TECHNOLOGIES FOR CONVERTING BIOMASS TO USEFUL ENERGY — COMBUSTION, GASIFICATION, PYROLYSIS, TORREFACTION AND FERMENTATION

A good environment and at the same time good economic living conditions—that is the goal for us as well as for our children and their children. To achieve that we need sustainable energy resources that do not harm the environment through pollution of water, air and food. At the same time we need food and thus should not compete between food and use of resources for other purposes.

Biomass resources is one of the key resources we have that can both give us the energy we need, the food we demand and also be a feed stock for many kind of products we use daily like paper, packages, furniture, plastic, chemicals etc. Estimates made from statistics on use of land area for agriculture, forestry or just more extensive use indicates a biomass production of approximately 270,000TWh/year, which should be compared to the total global energy use of approximately 140-150,000 TWh/year. As we also have huge amounts of solar and wind power potential, and already have explored a lot of our hydro power resources, there should principally be no problem to build a sustainable society without fossil fuels, although the distribution of resources is not always matching the demands locally or even regionally.

The major concern thus would be to use the biomass resources we have in best possible way. Conversion methods thus are important to refine. We could just burn the wood over an open fire, and then have a net efficiency of less than 10% between higher heating value of the wood compared to the energy taken up by the water you want to boil. Or we could use the biomass as fuel in a combined heat and power plant with exhaust gas condensation, where the corresponding efficiency as heat plus electricity would be 117%, which is common in Scandinavia.

In China the majority of the energy used for electricity production comes from coal. Installed capacity for electricity production from biomass is forecasted to increase from 5500 MWe in 2010 to 13,000MWe in 2015. 8000MW should come from agricultural waste, 2000MW from biogas and 3000 MW from municipal solid waste. The total available resources of biomass still are much higher. They amount about 690 million tonnes of straw, 840 million tonnes manure from live-stock, 3 million tonnes food waste for biodiesel, and 950 million tonnes solid industry waste. If all this could be used for energy purpose it could replace about 1000 million tonnes coal, or some 7000TWh/y. The main question then is how to do this in a sustainable way. Many different technologies would be needed. Easy to decompose biomass could be fermented to give biogas, but at the same time also give good fertilizer back to the farm land. More difficult materials can be combusted or gasified thermally. Ash might be brought back to at least forestry. The same wood could first be used as building material, furniture or paper boxes, and then be used as an energy resource in a power plant when the function as building material is over. Food waste can be used where manure or house hold waste is fermented in a biogas plant, etc. There are many technologies available, and many of them are covered in this book on biomass conversion with examples from all over the world.

Concerning the biomass resources these differ between different climate zones and soil types. Still, there is a major potential to enhance the production everywhere by introducing good conditions like enough water, nutrients and new more resistant species of the crops with respect to insects, fungus etc. The potential can be seen by comparing the production as tonne product per hectare 1970 compared to today. In middle income economies and high income economies, the production has approximately doubled during this time period, while it has increased by some 50% in low income economies, according to statistics from the United Nations for 213 countries. Still, there is a major gap between both the middle income economies and the high income economies, and even larger compared to low

income economies. A review of resources and crops used in different climatic zones, as well as new possibilities to use crops efficiently in e. g. biorefineries are covered in this book.

Yang Yong-Ping,

Professor, Vice President of North China Electric Power University Director of National Engineering Laboratory for Biomass Power Generation Equipment

Member of National Energy Expert Advisory Committee

150 years ago the modern world was developing as a consequence of cheap and easily accessed energy from fossil fuels. Together with this resource engineers developed new technologies for converting the fuels into useful products like mechanical power, electricity and heat. Today we are facing a situation where cheap fossil fuel is becoming more scarce, and the oil price has gone from around e. g. US$ 20/barrel in the mid-19th century to around US$ 100-110/barrel in 2012. Coal is principally still relatively cheap, but environmental concerns with respect to global warming as well as other negative impacts from spreading dust and sulfur are alarming. In August 2012 we heared that the Arctic ice cap is smaller than it has been for several thousand years. It is as small as the previous smallest size in 2007 already in August, while the minimum takes place in September. Heavy storms are causing problems in the USA and East Asia. The previous stable weather patterns are becoming unstable and unpredictive, probably as a main consequence of the global warming caused by emission of primarily CO2 from fossil fuel combustion. To avoid this effect we need to use renewable energy instead, and this as fast as possible. Here we have hydro power, wind power and solar power, but first of all Bioenergy, which can be both stored over the seasons as well as converted into all energy forms we need for heat and power, transportation and as a base chemical for manufacturing of anything from plastics and soap to buildings. As biomass is also food needed for a growing population, we need to look at biomass from a holistic perspective, where e. g. the cereal grain should be used primarily for food while the straw and other agricultural waste should be used for the other applications. To do this a number of different conversion techniques are needed.

