DE3111174A1 - Steam-jet condenser with a surge drum, in particular for superheated-steam and cold-steam power plants - Google Patents

Abstract

Published without abstract.

Description

Steam jet condenser with liquid separator,

in particular for hot and cold steam power plants The invention relates to a steam jet condenser with a liquid separator for condensation and precipitation of steaming, in particular of steaming from steam turbines of hot and cold steam power plants with a closed cycle.

In such steam jet condensers with a liquid separator is as complete a condensation as possible of the flowing out of the steam turbine Exhaust steam (wet steam) with the lowest possible kinetic energy of the steam jet he wishes.

It would be possible, for example, to meet these requirements a well-known steam jet chiller) to use by the heat-absorbing The evaporator would be relocated directly into the condenser vessel, which would carry the condensate cools down and absorbs the condensation heat of the steam to be precipitated.

In such an operating mode, by means of the on the steam jet nozzle generated underpressure the already separated condensate from the condenser vessel Taken from the evaporator via a control valve and from the vacuum chamber of the steam jet nozzle fed.

Since in this (attempted) embodiment a heat exchanger (evaporator) is necessary, a relatively large area would be used for the condensation of large amounts of evaporation Evaporator required. This would not only mean a relatively large amount of material and costs connected, but rather an incomplete one because of the loss of heat gradient at the evaporator Condensation linked so that additional (conventional) capacitors, +) Zum Example of a "water vapor jet chiller" according to the textbook "Technical Thermodynamics, 1st part, by F. BOSNJAKOVIC; 6th edition, pages 303-304, Fig. XIV / 2? ".

zg B, those with water cooling would be required, the rest of the Heat of condensation would have to give off to the environment.

The invention is based on the object with the existing exhaust steam jet optimal cooling and thus optimal condensation of the exhaust steam jet without Use of a separate evaporator and additional cooling equipment in the Use condensation chamber, with a minimum of condensation heat to the Environment must be released, and thus primary energy can be saved.

If one uses the present in the form of dry saturated steam Residual heat leads through further condenser stages or directly by means of an adiabat working compressor in the boiler of the superheated steam respectively.

returns to the evaporator of the cold steam power plant, one reaches a complete recovery at the expense of relatively minor technical work the heat of condensation and thus a complete conversion of the on the cycle transferred primary heat in technical (mechanical) work.

This object is achieved in that the from the Steam turbine with still relatively high speed BEZW. high kinetic energy exiting wet steam jet via a cylindrical guide tube (jet pipe) a likewise cylindrical so-called "condensation tube" is fed in such a way that that a vacuum chamber is formed between the guide pipe and the condensation pipe, consequently the expanding steam jet is directed towards the vacuum chamber Umbrella-shaped flow shape is obtained, with a strong turbulence at the same time Cooling and thus condensation of the steam on the wall of the condensation pipe is achieved.

The precipitated condensate collects at the lower opposite, conical end of the condensation pipe (liquid separator) and can be removed from there with a feed pump and the boiler BEZW. Evaporator be fed again.

The non-precipitated dry saturated residual steam is on the other hand removed separately from the condensation chamber via a pipe leading up steeply respectively via one or more downstream capacitors or directly via an adiabatic compressor to the boiler of the superheated steam or. the vaporizer fed back to the cold steam power plant.

When the dry residual steam is withdrawn from the condenser, it is through a bulge-shaped bead on the flue pipe ensures that the one on the condenser wall drops of liquid trickling down are not entrained by the residual steam flow, so the rest of the steam remains dry and thus its adiabatic recirculation the compressor requires a minimum of labor.

The aim is to achieve as intense a condensation as possible with the to achieve existing kinetic energy of the wet steam jet. By using an annular gap nozzle (instead of the nozzle with a circular cross-sectional area) it is possible for the wet steam jet emerging from the annular gap in the space of the condenser tube to distribute more regularly, d.

H. to transfer the condensation to more vapor molecules. It arise thus compared to the first variant (with a circular cross-sectional area steam jet pipe) with the same energy of the steam jet, more steam molecule associations, which, albeit with a smaller mass, are still on the condenser wall or on the surface of the liquid the separator are separated. Just a small residue of light particles (Vapor molecules) cannot be deposited due to a lack of kinetic energy and must - like the separated condensate - laboriously in the boiler respectively Evaporator to be returned to the thermal power plant. It is for reasons low workload important that both working media are "separated from each other" to be led back.

