Liquid spray, pulse combustion

FIGURE 23.6 A vertical pulse combustion spray drying installation and its pulse combustor developed by Pulse Combustion Systems, the United States, (a) Schematic of the PC spray dryer (1, air 2, unidirectional air valve 3, eombustion chamber 4, fuel 5, pilot 6, tailpipe 7, atomizer 8, quench air 9, liquid 10, drying chamber), (b) Photo of pulse combustor used in the PC spray dryer. 

Liquid suspension Drum Spray Fluid/spouted beds of inert particles Spray/fluid bed combination Vacuum belt dryer Pulse combustion dryers... 

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... 

Following on from the aforementioned characteristics, an advantage of pulse combustion is that the strongly oscillating hot-gas jet from the combustion chamber, and also from the tailpipe, can promote the dispersion of liquids, pastes and clumps of particulate materials (Wu et al., 2012). Hence, in the case of liquids, pulse combustion spray-dryers can refrain from using conventional disk or nozzle atomizers, which translates into a simple design and lower capital and operating costs, as well as an enhanced product quality due to the creation of finer droplets with a narrow size distribution. 

The most advantageous configuration of pulse combustion drying is to disperse a liquid material within a pulsating jet of flue gases (Fig. 2.20) which is then dried in a spray drying chamber (Stewart et al., 1991 Keller et al, 1992 Ozer, 1993 Ozer et cd., 1993 Zbicinski et al, 1998 Rehkopf, 2012). 

Plain-orifice atomizers are widely used for injecting liquids into a flow stream of air or gas. The injection may occur in a co-flow, a contra-flow, or a cross-flow stream. The best known application of plain-orifice atomizers is perhaps diesel injectors. This type of injectors is designed to provide a pulsed or intermittent supply of fuel to the combustion zone for each power stroke of the piston. As the air in the combustion zone is compressed by the piston to a high pressure, a very high pressure (83-103 MPa) is required to allow the fuel to penetrate into the combustion zone and disintegrate into a well-atomized spray. 

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