Fuel

FUEL, combustible substances used for obtaining heat. By physical state, fuels are divided into solid (firewood, peat, coal, anthracite, coke), liquid (mazut, petroleum, kerosene, alcohol) and gaseous (illuminating gas, water gas, etc.). By chemical composition, fuel consists of organic substances, mainly of plant origin, used either in their natural form (firewood, coal, petroleum, etc.) or after artificial processing (coke, briquettes, kerosene, mazut, etc.). During combustion, heat is formed in the process of oxidation of the carbon, hydrogen, and sulfur contained in it; the remaining part of the fuel is the non-combustible ballast. The content of combustible substances in various types of fuel determines its thermal-technical properties: 1) calorific value - the amount of heat released during the combustion of 1 kg, 2) pyrometric - the maximum temperature that can be obtained when burning this type of fuel, and 3) steam-forming - the amount of steam in kg from burning 1 kg of fuel. Sanitary requirements for fuel are: 1) the formation during combustion of the smallest possible amount of harmful gaseous products and unburned particles, 2) the formation of a smaller amount of ash and fly ash in particular, 3) less pollution and dusting of premises, especially residential ones, and 4) the highest calorific value at the lowest cost. The first requirement depends on the chemical composition of the fuel and the correctness of its combustion. The chemical composition of the main types of fuel in percentages is as follows: Fuel composition Firewood Peat Brown coal Coal Anthracite Coke Mazut Pine ^s Combustible parts 1 part 1 O \ S 36.8 4.6 88.1 38.0 4.6 31.a 38.8 £6.0 48.0 3.6 15.0 1.0 33.0-85.5 2.5-4.5 9.5-2.0 3.6-1.0 76.9-88.0 1.7-3.1 1.7-2.0 3.1-1.0 76.0 0.2 1.0 0.8 86.5 12.5 1.0 Non-combustible 1 ash parts 1 water 0.5 £5.0 0.5 £5.0 6.0 £5.0 7.4 £5.0 13.0-2.0 30.4-5.0 6.8-2.0 11.8-3.9 15.0 7.0 Volume of combustion products 1 kg at smoke temperature 200° in m³....... 15.3 15.8 Working calorific value in kcal/kg 2 800 3 000 3 220 2 715 5 635-6 795 7 170 6 350 9 870 The smoke usually contains: CO₂, CO, H₂O, SO₂, O₂, N₂ (from air), resinous substances, small particles of fuel (soot) and ash, sometimes ammonia, nitrous and nitric acids (total volume of combustion products is given in table 1). The most harmful product of combustion is SO₂, if the fuel contains sulfur. Brown coal, some grades of coal, anthracites and coke usually give smoke containing SO₂ in various quantities; on average, when burning coal with 2-3% sulfur, 3% SO₂ by weight of coal is formed. In addition to polluting the external atmosphere and consequently its harmful effect on humans, plants, soil, buildings and materials (see Smoke), SO₂ can enter residential premises with smoke when stoves are poorly designed and operated, as well as in boiler rooms when tending the fire and when embers burn out in ash pits. Here, in enclosed spaces, the harmful effect of SO₂ on the human body is even greater. In addition, SO₂ corrodes the metal parts of the furnace and the iron of smokestacks and roofs. The content of CO in the smoke depends more on the method of burning the fuel than on its chemical composition, as it increases significantly with insufficient air supply to the furnace. The harmful and often poisonous effect of CO poses the greatest danger to people in enclosed and working premises. The control of proper fuel combustion is the amount of CO₂ in the smoke, which should be from 12% to 14%. The formation of soot depends on both the type of fuel and the combustion process. Brown coal, dry long-flame coals produce a lot of soot, while lean coals, anthracite, coke, and mazut produce, on the contrary, little soot. Both a deficiency and an excess of air during fuel combustion and tending the fire cause an increase in soot in the smoke. On average, 4% soot by weight of fuel is formed (harmful effect of soot on humans, local climate, plants, houses, clothing, etc. - see Smoke). Soot entering residential and working premises with smoke during breathing easily penetrates the lungs with all the consequences of this. The formation of a large amount of soot during fuel combustion has great economic significance. Thus, in England, 3 million tons of unburned coal particles (soot) are thrown out with smoke annually, and in France, 18-20% of fuel is lost with smoke. The desire of industrial enterprises to reduce this loss and thereby increase the efficiency of coal has led to the improvement of fuel combustion and thus to the reduction of soot entering the air, while domestic stoves, especially non-central heating, usually do not undergo such improvement and are therefore significant sources of air pollution with soot in large cities. High ash content of fuel is undesirable from a sanitary-technical point of view, as it requires frequent cleaning of furnaces with dusting and pollution of indoor air. Besides peat, brown coal, coke, and some grades of coal and anthracite with high ash content, oil shales (up to 70%) also have high ash content; conversely, firewood, mazut, other grades of coal and anthracite produce little ash. Lighter ash particles when opening the furnace and tending the fire are carried away by increased air draft into the chimney and increase the dust content of the atmospheric air; especially a lot of fly ash (up to 70% of the total ash) is thrown into the air when burning powdered coal. Fuel that crumbles with the formation of a large amount of dust and dirt (peat, brown coal, shales, lean grades of coal) is undesirable from a sanitary point of view for heating residential apartments, as it leads to pollution and dusting of premises; it can only be allowed for boiler furnaces of central heating, however, even here it pollutes boiler rooms. Firewood, anthracite, coke, and dense types of coal crumble little and pollute premises much less. By calorific value, gaseous fuel ranks first (1 kg of illuminating gas gives up to 10,600 calories), then liquid and finally solid fuel (see table). Economic considerations and certain conveniences of use determine the greatest prevalence of solid fuel among us, then liquid and relatively very rarely gaseous fuel. In the USSR, for heating stoves in homes, firewood (without sulfur and dust, low ash content and ease of starting) are mainly used, then coal (spontaneous combustion, sulfur, sometimes dust) and anthracite (no spontaneous combustion and dust, sulfur may be present); for boiler firing, peat (dust, dirt, a lot of ash, poorly transported), brown coal (dust, dirt, sulfur, high ash content), coal, anthracite, coke (sulfur, high ash content), mazut (without dirt, sulfur and ash) are used, much less often shales and illuminating gas.

The fight against smoke and its harmful effects is carried out 1) by using smokeless fuel (anthracite, coke, mazut), 2) by rationalizing furnaces and the process of fuel combustion (automatic loading of fuel and removal of ash and slag, with grates for afterburning, improved blowing, etc.), 3) by burning soot, 4) by capturing gas and using CO₂ for fertilization in agriculture. Replacing apartment stoves with central heating in residential buildings and training stokers is also of great importance in the fight against smoke (see Smoke). Control of proper fuel combustion is carried out by determining the amount of CO₂, CO and O₂ in the smoke (more often with the Orsa apparatus), and the soot released - by weight, by counting particles or by the degree of blackening of a paper filter.