Secondary air

The steam generator is a balanced draft, controlled circulation, multichamber unit which incorporates NO control and final burnout of the fuel-rich MHD combustion gases. The MHD generator exhaust is cooled in a primary radiant chamber from about 2310 to 1860 K in two seconds, and secondary air for afterburning and final oxidation of the gas is introduced in the secondary chamber where seed also condenses. Subsequent to afterburning and after the gas has been cooled down sufftciendy to soHdify condensed seed in the gas, the gas passes through the remaining convective sections of the heat recovery system. 

Entrainment of Particles in an Air Stream. The lighter the particle and the finer its size, the longer it may remain suspended in an airstream such as upon filling of a bin. Secondary air currents can carry airborne particles away from a fill point into outer areas of a bin, scattering them in a way that bears no resemblance to the calculated trajectory. 

Modern central stations use the other burner-furnace configurations shown in Fig. 27-16, in which the coal and air are mixed rapidly in and close to the burner. The primary air, used to transport the pulverized coal to the burner, comprises 10 to 20 percent of the total combustion air. The secondary air comprises the remainder of the total air and mixes in or near the burner with the primary air and coal. The velocity of the mixture leaving the burner must be high enough to prevent flashback in the primaiy air-coal piping. In practice, this velocity is maintained at about 31 m/s (100 ft/s). 

A typical NO, le cl in the combustion gas is around 107 rng/lVlJ (0,25 lb/l(F Btii), and the (X) leyel tends to be high (near 86 rng/MJ [0,20 lb/l(f Btii]), Only one design has used secondaiv air, and this lowered the NO, to 86 rng/AlJ and the (X) to about 43 rng/AlJ (0,10 lb/l(h Btii), NO, reduction by selectiye noncatalytic reduction (SNCR) has not been tested in a bubbling AFBC, but without the assistance oF secondary air, it maybe diFFicult to distribute the ammonia adequately across the Freeboard to achie e the desired effect. 

Power house auxiliaries ID fans, FD fans, primary and secondary air fans, boiler feed pumps and slurry... 

When a jet is released into a free space, it induces into its body the room air. The air leaving the grille is the primary air, while that entrained from the room into the body of the jet is the secondary air. The degree of entrainment that takes place is related to the velocity of the leaving jet. The combined air stream is known as the total air. 

The following example provides some indication of the effects of induction. Primary and secondary air are mixed respectively at the rates of 0.5 m s , the primary air velocity at outlet being 5.0 m s , with the secondary air velocity assumed to be zero. 

Air ejectors (jet pumps) A device injecting high-velocity (pressurized) primary air into the secondary air. It allows air to be moved without passing through a fan, it may be a simple or Venturi-type ejector. 

Air, primary The actual quantity of air injected into a space before secondary air induction occurs. 

Air, secondary Air entrained in a primary airflow, or the additional air supplied to a combustion process. 

Air terminal unit Air distribution equipment that provides set conditions by the mixing of primary and secondary air. The device may be fixed, having no control or means of manual adjustment, automatically controlled or manually controlled. If automatically controlled, a sensor is used to indicate any required... 

Induced air The quantity of secondary air entrained into a primary airstream. 

Induction The process by w hich secondary air is entrained into the primary jet air. The mixing process is due to the momentum forces in the primary air jet. 

Induction terminal unit An air terminal assembly which by virtue of the configuration of the primary air inlet(s) within the unit can induce secondary air from the surrounding atmosphere before being discharged to the treated space. The tlow rate of the primary air may or may not be variable. The inlet aperture(s) for the secondary air may be fixed or adjustable by means of manual remote control. 

Secondary air Air that is introduced above a combustion process in addition to the primary air in an attempt to obtain complete combustion. 

BeAnft,/. admixed air secondary air. beim, abbrev. bei dem, beimengen, v.t. admix, add. 

Neben-hoden, m. Anat.) epididymis, -kem, m. Biol.) paranucleus, -kette,/. side chain, subordinate chain, -klasse, f. subsidiary class, -kosten, f.pl. extra costs, extras, -leiter, m. Elec.) branch conductor, -leitung, /. bypass branch line, -linie, /. secondary line branch line, -luft, /. admixed air secondary air, supplementary air. -niere, /. suprarenal capsule. 

All combustion equipment (oil, gas, solid fuel) requires primary air to support combustion and secondary air to permit adequate velocities in flue ways, etc. These requirements are governed by the minimum air/fuel ratio and operating flue-way parameters. There are also published recommended minimum requirements that are generally in excess of these. 

The majority of larger industrial burners, including furnace and boiler applications, are of the forced-draft type. These employ a combustion air fan to provide all the air needed for complete combustion. The burners are usually sealed into the combustion chamber so that there is no access to secondary air from the atmosphere as with natural-draft burners. Forced-draft burners may be of the premix type, where air and gas are mixed prior to the burner, or, more commonly, of the nozzle mix type, where the mixing takes place within the burner. 

The second method makes use of the pressure energy of the primary (fresh) air supply to induce room (secondary) air circulation. This air, at a pressure of 150-500 Pa, is released through nozzles within the coil assembly, and the resulting outlet velocity of 16-30 m/s entrains or induces room air to give a total circulation four or five times as much as the primary supply. This extra air passes over the chilled water coil. Most induction units are wall mounted for perimeter cooling, but they have been adapted for ceiling mounting. 

Serious research in catalytic reduction of automotive exhaust was begun in 1949 by Eugene Houdry, who developed mufflers for fork lift trucks used in confined spaces such as mines and warehouses (18). One of the supports used was the monolith—porcelain rods covered with films of alumina, on which platinum was deposited. California enacted laws in 1959 and 1960 on air quality and motor vehicle emission standards, which would be operative when at least two devices were developed that could meet the requirements. This gave the impetus for a greater effort in automotive catalysis research (19). Catalyst developments and fleet tests involved the partnership of catalyst manufacturers and muffler manufacturers. Three of these teams were certified by the California Motor Vehicle Pollution Control Board in 1964-65 American Cyanamid and Walker, W. R. Grace and Norris-Thermador, and Universal Oil Products and Arvin. At the same time, Detroit announced that engine modifications by lean carburation and secondary air injection enabled them to meet the California standard without the use of catalysts. This then delayed the use of catalysts in automobiles. 

The ideal exhaust gas composition is given in Table II, based on a fuel with an H to C molar ratio of 2.103, and assuming that the equilibrium is established and frozen at 4000°R 25). To complete the combustion in a rich exhaust, secondary air must be supplied to cover the deficiency in oxidants. 

Other variations of the dual-bed scheme exist as a combination of thermal oxidizing reactors and catalytic reducing reactors. The Questor company has developed a reactor with three zones the first zone is a thermal reactor with limited air to raise the temperature of the exhaust gas, the second zone is a catalytic bed of metallic screens to reduce NO, and the third zone is another thermal reactor where secondary air is injected to complete the oxidation of CO and hydrocarbons (45). 

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