General Plant Operations Engineering PDF

GENERAL PLANT OPERATIONS ENGINEERING 1  TABLE OF CONTENTS SL NO. TITLE PAGE NO. 1.0 RAW MATERIAL HANDLING PLANT 1.1 INTRODUCTION 5 1.2 DIFFERENT RAW MATERIALS AND THEIR...

GENERAL PLANT OPERATIONS ENGINEERING 1  TABLE OF CONTENTS SL NO. TITLE PAGE NO. 1.0 RAW MATERIAL HANDLING PLANT 1.1 INTRODUCTION 5 1.2 DIFFERENT RAW MATERIALS AND THEIR 6 SOURCES 1.3 QUALITY REQUIREMENTS OF RAW MATERIALS 10 1.4 PROCESS AND FLOW DIAGRAM OF RMHP 11 1.5 MATERIAL HANDLING EQUIPMENTS 11 1.6 CUSTOMERS OF RMHP 17 1.7 BENEFITS OF RMHP 17 1.8 SAFETY 17 2.0 COKE OVENS AND COAL CHEMICALS 2.1 INTRODUCTION 18 2.2 PROPERTIES OF COKING COAL 19 2.3 COAL HANDLING PLANT 20 2.4 CARBONIZATION PROCESS 22 2.5 PROPERTIES OF COKE 24 2.6 COAL CHEMICALS 25 2.7 BY-PRODUCTS OF COKE OVENS 26 2.8 POLLUTION CONTROL NORMS 30 2.9 SAFETY 30 2.10 ISO 45001:2018 – OH&SMS 31 3.0 SINTER PLANT 3.1 INTRODUCTION 32 3.2 SINTERING PROCESS 32 3.3 QUALITY PARAMETERS OF SINTER (SUBJECT TO 39 REQURIEMNT OF BF) 3.4 MAIN AREAS AND EQUIPMENTS 40 3.5 SAFETY HAZARDS AT SINTER PLANT 41 3.6 OHSAS- 18001-OCCUPATIONAL HEALTH & SAFETY 42 ASSESSMENT SERIES 4.0 BLAST FURNACE 4.1 INTRODUCTION 43 4.2 RAW MATERIALS AND THEIR QUALITY 43 4.3 BLAST FURNACE AND ACCESSORIES 48 4.4 B F ZONES AND CHEMICAL REACTIONS 55 4.5 HOT BLAST STOVES 57 4.6 CAST HOUSE AND SLAG GRANULATION PLANT 59 4.7 SAFETY & ENVIRONMENT 63 5.0 STEEL MAKING 5.1 INTRODUCTION 65 5.2 OPEN / TWIN HEARTH FURNACES - PROCESS 66 2 5.3 BASIC OXYGEN FURNACE (LD CONVERTER) 66 5.4 SECONDARY STEEL MAKING 73 5.5 CASTING 78 5.6 INGOT CASTING 87 6.0 ROLLING MILLS 6.1 BASICS OF ROLLING 90 6.2 PRODUCTS OF ROLLING MILLS OF SAIL 95 6.3 APPLICATIONS OF ROLLED PRODUCTS OF SAIL 98 6.4 HOT ROLLING 99 6.5 REHEATING FURNACES 99 6.6 ROLLING OF FLAT PRODUCTS 100 6.7 ROLLING OF LONG PRODUCTS 103 6.8 COLD ROLLING 109 6.9 MAJOR COLD ROLLING DEFECTS 115 6.10 INTRODUCTION TO PIPE PLANTS AND SILICON 116 STEEL PLANT 6.11 ROLLING OF SPECIAL STEELS (STAINLESS STEEL) 118 7.0 GENERAL MECHANICAL MAINTENANCE 7.1 INTRODUCTION 119 7.2 MAINTENANCE OBJECTIVES 122 7.3 TYPES OF MAINTENANCE SYSTEMS 123 7.4 LATEST TRENDS IN MAINTENANCE 126 7.5 LUBRICATION 127 7.6 BEARINGS & BEARING HOUSINGS 134 7.7 POWER TRANSMISSION AND POWER DRIVES 144 7.8 TECHNOLOGY OF REPAIR OF STEEL PLANT 148 EQUIPMENTS 7.9 AVAILABILITY AND RELIABILITY OF EQUIPMENTS 153 7.10 DOS, AND DONTS, & SAFETY 154 8.0 HYDRAULICS 8.1 INTRODUCTION 156 8.2 COMPONENTS OF HYDRAULIC SYSTEM & 159 FUNCTIONS 8.3 BLOCK DIAGRAM OF HYDRAULIC SYSTEM 172 8.4 APPLICATIONS OF HYD. SYSTEMS IN STEEL 173 PLANTS 8.5 MAINTENANCE OF HYDRAULIC SYSTEMS 175 8.6 SAFETY IN HYDRAULICS 177 9.0 ELECTRICAL AND ELECTRONICS 9.1 BASIC ELECTRICAL ENGINEERING 179 9.2 BASIC PRINCIPLES OF TRANSFORMER 184 9.3 BASIC PRINCIPLES OF MOTOR 188 9.4 POWER DISTRIBUTION 202 3 9.5 CIRCUIT BREAKERS 205 9.6 CABLES 214 9.7 RELAYS 218 9.8 ELECTRICAL INSULATION 221 9.9 ELECTRONIC DEVICES 223 9.10 TESTING, MEASURING INSTRUMENTS AND TOOLS 229 9.11 DRIVES AND CONTROL 230 9.12 UNINTERRUPTED POWER SUPPLY (UPS) 242 9.13 MAINTENANCE PRACTICES 244 9.14 ELECTRICAL SAFETY 248 9.15 SINGLE LINE DIAGRAM (SLD) 258 10.0 INSTRUMENTATION & PROCESS CONTROL 10.1 INSTRUMENTATION & PROCESS CONTROL FUNCTIONS 262 IN AN INTEGRATED STEEL PLANT 10.2 INSTRUMENTATION & CONTROL FOR DIFFERENT 277 PROCESS PARAMETERS 10.3 HISTORY OF PROCESS CONTROL AND AUTOMATION 294 11.0 COMPUTER 11.1 INTRODUCTION TO COMPUTER 303 11.2 HARDWARE AND SOFTWARE CONCEPTS 305 11.3 APPLICATIONS OF COMPUTERS IN STEEL 307 INDUSTRY 11.4 OPERATING SYSTEMS AND COMPUTER ARCHITECTURE 308 11.5 COMPUTER LANGUAGE AND APPLICATION SOFTWARE 310 11.6 DATA CENTRE MANAGEMENT 310 11.7 NETWORK AND CONNECTIVITY 311 11.8 INTRODUCTION TO WINDOWS 312 11.9 OFFICE AUTOMATION SOFTWARE (MS Office used in 313 SAIL) 11.10 DATABASE CONCEPTS 314 11.11 INTRANET AND INTERNET 314 11.12 INTRODUCTION TO ERP 316 11.13 DO’S AND DON’TS 318 11.14 DIGITAL TRANSFORMATION 320 12.0 MINING 12.1 INTRODUCTION 329 12.2 MINES OPERATION 334 12.3 SAFETY IN MINES 338 4  Chapter – 1 RAW MATERIAL HANDLING PLANT 1.1 Introduction : Raw Material Handling Plant (RMHP) or Ore Handling Plant (OHP) or Ore Bedding and Blending Plant (OBBP) play a very important role in an Integrated Steel Plant. It is the starting point of an integrated steel plant, where all kinds of raw materials ( Except coal) required for iron making/steel making are handled in a systematic manner, e.g., unloading, stacking, screening, crushing, bedding, blending, reclamation, etc. Different types of major raw materials used in an integrated steel plant are-  Iron Ore  Lime stone  Dolomite  Manganese Ore  Ferro and Silico manganese  Quartzite  Coal For Blast Furnace route Iron Making the main raw materials required are-  Iron ore lump  Blast furnace grade lime stone  Blast furnace grade dolomite  Coke  Sinter  Scrap  LD Slag  Mn Ore  Quartzite The main objective of raw material handling plant/ore handling plant/ore bedding and blending plant is to:-  homogenize materials from different sources by means of blending  supply consistent quality raw materials un-interruptedly to different customers  maintain buffer stock  unloading of wagons/rakes within specified time norm as permitted by Railway.  Raw material preparation (like crushing, screening etc.). The main functions of RMHP /OHP/OB&BP are – 1. Unloading& stacking of raw materials 2. Screening of iron ore lump & fluxes 3. Crushing & screening of coke/flux for base mix/sinter mix preparation 4. Dispatch of processed inputs to customer units 5 Different types of raw materials such as iron ore lump; iron ore fines, limestone, dolomite, manganese ore, etc. are supplied by SAIL mines (Jharkhand Group of mines, BSL, Odisha Group of Mines, RSP and Bhilai Group of Mines, BSP) or purchased from outside parties.. 1.2 Different Raw Materials and their Sources Sl. No. Raw Materials Sources 1. Iron Ore Lumps (IOL) Barsua,Kalta,Taldih,Kiriburu,Meghahatuburu, Bolani,Manoharpur,Gua,Dalli,Rajhara,Rowghat 2. Iron Ore Fines (IOF) Manoharpur,Gua,Dalli,Rajhara Barsua,Kalta,Taldih,Kiriburu, Meghahatuburu, Bolani, Rowghat 3. Blast Furnace( BF) Kuteshwar, Nandini, grade Lime Stone 4. BF grade Dolomite Birmitrapur, Sonakhan , Bhawanathpur & Tulsidamar, Bhutan. 5. Steel Melting Shop Jaisalmer, Imported from Dubai & Oman. (SMS) grade Lime Stone 6. SMS grade Dolomite Belha, Baraduar, Hiri, Bhutan. 7. Quartzite Bobbili (AP) 8. Manganese Ore Barjamunda, Gua Ore Mines, MOIL(Purchased) 9. Mixed Breeze Coke Generated inside the plant (Blast Furnace & Coke Ovens) also interplant transport as per requirement. 10. Mill Scale Generated inside the plant 11. Flue dust Generated inside the plant 12. LD Slag Generated inside the plant Recent trend in Raw Material Usage: Usage of pellet in Blast Furnace : Every attempt is being made to utilize low-grade iron ores, fines and industrial wastes. A huge amount of fine is generated during mechanized mining operation, which cannot be directly charged into blast furnace. The proportion of these fines is further increased due to narrow size distribution specification of iron ore required by blast furnace operators. For better utilization of low-grade ores, it is advised to beneficiate it after crushing and grinding. Such operations yield concentrate in finer form In addition to these fines there are good deposits of blue dust, which mostly remain unused due to its fineness These fines can be either used after agglomerations or utilized for direct reduction processes or production of powder metal products. Depending upon the size gradation of the ore fines the agglomeration can be done by sintering, pelletization, briquetting and nodulizing methods. Agglomeration generally refers to the process of forming a physically larger body from a number of smaller bodies. Thus, the major objectives of agglomeration processes are: (i) Economize mineral use by utilizing finer fraction of the minerals. 6  (ii) Energy conservation by preparing the burden so as to increase the efficiency of reduction process and decrease the coke rate. (iii) Environment improvement by utilizing the waste in-plant fines. Pelletising: Pelletization is an agglomerating process by balling in the presence of moisture and suitable additives like bentonite, lime etc. into 8-20 mm or larger size. These green pellets are subsequently hardened for handling and transportation by firing at 1200 – 13500C. Many times cement is added and pellet can be divided into (a) Acidic Pellets & (b) Basic Pellets Low grade iron ore, iron ore fines and iron ore tailings/slimes accumulated over the years at mine heads and generated during the existing washing processes, need to be beneficiated to provide concentrates of required quality to the Indian steel plants. However, these concentrates are too fine in size to be used directly in the existing iron making processes. For utilizing this fine concentrate, pelletization is the only alternative available. Advantages of Pellets: Iron ore pellet is a kind of agglomerated fines which has better tumbling index as compared to that of parent ore and can be used as a substitute for the same. Iron ore pellets are being used for long in blast furnaces in many countries where lump iron ore is not available. In India, the necessity of pelletisation is realized because of several reasons and advantages. The excessive fines generated from the iron ore mining and crushing units for sizing the feed for blast furnace and sponge iron ore plants are mostly un-utilized. Pelletisation Technology is the only route that is going to dominate the Indian steel industry in future. Pellets have:- Good Reducibility: Because of their high porosity that is (25-30%), pellets are usually reduced considerably faster than hard burden sinter or hard natural ores/lump ores. Good Bed Permeability: Their spherical shapes and containing open pores, gives them good bed permeability. Low angle of repose however is a drawback for pellet and creates uneven binder distribution. High uniform Porosity (25-30%): Because of high uniform porosity of pellets, faster reduction and high metallization takes place. Less heat consumption than sintering. Approx. 