An integral approach to evaluate the performance
of bagasse co-generation plants
A.F. Lau, K.T.K.F. Kong Win Chang and D. Gunness
Mauritius Sugar Industry Research Institute
Keywords: energy, bagasse, co-generation, electricity
Bagasse cum coal co-generation plants, in partnership with the cane sugar industry of Mauritius have become major players in the electricity production sector. In the larger plants, coal is used as fuel during the off-crop season to enable electricity export all year round, ensuring optimal plant operation and profitability. In the year 2003, power sales to the utility, using bagasse and coal as fuel was around 300 GWh and 430 GWh, respectively. The development phase is approaching completion, and the energy optimization stage has started.
In our quest to optimize the technical performance of bagasse co-generation plants, the factors influencing surplus electricity production were analyszed, using existing data. It appears that the large disparity between the electricity production of the least and the most efficient co-generation plants is not solely a matter of technological superiority, e.g., high-pressure boilers. The turbo-alternator, process steam consumption, imbibition % cane, fibre % cane, boiler efficiency, moisture % bagasse, electricity consumption in the mill and in the power plant have distinct influence on surplus electricity production.
Consequently, the performance of a co-generation plant can be accurately assessed only when all these factors are considered integrally and referred to a benchmarked figure for comparison. Energy inefficient areas can be detected for remedial actions to be taken. Electricity production and sugar recoveries are technical indicators for this performance evaluation.
Typical fFigures from Mauritian co-generation plants are used to benchmark the surplus electricity production for plants with low, medium and high-pressure boilers. Achievable targets with proven technologies shows that it ranged between 76 kWh/t cane to 143 kWh/t cane (433 to 815 kWh/t fibre) from the low- pressure to the high- pressure boiler range.
The financial incentives, endorsed by all stakeholders, under a bagasse energy co-generation program (1, 2, 3Deepchand, 2000, 2001; Kong Win Chang, 2001) aimed at enhancing the economic viability of the cane sugar industry and allowing Mauritius to diversify its energy base, were the key factors leading to a sharp rise in surplus electricity production. The inefficient back-pressure turbines and turbo-alternators are being phased out. New boilers have been installed, others upgraded, and the live steam is used to power the more efficient condensing-extraction turbo-alternators (CETA) to produce electricity for the entirely electrified factory and any surplus for export. The low-pressure steam, extracted from CETA is used, more efficiently in the quintuple, instead of quadruple effect evaporator stations. Energy surveys, aimed at optimizing the performance of co-generation plants, are being carried out by the MSIRI.
The technology and operating parameters for surplus electricity production are already well established and will not be discussed here. The prime purpose of this paper is to present a method to assess the performance of existing co-generation plants. In our approach, the real impact of each of the factors 2
influencing surplus electricity production is first overviewed, as it will allow us to rapidly identify, energy inefficient areas in a plant, i.e., where to concentrate our efforts. The next step is to consider all the influencing factors simultaneously and carry out a benchmarking process with existing equipment to ascertain that remedial action in a specific section of a plant will yield a significant rise in surplus electricity production. Lastly, benchmarking electricity...