CHEMICAL CLEANING OF PRE-BOILER SYSTEM
OBJECTIVES To remove dirt ,oil ,grease etc., from Condensate ,Feed water, Drip and Extraction steam lines of HP and LP heaters prior to putting these systems in regular service. This is to ensure flow of clean condensate and feed water to the boiler.
STATE OF THE PLANT • Hydro-test of the entire system to be flushed declared completed. • All the regenerative equipments are installed in position and temporary pipeline connection as per scheme is complete. • The bore of the temporary pipelines should preferably be the same as that used in permanent system. • All permanent support are provided for all the pipelines before flushing. • Plugs to be provided in the safety valves of LPHs,water seal inlets in flash tanks and LPH 1 and in C&I tapping. • Screens to be provided on booster pump suction line and acid cleaning pump suction line
• Availability of auxiliary steam. • Reagent preparation plant. • Sampling points for each circuit. • Level gauge on tank, pressure gauges and temperature indicators wherever required. • All the cutting and welding work on instrument tapping points are complete upto isolating root valves. • All the orifices,flow nozzles, control valves and NRV internals are removed and a checklist is prepared. Spool pieces are provided wherever required. • Installation of temporary chemical cleaning pumps(2 nos.) and connected piping along with required instrumentation is complete. • During post mounting cleaning it is proposed to use chemically clean water from condensate storage tank.
• Readiness of process water supply system,condenser circulating water system with pump house. • Availability of compressed air. • Proximate analysis laboratory facility. • Power supply to acid cleaning pumps,CEPs,condensate emergency make up pumps, condensate normal make up pumps, motor operated valves and lighting.
EQUIPMENTS AND RESOURCES FOR WATER WASHING • Condensate storage tanks. • Condenser of volume 1000m 3 as a reservoir for storing the dematerialized water. • Turbine condensate pumps (3 nos.). • Chemical cleaning pumps (q=300t/h,h=80mwg,n=1500rpm)- 2nos. • Compressor plant and pipeline Dn100 to supply air into the washing circuit with the parameters not less than q=20m 3 /min,p=0.6MPa • Pipelines and valves Dn 20-300,Pn 1.6MPa
EQUIPMENT AND RESOURCES FOR CHEMICAL CLEANING AND PASSIVATION • Deaerator and Feed Water Storage Tank. • Chemical cleaning pumps (q=300t/h,h=80mwg,n=1500rpm)- 2nos. • Pipelines and valves Dn 20-300,Pn 1.6MPa • SG Package neutralizing basin for collecting the spent solutions. • Reagent Preparation Plant designed for storage, preparation and supply of chemical reagents. • Chemical reagents. • Washing process controlling instruments (flow elements, pressure gauges, level gauges, temperature elements)
The pre-boiler system consists of • Condensate system • Drip system • Feed water system • Extraction steam lines to Regenerative Heaters
→ Condensate system comprises of 3 nos. of Condensate Extraction Pumps,Low Pressure Heaters, Gland Steam Cooler,Deaerator,connecting pipelines including excess condensate line upto Condensate storage tank.
→ Feed water system comprises 2 nos. of motor driven boiler feed pumps,2 nos. of Turbine driven boiler feed pumps ,their booster pumps and recirculation lines, high pressure heaters, their connecting pipelines upto econimiser inlet.Reheater and Superheater spray line are also included for the purpose of flushing.
→ Drip system comprises of the shell side of all LP and HP heaters and their normal and emergency drip lines.
→ Extraction steam system consists of bled steam lines from different stages of Turbines (HPT,IPT and LPT) to LP and HP heaters,Deaerator and TDBFPs.
CLEANING METHOD • Pre- mounting cleaning. Extraction steam lines to regenerative heaters • Post-mounting cleaning. Feed water line,Condendate line and heater drip lines. • Steam blowing. MS line,CRH line , HRH line ,steam line to TDBFPs etc.
METHODS AND SCOPE OF CLEANING Post Mounting Cleaning • Main Turbine and BFP Drive Turbine Condenser Cleaning. • Hydro-pneumatic Washing with Demineralized Water of Unit Circulating System. • Chemical Cleaning of Water – Steam path of Heater and Pipeline with hydrofluoric Acid solution. • Chemical Passivation of Water-Steam path of Heater and Pipeline with Hydrogen Peroxide solution added with Ammonia.
