DESIGN OPTIMISATION FOR STOCK HOUSES

OF LARGE BLAST FURNACESBy

Neeraj Mathur, S.K.Singh, A.R.Dasgupta and S.K.Bose

Centre For Engineering & Technology

Steel Authority of India Limited

Ranchi, Jharkhand – 834002

TOTAL NO. OF SLIDES = 21

• BF-BOF route is a worldwide accepted route for hot metal & steel production, although, DRI-EAF routes are also in practise now-a-days

• BFs consume various raw materials like iron ore, sinter, pellet, coke & additives

• Production of desired level of hot metal largely depends on the quality and quantity of the raw materials and the sequence of feeding

• Designing a stock house is as important as designing the Blast Furnace itself, since improper design of a stock house may lead to starvation of the BF due to non-availability of raw materials

INTRODUCTION

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WHAT IS A STOCK HOUSE ?

In a stock house, raw materials from various shops are received. These materials are stored in different bins in the stock house. These bins are provided at the bottom with gates, vibrating feeders, vibrating screens and weigh hoppers

For bigger BFs, raw materials are transported in a measured quantity in a proper sequence through a series of belt conveyors located inside the stock house and finally through a single charging belt conveyor feeding to the top of the BFs. However, in earlier days and even today in older BFs of SAIL, which are relatively smaller BFs compared to today’s sizes, burden materials were/are fed through skips at the top of BFs

All the equipment of a stock house are sized with calculations on the basis of control philosophy & timing cyclograms

The stock houses are provided with all necessary pollution control equipment to control dust as per pollution control norms

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TYPICAL FLOW DIAGRAM OF A STOCK HOUSE

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FEEDING BY SKIP

FEEDING BY CONVEYOR

TYPICAL FEEDING SYSTEM

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SCALE CAR IN A STOCK HOUSE WITH SKIP- TYPICAL

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BIG BELL & SMALL BELL SYSTEM IN FURNACE

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BELL LESS TOP SYSTEM

EQUIPMENT SIZING IN A STOCK HOUSE

For a typical BF of 4500m3 useful volume & Hot metal=9000tpd

•Hot metal (thm/d) capacity is based on useful volume (m3) of the Blast Furnace and its productivity (t/m3/day)

•Raw materials used are lump ore, sinter, pellets, additives, coke and nut coke. The typical sizes of raw materials are:

Sinter : 10 – 40 mm

Sinter : 5 – 10 mm

Centre coke : 60 – 80 mm

Surface coke : 34 – 60 mm

Lump ore : 10 - 40 mm

Pellets : 8 - 16 mm

Nut coke : 8 – 34 mm

Limestone : 6 – 30 mm

Quartzite : 6 – 30 mm

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EQUIPMENT SIZING IN A STOCK HOUSE Contd..

• A typical ratio of ore: pellet: sinter = 10:10:80 has been considered

• Total fuel rate (kg/thm) is to be finalised. Typical values considered are as below:

Coke rate without CDI injection (i.e. all coke) : 495 kg/thm

Coke rate with CDI injection @ 150 kg/thm : 330 kg/thm

Nut coke rate : 30 kg/thm

• Specific consumption of each of the iron bearing materials (kg/thm) based on Fe content and the ratio of ore: pellet: sinter is to be calculated

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EQUIPMENT SIZING IN A STOCK HOUSE Contd...

Typical specific consumption values calculated are as below:

Sl. No. MaterialSpecific consumption (kg/thm)

1Surface coke(all coke case)

372

2Centre coke

(all coke case)123

3Sinter

1206

4Small sinter

63

5Lump Ore

159

6Pellet

159

7Nut coke

30

8Additives (LS/QZ)

5011

EQUIPMENT SIZING IN A STOCK HOUSE Contd...Charging sequence:

(i) A typical option is 1 charge = 2 batches (CS+CC / S+P+O+M+Cn), where,CS = Surface cokeCC = Centre cokeS = Sinter + small sinterP = PelletO = Lump OreM= AdditivesCn = Nut coke

(ii) 1 batch comprises of surface coke + centre coke. Surface coke is 75% of total coke and centre coke is 25% of total coke

(iii) 1 batch comprises of sinter + small sinter + pellet + ore + additives + nut coke. Sinter is 95% of the total sinter and small sinter is 5% of the total sinter

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EQUIPMENT SIZING IN A STOCK HOUSE contd…

• Ore layer thickness (cm) at BF throat diameter is selected. Generally, it is considered as 70 cm

• Coke layer thickness (cm) at BF throat diameter is selected. Generally, it is considered as 70 cm considering “all coke” charge. However, considering CDI injection, the coke layer thickness is considered as 50 cm

• Retention time (h) in the bins for each raw material is finalised. A typical sizing of the bins for different raw materials are as below:

Sl.

