An Approach To Address the Low Concentration Methane Emission of

Article Cite This: Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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An Approach To Address the Low Concentration Methane Emission of Distributed Surface Wells Shengyong Hu,†,‡ Xiangqian Guo,§,∥ Chao Li,§,∥ Guorui Feng,*,†,‡ Xiaoyang Yu,† Ao Zhang,† and Guocai Hao† †

College of Mining Engineering, Taiyuan University of Technology, Taiyuan 030024, China Green Mining Engineering Technology Research Center of Shanxi Province, Taiyuan 030024, China § Shanxi Jincheng Anthracite Mining Group Co., Ltd., Jincheng 048000, China ∥ State Key Laboratory of Coal and CBM Co-mining, Jincheng 048006, China

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‡

ABSTRACT: The majority of gassy mines in China have been located in hilly areas, and distributed surface wells are widely used to recover the methane for mining safety and commercial purposes. However, a large amount of low concentration methane from distributed wells cannot be directly transported due to its high explosion risk, and have to be emitted into the atmosphere, resulting in air pollution and wasting energy. Conventional pressure swing adsorption (PSA) methods are mainly employed to increase the methane concentration for safe transportation. However, they typically adopt large-scale factory mode, which is not effective due to the lack of industrial land for distributed wells. In this study, an efficient approach is proposed to address the low concentration methane emission of distributed wells by designing a distributed purification system, including the units of security drainage, PSA purification, and pressurization. Low concentration methane was initially extracted by the security drainage unit, and then, its concentration was increased in the PSA purification unit. Eventually, after being pressurized in the pressurization unit, the methane parameters can meet the safety requirements of the long distance transportation. Field application of the system was carried out in Sihe Coal Mine in China. The results show that, after purification, the concentration of methane is stable at more than 60%, while the concentration of oxygen was remarkably decreased, and the methane recovery percentage is stable at more than 80%. The total profit of decade is 10936 k¥, and the average daily usable methane volume is 2857.39 m3 as well, which would reduce greenhouse emissions equal to approximately 60.01 km3 carbon dioxide. technique which is widely used in China11 to recover methane resources In China, major gassy coal mines with abundant methane reserves have been located in hilly areas, which caused distributed surface wells to be adopted to extract the gas.12 The distributed surface wells refer to traditional stress relief surface vertical wells, which are distributed in a relatively dispersed manner in coal mines. However, the concentration of methane in distributed wells drastically varies during the mining process. 13 As displayed in Figure 1, a high concentration of methane can be directly forwarded into the gas pipelines after pressurizing for a long distance transportation, while the low concentration methane cannot be directly transported because of some safety problems. For instance, low concentration methane always contains high

1. INTRODUCTION Nowadays, China is rapidly and economically developing and is becoming the largest consumer of coal, and it produces the highest amount of methane emissions, which is associated with mining as well.1 On a molecule-for-molecule basis, methane is a far more active greenhouse gas than carbon dioxide, but also one which is much less abundant in the atmosphere.2 Methane is a hydrocarbon gas produced both through natural sources and human activities, including the decomposition of wastes in landfills, agriculture, and especially rice cultivation, as well as ruminant digestion and manure management associated with domestic livestock.3 However, methane is also a clean, stable, and efficient source of energy.4 Thus, measurements should be conducted to control the methane emissions in coal mines in China.5 All gassy coal mines have established gas drainage systems to ensure safety during the mining process, leading to a reduction of methane emission and enhancement of the efficacy of commercial supply of methane.6−10 The stress relief coalbed methane drainage using surface wells is an efficient © XXXX American Chemical Society

Received: Revised: Accepted: Published: A

May 21, 2018 September 4, 2018 September 10, 2018 September 10, 2018 DOI: 10.1021/acs.iecr.8b02254 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research

Figure 1. Schematically representation of variation of methane concentration during mining process.

