There are many types of types of vegetation in the world, and many ways they can be used for energy production (Faaij, 2006; Karp and Shield, 2008). In general there are two approaches: growing plants specifically for energy use (energy crops), and using the residues from plants to be used for other things. The best approaches vary from one region to another according to climate, soil properties, geography, population, etc (Faaij, 2006).
11
The main sources for biomass are generally divided into these categories:
Energy crops can be grown on farms in potentially very large quantities, however in many cases replacing and competing with food crops, for example corn, sugar cane and sweet sorghum (Faaij, 2006, Demirbas, 2009).
Multifunctional crops could be used both for food and energy production simultaneously for example corn grain for food and corn stover for energy generation (Čuček et al., 2010).
Oil plants. Plants such as soybeans (Mandal et al., 2002), oil palm (Prasertsan , 1996; Lam et al., 2010d) and Jatropha (Achten et al, 2008) produce oil, which can be used to produce fuels. A rather different type of oil crop with great promise for the future is microalgae (Chinnasamy et al., 2010).
Forestry waste and woods. Forestry waste Schlamadinger and Marland, 1996) and wood waste are sawdust and bark from sawmills, shavings produced during the manufacture of furniture, and organic sludge (or "liquor") from pulp and paper mills (Joshi and Mehmood, 2010).
Other biomass residues. The forestry, agricultural, and manufacturing industries generate plant and animal wastes in large quantities (Faaij, 2006). City waste, in the form of rubbish and sewage, is also a source for biomass energy.
Biomass conversion technologies
The traditional way of converting biomass to energy, practiced for thousands of years, has been to simply burn it to produce heat. The heat can then be used directly, for heating, cooking, and also for industrial purposes. Today, new ways of using biomass are still being discovered and it always refer as analogy from waste-to-energy technologies (Vollebergh, 1997; Maniatis and Millich, 1998; Turkenburg et al., 2000;
Stehlík, 2007a, & 2007b; Celma et al., 2007; Stehlík et al., 2008; Demirbas, 2009;
Veringa 2010; Gregg, 2010). The general paths for biomass conversion and utilisation technology options are shown in Figure 2.1. The main routes are analysed next.
12
Thermochemical conversion Biochemical conversion
Combustion Gasification Pyrolysis Digestion Fermentation Extraction
Steam Gas Oil Charcoal Biogas Oil
Figure 2.1 Main conversion options for biomass (Turkenburg et al., 2000)
Combustion and incineration. A classic application of biomass combustion is heat production for domestic applications (Faaij, 2006; Stehlík, 2007a).
Traditionally, the use of wood generally takes place at low efficiency and generally emits considerable amounts of pollutants such as dust and soot.
Technological development has led to the application of improved heating systems, which are automated, have catalytic gas cleaning and make use of standardized fuels (Stehlík, 2007a & 2007b; Stehlík, 2009). Incineration of biomass combined with waste can be considered as a form of recycling energy contained in treated materials. It partly releases the energy consumed during their production. Biomass combustion is labelled as waste-to-energy technology (WTE) (Stehlík, 2009). WTE is also referred to as the thermal processing of waste, including energy utilization. The combustion (thermal processing, incineration) of various types of waste is substantially reducing the waste volume and in addition, WTE systems can provide relatively clean, reliable, and renewable (to some extent) energy.
13
Gasification. Gasification is one of the technologies for utilising the thermo chemical conversion of biomass through the generation of gaseous fuels suitable for more efficient consumption (Kirubakaran et al., 2009). Gasification with air is a conversion of organic matter into low-energy gas (syngas or synthesis gas) which, after some modification, is suitable for use in boilers, combustion engines, gas turbines and, after proper cleaning, even in high-temperature fuel cells (Varbanov and Friedler, 2008).
Anaerobic digestion is a biochemical process where, in the absence of oxygen, bacteria break down organic matter to produce biogas and digestate (De Baere and Mattheeuws, 2008). The digestate can be produced out of many different kinds of biomass such as energy crops, organic waste, manure or a combination of these raw materials.
Fermentation usually refers to the bioethanol production such as from corn (Mojović et al., 2006) , sugar cane and sweet sorghum (Nguyen and Prince, 1996) Selection of a convenient biomass utilisation method needs to conform to the applicable local environmental legislation. National environmental legislations are far from uniform;
large variations can be found when comparing different countries (Stehlík, 2007b). The differences among emission limits of EU, the USA, and China are displayed in Table 2.1 (Stehlík, 2007b).
The values in the Table 2.1 are related to allowable emissions limits based on concentration (mg/Nm3) and they are not measured in total volume. The limits are given by environmental legislation and are obligatory for medium and large sources of emissions generation. E.g. NOx concentration is re-calculated to NO2 concentration and measured before the stack in incineration plants. The same is valid for other emissions.
The measurement is collected at the end of the discharge point.
Table 2.1 Environmental limits for emissions from incineration (Stehlík, 2007b)
14
Pollutant Units EU USA China
Dust mg/Nm3 10 24 80
CO mg/Nm3 100 62.5 –
187.5
150
NOx mg/Nm3 200 – 400 308-370 400
SO2 mg/Nm3 50 85.7 260
HCl mg/Nm3 10 41.3 75
Hg mg/Nm3 0.05 0.08 0.02
Cd + TI mg/Nm3 0.05 0.02 0.1
As +Co+Ni+Cr+Pb+Cu+Mn+V+Sb mg/Nm3 0.5 0.2 1.6
Dioxins/furans TEGng/Nm3 0.1 0.1 – 0.3 1.0
Pros and Cons of Biomass Utilisation
All energy sources have advantages and disadvantages, and it is important to evaluate them to determine whether the particular source (e.g. biomass) is really clean, safe, efficient, and effective. Table 2.2 summarises the main pros and cons of biomass utilisation.
