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The Use of Plasma Torches in Blast Furnace Ironmaking
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Barry Hyde1
Mitren Sukhram1, Nishit Patel1, Ian Cameron1, Veena Subramanyam2, Alex Gorodetsky2
1Hatch Ltd. and 2Alter NRG Corp.
http://www.steel.org/making-steel/how-its-made/processes/how-a-blast-furnace-works.aspx
Plasma torches offer the opportunity to lower coke rate and carbon dioxide emissions by using a greater amount of electrical energy in blast furnace ironmaking. This presentation
will discuss: ‒ Coke rate savings ‒ Coal
consumption ‒ Electrical
purchase requirements
‒ CO2 reduction values
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Westinghouse Plasma Torch
2
Plasma torches are electric arc gas heaters that utilize a high temperature, ionized, and conductive gas to achieve direct heat transfer from the arc.
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Entering Process Gas
Power Terminals
Magnetic Field
Electrodes
Cooling Water Manifold
Heated Process Gas
Plasma Column
3
Westinghouse Plasma Corporation’s technology was initially developed in collaboration with NASA to produce clean high enthalpy gas flows to simulate reentry as part of the Apollo space program (1960’s).
‒ Plasma generated at extremely high temperatures
‒ Long electrode life was not required for these testing configurations
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http://science.howstuffworks.com/apollo-spacecraft7.htm
4
Pilot scale tests were conducted (1970’s) at the Centre de Recherches Métallurgiques (CRM) using 3 – 20 kW torches to produce heated reducing gas.
‒ Heated natural gas reformed
with CO2 at temperatures above 1750°C (3180°F)
‒ Electrode life was over 400 hours ‒ No electrical network problems
were experienced ‒ Tests showed that the blast
furnace process did not change
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In 1980, Westinghouse Electric Corporation in conjunction with Cockerill Steel implemented a plasma torch system for the injection of superheated air and natural gas into the tuyeres of a blast furnace.
‒ During tests a coke rate
reduction was observed ‒ The study proved that plasma
torches could be used to superheat reducing gas for co-injection with hot blast into a blast furnace
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The Westinghouse Plasma Corporation’s Plasma Torch Models.
‒ Power output: 80-300 kW
‒ Flexible cylindrical design
‒ Length of torch can be modified to suit process needs
‒ Conceived for pilot plant trials and R&D Activities
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‒ Power output: 280-530 kW
‒ Flexible cylindrical design
‒ Torch can be inserted into the hot zone of a furnace
‒ Robust industrial torch capable of delivering 500 kW of power to a process application
‒ Marc 11L power output: 350-800 kW
‒ Marc 11H power output : 860-2400 kW
‒ Fixed design
‒ Torches typically used externally due to mounting limitations
Our model utilizes the Westinghouse Marc 11H torch design to superheat hot blast.
‒ Power output: 2400 kW ‒ We assume the torch has a thermal efficiency of 85%
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Coke replacement cases studied:
‒ The largest cost savings in hot metal production is to lower coke consumption
‒ Use plasma torches to superheat blast air to high temperatures
Case Details 1 Base case – typical blast furnace
1150 °C (2100 °F)
2 Increase blast temperature to 1400 °C (2250 °F)
3 Increase blast temperature to 1600 °C (2900 °F)
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The base case was modeled to represent a typical blast furnace.
Parameter Units Value
Sinter kg/t HM 1000
Pellets kg/t HM 500
Coke kg/t HM 350
PCI kg/t HM 150
Fuel Rate* kg/t HM 485
Specific Blast Volume m3 (STP)/t HM 1000
Blast Temperature °C 1150
Flame Temperature °C 2220
Total Moisture in Blast g/m3 (STP) 15
O2 Content in Blast % 26
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*Fuel rate = Coke rate +0.9×PCI rate
A plasma superheated hot blast could enable the blast furnace to minimize coke close to theoretical minimum rates.
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‒ The PCI rate increases with blast temperature to reduce the flame temperature to the base case value
‒ The overall fuel rate of the furnace decreases with increasing blast temperature
0
50
100
150
200
250
300
350
400
450
500
1,150 1,400 1,600kg
/ t H
MBlast Temperature (°C)
PCICokeFuel Rate
12
10 Marc 11H plasma torches are required to superheat the blast temperature to 1600°C.
Parameter Units Case 1 Case 2 Case 3
Blast temperature
°C 1150 1400 1600
Specific electricity demand
kWh/t HM
150 205 245
Electrical demand for a 6000 t/day BF
MW 38 52 61
Number of Marc 11H Units
- 6 10
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13
An operating cost reduction of $6/t HM results when the blast air is superheated from 1150°C to 1400°C
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200.6 -12.0
-1.3-1.0
-0.2
3.8
5.1 194.9
175
180
185
190
195
200
205
BlastT=1,150°C
Coke CO2 credit Blast air Oxygen PCI Power BlastT=1,400°C
Ope
ratin
g C
ost (
$/t H
M)
Case 2, Blast Temperature = 1,400°C
CO2 credit
14
An operating cost reduction of $9/t HM results when the blast air is superheated from 1150°C to 1600°C
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200.6 -20.0
-2.0-1.6
-0.2
6.4
8.6 191.7
175
180
185
190
195
200
205
BlastT=1,150°C
Coke CO2 credit Blast air Oxygen PCI Power BlastT=1,600°C
Ope
ratin
g C
ost (
$/t H
M)
Case 3, Blast Temperature = 1,600°C
CO2 credit
15
The rate of return was based on a 10-year project life, a 1-year implementation period, an installed capital cost of $2.5 million for each plasma torch system, and electrical infrastructure upgrade costs at $100k per MW.
Parameter Unit Case 1 Case 2 Case 3
Blast Temperature
°C 1150 1400 1600
OPEX $/t HM 201 195 192
Change in OPEX
$/t HM - -5.6 -8.8
Change in OPEX
million $ /year
- -12 -19
CAPEX million $ - 16 27
Simple Payback
years - 1.4 1.5
Pre-tax IRR % - 71 67
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16
Superheating the hot blast using plasma replaces the chemical energy from coke combustion with electrical energy resulting in a reduction of CO2 emissions.
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Electrical grid emission factor 0.387 kg CO2 /kWh
108kg CO2 / t HM reduction
1,362 -253
122 22 1,254
500
700
900
1,100
1,300
1,500
BlastT=1,150°C
Coke PCI Power BlastT=1,400°C
CO
2 em
issi
ons
(kg
CO
2/t H
M)
Case 2, Blast Temperature = 1,400°C
17
Maximizing the blast superheating can potentially reduce CO2 emissions by about 13% without major changes to the blast furnace plant.
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175kg CO2 / t HM reduction
1,362 -419
209 37 1,189
500
700
900
1,100
1,300
1,500
BlastT=1,150°C
Coke PCI Power BlastT=1,600°C
CO
2 em
issi
ons
(kg
CO
2/t H
M)
Case 3, Blast Temperature = 1,600°C
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Superheating blast air using plasma torch technology offers an opportunity to reduce coke consumption below today’s best practices with oxygen enriched blast and coal injection.
‒ The financial payback is attractive ( ≤1.5 years) ‒ Lower coke consumption reduces the blast furnaces carbon emissions
an opportunity that merits consideration within a ‘cap and trade’ economy
‒ Engineering design work is needed to develop the best way to implement newer plasma torches from Alter NRG
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