DE1751750A1 - Process for the partial load operation of once-through steam generators and systems for carrying out the process - Google Patents

Description

' P-4192/4246

Sulzer Brothers, Aktiengesellschaft, Winterthur (Switzerland)

Process for partial load operation of forced once-through steam generators ^ and equipment for carrying out the method

The invention relates to a method for the partial load operation of once- through steam generators with a combustion chamber lined by pipe strings through which the working medium flows in parallel, with individual or groups of pipe strings working medium being metered by throttling devices . Such a method is known in which a temperature is measured on each pipe string group and regulated by influencing the associated throttle element. If such a steam generator is operated with a very low load , unstable behavior becomes noticeable: The working fluid is distributed unevenly within the groups across the various pipe strings, with individual pipe strings being insufficiently cooled. In highly loaded boilers, at low fire rates - due to the inherently low flow velocity or additionally stimulated by instability - fluid evaporation can occur, which results in local overheating of the pipe material and pipe rupture.

There are various ways of solving these difficulties Efforts have been made. So it was proposed in parallel

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to move to the Brennkaramerauskieidung forming pipe strings heating surfaces in boilers schwachbeheiztfe zones which can be shut off during part load operation to increase the working medium speed in dan Erennkammerrohren. Other possibilities have been seen in the installation of load-dependent operated throttle valves, floats, etc. All these swege solutions have not been able to prevail because they are too expensive to implement and / or operate, reduce efficiency or functionally unsatisfactory. In the case of high-performance boilers, the process of working medium circulation has become established, in which working medium is returned from the end of the combustion chamber tubing, preferably in a load-dependent amount, to the beginning of the combustion chamber tubing by means of a special circulating pump or a jet device. In the case of medium-capacity steam generators, people shy away from taking this route for reasons of profitability. In subcritical operation, there is also a risk of erheelidh cavitation for the circulation pump.

The aim of the invention is to eliminate distribution difficulties and film evaporation during start-up and during low-load operation in a way that is also suitable for older and smaller steam generators Performance is commercially viable and the powers mentioned are not having. This goal is achieved in that - at least in the lower part-load range - the pipe strings are loaded intermittently into the working equipment, with periodically alternating into the Stirring the flow rate (wipe a highest and a lowest value is changed · by dl · periodically

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alternately guided charging, it is possible in the feed pump, Turbine and superheater to a continuous mass flow reach.

The method offers the additional advantage that the overall coloration cross-section of the pipe strings can be enlarged, without the distribution of the agent on the individual strands becoming uneven. It therefore also allows Boilers of relatively low power with a combustion chamber formed from vertically running, densely fused tubes, these tubes to be connected in parallel on the work equipment side. It can therefore be applied to the In subcritical operation in the evaporator area, harmful downpipes are dispensed with.

To improve the stability at low partial loads, it is provided that the highest value of the flow velocity is one Fixed predetermined minimum value and that - considering any of the pipe strings - the time interval during which a certain value lying between the highest and the lowest value is exceeded, in the same sense as the load is changed. The "specified minimum value of the flow velocity" / represents a mean value at its height the duration of the impact can be measured.

Another object of the invention is to determine the mean flow of working medium in the pipelines using the intermittent flow penetrating work equipment inherent kinetic energy

Is otbei the value that is sufficient to make the film evaporation> to under-'JfUcken ,. while the "certain value of Ströraunf, speschv; iad.igke11"

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by recirculating the working medium - without using a circulation pump - to be able to further increase the thermal load capacity of the combustion chamber. This object is achieved according to a further embodiment of the invention in that from 6% of the exit side of the drill strings or groups of tubular strings, when the flow velocity drops therein, working fluid is periodically returned to the entry side of the relevant tubular string or group of tubular strings.

When the pipe strings are fed in bursts, this occurs in each case Ir interval of decreasing flow velocity at the inlet side of the pipe strings creates a negative pressure, which has the tendency to to decelerate advancing working equipment column. Due to the return of the working medium according to the invention, this negative pressure is reduced and at the same time working medium is reduced by the relevant one Strand uagevÄlit. In addition to better cooling, there is also a quieter one Operation achieved »By reducing under pressure peaks and thus * Avoid hydraulic shocks in the system.

The invention also relates to systems for carrying out the process mentioned, as described in the claims and, for example, are shown in the drawing.

