EP3017247B1 - Once-through steam generator - Google Patents

Description

The invention relates to a continuous steam generator according to the preamble of claim 1, and a method for operating such a continuous steam generator according to claim 5. Such a continuous steam generator is from the DE 19651678 known.

The invention relates specifically to continuous flow or forced flow steam generators for power plants, with a rectangular in cross-section combustion chamber, each combustion chamber wall comprises substantially vertically arranged and via tube webs gas-tight connected evaporator tubes, which are flowed through by a flow medium from bottom to top. The heating of these, the combustion chamber walls forming evaporator tubes, leads here to a complete evaporation of the flow medium in one pass. In principle, the evaporator tubes of the continuous steam generator can be arranged partially or over the entire length vertically or vertically and / or helically or spirally. Continuous steam generators can be designed as forced flow steam generator, wherein the passage of the flow medium is forced here by a feed pump.

Significant advantages of a pure vertical evaporator tube concept are a simple construction of the combustion chamber suspension, a low manufacturing and assembly costs and greater ease of maintenance. Compared to a spirally bored combustion chamber wall, the investment costs can be significantly reduced in this way. Due to the design, however, the temperature imbalances of such vertically drilled evaporator tube concepts are much greater in comparison to spirally bored combustion chambers. While the evaporator tubes in a spiral winding pass through almost all the heating zones of the combustion chamber and thus a good heat balance can be achieved, the individual combustion chamber tubes of the vertical bore remain from the upstream one Evaporator inlet collector to the downstream evaporator outlet collector in the respective heating zone. Thus, pipes in heavily heated combustion chamber areas, z. B. in the vicinity of the burner or in the middle wall region of combustion chambers with rectangular cross-section, over the entire length of the pipe continuous Mehrbeheizung. In contrast, pipes in weakly heated combustion chamber regions, in particular the corner wall pipes of the combustion chamber with a rectangular cross section, experience a lower heating over the entire pipe length. In concepts with spiral-shaped evaporator tubes, the excess and minor admixtures of individual tubes or tube groups are in the low single-digit percentage range. In the case of vertically bored concepts, on the other hand, with regard to the average heat absorption of a single evaporator tube, considerably greater increased and reduced heaters are known. The main challenge with vertically bored combustion chamber walls is therefore the controllability of these large heating imbalances between individual evaporator pipes.

A very effective and already in the DE 4 431 185 A1 The disclosed way of solving the problem described above is a design of the vertical pipe according to the so-called "low-mass-flux" design. In this approach, the lowest possible mass flow densities are sought in the vertical overflow, which open in a positive flow rate characteristic of the individual evaporator tubes. In concrete terms, this means that pipes with a multiple heating have a higher throughput and pipes with a lower heating have a lower throughput. Thus, the occurrence of inadmissibly high temperature imbalances can be counteracted effectively only by a targeted application of physical laws. However, since in recent years, the requirements in terms of plant efficiency have steadily increased and thus steam temperature and pressure have also continuously increased and also increasingly larger load ranges must be covered by the power plant, there is a need of this "low-mass flux" design further. The use of newly developed materials and their controllability in the processing and operation of the power plant make it also necessary to further reduce possible temperature imbalances.

It would be obvious to divide the mass flow distribution over individual combustion chamber wall regions and thus different groups of evaporator tubes and then manipulate these in a targeted manner. Concretely, this means that in a preferred manner wall areas with a high heating should have comparatively large flow rates and wall areas with low heating correspondingly lower flow rates. For this purpose, the combustion chamber must be subdivided into representative wall areas to take account of different heating zones. This is done by segmenting the inlet and outlet collectors. Each collector segment is assigned to a wall area with representative heating. In the inlet area, each collector segment is provided with its own feedwater supply line. By selecting a suitable geometric configuration of these supply lines, or by installing additional orifices in the region of these supply lines, the distribution of the total feed water mass flow can be made targeted to the individual collector segments depending on the particular heating situation.

