Air Requirement for Combustion

The air required for combustion is compressed by rotating piston compressors or turbo blowers. The air is preheated in heat exchangers by hot gases containing carbon black leaving the reactor. This conserves energy and thus improves the carbon black yield. Preheated air temperatures of 500-700 °C are common. 

Air required for combustion is furnished by turboblowers and preheated in hot-blast stoves lined with refractory-brick checker-work. Commonly,... 

Compute the quantity of air required for combustion. The combustion calculations show that... 

Compute the quantity of flue gas handled. The quantity of gas reaching the induced draft fan is the sum of the actual air required for combustion from step 1, air leakage in the boiler and furnace, and the weight of fuel burned. With an air leakage of 10 percent in the boiler and furnace (this is a typical leakage factor applied in practice), the gas flow is as follows ... 

This heat is used to raise the temperature of combustion products, i. e., 002(g) <1 H20( ) and also the N2 associated with air required for combustion. 

Air requirements for combustion vary with the need to ensure full utilization of the fuel s heating value but not generate excessive air pollutants. The excess air required in practice depends on the type of fuel, the furnace, and the burner. Fuel oil, for instance, requires 5 to 20% excess air depending on burner design. Excess air is recognized as a routine measure of heater performance. 

N.B. For the purposes of this model, additional excess air can be regarded as entering the calcining zone at ambient temperature as the heat in the lime entering the calcining zone is already insufficient to pre-heat the stoichiometric amount of air required for combustion to 900 °C.)... 

The mechanism behind the operation of a pulse combustor is a complex interaction between an oscillatory combustion process and acoustic waves that are propagated from the combustor (Figure 14.1). The process of pulse combustion is initiated when air required for combustion and fuel in the form of a gas jet or a liquid spray are drawn into the combustion chamber, mixed to... 

We have already discussed under practical stoichiometry how the air requirements can be estimated based on the fuel composition (ultimate analysis). The primary and secondary air requirements for combustion of pulverized coal or coke are best estimated by mass and heat balance at the mill. In Appendix 6A we show a calculation taken from Musto (1997) for the primary and secondary air required for coal pulverizer with 4.5 metric ton per hour (10,0(X)lb/hr) coal feed rate at initial moisture of 15 percent which is required to be ground and dried to 2 percent with a 200 HP mill. In order to estimate the actual primary and secondary air, one has to make some estimation of the evaporation rate, the amount of gas entering the coal mill, and the bleed air required so that the quantity of air that should be vented from the hood off-take can be properly estimated. It shows that for a take-off gas temperature of 315°C (600° F) and vent gas temperature of 76°C (170°F) and allowing ambient air infiltration of 10 percent at 15°C (60°F) the primary air will be about 22 percent of stoichiometric air and 21 percent of total air. The remaining air (about 79 percent) will be the secondary air. With this information we can size a burner using a burner pipe diameter based on a Craya-Curtet parameter of choice bearing in mind the conditions that ensure the desired jet recirculation patterns described in Chapter 3. 

The minimum amount of air required for combustion will depend on the heat consumption of the kiln and can be approximately calculated from ... 

A small portion of the air required for combustion (15 to 20 percent) is used to transport the coal to the burner. This is known as primary air and is also used to dry the coal in the pulverizer. The remainder of the combustion air (80 to 85 percent) is introduced at the burner... 

Air required for combustion Volume of air per 1-unit volume of the ideal gas Weight of air per 1-unit weight of the ideal gas Flammable limits in air, percent by volume Flash point... 

The mechanism behind the operation of a pulse combustor is a complex interaction between an intermittent combustion process and pressure/velodty waves that are propagated from the combustor (Fig. 2.1). The process of pulse combustion is initiated when air required for combustion and fuel in the form of a gas jet or a Uquid spray are admitted to the combustion chamber to make-up an explosive mixture, which is ignited by a spark plug and burns instantly in an explosion-like manner. At this moment, the air and fuel inlet ports are closed, either by mechanically operated valves or due to the hydrodynamic action of the rapidly rising pressure. The combustion-generated pressure forces the combustion products to flow out through the tailpipe to the process volume. As the hot flue... 

---