Figure 2. Location of Sihe Coal Mine.

have restricted the broad application of the membrane separation technique in the methane purification industry.20 Compared with these two methods, the PSA is a promising technique in the methane purification industry because of its low energy consumption, as well as cost-effectiveness.21,22 Several scholars have performed extensive researches on the PSA method for methane purification. Yang and Doong23 proposed a pore diffusion model for bulk separation to predict the PSA process. Fatehi et al.24 conducted experimental and theoretical studies on the separation of methane−nitrogen mixtures by using the PSA technique subjected to diverse conditions and interpreted the experimental results using a linear driving force dynamic model. Olajossy et al.25 presented a numerical simulation for the vacuum pressure swing adsorption process to retrieve methane from acoal mine. Qu et al.26 studied the carbon molecular sieves absorbent for coal mine methane. Thomas et al.27 reported dual-reflux pressure swing adsorption for capturing low concentration methane

oxygen content, and its explosion limit will be expanded after pressurization, thereby enhancing the explosion risk of gas pipelines.14 Thus, low concentration methane has to be directly emitted into the atmosphere, which not only causes severe air pollution, but also wastes energy resources. Hence, it is vital to address low concentration methane emission of distributed surface wells. A frequent approach to solve a challenge associated with low concentration methane emission is to increase the corresponding concentration, and then send it to the pipelines after pressurization for commercial purposes. Currently, a number of methods (i.e., pressure swing adsorption (PSA), cryogenic distillation, membrane separation technique, etc.) are used to enrich methane extracted from gas.15−18 The cost of supplying cryogenic distillation equipment is remarkable.19 The membrane separation method contains some disadvantages, including being expensive and low permeability, as well as selectivity of the N2 and CH4, which are the main reasons that B

DOI: 10.1021/acs.iecr.8b02254 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research from nitrogen gas. Zhang et al.28 proposed nonisothermal numerical simulations of dual reflux pressure swing adsorption cycles for separating N2 and CH4. Moreover, Li et al.29 presented the process of low methane enrichment by employing a PSA system to avoid the risk of explosion in the adsorption process. However, the majority of PSA systems mainly adopt a large-scale factory mode, represented by a large floor space and oversized gas treatment capacity, which us inappropriate for in situ purification of distributed surface wells due to the lack of industrial land, as well as low quantity of the daily drainage for a single well. In this paper, an efficient approach is proposed to address the low concentration methane emission in distributed surface wells by designing a proper distributed purification system, and a field practice is also undertaken in Sihe Coal Mine, Shanxi province, China. Eventually, environmental and economic aspects of the proposed approach are discussed as well.

wells of various sorts in the Sihe mining area.30 However, in terms of drainage gas from most of these distributed surface wells, the methane concentration is less than 30%, while the oxygen concentration is higher than 14%. As illustrated in Figure 4, if the drainage gas is directly forwarded into the gas pipelines after pressurization, the limit of corresponding explosion is expanded as well, causing the increase of explosion risk in the gas pipelines. Therefore, this part of gas has to be directly emitted into the atmosphere, which not only wastes energy resource, but also exacerbates the greenhouse effect. Regarding the problems mention above, for these parts of distributed surface wells, it is necessary to perform in situ purification for low concentration methane for gas transportation in the gas pipelines after pressurization in order to realize the recycling of the methane.

3. METHOD AND INSTRUMENTS 3.1. Method. Figure 5 shows a reliable method regarding safety purification and positive pressure transportation of low concentration methane of distributed surface wells through the units of the security drainage, PSA purification, and pressurization. First, low concentration methane (CH4 < 30%) enters to the security drainage unit. It presents a negative pressure as the drainage power and guarantees an isolation between the ground equipment and coal mine environment for safety of drainage. Then, the methane concentration increases to more than 60% in the PSA purification unit. Eventually, after being pressurized to approximately 0.2 MPa in the pressurization unit, the gas will be put forward into the gas pipelines for the long distance transportation. Exhaust gas (mainly N2 and O2), which is produced in the PSA purification process, is directly emitted into the atmosphere. On the basis of the method proposed in this study, as depicted in Figure 6, the distributed purification system, integrating security drainage unit, PSA purification unit, as well as pressurization unit, is particularly designed. The existing technologies for addressing low concentration methane mainly include the internal combustion power generation, low and high concentration methane mixture, and methane purification and transportation. For the internal combustion power generation technology, not only gas production and stability are strictly required, but also a large industrial open space area for factory construction is required. For the low and high concentration methane mixture technology, the construction of a new gas distribution pipeline is needed for high concentration methane transportation, which is extremely costly in a hilly area. Besides, the uncertain locations of the distributed surface wells make this technology hard to apply in this area. In contrast, the method proposed in this study is based on the methane purification and transportation technology; however, it is particularly appropriate for field, distributed, and small-scale surface methane drainage conditions. It can achieve gas purification and possesses a number of advantages, such as less land occupation, ease of installation, safety, and positive pressure transportation. 3.2. Devices. 3.2.1. Security Drainage Unit. As illustrated in Figure 6, the security drainage unit consists of gate value, one-way value, water drainer, explosion proof flame arrester, electric value, vacuum pump, compressor, buffer tank, and freeze-dryer. A vacuum pump used for gas drainage is the water-ring vacuum pump, and the compressor is arranged in the exit of the vacuum pump to integrate the gas drainage and compression functions. A one-way value is used to prevent

