Challenges and Prospects of Cogeneration and Energy Efficiency Improvement in Ethiopian Sugar Industry

Transcription

1 Proc. Ethiop. Sugar. Ind. Bienn. Conf., 1: (2009) FEATURE ARTICLE Challenges and Prospects of Cogeneration and Energy Efficiency Improvement in Ethiopian Sugar Industry Belay Dechassa Ethiopian Sugar Development Agency, P.O. Box , Addis Ababa, Ethiopia Abstract Price of sugar in the world market is very volatile and is in most cases below the cost of production of many countries. Moreover, sustainability of the sugar industries is becoming even worse with increasing petroleum price which is resulting in high rate of cost of sugar production. Thus, to ensure sustainability of their sugar industries many countries are taking different measures. In this regard, in Ethiopia, the government is planning to expand the existing three sugar mills and to establish a new sugar factory to operate four sugar mills with a total cane crushing capacity of 65,500 tons of cane per day (TCD) each having cogeneration and an ethanol plant. These sugar and ethanol production processes are energy intensive, requiring steam and electricity. While, the current scenario of the existing three sugar factories revealed that cogeneration in these factories is inefficient, operating with low pressure boilers and backpressure turbines generating electric power mostly for captive power use and partial requirements of irrigation and residential houses of the factory workers. Therefore, this paper was initiated to discuss prospects and challenges of cogeneration and energy efficiency improvement in the sugar industry of Ethiopia. Based on the analysis of the existing situation of the country with international scenario, the sugar industries of Ethiopia to become competitive in the international market, it needs to have an effective cogeneration scheme. However, a strong linkage between development in the sugar industry and power sector of the country is required. Moreover, unless there is an integrated policy of cogeneration linking sugar and electricity exports to the grid as a significant source of income to the industry, it is unlikely that cogeneration can be realized. Hence, Government s strong support in clearly defining the policy with respect to bagasse energy development is critical to the successful achievements of substituting bagasse cogeneration for imported fossil fuels or diversifying electric energy source based on renewable energy source. Introduction Increasing cost of sugar production from year to year and price volatility in sugar markets is substantially difficulty for many cane producing countries; hence the sugar industry is at stake. This could, however be reduced, by a number of methods that would increase revenues for non-consumable products derived from cane. Promotion of alcohol- fuelled vehicles (extensively carried out in ISSN print version,

2 Belay D. 138 Brazil) and expansion of bagasse-based cogeneration (extensively carried out in Mauritius and India) are measures taken to ensure sustainability and viability of the sugar industry (Aurelie, 2004). This is mostly done simultaneously with factory modernization and increasing scale of sugar production. Bagasse being a by-product of sugarcane industry has almost zero fuel cost. Historically, it is used in sugar industries for generating power to fulfill steam and electricity requirement of the mills. Feasibility studies of expansion and new sugar projects in Ethiopia have also showed that steam requirements of cane mills per ton of cane crushed vary between 550 and 400 kgs and the electric power requirement vary between 15 and 35 Kwh for low and high efficiency mills, respectively. Mass and energy balance computation showed that modern sugar factories with efficient cogeneration plant crushing cane of about 14 % fiber require about 60 to 70 % of bagasse produced for steam and electricity requirement of the mills. The remaining quantity can be used as raw material for paper production, other fibrous products or for production of extra electric energy in condensing mode turbines for sale to the grid. Whereas, old sugar factories with inefficient sugar mills and cogeneration plant consume the entire bagasse and in some cases even require additional fuel sources such as furnace fuel. Energy efficiency is defined as reducing the amount of energy used to accomplish exactly the same task. A well designed and operated cogeneration scheme will always provide better energy efficiency than conventional plant, leading to both energy and cost saving (Rick, nd ). Cogeneration is the simultaneous production of electric and thermal energy from a single energy system and source (Rick, nd). It is also known as combined heat and power technology. Cogeneration can be based on a wide variety of fuels. However, in the sugarcane growing countries, cogeneration from bagasse is becoming increasingly important (Kassiap, 2005). The reason cogeneration can make sense for production operations in sugar mills is that they can recover heat from exhaust steam of turbines, for juice heating, evaporation and sugar boiling. In addition, implementation of cogeneration will bring additional revenue to the sugar industry which is facing threats of price decline in the international sugar market. Besides cogeneration is a climate friendly technology that can attract Global Environmental Facility (GEF) funding as well as financing schemes such as Activities Implemented Jointly under the Kyoto Protocol Prototype Carbon Fund. Hence, most of the cane producing countries in African continent could benefit from such funding or scheme. In Ethiopia, the government is planning to expand the existing three sugar mills and to establish a new sugar factory to operate four sugar mills with a total cane crushing capacity of 65,500 tons of cane per day (TCD) each having cogeneration and an ethanol plant. These sugar and ethanol production processes are energy intensive, requiring steam and electricity. While, the current scenario

