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Energy for Sustainable Development 23 (2014) 266–274

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Energy for Sustainable Development

Review

Energy efficiency and greenhouse gas emission reduction potentials in sugar production processes in Thailand Sumate Sathitbun-anan a,b,⁎, Bundit Fungtammasan a,b, Mirko Barz c, Boonrod Sajjakulnukit a,b, Suthum Pathumsawad d,b a

The Joint Graduate School of Energy and Environment, King Mongkut's University of Technology Thonburi, Bangkok, Thailand Center for Energy Technology and Environment, King Mongkut's University of Technology Thonburi, Bangkok, Thailand HTW — Hochschule für Technik und Wirtschaft Berlin, Germany d King Mongkut's University of Technology North Bangkok, Bangkok, Thailand b c

a r t i c l e

i n f o

Article history: Received 12 March 2014 Revised 26 September 2014 Accepted 26 September 2014 Available online xxxx Keywords: Thai sugar industry Energy consumption Energy efficiency Energy efficient technologies and measures GHG emission

a b s t r a c t Sugarcane is one of the most promising sources of green energy for a major sugar producing country like Thailand. Any efforts to improve energy efficiency in sugar industry would result for green energy production and more avoided GHG emissions. This paper assesses the potentials for energy saving and GHG emission reduction in sugar production in Thailand. It is found that there is a wide gap between the most efficient mills and the less efficient ones among the country’s 47 mills, with specific steam consumption ranging from 400 to 646 kg steam/ ton cane. Thus significant potential exists for energy saving and GHG emission reduction in many mills, using some of the 17 commonly common technologies/measures identified. For the nine mills studied, which could have resulted in a combined saving savings of 23–32% of the total mill energy consumption, further savings of 5–14% could be achieved. © 2014 International Energy Initiative. Published by Elsevier Inc. All rights reserved.

Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . Methodology . . . . . . . . . . . . . . . . . . . . . . . . . Collecting baseline energy consumption data . . . . . . . . . Estimating the baseline CO2e emission . . . . . . . . . . . . Identification of energy efficiency technologies and measures . . Investigating the extent of energy efficiency improvement efforts Results and discussions . . . . . . . . . . . . . . . . . . . . . Overall energy consumption of sugar mills . . . . . . . . . . Baseline process steam and power demand . . . . . . . . . . Greenhouse gas emissions . . . . . . . . . . . . . . . . . . Energy efficiency technologies and measures . . . . . . . . . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . Appendix A. . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Introduction The industrial sector in Thailand is the largest energy-consuming sector with a share of 36% of total final energy consumption in 2012 ⁎ Corresponding author. E-mail address: [email protected] (S. Sathitbun-anan).

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(DEDE, 2012). Although there have been numerous efforts in improving energy efficiency in this sector over the years, well-structured approaches for specific industry types based on energy-saving potential analysis of process-specific technologies are lacking (Hasanbeigi et al., 2010). Since Thailand is the world's fourth largest sugar producer and the second largest sugar exporter after Brazil, producing annually about 95 Mt and 9.5 Mt of sugarcane and sugar respectively (OCSB,

http://dx.doi.org/10.1016/j.esd.2014.09.010 0973-0826/© 2014 International Energy Initiative. Published by Elsevier Inc. All rights reserved.

S. Sathitbun-anan et al. / Energy for Sustainable Development 23 (2014) 266–274

2012; Gudoshnikov et al., 2010), energy efficiency improvements in this sector can have a significant positive impact on both the Thai economy and the environment. Currently there are 47 sugar mills distributed throughout Thailand and the growth of sugarcane production is expected to reach more than 100 Mt of cane in 2012 (OCSB, 2012). These days sugar mills do not only produce sugar but also supply green electricity to the grid (PDTI, 2011; Ram and Banerjee, 2003; Nguyen et al., 2009). In fact the Thai sugar industry is already supplying approximately 610 MW of electricity to the grid using bagasse as fuel and generating a large amount of steam for its own use in the mills (PDTI, 2011). However the average export of electricity is only 14 kWh/tc (ton cane) as compared to 70 kWh/tc (Siemers, 2009) and 100 kWh/tc in more efficient mills in Thailand and in Brazil respectively (Isaias et al., 2008). In the Thai sugar production process, although the average specific steam consumption of about 369 kWh/tc (OCSB, 2010) is very close to the international average of 363 kWh/tc (Bocci et al., 2009), it is considerably higher than the specific consumption of 286 kWh/tc in highefficiency mills in Thailand (JGSEE, 2011). Therefore there is much room for energy efficiency improvement in this sector, which will result in more bagasse available for energy production and additional economic benefit to the sugar millers, particularly from selling surplus electricity to the grid. Since the generation of electricity from bagasse emits only 26 kg of CO2e per MWh as compared to 621 kg of CO2e per MWh from fossil fuels in the Thai context (Siemers, 2009), energy efficiency improvement in sugar production will result in significant CO2e savings as well. However open literature on energy efficiency and greenhouse gas (GHG) emission in sugar mills is scarce. Among the few reports that are available, only major forms of energy efficiency measures are reported (see Sattari et al. (2007) for example). A systematic study to determine the potentials and approaches for energy saving and GHG emission reduction in Thai sugar mills has thus been initiated by the authors, with an aim to identify best practices and provide policy recommendations for the removal of barriers to implementing energy saving technologies and measures. In this paper, we analyze the potentials for energy saving and GHG emission reduction by investigating the energy consumption patterns and the energy efficiency technologies and measures that could potentially be applied in the sugar production processes. Methodology The study begins with the collection of baseline steam and electricity consumption data for selected sugar mills; an estimation of the GHG emissions associated to sugar production; identification of currently available energy efficiency improvement technologies/measures and their potentials; and assessment of the extent to which these technologies and measures have been applied in Thai sugar mills. Collecting baseline energy consumption data Thai sugar mills can be categorized into three production capacity ranges: i) Small (less than 10,000 tc/d or tonnes of cane per day), ii) medium (10,000 to 20,000 tc/d) and iii) large (more than 20,000 tc/ d), each contributing about 41%, 42% and 17%, respectively, of the total sugar production capacity (OCSB, 2007). In this study, field surveys are to be carried out to collect the baseline data of nine mills from their daily production report and estimated electric and steam consumption in each process. The nine mills, with a combined capacity of 55% of the country's total capacity (OCSB, 2007), are categorized into three groups, each consisting of three mills, representing production capacities of 22%, 15% and 18% within the small, medium and large categories mentioned above. One sugar mill from each category, i.e. mills A, B and C, who has provided the most complete data set required for the analysis, is then selected for detailed analysis. The capacities of mills A, B and C are 9480; 12,000 and 32,160 tc/d, respectively.

