CONDENSATION METHOD This invention relates generally to steam condensing apparatus. More particularly, it relates to an apparatus that includes an air-cooled condenser of the kind in which the vapor to be condensed flows through tubes whose outer surface area is extended to be provided with fins on which the air flows. to eliminate the thermal energy provided by the steam as it condenses. The invention is applicable mainly to apparatuses wherein the pressure in the condenser is maintained at a sub-atmospheric value, to obtain high efficiency, for example, in a power generating system that uses steam. The usual arrangement of an air-cooled condenser comprises an arrangement of a large number of tubular elements with individual fins. The steam is led to said elements a large capacity duct connected to the discharge steam outlet of a turbine or other steam expansion device. In a first set of finned tubular elements, the steam generally travels downwardly condensing as it does so, the condensate being collected by a distributor or distributors at the lower ends of said tubular elements. He
The condenser may have an additional arrangement of tubular elements that complete the condensation of substantially all the steam discharged from the turbine, leaving only a trace amount of vapor together with any non-condensable substances such as trapped air to be extracted by a system of appropriate extraction so that the pressure in the condenser as an integer is maintained at the required sub-atmospheric value. The condensate collected in the distributor or distributors is conducted to a receiver tank from which it is extracted and finally returned to the system boiler. The nature of an air-cooled condenser is that the arrangement of finned tubular elements has a certain resistance to vapor flow, so that there is a pressure drop through the condenser. The pressure at the inlet side of the condenser, i.e. in the discharge vapor duct leading from the vapor expansion device, is higher than the pressure maintained at the outlet of the condenser, i.e., the collection manifold of the condenser. condensed. The pressure drop means that there is a difference between the water-vapor equilibrium temperatures at the inlet and outlet of the condenser. Therefore as the steam is
condenses in the tubular elements with fins and runs downwards from said elements to the distributor or distributors where it is collected, the temperature of the condensate is reduced to a value corresponding to the equilibrium temperature at the outlet of the condenser, below the temperature of the condenser. steam in the condenser inlet duct. This over-cooling of the condensate represents a small but significant energy loss, whose energy has to be replaced by the condensate when it is returned to the boiler of the system. In comparison, the condensate of a conventional surface condenser is generally at a temperature that is not significantly lower than the temperature of the vapor at the condenser inlet. It is broadly the object of the present invention to provide an improvement in the efficiency of a system including an air-cooled condenser, and more particularly to overcome the above described problem of over-cooling of the condensate in the condenser. In accordance with the invention provide a steam condensing apparatus comprising a duct for receiving discharge steam from an expansion mechanism; a number of air-cooled condensing elements connected to the duct to receive steam therefrom; a
distributor to collect condensate from the condensation elements; a receiver for the collected capacitor; means to take a portion of the discharge vapor to the receivermeans for sealing by steam and developing a pressure head in the condensate to cause it to enter the receiver, and means for causing the condensation to make contact between the condensate entering the receiver and the discharge steam portion, to condense the portion of steam and raise the temperature of the condensate in the receiver. The present invention, taking part of the discharge vapor to the receiver, establishes pressure and temperature conditions in the receiver substantially equal to those in the discharge steam pipe. The temperature of the condensate driven from the distributor to the receiver rises to the temperature which is not significantly lower than the water-vapor equilibrium temperature at the pressure of the discharge vapor in the duct leading to the condenser inlet, substantially eliminating the loss of energy described above due to overcooling of the condensate in the air-cooled condensing elements. Conveniently, the condensation contact between the condensate and the discharge steam portion can occur
in the capacitor receiver. The necessary intimate contact between the steam and condensate for effective condensation to occur when there is only a small temperature difference between the liquid and vapor is conveniently achieved by causing the condensate to enter the receiver as a jet or spray. A conventional surface condenser is generally disposed immediately adjacent to the discharge of a turbine, so that there are no losses involved in transmitting the discharge vapor to the condenser. On the other hand, an air-cooled condenser is usually a regularly large piece of equipment., Which requires that it be disposed outside the building in which the rest of the steam plant is accommodated and that it needs a long pipeline leading from the discharge from turbine to condenser. A small but significant pressure drop occurs in said duct, leading to an additional drop in condensate temperature and thus in the efficiency of the system in which the condenser is incorporated. In order to maximize recovery from this temperature drop, the discharge steam portion is preferably taken from the duct in a position as far from the upstream stream in it as possible.
