Document jygKE7wz5RVoJqqL20rLrrbbR

air and overfire excess air. About 85% of air (lows In above grote to complete combustion. Air biost Insures turbulence HUGE M000EG-FUEL PILES standing next ta Industrial ond thtrmol (tfMtoling plants ora common sight In our To Burn Wood Efficiently Choose Properly Designed Combustion Chambf Wo*to wood's value varies from a nuisance, to be gotten rid of as cheaply as possible, to a salable commodity In high de mand. To make best use of heating values, wood-fed furnaces must be engineered as carefully as those burning other fuels 8y M F ANDERS, Mtchmkof fajineor, P S Balden Co Lumber mills, remote from indus trial and residential areas, generally find their waste wood an operating lia bility- They can't locate a market, so must expend effort and money to get rid of the waste. Generally they use con veyors and refuse burners to dispose of it. This requires not only investment in equipment, but also labor to run and maintain It. Most mills, however, use steam to run engine drives, "shot guns'* for log carrioge propulsion, log kickers or hoisting cylinders, dry kilns, glue pots, plywood presses, and also electrical generating, distribution and application equipment. Lumber end paper mills use their wood wastes to fuel this apparatus. If the waste has a market value, It becomes especially important to burn it with maximum combustion efficiency, so a return can be realised from hogged-fuel sales. Dutch ovens are universally used for furnaces burning wood in steam boilers, see drawings p 91. They must be care fully designed to do a proper burning job. Dutch-oven layout controls the size of boiler, wood bio ond auxiliaries. Usual combustion principles govern de sign of these dutch ovens taking Into aecount, of course, the special charac teristics of wood as a fuel, especially high moisture content. Measures. Wood waste t> usually*8 on a volume basis, one unit oeCTP 200 cu ft. One unit is assumed to -- 4500 lb. Actual weight, however, pends ou entrained moisture, kkw tree the woste comes from, eoasld of the waste. This practioe iho**. "primitivenew" of waste-wood M. dustry and iho need for elacm: Wood refuse may consist ol ^ shavings, broken-up trltnmlnl** f bark, defective lumber pieces, S> dust, or any combination of the*contain carbon, hydrogen and nw ENGINEERING ANO MANAGEMENT SECTION cwure content is the most variable 1 wood-refuse fuels. For I* in furnace design, the ^ constants moy be used: Heating value, dry.9000 Dlu per lb One unit weighs...................4500 Ih Fixed carbon, as received.. .10% Volatile matter, as received - .40% Ash, as received.......................0.5% Moisture, ss received..............50% Detailed analyses lor specific woods are given in Table 1. Principal characteris tics of waste-wood fuels are high mois ture content, high volatile content, high oxygen content, low ash. Typical flue gas onalysis when burn ing Western fir shows CO of 12.5%. While the wood ash Is minute compared to most fuels, the constituents it con tains are large in number. Here is a typical analysis of the ash by weight: Silica, SiO....................... ...33.70% Alumina, AI,0................... 2.21% Lime, CeO....................... , .24.30% Magnesia, MgO................... 7.30% Iron, Fe,0,........................... 4.22% Phosphorous, P,0............... 5.44% Titania, TiO..........................0.01% Manganese, Mn,0,............. 0.54% Copper oxide, CuO ................ 0.87% Sulfur trloxide, SO, 2.90% Soda, Ne0............... 5.40% Potash. K0............. Nitrogen, N............. 8.87% 0.03% Moisture................................ 4.21% - Vaporization of moisture In the waste wood and gasification ol volatile matter absorbs appreciable amounts of heat cnergy, Toble U. These must be taken Into account when designing a dutch oven. For high moisture contents around 65%, use of fuel dryers and air pre heaters offers appreciable economies. Waste wood stored for prolonged periods loses heating value from a form of low-temperature spontaneous combus tion, called an isothermic reaction. If the storage pile Is heated, the .volatile mailer progressively disappears by dis tillation. whether air is present or not to burn it. In tho furnace, the fixed carbon com ponent of waste woods burns as fast as oxygen comes in eontaet with it. bixed carbon on the fuel-pile surface burns to CO* Fixed carbon within tbo pile burns to CO. CO, generated at the pile sur(ace reduces to CO if It comes in con tact with hot carbon before cooling. As fixed earbon burns, the ash deposits and foils through the grate, or Is carried up engineering and management section A