An Optimization Version of a Global Land Use and Energy Model GLUE

In order to evaluate economy of bioenergy as well as the bioenergy supply potential, the author developed an optimization version of the multiregional

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Fig. 3. Ultimate bioenergy supply potential of biomass residues a) Ultimate means all discharged biomass excluding biomass of material recycling such as timber and paper recycling

□ Kitchen refuse

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□ Cereal harvesting residues

□ Sawmill residues

□ Fuelwood felling residues

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Fig. 4. Share of ultimate bioenergy supply potential of biomass residues (in 2100)

global land use and energy model (GLUE 2.0). The author explains the outline of the model and the data. The data includes economic data of bioenergy concerning bioenergy resources and bioenergy utilization technologies.

6.3.1 Outline of an Optimization Version of a Global Land Use and Energy Model

The optimization model is described using a liner programming (LP) technique. The model consists of two parts: an energy systems part and a land use part. The energy systems part is based on a global energy systems model named New Earth 21 (NE21) (Fujii and Yamaji 1998) and the land use part is base on a global land use and energy model (GLUE) explained in the previous section.

NE21 includes a detailed description of energy resources and energy utilization technologies. The author added data of bioenergy resources and bioenergy utilization technologies to NE21 (see the following sub-section). The objective function of the model is the summation of the energy system costs.

6.3.2 Costs of Biomass Resources

Kinds of biomass resources can be used not only for energy but also for material or food. The costs of bioenergy in the model included opportunity costs of biomass for material or food. If the supply cost of a kind of bio-energy is less than the price of the biomass for material or food, the bio-energy cost includes the opportunity cost for material or food. On the other hand, if a kind of biomass residue has no use except for energy, there may be a disposal cost; the bioenergy resource cost may be negative when the supply cost is less than the disposal cost. The principle to set bioenergy resource costs is as follows.

• When an opportunity cost occurs:

(Bioenergy resource cost) = (supply cost) + (opportunity cost)

• When a disposal cost occurs:

(Bioenergy resource cost) = (supply cost) - (disposal cost)

(Bioenergy resource cost) = (supply cost)

The supply cost comprises costs of harvest, transportation and processing of the bioenergy. As an example, the author explains market prices of roundwood, timber, wood chips (for wood pulp) and sawdust in Japan. An average price of roundwood is about $84/m3 (about $7/GJ). Prices of timber and wood chips for wood pulp are about 45,000 yen/m3 (about $31/GJ) and about 8,000 yen/m3 (about $5/GJ), respectively. A market price of sawdust for energy or manure is about 1,000 yen /m3 (about $0.7/GJ) (Yamamoto et al. 2001b). The wood prices for non-energy are higher than (or equal to) the wood prices for energy.

Figure 5 shows the first-grade (or the lowest) costs of bioenergy resources in the model. The bioenergy resource costs were assumed to increase in proportion to the resource utilization ratios (that are resource uses per ultimate resource supply potentials) (Yamamoto et al. 2001b). The modern fuelwood cost is the most expensive because it includes the oppor-

Fig. 4. Costs of bioenergy resources in the model

tunity costs of material use. The cost of energy crops is the third most-expensive because it includes cultivation costs. Some kinds of biomass residues that are discharged at the factory or are collected by public garbage-collection systems can be used for energy at zero cost. Furthermore, some kinds of biomass residues with disposal costs such as animal dung and human feces can be used for energy at negative costs.

6.3.3 Costs of Bioenergy Utilization Technologies

The author considered costs and efficiencies of bioenergy utilization technologies such as power generation (steam power and gasified combined-cycle), and biomass gasification, biogas (anaerobic digestion) power generation and ethanol fermentation using cellulosic biomass. Synthesis gas (H2 + CO) made through biomass gasification processes are used for gaseous fuel (H2), methanol synthesis and syn-oil synthesis.

Fig. 5. Costs of bioenergy utilization technologies in the model

The author summarized the costs of the bioenergy utilization technologies using the costs per unit outputs ($/kW) (Figure 6).

Consequently, biogas power generation is the most expensive because the power output is small compared with the facility size. However, the biogas power generation improves the cost condition when it uses biomass resources with disposal costs such as animal feces.

Steam power, gasified combined-cycle and gasified methanol synthesis are developing technologies and the expected costs contain large uncertainty.

Co-firing of biomass and coal is the cheapest among the power generation technologies. However, the co-firing system is the system of retrofitting the existing coal power plant without increase in the plant capacity, and the cost of the co-firing cannot be compared with that of the other power plant technologies in a simple way. Therefore the author excludes the co-firing system from the model analysis.

6.3.4 CO2 Emission Scenarios

Below are three CO2 emission scenarios the author used for the simulation:

1. FREE

FREE is no CO2 constraint scenario.

2. CP3F

CP3F is COP3 forever scenario (UNFCCC 2005). In CP3F, the greenhouse gas constraints on the developed regions (including the former USSR) between 2008 and 2012 in COP3 will continue to be the same forever. There are no CO2 constraints on the developing regions. Tradable CO2 permits are allowed among the developed regions.

3. C30R

CO2 emissions in C30R in all the regions in the world will be 30% less than those in CP3F in and after 2020. Tradable CO2 permits are allowed among all the regions in the world.

6.3.5 Simulation Results

When CO2 emission constraints are imposed, it will be advantageous to bioenergy the CO2 intensity of which is close to zero. In 2050 the bio-energy used economically in the world is 74 EJ/year in no CO2 constraint scenario (FREE), 131 EJ/year in COP3 forever scenario (CP3F) and 337 EJ/year in CP3F where the CO2 emissions will be 30% less than

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Fig. 6. Bioenergy uses in primary energy (by resources, in 2050). a) Modern fuel-wood uses in C30R is 196 EJ/yr. The world bioenergy uses in primary energy is 74EJ/yr in FREE, 131 EJ/yr in CP3F and 337 EJ/yr in C30R

Fig. 6. Bioenergy uses in primary energy (by resources, in 2050). a) Modern fuel-wood uses in C30R is 196 EJ/yr. The world bioenergy uses in primary energy is 74EJ/yr in FREE, 131 EJ/yr in CP3F and 337 EJ/yr in C30R

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Fig. 7. Bioenergy uses (by utilization technologies, in 2050) (a). The bioenergy uses in C30R in Latin America is 127 EJ/yr. The world bioenergy uses in primary energy is 74EJ/yr in FREE, 131 EJ/yr in CP3F and 337 EJ/yr in C30R

those in CP3F (Figure 7). Biomass residues that can be used at low costs will be introduced even in FREE. Bioenergy plantation such as energy crops and modern fuelwood will be used on a large scale in CP3F.

Biomass gasifier and biomass-gasifier-combined-cycle (BGCC) will be used on a large scale in any case in 2050. Synthesis gas (H2 and CO) pro-

duced by biomass gasifiers will be used to make liquid fuel such as methanol and syn-oil (Figure 8). Anaerobic digestion power generation using animal dung and human feces, and waste incineration power generation using kitchen refuses, will be used even in FREE since the utilized biomass resources cost zero or negative. Ethanol fermentation using cellulosic biomass will not be selected since the ethanol fermentation is more expensive than the system of biomass gasification and syn-liquid production in the data in the model. However, both the ethanol fermentation using cellulosic biomass and syn-liquid production from biomass are developing technologies and the former might be less expensive than the latter in the future.

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