Radiation and convection losses will vary with boiler type, size, and operating pressure. The losses are typically considered constant in BTU/hr, but become a larger percentage loss as the firing rate decreases. Boiler design factors that also impact efficiencies of the boiler are heating surface, flue gas passes, and design of the boiler and burner package.
A condensing boiler can condense the water vapour in the flue gases and withstand the corrosive and acidic qualities of the flue gas condensate. Although most boilers can condense the flue gasses, only boilers that have heat exchangers constructed from materials able to withstand the corrosion should be used in condensing application. Condensing boilers with primary and secondary heat exchanger do not work well as they are not able to fully condense and defeat the purpose of using a condensing boiler. Also, boilers with this arrangement are prone to condensation in the primary heat exchanger at lower firing rate which can cause damage to the heat exchanger.
From wood burning to pellet-firing biomass, alternative fuel boilers and solid fuel fired boilers offer environmentally friendly energy options and cost efficiencies. With the push to become less reliant on fossil fuels, alternative fuel boilers provide a way for plant managers to save money on fuel sources as well as meet tightening emission regulation standards.
Combustion efficiency is an indication of the burner’s ability to burn fuel. The amount of unburned fuel and excess air in the exhaust are used to assess a burner’s combustion efficiency. Burners resulting in low levels of unburned fuel while operating at low excess air levels are considered efficient. Well designed conventional burners firing gaseous and liquid fuels operate at excess air levels of 15% and result in negligible unburned fuel. Well designed ultra low emissions burners operate at a higher excess air level of 25% in order to reduce emissions to very low levels. By operating at the minimum excess air requirement, less heat from the combustion process is being used to heat excess combustion air, which increases the energy available for the load. Combustion efficiency is not the same for all fuels and, generally, gaseous and liquid fuels burn more efficiently than solid fuels.
Excess air provides safe operation above stoichiometric conditions. A burner is typically set up with 15% to 20% excess air in higher firing ranges. Higher excess air levels result in fuel being used to heat the air instead of transferring it to usable energy, increasing stack losses and significantly decreasing efficiency. Boilers with lower excess air throughout the operating range have higher efficiencies.
The air in the economizer and condenser has not drained yet when firing. The safety valves of economizer and condenser need to be turned on to exhaust steam. Return pipe valves also need to be turned on, enabling the steam in the economizer and condenser to return to softened water tank.
The outlet water temperature is so high that economizer and condenser will have vaporization phenomenon. The outlet water temperature of economizer and condenser need to be controlled.
The check valve of the...
