The units are 250 MW negative draft boilers. Each has 16 burner guns, 4 at each level. At the time of the trial the unit burned 500 000 tones oil per year.
The plant’s main problem was severe deposits fouling the system. The production loss due to boiler cleaning downtime was 180 000 MW h per year.
This was an excellent opportunity to demonstrate that a Bycosin product could clean up a fouled boiler and out perform the other products in the market. It was decided to propose DP 99004.
The organic magnesium based deposit inhibitor had proved to be excellent at demonstrating a fast reduction of slag deposits.
It also reduces stack solids, both hot and cold end corrosion and makes the remaining deposits soft, porous and easy to remove.
Bycosin DP 99004 is a slag inhibitor combined with a combustion catalyst that rapidly reduces existing slag deposits. It also reduces soot/stack solids and makes the remaining deposits soft, porous and easy to remove.
• The organic Mg penetrates easy into the deposits and slag, due to the smaller size of the organic Mg, and makes the deposits soft and friable.
• DP 99004 rapidly cleans tubes and walls throughout the whole system from furnace to air pre heater.
• The DP 99004 raises the melting point of the ash and prevents corrosion at high and low temperatures.
It is important to keep the furnace surfaces clean in order to get maximum heat transfer (heat radiation).
In most cases, a surface with deposits will reduce heat transfer to the water in the tubes and increase the temperature of the flue gases out the stack. This can result in more deposits and high temperature corrosion in the back end of the boiler.
The trial was carried out between April 6 and July 30.
A base line measurement was taken in February, prior to the trial, and is referred to in the diagrams as a reference point.
Measurements were taken from both boilers, but this report will be based only on boiler #1.
During the trial Bycosin DP 99004 was used to treat the existing deposits and to inhibit corrosion attacks from sodium vanadium deposits.
All this data was taken in co-operation with the plant. The acid dew point was taken at the air heater inlets and outlets.
Dust burden was measured at EP (Electric Precipitator) inlet A & B.
The O₂ was measured at EP outlet A & B. Fly ash samples were taken at air heater inlets and outlets. Monitoring the DP99004 dosage was done on a daily basis.
The field inspection showed the lack of deposits from the DP99004 treatment. The photo inspection gave a clear image of how well DP 99004 had cleaned the boiler.
All through the boiler the clean surfaces could be seen and the small amount of remaining deposit was dry and very friable. In the superheater section even the old corrosion damage could be seen because the surfaces were so clean.
By June the ash pH had increased on all sides of the air heater and the pH was almost 1 point higher than the trial reference point (from pH 2,2 to pH 3).
When using DP99004 the acidity dropped to very low levels. The drop in acid dew point is an important confirmation of the fact that the ash is less acidic and less corrosive.
The lower high temperature super heater looked like it had deposits but they were marks from earlier corrosion attacks that DP99004 uncovered from the tubing.
It is a well-known fact that there can be no corrosion without deposits as it is a “dry” corrosion process at the temperatures we have at the super heaters.