When a boiler setting is required to stand an intense heat and carry a heavy load at the same time, it is well to construct the walls with two courses of fire brick. The inner course should be of highly re fractory brick, and the outer course of strong brick. All fire brick should be dry when placed, and only a thin wash of fine clay used for a mortar. The bricks should be "tamped" until in contact with one another; for if a poor quality is used, or if the bricks are not tamped into place, they are likely to melt and run.
Common brick require from 35 to 50 gallons of crude oil per thousand bricks burned and about 5 days are necessary to water smoke and burn. The con sumption of oil varies somewhat with the analysis of clay and percentage of water. The table below gives typical analyses of common brick clays : In order to determine the length of time, the amount of fuel, and the air required for burning brick, one of the largest manufacturers of oil burning equip ment has gathered the following data: The oil for burning brick varies with different clays from 20 to 80 gallons per thousand brick—an average being 50 gal lons per thousand. The burning of most clay wares can be divided into three periods, namely: First—The drying out or water smoking period, requir ing from 1 to 4 days of 24 hours each, with an average of 21/2 days. During this period from 10 to 30 per cent of the gross amount of fuel • required is burned, the average being 15 per cent.
Second—The period during which the temperature is raised from that of the water smoking period to the extreme temperature necessary to burn the ware, requiring from 2% to 6% days of 24 hours each, with an average of 4% days. During this period from 45 to 75 per cent of the gross amount of fuel is required, the average being 65 per cent.
Third—The oxidization period, during which the maxi mum temperature is maintained, in order to thoroughly burn or vitrfy the product. This varies from % to 2% days, with an average of 1% days, about 20 per cent of the gross amount of oil being burned.
The process of burning fire brick is similar to that of common brick, except that longer time, higher temperature, and much more oil is required. The average time being from 7 to 8 days, and the oil con sumption per 1000 bricks varying from 120 to 140 gallons.
With oil burners only 8 cu. ft. of air or steam per lb. of oil is required for atomizing when the furnace shows a draught of in. to Y8 in. of water in a U glass. The amount of air required for atomizing is thus determined by the amount of oil burned during the second period, for during this period more oil is burned per burner per minute than during any other.
Computations for a typical kiln are given below : Assuming a kiln of 120,000 capacity : First Period: Total time-2% days = 60 hours = 3600 minutes.
Total brick in kiln-120 M. divided between 10 burners, or 12 M. to each burner.
Total oil required per M. brick, 50 gallons.
During the 1st period, 15 per cent or 7.5 gal. = 56.25 lb. X 12 (M. brick) =675 lb. of oil, divided by 3600 minutes= .1878 lb. per minute.
Air required for atomizing 8 cu. ft. per lb. of oil, or 8 X ,1875, or 1.5 cu. ft. per minute X I A burners or 15 cu. ft. per minute.
Second Period: Total time-41 days = 108 hours = 6480 minutes. During the second period 65 per cent or 32.5 gal. = 243.75 X 12=2925 lb., divided by 6480 = .451 lb. per minute.
Air required for atomizing 8 cu. ft per lb. of oil or 8 X .451 = 3.40 cu. ft. per minute X 10 burners, or 34 cu. ft. per minute. Third Period: Total days or 36 hours = 2160 minutes.
During the third period 20 per cent or 10 gal. = 75 lbs. X 12 = 900 lb., divided by 6480 = .412 lb. per minute. Air re quired for atomization 8 cu. ft. per lb. of oil, or 8 X 4.12 = 32.96 cu. ft. per minute.
Since the kiln selected above burned 120,000 bricks in days, or 16,000 bricks per day, the amount of air required for a similar kiln of any given capacity may be easily computed. Thus, for a kiln with a capacity of 30,000 bricks per day, a compressor capable of furnishing 65 cu. ft. of free air per minute is re quired. The most favorable working pressure for kilns is 20 lbs. per sq. in.
Lime is an oxide of calcium (CaO), and in one form or another is the basis of all mortars and cements. It is produced commercially by heating common lime stone in specially constructed kilns. Fig. 50 shows a modern type of continuous oil burning lime kiln.
Limestone is calcium carbonate, CaCOs. When heated to high temperature, it gives up carbon diox ide, which passes off as a gas, and oxide of calcium, or quicklime, remains. Carbon dioxide begins to come off at about 750 degrees F., but a temperature of over 1300 degrees F. is required to completely reduce the stone to calcium oxide. Commercial limestone nearly always contains considerable quantities of moisture and organic matter, which are driven off in the burn ing process. Clay, magnesia and iron oxide are other impurities often present, with the result that the actual yield of lime may vary from 55 per cent to 30 per cent or less of the stone.