J. Sci. Dev. 2009, 7 (Eng.Iss.1): 70 - 78 HA NOI UNIVERSITY OF AGRICULTURE 70 Energy recovery potential from landfill and environmental evaluation of landfill gas power generation system at nam son landfill, Vietnam Tiềm năng thu hồi năng lượng từ bãi rác và đánh giá lợi ích môi trường của hệ thống phát điện sử dụng khí từ bãi rác tại bãi rác Nam Sơn, Việt Nam Pham Chau Thuy 1 , Sohei Shimada 2 1 Department of Environmental Technology, Faculty of Natural Resource and Environment, Hanoi Agricultural University, Trau Quy, Gia Lam, Hanoi 2 Graduate School of Frontier Sciences, Institute of Environmental Studies, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, JAPAN TÓM TẮT Khí từ bãi rác là nguồn năng lượng xanh, sạch, có thể tái tạo được và có thể sử dụng để tạo ra điện, hay sử dụng trong công nghiệp năng lượng. Bài báo này đánh giá tiềm năng thu hồi năng lượng từ khí bãi chôn lấp chất thải rắn đô thị, mục đích làm giảm lượng phát thải methan nói riêng và giảm phát thải khí nhà kính nói chung. Ngoài ra, bài báo cung cấp cách sử dụng mô hình đánh giá lượng khí methan tạo ra từ bãi chôn lấp chất thải rắn đô thị và tiềm năng tạo ra năng lượng từ khí đã thu hồi. Đặc biệt, bài báo sử dụng phương pháp đánh giá vòng đời để đánh giá việc giảm phát thải khí nhà kính của hệ thống phát điện sử dụng khí từ bãi rác. Kết quả nghiên cứu chỉ ra rằng, bãi rác Nam Sơn là một bãi rác có tiềm năng lương lượng lớn cần thu hồi và sử dụng, góp phần đáng kể vào việc làm giảm phát thải khí nhà kính, hướng tới sự phát triển bền vững. Bài báo cung cấp một cách nhìn mới về công nghệ năng lượng sử dụng khí từ bãi rác cho Viêt Nam: hệ thống phát điên sử dụng động cơ khí và tuabin khí. Kết quả còn chỉ ra rằng, hệ thống phát điện bằng động cơ khí tỏ ra hiệu quả hơn về lợi ích về môi trường so với hệ thống phát điện bằng tuabin khí. Hệ thống này có thể ứng dụng cho bãi rác Nam Sơn và ứng dụng cho các bãi rác khác của Việt Nam trong tương lai. Từ khóa: Đánh giá vòng đời, giảm phát thải khí nhà kính, khí từ bãi rác, mô hình phát thải khí bãi rác. SUMMARY Landfill gas (LFG), a green, clean, and renewable energy source can be used for electricity generation or fuel industries. This research presents an attempt to assess the energy recovery potential from the Municipal Solid Waste (MSW) landfill, targeting at gas recovery and gas utilization, in mitigating methane emission in particular and green house gas (GHG) emission in general. Our research provides the using of landfill gas emission model (LFGEM) to quantify the methane generation volume for MSW landfill. We then evaluate of energy generation potential from recovered gas. Especially, this research conducted the Life Cycle Inventory to evaluate GHG emission mitigation of power generation system using LFG. The results show that the methane gas flow at Nam Son landfill can provide a considerable energy potential. LFG recovery and utilization could contribute remarkable to GHG emission mitigation, toward to sustainability. The research supplies a new vision of energy technology from LFG for Viet Nam: Gas Engine and Gas Turbine. The research found that Gas Engine is more attractive in term of environmental benefit, which can be applied primarily for Nam Son landfill and continue applied for other landfill in Vietnam for the future. Journal of Science and Development 2009: Tập VI, No 6: 69-77 HA NOI UNIVERSITY OF AGRICULTURE 71 Key words: Green House Gas emission mitigation, landfill gas, landfill gas emission model, life cycle Inventory. 1. INTRODUCTION Climbing LFG is considered as the largest anthropogenic emission source in the developed countries and also as a considerable emission source in developing countries up to now. Landfill gas (LFG) is produced from anaerobic biodegradable decomposition of organic content of landfilled waste. Release of LFG is one of the dangerous contaminations due to high methane content contributing to GHG emission and global warming. Hence, collecting LFG and using it not only to avoid the pollution and explosion, but also can get attractive benefits. The main mechanism for reducing future methane emission from landfill sites is the use of engineered sites and the collection and utilization of LFG. There are several ways