2. BACKGROUND As shown in Figure 2, the Sihe Coal Mine is located in the Southern Qinshui Basin of Shanxi province, in China. It is in an area with low mountains and hills; the maximum relative elevation difference of the terrain is approximately 240 m. It has a length of approximately 23 km in a west-to-east direction, width of almost 12 km in a north-to-south direction, and covers a total area of approximately 230 km2. The Sihe Coal Mine is considered as a gassy coal mine, with a methane content of approximately 13 m3/t, and a pressure rate of approximately 0.29 MPa as well. The estimated methane resources measure 1.03 × 1010 m3. The rate of coal production is 12 Mt/a, the main minable coal seam for beneficial production is No. 3 coal seam, containing an average thickness of 4.45 to 8.75 m. The gas content is generally 15.04 to 19.52 m3/t in the coal seam, and pressure of the coal mine gas is 0.2 to 2.12 MPa. However, with the increase of the depth of mining, the rates of emission of coal mine methane and coal seam methane content subsequently increased, while gas has imposed tremendous challenges in the aspects of production and safety of coal mine. To date, in Sihe Coal Mine, an accident due to gas explosion has occurred, and the gas power phenomenon as well as the coal and gas outburst accidents have already happened four and two times, respectively. To control and mitigate disasters caused by gas explosions, many surface wells were established in Sihe Coal Mine for coal seam gas drainage. As shown in Figure 3, the Sihe Coal Mine is located in a hilly area. This means that distributed surface wells are adopted to extract gas in the field. According to the statistical results, there are more than 60 distributed surface

Figure 3. Sihe Coal Mine in a hilly area. C


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Figure 4. Transportation problems of low concentration methane after pressurization.

Figure 5. Proposed purification method appropriate for low concentration methane in distributed surface wells.

Figure 6. Proposed purification system of low concentration methane of distributed surface wells.

pressure fluctuations of the pipes to maintain the stability of the system. Low concentration methane is released from the distributed surface well with the negative pressure, passing through the gate value, one-way value, a water drainer, an explosion proof flame arrester, and an electric value, and enters into the vacuum pump and compressor. In the outlet of the compressor, its pressure is roughly increased to about 0.2 MPa. Next, most of the water of the compressed gas is eliminated by a freeze-dryer. After being compressed and dried, the gas will be directly forwarded to a subsequent processing unit.

reversed flow of the explosive gas into the mine to guarantee the safety during the unexpected shut-down period of the vacuum pump. The major role of an explosion proof flame arrester is to prevent a flame caused by mine gas explosion from spreading to the ground for the safety of ground equipment. By automatically adjusting the open degree of an electric valve, the drainage native pressure and gas flow rate can be appropriately matched to improve the efficiency of a vacuum pump. A water drainer can release the water into the pipes to decrease the pump load. A buffer tank can stabilize D


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Industrial & Engineering Chemistry Research 3.2.2. PSA Purification Unit. As displayed in Figure 6, a PSA purification unit mainly consists of six adsorption beds, vacuum pump, separating tanks, sequencing valves, and console. It is used in order to increase the methane concentration to more than 60%. Figure 7 illustrates the internal structure of an

