EP2321578B1 - Continuous steam generator - Google Patents

Description

The invention relates to a continuous steam generator having a combustion chamber with a number of burners for fossil fuel, the heating gas side in a top region via a horizontal gas is followed by a vertical gas train, the Umfassungswand the combustion chamber of gas-tight welded together, a Wasserabscheidesystem flow medium side upstream evaporator tubes and gas-tight with each other welded, the Wasserabscheidesystem flow medium side downstream superheater tubes is formed, wherein the Wasserabscheideystem comprises a number of Wasserabscheideelementen, each of the Wasserabscheideelemente comprises a connected to the respective upstream evaporator tubes Einströmrohrstück, seen in its longitudinal direction merges into a Wasserableitrohrstück, wherein in the transition region, a number of Abströmrohrstücken branches off, the verb with an inlet header of the respective downstream superheater tubes verb are unden.

In a fossil-fueled steam generator, the energy of a fossil fuel is used to generate superheated steam, which can then be supplied to power a steam turbine, for example, in a power plant. Steam generators are usually designed as water tube boilers, in particular in the steam temperatures and pressures typical in a power plant environment, that is to say the supplied water flows in a number of tubes, which store the energy in the form of radiant heat of the burner flames and / or by convection and / or by heat conduction from the flue gas produced during combustion.

In the field of burners, the steam generator tubes usually form the combustion chamber wall by being welded together in gas-tight fashion. In further, the combustion chamber Smoke gas side downstream areas can also be provided in the exhaust duct arranged Dampfzeugerrohe.

Fossil fueled steam generators can be categorized by a variety of criteria: based on the flow direction of the gas flow, steam generators can be classified, for example, into vertical and horizontal types. In fossil-fueled steam generators in vertical construction usually a draw-in and two-pass boiler are distinguished.

In a feeder or tower boiler, the flue gas produced by the combustion in the combustion chamber always flows vertically from bottom to top. All arranged in the flue gas heating surfaces are flue gas side above the combustion chamber. Tower boilers offer a comparatively simple construction and easy control of the stresses caused by the thermal expansion of the tubes. Furthermore, all heating surfaces of the arranged in the flue gas duct steam generator tubes are horizontal and therefore completely drainable, which may be desirable in frost-prone environments.

When Zweizugkessel a horizontal gas train is downstream of flue gas side in an upper region of the combustion chamber, which opens into a vertical gas train. In this second vertical throttle cable, the gas usually flows vertically from top to bottom. It takes place at the two-pass boiler so a multiple deflection of the flue gas. Advantages of this design are, for example, the lower height and the resulting lower production costs.

Steam generators may continue to be designed as a natural circulation, forced circulation or continuous steam generator. In a continuous steam generator, the heating of a number of evaporator tubes leads to a complete evaporation of the flow medium in the evaporator tubes in one pass. The flow medium - usually water - is after its evaporation to the evaporator tubes downstream superheater tubes fed and overheated there. The position of the evaporation end point, ie the location at which the water content of the flow is completely evaporated, is variable and mode-dependent. During full load operation of such a continuous steam generator, the evaporation end point is for example in an end region of the evaporator tubes, so that the overheating of the vaporized flow medium already begins in the evaporator tubes (with the nomenclature used this description is strictly valid only at partial loads with subcritical pressure in the evaporator.) For the sake of clarity however, this representation will be used throughout the following description).

In contrast to a natural or forced circulation steam generator, a continuous steam generator is not subject to any pressure limitation, so that it can reach steam pressures far above the critical pressure of water (P _Kri ≈ 221 bar) - where at no temperature water and steam can occur simultaneously and therefore no phase separation is possible is - can be designed.

During low load operation or during startup, such a continuous steam generator is usually operated with a minimum flow of flow medium in the evaporator tubes in order to ensure reliable cooling of the evaporator tubes. For this purpose, just at low loads of, for example, less than 40% of the design load, the pure mass flow through the evaporator usually no longer suffices for cooling the evaporator tubes, so that an additional throughput of flow medium is superimposed on the passage of flow medium through the evaporator in circulation. The operationally provided minimum flow of flow medium in the evaporator tubes is thus not completely evaporated during startup or during low load operation in the evaporator tubes, so that in such an operating mode at the end of the evaporator tubes still unevaporated flow medium, in particular a water-steam mixture is present.

