Abstract
Rice straw as a source of energy could substitute for fossil fuels and reduce greenhouse gas (GHG) emissions. Thus, the aim of this paper was to analyze the energy and GHG emissions of rice straw to the energy chain in Egypt. The analysis was performed starting from paddy production, straw collection and transportation, and energy generation for two scenarios: power plant and anaerobic digestion plant. The results showed that the paddy production and transportation stage represented the highest contribution of the total energy consumption and GHG emissions for the two scenarios, respectively. The energy potential was estimated with 4193 GWh electricity and 25,647 × 106 MJ of biogas energy. It was also found that use of rice straw as an energy source could reduce the use of fossil fuel and mitigate air pollution from direct burning of rice straw by 3 Mt CO2-eq of GHG emissions.
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Analysis of Energy and Greenhouse Gas Emissions of Rice Straw to Energy Chain in Egypt
Noha Said,a Adel Alblawi,b Ibrahim Hendy,a and Mahmoud Abdel Daiem a,c,*
Rice straw as a source of energy could substitute for fossil fuels and reduce greenhouse gas (GHG) emissions. Thus, the aim of this paper was to analyze the energy and GHG emissions of rice straw to the energy chain in Egypt. The analysis was performed starting from paddy production, straw collection and transportation, and energy generation for two scenarios: power plant and anaerobic digestion plant. The results showed that the paddy production and transportation stage represented the highest contribution of the total energy consumption and GHG emissions for the two scenarios, respectively. The energy potential was estimated with 4193 GWh electricity and 25,647 × 106 MJ of biogas energy. It was also found that use of rice straw as an energy source could reduce the use of fossil fuel and mitigate air pollution from direct burning of rice straw by 3 Mt CO2-eq of GHG emissions.
Keywords: Rice straw; Energy; GHG emissions; Electricity; Biogas
Contact information: a: Environmental Engineering Department, Faculty of Engineering, Zagazig University, Zagazig, 44519, Egypt; b: Mechanical Engineering Department, College of Engineering, Shaqra University, 11911, Dawadmi, Ar Riyadh, Saudi Arabia; c: Civil Engineering Department, College of Engineering, Shaqra University, 11911, Dawadmi, Ar Riyadh, Saudi Arabia;
* Corresponding author: engdaim@ugr.es
INTRODUCTION
Widespread and massive consumption of fossil fuels has led to rapid economic growth in advanced industrial societies, but it has also increased carbon dioxide (CO2) in the atmosphere and consequently caused global warming and climate change (Bilgen et al. 2008). In consequence, alternative energy sources, such as renewable energies, are an opportunity to replace and/or subsidize fossil fuels and obtain the safest, most cost-efficient, and most practical energy (Bilgen et al. 2008; Demirbas et al. 2009). Currently, renewable energy supplies 17% of the world’s primary energy, counting traditional biomass that represents 9%, nevertheless, it is projected to double the share of renewable energy in the global final energy consumption by 2030 (Demirbas et al. 2009).
Rice straw as a biomass source is produced in great amounts, and it represents the largest unutilized crop residue in Egypt (Said et al. 2013b). Field burning is the major practice for removing rice straw, but it results in air pollution and consequently affects public health (Sarkar et al. 2012). However, rice straw has a high energy potential and thus can become a source of alternative energy that substitutes fossil energy for reducing GHG emissions as well as avoid the local pollution problems from open burning (Said et al. 2013a, 2014). Today, densified rice straw can be easily handled and transported to recover its energy (Said et al. 2015). Energy from rice straw can be recovered directly in the form of heat through a combustion process, or it can be converted to a valuable energy product through indirect techniques such as anaerobic digestion (AD) (Said et al. 2013a; Abdel Daiem et al. 2018; Ahmed et al. 2019).
