DESIGN OPTIMISATION FOR STOCK HOUSES OF LARGE BLAST FURNACES By 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

INTRODUCTION 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

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

TYPICAL FLOW DIAGRAM OF A STOCK HOUSE

TYPICAL FEEDING SYSTEM FEEDING BY SKIP FEEDING BY CONVEYOR

SCALE CAR IN A STOCK HOUSE WITH SKIP- TYPICAL

BIG BELL & SMALL BELL SYSTEM IN FURNACE

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

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

EQUIPMENT SIZING IN A STOCK HOUSE Contd... Typical specific consumption values calculated are as below: Sl. No. Material Specific consumption (kg/thm) 1 Surface coke (all coke case) 372 2 Centre coke 123 3 Sinter 1206 4 Small sinter 63 5 Lump Ore 159 6 Pellet 7 Nut coke 30 8 Additives (LS/QZ) 50

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 coke CC = Centre coke S = Sinter + small sinter P = Pellet O = Lump Ore M= Additives Cn = 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

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 3 Sinter 8 1200 4 Small sinter 5 Lump Ore Pellet 7 Nut coke 200 Additives (LS/QZ) 400

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

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

TYPICAL CYCLOGRAM

VIBRATING FEEDERS/ VIBRATING SCREENS Sl. No. Material Nos. installed Nos. in operation Capacity (tph) Remarks 1 Surface coke 6 4 75 Feeder + screen 2 Centre coke 100 3 Sinter 8 250 Small sinter 60 Feeder only. No screen 5 Lump Ore 150 Pellet 7 Nut coke 30 Additives (LS/QZ) 45

Effective volume (m3) for each Main charging conveyor WEIGH HOPPERS Sl. No. Material Nos. installed Nos. in operation Effective volume (m3) for each 1 Surface coke 6 4 45 2 Centre coke 3 Sinter 8 35 Small sinter 20 5 Lump Ore 25 Pellet 7 Nut coke 10 Additives (LS/QZ) BELT CONVEYORS Sl. No. Material Capacity (tph) 1 Main charging conveyor 5000

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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