2.4.1 Indicators of biomass energy content

In order to establish biomass energy systems, the energy content of each type of biomass feedstock should be determined at first. Heating value is often used as an indicator of the energy that biomass contains. Heating value is the amount of heat generated when a substance undergoes complete combustion, and is also called the heat of combustion. Heating value is determined by the ratio of components and the kinds and ratios of elements (especially carbon content) in biomass.

(a) Higher and lower heating value

Biomass comprises organic substances composed mostly of carbon, hydrogen, and oxygen, and when it is completely combusted, it produces water and carbon dioxide. The generated water and water vapor contain much latent heat that is given off upon condensation. The heating value which includes latent heat is the high heating value (HHV), while that from which latent heat is subtracted is the low heating value (LHV).

(b) Available heat

Heating value Q0 is the amount of heat that arises from complete combustion per unit material under standard conditions. Actual biomass contains much moisture and ash, which must be taken into consideration when energy is producing. Merely evaluating low heating value is inadequate as an indicator whether biomass in its natural state will sustain combustion. The energy to raise ambient air to the temperature that maintains the fire and the endothermic energy of ash should also be taken into account. The heat amount that takes them into account is the available heat, and is expressed with this equation:

Available heat Q = Q0 (1 — w) — 1000 w — [flue heat absorption] — [ash heat absorption]

(w: moisture content)

Fig. 2.1.3. uses values calculated for available heat Q at 900°C. A positive (+) value for available heat Q is the condition for combustion to occur.

2.13.1 What is animal waste?

Livestock feces and urine are the major animal waste products and the amounts of livestock feces and urine account for the greatest portion of domestic organic waste in Japan. The feces and urine contain many easily degradable organic materials and many nutrient materials, such as nitrogen and phosphorus. The quantity and quality of feces and urine are very different depending on the kind of livestock, weight, feed, amount of drinking water, breeding system, season, and livestock conditions. According to their characteristics, feces and urine are processed and stored or used by suitable methods. Other animal waste products include slaughterhouse residue and other by-products of meat processing.

Examination of biomass material properties is necessary before planning gasification.

(a) Element analysis

Carbon (C), hydrogen (H), oxygen (O), sulfur (S), nitrogen (N) and chlorine (Cl) are observed through element analysis (HCN coder etc.). Excessive sulfur and/or chlorine can cause corrosion of plant equipment. The abbreviated molecular formula CnHmOp can be determined by obtaining the mol ratios for carbon (C), hydrogen (H) and oxygen (O). For biomass consisting of grass and wood, n=1.2-1.5 and p=0.8-1.0 when m=2.

(b) Ash composition and fusion point

The ash softening point, fusion point and flow point are to be measured in both oxidizing and reducing atmospheres. Problems with plant equipment occur more easily when the fusion point temperature is low.

(c) Technical analysis

Technical analysis is to be performed on raw material biomass to determine surface moisture, inherent moisture, volatile matter content, fixed carbon content and ash content, as well as high and low calorific content. These material property values are essential for gasification analysis.

5. 4. 1 What is hydrogen fermentation?

Anaerobic fermentation is a reaction in which anaerobic microorganisms oxidatively decompose organic materials to get energy under anaerobic conditions. We call fermentative reactions in which hydrogen is the final product as hydrogen fermentation. In hydrogen fermentation, some organic materials and alcohols are produced with hydrogen. Although final electron acceptor is oxygen or inorganic materials in respiration, oxidatively degraded organic materials and carbon dioxide etc. from substrate materials are final products in fermentation. For example, final products are ethanol and carbon dioxide from glucose during ethanol fermentation. While ATP synthesis is coupled with electron transfer chain in respiration, ATP is produced in reactions at substrate level in fermentation. Energy gained from fermentation is smaller than that from respiration for the same amount of substrate.

5.4.2 Characteristics of hydrogen fermentation

The role of hydrogen production is to regulate oxidation-reduction level in bacterial cells by converting excess reducing power to hydrogen. There are bacteria which can take in and utilize such hydrogen. In order to increase hydrogen yields, the reverse reactions consuming hydrogen should be suppressed. Generally, it is needed to treat waste water from hydrogen fermentation, since hydrogen fermentation includes the production of some organic materials.

By the use of the plant described above, the farmer did not need to pay 350 bahts a month (100 bahts = 2.85 US$, as of December 2006), which was the cost of propane gas. This was a fair amount for a farmer’s family, and they said that they were happy with the reduction of this cost.

The fermentation residue was placed in a bag by 30 kg and sold at 12 bahts per bag.

The system was quite simple, and the plant

could be fabricated by villagers in 9 days. The material cost 5,000 bahts and total cost was 7,400 bahts, so the economic payback period was 21.1 months. A person from the local government who knew the know-how could help the farmer for building. The means to make the process economically feasible is simple structure and free labor to help each other in the village. The materials are cheap. No special skill was needed for operation, the main body of operation is farmers themselves, and this reduces the labor cost. The simplicity results in no necessity of operation person or labor cost, and farmers themselves can construct the plant.

Incidentally, income of farmers living around an ethanol production plant in Thailand is discussed here (Fig. 6.5.2.). The plant is planning to construct a 100,000-L/day ethanol plant and its feedstock is assumed to be cassava. It is because the market price of cassava is rather stable than that of molasses. The farmers could not get income when the plant used molasses
since the plant paid to sugar production factories. Therefore, the plant thinks that increase in the ethanol production from cassava will make cassava cultivation more attractive and people in rural area remain. The unit price of cassava chips is now 3.7 bahts/kg. In order to sell cassava to the plant, farmers have to chip and dry (below 18% of water content) for pretreatment. Considering this, they can earn 1 baht/kg and this profit is quite attractive for them.

There are mainly two ways to support farmers. One is to supply energy so that they have the access to useful fuels. In Thailand, small-scale biomethanation provides cooking gas to farmers, so they need not to buy propane gas for cooking. This support to farmers is also effective for sustainable agriculture due to the reduction of fossil fuel utilization. The other support is by cash. When they grow feedstock for ethanol production and sell it at a higher price, they can get money for buying electricity. Since those who use ethanol as fuel are richer compared to farmers, this mechanism can be considered as ‘redistribution of wealth.’

Singapore has always enjoyed a reputation as a “Garden City” for being “clean and green” due to its effective management of the urban environment and maintenance of the green space. With a land mass of approximately 700 square km and population of 4.5 million, it has also invested heavily on the environmental infrastructures such as waste water treatment and waste disposal facilities. Most recently, it has embarked on the recycling and reuse of the water resources under a program called “Newater” which has become a model for many countries to follow.

It is now 2008, energy security dominates international stage, crude oil price is nearing a record high of over $100 US a barrel, global warming and climate change are now household concerns. Europe-led market demand for biofuels is all the rage. Singapore claims to be the world’s second largest petroleum refinery center with installed capacity of well over 1 million barrels/d. However, Singapore relies on the import of nearly100% of its raw energy supply. This reliance on imported fossil energy necessarily subjects Singapore’s economic and environmental sustainability to external factors that all energy importing countries must also face. These included global oil/gas market fluctuations; political instability of the oil exporting countries; international protocol (Kyoto Agreement) to limit CO2 emission from fossil energy use, as well as changes in public energy consumption patterns.

Government has encouraged development of clean, alternative energy programs such as the Sinergy Program which provided a testbed for hydrogen based fuel cell vehicles since the 1990’s. More recently, it has announced major R&D funding program on clean and renewable energy. It has successfully attracted major investments for the manufacturing of solar-PV panels with the announced capacity of 1,500 MWe per year, as well as a wafer manufacturing plant to provide the mono-silicon materials needed for the solar cells.

On the other hand, private sector investors have taken advantage of Singapore’s strategic location in the tropical SE Asia together with its well established infrastructures for crude oil handling, storage, and refineries. Singapore is benefiting directly from its proximity to this rich repository of biomass resources. In recent years, Singapore has attracted major foreign direct investments in biodiesel production facilities. All together, 6 biodiesel production projects have been confirmed, with a total combined capacity of close to 2 million tonnes/per year and the total investment dollars is close to S$2 billion. All of these investments aim to bring in crude plant/seed based oil from the region and refine them in Singapore. A regional biofuels analysis center is also being set-up to cope with the anticipated demand from all these activities.

Domestically, Singapore generates about 650,000 Tonnes/year of biomass wastes which includes food waste, wood/timber wastes and sludge/biosolids. Many of the woody biomass comes from the thriving shipping/trans-shipping industry in Singapore where wooden pallets are routinely disposed when they become unrepairable. Increasingly, the government of Singapore, through the National Environment Agency (NEA) and private sector investors are exploring opportunities for their energy recovery and utilisation. Once plant has been built by local investor to convert food waste to biogas, another diverts about 600 tonnes/d of municipal solid waste (MSW) for recycling and reuse, of which about 300 tonnes/d of woody biomass are used as fuel for cogen. The third recovers energy and generates hot water from horticultural wastes. Government is now encouraging more opportunities for diverting biomass waste from the incinerators and landfill sites. It is expected that more private sector investment will see the economic benefit for recovering energy from the biomass resources.

In summary, Singapore is in the forefront of bioenergy R&D, it is also racing ahead to explore more sustainable 2nd and 3rd generation of biofuels technology and will likely to lead the commercial developments of these renewable energy due to its pro-active government policies for attracting investments.

It is a great pleasure and honor for me to give some words for this Biomass Handbook. In 2002 we had already published Biomass Handbook in Japanese edition with the help of more than 60 contributors who are distinguished specialists in this field. This time English version has been issued with the cooperation of scientists and engineers of Asian countries in addition to domestic contributors.

As we are aware, negative impacts of global warming has been remarkably coming out. Carbon dioxide discharged from fossil fuel combustion has been accumulated in the atmosphere as far as we consume coal, petroleum, and natural gas. On the other hand, it is clear that the life of fossil fuels is limited, for example, the life, the ratio of reserve divided by the production, of petroleum, coal, and natural gas will be about 41, 160, 65 years, respectively. I believe that we are at the gateway to the new age independent on the fossil fuels and biomass is a key resource to open up a new vista of the future.

Biomass means, in general, a substantial amount of bioorigin resources which can be utilized in the form of energy and materials. Wood, grass, marine algae, micro algae, agricultural wastes, forestry wastes, and municipal wastes fall into this category. Energy crops are one of promising biomass which could make energy plantation possible in a large scale, though it has not yet been commercialized at the present.

One of the strong countermeasures to suppress carbon dioxide emission is the introduction of renewable energies. Renewable energies mean biomass, photovoltaics, geothermal, wind, hydro, tidal, and wave energies. How does differ biomass from other renewable energy?

Biomass forms own body by photosynthesis. The concentration of carbon dioxide in the atmosphere remains unchanged as far as carbon dioxide, which is emitted by combustion of biomass after energy utilization, is refixed by, for example, reforestation. It is called the carbon neutrality of biomass. Energy which replaces fossil fuels can be derived from the cycle, that is, biomass combustion, carbon dioxide emission, and carbon dioxide refixation. Thus, the carbon dioxide emission can be reduced by replacing fossil fuels by biomass.

Biomass is only organic or carbonaceous among renewable energies. In other words, ethanol, methanol, dimethyl ether, and hydrocarbons can be produced only from biomass among renewable energies. It has the same meaning that biomass can be transportable and storable in the form of material. It should be emphasized that wind, photovoltaic, tidal, wave, and geothermal energy can produce heat and power but not chemicals and fuels. However, carbon dioxide emitted from biomass utilization will be accumulated irreversibly into the atmosphere in a similar manner with fossil fuel utilization unless otherwise reforestation is made. Sustainable forestry management is essential to the long and stable supply of bioenegy.

This Biomass Handbook deals with the characteristics and resources of biomass, thermochemical and biochemical conversion of biomass, and system development of sustainability. However, the most important aspect is the contribution of many specialists of Asian countries, that is, Brunei, Cambodia, China, India, Indonesia, Korea Malaysia, Myanmer, Philippines, Singapore, Taipei Chinese, Thailand, Viet Nam. I should like to appreciate all the people who contributed this Handbook. Also I appreciate the Ministry of Agriculture, Forestry and Fisheries which gave an opportunity to enable us to issue this Handbook by financial support.

January 2008 Editor-in-chief Shinya Yokoyama

Existing biomass of tropical savanna is lower than that of tropical rainforest. The primary production of the tropical savanna, which has rich rhizosphere and the grasses vigorously grow under heavy grazing of animals, is similar to that of tropical rainforest, whose rhizosphere is shallow, of poor quality. As such, tropical savanna greatly contributes to the reduction of CO2 when compared to tropical rainforest1. As advancements in fermentation and gasification techniques, the utilization of herbaceous biomass as a biofuel, has attracted much attention. Annual production of herbaceous by-products is estimated at 18.95 million tons (Mt) from rice straw and husks, 1.90 Mt from barley and wheat, 0.5 Mt from sugarcane. Furthermore, estimated data of forage production of 40 t/ha in 560,000 ha of abandoned fields, 40 t/ha in 79,000 ha of abandoned paddy field, 5-20 t/ha in un-utilized land comes to 32.08 Mt. The total of available herbaceous biomass comes at least to 53.43 Mt/year in Jpan. But these are utilized partly for forages of cattle now.

As described, burning black liquor in a recovery boiler is a process to get energy. At the same time, it reproduces the chemicals for pulp production. It’s necessary to use black liquor in a kraft pulp manufacturing plant. Therefore, all kraft pulp plants have a process to burn black liquor.

2.0 tones of black liquor are produced as a by-product from 1 tone of a hard wood pulp or 1.5 tones of a soft wood pulp. Generally, almost all amount of black liquor is used as biomass energy. The production of the kraft pulp in Japan is about 9,000,000 tones a year and

14.0. 000 tones of black liquor are produced during the process. And the amount of the liquor is equal to 4,710,000 kiloliters of crude oil in terms of energy.

In 1999, the production of chemical pulp in the world was 119,000,000 tones. In consequence, the production of black liquor was calculated to be about 200,000,000 tones. And it’s equal to

60.0.000 kiloliters of crude oil (Table 2.16.1).

Pulp and paper industry in Japan and Asian countries has been using planted woods as a material of pulp in these days and the production has been increasing. The industry is able to be developed by means of producing both material and energy from sustainable forest management which produces the resources for pulp. The utilization of black liquor is surely the foundation for the management.

Now that the utilization of black liquor is limited to the energy source in pulp and paper mills, however, various kinds of materials are produced such as lignosulfonic acids by dividing lignin from black liquor and nucleic acids by culturing of the yeast using sugars in the black liquor. It’s expected that biorefinery of black liquor utilization will be more and more developed in the future.

Further information

Keiichi Tsuchiya, Makoto Iwasaki, Tadanori Oihata, Yoshihiro Sakaguchi, Keiichi Tushiya, “Pulp and Paper Manufacturing Technology Complete Book, Vol. 2 Kraft Pulp”, 11-20, 185-223 (1996) JAPAN TAPPI (in Japanese)

JAICAF Edition, “World Forest White Paper 1997”, JAICAF (in Japanese)

JAPAN TAPPI Energy Committee, “Survey on Energy Consumption in the Pulp and Paper Mills in Japan Part 1”, 55, 573-591 (2001) JAPAN TAPPI (in Japanese)

JAPAN TAPPI Edition “Pulp and Paper technical handbook”, 105-136 (1971) JAPAN TAPPI (in Japanese)

Yuuichi Hayase, “Seishi-koujou kara-no Fukuseigenryou ”, 50, 1253-1259, Thermal and Nuclear Power Engineering Society (in Japanese)

Masahiro Kitazume, “Sekai no Kami Parupu”, 8-15, September (2000) Kami-Parupu (in Japanese) Keiichi Nakamata, “Kami to Shinrin no Kakawari”, Global Environmental Policy in Japan the 1st report, 1-9 (1999) Chuo University Press (in Japanese)

Hydrothermal gasification is suitable for wet biomass treatment. When wet biomass is to be gasified, usual thermochemical gasification is not employed due to its high moisture content. Hydrothermal gasification, on the other hand, uses water as reaction medium, and thus wet biomass can be treated without costly, energy-consuming drying pretreatment. Since reactivity of water is high under these conditions, hydrothermal gasification enables quick and almost complete gasification of biomass. Biomethanation is employed to obtain methane gas from wet biomass, but usually it takes a few weeks for the reaction to complete, and treatment of unreacted fermentation sludge and waste water can be a large problem. Reaction time as long as a few weeks results in bulky reactor. Fermentation sludge can be converted to compost, but when sufficient land is not available for the use of the compost, it is just a waste to be treated. In hydrothermal gasification, reaction is completed in a few minutes at longest, and almost complete gasification is possible when reaction condition is properly adjusted. Sometimes, addition of catalysts such as alkali, metal, or carbon catalysts enhances the reaction.

To investigate the reactions taking place in hydrothermal gasification, tube-bomb reactors of the volume of several mL and autoclaves are often used. However, when you want to develop a commercial plant, a continuous reactor such as is shown in Fig. 4.5.2 is a must. Biomass is fed to the reactor at a high pressure, and then heated to the reaction temperature. In the reactor, biomass is gasified under hydrothermal condition, and the effluent is cooled down to the room temperature. Heat released at this time is recovered by the heat exchanger, and used to heat up the feedstock. After reaching the room temperature, the effluent is depressurized to atmospheric pressure, and the product gas is recovered. The continuous reactor is needed because of the large amount of heat needed to attain the hydrothermal condition. This heat sometimes matches the heat of combustion of the biomass to be gasified, and thus heat recovery using a heat exchanger is needed. Only flow reactors allow this heat recovery. In Fig. 4.5.2, heat balance for the ideal case is also shown. Combustion heat of biomass is maintained in the product gas while heat required to attain hydrothermal condition is recovered so that no heat is added from outside during gasification operation. In practice, the efficiency of the heat exchanger cannot be unity, and endothermic reaction results in necessity of additional heat supply to the reactor.