OCR Text |
Show A high rate of heat transfer in the exhaust gases L o w N O x and acceptable C O emissions in the exhaust Ability to disperse agglomerative materials Production of high velocity exhaust gases Proven combustor design Reasonable fabrication costs These attributes seemed ideally suited to industrial drying and process heating. Equipment Description The pulse combustors utilized by Novadyne in the development of applications are as shown in Figure 1. The cylindrical combustion chamber is mounted within an air cabinet, with the valve plate mounted at one end. The valve plate has a number of flapper valves mounted on it, which open and close each cycle. A blower provides air to the air cabinet for starting, however the blower remains on during operation even though the combustor itself is self aspirating. Gas is provided by means of a cushion chamber. (It is interesting to note that this chamber can have a negative pressure.) The valve train for the combustor (not shown) is similar to a conventional burner. Gas is emitted to the combustion chamber through the gas distributor. The combustion chamber and tailpipe have cooling fins welded to them. Cooling air is blown along the tailpipe through a shroud. At the outlet of the tailpipe, the cooling air and combustion gases are mixed. In other arrangements, the tailpipe is not cooled, however materials which can withstand high temperatures are then required for its construction. The operation of the pulse combustor is as follows. Ignition is provided by a spark plug and a rapid increase in pressure follows. The gases are driven out through the small diameter tail pipe. A vacuum follows the explosion and a new charge of fuel and air are drawn into the combustion chamber. This new charge is ignited by residual flame fronts from the previous cycle. (1) It has been found useful in discussing pulse combustors to describe them as internal combustion engines, rather than gas burners. They do burn fuel in cycles and they do produce kinetic energy, ie. usable work, in addition to heat. Operating Characteristics Pulse combustors have unique characteristics. Some of these are discussed below. Kinetic Energy The kinetic energy produced by a pulse combustor is significant. For example, firing a 1,000,000 BTU/hr combustor with 1 0 % excess air, and an exhaust temperature of 2000°F, produces an exhaust gas volume of 944 cfm. Exhausting through a 2" N P S Sch 2 |