FIELD OF INVENTION
The present invention relates to an improved condensing system with three surface condensers fixed to Low Pressure (LP) turbine of 700 MW unit nuclear turbine to condense 100% steam after expansion from turbine. More particularly the invention relates to an in-house improvement of a surface condenser of required size and capacity which can condense all the steam exhausting out of three LP turbines of 700 MW Nuclear turbine.
BACKGROUND OF THE INVENTION
Till date, there was no design available for 700 MW Nuclear Surface Condenser. The newly designed Surface Condenser have many new and unique features which are detailed below. The Surface Condenser designed earlier did not have any of these features and were generally supplied for smaller ratings and for thermal power plants.
The complete Surface Condenser was designed in-house catering to the specific requirements of Nuclear Power plant.
The design of Surface Condenser for Thermal Power plants for sub-critical and supercritical sets was available. However no such design for 700 MW Nuclear Power

Plant was available. Hence design for the same needs to be established not only to cater the heat load of the incoming steam, but to meet all the specific requirements of the customer, which led to the development of a new variant of Surface Condenser for the first time.
OBJECT OF THE INVENTION
Therefore an object of the invention to propose an improved condensing system with three surface condensers fixed to three Low Pressure (LP) turbines of 700 MW nuclear turbine to condense 100% steam after expansion from turbine, which is capable of meeting the requirement of condensation of steam coming out of LP exhaust of the said turbine.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1: Shows implementation of 3D PDMS (Plant Design Management System)
models.
Fig. 1A: Shows 3D Model of the Surface Condenser along with its technical details.
Fig. 2: Shows introduction of SEISMIC RESISTANT LUGS (SRLs) to withstand
seismic forces where the condenser is anchored or guided at the bottom by two Nos. of transverse lugs and two Nos. of axial lugs.

Fig. 3 & 3A: Shows introduction of Retractable conductivity measurement probe for early detection of tube to tubesheet joint leakage.
Fig. 4 & 4A: Shows introduction of Thermal Mass flow Meter for Air ingress
Measurement in the surface condenser according to the invention.
Fig. 5: Shows introduction of technological pulling Lugs in the surface condenser
to facilitate weld joint between waterboxes with their respective water chambers according to the invention.
Fig. 6: Shows introduction of two specially designed Steam bypass diaphragm
nozzles with varying capacities in accordance with the invention.
Fig. 7: Shows introduction of Ergonomically routing of stand pipes towards the
front waterboxes to suit the site conditions as per the invention.
Fig. 8: Shows introduction of strainer assembly to prevent entry of any foreign
particle into the CEP (Condensate extraction pump).
Fig. 9: Shows introduction of Air Vent Valve to remove formation of any air
pockets in water boxes according to invention.
Fig. 10: Shows bundles of tube in a condenser.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Each 700 MW unit consisted of 1 HP Turbine coupled with 3 LP Turbines (in parallel). Three (3) surface Condensers per unit with neck mounted LP Heater no 1, were finally designed to be welded to each LP turbine exhaust to condense 100% steam after expansion from the turbine. The 700 MW Surface Condenser is a large sized, rectangular shaped, metallic heat exchanger (of size approx. 15 metres long, 7 metres wide x 17 metres high) where the steam exhausting from the LP Turbine Exhaust neck gets condensed. The steam entering the condenser faces two separately placed tube bundles in a “twin shell” condenser, thus the steam follows a “divided flow concept”. The steam is guided and spread over the tubes by the specially designed pyramid shaped “Dome walls” for maximum heat transfer.
The Condenser, supported on a stiffened “Bottom plate”, is fitted with a large number of straight, long but thin Stainless Steel “tubes” placed in a very specific pattern/layout for effective heat transfer. The raw cooling water (sourced from river) flows through these tubes which condense all the steam into a long semi cylindrical shaped “hotwell” connected to the bottom plate.

The tube bundles are stiffened by thick, solid carbon steel rods, also supported by a series of “tube support plates” and are fixed at the ends by large sized perforated “stainless steel cladded tubesheets” which also acts as tough partition walls between the condensing stream (at sub-atmospheric pressure) on one side and pressurized cooling water on the other side. The complete bundle is enveloped by “side walls” on sides.
The raw cooling water, before entering the tubes is collected in the lower half of the two large vertical reservoirs called “front water boxes (3)”, through large size “cooling water inlet nozzles (4)”, which are suitably shaped and designed to redirect the flow into the tubes, in case of “divided waterbox condenser”. Similarly the water after coming out of tubes after Heat Transfer process is also collected in the upper half of the same water box before exiting out through Cooling Water outlet nozzles. The similar shaped reservoirs called “reverse end waterboxes” (but without nozzle connections) at the rear end of the condenser are provided to reverse the flow in the “two pass condenser”. The main advantage of a twin shell, divided water box, divided flow type configuration of a condenser is that the condenser can function for 50% duty in case of any tube leakage/leakages, which can be attended for repair in one half of the condenser without isolating it completely.

