Best practice no 22

LOSSES DUE TO HIGH TEMPERATURE CONDENSATE PURGE

The water used to feed the boilers contains dissolved salts that are concentrated because the steam generation process only evaporates water, due to this we must throw away a certain amount of water concentrated with salts at high pressure and temperature, therefore that we lose heat invested in bringing the water to those conditions, this loss is a direct relationship of the amount of water that must be thrown away.

MOISTURE LOSSES IN THE GENERATED STEAM

The presence of humidity in the steam is due to the dragging of liquid in the generation of steam, this water does not intervene in the heating processes, so it is discarded as condensate, losing the latent heat it has.

The acquisition of a boiler is normally done by calculating the maximum demand of our steam-consuming equipment and increasing it by 30 to 50% more due to future expansions, so that finally the boiler operates at 30 to 60% of its design capacity. Conventional boilers at low operating loads decrease their design efficiency.

The capacity of a boiler is normally given with feed water at 100°C and one atmosphere of pressure, but the water we feed to our boilers is normally at room temperature, so we need to use part of the steam generated to preheat the boiler water. feeding from 20°C to 100°C, lowering the real efficiency of the boiler.

CALCULATION OF CAPACITY LOSS DUE TO PREHEATING

Assuming steam is generated at 10 kg/cm² DATA: T = 185°C

Enthalpy of the saturated liquid........................hf = 185.6 kcal/kg. Enthalpy of vaporization ..................................hfg = 478.4 kcal/kg. Enthalpy of saturated vapor.............................hg = 663 kcal/kg.

HEAT REQUIRED TO CARRY A BHP FROM 20°C TO 100°C

Q = 15.6 kg/h x 1 kcal/kg°C x 80°C = 1,248 kcal/h

HEAT REQUIRED BY BHP FROM 100°C TO 185°C AS STEAM

Q = 15.6 kg/h x 1 kcal/kg°C x 85°C + 15.6 kg/h X 477 kcal/kg

Q = 8,767 kcal/h

CAPACITY LOSS = 1,248 Kcal/h / 8,767 Kcal/h = 14.2 %

The monotubular forced convection Steam Generators by design recover 25% in humidity of the amount of steam that is being generated in the separator, this condensate is recovered to the condensate tank acting as a preheating system.

RECOVERED HEAT

QR= 15.6 Kg/h x 0.25 x 186 kcal/kg = 725 kcal/h

HEAT NECESSARY BY BHP TO TAKE FROM 20°C TO 100°C

Q = 1,248 Kcal/h - 725 kcal/h = 523 kcal/h

CAPACITY LOSS = 523 Kcal/h / 8,767 Kcal/h = 6.0 %

FOR-IM-024

REVISION DEL FORMATO: C

FECHA DE EFECTIVIDAD DEL FORMATO:10/03/2022