267

Estimating the baseline CO2e emission Since bagasse is practically the only source of energy in the sugar mill production process in Thai sugar mills, the associated GHG emissions are estimated from the burning of bagasse only. According to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, during biomass combustion carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are released. Since CO2 emissions from bagasse burning are not deemed as contributing to net greenhouse gas emissions because the CO2 emitted is re-absorbed by plants in the next cultivation season, this study therefore takes into account only other gases aside from CO2 and converts them into their carbon dioxide equivalent (CO2e). It is generally known that burning 1 TJ energy equivalent of bagasse emits about 30 kg of CH4 and 4 kg of N2O, (IPCC, 2006; Yuttitham et al., 2011). According to the Thai Office of Cane and Sugar Board (OCSB) report, 5 kg of bagasse burnt is sufficient to generate 10 kg of steam (20 bar 360 °C); and 10 kg of steam can produce 1 kWh of electricity. Therefore CO2e emission from electricity and steam consumption in sugar mill processes can be estimated by using the CO2 equivalent factor for CH4 and N2O, which are 25 and 298 respectively (IPCC, 2007; Yuttitham et al., 2011). The CO2e emission in the sugar mill process is calculated from Eqs. (1)–(3) as shown in Appendix A. Identification of energy efficiency technologies and measures Energy efficiency technologies and measures that could potentially be applied to the Thai sugar industry are to be identified by i) reviewing the best practices that had been reported earlier by the OCSB based on the experiences of 4 sugar mills (OCSB, 2007), and ii) examining the experiences of 5 additional energy-efficient mills belonging to a large sugar production group. Investigating the extent of energy efficiency improvement efforts To investigate the extent to which the energy efficiency technologies and measures identified in the previous section have been implemented in both efficient and inefficient Thai sugar mills, a detailed survey is to be conducted at the 3 sugar mills (A, B and C) mentioned above, each representing a production capacity range (see Overall energy consumption of sugar mills section). A correlation will then be made between the energy performance of these mills and the number and type of technology/measure implemented. Results and discussions Overall energy consumption of sugar mills Based on the overall steam and electricity consumption data and the amount of cane processed in each mill, the specific steam consumption (SSC) (kg steam/tc) and corresponding specific energy consumption of the nine selected sugar mills can be calculated. The result is plotted in Fig. 1 according to the mill capacity. From this figure, it may be inferred that the energy performance of the nine sugar mills may be roughly classified into three groups on the basis of their SSC as follows: high efficiency mills (less than 450 kg steam/tc), medium efficiency mills (between 450 and 600 kg steam/tc), and low efficiency mills (more than 600 kg steam/tc). As a consequence, 3 of the 9 mills are in the high efficiency category with SSC around 400–420 kg steam/tc, 2 are in medium efficiency category, and 4 are in the low efficiency category. A previous study (OCSB, 2007) also reported SSC for 3 other mills that fall in this range, namely 526, 533, and 630 kg steam/tc, as shown the figure (triangle). It should be noted that there is wide gap between high and low efficiency mills, with SSC ranging from 400 to 650 kg steam/tc.