to utilize LFG. The most prevalent use is converting LFG to electricity for utilization. Power generation is advantageous because it produces a valuable end product - electricity – from waste. LFG recovery and converting to electricity is optimum solution for environmental burdens decrease by CH 4 emission mitigation from landfills, a large emission source from human’s activities. Hence, the purpose of this study is to make an attempt to assess the energy recovery potential from LFG and utilize it, targeting at gas recovery and gas utilization, in mitigating methane emission in particular and GHG emission in general. For initial assessment, an estimate of landfill gas quantity is all needed to estimate power potential, which is necessary for LFG power generation design. This research presents the method with the combination of using theoretical model and experimental research to estimate LFG quantity in more accurate. Then energy recovery potential from LFG continuing is estimated. Several good conversion technologies exist for generating power from LFG – Internal combustion engine (Gas Engine), combustion Turbine (Gas Turbine) and steam turbine. Steam turbine is applicable in very large landfill. Other technology is fuel cell. However, this application is too expensive. This research considers on Gas Engine (GE) and Gas Turbine (GT) in converting LFG to electricity. Use of Life Cycle Inventory will analyzed attractive in term of environmental advantages obtained from power generation plant. Viet Nam has carried out a number of studies and project relevant landfill gas recovery and power generation, for example: project of Landfill gas capture and power generation in Dong Thanh and in Go Cat landfill. Landfilling is the common way for Municipal Solid Waste treatment in Viet Nam. There are a lot of landfills in Vietnam with high capacity which are not considered in landfill gas capture and power generation. The research approaches a new vision of LFG technology, which is necessary in environmental protection and sustainability development for Viet Nam in particular and for the world in general. 2. MATERIALS AND METHODS 2.1. Case study- Nam Son landfill Nam Son (NS) landfill is the biggest landfill in Hanoi city, with the largest area (83.5 ha) compared to other landfills opened in Hanoi. It is the important site, which is active now and prospect of use is in a long time (it will be closed in 2020). With a large area and high capacity, NS landfill receives 1850 tons of solid waste per day today and more in the future. The waste volume is expected to be 12 million tons when landfill close. Gas migration in NS landfill has made serious consideration to the government. The question to them is how to collect landfill gas and how to use it with the aim of getting advantages including environmental pollution reduction and economic yield. 2.2. Materials and methods The first method used in this study is investigation at field and gas measurement. The data obtained from this method includes: characteristic and structure of the landfill, quantity and composition of waste disposed at NS landfill daily, local weather condition and other relevant characteristics around the landfill. Gas measurement includes sampling landfill gas and analyzing the samples, which focused on methane and carbon dioxide concentration determination. Using vacuum pump and Tedlar bag carried out Pham Chau Thu, Sohei Shimada 72 LFG sampling. GC-FID and GC-TCD machine analyze gas samples. The continuing method in this study is using landfill gas emission model (LFGEM) to estimate landfill gas emission and energy recovery potential at NS landfill. There are several ways used to evaluate the theoretical production of methane from MSW landfill. This study uses the theoretical model for evaluating of LFG emission. The model is based on the first order decay equation, which can be run by site-specific data for parameters need to estimate emission. If the data is not available, the method will use default value sets included in landfill. Site-specific data in this study is determined by on-site testing and through IPCC guideline. For the sites with known (or estimated) year- to-year solid waste acceptance rates, the model