In order to develop new corrosion resistant superheater tubes capable of functioning efficiency under temperature and pressure conditions of 500ºC and 100ata used in high efficient waste-to-energy (WTE) plants, field corrosion tests were conducted m eight single tube materials and two welded overlay materials at metal temperatures of 450ºC and 550ºC for 700 and 3000 hours, respectively, in three typical Japanese waste incineration plants.
The test results indicate that austenitic alloys containing higher concentrations of [Cr + Ni + Mo] show excellent corrosion resistant properties and new alloys of JHN24 and HR30M have good corrosion resistance.
The different corrosion rate found for each of the three plants could be explained by differences in the severity of corrosion factors, such as, gas temperature, concentration of molten salts due to C1 content of deposits, and heavy metal [ZnO+PbO] content etc. h was also confirmed that the corrosion rate of materials positioned in the first tube row facing the oncoming flow of gas show somewhat higher rate than those in the second row due to higher C1 content in the deposits.
Applying the above information, a pilot plant capable of processing 50 tons of waste per day, under respective temperature and pressure conditions of 500ºC, 100ata is now under construction, and eleven conventional and new tubings will be tested over a two year period.
There is a strong demand in Japan for the high efficiency of waste-to-energy (WTE) plants to be improved in order to achieve greater energy savings and protection of the environment. Legislative initiatives, as demonstrated by the recent revision of the Electricity Enterprises Act, are also creating conditions which make it easier to sell the power generated by small scale power plants.
Higher temperatures and higher pressures in boiler steam are essential to improving the efficiency of power plants, Consequently, state-of-the art plants capable of operating at 400ºC and 40ata levels are starting to be constructed and operated in plain of conventional plants which operate at temperatures of 300ºC and pressures of 30ata. At present, there are approximately 130 waste incineration plants in operation in Japan which have their own power generation facilities. The total amount of power being generated by WTE plants is on the rise as shown in FIGURE l(l). However, in order to secure a stable power supply and satisfy requirements for cost petiomnce, tie prevention of high temperature corrosion damage to boiler tubes has become a major topic of concern. In order to prevent high temperature corrosion, it is necessary to study both how to reduce the severity of high temperature corrosive environments and the use of corrosion resistant alloys. Such efforts will serve to address demands for the realization of plants in which total costs including maintenance costs can be reduced through a proper combination of both approaches.
NEDO (New Energy and Industrial Technology Development Organization) has been engaged in a project to develop high efficiency waste-to-energy plant technology since 1991, for purpose of developing a plant capable of generating 500ºC and 100ata steam.