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Baseline process steam and power demand Detailed steam and electricity consumptions of three mills (A, B and C) have been accounted. The energy used in a sugar mill is supplied primarily by bagasse, which could be estimated from the amount of bagasse utilized and its heating value. Since 100 kg of crushed sugarcane could produce 29 kg of bagasse and the net calorific value (NCV) of bagasse (at 50.7% moisture) is 7.37 MJ/kg of bagasse (OCSB, 2007), the amount of energy that can be derived from the bagasse for mills A, B and C is about 706, 824 and 1667 GWh, respectively. A portion of this energy input is used to generate electricity in the co-generation plant: 30 GWh or 4% in mill A, 75 GWh or 9% in mill B, and 90 GWh or 5% in mill C (see Fig. 2). 73–79% of the bagasse energy is used in the sugar production processes, and the remaining 16–20% is lost. Their detailed usage of steam and electricity is described in the following section. A simplified flow diagram for the sugar production process is illustrated in Fig. 3 which indicates the major energy flows (steam and electric power) in each process. The information is obtained from a mill with a production capacity of 12,000 tc/d (mill B) (PDTI, 2011; OCSB, 2007). Similar energy flow diagrams have also been obtained for mills A and C. In this particular mill bagasse is used in the boiler to produce steam at 30 bar, about 60% of which is used to generate electricity in a co-generation plant, with the remaining 1.2 bar being supplied to the sugar production process. Surplus electricity from in-house usage in the boiler and sugar production is sold to the grid. The first step in sugar production is the extraction of juice from the cane in a mixed-juice process. The unloaded cane is cleaned and then fed to size reduction and milling processes, which consume 230 kg steam/tc (30 bar, 390 °C) and use 2540 kW of power. The juice is then evaporated in two stages in the raw syrup production process. The first stage is juice-concentration. The clarified juice is passed through a station consisting of five-effect evaporators. Evaporation is one of the most energy intensive operations in sugar mills (Ecoinvest, 2000). The resulting syrup is then filtered and fed to the vacuum pans for crystallization. This syrup production process in the first stage consumes 560 kg steam/tc (1.2 bar, 130 °C) and requires 26 kW of power. The second evaporation stage is sugar crystallization in which 120 kg steam/tc (0.5 bar, 115 °C) and 1595 kW are required. The mother liquor resulting from crystallization is passed on to a vacuum pan to produce raw sugar, which is then separated from the molasses and introduced to storage in a raw sugar silo (OCSB, 2007). The energy consumed is 70 kg steam/tc (0.5 bar, 115 °C) with the power demand being 301 kW. The resulting molasses (B-molasses), being of much lower purity than the first molasses, goes through a series of re-boiling, crystallization and centrifugal separation to produce low-

grade cane sugar and the final molasses — a heavy and viscous material. The total power demand here is 376 kW with the steam consumption being 14 t steam/h (0.5 bar, 115 °C). In addition 1860 kW is needed for the lighting and liquid pumping system. Table 1 summarizes the electricity and steam demand in each process of the A, B, and C mills. It can be seen that the main energy requirement of sugar production is thermal energy, being 10 times more than electrical energy. The highest thermal energy demand is evaporation in raw syrup production, followed by crystallization, and the raw sugar process involving crystallization in vacuum pans. The electrical, steam and total energy consumption of A, B, and C mills are: 25, 21 and 21 kWh/tc; 646, 410 and 418 kg steam/tc, and 476, 414 and 339 kWh/tc, respectively. Internationally the specific electricity consumption ranges from 15 to 35 kWh/tc, the average specific steam consumption being 500 kg steam/tc or 338 kWh/tc, and the specific energy consumption (electric and thermal) being 363 kWh/tc (Bocci et al., 2009). The energy consumption of mill A, which is an old mill, is therefore significantly higher than international average, while that of mill B, being a relatively new mill, significantly lower. Although mill C is also a relatively old mill, its performance is significantly better than the international average because the mill management implemented a number of efficient technologies and measures, including a strong commitment from management (see Table 5). Raw syrup production is the most energy intensive process in sugar production, involving a high percentage of steam consumption (about 85% of total energy consumption) in evaporation, followed by crystallization (15–18%) and raw sugar production (9–13%). Greenhouse gas emissions The estimated CO2e emission of each process in mills A, B and C is summarized in Table 2. It should be pointed out that because process 3 (crystallization), process 4 (raw sugar) and process 5 (molasses) use steam generated from the evaporator in process 2 (raw syrup), not fresh steam from the boiler. A reasonable estimate of the CO2e emission for process 2 itself is the difference between the emission due to steam input into process 2 and that due to the three processes mentioned above. The total CO2e emission of A, B, and C mills are found to be 7, 6 and 5 kg CO2e/tc, respectively, with more efficient mills emitting less CO2e as expected. They are significantly higher than the emission reported in a previous study that shows 4 kg CO2e/tc or 0.04 kg CO2e/kg sugar, based on an average of 4 very efficient Thai mills (Yuttitham et al., 2011). However even this is still significantly higher than the Brazilian

Fig. 1. Specific steam consumption (kg steam/tc) and specific energy consumption (GJ/tc) (in brackets) of selected sugar mills; nine mills from this study, and 3 mills (triangle) from a previous study (OCSB, 2007).