Some scientific articles have studied the life cycle assessment of rice straw-based power generation and analyzed energy and environmental aspects related to the use of rice straw as an energy source in different countries (Singh et al. 2010; Delivand et al. 2011; Shafie et al. 2013, 2014; Soam et al. 2017). Due to the low number of studies and lack of information about rice straw utilization for energy generation in Egypt, the main objective of this paper was to analyze the energy and GHG emissions of rice straw preparation stages for energy generation in Egypt. The analysis was performed starting from paddy production, straw collection, straw transportation, and energy generation.
EXPERIMENTAL
Materials
Data collection
Data of paddy production and cultivated areas was collected from the Central Agency for Public Mobilization and Statistics (CAPMS 2018). The different rice producer governates in Egypt are Port Said, Damiietta, Dakahliya, Sharkia, Qalyoubia, Kafr Elsheikh, Gharbia, Behera, Ismailia, Beni suef, and Fayoum, as illustrated in Fig. 1. Paddy production, cultivated areas in these governates are indicated in Table 1. As indicated in the table, Dakahlia, Kafr Elsheikh, Sharkia, Behera, and Gharbia are the largest rice cultivation areas. These governates contribute 97.41% of the Egyptian rice production. The amount of rice straw production was derived according to Shafie et al. (2014), using the value of straw to grain ratio (0.75). As indicated in the table, approximately 97.41% of the total rice straw production was generated in the six major rice producer governates as mentioned before with respect to paddy production.
Fig. 1. An overall map of paddy production governates in Egypt
Table 1. Paddy Production, Cultivated Area, and Straw Production for the Different Governates in Egypt in 2015 (CAPMS 2018)
Methods
The analysis of straw to energy chain included straw preparation; starting from paddy production, straw collection and transportation, and finally energy generation from two scenarios: power plant and AD plant, as illustrated in Fig. 2. Energy consumption and GHG emissions emitted through those processes were investigated according to inventory data displayed in Table 2. The energy consumption of straw collection included all machinery using baling technique and considered the diesel consumption in machinery (Shafie et al. 2014). Transportation from farm to power plant included two steps, where straw is first transported to the collection center with a tractor trolley, then transported to the power plants with a truck (Bakker 2011; Soam et al. 2017). For the AD process, the transportation was considered from farm to the collection center only where the straw can be directed easily to the plant to produce biogas, therefore, rural people could use the biogas for cooking (Singh et al. 2014; Soam et al. 2017).
Fig. 2. System boundaries for rice straw-energy generation
Note: Material (M), Energy (E), Waste (W), and Emission (S)
The analysis quantified equivalent CO2 emissions of the three primary GHG: CO2, methane (CH4), and nitrous oxide gases (NOX) (Delivand et al. 2011; Shafie et al. 2013). The GHG emissions from straw collection were computed considering diesel consumption (Bakker and Poppens 2011). Transport emissions are expressed in grams CO2-eq emitted for every ton moved over one kilometer (g CO2-eq per ton.Km), considering loaded and unloaded travel distances in kilometers and rice straw yield in tons (Bakker 2011). Biogenic emissions of CO2 from the power plant were considered zero because the amount of CO2 produced during combustion is utilized during photosynthesis while growing crops (Shafie et al. 2014). However, CO2-eq straw fuel emissions could be estimated respecting CH4 and NOX gases according to Delivand et al. (2011), Soam et al. (2017), and Shafie et al. (2014). In contrast, CO2 emissions from biogas combustion are biogenic and hence considered not applicable. Therefore, CH4 and NOX gases have been taken in consideration (Soam et al. 2017).
