The heat value of briquettes will depend on the kind and quality of material that enters into their composition. Quite generally, they produce heat equal to the average grade of soft coal. In the Northwest briquettes made of West Virginia semi-bituminous coal sell at the same price as run-of-mine coal of the same quality. Their use has proven satisfactory as a furnace fuel and they will very likely be sold in increasing quantities.
Comparative Value of Coal to Other Fuels.
—Until a comparatively recent time, coal has been sold by weight and reputation alone; but conditions are rapidly approaching, which will require it to be sold according to its composition and heating value. Among manufacturers and others using large quantities of fuel, the practice of contracting for coal by specification is becoming increasingly common. The determining factors are the amounts of moisture, ash, sulphur, carbon, and volatile matter the coal contains, as well as the size of the pieces and freedom from dust. In a few of the most progressive cities, coal dealers are required to supply coal for schools and other municipal uses, which has been subject to the approval of the City Engineer. The time is not far distant when dealers will be required to submit samples of all fuel, for sale to the public, to the examination of the municipal authorities.
The following table of the heating values of various fuels is taken from Benson’s “Industrial Chemistry.”
British Thermal Units for One Cent from Different Fuels
| Acetylene, from carbide at 10 cents per pound | 600 |
| Denatured alcohol, at 40 cents per gallon | 2,000 |
| Air gas (from gasoline, 80°Bé at 25 cents per gallon) | 3,000 |
| Water gas, at $1 per 1000 cubic feet | 3,000 |
| Coal gas, at $1 per 1000 cubic feet | 6,500 |
| Gasoline, at 20 cents per gallon | 7,500 |
| Kerosene, at 15 cents per gallon | 11,000 |
| Natural gas, at 50 cents per 1000 cubic feet | 18,000 |
| Charcoal, at 10 cents per bushel (15 pounds) | 20,000 |
| Petroleum at 5 cents per gallon | 30,000 |
| Producer gas, from anthracite, $7 per ton | 30,000 |
| Producer gas, from coke, $5 per ton | 36,000 |
| Anthracite, at $7 per ton | 46,000 |
| Producer gas, from soft coal, at $3 per ton | 50,000 |
| Coke, at $5 per ton | 54,000 |
| Mond producer gas from soft coal, at $3 per ton | 65,000 |
| Soft coal, at $3 per ton | 80,000 |
Price of Coal.
—The value of coal as a fuel will depend on the amount of heat it is capable of producing when burned; its price should therefore be determined by the heating value per pound of fuel as purchased. Secondary determining factors in price are those of convenience of handling and the difficulty in burning the fuel such as the size and uniformity of the pieces, the formation of clinkers, smoke and accumulation of soot. Soft coals, containing a large amount of volatile matter, usually produce much soot and smoke and as a consequence sell for a lower price than coals that produce little smoke.
The selection of fuels will depend on the type of heating plant in use, whether by stoves or by furnaces. If by stoves, whether it is possible to use soft coal as a fuel. The automatically fed stove, of the base-burner type, are usually designed for the use of hard coal and in such stoves the use of soft coal would not be possible. Other stoves and furnaces are usually capable of burning soft coal with varying degrees of satisfaction, depending on the design and surrounding conditions.