Document zoN5axrvdypYVn3YN41OxpY7m

American Society of Heating and Ventilating Engineers Guide, 1934 s A chimney for a gas-fired boiler or furnace should be constructed in accordance with the principles applicable to other boilers. Where the wall forming a smoke flue is made up of less than an 8 in. thickness of brick, concrete or stone, a burnt fire clay flue tile lining should be used. Care should be used that the lengths of flue tile meet properly with no openings at the joints. Cement mortar should be used for the entire chimney. Table 2. Height op Feet Minimum Round Chimney Diameters for Gas Appliances (Inches) Gas Consumption in Thousands op Btu pee Hour ' 100 200 300 400 500 750 1000 1500 2000 20 40 60 81) 100 4.50 4.25 4.10 4.00 3.90 5.70 5.50 5.35 5.20 5.00 6.60 6.40 6.20 6.00 5.90 7.30 7.10 6.90 6.70 6.50 8.00 7.80 7.60 7.35 7.20 9.40 9.15 8.90 8.65 8.40 10.50 10.25 10.00 9.75 9.40 12.35 12.10 11.85 11.50 11.00 13.85 13.55 13.25 12.85 12.40 Table 2 gives the minimum cross-sectional diameters of round chim neys (in inches) for various amounts of heat supplied to the appliance, and for various chimney heights. This is in accordance with American Gas Association recommendations. The flue connections from a gas-fired boiler or furnace to the chimney should be of a non-corrosive material. In localities where the price of gas requires the use of highly efficient appliances, the material used for the flue connection not only should be resistant to the corrosion of water, but should resist the corrosion of dilute solutions of sulphur trioxide in water. Sheet aluminum, as well as some other materials, seems to serve this purpose very well. 364 Chapter 27 FUELS AND COMBUSTION Classification of Coal, Air for Combustion, Draft Required, Com bustion of Anthracite Coal, Firing Bituminous Coal, Burning Coke, Pulverized Coal, Hand Firing, Classification and Use of Oil, Classification, and Use of Gas COAL, oil, and gas are the principal fuels used for heating. The choice of the fuel to be burned is a question of economy, cleanliness, fuel availability, operation requirements, and control. Information con cerning fuel burning devices will be found in Chapter 28. COAL The complex composition of coal makes it 'difficult to classify it into clear-cut types. Its chemical composition is some indication but coals having the same chemical analysis may have distinctly different burning characteristics. Users are mainly interested in the available heat per pound of coal, in the handling and storing properties, and in the burning characteristics. A description of the relationship between the qualities of coals and these characteristics requires considerable space; a treatment applicable to heating boilers is given in U. S. Bureau of Mines Bulletin 276. Fig. 1 illustrates the distribution of the kinds of coal by states and shows the average calorific values and the ash and moisture contents of a limited number purchased on the open market. Five hundred tests in a small domestic boiler were made with these coals by the U. S. Bureau of Mines and the lower curves show the averages of the pounds of water evaporated per pound of coal under similar and normally good operating conditions. A brief description of the kinds of fuels is given in the following para graphs, but it should be recognized that there are no distinct lines of demarcation between the kinds, and that they graduate into each other: Anthracite is a clean, dense, hard coal which creates very little dust in handling.. It is comparatively hard to ignite but bums freely when well started. It is non-caking, bums with a short flame, creates very little smoke, burns uniformly, and requires little attention to the fuel beds between firings. It is capable of giving a high efficiency in the common types of hand-fired furnaces. Semi-anthracite has a higher volatile content than anthracite, is not as hard and ignites somewhat more easily; otherwise its properties are similar to those of anthracite.- Semi-hituminous coal is soft and friable, and fines and dust are created by handling. It ignites somewhat slowly and bums with a medium length of flame. Its caking prop erties increase as the volatile matter increases, but the coke formed is relatively weak. Having only half the volatile matter content of the more abundant bituminous coals it can be burned with less production of smoke, and is sometimes called smokeless coal. 365