ARRANGEMENT IN A FIRE WATER SYSTEM

Abstract: An arrangement in a fire water system, especially for an offshore platform, wherein the system comprises one or more fire water pumps (6) connected through a pipe system (2-5) to a number of deluge valves (812) coupled to associate with pipe stretches leading to respective fire sections. The arrangement comprises a distribution manifold (2) having an upstream side (3) which is in open connection with the fire water pumps (6) and with a buffer tank (7) for water, and having a downstream side (4) conected to the deluge valves (12) which are coupled to said pipe stretches, and there is also provided a gas supply means (10) connected to the buffer tank (7) and having a pressure which is sufficient to see to it that the water pressure at the upstream side of the distribution manifold does not sink below a predetermined level after activation of the deluge valves (12). The distribution manifold (2) and the deluge valves (12), preferably also the buffer tank (7) and the gas supply means (10), are arranged as an integrated unit within a_delimited area which may advantageously be constituted by a container (1).

Description: Arrangement in a fire water system The invention relates to an arrangement in a fire water system, especially for an offshore platform, wherein the system includes one or more fire water pumps connected through a pipe system to a number of deluge valves coupled to associated pipe stretches leading to respective fire sections. A fire water system for an offshore installation normally will include a large pipe system having large variations in static and dynamic pressure. The system often includes one or more ring mains having branches to the different fire sections. In a normal situation the pipe system is maintained water- filled by means of feeding pumps of moderate capacity. When a fire is warned in an area, deluge valves are activated opening for the supply of water from the pipe system to sprinkler heads/nozzles and to other extinguishing means at the relevant fire location. At the same time strong fire water pumps are started, which pumps are to provide for the necessary supply of water. These pumps, having a power of 0,5 - 2 MW, have a start-up time of 10 - 30 seconds. The deluge valves of the system open more quickly. During the time before the fire water pumps have come into operation, there will often be drawn more water from the pipe system than that which is supplied. Therefore, column separation may take place in parts of the pipe system, with the consequence that strong pressure pulses arise when the fire water pumps force fresh water into the regions where column separation has occurred. The result may be that the pipe system becomes overloaded, so that the fire water system is put completely or partly out of operation. This is a substantial problem in the design and operation of fire water systems. It is wanted that the fire sections are to supply water as quickly as possible in order to prevent the fire from developing. In principle, this implies that the relevant deluge valves should be open by the time when the fire water pumps have come into operation. Great resources have been laid down in order to arrive at technical solutions causing the different fire water systems to be operative as fast as possible without pressure surge problems etc. arising. Generally, it cannot be said that the existing solutions are functioning entirely satisfactorily. A solution which has been used in some situations, is to install a so-called semaphore tank. This is a large, partly air-filled pressure tank which is normally placed at a high level on the platform, a passive unit connected to the pipework and keeping the pipe system water- filled for the purpose of eliminating pressure surge problems. A substantial drawback of such a tank is that the internal pressure varies with the water content, and the lack of desired control of the water flow from the tank. An alternative solution is to use gas valves (a pressure surge compensator) for replenishing with compressed air and providing an air cushion for attenuating pressure surge attempts. A common feature of these solutions is that they become relatively expensive, either because the unity price is high or because several units are required in order to solve the pressure surge problems. On this background it is a general purpose object of the invention to provide a cost efficient fire water system wherein the above-mentioned drawbacks and problems of the known systems are eliminated. Another object of the invention is to provide a fire water system giving an increased security as a result of a reduced total start-up time, and no harmful pressure pulses during start-up and operation, and wherein manual intervention of deluge valves during fire and explosions can be carried out within secure areas at the topical installation. A further object of the invention is to provide a fire water system which is without the above-mentioned fire water ring mains with associated components, and wherein the system has a modularised construction and offer a great flexibility with respect to design and location. For the achievement of the above-mentioned objects there is provided an arrangement in a fire water system of the introductorily stated type, which arrangement is characterised in that it comprises a distribution manifold having an upstream side which is in open connection with the fire water pumps and with a buffer tank for water, and having a downstream side connected to the deluge valves which are coupled to said pipe stretches, and that there is also provided a gas supply means connected to the buffer tank and having a pressure which is sufficient to see to it that the water pressure at the upstream side of the distribution manifold does not sink below a predetermined level after activation of the deluge valves, said distribution manifold and the deluge valves, preferably also the buffer tank and the gas supply means, being arranged as an integrated unit within a delimited area. An advantageous embodiment of the arrangement according to the invention is characterised in that the distribution manifold and the deluge valves are mounted in an enclosure constituting the delimited area, and preferably consisting of a container, the deluge valves being coupled to respective outlets from the container to the said pipe stretches. It is advantageous that also the buffer tank and the gas supply means, and possibly also the fire water pumps, are installed in the container. Further, the container advantageously may be heated, and preferably also fire insulated. When said delimited area is constituted by a container, this will be placed at a good distance from the fire sections to be served by the system. From the container, the respective fire sections are supplied with water via long pipe stretches which are filled with water as long as the fire water system is activated. In the present system, these pipe stretches in a fire situation will be quickly filled with water, the distribution manifold at the upstream side being in open connection with a water- filled buffer tank which, in cooperation with a supply unit for gas, is arranged to prevent the water pressure upstream of the manifold to sink below a defined level. Consequently, when deluge valves are activated, water will quickly be forced into the relevant pipe stretch by a driving pressure corresponding to the defined level. This level is chosen such that the pipe stretches are filled quickly, but not so quickly that there is a risk that harmful pressure surges will arise. In this manner the fire extinction can start quickly, independently of whether the fire water pumps require a long start-up time. When the fire water system is installed on an offshore platform, the container preferably should be placed on the platform deck proper. By collecting the elements of the system in this manner, one achieves a number of economic and operation-technical advantages as compared with the traditional solutions wherein the different elements in different ways are distributed around the platform. In this manner the pipe work can be considerably simplified. As mentioned above, it is common today to use one or more ring mains having an outlet to the different fire sections. The ring mains now can be replaced by a short distribution manifold without isolating valves. The reason that isolating valves are not needed, is that the container which contains the distribution manifold, can be placed at a secure place of the platform. The isolating valves in a ring mains are necessary to prevent damage of the pipes, and that parts of the ring mains must be isolated, for example in connection with fires and explosions. Another cost-saving effect is that one is let off providing for heated compartments for the deluge valves and frost-proofing of divers shut off valves, since these may be placed within the container, which preferably should be heated in order to ensure a reliable starting of the pumps. In a further advantageous embodiment the buffer tank comprises a number of tubular containers, e.g. long water-filled tubes having tight end surfaces. These tubes can be installed beneath the ceiling or along the walls in the container. Tubes having a relatively large cross-section connect the lower part of the buffer tank with the distribution manifold, and the buffer tank is cooperating with said gas supply unit. This supply unit in principle comprises a gas pressure control valve that can supply a sufficient quantity of gas for maintaining a predetermined minimum pressure in the buffer tank. The buffer tank thereby can provide for the necessary supply of water to the relevant fire site until the time when the fire water pumps have come properly into operation. The invention will be further described below in connection with an exemplary embodiment with reference to the drawings, wherein Fig. 1 shows a schematic perspective view of an arrangement according to the invention, and Fig. 2 shows a perspective view of a platform on which there is installed a fire water system designed in accordance with the invention. In the embodiment of Fig. 1, the elements of the arrangement are shown to be installed within an enclosure in the form of a container 1 (shown with broken lines). The arrangement comprises a distribution manifold 2 having an inlet or upstream side 3 and an outlet or downstream side 4. Via a conduit or pipeline 5, the upstream side is in open connection with a number of fire water pumps of which one is symbolically shown at 6. The upstream side 3 also is in connection with a buffer tank 7 for water via a number of conduit lengths 8 on which associated valves 9 are connected. In the illustrated embodiment, the buffer tank is a tubular container installed beneath the ceiling in the container and which extends in the longitudinal direction thereof. The buffer tank is coupled to a gas supply means 10 via a conduit 11. The downstream side 4 of the distribution manifold 2 is connected to a number of deluge valves 12 which, via respective conduit lengths 13, are coupled to associated outlets 14 from the container 1 to the relevant pipe stretches (23 in Fig. 2) leading to the respective fire sections. On the conduit lengths 8 and 13 there are further shown to be connected respective pairs of shut-off valves 15 and 16, respectively, more specifically a valve 15 on each side of the valves 9, and a valve 16 on each side of the deluge valves 12. These shut-off valves are necessary in order to isolate the different types of valves when overhaul or replacement is to be carried out. As regards the gas supply means 10, this is designed and dimensioned so as to have a pressure which is sufficient to see to it that the water pressure on the upstream side of the distribution manifold 2 does not sink below a predetermined level after activation of the deluge valves 12. In a normal situation the buffer tank 7 will be approximately 100 % water- filled. When a fire is warned, a deluge valve 12 opens and thereby opens the connection between the distribution manifold 2 and the associated outlet 14, here fed through the ceiling of the container and bringing the water supply to the relevant fire site. ,,\ ' It is here to be remarked that the deluge valves in a traditional fire water system are placed relatively close to the fire section they are to provide with water. The pipe connection between the deluge valves and the relevant fire site therefore is normally relatively short and is not filled with water before the deluge valves open. In the arrangement according to the invention, the pipe stretches between the deluge valves and the fire site can be substantially longer. The pressurised water supply means 7, 10 thereby has an important function, as it can be dimensioned so as to fill the relevant pipe stretch with water during the time from the opening of the relevant deluge valves until the time when the fire water pumps have come into operation. This implies that the size of the buffer tank 7 and the predetermined delivery pressure to the gas supply means 10 must be adapted to the relevant fire water system. Important factors here will be the characteristics of the deluge valves which are used. Traditional deluge valves will adjust themselves to a maximum opening until the pressure in the pipe system to the fire site has risen to the operational pressure. When this type of deluge valves are utilised, one will normally chose to keep the predetermined delivery pressure of the supply means 10 relatively low. Soon deluge valves will be on the market, which do not open until their upstream pressure has reached a given level. When these valves are to be used in connection with the invention, it may be necessary to set the delivery pressure of the gas supply means higher in order that the pipe system shall be filled with water ahead to the fire site until the pumps have come into operation. The buffer tank 7 will be provided with a venting valve (not shown) letting out the gas in the buffer tank until it again is almost completely filled with water. This water is supplied via a non-illustrated permanently open duct between the distribution manifold and the buffer tank. Fig. 2 shows a prospective view of an offshore platform 20 of which is installed a schematically shown fire water system designed in accordance with the invention. As will be seen, the system is provided with a duplicated arrangement according to the invention, namely two containers 1 arranged at a large distance from each other on the platform deck 21. Fire water for all fire sections 22 is provided by a pair of dedicated pipe stretches 23 having a maximum physical separation. In this manner an increased system security is obtained. As will be understood from the foregoing description, the arrangement according to the invention constitutes a commercial, modularised unit wherein the products requiring expertise are placed within a delimited area. The remaining work including the laying of pipes, the choice of nozzles and the nozzle positioning, the placing of hydrants and water guns and the purchase of such equipment will in this connection become "low technology". This work is also to a larger extent dependent on the arrangement on the platform and will require more personal resources to get the equipment in place. The assembly of the equipment on the platform is very simple in that it in principle represents one crane lift per container onto the platform. Among other advantages there may be mentioned that inspection and maintenance become substantially simpler because the different elements are collected within a delimited area. The whole distribution manifold is physically separated from fires and explosions in that it is preferably placed in a fire-insulated container. Generally, the fire water pumps will be placed where there is a minimum probability that they will be affected by such events as fires and explosions. The integrated solution also improves the possibility for standardising the construction and production of fire water systems.

Claims: P a t e n t c l a i m s 1. Arrangement in a fire water system, especially for an offshore platform (20), wherein the system includes one or more fire water pumps (6) connected through a pipe system (2-5) to a number of deluge valves (12) coupled to associate pipe stretches (23) leading to respective fire sections (22), characterised in that it comprises a distribution manifold (2) having an upstream side (3) which is in open connection with fire water pumps (6) and with a buffer tank (7) for water, and having a downstream side (4) connected to the deluge valves (12) which are coupled to said pipes stretches (23), and that there is also provided a gas supply means (10) connected to the buffer tank (7) and having a pressure which is sufficient to see to it that the water pressure at the upstream side of the distribution manifold does not sink below a predetermined level after activation of the deluge valves (12), said distribution manifold (2) and the deluge valves (12), preferably also the buffer tank (7) and the gas supply means (10), being arranged as an integrated unit within a delimited area. 2. Arrangement according to claim 1, characterised in that the distribution manifold (2) and the deluge valves (12) are mounted within a container (1) constituting the delimited area, the deluge valves (12) being coupled to respective outlets (14) from the container (1) to said pipe stretches (23). 3. Arrangement according to claim 2, characterised in that also the buffer tank (7) and the gas supply means (10) are installed in the container (1). 4. Arrangement according to claim 2 or 3, characterised in that also the fire water pumps (6) are installed in the container (1). 5. Arrangement according to claim 3 or 4, characterised in that the buffer tank (7) comprises a number of tubular containers. 6. Arrangement according to one of the claims 2-5, characterised in that the container (1) is heated. 7. Arrangement according to one of the claims 2-6, characterised in that the container (1) is fire insulated.

Inventors: OTTESTAD NILS T, WICHSTROEM FINN, OTTESTAD, NILS, T., WICHSTROEM, FINN
Applicants: AKER TECHNOLOGY AS, OTTESTAD BREATHING SYST AS, OTTESTAD NILS T, WICHSTROEM FINN, OTTESTAD BREATHING SYSTEMS AS, OTTESTAD, NILS, T., WICHSTROEM, FINN
Application year: 2001
Main classification: A62C35
IPC codes: A62C3, A62C35