hot metal flow scheduling

Hot-metal flow SchedulingSébastien MouthuyMay, 2015

May 3, 2023(c) n-Side

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Summary

•Steel-making process•Hot-metal flow•Hybrid solution to the HMF•Challenges•Future


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Steel-making process


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Hot-metal flow


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Hot-metal flow


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Steel-making process: Blast furnaces> Alternated Mix of coke and Iron

Ore> Coke provides heat to melt Iron

Ore

> BF produces hot-metal with> A given temperature> A given chemical content:

> S, Si, Mn and P

> A lot of inertia

> Hot-metal is poured into torpedo cars

> Alternating through tapping holes

> 2 lanes per tapping hole

> Torpedoes have to be on time under BF!!!


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Steel-making process: O2 converters> Mix Hot-metal and scraps

> Pressurize O2 in order to remove C content from Hot metal

> Schedule set by another process> Quantity of Hot-metal> Maximum sulfur content> Time of rendez-vous

> 204t with Smax= 9‰ at 11:23am> 215t with Smax= 3‰ at 11:45am> 224t with Smax= 5‰ at 12:05am> …


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Steel-making process: Desulfurization

CaD

> Adding a desulfurizing agent in the torpedo

> Precipitation of sulfur by adding calcium sulfice

> Desulfurization equation linking> Quantity of HM in torpedo> CaD flow into torpedo> Initial sulfur (from BF)> Target sulfur

> Highly non-linear desulfurization equation

> 2 desulfurization stations available


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•Cleaning of the TC▫Remove sulfur that would remain at the top of the

torpedo car▫At least once in every N rotations▫At most once in every M rotations

•Emergency pit▫Used when Steel Making shop does not consume as

much HM as BF are producing▫Only way to free a torpedo to get back under the BF▫Only one torpedo at the EP at a time


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Steel-making process: Pouring> 2 pits at the Steel making shop> 2x2 lanes

> 1 torpedo pouring at a time

> Torpedo cars and ladles have different capacity: 3/2 ratio

> A torpedo car can pour into max 3 ladles

> A ladle can be filled by at most 2 torpedo cars

> Mix !!!


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Hot-metal flow

> 3 BF, 8 tapping holes> >15 torpedoes> 2 desulf stations> 2 pits> 4 ladles> 3 converters> 3 locomotives

> …and many more business constraints

GOAL: MITIGATE RISK AND INCREASE PRODUCTIVITY

Our solution aims to mitigate risk and increase productivity of equipment, thanks to industry expertise and advanced mathematical modeling techniques

RISKMITIGATION+INCREASED PRODUCTIVITY

INTEGRATED

MODELING OF HOT METAL FLOWS

FROM A 2-HOUR TO A 8-

HOUR HORIZON

> Emergency pit use minimization: reduce waste by knowing evolution in time

> Less over-desulfuration

> Planning maintenance of tools correctly

> Improved communication

> Better use of resources: increasing use of cleaning stations (torpedos, ladles), desulfuration stations

> Flux minimization by optimal blending from torpedo to ladle

> Minimization of thermal losses

HYBRID SOLUTIONOur HMF optimizer is used as a real-time operational tool, taking all operational constraints into account to determine optimal HMF planning for the next 8 hours

Steel production planning Blast furnace prediction Localization of torpedos and ladles Quantity and quality of HM in each torpedo

and ladle Status of torpedos: cleaniness Status of ladles: cleanliness Unavailabilities of the tools

Planning of the all the tools for next 8 hours

Quantity of HM in torpedos for next 8 hours

Target sulfur for all torpedos, to minimize flux usage

Availability of torpedos over time

INPUTS

Moves of torpedos and ladles+ Complex moves of torpedos (2 torpedos per locomotive at desulfuration)

Desulfuration equation (non-linear) Cleaning of torpedos (e.g. 1 cleaning

out of 5 cycles) Variable numbers of locos over time …

OUTPUTS

Varia

bles

Ope

ratio

nal

cons

trai

nts


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Demo

•Main result of the solution


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Hybrid solution in OscaR• Constraint programming model▫Priority is given to finding a solution▫Easily state combinatorial operational constraints▫High scheduling components▫Sometimes data is invalid need for proving or explaining

infeasibility

• Search heuristics▫Highly based on business knowledge we got through interviews▫Based on LP, clustering algos

•Optimization▫Using LNS: easy when you have model and search


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CP Model

•Designing jobs with consecutive or collated activities and posting redundant constraints was key

Complex model1. All activities of a torpedo have to be collated2. Some activities are optional, other are mandatory

if the job is performed


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Search heuristics

•Constraint programming model•Search heuristics:

many different kind of decisions:▫Mix▫Emergency pit▫Desulfurization setup▫Assignment of the torpedoes▫Start times of the activities

• Learn how to find a good solution through interviews with operators


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Search heuristics

•When to take non-scheduling – and important – decisions ?▫At first ? Then there is a risk of infeasible schedule▫At the same time we are doing the schedule ?

Reinforce pruning

Take the good decision


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Infeasibilities

•Pay attention of validation of ▫Real-time data▫Requirements from the customer

•Strong need for highlighting these inconsistencies

Garbage In Garbage Out


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Infeasibilities

•Most time-intensive task: proving inconsistencies▫ If the model fails with no search

Post model several times with constraints shuffled randomly▫Else

we had a set of relaxations We applied them all We minimized the set until finding the smallest for which

we found a solution

Garbage In Garbage Out


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Questions ?

hot metal flow scheduling

Data & Analytics