Trong quá trình nghiên cứu thực hiện luận văn: "nghiên cứu mô phỏng và thực nghiệm q trình khí hố than ngầm", Tác giả thực hiện song song việc nghiên cứu tài
liệu q trình khí hóa than ngầm, tìm hiểu, ứng dụng phần mềm mô phỏng Comsol Mutilphysics kết hợp với q trình thực nghiệm khí hóa than.
Qua q trình nghiên cứu thực hiện luận văn, tác giả đạt được những kết quả sau: - Nắm bắt được cơ sở cơng nghệ khí hóa, vận dụng vào nghiên cứu thực nghiệm được thử nghiệm trên mơ hình thực nghiệm khí hóa tại xưởng Nhiệt cho ra sản phẩm khí cháy có thể cháy được.
- Tìm hiểu và sử dụng phần mềm mơ phỏng Comsol Mutilphysics để mơ phỏng q trình truyền nhiệt, q trình truyền chất xảy ra trong mơ hình khí hố. Đã khắc phục được các lỗi thường gặp trong q trình mơ phỏng.
- Mơ phỏng chậy được q trình truyền nhiệt và truyền chất của q trình khí hóa than. nhưng vẫn chưa đủ để đáp ứng yêu cầu và điều kiện để áp dụng q trình mơ phỏng này vào thực nghiệm.
- Nhờ kinh nghiệm thu được sau nhiều lần vận hành thử nghiệm, đã vận hành lò ở chế độ tạo ra sản phẩm khí có thể cháy được. Điển hình là lần đốt thử nghiệm cuối cùng vào ngày 24/07/2016, sau 20 phút vận hành đã cho ra hỗn hợp khí đốt ra ngọn lửa đầu màu xanh nhạt.
- Bên cạnh đó việc áp dụng phần mềm Comsol Multiphysics 5.2 vào q trình khí hóa than hỗ trợ rất nhiều trong điều kiện thiếu các thiết bị đo đạc đắt tiền và hiện tại chưa có nghiên cứu cụ thể nào về ứng dụng phần mềm này vào q trình khí hóa than.
Mặc dù vậy, kết quả nghiên cứu lý thuyết cũng như nghiên cứu thực nghiệm cịn khá
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hố, mà mới chỉ được xem như là sản phẩm quá trình cháy thiếu Oxy. Tuy nhiên có thể coi đây là kết quả bước đầu trong lĩnh vực nghiên cứu hóa khí than ngầm tại Việt Nam.
- Yếu tố thời gian: thời gian thực hiện luận văn có giới hạn, trong khi q trình thực hiện cần nhiều thời gian để nghiên cứu và tìm ra giải pháp thực hiện mơ phỏng một cách chính xác.
- Độ chính xác của thiết bị đo cịn chưa mang lại tính chính xác cao.
- Yếu tố kinh phí cũng ảnh hưởng rất lớn đến chất lượng luận văn do một lần thực hiện khí hóa tốn rất nhiều kinh phí mà em chưa đáp ứng được.
Kiến nghị hướng phát triển đề tài:
- Từ những bước đầu tìm hiểu tài liệu cũng như sử dụng phần mềm Comsol 5.2 đã phần nào mang lại kết quả có tính tương đối, nhưng để đạt được kết quả cao hơn và chính xác thì chúng ta cần thêm nhiều nỗ lực để nghiên cứu về phần mềm mô phỏng Comsol.
- Do điều kiện thực nghiệm khó khăn, kiến thức và kỹ thuật hạn chế nên mơ hình thực nghiệm chưa thể đưa vào thực tế. Để đưa cơng nghệ khí hóa vào thực tế cần sự giúp đỡ từ chuyên gia, sử dụng công nghệ tiến tiến và cần hỗ trợ đầu tư từ các nguồn khác.
- Bên cạnh đó tiếp tục phát triển, nâng cấp mơ hình khí hóa than có sẵn để có thể tiếp tục tiến hành thí nghiệm, mang lại những số liệu thống kê tốt hơn, nâng cao hiệu suất khí hóa.
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TÀI LIỆU THAM KHẢO
[1] Đặng Quốc Phú, Trần Thế Sơn, Trần Văn Phú, Truyền nhiệt , NXB giáo dục, 2004. [2] Patankar S.V, Numerical Heat Transfer and Fluid Flow, McGraw Hill, 1980.
[3] Phạm Lê Dzần, Nguyễn Công Hân. Cơng nghệ lị hơi và mạng nhiệt. Nhà xuất bản Khoa Học và Kỹ Thuật Hà Nội – 2008.
[4] PGS.TS Bùi Hải, PGS.TS Trần Thế Sơn, Bài Tập Truyền Nhiệt - Nhiệt Động Và Kỷ Thuật Lạnh, Nhà xuất bản khoa học và kĩ thuật Hà Nội, 2001.
