Biofuel


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This page currently need further attention. It should also include some of the pros and cons of biofuels for household use in developing countries, present the issues from a more neutral point of view. If you have the necessary expertise we would greatly appreciate improvements on this page.

Introduction

Liquid biofuels can be used to produce heat, electricity, and fuel for transportation. Currently most important biofuels are pure plant oil (PPO), bioethanol, and biodiesel, that are capable to conventional gears. Liquid biofuels are disposed in 1. and 2. generation fuels. PPO, Bioethanol and Biodiesel belong to 1. generation that can be produced by conventional technology. Synthetic biofuels (e.g. BtL Biomass to liquid) and ethanol from cellulose belong to 2. generation. In this case the total biomass (plant, residues etc) is used and transformed to fuel by a highly developed technology.

In the household energy context, liquid biofuels can be used to power farm equipment, to run small generators for individual households or minigrids, and as cooking fuels.

How are biofuels produced?

To gain PPO any type of oil seed is pressed. Another option is to recycle wasted cooking oil. Wasted oil has to be filtered in order not to plug filter and fuel lines. The so called "Elsbett engine" was developed in the 70ies and runs purely on PPO. Cars used today need a modification to run on PPO.

Biodiesel

Biodiesel is produced by transesterfying PPO (with additional methanol). Apart of biodiesel gylcerine is produced as by product. Not all engines are able to run on 100% biodiesel but a nearly 10% blend into diesel is possible.

Bioethanol

Petrol is substituted by ethanol. Bioethanol is produced by a fermentation of sugar or starch (cereals, maize). During the fermentation process a lot of mash is produced as by product that could be used as cogeneration within the plant. In Brazil ethanol is sold even in 100%. Flex Fuel Vehicles (FFV) are able to run on any mixture of ethanol/petrol. Today 60% of all new released cars in Brazil are FFV.

Newly cellulose is used to produce bioethanol. Cellulose is split by a hydrolysis of enzyms. After the split it is fermented and destilled like sugar (e.g. synfuel of IOGEN in Canada). In case of the production of «Biomass to Liquid» (BtL) total biomass is gasfied (thermochemical).

Bio Oil

BioOil is another form of liquid fuel from biomass using a pyrolysis process. There are various technologies, including a method called "fast pyrolysis". In general pyrolysis comes about when biomass is burned in the absence of air. This process can convert forest and agricultural residue (including bark) into liquid BioOil and char. It is currently at an experimental stage and not fully commercial.

Fast pyrolysis refers to the rapid heating of biomass (including forest residue such as bark, sawdust and shavings; and agricultural waste such as wheat straw and bagasse) in the absence of oxygen.

There are many approaches, including bubbling fluidized bed reactors and rotating kilns. Three products are produced: biooil (60-75% by weight), char (15-25% wt.) and non-condensable gases (10-20% wt.). Yields vary depending on the feedstock composition. Bio oil and char are commercial products and non-condensable gases are recycled and supply a major part of the energy required by the process.

What Biofuels Are In Development?


Feedstocks for biofuels with the greatest potential to displace imported petroleum are in the form of cellulosic biomass, including residues from agriculture and forest operations, urban woody waste, and energy crops such as hybrid poplar, hybrid willow and switchgrass,jatropa . Biofuels may be derived from woody biomass.

Ethanol can be produced from woody biomass, as it can from corn. However, there are several important differences between cellulosic ethanol and corn-starch ethanol. The sugars derived from woody biomass are a mixture of 5- and 6-carbon sugars, and as a result, fermentation organisms and processing conditions are more challenging than for corn ethanol.

Research continues to improve the enzymes and microorganisms needed to boost sugar and ethanol yields from woody biomass and to reduce costs of production. A fraction of the woody biomass known as lignin, which is not converted to sugars, is dried and burned to produce heat and power for the conversion process. This eliminates the need for fossil energy resources for the conversion steps to ethanol. As a result, the life-cycle reduction of fossil energy and greenhouse gas from cellulosic ethanol compared to petroleum gasoline on an equivalent energy basis is much improved compared to fossil gasoline and corn ethanol.

Thus far biofuels other than ethanol have not been discussed . Woody biomass can also be converted to a true hydrocarbon fuel (no oxygen in the fuel) that is nearly identical at a molecular level to petroleum liquid fuels, using thermochemical conversion steps: gasification and pyrolysis. Gasification converts the solid biomass into a synthesis gas comprised mostly of CO and H2. Pyrolysis converts solid biomass into an oily substance. In either case, these components are catalytically converted to hydrocarbon fuels called synthesis gasoline and synthesis diesel (syngas and syndiesel).

By adjusting reaction conditions, other fuels like jet fuel can also be produced. The obvious advantage of producing these synfuels is that their compatibility with existing vehicular transportation infrastructure is almost perfect, requiring very little if any modification. Studies have shown that the life-cycle, fossil energy, and greenhouse gas reduction of woody biomass-based synfuels compared to petroleum gasoline on an equivalent energy basis also is much improved compared to fossil gasoline and corn ethanol.

Biofuels are not a total solution to the issues of energy security or greenhouse gas reduction, but significant benefits are expected in the near future, at the same time that technology continues to advance in other sustainable energy technologies like solar power, hydrogen fuels, carbon capture and sequestration, etc.

Resources


Pyrolysis

Biofuels and potential negative impacts

  • UNEP warns of dangers
  • This important issue was covered in some depth by several speakers at the recent UK Soil Association conference - you can get transcripts and audio recordings here: http://www.soilassociation.org/conference. In particular, have a look at what was said by Jonathon Porritt, Richard Heinberg and Peter Melchett







Last edited by Miriam Hansen , based on work by Karabi Dutta .
Page last modified on Wednesday 13 of October, 2010 15:49:43 GMT. @HEDON: HRDB

Technologies » Biofuels
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