3 Cogeneration in Ethiopia 139 of the existing three sugar factories revealed that cogeneration in these factories is inefficient, operating with low pressure boilers and backpressure turbines generating electric power mostly for captive power use and partial requirements of irrigation and residential houses of the factory workers. Therefore, this paper was initiated to discuss prospects and challenges of cogeneration and energy efficiency improvement in the sugar industry of Ethiopia. Significance and Experience of Cogeneration in African Sugar Industry The sugar and alcohol production process is energy intensive, requiring both steam and electricity. Historically, sugar mills have been designed to meet their energy requirements by burning bagasse. This was seen as an economic means of producing electricity whilst cheaply disposing of bagasse. This, however, is often not in cogeneration mode since, until very recently, there has been no incentive to produce electricity efficiently due to the unavailability of tariffs for electricity produced by Independent Power Producers (IPPs) and sold to the grid. Much of the potential for energy generation has thus, so far, been wasted as there was no requirement for it. With the introduction of biomass feed-in tariffs in countries such as Brazil, Mauritius and parts of India, there are now great opportunities for sugarcane-producing countries to learn from the best practices around the world. In addition, over the years the energy requirements of sugar mills have increased, both in and out of season. This has mainly been due to the development of downstream units such as distilleries as well as ethanol, chemical, paper, effluent treatment and biogas generation plants. The establishment of settlements around mills, with their related social, educational and commercial activities, has also contributed to increased electricity demand. In countries such as India, this has compelled sugar mills to buy electricity from utilities and use non cane-based fuels to meet energy requirements, particularly out of season (Source). In the case of the least energy-efficient mills, such demand would be quite high. The main reasons for viability of cogeneration are due to the following facts as stated by Aurelie (2004): Cogeneration helps to reduce CO 2 emissions significantly there by deliver significant CO 2 benefits. It also reduces investments into electricity transmission capacity, avoids transmission losses, and ensures security of high quality power supply. The initial investment in cogeneration projects can be relatively high but payback periods is between 3-5 years might be expected.