35-40% less heat required than sintering. Uniform chemical composition & very low LOI: The chemical analysis is to a degree controllable in the concentration processing within limits dictated by economics. In reality no LOI makes them cost effective. Easy handling and transportation. 7 Unlike Sinter, pellets have high strength and can be transported to long distances without fine generation. It has also good resistance to disintegration.. Pellets Green Balls Fired Pellet Good Quality Fired Pellet Bad Quality 8 Pellet - Blast Furnace Grade: Chemical Quality (Typical) Parameter Specification Fe 65% min SiO2+Al2 O3 5% max Al2 O3 0.60% max Na2O 0.05% max K20 0.05% max TiO2 0.10% max Mn 0.10% max P 0.04% max S 0.02% max V 0.05% max Basicity (CaO+MgO)/(SiO2+Al2O3 ) 0.40 Moisture (free moisture loss at 1050C) 4% max (fair season) 6% max (monsoon) Screen Analysis Specification +16mm 5%max -16mm ,+9mm 85%min -9mm,+6.35mm 7.00%max -5mm 5%max Tumbler test (ASTM) Tumble index (+6.35 mm) 94.00 % min Abrasion index (+ 0.6 mm) 5.00 % max Specification Swelling 20% max. Compression Strength 250 KG/PELLET min Porosity 25.00 % min Reducibility 60% min Right quality raw material is the basic requirement to achieve maximum output at lowest operating cost. Quality of raw materials plays a very important and vital role in entire steel plant operation. Quality of 9 raw materials (incoming) and processed material (outgoing) is monitored by checking the incremental samples collected from the whole consignment. Samples are collected at Auto Sampling Unit or Sampling Unit. The samples prepared after quarter and coning method are sent for further analysis. 1.3 Quality Requirements of Raw Materials Sl. No. Material Chemical Physical 1. Iron Ore Lump Fe SiO2 Al2O3 -10mm= 5% Max 62.3-63.2 % 1.8-2.8% 2.6-3.0 % +40mm= 5% max 2. Iron Ore Fines Fe SiO2 Al2O3 +10mm= 5% Max 62-63% 2.3 – 3.6% 2.8 – 3.3% - 1mm= 30 % max 3. Lime Stone (BF) CaO MgO SiO2 -5mm= 5% max grade. 43 - 50% 2.25-5% 3.5-6.5% +40mm= 5% max 4. Dolomite (BF) CaO MgO SiO2 -5mm= 5% max grade. 30% 18% 5% +50mm= 5% max 5. Lime CaO MgO SiO2 -40mm= 7% max Stone(SMS) 52% 1% 1.5 % (max.) +80mm= 3% max grade(Jaisalmer), (30-60mm) Imported(Dubai & Oman) 6. Dolomite(SMS) CaO MgO SiO2 -40mm= 5% max grade 29 % 23.5% 2.5 % +70mm= 5% max 7. Mn Ore Mn= 30% (min.) 10-40mm size 8. Coke Breeze Fixed C>70%, SiO2-12-15% < 15mm Moisture- 10-15% (max.) 10 1.4 Process Flow Diagram of RMHP/OHP/OBBP Iron Ore (Lump +Fines), Lime Stone, Dolomite (Lump + Fines), Mn Ore From Mines Auto Sampler/ Wagon Tippler/ Track Hopper Sampling Unit Base Mix Designated Beds Screening Unit Preparation Unit Bedding & Blending Despatch to Customer 1.5 Material Handling Equipments Major equipments which are used in RMHP/OHP/OBBP are- Sl. No. Major Equipments Main Function 1. Wagon Tippler For mechanized unloading of wagons 2. Car Pusher / Side Arm For pushing / pulling the rakes for wagon Charger. placement inside the wagon tippler. 3. Track Hopper For manual unloading of wagons 4. Stackers/ Stacker- cum - For stacking material and bed formation Reclaimer (SCR) 5. Barrel / Bucket wheel For reclaiming materials from the beds /SCR 6. Transfer Car For shifting equipments from one bed to another 7. Screens For screening to acquire desired size material 8. Crushers For crushing to acquire desired size material 9. Belt Conveyors For conveying different materials to the destination /customer. 11 Logistics: For smooth operation, the planning of Raw Material requirement for the set target is of prime importance. Raw material requirement plan is to be made ready and communicated to the concerned agencies well in advance to avoid any setback for the process. The different agencies which are involved in this process are - -RMHP/OHP/OBBP -Traffic and Raw Material Department -Raw Materials Division (RMD) -Production Planning Control (PPC) -Finance - Materials Management (Purchase) -Railways, etc, Indian Railway acts as a linkage between mines and steel plant as major mode of Raw Material transport. Inside the plant, Traffic Department (of the Plant) plays the major role for foreign wagons (Railways) rakes movement and the processed/waste material movement by the plant wagons. Depending on the types of wagons, raw materials rakes supplied by the mines through railways are being placed either in wagon tippler or track hopper for unloading. The types of wagons for unloading in wagon tippler and /or track hopper is as given below – For Wagon Tippler - BOXN, BOXC, BOST, NBOY For Track Hopper - BOBS, NBOBS. The material such as Iron Ore Lumps, Iron Ore Fines, Lime Stone, Dolomite, Quartzite etc, unloaded in wagon tippler or track hopper is being conveyed through series of belt conveyors to the designated bed and stacked there with the help of stackers/ SCR. Bed formation takes place by means of to and fro movement of stacker. Number of optimum layers in a bed is controlled by stacker speed. Number of layers in a bed determines the homogeneity of the bed and is reflected in standard deviation of final bed quality. More is the number of layers more is the bed homogeneity and lower the standard deviation. Blending is the mechanized process of stacking & reclaiming to get optimum result in physical & chemical characteristics of raw material; this means that blending is a process of homogenization of single/different raw materials over a full length of pile/bed. Homogenization increases rapidly as the no of layers exceeds 400 and the effect becomes constant after 580 layers. 12  Std dev. Of Fe against No of layers 1 Std. Dev. of Fe 0.5 0 200 400 600 800 1000 No. of Layers Fig.:Change of Homogeneity of co-efficient with no. of layers after Blending Iron Ore Lump Screening: Screening of Iron Ore Lump is necessary because Iron Ore Lump coming from mines contains lot of undersize fraction (-10 mm), which adversely affects the blast furnace operation. Therefore, this undersize fraction (fines) is screened out at Iron Ore Lump screening section and then stacked in the designated Iron Ore Lump beds, from which this screened ore is supplied to blast furnace. Screened Iron Ore Lump also called sized iron ore. Screening plays a very important role as size of material is very important as far as blast furnace operation is concerned. Incoming Iron Ore Lump contains -10 mm fraction as high as 15 to 20 %. To get rid of this -10 mm fraction, vibratory screen of 10 X 10 mm mesh size is used. Base Mix Preparation: In some plants, base mix or sinter mix or ready mix for sinter is being prepared at RMHP/OHP/OBBP for better and consistent quality sinter and also for increasing sinter plant productivity. Base mix is a near homogeneous mixture of Iron Ore Fines, crushed flux (limestone and dolomite), crushed coke, LD 13 slag fines, mill scale, flue dust, return sinter etc, mixed at certain proportion. Before mixing, above said materials are stored in individual bunkers, also called proportioning bins. Prior to stacking, required ratio is to be set for Iron Ore Fines, flux, coke fines, return sinter etc., so that prepared base mix should satisfy the requirement of sintering plant. Panoramic view of RMHP/OHP/OBBP Steel Plant Panoramic view of RMHP/OHP/OBBP Iron Ore Fines: Iron Ore Fines is the base material for base mix preparation. Nearly 70-80 % Iron Ore Fines is used in base mix preparation. Fe content in Iron Ore Fines is around 62-64%. 14 Flux: Flux is a mixture of Lime Stone and Dolomite in certain proportion required in sinter making. Fraction of (-3mm.) in crushed flux is 90% and more. The main function of flux is to take care of gangue in blast furnace and also to increases the rate of reaction to form the good quality slag. Flux acts as a binder in sinter making to increase the sinter strength. Nearly 12-16% flux used in base mix preparation. Hammer crushers are used for crushing Limestone and Dolomite Lumps to required size i.e. (-3mm.) > 90%. BF Grade Dolomite 15  BF Grade Lime stone Dolo-fines Coke Breeze: Another important ingredient in base mix is crushed coke of size fraction (-3mm.) 85%.(Minimum) Coke for base mix preparation is received from Coke Ovens and Blast Furnace, called mixed breeze coke. The size fraction (+ 12.5 mm.) is screened out and sent along with sinter to blast furnace as a nut coke. The under size material is crushed in the two stage roll crusher i.e. primary and secondary roll crusher to achieve requisite size fraction of (-3mm.) 85%. Nearly 5-6% crushed coke used in base mix preparation. 16 Plant Return & Metallurgical Waste: Plant Return or BOF (LD) slag is used as a replacement of Blast Furnace grade Lime Stone. Nearly 3.5 – 4 % BOF slag is used for base mix preparation. Metallurgical Waste such as mill scale, flue dust, sludge, spillage also used in base mix preparation @ 1%. 1.6 Customers of RMHP Sl. No. Customer Product/ Material 1. Blast Furnace Size Ore (Screen Iron Ore Lump) & Quartzite. 2. Sinter Plant Base Mix/Sinter mix, crushed limestone & dolomite (Flux), crushed coke & nut coke 3. Calcining/ Refractory SMS grade Limestone & Dolomite. Plant 1.7 Benefits of RMHP/OHP/OB&BP Provides consistent quality raw materials to its customer and also controlling the cost by:  Centralized Raw Material facility  Mechanized & faster unloading facilities  Facility for sizing of materials for base mix preparation.  Minimizing undersize in iron ore lump by means of screening  Consistency in chemical & physical properties by means of bedding & blending.  Input quality over a time period is known.  Base mix preparation for Sinter Plants  Supply prepared Raw Materials to Units  Utilization of metallurgical waste. 