The advantages achieved with the invention are in particular: that with a relatively small kinetic energy of the exhaust steam an almost complete Condensation is achieved in a relatively small condenser vessel and thus relatively little condensation heat dissipated to the environment resp. with relatively little effort this can be returned to the district processor.

Thus, the primary heat that can still be absorbed from the outside in the cycle With such a condenser equipped thermal power plant theoretically complete converted into equivalent work (useful work). So you save that one Amount of primary energy that is still in the form of today's thermal power plants condensation heat must be dissipated to the environment (water, air). this applies especially for Superheated steam power plants, such as for coal and nuclear power plants, which in the working group process bezv as working material water. Steam use.

Since when using the steam jet condenser according to the invention no waste heat has to be dissipated into the environment, the expansion end temperature can be reached on the expansion machine (steam turbine or piston machine) far below the the ambient temperature and thus the heat gradient that occurs during expansion take full advantage of it. This great advantage can be particularly useful in cold steam engines be used wherever it is necessary, low-temperature heat, which is used on a large scale Is available to use such. B. Environmental heat in the form of water, air or Geothermal heat.

It is also necessary to implement such a cold steam engine necessary that the upper gas temperature of the cold steam at a sufficiently high Operating pressure selects so low that a sufficiently high heat gradient between the ambient heat to be absorbed and the gas heat of the cold steam arise. In in this case there would be an independent heat transfer from the primary heat source on the working substance in the evaporator of the cold steam engine ensured.

So in order to be able to use low-temperature environmental heat, is for the present cold steam engine with steam jet condensation a working substance with a very low boiling point (T5 at 1.013 bar) required, which - depending on Ambient temperature - should be between about -40 ° C to about -140 oC.

There are such low-boiling substances in the known refrigerants R 14 (CF4) with Ts = 1280C, R 23 (CHF3) with Ts = -82.1 ° C, R 13 Bi (CF3Br) with T5 = -57.8 ° C and R 22 (CHF2Cl) with Ts = -40.8 ° C.

This would give the real opportunity for the first time to be self-balanced Environmental heat, ie heat "without temperature differences" respectively. heat from a single one Heat container ", i.e. to convert it into technical (mechanical) work. Since the heat flow when the primary heat is absorbed into the working group in Flows in the direction of falling temperature, it works in the direction of natural occurrences, is therefore with the laws of nature - and thus with the so-called "2nd law of the Heat theory "-compatible. The 2nd HS with all its negative formulations regarding one any use of heat from a 'single heat tank' refers exclusively on heat engines with a closed cycle process that still absorb their waste heat have to discharge the environment.

With the possibility of obtaining mechanical work from the environment At the same time, heat is the reversibility (reversibility) of natural occurrences proven, d. H. the 'doughy cycle of energy that is bound to matter ", documented. So far this was only conceivable for energy that was present in pure form, So for radiant energy, a so-called "Perpetuum mobile des Universe "is postulated. Five exemplary embodiments of the invention with three possible applications are shown in the drawings and are described in more detail below. It Fig. 1 shows the steam jet condenser with liquid separator and cylindrical Nozzle Fig. 1.1 a partial drawing of Fig. 1 with a view in the direction of the exhaust pipe opening Fig. 2 is the same as Fig. 1, but with an annular gap-shaped nozzle Fig. 2.1 is a partial drawing to Fig. 2 with section through the condensation chamber Fig. 3 an arrangement with several Steam jet condensers with a common separator and exhaust pipe Fig. 4 the steam jet condenser in 2-stage design Fig. 5 the steam jet condenser in 3-stage design Fig. 6 an application example on a simple superheated steam power plant z. Am a thermal power plant (fossil or nuclear power plant) 7 with status information of a possible Operating sequence Fig. 7 with an application example on a cold steam power plant Status information of a possible operational sequence Fig. 8 shows an application example a superheated or cold steam power plant when using piston engines Fig. 9 the pressure-volume diagram (P, v diagram) for the two possible applications Fig. 6 and 7 Fig. 10 the vapor pressure curves of the refrigerants in question, in particular of the refrigerant R 14 (CF4), which is used as a working substance for the cold steam engine according to Fig. 7 or 8 is used.