A typical variation of pressure with time is depicted in Figure 8. The total duration of a cycle is 150 s, and the adsorption pressure is 0.2 MPa. To ensure the continuity of the flow, simultaneously, two adsorption beds are normally available in the AD and EV steps, respectively. A one-sixth-sequence of the PSA cycle is detailed in Figure 9, and the same step arrangement is transposed to other column numbers accordingly. An adsorption bed A is taken as an example. (1) AD: After being pressurized by a gas compressor and dried by a freeze-dryer, the feed gas goes through buffer tank A and flows into bed A, in which CH4 is selectively adsorbed and other ingredients, which mostly involve N2 and O2 are released. (2) ED1: A gas control valve in the entrance of bed A is closed, and bed A is connected to bed C, which led to completion of the ER2 process, and then, the first depressurization occurs. The gas flows from a bed with a high-pressure bed to another one with a low pressure until pressures are the same between these two beds (3) ED2: The gas control valve is connected with bed A, and bed C is closed, and bed A is also connected with bed D, which leads to the completion of the ER3 process. Next, the second depressurization occurs. (4) ED3: The gas control valve is connected with bed A, and bed D is closed, and bed A is connected with bed E, which leads to completion of the IS process, and then the third depressurization occurs. (5) IS: The bed also idles during certain periods of the cycle, as they have to wait until an interaction gas becomes available. (6) EV: Bed A is connected to a vacuum pump for evacuation. CH4 is desorbed and flows into buffer tank C, and then it will be forwarded into the next unit. (7) ER3: Bed A is connected with bed C, which leads to completion of the ED2 process and the start of the first repressurization. The sequence is counted in an inverted order to match with the sequence of depressurization. (8) ER2: Bed A is connected with the bed D, and the second repressurization is started. (9) ER1: Bed A is connected with the bed E and the third repressurization is started. (10) FP: The gas control valve is opened and the exhaust gas, after being throttled, flows into bed A, from the buffer tank B until the pressure of the bed is equal to the adsorption pressure. Then, bed A undergoes the next round of circulation. After being treated by the PSA unit, the methane concentration is increased to more than 60%, and the oxygen content of gas is low, indicating that the gas meets the safety requirement of concentration for long distance transportation. However, the gas pressure is between −0.2 and 0.1 MPa, which is less than the transmission pressure of gas pipelines. Accordingly, the gas also needs to be sent to the pressurization unit. 3.2.3. Pressurization Unit. As shown in Figure 6, the pressurization unit involves compressor, pressure sensor, methane sensor, flow sensor, temperature sensor, console, gasholder, and gate valve. It is used to realize the safety of

Figure 7. Internal structure of the adsorption beds.

adsorption bed. There are two layers in the adsorption bed involving an alumina molecular sieve and an adsorbent, which are filled in the lower and upper layers, respectively. The alumina molecular sieve is utilized for dehydration of the compressed gas entering the adsorption bed to prevent entrance of water to the adsorbent. An activated carbon, particularly applied for methane adsorption, is adopted as the adsorbent, containing characteristics of explosion proof, dust proof, and high adsorption efficiency as well.31 In detail, the adsorbent possesses an excellent electrostatic conductivity and can prevent static electricity from accumulating in beds. Besides, the special chemical material is wrapped, so dust would not be easily produced and accumulated. A PSA cycle consists of 6 adsorbent beds and 10 steps. Table 1 represents an operational schedule for all six beds, showing the interactions/couplings among the beds. The next steps, which are performed for each bed in a complete cycle, are as follows: adsorption (AD), equalization depressurization (ED), equalization repressurization (ER), final pressurization (FP), evacuation (EV), and insulation (IS). Table 1. Cycle Sequence of the PSA Process bed A B C D E F

step AD ER1 ER3 EV ED3 ED1

AD FP ER2 EV IS ED2

ED1 AD ER1 ER3 EV ED3

ED2 AD FP ER2 EV IS

ED3 ED1 AD ER1 ER3 EV

IS ED2 AD FP ER2 EV E

EV ED3 ED1 AD ER1 ER3

EV IS ED2 AD FP ER2

ER3 EV ED3 ED1 AD ER1

ER2 EV IS ED2 AD FP

ER1 ER3 EV ED3 ED1 AD

FP ER2 EV IS ED2 AD


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Figure 8. Profile of pressure in the adsorption beds at each purification step.

Figure 9. Schematic profile of one-sixth-sequence PSA cycle.

pressurization for methane emissions after purification. The injection screw turbocharger is adopted as a compressor, while its circulating medium is water. As water has an impact of cooling and explosion suppression, it can avoid the generation of high temperature and electric spark made by a friction between dust and screws. The front section of the compressor is equipped with pressure, methane, and temperature sensor. The parameters, including methane concentration, temperature, and gas pressure, can be continuously monitored by these sensors. When one of these parameters is out of gauge, the pressurization unit will automatically shut down. After passing through the injection screw turbocharger, the gas pressure is increased to approximately 0.2 MPa and the methane concentration, gas pressure, and oxygen content meet the safety requirement of long distance transportation. Therefore, this part of gas can be sent into the pipelines for safe transportation, preventing the methane emission, as well as wasting energy.