Table 2. Inventory Data Used for Energy Consumption and GHG Emission Calculations
A power plant uses a combustion boiler with steam turbine for electricity generation. Straw characteristics are critical factors influencing the operation and maintenance of plants (Soam et al. 2017). The straw characteristics were used in determining lower heating value (LHV) in MJ/kg, which is used in determining electricity output power of straw (E) in KWh. The LHV and E were calculated according to Eq. 1 and 2, respectively (Gadde et al. 2009), where straw characteristics were taken according to Said et al. (2013a) as follows: moisture content (MC, 7.18%); carbon (C, 39.01%); hydrogen (H, 6.59%); nitrogen (N, 0.64%); oxygen (O, 53.32%), and sulfur (S, 0.009%). The estimate LHV is 13.82 MJ/Kg, W is the amount of straw in ton and the conversion efficiency of the plant (CE) was taken as approximately 30%. Equations 1 and 2 are as follows:
In the AD process, the plant consists of one stage operating at 30 to 40 °C, where straw is mixed with water and cattle dung to reach desired solid content of 10%. The biogas system was assumed to be a fixed dome, 2 m³ household type, and the process operated in continuous feeding mode for 350 days/year operating cycle, and with 10 years of operational life (Singh et al. 2014; Soam et al. 2017). The energy production from the AD plant was estimated according to Börjesson and Berglund (2007) and Soam et al. (2017), where one ton of rice straw produces 7.1 GJ energy from biogas.
RESULTS AND DISCUSSION
Energy consumption of paddy production and straw collection for the six major governates and other governates are illustrated in Table 3. The Dakahliya governate had the highest energy consumption for both paddy production and straw collection, accounting for 31.3% of total energy consumption. Meanwhile, energy consumption of paddy production was higher than straw collection due to the high energy consumed in the farming stages due to the consumption of fertilizer and agriculture machinery activities (Farag et al. 2013). Kafr Elsheikh recorded the second governate for energy consumption followed by Sharkia, representing 20.5% and 18.2% of the total, respectively. The annual total energy consumption for all governates reached to 6,241 × 10⁶ MJ and 137 × 10⁶ MJ for paddy production and straw collection, respectively. The energy consumption of paddy production and straw collection for one kg of rice straw are 1.73 MJ and 0.038 MJ, which are lower than 2.52 MJ and 0.11 MJ estimated by Shafie et al. (2014), respectively.
Table 3. Energy Consumption (106 MJ) for the Different Governates at Different Stages
Transportation energy for the energy consumption-based power plant was higher than AD due to the high transportation distance. The highest transportation energy consumption was found in Dakahliya, as it had the highest straw yield. Transportation energy for the energy consumption-based power plant and AD plant is indicated in Table 3. As demonstrated in the table, transportation energy consumption-based power plant for Dakahliya accounted to 2026.21 × 10⁶ MJ/ year, while its value was 129.45 × 10⁶ MJ/year for the AD-base plant. Dakahliya, Kafr Elsheikh, Sharkia, Behera, Gharbia, and Damietta accounted approximately 35.01%, 19.80%, 18.04%, 12.93%, 7.86%, and 2.59% of the total, respectively. The annual total transportation energy of the consumption-based power plant and AD plant reached to approximately 5,788 × 10⁶ MJ and 370 × 10⁶ MJ, respectively.
Considering all stages of rice straw preparation, the total energy consumption-based power plant and AD accounted to 12,160 × 10⁶ MJ/year and 6,750 × 10⁶ MJ/year, respectively. For the power plant, the highest contribution to the total energy consumption was from paddy production (51.3%), followed by transportation (47.6%), and straw collection (1.12%). In case of AD, the transportation energy consumption represented only 5.48% of the total followed by straw collection (2.02%) and the highest energy consumption was from paddy production (92.5%). The high energy consumption in paddy production stage can be attributed to the high energy consumed in farming stages due to consumption of fertilizers and agriculture machinery use as found and described by Shafie et al. (2014).
Energy production from rice straw for the different governates power plants and AD plant is illustrated in Fig. 3a and b, respectively. As indicated in the figure, Dakahliya had the maximum annual energy production, accounting for 35.0% of the total energy production. The annual electricity output from rice straw fuel-based power plant in Dakahliya was 1,468 GWh, while energy from biogas generated from AD plant was 8,980 × 10⁶ MJ. The annual total energy obtained for all governates was 4,193 GWh electricity and 25650 × 10⁶ MJ of biogas energy for straw fuel-based power plant and AD plant, respectively. Thus, the electricity production from one ton of rice straw was 1165 KWh, which was higher than 938 KWh found by Shafie et al. (2014) and lower than 1367 KWh estimated by Soam et al. (2017). The variation in energy obtained by these studies may be attributed to the different characteristics of the used rice straw and according to the power plant efficiency (Soam et al. 2017).
