Feedwater flow

Fig. 13. A hoUow-fibet reverse osmosis membrane element. Courtesy of DuPont Permasep. In this twin design, the feedwater is fed under pressure into a central distributor tube where half the water is forced out tadiaUy through the first, ie, left-hand, fiber bundle and thus desalted. The remaining portion of the feedwater flows through the interconnector to an annular feed tube of the second, ie, right-hand, fiber bundle. As in the first bundle, the pressurized feedwater is forced out tadiaUy and desalted. The product water flows through the hoUow fibers, coUects at each end of the element, and exits there. The concentrated brine from both bundles flows through the concentric tube in the center of the second bundle and exits the element on the right.

Eig. 19. Flow diagram of the experimental solar RO unit at Cadatache, France. Feedwater flow = 1.38 L/s, product water flow = 0.69 L/s, energy... 

In a ouce-throiigh system, the feedwater entering the unit absorbs heat until it is completely couveided to steam. The total mass flow through the waterwall tubes equals the feedwater flow and, during uorm operation, the total steam flow As only steam leaves the boiler, there is no need for a steam drum. 

Loss of RCS flow (one loop) 22. Feedwater flow instability from mechanical can... 

Total loss of feedwater flow (all loops) 39. Automatic trip - no transient condition... 

The large water inventory above the core provides a long time to respond to a feedwater flow interruption or a loss-of-cool accident. 

Thus, in this example, assumption of the deaeration steam allows the steam balance to be closed. However, this is based on an assumed deaerator flow. The actual flow to the deaerator can be calculated from a heat balance around the deaerator. Figure 23.23 shows the flows into and out of the deaerator. If the boiler feedwater flow and condensate flows are known, together with an assumed value of the vent steam, then the flowrate of deaeration steam can be calculated from an energy balance. 

The BWR reqnires substantially lower primary coolant flow through the core than pressurized water reactors. The core flow of a BWR is the sum of the feedwater flow and the recirculation flow, which is typical... 

Figure 15.54b is a schematic of a feedforward controller applied for steam drum level control. If the flow rate of the makeup feedwater is equal to the steam usage, the drum level remains constant. One is tempted to conclude that the feedforward controller is aU that is needed for this application. Unfortunately, the measurements of the steam usage and the feedwater flow rate are not perfectly accurate. Even small errors in measured flow rates add up over time, leading to one of two undesirable extremes. The drum can till with water and put water into the steam system, or the liquid level can drop, exposing the boiler tubes, which can damage them. As a result, neither feedback nor feedforward are effective by themselves for this case. In general, feedforward-only controllers are susceptible to measurement errors and umneasured disturbances, and, as a result, some type of feedback correction is typically required. 

The relatively simple, lumped-parameter system model described above has been tested against and used in earnest to analyse the behaviour of the boiler recirculation loops of a number of power stations. It has been found to give excellent quantitative predictions of all the variables whose trends are important for control engineering purposes, namely steam drum pressure and temperature, feedwater flow, steam production, downcomer flow and, very important, drum water level. 

An industrial reverse osmosis plant usually will consist of three separate sections which are shown in Figure 4.2. The first section is the pretreatment section in which the feedwater is treated to meet the requirements of reverse osmosis element manufacturers and the dictates of good engineering practice. Following pretreatment, the feedwater is introduced into the reverse osmosis section where the feedwater is pressurized and routed to the reverse osmosis elements which are in pressure vessels. The feedwater flows across the membrane surface where product water permeates through the membrane and a predetermined amount remains behind as reject. The reject is discharged to waste while the product water is routed to the posttreatment section. The third or posttreatment section treats the product water to remove carbon dioxide and adds chemicals as required for industrial use of the product water. 

Low system pressure Steam/feedwater flow xnistnatch in B SO ... 

U-12 Loss of feedwater flow to one steam generator loop 3 per loop... 

The fuel element hole pattern of two fuel holes per coolant hole and the pitch between the holes was selected to meet the core pressure drop limit in addition to limits on fuel temperature. In addition, the coolant channel roughness and the minimum pressure drop through the plenxim elements are limited to ensure that the active core pressure drop limit of 5 psi is met. The calculated equilibrivun cycle peak active core pressure drop at the nominal 100 percent feedwater flow operating conditions is 4.33 psi. 

Notes Feedwater flow rate = 45 rn /h. Reiect/brine osmotic pressure range = 3.1 (I)—7 (VI) bar. RO pump w = 80%. RO pump motor w = 90%. Calculated specific energy for the BWRO unit only. Source [8]. 

The heat exchanged (in either direction) by the primary system with the steam generators during the accident can be simulated by a term decreasing from a given value at an initial time down to zero at a given subsequent time. This term may simulate, for example, the heat absorbed by the residual water of the secondary side of the steam generators after a stop of the feedwater flow. 

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