CoOLING TOWER
The Towers also known as refrigeration or cooling towers are structures for water cooling and other means to temperatures close to the environment. The main use of large industrial cooling towers is to lower the temperature of the cooling water used in power plants, oil refineries, petrochemical plants, processing plants, natural gas and other industrial facilities. The main types are: wet cooling towers operated by the principle of evaporation dry cooling towers, which operate by heat transfer through an area that separates the fluid to cool ambient air. In a cooling tower wet hot water can be cooled to a temperature below that of the environment, if the air is relatively dry. With regard to the shooting in the air tower there are three types of cooling towers: natural Tyre, which uses a high chimney. Tyre helped by natural Tyre mechanical ventilator (or forced draught), which uses the power of engines ventilation led to the air force or pushing for the tower. Under certain environmental conditions, clouds of water vapor (fog) can be seen emerging from a cooling tower dry (see picture). The cooling towers used evaporation of water to reject heat from a process such as electric power generation. The cooling towers vary in size from small to very large structures that can exceed 120 metres high and 100 metres long. Torres smaller are usually built in factories, while larger are built on the site where required.
Balance of material from a cooling tower wet.
Quantitatively, the balance of material around a cooling tower system is controlled by the wet operating variables structural rate of flow, and evaporation losses from wind, trasegado rate, and cycles of concentration.
M = Water
structure in m³ / h
C = Water circulating in m³ / h
D = Trasegado water m³ / h
E = Water evaporated in m³ / h
W = Loss on wind water m³ / h
X = Concentration in ppmw (from completely soluble salts,
usually chlorides)
XM = concentration of chloride in the water structure (M),
ppmw
XC = concentration of chloride in the water circulating (C),
ppmw
Cycles Cycles concentration = = XC / XM (dimensionless)
ppmw = parts per million by weight
In the sketch above, the water pumped from the tank of the
tower is aimed coolant water coolers across the process and
capacitors in an industrial plant. The cold water absorbs
heat from the warm currents of the process that need to be
cooled and condensed, and the heat absorbed heats the water
circulating (C). The heated water returns to the top of the
cooling tower and falls in thin jets - introducing great
surface for cooling the air - on cushioning material inside
the tower. As drips, contact with the air rises by the tower,
shot by natural or forced by large fans. This contact causes
a small amount of water is lost by wind drag (W) and part
water (E) through evaporation. The heat needed to evaporate
the water itself is derived from water, which cools the
water to return to their original deposit and where it is
available to re-circulate. The water evaporated leaves salts
dissolved from carrying the bulk of which has not suffered
water evaporation, which makes the increased concentration
of salts in the cooling water circulating. To prevent the
concentration of salts in the water becomes too high, a
portion of water is removed (D) for disposal. It provides
the deposit of the tower new cadre of fresh water (M) to
offset losses from the evaporated water, wind and water
withdrawn.
The balance of water in the entire system is:
M = E & D & W
As the water evaporated (E) has no sales, the balance of
chloride of the system is:
M (XM) = D (XC) + W (XC) = XC (D & W)
and, accordingly:
XC / XM = Cycles concentration = M ÷ (D & W) = M ÷ (M - E) =
1 + [E ÷ (D & W)]
From a balance of heat simplified the tower:
E = C ÷ Δ T cp HV
Where:
HV = latent heat of vaporization of water around = 2260 kJ /
kg
Δ T = temperature difference of water from the top of the
tower to its base, in ° C
cp = = specific heat of water about 4,184 kJ / kg / ° C
Losses by wind (W), in the absence of information from the
manufacturers, can be estimated that are:
W = 0.3 to 1.0% of C for cooling towers shooting naturally.
W = 0.1 to 0.3% of C for cooling towers induced draught.
W = approximately 0.01% of C if the cooling tower disposers
have the effect of wind.
The cycles of concentration in the cooling towers at an oil
refinery normally are between 3 to 7. In some large power
plants. Cycles of concentration of cooling towers may be
much higher.
SOME IMAGES OF COOLING TOWERS
|
Information compiled on
june 17, 2008 by Webmaster of wide tec Ricardo Nava |
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