CONDENSER & HEAT EXCHANGERS

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__CONDENSER AND AUXILIARIES

1.1.0STEAM CONDENSER

1.1.1Introduction The condenser is single pass design having box type construction with divided water box design which facilitates the operation of one half of the condenser while the other half is under maintenance. The steam space is of rectangular cross-section condensing surface. The condenser is provided with integral air cooling section from where air and non-condensable gases are drawn out with the help of air evacuation equipment.

1.1.2Construction The surface condenser is mounted on the springs which take the load of empty condenser and also a portion of operational weight of condenser. The springs are also designed for taking up thermal expansion during operation. The condenser is welded with the exhaust-hood of the low pressure turbine. The tube plates are with water chamber. Condenser is provided with domed shape water box. The condenser tubes are supported within the condenser shell by internal tube support plates and these are so spaced that vibrations of the tubes induced by flow of steam are prevented under normal operating conditions. The condenser during erection is installed in such a way that all condenser tubes are drained automatically into the condenser water boxes and there is no stagnation of water inside tubes. 10% UT/RT of weld seams and the other quality checks are made during erection at site to produce air-tight condenser.

1.1.3NeckCondenser has been provided with an extension neck suitably reinforced to connect it to the turbine exhaust opening. Provision has been made in the condenser neck to accommodate steam dumping devices and extraction steam connections for low pressure heaters. Adequate internal stiffening grid is provided to ensure deflections within permissible limits avoiding dislocation of turbine bearings. The rigid construction results in sound turbine-condenser combination for trouble free operation.

1.1.4Tube LayoutThe tube layout is of modular type having properly sized tube bundles. Each module is separately vented. Steam lanes are designed from thermo-hydraulic considerations resulting into better heat transfer, effective de-aeration and minimum pressure drop. Air cooling zone is suitably located for effective venting. The lower most horizontal band of tubes provide reheating of falling condensate which further helps in de-aeration and minimizes sub-cooling.

1.1.5Water Box The water boxes of the condenser have been designed for smooth entry and uniform distribution of cooling water to all the tubes. The water boxes are removable type and have been provided with necessary hinged manholes for easy access to the interior for inspection. Each water box has been provided with a vent and drain connection. The circulating water connections of adequate size have been provided with water boxes. Safety guards have been provided at CW inlet and outlet connections to protect the operating personnel from falling-in, during inspection or maintenance.

1.1.6Hot WellHot well (of adequate capacity) is divided longitudinally for detecting contamination of the condensate in each condenser half. Suitable man holes are provided in each of the hot well sections for easy access and inspection. The provision of drainage of condensate has been provided at the bottom of the hot well to drain it completely, if required.

The condensate produced in the condenser and the drains entering through flash vessels collect in the condenser hot well from where they pass to the condensate pumps.

1.1.7Thermal Design The thermal design of surface condenser is based on HEI standards.

1.2.0GLAND STEAM CONDENSER

The gland steam condenser is used to condense the steam- air mixure extracted from turbine glands and to maintain slight vacuum at turbine glands for avoiding leakage of steam to atmosphere. Gland steam condenser is placed in the feed heating cycle to serve as a feed heater. The gland steam condenser is of surface type design with horizontal arrangement. It is a single pass heat exchanger with the main condensate flow entering from one end and leaving from other end. Air steam mixure is made to pass over the tubes in zig-zag path by provision of baffles and thus steam is condensed thereby heating the condensate inside the tube. Cooled air is sucked by the electric motor driven Air exhauster which maintains vacuum inside the gland steam condenser and turbine glands. Condensed drain is led to the condenser while heated condensate from tubes enters into L.P. feed heating cycle.

The shell is fabricated from carbon steel plates. It houses necessary connections for the air-steam mixure inlet, drain outlet and air exhaust to Air exhauster. Baffles are welded to the shell. Water boxes are welded to tube plates at both ends. Gland steam condenser is directly connected into the condensate line of feed heating cycle with suitable welded joint.

The tubes of stainless steel are roller expanded at both ends into the steel tube plates. This ensures trouble free operation against corrosion and erosion. Each tube is subjected to a hydraulic test pressure of 70 kg/cm2(g) at tube supplier's works. All the tubes are heat treated throughout their length for better grain structure and long life.Gland steam condenser is subjected to hydraulic test to a pressure of one and a half times the maximum working pressure.

The vessel is cleaned, degreased and painted with suitable paints. All the openings are properly blanked off before despatch.

1.3.0VACUUM PUMPS

2X100% Vacuum Pumps are supplied for maintaining the vacuum in the condenser.

