| OCR Text |
Show I ; Combustion ? V . By O. W. Ott. . . NOTE Thin In Uio first of a. scries of nrtlrlw wltlcli Mr. Ott r, writing on tlio 6moko nulsnnco Rt Uic BUffKcnllon or tho ritlIco Mtormy clnb. Tho artlclna will appear in Tho Tribune. COMBUSTION may bo defined as the rapid chemical combination of any fuel element with oxygen. oxy-gen. Tile chemical combination combina-tion of two elements Is a much more Intimate combination than that which occurs in the mechanical mixture mix-ture of two liquids (such as milk and water), The chemical combination of two elements is usually accompanied by the liberation of heat and light and thlH Is invariably the case with the chemical combinations which come under the classification of combustion. com-bustion. The ordinary process of combustion consists in. the rapid chemical combination com-bination of the various combustible elements of the fuel with theoxygen of tho air. As tho principal combustible combust-ible elements of fuel are carbon and hydrogen with a small trace of sulphur, sul-phur, the products of complete oxidation oxi-dation or combustion will be carbon dioxide and will contain no opaque substances. Tn order to get complete combustion combus-tion three fundamental requirements are necessary. First, there must bo a sufficient supply of air to furnish the necessary amount of oxygen for proper chemical combination with the fuel. Second, the temperature or degree de-gree of heat at the place where the mixture of air and fuel occurs must be sufficient to Insure the Ignition and complete chemical combination of the elements of the fuel with this supply of oxygen. Third, the -oxygen of the . air must come Into inttmato contact with every part of tho fuel. Coal Analysis. The coal that is used in Salt Lake City Is a high class bituminous coal and contains from -10 to 50 per cent-fixed cent-fixed carbon; about tO per cent to 550 i per cent hydro-carbon; 4 per cent to S per cent of ash and a trace of sulphur. sul-phur. The hydro-carbons of the coal are volatile compounds which distill at a. low temperatur.o producing a gas commonly called methane or marsh gas. which Js composed of one part carbon and four parts of Hydrogen. The principal combustible elements in coal are carbon (olther in combined or uncombined form), and hydrogen, and . therefore, the products of com-bualion com-bualion will consist of oxygen compounds com-pounds or these elements; carbon dioxide and other impurities. As the air from which the supply or oxygen for combustion, is obtained contains a large amount of nitrogen Cwhlch is an Inert gas, and has no value whatever In the process of combustion), com-bustion), this nitrogen gas. associated asso-ciated with the above products of combustion, has to be heated up in the furnace nnd expelled through the stack without any chemical change. Oxygen Required. j The complete combustion of ono I pound of coal requires theoretically about three pounds of oxygen, and this amount of oxygen Is contained In thirteen pounds of air. By reason of the large proportion of inert nitrogen ni-trogen In air (80 per cent by volume), It Is impossible ta obtain Intimate contact between the 'oxygen and the , fuel, and therefore a'n excess of air has to be furnished. The exact amount of excess air required over and above the theoretical thirteen pounds will vary greatly, according to the conditions of the fire, boiler selling and various other factors. In ordinary hand tiring with natural draft, approximately 100 per cent excess ex-cess of air will be required. With some stoker settings and forced draft Ihe excess of air may be reduced considerably con-siderably below this amount. Any excess of air above that which Is theoretically the-oretically required for combustion pimply causes a waste of heat, the amount of which depends on the quantity In excess and the temperature tempera-ture at which it Is finally discharged into the chimney. The process of combination Is best understood .by a description of what happens tor the cool In Its progress through the furnace, The coal is first "heated to a point at which the molw-ture molw-ture Is driven off and the hydro-carbons are volatilized. The hydro-carbon gases, mixed with air, then come in contact with a high temperature part of the fire, arc Ignited and continue con-tinue to burn until combustion is. complete. The residue of the fuel consisting of red hot coke continues its progress through the furnace, re- celvos Its proper supply of air and is completely consumed with the exception excep-tion of any incombustible part of tho coal which will be ejected as ash. Ideal Consumption. The foregoing is a description' of . the ideal process of consumption m a furnace and this Ideal process Is actually actu-ally attained In certain high class large unit boiler furnaces. In the process of distilling and burning burn-ing the hvdro-carbon gas If the temperature tem-perature bf the urc Is not sufficient, the hydro-carbons arc neither ignited nor" completely gasified and they pups out or the stack in tbc form of poisonous poi-sonous gases mixed with slight particles par-ticles of coal tar and free carbon, producing what. Is known as jjmokc. If the temperature Is sufficiently hlcrh and If there is .sufficient air the hvilro-carbons are completely burned' and the products of combustion combus-tion consisting of carbon dioxide and water vapor continue their progress through the furnace. Wheh fresh coal is added to a tire the first action to take place is the driving off of the moisture and as soon ns the moisture has been all driven off the distillation of the hydro-carbons comniences. As this distillation process starts in at a temperature close to 500 degrees de-grees Fahrenheit, and is very rapid up to S00 degrees Fahrenheit, and a:i the temperaturo of the bed of fire on to which the fresh coal Is thrown (at a cherry beat). Is close to 1S0O degrees Fahrenheit, It will ' be seen thai the volatile matter In tho fresh coal will be quite rapidly distilled. As It lakes a temneraturc of ap-proxlmatclv ap-proxlmatclv 1200 degrees Fahrenheit to brine about the chemical combination combina-tion of these distilled gases with the oxygen of the air, and as the gases travel quite rapidly away from the fuel bed into cooler parts of the furnace, it will be seen that It is quite a difficult matter to insure their proper liailtion, especially If a very large portion" of the fire Is covered cov-ered over at one time with fresh fuel, thus materially reducing the furnace temperature. Proper Combustion. The final combustion of the fixed carbon car-bon of the fuel necessitates the ac-, cess" of the proper amount of air to each particle of the red hot portion. The complete combustion of the fixed carbon produces carbon dioxide which consists of one part of carbon to two parts of oxygen. Incomplete combustion com-bustion results in tho produotlon of carbon monoxide which la a gas consisting con-sisting of one part of carbon and one part of oxygen. The former eras (carbon (car-bon dioxide) is an inert non-poisonous gas, whereas the latter gas (carbon (car-bon monoxide) Is poisonous. Carbon dioxide gas'aftor being onca produced mav bo reconverted to cartoon car-toon monoxide, if It passes over or through the red hot coke with an Insufficient air supply, the chango from dioxide to monoxide being caused b3' a combination between the carbon dioxide gas and carbon. Carbon monoxide gas may be converted con-verted to dioxide provided it comes in contact with oxygen at a sufficiently suffi-ciently high temperature, otherwise the additional air will simply dilute the monoxide and the air and gas will pass out of the stack uncon-sumcd. uncon-sumcd. Now that the three fundamental requirements re-quirements of proper combustion, namely, proper air supply, proper temperature for ignition, and proper mixing of the air supply with the fuel, have been pointed out, they can be taken up In order in subsequent articles |
