Document yb2w8Jepxd13jgdJRXzdL4Ln4

TO BURN WOOD continued the stack as flyash. Extraneous matter, like earth, stones, sand, (orms clinkers on the grates. I: Typical Analyte, of Waste-Wood Fuel, Percentages by Weight Combustion air enters the furnace, up through the grates, through openings in the furnace doors to pais over the fire, through the leed-hote openings in uncontrolled form, horixontally through special tuyeres in side and center par* tition wells above the grates. Air may also he admitted through tuyeres in the bridge wall and through nozxles in the arch, nose- All oxygen passing up through the first two inches of burning fuel bed com bines with the carbon to form CO*. Above this level, CO. reduces to CO on contacting further hot carbon. Combus tible gas leaving the fuel bed contains CO and hydrogen, a combination known as producer gas, which has a heating value of about 200 Btu per cu (l. Increasing air-flow rate through the grate raises the gas production rate without affecting completeness of com Fuel Moisture: As received, *fc Air dried, % CoHf. tWvood 50.4 7.3 Proximate analysis (dry): Volatile, % 52.5 Fixed carbon, % 17.3 Ash, % 0.2 Ultimata analysis (dry): H, % C, % N,, % 0, % 5, % Ash, % 5.9 53.5 0.1 40.3 0.0 0.2 Higher hooting value (dry): Btu par lb 9920 hemlock 57.9 7.3 Ur 35.9 6.5 74.2 23.6 2.2 B2.0 17.2 Q.B 5.8 50.4 0.1 41.4 0.1 2.2 0520 43 52.3 0.1 40.5 o.o o.e 9050 Heg > 6.3 79.4 0.5 6.3 51.8 414 0.0 04 9130 bustion. Producer gat bo/ns at the sur face of the cone-shaped $cl pile. To complete this burning, obout 05% of the combustion air must be supplied over the fire, the remainder through the grete. Air for burning the gas must be Ap plied near the fuel-pile surface with a velocity great enough to insure contact IVi Firing Data of West Coast Waste Wood Hroflnt vela., Cry Stton pttliuK FmI mofitiflp, % *000 St* par IS iso pitg 10 feedvete* featperatare Sleek lempetahite 20 to 40 sa and turbulence. This Insures maintain ing a high temperature end causes e high rate of heal transfer to freshly fired fuel to force rapid distillation of moisture and volatile. Hearing value, et rir*4, lie per lb.......1100 Fuel melslio* leu, ate pc lb_.......... SSI Vetatlfe (Utilitarian Ian, Ola pat lb.... M4 toa 4)00 H) )4 S400 4S0Q 1400 'i S2S Theoretical combustion air Nat beatkf value. Bte per lb_______ 712} 4779 J7S) 2741 . _ 11.61C+ 34.8(ff-5) Lb iteaia greereted par lb feel Iked: At 40ft owr-aU efficiency where C, H and O are weights of these components per lb fuel as shown by the ultimate analysis. Actual air needed Iot combustion varies from the theoretical over a wide range depending on furnace layout, load, fuel type, firing method, as it does for any fuel. Excess air must be de At SOft aver-an efficiency At SOft evci-efl tfr<lmv termined experimentally for each in stallation. In general, hogged fuel needs bout 33% more air than No. 6 fuel oil. To recapitulate well-known relation ships: (1) CO. in flue gas is an index of combustion efficiency. (2) Exit-gas temperature is an index of boiler effi ciency. (3) Combustible in the ash is an index of grate efficiency. Within lim its each of these indexes influences the other. Burning Behavior. Small particles, like sender dust, ignite and burn in stantaneously. Pieces the sice of saw dust take a few seconds to burn com pletely. Large pieces up to 2x2xC in. may take hours to burn up. With these large pieces, the surface loses volatile matter nd moisture first, and time elapses before the inner fibers give up these components. This delay results from the low heat conductivity of wood. Loss of moisture and 'volatile# causes (he outer wood layers to shrink and crack., This permits the inner layers to give up their gaseous components. Waste wood burns slowly because of .the high moisture content. It can be burned as last as water and volatile mat ter distill off. This matter in turn de pends on the rapidity of heat supply. Fresh fuel receives heat by radiation from the burning fuel, walls and arch, and by conduction through the wood and furnace gases. For rapid combustion, fuel should be finely shredded. Combustion temparaturo depends s great deal on moisture content. Max imum temperatures obtainable with 20% excess air at 70 F range as follows: 33% moisture 50% moisture 60% moisture ......... 22S0;rl 67% moisture ..............19'fJ 71% moisture 75% moisture .............. 170b;Fl ..............14$/1 Maximum temperatures obtiis*jj^ will) an air preheater, passing 8Sfy the combustion sir entering the b*` at 70 F and leaving st 600 F, vi^. remainder leaking Into the /urns* 70 F, range as follows: 33% moisture ....................372JvJ 50% moisture ............... 60% moisture .................... 67% moisture ....................*155*3 71% -moisture .................... 75% moisture ..................... IWgL With moistures in excess dfM improved operation and eflieiuitfLi^ fists*!. KV ,, gkihBi5r**s1"*ETL',\l*b --4 -d'r".kaB.", f.wd -- ......... M[(iu-18 + 1- #.