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38 Cards in this Set
- Front
- Back
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What is direct reduction |
1. Direct reduction (reduction by CO accompanied by boudouard reaction) stiochiometrically looks like carbon is directly reducing the FeO 2. FeO +CO=Fe +CO2 +3990 CO2 +C =2CO-41210 |
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CO utilization |
extent of CO utilization: %n CO= 100 %CO2/ (%CO +%CO2) maximum only for 30% for wustite/iron at 900 C |
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What are the differences between direct and indirect reduction |
1. direct reduction needs less carbon than indirect but needs more heat 2. Indirect FeO+CO =Fe+CO2 |
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Describe Fe-O-H System |
1. H2/H2O is analogous to CO/CO2 2. Reducing power of CO greater at lower temperature 3. H2 does not have a Boudouard-type reaction |
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Describe cost of coke, coke rate, how it impact environment and how to calculate and other variables |
Coke is one of the major costs in BF ironmaking. Operators want to lower coke rate. major contributor to GWP. difficult to calculate because of variations in reducibility of wustite. other variables: flame temperature, othher heat requirements |
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What does coke provides support for and what are the chemical requirements? |
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What do all reaction require? |
evaporation of moisture, calcination,heating and melting, sensible heat for gases, heat losses |
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What are the highest heat demands in the lower furnace for? |
-direct reduction of FeO -calcination of limestone -melting of slag and iron -reduction of metalloids |
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Why is it convenient to divide the furnace into two zones at what temperature? |
Because of chemical reserve zone, at 900 C |
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The amount of carbon must satisfy........ The gas leaving this zone will..... Any excess gas will..... |
1. the thermal requirements in the lower furnace 2. have the thermal and chemical capacity to satisfy the upper furnace 3. raise the top gas temperature |
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What does RAFT stand for? for normal air blast how much percent oxygen? |
Raceway Adiabatic Flame Temperature. 21% |
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What temperature must RAFT be above? Excess heat is used..... What is Q > 900 hf and h900 stand for? |
-900 C. -supply the thermal requirement above 900 C -heat content of gas from burning carbon at Tf and 900 C |
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heat balance equation for Carbon burned at tuyeres Ct |
ct = Q >900/ hf-h900 |
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What happens when Ct drops? |
less gas is generated and transferred to upper furnace |
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What is top gas temperature fixed at for upper furnace and what is it fixed by? |
100-150 C. Q <900 and Ct |
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What happens if heat demand increases? (3) |
-requires more Ct -if indirect/direct reduction remains the same, then more CO exits furnace (less efficient) -can compensate by increasing indirect reduction, finer ore |
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What are measures of fuel efficiency? |
CO/CO2 ratio or CO utilization |
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Coke rate can be reduced by... |
-increasing indirect reduction -decrease thermal load -increase heat supply -replace coke with other fuels |
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What are some techniques of reducing coke rate? |
-increased blast temperature -burden preparation -blast additives -high top pressure -pre-reduced feed |
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blast temp- what is air preheated to |
1000-1250 |
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Blast temperature is |
1. mainly increase in sensible heat. 2. 100 C increase gives sensible heat saving equivalent to 6% coke rate -less CO generated, so less indirect reduction occurs -more direct reduction required, so saving only 4% -more CO utilization -limits due to "hanging" 3. actual heat savings somewhat less than theoretical |
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What is Burden? |
Burden is the name for the iron-bearing materials charged to the furnace. (lump ore, pellets, sinter) |
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What is burden prepared for? |
-optimum size, large enough for gas permeability, but small enough for reducing gas diffusion to interior of particle. -ease of reducibility, by adding fluxing materials to make the oxides reduce at lower temperatures -low thermal load, removing unwanted components, like silica and alumina. |
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how is burden prepared at mine site? |
Crushing, screening, washing, concentrating, Pelletizing, (pre-fluxing) Induration or firing |
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burden preparation: sintering is also used for... |
waste oxides |
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What is shaft work? |
shaft work is calcination of carbonates, evaporation of water and hydrated water. Higher for low burden yields. Modern furnaces minimize shaft work. |
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reducibility is measure in... |
single-pellet experiments and has a huge effect |
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What is fluxed burden and what effect does it have? |
CaO and MgO added to pellets to make slag. better reducibility and enhanced indirect reduction. slag melts at higher temperature and softens over a narrow range. no heat requirement and CO2 generation from calcination. |
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how much slag is saved when used fluxed burden? |
normal slag is 45% CaO, so reducing calcination saves 20-25kg/100kg slag |
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what is super burden and what is it's purpose? |
charge scrap, DRI or HBI to furnace to improve productivity. Also reduces coke rate. |
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Replacement ratio |
=[kg coke saved/THM]/[kg of injectant/THM] |
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Blast additives include.... |
gases: oxygen, steam, natural gas, coke-oven gas liquid: oil, tar solids: pulverized coal, waste plastics |
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____ cannot replace role of coke for support and permeability |
blast additives |
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steam is reduced to _____ that reduces ______ steam moderates |
1. H2 2. iron faster 3. RAFT |
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the carbon and hydrogen in oil.... does oil increase or decrease reduction? soot is a problem: T or F Over long term oil prices...... |
reduce coke consumption. increase. True. greater than natural gas and coal |
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Replacement ratio of oil, natural gas and coal |
oil:1.3-1.4 natural gas: theoretical 1.6- 1.4 achieved coal:0.8-0.9 |
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coal injection is used with... |
O2 enrichment -raceway coal combustion -flame temperature |
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High top pressure reduces coke rate by... |
-increases gas reaction rate, decreasing direct reduction -decreases linear velocity, increasing gas residence time -improve gas permeability and makes gas distribution more uniform |
