OCR Text |
Show 3. APPLICATION T O BOILER SYSTEM 3.1 Small Water Tube Boiler System -p Steam Fuel Water Separator Combustion Air Various sizes of small water tube boilers are used for producing steam in the range of 150 - 2000 kg/h at a pressure of 5 -10 kg/cm-. These types of boilers are popular in Japan due to their high performance, compactness, simple operation, quick response to variation in steam load demand, and high (85 - 9 0 % ) thermal efficiency. A schematic diagram of typical water tube boiler is shown in Figure 3.1. The arrangement of the boiler tubes is cylindrical and surrounds the burner flame. The inside section of the boiler arrangement is radiative while that on the outside is convective, see Figure 3.1. The boiler water supplied via the header, reaches the steam header in the form of steam-water mixture through the boiler tubes. The mixture is then separated out into steam and water in the water separator. The difference in specific gravity between separated water and steam-water mixture in the boiler tubes provides the driving force for circulating the fluid. This type of boiler has the desired characteristics of quick response and good stability of operation for raising steam. The safety in boiler operation is accomplished through the use of a quite simple High- Low control. Since there are many small water tube boilers in Japan, any improvement in the heat transfer from this type boiler provides significant improvement in efficiency and subsequent savings in energy. A finite improvement in heat transfer characteristics can yield large amount of energy saving. W e have used this type of boiler as the experimental system for examining the role of high temperature excess enthalpy combustion on boiler characteristics including boiler efficiency and emission of NOx. Ct lue Gi , Water Fig 3.1 Small Water Tube Boiler 3.2 C o m b u s t i o n Test Results In order to determine the improvement in heat transfer when the H R S technology is applied in a commercial boiler, experiments were carried out on a small water tubes boiler, see Fig. 3.1. The experimental arrangement used is shown in Fig. 3.2. The original burner and control system was replaced with the one specially made for the H R S. 7 11-8 |