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Show 2. REPOWERING 2. 1 Improvement in Steam Conditions The most effective way to improve the power generating effeciency is to raise the steam temperature and pressure. In Japan, however, temperature below 300°C had been used to avoid high-temperature corrosion of the superheater caused by the corrosive elements in the flue gas. This was becasue the main purpose of MSW incinerator had been considered as a means of hygenical Iy treating MSW, and power generation was given a secondary role. Therefore, it was generally accepted practise to maintain a stable operation of the plant, rather than increasing the power generation at the expense of frequent superheater repair. Due to recent environmental concerns such as fossi I fule depletion and global warning caused by CO 2 , studies on more efficient power generation by the MSW incineration plants began to be taken UP by various groups such as Waste Innovation 21C Project and NEDO (New Energy/New Industrial Technology Development Organization). As mentioned eal ier, superheater temperatures has been capped in order to avoid high-temperature corrosion. It is now acknowledged that given a proper superheater design, a much longer I ife span can be expected. Figure 10 I I lustrates the relationship between the steam temperature and the service I ife of steam pipe based on the field operation data. It shows that the pipe has at least 15,000 to 16,000 hours of I ife with the steam temperature of 400°C. (Of course the difference in MSW and flue gas compositions between USA and Japan should be considered.) Service Life [h) 40,000 30,000 20,000 10,000 300 350 400 450 500 550 Temperature of l ive-steam rOC] Figure 10 SERVICE LIFE OF THERMAL HEAVILY STRESSED BOILER HEATING SURFACES IN INCINERATION PLANTS 9 |