Development of Rice Husk Power Plants Based on Clean Development Mechanism: A Case Study in Mekong River Delta, Vietnam

In this research, we planned and conducted estimations for developing a pilot-scale Clean Development Mechanism (CDM) project for group plant activities in the Vietnam electricity/energy sector. The overall aim of this paper is to assess the power generation potential of rice husk power plants in the Mekong Delta. We intend to set up a rice husk energy balance flowchart for the whole Mekong River Delta in the year 2021 and suggest policies that can be used for the power generation of unused rice husk, to avoid having them pollute rivers and canals. We put forward a safe and environmentally friendly solution to thoroughly minimize the current serious pollution of rivers and canals in the Mekong River Delta caused by the increasing quantity of unused rice husk. The results of this paper are based on the estimation of electricity potential of a group of rice husk power development plants in the Mekong River Delta with a capacity of 11 MW per plant, including carbon dioxide emission reductions (CERs) and CER credits, along with estimations of their economic criteria (NPV, B/C, IRR), both W/CDM and W/O CDM.


Introduction
Vietnam has an impressive economic growth rate, and it has succeeded in transforming itself from a command economy to a market economy, especially in transforming and developing its agricultural sector. With a major impact on employment, GDP, and export, the importance of the agricultural sector in Vietnam is profound. Having both a continuing agricultural development in general and a rapid paddy production growth in particular is very necessary. The Mekong River Delta is an important agricultural area amongst the agricultural areas in Viet Nam.
Vietnam's renewable energy report of 2018 [1] highlighted some future plans and key points, including an electricity growth rate demand of about 9% per year, in which the demand of renewable energy demand growth rate is around 10% per year. The report pointed out that the growth rate of renewable energy supply is likely to increase the fastest at 23.2%, compared with hydropower at 2.6% and coal gas fire at 7.8%, in the period between 2020 and 2030.
The intensive paddy farming and rapid growth of rice production in the Mekong River Delta has led to dumping and discharging a large amount of rice husk from the local dense milling center networks. Currently, rice husk discharged from milling centers can be used for fueling brick kilns, porcelain furnaces, and rural household cooking (under 20% total), for open-air burning to fertilize the planted areas (not considerable; under 20% total), or it can be dumped (uncontrollable at over 70%) [2].
Most of paddy milling plants in the Mekong River Delta are located on the banks of canals and two major rivers. About 1.4-1.5 million tons of rice husk discharged from dense milling center network into rivers cause serious negative environmental impact (See Figure 1). Amongst the three aforementioned rice husk disposal modes (i.e., used as fuel source, open-air burning of rice husk for fertilizing the planted areas, uncontrollable dumping of unused rice husk into rivers), power generation using rice husk is considered to be the only mode with an environmentally friendly context. pointed out that the growth rate of renewable energy supply is likely to increase the fastest at 23.2%, compared with hydropower at 2.6% and coal gas fire at 7.8%, in the period between 2020 and 2030.
The intensive paddy farming and rapid growth of rice production in the Mekong River Delta has led to dumping and discharging a large amount of rice husk from the local dense milling center networks. Currently, rice husk discharged from milling centers can be used for fueling brick kilns, porcelain furnaces, and rural household cooking (under 20% total), for open-air burning to fertilize the planted areas (not considerable; under 20% total), or it can be dumped (uncontrollable at over 70%) [2].
Most of paddy milling plants in the Mekong River Delta are located on the banks of canals and two major rivers. About 1.4-1.5 million tons of rice husk discharged from dense milling center network into rivers cause serious negative environmental impact (See Figure 1). Amongst the three aforementioned rice husk disposal modes (i.e., used as fuel source, open-air burning of rice husk for fertilizing the planted areas, uncontrollable dumping of unused rice husk into rivers), power generation using rice husk is considered to be the only mode with an environmentally friendly context. The study in [3] provided a comprehensive overview of three main types of renewable energy in Vietnam: solar, mini-hydro power, and biomass energy. In this present study, the use of rice husk and bagasse to fuel the bioelectricity generation plants is first considered in details on both a qualitative and quantitative basis. The preliminary data and analysis of the study on the rice husk potential in the Mekong River Delta (South Vietnam) are very useful for preparing the CDM-PDD of a 11 MW rice husk fueled biopower plant and for achieving the policy recommendations for using the rice husk potential of provinces in the Mekong River Delta [4].
The objectives of the study are to assess the CDM-based potential of rice husk power development plants and to recommend a regional strategy for developing a group of rice husk power generation plants with a 11 MW installed capacity per plant for minimizing the uncontrollable dumping of unused rice husk produced from paddy milling plants to rivers.

