Título

REDUCTION IN THE COKE-RATE AT CSN ́S BLAST FURNACES BY DECREASING THE PULVERISED COAL MOISTURE CONTENT

REDUCTION IN THE COKE-RATE AT CSN ́S BLAST FURNACES BY DECREASING THE PULVERISED COAL MOISTURE CONTENT

Autoria

Motta, Ricardo Sebastião Nadur; Zanetti, Carlos Hilton; Filho, José de Souza; Silva, Alcides José Lucena; Carvalho, Valmir Soares de; Vianna, Leandro Nonato

DOI

10.5151/2594-357x-0132

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Resumo

The Pulverised Coal Injection System – CSN ́s PCI – comprises two grinding plants of indirect drying mineral coal, which utilise recirculation gases from the plant itself, aiming at better energy efficiency. Every coal grinding plant grinds about 66 t/h of raw material to produce around 60 t/h of pulverised coal with maximum of 2.2 % of final moisture. The raw coal moisture varies from 8 to 12 % in average, and the final product moisture varies from 1.5 to 2.2 %, depending on the season of the year, inherent moisture, coal hygroscope, amongst other factors. The hot gas generator, HGG, supplies gases for drying and grinding the coal in the roll mill. The less the moist is, the less the water introduction in the Blast Furnace will be, and better the coal combustion efficiency in lance will be. The introduction of the automatic control system for oxygen content in the plant carried out by Flap 5, and motorised positioning for the recirculation flow control valve, Flap 13, has improved both coal grinding plants. These two new loop controls along with its equipment, instruments and interlocks allowed the controlled suction of fresh air from the atmosphere, as well as the remote control of recirculation gas flow. The Flap 5 has got an intelligent pneumatic positioner, position transducer and new pressure transmitter, allowed the controlled introduction of fresh air in the grinding plants. The function of such fresh air is to dilute the steam contained in the recirculation gases, which are recycled for the grinding processes. Besides, a latest generation on-line pulverised coal moisture meter has been installed to adjust the grinding plant in order to obtain their best parameters for minimum moisture, complying with the granulometry. The two grinding loop controls made new operating functions possible, as well as a new knowledge for grinding parameterisation to obtain the lowest on-line moisture content for coal injection. The results obtained reduced the pulverised coal moisture down to the range of 0.6 to 1.2%, even during rain seasons. This meant the reduction of water introduction in Blast Furnaces 2 and 3 via pulverised coal injection, from around 3000 l/h down to 1000 l/h, making possible the decrease in coke-rate in approximately 3 kg/ton of pig iron.

 

The Pulverised Coal Injection System – CSN ́s PCI – comprises two grinding plants of indirect drying mineral coal, which utilise recirculation gases from the plant itself, aiming at better energy efficiency. Every coal grinding plant grinds about 66 t/h of raw material to produce around 60 t/h of pulverised coal with maximum of 2.2 % of final moisture. The raw coal moisture varies from 8 to 12 % in average, and the final product moisture varies from 1.5 to 2.2 %, depending on the season of the year, inherent moisture, coal hygroscope, amongst other factors. The hot gas generator, HGG, supplies gases for drying and grinding the coal in the roll mill. The less the moist is, the less the water introduction in the Blast Furnace will be, and better the coal combustion efficiency in lance will be. The introduction of the automatic control system for oxygen content in the plant carried out by Flap 5, and motorised positioning for the recirculation flow control valve, Flap 13, has improved both coal grinding plants. These two new loop controls along with its equipment, instruments and interlocks allowed the controlled suction of fresh air from the atmosphere, as well as the remote control of recirculation gas flow. The Flap 5 has got an intelligent pneumatic positioner, position transducer and new pressure transmitter, allowed the controlled introduction of fresh air in the grinding plants. The function of such fresh air is to dilute the steam contained in the recirculation gases, which are recycled for the grinding processes. Besides, a latest generation on-line pulverised coal moisture meter has been installed to adjust the grinding plant in order to obtain their best parameters for minimum moisture, complying with the granulometry. The two grinding loop controls made new operating functions possible, as well as a new knowledge for grinding parameterisation to obtain the lowest on-line moisture content for coal injection. The results obtained reduced the pulverised coal moisture down to the range of 0.6 to 1.2%, even during rain seasons. This meant the reduction of water introduction in Blast Furnaces 2 and 3 via pulverised coal injection, from around 3000 l/h down to 1000 l/h, making possible the decrease in coke-rate in approximately 3 kg/ton of pig iron.

Palavras-chave

Coal grinding plant; Pulverized coal; Moisture

Coal grinding plant; Pulverized coal; Moisture