4 Belay D. 140 The payback period and profitability of cogeneration schemes depends crucially on the difference between the fuel price and the sales price for electricity. Global environmental concerns, ongoing liberalization of many energy markets, and projected energy demand growth in developing countries are likely to improve market conditions for cogeneration in the near future. Near-zero fuel costs (paid in local currency), commercial use of a waste product and increased fuel efficiency leading to an increase in the economic viability of sugar mills Cogeneration plants using bagasse and other biomass could mitigate the impacts of drought on hydropower availability. A number of countries, in particular those devoid of any fossil fuel, have implemented energy conservation and efficiency measures so as to minimize cogenerated energy (steam and electricity) utilized in cane processing and export excess electricity to the grid (Kassiap, 2005). Most of cogeneration plants in African sugar mills are inefficient, operating with low-pressure boilers generating electric power mostly for captive power use. According to the assessment of AFREPREN/FWD Cogen for Africa project cogeneration system almost in all seven Eastern and Southern African countries namely Kenya, Ethiopia, sudan, Tanzania, Malawi, Swaziland and Uganda is inefficient and can only meet their factory energy demand Almost all the sugar factories of these countries use low pressure boiler and backpressure turbine systems for cogeneration to meet their factory energy demand. In some of the sugar factories of Kenya because of old equipment used for energy generation, are net importers of electricity (Stephen and Kithyoma, 2006). The Ethiopian sugar factories use electricity from the national grid for fulfilling the partial requirement of irrigation and residential houses of the factory workers. Tanzania, Malawi, Ethiopia, Sudan, Swaziland and South Africa have plans to expand their sugar industries, which include expansion of cogeneration to cover their energy requirements and sell excess power to the grid (Stephen and Kithyoma, 2006). Mauritius has progressed quite well in implementing efficient cogeneration plants. Currently it meets close to 40 % of its electricity supply from bagasse and coal cogeneration. Bagasse constitutes about 44 % of the cogenerated power. It is reported that the average kwh/ton cane processed in 1988 was 13 and even after implementation of the projects up to the year 2000, the value has reached 60 kwh per ton of cane. In Mauritius 10 out of 11 factories are exporting electricity to the grid during crop season out of which three are using coal as a complementary fuel to export electricity during the offseason (Kassiap, 2005).

5 Cogeneration in Ethiopia 141 Opportunities for Raising Scale of Cogeneration in Ethiopia The Existing Cogeneration and Future Plan There are four sugar mills with a total cane crushing capacity of 12,500 tons of cane per day (TCD). Total annual sugar production from all factories varies between 275,000 and 315,000 tons. The existing cogeneration capacity of the existing Ethiopian sugar factories is shown in Table 1. Table 1. Cogeneration status in the existing sugar factories of Ethiopia Sugar Factory Factory Capacity (TCD) Boilers capacity (t hr -1 ) Steam pressure bar (g) Steam temperature ( o C) Turbo alternator, (MW) Steam/power rate (kg kw -1 ) Wonji x x Shoa x x Metahara x x x x3.3 9 Finchaa x x3.3 9 Source: Finchaa Sugar Factory, 2004; Metahara Sugar Factory, 2006; Wonji-Shoa Sugar Factory, 2001 The Ethiopian Government, with an ambitious plan of boosting sugar production capacity of the country to the extent of 5 fold of the present capacity has embarked upon development program of expanding the existing three sugar factories and installing a green field sugar factory with a capacity of 26,000 TCD. At steady state Ethiopian sugar production from all the sugar factories is planned to reach 1.5 million tons after 6 years. The total cogenerated power for sale to the national grid from all the sugar factories is planned to be about 178 MW and ethanol production about 128 million litres per year. The mechanisms by which this plan to be realized is through improving energy efficiency and expanding existing factories and by installing new sugar factory. Improving Energy Efficiency of the Existing Sugar Factories Bagasse is a fibrous sugar cane by-product obtained after crushing and extraction of juice. The quantity of bagasse is directly proportional to the fibre content of cane. The fibre content of cane generally lies in the region of %. Therefore the quantity of the bagasse varies between 25 and 32 % by weight of cane.

6 Belay D. 142 The net calorific value (NCV) of bagasse with 50 % moisture content is about 1800 Kcal/kg and depending on the boiler efficiency (low to high) steam ratio to bagasse varies between 1.8 and 2.5. Also depending on the pressure and temperature of steam and type and technology level of turbo-alternators electric power generation rate per unit amount of steam for typical low pressure and high pressure turbo-alternators varies as shown in Table 2. Table 2. Power generation rate per unit amount of steam Type of Turbo-alternator Initial steam temperature ( o C) Pressure bar (a) inletoutlet Power production rate Kg Kwh -1 Back pressure Single extraction back pressure Average ( based on the process and cogeneration steam demand) Double extraction condensing Average (based on steam demand of the process and cogeneration) 5.57 Moreover, the power production per ton of cane processed depending on the efficiency of power plants varies as follows: Conventional low efficiency power plants with low pressure boilers (20-30 bar (g)) and back pressure turbines kwh t -1 cane Power plants operating with 40 bar (g) 60 kwh t -1 cane Power plants operating with 64 bar (g) kwh t -1 cane Power plants operating with 82 bar (g) 125 kwh t -1 cane The two key measures of energy improvement in the sugar factories are replacing inefficient, often single wheel turbines with electric drives and