estimate LFG generation rate for given year using the following equation: i n kt M 0 i i 1 Q kL M (e )     (1) Where: M Q = Maximum expected generation flow rate of methane for Mi tons of solid waste (m 3 /year)   n i 1 = Sum from opening year + 1 (i=1) through year of projection (n) k = methane generation rate constant (1/year) Lo = methane generation potential (m 3 /t) Mi = mass of solid waste disposed in the i th year (ton) t i = age of the waste disposed in the i th year (years). The life cycle inventory of power plant was considered in four lifecycle phases, namely, upstream LFG, construction, operation, and decommissioning. Upstream landfill gas includes waste collection, transportation and operation of landfill. The construction phase considered both of LFG collection system and power plant construction. In the decommissioning phase, demolition of power plant, material recycling and material reusing was included within the system boundary. LFG recovery and utilization of it is optimum solution for environmental burdensdecrease by CO 2 and CH 4 emission mitigation from landfills, a large emission source from human’s activities. The aim of this method is to evaluate environmental impacts associate to the whole life cycle of LFG energy conversion systems. This method is important in accounting of GHG emission mitigation from utilization of recovered LFG. 3. RESULTS AND DISCUSSION 3.1. Determining site-specific input of NS landfill 3.1.1. Determining the concentration of LFG in Nam Son landfill To define the concentration of landfill gas, total 9 samples were taken in the different cells and locations and analyzed on GC machine. Using of vacuum pump and Tedlar bag carried out LFG sampling. Microclimate factors including temperature, moisture, and wind velocity were measured also. The samples were analyzed on GC- FID or GC-TCD in laboratory. LFG analyzing focuses on the measurement of methane and carbon dioxide concentration. By volume, LFG typically contains 45% - 65% methane and 40-60% carbon dioxide. The rate and volume of LFG produced at a specific site depends on characteristic of waste (waste composition and age of refuse) and a number of environmental factors (present of oxygen in the landfill, moisture content and temperature). Typically, the more organic waste present in the landfill, the more landfill gas produces. Waste component in NS landfill was described in Fig. 1. The results of sample analysis are shown in Table 1. These results are not so different due to a stable component of waste and the time of refuse of each cell. The result of analyzing samples is around 50% of CH 4 in LFG (53% CH 4 concentration in average level). 51.9 2.7 3.1 1.3 1.6 0.5 6.1 0.9 31.9 organic papers plastic leather, rubber, wood textile glass stone, clay,percelain metal fine fraction 1. 31.9 51.9 0. 6. 1 0.5 2.7 3. 1 1. Energy recovery potential from landfill and environmental evaluation 73 Figure 1. Composition of Municipal Solid Waste Table 1. Results of LFG sample analysis at NS landfill Microclimate Location of sampling No of Sample Temperature ( 0 C) Moisture (%) Wind velocity (m/s) CH 4 (%) CO 2 (%) 1 20.2 66.9 0.12 57.6 40.3 2 19.8 65.3 0.15 56.2 34.5 Cell 1 3 19.2 67.9 0.14 55.2 0.92 4 18.4 74.2 0.17 55.2 42.0 5 23.5 75.3 0.11 50.2 36.5 Cell 3 6 21.3 77.4 0.15 54.2 35.6 7 18.4 74.2 0.11 53.2 12.3 8 19.2 78.3 0.12 50.1 33.5 Cell 4B 9 20.1 75.6 0.15 48.2 45.3 Table 2. Input parameters used in calculation of Lo Input parameters Category MCF DOC (%) DOC d F (%) Lo Result 1 26.6 0.84 0.53 158 m 3 CH 4 /ton of waste 3.1.2. Determining methane generation potential of waste disposed at NS landfill (Lo) This data was defined through IPCC guidelines. IPCC guidelines presented that Lo correspond to MCF x DOC x DOCd x 16/12 x F. Where: MCF = methane correction factor (= 1 with well managed landfill, supposing that MCF of NS landfill is 1) DOC = fraction of degradable organic carbon DOCd = fraction DOC dissimilate F = fraction of CH 4 in landfill gas Defining of DOC and DOCd was carried out depending on waste component, calculated by IPCC guideline also. DOC = 0.4 (A) + 0.17(B) + 0.15 (C) + 0.3 (D), where A: percentage of paper and textile; B: percentage of garden waste, park waste