Steam Condenser types,function, tube test, condenser vacuum

steam condenser types, function, condenser vacuum, importance in power plant , air ingress prevention,fouling

1. Condenser Waqar ahmed Hubco power plant

2. Contents Introduction Types Condenser vacuum Function of condenser Tube materials Importance Leak test methods Cleaning of tubes

3. Introduction A steam condenser is a closed vessel which is maintained at low pressure, (lesser than atmospheric pressure). The condenser acts as a heat exchanger where exchange of heat occurs between steam and cold circulating water. In this system, heat rejection at atmospheric temperature takes place by condensing exhaust steam from prime mover. The condensate can be reused as feed water to the boiler. The steam turbine condenser is located under LP turbine.

4. Types of Steam Condensers The  steam condensers  are broadly classified into two types : Jet condensers  (or mixing type condensers). In jet condensers there is direct contact between the exhaust steam and cooling water. Surface condensers  (or non-mixing type condensers). In surface condensers, there is no direct contact between the exhaust steam and the cooling water.

5. Jet Condenser In jet condensers, the cooling water is sprayed on the exhaust steam and there is  direct contact  between the exhaust steam and cooling water . The process of condensation is  very fast  and efficient, but here cooling water and condensed steam are  mixed up . The condensate then cannot be reused as feed water to the boilers. 

6. Surface Condenser In surface condensers, there is  no direct contact  between the exhaust steam and the cooling water. The exhausted steam from the LP turbines is condensed by passing over tubes containing water from the  cooling system . 

7. Surface Condenser These tubes are usually made of stainless steel, copper alloys, or titanium depending on several selection criteria (such as thermal conductivity or corrosion resistance).   Titanium condenser tubes  are usually the best technical choice, however titanium is very expensive material and the use of titanium condenser tubes is associated with very high initial costs. In general, there are two types of surface condensers: water-cooled surface condenser air-cooled surface condenser

8. Condenser vacuum For water-cooled surface condensers, the shell's internal vacuum is most commonly supplied and maintained by an external ejector  system. Such an ejector system uses steam as the motive fluid to remove any non- condensible gases that may be present in the surface condenser. Motor driven mechanical vacuum pump such as the liquid ring type , are also popular for this service.

9. Why vacuum is necessary T o pull out non condensable gases/air M ake faster the process of condensation otherwise the gases will react , can cause of serious material fatigue & tubes failure. T o achieve the process/plant efficiency. To pull the low pressure steam. To change the phase steam to water rapidly. To prevent the turbine back pressure. To protect the tubes failure.

10. Sources of air ingress Atmospheric relief valves Rapture disks LP heaters / re-heater Drain valves Turbine seals Condenser expansion bellow From ejector lines Instruments /sight glasses Valve stems/bonnets Hot well man hole covers Piping weld joints Condensate pump seals

11. Effects of air ingress Efficiency of condenser decreases Condensation process will slow Failure to remove non condense able gases , that may cause of corrosion or material failure Lower heat transfer properties Unconscious temperature occur in turbine last stages Pressure can generates on last stages Rotor blades can effected

12. Function of Condenser Create the vacuum for condensing steam Removing dissolved noncondensable gases from steam Change the phase, steam to condensate Re use the demin water Providing a barrier between condensate and non treated cooling water Providing a barrier against the air ingress Preventing excessive back pressure to turbine Serving as a drain receptacle ,receiving vapors & condensate from many exchanger, from valve leak off Facility of storage and makeup water

13. Condenser tube materials Copper base alloy (ASTM B111 , B543) Stainless steel (ASTM A213, A249, A268, A269, B268) Titanium (ASTM B338 , Gr1&2) Carbon steel (ASTM A179, A214)

14. Why condenser is important in power plant

15. Why condenser is important Can get Maximum steam energy For Rankine cycle High vacuum can obtained easily increases of plant efficiency Reuse of condensate water Saving of Water treatment plant cost Power saving

16. Condenser Leak Test Methods Hydro testing Soap test Electronic device test

17. Hydro testing Take permit and open the water box covers. Check the oxygen level in confined space. Fill the shell with water until all tubes get dip in water Insert the fluorescent powder in water and mix it well. Give some time to penetrate the water in cracks. Check tube sheet from both sides, if any water leak find then mark and plug both end of tube After it , use the fluorescent light to detect leak(off other light while using F.light) The fluorescent light identify the minor leaks, then plug the tube both ends. After all , drain the water and close the covers. Check housekeeping , return permit . Fill the box up sheet.

18. Soap testing Take permit and open the water box covers. Check oxygen level in confined space. Clean the tube and tube sheet. Start the ejector / vacuum pump for vacuum , because we need vacuum . Use rubber gloves and Prepare the soap water & mix well to obtain the bubbles. Put the soap bubbles to the tube ends and check the bubbles is cracking or not, because if the bubbles are cracking it means the tube is sucking air, and that particular tube is leak. Identify the leak tube and install plugs on both ends. After all check housekeeping and close covers.

19. Electronic tube detector Take permit and open water box covers Check the oxygen level in confined space. Start the ejector for vacuum. Use electronic device on the end of every tube. Check the air passing, when air passing in tube it means tube sucking air, and that tube is leaking. Identify the tubes and plug it. Update the tube sheet check list.

20. Eddy current Eddy current testing  uses electromagnetic induction to identify defects in  tubing . A probe is inserted into the  tube  and pushed through the entire length of the  tube .  Eddy currents  are generated by the electromagnetic coils in the probe and monitored simultaneously by measuring probe electrical impedance.

21. Fouling Fouled condenser tubes cause significant economic problems for power station operation. Reduced heat transfer capability results in a higher backpressure in the condenser and less efficient turbine performance , requiring increased fuel or even limiting generation capacity . A second serious concern is that condenser tube leaks commonly occur as a consequence of fouling.

22. Types of fouling Condenser tube fouling is mostly a tube interior concern, generally into the categories Microbiological Scale Deposition Corrosion Tube sheet plug gage

23. Fouling prevention Steps can be taken to significantly reduce the possibility of condenser tube fouling .incoming water may be treated for particular removal by the use of settling ponds or by filtration. The chemical dosing system can reduce the fouling effect (to improve water quality) . The travelling mesh can prevent from fouling. Mechanical system of sponge ball can also be use to prevent the tube fouling.

24. Condenser tube cleaning Condenser tube cleaning can occur: With steel rod When just debris on tube ends then we can use steel rod. Pressurized water gun: When tubes are fouling , pressurized water gun will remove the accumulated debris internally.

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