Primary combustion air

Chemical Regeneration. In most MHD system designs the gas exiting the toppiag cycle exhausts either iato a radiant boiler and is used to raise steam, or it exhausts iato a direct-fired air heater and is used to preheat the primary combustion air. An alternative use of the exhaust gas is for chemical regeneration, ia which the exhaust gases are used to process the fuel from its as-received form iato a more beaeftcial oae. Chemical regeaeratioa has beea proposed for use with aatural gas and oil as well as with coal (14) (see Gas, natural Petroleum). 

Air-staged burners Low-NO air-staged burners for firing gas (or oil) are shown in Fig. 24-28. A high-performance, low-NO, burner for high-temperature furnaces is shown in Fig. 24-32. In this design, both air-staging and external flue-gas recirculation are used to achieve extremely low levels of NO emissions (approximately 90 percent lower than conventional burners). The flue gas is recirculated by a jet-pump driven by the primary combustion air. 

The LFJSC has a spherical jet-stirred zone (diameter 5.08 cm) followed by a cylindrical plug flow zone (diameter =2.2 cm length - 7.6 cm) both zones are refractory lined. Primary combustion air enters the jet-stirred zone through two nozzles positioned 180° apart. A set of four 1.1 mm diameter air jets from each nozzle is aimed towards the corners of a cube imagined to sit within the spherical zone. One set of air jets is rotated 45° with respect to the other to allow the opposing jets to mesh rather than to collide. Flow rates are chosen to produce near... 

The primary combustion air is also controlled in a separate control circle in a way, that maximum glowbed volume (glowbed height) is reached. Glow bed height can be measured more or less easily by an infrared barrier with a modulated signal. This, as described above, ensures, that in any operation conditions minimuin NO, emissions are reached. 

Each burner, regardless of type, is usually mounted in a refractory block or ignition tile (see Fig. 1). This is necessary to confine the primary combustion air introduced through the burner, ensure proper air-fuel-waste mixing, and maintain ignition. Manufacturers each have their own geometric specifications, which have been developed through past experience. 

The energy utilization in the production of 1 kg of oil-fumace carbon black is in the range of (9-16) x 10 J, and the yields are 300-660 kg/m depending on the grade. The energy inputs to the reactor are the heat of combustion of the preheated feedstock, heat of combustion of natural gas, and the thermal energy of the preheated air. The energy output consists of the heat of combustion of the carbon black product, the heat of combustion and the sensible heat of the tail gas, the heat loss from the water quench, heat loss by radiation to atmosphere, and the heat transferred to preheat the primary combustion air. 

Operating experience and design wiU likely improve the concepts. It should be noted that while normal kiln coal burners receive their primary combustion air directly with the fuel, low-NO burners require an independent air supply (indirect firing) largely fed from the chnker cooler. On an existing kiln, this represents a significant cost compared to that of the new burner. 

---