Author: Sumit Waghmare

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%

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

About Me…

Hi all..
Hope you all are enjoying the life to the fullest..

Let me take pleasure to introduce myself, I’m Sumit Y Waghmare (BE Mechanical) residence of Pune, India.
Currently I’m working in reputed Boiler Manufacturer in pune as Asst, Manager Design. Now guess the kind of work a design engineer is doing in a Steam Insustry.. yes lots of thermal, mass & heat balance!
Thou thermal was not my major in my engineering.. it was now bread & butter for me. I’ve learn a lot many things in my stay in company & all creadit goes to my learnign capacity 😉 and off-course to the company.
I’m looking forward your discussion on the topic.. the Queries, the Troubleshooting, Your on site design experience..
I also developed small package software which i think is be very useful tool for any thermal engineer..
What I’ll share?
I’ll share my knowledge, I’ll introduce you with my small soft tools! You may ask for a trial copy 🙂 till date I’ve not thought of making it commersial but it all start if there is a good response!