However, geometrically matched supply lines or throttle diaphragms have the decisive disadvantage that their throttle power changes with the load. Thus, the mass flow distribution in the evaporator and the associated temperature imbalances at the evaporator outlet system can be optimized only for a specific load range. In addition, both the supply lines and the orifices can be targeted and matched to one another only with precise knowledge of the heat distribution over the combustion chamber circumference. Then differs in the operation of the power plant, the occurring heat distribution of the in From the design calculations of the supply lines or orifices used distribution, so in the worst case, the temperature imbalances may even increase. The idea of further securing the design by means of the geometrical adaptation of the supply lines with or without restrictor orifices may even reverse the opposite.

The object of the invention is therefore to provide an improved continuous steam generator and a corresponding method for operating such a continuous steam generator.

This object is achieved with the continuous steam generator with the features of claim 1 and the method with the features of claim 3.

The advantage of the present invention is that the fact that evaporator tubes of the combustion chamber walls are summarized according to their degree of heating by upstream inlet collector respectively to mehrbeheizten pipe groups and underheated pipe groups and in the region of the corresponding feed water supply at least one control valve for controlled throttling of the mass flow of the feedwater and thus the The evaporator tubes flowing through the flow medium is provided, and for determining a controlled variable for the at least one control valve in the range of downstream outlet collectors temperature measuring means are provided for measuring outlet temperatures of the flow medium from the evaporator tubes, so even with almost unchanged design of the continuous evaporator, temperature imbalances a perpendicular bored Combustion chamber in the entire load range of the power plant, with minimal effort effectively minimized. In the best case, this is only an additional control valve to provide as a control valve and a corresponding control concept. The inventive method for operating such a continuous steam generator provides that the feedwater supply throttling of the at least one control valve is reduced to such an extent that the outlet temperatures of the reheated pipe groups are equal to those of the underheated pipe groups or are at a similar level.

Preferably, each of the more heated pipe groups and the lower heated pipe groups are respectively associated with one of the inlet header and one outlet header, and each of the outlet header includes one of the temperature measuring means. Preferably, the temperature measuring means are installed in the outgoing from the outlet headers lines, since a mixing temperature is measured here.

Especially in the case of essentially rectangular combustion chambers, which have pronounced, less heated tube groups in the corner wall regions, it can be advantageous if each of the four corner wall regions has its own feedwater supply line, each with its own control valve. Due to this expansion, which can also be modular if required, a further homogenization of the temperature distribution at the outlet of the vertical perforated evaporator wall of a continuous steam generator can be achieved. Under these circumstances, it is even conceivable that the continuous steam generator from the entrance to the ride in a complete run to bore, so that previously provided reversing collector can be omitted. The possibly necessary for dynamic stability pressure equalization could be realized here with a much cheaper pressure equalization collector.

Further advantageous developments of the continuous steam generator according to the invention or of the forced flow continuous steam generator can be found in the further subclaims.

FIG 1

schematisch im Querschnitt eine erfindungsgemäße Ausbildung eines Durchlaufdampferzeugers mit rechteckiger Brennkammer,

FIG 2

schematisch eine zweite erfindungsgemäße Ausbildung.

The invention will now be explained by way of example with reference to the following figures. Show it:

FIG. 1

schematically in cross-section an inventive design of a continuous steam generator with a rectangular combustion chamber,

FIG. 2

schematically a second embodiment of the invention.

The present invention is based on the idea of segmenting in a combustion chamber 1 the mass flow distribution of the flow medium flowing through the evaporator tubes into reheated tube groups 10 and sub-heated tube groups 11 and then selectively manipulating their flow rates. Concretely, this means that wall sections with high heating should have comparatively large flow rates and wall sections with low heating correspondingly lower flow rates. For this purpose - as in 1 and FIG. 2 illustrated by way of example - the complete combustion chamber 1 divided into representative wall areas E1 to E4 and M1 to M4 with different heating zones. This is done here at least by segmentation of the evaporator tubes in tube groups 10 and 11 by means not shown inlet collector at the bottom of the (forced) continuous steam generator.