>!" ' *' *000 4*00 thi -Jfllw. * m-01 TiS Sip 1744 # III: Typical Test Result*, Boilers Burning Waste Wood in Producer-Gas-Type Units ttlW A-- IfMrgtaey flvgt ty, U.S. CmI Qf,, ertit 4M", toctsMd Ittfllgkt tabu 0--Faurdruai vattrtebt FfP4 Soiir I. laftrr htlng iwlm, iq II I. Tvial iIhx baf 1. FimI < )*! Inpvl, etu 4. Efficiency, bvilef, fainecc, '#*. % 5. Avt'og* ttian prmni, tl* S, Avvrggc fctevolw F 7. Avgregs fuinae* Crgll, in. *g I. Avcregi draft at Samper, in. e . *. Avirogc f<f mof*F*r, at FlraS, % till U.37>I0V 71.0MIP* SI.* 17* saoo nrnio* )T.?litO* 47.0 171 210 M` ' wtjL,,, ol 0 tU hotTM- Th contact with from end sides of the fuel This feature practically eliminates coo.bo.aon lempeioISBSi jM F 1m iN ,,e" co"a`' |sK"V,,. Wu,lns <h beater mutt alt to keep * hM,'r I&u,.dropol3>F-*" ftSkwhpecaiure rise ol 520 F. beSufeiTtho diflorenec in speclfio heats pile. A large part of this air rises and scrubs the arch and upper side walls, reducing tho temperature of these sur faces. Air leaking in through the feed-hole openings reduces air coming in through the furnace-door openings. It also eools the arch, aggravating the loss of ra diated heat. Air and gas enter the boiler In uncontrolled fashion markedly efinker formation. Center-wall oven partitions allow cleaning one side of the furnace at a time. For the producer-gas oven they provide space for installing, more air tuyere eastings. This breaks up the fuel bed into smaller units, exposing more fuef-pile surfsea to contact with oxygen. This more nearly approaches conditions in coal-fired furnaces with- level fuel TUJfWtirffiai'lal iirn.cTrebailei adUaIterteltneeIen>el rn>ola'- JSffii&UM and at the amonnt ol |SaVti:.lt leaking tHtough the lees reducing combustion efficiency. The conventional-type dutch oven, comparable with the hand-fired coal grate, -is on inefficient burner. It Is a beds. Cost Compsirin. To give an Ides how various fuels effect steam coats here are results of one study we made OTw^Detign. Two type* "I dutch- iSffita* * conventional, and SiSeilM produeer-soi !7P. P ' teT! '",;ioveotlonal lypa air lor enm- low-cost installation, but for given steam output requires a larger boiler and stack than does the producer-gas type. PrQduer-9as4yp evens have distil lation air forced into the ashpit under for a West Coast lumber mill: Hogged fuel, 45% moisture, 4500 lb per unit, 9000 Btu per lb dry, 13.10 per unit deliverod into dutch oven includ ing a charge of 10c per unit for storage Wtera through the grate, helow SJ(d opening. In the roof. In %loa to coating through tho lurnaoo- SSfSW Nono ol thl. oir I* uVecattel either hr rale ol dew, dlreo''SroriiiitnihT of blast, filiation sir enters through- the positive pressure by a blower, controlled by steam pressure- Much of the sir finds (ts way through the thinner edges of the fuel bed, but the flow varies In response to steam demand. This feature reduces the grate and arch area needed. Distillation air Is not affected by the air and conveying. No. 6 fuel oil, 42-gal barrels, 150,090 Btu per gallon, $2.27 per barrel, in cludes 12c per barrel for storage, heat ing, pumping. The resulting costa per 1000 lb of team burning hogged fuel or oil were: `tpit/doora and come* up through the 3s*uadet the Impetus of tnophenc Jjofpnly. I finds Us way through Jflorijhed mostly where the pile [itoo&L-, This prevent* uniform dtiiri* distillation air end ntimnute* ^aWgeoemtlng capacity o! the fuel ^Airflow depends on the furnace iftCJxbieh In turn varies with fuel-bed jjktiVm, cue of fuel particles and rela$TbJ?psc>lng."-'This type inattllotion M.JOjfposltlv^controlled gw generojfjwrfire air is 'drawn through small Wjdjvihe furnace doors, or through riW'vhsmes if the doors ere openfiraftTre amgUy kept closed to prevent K:$ifog out This eir is largely vin* At best U can only cm0 ,n leaking In through the fuel-feed open ing. Overfire .air enters under forced pressure through wotercooled eset-iron tuyeres in side and center waits. This air blasts against the hot fuel pile where it contacts the hot earbon for good com bustion. PrneileaJly the whole surface of the fuel pile has good oxygen supply. In this type dutch oven there is s slight positive pressure. Hence the fur nace and ashpit doors must be gas tight.' The main combustion space below the boiler receives well-mixed gas and air from the dutch oven in controlled quan tities. Because of iredoead operating and maintenance costs, wstercooled grates are recommended for both type ovens. Wood in conventional oven___ 40c Wood In producer-gas oven... .26c Oil in conventional furnace___ 52c These figures do not include ash-dispowl and aoot-blowlng equipment. Table HI shows some typical tests of industrial boilers burning waste wood. Table IV shows variation in boiler per formance for different fuel and boiler conditions. Most of this information was obtained from Frank Balden, president ol F E Balden, Inc, Portland, Oregon. Ho has conducted research work in the field of waste-wood burning for many years. He also pioneered the producer-gas-type dutch oven. There iro many of these plants on the West Coast. n CNOtNEERINO AND MANAOEMENT SECTION NT gjtf.lJjj ENOINEERINO AND MANAOEMENT SECTION