Fig. 1 shows the structure of the steam jet condenser with a liquid separator and dry steam exhaust pipe shown in sectional view.

The representation also shows the flow profile of the to be condensed Wet steam as well as the condensate loss and the dry steam extraction by appropriate Arrows are also drawn in. (The flow path in the condenser could be seen on a transparent Test model, which consisted of glass tubes, can be determined.) Fig. 1.1 shows - with the condenser cylinder open - the side view of the dry steam exhaust pipe with the bead attached to the beginning of the pipe.

This is supposed to suck off the trickling down on the condenser cylinder wall Prevent liquid droplets over the flue pipe. As indicated by arrows, the drops of liquid slide "protected" between the wall and the bead around the flue pipe around in the separation vessel.

As can be seen from Fig. 2, the feed pipe for the wet steam at its end also be provided with an annular gap nozzle, which allows more effective condensation with the same kinetic energy of the steam jet. Around the separation area for the steam flow directed towards the condenser axis are to be increased accordingly Arranged surface elements that pull through the capacitor in the axial direction. As from the associated cross-sectional drawing, Fig. 2.1, there are four such Longitudinal surface elements arranged respectively on the inner cylinder. connected to this.

In order to be able to effectively knock down large masses of steam, a Arrangement with several nozzles can be used, as shown in principle in Fig. 3 is. In this embodiment there are many individual ones at their exit condensation cylinders kept open in a common separation vessel to which also a common exhaust pipe for the dry steam for all condensation cylinders connected.

To suppress a given vapor mass as completely as possible two or more stages can be used.

A two-stage arrangement is shown in Fig. 4. To get from the 1st Level coming dry steam to precipitate, he is by means of a compressor brought to the required pressure and fed to a second steam jet condenser, which - according to the residual amount of steam from the first stage - is relatively small can be. The dry steam from the second stage can then with the compressor to the required operating pressure with a relatively small volume brought and the boiler respectively. Evaporator are supplied. The condensate can come out both stages with a separate condensate pump each or a common feed pump the boiler respectively. To be returned to the vaporizer.

In order to be able to completely suppress a given amount of steam, several stages may have to be connected in series. In Fig. 5 is a 3-stage arrangement is shown in which only condensate remains at the end of the 3rd stage accrues. This is, as indicated, via three separate condensate pumps (due to possible different pressure in the individual capacitors) discharged respectively. over a common feed pump respectively the boiler. Evaporator fed.

If it is the condensation of static vapors with air admixtures acts, such as B. of water vapors, cold gas vapors or acid vapors, can proceed in a similar way according to the arrangement in Fig. 5.

The one to be knocked down respectively. Steam to be condensed is with a Compressor sucked into the 1st stage and adjusted to the required level (approx. 2-3 bar) compressed and fed to the steam jet condenser. The non-condensed residual steam becomes a correspondingly smaller 2nd steam jet condenser via an additional compressor supplied and condensed there again except for a small residual vapor. The residual steam from this 2nd stage is finally fed to the 3rd steam jet condenser, its Residual steam consists essentially of the non-precipitable air. This can - if the vapors are aggressive, use a suitable filter taken from the condenser chamber of the 3rd stage and with a suction pump to the environment be discharged.

To avoid heat losses through the wall of the condenser vessel (Fig. 1-5) as well To be avoided via the inlet and outlet pipes, these must be provided with appropriate thermal insulation to provide. The condensation of the steam is not supposed to be caused by heat dissipation the metal walls can be reached to the outside, but solely through the transfer of the heat of condensation (= Residual heat of evaporation) on the condensate cooled by expansion, according to the applied kinetic energy of the steam jet The secluded The amount of liquid depends on the vapor pressure and the geometric dimensions of the steam jet condenser addicted. The maximum of the separation must be determined by experiments one z. B. for a certain (given) arrangement, the vapor pressure varies and too the amount of vapor deposited is determined for each pressure.

For example, with a test model from 1 kg of water vapor At a steam temperature of 1200C and a steam pressure of 2 bar, about 0.960 kg of steam are condensed. The remainder of 40 gr was in the form of dry steam to the outside, to the ambient air, submitted.

