Abstract
The invention relates to a valve system of a fuel tank, especially of an LNG tank, which valve system includes at least two pressure relief safety valves, in which valve system one pressure relief safety valve is located in one safety valve branch branching from an outlet line from the LNG tank. The valve system further comprises interconnected shutoff valves for shutting off one of the safety valve branches at time and that the shutoff valves are diverter valves with a T-bore.
Claims
1. A valve system for liquefied natural gas (LNG) fuel tank, which valve system comprises two pressure relief safety valves, in which an outlet line from the LNG fuel tank is divided into two safety valve branches each comprising at least one of said two pressure relief safety valves, wherein the valve system further comprises interconnected shutoff valves for shutting off one of the safety valve branches at a time so that at least one of said two pressure relief safety valves is in operation at all times, that the safety valve branches connect to a common outlet line and one of the shutoff valves is located at a branching point of the outlet line for the LNG fuel tank and one of the shutoff valves is located at a connecting point to the common outlet line; and the shutoff valves are diverter valves with a T-bore.
2. The valve system according to claim 1, wherein the shutoff valves are interconnected by a mechanical connector.
3. The valve system according to claim 1, wherein the interconnected shutoff valves are interlocked with a mechanical key and lock system with free keys and trapped keys.
4. The valve system according to claim 1, wherein the shutoff valves are controlled such that when one of the shutoff valves is turned to an open or closed position, the other one of the shutoff valves is turned to the open or closed position, thereby allowing passage through one of the safety valve branches.
5. The valve system according to claim 1, wherein the valve system is located in a tank connection space of a marine vessel.
6. A marine vessel comprising a valve system according to claim 1.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) In the following the invention is described in more detail by reference to the accompanying drawing in which
(2) FIG. 1 shows schematically a simplified example of a valve system of an LNG tank according to prior art and
(3) FIGS. 2A-2D show schematically a simplified example of a valve system of an LNG tank according to an advantageous example of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
(4) During the course of the following description of FIGS. 1-2C corresponding reference numbers and signs will be used to identify like elements, parts and part components unless otherwise mentioned. In the figures some references sign have not been repeated for clarity reasons. In the following the examples are described mainly by reference to an LNG tank of a marine vessel in view of simplifying the disclosure but it should be noted that instead of this example any type of a valve system of an LNG tank or a LPG tank or ethane tank can have similar features and properties in accordance with the invention.
(5) In FIG. 1 is shown a simplified example of a valve system of an LNG tank according to prior art, in which an outlet line 21 from the LNG tank 10 is divided into two safety valve branches 23, 24 each comprising a pressure relief safety valve 12, 15 with shutoff valves 7, 9 before and shutoff valves 13, 14 after each of the pressure relief safety valves 12, 15. After the after the pressure relief safety valves 12, 15 located shutoff valves 13, 14 the safety valve branches connect to a common outlet line 22 for ventilation out to the ventilation mast. The pressure relief safety valves 12, 15 will open for safety reasons when the pressure of the LNG tank exceeds the set safety limit. In this prior art system the shutoff valves 7, 9; 13, 14 are globe valves and interlocked with key and lock system with free keys FA, FB, FD and trapped keys TB, TC, TD, TE. The keys are mechanical keys for mechanical locks. For shutting off the pressure relief safety valve 12 in the safety valve branch 23 first free key FA is used to release the shutoff valve 7 to be closed and to release trapped key TB to be used for releasing the shutoff valve 13 to be closed and to release trapped key TC, which cannot be used for the other safety valve branch 24. As free key FA is in use the other safety valve branch cannot be closed. When the pressure relief safety valve 12 is ready to be used again the safety valve branch 23 is opened again in using the keys in reverse order. After this the free key FA is released and ready for use for example for closing the other safety valve branch 24 correspondingly.
