What are sub critical boilers?
What is a Subcritical Boiler? Subcritical boilers are boilers that work at temperatures up to 374°C and at a pressure of 3,208 psi (the critical point of water). These boilers compose a system with constant evaporation endpoint. A typical example for a subcritical boiler is the drum-type steam generator.
What are critical and super critical boilers?
Super Critical Boilers are the boilers which operate at steam pressure higher than critical point. Critical point is 22.064 Mpa, 373.946 deg cen. at this point latent heat of evaporation is zero & there is no difference in density of steam & water.
What is the average efficiency of sub critical boiler?
In subcritical boiler higher GCV coal are used like semi- bituminous coal and Indian lignite coal gives 80% efficiency near about.
Which boiler is critical?
Subcritical consists, preheater, evaporator and superheater while supercritical boiler requires only preheater and superheater. Supercritical boilers operate at a pressure greater than 22 MPa and also referred to as Once through boilers since the feed water circulates only once through boiler in each steam cycle.
What is sub critical condition?
The condition of a nuclear reactor system, in which nuclear fuel no longer sustains a fission chain reaction (that is, the reaction fails to initiate its own repetition, as it would in a reactor’s normal operating condition).
What is the difference between supercritical and subcritical flow?
Subcritical flow is dominated by gravitational forces and behaves in a slow or stable way. It is defined as having a Froude number less than one. Supercritical flow is dominated by inertial forces and behaves as rapid or unstable flow.
What is the difference between subcritical and supercritical flow?
Subcritical Flow: Depths of flow greater than critical depths, resulting from relatively flat slopes. Froude number is less than one. Flow of this type is most common in flat streams. Supercritical Flow: Depths of flow less than critical depths resulting from relatively steep slopes.
What is boiler efficiency formula?
η=(Energy output)/(Energy input) X 100
In order to calculate boiler efficiency, we divide the total energy output by total energy input, multiplied by hundred.
What is boiler critical pressure?
The critical pressure and critical temperature of water and steam are 22.12 MPa and 647.14 K, respectively. Any boiler that operates below the critical point is called a subcritical boiler, and one that operates above the critical point is known as a supercritical boiler.
What is pressure of supercritical boiler?
In contrast to a subcritical boiler in which bubbles can form, a supercritical steam generator operates at pressures above the critical pressure – 22 megapascals (3,200 psi). Therefore, liquid water immediately becomes indistinguishable from steam.
What is sub critical depth?
Subcritical occurs when the actual water depth is greater than critical depth. Subcritical flow is dominated by gravitational forces and behaves in a slow or stable way. It is defined as having a Froude number less than one. Supercritical flow is dominated by inertial forces and behaves as rapid or unstable flow.
What are two advantages of supercritical boilers?
Specific advantages include:
Steam temperature at the inlet and outlet of the reheater is nearly constant over a wide load range. The boiler feedwater pump power is significantly reduced at lower loads. Short startup times. Higher plant efficiency over the entire load range.
What is boiler capacity?
Since the amount of steam delivered varies with temperature and pressure, a common expression of the boiler capacity is the heat transferred over time expressed as British Thermal Units per hour. A boilers capacity is usually expressed as kBtu/hour (1000 Btu/hour) and can be calculated as. W = (hg – hf) m (1)
What is boiler calorific value?
Gross Calorific Value
This is the theoretical total of the energy in the fuel. The gross calorific value of the fuel includes the energy used for evaporating the water in the combustion process. The flue gases from boilers are in general not condensed.
What is critical pressure formula?
expression for critical pressure is Pc=27b2a.
What is critical temperature in boiler?
The water being heated to the critical temperature (706° F.) turns completely and instantaneously into steam.
What temperature is supercritical steam?
Supercritical water exists at temperatures above 374 °C and pressures above 220 atmospheres.
What is supercritical temperature and pressure?
The supercritical condition of a steam-water cycle is a state at which its temperature and pressure are above its thermodynamic critical point, where the pressure of the steam water is 22.12 MPa, the temperature is 647.14 K, and the density is 324 kg/m3.
What is normal depth?
Normal depth is the depth of flow in a channel or culvert when the slope of the water surface and channel bottom is the same and the water depth remains constant. Normal depth occurs when gravitational force of the water is equal to the friction drag along the culvert and there is no acceleration of flow.
Why supercritical boiler is used?
B&W’s supercritical and ultra-supercritical boilers are designed to take full advantage of variable pressure turbine operation. Specific advantages include: For a given output, lower fuel consumption, and thus lower carbon emissions, than other less efficient systems.
What is the unit of boiler?
Steam boilers output can be expressed in Boiler Horsepower, MBTU or in Pounds of Steam delivered per hour. Boiler load – the capacity of a steam boiler – is often rated as boiler horse powers, lbs of steam delivered per hour, or BTU.
What is the formula for boiler?
How do you calculate LCV and HCV?
L.C.V. = H.C.V. – ms x 2466 L.C.V. = H.C.V. – 9 H2 x 2466 KJ/Kg. Dulong’s formula used to calculate the theoretical calorific value of fuel if ultimate analysis is available and the calorific value of elementary combustibles are known.
What is called critical pressure?
The critical pressure is the vapor pressure of a fluid at the critical temperature above which distinct liquid and gas phases do not exist. As the critical temperature is approached, the properties of the gas and liquid phases become the same, resulting in only one phase.
What is the critical pressure ratio?
The critical pressure ratio is the ratio of the downstream pressure to the upstream pressure at which the flow becomes sonic. Below the critical pressure ratio, the mass flow rate is constant for a given upstream pressure. The flow is choked, and it does not change if the downstream pressure is decreased.