1.8 Safety and Environment RMHP/OHP/OB&BP is a dust prone department due to handling of various types of Raw materials and conversion of lumpy mass into fines by crushing & screening, hence use of dust mask, safety goggles, safety helmet, safety shoes etc. is of prime important. To take care of surrounding area Dust Extraction & Dust Suppression system is installed. In some plants dry fog dust suppression (DFDS) system is also in use. Housekeeping is a major challenge for smooth operation in this department and requires special attention. Spillage materials are collected & reused by effective housekeeping. Scrap conveyor belts are regularly collected and disposed at designated place for proper disposal. This helps in maintaining personal and equipment health and safety. It makes the surrounding operation friendly. --- 17  Chapter – 2 COKE OVENS AND COAL CHEMICALS 2.1 Introduction Coke making is the process to convert coking coal, through a series of operations, into metallurgical coke. The process starts from unloading of the coal at the wagon tipplers & ends at sizing & transportation of coke to Blast furnace. Formation of Coal: The plant & vegetations buried under swamp bottom during earthquakes or due to other environmental changes were subjected to heat & pressure. During the initial period plant & vegetations decay to form PEAT. Over a long period of time water is forced out due to tremendous pressure of the overburden & due to heat generation, converting the mass to LIGNITE. Continuous compaction & ageing converts the Lignite to Bituminous coal. This process takes million of years. Types & Sources of Coking Coal: Coals are primarily divided into two categories i.e. coking coals and non coking coals. Coking coals are mainly used in steel industries for coke making. Indigenous coking coals are classified as:  Prime Coking Coal (PCC)  Medium Coking Coal (MCC) While imported coking coals are classified as.  Hard coking coals (HCC)  Soft Coking Coal (SCC) Coal is extracted from coal mines & processed in the coal washeries to lower down the ash content to make it fit for coke making. The different sources of Indigenous coking coal are named after the respective washeries while imported coking coals are named after the name of countries and are as follows in next page: PCC - Bhojudih MCC - Kathara - Sudamdih - Swang - Munidih - Rajrappa - Patherdih - Kedla - Dugda - Nandan - Mahuda - Dahibari -Chasnala - Jamadoba - Bhelatand 18  ICC (Hard) – Australia SCC -Australia - USA -USA -Mozambique Benga) - Indonesia - Canada 2.2 Properties of Coking Coal Percentage of Ash: Lower the ash percentage better is the coal. Indian coal normally contains a high percentage of ash. This is reduced to some extent by suitable beneficiation process at the washeries. Volatile Matter (VM): This is the volatile matters present in the coal which goes out as gas during carbonization. Free Swelling Index (FSI): The free- swelling index is measure of the increase in volume of coal when heated under specific conditions. It is also known as Crucible swelling number (CSN) Low Temperature Gray King coke Type (LTGK): The purpose of the test is to assess the caking properties of coal or coal blend and the yield of the various byproducts during carbonization. Gieseler Fluidity: This test measures the rheological properties of coal. This test tells about the initial softening temperature, temperature at which maximum fluidity occurs, Plastic range, maximum fluidity and re-solidification temperature. This is expressed in dial division per minute (DDPM). This test tells about the compatibility of different coals in coal blend. Inherent Moisture: This gives a very good idea about the maturity of the coal with advancement of rank the inherent moisture generally comes down. Mean Max Reflectance (MMR): Rank of coal is determined by measuring the reflectance of coal, which is determined by MMR value. MMR is directly proportional to the strength of COKE. Table -1: Properties of incoming Indigenous and Imported coking coals Coal Ash VM FSI LTGK Inherent MMR moisture PCC 19 - 23 21-23 >2.0 >E < 1.5 1.10 MCC 20 – 25 23-25 >1.0 >E < 1.5 0.85 Imported 8-10 25-30 >5.0 >G4 < 1.5 0.9 Soft Aust Hard 8-10 18-20 >5.0 >G4 < 1.5 1.25 USA Hard 8-10 24-26 >5.0 >G4 < 1.5 1.10 Mozambique 12 - 14 24-26 >5.0 >G4 < 1.5 1.15 (Benga) Indonesia 10-12 24-26 >5.0 >G4 < 1.5 1.10 Hard 19 2.3 Coal Handling Plant Coke is one of the most important raw materials used to extract iron from the iron ore. The success of Blast Furnace operation depends upon the consistent quality of coke, which is used in Blast Furnace. The quality of coke depends upon the pre-carbonisation technique, carbonization & post-carbonization techniques used in Coke ovens. Pre-carbonization technique is controlled by Coal handling Plant. Unloading & lifting of coal: Washed coals from washeries are received at the Coal Handling Plant by Railways wagons. Generally 59 wagons, called a rake, are brought to the plant at a time. These wagons get unloaded in wagon tipplers. Here the wagons are mechanically clamped & turned up to 172° to discharge the coal onto down below conveyors. Then through a series of conveyors the coal is stacked in coal yard through a Stacker or directly to the silos by tripper car. The coal yard is divided into separate segments where different types of coal can be stacked in respective earmarked areas. It is very important to stack different types of coal separately so as to avoid mix up of two types of coal. Mix up of coal is highly detrimental for coke making. From the coal yard, coal is reclaimed through Reclaimer & by a series of conveyors gets transported to either crushers or silos as per prevailing system in different SAIL plants. In some plants, coal from different sources are tippled and carried by conveyors directly to the silos. Care is taken to load same grade of coal in the same silos, from where it is taken through weigh feeders to the hammer crushers and then the entire blended coal is transported to different coal towers by conveyors. Crushing & Blending: The sequence of crushing & blending is different in different SAIL plants. The system of crushing the coal & then blending is followed in RSP, whereas blending is done before crushing in other SAIL Plants. Importance of Crushing: Coal is a heterogeneous mixture of organic and inorganic materials. Finer crushing of good coal leads to increase in specific surface area of coal grains which will increase the quantity of plastic material required for wetting and enveloping the inert material. Courser crushing of inferior coals leads to generation of courser particles which are centers of weakness in coke matrix. Due to difference in the plastic and shrinkage behavior of these inert rich particles and rest of the charge, local stresses are developed and cracks appear adversely affecting coke quality. Crushing should ensure minimum differences between different size fractions. Organic materials-rich particles are softer than those of inorganic-rich or ash-rich particles. Ash or inerts content is higher in larger size particles (>5 mm size) and such particles needs finer crushing The mineral matter/inert reach component should be crushed to finer sizes compared to the reactive component for even dispersion of inert particles in the coal charge. Fine crushing of coal is essential to homogenize the different inherent constituents of coal blend. Crushing of coal is done by hammer crusher. Crushing also influence the bulk density of coal charge in 20 the ovens. Bulk density is the compactness or close packing of the coal charge in the oven. Higher the bulk density better is the coke strength. It is desirable to have 80% to 82% of -3.2mm size coal after crushing. This is known as crushing Index. However over crushing is not desirable as this reduces the bulk density & increases micro fines which cause jamming in gas off-take system. Fig : Bulk density variation with Crushing Index and +6.3 mm content in coal charge Importance of Blending: Different coal has different properties. Some coals may be good in coking properties but high ash and poor rank while others may have low ash and desired rank but poor coking properties. These properties are additive in nature except Fluidity. As evidenced from the table under properties of coal the Indigenous coals contain a relatively higher percentage of ash and poor coking properties & Imported coals contain a relatively lower percentage of ash and better coking properties. Hence blending of both types of coal is necessary for obtaining the desired quality of coal blend. Blending plays a vital role in producing good metallurgical coke. Blending is a process of mixing the different types of coal, i.e. PCC, MCC, Imported Soft & Hard, in different percentage to obtain the desired quality of the blend coal. However blending is to be done in a very accurate manner so that required coke property does not get adversely affected. Blending is generally done by adjusting the discharge of different types of coal from bunkers or silos to a common belt. The different type of coals gets thoroughly mixed during crushing where blending is done before crushing. In case where blending is done after crushing proper mixing takes place at several transfer points, i.e. during discharge from one conveyor to another conveyor through a chute, during transportation to coal towers or service bunkers. 