The physical process during the condensation of the wet steam in the condensation vessel goes something like this based on observations on a transparent condensation tube follows in front of it: The one emerging from the steam turbine at a relatively high speed Steam has already been depressurized and cooled down (= processed) to such an extent that it is oversaturated is (wet steam), d. H. Molecular assemblies have already formed in the vapor volume (e.g. H20 molecular assemblies) formed with one proportional to the number of molecules Dimensions.

When this already so "precondensed" steam occurs with a high Velocity (v) in the condensation tube becomes the kinetic energy of the large Steam jet uses a more or less large vacuum in the annular chamber to build. The light to medium-weight particles (molecules and smaller groups of molecules) are umbrella-like upwards, in the direction of the vacuum chamber, with vortex formation, diverted and cool down and become increasingly with increasing expansion with the remaining kinetic energy finally hurled against the condenser wall, to which they stick to the wet wall as a result of adhesion. For larger accumulations of liquid they finally trickle down the cone in the form of large drops of liquid down the wall into the condensate trap.

The heavier ones formed during vacuum formation and turbulence Cores of condensation become less strong in the direction of the vacuum chamber deflected and, due to their weight, fall immediately down into the condensate separator. Only the very light particles (molecules) with low kinetic energy (vklein) are sucked off via the exhaust pipe in the form of dry saturated steam.

When the light to medium-weight particles precipitate on the The super-saturated wet steam with its heat content is absorbed by the condenser wall smaller room volume over, d. H. the internal energy of the condensate increases, because in this liquid state the particles are packed closely together. this is shown in the higher specific heat of the liquid compared to that of the vapor at the same temperature.

When the vapor is deposited on the condenser wall, Cv Liquid> t Cv vapor cal (Cv = specific heat per unit volume, e.g. measured in cm3.oC> According to this transition from the vapor to the liquid state the kinetic energy expended by the steam jet, the vacuum in the condenser is created increasingly larger, so that the pressure gradient for the wet steam jet - and thus also its kinetic energy - correspondingly increases. This increases the condensation effect in the condenser additionally.

Fig. 6 shows an example of the application of the steam jet condenser a simple superheated steam power plant with a closed cycle process. Here was Water resp. Water vapor used as a working substance. So it's a single-circuit thermal power plant with closed cycle and one of the environment independent condensation of the exhaust steam with complete recirculation of the condensation heat in the form of liquid heat and residual steam heat.

The circuit diagram in Fig. 6 shows a possible operating state with corresponding Temperature and pressure information given. The pressure and volume course on the individual Points in the circuit diagram is described with the P, v diagram in Fig. 9. In repatriation of the dry steam with the compressor (e) must be at least up to the operating pressure be adiabatically compressed. The starting temperature that may not be attainable (325 OC) as a result of heat losses, is in the steam boiler through additional heat absorption balanced. Instead of the 1-stage arrangement used in Fig. 6, a 2- resp. 3-stage arrangement according to Fig. 4 or 5 can be used.

The superheated steam power plant consists of the following, basically required Components: a boiler (evaporator in the cold steam engine), a "steam volume, b steam turbine, c steam jet condenser, d condensate pump, e compressor, f condensate vessel, g feed pump.

This system works in a completely closed cycle process. If one on the return of the relatively small amount of dry steam produced waived or gives off to the environment - that is, only one;> I am the separated Condensate returns to the boiler - you get a so-called "partially closed" Cycle 1 ,. Compared to the previously completely "openly operated steam cycle" (e.g. with the steam locomotive) this would have the advantage of low water and waste heat losses.

The non-condensable residual steam here could of course be used also feed a separate, customary condenser and thus discharge this relatively small heat of condensation obtained a completely closed cycle. In addition, a 2- or 3-stage arrangement according to Figs. 4 and 5 could be used and thus with a correspondingly small amount of work - since only essentially Condensate accumulates - achieve a completely closed cycle process.

Fig. 7 shows another application example of the steam jet condenser on a cold steam engine. The cold steam engine basically has have the same components as the superheated steam engine according to Fig. 6. These have however, some other names. The evaporator takes the place of the boiler and instead of the volume of steam accumulated in the boiler, a separate one became here Steam reservoir a used.

A 2-stage condenser design was chosen here and at the same time provided that the entire residual steam from the 1st stage is precipitated in the 2nd stage will. If not, the dry steam from the 2nd stage could in principle also be used a compressor - as indicated in Fig. 6 for the 1st stage - the vapor volume a ' are fed.

