Document 9R1VNm1j7bLLkZZZoVYq93ee

BLASTFURNACE GAS leaves furnace (center) it top by downcomer, large-diameter pipe, to duet catcher (below) WASTE-HEAT BOILERS, outilde the engine house, r%\ celve exhaust from englnee fired by blast-furnaee gn BATTERY OP GAS-POWERED BLOWING ENGINES furnish requirements for blast furnseee are shared by seme steam heated air-In volumes up to 100,000 cfm at 20 pal. Air lurblne-drtven blowers to give a flexible supply source How Gas Engines Serve Today's A one-lime major tource of steel mill power now share, the kw load. W M Cline ir, combustion engineer, Belhle-; hem Steel Co, tells how typical steel mill uses gas engine, to advantage, gives operat ing and heat-balance detail. ROUGHLY 209L OF FLANT EUCTRICAL LOAD Como, from gai-ctcclrlc 29cyclo 00,(00, at 25% thermal emcleocy loctudlog pickup from waoto-heat bollero 102 00) Steel mills, with gat-electric en gines installed, find their continued utt on operating advantage. A combiastion of gas engine wlih a waite*hetl boiler, working from the engine eshautt, produces power at a rale of 9400 Rtu per kwhr. This includes a credit of about 2 to 4 lb of steam per kwhr developed in the waste-heat boiler. With out this recovery thermal efficiency row about 25%, or 13,600 Btu per kwhr. j A typical steel plant today requlrd. about 65,000,000 kwhr per month. Csj engines alreedy on the line supplj about 20% of thia load, with the r*; mainder split roughly between P^i chased power and steam-generated eej ergy. This division of load has com* J;POWER jnusrv-r Steel Mills bout from changes within the eteel industryFor instance, in the eorly days the gas engine enjoyed the favored spot as prime mover in the steel mill. This was so beesuse (1) plant electric loads were small, individual steam drives common (or most equipment (2) blastiurnaee fit-fired boilers suffered from using raw gas without cleaning (3) smaller quantity demand of the indi vidual gas engine permitted cleaning gas without too heavy a eapital outlay (4) efficiency of the current gas engine ran 114 to 2 times that of the con temporary steam engino ond boiler in stallation (5) capital costs for gas en gine and equivalent steam boiler ond turbine were about even. Today's Gos Engine. Since 1930 the picture has changed. # Cas-electric en gines have lost ground to newer con densing and noncondensing steam tur bine-generators. The reasons are (1) enormous electrical load growth within the plant making )arge<apacity tur bines justifiable (2) increase in reli ability and efficieney ol blast-furnace s-fired boilers at higher operating pressures <3) decrease in capital in vestment lor steam stations to the point here they run about half that of an ^uivalent engine installation (4) Iran`Hon to 60-cycle power, which rules oul the gas engine because of sice requirements (number of poles in gen erator) ond speed (present speed runs about 86 rpm) (5) advent of tbe top ping turbine that permits use of higherpressure higher-temperature steam in this unit and its exhaust to existing lower-pressure condensing machines, or direct to process. Operating Characteristics. Now let's look at a typical gas engine. Spaed is based on frequency of the electric current produced and number of poles in the generator field. With a current requirement of 2S cycles and a machine with 34 field poles, engines must op erate at 25 X 60 4- 34/2, or 88.24 rpm. This speed is critical because the gas engines are synchronized with other units and purchased power supply from utilitiea. Governing for speed control consists of a pilot-operated hydraulic cylinder mechanically tied into the gas-regulat ing valve. A centrifuge] or flybatl gov ernor operates the pilot valve, which admits oil under 45 to SO pal to the cylinder. A pump driven off the en gine camshaft develops the hydraulic pressure. A spring-loaded overspeed trip at tached to the flywheel cuts off ignition if flywheel exceeds a preset speed. Starting up and putting an engine under load involves a somewhat stand- DISTRIBUTION OR BLAST-FURNACE GAS within the mill follows chart with eertaln load* given first call, and blastfurnace gat bolters as '`flywheels'* *OW|R January 1941 (39| 10)