2.3.1 Overview of biomass composition

There is a wide variety of biomass, and composition is also diverse. Some primary components are cellulose, hemicellulose, lignin, starch, and proteins. Trees mainly consist of cellulose, hemicellulose, and lignin, and so herbaceous plants, although the component percentages differ. Different kinds of biomass have different components: grains have much starch, while livestock waste has many proteins. Because these components have different

chemical structures, their reactivities are also different. From the standpoint of energy use, lignocellulose biomass, which consists mainly of cellulose and lignin such as trees, exist in large amounts and have great potential.

2.12.1 Characteristics and environmental significance

Wood-based carbon from sustainable forestry, in which the amount harvested is less than or equal to the amount of growth, circulates in forests, human communities, and the atmosphere. Wood from sustainable forestry is called “carbon neutral” as it will not cause a rise of carbon dioxide concentration in the atmosphere. Fossil fuel consumption for forestry production is less than in agriculture or fisheries, and less energy is used for producing wooden products like sawn timber or wooden buildings than for producing steel products etc. The promotion of wood utilization could contribute to carbon dioxide reduction. However, only 30% of tree biomass carbon can be stocked in final wood products like wooden buildings. Thus, it is important to achieve a balance between resource saving through material-recycling and fossil fuel saving by consuming wooden residuals for energy.

Densities of wood and wooden composites vary from 0.2 to 1.0 g/cm3, and the weight of low-density wood can vary by up to 3-fold, depending on moisture content conditions. Thus in most cases, wood statistics are listed using volume as the unit. Average oven dry density of wood used in Japan is estimated to be 0.42 g/cm3. Carbon content is 0.5. However, sometimes a carbon content value of 0.45 is used for wooden composites like particle board or medium density fiber board, which contain 10% weight ratio of adhesives, as a wood-derived portion.

(a) What is CHP?

Production of electricity and heat from one energy source at the same time is called Combined Heat and Power (CHP). Because the energy efficiencies are higher than the cases to produce only electricity, attention is paid to CHP by the viewpoint of effective use for energy.

(b) Energy conversion in CHP

To generate electricity from biomass, the energy of the biomass is changed into the kinetic energy, the dynamo is turned by it, and the electrical energy is obtained. The main method of changing the energy of the biomass into the kinetic energy is as follows; 1) Steam is made by heat of combustion of the biomass and the steam turbine is turned, 2) The combustible gas is made by pyrolysis or microbial degradation of biomass and the gas engine or the gas turbine is turned using the gas. In any case, the heat obtained by the combustion is converted into the kinetic energy. As all thermal energy cannot be converted into the kinetic energy, a part of the heat is discharged. The energy efficiency of the biomass utiliazation can be improved if this heat is collected and supplied with the electricity. The CHP has the advantage of raising the energy conversion efficiency in this way.

(c) Possibility of a large-scale plant

CHP can be applied even in a large-scale power plant. The reason for locating a thermal power plant and a nuclear plant near the coast or the big river is to use a large amount of seawater or river water to throw away heat. On the other hand, there is a case to sell the heat that occurs from the power plant to the nearby factories. It would be desirable to consider heat
supply when a large-scale power plant is planned.

(d) Applicability of factories and housing complexes

The CHP facilities can be designed and be set up in a factory or a housing complex according to the demand for the electric power and heat. There are various specifications for the obtained heat from the steam of high temperature and high pressure to the warm water. The collections and supplies of the heat are easier at low temperature and low pressure. The steam and the hot water can also be supplied by combining the CHP facilities with the existing boiler. When the biomass is used as fuel, the generation efficiency decreases when the scale of the facilities gets smaller. In case of the boiler and turbine processes, the scale of 2,000 kW or more in electrical output is necessary and in case of the gasification and gas engine process, the scale of 50 kW or more in electrical output is also necessary.

(e) Examples

An example of the small-scale CHP facility using woody biomass is shown below. In this facility, the wood scrap from the factory is used as fuel, pyrolysis and gasification is performed and electricity, hot air, hot water and cold water are supplied to the factory. The process flow diagram is shown in Fig. 4.1.1.