S. Sathitbun-anan et al. / Energy for Sustainable Development 23 (2014) 266–274 Heat losses 20%

Bagasse energy 706 GWh/year

Mill A

Bagasse energy 824 GWh/year

Bagasse energy 1,667 GWh/year

Heat losses 18%

Mill B

Process heat 75.7%

Heat losses 16%

Mill C Process heat 78.6%

Process heat 72.9%

Electric power 9.1%

Electric power 4.3%

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Electric power 5.4%

Fig. 2. Overall steam and power flow of sugar mills (mill B, 12 Mtc/d).

average of 2.2 kg CO2e/tc (based on a average of 44 mills with integrated ethanol production) (Isaias et al., 2008). In general, Brazilian sugar mills are more efficient because they adopt an integrated process in which typically half of the juice from the extraction system is used for sugar production and the other half for ethanol production (Ensinas et al., 2007). The highest CO2e emission is found to be in the raw syrup process, being in the range of 43–50% of total emission, followed by crystal production in the range of 6–10% of total emission. Energy efficiency technologies and measures Seventeen energy efficiency technologies and measures are found to have been already applied in Thai sugar industry. Out of these, eleven are cited from the OCSB report (OCSB, 2007), which includes: extended period of blow down inside the boiler, optimum/sufficient hot water use in cane crushing, raw syrup brix improvement, effective insulation, more efficient bagasse dryer, replacing steam turbine by motor drive

in furnace, replacement of open gear by planetary gear on first crusher stage, additional jet vacuum on the evaporator and vacuum pan, replacement of AC motor by DC motor on the vacuum pan, and replacement of an optimum (smaller) motor on the drying blower. The remaining technologies and measures identified in this study are those applied in an efficient Thai mill (ETM), which include: replacement of a turbine drive by an AC motor for cane cutting knives, replacement of a turbine drive by an AC motor drive for feed water pumps, installation of an inverter to modulate the motor for driving feed water pumps, use of high efficiency lighting, installation of a capacitor for adjusting the power factor from 0.75 to 0.85, and installation of an additional evaporator for improving the raw syrup brix (70). A description of these technologies and measures and their estimated energy saving potentials are given in Table 3. The efficiency values mentioned in Table 3 are derived from literature (OCSB, 2007) and from the present study (survey result of efficient Thai mills or ETM). The above list reveals that there are a number of energy efficient measures/technologies that could potentially

13 MW e supply to the grid 390 kg steam/tc (30 bar 390 ºC)

Co-generate plant 9 MW e supply to sugar process

Boiler Bagasse input 39kg/s output: 640 kg steam/tc (30 bar 390 ºC) inhouse:20 kg steam/tc (30 bar 390 ºC)

60 kg steam/tc (1.2 bar 130 ºC)

230 kg steam/tc (30 bar 390 ºC)

330 kg steam/tc (1.2 bar 130 ºC)

Mix juice process

560 kg steam/tc (1.2 bar 130 ºC)

Raw syrup process 300 kg steam/tc (0.5 bar 115 ºC) by evaporating clarified juice

560 kg sat water/tc (0 bar 99 ºC) 82 kg steam/ tc (0.5 bar 115 ºC) 82 kg sat water/ tc (0 bar 99 ºC)

Refine sugar

28 kg steam/ tc (0.5 bar 115 ºC)

70 kg steam/tc (0.5 bar 115ºC)

120 kg steam/ tc (0.5 bar 115 ºC)

Pre-heat

Water Tank

28 kg sat water/tc (0 bar 99 ºC) 70 kg sat water/tc (0 bar 99 ºC)

Molasses process

Raw sugar process steam condensed in B-Vacuum pan (0 bar 99 ºC)

Crystallization process steam condensed in A-Vacuum pan (0 bar 99 ºC)

120 kg sat water/tc (0 bar 99 ºC) Fig. 3. Schematic diagram of sugar production processes and their steam consumption in a typical sugar mill (mill B).

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Table 1 Summary of steam and electricity consumption in sugar production in mills A, B and C. Process

Boiler (in house)

Mill

A B C Mixed juice production A B C Raw syrup production A B C A Crystal productiona B C a A Raw sugar production B C A Molasses productiona B C Lighting and liquid pump system A B C Other process system A B C Office & service A B C A Overall SECb B C International SEC (Bocci et al., 2009, Ecoinvest, 2000 and Morand et al., 2004) c Brazil (Isaias et al., 2008) a b c d

Electricity consumption

Steam consumption

kWh/tc

kg steam/tc

kWh/tc

kWh/tc

Total energy consumption

4.6 4 3 2.5 5.08 NA 1.12 0.05 1.5 1.8 3.19 5.33 1.08 0.6 1.3 2.47 0.75 2.11 3.75 3.72 3 4.7 0.61 0.21 3 3 4.5 25 21 21 15–35 30

25 (20 bar, 360 °C) 20 (30 bar, 390 °C) 15 (20 bar, 360 °C) 401 (20 bar, 360 °C) 230 (30 bar, 390 °C) 239 (20 bar, 360 °C) 621 (1.2 bar, 130 °C) 560 (1.2 bar, 130 °C) 448 (1.2 bar, 120 °C) 101 (0.5 bar, 115 °C) 120 (0.5 bar, 115 °C) 90 (0.5 bar, 115 °C) 88 (0.5 bar, 115 °C) 70 (0.5 bar, 115 °C) 49 (0.5 bar, 115 °C) 38 (0.5 bar, 115 °C) 28 (0.2 bar, 105 °C) 30 (0.5 bar, 115 °C) NA

