Pyrolysis of Biomass

 

Pyrolysis of Biomass

Pyrolysis

Pyrolysis is the heating of something without air and decomposing it in the process. It is sometimes called destructive distillation. It is a simple way of pulling apart wood to produce useful products.

A wood fire

When you start a fire, you need to heat the wood enough to drive smoke off, then if this is heated enough, it will catch fire producing flames. A cold pot sitting in the flames will pick up a layer of brown tar. Over time the heat will convert this to carbon giving us a black pot to clean. A pot above the flames will stay clean.

The charcoal left when the smoke has been driven off, will burn with a red glow without flame. The coals as they are called. With bellows supplying air, they become white hot and can soften iron in a forge.

Pyrolysis

If the wood is heated in a sealed container without air, then it gives off the smoke and charcoal remains.

The charcoal is biochar

The smoke, or wood gas, can be separated into gas and liquid.

The gas can be burnt to provide heat for the process. Some can be converted to oil using microorganisms or catalyst.

The liquid can be converted to various biofuels.

 

Coskata Makes ethanol from gas produced by pyrolysis using microorganisms.

Low temperature pyrolysis

In low temperature pyrolysis at 450-500 degrees C, the process produces

  • 20% gas which is used to do the heating,
  • 60% oil, and
  • 20% bio-char.

Airlines are looking at this as  a future fuel source.  Virgin is investing nearly all of its profits in finding the low-carbon fuels of the future.

Pyrolysis oil.

Renewable oil corporation - low termperature pyrolysis

Dynamotive process bio-oil for use in engines

Patent details for liquefaction by thermolysis (Pyrolysis)

Kior process of Fluid Catalytic Cracking similar to oil refining

Pyrolysis

High temperature pyrolysis of biomass

800-1,000 oC. rapid pyrolysis of agricultural residues such as olive waste, straw and sugar cane bagasse at high temperature (800°C-1000°C) in a free fall reactor

The higher treatment temperature has led to lower yields of tar and more tar cracking leading to higher yields of gaseous products. The char yield decreases when temperature is increased from 800°C to 1000°C.

The char obtained by rapid pyrolysis contains a fraction that can be further volatilized by slow pyrolysis.

Higher treatment temperatures favour cracking of the hydrocarbons in the gaseous products and thus increase the yield of hydrogen. Higher temperature has also decreased the content of CO2 in the gases and increased the CO content for the agricultural residues.

 

 

High or low temp?

So low temperature if for production of products, and high temperature for production of gas as fuel.

 

Biochar in the soil

Biochar is special as it can be used to increase the fertility of soil. For details of this and as a way of fixing carbon in the soil see the page on Biochar

 

Gasification to liquid fuel

Energy yield presently of bioenergy crops converted via silage to methane is about 2 GWh/km²

Ineos produce ethanol from waste via gasification

Rentech ClearFuels biomas gasification process

 

Bio oil

Bio-oil contains organic acids which are corrosive to steel containers, has a high water vapor content which is detrimental to ignition, and, unless carefully cleaned, contains some biochar particles which can block injectors. 

The greatest potential for bio-oil seems to be its use in a bio-refinery, where compounds that are valuable chemicals, pesticides, pharmaceuticals or food additives are first extracted, and the remainder is either upgraded to fuel or reformed to syngas. Wikipedia

 

Pyrolysis of Mallee

(Mallee is an area with various Eucalyptus trees)

One project was run by Curtin university looking into pyrolysis of mallee grown in tthe WA wheat belt. They estimate the liquid fuel could be produced for AU$ 0.49/litre.

Most other biomass is suitable for this process.

If the biochar is buried it would result in CO2 being removed from the atmosphere.

Final report published 20 March 2013 

 A novel two-step pyrolysis-biorefinery technology.

1 Biomass grinding

2 Pyrolysis

3 Biorefinery technology:  (esterification and hydrotreating). Acid-catalysed reactions between pyrolysis green biocrude and methanol, which transform methanol into a much better liquid fuel.  A novel process (bio-crude hydrotreatment reactor configuration) was also developed to produce drop-in biofuels using cheap catalysts. This reduced coke formation on catalyst surface and increased energy efficiency.

4 Carbon sequestratioin: up to 0.6 kg of carbon dioxide can be sequestrated for every litre of biofuel produced. Or 22.4 kg of sequestrated carbon dioxide (or its equivalent) for every GJ of biofuel produced.