The invention also provides a method for condensing discharge vapor from an expansion mechanism by use of an air-cooled condenser, wherein the condensate collected from the condenser is brought into condensation contact with a portion of the discharge vapor to condense the latter and raise the temperature of the condensate. In some previously known air-cooled condenser installations, a condensate receiving tank release pipe may be provided at the inlet of the condenser, to allow the tank to escape from the evaporated steam that could be generated under certain transient conditions. However, there is no steam flow through said pipe to the receiver tank, because the receiver tank is sealed to the liquid in this case to prevent the bypass of the condenser. Therefore, said arrangement has no significant effect on the temperature of the condensate. These and other features of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows diagrammatically a capacitor system that modalizes the invention; Figure 2 shows a modification of part of the
apparatus. The illustrated system comprises a duct 10 which is arranged to be connected at 11 to a steam expansion device such as a turbine, to receive the discharge vapor thereof. An air-cooled condenser arrangement is generally indicated at 12, comprising a first series of condenser elements 13 receiving steam from the duct 10. The elements 13 comprise arrangements of tubes provided with external fins to increase their surface area and provide effective thermal transfer to the surrounding air. The condenser elements 13 are connected at their lower ends to a distributor 14 to receive condensate thereof, and any non-condensed vapor and non-condensable gases. The air-cooled condenser 12 further comprises condensing elements 15 which extend from the distributor 14 and are connected together in 16 to an air extraction system, usually a pump or ejector. The condenser elements 15, called the condensing section of the condenser, substantially complete the condensation of the vapor leaving only non-condensable gases with some trace vapor that is to be extracted by the air pump or expeller to ensure that the pressure
of the condenser is maintained below atmospheric pressure. A receiver 17 is provided to receive condensate from the distributor 14, and to retain said condensate ready for final return to the boiler of the steam system, not shown, by a condensate extraction pump 18. The condensate enters the receiver 17 by gravity from the distributor 14, through a pipe 19. In accordance with the invention, a pipe 20 is provided to take a small proportion of the steam flowing in the pipe 10 to the receiver 17. The condensate which enters the receiver from the pipe 19 is delivered to the receiver from a sprinkler arrangement 21, so that the condensate is brought into intimate contact with the vapor in the receiver, thereby condensing the vapor and bringing the condensate up to the equilibrium temperature corresponding to the pressure prevailing in the receiver 17. A pipe 22 leads from the receiver 17 to the distributor 14, for any excess steam and non-condensable gases carried by it. Said excess steam, and non-condensable, are treated by the deflegmentation condenser elements 15 and air extraction system, and it is these components that enter the distributor 14.
from the condenser elements 13. It will be appreciated that steam flow through the pipe 20 to the receiver will occur because the prevailing pressure in the pipeline will be higher than that in the distributor 14, due to the pressure drop occurring in the condenser elements 13. The receiver pressure is maintained at a value close to that in the duct 10 by appropriately restricting the pipe 22: it may be advantageous to provide an adjustable valve in the pipe 22 for this purpose. The pipe 19 incorporates a water seal 19a. This prevents the possibility of steam flow directly from the pipe 20 to the distributor 14 through the receiver 17, which could occur due to the difference between the pressure in the duct 10 and that in the distributor 14, and that if it would occur it would tend to enter the condenser elements 13 and trap the non-condensable elements therein. Sufficient head in the condensate of the distributor 14 to enter the condensate receiver 17 and to ensure satisfactory operation of the spray arrangement 21 if appropriate is provided by the water present in the pipe 19. In use of the system described above, the condensate temperature stored in the receiver 17 is
substantially equal to the equilibrium temperature corresponding to the pressure of the discharge vapor in the duct 10. In this way, the loss of energy and the loss of efficiency in the total system, which results from the over-cooling of the condensate in the elements 13 and 15 condenser is avoided. In the example described above, the condemned is brought into condensation contact with the portion of the discharge vapor that has entered the receiver through the pipe 20 by sprinklers 21 in a part of the receiver 17. Figure 2 shows a modification where , instead of the spray or jet arrangement, an arrangement comprising a cascade of perforated trays 23 is arranged in a part of the receiver 17. The condensate entering the receiver passes over the trays 23, which provide the necessary contact between the vapor and the condensate over a large surface area. In a further modification, instead of causing the condensation contact between the vapor from the pipe 20 and the condensate currently in the receiver 17, a separate device could be provided between the distributor 14 and the receiver 17 for this purpose. Alternatively, an appropriately enlarged section of
Piping work between the distributor 14 and the receiver 17 could provide the necessary condensation contact between the steam and the condensate. Figure 2 of the drawings shows part of the apparatus that includes a further modification of the apparatus shown in Figure 1. A pipe 24 leading from the receiver is shown, whose pipe is directly connected at 25 to the air extraction system of the apparatus in place to be connected to the distributor 14 in the manner of the pipe 22 in Figure 1. The remaining vapor and non-condensable vapor remaining from the steam that has entered the receiver through the pipe 20 are removed by the air extraction system together with said substances from the distributor 14 and condenser elements 15. The pipe 24 would also be sized so that the air extraction system is capable of removing the non-condensable from the receiver while the pressure of the receiver remains substantially equal to that in the pipeline 10. By way of example, the amount of steam that passed through the pipe 20 may be of the order of only 1% of the steam that passes through the pipeline 10. A further advantage of the invention is that it helps
to ensure that the oxygen content of the condensate held in the receiver is minimized.