Mer effektiv bruk av kull i metallindustrien

Metall-legeringer med jern blir produsert ved at karbon – i form av trekull – reagerer med jernmalm når det blir utsatt for høy temperatur i smelteovner. Trekull er en fornybar ressurs, men produksjonen betyr likevel utslipp av drivhusgasser.

I sin doktorgradsavhandling «Renewable reducing agents for the use in ferroalloy industries» viser Gerrit Ralf Surup hvordan volumet av kull-pellets kan øke med 20 prosent ved produksjon med høy temperatur og bruk av bio-olje som bindemiddel i pelletsen. Mer effektiv kullproduksjon innebærer også redusert utslipp av drivhusgasser fra smelteverksindustrien.

Gerrit Ralf Surup disputerer for ph.d.-graden torsdag 29. august 2019. Han har fulgt doktorgradsprogrammet ved Fakultet for teknologi og realfag med spesialisering i fornybar energi. 

Slik beskriver kandidaten selv essensen i avhandlingen:

Renewable reducing agents for the use in ferroalloy industries

Biocarbon or charcoal as a renewable reducing agent has attracted a large interest in the metallurgical industry as a way to reduce the anthropogenic (“man-made”) greenhouse gas emissions in the upcoming decades.

Relies on fossil based reducing agents

To retain the high throughput and high quality of metallurgical products, specific properties are demanded for the reducing agents.

Although charcoal is produced within different processes in for example Brazil, Nigeria or Ethiopia, none of these products provide completely the required properties or is produced sustainable.

In addition, most companies continue to rely on fossil based reducing agents due to the limited knowledge of biocarbon properties and the knowledge gaps in required process conditions to produce charcoal with acceptable properties at low costs.

Biooil increases the charcoal yield

In this dissertation, different process routes of two wood species were investigated to produce tailor-made charcoal.

The research comprised of operating parameters such as a primary heat treatment (500 to 1300 °C), secondary heat treatment (700 to 2800 °C) and biooil conditioning.

The heat treatment to 900 °C reduced mainly the volatile matter of the charcoal, whereas the biooil conditioning increased the charcoal yield by about 20 %.

In addition, supercritical CO₂ extraction enables the extraction of more than half of the value-added compounds without any significant influence on the charcoal yields.

Proposes process route

The volatile matter content of charcoal at heat treatment temperature of 1600 °C is like that of metallurgical coke. https://en.wikipedia.org/wiki/Metallurgical_coal

The reactivity of charcoal heat treated at 2400 °C is similar to those of metallurgical coke, emphasizing the importance of high heat treatment temperatures on the charcoal structure.

It was shown that high heat treatment temperatures resulted in the ordering of the charcoal carbonaceous matrix.

The pelleting of charcoal with biooil as binder showed that biooil can be used as a binding agent to produce thermally stable charcoal-based pellets. We propose a process route to produce charcoal pellets with improved properties.