| Application of biomass-energy technologies |
|VI. Conversion of biomass into electricity|
Rice husks are one of the most widely available agricultural residues in Indonesia, but they have few uses. They are a significant potential energy source if reliable conversion technologies can be developed. In Indonesia in 1986, milled rice production was over 26 Mt and 6.5 Mt of rice husks were subsequently produced - husks are estimated at 20 per cent of unmilled paddy weight. Use of 25 per cent of these husks (about 1.8 Mt) and a similar amount of available straw would yield about 3.6 Mt of energy feedstock which could produce an estimated 155 or 300 MW electricity depending of the amount of capital invested in the facility (USAID, 1988). Research and development work in gasifier technology has expanded considerably in Indonesia, and has been supported by the Government In 1987, the Government mandated that 10 gasifiers, manufactured in Indonesia, should be placed in field operation to help demonstrate their technical and economic viability.
This case study is based on a system designed by Manurung and Beenackers (1990). Their continuous, small-scale down-draft rice-husk gasification system appears to have overcome many of the previous problems related to the gasification of rice husks. Based on laboratory experience the first unit (10 kWh) was installed in a village, 100 km east of Bandung, West Java, in 1986. This was followed up by two scaled-up versions each with a capacity of 35-40 kWh. One powers a 1000 kg/hr rice mill and the other provides 10 kWh of electricity for 320 rural consumers.
Typical performance of these field units (called Gasifier I and II) are illustrated in table 15. Diesel fuel replacement up to 70 per cent was achieved; the rice husk to electricity conversion is about 2.4 and 2.0 kg/kWh for Gasifier I and II, respectively. The economic analysis shown in part C of the table is based on Gasifier II only, and demonstrates the pay-back period (PBP) and the net present value (NPV) of the investment. In addition, the economics of the gasification unit are compared with those of a conventional diesel-engine generating set of the same capacity. The costs are based on 1989 economic data and on the present actual performance of Gasifier II for that year.
Under present conditions, according to Manurung and Beenackers (1990), the operating costs of the dual-fuel plant were lower than the plant revenues, resulting in a positive income, with a pay-back period of 7 years compared with 8 years for the full diesel plant. Since the diesel costs for a full diesel plant are 66 per cent of its operating costs, and only 22 per cent for a dual-fuel plant, the economics are particularly sensitive to the price of diesel, and also to load capacity, total annual operating hours and the level of diesel substitution. If applied to rural electricity production, economic feasibility appears to be good with capacities of 30 to 50 kWh and upward, under Javan conditions of 1989.