An LP Heater 1 is also positioned inside the dome wall and properly anchored on the bottom plates through vertical supports passing through two (2) of the support plates. In fact the entire load inside the condenser is transferred to the ground through the support plates only which rests on a series of “Spring Support assemblies” consisting of a pair of heavy duty coil springs caged in a specially designed Spring cages.
The thermo-mechanical design of the surface condenser to suit the thermodynamics of the steam coming out of the LP turbine exhaust, has been successfully carried out and implemented.
The in-house developed Surface Condenser contains many significant and distinct features catering to the stringent requirements of the turbine.
The salient features of this newly developed Surface Condenser are given below with a comparison with prior Art.
1. As shown in Fig 1 and 1A, each 700 MW unit, consisting of three Surface Condensers (of twin shell, divided water box two pass, divided flow, welded water boxes) welded to the LP Turbine exhaust from the top and is supported on a series of spring support assemblies at the bottom. The three condensers are connected with four

nos of Air Evacuation system (Vacuum Pumps) of 30 SCFM capacity each to maintain the desired back pressure during operation by three Pumps in continuous operation; the fourth standby pump shall be operating during startup/hogging operation. 3D PDMS (Plant Design Management System) models were developed for the first time for Surface Condenser including air Evacuation System to integrate with the main Plant layout and piping thereby minimizing mismatch and fouling with the piping and other equipment including civil structures.
Prior Art: None of the Surface Condenser supplied earlier had such a three LP Cylinder configuration, integrated to three individual condensers coupled with four Air Evacuation units.
2. Fig. 2 shows introduction of specially designed “Seismic Resistant Lugs (SRL)” at the bottom face of the Bottom Plate of Surface Condenser to resist and absorb the probable seismic loads corresponding to the geographical conditions of the site. The fixed point of the Surface Condenser is offset from the main center lines and is located at the LP Turbine foundation. As a result, the condenser was anchored at the bottom by two pairs of the SRLs (two Nos. transverse lugs and two Nos. axial lugs), in such a way that the condenser shall withstand horizontal impact load in any direction, arising

out of Seismic condition but at the same time the movements due to thermal expansion are not restricted.
Prior Art: None of the Surface Condenser supplied earlier had such inbuilt feature of Seismic Resistant Lugs to resist seismic forces.
3. Fig. 3 and 3A shows introduction of special “Catch Troughs” arrangement in
individual water chambers for “online” monitoring of the condensate for its change in
conductivity (due to contamination) in the connected U-tube siphon pipe by
“Conductivity probe with retraction assembly kit” for early detection of Tube to tube
sheet joint leakage. The most significant work was to extract the condensate from the
condenser shell, which is working at sub-atmospheric pressure (nearly vacuum) and
feed it back into the condenser.
Prior Art: None of the Surface Condenser supplied earlier for any of the power plants had such inbuilt feature for early detection of tube to tubesheet joint leakage.
4. Fig. 4 and 4A shows the introduction of the “Thermal Mass Flow meter” at the
outlet of Separator Tank of Air Evacuation System for continuous monitoring of Air
ingress inside the condensing system. This will result in diagnosis for deterioration of

condenser performance attributed to any Air Ingress into the condenser system, which is operating in sub-atmospheric condition.
Prior Art: None of the Surface Condenser supplied earlier had such a facility/arrangement to “online” monitor the total non condensibles/air-ingress into the system. Only Rotameter was provided for monitoring manually in all the past supplies.
5. Fig.5 shows introduction of specially designed technological pulling lugs provided
on the water box and water chambers which can be tightened by suitable fasteners to
align and assist the welding assembly between two major assemblies at site.
Prior Art: Most of the Surface Condensers supplied earlier have flanged water box to water chamber joint. Technological pulling lugs on water chambers and water boxes have been introduced for the first time.
6. Fig.6 shows the surface condenser equipped with two different sizes of specially
designed Steam Bypass diaphragm nozzles catering for High flow (for 20% of main
steam flow) and Low flow (for 3.50% of main steam flow) requirements of steam under
Turbine Bypass condition.