There are always topics for the discussion about the pros and cons of biomass utilisation, for example: Is biomass energy better in production cost? Biomass is usually locally available. The typical locations of biomass sources (farms, forest, etc.) have the relatively low energy density, and the distributed nature of the sources require extensive infrastructures and huge transport capacities for implementing the biomass supply networks. For regional biomass supply chains road transport is the usual mode for collection and transportation. This tends to increase the cost of the biomass based energy. From the regional development point of view, biomass energy can be produced and supplied in the area, so there is no need for large pipelines or other massive infrastructure building. This also eliminates or decreases the cost and maintenance fees
15
caused by vehicles transporting the energy source from a long distance source point, e.g., the natural gas sending over from Russia.
Table 2.2 Pros and Cons of Biomass Utilisation (Hall and Scrase, 1998; Demorbas, 2009; Biofuel Watch, 2010)
Impact Advantages Disadvantages
Environmental Cleaner energy alternative to Fossil fuels
-economical Can reduce the dependence of fossil fuels (imported in most countries)
Can stimulate regional growth
Maximise the usage of local energy sources and increase the productivities
Increase the local job opportunity for rural areas
Security of energy supply
Development of related considered ―clean – low carbon emission‖.
Biomass is considered as Clean Energy because it can be naturally replenished (Karp and Shield, 2008; Demirbas, 2009) through the process of photosynthesis, chlorophyll in plants captures the sun's energy by converting CO2 from the air and water from the ground into carbohydrates, complex compounds composed of C, H2 and O2. When these carbohydrates are burned, they turn back into CO2 and water and release the sun's energy they contain. On the down side, the biomass process plant has to be
16
properly designed else It can release greenhouse gases into the atmosphere when burned. Therefore, biomass energy plants need to be equipped with exhaust gas cleaning technology to make them completely environmentally friendly. Furthermore, biomass processes required a huge amount of power for the pre-treatment such as drying, chipping, compacting, cutting and shredding massive volumes of biomass is frequently required.
The higher production cost as compare to fossil fuel would put biomass at disadvantage in purely economic terms (Krotscheck et al., 2000). The nature of biomass: distributed source points and low energy - mass density increase the load of transportation, which directly affected the biomass production cost. Moreover, harvesting, collecting, and storing raw biomass materials can be very costly, especially if we take into consideration the large volumes needed in comparison to fossil fuels. This observation contradicts the conventional industrial wisdom regarding the economy of scale, where larger plants are usually favoured, and processing is centralized. Centralised biomass processing over a larger area would eventually lower transportation efficiency in the case of transporting raw biomass, due to the unnecessary amounts of water and the low physical density of the transported materials’ volumes. Even though, such cleaning technology is often not economically feasible for smaller plants. There are always a pay-off for the economical impact, especially the development of regional scale biomass utilisation always bring a potential job and export (energy and other biomass products) opportunities.
The pre-treatment step has a significant influence on the performance of bioenergy networks, especially on logistics. Densification, compaction, and drying prior to transportation is crucial, as converting biomass into a higher density intermediate product can save transport and handling costs. It can improve the efficiencies of the conversion stages (Uslu et al. 2008).
17
The importance of pre-treatment is supported by studies on the types of biomass transportation. Gwehenberger and Narodoslawsky (2008) evaluated the energies used by several modes when transporting biomass. Figure 2.2 shows that transportation using ships uses the smallest amount of energy, whilst, in contrast, transportation of low-density raw materials such as straw using tractors uses a greater amount of energy.
0
Energy for Transportation of I MJ Biomass kJ/MJ km
Figure 2.2
Energy used for transporting 1 MJ of biomass energy content 1 km (Gwehenberger and Narodoslawsky, 2008)
Because of the growing demand for biomass energy crops, agricultural production, the space for settlement, and land use management, form an environmental and societal trade-off. The large land areas required for growing energy crops and refining them into
18
marketable fuels can result in food price increases and deforestation (Koh and Ghazoul, 2008). This in turn could lead to the loss of biodiversity and create a conflict between the atmospheric carbon balance and natural ecosystems (Huston and Marland, 2003).
Land use conflict occurs when the land in an area is limited and the same land can support a variety of different uses. The latter define a trade-off scenario for the region.
Because of the significant growth in world population and the resource demand per capital, it makes land use management more critical: to produce food, energy and space for living in a competing resource base. Consequently land use strategy is required to be properly planned for sustainable development (Chen et al., 2005). The planning should be focused on the social and economic needs with integral considerations of the environment to be sustainable in the long term.
The concepts of sustainable regional resource and land use management have been presented elsewhere. Yamamoto et al. (2000) developed a global land use and energy model (GLUE) to evaluate bioenergy supply potentials, land use changes, and CO2
emissions in the world. The model analyses the land use competitions and overall biomass flows. Silalertruksa et al. (2009) used consequential life cycle assessment (LCA) approach to evaluate the environmental consequences of bioenergy (bio-ethanol) policy target on land use and greenhouse gas emissions. A strategic method focused on the land-use trade-off between biomass production and other land uses such as for food crops and urbanisation development is needed.