OCR Text |
Show 4.4 Combustion Test Regarding the combustion, there are some important aspects to be evaluated for good combustion performance. They are as follows; © Ignitability • Flame stability © Contents of Flue Gas (NOx , Unburned carbon , SOx , CO) © Ash properties (1) Ash Properties CWM firing has different characteristics from that of the parent coal. One of them is the ash deposition problem caused by chemical additives. Figure-16 shows the ash deformation and flow temperature at heating by a Reitz pyro microscope when the sodium content in CWM is increased by adding as NaOH. Ash properties of the raw coal are shown in Table-3. In Figure-16, it appears that both flow temperature and deformation temperature except the case of TA-coal decrease with the increase of sodium addition. This is a severe tendency for slagging or fouling in the boiler. By these results, the selection of additive containing sodium is not preferable for CWM preparation. Non-sodium, non-sulfur additives with lower costs for CWM should be developed in future. However, the addition of 0 - 0.1 % has little effect on the ash deposition and can be fully tolerable for ash properties because of little temperature decrease in this range. (2) Multi-Burner Test © Flame Temperature The flame temperature and ignition stability are influenced by each other and affect not only combustion efficiency but also NOx emission. The data were obtained by means of an optical pyro-meter and are shown in Figure-17. Adiabatic flame temperature of the CWM combustion is estimated to be about 150 to 200 °C lower than that of the parent pulverized coal combustion. Actually, the difference between CWM flame temperature and the parent pulverized coal is about 100 ~ 150 °C. As shown, the lower XBNR becomes, the less the difference of the temperature is. XBNR is defined as follows ; NR Actual Air Quantity to Burners Theoretical Air Quantity The difference of combustion flame temperature is considered to mainly result from the presence of water. 6 |