Once-through steam generator

Abstract

A once-through steam generator includes a combustion chamber, the walls of which comprise vertically arranged evaporator pipes connected to one another in gas-tight fashion by pipe webs, through which evaporator pipes flows a flow medium from bottom to top. The evaporator pipes are combined by upstream inlet collectors to form more intensely and less intensely heated pipe groups. A feed water supply is assigned to respective inlet collectors. At least one regulating valve regulates throttling of the mass flow of the flow medium into the evaporator pipes. To determine a control variable for the regulating valve, temperature measurement device measures outlet temperatures of the flow medium exiting the evaporator pipes. Each of the more intensely and less intensely heated pipe groups is assigned to one of the inlet collectors and to an outlet collector, and each of the outlet collectors has one of the temperature measurement devices.

Claims

1. A once-through steam generator, comprising: a burning chamber of substantially rectangular cross section, the burning chamber walls of which comprise substantially vertically arranged evaporator tubes of the once-through steam generator which are connected to one another in a gastight manner via tube webs and are flowed through by a flow medium from the bottom to the top, wherein the evaporator tubes of the burning chamber walls are combined in accordance with their degree of heating by inlet headers which are arranged upstream in each case to form more heated tube groups and less heated tube groups, and wherein the respective inlet headers are assigned a feed water supply, at least one control valve provided in the region of the feed water supply for the controlled throttling of the mass flow of the flow medium in the evaporator tubes, temperature measuring devices for measuring outlet temperatures of the flow medium from the evaporator tubes located in the region of outlet headers which are arranged downstream in order to determine a control variable for the at least one control valve, wherein each of the more heated tube groups and less heated tube groups are assigned in each case to one of the inlet headers and an outlet header, wherein each of the outlet headers has one of the temperature measuring devices, and wherein the less heated tube groups being corner wall regions of the substantially rectangular burning chamber, and wherein each of the four corner wall regions has a dedicated feed water supply line with in each case one control valve, and a controller configured to reduce the feed water supply of the less heated tube groups by throttling of the at least one control valve to such an extent that outlet temperatures of the more heated tube groups are equalized to those of the less heated tube groups.

2. The once-through steam generator as claimed in claim 1, wherein the more heated tube groups are middle wall regions of the substantially rectangular burning chamber, and each of the four middle wall regions has a dedicated feed water supply with in each case one control valve.

3. The once-through steam generator as claimed in claim 1; wherein the controller is further configured to reduce the feed water supply of the more heated tube groups by throttling of the at least one control valve to such an extent that the outlet temperatures of the more heated tube groups are equalized to those of the less heated tube groups.

4. The once-through steam generator as claimed in claim 1; wherein the controller is further configured to establish an equalization of the outlet temperatures between the more heated and less heated tube groups.

5. The once-through steam generator as claimed in claim 1, wherein the once-through steam generator comprises a forced-flow steam generator.

6. A method, comprising: operating a once-through steam generator comprising: a burning chamber of substantially rectangular cross section, the burning chamber walls of which comprise substantially vertically arranged evaporator tubes of the once-through steam generator which are connected to one another in a gastight manner via tube webs and are flowed through by a flow medium from the bottom to the top, wherein the evaporator tubes of the burning chamber walls are combined in accordance with their degree of heating by inlet headers which are arranged upstream in each case to form more heated tube groups and less heated tube groups, and wherein the respective inlet headers are assigned a feed water supply; at least one control valve provided in the region of the feed water supply for the controlled throttling of the mass flow of the flow medium in the evaporator tubes; and temperature measuring devices for measuring outlet temperatures of the flow medium from the evaporator tubes located in the region of outlet headers which are arranged downstream in order to determine a control variable for the at least one control valve; wherein each of the more heated tube groups and less heated tube groups are assigned in each case to one of the inlet headers and an outlet header, wherein each of the outlet headers has one of the temperature measuring devices, and wherein the less heated tube groups being corner wall regions of the substantially rectangular burning chamber, and wherein each of the four corner wall regions has a dedicated feed water supply line with in each case one control valve; and reducing the feed water supply of the less heated tube groups by throttling of the at least one control valve to such an extent that outlet temperatures of the more heated tube groups are equalized to those of the less heated tube groups.

7. The method of claim 6, further comprising: reducing the feed water supply of the more heated tube groups by throttling of the at least one control valve to such an extent that the outlet temperatures of the more heated tube groups are equalized to those of the less heated tube groups.