In the in FIG. 1 schematically represented cross section through the continuous steam generator of the combustion chamber 1 are twelve segmented pipe groups 10 and 11 can be seen. Each combustion chamber wall are assigned to two inlet collector segments at the corners and an inlet collector segment lying therebetween. Each of the inlet collector segments is assigned to a wall region with representative heating, in this case the less heated corner wall regions E1-E4 and the more heated middle wall regions M1-M4, wherein the corner wall regions E1-E4 are each assigned two inlet collector segments at the corner of two adjacent combustion chamber walls. Each Eckwandbereich E1 to E4 is a feedwater supply line S1 to S4 for supplying feed water to the corresponding inlet headers. These can, as in FIG. 1 represented branch out of a feedwater main supply line 20 and supply in each corner wall region in each case two pipe groups of adjacent combustion chamber walls via the corresponding inlet collector segments with feed water (in FIG. 1 indicated by arrows). The feedwater main supply line 20 and the feedwater supply lines S1 to S4 thereby form the feedwater supply to the tube groups 11 of the corner wall portions. Now, if a control valve R is provided in the feedwater main supply line 20, it can be adequately responded to different loads and to design uncertainties in the assumed heat distribution to the individual Eckwandbereiche E1 to E4, by controlled by opening or closing the control valve R, the evaporator tubes the pipe groups 11 of Eckwandbereiche E1 to E4 supplied feedwater mass flow, the current operating requirements is adjusted. Not shown in the FIG. 1 the supply of the pipe groups 10 of the middle wall portions M1 to M4 with feed water from the feedwater main supply line 20th

By means provided in the region of downstream outlet headers temperature measuring means for measuring the outlet temperatures of the flow medium, the feed water supply 20 of the underheated pipe groups 11 is reduced by throttling the control valve R extent that match the outlet temperatures of the underheated pipe groups 11 of the reheated pipe groups 10 and thus the entire temperature profile at the outlet of the continuous steam generator uniformed. Inadmissibly high temperature imbalances can be prevented so effectively and without much effort, since depending on the measured temperatures, wall areas with low heat absorption now lower flow and wall areas with high heat absorption have a high flow.

Preferably, at the evaporator outlet, the temperature measuring means of the reheated tube groups 10 from the middle wall regions can be summarized as "high-heated" and the temperature measuring means of the underheated tube groups 11 from the corner wall regions as a "low-heated" system. If the measured temperature of the combined "high-heated" system is too large, so can be reduced by additional throttling of the control valve, the flow through the corner wall areas and reversed in the middle wall areas are raised, so that lower the mean temperature of the middle wall areas to the desired level leaves.

In order to keep the additional costs and the control engineering effort manageable or to limit, the maximum number of individual collector segments and associated control valves should be limited as much as possible. The simplest system is, as in FIG. 1 It is assumed that the four corner wall portions E1 to E4 of the combustion chamber undergo almost the same heating to one another and so via the feedwater supply lines S1 to S4 and the feedwater main supply line 20 as a common tube group with a common feedwater supply can be summarized. Analogously, the remaining wall center regions M1 to M4 are combined by a corresponding, but not shown, feedwater supply to a common pipe group.

If skewed positions between the individual corner wall regions E1 to E4 (and possibly also also between the individual middle wall regions M1 to M4) are to be taken into account and compensated for each other, then - as in FIG. 2 illustrated - to install at least four control valves R1 to R4 in each of the feedwater supply lines S1 to S4. This means that each corner wall region E1 to E4 can be regulated independently of the other corner wall areas feed water be supplied. Advantageously, here each of the four corner wall systems E1 to E4 has its own temperature measuring means. Depending on the temperature distribution of the flow medium at the outlet of the respective corner wall region, these are now throttled individually in a manner such that a relatively uniform outlet temperature profile is established over the entire wall circumference of the evaporator of the continuous steam generator. With regard to the coordination of the individual control valves R1 to R4 with each other but also increases as expected, the control engineering effort.

