Page 382 - Handbook of Energy Engineering Calculations

FIGURE 7 T-S diagram of the cycle shown in Fig. 6.

Calculation Procedure:

1. Determine the enthalpy of steam in the reservoir at 460 ° F (238° C)

Therefore,

x = 0.161
3

2. Find the enthalpy ratio
Mass of water from well per unit mass of steam = 1/x = 6.21.
3
Mass of reinjected brine per unit mass of steam = 6.21 − 1 = 5.21.
Ratio of enthalpy at 5 to enthalpy at 4 = 5.21(h /h ) = 5.21 × (298.
4
5
54/1187.2) = 1.31.

Related Calculations. The flashed-steam system is reserved for water in the
higher-temperature range, and is illustrated by the flow and T-S diagrams of
Figs. 6 and 7. Water from the underground reservoir at 1 reaches the well

head at 2 at a lower pressure. Process 1-2 is essentially a constant enthalpy
throttling process that results in a two-phase mixture of low quality at 2. This
is throttled further in a flash separator resulting in a still low but slightly
higher quality at 3. This mixture is now separated into dry saturated steam at

4 and saturated brine at 5. The latter is reinjected into the ground.
The dry steam, a small fraction of the total well discharge (because of the
low quality at 3), and usually at pressures below 100 psig (8 bar), is expanded
in a turbine to 6 and mixed with cooling water in a direct-contact condenser

with the mixture at 7 going to a cooling tower in the same fashion as the
vapor-dominated system. The balance of the condensate after the cooling
water is recirculated to the condenser is reinjected into the ground.
The flashed-steam system is a more difficult proposition than the vapor-

dominated system for several reasons: (1) much larger total mass-flow rates
through the well, as shown by the preceding example; (2) a greater degree of