and other non-food organic putrescible waste; C: percentage of food waste; D: percentage of wood or straw. Apply datum from analyzed sample of waste in Nam Son landfill, the percentage of DOC is 26.6%. DOCd is calculated based on the theoretical model that the variation depends on the temperature of anaerobic zones of the landfill. DOCd= 0.014 x T + 0.28 Where: T is temperature. This factor may vary from 0.42 for 10 0 C to 0.98 for 50 0 C. In fact, in many deep landfills (>20m), temperatures of more than 50 0 C have been registered in gas streams from highly productive gas wells (thus clearly anaerobic). In the Nam Son landfill, the height of site now is 18 m. Expected height in the future is 30m. In this case, assumption of average temperature of anaerobic zone is 40 0 C, therefore DOCd = 0.84. Taking account the value of methane concentration in landfill gas F, fraction of degradable organic content DOC and dissimilate fraction of degradable organic content DOCd, Lo is calculated in the Table 2. Lo calculated in NS landfill is suitable with range of Lo in IPCC guidelines and also suitable with two set of default value used in US-EPA standards. 3.1.3. Methane generation rate constant k As mentioned above, k is a parameter to reflect the LFG emission rate. The k relates to waste component, landfill condition and local weather. Commonly, if easy-digest organic waste has a higher proportion, landfill is under the Pham Chau Thu, Sohei Shimada 74 warmer climate condition, and waste has a reasonable press by compactor, the k will be larger, waste easy to digest; the time of digestion will be shorter. In converse, if the waste has a lower proportion of easy-digest organic waste, landfill is under the colder climate condition, waste has an un-well press, k will be smaller, waste difficult to digest, and time of digestion will be longer. For a landfill, the k can be obtained via site test for accurate calculation. In this study, a k value was suggested depending on the consideration to the climate condition at Nam Son landfill, landfill design, landfill condition, and reference of other default k values. K = 0.04 is assumed for using in estimation of landfill gas in Nam Son landfill. 3.2 Estimation of methane emission at NS landfill This study used Landfill gas emission model (LFGEM) to evaluate methane emission from landfill. This model was be run by site - specific data supplied by above calculation. With the methane concentration of 53% in LFG, methane generation potential Lo of 158 m 3 CH 4 per ton of waste, and the methane generation rate constant k of 0.04, landfill gas emission model calculates the methane emission for NS landfill and presents the development of methane emission with the time. Figure 2 shows the change of methane emission at NS landfill with time. Methane emission from landfill decreases according to the exponential curve after reaching peak gas production. The results show Nam Son landfill has been exposed with an abundant volume of methane. Maximum of methane emission occurs at the time of closed landfill operation. It takes account for 60 million m 3 at 2020 approximately. Minimum of emission is 2.3 millions m 3 of methane at the second year of landfill operation (2000). Suppose that gas collection efficiency of recovery system is 70%, maximum of methane collected will be 42 millions m 3 . These results will be used to estimate energy recovery potential of NS landfill, which can be useful for good design of power generation plant in energy recovery orientation. 3.3. Energy recovery potential of NS landfill Methane has a high calorific potential considered as ideal energy source (39700 MJ/m 3 ). Estimation of energy recovery potential from LFG is useful for good designing power capacity of plant. Figure 3 shows the possible ways for using recovered gas and energy generation potential attaining from recovered gas. Energy generation potential in Nam Son landfill can be started to exploit in 2006 for power generation. At this time, methane flow can support enough for power generation with a minimum capacity of 6MW. The lifetime of power plant is projected for 20 year. In the case of LFG flow excess the design capacity of generator, the gas redundancy should be