8. The method of claim 6, further comprising: establishing an equalization of the outlet temperatures between the more heated and less heated tube groups.

9. A once-through steam generator, comprising: a burning chamber of substantially rectangular cross section and comprising burning chamber walls which comprise substantially vertically arranged evaporator tubes connected to one another in a gastight manner via tube webs and which conduct a flow medium from the bottom to the top of the burning chamber, wherein the evaporator tubes are combined to form more heated tube groups in middle wall regions of the burning chamber and less heated tube groups in corner wall regions of the burning chamber; a dedicated inlet header and a dedicated outlet header for each tube group; a dedicated feedwater supply line in fluid communication with each inlet header of the less heated tube groups; a control valve in the feedwater supply line for controlling a mass flow of the mass flow medium; a temperature measuring device for measuring outlet temperatures of the flow medium; a controller in signal communication with the temperature measuring device and the control valve and configured to control the mass flow rate of the flow medium in the dedicated feedwater supply line independent of a mass flow rate of the flow medium in the more heated tube groups in order to homogenize an outlet temperature of the flow medium of the less heated tube groups with an outlet temperature of the flow medium of the more heated tube groups.

10. The once-through steam generator of claim 9, further comprising: a dedicated feedwater supply line for each corner region; a dedicated control valve in each feedwater supply line; and a dedicated temperature measuring device for each outlet header; wherein the controller is further configured to control the mass flow rate of the flow medium in each of the corner regions independent of the mass flow rate in other corner regions in order to homogenize an outlet temperature of the flow medium of the corner regions with an outlet temperature of the flow medium of the more heated tube groups.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is now to be explained by way of example using the following figures, in which:

(2) FIG. 1 diagrammatically shows a cross section of an embodiment according to the invention of a once-through steam generator with a rectangular burning chamber,

(3) FIG. 2 diagrammatically shows a second embodiment according to the invention, and

(4) FIG. 3 diagrammatically shows a top view of the embodiment of the once-through steam generator of FIG. 2.

DETAILED DESCRIPTION OF INVENTION

(5) The present invention is based on the concept of segmenting the mass flow distribution of the flow medium which flows through the evaporator tubes in a burning chamber 1 into more heated tube groups 10 and less heated tube groups 11 and to then manipulate their throughflow rates in a targeted manner. In specific terms, this means that wall regions with high heating should have comparatively great throughflow rates and wall regions with low heating should have correspondingly lower throughflow rates. For this purpose, as shown by way of example in FIG. 1 and FIG. 2, the complete burning chamber 1 is divided into representative wall regions E1 to E4 and M1 to M4 with different heating zones. This takes place here at least by way of segmenting of the evaporator tubes into tube groups 10 and 11 by means of inlet headers (not shown in greater detail) at the lower end of the (forced-flow) once-through steam generator.

(6) In the cross section (shown diagrammatically in FIG. 1) through the once-through steam generator of the burning chamber 1, twelve segmented tube groups 10 and 11 can be seen. Here, each burning chamber wall is assigned two inlet header segments at the corners and an inlet header segment which lies in between. Here, each of the inlet header segments is assigned to a wall region with representative heating, the less heated corner wall regions E1 to E4 and the more heated middle wall regions M1 to M4 here, the corner wall regions E1 to E4 being assigned in each case two inlet header segments at the corner of two adjacent burning chamber walls. Here, each corner wall region E1 to E4 is assigned a feed water supply line S1 to S4 for supplying feed water to the corresponding inlet headers (14). Here, as shown in FIG. 1, they can branch off correspondingly from a feed water main supply line 20 and can supply in each case two tube groups of adjacent burning chamber walls in each corner wall region via the corresponding inlet header segments with feed water (indicated by way of arrows in FIG. 1). Here, the feed water main supply line 20 and the feed water supply lines S1 to S4 form the feed water supply to the tube groups 11 of the corner wall regions. If a control valve R is then provided in the feed water main supply line 20, different loads and also design uncertainties in the assumed heat distribution to the individual corner wall regions E1 to E4 can be reacted to adequately, by the feed water mass flow which is supplied to the evaporator tubes of the tube groups 11 of the corner regions E1 to E4 being adapted to the current operating conditions by way of controlled opening or closing of the control valve R. FIG. 1 does not show the supply of the tube groups 10 of the middle wall regions M1 to M4 with feed water from the feed water main supply line 20.