3.1 2.7 1.8 48.3 30.9 28.9 399.4 359.4 287.2 64.1 76.1 56.8 56.0 44.4 30.6 24 17.6 18.9

7.7 6.7 4.8 50.8 36.0 28.9 400.5 359.5 288.7 65.9 79.3 62.1 57.1 45.0 31.9 26.5 18.4 21.0 3.7 3.7 3.0 4.7 0.6 0.2 3.0 3.0 4.5 475.8 414.0 338.9 363.1 308.9

NA

NA

646 (20 410 (30 418 (20 500 (21 340 (65

bar, 360 bar, 390 bar, 360 bar, 300 bar, 480

°C) °C) °C) °C) °C)

450.8 393.0 317.9 338.1 278.9d

Steam consumption from evaporation process in raw syrup production. Specific steam consumption calculated from the sum of: the proportion of steam used for generating process steam, and steam used in boiler and mixed juice production. Average of 44 mills with integrated ethanol production. Energy consumption calculated from steam consumption.

be applied in Thai sugar mills, with potential savings being up to 11% of the total energy consumption of the mill. The provision of optimum hot water supply to the cane crusher (for juice extraction) appears to have the highest potential (10–11% saving), followed by replacing the open gears by planetary gears on the first crusher stage (5.5–7% saving) and installing a bagasse dryer (2–9% saving). Other measures of interest include: syrup concentration control in the evaporator (2–3% saving), installing an additional jet vacuum in the evaporator (0.3–0.7% saving) and vacuum pan (1–3.5%), replacing inefficient steam turbines by electric motors (0.4–6.5%), and installing a power factor adjustment capacitor (1.25%). Table 4 shows the sum of the typical potential savings when the technologies and measures are applied to the main production processes. It can be seen that, typically, the highest saving potential exists in the mixed juice production process (19–26% of the total mill consumption), followed by boiler house (3–10%), raw syrup production (3–5%) and crystal production (2–5%). In order to determine the extent to which the above energy efficiency technologies and measures have been applied in Thai sugar mills, a survey based on questionnaires was conducted for nine sugar mills (mills A–I), and the results are summarized in Table 5, which shows the sum of the estimated savings that could have been achieved from energy-efficiency technologies and measures already applied, and the estimated potential saving if the remaining technologies/measures listed above were applied. The number of technologies/measures already applied in each mill surveyed ranges from 7 to 13 (out of a total of 17), suggesting that each of the mills could have saved 23–32% of total plant energy

consumption based on the typical saving potentials of each measure. Generally higher efficiency mills (mills B, C and I) have applied 10 or more technologies/measures. However, the age of the mill is also an important factor. Mills B and I, with about 400 kg steam/tc, for example are relatively new mills that use more advanced technology. Mill I in particular is a new plant that uses the most advanced technology in Thailand, with integrated sugar and ethanol production like those in Brazil. Mill A, on the other hand is a very old one that lacks not only energy management but also preventive maintenance of its production facilities. It should be noted that out of the 17 energy efficiency technologies and measures described in Table 3, only 3 technologies (3, 8, and 17), each with a saving potential in the range of about 0.3–3%, could be applied for the raw syrup production process, which is the most energy intensive process, and that the total potential saving that could result from applying these technologies in this process are in the range of only 3.1–5.3% of mill consumption (Table 4). Therefore, additional energy-efficient technologies and measures that have not been tried in the mills surveyed here will be needed to yield greater energy savings and GHG emission reductions. Examples of these technologies/measures include: maximizing evaporation efficiency by adding a higher number of effects of evaporators or multiple effect evaporators, thus increasing the solid content of the syrup as high as possible (Ensinas et al., 2007; Ram and Banerjee, 2003); and the use of heaters for the first stage heating of mixed juice (from the mixed juice process) with waste steam from the cogeneration plant. In the latter measure, the temperature of the mixed juice is increased before entering the next stage of raw sugar syrup production, which would then help

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Table 2 Summary of CO2e emission in sugar production in mills A, B and C. Process

Boiler (in house)

Mill

A B C Mixed juice production A B C Raw syrup production A B C Crystal production A B C Raw sugar production A B C Molasses production A B C Lighting and liquid pump system A B C Other process system A B C Office & services A B C A Total CO2e emission B C CO2e emission (average of 4 mills) (Yuttitham et al., 2011)

CO2e emission due to electricity consumption

CO2e emission due to steam consumption

kg CO2e/tc

kg CO2e/tc

kg CO2e/tc

0.33 0.29 0.21 0.18 0.36 NA 0.08 0.004 0.11 0.13 0.23 0.38 0.08 0.04 0.09 0.18 0.05 0.15 0.27 0.27 0.21 0.34 0.04 0.02 0.21 0.21 0.31 1.79 1.50 1.48 NA

