efficient furnace operation1

7/28/2019 Efficient Furnace Operation1

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Efficient furnace operation

A. Air and gas ratio control1. Producer gas is low C.V gas 1000-1200 Kcal/NM2. As there is no meter in the furnace to know amount of gas in the burner , air should be

controlled by trial and error and should be adjusted with respect to rise in temperature of the

furnace with help of handle provided in the suction side of the blower.

3. Once the O-analyzer comes the flue gas can be analyzed 2/3 times in the shift and accordinglyair to be adjusted. The maximum O in the flue gas should not be more than 2.0%

B. Furnace draught/ damper control1. Damper controls pressure inside the furnace.2. The furnace in no case should run in negative pressure. This can be checked by flowing dust in

front of charging door inspection hole. If the dust is sucked in the furnace, it is in suction. The

damper should be closed in this case till suction of dust inside the furnace stop otherwise it will

suck air from atmosphere.

3. Similarly, furnace should also not run on high pressure by closing damper as hot flue gasseshaving lot of sensible heat will go out of furnace from charging door and any other opening in

the furnace instead of going to the recuperator. Lot of sensible heat of the furnace is wasted in

this manner. Moreover high pressure furnace operation by closing damper during running leads

to roof failure by creating opening in the furnace roof and burning hanger and loosening of roof

bricks which fall during running.


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4. Furnace should run at optimum pressure i.e nether on high nor to low pressure. The furnaceshould be slightly on positive pressure to avoid suction of cold air from atmosphere and in no

case on negative pressure.

5. Depending on volume of the flue gas damper should be adjusted accordingly. Therefore furnaceoperator should check pressure frequently and adjust the damper position.

C. Maximization of Air preheats temperature through Recuperator.

Recuperators are installed in the furnace for recovery of sensible heat of flue gas before

going to chimney. It is one of the most important activities in reducing energy consumption.

There is a metallic recuperator located in the ground between the flue gas tunnel and

chimney. It is shell and tube type of heat exchanger.

If furnace runs on high pressure lot of gas goes out of the furnace mostly from charging door

instead of going to recuperator which in turn heats the cold air. Therefore to extract

maximum sensible heat of the flue gas efficientally, most of the flue gas should pass through

the recuperator. It can only be possible by opening the damper. But while opening the

damper precaution should be taken to avoid suction in the furnace. It is always advisable to

run the furnace slightly at positive pressure instead of negative pressure.

Air preheat temperature from metallic recuperator should be about 45-50%of the flue gas

inlet temp. All efforts to be made to maximize it. Hot air line should be covered with ceramic

fiber blanket.


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Recuperator should be inspected to find leakages in tube joints.

D. Heating control. Heat losses through the opening should be avoided opening of charging and

discharge door should be kept at minimum.

Maximum rate of heating should be realized by controlling air flow in the furnace.Excess and less air reduces rate of temperature rise. Therefore optimum air should

be maintained in the furnace by controlling suction valve of air blower.

Maximum heating should be done upto heating zone thereafter billet should beheated to equalize the temperature from surface to centre in the soaking zone.

As per requirement of gas operation of gassifire should also be controlled.Unnecessarily increasing pressure in the gassifire , increases coal consumption and

also chokes gas lines.

Gas temperature is above 200 C, therefore gas line pipes should also be coveredwith ceramic fiber blanket.

E. REDUCTION OF SCALE

Scale is nothing but oxides of iron in the form of Fe2O3, Fe3O4 & FeO. Steel oxidizes inthe presence of oxygen (Air) at high temperature beyond 900 degree C


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Between 900 degree c -100 degree C scale formation is slow but beyond 1000 degree Cit increases very rapidly and at about 1200-1300 degree C it is maximum

Therefore in case of longer delays the furnace temperature should be brought downbetween 900-1000 C as quickly as possible. In rapid cooling upto 900 degree C there is

no damage to refractory but below 800 degree furnace should be cooled very slowly

upto at least 200 degree C and thereafter also if can be cooled faster for any refractory

repair work.

All effort should be made to avoid retention of the billets in the furnace at highertemperature (>1000C) and this can be accomplished either by faster rolling or by

reducing temperature during longer delays.

As scale formation predominantly depends on surface temperature and residence timeof the billet inside the furnace, heating as well as cooling (upto 900 C) should be faster.

F. Maintenance of furnace. All gas valves should be leak proof.

Air blowers should be checked once in 2-3 months for dynamic balancing.

All temperature display should be calibrated once in 2-3 months.


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During mill stoppage furnace roof should be inspected every month and any leakageshould be filled with mortar.

Hot air pipe should be covered with ceramic fiber to avoid heat loss.

Charging and discharge door should be checked and should be kept at minimumopening.

Ejector and pusher to be cheeked every month

Gas leakage from pipe joints should not be allowed.

Booster should run at 3000 rpm to supply adequate amount of air at desired pressure.There should not be any leakage in air line.

Burner and valves should be checked. It has been observed that front portion of theburner is damaged due to which air and gas mixing near the burner is not proper

reducing flame temperature.

Damaged burner should be replaced

Other refractorys like burner block, hearth , door bricks, wall etc should also beinspected and should be repaired as and when required


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Burner in heating zone is inclined as a result the flames is impinging on metal surface.Since flame temperature is very high it is melting scale over the billet while heating is

carried out in stationary billet, therefore furnace operators do not open burner of

heating zone during heating period and carry out heating from soaking zone which is not

desirable. In no case flame should come in contact with billet.

Wrong practices prevailing in furnace operation

Air flow was never controlled. Damper used to be keep at fixed position irrespective of furnace pressure. Furnace was running at very high pressure which has damaged the roof and burnt almost all the

cast iron hangers. It was observed when roof of soaking zone collapsed.

Even damage roof was not inspected and repaired during a few days planned stoppages of themill. While making new roof the cast iron hangers were covered with 100 mm thick refractory

mortar. Hanger is never covered under mortar. It affects more in soaking zone as temperature

is high and burns the hanger.

The furnace was designed for running with furnace oil. In case of oil the flue gas volume is lowand the chimney and flue tunnel were designed keeping in view low volume of flue gas. After

changing to producer gas fired operation no changes were made (increasing chimney height). It

was observed that after opening of all the burners, the volume of flue gas is so high that even

after opening full damper, the furnace still remains pressurized. But the old operators still follow

the old practices and close the damper in half position thereby pressurizing the furnace further.

Heating zone burners were installed in inclined position. As in oil fired burner, the flame lengthis short but in low C.V gas (Gassifier producer gas) the flame length is large thereby hitting the


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billet surface . Since flame temperature is very high it melts the scale resulting in sticking of

billets. Thats why during stationary furnace heating, operators never opens heating zone

burners due to the fear of billet sticking.

When the mill stops for longer duration the temperature of furnace (about 1200 C) ismaintained high resulting in large scale formation upto the length of furnace where

temperature is above 900 C.

efficient furnace operation1

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