The conventional boiler unit for Municipal refuse incinerator is operated at about 30 kg/cm²g and 300 deg.C for the prevention of high temperature corrosion of superheated steam tube by the HCl corrosion at gas temperature of 350 deg.C or more. This condition results in low energy recovery efficiency as about 15 percent in total, and some improvement is expected for better energy recovery.
Recent advanced technology development has brought about these conditions into 35 kg/cm²g and 310 deg.C, which gives the efficiency of 18 percent, that is, 20 percent improvement of total energy recovery efficiency against the conventional system.
The new exhaust gas boiler that has been developed by Mitsubishi Heavy Industries, Ltd. allows for high temperature corrosion preventive measures to offer steam conditions of 40 kg/cm²g and 400 deg.C for a higher efficiency with energy recovery of about 20%.

2. Characteristics

This achievement is performed by the following technologies:

(1) Set the superheater tube at gas temperature of lower than 600 deg.C
(2) Make the tube thickness doubled at high temperature zone
(3) Increase the flue gas passing time up to superheater to 6 seconds or more.
(4) Change the materials of tube at high temperature to alloy.

Through these improvements, this system has low corrosion (0.1 to 0.2 mm/year) and has been safely operated.

3. Performance

For example, as for the capacity of 800 tons per day incinerator with the calorific value of 3000 kcal/kg, the generated electricity will increase greatly as:

  Normal condition as 30 kg/cm2g and 300 deg.C  : l9,000kW generation
  New high condition as 40 kg/cm2g and 400 deg.C: 24,000kW generation

Exhaust gas boiler side view