The measurement of thermal characteristics in boiler furnace

The power-up tendency of marine power plant in recent years has led to great increase of heat release rate of boiler furnace, which may cause a serious problem such as local overheat of boiler tubes and the reinvestigation of thermal design method. In order to get some information about these problems, we carried out a test on a natural circulation boiler (steam generating rate; 30T/H) . Here are shown the test results of gasflow pattern, temperature distribution and heat flux distribution which are considered to have much to do with these problems. Firstly, an observation of flow pattern was done using a 5-hole pitot tube and a smoke generator etc.. And the results are as follows; (1) the flow pattern was kept approximately the same to the both case whether there was flame or not, (2) flame shape was like an egg and independent from the shape of the furnace, (3) there existed a strong reversal flow in the narrow range between the flame and the floor, (4) there was no flame in the upper half of the chamber and the gas flow was stagnated here. Secondly, the temperature distribution in the furnace was measured with a suction pyrometer and the result showed a good correspondence with the observed flow pattern and flame shape. The maximum temperature was recorded at the position, downward about one-third of the flame length from the burner tip. The gas temperature at the chamber outlet showed fairly good agreement with the calculated one. Lastly, heat flux distribution was measured using a heat flux probe of our own idea, by which not only the radiation component but the whole heat flux was measured. The maximum heat flux was recorded at the midway of the flame length and was 67-84% greater than the average value, which resulted in fairly large unbalance of heat absorption rate of each boiler tube. And this unbalance nay have a great influence on water circulation and safaty of boiler. The radiation component of whole heat flux was about 84% at half load.