Document YrMYvwdNBbGZvbQRBVOe7Dz2E

HEATINC VENTILATING AIR CONDITIONING CUIDE 1944 Two or more chimneys, either large or small, should never be connected together especially near the bottom. Hot gases in an inverted U-tube thus formed will be in unstable equilibrium. Cold air will descend through one such chimney, from the top, and drive the hot gases out of the other and thus annul the draft. More than one device can be served by one chimney. Batteries of boilers are commonly connected to a single chimney in power plants. However, if more than one chimney are used, each chimney should be used separately for part of the boilers, and not connected in manifold with another chimney, in order to avoid the difficulty described previously. In domestic installations it is sometimes necessary to serve a space heater or cooking stove and a water heater with the same chimney flue. This is not desirable, especially for low chimneys, since doors left open on one device while it is un-fired will tend to annul the draft on another device. Gas burning devices, with their draft hoods and lack of draft dampers, are especially bad in this respect. The traditional means of avoiding this with brick chimneys was to construct multiple-flue chimneys, so that each fuel-burning device could be served by a separate opening. If two devices must be served by one flue-opening in a chimney, their connections to the chimneys should not be located opposite each other. The connection from the larger device should be reasonably low down and that from the smaller, up near the ceiling, so that each device can be serviced as well as possible, regardless of the treatment of the other. Excessive size in a chimney does no harm but means for controlling the draft are more than ordinarily essential if the chimney is too large in capacity. Coal-burning devices often have air leaks around the fire-box and the draft doors sometimes fit poorly so that the fire cannot be con trolled at a low rate. Perhaps the simplest remedy for such cases is the barometric damper which admits air into the flue pipe and thus reduces the draft. Directions for building chimneys for fireplaces are contained in Depart ment of Agriculture Farmers' Bulletin No. 1230.------ It is considered bad practice to connect any heating device to a fireplace flue unless the fireplace is effectively sealed. 200 CHAPTER 10 Automatic .3uei daunting. cfruipment Classification of Stokers, Combustion Process and Adjust ments, Furnace Design, Classification of Oil Burners, Combus tion Chamber Design, Classification of Gas-Fired Appliances AUTOMATIC mechanical equipment for the combustion of solid, liquid and gaseous fuels is considered in this chapter. MECHANICAL STOKERS A mechanical stoker is a device that feeds a solid fuel into a combustion chamber, provides a supply of air for burning the fuel under automatic control and, in some cases, incorporates a means of removing the ash and refuse of combustion automatically. Coal can be burned more efficiently by a mechanical stoker than by hand .firing because the stoker provides a uniform rate of fuel feed, better distribution in the fuel bed and positive control of the air supplied for combustion. CLASSIFICATION OF STOKERS ACCORDING TO CAPACITY Stokers may be classified according to their coal feeding rates. The following classification has been made by the U. S. Department of Com merce, in cooperation with the Stoker Manufacturers Association. Class 1. Capacity under 61 lbof coal per hour. Class 2. Capacity 61 to 100 lb of coal per hour. Class 3. Capacity 101 to 300 lb of coal per hour. Class 4. Capacity 300 to 1200 lb of coal per hour. Class 5. Capacity 1200 lb of coal per hour and over. Class 1 Stokers These stokers are used primarily for home heating and are designed for quiet, automatic operation. Simple, trouble-free construction and, attractive appearance are desirable characteristics of these small units. A common stoker in this class (Fig. 1) consists essentially of a coal hopper, a screw for conveying the coal from the hopper to the retort, a fan which supplies the air for combustion, a transmission for driving the coal feed worm, and an electric motor for supplying power for coal feed and air supply. Air for combustion is admitted to the fuel through tuyeres at the top of the, retort, and in this class, the retort may be either round or rectan- 201