The GHG emissions of rice straw-based energy generation begins with paddy production and continues to energy generation. The CO2 gases represent a high percentage of GHG emissions (Shafie et al. 2014). Only as an exception, the paddy production process has a great advantage in relation to the global warming impact, due to the absorption of carbon through photosynthesis (Abdelhady et al. 2014; Shafie et al. 2014). Table 4 shows GHG emissions (CO2-eq) for paddy production and straw collection. As shown in the table, the highest annual GHG emissions emitted from paddy production and straw collection were found in Dakahliya with values of 2,050 t CO2-eq and 3,582 t CO2-eq, accounting for 35.0% and 31.3% of the total, respectively. Meanwhile, the total GHG emissions emitted from paddy production and straw collection for all governates were 5,857 t CO2-eq/ year and 11,435 t CO2-eq/year, respectively. The obtained CO2-eq from straw collection was approximately 0.003 Kg CO2-eq/Kg straw, which is lower than 0.012 Kg CO2-eq/Kg straw calculated by Bakker and Poppens (2011). Furthermore, The GHG emissions from both paddy production and straw collection were equivalent to 0.01 Kg CO2-eq/Kg straw, which is lower than 0.10 Kg CO2-eq/Kg straw estimated by Shafie et al. (2014). The difference in emissions is likely due to differences between studies in farming location, type, allocation method, energy, and emission coefficients (Miller and Kumar 2013).
Fig. 3. Energy production for the different governates from rice straw-based a) power plant and b) AD plant
Table 4. GHG Emission (t CO2-eq) for the Different Governates at Different Stages
Transportation distances play a major role in GHG emissions. Increases in the transportation distance from the collection center to power plant contribute to increased GHG emissions, as detected by Shafie et al. (2014). Table 4 includes GHG emissions emitted from the transportation of rice straw fuel-based power plant and AD plant, respectively. As can be seen in the table, a remarkable increase in emissions emitted from transportation to power plant comparing AD plant was detected, as found by Soam et al. (2017). Dakahliya as the highest governate in GHG emissions emitted from transportation, has annual values of approximately 33,540 t CO2-eq and 5,590 t CO2-eq for the power plant and AD plant, respectively. Meanwhile, the annual total GHG emissions emitted from transportation to power plant and AD plant for all governates were 95,800 t CO2-eq and 15,970 t CO2-eq, respectively.
The GHG emitted from plants includes emissions from the combustion boiler of the rice straw power plant and combustion of biogas generated from the AD process. As mentioned before, CO2 emissions from the straw-based power plant and biogas combustion are biogenic and considered zero; therefore, GHG emissions included CH4 and NOX gases. Figure 4 illustrates the GHG emissions generated according to boiler and biogas combustion. As indicated in Fig. 4, GHG emission was higher for the combustion boiler compared to biogas combustion, similar to Soam et al. (2016). This indicated that the straw fuel-based AD process has more environmental benefits than the power plant (Soam et al. 2016). The annual GHG emitted in Dakahliya, as the greatest values among different governates, reached to 1,468 t CO2-eq and 727 t CO2-eq from the power plant and AD plant, respectively. Meanwhile, the total GHG emissions emitted from the combustion boiler of the rice straw power plant and combustion of biogas generated from the AD process for all governates accounted to 4,190 t CO2-eq/year and 2,080 t CO2-eq/year, respectively. The difference in emissions for the two plants arises due to different processing technologies and the displaced product (Soam et al. 2016).