(6) FIGS. 2A-2D show schematically a simplified example of a valve system of an LNG tank, which valve system is located advantageously in a tank connection space of a marine vessel, according to an advantageous example of the invention. In FIG. 2A the valve system is as used in normal conditions and in FIG. 2B, when one of the pressure relief safety valves is under maintenance; in this figure the pressure relief safety valve in the left hand side safety valve branch. In FIG. 2C, when the other of the pressure relief safety valves is under maintenance: in this figure the safety valve of the right hand side safety valve branch. In FIG. 2D, the valve system controls the gas flow using the interconnected shutoff valves that are interlocked with a mechanical key and lock system with free keys FA, FB, FD and trapped keys TB, TC, TD, TE. In FIGS. 2A-2D gas flows from the LNG tank 10 and through the valve system to the outlet line 22 out via the ventilation mast are shown by arrows. As shown in the FIGS. 2A-2D an outlet line 21 from the LNG tank 10 is divided into two safety valve branches 23, 24 each comprising a pressure relief safety valve 12, 15 and the safety valve branches 23, 24 connect to a common outlet line 22 for ventilation out to deck and to air. The pressure relief safety valves 12, 15 will open for safety reasons when the pressure of the LNG tank exceeds the set safety limit The valve system comprises two shutoff valves 11, 16 that are diverter valves with T-bore i.e. three-way valves. One shutoff valve 11 is located at the branching point where the outlet line from the LNG tank 10 branches to the safety valve branches 23, 24, in which the pressure relief safety valves 12, 15 are located. The other shutoff valve 16 is located at the connecting point where safety valve branches 23, 24 connect to each other to a common outlet line 22 from the valve system. The shutoff valves 11, 16 are in this embodiment mechanically connected by a mechanical connector 18 for example by a chain, a bar or a pinion. Thus the shutoff valves 11, 16 are interlocked mechanically such that when one shutoff valve 11 is turned to another position, for example to close one safety valve branch 23 and keep the other valve branch 24 open, the other valve 16 will turn at the same time to corresponding position, i.e. closing the same safety valve branch 23 and keeping the other safety valve branch 24 open. In FIG. 2A the valve system is as used in normal conditions and the gas can flow through both safety valve branches 23, 24 as the T-bore of the shutoff valves 11, 16 allows the flow to each of the safety valve branches 23, 24 and both pressure relief safety valves 12, 15 are in use. In FIG. 2B one pressure relief safety valve 12 is under maintenance and the safety valve branch 23 is shut off by the shutoff valves 11, 16, which are turned such that the T-bore of the shutoff valves 11, 16 closes the safety valve branch 23 and keeps the other safety valve branch 24 open. In FIG. 2C the other pressure relief safety valve 15 is under maintenance and the safety valve branch 24 is shut off by the shutoff valves 11, 16, which are turned such that the T-bore of the shutoff valves 11, 16 closes the safety valve branch 24 and keeps the other safety valve branch 23 open. The shutoff valves 11, 16 are operated manually or by an actuator (not shown).
(7) In another embodiment instead of the mechanical connector 18 the shut off valves 11, 16 are interlocked with key and lock system with free keys and trapped keys as described in reference to FIG. 1. In this embodiment there are mechanical locks on both left and right sides of both the shutoff valves 11, 16 for preventing or allowing to turn the shutoff valve to left or right. The keys are mechanical keys for the mechanical locks. For shutting off one of the pressure relief safety valves 12; 15 in either of the safety valve branches 23; 24 the keys are used correspondingly as explained in connection with FIG. 1. When the pressure relief safety valve 12; 15 is ready to be used again the safety valve branch 23; 24 is opened again in using the keys in reverse order.
REFERENCE SIGNS USED IN THE DRAWING
(8) 7 shutoff valve
(9) 9 shutoff valve
(10) 10 LNG tank
(11) 11 shutoff valve
(12) 12 pressure relief safety valve
(13) 13 shutoff valve
(14) 14 shutoff valve
(15) 15 pressure relief safety valve
(16) 16 shutoff valve
(17) 18 mechanical connector
(18) 21 outlet line from the LNG tank
(19) 22 outlet line from the valve system
(20) 23 safety valve branch
(21) 24 safety valve branch
(22) FA, FB, FD free key
(23) TB, TC, TD, TE trapped key