Literature Review
Cheewaphongphan et al. [5] studied the rice straw in Thailand and calculated its potential to serve as a fuel source. The study results of Ji and Nananukul [6] assisted in the decision making of biomass projects based on the study of supply chains for sustainable renewable energy from biomass. Weldekidan et al. [7] concluded that "gases have a high concentration of combustible products and as fuels in engines". Another fuel source is industrial wastewater and livestock manure resources, which have a potential of 7800 to The study in [3] provided a comprehensive overview of three main types of renewable energy in Vietnam: solar, mini-hydro power, and biomass energy. In this present study, the use of rice husk and bagasse to fuel the bioelectricity generation plants is first considered in details on both a qualitative and quantitative basis. The preliminary data and analysis of the study on the rice husk potential in the Mekong River Delta (South Vietnam) are very useful for preparing the CDM-PDD of a 11 MW rice husk fueled biopower plant and for achieving the policy recommendations for using the rice husk potential of provinces in the Mekong River Delta [4].
The objectives of the study are to assess the CDM-based potential of rice husk power development plants and to recommend a regional strategy for developing a group of rice husk power generation plants with a 11 MW installed capacity per plant for minimizing the uncontrollable dumping of unused rice husk produced from paddy milling plants to rivers.

Literature Review
Cheewaphongphan et al. [5] studied the rice straw in Thailand and calculated its potential to serve as a fuel source. The study results of Ji and Nananukul [6] assisted in the decision making of biomass projects based on the study of supply chains for sustainable renewable energy from biomass. Weldekidan et al. [7] concluded that "gases have a high concentration of combustible products and as fuels in engines". Another fuel source is industrial wastewater and livestock manure resources, which have a potential of 7800 to 13,000 TJ/year (terajoule per year) [8]. Kinoshita et al. [9] found that biomass production is Sustainability 2021, 13, 6950 3 of 10 an important target of the Japanese government. In the study by Beagle and Belmont [10], they considered the power plants near beetle kill mortality to be ideal candidates for co-firing. Jasiulewicz [11] described the conditions when making a decision on replacing hard coal with local biomass. The results of the study by Luk et al. [12] showed that the overall efficiency with proper drying and heat integration is improved by about 5% when compared to a process without drying. In the study by Botelho et al. [13], they concentrated on the importance of performing an equity analysis; they also found that while the sulfur content of coal can reach 4%, the biomass sulfur content is between 0 and approximately 1%. Tokarski [14] showed that the most widespread method of producing electricity from renewable sources in power plants involves the co-firing of biomass with fossil fuels. Cereals were found to have a major contribution (about 74.67%) in the surplus biomass [15]. The results of Zhang et al. [16] showed that the proposed feedstock supply pattern is able to significantly increase the profits of biomass plants. The study by Gao et al. [17] encouraged building wind power plants in desert areas where possible. In the study by Moretti et al. [18], they compared benchmarks of biomass-fueled combined heat and power systems (CHPs) with conventional separate production technologies; they also identified the main sources of environmental impacts and assessed the potential environmental performance.
The study by Wang and Watanabe [19] on straw-based biomass power generation showed that risk changing in the biomass supply chain is one of the reasons why farmers are unwilling to supply straw. Visser et al. [20] showed the details of the cost of biomass power plants in South Africa. Yang et al. [21] pointed out that a pulverized biomass/coal co-firing power plant with carbon capture and stores (CCS) can achieve near-zero emissions. Thakur et al. [22] found that the bundled and chipped forest harvest residues used at a power plant ranges from 21.4 to 21 g CO 2 eq/kWh. Ferreira et al. [23] pointed out that the total potential estimated for various sectors of Portugal is 42.5 GWh/year. The economic and environmental results given by Mohamed et al. [24] showed the efficiencies of the carbon capture and stores and non-CCS plants. Singh [25] examined the cereal crops, sugarcane, and cotton contribution in the production of surplus biomass. In the study by Song et al. [26] on hydro power plants, they concluded that the electricity price would have to be increased to 5.7 US cents/kWh in order to cover the full costs of the Yali hydro power plant. In the environmental analysis of Roy et al. [27], they found an environmental benefit value of about 430,014 USD/year of using biomass power plants.

