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PROCESS ENGINEERING OF HOT METAL PRODUCTION IN BLAST FURNACE Heat and mass balance calculations for Pellets & Sinter as charge material [MH2039 HT17-1 Process Engineering]
Abstract
Alva Army Gerry, Daniel Haster Olsson, Fikan Mubarok Rohimsyah and Thales Rossi
[email protected]
ABSTRACT
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NOMENCLATURE
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TABLE OF CONTENTS 1 INTRODUCTION................................................................................................................... 1 2 THE BLAST FURNACE ........................................................................................................ 2 3 MASS AND HEAT BALANCE ............................................................................................. 3 4 RESULTS................................................................................................................................ 5 5 DISCUSSION AND CONCLUSIONS................................................................................... 6 6 RECOMMENDATIONS ...................................................................................................... 13 7 REFERENCES ...................................................................................................................... 14 APPENDIX A: CALCULATIONS ......................................................................................... 15
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1 INTRODUCTION
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2 THE BLAST FURNACE
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3 MASS AND HEAT BALANCE The procedure and results of mass and heat balance calculations will be presented in the following chapter. This includes: the industrial data used in the calculations, general and specific assumptions, one calculation with pellets as iron-bearing charge material and two calculations with sinter as iron-bearing charge material.
3.1 Collection of industrial data The data used in the calculations was collected from articles and reports regarding SSAB’s blast furnaces in Oxelösund and Luleå. As the real blast furnace process is continuous only average data could be obtained. All necessary data could not be obtained from one article or report solely. Thus, the data used in the calculations are combinations from different reports and articles. E.g. mass of input materials from one report/article and the chemical composition of the input materials from another one. As SSAB’s blast furnaces are exclusively charged with pellets as main iron-bearing material, it was difficult to find corresponding operational data about the outdated sinter method. This resulted in the usage of mostly the same operational data in the first sinter calculation as in the pellet calculation. This matter will be discussed further in the calculation section. Input materials taken into consideration was: iron-bearing material (pellets or sinter ), additives (lime stone, BOF-slag and dust briquettes ), reducing agent (coke) and hot blast. The chemical compositions of iron-bearing materials are presented in Table I, while mass and chemical composition of remaining input materials are presented in Table II.
Table I . Chemical composition of iron-bearing materials [wt-%]. Pellet Sinter
Fe
CaO
SiO 2
MgO
Al 2O 3
66,8 60,4
0,35 7,95
1,7 3,2
1,5 1,96
0,32 0,59
3.2 Assumptions As described in the previous chapter the blast furnace is a highly complex process. Some assumptions were necessary to enable calculations. General assumptions:
No mass or heat loss (closed system)
Iron-bearing material:
The iron content in sinter and pellets are in the form of hematite.
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The small amount of iron in other input materials (BOF-slag, dust briquettes, lime stone…) are in the form of pure iron. 3% of total iron input is lost as dust (2%) and into slag (1%) in the form of FeO.
Slag formers:
Slag forming elements are in their reduced oxide states (e.g. CaO instead of CaCO3). Slag forming elements are just heated within the system, they do not take part in any chemical reaction, except for a small amount of SiO2 that is reduced to enable dissolution of Si into the hot metal.
Reducing agents:
Coke is the only reducing agent. Sulphur content in the coke is in the form of elemental sulphur. The excess of sulphur after dissolution into hot metal will end up in the slag as elemental sulphur.
Hot blast and off gas:
Hot blast consists of pure preheated oxygen and nitrogen The excess of carbon after dissolution into hot metal will result in an equal amount (1:1 ratio) of CO and CO2 in the output off gas.
3.3 Pellet 3.4 Sinter
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4 RESULTS
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5 DISCUSSION Sinter case Background
In the Nordic countries sintering has recently been eliminated altogether. The role of the sinter plant has been taken over by recycling waste product into briquettes. Nowadays, The Nordic blast furnace charging consist of almost 100% pellets plus briquettes and additives. However sintering still dominates in much of Asia and Europe region where raw materials are imported largely from Australia and Brazil. However, there has been a decline in run of mine ore grades and exploitation of lower grade deposits that is increasing the need for further beneficiation. The elimination of sintering resulted in a net gain in energy efficiency in the chain from mine to steel.
