipped by a separate pump or ejector 10, or this may be common for several tanks. Air or gas is supplied for inlet 13.

The internal pressure- and fluid levels for the pilot tanks 2 is controlled by operation- and controlling units 11, either manually or automatically, connected with one or more vacuum pumps or ejectors 10. Emissions of air or gas from the pilot tanks 2 during operation may either pass to free air, or may be reinjected to the tank, via outlet 14.

In some instances there may be a substantial counter pressure in the drain pipe 6 during draining of the tanks 1, and it may therefore be necessary to fit a pressure pump 12 in the drain pipe 6, preferably outside the tank, in order to reduce the fire- or explosion risk, as well as simplifying maintenance and repair of the pressure pump 12.

When draining the tank 1, the procedure will be based on the pilot tanks 2, which are either placed within the tank, or are connected to the tank 1 via suitable pipelines; being filled up by the static fluid pressure existing at the bottom of the tank. Air or gas inside the pilot tanks 2 escapes via pipelines 9 to outlet 14.

When draining the tank 1, one of the pilot tanks 2 are pressurized through outlet 15 via vacuum pump 10 or injector 10 via pipelines 8. The fluid is pressed out through pipelines 5 and drain pipes 6, possible via the pressure pump 12. The pressure pump 12 may be necessary when, for instance, the difference in vertical level between tank and outlet 15 is substantial, or there exists counter pressure at the point where the fluid is to be drained. When the pilot tank 2 is drained of fluid, the gas pressure inside the pilot tank 2 is reduced again by means of vacuum pumps or ejector 10, and the pilot tank 2 is refilled when fluid flows in from the tank 1 via the pipe 3.

By connecting two or several pilot tanks 2 in one installation, and fitting one or several valves 7 at the pipe connection and drain valve, one obtains continuous drainage, since the pilot tanks 2 are drained and filled in different phases. Valves in the drain pipe 6. or the connection to the vacuum pump or ejector 10 may, via control unit 11 provide desired opening or closure, for suitable control.

Claims

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1. Apparatus for continuous drainage or "stripping" of a fluid tank, characterized in at least two pilot- or support tanks (2) which both are mounted in- or outside the fluid tank (1), equipped with inspection hatches (9) and internally connected through one or more pipelines (5) which are connected with a drain pipeline (6) and equipped with change-over valve (7), and connected, through separate pipelines (16), with an inlet pipeline (13) from a pressure medium source and connected, through an outlet pipeline (6), with a fluid outlet (15) and connected, through separate pipelines (8) from the top of the tank, with one or more pilot tank pumps or -injectors (10) connected with a air/gas outlet pipeline (14) and connected with the pressure medium source through the inlet pipeline (13), for creation of negative pressure and overpressure intermittently in the pilot tanks, for respectively suction of fluid into the tank (1) through fluid inlet (3) directly above the tank's bottom and expelling of the fluid, when inlets (3) are closed, through the drian pipeline (6) and the fluid outlet (15).

2. Apparatus according to claim 1, characterized ill that the drain pipeline (6) is coupled with a pressure pump (12) which functions at times of possible existence of considerable counter pressure in the outlet pipeline (6).

3. Apparatus according to claim 1, characterized in that the pipelines (8) from the top of the pilot tanks (2) are supplied with control valves (16) for creation of negative pressure and overpressure intermittently or simultaneously in the pilot tanks (2) for intermittent or simultaneous suction and expelling of fluid, respectively, and that pressure- and fluid levels in the pilot tanks (2) are controlled by regulators (11).

4. Methods for continuous draining or "stripping" of fluid tanks by use of apparatus according to claim 1, c h a r a c t e r i z e d i n process stages comprising pressure medium controlled creation of negative pressure and overpressure intermittently in the pilot fluid tank by means of the pilot tank's pump/injector, for suction of fluid from the fluid tank through inlets and expelling of the fluid, respectively, when the inlet is closed, through connecting pipeline(s) outlet pipeline and fluid outlet, control of pressure- and fluidlevels in the pilot tanks by means of the fitted regulators, and bypass of air/gas from the pilot tanks to free air through the air/gas pipeline or to the tank.