OCR Text |
Show (3) Circular slit high speed ejection of teritary air 6 Perfect combusion of char is conducted by a homogeneous mixture of the tertiary air and promotion of exhaust circulation. This reduces NOx and prevents ash from adhering to the quarl. (4) Installment of choke to the tertiary quarl air ejection hole Ignition is improved by a reverse circulation into the inside of in-furnace high temperature gas quarl, and unburned soot particles are reduced. (S) Possibility of heat resistant metalization of quarl Adhesion of ash can be prevented and the quarl burner can be made compact. (Fig. 6) 3.2 . 3 Combustion characteristics Combustion is conduced in a castable refractory furnace using a short flame type burner of 1200 x 1~kcal/h and 300°C air with by-product gas (blast furnace gas + coke oven gas: 1600kcal/ Nm 3) and three kinds of main fuels pulverized coal, petroleum cokes, and powder cokes. (Table 4) (1 ) Pulverized coal can be burned by itself at rate of 30-1S0 kg/h. Petroleum cokes and powder cokes can be combusted with a 1/3 turndown at 10% auxiliary fuel gas and a 1/2 turndown at 15% auxiliary fuel gas respectively. (Fig. 7 and Fig. 8) (2) When the excess air ratio is more than 1.05 with the three kinds of pulverized fuel, unburned carbon is not observed. (3) NOx emissions of petroleum cokes and powder cokes is generally low compared with pulverized coal. NOx emissions of pulverized coal, petroleum cokes, and powder cokes becomes 300, 120 and 100 ppm respectively proportionally large to volatile. (Fig. 9) (4) NOx emissions of pulverized coal and powder cokes is reduced to half by a reduction in the excess air ratio from 1.2 to 1.05. but the reduction ratio of NOx is small in case of petroleum cokes. (Fig. 10) (S) With both pulverized coal and petroleum cokes. NOx is reduced by a half to SOppm or less by twostage combustion. (Fig. 11) 3.2.4 Burner application results (Table S) (1) Reduced pellet kiln at the Wakayama Steel Works The conventional LPG fuel has been changed to pulverized coal and by-product ga~ (Blast furnace gas + coke oven gas: 1S00 kcal/Nm ) a. Fuel costs were reduced by 6S% compared with those with the conventional fuel. b. NOx emissions are extremely low for pulverized coal combustion. (2) Sintering iginition furnace at the Wakayama Steel Works The fuel for the largest sintering ignition furnace at the Wakayama Steel Works was converted from a coke oven gas to a pulverized coal and coke oven gas mixture . '-" - " ( . I .~Aor ~·-{11-·r ' ''I : : !I Mixed com· :,/ . bunion fuel Solid line: Fuel 8roken line: CombuSlion gas Fig. 6 Combustion now of SSF burner T3bJe 4 Properties of tested pulvarized fuels -------- Pulverized Pulverized PetrOleum coal cokes cokes Heat ing value (kc;al/ltg) 6400 6000 8760 ie C 80.7 85.0 89.2 i H co:' 4 .9 <0.2 3.5 E~ .. to N 1.75 0 .82 2.12 w- .C. S 0 .89 0 .34 1.48 Water ~ 0 .9 0 .2 0.1 i Ash 9 .6 11 .6 0.3 .~ Volatile 32 .3 <1 12.1 'ii ~ o2r0 0le sms esh 85 95 97 ~ 40 0 Petroleum cokes .. 0 Pulverized coal ." 30 L::!. Powder cokes 0; ~ .2 , , ~ 20 , ~, 'x --A ___ _ ~ ___ __ ~----6 :::l c( 10 ~ \ . E 400 Co Co i 300 ~ • .-J 2 200 ~ 0 Z 100 ~ -Jr- 6-.fiF. '- 20 40 60 80 100 120 140 160 Fuel rate (kg/h) Fig. 7 Combustion characteristics |