0.04 0.03 0.02 0.57 0.37 0.34 3.03 3.06 2.12 0.76 0.66 0.67 0.66 0.39 0.36 0.28 0.15 0.22 NA

0.37 0.31 0.23 0.75 0.63 0.34 3.11 3.06 2.23 0.89 0.89 1.05 0.74 0.43 0.45 0.46 0.20 0.37 0.27 0.27 0.21 0.34 0.04 0.02 0.21 0.21 0.31 7.14 6.15 5.21 4

lower energy consumption and reduce the GHG emission (Ensinas et al., 2007). It is also noted that all the nine mills have applied the “optimum hot water application in cane crushing” (Measure 2) and “raw brix improvement” (Measure 3) because of their high saving potentials. Application of efficient insulation (Measure 4) has also been done by all mills due to its ease of application. Based on the above observations, it is clear that opportunities exist for Thai sugar mills to improve their energy efficiency and reduce GHG emissions if they apply additional technologies and measures listed, the number of which ranges from 4 to 10 per mill. This could result in potential savings of 5 to 14% of total energy consumption in each mill, and hence surplus steam for other uses or additional bagasse available for electricity generation. In the case of surplus steam, it could be used for replacing electrically driven vacuum pumps with steam jets vacuum systems (OCSB, 2007), resulting in reduced plant electrical load and hence more electricity can be sold to the grid. The surplus steam could also be sold to nearby users, such as ethanol plants. Alternatively, as is the case for a number of mills in Thailand, the bagasse saved could be used in off-season electricity generation, either in low-pressure condensing turbines or high-pressure extraction/condensing turbines. Note that the cane crushing season only lasts about 5 months and so almost all sugar mills have installed condensing turbines for off-season generation using other biomasses, such as rice husk and wood waste, as supplementary fuel. Assuming an annual average operating time of 120 days, the additional electricity that could be generated amounts to about 82 GWh per year, with a minimum saving of 4 GWh and a maximum of 15 GWh. It should also be noted that even the most efficient mills still have room for improvement. However the potential based on these measures (and their typical saving potential) could be lower for newer plants because more advanced technologies would have been already employed.

NA

NA

5.34 4.66 3.73 NA

Total CO2e emission

Conclusions This study analyzed the overall and process-specific energy consumption and GHG emission patterns in three selected Thai sugar mills, common energy efficiency technologies/measures that have been applied in Thai sugar mills, the status of application of energy efficiency technologies/measures in nine selected mills, and the typical potential for energy saving (and hence GHG emission saving) if these mills were to apply all the common technologies/measures identified. The main conclusions are the following: 1. For the nine mills studied, there is a significant gap between the most efficient mill (400 kg steam/tc) and the most inefficient one (646 kg steam/tc), or a potential steam consumption reduction of 40% for the inefficient mill. 2. Generally newer mills using more advanced sugar production technologies have reached a specific steam consumption as low as 400 kg steam/tc, which is better than the international average of 500 kg steam/tc, but still behind the Brazilian average of 346 kg steam/tc. However, with the extensive application of energy efficiency technologies/measures and better energy management, older mills could also achieve the 400 kg steam/tc mark. 3. There are at least 17 common energy efficiency technologies/measures that have been applied in Thai sugar mills. The nine mills studied have each applied 7–13 of these technologies/measures. If the remaining technologies/measures were applied in these mills, the potential saving could range from 5 to 14% of the total energy consumption per mill. This would result in additional bagasse available for generating more than 80 GWh of electricity. 4. For the three mills selected for detailed analysis, it was found that their GHG emission ranged from 5 to 7 kg CO2e/tc. This is significantly higher than the 4 kg CO2e/tc average emission reported by a previous study of a group of 4 Thai mills that are known to the local

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Table 3 Energy-efficiency technologies and measures and their saving potentials in sugar production (ETM refers to information obtained from an efficient Thai sugar mill). NO Technology/measure

Process applied

Description

Saving potential

1

Extended period of blow down inside the boiler (OCSB, 2007)

Boiler

0.2–1%

2

Optimum hot water supplication to cane crushing process (OCSB, 2007)

Mixed Juice

3

Raw syrup brix improvement (OCSB, 2007)

Raw Syrup

4

Energy efficient insulation (OCSB, 2007)

Boiler, steam piping

5

Bagasse dryer (OCSB, 2007).

Boiler

6

Replace steam turbine drive by motor drive for ID fan (OCSB, 2007). Replace open gears by planetary gears on first crusher stage (OCSB, 2007)