7 Cogeneration in Ethiopia 143 reducing the evaporator steam consumption, these being the main users of steam in the factory. In addition changing from milling to diffusion also reduces the electric power consumption of the factory although it increases the evaporation load. Modern cogeneration turbines have specific steam consumptions approaching half that of typical mechanical drive turbines. Installing pre-evaporator and increasing the number of effects on the evaporator, using continuous vacuum pans for sugar boiling can also have a dramatic impact on the availability of power for export. Other way of improving the overall sugar factory energy efficiency is by improving the quality of bagasse fed to the boilers. It is important when considering bagasse quality to look at the total non-combustibles-ash and moisture-combined. There are therefore two possibilities, improving the moisture content and reducing the ash. The effect is predicted by the South African Mill Research Institute (SMRI) formula: NCV= B W C kcal kg -1 Where: B= Brix (soluble solids) % bagasse C= ash % bagasse W= moisture % bagasse For each 2 % decrease in moisture content of bagasse NCV bagasse increases by 5.6 %. The possible modifications to decrease bagase moisture content are: Flue gas drying of excess bagasse to increase combustion efficiency; Baling of surplus bagasse to improve its storability and use beyond the milling season and Installing air pre-heaters and economizers on the boilers Given that the bagasse is a constant, what does one do with the surplus steam arising from adding effects to the evaporator station and taking other efficiency measures? There is a spectrum of possibilities to answer this question ranging from condensing it all to not generating it but storing the bagasse instead. The correct solution needs to consider ensuring firm power by arranging auxiliary fuel and a low grade heat dump. In high fibre cane areas with low power price the correct solution may be not to make the factory too efficient and thereby hold down capital cost. Before considering cogeneration, one must first examine steps to optimize existing operations with minimal investment. In other words, one should find and implement the low cost or no-cost investment steps to improve site efficiency. An example might include burner management. Bagasse energy projects are linked with sugar factory modernization in that boilers, turbo

8 Belay D. 144 alternators and energy efficient equipment represent a major proportion (up to 50 %) of the cost of sugar factory. Linking energy projects to modernization and higher scale of production brings about reduction in cost of production. The sale of electricity adds to the revenue of sugar companies. Expansion of Existing Factories The existing two old mills of Wonji-Shoa sugar factory will be scrapped and one factory of TCD will be installed in two phases. Metahara and Finchaa sugar factories will be expanded to capacities of 15,000 TCD and 12,000 TCD respectively, both in two phases (Table 3). Table 3. Cogeneration plan in Ethiopian Sugar Factories after expansion Parameters Wonji-Shoa Metahara Finchaa Crushing capacity(tcd) Boiler capacity (t hr -1 ) 2x30 2x165 2x110 Steam pressure bar(a) Steam T o ( o C) Steam to bagasse ratio (Kg kg -1) DEC-TA (MW) 2x30 2x30 2x8.5 Steam/power rate (kg/kwh -1 ) Total power (MW) Expansion power (MW) Source: Finchaa Sugar Factory, 2004; Metahara Sugar Factory, 2006; Wonji-Shoa Sugar Factory, 2006 Installing New Factory New Tendaho sugar Factory project will be installed in two phases. The initially capacity will be 13,000 TCD and final one 26,000 TCD. Estimated investment cost of Tendaho Sugar factory including the complete cogeneration plant is US$ 366 million. Out of this amount US$ 180 million is the cost of the cogeneration plant. The estimated investment cost of cogeneration plant devoted for export power amounts to US $ 110 million. Economic Feasibility of Cogeneration in Ethiopia with Special Emphasis to Tendaho Sugar Project The expansion and new sugar factory projects have plans to integrate sugar and electricity production. With this plan, from Wonji-Shoa, Metahara, Finchaa and Tendaho sugar factories, 40.7,41.82, 9.00 and MW power will be congenarted and be available and to be sold to the national grid after fulfilling the captive requirement for sugar and ethanol processing, respectively (Table 2). In general a total of 178 MW cogenerated power will be sold to the national grid from all the sugar factories during the season days.