[5] Nguyễn Bin, Đỗ Văn Đài, Long Thanh Hùng, Đinh Văn Huỳnh, Nguyễn Trọng Khuông, Phạm Văn Thơm, Phạm Xuân Toàn, Trần Xoa, Sổ Tay Quá Trình Và Thiết Bị Cơng Nghệ Hóa Chất – Tập 1, Nhà xuất bản khoa học và kĩ thuật Hà Nội, 1999.
[6] Nguyễn Thanh Quang (ĐHBK - Đà Nẵng), Đặng Thế Hùng (Công ty TNHH Trường Quang II), “Nghiên Cứu Chế Tạo Hệ Thống Hóa Khí Than Tầng Cố Định Ngược Chiều”, Tạp Chí Khoa Học Và Cơng Nghệ Nhiệt Số 77.
[7] Gasification Technology, Technical Issues in the Design of Gasifiers, 1999.
[8] Krzysztof Stanczyk, Krzysztof Kapusta, Experimental simulation of hard coal underground gasification for hydrogen production, Fuel, 2012.
[9] Krzysztof Stanczyk Hydrogen-oriented underground coal gasification for Europe (HUGE)-Euro commission, 2009.
[10] Krzysztof Stanczyk, Krzysztof Kapusta, Pollution of water during underground coal gasification of hard coal and lignite, Fuel, 2011.
[11] G. X. Wang, Semi industrial tests on enhanced underground coal gasification at Zhong- Liang-Shan coal mine, Curtin university technology, 2009.
[12] M.Wiatowski Kstanczyk, Semi-technical underground coal gasification (UCG) using the shaft method in Experimental Mine “Barbara”, Fuel, 2012.
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[13] Results of the tracer tests during the El-Tremedal underground coal gasification at great depth, Fuel, 2000.
[14] Review of Underground Coal Gasificationwith Reference to Alberta's Potential.
[15] Sateesh Daggupati - Laboratory studies on combustion cavity growth in lignite coal
blocks in the context of underground coal gasification, Elsevier, 2009.
[16] V. Prabu- Simulation of cavity formation in underground coal gasification using bore hole combustion experiments- Elsevier, 2009
[17] Lanhe Yang, Jie Liang, Li Yu, Clean coal technology - Study on the pilot project experiment of underground coal gasification, 2002.
[18] Lanhe Yang, Study of the model experiment of blinding - hole UCG, 2002. [19] Ahad Sarraf Shirazi - CFD Simulation of Underground Coal Gasification, 2013.
[20] PGS.TS Phạm Lê Dần - Cơng nghệ lị hơi và mạng nhiệt.Nhà xuất bản Khoa Học và Kỹ Thuật Hà Nội – 2005.
[21] Đồ án các anh chị khóa trước. [22] COMSOL Mutiphysics Library.
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Review Of Underground Coal Gasification Technologies
Nguyen Le Hong Son Nguyen Hoang Anh
Ho Chi Minh City University of Technology and Education Ho Chi Minh city, Vietnam
Sonnlh@hcmute.edu.vn , hoanganhskill@gmail.com
Hoang Ngoc Dong
Da Nang University of Technology Da Nang city, Vietnam
Abstract—In thewake of increasingchallenges of highprices
of oil and gas and uncertaintiesaboutpoliticalstability in many oil and gas producingcountries, coalbecomesmore and more important in the comingyearsforitsvastreserves and widedistributionallover the world. The technology of Underground Coal Gasification (UCG), converting in-situ, unmined coal intocombustiblegases, hascontinued to attractworldwideinterestbecause of its ability to exploit coal whichisotherwiseunminablebyconventionalminingtechniquesdue to deepdepositdepths, thin seam thickness or low quality, in an economical, safe and environmentally friendly manner. We have recently reviewed the current status of UCG throughout the world and analyzed the criteria for selecting UCG in the Red River Delta (RRD)- Viet Nam. This article presents the main results of this work.
Keywords—underground coal gasification, ucg, syngas, coal seam, unmined coal seams.
INTRODUCTION
The quest for energy resources delineates the progress of mankind from the stone age to the modern era. For the sustainable development and raising the living standards, man has tried all possible energy resources offered by the nature and used them creatively, for the better quality of life. The conversion of available fossil fuel into useful heat energy has been an area of interest for long time. This rudimentary practice was encouraged by the abundant availability of the fossil fuels such as coal, natural gas and crude oil. The burgeoning energy demand was the main motivation behind the development of various technologies that converted fossil fuel into heat energy. The coal gasification is one of the important energy harnessing technologies, which converts coal into useful gaseous fuel
The Underground Coal Gasification technology (UCG) is a technology for recovering the energy content of coal reserves by gasifying it in-situ with the application of the skilful utilisation of operating conditions and the geological position of the coal seam. This process aims at converting coal into combustible fuel gas by the gasification of the coal seam in the presence of air, oxygen and steam. This technology has been proven to be very useful in situations where coal deposits can
not be exploited economically or technically by conventional mining processes.
