Calculation and Analysis

Referring to Figure 5.17. Determine Flash % using Chart B:

Entering chart B with a boiler drum pressure of 150 psig and following a live to the curve for a flash tank pressure of 20 psig, read the Steam percentage (Flash %) to be 12.5%.

Determine COND %:

COND % = 100 - Flash % COND % = 100 - 12.5 % COND % = 87.5% Determine htk using Chart A:

Entering chart A with a flash tank pressure of 20 psig and following a line to the curve for saturated liquid, read the enthalpy of the drum water (htk) to be 226 Btu/lb. Determine hex using Chart C:

Assuming a 30°F approach temperature between condensate discharge and makeup water temperature, the temperature of the blowdown discharge is equal to the makeup water temperature plus the approach temperature which equals 100°F (70°F + 30°F).

Entering chart C with a blowdown heat exchanger rejection temperature of 100°F and following a line to the curve, read the enthalpy of the blowdown discharge water to be 68 Btu/lb. Determine the % QC:

Determine the % Q:

% Q = % QC + Flash % % Q = 61.2% + 12.5% % Q = 73.7%

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