Figure 10. Low concentration methane in the distributed purification system.

4. FIELD APPLICATION A typical surface well of Sihe Mine Coal was selected as a case study. Figure 10 shows a low methane concentration in the

distributed purification system in the field. The system abandons the design characteristics of factory mode, and F


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relief zone, gradually compacted zone, and fully compacted zone.32 The permeability in the pressure-relief zone is maximized due to a well-developed fractured within this zone, and the amount of methane flow rate and concentration reaches its peak value. The permeability in the gradually compacted zone declines slowly, causing methane flow rate and concentration to decrease gradually. The permeability in the fully compacted zone is minimized to guarantee stability, allowing that methane flow rate and concentration would be limited and relatively stabilized. The variation of methane flow rate and concentration of methane in the distributed wells are relatively small during mining processes, reflecting that they are located in the fully compacted zone. Research concerning the gas composition and concentration variation was carried out through the experimental testing. As shown in Table 2, after purification, the concentration of

contains the miniaturization’s features, low-cost, easy deployment, as well as high integration of each unit. The whole system covers an area of 120 m2 as well. In the PSA process, the duration of adsorption is proportional to the concentration of methane, while is inversely proportional to the methane flow rate. To meet the local demand of methane flow rate, the concentration of methane cannot be remarkable after purification, otherwise, the flow rate of methane will be decreased. Therefore, the duration of adsorption is determined in the premise of ensuring the methane concentration for safe transportation in addition to the local demand for methane flow rate. Figures 11 and 12 show the percentage of the methane recovery and the comparison of the methane concentration

Table 2. Gas Composition Rates before and after Purification gas composition rates gas type gas before doing purification (feed gas) gas after doing purification (product gas) exhaust gas

CH4 (%) O2 (%)

N2 (%)

CO (%)

other gas (%)

29.1

14.3

54.9

0

1.7

69.5

4.6

23.3

0

2.6

4.2

20.2

74.3

0

1.3

methane was increased from 29.1% to 69.5%, whereas the concentration of oxygen was decreased from 14.3% to 4.6%, meaning that this part of the gas has lost the risk of explosion. The main components of the exhaust gas are nitrogen and oxygen, and the concentration of methane is very low as well. The concentration of nitrogen, oxygen, and methane in the exhaust gas is 74.3%, 20.2%, and 4.2%, respectively. These indicate that most of methane concentration is recycled. The main component of the detected gas also includes carbon monoxide, which is used to detect the coal fire in a coal mine to prevent the underground fires.

Figure 11. Comparison of the methane concentration before and after purification.

5. ENVIRONMENTAL AND ECONOMIC ASSESSMENT 5.1. Environment Evaluation. To perform a significant environment evaluation, on the basis of data shown in Figures 11 and 12, the average daily methane flow rate before and after purification along with the average daily methane recovery percentage are summarized in Table 3. As shown in Table 3, the average daily methane flow rate before and after purification is 3420.48 m3/d and 2857.39 m3/d, respectively, and the average daily methane recovery percentage is 83.5%. Before utilizing the system, all the extracted low concentration methane is emitted into the atmosphere. However, in the

Figure 12. Methane recovery percentage and comparison of the methane flow rate before and after purification.

and flow rate before and after purification. As can be seen in Figures 11 and 12, before purification, the concentration of methane is in the range of 20% to 35%, and the methane flow rate is between 2800 and 4200 m3/d. After purification, the methane concentration is stable at more than 60%, and the methane flow rate varies between 2000 to 3200 m3/d. The methane recovery percentage, which is the ratio of the methane flow rate in the product gas after purification to that of in the feed gas before purification, is stable at more than 80%. A gob can be divided into three zones along the mining direction as the working face advances, including the pressure-

Table 3. Key Performance Indicators Used for Environmental Evaluation

G

indicator

value

average daily methane flow rate before purification (m3/d) average daily methane flow rate after purification (m3/d) average daily methane recovery percent (%) average daily volume of emission reduction (equivalent to carbon dioxide) (Km3)