Data Collection
We determined rice husk availability based on estimating the rice husk potential of milling centers located alongside the Tien Giang River in the Mekong Delta. We also considered the capability needed to transport the rice husk that is needed by not only the considered pilot rice husk power plant but also similar ones planned at the Mekong Delta for future use, and we found that waterways are the most economical method. We also found the current local rice husk using and pricing by interviewing the relevant companies and stakeholders. In the data collection process, we asked them questions (Appendix A) in a number of areas, such as their willingness to participate in the pilot plant of the current local milling centers in the capacity of the plant developers; their willingness to sell the stored rice husk; the rice husk selling capability, and the acceptable rice husk pricing level of current rice milling centers. The steady rice husk availability and procurement for bioelectricity generation was considered for provinces of the Mekong River Delta (South Vietnam).

Estimation of GHG (Greenhouse Gas) Emissions by Sources
In this section, we present the estimation of GHG emissions in the project. All equations were created based on the Clean Development Mechanism and GHG emission reduction requirement.
where E j is the CO 2 emissions per year of the generation mode j, calculated as: where PG j is the electricity generation of power plant j; EF j is the emission capacity of the fuel-fired power plant j; OF j is the oxidation factor; CF is the unit conversion factor, i.e., 44/12 (C−CO 2 ) × 0.36 (TJ−MWh); and TE j is the thermal efficiency of the electric generation mode j. The weighted average emission (E), representing the emission intensity, is given by:

Total Cost
The total cost is calculated as follows: where Ct inv. is the investment cost; Ct O&M is the operation and maintenance cost; and Ct fuel (RH) is the fuel rice husk cost (including rice husk transport and storage costs).

Total Benefit
The total benefit is calculated as follows: where Bte is the benefit given by rice husk electricity sale = peWt; BtCER is the benefit given by CER sale = pCO 2 CER; Bt ask is the benefit given by rice husk ash sale = pashWt; Pe = rice husk electricity sale price; pCO 2 is the CER sale price; pash is the rice husk ash sale price; and Wt is the rice husk electricity sale to the Vietnam Electricity (EVN) grid in year t.

Assessment of the CO 2 Emission Reductions (CERs) and CER Credits Determined by Different Assumed CO 2 Prices
Assessment of the CO 2 (CERs) and CER credits determined by different assumed CO 2 prices was realized for a group of five similar pilot grid-connected rice husk power development plants 5 × 11 MW installed capacity. As presented in Section 3, these five identified and recommended power plants are similar in relation to their size and employed technology. Although they are originally presented as a single CDM plant, this single plant in actuality comprises five similar rice husk power plants with the installed capacity of 11 MW per plant. The assessment of their CERs and CER credits is carried out only for an individual rice husk power plant, and then its assessed CER and CER credit is multiplied by 5 to make the CER and CER credit account for the whole CDM power plant. The rice husk ash price of proposed rice husk power plant, which is assumed to be at a constant pricing level, is 0.02 USD/t of ash. The calculations are given in Table 1. We made calculations using the maximal running number of days (332 days/year) as given above, and the average running day number (200 days/year), which is the realistic case, based on realistic input parameters (Table 1).
We took into consideration the current serious pollution of Mekong Delta's rivers and canals caused by unused rice husk, as river pollution is a threat to the health of local communities and their livelihood, especially their traditional aquaculture and pisciculture. This region-wide environmental threat is expected to rapidly increase with the following contexts: • Mekong River Delta, which leads to a rapid increase in the local rice husk generation; • Basic change in rice husk end-uses of local communities from using rice husk fuel to using the commercial energy types, leading to the rapid reduction of the local rice husk consumption and the increase of the local unused rice husk dumping; • Lack of region-wide cooperation in looking for an environmentally friendly and effective solution to thoroughly minimize the pollution of the Mekong Delta's rivers and canals with rice husk pollution by paddy milling centers.
From 2004, the search for a thorough solution to eliminate the increasing pollution of rivers in the Mekong River Delta became an urgent task faced by local authorities, administrators, agriculture, and energy development planners. Safe and environmentally friendly disposal of 3.7 million tons of rice husk per year with over 70% of that (2.5 million tons per year) to be dumped is one of the major problems of the Mekong Delta's sustainable development.
In this context, the development of a group of 5 rice husk power plants with an installed capacity of 5 × 11 MW was selected as the most thorough and sustainable solution to solve this problem.