FIr. 1 shows schematically a first embodiment of a system according to the invention,

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represents a section through the distributor 2 according to FIG. 1,

shows a variant of Fig. 1,

a schematic representation of an embodiment of a system according to the invention,

Mass flow diagrams of the system according to FIG. 4,

also in a scheratical representation a third Embodiment of a system according to the invention and

a section through a distributor slide according to the line A - B in FIG. 6.

In the system according to Fig. Γ a feed pump 1 promotes working medium in a distributor 2 having throttle elements with four outlets 3, via which there are four groups 4 of pipe strings 4 »flows in. The working equipment is located downstream of the pipe groups "Combined in a collector 5 and fed through a superheater 6 to a consumer not shown ·

The distributor 2 has a rotating distributor slide 7, which receives the working medium axially and alternately periodically four chambers 3, where the exit nozzles 3 are connected.

FiK 2 3 FlP. A. FiR. 5 FiR. 6th Fi R. 7th

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In B ¹ Ig. 2 ift cer distributor 2 is represented. It consists of a pot-like housing 10, which is closed by a cover 11 with a Lridgman closure, which has an inlet nozzle 12. The four outlet nozzles 3 are arranged in a radial plane 13, starting from the chambers 8.

The bottom of the housing 10 is penetrated by a shaft 14, which carries the distributor slide 7 at the inner end. The end face j5 of the distributor slide 7 is inclined to the axis and forms with it the cylinder surface of the distributor slide 7 together approximately after two crossing helical lines running control edges 16. Up an invisible shoulder of the partial slide 7 is seated inner Kugella £ errijn 17 with balls, which the distributor slide 7 Center in the bore of housing 10. The rooms on both sides of the distributor * sin <? through an opening 18 which extends between shaft 14 and ball bearing ring 17 through, for Pressure equalization connected to each other.

On the outside loading of the shaft 14 sits, axially displaceable, a V-belt pulley 19 driven by a gear motor 20 will. Shaft 14 and Vei'teilschieber 7 are axially displaceable depending on the load by a rebel 21 engaging on shaft 14, in a * so large area that on the one hand a The dash-dotted mark 22 attached to the distributor is brought into the plane 13 and, on the other hand, the control edges 16 to the right the area of the chambers 6 can be pushed out.

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The distributor slide rotates when starting up and during low-load operation 7 in its left end position, so that the work equipment essentially only one of the groups 4 of pipe strings is fed in at a time, and two of them when switching over. With increasing The load is shifted to the right by means of the lever 21, whereby the time interval during which a considered pipe is charged by the working medium per period is increased will. At maximum load the distributor, the chambers 8, is released, in its right-hand end position. The motor 18 can then be stopped.

By increasing the number of groups into which the parallel Pipe strings are divided, the distribution of the work equipment improved and pressure surges that occur in the pipe system are reduced. Should the distribution even at maximum load are improved, the distributor slide 7 will not be pushed all the way to the right, but it will periodically move the chambers Cover B.

While in FIGS. 1 and 2, the distributor slide 7 is formed in numbers is, it is according to the embodiment of FIG. 3 shown in two digits, i.e. it points two at right angles to each other standing, axially extending planes of symmetry on and also the housing carries twice the number of outlet nozzles 3, measured on the single arrangement, with two opposite each other Nozzles are connected to one another by lines.

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This arrangement has the advantage that the working medium pressures acting on the distributor slide 7 cancel each other out, so that the Ball bearing 17 of which is not loaded. At the exit of the Pipe strings 4 arranged non-return flaps 23 prevent one Backflow of working fluid from the pipe strings that have just been fed into the strings that are not currently fed.

The speed of the distributor slide 7 is in a range that is due to the permissible temperature fluctuations in the pipes and below above by the inertia of the. Pipelines located Work equipment is limited. If the switchover is too fast, the working equipment column could not move into it quickly enough. Set movement, unless the speed comes into resonance with a vibration form of the work equipment,

In deviation from the examples shown, this could The throttle element 2 and the collector 5 are interchanged and / or the superheater is related to the periodically fed Rohrstrtnggruppen will. Compared to these variants, however, the embodiments shown have the advantage that the throttle member because of the lower specific volume of the working fluid can be built smaller, or that the superheater as a damping Volume protects the turbine from vibrations of the working medium.

The distributor 2 or equivalent, periodically opened throttling devices (e.g. valve manifold controlled by a camshaft) a normal work equipment feeding event11 can be connected upstream,

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but he would also be able to take over its function, in which case the feed regulator would have to act on the lever 21.

Sin Economizer can be connected upstream or downstream of the throttle element 2.

According to FIG. 4, a feed pump 1 conveys working medium into a distributor 2 ¹ , from which four branch lines 93a, 93b, 93c and 93 ^ d extend. Each of these branch lines leads via a valve 94a, 'Mb,? 4c or 94d, to a pipe string group 4a, 4b, 4c or 4d, which opens into a common collector 5 via a non-return cap 23a, 23b, 23c or 23d a line 98 leads away the working fluid. The valves 94a to 94d are opened and closed alternately via a spring-loaded plunger 90a to 90d each by a cam 92a to 92d, which are jointly driven by a motor 91. A return line 83 is now provided, which is connected on the one hand to the collector 5 and on the other hand, forked into four branches, via non-return flaps 84a to 84d with the inlet sides of the pipe string groups 4a to 4d.

In the cam position shown in FIG. 4, the pump 1 delivers Working fluid through the open valve 94 · and the pipe string group 4a in the collector 5.

Las valve 94d was open for the last quarter period, well but it is closed. The work equipment in the pipe string

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Group Ad is - due to its inertia - still in motion} it is therefore returned from the return line 83 via the backlash cap 84d into the inlet side of the group 4d.

Valve ^Q 4c, which was open during the penultimate quarter period, is also closed. 4c in the associated pipe string group, the working fluid movement is already almost off W ge ^ ^ payments being returned very little working tools over which only partially opened check valve 84c into the group 4c.

In the pipe string group 4b, the working equipment is completely idle. Both Non-return flaps 23b and 84b are closed.

In FIG. 5, the diagrams a to d show the course over time of the mass flow in the pipe string groups 4a to 4d, the areas circumscribed with solid lines representing the mass flow Jk. through valves 94a to 94d and those of dashed lines limited areas represent the mass flow through the corresponding non-return flaps 84 «to 84d. The diagrams show that By arranging the return line 83 with the non-return flaps 84a to 84d, the time interval during which a pipe string group is flushed through is approximately tripled.

The diagram e in Flg. 5 shows the sum of the mass flows passed through the valves 94a to 94d as a slightly toothed curve,

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while the diagram f is the sum of the through the check valves B.4a to 84cj indicates returned mass flows. The hatched ones Areas of the diagrams e and f are almost the same size, so there is about the same amount of work equipment in the example according to FIG. 4 '. returned' as / requested by the pump and the entire in the The amount of working fluid that penetrates pipe string groups is roughly double as large as the amount required by Punipe 1.

According to FIG. 6, a distributor is used instead of cam-controlled valves 30 used;

The feed pump 1 conveys working medium through a line 31 into a housing 32 of the distributor 30, in which a rotary slide valve 33 rotates, which is driven via a shaft 34 (FIG. 7). In the housing 32, four nozzles 3 are arranged in a first axis-normal plane E ₁ (FIG. 7) (only one of which is shown in FIG. 7), which are connected to the four pipe string groups 4a to 4d via line branches 36a to 36d. In a second axis-normal plane Er, (FIG. 7), two return nozzles 37 are provided in the valve housing 32, which are connected to the collector 5 via a return line 83 'with a non-return valve 86. The rotary slide valve 33 has two axial bores 39 and 40, which serve to balance the working medium pressure on the two slide end faces. The end face 41 on the left in FIG. 7 is cut off at an angle, so that when the slide is rotated, a control edge 42 that oscillates in the axial direction with respect to the connector 3 results. Between the right end face 43 of the rotary valve in FIG. 7 and

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the control slide has an undercut on the control edge 42 through which a second control edge 45 is formed.

The rotary valve 33 is rotated uniformly by a motor (not shown), possibly with a load-dependent speed and is moreover displaceable to the right in FIG. 7 by a load-dependent device (not shown). The one shown in FIG The position of the slide corresponds to the minimum load of the steam generator.

In the position shown in Fig. 7, the supply is to the drawn Connection 3 blocked. After about an eighth of a turn of the rotary valve, it flows via the line 31 'into the left housing part incoming work equipment during about a quarter turn through the port 3 drawn, whereupon this Trim the socket over the back milled 44 with the back 37 communicates, so that now work equipment via the non-return valve 86 is sucked in and circulated.

As the load increases, the rotary valve is moved to the right, with the intervals of direct feeding of the pipe string groups 4a to 4d are enlarged so that they overlap.

In the example of FIG. 7, the slide is dimensioned such that when it is pushed completely to the right at full load, its control edge all the nozzle 3 are simultaneously free 42. Depending on the desired mass flow in the pipe string groups 4a to Ad , it can be useful, even with full load through both control edges

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and 45 to have the connection 3 still covered, so that working fluid is still returned via the non-return valve 86 even at full load. -

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Claims (1)

Patent claims: 1. A method for the part-load operation of once-through steam generators with a combustion chamber lined with pipe strings through which the working fluid flows in parallel, with individual or groups of pipe strings working fluid being metered by throttling devices, characterized in that the pipe strings (4 ¹ ) are charged with working fluid in bursts at least in the lower part-load range are periodically alternating in the pipe strings (4 ·) the flow velocity is changed between a highest and a lowest value. 2. The method according to claim 1, characterized in that the lowest value of the flow velocity is practically zero. 3. The method according to claims 1 or 2, characterized in that, with a constant load, the course of the flow velocity over time, apart from the phase shift, is 4 · the same in the different pipe strings. 4. The method according to claims 1, 2 or 3, characterized in that · draws that - considering any of the pipe strings (4 ·) - the highest value of the flow velocity 009849/0718 BATH ORIGINAL exceeds a fixed, predetermined minimum value and d-äss the time interval during which a between the The lowest and highest specific value is exceeded j when the load changes in the same way as the load is changed. 5. Plant for performing the method according to one of the preceding claims, with a once-through steam generator with a combustion chamber lined with pipe strings through which the working medium flows in parallel, with individual Pipe strings or groups of pipe strings each have a throttle body is connected in series and the Rohrsträng'en at least one feed pump is connected upstream, thereby characterized in that one on the throttle organs (7, 8) acting control element (20) is provided, which periodically alternates between opening and opening the throttle elements ■ 'actuated in the closing sense. 6. Plant according to claim 5, characterized in that the control member (20) and the throttle members (7, 8) from one Distributor (2) with at least two outlet nozzles (3) exists, and that each outlet nozzle (3) with a of the pipe strings (4 ·) or with a group (4) of pipe strings (4 ·) is connected. 7. Plant according to claims 5 or 6, characterized in that that the control element (20) and the throttle elements (7.3) 009849/0718 .respectively. the vertfailer (2) is designed and the pipe strings (4 ¹ ) are grouped in such a way that, in order to keep pressure fluctuations small, regardless of the phase position, the total cross-section of the pipe strings (4 ·) currently flowing through is approximately the same over the period is. ü. Plant according to claims 6 or 7, characterized in that that the distributor slide (7) is designed as a rotary slide and is axially adjustable, that the distributor slide (7) has control edges (16) running according to crossed helical lines and that in the valve body (10) provided outlet nozzle (3) are all arranged in a radial plane (13). 9. Plant according to one of the claims 6 to 8, characterized in that that the distributor slide (7) has two digits, seen in the axial direction. 10. Plant according to one of claims 5 to 9, characterized in that that the control unit or the distributor (2) is connected to a boiler load sensor. 11. The method according to claim 1, characterized in that _$ of the exit side of RohrstrSnge or group of RohrstrSngen at sinking therein flow speed working means periodically alternately into the inlet side of the respective pipe string the group ODTR 00984 9V0718 BATH is returned by pipe strings. 12. The method according to claim 11, characterized in that the return of work equipment is maintained, . as long as there is a negative pressure on the inlet side of the respective pipe string or the group of pipe strings opposite the outlet side. · 13. · The method according to claim 11, characterized in that the return of the work equipment is controlled depending on the load. 14. Plant for carrying out the method according to one of the Claims 11 to 13, characterized in that at least one return line is provided, which is from a Place strora below the exit side of the pipe strings or the groups of pipe strings and over- _ locking organs leads to the inlet side of the individual pipe strings or groups of pipe strings. 15. Plant according to claim 14, characterized in that the Shut-off devices are designed as non-return devices. 16. Plant according to claim 14, wherein the control member and the Throttle body consists of a distributor with at least two outlet nozzles and each outlet nozzle with one the pipe strings or with a group of pipe strings 009849/0718 _ßA0 original - 13 - is connected, characterized in that the distributor is connected to the Riickführleitung and formed so that it assumes and periodically alternating the working fluid releases the puncture of the shut-off the path from the back-circulation line to the inlet side of the Hohrstränge the group of pipe sections. 0098A9 / 0718 BATH ORIGINAL I, « _a t & lt 'J-vj * ■ * - Read it