Hot water for air-conditioning

Fig. 4.1.1. Outline flow diagram of a small CHP using woody biomass

Gross power output of electricity is 175 kW and net power output is 157 kW. Heat outputs are 174 kW (150 Mcal/h) as hot air (67oC), 116 kW (100 Mcal/h) as hot water (80oC) and 70 kW (60 Mcal/h) as cold water (7oC). The energy efficiency in the facility can be raised by using heat that is originally thrown away as exhaust and cooling water.

4.1.4 What is acetone-butanol fermentation?

Aceton-butanol fmentation is a reaction in which acetone and butanol are produced from glucose using Clostridium, a strictly anaerobic bacterium. Further, ethanol is also produced. Therefore, acetone-butanol fermentation is also called as ABE fermentation. Clostridium is widely distributed in soil, and secretes amylase, xylanase, protease and lipase out of cells. There are two types of strain in acetone-butanol fermentation. One is Weizmann-type which produces butanol from starch, and the other is Saccaro-type which produces butanol from sucrose.

4.1.5 Characteristics of acetone-butanol fermentation

Acetone-butanol fermentation has a long history and is industrialized technology. Acetone-butanol fermentation was utilized to produce acetone as a raw material of smokeless powder in WWI and butanol for fuels of fighter planes in WWII. After WWII, acetone-butanol fermentation fell out of use due to development of petroleum chemistry. Recently, butanol is reviewed as biofuel.

Traditional biomass is directly used as wood or charcoal. Modern biomass is consumed as useful energy carrier such as electricity, liquid fuels, and gaseous fuels. There are several types of conversion technologies such as electricity generation (steam generation, integrated gasification generation), pylorysis, and fermentation (anaerobic digestion generation, ethanol production).

Generation cost of biomass integrated gasification was evaluated as follows. Installation cost was projected to be 2102 $/kWe (capacity 75 MWe, efficiency 36%) in 1997 , 1892 $/kWe (capacity 100MWe, efficiency 37%) in 2000, 1111 $/kWe (capacity 110 MWe, efficiency 45%) in 2030 (price in the year of 1996). But still it is in experimental stage in 2001. Another evaluation estimates installation cost to be 1221 $/kWe with 100 MWe capacity (1990 price). Annual expenditure (as a portion of annualized installation cost and operation cost) is assumed to be 12%.

Fig shows bioenergy conversion cost of typical technologies. Though cost of fermentation technology is higher than others, it can be moderated to include waste management cost of livestock manure. Technology cost for steam generation, integrated gasification generation, and pylorysis is expected to be cheaper due to technology development and deployment, but it is uncertain. Cost of co-firing generation is the additional cost to reform existing coal fired plant.

7.9.1 Fundamental energy policy

The Philippine Energy Plan is focused on its primary goal of energy independence and power market reforms.

As a major reform agenda of the Arroyo Administration, the objective of the energy independence package is to reach an energy self sufficiency level of 60% by 2010 and beyond. To realize this goal, five major strategies have been identified and this includes two major strategies directly related to renewable energy (RE) to include biomass energy. The two major strategies are the following: 1) intensifying renewable energy resource development and
increasing the use of alternative fuels.

According to the FAO statistics, total forest area is 4 billion ha, corresponding to an average of 0.62ha per capita. This forest area accounts for one-third of total global land. However, deforestation is a significant problem and 13 million ha of forest land has annually disappeared. On the other hand, China and India have aggressively expanded new plantation every year, then net loss of world forests area in the period of 2000-2005 is estimated at 7.3 million ha per year. In addition to deforestation, there are about 1.6 billion ha of degraded forests. It is important to rehabilitate degraded forests for global environment and sustainable development. If woody biomass is limited to stem biomass, there is 350 billion tons of dry-biomass in the world forest ecosystem. One third of dried woody biomass is existed in South America.

The area of forest plantation is 140 million ha and has increased by about 2.8 million ha annually in the period of 2000-2005. Forest plantations in tropical countries consist primarily of introduced species which growth rates are 15-50 m3 per year of Eucalyptus grandis, 14-25 m3 of Acacia mearnsii, 12-35 m3 of Pinus radiate, and 20-50 m3 of Pinus caribaea. These annual growth rates are three times of Japanese species for forest plantation. The forest plantations in tropical countries have a big potentiality to provide woody biomass with short rotation and low costs. Though a large-scale of forest plantation is sometimes criticized for poor biodiversity, forest plantation can be harmonized timber production operation with other forest function and services if it will be well managed under a concept of sustainable forest management. This concept usually requests forest managers to take care not only forest plantation but also natural forest with indigenous species.