No.

Material No. of Bins Useful volume of each

bin (m3)

1 Surface coke 6 850

2 Centre coke 2 850

3 Sinter 8 1200

4 Small sinter 2 850

5 Lump Ore 4 850

6 Pellet 2 850

7 Nut coke 2 200

8 Additives (LS/QZ) 2 400 13

EQUIPMENT SIZING IN STOCK HOUSE contd…• “Catch-up rate” or “force filling factor”, is defined as a ratio between

no. of charges available per day based on design of equipment of stock house/ no. of charges required per day for the target hot metal production. Typical value considered is 1.3

• Quantity (t/batch) of coke (CS+CC) for “all coke” as well as coke along

with CDI injection is calculated based on the volume required at throat diameter for the desired thickness of coke at throat

• Quantity (t/batch) of iron bearing material including nut coke (S+P+O+M+Cn) is calculated based on the volume required at throat

diameter for the desired thickness of iron bearing materials at throat

• Batches of coke per day is calculated as (Specific consumption of coke x hot metal per day)/(quantity per batch). In this case, normal batches = 130 per day

• Batches of iron bearing materials including nut coke per day is calculated as (Specific consumption of iron bearing materials x hot metal per day)/(quantity per batch). In this case, normal batches = 130 per day

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EQUIPMENT SIZING IN STOCK HOUSE contd…• Timing (secs.) for each batch formation for coke as well as iron bearing

material is calculated as (24 x 3600)/no. of batches

• Total no. of equipment (vibrating feeder, vibrating screen, weigh hoppers etc.) operating at a time out of total nos. installed is decided

• Development of a cyclogram considering operation of equipment for Bell Less Top (BLT) (bigger BFs are generally provided with BLT system) and operating time of all stock house equipment is carried out. Cyclograms are prepared after calculating time of operation of all the equipment in the stock house and total time required for each batch. Two cyclograms are prepared. One with “normal rate” and the other with “catch-up rate”

• Sizing of all equipment like gates, vibrating feeders, vibrating screens, weigh hoppers, belt conveyors including main charging conveyor finally feeding at the top of the BF in the receiving hoppers of BLT is done. The equipment is designed based on coke rate along with CDI injection option and providing consideration for “all coke” burden operation

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TYPICAL CYCLOGRAM

VIBRATING FEEDERS/ VIBRATING SCREENS

Sl. No. Material Nos. installed

Nos. in operation

Capacity (tph) Remarks

1Surface coke 6 4 75 Feeder + screen

2Centre coke 2 1 100 Feeder + screen

3Sinter 8 6 250 Feeder + screen

4Small sinter 2 1 60 Feeder only. No

screen

5Lump Ore 4 3 150 Feeder + screen

6Pellet 2 1 150 Feeder + screen

7Nut coke 2 1 30 Feeder only. No

screen

8Additives (LS/QZ) 2 1 45 Feeder only. No

screen

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WEIGH HOPPERS

Sl. No. Material Nos. installed

Nos. in operation

Effective volume (m3) for each

1Surface coke

6 4 45

2 Centre coke 2 1 45

3 Sinter 8 6 35

4 Small sinter 2 1 205 Lump Ore 4 3 25

6 Pellet 2 1 257

Nut coke2 1 10

8Additives (LS/QZ)

2 1 10

Sl. No. Material Capacity (tph)

1 Main charging conveyor 5000

BELT CONVEYORS

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TYPICAL GENERAL LAYOUT OF A STOCK HOUSE

CONCLUSION

In near future, all steel plants will be installing bigger BFs with above mentioned type stock houses. In this regard, an endeavour may be made for a uniform design of the stock house equipment which will lead to standardisation of equipment and less inventory.

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THANK YOU