Problem 1: 1000 kg/hr of water at 1 bar is fed to (Total points 30)
a pump where the pressure of the water is increased to 20 bar in
an adiabatic manner.
The high-pressure water is fed to a isobaric furnace. In the
furnace natural gas (primarily CH4) is burnt and most of the
heat generated is transferred to the water which leads to steam
at 300 C and 20 bar being produced. The steam is then fed to an
adiabatic turbine where it is expanded and then exits as saturated
vapor at 1 bar. This exhaust steam is sent to an isobaric condenser
to cool and produce saturated liquid. This saturated liquid is the
feed to the pump. During the pumping the temperature of the
water increases slightly to 110 C.
The complete steady cyclic process is as shown. The work generated in the turbine is in the
form of electricity and the pump operates by an electric motor that consumes electricity. Thus the
cyclic process produces net electricity.
(i). Calculate the work produced by the turbine the heat that has to be transferred to the water in
the furnace from natural gas the heat removed in the condenser and the shaft work required
by the pump. Clearly state assumptions for each unit.
(ii).If the furnace efficiency is 81% i.e. 81% of the heat generated by combusting methane is
transferred calculate the amount (kg/hr) of natural gas burnt in the furnace using the results
from above part. The heating value of natural gas can be assumed to be 55.6 MJ per kg CH4
burnt.
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