treated and sale for nearby site. Other incentive is burning excess gas in purpose of environmental pollution mitigation only. The designed capacity for LFG power generation system at Nam Son landfill further depends on the energy consumption requirement in Nam Son commune. The electricity capacity of 6MW could provide enough for the resident’s consumption need located nearby Nam Son area. In the Nam Son landfill, there will have compost processing plant, incineration plant and plant for industrial waste treatment in the future. Therefore, recovered gas can be also supplied for waste treatment units located on site as a replacement of energy power or supplementary fuel. 0 10 20 30 40 50 60 70 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 Time(year) Methane emission (millions m3) Lo=158,k=0.04 Figure 2. Development of methane emission in NS landfill LFG emission curve by the waste filled in a year ( for Mi tons of waste) Total methane emission volume in a year (for   n i Mi 1 tons of Energy recovery potential from landfill and environmental evaluation 75 0 2 4 6 8 10 12 14 16 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 Time(year) Electricity Capacity (MW) Sale medium Btu LFG Power generation Sale medium Btu LFG or LFG burning Figure 3. Energy recovery potential from LFG at Nam Son landfill 3.4. Life Cycle Inventory of LFG power generation system 28% Landfill gas Gas Engine Gas Turbine 2 MW 2 MW 2 MW 6 MW Annual electricity generation:42,048 MW 37.7% 20 years Total life cycle electricity outputs: 840,960 MW Steam Turbine Applicable in very large landfill Figure 4. Outline of Nam Son Landfill gas power generation system Pham Chau Thu, Sohei Shimada 76 3.4.1. Options to be compared for LFG conversion systems Due to high landfill gas generation potential of Nam Son landfill, the most appropriate use for landfill gas is as a fuel for power generation. Several good conversion technologies exist for generating power: Internal Combustion Engines, Combustion Turbine, and Boiler/Steam Turbine. Among them, both Gas Turbine and Gas Engine are capable used in the Nam Son landfill, where landfill gas volumes are sufficient to generate a minimum of 3 to 4 MW. The comparison should be done between 3 units of GE with a 2MW capacity of each and 1 unit of GT with a 6MW capacity. The next section will analyze and compare energy consumption and emission each system. The electricity can be used on-site to displace purchased electricity or be sold to a nearby electricity user. Table 3. Summary of energy consumption and CO2 emission in whole lifecycle of GE power plant Phases Energy consumption (kcal/kWh) CO 2 emission (kg/kWh) E.C (%) CO 2 emission (%) Upstream material 72.6 0.0225 3.047 4.099 Construction phase 5.59 0.0016 0.234 0.297 Operational phase 2307.7 0.513 96.7 95.3 Decommissioning phase -0.046 0.0016 -0.0019 0.3055 Total 2385.8 0.538 Table 4. Summary of energy consumption and CO 2 emission in lifecycle of G.T power plant Phases Energy consumption (kcal/kWh) CO 2 emission (kg/kWh) E.C (%) CO 2 emission (%) Upstream material 72.63 0.0221 2.176 2.910 Construction phase 4.93 0.00148 0.1477 0.195 Operation phase 3259.58 0.732 97.67 96.690 Decommissioning phase 0.063 0.0015 0.00189 0.200 Total 3337.21 0.759 3.4.2. Life cycle energy use and CO 2 emission of Gas Engine power generation system The results were attained from analytical accounting of the matter and energy flux, which can enter or go out of system. The energy per functional unit (kcal/kWh) was calculated from the life cycle energy use and total electricity generation during the entire lifetime of power plant. The results in Table 3 show that the energy- intensive phase is operational phase. Operational phase consumed 2307.7 kcal/kWh while total thermal energy consumption for lifecycle of system is 2385.8 kcal/kWh (accounting for 96.7% of total energy consumption (EC) of system). The negative value in decommissioning phase shows that energy can be saved from reusing of materials. The primary source of used energy was traced back to estimate the CO 2 emission then GHG emission evaluation. The result presents the emission in operational phase contributed 95.3% of total emission from whole life cycle of system. It