A system consisting of an exhaust gas boiler (EGB)

Question: A system consisting of an exhaust gas boiler (EGB) and an auxiliary boiler is used for producing saturated steam in a bulk carrier. The exhaust gas boiler uses the exhaust gas of the ship main engine. The following parameters are given: main engine exhaust gas mass flow rate: 129 t/h Temperature of exhaust gas entering the EGB: 235oC specific heat at

A system consisting of an exhaust gas boiler (EGB) and an auxiliary boiler is used for producing saturated steam in a bulk carrier. The exhaust gas boiler uses the exhaust gas of the ship main engine. The following parameters are given:

main engine exhaust gas mass flow rate: 129 t/h
Temperature of exhaust gas entering the EGB: 235oC
specific heat at constant pressure of the exhaust gas: 1.07 kJ/kgK
EGB efficiency: 100%
produced saturated steam when the auxiliary boiler is switched off: 3.25 t/h Pressure of saturated steam/water: 8 bar (absolute)
Temperature of saturated steam/water: 170.4oC
Temperature of water entering the boiler: 130oC
Saturated steam specific enthalpy: 2768.3 kJ/kg
Saturated water specific enthalpy: 720.86 kJ/kg
Feed water specific enthalpy: 251.3 kJ/kg
Auxiliary Boiler efficiency: 0.93
Auxiliary Boiler fuel lower heating value: 40800 kJ/kg

1. Calculate the thermal power recovered from the main engine exhaust gas at the EGB when the auxiliary boiler is switched off.

2. Calculate the temperature of the exhaust gas exiting the EGB when the auxiliary boiler is switched off.

3. Calculate the minimum temperature difference at pinch point of EGB and compare it with the typical values required for normal boiler operation.

4. Calculate the economiser thermal power, the evaporator thermal power and the respective percentages out of the total boiler thermal power and plot the temperature/thermal power diagram for the EGB.

5. Calculate the mass flow rate of the fuel required to be burnt in the auxiliary boiler for the case where an additional saturated steam mass flow rate of 3 t/h needs to be produced.

6. Consider that the EGB and AB simultaneously operate. Calculate the electric power required to drive the feed water pump. Make appropriate assumptions to estimate the parameters that are not provided.