Advantages of forced circulation boiler, Steam accumulator, Equivalent Evaporation

Advantages of forced circulation boiler

• The evaporator tubes may be built in any orientation. Natural circulation requires vertical piping whereas the forced circulation ensures flow in any direction.^[6]
• The walls of the tube may be built smaller due to the greater tolerance of higher pressure losses.^[6]
• The general forced circulation boiler has a low circulation ratio of range between three and ten. The circulation ratio is how much steam is produced per how much feed was put in. Natural circulation boilers have a huge range of circulation ratios all the way from five to one hundred.

Steam accumulator

 Steam Accumulator is an equipment which accumulates energy in form of pressurized hot water which can be used later when the steam demand of the process goes above the boiler capacity. The accumulator stores energy in the form of pressurized hot water which flashes to produce steam at lower pressure for the process. The accumulator is constructed in form of a horizontal cylindrical steel tank with dish-ends and control instrumentation to control the charging and discharging cycle with level controls.

  Working principle of steam accumulators

 When the saturated water at high pressure is exposed to low pressure, some amount of this water will flash off into steam by using excess sensible heat in the water. The proportion of flash steam (kg of steam/ kg of water) depends on the pressure difference to which the hot water is exposed.  

When steam demand from the plant is low, and the boiler is capable of generating more steam than required (i.e. at maximum continuous rating of boiler), the surplus steam available is injected into a mass of water stored under pressure in the accumulator. 

After a while, the temperature of stored water will increase to saturation temperature with respect to the pressure at which the boiler is operating. And when steam demand is high such that it exceeds the maximum capacity of the boiler, then this leads to drop in pressure at accumulator which in turn leads to flashing of some proportion of water into steam, thus fulfilling the high steam demand without affecting the normal operation of the boiler.

Definition of equivalent evaporation

1. the rate in pounds per hour at which water would be vaporized in a given steam boiler if supplied and evaporated at the normal boiling point and normal atmospheric pressure

What is BOILER TRIAL?

A test where exact ammounts of fuel and feed-water are used in a boiler in order asses specific sources of loss.

BOILER TRIAL: "The boiler trial was inconclusive."