(7) By means of temperature measuring means which are provided in the region of outlet headers which are arranged downstream in order to measure the outlet temperatures of the flow medium, the feed water supply 20 of the less heated tube groups 11 can be reduced by way of throttling of the control valve R to such an extent that the outlet temperatures of the less heated tube groups 11 are equalized to those of the more heated tube groups 10, and therefore the entire temperature profile at the outlet of the once-through steam generator is homogenized. Impermissibly high temperature imbalances can be prevented effectively and without great outlay in this way, since wall regions with low heat absorption then have lower throughflows and wall regions with great heat absorption have a high throughflow in a manner which is dependent on the measured temperatures.

(8) Here, advantageously, at the evaporator outlet, the temperature measuring means of the more heated tube groups 10 from the middle wall regions can be combined as a highly heated system and the temperature measuring means of the less heated tube groups 11 from the corner wall regions can be combined as a lowly heated system. If the measured temperature of the system which is combined as highly heated is too great, the throughflow through the corner wall regions can be reduced by way of additional throttling of the control valve and the throughflow in the middle wall regions can be raised conversely, with the result that the mean temperature of the middle wall regions is lowered to the desired level.

(9) In order to keep the additional costs and the outlay on control technology manageable or to limit them, the maximum number of individual header segments including associated control valves should be as limited as possible. Here, as shown in FIG. 1, the simplest system consists of only one additional control valve R in the feed water main supply line 20. It is assumed here that the four corner wall regions E1 to E4 of the burning chamber experience virtually the same heating among one another and can therefore be combined via the feed water supply lines S1 to S4 and the feed water main supply line 20 as a common tube group with a common feed water supply. In an analogous manner to this, the remaining wall middle regions M1 to M4 are also combined by way of a corresponding feed water supply (not shown in greater detail, however) to form a common tube group.

(10) If imbalances between the individual corner wall regions E1 to E4 (and possibly additionally also between the individual middle wall regions M1 to M4) among one another are also to be taken into consideration and equalized, a minimum of four control valves R1 to R4 are to be installed in each of the feed water supply lines S1 to S4, as shown in FIGS. 2 and 3. That is to say, each corner wall region E1 to E4 can be supplied with feed water in an individually controlled manner independently of the other corner wall regions. Here, each of the four corner wall systems E1 to E4 advantageously has its own temperature measuring means. Depending on the temperature distribution of the flow medium at the outlet of the respective corner wall region, they are then together throttled individually in such a way that a relatively homogeneous outlet temperature profile is set over the entire wall circumference of the evaporator of the once-through steam generator. However, the outlay on control technology also rises here as expected with regard to the coordination of the individual control valves R1 to R4 among one another. In such an embodiment, there may be an outlet header 16 for each tube group 10, 11, a temperature measuring device 22 for each outlet header 16, and a controller 30 controlling the control valves R1 to R4 in response to information provided by the temperature measuring devices 22.

(11) Combinations of the above-described exemplary embodiments and further additions are conceivable against the background of increasing requirements made of the flexibility during the operation of a power plant facility, and are also included in the invention. For instance, imbalances of the individual middle wall regions M1 to M4 among one another and in relation to the corner wall regions E1 to E4 can additionally also be taken into consideration and equalized if corresponding feed water supply lines and control valves for throttling said highly heated middle wall regions are provided. If dedicated control valves in the supply lines of the tube groups of the corner wall regions E1 to E4 were dispensed with at the same time, the throughflow through the corner wall regions could be limited in this special case in advance, for example by means of fixedly installed throttles, to such an extent that control of the feed water mass flow of the middle wall regions is made possible in the first place. It is only in said circumstances, in the case of a fully open control fitting in the supply lines of the highly heated middle wall systems, that their throughput would be so great that, despite higher heating, the middle wall systems would have lower outlet temperatures in comparison with the corner tube systems. By way of additional throttling of the control valves of the middle wall systems, the throughput through the middle wall systems which has then become too great might be reduced again, in order to homogenize the outlet temperatures of all systems.

(12) In addition to the projected design of the once-through steam generator in order to compensate for temperature imbalances, faulty designs of the distributor system of the feed water supply can also be absorbed comfortably by way of the design according to the invention of the once-through steam generator and the method according to the invention. In addition, heating imbalances which were not taken into consideration during the design of the burning chamber can be handled reliably by way of the present invention without negative consequences. In addition, in some circumstances, fuel combinations can be used which were previously not possible, because heating imbalances can be reacted to flexibly. All in all, the present invention increases the uptime of the once-through steam generator and therefore of the entire power plant facility.