21 COAL BLEND QUALITY: ASH 12% max VM 23 - 25% MMR 1.15 to 1.20 SULPHUR < 0.7 % FSI 5 to 6 MAXIMUM FLUIDITY 300 to 600 MOISTURE 7 to 9 % 2.4 Carbonization Process The process of converting blend coal to metallurgical coke is known as carbonization. It is defined as heating the coal in absence of air. It is also the destructive distillation of coal. The carbonization process takes place in a series of tall, narrow, roofed chambers made of refractory bricks called ovens. A specific number of ovens constitute a Battery. The ovens are mechanically supported by Structural & Anchorage. A battery can be classified as per size & design. The most common classifications are: a. Tall Battery – 7.0 m height. Small Battery – 4.5/5.0 m height. b. Recovery type battery – Gas evolved during carbonization is collected and cleaned at by- product plant. This clean gas is then used as a fuel gas throughout the Plant. Different chemicals are extracted as by-products during cleaning of gas. Non-Recovery type battery – No by products are formed as the generated gas acts as the fuel. c. Top charge battery – Conventional battery with charging from the top. The charging cars (machine that takes coal from coal tower to charge the ovens) run over the oven top and discharge the coal into the ovens through charging holes on the oven top. Stamp charged battery – A cake like mass is formed by ramming the coal and is charged by pushing the cake into the oven from Pusher/Ram side. Blend coal from coal tower is charged from top to the ovens. Each oven is sandwiched between two heating walls from which heat is transmitted to the coal charge inside the oven. When coal is charged inside an oven, it gets heated up to form a plastic mass which re-solidifies to form coke near the heating walls. The heat passes to the next layer of coal and so on till they meet at the center. During the process of carbonization the coal charge first undergo de-moisturisation (drying) upto a temperature of 250°C. Then it starts to soften at around 300°C. It then reaches a plastic or swelling state during 350°C to 550°C. The entrapped gasses are then driven out at 400°C to 700°C. The calorific value (CV) of Coke ovens gas is around 4300 kcal/m3.The gas is cooled to 800C by ammonia liquor/ flushing liquor. The mass inside the oven then re-solidifies (shrinkage) beyond 700°C. Finally coke is produced as a hard & 22 porous mass at around 1000°C.The total time taken for full carbonization is called coking time or coking period. The hot coke is then pushed out from the ovens. The hot coke is then cooled by water spray or dry nitrogen purging. This process is called quenching of coke. Generally coke is cooled by water spray for a period of 90 seconds and termed as quenching time. The cooled coke is then sent to Coke Sorting Plant for proper sizing & then to Blast Furnace. Major Equipments: Major equipment’s/machines used in the process of coke making are:  Charging car: It collects the blended coal from coal tower & charges to empty ovens.  Pusher Car or Ram Car: Its functions are to level the charged coal inside the oven during charging & to push out the coke mass from inside the oven after carbonization.  Coke Guide Car: It guides the coke mass during pushing to the Quenching car.  Quenching Car: It carries the hot coke to quenching tower & dumps the coke in the wharf after cooling. These machines have a lot of mechanical and electrical engineering devices in them. They have hydraulic operating systems run by VVFD (Variable voltage and variable frequency drive) drives controlled by PLC (Programmable Logical Controller) system. They are connected by radar based communication system which involves state of art technology. Quenching of Coke: There are two method of quenching the hot coke: 1. Wet Quenching: This is the conventional quenching system, where the red hot coke is cooled by spraying it with water (phenolic water / BOD water). The coke thus produced contains around 5% of moisture. 2. Dry Quenching: In this system, the red-hot coke is discharged into a closed chamber, where it is cooled by purging nitrogen into it. The sensible heat of the hot coke is recovered to produce steam. The coke thus produced contains around 0.2% of moisture and is of good quality. COKE SORTING PLANT: The coke, after wet quenching is dumped from the quenching car to a long inclined bed called wharf. The Quenching car operator should dump the quenched coke uniformly on the wharf from one end to the other. Quenched coke should be allowed to remain in the wharf for about 20 minutes (retention time) so that the heat remained inside the coke comes out & evaporates the surface moisture. To maintain this retention time, wharf is to be emptied out from one side & gradually progressing to the other side. If any hot coke remains after quenching, then they are cooled by manual water spray and is known as spot quenching. However this spot quenching is undesirable as it increases the moisture content in coke. The cooled coke is then taken to an 80 mm screen. The +80mm coke fractions are sent to coke cutter / crusher to bring down the size. The hard coke of size +25mm to -80mm size are then segregated to send to Blast Furnace. Coke fraction of +15mm to -25mm, which is called Nut coke, is also segregated & sent to Sintering Plants. The -15mm fractions, called fine breeze or breeze coke, are also sent to Sintering Plants. 23 In case of dry quenching, the coke is discharged from the chamber and passes through the same process of sizing and screening. 2.5 PROPERTIES OF COKE ASH: Ash in coke is inert & becomes part of the slag produced in the Blast Furnace. Hence, ash in coke not only takes away heat but also reduces the useful volume of the furnace. Hence it is desirable to have lower ash content in the coke. The desired ash content is less than 15%. VOLATILE MATTER (VM): The VM in coke is an indicator of completion of carbonization & hence the quality of coke produced. It should be as low as possible, i.e. < 1% GROSS MOISTURE (GM): It has got no role to play in the furnace. It only takes away heat for evaporation. Hence least moisture content is desirable. However during water quenching certain amount of moisture is inevitable. A level around 4.5% is desirable. MICUM INDEX: Micum index indicates the cold strength of coke. M10 value indicates the strength of coke against abrasion. Lower the M10 value better is the abrasion strength. A M10 value of around 8.0 indicates good coke strength. M40 value indicates the load bearing strength or strength against impact load. Coke having lower M40 value will crumble inside the furnace which will reduce the permeability of the burden and cause resistance to the gasses formed in the furnace to move upwards. A good coke should have a M40 value more than 80. COKE REACTIVITY INDEX(CRI): Coke reactivity determines percent weight loss of coke, as a result of carbon dioxide action on the coke at temperature 1100℃. It is the capacity of the coke to remain intact by withstanding the reactive atmosphere inside the furnace. Hence less the CRI value, better is the coke. Desirable value should be in the range of 21 - 24. COKE STRENGTH AFTER REACTION (CSR): It denotes the strength of the coke after passing through the reactive environment inside the furnace. CSR for a good coke should be in range of 64-66. It is also known as hot strength of coke. CRI &CSR are also known as hot strength of coke. 24 COKE SIZE: The size of coke is most important to maintain permeability of the burden in the furnace. The required size for Blast Furnace is more than 25mm size & less than 80mm size. If the undersize is more the permeability decreases as smaller coke pieces fill up the voids & increase the resistance to the flow of outgoing gasses. If the oversize is more the surface area of coke for the reactions reduces. Hence the size of the coke is to be maintained between +25mm & -80mm ROLE OF COKE IN THE BLAST FURNACE: Coke plays a vital role in Blast Furnace operation. For stable operation of the furnace, consistent quality of coke is most important. Variation in coke quality adversely affects the Blast Furnace chemistry. The roles of coke in Blast Furnace are: It acts as a fuel. It acts as a reducing agent. It supports the burden inside the furnace. It provides permeability in the furnace. 2.6 Coal Chemicals Process of heating coal in absence of air to produce coke is called coal carbonization or destructive distillation. Purpose of coal carbonization is to produce coke whereas co-product is coke oven gas. From coke oven gas, various by products like tar, benzol, naphthalene, ammonia, phenol, anthracene etc. are produced. Generally high temperature coal carbonization is carried out in coke oven battery of integrated steel plants at temp of 1000-1200 deg. Centigrade. In the by-product plant major byproducts like tar, ammonia and crude benzol are recovered from the coke oven gas evolved during coal carbonization. The output of the gaseous products, their composition and properties depend on the coal blend used for coking, the heating regime & the operating condition of the battery. Tar separated out of coke oven gas as a mixture of large quantities of various chemical compounds. From tar, a number of products are separated in the tar distillation plant which have market demand. Among the tar products, naphthalene is the costliest item & its yield is 50-55 % of the tar distilled. Other tar products are road tar, Anthracene, pitch creosote mixture, medium hard pitch & extra hard pitch etc. Ammonia in the coke oven gas is recovered as Ammonium sulphate, which is used as a fertilizer in agriculture sector. Output of crude benzol depends on the V.M content in the coal blend and temperature of coking. Light crude benzol is rectified in benzol rectification plant and the benzol products obtained are benzene, toluene, xylene, solvent oil etc. Yield of benzol products varies from 86-88% of the crude benzol processed. The by products recovered in the process are very important and useful.Tar is used for road making and as fuel in furnaces. Pitch is used for road making. The benzol products like benzene, toluene, phenol, naphthalene and xylene etc. are important inputs for chemical industries producing dyes, paint, pharmaceutical, insecticide, detergent, plasticiser and leather products. 