VERTICAL HEAT RECOVERY STEAM GENERATOR

Abstract

A vertical heat recovery steam generator, the low-pressure stages of which are designed as a once-through system, having a condensate preheater with at least one condensate preheater heating surface, through which a flow medium flows and which is disposed in a hot gas channel through which hot gas flows, a low-pressure preheater with at least one low-pressure preheater heating surface through which the flow medium flows and which is disposed in the hot gas channel, and a low-pressure evaporator with at least one low-pressure evaporator heating surface through which the flow medium flows and which is disposed in the hot gas channel. The flow medium flows successively through the at least one low-pressure preheater heating surface and the at least one low-pressure evaporator heating surface in one pass and without additional pressure compensation.

Claims

1.-7. (canceled)

8. A vertical heat recovery steam generator, low-pressure stages of which are designed as a once-through system, comprising: a condensate preheater with at least one condensate preheater heating surface, through which a flow medium flows and which is disposed in a hot gas channel, through which hot gas flows, a low-pressure preheater with at least one low-pressure preheater heating surface, through which the flow medium flows and which is disposed in the hot gas channel, a low-pressure evaporator with at least one low-pressure evaporator heating surface, through which the flow medium flows and which is disposed in the hot gas channel, wherein the flow medium flows successively through the at least one low-pressure preheater heating surface and the at least one low-pressure evaporator heating surface in one pass and without additional pressure compensation and wherein a first of the at least one low-pressure preheater heating surfaces in the hot gas channel is disposed in a region of a hot gas channel outlet and after a first of the at least one condensate preheater heating surfaces in the hot gas direction or largely in the same region as the first of the at least one condensate preheater heating surfaces.

9. The vertical heat recovery steam generator as claimed in claim 8, wherein the condensate preheater comprises two condensate preheater heating surfaces, through which the flow medium flows successively and which are disposed in a spatially separate manner in the hot gas channel, and wherein the low-pressure preheater comprises two low-pressure preheater heating surfaces, through which the flow medium flows successively and which are disposed in a spatially separate manner in the hot gas channel, wherein a first low-pressure preheater heating surface, through which flow medium flows, is disposed in the hot gas channel after a first condensate preheater heating surface in a hot gas direction, and a second low-pressure preheater heating surface, through which the flow medium subsequently flows, is disposed between the first condensate preheater heating surface and a second condensate preheater heating surface in the hot gas direction.

10. The vertical heat recovery steam generator as claimed in claim 8, further comprising: a branch for feeding the low-pressure preheater with some of the flow medium in a first feed line of the flow medium toward the condensate preheater.

11. The vertical heat recovery steam generator as claimed in claim 10, further comprising: a control valve after the branch, in a second feed line toward the low-pressure preheater, said control valve controlling a quantity of flow medium diverted to the low-pressure preheater.

12. The vertical heat recovery steam generator as claimed in claim 10, further comprising: a circulating pump for the condensate preheater, said circulating pump returning the flow medium heated in the condensate preheater heating surfaces to the first feed line via lines and a first connection point, wherein the first connection point is disposed in the first feed line, ahead of the branch.

13. The vertical heat recovery steam generator as claimed in claim 8, further comprising: a low-pressure circulating pump for the low-pressure preheater and the low-pressure evaporator, said pump returning unevaporated flow medium flowing through the low-pressure preheater and the low-pressure evaporator heating surfaces, via a water/steam separator, a return line and a second connection point, to a second feed line toward the low-pressure preheater.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The invention will now be explained by way of example with reference to the following figures. In the drawing:

[0015] FIG. 1 shows schematically an illustrative embodiment according to the invention of the low-pressure stages of a vertical heat recovery steam generator,

[0016] FIG. 2 shows schematically an illustrative embodiment according to the invention of a vertical heat recovery steam generator with subdivided heating surfaces,

[0017] FIGS. 3-4 show schematically two further illustrative embodiments according to the invention.