Combinations of the embodiments described above and other additions are conceivable against the background of increasing demands on the flexibility during the operation of a power plant and are included in the invention. Thus, in addition, inclinations of the individual center wall regions M1 to M4 can also be taken into account and compensated for one another with respect to the corner wall regions E1 to E4 if corresponding feedwater supply lines and control valves for throttling these highly heated central wall regions are provided. If at the same time one would do without separate control valves in the supply lines of the tube groups of the corner wall regions E1 to E4, the flow through the corner wall regions, for example by means of permanently installed throttles, would have to be limited to such an extent in the first instance that regulation of the feedwater mass flow of the central wall regions would be possible in the first place becomes. Only in these circumstances would be at full open control valve in the supply lines of the highly heated central wall systems whose throughput so large that despite higher heating, the center wall systems would have lower outlet temperatures compared to the Eckrohrsystemen. By an additional throttling of the control valves of the center wall systems, the now too large throughput through the center wall systems could be reduced again to even out the outlet temperatures of all systems.

In addition to the projected design of the continuous steam generator for the compensation of temperature imbalances can be cushioned comfortably with the inventive design of the continuous steam generator and the method according to the invention but also misinterpretations of the distribution system of the feedwater supply. In addition, heating imbalances that were not taken into account in the design of the combustion chamber, by the present invention safely handled without negative consequences. In addition, under certain circumstances fuel combinations can be run that were previously not possible, because it can respond flexibly to heating imbalances. All in all, the present invention increases the availability of the continuous steam generator and thus the entire power plant.

Claims (5)

1. Once-through steam generator, in particular forced-flow steam generator, having a burning chamber (1) 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 can be flowed through by a flow medium from the bottom to the top, the evaporator tubes of the burning chamber walls being combined in accordance with their degree of heating by inlet headers which are arranged upstream in each case to form more heated tube groups (10) and less heated tube groups (11), and the respective inlet headers being assigned a feed water supply (20, S1, S2, S3, S4), and at least one control valve (R, R1, R2, R3, R4) being provided in the region of the feed water supply (20, S1, S2, S3, S4) for the controlled throttling of the mass flow of the flow medium in the evaporator tubes, and temperature measuring means for measuring outlet temperatures of the flow medium from the evaporator tubes being provided in the region of outlet headers which are arranged downstream in order to determine a control variable for the at least one control valve (R, R1, R2, R3, R4), and each of the more heated tube groups (10) and less heated tube groups (11) being assigned in each case to one of the inlet headers and an outlet header, and each of the outlet headers having one of the temperature measuring means and the less heated tube groups (11) being corner wall regions (E1, E2, E3, E4) of the substantially rectangular burning chamber (1), and each of the four corner wall regions (E1, E2, E3, E4) having a dedicated feed water supply line (S1, S2, S3, S4) with in each case one control valve (R1, R2, R3, R4)
2. Once-through steam generator according to Claim 1, characterized in that the more heated tube groups (10) are middle wall regions (M1, M2, M3, M4) of the substantially rectangular burning chamber (1), and each of the four middle wall regions (M1, M2, M3, M4) has a dedicated feed water supply with in each case one control valve.
3. Method for operating a once-through steam generator which is configured according to one of Claims 1 to 2, characterized in that the feed water supply (20, S1, S2, S3, S4) of the less heated tube groups (11) is reduced by way of throttling of the at least one control valve (R, R1, R2, R3, R4) to such an extent that outlet temperatures of the more heated tube groups (10) are equalized to those of the less heated tube groups (11).
4. Method according to Claim 3, characterized in that the feed water supply of the more heated tube groups (10) is reduced by way of throttling of the at least one control valve to such an extent that the outlet temperatures of the more heated tube groups (10) are equalized to those of the less heated tube groups (11).
5. Method according to Claim 3 or 4, characterized in that an equalization of the outlet temperatures is established between the more heated (10) and less heated (11) tube groups.

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