25 The coke oven gas from Coke ovens contain lot of impurities, which needs to be properly cleaned before being used as a fuel gas for Coke Oven heating as well as elsewhere in Steel Plant. The impurities in coke oven gas are mainly tar fog, ammonia, naphthalene, hydrogen sulphide, benzol, residual hydrocarbon and traces of HCN. Cleaning of coke oven gas is done by passing it through a series of coolers & condensers and then treating the gas in ammonia columns, saturators, washers, tar precipitators, naphthalene washers, benzol scrubbers etc. for removal of these impurities. After the cleaning operation, the final coke oven gas still contains traces of impurities. Quality of coke oven gas depends on the contents of various impurities and its heat value. Typical analysis of impurities in good quality coke oven gas is as follows:-Tar fog: 30 mg/Nm³ ± 10mg, Ammonia- 30 mg/Nm³ ± 10mg, Napthalene- 250mg/Nm³ ± 50mg, Hydrogen Sulphide- 200 mg/Nm³ ± 50mg, HCN- Traces, CnHm- 1.5 to 2.5%. 2.7 By Products Plants of Coke Ovens The Gas generated in the Coke oven batteries during carbonization process is handled and cleaned in the By Product Plant. During the process of cleaning the gas some By Products are separated out and clean Gas is used as fuel in the plant. Following process are involved in cleaning the gas. TAR AND LIQUOR PROCESSING PLANT The tar and liquor processing plant process the flushing liquor that circulates between the by product plant and the coke oven battery. It also processes the waste water that is generated by the coke making process and which results from coal moisture and chemically bound water in the coal. The main functions of these plants are as follows:  Continuous rapid separation of a suitable flushing liquor streams. This is the very important function since flow is needed to cool the hot oven exit gases down to a temperature which can be handled in the gas collecting system.  Separation of a clean and tar free excess ammonia liquor for further processing.  Separation of clean tar essentially free from water and solids. Since the flushing liquor supply is very important, stand by equipment are normally provided for flushing liquor decanting and recirculation. The flushing liquor flows into tar decanters where the tar separates out from the water and is pumped to tar storage for processing in tar distillation plant. Heavier solid particles separate out from the tar layer and these are removed as tar decanter sludge. The aqueous liquor is then pumped back to the battery, with a portion bled off from the circuit which is the coke plant excess liquor or waste water. This contains ammonia and after the further removal of tar particles, it is steam stripped in a still. PRIMARY GAS COOLER After separation of tar and ammonia liquor from gas, gas is fed into gas cooler where temperature of gas is lowered down by means water sprinkling. Primary gas cooler are two basic types, the spray type cooler and the horizontal tube type. In spray type cooler the coke oven gas is cooled by direct contact with recirculated water spray. As the coke oven gas is cooled, water, naphthalene and tar condensed 26 out. The condensate collects in the primary cooler system and is discharged to the tar and liquor processing plant. ELECTROSTATIC TAR PRECIPITATOR As the raw coke oven gas is cooled, tar vapour condenses and forms aerosols which are carried along with the gas flow. These tar particles contaminate and foul downstream processes and foul gas lines and burner nozzles if allowed to continue in downstream. The tar precipitator typically uses high voltage electrodes to charge the tar particles and then collect them from the gas by means of electrostatic attraction. The Tar precipitator can be installed before or after the exhauster. EXHAUSTER Exhausters are installed which sucks the gas generated in the batteries and sends to the desired destination for further processing. Another function of the exhauster is to maintain steady suction as per requirement so as to maintain the hydraulic main or gas collecting main (GCM) pressure. The exhauster is of prime importance to the operation of the coke oven battery. It allows the close control of the gas pressure in the collecting main, which in turn affects the degree of emission in the battery like door emission. A failure of the exhauster will immediately result in venting to atmosphere all the generated the raw coke oven gas through the battery flares / bleeder. AMMONIUM SULPHATE PLANT (ASP) Due to the corrosive nature of ammonia, its removal is very much necessary in by-products plants. The removal of ammonia from coke oven gas results into yield of ammonium sulphate. The ammonium sulphate processes are basically involves contacting the coke oven gas with solution of sulphuric acid. Raw coke oven gas from Exhauster outlet is passed through the saturators filled with Sulphuric Acid (H2SO4), where ammonia present in the gas is precipitated in the form of ammonium sulphate. Acidity of the saturator liquor is maintained at 3 % to 5 %. This ammonium sulphate is sold as Fertilizer. FINAL GAS COOLER (FGC) Final gas cooler removes the heat of compression from the coke oven gas which it gains while flowing through the exhauster. This is necessary since the efficiency of many of the by-product plant processes greatly improved at lower temperature. Gas coolers typically cool the coke oven gas by direct contact with a cooling medium. BENZOL RECOVERY PLANT (BRP) Benzol present in the raw coke oven gas is removed in this unit. The gas is passed through solar oil / Wash oil in the scrubbers. The benzol gets absorbed in the oil. Benzol rich oil is fed to distillation unit where oil and crude benzol are separated. The oil is reused in the scrubbers. The clean coke oven gas is used by the consumers through gas net work maintained by Energy Management Department. NAPTHALENE REMOVAL Naphthalene is removed from coke oven gas in a gas scrubbing vessel using wash oil. The vessel can be of packed type and it can be of the void type in which the wash oil is sprayed into the gas in several stages. 27 BENZOL RECTIFICATION PLANT Light crude benzol from benzol recovery plant is further processed in this unit and following by products are recovered: a. Benzene b. Toluene c. Xylene d. Carbon di-Sulphide (CS2) TAR DISTILLATION PLANT (TDP) Tar recovered from GCPH is further processed in TDP. The main products of TDP are: (a) Tar (b) Pitch (c) Pitch Creosote Mixture ( PCM ) (d) Naphthalene (e) Anthracene oil ACID PLANT Sulphuric acid is produced in acid plant by DCDA (Double Conversion Double Absorption) process. In this process sulphur is converted to Sulphur tri oxide (SO3) in presence of catalyst Vanadium pentoxide (V2O5) and then to Sulphuric acid. This acid is used in Ammonium Sulphate plant for removal of ammonia from raw coke oven gas. PETP / BOD PLANT In Phenolic Effluent Treatment Plant (PETP) or Biological Oxygen Demand (BOD) Plant, the contaminated water generated from whole of coke oven is treated to make it clean from the effluents with the help of Bacteria. The treated water is then used for quenching hot coke in the quenching towers. The norms for different effluent after treatment at BOD plant are: Ammonia : 50 ppm Phenol : 1 ppm Cyanide : 0.2 ppm Tar & Oil : 10 ppm Coke Oven Gas (CO Gas): The most important byproduct of Coke oven is the raw Coke oven gas. The basic constituents of clean coke oven gas are: Hydrogen - 50 to 60% Methane - 25 to 28% Carbon Monoxide - 6 to 8% Carbon Dioxide - 3 to 4% Other Hydrocarbons - 2 to 2.5% Nitrogen - 2 to 7% Oxygen - 0.2 to 0.4% Calorific value - 4300 kcal / m3 28  PROCESS FLOW DIAGRAM OF COKE OVEN & CCD Washed Coal from Washeries Wagons Wagon Tippler Unloading of coal Coal Yard / Silos Reclaiming Crusher Crushing & Blending Coal Tower +25 to -80 B.F. Hard Coke Batteries Coke Sorting +15 to -25 (Carbonization) Plant S.P. Nut Coke -15 S.P. Coke Breeze Raw CO Gas Extra hard pitch By Product Wash oil Plant Tar Anthracene oil Clean CO Gas Carbolic oil Light oil Benzol (BTX) Ammonium Sulphate Naphthalene 29 2.8 Pollution Control Norms To protect the environment, Central Pollution Control Board (CPCB) has laid down strict pollution control norms. The different norms for coke ovens with respect to PLD (Percentage Leaking Doors), PLO (Percentage Leaking Off take), PLL (Percentage Leaking Lids) and Stack Emission are as follows: FACTORS NEW BATTERY EXISTING BATTERY PLD 5 10 PLL 1 1 PLO 4 4 SO2 800 mg/Nm3 800 mg/Nm3 Stack Emission 50 mg/Nm3 50 mg/Nm3 Charging Emission 16 sec/charge 50 sec/charge ISO 14001: 2004 is an environment management system which deals with the ways and means to make the environment pollution free. Its main thrust is to make Land, Air & Water free of pollutants. 2.9 Safety Safety is the single most important aspect in the steel industry. This aspect covers both personal as well as equipment safety. The use of PPE s (Personal Protective Equipment) is a must for the employees in the shop floor. The use of PPEs like safety helmet, safety shoes, hand gloves, gas masks, heat resistant jackets, goggles and dust masks are to be used religiously while working in different areas of coke ovens. Different laid down procedures like EL 20 / permit to work, as followed in different steel plants, are to be strictly followed before taking any shut-down of equipment for maintenance. The stipulated SOPs (Standard Operating Procedure) and SMPs (Standard Maintenance Procedure) should be adhered to strictly. Persons should be cautious about the gas prone areas and should know about the gas hazards. EMD clearance is a must before taking up any job in gas lines or gas prone areas. A life lost due to any unsafe act is an irreparable loss to the company as well as to the family which can not be compensated. 