Boiler Education: Ask the Energy Expert
Dear Energy Expert,
My plant is looking for recommendations for achieving boiler combustion control more efficiently. Do you have any suggestions?
Check Burner Air to Fuel Ratios
In light of the continued rise in fuel and labor costs, a good understanding of basic combustion theory is more important today than ever before. In addition, increasingly stringent environmental regulations and concerns make the selection, design, and maintenance of combustion control systems of paramount importance. There must always be more air supplied to the combustion process than the theoretical or stoichiometric air requirement. This is because no burner made is this “perfect”. This “extra” air is referred to as “excess air”. If 20% more than the theoretical air requirement is supplied, we say that the burner is operating at 20% excess air. Another way of stating the same thing is to say that the burner is operating with 120% “total air.”
Eclipse Combustion Engineering Guide
Click to open the engineering guide to Eclipse products. The Eclipse combustion engineering guide (EFE 825, 1/00 Electronic Edition Published by Eclipse, Inc. All Rights Reserved) contains chapters on Orifices & Flows, Fan Laws & Blower Application Engineering, Gas, Oil, Steam & Water, Electrical Data, Process Heating, Combustion Data, Mechanical Data, and more. Please reference the Eclipse combustion engineering guide below.
Furnace Pressure Controllers
Furnace draft, or negative pressure, is created in fuel-fired furnaces when high temperature gases are discharged at a level higher than the furnace openings. This is commonly known as the chimney effect. The negative pressure in a furnace that operates at a fixed temperature changes with the heat input rate or mass flow of flue gases moving through the stack. This negative pressure causes ambient air to leak into the furnace. Furnace pressure controllers regulate and stabilize the pressure in the working chamber of process heating equipment. Pressure controllers use a pressure gauge in the furnace chamber or duct and regulate the airflow to maintain a slightly positive pressure (a few inches of water gauge) in the furnace chamber. Airflow can be regulated by varying the speed of draft fans or by changing damper settings for the incoming combustion air or the exiting flue gas.
Install Waste Heat Recovery Systems for Fuel-Fired Furnaces
Load Preheating: Load Preheating Using Flue Gases from a Fuel-Fired Heating System
Oxygen Enriched Combustion
Reduce Air Infiltration in Furnaces
Fuel-fired furnaces discharge combustion products through a stack or a chimney. Hot furnace gases are less dense and more buoyant than ambient air, so they rise, creating a differential pressure between the top and the bottom of the furnace. This differential, known as thermal head, is the source of a natural draft or negative pressure in furnaces and boilers. A well-designed furnace (or boiler) is built to avoid air leakage into the furnace or leakage of flue gases from the furnace to the ambient. However, with time, most furnaces develop cracks or openings around doors, joints, and hearth seals. These openings (leaks) usually appear small compared with the overall dimensions of the furnace, so they are often ignored. The negative pressure created by the natural draft (or use of an induced-draft fan) in a furnace draws cold air through the openings (leaks) and into the furnace. The cold air becomes heated to the furnace exhaust gas temperature and then exits through the flue system, wasting valuable fuel. It might also cause excessive oxidation of metals or other materials in the furnaces.
Save Energy Now in Your Process Heating Equipment
Process heating accounts for about 36% of the total energy used in industrial manufacturing applications. And in some industries, this percentage is much higher. In the glass industry, for example, process heating accounts for about 80% of energy consumption, according to the U.S. Department of Energy’s (DOE) Manufacturing Energy Consumption Survey. The thermal efficiency of a heating system can be improved significantly by using heat contained in furnace flue gases to preheat the furnace load (material coming into the furnace). If exhaust gases leaving a fuel-fired furnace can be brought into contact with a relatively cool incoming load, heat will be transferred directly to the load. Since there is no intermediate step, like air or gas preheating, in the heat recovery process, this can be the best approach to capturing waste heat. Load preheating is best suited for continuous processes, but it can sometimes also be used successfully with intermittently operated or batch furnaces.
Waste Heat Recovery 101
Thermal efficiency of process heating equipment, such as furnaces, ovens, melters, heaters, and kilns is the
ratio of heat delivered to a material and heat supplied to the heating equipment. For most heating equipment, a
large amount of the heat supplied is wasted in the form of exhaust or flue gases. These losses depend on various factors associated with the design and operation of the heating equipment. This technical brief is a guide
to help plant operators reduce waste heat losses associated with the heating equipment.
This technical brief supports or complements the software tool Process Heating Assessment and Survey Tool
(PHAST) developed jointly by the Industrial Heating Equipment Association (IHEA) and the U.S. Department
of Energy’s (DOE) Industrial Technologies Program.