The soot from residual fuel oil shows similar structure to that of conradson carbon. When X-ray analysis were performed on soot produced in a practical furnace (cenospher) and on conradson carbon, similar values were obtained.
With the object of determining whether addition of metal naphthenate would improve combustion of fuel oil less formation of soot, a study on the effect of metal naphthenate on conradson carbon was made. The results are summarised as follows:
(1) In general, the addition of metal naphthenate to residual fuel oil has no effect in reducing the formation of conradson carbon. Ferrous naphthenate, however, reduce the formation of conradson carbon.
(2) Cuprous and ferrous naphthenate tend to decrease the activation energy and lower the ignition point of residual carbon in combustion. These effects are considered to result from the catalytic action of the metals.
(3) The addition of metal naphthenate did not change the crystal structure of conradson carbon. No particular relation was noted between crystal structure of carbon and its combustion rate.
(4) From the above results, conclusion was reached in that proper metal naphthenate (Cu, Fe salts) improves the burning qualities of fuel oil soot (Cenospher).

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Corrosion and deposit formation in the air-heater has always been an obstacle to continuous operation of oil-fired boilers. To overcome the difficulties, changes in design and construction of the air-heater section constituted a part of countermeasures. In addition, injection of ammonia gas into combustion gas has been a common practice so as to neutralize the sulfuric acid as formed in the process of combustion of fuel oil containing sulfur. A major trouble encountered here, however, lies in the fusion and accumulation of NH₄HSO₄, a combustion by-product with the low melting point, in the air-heater.
On the basis of our studies on the condensation temperature of sulfuric acid and the decomposing temperature of (NH₄)₂SO₄, the ammonia injection temperature zone has been found to be an important factor in this method. The ammonia injection was then applied to a boiler of the thermal power plant for a one-month period, using the following operating conditions; ammonia injection rate-0.06/0.07wt.% of fuel oil fired, injection temperature zone -180°C in flue gas. Satisfactory results were obtained from this test as indicated in the reduced accumulation of deposit. An inspection of the deposit also confirmed the above statement.
As regards the powder injection, dolomite powder which is known as an effective agent for eliminating the high temperature corrosion was used to remove sulfuric acid from the combustion gas. Corrosion as observed in the test using air-cooled corrosion probe started dropping at the injection level of 0.3wt.% of fuel oil fired. Contrary to an anxiety about the formation of undesirable gypsum, none of them was traced by an X-ray diffraction analysis of the deposit in the air-heater. How to efficiently mix the powder with the combustion gas, and what economical dosage of powder to be used must further be analyzed. A fly-ash injection also proved somewhat effective from the corrosion reduction viewpoint.

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