Midterm 2 – ENERGY 293B – Winter 2021

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2. Geothermal Dual-Flash Power Plant? [50 points]



The Te Mihi geothermal power plant in New Zealand is a dual-flash plant that uses intermediate
pressure (IP) and low pressure (LP) steam inlets. The LP steam is obtained by flashing the water
from the first (IP) separator down to a lower pressure in the second (LP) separator. The first (IP)
turbine produces 50 MW of electricity.

Using Xsteam (or your program of choice), determine the following answers:
(a) What is the steam consumption rate (kg/kWh) in each of the two turbines?
(b) What is the geofluid consumption rate (kg/kWh) in the first turbine?
(c) The first (IP) turbine produces 50 MW of electricity. How much steam does it require?
(d) How many MW of electricity does the second (LP) turbine produce?
(e) What is the geofluid consumption rate (kg/kWh) of the combined plant (IP + LP)?

Assume a generator efficiency of 1.0, and a dry turbine efficiency of 0.85. Other parameters are:
IP separator pressure 5.2 bar.a
LP separator pressure 1.14 bar.a
Condenser pressure 0.065 bar.a (same for both IP and LP units)
Reservoir temperature 200°C


[The actual plant uses a single, dual-inlet turbine, however to simplify the question we will
consider it as if there were two separate turbines. Also, the actual plant takes an additional flow
of LP steam from lower pressure wells in the field. Again, we will ignore this to simplify the
problem.]