COMMISSIONING BOILER ALKALI BOIL OUT ,ACID /EDTA CLEANING PART -VI-ABC OF THERMAL POWER PLANT

EDTA cleaning of Boiler 

Ammoniated EDTA with initial concentration of 4 +/- 1% is used for chemical cleaning of Boiler now a days instead of HCL acid cleaning.

Following Preliminary cleaning steps are taken before EDTA cleaning take place.

a. Alkali flushing with Tri Sodium phosphate ( 1000 ppm) and di-sodium phosphate (500 ppm) with boiler water temperature measuring at DRUM 140 degree centrigrade.

b. Hot water flushing with water temperature of 140 degree centrigrade.

c. Cold water flushing with completion criteria as phosphate < 10 ppm and pH = 7.0.

Special inhibitor is required for EDTA is already patented by BHEL ( an Indian Power Plant

manufacturer ) for their use.

Process :- EDTA Pickling

Material required:- Ammoniated EDTA ( 4 +/_ 1%) ; Hydrazine - 1000 ppm; inhibitor-

BHEL Max ( 0.15 % w/w) and BHEL Sol ( 0.15 % w/v) ; Ammonia to maintain PH 9.2-9.8.

Completion criteria :- Iron concentration stabilizes in three concurrent values or EDTA

process continuing  for more than 8 hrs.

Treated DM water rinsing :-  Material required Hydrazine 200 ppm  ,Ammonia to

maintain PH 9.2- 9.8.

Material required for EDTA cleaning Process  500 MW                    250 MW  ( Typical)

Tri sodium Phosphate (  Na3(PO4) 12 H2O     400kg                        250 kg

Di sodium Phosphate (Na2H(PO4) 7 H2O       200kg                        125 kg

Ammoniated EDTA ( C6H12N2O8(NH4)4       42000kg                      22000kg

Ammonia (NH3)                                                1500Ltrs                     1000Ltrs

Hydrazine ( N2H4)H2O                                   1500 Ltrs                     1000 Ltrs

BHEL max                                                         700 kg                         350 kg

BHEL Sol                                                          700 Lit                         350 Lit.      

Beside that well furnished chemical laboratory with necessary reagent and instrument 

like  Spectrophotometer, pH meter , Electronic mass balance , pipette ,burette , measuring


cylinder , volumetric flask etc.

Chemical analysis is carried out to monitor and control the chemical parameters

of the chemical cleaning process for ensuring safe and efficient chemical cleaning

of boiler.

Following chemical parameters are monitored during the process:

   Phosphate Concentration

   pH

  Total EDTA Concentration

  Hydrazine Concentration

  Iron Concentration

The chemical analysis to be carried out during various steps of Chemical Cleaning of Boiler

using EDTA.

A Typical sketch for 660 MW super critical set is given below.





 CONTINUED TO PART -VII EDTA CLEANING.