However, since the evaporator tubes of the continuous steam generator are usually designed for a flow through unvaporised flow medium after passing through the combustion chamber walls, continuous steam generators are usually designed so that even when starting and in low load operation, a water ingress into the superheater tubes is reliably avoided. For this purpose, the evaporator tubes are usually connected to the superheater tubes connected downstream via a Wasserabscheidesystem. The water separator causes a separation of the emerging during the start or in low load operation of the evaporator tubes water-steam mixture in water and in steam. The steam is supplied to the water separator downstream superheater tubes, whereas the separated water can be fed back to the evaporator tubes, for example via a circulating pump or discharged through a decompressor.

The Wasserabscheidesystem can include a variety of Wasserabscheideelementen that are integrated directly into the tubes. In particular, each of the parallel-connected evaporator tubes may be assigned a water separation element. The Wasserabscheideelemente can continue to be designed as a so-called T-piece Wasserabscheideelemente. In this case, each T-piece water separation element in each case comprises an inflow pipe piece connected to the upstream evaporator pipe, which, as seen in its longitudinal direction, merges into a water drainage pipe piece, wherein an outflow pipe piece connected to the downstream superheater pipe branches off in the transition region.

By this construction, the T-piece Wasserabscheideelement is designed for a Trägheitsseparation of the flowing from the upstream evaporator tube in the Einströmrohrstück water-steam mixture. Due to its comparatively higher inertia, the water content of the flow medium flowing in the inflow pipe section flows at the transition point preferably in the axial extension of the inflow pipe section and thus passes into the Wasserableitrohrstück and from there usually further into a connected collecting container. By contrast, the vapor portion of the water-steam mixture flowing in the inflow pipe section can better follow an imposed deflection due to its comparatively lower inertia and thus flows via the outflow pipe piece to the downstream superheater pipe section. A continuous steam generator of this type is for example from the EP 1 701 091 known.

In a continuous steam generator with such a designed Wasserabscheidesystem can be done by the decentralized integration of the water separation in the individual tubes of the pipe system of the continuous steam generator water separation without prior collection of effluent from the evaporator tubes flow medium. For a direct transfer of the flow medium in the downstream superheater tubes is possible.

Due to the design, the transfer of flow medium to the superheater tubes is not only limited to steam, but now a water-steam mixture can be continued to the superheater tubes by the Wasserabscheideelemente be fed. As a result, the evaporation end point can be pushed into the superheater tubes as needed. Thus, a particularly high operational flexibility can be achieved even in start-up or low load operation of the continuous steam generator. In particular, the live steam temperature can be controlled in comparatively large limits by influencing the feedwater quantity.

However, it should be noted in such systems that, due to the integration of the water separation function into the individual tubes, a comparatively high number of individual tube pieces or elements is required, especially in the region of the separation system.

The invention is therefore based on the object to provide a continuous steam generator of the type mentioned above, while maintaining a particularly high operational flexibility brings a comparatively lower design and repair costs.

This object is achieved according to the invention by a distributor element being arranged on the steam side between the respective water separation element and the inlet collector.

The invention is based on the consideration that the decentralized separation of water, which takes place separately in each of the parallel-connected evaporator tubes in the construction described above, a comparatively large number of T-piece Wasserabscheideelementen can lead to design problems in large-scale application. Due to the space problems that may be associated with the necessity of accommodating such a large number of water separation elements, such a construction can also entail significant additional costs and limitations of the continuous flow steam generator due to the high design effort involved.

Reducing the design cost of the continuous flow steam generator could be achieved by simplifying the design of the water separation system. For this purpose, the number of Wasserabscheideelemente used can be reduced. However, in order to obtain the advantages of decentralized water separation, such as the possibility of feeding with water-steam mixture, the basic construction in the form of T-piece water separation elements should be maintained. The combination of the two aforementioned concepts can be achieved by a collection of the flow medium from a plurality of evaporator tubes in each case a Wasserabscheideelement.

Due to a reduced number of tee-Wasserabscheideelementen direct steam-side forwarding to the Entrance collector of the downstream superheater tubes, however, lead to inhomogeneities in the distribution of the various superheater tubes. Therefore, in order to achieve a uniform distribution to the downstream superheater tubes after the exit of the steam or water-steam mixture from the T-piece Wasserabscheideelement, a distributor element is arranged on the steam side between the respective Wasserabscheideelement and the inlet header.

Advantageously, the geometric parameters of a number of outlet pipes are chosen such that a homogeneous flow distribution is ensured on the inlet header of the respectively downstream superheater pipes. As a result, a homogeneous entry is already achieved in the inlet header, which continues accordingly in the downstream superheater tubes. The outlet tubes can, for example, have the same diameter and be guided at equal intervals parallel to one another in the inlet header.

In an advantageous embodiment, the distributor element is designed as a star distributor, d. H. it comprises a baffle plate, an inlet tube arranged perpendicular to the baffle plate, and a number of outlet tubes arranged in a star shape around the baffle plate in the plane thereof. The inflowing water impinges on the baffle plate and is distributed in a symmetrical manner perpendicular to the inflow direction and directed into the outlet tubes. In this case, the baffle plate in a particularly advantageous embodiment is circular and the exit tubes arranged concentrically to the center of the baffle plate at equal intervals to the respective adjacent outlet tubes. In this way, a particularly homogeneous distribution is ensured on the different outlet pipes.

It is advantageously provided between 5 and 20 outlet pipes per distribution element. With a smaller number, sufficient homogenization of the entry of steam or water-steam mixture into the inlet header could not more can be ensured, while a higher number can be problematic in the geometric configuration of the distributor element, in particular if this is designed as a star distributor.

The advantages achieved by the invention are in particular that a uniform distribution of the flow medium is achieved on the superheater tubes by the vapor-side arrangement of an additional distribution element between the respective Wasserabscheideelement and the inlet header of the superheater superheating even at a much lower number of Wasserabscheideelementen. These measures make it possible to reduce the number of water separation elements in the first place. This means a much lower production cost and a comparatively lower complexity of the pipe system of the continuous steam generator and it is a particularly high operational flexibility even in start-up or low load operation achievable.

Furthermore, a homogeneous temperature distribution over the downstream superheater tubes is possible, which leads to significantly lower mechanical loads due to different thermal expansion of the individual superheater tubes. At the same time, all advantages of using T-piece Wasserabscheideelementen obtained, such. B. the possibility of forwarding water-steam mixture to the superheater pipes, which allows a needs-based control of the steam temperature at the steam outlet of the continuous steam generator by the control of the introduced flow medium amount.

An embodiment of the invention will be explained in more detail with reference to a drawing. Therein, the figure shows a continuous steam generator in Zweizugbauweise in a schematic representation.

The continuous steam generator 1 according to the figure comprises a combustion chamber 2 designed as a vertical gas train, which is located in an upper combustion chamber Region 4 a horizontal gas train 6 is connected downstream. At the horizontal gas train 6, another vertical gas train 8 connects.

In the lower region 10 of the combustion chamber 2, a number not shown burner is provided which burn a liquid or solid fuel in the combustion chamber. The surrounding wall 12 of the combustion chamber 2 is formed from steam generator tubes which are welded together in a gastight manner and into which a flow medium, usually water, is pumped in by a pump (not shown in greater detail), which is heated by the heat generated by the burners. In the lower region 10 of the combustion chamber 2, the steam generator tubes can be aligned either spirally or vertically. Due to differences in both the geometry of the individual tubes and in their heating, different mass flows and temperatures of the flow medium (imbalances) in parallel tubes set. In a helical arrangement, a comparatively higher design effort is required, but the resulting imbalances between parallel connected pipes are comparatively lower than in the case of a perpendicularly annealed combustion chamber 2.

The continuous steam generator 1 shown further comprises, to improve the flue gas duct, a nose 14, which merges directly into the bottom 16 of the horizontal gas flue 6 and projects into the combustion chamber 2. Furthermore, a grid 18 is arranged from further superheater tubes in the transition region from the combustion chamber 2 to the horizontal gas flue 6 in the flue gas duct.

The steam generator tubes in the lower part 10 of the combustion chamber 2 are designed as evaporator tubes. The flow medium is first evaporated in them and fed via outlet collector 20 to the water separation system 22. In Wasserabscheidesystem 22 not yet evaporated water is collected and removed. This is necessary, in particular during start-up operation, when a greater amount of flow medium has to be pumped in to ensure reliable cooling of the evaporator tubes than in an evaporator tube passage can be evaporated. The generated steam is conducted into the walls of the combustion chamber 2 in the upper region 4 and optionally distributed to the arranged in the walls of the horizontal gas flue 6 superheater tubes.

In addition to the two-pass boiler shown in the figure are of course also other configurations for fossil-fired boiler, z. B. in the manner of a tower boiler, possible. The components to be described below can be used in all these variants.

The Wasserabscheidesystem 22 includes a number of T-piece Wasserabscheideelementen 24. Each number of evaporator tubes opens via an outlet header 20 into a common transition pipe piece 26, each of which a T-piece Wasserabscheideelement 24 is connected downstream. The T-piece Wasserabscheideelement 24 includes an inflow pipe section 28, which, viewed in its longitudinal direction merges into a Wasserableitrohrstück 30, wherein in the transition region a Abströmrohrstück 32 branches off. The Wasserableitrohrstück 30 opens into a collector 34. To the collector 34 is connected via connecting lines 35, a collecting container 36 (bottle) downstream. To the collecting container 36, an outlet valve 38 is connected, via which the separated water can either be discarded or re-fed to the evaporation cycle.

In the T-piece water separation element 24, flow medium M enters through the inflow pipe piece 28. The proportionate water flows due to its inertia in the longitudinally following Wasserableitrohrstück 30. The steam, however, follows due to its lower mass imposed by the pressure conditions deflection in the Abströmrohrstück 32. The Abströmrohrstück 32 are the superheater tubes in the upper region 4 of the combustion chamber 2 and optionally in the grid and in the region of the horizontal gas train 6 via an inlet collector 40 downstream. In the wall heating surfaces and the subsequent Konvektivheizflächen the steam is overheated and then its further use supplied; Usually, a device not shown in detail in the figure, such as a steam turbine is provided.

If necessary, the outlet valve 38 can be closed and thus an overfeed of the T-piece Wasserabscheideelemente 24 brought about. In this case still unevaporated water enters the superheater tubes, so that they can still be used for further evaporation, d. h., The evaporation end point can be moved into the superheater tubes, which allows a relatively higher flexibility in the operation of the continuous steam generator 1.

In order to allow a particularly simple construction of the continuous steam generator 1, a comparatively smaller number of T-piece Wasserabscheideelementen 24 should be used. In order to compensate for the resulting inhomogeneities in terms of distribution to the superheater tubes and thus to allow such a configuration in the first place, the T-piece Wasserabscheideelementen 24 distributor elements 42 are interposed in the manner of star distributors. These provide for a pre-distribution of the flow medium in the event of over-feeding of the T-piece Wasserabscheideelemente 24 on the inlet header 40th

In the distributor elements 42 designed as a star distributor, the flow medium strikes a circular baffle plate and bounces from there into star-shaped, concentrically-symmetrically arranged outlet tubes 44. The symmetrical arrangement allocates approximately the same amount of flow medium to each outlet tube 44. These open at equal intervals in the inlet header 40, so that there is already a pre-distribution of the flow medium over the entire width of the inlet header 40.

In a direct introduction of the flow medium via a single line per tee-Wasserabscheideelement 24, the flow medium in the inlet manifolds 40 would not be uniform can be distributed because they are not suitable due to their width for such a homogeneous distribution of, for example, a single supply line.

By designed as a star distributor distribution elements 44 thus a simpler and thus more cost-effective construction of the continuous steam generator 1 is possible because a comparatively smaller number of T-piece Wasserabscheideelementen 24 can be used. Furthermore, temperature differences are better compensated by the better mixing of the flow medium compared to a fully decentralized water separation with a larger number of T-piece Wasserabscheideelementen 24 and thus achieves a more homogeneous temperature distribution to the subsequent superheater tubes. This avoids damage caused by different thermal expansion of pipes welded together.

Claims (4)

1. Once-through steam generator (1) which comprises a combustion chamber (2) having a plurality of burners for fossil fuel and downstream of which a vertical gas duct (8) is connected on the hot gas side in an upper region (4) via a horizontal gas duct (6), wherein the external wall (12) of the combustion chamber (2) is formed from evaporator tubes that are welded to one another in a gas-tight manner and disposed upstream of a water separation system (22) on the flow medium side and from superheater tubes that are welded to one another in a gas-tight manner and disposed downstream of the water separation system (22) on the flow medium side, wherein the water separation system (22) comprises a plurality of water separating elements (24), each of the water separating elements (24) comprising an inflow tube section (28) which is connected to the respective upstream evaporator tubes and, viewed in its longitudinal direction, transitions into a water discharge tube section (30), wherein a plurality of outflow tube sections (32) branch off in the transition zone, characterised in that said outflow tube sections (32) are connected to an inlet collector (40) of the respective downstream superheater tubes, and wherein a distributor element (42) is disposed on the steam side between the respective water separating element (24) and the inlet collector (40).
2. Once-through steam generator (1) according to claim 1, wherein the respective distributor element (42) comprises a baffle plate, an inlet tube disposed vertically with respect to the baffle plate, and a plurality of outlet tubes (44) arranged in a star shape around the baffle plate in the plane thereof.
3. Once-through steam generator (1) according to claim 2, wherein the baffle plate is circular and the outlet tubes (44) are arranged concentrically with respect to the centre of the baffle plate at equal spacings from the respective adjacent outlet tubes (44).
4. Once-through steam generator (1) according to one of claims 1 to 3, wherein the respective distributor element (42) comprises between five and twenty outlet tubes (44).

Images