Prior Art: All Surface Condensers supplied earlier had a pair of identical Steam Bypass nozzles to cater for the total bypass requirement. Two specially designed nozzles with varying capacities have been designed and developed for the first time.
7. Fig. 7 shows stand pipes which are ergonomically routed towards front water
boxes to suit the site requirements and are equipped with latest State of the art
instrumentations like Guided Wave Radar type Level transmitters, Magnetic Level
Indicators & Vibrating Fork Type Level Switches for accurate indications of the
condensate levels inside the Condenser Hotwell.
Prior Art: All Surface Condensers supplied earlier had standpipes (fitted with conventional level monitoring instrumentations) mounted on the side walls occupying extra space on sides, thus increasing the condenser required width.
8. As shown in fig. 8, the condensate outlet connection in the condenser hotwell is
provided with in-house developed removable Stainless Steel strainer arrangement to
ensure clean condensate entry into the Condensate Extraction Pump (CEP) thereby
enhancing the life and durability of the pump.
Prior Art: The strainer at the Condensate outlet has been introduced for the first time, thus preventing any foreign particle entering into the CEP.

9. Fig. 9 shows the introduction of Air Vent Valve in the reverse end Water Box to prevent formation of any air pocket during Condenser operation. Any air pocket formation in the waterbox shall prevent the cooling water to flow into the top rows of the tubes thereby deteriorating the condenser performance.
Prior Art: The arrangement of introducing air vent Valve (which will release any unwanted air into the atmosphere) is being implemented for the first time.

WE CLAIM
1. An improved condensing system with three surface condensers (2) fixed to Low Pressure (LP) turbine of 700 MW unit nuclear turbine to condense 100% steam after expansion from turbine comprising;
a metallic rectangular heat exchanger for condensing the steam exhausted from the LP turbine exhaust;
two separately placed tube bundles (19) disposed in a twin shell condenser for allowing the steam to follow a divided flow pattern;
a pyramid shaped ‘dome walls’ (8) disposed for guiding and spreading steam over the tubes (17) for maximum heat transfer;
stiffened bottom plate (18) for supporting the condenser (2);
a plurality of straight, long, thin tubes (17) fitted to the condenser in a specific pattern for effective heat transfer;
a long semi cylindrical shaped hotwell (6) connected to the bottom plate (18);
two large vertical reservoirs disposed as front water boxes (3) having cooling water inlet nozzles (4) directing the flow into the tubes (17);

two similar reservoirs disposed at the rear end of the condenser as reverse end waterbox without having any nozzle, for reversing the flow in the two pass condenser;
an LP heater disposed inside the dome wall (8) and anchored on the bottom plates through support plates resting on a series of spring support assemblies;
a condensate extraction pump;
characterized in that,
each of 700 MW L.P. turbine unit consisting of three surface condenser (2) in parallel welded to the LP turbine exhaust from the top and supported on a series of spring support assemblies (5) at bottom, the said three condensers connected to four Nos. air evacuation system/vacuum pumps for maintaining the desired back pressure during operation of the three condenser; wherein,
a plurality of seismic resistant lugs (10A,10B) disposed at the bottom face of the bottom plate of surface condenser (2) for resisting and absorbing the probable seismic loads corresponding to the geographical conditions of the site; wherein,
a ‘catch Troughs’ arrangement disposed for monitoring of the condensate for change in conductivity by conductive probe (11) with retraction assembly kit for early detection of tube to tube sheet joint leakage;
when a thermal mass flow meter (12) disposed at the outlet of separate tank of Air Evacuation system for continuous online monitoring of Air ingress inside the condensation system; wherein,

a plurality of pulling lugs (13) provided on the water box and water chambers for lightening the welding assembly;
two different sizes steam bypass diaphragm nozzles (4) for catering high flow and low flow requirements of steam under turbine bypass condition; when a plurality of stand pipes (14) routed towards front water boxes (3), the said pipes equipped with special instrumentation for accurate indications of the condensate levels inside the condenser Hotwell; wherein, the said condensate hotwell having condensate outlet connection is provided with stainless steel strainer arrangement (6) to ensure clean condensate entry into the condensate extraction pump for enhancing the life and durability of the pump when air vent valve is provided in the reverse end water box for preventing formation of any air pocket during condensation operation.
2. The improved system as claimed in claim 1, wherein the capacity of the vacuum pump disposed in the said system is 30 standard cubic feet per meter.