can be recorded that most of EC and emission occurs on the operational phase of GE power generation system using LFG. 3.4.3. Life cycle energy use and CO 2 emission of Gas Turbine power generation system Calculating of LCI energy used and GHG emission of G.T system was carried out similar to GE system. The results once more demonstrates that energy consumption and GHG emission of LFG power generation system concentrated mainly on operational Energy recovery potential from landfill and environmental evaluation 77 phase. Gas Turbine has a high compression requirement, but lower lubricating oil consumption than Gas Engine. The results in Table 4 shows that energy consumption is accounted for 97.67% and CO 2 emission is 96.69% in operational phase of GT system, slightly higher than that of GE system. 3.4.4. Comparison of energy consumption and GHG emission between G.E and G.T power generation system G.T power generation system using LFG consumed energy and emitted CO 2 much more than that of GE system. The different of them shows in Table 5. Although the difference of each phase, Gas Turbine power plant presents energy consumption and also CO 2 emission is higher than that of Gas Engine power plant. The reason for this mainly is efficiency of G.T (27%) is lower than that of G.E (37.7%). This estimation is important in comparison of GHG emission mitigation obtained from each of LFG power generation alternative. Table 5. Comparison between Gas Engine power plant and Gas Turbine power plant Thermal energy consumption (%) CO 2 emission (%) Phase G.E G.T G.E G.T Upstream LFG 3.04 2.18 4.1 2.92 Construction 0.23 0.148 0.297 0.195 Operation 96.72 97.67 95.3 96.69 Decommissioning -0.0019 0.0019 0.306 0.200 Total 2385.8 (kg/kWh) 3337.2 (kg/kWh) 0.538 (kcal/kWh) 0.759 (kg/kWh) 3.4.5. Green House Gas (GHG) emission mitigation attained from LFG power generation system GHG emission mitigation obtained from installation of LFG power generation system is evaluated from total emission reduction by methane combustion, CO 2 emission from whole life cycle of electricity production (as calculated in previous section), and CO 2 emission offset for electricity production. Because methane emission is a global climate change agent with 23 times the negative impact of CO 2 . Hence: GHG emission mitigation from whole life cycle of Gas Engine power plant is: -[(1*22-5695*0.538/1000)+5695*0.5/1000]*28.88*365*20 = - 4.6 million tons (CO 2 equivalent) = - 2.35 billion m 3 (CO 2 equivalent) Where: 1*22 is CO 2 mitigation from 1 ton CH 4 combustion 5696*0.538/1000 is CO 2 emission from whole life cycle of LFG power generation system by combustion of 1ton methane 5695*0.5/1000 is CO 2 emission offset for electricity production GHG emission mitigation from whole life cycle of Gas Turbine power plant is: -[(1*22-4283*0.759/1000)+4283*0.5/1000]*28.88*365*20 = - 4.4 million tons (CO 2 equivalent) = - 2.24 billion m 3 (CO 2 equivalent) Negative sign indicates the net positive reduction of CO 2 emission using power generation system. Both Gas Engine and Gas Turbine contribute remarkable to GHG emission mitigation. The results indicate that Gas Engine power generation plant was considered more friendly environmental than Gas Turbine system. In the consideration of environmental benefits, Gas Engine system appears more attractively than Gas Turbine. Gas Engine power generation system could be an ideal style insuring sustainable development for converting LFG to electricity for Nam Son landfill. 4. CONCLUSION By using of LFGEM, the study found the methane gas flow at Nam Son landfill could provide a considerable potential that has many options to be used as a source of energy, where Pham Chau Thu, Sohei Shimada 78 LFG electricity generation option is most preferable. Both of GE and GT contribute remarkable to GHG emission mitigation. Comparison between two LFG power generation systems with the same capacity, the analysis shows that the Gas Turbine power generation system presents a higher thermal energy consumption and also higher GHG emission. However, considering in whole life cycle, G.E contributes to GHG emission mitigation more remarkably than that of G.T system. 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