3420.48 2857.39 83.5 60.01


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6. CONCLUSIONS An approach is proposed to address the low-concentration methane emission of distributed surface wells by designing a low-concentration methane distributed purification system. The proposed system includes the units of security drainage, PSA purification, and pressurization, with the characteristics of less land occupation, easy deployment, safe drainage, savingenergy, and environmental protection. Low concentration methane is first extracted by a security drainage unit, providing negative pressure as the drainage power, as well as ensuring the safe drainage. Then, the methane concentration is enriched by a PSA cycle which consists of 6 adsorbent beds and 10 steps in the PSA purification unit. Eventually, after being pressurized in the pressurization unit, the gas parameters, mainly including methane concentration, oxygen concentration, and gas pressure, can meet the safety requirements for transportation, and then, the gas will be sent into the pipelines for the long distance transportation. In this study, results of industrial application in Sihe Coal Mine in China shows that, after purification, the methane concentration is stable at more than 60%, while the oxygen concentration is significantly decreased, and the methane recovery percentage is stable at more than 80% as well. The results of the environmental evaluation indicated that the average daily usable methane volume is 2857.39 m3, which can reduce greenhouse emissions equal to about 60.01 km3 carbon dioxide. Meanwhile, according to the results of an economic evaluation, the capital costs will be recovered in less than two years and the total profit of the decade is 10936 k¥. As can be seen from the results mentioned above, there are wide prospects for the application of the proposed distributed purification system to address the low concentration methane emission.

proposed approach, most of the extracted low concentration methane is used as the produced gas for transportation after purification, thereby avoiding the methane emission. The average daily usable methane volume is 2857.39 m3 which would reduce greenhouse emissions equivalent to about 60.01 km3 carbon dioxide. Therefore, the proposed approach can significantly address the methane emission in distributed surface wells. 5.2. Economic Evaluation. An economic evaluation study is performed for the proposed approach described above. In addition, the key performance indicators for the economic evaluation of the proposed approach is listed in Table 4. As Table 4. Key Performance Indicators for the Economic Evaluation of the Proposed Approach key performance indicator capital costs breakdown equipment costs (k¥) installation costs (k¥) engineering and contingency costs (k¥) total capital costs (k¥) operational costs breakdown electricity costs (k¥/a) labor and operating charges costs (k¥/a) sales tax costs (k¥/a) total annual operational costs (k¥/a) annual gas sales breakdown average daily volume of methane production (Km3/d) estimated yearly volume of methane production (350 working days) (Km3/a) unit volume price of methane (including subsidies) (¥/m3) total annual gas sales revenue (k¥/a) annual profit (k¥/a) time required for capital recovery (years) profit during the system’s lifetime (10 years) (k¥)

value 1631 20 200 1851 241 72 110 423 2.86 1001 1.7 1701.7 1278.7 1.45 10936

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel (Fax): +86 351 6010177.

demonstrated in Table 4, the total production cost includes capital and annual operational costs. We initially estimated the capital and annual operational costs. The capital costs involve direct costs (e.g., equipment and installation costs) and indirect costs (e.g., engineering and contingency costs). The operational expenses include variable operating costs (costs of materials and utilities, such as electricity and activated carbon), fixed operating expenses (labor costs, operating charges, and sale tax costs), and other expenses. In the proposed approach, the capital and annual operational costs are 1851 and 423 k¥/a, respectively. To calculate the beneficial sale of methane, the unit volume price of methane (i.e., subsidies) is equal to 1.7 ¥/m3, the system’s lifetime is assumed to be 10 years, and the number of annual working days is 350. Although the additional PSA equipment and pumps lead to an increase of capital and annual operational costs in the proposed approach, the selling amount of methane brings high revenue, reaching 1701.7 k¥/a. According to further calculation, after applying the proposed approach, we can recover capital costs in less than two years and the profit of the decade is approximately 10936 k¥. These economic analyses show that the proposed approach is potentially ideal to gain high profit.

ORCID

Guorui Feng: 0000-0002-8602-7508 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported by the National Natural Science Foundation of China (51504160, 51574172) and the Joint Funds of the National Natural Science Foundation of China (U1710258, U1710121). This work was also supported by the Program for the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi and the Training Program of First-class Discipline for Young Academic Backbone of Taiyuan University of Technology.

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REFERENCES

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An Approach To Address the Low Concentration Methane Emission of

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