the use of plasma torches in blast furnace...

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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

18

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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