Pre-Mounting Cleaning • Chemical Cleaning of Pipelines in a bath of Hydrofluoric Acid solution. • Spent solution displacement. • Chemical Passivation of Pipelines with Hydrogen Peroxide solution added with ammonia. • Air Blowing of Passivated pipelines for drying.
Main Turbine and BFP Drive Turbine Condenser Cleaning or Condenser Degreasing. STEP- I • The demineralized water is heated upto 70 0 c in the De-aerator FST. • The Chemical solution prepared in reagent preparation plant is mixed with the hot water in the De-aerator FST.
• The hot solution is transferred to Condenser with the help of temporary chemical cleaning pump through temporary pipelines connecting pump discharge header to the CEP discharge header and the cooling device sprayers of Condenser. • Circulation is completed by bringing this solution from condenser to Chemical Cleaning pump suction header through CEP suction header and temporary pipeline connection. • Circulation is continued for 4 hrs. • System is isolated after closing one temporary gate valve provided in the circuit (refer to scheme.)
DEAERATOR CHEMICAL AUX.STEAM FST BP BP BP BP ACID CLEANING PUMPS CONDENSERS CEPS
STEP – II • CEPs are charged from water side by opening suction valve and through proper venting, keeping discharge valve in closed condition and suction strainer in position. • Flushing started by alternately starting and stopping CEPs and completing the circulation from CEP discharge to CEP suction line through recirculation line and condenser.
• Circulation is continued for 4 hrs. • After cleaning the spent solution is pumped from condenser to neutralizing basin. • Water washing of Condenser started and continued for 4 hrs. using the two circuits already described..
DEAERATOR CHEMICAL AUX.STEAM FST BP BP BP BP ACID CLEANING PUMPS CONDENSERS CEPS
Hydro-pneumatic Washing of Unit Circulating System with Demineralized Water and air. → Hydro-pneumatic washing of unit circulating system is carried out step by step with simultaneous water and air supply. → Demineralized water for washing is stored in the De-aerator FST and Condenser. → Hydropneumatic washing is declared completed if suspended matter content of the washing water reaches no more than 100mg/kg. → Hydro-pneumatic washing of unit circulating system is done using following four circuits.
CIRCUIT 1: Circuit 1A De-aerator FST – TDBFP A booster pump suction line – BP strainers – Temporary header connecting the BP suction lines downstream of the strainers – Acid cleaning pumps – Temporary discharge header – Temporary lines to the discharge gate valves of four feed pumps – Feed lines to HPH – Bypass line of all HPH – HPH bypass lines – Water path of HPH 6,7,8 – Feed water line upto boiler feed control unit – Temporary discharge line to the circulating water line - De-aerator FST.
Circuit 1B De-aerator FST – TDBFP B booster pump suction line – BP strainers – Temporary header connecting the BP suction lines downstream of the strainers – Acid cleaning pumps – Temporary discharge header – Temporary lines to the discharge gate valves of four feed pumps – Feed lines to HPH – Bypass line of all HPH – HPH bypass lines – Water path of HPH 6,7,8 – Feed water line upto boiler feed control unit – Temporary discharge line to the circulating water line - De-aerator FST.
Circuit 1C De-aerator FST – MDBFP booster pump suction line – BP strainers – Temporary header connecting the BP suction lines downstream of the strainers – Acid cleaning pumps – Temporary discharge header – Temporary lines to the discharge gate valves of four feed pumps – Feed lines to HPH – Bypass line of all HPH – HPH bypass lines – Water path of HPH 6,7,8 – Feed water line upto boiler feed control unit – Temporary discharge line to the circulating water line - De-aerator FST.
Circuit 1D De-aerator FST – Booster pump suction line – BP strainers – Temporary header connecting the BP suction lines downstream of the strainers – Acid cleaning pumps – Temporary discharge header – Temporary lines to the discharge gate valves of TDBFP A – Feed lines to HPH – Bypass line of all HPH – HPH bypass lines – Water path of HPH 6,7,8 – Feed water line upto boiler feed control unit – Temporary discharge line to the circulating water line - De-aerator FST.
Circuit 1E De-aerator FST – Booster pump suction line – BP strainers – Temporary header connecting the BP suction lines downstream of the strainers – Acid cleaning pumps – Temporary discharge header – Temporary lines to the discharge gate valves of TDBFP B – Feed lines to HPH – Bypass line of all HPH – HPH bypass lines – Water path of HPH 6,7,8 – Feed water line upto boiler feed control unit – Temporary discharge line to the circulating water line - De-aerator FST.
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