[Gasification] Gasification Digest, steel making

[Sanjeev Sharma]

Dear Rex ,

Please give me your company details,

Regards

Sanjeev Sharma

-----Original Message----- 
From: Rex Zietsman
Sent: Saturday, August 16, 2014 2:59 PM
To: 'Geoff Thomas' ; gasification at lists.bioenergylists.org
Subject: Re: [Gasification] Gasification Digest, steel making

Hi Geoff,

South Africa exports some 65m tons of iron ore per year. All of this ore is
>6.3mm as fines block gas flow in blast furnaces. We have millions of tons
of fines on dumps as a result. We have developed a biogas from biomass
process that can provide methane into the iron ore industry. Initially this
gas will be compressed and used to replace diesel in the mine haul trucks.
The second use for the gas is to supply a pellet plant that feeds an HBI
(hot briquetted iron) plant. Milling and upgrading the fines (upgrading
removes clay and other impurities) raises the iron content in the milled ore
to about 67% Fe. These fines are made into 10 to 15mm diameter pellets.
Carbon is added to the mix when making the pellet. The pellet is then fed to
the HBI plant. Methane (CH4) is steam reformed to syngas - CO and H2 and fed
to the HBI plant. The H2 and CO react with the iron oxide stripping away the
oxygen. Typically pellets leaving the HBI have about 93% metallisation.
While still hot, the reduced pellets are fed to compactors that produce a
high density briquette. The briquettes are cooled and exported.

When the briquettes are fed to a blast furnace, they have three major
benefits:
  - they require less carbon to strip out the balance of oxygen
  - they bring their own carbon into the blast furnace
  - the high strength of the briquettes reduces mechanical breakdown in the
blast furnace providing low pressure drop gas flow paths

All three benefits result in high blast furnace productivity that uses less
coke. Coke is devolatalised coal as volatiles cause operational difficulties
in blast furnaces. Coking coal is rare compared to thermal coal and its
price is significantly higher. Hence a saving in coke and an increase in
production results in a reduction in the cost of hot metal production.

This addresses part of the story. The second part is that there is always a
solid fraction coming out of anaerobic digestion. These solids will be
filtered, dried and pyrolysed with pyrolysis gas used as a thermal energy
source while the char is sent to pelletization for mixing in with the iron
ore.

The main problem with replacing coke in blast furnaces is the amount of
char(coal) required. One industry we have smelts silicon. As silicon reports
to the "slag" in the furnaces, the purity is affected by all elements that
report to the slag fraction. This includes the ash fractions in coal. As a
result, coal is not suitable as a reductant. Charcoal has the double benefit
of high fixed carbon and low ash making it the only realistic carbon source
that can be used. These guys have charcoal retorts spread across the entire
country. The cost of charcoal delivered to the furnace consequently has a
high transport element. As charcoal has low density, this simply exacerbates
the transport problem. Needless to say, charcoal for the metallurgical
industry is a major challenge. I simply cannot see how the world can grow
enough biomass to be able to supply the requirements adequately as long as
there is "cheap" coal available.

There - my 2c worth.

Rex Zietsman


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