Karakterisering av agglomererte biokokser og vurdering av egnetheten som reduksjonsmiddel i produksjon av manganlegeringer

lloy production is performed by recovery of the metal from ores, where ores are the designation of metals in an oxidized state, bound to oxygen. To remove the oxygen the ores are heated with a carbon source who acts as an oxygen remover and releases the metal we are interested in from the ore. The byproduct of this process is then CO gas, which is combusted into CO2 and released into the atmosphere increasing CO2 emissions. Dependent on what sort of alloy is being produced there are several possible sources of carbon, but for manganese production only metallurgical coke produced from fossil coal has so far proven to work adequately and not give additional problems. The ambition of the alloy producing process industry is to be carbon neutral within 2050. This means the industry will not contribute to an increase in CO2 emissions and only use environmental friendly sources of carbon. Environmental friendly sources, such as wood or other plant matter grown during the last 5-50 years, and not several millions years old carbon sources as is the case with fossil coal. Using wood will be keep the total carbon amount in the atmosphere the same in a 5-50 years perspective as the amount of CO2 emitted when burning the wood will be the same amount of CO2 the three consumed from the atmosphere during growth. In order to use wood or plant matter as a carbon source in manganese production it need to meet a few criteria. This project goal is to map these criteria on fossil-based cokes used today and then see how the production process of bio-carbon can be tuned to meet the criteria for use in manganese alloy production. For the characterization of the different carbon materials suitability as a reducing agent, a method where the ore mixture is placed on a flat surface of the carbon material of interest is used. This is then heated to 1200 degrees Celsius, where the ore melts and forms a liquid drop of the top of the carbon material. This is called the sessile drop technique. The ore when melted is usually referred to as a slag. After further temperature rise up to 1600 degrees, the carbon material begins to react with the slag drop and produces the desired metal and CO gas. This CO gas is later combusted into CO2. The furnace these experiments are performed on is equipped with windows so you can study the behavior of the drop during reaction at the temperature of interest. The wetting angle between the slag drop and the carbon material is of interest. Poor wetting means that the drop crawls up on itself and tries to minimize contact with the substrate. With good wetting, the slag drop rests more like a semicircle on the surface. Good wetting between the slag and carbon material will thus mean a larger area where the reaction between the slag and the carbon material can occur and is a desired property of the carbon material. In addition to wetting angle, you can continuously measure changes in the drop volume during reaction. Volume changes in the drop is a result of the reaction since the produced CO gas escapes the drop and the remaining metal produced has a lower density compared to slag. This volume change can then be used to estimate how much of the slag has been reduced as a function of time and thus the reduction rate of each carbon material. In the initial trials so far in the project two different fossil cokes, anthracite, which is also a fossil carbon source and charcoal produced from hardwood has been tested. The result of these trials is that the reduction rate of the two coke is approximately the same as for anthracite, and the speed of these is twice as high as for charcoal. The most obvious difference between these materials is the density, where charcoal stands out as the lowest weight per volume and is a very porous material relative to the fossil materials. This means that the effective contact surface between the slag and charcoal is lower than the case of anthracite and coke. The next step in the project is to crush the materials and make briquettes of them to reduce porosity and examine the different carbon materials against each other when they have comparable contact surfaces to the slag.

Produksjon av ferromanganlegeringer skjer ved karbotermisk reduksjon i elektriske smelteovner, hvor elektrodene står i en koksseng som både fungerer som reduksjonsmiddel og motstandselementet som gir den nødvendige varmen. Karbonmaterialet er typisk metallurgisk koks produsert fra fossile karbonkilder. Det er en visjon i prosessindustrien at industrien skal være karbonnøytral innen 2050, skal det skje må det introduseres biokarbon produsert fra en klimanøytral karbonkilde. Prosjektet vil gå ut på karakterisering av forskjellige biokarbonmaterialer med tanke på bruk som reduksjonsmiddel i ferromanganindustrien. Hovedmål: Redusere GMNs CO2 avtrykk i manganlegeringsproduksjon ved bruk av klimanøytralt biokarbon som reduksjonsmiddel. Kvantifisere og optimalisere kritiske produktegenskaper for agglomererte biokarbonmaterialer for bruk i produksjon av manganlegeringer. Delmål 1 og 2: Litteraturstudie på karakterisering av koks med hovedfokus på slaggreaktivitet og konkludere med beste målemetode på slaggreaktivitet. Søker et svar på hvilke parametere som har betydning for slaggreaktiviteten. Delmål 3. Karakterisere biokoksmaterialer for å konkludere med hvilken fremstillingsprosess som gir best egnet koks ut fra et slaggreaktivitetssynspunkt. Delmål 4. Teste biokarbon som reduksjonsmiddel i laboratorieskala og som reduksjonsmiddel i laboratorieskala elektrisk smelteovn. Sentrale utfordringer: For å kunne bestemme kritiske egenskaper angående slaggreaktivitet må man finne en metode som måler forskjellig på det som erfaringsmessig er «gode og dårlige» kokser for manganproduksjon. Finner man ikke forskjell må man foreløpig konkludere med at det ikke er viktig og se på CO2 reaktivitet og elektriske egenskaper som guide angående design av et agglomerert biokarbon. Bedriften søker å øke sin kunnskap om koks for å forbedre produksjon ved å unngå å kjøpe koks med dårlige egenskaper. Håpet er at prosjektarbeidet skal bidra til å øke den kunnskapen.