Mixed Juice

To keep the total dissolved solid (TDS) concentration in a boiler below 3000 ppm, Thai sugar mills usually drain off water from the boiler every 12 h without measuring TDS, causing unnecessary heat loss. Based on a review of best practice in Thailand the period of blow down should be extended from 12 to 18 h when it is found that TDS would normally reach the allowed limit of 3000 ppm. This measure is applied in the juice extraction process. The juice extraction is aided by introducing hot water to cane crushing process. The optimum hot water is 28% by weight of cane. This measure is used by almost all sugar factories in Thailand but they may use more than 28% of hot water, which is not optimum. This measure is applied in the evaporation process. Some plants do not control the syrup concentration, which leaves continuously at the last evaporator. The syrup, which contains about 65% solids and 35% water, is suitable for crystallization in vacuum pans. When solid content is less than 65%, more energy is needed for crystallization in the vacuum pans. Surface temperatures of boiler walls and steam pipes should be insulated to prevent heat loss. Ceramic Rockwood is generally used as wall insulation for boilers and steam pipes. With this insulation the surface temperature should not exceed about 50 °C. Bagasse from the milling process usually contains high moisture of about 51%, which causes a reduction in combustion efficiency in the furnace. To lower the moisture content to 35%, a bagasse dryer should be used prior to combustion. Many of the ID fans of the old plants with steam turbine drives have been remodeled by motor drives, which have better control, easier maintenance and are more energy-efficient. Older plants in Thailand use open gears for power transmission in the cane crushers. These gears can be replaced by the higher efficiency planetary gears, which have been introduced in Thailand recently. For efficient evaporation in the evaporator, a number of plants use vacuum pumps to lower the pressure. A jet vacuum, utilizing the pressure from the cooling water pump, can be more energy-efficient. Many of old plants use vacuum pumps to lower the pressure in the vacuum pan. For energy-efficient evaporation, the vacuum pumps have been remodeled by jet vacuums, which utilize the pressure from the cooling water pump. The operation of a vacuum pan is controlled by a motor whose speed is varied continuously. The use of DC motor consumes only 1/3 of the electric energy needed to drive the AC motors. Moreover the DC motors can re-generate power back into the system more than AC motors do. Many of the motors used for driving hot air blowers in dryers have been over designed, causing excess electricity usage. Replacing them with optimum (smaller) motors can potentially save electricity use. Many of the old designs of cane cutting knives with steam turbine drives have been remodeled by AC motor drives, which have better control, easier maintenance and are more energy-efficient. Many of the old boiler feed-water pumps with steam turbine drives have been remodeled by motor drive, which have better control, easier maintenance and are more energy-efficient. AC motors consumes more energy at startup and while changing speed. An inverter can help save energy by providing soft start and gradually changing the speed of the motor. Replacement existing lighting by energy efficient lighting.

7

Mixed Juice

8

Additional jet vacuum for evaporator (OCSB, 2007)

Raw Syrup

9

Additional jet vacuum for vacuum pan (OCSB, 2007)

Crystallization

10

Replace AC motor by DC motor on vacuum pan (OCSB, 2007)

Crystallization

11

Optimum (smaller) motor for drying blower (OCSB, 2007)

Raw Sugar

12

Replace steam turbine drive by AC motor drive for cane cutting knives [ETM]

Mixed Juice

13

Replace steam turbine drive by motor drive for boiler feed-water pumps [ETM] Install inverter to AC motors in feed water pumps [ETM] Efficient lighting [ETM]

Boiler

14 15

16 17

Install power factor adjustment capacitor from 0.75 to 0.85 [ETM] Install additional evaporator to improve raw syrup brix [ETM]

Boiler Lighting and liquid pump system Other Raw Syrup

Changing the power factor from 0.75 to 0.85 at fixed power and voltage reduces the current and hence saving energy. Experience in some plants has shown that additional evaporator could increase syrup concentration to about 72% solids and 28% water (OCSB, 2007). This concentration aids energy saving in the vacuum pans by accelerating crystallization.

10–11%

2–3%

0.02– 0.07% 2–9%

1.5–6.5% 5.5–7%

0.3–0.7%

1–3.5%

0.6–1.5%

0.01– 0.05% 1.8%

0.4% 0.16% 0.1%

1.25% 0.8%

Table 4 Typical energy saving potential in each of sugar production process. Process

Technology/measure

Typical saving potential (% of mill consumption)

Boiler (in house)

Extended period of blow down inside the boiler Energy efficient insulation Bagasse dryer Replace steam turbine drive by motor drive for boiler feed-water pumps Install inverter to AC motors in feed water pumps Optimum hot water supply to cane crushing process Replace steam turbine drive by motor drive for ID fan Replace open gears by planetary gears on first crusher stage Replace steam turbine drive by AC motor drive for cane cutting knives Raw syrup brix improvement Additional jet vacuum for evaporator Install additional evaporator to improve raw syrup brix Additional jet vacuum for vacuum pan Replace AC motor by DC motor on vacuum pan Optimum (smaller) motor for drying blower Install power factor adjustment capacitor from 0.75 to 0.85 Efficient lighting

2.8–10.6

Mixed juice production

Raw syrup production

Crystal production Raw sugar production Other process system Office & Service

18.8–26.3

3.1–5.3

1.6–5 0.01–0.05 1.25% 0.1%

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273

Table 5 Summary of energy efficient technologies and measures applied in mills A–I. Technology/measure (saving potential)

Sugar Mills/SEC (kg steam /tc)