Conclusions and Recommendations
In this study, we investigated the potential of rice husk power plants using secondary data and direct survey data in the study area and applying methods of project analysis along with emission reduction estimations based on the Clean Development Mechanism. The prices of electricity generated by rice husk power plants and sold to Vietnam Electricity (EVN) through national power grids should be considered by the government and EVN with the concession of electricity pricing to small renewable (rice husk) power producers so that EVN could agree to purchase rice husk electricity with the electricity pricing level from 0.045 to 0.050 USD per KWh.
During a plant's projected lifespan of 20 years (2020-2040), the average annual CER of a proposed rice husk power plant is calculated to be 26,700 tons of CO 2e with a time of use (TOU) of 4800 h/year (or 200 operating days per year), and its average annual CER credits by CO 2 prices of 9 and 15 USD per ton of CO 2e is expected to be from 240 to 400 thousand USD, respectively. For the whole group of five similar rice husk power plants with a 5 × 11 MW installed capacity, these figures are 5 × 26,700 = 133,500 tons of CO 2e per year, and 1200-2000 thousand USD per year, respectively. Initial construction and installation costs are still high compared to other types of electricity power sources. Currently, the cost of rice husk is almost zero, and the only costs involved are shipping costs. In the future, if rice husk power plants are developed in the area, rice husk prices are likely to increase, and so further studies are needed to ensure the sustainable development of these rice husk power plants.
The research recommends developing in the Mekong River Delta a group of five similar pilot rice husk power plants having a total installed capacity of 5 × 11 MW at five locations, namely An Hoa (An Giang province), Thoi Hoa (limitrophe area of three provinces: An Giang, Dong Thap, and Can Tho), Thoi Lai (Can Tho province), Cai Lay (Tien Giang province), and Tan An (Long An province) (Figure 2). Besides these five locations, a reserved location in Tan Chau (limitrophe area of two provinces such as An Giang and Dong Thap, and the Kingdom of Cambodia) was selected for the future development of a paddy milling center network as well as rice husk power centers. Initial construction and installation costs are still high compared to other types of electricity power sources. Currently, the cost of rice husk is almost zero, and the only costs involved are shipping costs. In the future, if rice husk power plants are developed in the area, rice husk prices are likely to increase, and so further studies are needed to ensure the sustainable development of these rice husk power plants.
The research recommends developing in the Mekong River Delta a group of five similar pilot rice husk power plants having a total installed capacity of 5 × 11 MW at five locations, namely An Hoa (An Giang province), Thoi Hoa (limitrophe area of three provinces: An Giang, Dong Thap, and Can Tho), Thoi Lai (Can Tho province), Cai Lay (Tien Giang province), and Tan An (Long An province) (Figure 2) . Besides these five locations, a reserved location in Tan Chau (limitrophe area of two provinces such as An Giang and Dong Thap, and the Kingdom of Cambodia) was selected for the future development of a paddy milling center network as well as rice husk power centers.

Appendix A
Annex of the paper: Questionnaires Four kinds of questionnaires needed for this study: