| 摘要 |
Combustion assisting devices (50, 52) for heating exhaust gas at the upstream of one of the heat exchangers and a fuel supply system for supplying fuel to the combustion assisting devices are disposed. In order to avoid damaging a heat-conducting tube by means of high-temperature exhaust gas, an index value for restricting the amount of fuel supplied to the combustion assisting devices (50, 52) is set and the amount of fuel supplied to the combustion assisting devices (50, 52) is restricted so as to not surpass the limit of the index value. |