Fig. 8 shows the superheated or cold steam power plant in the embodiment as a piston engine. Corresponding valves have to be installed in the supply and discharge lines be arranged to the components. EV = inlet valve for a defined inlet volume, R1 to R5 = opening resp. Closing valves.

The designations for the components correspond accordingly to those of Fig. 6 or 7. The steam jet condensation is here when ejecting the relaxed Wet steam caused during the backward movement of the piston via the outlet valve R1. The condensate is returned via pump d and the dry steam return via the pump e.

To avoid power losses that occur in the cold steam power plant can occur through unintentional heat absorption from the outside, all components, except for the evaporator, the steam storage tank and the inlet and outlet pipes to these Components are well insulated.

In order to be able to use heat sources at the temperature level of the Environment, such as B. water heat, a refrigerant must be used as an agent are already below the temperature of the heat source one for the operational sequence relevant gas pressure reached.

For the exemplary embodiment according to Fig. 7, the working substance was Refrigerant R 14 (CF4) is used, which has a boiling point of around -130 OC (at 1 bar) has - (Fig. 10). This z. B. at a heat source temperature of +10 ° C and a temperature gradient of #t = 30 ° C, the refrigerant in the gaseous state transfer whose saturation point (approximately operating point) is -20 OC, 30 bar. The pressure-stressed cold steam obtained in this way can be used with the cold steam engine according to Fig. 7, for example, by relieving it to 3 bar and -85 ° C. A pressure gradient of dP = (30-3) bar = 27 bar and a temperature gradient can be achieved Use from AT = (-200C) - (-850C) = 65 OC. The rest of 3 bar steam pressure would stand then available for condensation of the saturated exhaust steam in the steam jet condenser. In the 2nd stage, the same steam pressure (3 bar) would then have to be used for the residual steam the now much smaller steam volume are used again to a to achieve complete condensation in the 2nd stage.

In the circuit diagram of Fig. 7, such an operating state is shown with the corresponding Temperature and pressure information given.

Fig. 10 shows, among other things, the vapor pressure curve for the refrigerant R 14 (CF4) with the saturation values used in the circuit diagram in Fig. 7.

The effective useful work, i.e. the work of the thermal power plant can be discharged to the outside and used, arises for the superheated steam as also for the cold steam power plant in general as Weff = Wt (Wk + Ws) (Eq. 1) Herein mean: Wt = turbine work, Wk = compressor or compressor work, W5 = feed pump work.

The smaller the amount of work, the greater the effective work for the return of the condensate and the residual steam in the boiler BEZW.

is in the evaporator of the thermal power plant.

To return the residual steam (dry steam) to its original state (according to Fig. 6 to P = 100 bar, T = 3250C) - at least in its pressure - to be traced back, an amount of work is required that is theoretically just as large as the previous one work gained on the steam turbine by this steam portion.

If you place this non-condensed vapor fraction according to the test result with 5% (of the total steam entering the turbine), one needs to Recirculation for the adiabatically operated compressor is theoretically 5% of that at the Steam turbine previously obtained mechanical work.

So it is Wk = 0.05 Wt If you put a W5 for the feed pump work The lump sum of 1% of the turbine work results in the effective Mechanical work (which can be carried away from the system to the outside) to Weff = Wt - (Wk + W5) = Wt - (0.05 + 0.01) Wt = 0.94 Wt Because of the feedback of these two mechanical Working amounts Wk + W in the form of heat amounts IWkI + 1W51 + 1 s can add to the cycle only the missing difference amount from the outside - through the primary heat source - is replaced respectively continuously fed. The amount of heat that can be supplied from outside corresponds to Qp thus the effective work Weff that can be transferred to the outside, or Qp tS Weff = 0.94 Wt There both energies are equal in magnitude, so | Qp | = | Weff | is, and, except mechanical work, no energy is dissipated to the outside, is obtained for the Primary heat has a conversion value of 100%. This enables a so-called "thermal Plant efficiency "generally define to be discharged to the outside of the plant Work nth plant of the plant externally supplied heat Wt - (Wk + Ws) = W Weff = 1 Qp - Qp - 1 (Eq. 2) Here: Weff = effective work dissipated to the outside, Q = primary heat that can be supplied to the cycle from outside p Wt = turbine work, Wk = Compressor work, W5 = feed pump work.

