The conventional BFW treatment was carried out with Amine base product comprising of Neutralizing and Filming Amine. The function of Filming Amine is to form a Film against and protect the equipment from dissolved oxygen. However, the film formation requires a narrow pH control in feed water system and can be non-uniform if high dissolved oxygen is present in feed water. Due to absence of oxygen scavenger in the treatment chemical, the high dissolved oxygen in feed water resulted in non-uniform film resulting in pitting type of corrosion. Also, due to higher m-alkalinity in BFW there was substantial generation of CO2 in the boiler resulting in low pH in the steam circuit. The problem was further aggravated during hardness slippage in BFW due to poor softner performance resulting in deposition in boiler tubes.
To avoid the above a new multiproduct phosphate based chemicals with oxygen scavenger and neutralizing amine was tried. Oxygen scavenger is found to be very effective in reducing the dissolved oxygen in BFW thereby minimizing pitting type of corrosion. The observation of phosphate residue in the boiler water indicated that all calcium magnesium hardness slippage in the boiler was getting fully consumed with phosphate and taken out thru boiler blow down system. This has resulted in reduced scaling inside the boiler tubes. Also, due to antifoaming action of the chemical carry over of silica and volatile in the super heater section was minimized. Thus, during the treatment, the boilers were operated at maximum possible cycles.
The conventional treatment of Boiler Feed water with Phosphate (TSP), Hydrazine, Caustic Soda & Ammonia was common in HPCL Mumbai Refinery. The limitations of this treatment were mainly in terms of hardness slippage, safety hazards and unsafe handling of carcinogenic hydrazine as an oxygen scavenger. The conventional treatment was changed in 1993 to amine based single product comprising of Neutralizing and Filming Amine.
The filming amine chemical forms film on metal surfaces and protect the equipment from direct contact of dissolved oxygen. However, the film formation requires a narrow pH control in feed water system and can be non-uniform if high dissolved oxygen is present in the feed water.
The performance of amine base single product was not satisfactory resulting in changing to new phosphate based multi-product chemical treatment. The new program found to be cost effective for improving the reliability of the boiler operation. The performance of these new phosphate based chemical was evaluated and the details are presented.
This product is a blend of film forming aliphatic polyamines, neutralizing amine and dispersing amine. Aliphatic primary polyamines forms adhesive films on clean metallic surface and prevent even the growth of microcrystalline calcium and magnesium salts. This is totally organic formulation, safe, non-toxic and non-carcinogenic product. The elimination of salts based treatment results in substantial reduction of blow down losses. It allows higher level of TDS in boiler further adding to the reduction of blow down.