5-S SYSTEM (WORK PLACE MANAGEMENT): 5 S system is an integrated concept originated by the Japanese for proper work place management. Takasi Osada, the author of this concept says 5 s activities are an important aspect of team work applicable to all places. 30 1 S : s e i r i – It is the process of distinguishing, sorting & segregation between wanted & unwanted items in a work place & removal of the unwanted. 2 S : s e i t o n – It is the process of systematic arrangement of all items in a suitable place. 3 S : s e i s o – It is the process of proper house keeping of the work place including cleaning of all equipments. 4S:seikestu– It is the process of standardization 5 S : s h i t s u k e – Literal meaning of shitsuke is discipline. It is the process of following the system meticulously. 2.10 ISO45001:2018 (Occupational Health and Safety Management System: OH&SMS provides a formalized structure for ensuring that hazards are identified, their impact on staff assessed and appropriate controls put in place to minimize the effect. It further assists a company in being legally compliant, ensuring appropriate communication and consultation with staff, ensuring staff competency and having arrangements in place to deal with foreseeable emergencies. It is not concerned with the safety of the product or its end user. It is compatible with the established ISO 9001(Quality) and ISO 14001 (Environmental) management system standards. This helps to facilitate the integration of the quality, environmental and occupational health and safety management systems within the organization. Impacts of fully implemented OH&SMS are: (a) Risks and losses will be reduced and/or eliminated (b) Reduced accidents, incidents and costs (c) Reliable operations (d) Compliance to rules, legislation, company standards and practices (e) A systematic and efficient approach to health and safety at work (f) Positive company image and reputation --- 31  Chapter – 3 SINTER PLANT 3.1 Introduction Sinter Plant agglomerates iron ore fines with other fine materials at high temperature, such that constituent materials fuse together to make a single porous mass. A large quantity of iron ore fines is generated in the mines, which cannot be charged directly into the Blast furnace. Moreover many metallurgical wastes are generated in the steel industry itself, disposal of which is very difficult. In order to consume this otherwise waste fine materials, they are agglomerated together and made into lumps by a process known as SINTERING. Sintering is the process of agglomeration of fines (steel plant wastes) by incipient fusion caused by heat available from the fuel contained in the charge. This technology was developed for the treatment of waste fines in the early 20th century. Since then sinter has become the widely accepted & preferred Blast furnace burden material. Raw materials used in Sinter Plant 1. Iron ore fines 2. Lime stone fines 3. Dolomite fines 4. Coke breeze fines 5. B.O.F.Sludge 6. Burnt Lime 7. Mills Scale 8. B.O.F.Slag / L D slag 9. BF Return fines 10. Internal Sinter Return fines 3.2 Sintering Process The Iron ore fines, lime stone fines, dolomite fines, lime dust, coke breeze and other metallurgical wastes are proportioned based on charge calculation. These charge thus mixed in a balling drum with the addition of water and then loaded into grates of moving pallets. The purpose of Balling drum is to mix the raw materials (called base mix) with water and make balls. After mixing and ball formation( nodulization ) this base mix (now called green mix) is loaded on moving sinter machine pallets. HEARTH LAYER which consists of finished sinter of size fraction 10 to 20mm forms the bottom layer. Green mix is loaded above the hearth layer. As soon as these raw materials reaches the ignition furnace, Top layer of green mix charge is ignited in the IGNITION FURNACE by burning of gases mainly CO gas. Air is drawn 32 downwards through Exhausters or Waste Gas Fans. The heat from top layer is gradually transferred to subsequent bottom layers.. Due to burning of coke particles bonding take place between the grains and a strong & porous aggregate is formed known as “SINTER”. This sintering process is over when bottom layer coke fine burning is completed. The sinter cake is then crushed, cooled, screened and dispatched to Blast furnace. The ideal size of sinter required in blast furnace is in between 5mm to 40mm. The - 5mm size sinters are screened & returned back to sinter bins. Fig1: Sinter Machine at SP3 , Machine 1 Sinter Making Sintering of fines by the under grate suction method consists of the mixing of fines 33 with finely crushed coke as fuel and loading the mixture on the pallet grates. Ignition of the fuel proceeds on the surface of charge by a special ignition arrangement, called ignition furnace (where gaseous fuel is burnt to produce high temperature to ignite the fuel in sinter mix) The gases used in ignition furnace are mainly coke oven gas or mixed gas. Mixedgas is combination of coke oven gas and blast furnace gas. Further the combustion is continued due to suction of air through the layers of the charge by means of Exhausters. Due to this, the process of combustion of fuel gradually moves downwards up to the grates. From the scheme obtained in a few minutes after ignition, it is observed thatthe sintering process can be divided into six distinct zones: 1. Zone of Cold Sinter (60 to 100 0C) 2. Zone of hot Sinter (100 to 1000 0C) 3. Zone of intensive combustion of fuel (1000 to 1350 0C) 4. Heating zone (1000 to 700 0C) 5. Zone of Pre-heating of charge (700 to 60 0C) 6. Zone of Re-condensation of moisture (60 to 30 0C) In all the zones except the zone of combustion, the reactions taking place are purely thermal wherea s in the zone of combustion reactions are thermal and chemical. The maximum Temperature attained in the zone of combustion will be 1300-1350 0C. The vertical speed of movement of the zones depends on the vertical speed of sintering. Heat from the zone of ready sinter is intensively transmitted to the sucked air. In the 34 zone of combustion of fuel hot air and preheated charge comes into contact with each other which with the burning fuel will result in the formation of high temperature. Maximum temperature will be developed in this zone and all the physical-chemical process takes place resulting in the formation of Sinter. In the zone of pre-heating the charge is intensively heated up due to transfer of heat from the sucked product of combustion. In the zone of re- condensation of moisture, the exhaust gases during cooling transfer excess moisture to the charge. Temperature of this zone sharply decreases and will not increase till all the moisture is driven off. As the fuel in the zone of combustion is burnt away, Sinter, the height of which increases towards the grates, is formed above this zone from the red hot semi-fluid mass, forcing out subsequent zones. Disappearance of the zone of combustion means the end of sintering process. The sinter cake is then crushed, cooled, screened and dispatched to Blast furnace. The ideal size of sinter required in blast furnace is in between +5mm to 40mm. The - 5mm size are screened & returned back to sinter bin. (Called In plant return fines) Following Approximate charge proportion will be required to make one ton of sinter (Wet basis):- Ore fines : 750-825kg Coke : 65-70 kg Mill scale + fines : 26 Kg Lime stone : 150-180 kg B.O.F. Sludge : 02kg B.O.F. Slag : 20Kg Dolomite : 3 0 - 4 0 kg Burnt Lime : 20 kg BF Sinter return : 100 kg In plant sinter return : 456 kg Note- All above mentioned data varies in different plants under SAIL. Factorsaffecting sintering process: 1. Quality of Input raw materials a. Quality of Iron ore fines : : +10 mm should be nil : -1mm should be 30% maximum : Alumina (Al2O3) 2.55% maximum : Silica (SiO2) 2.91% maximum Increase in +10mm fraction will result in weak sinter & low productivity Increase in –1mm fraction will decrease bed permeability resulting in low productivity Increase in % of Alumina increases RDI (Reduction Degradation Index) resulting ingeneration of –5mm fraction & also resulting in chutejamming (Due to high Alumina in Base/Mix. 35 With increase of SiO2 level in Iron ore fines, glassy phase in sinter increases and causes brittleness in sinter. 36 b. Quality of Flux : -3mm fraction should be 90% minimum (Crushing index) : Less crushing index results in free lime, causing weak sinter c. Quality of Coke : -3mm fraction should be 85% minimum (Crushing index of coke) : +5mm fraction should be nil : Increase in 5mm fraction decreases the productivity : Increase in less than 0.5 mm particle size in coke causes increase in coke consumption during sintering 2. Moisture : Moisture in the form of water is added in the base mix in Mixing/Nebulizing drum. Water acts as binder of base mix. Addition of water in base mix plays an important rolein sinter bed permeability. Ideally 7 to 8% of total base mix of water is used. Higher % of water results in low permeability & less sintering speed. Less % of water results in less balling, hence less permeability, resulting in low productivity. 3. Ignition furnace temperature: Ignition of sinter mix is carried out through ignition hearth where a temperature of 1150 to 1250 0C is maintained by burning gaseous fuel by the help optimum air/gas ratio. 32.5% of CO gas & 67.5% of BF gas is used to maintain calorific value 1900kcal/m3. Now a day Sintering Plant, Bhilai Steel Plant uses Coke Oven Gas of calorific value 4150 Kcal/Nm3. Very Higher hearth temperature results in fusing of sinter at top layer. This reduces the bed permeability, hence low productivity. Low hearth temperature results in improper ignition. The sintering process will not be completed, hence –5mm fraction will increase, i.e. re- circulating load will increase. Note- BF&CO gas mixing ratio and calorific value varies in different plants of SAIL 4. Coke rate : Coke acts as a solid fuel in base mix in the sintering process. It is normally 3.5 to 6% of total charge. Higher coke rate will fuse the top layer, thereby decreasing the bed permeability. Sticker formation will increase. Low coke rate will result in incomplete sintering. 