There are mainly two ways to support farmers (The Japan Institute of Energy, 2007). 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.’

2.10.1 What is aquatic plant biomass?

Aquatic plant biomass is produced in freshwater and marine environments and has some potential human uses. Most current aquatic plant biomasses include seed plants, seaweeds and micro-algae, which are mostly produced naturally as well as some with man-made culture production.

Seed plant biomasses in freshwater are a water plant (Eichihornia crassipes (Mart.) Solms) and duckweeds. E crassipes native to Brazil grows actively at 18-32 oC but shows no positive growth above 34 oC and below 0 oC. No duckweed species including about 30 species recorded has been selected as biomass utilization yet.

Within 60 species belonging 13 genera of 3 families (Hydrocharitaceae, Zosteraceae and Cymodoceaceae) as marine seed plants (sea grasses) in the world, eel grass (Zostera marina L.) and related species distributing at middle and high latitudes attract mostly for biomass uses (Hartog, 1970).

Algae include multi-cellular macro-algae (seaweeds) and unicellular micro-algae (phytoplankton). Seaweed inhabits, mostly in seawater and active biomass utilization is made with 220 species of red algae, 88 species of brown algae and 27 species of green algae in the world (Indergaard, 1982).

Micro-algae are distributed widely both in fresh — and marine waters although species are different. Current attractive species for biomass are green algae belonging Chlorella, Scenedesmus and Dunaliella and blue green alga of Spiriluna in freshwater. Selected strains are cultured artificially for biomass uses, and some freshwater strains are cultured in seawater after acclimation treatment.

(a) Wood pellet

It is thought that the factors that affect on pelletizing condition are pressure, temperature, compression time, particle size of raw materials, moisture content and chemical composition of wood. As for the boundary condition on pelletizing, it is not clear yet. It is actual that pellet is produced on the basis of experience of operator. It is different with a kind of wood material, but the experience value of pelletizing pressure and temperature is 70MPa and 100-150 degrees. However, there is no doubt that lignin, glucide and pectin play as a binding agent.

(b) CCB

We use a high pressure roll type briquetting machine for production of CCB. Tablet tests are carried out to obtain the optimum blending ratio of the raw materials and indispensable as a preliminary step in briquette manufacturing. The blended material is compressed to tablet of 25 mm diameter. A steel ball with a diameter of 20 mm is placed on a tablet and the ball is forced down onto the tablet until the tablet breaks. The breaking strength is measured as the criteria of quality. Fig. 3.2.5 shows the breaking strength of the tablets prepared from coal and biomass. The breaking strength becomes increasingly higher as the content of the biomass increases. Heating the raw materials under briquetting is an effective way to increase the breaking strength. Fig. 3.2.6 shows that a higher temperature of molding increases the breaking strength of tablet. This is attributable to the enhancement of the plastic deformation of the biomass by heat. The blending ratio of coal and biomass that achieves a breaking strength of briquette of 1 kN is 20% of biomass content and molding temperature 50 degrees. Based on these results, the standard blending ratio of coal and biomass is determined. When a CCB was produced with high pressure roll press machine, the shearing stress occurs between roll tire and raw materials, and raw materials is heated in about 70-80 degrees. Therefore heating control of raw materials is not done in briquetting process.

4.1 Biomethanation

4.1.1 What is biomethanation?

“Methane fermentation” or “anaerobic digestion” is usually used to indicate “biomethanation”. Biomethanation is a complex microbial process in which organic compounds are degraded into methane and carbon dioxide by variety of anaerobes. This biogas has a low heating value of 20-25 MJ/m3-N (5,000~6,000 kcal/m3-N) and can be used for fuel after desulfurization of hydrogen sulfide. Biomethanation is used as a technique of biofuel recovery from biomass and treatment of waste biomass. Fermented residue can be used for liquid fertilizer and raw material of compost.

4.1.2 Feature of biomethanation

First of all, organic compounds are decomposed to organic acid or hydrogen by variety of anaerobes. At the final stage, acetate or hydrogen and carbon dioxide are converted to methane. Biomethanation takes place under anaerobic conditions, especially, methanogens require absolute anaerobic conditions for methane production. Biomethanation is a microbiological process; therefore, this process proceeds under normal temperature and pressure. Biomethanation can be applied for variety of biomass compared with ethanol fermentation due to activities of complex microflora.

