Forced-circulation once-through

Figure 5.6 Forced-circulation once-through reboiler.

A2.2.2 Fuel System—Freshly filtered and aerated fuel is initially placed in a reservoir, then circulated once through the apparatus to a spent sample receptacle. Motive force for the sample is a positive displacement pump that will maintain flow at 3.0 mL/min and overcome any tendency of initial filter blockage from affecting the flow rate. Deviation of 10 % in flow rate is permitted. If filter blockage becomes severe, the bypass valve located before the test filter can be opened in oi r to finish the test. Then, any deposit on the... 

Certain boilers employ forced circulation, whereby a pump helps impart the circulation through the downcomer lines to the waterwaH header, particularly to improve or control circulation at low loads. Forced-circulation pumps are also required in high pressure and supercritical pressure boilers, because once the pressure within a boiler approaches the critical pressure, 22.1 MPa (3208 psia), the densities of the water and steam become similar, limiting or eliminating the potential for natural circulation. 

Steam-Generator Circulation System Circulation systems for utility application are generally classified as natural circulation and forced or pump-assisted circulation in drum-type boilers, and as once-through now in subcritical- and supercriticaf-pressure boilers. The... 

Figure 5.6 shows a once-through forced-circulation reboiler. Such a reboiler differs from a thermosyphon reboiler in that it has a pump to force circulation, rather than rely on natural or thermosyphon circulation. This seems rather wasteful—and it is. 

Thus, it is not uncommon for heat sensitive products to be concentrated in two different evaporator types in series—in natural or forced circulation evaporators to perform the bulk of the solvent removal and in a low mean residence time evaporator to finish the concentration step. Because of the recycle and back mixing effects of a natural or forced circulation evaporator, the mean residence time of the average molecule can be several hours. Some evaporators operate without recycle these are called once-through or single... 

The heat produced in reactor is transferred to tertiary circuit through steam generator. There are four identical modules of 12.5 MWt capacity located inside an insulated casing. It is a forced circulation, counter current, shell and tube once through type of steam generator. 

Canned motor MCPs eliminate the need for an MCP seal, and basically eliminate a potential for SBLOCA associated with seal failure. The modular type once-through SGs is located relatively high above the core to provide a driving force for natural circulation flow. This design feature along with low flow resistance enables the capability of the system to have natural circulation with the maximum power of 25%. 

A deep bed, sufficiently small or stratified particle sizes, and/or a small coolant fraction could produce dryout in the bed even after it is initially quenched. Forced circulation of coolant through some possible configurations of in-vessel debris bed would be required to prevent dryout. Maintaining forced circulation was considered to be of paramount importance once it was re-established at TMI-2. 

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