Feed Pump Selection

Lets do the Quick Caclulation
Actul Flow in m3/hr ?
Design head MWC ?
Operating head MWC ?

Minimum Flow required for safer operating of the pump ?
How the by pass is maintained, using Orifice or control Valve ?
Let Boiler Steam flow rate is 31000 kg/hr

32.488 m3/hr X 1.05 (design factor) + Min. bypass flow via orifice = 40.87 m3/hr
(Boiler pressure + pr. drop in system ) x 1.05 (design factor) = 207.38 MLC

Pr. Drop Flow Head Density
Flow Rate 31000 m3/hr MLC kg/m3
Working pr 18 1.75 40.87 207.38 955.317
Design Pr 20 1.75 40.87 228.38 995.331
Temp 105
Rated Flow 34
% Bypass 20

Select the pump for 40.87 m3/hr & 207MLC & 228MLC Condition

Superheater – Gas Flow

Design of any heat exchanger is manly depend upon the flow configuration.
As discussed before the configuration could be of three type (majourly)

  1. Parallel Flow
  2. Counter Flow
  3. Cross Flow

The compactness increases from Parallel flow to Counter Flow to Cross Flow

While complexity increases in reverse direction.

The superheater has flue gas on one side & Ideal gas on other. As steam has less capacity of carring the heat than water, we have to give more area.

The velocity of steam & flue gas plays a majour role in deciding the compact ness of heat exchanger.
More the velocity, more will be reynold’s number, higher will be nusselt number, higher will be heat transfer co-efficient which leads to higher over all heat transfer co-efficient & hence
lesser Area.

Superheater – Performance Optimization

One thing we must remember while designing super heater.. Better the steam dryness compact will be the super heater.

One must always ensure that dry steam (99%) is coming in the superheater.
Just to give you the picture..

  • for 98% Dry steam.. the unit energy required to make steam 100% dry+70ºC superheat

is : 61.5kcal/kg

  • for 99% Dry steam.. the unit energy required to make steam 100% dry +70ºC superheat

is : 56.1kcal/kg

i.e if you give 99% dry.. 61.5-56.1 = 5.4Kcal/kg i.e for 6000kg/hr its 40KW less energy is required.

Lower heat demand.. means lower heat transfer area.

“Higher dryness fraction, lower heat load, lower heat transfer area, compact heat exchanger”

Now Dryness can be improved by giving dimister pad or giving external equipment to improve steam dryness.

Superheater Design

A Major component of the Boiler

Superheater are of Two Type
1. Convective type
2. Radiant type

Convective super heater gives maximum of 80ºC of Superheat while, Radiant Superheat can give 150-300ºC Superheat. Former is more prone to thermal failure & rarely used in ‘flue gas boiler’.

I’ll discuss the convective type super heater.
The basic criterion for the design are
1. Degree of superheat required
2. Steam Dryness available at inlet of super heater
3. Heat duty available.
4. Maximum pressure drop allowed in the system.
5. Flue gas maximum temperature.
6. Type of heat exchanger configuration flow, Cross/Parallel/counter etc.
Flue gas maximum temperature is required to select the MOC of the super heater tubes

for Heat duty following equation shall be validated
M Cp DT = m. (Unit enthalpy of steam)
M = Mass of flue gas
cp = Heat capacity of the flue gas
DT = Temp. drop across super heater
m = mass of Steam

NOx of the Boiler

Nox is majourly a function of Burner & then a Boiler.

Mainly in retrofit market Nox commitment can be achieved by changing burner design & Burner refractory.

Type of Nox
1. Thermal Nox Contributes to 80% of Total Nox
2. Instant Nox Contributes to 15% of Total Nox
3. Fuel Nox Contributes to 5% of Total Nox

I’ll write in details later..

Burner Design

Burner Design

Three parameters decides performances of the burner
1. Turbulence,
May be created by ‘Swearler’ & high velocities, which results in better fuel atomization. optimum size of fuel droplet is 50 microns
2. Time,
Time of residence, residence time of the fuel during combustion, for gas its low, for LDO its high & for FO its highest
3. Temperature,
Right & high temperature at core, wil yield better combustion.


O2% gives excess air level, excess air decides fuel qty, more excess air, more the fuel gases, more stack temperature & hence more stack losses, as more air is carrying the heat with it.

Heat is carried away with the N2 in the flue gases, which can’t be recovered & hence carried away in stack.

Fast Burner Funda!!

Hi I’m making this live again.. lets start with Burner!!

The Flame Visibility
1. Low Luminous flame causes, Non uniform Temperature & heat flux distribution
2.Low Luminous flame causes Poor radiant heat transfer & hence lower thermax efficiency
3. While More luminous flame gives Good radiant heat transfer, Low flame temperature & low NOx

Flame Geometry & O2
Blue Whitish flame,7.5% O2 Whisling Noise
At high excess air & velocity, molecules of the fuel start burning in fractions. on-off in this manner they produce small explosion along the length.
Hence flame will be bright & fluctuating in nature

Blueish pinkish flame
Less blue, more pink gives less NOx, higher blue flame suggest excess air & higher NOx

Critical Heat Flux for Any Flue gas Tube Steam Genrator

CHF (Critical Heat Flux)

During the brainstorming session, we have come with a critical question on ‘Furnace life’ due to higher heat loading in the furnace. during the ‘research’, I came across a term, Critical heat flux(CHF) or the ‘burn out point’.

The past decade has witnessed unprecedented improvements in the performance of packaged boiler which were brought about, for the most part, by a restless pursuit of reducing the foot print of boiler. These advances have led to increases in the amount of heat that is dissipated and has to be removed from these furnaces to keep its life up & good heat transfer, large increase in heat dissipation per unit surface area is now the benchmark for designing of the furnace.

The CHF is a very interesting and important phenomenon from both fundamental and practical points of view. From the fundamental point of view, CHF accompanies tremendous changes in heat transfer, pressure drop and flow regime.

The critical heat flux (CHF) condition is characterized by a sharp reduction of the local heat transfer coefficient that results from the replacement of liquid by vapor adjacent to the heat transfer surface (Collier & Thome, 1994). The occurrence of CHF is accompanied by an inordinate increase in the surface temperature for heat-flux-controlled systems, and an inordinate decrease in the heat transfer rate for temperature-controlled systems. The CHF condition is generally more important in the heat-flux-controlled systems, since the temperature increase can threaten the physical integrity of the heated surface.

Dissipation of large heat fluxes at relatively small temperature differences is possible in systems utilizing boiling phenomenon as long as the heated wall remains wetted with the liquid. With the wetted wall condition at the heated surface, heat is transferred by a combination of two mechanisms:
(i) bubbles are formed at the active nucleation cavities on the heated surface, and heat is transferred by the nucleate boiling mechanism, and
(ii) heat is transferred from the wall to the liquid film by convection and goes into the bulk liquid or causes evaporation at the liquid-vapor interface. The large amount of energy associated with the latent heat transfer (compared to the sensible energy change in the liquid corresponding to the available temperature potential in the system) in the case of nucleate boiling, or the efficient heat transfer due to liquid convection at the wall, both lead to very high heat transfer coefficients in flow boiling systems. Removal or depletion of liquid from the heated wall therefore leads to a sudden degradation in the heat transfer rate.

The way in which the heated surface arrives at the liquid starved condition in a flow boiling system determines whether it is termed as Critical Heat Flux

At atmospheric pressure, The critical heat flux is slightly above 1MW/m². The formula for calculation of heat flux is given below.

This formula is derived by Zuber,N and its more in line with the practical values