Vapor generator start-up system

Claim 2

A once-through vapor generator comprising: a main flow path including a plurality of heating surfaces, a point of use, and an outlet end of said heating surfaces connected to said point of use; a startup bypass system which includes; a first conduit leading from the main flow path from said heating surfaces outlet end; a pressure-reducing means in said conduit; a second conduit connected adjacent the inlet end of the pressure-reducing means leading back to said main flow path, connected to the latter at a point downstream of the first conduit in communication with said point of use; the second conduit also containing a pressure-reducing means including control means comprising a first input means responsive to vapor temperature at the heating surfaces outlet end, and a second input means responsive to vapor conditions at said point of use, said second input means being responsive when said heating surfaces outlet end reaches a predetermined temperature.

Claim 3

The generator of claim 1 further including a shutoff valve positioned in the main flow path between the points of connection of the first and second conduits.

Claim 4

The generator of claim 2 including a turbine at said point of use, wherein said second input means comprises a first pressure control means responsive to the pressure upstream of the turbine inlet end and a second load control means responsive to the load demand on the turbine; said first input means sensitizing said pressure and load control means when the temperature reaches a predetermined value at said heating surfaces outlet end.

Claim 5

The generator of claim 3 wherein said pressure-reducing means in said first conduit includes control means therefor responsive to the pressure at the outlet end of the generator-heating surfaces.

Claim 6

The generator of claim 4 further including burner means, and control means therefor responsive to the temperature at the outlet end of said heating surfaces.

Claim 7

The generator of claim 5, wherein said heating surfaces include primary and finishing superheating surfaces, said generator further including; pressure-reducing means upstream of said finishing superheating surface arranged to reduce the pressure in the finishing superheater and reduce the pressure breakdown in the pressure-reducing means in said second conduit during a hot restart.

Claim 8

A once-through vapor generator for use with a vapor turbine which comprises a main flow path including in series flow relationship radiantly heated surfaces and primary and finishing superheating surfaces, an outlet end for said finishing superheating surface, said primary and finishing superheating surfaces being positioned in high temperature convection zones of said generator; a reheating surface positioned in a lower temperature convection zone of said generator; a startup bypass system including a first conduit which leads from said main flow path from said finishing superheating surface outlet end; pressure reducing means in said conduit; a second conduit connected adjacent to the inlet end of said pressure-reducing means leading back to the main flow path, connected to the latter to a point downstream of said first conduit; the second conduit containing a pressure-reducing means including control means therefor responsive to turbine inlet pressure and load once the flow at the finishing superheating surface outlet end reaches a predetermined temperature; shutoff valve means positioned in the main flow path between the points of connection of the first and second conduits; said generator further including between said vapor turbine and radiantly heated surfaces a condenser means, a deaerator and high pressure heat recovery means, in series flow relationship; said bypass system including first, second and third branch conduit means extending from the outlet end of the first conduit pressure-reducing means to said high pressure heat recovery means, deaerating means and condenser means, respectively; valve means in said branch conduit means, the valve means in said third branch conduit means to said condenser means being responsive to the pressure upstream thereof to maintain a set pressure on the downstream side of said first conduit pressure-reducing means.

Claim 9

A once-through vapor generator for use with a vapor turbine which comprises a main flow path including in series flow relationship radiantly heated surfaces and primary and finishing superheating surfaces, an outlet end for said finishing superheating surface, said primary and finishing superheating surfaces being positioned in high temperature convection zones of said generator; a reheating surface positioned in a lower temperature convection zone of said generator; a startup bypass system including a first conduit which leads from said main flow path from said finishing superheating surface outlet end; pressure reducing means in said conduit; a second conduit connected adjacent to the inlet end of said pressure-reducing means leading back to the main flow path, connected to the latter to a point downstream of said first conduit; the second conduit containing a pressure-reducing means including control means therefor responsive to turbine inlet pressure and load once the flow at the finishing superheating surface outlet end reaches a predetermined temperature; shutoff valve means positioned in the main flow path between the points of connection of the first and second conduits; said generator further including between said vapor turbine and radiantly heated surfaces a condenser means, a deaerator and high pressure heat recovery means, in series flow relationship; said bypass system including first, second and third branch conduit means extending from the outlet end of the first conduit pressure-reducing means to said high pressure heat recovery means, deaerating means and condenser means, respectively; valve means in said branch conduit means, the valve means in said third branch conduit means to said condenser means being responsive to the pressure upstream thereof to maintain a set pressure on the downstream side of said first conduit pressure-reducing means.

Claim 10

The generator of claim 7 wherein the pressure-reducing means in said first conduit includes control means responsive to the pressure at said finishing superheating surface outlet end.

Claim 11

The generator of claim 8 wherein the control means for said second conduit pressure-reducing means comprises a first input means responsive to vapor temperature at said finishing superheating surface outlet end, and a second input means responsive to the turbine inlet pressure and load once the flow at the finishing superheating surface outlet end reaches a predetermined temperature.

Claim 14

The method of claim 10 wherein said bypassed flow is reduced in pressure and used in the reduced pressure state for the recovery of heat therein.

Claim 15

The method of claim 11 wherein the portion of the bypassed flow returned to the main flow path is also reduced in pressure to a set pressure, the amount returned to the main flow path during part of the startup period being that required to maintain said set pressure.

Claim 16

The method of claim 10, wherein said generator includes primary and finishing superheating surfaces further including the step of reducing the pressure upstream of said finishing superheating surface to a pressure intermediate the pressure upstream of the finishing superheating surface and the reduced pressure of the flow returned to said main flow path.