Pellets Case Background
Pelletizing is more energy efficient than sintering, however the sinter plant performs the important function of recycling materials within the steel plant and thereby improving the material efficiency. Because pelletizing is more energy efficient, a recent European Commission report recommends increasing the ratio of pellets in the ferrous burden to at least 50% on average in blast furnaces. From the data above, we consider that sinter still has important role as a steelmaking process in the world. Sintering and pelletizing are only a part of the steelmaking system. The objective of this work is to compare mass and energy balance differences between the use of sinter and pellets for blast furnace steelmaking systems. Further more, optimization of each process will be obtained. Mass and energy balance was used to calculate energy consumption of each steelmaking process for selected cases with different charge and source pellets and sinter are assumed made from hematite ores. Coke and Slag formers are considered. The unknown parameter are the input charges of Pellets and Sinter by steelmaking process.
Result discussion
In sinter based blast furnace, the sinter mass input are within expected results. With the same parameter we got higher mass input for the sinter case than pellets case. In sinter blast furnace we need 1573.5 Kgs charges and in pellet s based need 1411 Kgs pellets charges. As we expected, the slag amount of sinter based BF larger than pellets based BF. This is happened because sinter has lower iron content and higher slag formers. As the concequencies, the produced slag will be higher than pellet based BF. Further more, the energy required in each process will be different.
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Hot Blast 1223.2 kg (38.49%) Dust Briquettes 25.6 kg (0.81%)
Pellets 1411 kg (44.41%)
BOF Slag 38.5 kg (1.21%) Quartzite -
Hot Blast 1223.2 kg Dust (36.08%)
Input Pellets based BF
Limestone 22.35 kg (0.70%)
Input Sinter based BF Sinter 1573.5 kg (46.42%)
Briquettes 25.6 kg (0.76%) BOF Slag 38.5 kg (1.13%) Quartzite 72 kg (2.12%)
Coke 456.7 kg (14.38%)
Total Input mass = 3177.7 kg
Limestone - (0%)
Coke 456.7 kg (13.47%)
Total Input mass = 3389.5 kg Output Sinter based BF
Output Pellets based BF
Hot Metal 1000 kg (29.51%)
Hot Metal 1000 kg (31.47%)
Slag 165 kg (5.2%)
Off gas 1988.8 kg
Dust 24.14 kg (0.76%)
Slag 165 kg (11.08%)
Off gas 1988.8 kg Dust 24.14 kg (0.71%)
Total output mass= 3388.4 kg
Total output mass= 3177.9 kg
Sinter Second calculation coke addition
The total energy consumption of BF then calculated in both sinter based and pellets. After calculation we found that sinter based blast furnace were lacking of energy. HEAT BALANCE SINTER BASED BF
10000 9500 9000 8500 8000 7500 7000 6500 6000 J 5500 M 5000 4500 4000 3500 3000 2500 2000 1500 1000 500 0
119
14.5
7749.6
1470.1 Heat Input
7085.7
357.8 624.7 1310.9 Heat Output
Hot blast (1470.1 MJ) Exothermic mixing (14.5 MJ) Slag (624.7 MJ) Endhotherm. Reaction (7085.7 MJ)
Exothermic reaction (7749.6 MJ) Hot Metal (1310.9 MJ) Off gas & Dust heat content (357.8 MJ) Edhotherm. Reaction (119 MJ)
Figur 2. Heat balance Sinter Blast Furnace 7
This was assumed because Sinter based blast furnace has lower grade of iron content and larger amount of formed slag which need more energy to be heated. Since we are using same parameter with pellets due to lack of data this calculation result as expected. Sinter BF will need more energy than Pellets based BF. To fulfil the energy required in sinter based blast furnace, we assumed that more energy will be generated if amount of coke addition were slightly increased based from data that coke consumption in sinter based blast furnace larger than sinter based blast furnace. In table below shows industrial reported reductant consumption for European BFs, charged predominately with sinter plus pellet and lump ore, and the Nordic for both sinter and pellet operations. Table 1. Coke Consumption Comparation Pellets vs Sinter
