OCR Text |
Show 4 (6) Since in the two-stage air combustion method, air fed at the second staqe hardly reaches at the center of the main stream of combustion gas, formation of soot due to delayed combustion, difficulty in low air ratio (below 1.0) combustion and other problems are encountered. However, by applying this new method, as oxygen always exists in the center of the main stream of combustion gas, soot is hardly formed, and thus low excess air combustion becomes possible. (7) In the flue gas self-recirculation method, the draft pressure has to be made high because of its characteristics. In this new method, it is not necessary to make the draft pressure high. (8) In the water injection and flue gas re-circulation method, such problems as decrease of heat transfer or increase in thermal loss, etc. are encountered. In this new method, such problems are not encountered. As described above, it can be said that the two stage fuel system has many features. 4. Control Effect on NOx Formation : 4.1 The case of single burner The following shows the results on study of the control effect on formation of NOx by installing the burner with the specification as shown in Table 1 in the horizontal cylindrical furnace with water cooled wall (in some cases, the inner surface of the water-cooled wall is lined with thermal insulating materials such as ceramic fiber to check the characteristic of NOx formation when the furnace temperature is increased). The fuels used in the test were natural gas with 99 % CH4 content, industrial propane, kerosene and A heavy oil which nitrogen content is less than 0.01 %. Measurement of NOx was done by chemiluminescence analyzer, 02 by magnetic or zirconia analyzer, and temperatures inside the furnace and at the exit of furnace by suction pyrometer. 10-4 |