Further Information

FAO, Global Forest Resources Assessment 2005, FAO, 2006 FAO, Forest Resources Assessment 1990, 7, FAO, 1995

Refuse-derived fuel (RDF) is fuel recovered from waste. It includes a wide range of fuel including gas and oil, but usually refers to shredded waste from which incombustibles have been removed. In Japan, RDF was first produced from uniform commercial waste, such as plastics or paper, and in the late 1980s, RDF production began to include household waste. Produced after a series of processes including separation of incombustibles, drying, shredding, and palletizing, RDF can be easily stored and transported, and therefore has been selected as an alternative method of incineration in small — and medium-sized cities. After problems related to dioxins limited RDF use as fuel for small-scale boilers, regional RDF power generation (in which RDF produced in member municipalities is used in a central power plant) became a promising option when decentralized small-scale incineration was not possible.

Compared to unprocessed waste, RDF provides a higher heating value and uniform composition, and yields improved power generation efficiency. Five RDF power generation plants have been in operation since 2001 in Japan. They were expected to yield throughput of 160 to 310 tons/day, power generation efficiency of 20 to 30%, and output of 3000 to 20,000 kW.

However, a RDF storage tank exploded at one plant in 2003, and extensive surveys revealed that similar accidents were not rare; a considerable fraction of RDF is now being sent to landfills. As of 2003, 43 RDF production facilities were in operation or under construction, but this technology has been discredited in Japan due to its poor safety record. The United States currently has 15 large RDF incinerators in operation, but in that country, RDF contains only shredded combustible waste, termed “fluff RDF” (or coarse RDF).

Continuous carbonization of a mixture of pine bark and sawdust by Tech-Air pyrolysis system (Fig. 4.4.2) is described as an example. This is an internal heat supply process with a vertical fixed bed reactor. The raw material is fed at the top of the reactor after reducing the initial moisture of 25-55% to 4-7%. Heat for carbonization is provided by partial combustion of the feed with air introduced from the bottom of the reactor. Charcoal produced is drawn out with a screw from another bottom section, while the product vapor passes through a cyclone where fine solid particles are removed to enter a condenser for tar (oil) recovery. The non-condensable gas is then combusted in a burner, and the discharged gas (204-316°C) is used for drying the raw material. The reactor temperature that is variable from 430° to 760°C is so controlled as to allow the heating value of the pyrolytic gas to have the energy necessary for drying the feed. Table 4.4.1 summarizes product distribution and two process efficiencies, which are defined as Net Thermal Efficiency (NTE, %) calculated as [{heating value of products — heat of process (gas for drying)}/heating value of raw material] x 100, and Energy Benefit Ratio (EBR, %) obtained as [energy of products/energy consumed] x

100, respectively, in terms of energy for the maximum yield of each product. Because of no great difference for all of the operations, the optimal conditions are decided by quality, use, cost, and so on for charcoal and oil.

Japan is a narrow country and has higher population density. That is why we cannot use a simple dumping method for the garbage treatment in Japan. Thus we have around two thousand incinerators for burning the garbage. Every day, garbage is collected in the incinerators and burned to get heat energy, part of which is used for power generation. Therefore, unused steam with lower pressure is available. Kitchen garbage comprises 30% in the total garbage in Japan. Especially, kitchen garbage from business sectors including supermarket and convenience stores can be easily separated form the others. Japanese kitchen garbage should be a good resource for sugars because half of the solid in the kitchen garbage is composed by starch, even though the compositions of the kitchen garbage should be changed every day. Then kitchen garbage contains a variety of nutrients including vitamins and it is good for the lactic acid fermentation. Fig.5.5.1 shows the lactic acid yield from kitchen garbage in the lactic acid fermentation after enzymatic treatment with glucoamylase using Lactobacillus rhamnosus. Generally, kitchen garbage contains 80% of moisture and indicating that around the 10% of the lactic acid yield shown in the figure should be quite high.