E Ireland wrote:
As I understand it yes, you simply need a feedwater pump group (with redundancy) for each heater, which in the traditional calculation adds more complexity than can be justified.
However now nuclear boilers cost an enormous sum and pumps and drives for the same get relatively cheaper every year.
Additionally building pressure vessels large enough for high pressure open heaters becomes problematic - but I think prestressing largely solves that issue.
Building big pressure vessels without excessive wall thickness is pretty easy, using shipyard type steel plate - beam technology. Basically submarine tech, but easier as you only have to deal with internal pressure rather than much more limiting external pressure in a sub.
My question on open FW heaters all the way is more along the lines of can it work at all, from several angles. Basically does it work for all the 6-9 stages of FW heating, or is there some problem that prevents this (to my knowledge this is never done?)
Quote:
In my last flow sheet the condenser pressure was 3kPa, and the first three feedwater heaters were 7.4kPa, 25kPa and 70kPa, which means there is a total head of only 7m across them, so now that we have 72" blade turbines with exhaust diameters of over seven metres, we could potentially stack the first three heaters on top of each other and use the weight of the water in the heater 'hotwells' to provide the necessary pressure increase, whilst only requiring a single pump, the lowest pressure heaters could draw from the top of the turbine housing and the higher pressure heaters from the bottom fo the turbine housing, thus keeping the feed lengths short.
That's pretty ambitious but sounds workable. Generally I'm not a big fan of stacking equipment due to access/maintenance/inspection/replacement reasons. I generally prefer larger floor plans with access from the top - 360 deg. access becomes unnecessary so a lot of space and complexity is saved in the end.
Steam injectors can have big applications, I think, in LWRs. A lot of the FW pump duty can be replaced by the steam injector and simultaneously allow open FW heaters. Two in one blow. I would not underestimate the issues with FW pump capacity - for the ESBWR for example, the FW pumps set the plant electrical (house) loads, as they have to be sized for transient water flow (some ATWS events IIRC) as well as having redundancy. These things are massive. Having lower pressure drop throughout the FW chain by using open FW heaters and/or airfoil PCHE would help a lot here, limiting house loads and improving efficiency.