To improve the steam production on board via the exhaust gas economizer, X-engines can be equipped with a controlled exhaust gas bypass valve.
Such a valve can be opened on demand when the exhaust gas temperature is lower than the target temperature, or when the steam pressure is lower than required. As a consequence of the exhaust gas bypass opening, the exhaust gas temperature increases and steam production through the boiler is increased.
As an example, the below figure shows the same X-engine with and without the variable bypass. With the variable bypass it is possible to target exactly the minimum steam production needed if the exhaust gas temperature is lower than that required. Where
no variable bypass is installed, it is necessary to switch on the thermal boiler to reach the targeted steam production.
Increasing the steam production with an engine variable bypass is more efficient than switching on the thermal boiler, and fuel consumption savings of 2-6 g/kWh are possible