The assumption as shoen in Table 6.2.1 is set, although growth quantity and caloric value of biomass depend on tree types and/or local meteorological conditions.

Table 6.2.2-Table 6.2.4 obtained from references shows energy required for tree planting, describing electricity as primary energy based on power generation efficiency (38.1%) in Japan.

Table 6.2.4 shows the inventory of afforestation for pulp production in Brazil, which can be considered as an example of biomass energy production technology.

The growth rate is a value per each unit area and depends on intervals between trees. For Brazilian case, plenty of human work (task) reduces energy consumption. Energy efficiency of biomass production can be found by comparing calorific value of Table 6.2.1 and energy consumption of Tables 6.2.2- 6.2.4.

For example, North American case shows that 1.4 MJ of energy (about 7.4%) is consumed to produce biomass which has 18.8 MJ of caloric value per unit mass.

There are biomass fuelled electricity generation facilities in Cambodia.

(i) Centre for Livestock and Agriculture Development (CelAgrid)

CelAgrid is the institute conducting various research on rural development mainly based on agricultural technologies. There are 17 academic staff and 40 students working in the institute. They purchased a 9 kWe (gross) biomass gasification electricity generation system from Ankur Scientific (India) in September 2004. Center’s currently conducting a research on comparing different biomass such as coconut husk, cassava stem, mulberry stem and Cassia tree for suitability and efficiency for gasification.

(ii) Anlong Ta Mei Community Energy Project

Anlong Ta Mei village (Bannan District, Battambang Province) community energy cooperative project is the only biomass electricity supply system operated profitable base rather than research. The project introduced a 9 kWe biomass gasification electricity generation system (same model as CelAgrid) and set up a mini grid. They use planted Leucaena branches for the fuel. They started the operation in February 2005.

(iii) NEDO and Biogas Hybrid Power Generation Project

In December 2003, Japan’s NEDO completed the construction of a hybrid electricity generation system consist of a solar photovoltaic (50 kW) and 2 x 35kWe duel fuel biogas engine near Sihanoukville. The biogas is extracted from cattle excrements from a farm. The system is currently operating but the project is considered to be mainly a demonstration and research venture and would not economically viable yet.

Despite many biomass power plants, some of them are still running at the low efficiency using conventional burning to produce a steam for power generation. Hence, thermo-mechanical conversion process like gasification technology can help solve the problem. Rice husk is another attractive feedstock for biomass power plant due to its plentiful availability from the rice mills, its small size and low moisture. Recently, Ministry of Energy has funded a project to demonstrate the feasibility of constructing the community biomass gasification system (using rice husk) to Kasetsart University and Great Agro Co., Ltd. This project was initiated to foster Sufficiency Economy philosophy by His Majesty the Kind of Thailand. The system produces not only 80kW electricity but also heat and biomass ash for fertilizer, as shown in Fig. 8.4.3. The system design uses three-stage fluidized bed pyrolysis and gasification, comprising of 5 main units: drying, pyrolysis, gasification, cooling system and engine/generator set, as shown in Fig. 8.4.4.

As shown in Fig. 8.4.5 and 8.4.6, the system was installed at Lamlukka Cooperative Rice Mill & Paddy Center Market Co., Ltd for demonstration and test run for more than 360 hours. With gas flow rate of 240 m3/hr (heating value at 4.5 MJ/m3) and rice husk consumption of 85 kg/hr, the overall gasification system efficiency is 92%. In other words, 1.25 kg/hr consumption of rice husk generates 1 kW of electricity. Furthermore, the residue tar volume from the system is approximately 22 mg/m3. On the economic analysis, this 80kW system requires a capital investment of ~3.9M Baht with the operating cost of ~1.79 Baht/unit. Assume that the system produces the electricity at 460,800 unit/year, which substitutes the electricity cost of 3 Baht/unit, the net profit is estimated to be 0.56M Baht/year with the
payback period of 7 year. The next step would be the collaboration between MTEC and Great Agro Co., Ltd to scale up the system to 1MW capacity.

Further information

S. Nivitchanyong, Alternative Energy Cluster, National Metal and Materials Technology Center: MTEC (siriluck@mtec. or. th)