1 2 3 4 5 6 7 8

Extended period of blow down inside the boiler (0.55%) Optimum hot water supplication to cane crushing process (10.85%) Raw syrup brix improvement (2.5%) Energy efficient insulation (0.05%) Bagasse dryer (5.85%) Replace steam turbine drive by motor drive for ID fan (1.61%) Replace open gears by planetary gears on first crusher stage (6.77%) Additional jet vacuum for evaporator (0.48%) 9 Additional jet vacuum for vacuum pan (2.71%) 10 Replace AC motor by DC motor on vacuum pan (0.8%) 11 Optimum (smaller) motor for drying blower (0.03%) 12 Replace steam turbine drive by AC motor drive for cane cutting knives (1.8%) 13 Replace steam turbine drive by motor drive for boiler feed-water pumps (0.4%) 14 Install inverter to AC motors in feed water pumps (0.16%) 15 Efficient lighting (0.1%) 16 Install power factor adjustment capacitor from 0.75 to 0.85 (1.25%) 17 Install additional evaporator to improve raw syrup (0.8%) Total number of measures applied Total estimated savinga Total saving potentialb Estimated potential for electricity generation from bagasse saved (GWh)c a b c

A/646

B/410

C/418

✓ ✓ ✓ ✓

✓ ✓ ✓ ✓

✓ ✓ ✓ ✓ ✓

✓ ✓ ✓ ✓ ✓

✓ ✓

✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓













✓ ✓

D/640

E/590

F/550 ✓ ✓ ✓ ✓ ✓ ✓

G/610 ✓ ✓ ✓ ✓

H/600 ✓ ✓ ✓ ✓ ✓

















8 25.5% 11.2% 14.7

9 27.1% 9.6% 14.5

✓ ✓ ✓ ✓







✓ ✓ ✓

✓ 7 22.7% 13.9% 10.2

✓ 10 26.5% 10.2% 6.0

10 31.7% 4.9% 7.9

8 25.9% 10.9% 7.1

9 27.1% 9.6% 4.4

10 25.4% 11.3% 8.2

I/400 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

13 28.7% 8% 8.4

Estimated by summing the typical energy saving potential of the technology/measure already applied by the mill. The number is indicative only, not the actual saving achieved. Estimated by summing the typical energy saving potential of the technology/measure that has not been applied by the mill. Based on 120-day/year operation; 20 kg bagasse generates 1 kWh (OCSB). Total potential = 81.6 GWh.

miller's community as among the most efficient mills. Therefore there is a substantial scope for GHG reduction in most Thai mills. 5. The evaporation process in raw syrup production is the most energy consuming process in a sugar mill. However the energy saving and CO2 reduction potentials that could result from applying the technologies and measures found in the mills surveyed in this study are not significant. It is found in literature that additional potential technologies/measures specifically for raw syrup production are available. Therefore it is recommended that their actual potential and economic feasibility in the context of Thai sugar mills be investigated in future studies.

CO2 e emission from electricity consumption ¼ NCV f ep  ½ðDefault emission factors f or CH4  CO2 equivalent factor f or CH4 Þ þðDefault emission factors f or N2 O  CO2 equivalent factor f orN2 OÞ ð2Þ where Default emission factorsfor CH4 is the amount of CH4 which is emitted by burning 1 MJ bagasse (3 × 10−5 kg of CH4 per MJ) (IPCC, 2006),CO2 equivalent factor for CH4 is the conversion factor for converting CH4 into CO2e (25) (Yuttitham et al., 2011), Default emission factors for N2O is N2O which is emitted by burning 1 MJ bagasse (4 × 10−6 kg of N2O per MJ) (IPCC, 2006), and CO2e equivalent factor for N2O is the conversion factor for converting N2O to CO2e (298) (Yuttitham et al., 2011).

Acknowledgment The financial support provided by the Center for Energy Technology and Environment (5292006) through the Joint Graduate School of Energy and Environment (JGSEE) is gratefully acknowledged. The cooperation of the OCSB (Office Of The Cane and Sugar Board), the Pilot Plant Development and Training Institute, King Mongkut's University of Technology Thonburi, and various sugar mills in providing information and assistance are deeply appreciate. Thanks are also due to the support of the National Research University Program (NRU). Appendix A NCV f ep ¼ Electricity consumption  Energy conversion factor  Solid biomass combustion factor  NCV ðbagasseÞ

CO2 e emission from steam consumption ¼ NCV f sp  η steam generation  ½ðDefault emission factors f or CH4  C 2 equivalent factor f or CH4 Þ þðDefault emission factors f or N2 O

 CO2 e equivalent factor f or N2 OÞ

ð3Þ where NCV fsp is the net calorific value from the steam consumption of each process (MJ per ton of cane), and η steam generation is 80% (Pilot Plant, 2011). References

ð1Þ

where NCV fep is net caloric value from electricity consumption of each process (MJ per ton of cane), Electricity consumption is the electricity supply to each process (kWh per ton of cane), Energy conversion factor is the amount of steam (at 20 bar 360 °C) required to produce 1 kWh of electricity (10 kg of steam per kWh), Solid biomass combustion factor is the amount of baggase required for generating 1 kg of steam (0.5 kg of bagasse per kg of steam), and NCV(bagasse) is the net calorific value of bagasse (7.37 MJ per kg of bagasse).

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