The data above shows per ton Hot Metal produce, pellets has slightly lower coke consumption than sinter in steelmaking process. So, we performed second calculation with more coke addition. By increasing coke rate, we gained sufficient energy needed to operate the blast furnace using Sinter charge. HEAT BALANCE SINTER BASED BF WITH COKE ADDITION
10000 9500 9000 8500 8000 7500 7000 6500 6000 J 5500 M 5000 4500 4000 3500 3000 2500 2000 1500 1000 500 0
14.5
119
7951.2
7085.7
1588.4
327.6 626.6 1310.9
Heat Input
Heat Output
Hot blast (1588.4 MJ)
Exothermic reaction (7951.2 MJ)
Exothermic mixing (14.5 MJ)
Hot Metal (1310.9 MJ)
Slag (626.6 MJ)
Off gas & Dust heat content (327.7 MJ)
Endhotherm. Reaction (7085.7 MJ)
Edhotherm. Reaction (119 MJ)
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Comparation Pellets and Real Problem
To gain confident in our report we try to compare our calculation with the real data from SSAB Luleå and SSAB Oxelshund. In our calculation of pellets blast furnace we need 9235 MJ to produce one ton of Hot Metal. Tabel 2. Operation Datasheet BF No. 3 Lulea
Table above shows energy needed per year of operations. By assuming parameter in our case and converting Energy from GWh into MJ and production in 1 ton hot metal by calculation: Known, 1GWh = 3600 GJ Energy needed (output) = Energy content hot metal + Energy content slag + Energy lost in dust+ Energy content off gas = 2395,04 GWh + 78,37 GWh + 17,56 GWh + 72 GWh = 2562,97 GWh / 873000 THM =9,226x109 MJ/873000 THM =10568,94 MJ/THM
Table above shows energy balance per year of BF operation. At the real operation, they are using pellets as input materials. We compared our calculation with the real data operation. In this case we compared pellets energy balance calculation with real energy balance in BF No.3 Lulea.
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Heat calculation Pellets based BF Vs Heat Real data HEAT INPUT COMPONENT CALCULATION VS REAL DATA
100% 80%
t n e t 60% n o C t 40% a e H
20% 0% Heat Input Calculation
Hot Blast COG (coke oven gas) Nut Coke
Heat Input real data Exothermic reaction BFG (blast furnace gas) Electric
Exothermic mixing Coke PCI
HEAT OUTPUT COMPONENT CALCULATION VS REAL DATA
100% t n e t n o C t a e H
80% 60% 40% 20% 0% Heat Output Calculation
Hot metal COG (coke oven gas) Nut Coke
Heat Output real data Exothermic reaction BFG (blast furnace gas) Electric
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Exothermic mixing Coke PCI
COMPARATION HEAT INPUT CALCULATION VS HEAT INPUT REAL OPERATION
10000 9500 9000 8500 8000 7500 7000 6500 6000 J 5500 M 5000 4500 4000 3500 3000 2500 2000 1500 1000 500 0
14.5
7749.6
1470.1 Heat Input Calculation
357.8 273.5 1310.9 Heat Input real operation
Hot blast (1470.1 MJ)
Exothermic reaction (7749.6 MJ)
Exothermic mixing (14.5 MJ)
COG (coke oven gas)
BFG (recycled blast furnace gas)
coke
nut coke
Column1
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Compared with the real data, our pellets based BF slightly different with the real data. We assumed this caused by simplified assumption compared to real complexity of the real blast furnace operation.
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6 RECOMMENDATIONS
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7 REFERENCES Det finns inga källor i aktuellt dokument.
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APPENDIX A: CALCULATIONS
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