9 Cogeneration in Ethiopia 145 On the other hand, an economic analysis of cogeneration for Tendaho sugar factory project indicated that cogeneration will result in an estimated profit of US$ 2.0 per ton of cane at electric power tariff of 0.04 US$ kwh -1 or US$ 3.4 kwh -1 at power tariff of US$ 0.06 kwh -1. Payback period is 9 and 5 years respectively. Table 4. Economic benefits from cogeneration of power at Tendaho Sugar Factory Project Description Unit Tendaho Bagasse available to burn in boilers after deducting 0.5 % windage loss (28.37 %) t h Steam to bagasse(50 % moisture) ratio Steam utilized at DEC TA set t h Estimated average specific steam consumption for steam flow condition considered for Kg KWhr diffusion option Estimated power generation per ton cane kwh Estimated captive power required to process one ton cane (in diffuser option) kw Balance power available for export, per ton cane Kw Considered 90 % of this figure, net available for export (0.9 x 80) Kw Power US$ 0.04/kWhx US$ Estimated renewable energy credit per kwh US$ Estimated revenue from one ton cane from power export US$ Estimated cane processed per year tons Estimated annual Revenue US$ 19, 235,666 Less estimated annual operating cost (excluding bagasse cost) US$ (5,930,000) Less financial cost per annum US$ (909,000) Revenue less operating & financial cost US$ 12,396,666 Estimated additional investment cost for co-generated export power US$ 110,000,000 Payback period based on US$ 0.04/kwh years 9 Payback period based on US$ 0.06/kwh years 5 Challenges for Cogeneration and Energy Efficiency Improvement Energy Efficiency Improvement In order to increase energy efficiency in the old sugar mills, one needs to initially make thorough assessment of the condition of plant and equipment, process parameters and record the findings including the data of inputs and outputs at each process stage. Following which mass and energy balance calculation and proper diagnosis and analysis is done in order to identify the correct measures to

10 Belay D. 146 be taken. The result may indicate to either renovate the existing equipment or substitute them with new and better capacity once. Energy efficiency improvement is effectively done if coupled with expansion of sugar production. Some times complete substitution of the plant is preferred if the equipments are very old and their renovation require large investment with out resulting any or small increase of production or productivity. Wonji-Shoa factory Rehabilitation, Optimization and expansion study revealed that it was preferable to scrap the existing old sugar mills and substitute by one new and better capacity sugar factory in order to maximize profitability. Cogeneration Moderate cogeneration efficiency increase could be done in old sugar factories by renovating the necessary equipment, optimizing process and substituting or installing additional once. However, the additional investment incurred should be weighed against the additional profit obtained from the electric energy sales. Cogeneration efficiency improvement is better coupled with expansion of sugar production in order to optimize the benefit. Very efficient and complete cogeneration efficiency could be carried out with integration to establishment of big scale new sugar factories preferably with capacities of 500 tons of cane per hour and above. This allows utilization of cogeneration equipment with state of the art technologies. The planned Tendaho Sugar Factory Project evidences this fact. Conclusion and Suggestions The sugar industries of Ethiopia to become competitive in the international market, it needs to have an effective cogeneration scheme. However, a strong linkage between development in the sugar industry and power sector of the country is required. Moreover, unless there is an integrated policy of cogeneration linking sugar and electricity exports to the grid as a significant source of income to the industry, it is unlikely that cogeneration can be realized. Hence, Government s strong support in clearly defining the policy with respect to bagasse energy development is critical to the successful achievements of substituting bagasse cogeneration for imported fossil fuels or diversifying electric energy source based on renewable energy source. References African Regional Coverage Reporting Service,UNIDO First High-level Biofuels Seminar in Africa. International Institute for Sustainable Development Bulletin.

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