Method and plant for the condensation of excess steam

Referring to method and plant for the condensation of excess steam obtained from steam-producing and steam-consuming facilities it is intended to provide a solution which avoids the release of steam into the atmosphere and the absorption of oxygen by the condensate. The problem is solved by indirect heat-exchange in a condenser that is filled with an oxygen-free fluid which is displaced by the excess steam into a receiver, the fluid being returned to the condenser in the absence of an excess steam flow. Referring to the plant, the problem is solved in that a condensate receiver (5) with gas dome is arranged downstream of the condensate header (4) of condenser (2), a line (11) for condensate discharge being provided between condensate header (4) and condensate receiver (5) while a line (10) for the inert gas is connected to the gas dome (9).

The invention relates to a method and plant for the condensation of excess 
steam obtained from steam-producing and steam-consuming facilities in a 
condenser designed for indirect heat-exchange. 
Steam is needed for a great number of industrial operations apart from the 
utilisation of steam for heating purposes or for the production of energy 
through steam turbines. Excess steam, especially low-pressure steam, may 
temporarily be available in such steam systems without any possibility of 
utilizing it directly for heating purposes or as turbine live steam. 
It is known to discharge excess steam to the atmosphere or to pass it to 
emergency condensers that are open to the atmosphere. It is also known to 
provide such emergency condensers with liquid discharge facilities. 
A marked disadvantage inherent in releasing the steam to the atmosphere is, 
for example, the loss of water that has generally undergone expensive 
treatment; in addition, environmental conditions are adversely affected by 
noise and water vapour. When the steam passes through such emergency 
condensers, the condensate is liable to absorb oxygen from the atmosphere, 
which may cuse corrosion and entrainment of corrosion products into the 
steam system. It should be added that liquid discharge facilities of the 
condensers feature slow response so that they can be used within narrow 
limits only. 
The object of the invention is to provide a method which avoids the release 
of steam to the atmosphere while preventing absorption of oxygen by the 
condensate. 
For a method as defined above, the problem is solved according to the 
invention in that the condenser is filled with an oxygen-free fluid which 
is displaced by the excess steam into a receiver and is allowed to return 
into the condenser in the absence of excess steam. 
Condensation of the excess steam by indirect heat-exchange avoids 
environmental pollution because the steam remains within the system. Since 
the condenser system, which is needed temporarily only, is filled with an 
oxygen-free fluid, no oxygen-bearing condensate goes into the process 
water. The specific requirements are satisfied by a multitude of fluids, 
i.e. they must permit to be displaced by water and steam and must be free 
of oxygen. Light-weight fluids will generally be preferred. 
Although the method according to the invention is not restricted to the use 
of a specific fluid, it has been found that an inert gas, especially 
nitrogen, is particularly recommended. 
It was mentioned before that the requirements are satisfied by a multitude 
of fluids, for example by industrial oils, which must be displaced into 
special receivers. But the use of an inert gas is particularly indicated 
because gases are compressible. 
The invention also provides for the condenser to be equipped with a 
downstream condensate receiver with gas dome which serves for 
accommodating the inert gas and for its compression, if any. This 
embodiment has the advantage that displacement of the inert gas from the 
condenser into the gas dome produces a pressure rise which causes an early 
reflux of the inert gas into the condenser when the volume of condensate 
is reduced or the flow of excess steam is stopped. This procedure 
facilitates the flow control and shortens the response periods of the 
system. 
The invention also provides for a plant for solving the subject problem, 
said plant being characterized in that a condensate receiver with gas dome 
is arranged downstream of the condenser condensate header, a condensate 
discharge line being arranged between condensate header and condensate 
receiver while the gas dome is provided with an inert gas line. 
This solution which is particularly intended for the use of inert gas 
offers the advantage of quick response, simple design, economical 
operation, and a great variety of applications. 
A further embodiment of the invention provides for the gas dome with 
connecting line to the condensate header to be sized for accommodating the 
entire inert gas volume contained in the condenser. 
This embodiment permits the maximum working pressure to be achieved at full 
admission of steam to the condenser. The elevated pressure is markedly 
higher than the working pressure prevailing in open condensers, that is 
the atmospheric pressure. The elevated pressure level raises the 
condensation temperature of the steam and, consequently, the mean 
logarithmic temperature difference, so that less heat-exchange surface is 
required as compared with atmospheric condensers. 
Considering that no oxygen corrosion can occur in the condensate system, 
inexpensive piping materials may be selected for the service conditions 
involved.

