Patent EA-001162-B1 (EA)
Title: System for draining a liquid storage tank
Inventor: WITTER ALDYR
IPC: B01D17/032
Filed: 1997-09-18
Abstract: 1. System for draining a liquid storage tank, which is intended to promote removal, from inside the storage tank, of denser phase which is deposited in the bottom of the tank below a less dense phase which is not to be drained comprising a drainage device (30) to be fitted at the lowest level of said liquid storage tank (1), said drainage device (30) comprising a concave body (31) which ends in a seat (26), an interface float (8) which sinks into the less dense phase and floats on the denser phase and thus prevents the formation of a vortex when the denser phase is being drained off, means (25) actuated by the float (8) for plugging the seat (26), and stop means (9) which limits the travel of the interface float (8) inside the drainage device (30) but allows the passage of liquids; a drainage box; a drainage conduit (10) connecting the seat (26) of the drainage device (30) to a drainage box (13) which is connected to a drain line (22); a shut-off valve (11) fitted in the drainage line (10) and which is intended to control the flow of liquid which passes to the drainage box (13); characterized in that the system comprises a pressure-equalization conduit (23) connecting the concave body (31) of the drainage device (30) to the drainage box (13); a pressure-equalization valve (24) fitted in the pressure-equalization line (23), said pressure-equalization valve (24) and functioning to promote the equalization of the pressures below and above the interface float (8) after the plugging means (25) has settled on the seat (26) of the drainage device (30); and a sensor (12) functioning to detect the presence of the denser phase which is deposited in the bottom of the tank; a sensor functioning to emit a command signal to open the shut-off valve (11) which makes it possible to drain off to the drainage box (13) the denser phase which has accumulated in the drainage line (10) and to emit a command to close the shut-off valve upon the completion of drainage; and a sensor functioning to emit a command signal to open the pressure-equalization valve (24) which causes an equalization of the pressures to which the upper and lower parts of the interface float (8) are subjected. 2. The system according to claim 1, characterized in that the shut-off valve is provided with a first actuator; the pressure-equalization valve is provided with a second actuator, associated with a detection means, wherein a detection means for the presence of the denser phase deposited in the bottom of the tank for storing the liquid comprises the monitoring and controlling system wherein the monitoring and controlling system is adopted for detecting a denser phase and providing a control signal to the first actuator to open the shut-out valve for a predetermined period of time which makes it possible to drain off to the drainage box the denser phase which has accumulated in the drainage conduit, wherein after a predetermined period of time during which the shut-off valve (11) has remained closed, the monitoring and controlling system enabling to emit a command signal to the actuator to open the pressure-equalization valve for a predetermined period of time, which causes an equalization of the pressurea to which the upper and lower parts of the interface float (8) are subjected, enabling said interface float (8) to float again on the denser phase, thereby initiating a new drainage flow. 3. The system according to claim 2, characterized in that the system further comprising a second monitoring and controlling means fitted in the drainage conduit operative to detect passage of less dense phase through this drainage conduit (10) which would signify an operational failure of the drainage device (30) and in response to detection of such passage to emir a command signal to the actuator (11A) to command closure of the shit-off valve (11), thereby halting drainage. 4. The system according to claim 3, characterized in that comprising a remote panel installed in a control room where a type of alarm would emit an alert vis-a-vis the problem, to receive the signal emitted  by the sensor (17) and in response thereto to signal an alarm which would enable an aperator in charge to take the necessary measures to rectify said problem. 5. The system according to claim 1, characterized in that comprising a level gauge (28), for inspecting the liquid level in the tank, fitted in the bottom of the side wall (6) of the storage tank (1) slightly above the level of the drainage device (30), and operative to enable an operator to detect the presence of aqueous phase in the bottom of the storage tank (1), the shut-off valve and the pressure-equalization valve can be operated by an operator, whereupon after the predetermined period of time the operator inspects the liquid level in the tank by the level gauge and after detecting the presence of the denser phase in the bottom of the storage tank (1) the operator opens manually shut-off valve (29) for draining the denser phase and keep it open until the end of the drainage operation, close it at that end of the drainage operation, and subsequently opens manually the second shut-off valve (27) and keep it open for a predetermined period of time to equalize the pressures to which the top and bottom of the interface float (8) are subjected, thereby enabling the said interface float (8) to float again on the denser phase, thereby initiating a new drainage flow. 6. The system according to any one of the preceding claims, characterized in that the height of the drainage box (13) is greater than the useful height of the containment basin of the storage tank (1), and in that the drainage box has, at its bottom, a drainage conduit (20) with a second shut-off drain valve (21), these enabling the containment basin of the storage tank (1) to be drained through the drainage box (13) when the second drain valve (21) is opened. 7. The system according to any claims 1 to 5, characterized in that said plugging means comprise a valve portion (25) on the lower face of said interface float and, intended to settle on the seat (26).