The purpose of this book is to give a concise overview of all major conversion techniques for biomass. We start with thermal conversion and follow with torrefaction, biogas production using biological methods and finally mechanical processes like briquetting and pelletizing.

Combustion, biogas production using microbiological methods and polarization are already used extensively, while gasification, pyrolysis and torrefaction are still under development. Some countries are utilizing biomass a lot while others very little. In Sweden 1/3 of all primary energy used is as biomass, or 132TWh/y out of a total 400TWh/y 2010 (when we exclude the waste heat from nuclear power plants). That is one of the highest percentages in developed countries, while many still developing countries may have similar or even higher figures, at least if we include also biomass collected and used locally.

From a future perspective biomass could replace most of our energy needs if it was utilized in a most efficient way. Still, the use must be in a sustainable way. Here for instance it is important to see that organic material and nutrients like phosphorus and nitrogen are recirculated to farmland, and thus biogas production is good from a system perspective. The organic residues then will be a fertilizer to keep the production high in the long term, but we also have to see that we do not bring negative substances from anaerobic digestion into the food, and precautions have to be made. On the other hand some materials like wood are not very suitable for biogas production and here gasification and combustion are more suitable. We can also produce ethanol from pre-treated cellulosic material like straw, and then it is useful to combine it with biogas production of the residual brine. Also pyrolysis to replace oil and torrefaction to replace coal are new alternatives. All these aspects are highlighted in this book.

If we just look at EU27 I have tried to estimate the total annual biomass production from the data on crops grown and areas used for agriculture and forestry. The rough figures come to around 8500 TWh/y biomass produced. A very small portion of this is really utilized for our different needs. If we could use e. g. straw efficiently for biogas production or for production of ethanol using fermentation

we could produce most of the fuels needed for our vehicles. By introducing a series of hybrid electric vehicles the total energy for transportation could be decreased by roughly 70-80%, where half would be as electricity, and the rest as methane, ethanol or bio-diesel. The electricity then could be produced in CHP plants using biomass as the fuel, aside from wind power, hydro power and solar power.

To make this economically attractive still we need to have good conversion techniques, and these will be the focus of this book. If we can combine these conversion techniques with robust agriculture and forestry, and reuse materials in a most efficient way, we can see a bright future without fossil fuels. The advantage also would be a solution to the upcoming climate problems with global warming. This is the motivation for this book.

The book is using SI units as the standard. Still, SI units can have different forms as well. It is common to use MJ (million Joules) for energy in SI units, but as kWh, (kilo watt hours), MWh (mega watt hours), TWh (terra watt hours) and toe (tonne oil equivalents) are used by e. g. UN and the World Bank for energy these units have been used as well. One toe is approximately 10 MWh. For electric power usually MW has been used. China is using t. c.e (tonne coal equivalent) for energy as well, and in a few places this unit has been used relating to Chinese energy data. For surface area ha (10,000 m2) and km2 (100 ha) have been used concerning calculations related to production of different crops, yield, etc. Both m3 (1000 liters) and liters have been used for volume. Concerning pressure this is MPa in SI, but as bar is very common also this is used. Parts per million, or ppm is also used commonly, and thus also is used here and there in the book, although kg/kg is the SI sort. Where it is used in the book is just because it is difficult to change in some already produced diagrams and similar. Both kg and tonnes have been used as well, where we refer to metric tonne (tonne = 1000 kg). Sometimes also other units like Pg for weight (1015 g) and TJ (1012 J) for energy are used, and probably will be used even more in the future.

The authors are all well established in different fields of biomass conversion and also cover most parts of the world. This book is written in parallel with volume 3 in this book series on sustainable energy developments, where biomass resources are presented.

Erik Dahlquist January 2013

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