The plant designated by 1 comprises an air-cooled condenser 2 of shed-roof 
design. The blower is designated by 3. It should be said that all plant 
components are shown schematically only. 
Condenser 2 is provided with a condensate header 4, with a condensate 
receiver 5 being arranged downstream in the direction of condensate flow. 
Excess steam is admitted to the condenser through line 6 which branches off 
the mains 7 and is equipped with control facilities 8. 
The Figure shows that condensate receiver 5 is equipped with a gas dome 9. 
Provision is made for an inert gas line 10 between gas dome 9 and the top 
of condensate header 4 and for a condensate discharge line 11 connected to 
the bottom of condensate header 4. 
FIG. 1 also shows an inert gas feed line 12 with control facilities 13 and 
a condensate reflux line 14 with control facilities 15 and a pump 16. 
Operation of the plant may be described as follows: 
Excess steam from mains 7, for example the low-pressure steam system, is 
admitted through line 6 and control station 8 to condenser 2. Under 
no-load conditions, this condenser 2 is completely filled with a fluid, 
for example nitrogen. The incoming excess steam displaces this nitrogen 
from the system into the gas dome of condensate receiver 5. The nitrogen 
is displaced through line 10 while the condensate is admitted throough 
line 11 to condensate receiver 5. The condensate is finally returned 
through pump 16 and line 14. 
As soon as no further excess steam arrives from system 7, valve 8 moves 
into the closed position, and the condensate leaves the system. The 
elevated pressure produced by the displacement of the nitrogen into gas 
dome 9 will immediately force the nitrogen through line 10 and condensate 
header 4 back into the condenser. This procedure prevents oxygen to 
contact the condensate at any point of the system. 
Referring to FIG. 2, the plant incorporates an ejector 17 with a downstream 
cooler 18. 
For reducing the heat-exchange surface, this design provides for the inert 
gas to be withdrawn through ejector 17 for admission to a separate section 
of the heat exchanger. This method is applied to raise the flow velocity 
in the heat-exchanger tubes and the heat transfer rate. 
The plant designated by 1 as in FIG. 1 is also equipped with an air-cooled 
condenser 2 of shed-roof construction. In addition, it comprises the 
ejector 17 and a separate aftercooling section 18. Excess steam from line 
7 passes through line 6 and control valve 8 into condenser 2. 
Condensate flows through downpipe 11 into condensate receiver 9. Displaced 
inert gas passes through line 19 to ejector 17. 
As the pressure rises in line 19, steam arrives at ejector 17, and the 
inert gas passes through line 21 to the aftercooling section 18; the inert 
gas is cooled, motive steam and water vapour undergo condensation. The 
condensate flows through a downpipe 22 into the condensate receiver while 
the inert gas passes through connecting line 10 into the gas dome. 
The water level which builds up in downpipe 11 depends on the pressure 
difference between condensate pipe or condenser 2 and aftercooling section 
18. 
The embodiments of the invention, referring to method and plant, described 
before by way of example permit, of course, a plurality of modifications 
without deviating from the basic idea of the disclosure. Provisions may be 
made, for example, for an additional inert gas control station or 
facilities which prevent excessive diffusion of inert gas into the process 
water, etc. If, for example, oil is used instead of gas, pressure 
equalizing vessels may be recommended. Moreover, condensers may be used 
which are designed for being cooled with water or any other fluid. If a 
water-cooled condenser is used instead of the air-cooled condenser it is 
recommended, for the arrangement described above, to admit the steam to 
the tubeside and the cooling fluid to the shellside in order to achieve a 
distinct flow and displacement of the inert gas.