The vacuum pumps are of liquid ring type with rotor eccentric to the casing, giving variable space between water ring (which is concentric to the casing due to centrifugal force) and the impeller for air to be sucked in and compressed during one complete rotation to vent out air into the atmosphere. Pumps will perform for hogging as well as holding operation. During hogging operation, both the pumps will work simultaneously for quick evacuation,while during holding operation,one pump will operate.Capacity of each pump in free dry air at standard conditions is suitably selected to meet the design requirements.Pressure drop in the suction line between pump and condenser is also taken into account while sizing the pump capacity for operating conditions.

Air steam mixture is sucked from condenser through system inlet valve. Compressed air alongwith water is pushed into the air water separator where air is separated and vented to atmosphere through outlet check valve. Due to churning and due to condensation of steam carried away by entrapped air in the pump, sealing water gets heated up before going to the air water separator. Hot sealing water from air water separator is pumped to main pump (by either separate sealing water re-circulation pump or built in arrangement within the main pump) through a heat exchanger, where sealing water is cooled preferably by raw water.The operation of each pump is fully automatic during both holding and hogging.

Each vacuum pump is despatched as a separate package with inter connecting wiring and piping. Vacuum pumps and all accessories are mounted on a fabricated steel base plate.

1.4.0L.P.HEATERS

L.P.Heaters are horizontally mounted shell and tube heat exchanger. L.P.Heaters are designed for shell removal for ease in maintance. Condensateflowinsidethe tubes whilesteam flows outside the tubes .Each heater is of two pass design and has following main parts:

1.Shell

2.Tube nest

3.Water Box

Shell is compeletely welded type, fabricated from carbon steel plates. Shell accommodates steam inlet, shell drains, drains inlet from higher heater, shell vent and shell relief valve connections. Shell is cylindrical vessel with dished end welded at one end and other end is welded with tube plate through shell skirt. Steam inlet connection is kept at thermal balance of tube Dest. Lugs are provided for transportation and lifting during its withdrawal.

Tube nest consists of welded stainless steel U-tubes to ASTM-A688 TP304, Carbon steel tube plate, baffles, impingement baffles for steam inlet and drain inlet. Tubes are roller expanded in steel tube plate. For best utilisation of tube surface, central air duct is provided for continuous venting of non-condensibles. With central air ducting, steam from all round is directed to centre, thus air blanketing is avoided. A short skirt which form part of shell during assembly is welded to tube plate. Stainless steel ring is welded over the tube nest at the location of shell cutting to avoid approach of flame at the tubes while shell cutting. Water box of carbon steel plate is welded to tube plate on the other side. Pass partition is welded to tube plate on one side and bolted to inner cover on other side, so that tube plate is accessible for plugging and inspection. Suitable supports are provided for mounting of heater.

All pressure bearing parts are fabricated from tested quality material. All the tubes individually are hydraulically tested at 70 kg/cm2 (g) at suppliers works. Each tube is eddy current tested before bending. Welders and welding process for pressure parts are quallified as per ASME section IX.

Completed vessel is individually tested on shell side and tube side at 1.5 times of corresponding design pressure.

1.6.0TURBINE OIL COOLER

Turbine oil cooler is provided for cooling the oil for T.G. lubrication system. One extra cooler is supplied as stand by. The function of the cooler is to reduce the bearing oil temperature to a desired value as required for lubrication:-

The main assemblies of cooler are as follows:1.Main shell (Outer shell)

2.Tube nest

3.Upper (reverse) water box

4.Lower (inlet/outlet) water box

The tube nest consists of plain tube of admiralty brass material. Water enters from the lower water box, flows through the tubes to upper water box and then flows down through the tubes before going out from lower water box. Oil flows over the tube bundle with cross flow encountered due to disc and through baffles. This ensures low pressure drop while maintaining good heat transfer rate. Complete nest is enclosed by inner shell around doughnut baffles to avoid oil bypass. Lower tube plate is bolted with lower water box while upper tube plate is kept floating to cater for differential expansion of tube nest and shell. This arrangement also ensures easy removal of tube nest and shell.

A suitable O-ring arrangement is provided at the floating end tube plate to ensure oil tight joint while allowing tube plate to move.

The tubes are roller expanded into the upper and lower tube plate to get leak proof joint. Lower (inlet/outlet) water box is fixed with foundation to hold the complete cooler. Complete tube nest (including inner shell) is enclosed by the main shell which is bolted to lower water box.

Thermometers are provided to measure inlet and outlet temperature of cooling water and oil. Both oil side as well as water side vent valves and drain valves/plugs are also provided.

Inner surface of water boxes are painted with coaltar epoxy paint.. External surfaces of shell and water boxes are painted with suitable paint.

Shell side and tube side are individually hydraulically tested at one and half times the maximum working pressure on respective sides.

All openings are properly blanked off before dispatch to avoid ingress of dirt and dust during transportation and storage.