Process Integration in Iron and Steel Industry – Some Examples

Henrik Saxén Åbo Akademi University

Finland

International Process Integration Jubilee Conference Göteborg, 2013

Contents

Why Process Integration in Steelmaking?

PI in Steelmaking − Opportunities and Challenges

Primary Steelmaking - Basics

Some Examples PI within the plant: Minimize energy use, emissions or costs PI with external plant: Methanol production

Conclusions

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Why Process Integration in Steel Industry?

Growth mainly due to China, Brazil and India to follow.

Globally: Energy demand about 25 EJ, results in 5-6% of the global CO2 emissions.

Many of the unit processes already have high efficiency: only marginal improvements possible.

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Primary Steelmaking - Basics Iron concentrate

Coal Limestone

Coking plant - Coke

Sintering plant - Sinter

Oxygen plant - Oxygen Blast furnace

Recycled steel

Slab

Hot metal Desulphuri- sation

LD-KG converter - Steel

Continuous casting

Lime kilns

Granulation

Pellets

Steel

Roughing mill

Finishing mill Strip cooling

Cut lengths

Slit coils

Pickled coils Pickling line

Slitting line

Cutting line Skin pass mill

Coilers

Patterned plates

Edging mill

Walking beam furnace

Hot-rolled coils

Coil box

Hot strip rolling

Pusher type slab reheating furnaces

Plate mill

Direct quenching and

Hot leveller Hot leveller

Marking Normalising furnace

Inspection

Flame cutting

Plate products

Marking

Cooling banks Crop shears

Mechanical cutting

Cold leveller

Prefabricated plate products Precision and shape cutted plates Bending

machine

Thick-walled tubes and profiles Curving of tubes and welding

Plate rolling

Slag

Pre-leveller accelerated cooling

CAS-OB, ladle furnace and vacuum degassing

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More Detailed View

Limestone

Iron concentrate

Coal

Oxygen

Oil

Sinter

Pellets

Coke

Coking plant

Sintering plant

Oxygen plant Lime burning kilns

Blast furnace

Recycled steel

Slab

Desulphurisation

Converter

Continuous casting

Pig iron Steel

Oxygen

Ladle furnace

Vacuum

2 x CAS-OB

CO,H2

Heat

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Blast Furnace (BF) – the Core

Major Flows Including Recycled Ones

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Steelmaking PI – Opportunities and Challenges?

O. Big business – large saving opportunities. O. High temperatures, large amounts of rich residual gases O. Large quantities of waste heat, traditionally of little interest O. Steelmaking seldom integrated with other production (except to

heat and power production)

C. High temperatures and hostile environment (liquid metal and slag, dust, mechanical wear, etc.)

C. Complex entities, difficult time constraints C. Very specific unit processes C. Internal integration sometimes quite efficient

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Case 1: PI within the Steel Plant

In a steel plant, there are numerous ways to save material and energy, but the complexity of the plant makes the realization difficult.

An example on evaluating different potentials by optimization will be presented, where ten different ways to save energy and/or costs, and to reduce emissions were considered. Each case was separately optimized. Larsson, M. and Dahl, J. ISIJ International 43 (2003), 1664.

The problems were solved by MILP An alternative formulation studied the BF-BOF system with

optimal distribution of scrap under different goals (minimize energy, emissions or costs). Wang et al., Int. J. Greenhouse Gas Control 3 (2009), 29.

Systems in Consideration

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BF

BOF

CHP

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Formulation, constraints and results

Alternative formulation: BF vs. BOF scrap use

Pig iron

Pellet Coke Coal NG O2

Flux Power

Scrap

Steel Gas

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Some results: Optimized scrap use

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ULCOS by K. Meijer

Case 2: PI of Plant with Future Blast Furnace

Early idea to use heavy oxygen enrichment in the BF to yield a top gas suitable for ammonia synthesis Okamoto et al., Trans ISIJ 14 (1975) 122.

Top gas recycling with CO2 strip-ping opens up new possibilities as the top gas can change to very low N2, high CO and CO2 contents. Tseitlin, M. A. et al. ISIJ International 34 (1994), 570.

Top gas recycling also reduces the dependence on coke and makes CO2 separation easier

CP: Coke Plant, SP: Sinter Plant, ST: Hot Stoves, CCP: CO2 Capturing Plant, BF: Blast Furnace, BOF: Basic Oxygen Furnace and CHP: Combined Heat and Power Plant, GR: Gas Reforming unit, MP: Methanol Plant

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System Studied

”1”

”2”

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Heat & mass balances using “yield factors” from reference plant Three different BF gas preheating concepts (see below). Three auxiliary fuels: Oil, natural gas or biomass. Biomass

preprocessed in pyrolysis unit. Gas phase methanol process with gas reforming Solution: SQP and comparison of different alternatives

Models and Gas Preheating Concepts

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Some Results: OBF plant with auxiliary fuels

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Approach developed together with Prof. Grossmann’s group

Reduced complexity by applying surrogate linear BF model

Increased complexity by evaluating different gas treatment and upgrading alternatives, including ways to handle the CCS problem

MINLP problem solved by Generalized Disjunctive Programming (BARON or DICOPT from GAMS)

Solution provides details about the polygeneration plant as well as its optimal integration with the steel plant

Extended Model

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Superstructure of Polygeneration System

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Optimal solution for gas processing

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Optimal states vs. emission & CCS costs

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Pareto Frontier: NPV vs. Emissions

Some States

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Case (see arrows) 1 2 3 4

Coal rate (t/h) 0.0 0.0 80.1 80.2

Ore rate (t/h) 133.1 133.1 153.6 153.6

Ext. coke rate (t/h) 56.1 52.6 0.0 0.0

Pellet rate (t/h) 90.0 90.0 70.2 70.2

Blast volume (knm3/h) 106.5 113.0 113.0 113.0

Oil rate (t/h) 21.6 21.9 18.0 18.0

Oxygen rate (knm3/h) 22.0 17.3 17.8 18.7

DME flow rate (t/h) 0.0 0.0 0.0 0.6

CO2 sequestrated (t/h) 148.7 118.8 116.1 81.6

Methanol production (t/h) 23.4 20.9 21.2 19.3

Sp. emission (tCO2/tls) 0.45 0.55 0.75 0.98

NPV (G$) 0.49 1.28 1.89 2.05

Steel Cost ($/tls) 358.4 355.1 300.3 311.0

4 3 E 2 1 NPV

Conclusions

A steel plant has been presented as a potential industrial system that could be improved by process integration

The basic operation and units of a steel plan have been reviewed

Two examples of process integration – internally and externally

– have been selected to illustrate some features.

An abundance of alternative PI concepts exist and should be explored in the future

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