Steam atomizing burners

Oil-, gas- and dual-fired boilers are available with a range of combustion appliances. The smaller units have pressure jet-type burners with a turndown of about 2 1 while larger boilers may have rotary cup, medium pressure air (MPA) or steam-atomizing burners producing a turndown ratio of between 3 1 and 5 1, depending upon size and fuel. The majority has rotary cup-type burners, while steam- or air-atomizing burners are used where it is essential that the burner firing is not interrupted even for the shortest period. 

Using pressurized steam or air (air-steam atomizing burner)... 

The Burning of Oil Fuels. Although steam-atomizing burners a e... 

Acid sludge Cone and flat-flame type burners, steam-atomized 10-15... 

Liquid fuel burner using pressure steam atomization. 

Steam is the preferred atomizing medium, since it is more economic than compressed air. Steam consumption is typically less than 0.5 per cent of the fuel burnt on a mass basis, although this rises in direct proportion to turndown ratio. On very large burners, the steam flow is modulated in proportion to fuel burnt. Turndown ratios range from about 5 1 for small shell boilers to 12 1 in watertube applications, making this one of the most versatile burners. The steam condition is important in that it must be dry saturated or slightly superheated at the nozzle to avoid condensate formation. On small or non-continuously running plant where no steam is available for start-up a compressed air supply must be provided until steam becomes available from the boiler. 

These are particularly applicable to burners firing the heavier grades of oil which contain long-chain molecules called asphaltines. The superheating of the water in the emulsified fuel droplet enhances atomization. The effect is to provide secondary atomization to the droplet as the steam is formed. 

The observed flame features indicated that changing the atomization gas (normal or preheated air) to steam has a dramatic effect on the entire spray characteristics, including the near-nozzle exit region. Results were obtained for the droplet Sauter mean diameter (D32), number density, and velocity as a function of the radial position (from the burner centerline) with steam as the atomization fluid, under burning conditions, and are shown in Figs. 16.3 and 16.4, respectively, at axial positions of z = 10 mm, 20, 30, 40, 50, and 60 mm downstream of the nozzle exit. Results are also included for preheated and normal air at z = 10 and 50 mm to determine the effect of enthalpy associated with the preheated air on fuel atomization in near and far regions of the nozzle exit. Smaller droplet sizes were obtained with steam than with both air cases, near to the nozzle exit at all radial positions see Fig. 16.3. Droplet mean size with steam at z = 10 mm on the central axis of the spray was found to be about 58 /xm as compared to 81 pm with preheated air and 96 pm with normal unheated air. Near the spray boundary the mean droplet sizes were 42, 53, and 73 pm for steam, preheated air, and normal air, respectively. The enthalpy associated with preheated air, therefore, provides smaller droplet sizes as compared to the normal (unheated) air case near the nozzle exit. Smallest droplet mean size (with steam) is attributed to decreased viscosity of the fuel and increased viscosity of the gas. 

Burners may be located in the floor or on the ends of the heaters. Liquid fuels are atomized with steam or air or mechanically. A particularly effective heater design is equipped with radiant panel (surface combustion) burners, illustrated in Figure 17.16(a), (b). The incandescent walls are located 2-3 ft from the tubes. The furnace side of the panel may reach 2200°F whereas the outer side remains at 120°F because of continual cooling by the air-gas mixture. Radiant panel burners require only 2-5% excess... 

Fig. 3.3. Burner end of sulfur burning furnace. Atomized molten sulfur droplets are injected into the furnace through steam-cooled lances. Dry combustion air is blown in through the circular openings behind. The sulfur is oxidized to S02 by Reactions (3.1) and (3.2). Atomization is done by spiral or right angle flow just inside the burner tip.

For combustion, liquid phosphorus is displaced from a closed, steam-heated storage tank by metering in hot water (Fig. 10.2), to a burner which uses compressed air to finely atomize the phosphorus. Additional combustion air then completes the oxidation to produce phosphorus pentoxide and a great... 

Due to high viscosity, heavy oils are often heated by an electrical heater or steam before they are pumped to delivery lines. The resulting temperature is required to be high enough so that the oil can be easily atomized. Otherwise, a spray of undesirably large oil droplets will be formed. It leads to an unstable flame and carbon buildup on the atomizer and burner block. The American Society for Testing and Materials (ASTM) reported the relationship between the viscosity and temperature for different fuel oils, as shown in Figure 11.3.18... 

Railroads have made great progress in locomotives, from the high-stacked wood-burners of the 1850 s to steam locomotives, electric locomotives, and finally the diesels of today. Railroad planners are now studying the possibilities of a locomotive powered by atomic energy. 

Diagram c in Fig. 114 gives the metal skin temperatures of the vertical tubes for a terrace wall furnace, as well as the temperatures reached by the wa s and supports. The top part of the figure shows the suspension of the coils by hangers, rod and counterweight Heating is provided in this case by combination burners running both on gas and fad oil atomized with steam, in the form of a line burner for the gas. and a tunnel burner for the fuel. 

Combination burners are typically freestanding burners that can fire both gas and liquid fuels. The liquids that are commonly burned are fuels such as No. 2 fuel oil (diesel) or No. 6 fuel oil. These burners also require connections for the medium used to atomize the liquid fuel, which is typically steam or air. The burner can be used to fire only gas, only liquid, or some combination of the two. Figure 18.12 is a rendering of an up-fired combination burner. 

Fuel oil must be atomized to bum. Steam in the burner tip may be used or the oil can be brought in at hi pressures to furnish the energy for atomization by so-called mechanical burners. 

Many systems use steam to help atomize the heated fuel at the point of ignition. Primary air provides oxygen to the fuel mixture. Primary air is located at the point on the burner where air and fuel mix, whereas secondary air registers are located on the bottom and sides of the burner. Flame patterns are important to an experienced technician and can provide an indication of how the system is working. Visual checks are possible at different points on the fired heater. 

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