Fig. 4. GHG emissions from energy generation processes
Based on the results of the current study, the total annual GHG emissions generated from rice straw-based power plant are 117,280 t CO2-eq, which are higher than 35,340 t CO2-eq from the AD plant. Figures 5a and b indicate the GHG emission contribution of the different stages for rice straw fuel-based power plant and the AD plant. For the power plant, transportation had the highest emissions, accounting for 81.7% of the total emissions, followed by straw collection and paddy production. Similar results were found by Soam et al. (2017) and Shafie et al. (2014), where they found that the highest contribution to the total GHG emissions was from straw transportation with 92% and 57.5%, respectively. Meanwhile, combustion boilers of the power plant had the lowest emissions among the different stages. Although transportation emission represented the highest contribution among the different stages-based AD plant, its contribution percentage (45.2%) was lower than that (81.7%) from the power plant. For the straw fuel-based AD, the second highest contribution was for straw collection followed by paddy production, while biogas combustion emission had the lowest percentage (5.88%), as can be seen in the figure.
According to the obtained results, the annual air pollution of 3.2 Mt CO2-eq from the direct burning of rice straw (Farag et al. 2013) could be mitigated by using rice straw for electricity generation and biogas energy source to 0.12 Mt CO2-eq and 0.035 Mt CO2-eq, respectively. Therefore, it is expected to have a GHG emission reduction of approximately 3 Mt CO2-eq per annual country emissions from non-open field burning and using rice straw as an energy source. This reduction represents approximately 0.94% reduction of the total annual country’s GHG emissions (Nakhla et al. 2013). Similar results were found by Delivand et al. (2011) who expected to have a GHG emission reduction of approximately 2 to 3.5 Mt per year, which is equivalent to approximately 1 to 1.13% reduction to the total annual Thailand’s GHG emissions. Additionally, Shafie et al. (2014) found that the power generation of rice straw, if applied, can reduce the GHG emission up to 1% of total GHG emissions in Malaysia. These small percentages of reduction will become more attractive in the future as these countries strive to reduce their carbon emissions. According to Delivand et al. (2011), 0.368 t CO2-eq/t dry straw and 0.683 t CO2-eq/t dry straw could be avoided if straw is used instead of natural gas or coal fuel in the power generation sectors. In consequence, 1.24 Mt CO2-eq and 2.29 Mt CO2-eq could be mitigated annually by substituting the natural gas and coal fuels with rice straw for power generation, respectively. Moreover, 152 m³ natural gas/t dry straw or 0.285 t coal/t dry straw could be saved (Delivand et al. 2011). As a result, an annual amount of 510 × 10⁶ m³ natural gas and 957,400 t coal could be saved. Based on the country, fossil fuel consumption for electricity generation of 230 ton of oil equivalent (toe)/GWh (Abdelhady et al. 2014), the straw fuel power plant could be able to reduce the use of fossil fuel by an amount of 964,400 t/year. Thus, the utilization of rice straw for energy generation not only removes the rice straw from field without open burning, but also saves GHG emissions that can contribute to climate change, acidification, and eutrophication, among other environmental problems, as well as it would contribute to savings on the fossil fuel consumptions (Delivand et al. 2011; Shafie et al. 2014).
Fig. 5. GHG contribution of the different stages to the total emissions of rice straw fuel-based a) power plant and b) AD plant
CONCLUSIONS
- The paddy production and transportation stage represented the highest contribution of the total energy consumption and greenhouse gas (GHG) emissions, respectively.
- The annual total energy obtained amounted to 4193 GWh electricity and 25,650 × 106 MJ of biogas energy from straw fuel-based power plant and AD plant, respectively.
- Air pollution from direct burning of rice straw could be mitigated by 3 Mt CO2-eq of GHG emissions by using rice straw as an energy source.
ACKNOWLEDGMENTS
The authors are grateful to the teamwork at the Environmental Engineering Department in Zagazig University in Egypt for their valuable suggestions and to Shaqra University for its financial supporting through Research Support Program.
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Article submitted: October 23, 2019; Peer review completed: December 31, 2019; Revised version received and accepted: January 8, 2020; Published: January 13, 2020.
DOI: 10.15376/biores.15.1.1510-1520