- A boiler designed to generate 5000 kg/hr steam for & at,100-degree Celcius at mean sea level will not give the same quantity of steam if shifted to an elevated place. It will give less steam.
- Due to decreased air density at higher altitude, it will consume the same volume of air but will not consume the same mass of air.
- This results in less fuel consumption & less steam generation rate.
- Due to the reduction of mass flow of gases through tubes of a boiler, convective heat transfer also decreases which further results in reduced evaporation rates.
Combustion is a process which needs the constant air supply for its survival, but as we move up the earth i.e. at higher altitudes, things aren’t the same as they used to be at sea level. The oxygen content in the air reduces exponentially. Unlike human body, a Steam Boiler doesn’t acclimatize itself to this shortage.
Though the Blower provides the same volume of air the reduced density of air (oxygen to be specific) leads to reduced combustion, lesser fuel consumption hence reduced steam generation.
So, it can be concluded that a Steam Boiler at its rated capacity, won’t keep up the promise of desired output at elevated levels. So, one should focus on the mass flow rate of air supplied for combustion instead of volumetric flow. Knowledge of De-rating factor can help in quantifying the reduced output of the Boiler. A Proper volumetric flow of the Blower should be selected as per the conditions.
At higher altitudes, atmospheric temperature decreases, so to increase the efficiency of the boiler one must focus on increasing the temperature of feed water and air. Also, the proper insulation of all the equipment must be ensured in order to prevent the heat losses due to convection and radiation.