5. Machine speed : The speed of sinter machine can be varied as per the condition of sintering process. BTP (Burnt Through Point) temperature decides the completion of sintering process. It is observed normally in second last wind box from discharge end side of sinter machine where the temperature reaches up to 400 0C (approximately). Higher machine speed, lower 37 BTP causes more–5mm generation, hence lower productivity. Lower m/c speed, higher BTP temperature causes low productivity. Note: BTP: Exhaust gas temperature which indicates the completion of sinteringprocess iscalled BTP. It is approximately around 400 degree centigrade. Crushing, Cooling & Screening of Sinter The finished Sinter cake is then crushed to the size of 100mm by using crushers. Cooling of finished crushed Sinter is then done on cooler by means of air blowers (forced draught fans), so that cooler discharge end temperature is about 60-80 degree centigrade. For effective cooling, bigger size of sinter should be on bottom portion & smaller size should be on the top. Finally various fractions of Sinter are screened out. -5mm fraction of sinter, returns back to bunkers. 15 to 20mm fraction is also screened out to be used as hearth layer. Rest sizes goes to blast furnace. After screening, +10mm fractionshould be 65%minimum and –5mm fraction should be 6% maximum as per requirement of blast furnace. Advantages of using Sinter 1. To utilize the ore fines generated at mines to transform to an acceptable feed in blast furnace 2. To utilize economically all the metallurgical wastes like Mill scale, L.D slag, B.O.F slurry, Flue dust, Ferro scrap etc. 3. To utilize the coke breeze generated in coke screening at coke ovens as fuel, otherwise has no metallurgical use 4. As the calcination of flux takes place in sinter strand, super-fluxing saves much more coke in the furnace. 5. Increase of sinter percentage in Blast Furnace burden, increases the permeability, hence reduction and heating rate of burden increases, so the productivity also increases. Coke rate is also reduced in Blast furnace. 6. Minimal fraction of total mass of impurities, Viz. sulphur, phosphorous, zinc, alkali is reduced. 7. Improved quality of hot metal. 8. The softening temp. of sinter is higher and melting zone is narrow. This increases the volume of granular zone and shrinks the width of cohesive zone consequently,the driving rate of BF become better. 38  PROCESS FLOW DIAGRAM OF SINTER PLANT 3.3 Quality Parameters of Sinter (Subject to Requirement of BF) Chemical composition Physical composition 1. FeO % 8.0 to 11.0 Sinter size 5mm to 40mm 2. MgO % 2.6 to 3.0 Mean size 18mm to 21mm 3. Available lime 3.4 to 6 DTI 70% MIN (CaO-SiO2)% 4. As per BF RDI 30% MAX Requirement 5. SiO2 % 4.8 to 5.2 + 10 mm 65 % min. 6. Al2O3 % 3.0 +40 mm 9 % max. 7. Basicity. 1.6 to 2.1 - 5 mm 6% max. Note- Quality parameters of sinter varies in different plants under SAIL. 39 Quality parameter definitions: Tumbler index (DTI): The cold strength of sinter is determined by the tumbler test , and depends on the strength of each individual ore component, the strength of the bonding matrix components and the ore composition. This test determines the size reduction due to impact and abrasion of the sinters during their handling, transportation, and in the blast furnace process. Studies of the fracture strength of several mineral phases have allowed the following order to be established: primary (or residual) hematite > secondary hematite > magnetite > ferrites. Cold mechanical strength is directly related with the tendency for fines to form during transportation and handling between the sinter machine and the blast furnace throat. Reduction Degradation Index (RDI) Sinter degradation during reduction at low temperature is more usually determined by the RDI static test ,which is carried out at 550 °C. Low values are desirable for this index. The RDI is a very important parameter that is used as a reference in all sintering work and servesto predict the sinter's degradation behavior in the lower partof the blast furnace stack. Some critical terms/parameters used/monitored in sinter plant: Coke crushing index Percentage presence of –3mm fraction of coke in any sample is termed as coke crushing index. For better sintering process coke crushing index should be more than 85% Flux crushing index Percentage presence of –3mm fraction of flux in any sample is termed as Flux crushing index.For better sintering process Flux crushing index should be more than 90% Burn Through Point Burn through point temperature indicates the completion of (BTP) sintering process. It is normally around 400 degree Celsius and is normally found in second last of wind box from discharge end of sinter machine. 3.4 Main Areas & Equipment Main Areas Equipments Functions Sinter making & Balling drums To mix & pelletize Cooling bldg. Sinter pallets Sintering takes on it Screens Screens out diff. sizes Crushers Crushes sinter cake Coolers Cools/ Normalize sinter Exhausters High capacity fans To suck air below grates Battery cyclones To clean Exhaust air ESP To clean Exhaust air 40  Proportioning Bins Electronic feeders For adjusting feeding Conveyors Transport charge mix. Bunkers Store raw materials Coke & Flux Roll crushers For crushing coke Crushers Rod Mills For crushing coke Hammer crushers For crushing Fluxes Grab cranes For lifting coke Techno Economics 1. Specific Productivity : Sinter produced per square meter per hour 2. Specific Heat consumption : Gas consumed per ton of sinter 3. Specific Power consumption : Power consumed per ton of sinter 4. Specific Coke consumption : Coke consumed per ton of sinter 5. Specific Flux consumption : Flux consumed per ton of sinter In order to produce sinter at less cost, specific productivity of sinter should be as high aspossible & all other four parameters should be as low as possible keeping quality parameters under consideration. Advantages of Sintering 1. Better use of the huge quantity of iron ore fines generated at mines. 2. Gainful use of various metallurgical wastes like flue dust, mill scale, lime dust, sludge, etc. 3. Use of super fluxed sinter eliminates raw flux from the blast furnace burden. This leads toconsiderable coke saving and productivity improvement in blast furnaces. 4. Due to the higher reducibility of super fluxed sinter, direct reduction of iron oxide is enhanced, which contributes to further coke saving. 5. The softening temperature of sinter is higher and the softening melting zone is narrower. This increases the volume of granular zone and shrinks the width of the cohesive zone. Consequently, the driving rate of the blast furnace improves. 6. Hot metal quality (from the SMS point of view) improves due to lower silicon content and higher hot metal temperature. A higher hot metal temperature contributes to better sulphur removal from the hot metal. 7. Material handling in the charging section of the blast furnace is reduced, and fewer logistics are needed. 8. Blast furnace operation is more reliable and efficient 3.5 Safety hazards at Sinter plant 1. Dust pollution : As lot of finer particles are used in sintering, there causing lots of dust pollution. Efficient running of ventilation is must. Use of dust mask is essential. Chimney Stack Emission is 50mg/nm3. Fugitive Emission(ambient) is 2mg/nm3 2. Gas safety : Gases (usually Mixed gas & Coke oven gas) are used for igniting charge mix, It is very important to follow all the protocols for gas safety. Use of gas mask and Carbon mono oxide (CO) gas monitor while working on gas line is must. 41  3. Noise pollution: Tremendous amount of air is sucked through exhausterfans. Slight leakages anywhere in suction line or exhauster results in high level of noise. Air compressor, chiller unit, hammer crusher, coke crusher are also high noise generating areas in Sinter plant. Use of Ear plug is essential. 3.6 ISO 45001:2018 (Occupational Health and Safety Management System): OH&SMS provides a formalized structure for ensuring that hazards are identified, their impact on staff assessed and appropriate controls put in place to minimize the effect. It further assists a company in being legally compliant, ensuring appropriate communication and consultation with staff, ensuring staff competency and having arrangements in place to deal with foreseeable emergencies. It is not concerned with the safety of the product or its end user. It is compatible with the established ISO 9001(Quality) and ISO 14001 (Environmental) management system standards. This helps to facilitate the integration of the quality, environmental and occupational health and safety management systems within the organization. Impacts of fully implemented OH&SMS are: a) Risks and losses will be reduced and/or eliminated b) Reduced accidents, incidents and costs c) Reliable operations d) Compliance to rules, legislation, company standards and practices e) A systematic and efficient approach to health and safety at work f) Positive company image and reputation 42  Chapter – 4 BLAST FURNACES 4.1 Introduction BF is a counter current heat and mass exchanger, in which solid raw materials are charged from the top of the furnace and hot blast, is sent through the bottom via tuyeres. The heat is transferred from the gas to the burden and oxygen from the burden to the gas. Gas ascends up the furnace while burden and coke descend down through the furnace. The counter current nature of the reactions makes the overall process an extremely efficient one in reducing atmosphere. The real growth of blast furnace technology came with the production of high strength coke which enabled the construction of large size blast furnaces. 