If the so-called ideal "Carnot cycle" is carried out, one obtains with the inputs indicated in Fig. 6 on the turbine and output temperatures for the superheated steam power plant a theoretically thermal Efficiency of maximum T1 - T2 (273 + 325) - (273 + 150) 180 nc turbine T1 273 + 325 = 30% T1 273 + 325 600 With the in Fig. 7 the inlet and outlet temperatures given on the turbine show a Carnot efficiency of maximum T1 - T2 (273 - 20) - (273 - 85) 65 ntc turbine = T1 = 273 - 20 = 253 = 25%.

In the case of the superheated steam power plant, (100 - 30)% = 70% of the total heat supplied to the turbine as waste heat (anergy) to the cycle like which is returned and in the case of the cold steam power plant accordingly (100 - 25)% = 75 %. The primary heat that can be absorbed from the outside of the cycle is supplemented in both 100% of these cases by absorbing heat at a higher temperature or pure exergy. The amount of usable The heat gradient is a measure of the Size of the convertible amount of heat respectively. a measure of the "energy density" of the concerned Thermal power plant.

When using environmental heat as the primary heat source, next to the air and ground heat, the most abundant is the heat of the water. Large water masses have a relatively high temperature constancy all year round and are therefore particularly good as a heat source (for generating cold gas with a constant upper Temperature). Since the latent heat of the water (80 kcal / kg) is also used can be, there is a particularly large amount of energy at a constant temperature to disposal.

With the aforementioned cold steam engine you can, for example from 1 m3 of water from 20 ° C to complete ice formation, i.e. including with use the latent heat, a mechanical work of theoretically Amech QR / m3 100 kcal / l . lOOn l / m3. 1 = ~ 60 kcal / kWh 100,000 kcal / m³ = 116.3 kWh / m³ 860 kcal / kWh gain.

In practice, this could generate around 100 kWh of electrical energy using generators Work to be generated.

In this case, the latent heat of the water alone provides this 80 «0 of this energy at constant work source temperature at 0 0C.

This means that so-called cold steam power plants can be built on a large scale will work with a relatively high energy density and get their heat from the sea, Get lake or river water.

Since the mechanical BEZW obtained from the water. Electrical work in the end almost completely back to its original form of energy (environmental heat) flows back and anyway is constantly radiated solar heat onto the earth and not is used, there is no doubt about the inexhaustibility of this regenerative Energy source.

Today's energy problem could thus be complete for all time and be solved in an environmentally friendly way.

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Claims (5)

Claims steam jet condenser with steam jet condenser with liquid separator for condensation and precipitation of saturated vapors in particular from side and cold steam power plants with a closed cycle process, characterized in that the expansion machine (steam turbine or piston steam engine) A jet of wet steam flowing out at a relatively high speed into a condensation pipe is inserted in such a way that between the steam-carrying supply pipe (jet pipe) and the condensation tube a vacuum chamber is formed in which the wet steam jet Expands like an umbrella in the direction of the vacuum chamber, cools down, condenses and is deposited on the condensation pipe wall, the condensate being deposited on the opposite lower end - the liquid separator - accumulates while the non-separated residual steam (dry saturated steam of small kinetic Energy) via a flue pipe leading up steeply to a compressor and - to further condensation - a 2. or even 3rd steam jet condenser is supplied. 2. Steam jet condenser with liquid separator according to claim 1, characterized in that the steam-supplying jet pipe is in the form of an annular gap nozzle opens into the condensation tube and that in the direction of the condensation tube axis Wet steam jet expanding out of the annular gap nozzle at several, in the longitudinal direction to the condensation tube axis arranged separation surfaces is deposited. 3. Steam jet condenser with liquid separator according to claim 1 and 2, characterized in that the exhaust pipe for the dry steam on the The side opening into the condensation tube with a .valst-shaped flared area is provided, which prevents liquid droplets from being sucked into the drain pipe. 4. Steam jet condenser with liquid separator according to claim 1 to 3, characterized in that several steam jet condensers operated in parallel are and for this a common separation vessel for the condensate and a common one Flue pipe is used for the dry steam. 5. Steam jet condenser with liquid separator according to claim 1 to 4, characterized in that two or more steam jet condensers are operated in series and each consists of one or more connected in parallel Units exist.