DETAILED DESCRIPTION OF INVENTION

[0018] FIG. 1 shows schematically the variant embodiment of a once-through low-pressure system of a vertical heat recovery steam generator, this variant being the advantageous one for ensuring flow stability. Said generator comprises a condensate preheater with a condensate preheater heating surface 20, through which a flow medium (S) flows and which is disposed in a hot gas channel 1, through which hot gas H flows, a low-pressure preheater with a low-pressure preheater heating surface 30, through which the flow medium S flows and which is disposed in the hot gas channel 1, and a low-pressure evaporator with a low-pressure evaporator heating surface 40, through which the flow medium S flows and which is disposed in the hot gas channel 1. Here, the low-pressure preheater heating surface 30 and the low-pressure evaporator heating surface 40 are designed in such a way that the flow medium S flows successively through them in one pass and without additional pressure compensation. Moreover, the low-pressure preheater heating surface 30 in the hot gas channel 1 is disposed after the condensate preheater heating surface 20 in the hot gas direction.

[0019] Moreover, a branch 50 for feeding the low-pressure preheater with some of the flow medium S is provided in a first feed line 24 of the flow medium S toward the condensate preheater. Furthermore, a control valve 35 is provided after the branch 50, in a second feed line 34 toward the low-pressure preheater, said valve controlling the quantity of flow medium S diverted to the low-pressure preheater. Moreover, a circulating pump 23 is provided here for the condensate preheater, said pump returning the flow medium heated in the condensate preheater heating surfaces to the first feed line 24 via lines 25 and 27 and a first connection point 26, wherein the first connection point 26 is disposed in the first feed line 24, ahead of the branch 50.

[0020] FIG. 2 shows a development of the above-described embodiment of a vertical heat recovery steam generator but with a condensate preheater comprising two condensate preheater heating surfaces 21 and 22, through which the flow medium S flows successively and which are disposed in a spatially separate manner in the hot gas channel 1. Moreover, in this case the heat recovery steam generator has a low-pressure preheater with two low-pressure preheater heating surfaces 31 and 32, through which the flow medium S flows successively and which are disposed in a spatially separate manner in the hot gas channel 1, and has a low-pressure evaporator with at least one low-pressure evaporator heating surface 40, which is disposed in the hot gas channel 1 and through which the flow medium S flows after the low-pressure preheater heating surfaces. According to the invention, provision is now made for the first low-pressure preheater heating surface 31, through which flow medium S flows, to be disposed in the hot gas channel 1 after the first condensate preheater heating surface 21 in the hot gas direction and for the second low-pressure preheater heating surface 32, through which the flow medium S subsequently flows, to be disposed between the first and the second condensate preheater heating surface 21 and 22 in the hot gas direction. Furthermore, a branch 50 for feeding the low-pressure preheater with some of the flow medium S is provided in a feed line 24 of the flow medium S to the condensate preheater, wherein the quantity of flow medium S diverted is controlled by a control valve 35. By virtue of the fact that a circulating pump 23 is furthermore provided for the condensate preheater in order to return the flow medium heated in the condensate preheater heating surfaces to the feed line 24 via a line 27 and a connection point 26 and that the branch 50 is disposed downstream of the connection point 26, a flow medium with virtually the same temperature level is now available to both systems.

[0021] FIG. 3 and FIG. 4 show an alternative embodiment of a vertical heat recovery steam generator. In contrast to the embodiment illustrated in FIG. 1 and FIG. 2, a low-pressure circulating pump 52 is also provided here for the low-pressure preheater and low-pressure evaporator circuit in order to return the unevaporated flow medium S flowing through the low-pressure preheater and evaporator heating surfaces to the second feed line 34 via a water/steam separator 60, a return line 51 and a connection point 53. With the aid of suitable evaporator overfeeding, the circulated mass flow passed via the low-pressure circulating pump 52 and the return line 51 can be set precisely to ensure that the desired temperature of the flow medium S is achieved at the inlet to the first low-pressure preheater heating surface.