4.2 Raw materials and their quality In India steel is being produced largely through the blast furnace. Iron ore, sinter and coke are the major raw materials for blast furnace smelting. Raw materials: The following raw materials usedfor the production of pig iron: - (i) Iron ore (ii) Limestone / L D Slag (iii)Dolomite (iv) Quartzite (v) Manganese ore (vi) Sinter (vii) Coke (viii) Pellets (ix) Scrap (Steel / Iron) (x) Coal Dust / Coal Tar Iron ore: Iron bearing materials; provides iron to the hot metal. Iron ores is available in the form of oxides, sulphides, and carbonate, the oxide form known as hematite (red in colour) is mostly used in SAIL plants. It is the principal mineral in blast furnace for extraction of pig iron, generally rich in iron content varying from 62 % to 66 % associated often with naturally occurring fines (-10 MM) to the extent of 20 %. Although relatively free from impurities like phosphorous, sulphur and copper, they have high aluminaand silica contentas gangue. The high alumina content makes the slag highly viscous and creates problems for stable furnace operation. Limestone / LD Slag: Acts as flux. Helps in reducing the melting point of gangue present in the iron bearing material and combines effectively with acidic impurities to form slag in iron making. LD slag is a substitute for limestone which is easily available in a steel plant. Its usage helps in waste utilization and thus reduces production cost. 43 Quartzite: It acts as an additive.Quartzite is a mineral of SiO2 (silica) and under normal circumstances contains about 96 – 97 % of SiO2 rest being impurities. Quartzite plays its role in counteracting the bad effects of high alumina in slag through maintaining optimum slag basicity. Manganese ore: It acts as additive for the supply of Manganese in the hot metal. Manganese ore is available in the form of combined oxides of Mn and Fe and usual content of Mn is about 28 – 32 % for steel plant use, However Manganese ore available with SAIL is having high alkali contents so it should be used judicially. Coke: Itacts as a reductant and fuel, supports the burden and helps in maintaining permeable bed. Coke (metallurgical) used in blast furnace both as fuel & reducing agent. The Indian coal is characterized by high ash (25 – 30 %) and still worse, a wide fluctuation in ash content, poor coke strength leading to excessive generation of fines, rapid fluctuation in moisture content etc. The problem of poor quality coke has been tackled by adding imported coal (75-95%) in the indigenous coal blend to get a coke ash of 13 – 16 %. Sinter: It is iron bearing material. Fines that are generated in the plant/mines are effectively utilized by converting them to sinter. It provides the extra lime required for the iron ore and coke ash that is charged in the blast furnace. Sintering is the process of agglomeration of fines (steel plant waste and iron ore fines) by incipient fusion caused by heat available from the coke contained in the charge. The lumpy porous mass thus obtained is known as “sinter”. Scrap (Steel / Iron): Scrap is generrated in the process of product making in a steel plant which is gainfully utilized by back charging in the Blast Furnaces. It increases the furnaces productivity and reduces the production cost. Pellets: It is also an iron bearing materials. The micro-fines which cannot be used for sinter making can be used for pellet manufacturing and the pellets formed will be charged in the BF. Coal dust Injection: It acts as an auxiliary fuel, reduces coke consumption in the blast furnaces. The coal is injected through the tuyeres. 44  Different sources of raw materials Sl. Raw BSP RSP DSP ISP BSL No. material 1. Iron ore Dalli Barsua Bolani Gua Kiriburu Rajhara Kalta GuaMeghaha Bolani Meghahatubur Raoghat Meghahatuburu tuburu Meghahatubu u Meghahatubur Kiriburu ru Bolani u Barsua Kiriburu Gua Manoharpur 2. Limestone Nandini Kuteswar Kuteswar Jaisalmer Nandini Kuteswar Jaisalmer Jaisalmer Imported Kuteswar Jaisalmer Imported Imported Jaisalmer Imported Imported 3. Dolomite Hirri Baraduar Belha Baraduar Belha Birmitrapur 3 Imported Imported Baraduar Belha Imported Imported Quality of raw materials Material Chemical Analysis Specification Size Other properties Softening Melting Fe 61.0% min. range: Iron 10 – 40 SiO2 2.5 ± 0.5 % 1100 - 1400˚C Ore(Lumps) mm P 0.10% max. Al2O3/SiO2 0.70 max. RDI(Reduction Fe 50-58% Degradation Index) 65 Sinter SiO2 4-6% mm Tumbler Index >70 Softening Melting Al2O3 2-3% range: CaO 9 – 13% 1200 – 1450oC MgO 2 – 3% CRI(Coke Reactivity Ash 13 – 15% 25 – 80 Index): 21 -23 Coke VM(VOLATILE mm CSR(Coke Strength 64 45  Moisture 5 ± 0.5% M40 >80% S 0.5 - 0.6% M10 6 mins  Tap hole life >110 heats Practices to be followed for convertor nurturing: Splashing of retained slag for 3 mins by nitrogen blow through lance Addition of coke for better splashing Coating of converter Slag dumping in slag pot after splashing and coating before next charging 5.4 Secondary Steel Making Objective: Achieving the required properties of steel often requires a high degree of control over carbon, phosphorus, sulphur, nitrogen, hydrogen and oxygen contents. Individually or in combination, these elements mainly determine material properties such as formability, strength, toughness, weldability, and corrosion behaviour. There are limits to the metallurgical treatments that can be given to molten metal in high performance melting units, such as converters or electric arc furnaces. The nitrogen and phosphorus content can be reduced to low levels in the converter but for further reducing carbon, sulphur, oxygen and hydrogen contents (< 2 ppm) to very levels it can only be obtained by subsequent ladle treatment. To ensure appropriate conditioning of steel before the casting process, the alloying of steel to target analysis and special refining treatments are carried out at the ladle metallurgy stand. The objectives of secondary steelmaking can be summarized as follows:  Refining and deoxidation  Removal of deoxidation products (Mn0, SiO2, Al2O3)  Desulphurization to very low levels (< 0,008%)  Homogenization of steel composition  Temperature adjustment for casting, if necessary by reheating (ladle furnace)  Hydrogen removal to very low levels by vacuum treatment. The high oxygen content of the converter steel would result in large blow-hole formation during solidification. Removal of the excess oxygen ("killing") is therefore vital before subsequent casting of the steel. Steels treated in this way are described as killed steels. All secondary steelmaking processes allow deoxidising agents to be added to the ladle 73 Deoxidation can be performed by the following elements classified by increasing deoxidation capacity; carbon - manganese - silicon - aluminium.The most popular are silicon and aluminium. After addition, time must be allowed for the reaction to occur and for homogeneity to be achieved before determination of the final oxygen content using EMF probes (electro- chemical probe for soluble oxygen content). Secondary Refining Secondary steel making units can be categorized as: a) Stirring Systems b) Ladle Heating Systems c) Vacuum Degassing Systems and d) Addition Systems (RH Process and Tank degassing unit) a. Stirring systems These systems involve in stirring the molten steel bath for obtaining homogenous temperature, composition, floatation of inclusions and promotion of slag-metal refining reaction.As most of deoxidation agents form insoluble oxides, which would result in detrimental inclusions in the solid steel, they have to be removed by one of the following processes during the subsequent refining stage: Argon stirring and/or injection of reactants (CaSi, and/or lime based fluxes) achieves:  Homogeneous steel composition and temperature  Removal of deoxidation products  Desulphurisation of aluminium-killed steel grades  Sulphide inclusion shape control. Argon stirring can be done by refractory lined lance (Top lance) or by means of porous plug made by high alumina material (bottom purging). b. Ladle heating systems These furnaces, act as buffer between the primary melting unit and the continuous casting unit giving precise temperature and compositional control. This provides an option to the primary melting unit to tap at low temperatures leading to saving in time and energy and also the cost of Ferro-Alloys / De-oxidisers apart from increasing the refractory life of BOF. Through appropriate slag composition control, de-oxidation practice and argon stirring, it is possible to produce clean steels through Ladle furnace. Stirring of the melt by argon or by an inductive stirring equipment and arc heating of the melt (low electric power, typical 200 KVA/t) allows:  long treatment times  high ferro-alloy additions  high degree of removal of deoxidation products due to long treatment under optimized conditions  homogeneous steel composition and temperature 74   desulphurisation, if vigorous stirring by argon. In ladle furnace the produced exhaust waste gases are cleaned by means of bag filters/ESP. c. Vacuum Degassing Systems The concept of degassing started primarily to control the hydrogen content in steels but sooner it served many purposes for production of clean steels. The degassing systems can be further classified as Circulation Degassers, Tank Degassers. Vacuum-Treatment: RH process (Ruhrstahl-Heraeus) In the RH process the steel is sucked from the ladle by gas injection into one leg of the vacuum chamber and the treated steel flows back to the ladle through the second leg. Tank degassing unit In the tank degasser process, the steel ladle is placed in a vacuum tank and the steel melt is vigorously stirred by argon injected through porous plugs in the bottom of the ladle. Millibar is term used for measurement of vacuum. Steam is used for creating vacuum. Vacuum treatment achieves: