Feed water distribution piping

The module structure also consists of two elements and is shown in Figure 2.20. The center pipe of the RO module is composed of a concentric pipe. Permeate flows in the inner tube of the concentric pipe, and feed water flows between the outer tube and the inner tube of the concentric pipe. Feed water enters the feed center pipe of the feed-side element through the feed-side distribution connector. The distribution connector divides intersecting flow of the feed and permeate. Feed water flows radially outward from the center pipe, past the hollow fibers in the bundle, and away from the element as concentrated brine flow. Feed flow is uniformly distributed in the RO module throughout the crosswound hollow-fiber bundle. 

The CUSH code has been developed to provide a complete representation of a primary circuit containing.several hundred channels with appropriate pumps, steam drums, headers, tall pipes and other features associated with a practical arrangement. Each channel is represented one-dimensionally and such aspects as the appropriate single- and two-phase pressure drops and coolant density distribution are calculated. A three-dimensional specification of the nuclear power distribution is required as input to CUSH. Specifications of the feed-water flow for a given steam output are also needed to determine the sub-cooling at channel entry and may be derived from the JAVAN complete steam plant model. 

Gidropress according to the Russian norms. The Russian designer and manufacturer made the feed water pipelines (secondary side) from carbon steel (GOST norms 20K and 22K). The water inlet pipe was connected to the T-junction. From this point, two pipelines with nozzles distributed the cooling secondary water within the space between the primary pipes. Several problems that had occurred in other NPPs were published in [195,197,198,203]. One disadvantage of such steam generators is the poor accessibility to the T-junction and the pipes in the bundle. 

The basic 1977 design was improved after 1994 by installing a new feed water pipeline system. There was also a change in the type of steel used in these pipes. Instead of conventional carbon steel, austenite steel was used in the distribution boxes as well as the feed water pipes. 

The feed water enters the pipeline distribution system via a nozzle and passes into the left and right inlet lines. From there, the water flows into chambers via pipes (p = 44.5 x 4 mm) and exits via ejectors. This flow is mixed with boiler water, so the final flow in the small primary pipes is not extremely hot and does not cause a very high thermal load. The circulation in the SG tank was also improved in the renovations, and locations with increased salt concentration were reduced. 

The main advantage of this approach is that a visual inspection of the feed water pipe can be performed directly due to the placement of the whole water distribution system over the primary pipe bundle. Using this system, any potential defects are easier to observe. Another advantage arises from the seven boxes with ejectors that mix the feed water with boiler water, thus decreasing the thermal load. An additional advantage is that it is possible to check and exchange of the distribution boxes if they get damaged. 

After five years of operation in SG35, one feed water box and the corresponding distributing pipes were replaced with new ones during an NPP outage in order to allow an analysis of their overall condition and the corrosion products on their walls. For comparison, some parts of the original feed water distribution system from SG46 were cut out and analysed. 

In connection to the planned commissioning of Mochovce NPP 3 and 4 (announced officially on 3 October 2008), it is recommended that all feed water pipes and water distribution systems in the steam generators should be replaced immediately before starting operation with new ones constmcted from austenitic steels. The Bohimice design with feed water distribution boxes is highly recommended, and seems to be acceptable from a practical point of view. 

The blowdown from the boiler(s) will be run to a flash-steam vessel mounted adjacent to the feed tank. Flash steam will be introduced into the feed tank through a dip pipe terminating in a distribution manifold. The drain from the flash vessel may then be taken to a residual blowdown heat exchanger. Any remaining heat is then transferred to the make-up water to the tank before the blowdown runs to drain. 

Almost all feedstocks of interest have such properties that they do not flow readily through cither pipes or shell of a conventional heat exchanger without distribution problems. Afler a number of alternatives had been considered it was concluded that the most adequate way of preheating is direct injection of hot water. In Fig. 3 this is done in vessel V where a stream of hot recycle water is mixed with the feed. A special way of contacting achieves efficient heat and mass transfer. It has been verified in our experiments that at 200-250°C biomass feedstocks of different origin, including wood chips, arc softened and form a pastc-like substance [7,8]. The... 

Water coolant is fed to each fuel channel from below and the steam-water mixture is removed from the top. In order to compensate for variations in power distribution, the coolant supply to individual channels is regulated by isolating and regulating valves which are installed in the channel feed pipes. 

The superficial velocity of the dissolving fluid at the bottom of an upflow dissolver is typically about 2.5 mhr i (say, 2-4). The depth of the salt bed usually is kept above 1.5 m. The feed brine or water enters a sparger-pipe arrangement through one or more peripheral connections. Proper design of the sparger is necessary for good flow distribution. 

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