Atomiser nozzle

The feed system consisted of a reservoir, a plunger-type feed pump, a twin-fluid atomising nozzle (giving a round spray of angle 13° in free air) and a mini-compressor. Inert gas for the twin-fluid nozzle was drawn between the outlet of the heat exchanger and the rotameter... 

Blocking of the atomiser nozzle due to the agglomerates and solid particles contained in the pyrolysis liquid created difficulties in the ftiel supply. 

Spare atomising nozzles of different sizes shall be available with plant... 

Spray dryers are normally used for liquid and dilute slurry feeds, but can be designed to handle any material that can be pumped. The material to be dried is atomised in a nozzle, or by a disc-type atomiser, positioned at the top of a vertical cylindrical vessel. Hot air flows up the vessel (in some designs downward) and conveys and dries the droplets. The liquid vaporises rapidly from the droplet surface and open, porous particles are formed. The dried particles are removed in a cyclone separator or bag filter. 

In a pressure atomiser, liquid is forced under pressure through an orifice, and the form of the resulting liquid sheet can be controlled by varying the direction of flow towards the orifice. By this method, flat and conical spray sheets can be produced. From the Bernoulli equation, given in Volume 1, Chapter 6, the mass rate of flow through a nozzle may be derived as ... 

The principle of operation of the impinging jet nozzle resembles that of the fan spray nozzle with the exception that two or more independent jets are caused to impinge in the atmosphere. In impact atomisers, one jet is caused to strike against a solid surface, and for two jets impinging at 180o(34), using SI units ... 

With this atomiser, the drop size is effectively independent of viscosity, and the size spectrum is narrower than with other types of pressure nozzle. 

Pressure nozzles are somewhat inflexible since large ranges of flowrate require excessive variations in differential pressure. For example, for an atomiser operating satisfactorily at 275 kN/m2, a pressure differential of 17.25 MN/m2 is required to increase the flowrate to ten times its initial value. These limitations, inherent in all pressure-type nozzles, have been overcome in swirl spray nozzles by the development of spill, duplex, multi-orifice, and variable port atomisers, in which ratios of maximum to minimum outputs in excess of 50 can be easily achieved(34). 

Break-up of the jet occurs as follows. Ligaments of liquid are tom off, which collapse to form drops. These may be subsequently blown out into films, which in turn further collapse to give a fine spray. Generally, this spray has a small cone angle and is capable of penetrating far greater distances than the pressure nozzle. Small atomisers of this type have been used in spray-drying units of low capacities. 

Pressure nozzles are most suited to low viscosity liquids and, where possible, viscous liquids should be preheated to ensure the minimum viscosity at the nozzle. Because of their simplicity, pressure nozzles are also employed to atomise viscous liquids with a kinematic viscosity up to 0.01 m2/s, depending upon the nozzle capacity. Under these conditions, injection pressures of up to 50 MN/m2 may be required to produce the required particle size. With slurries, the resulting high liquid velocities may cause severe erosion of the orifice and thus necessitate frequent replacement. 

It is far from certain that such a high-voidage spray zone can exist within a fluidized bed a spray zone, with a submerged nozzle, would require a jet to be blown in the dense phase by the atomising air. Work by Rowe et al. (1979) and by Smith and Nienow (1982), using X-ray... 

Automatic fogging systems are available to disinfect rooms. A dense fog is quickly achieved by atomising disinfectant solution through nozzles. 

While possible to obtain satisfactory products with the pneumatic nebuliser, the experimental difficulties due to clogging and the strong dependence on many interrelated variables indicated that another type of atomiser should be investigated. An ultrasonic nozzle, in which high frequency electrical energy is converted into vibratory mechanical motion at the same frequency, was therefore examined. The ultrasonic nozzle was chosen because the average droplet size was small, about 25 microns, and... 

Technol. 15 (1992) 224—231 Atomisation of Liquids and Suspensions with Hollow Cone Nozzles... 

I Nozzle I Atomisation I Vessel I Filter Two Fluid Nozzle U Oven... 

Fig. 4 Atomisation cone with BCO (nozzle hole 0.8 ixitn BCO flow 8 1/h air... 

A traditional propane burner of WS was modified for BCO combustion. The burning chandwr with the modified burner was pre heated up to 900°C with an auxiliary burner placed opposite to the BCO atomiser (Fig. 5). The nozzle was cooled down to 30°C. Once 900°C was reached in the burning chamber, the BCO injection was started. After the ignition of BCO, which occurred immediately with supply of the first amount of BCO, the auxiliary burner was turned off. The supply of BCO was started with about 2 1/h and than increased to about 9-10 1/h (liquid pressure 0.9 bar). The air supply was adjusted to about 3% O2 in the flue gases. The burning of BCO in FLOX mode continued stationary without any difficulties for several hours. Table 1 summarises the main experimental results. 

The experiments proved that BCO can be burned without any noticeable residues or soot formation and with practically no CO emission in stationary FLOX mode. Inqnovement in NO emission can be expected by varying excess air and exhaust gas recirculation ratio. However, the nitrogen content of BCO is itself a source of NOx which can not be reduced below a certain limit. The low CO concentration provides evidence for a high quality atomisation which allows a total carbon bum out. Fig. 6 shows the combustion chamber fuelled with BCO (FLOX mode). The temperatures in the burning chamber (on different places) and in the nozzle were recorded, (see Fig. 5). In order to avoid the nozzle plugging, the BCO temperature in the nozzle was controlled closed to the nozzle tip and was kept at 25-30°C, therefore a tenperature caused blocking (coke formation) can be excluded. 

In order to avoid the blocking of the nozzle due to the solid particles and agglomerates In the BCO, a mechanical cleaning system was integrated in the atomisation system. The cleaner was activated only when due to break of BCO supply a temperature decrease at the heater was observed. During the experiments engine performance and emission data were recorded. A summary of the records is presented in Table 2. 

The atomisation viscosity should be adjusted suitably so that the size and size distribution of oil droplets are correct and their penetration into the air pattern of the burner is as desired. A burner dimensioned for oil combustion can be used or it should at least be slighly modified. However, if the best result is wanted a special burner should be designed. A too high temperature (> 60 °C) increases the risk of nozzle blockage. Particle emissions, soot and usually also nitrogen oxide emissions increase... 

As regards adjustments, the following factors ii proved combustion and flame clean nozzle, strong swirl, intense symmetrical flame, pressure air atomisation compared to steam), increase of air coefticient and combustion power (having enough residence time though), suitable atomisation viscosity (abt 15-20 cSt). At the optimum adjustments of this combustion system, the mean conibustion results and emission values of typical pyrolysis oils were as follows O2 3 5 vol%, NO 88 mg/MJ, CO 4.6 mg/MJ, hydrocarbons 0.1 mg/MJ, soot 2.4 Bac., and particles 86 ing/MJ. 

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