The basic principles of UCG are similar to that of conventional surface gasification of coal. The UCG process is illustrated in Fig.1. The process of UCG involves the injection of steam and air or oxygen into a coal seam from an injectionwell and recovering combustible fuel gases from the production well. These bore wells are drilled into the coal seam from the surface and combustion is initiated at the bottom of one of the bore holes. Both bore wells are linked with various available linking techniques to enable gas flow
In recent years, people have applied many methods of burning and transfer coal fuel to other fuel types are very effective, it reduce emissions source pollute the environment, as well as transforming coal into liquid fuel, coal washing ... and especially the coal gasification. Coal gasification is a method to transfer coal to gas or used as raw materials for chemical synthesis.
Figure 1: Principle of underground coal gasification. REVIEW OF LITERATURE:
Gasification Process- Chemical reactions
The gasification process occurs in the coal of the gasifier was shown in Fig. 2. Based on the differences in major chemical reactions, the temperature, and the gas compositions, the gasification channel can be divided into three zones: oxidization zone, reduction zone and dry distillation zone.
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Figure 2: The diagram of UCG.
In the oxidization zone, the multi-phase chemical reactions between oxygen contained in the gasification agent and the carbon in the coal seam occur, producing heat and making the coal seamfull-hot.
C + O2 → CO2 + 393,8 MJ/kmol (1)
2C + O2 → 2CO + 231,4 MJ/kmol (2)
2CO + O2 → 2CO2 + 571,2 MJ/kmol (3)
In the reduction zone, the major reactions are that H2O(g) and CO2 are reduced to H2 and CO under the effect of high temperature, when they meet with the incandescent coal seams.
C + CO2 → 2CO + 162,4 MJ/kmol (4) C + H2O(g) → CO + H2 + 131,5 MJ/kmol (5) Additionally, under the catalytic action of coal ash and metallic oxides, a certain methanation reaction occurs.
C + 2H2 → CH4 + 74,9 MJ/kmol (6)
Heat Transfer and Species Transport Process- Thermodynamics
Model of the temperature field of the coal layer.
Considering the heat conduction within the coal layer, according to the law of conservation of energy, the temperature field equation of the coal layer is obtained as
1 s s s s s s s s s s s T T T T C K K K F T z z r r r r where
+ Cs is the specific heat of the solidphase, KJ/kg.K; + Fs is the heat losscoefficient of the solid phase, KJ/kg.s.K;
+ Ks is the heat conduction coefficient of solid
phase, KW/m.K;
+ Tsr0 is the temperature of the external coal layer, K;
+ and rs is the density of the solid phase, kg/m3.
Flow equation for the gas phase.
According to the law of conservation of momentum, for the conditions of UCG, the flow equation of fluid in the gasification channel can be explicitly expressed as
2 2 2 1 g g g g P P P RT r z r r r k
where, Pg is the fluid pressure, Pa; is the cohesiveness
coefficient, Pa.s; is a source or convergence item; R is the gas constant, J/mol.K and k is the seepage rate, m2.
Brinkman Equations theory
1 2 . . 1 2 . . 3 p br p p T br p p u Q t u u u t Q p u u u I k u F In theseequations : + u: is a velocity vector (m/s) + p: is the pressure (Pa)
+ : is the density of the fluid (kg/m3)
+ : (SI unit) is a dynamic viscosity of the fluid(Pa.s) + p: is the porosity
k: is the permeability tensor of the porous medium. + F: hệ số Forchheimer
+ Qbr: is a mass source or mass sink (kg/m3.s) + : is the Laplace
When the neglect inertial tern check box is selected, the tern .
p u u
is disabled. For incompressible flow, the density stays constant in any fluid particle, which can be
expressed as p u. 0 t and equation p . u Qbr t reduces to .u Qbr.
Heat transfer in a porous media:
peff p . . vd eff T C C u T q Q Q t q k T where:
+ : (SI unit: kg/m3) is the fluid density.
+ Cp: (SI unit: J/(kg·K)) is the fluid heat capacity at constant pressure.
+ (ρCp)eff (SI unit: J/(m3·K)) is the effective volumetric heat capacity at constant pressure defined by an averaging model to account for both solid matrix and fluid properties.
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+ u: (SI unit: m/s) is the fluid velocity field, either an analytic expression or the velocity field from a Fluid Flow interface. u should be interpreted as the Darcy velocity, that is, the volume flow rate per unit cross sectional area. The average linear velocity (the velocity within the pores) can be calculated as uL = u ∕ θL, where θL is the fluid’s volume fraction, or equivalently the porosity.
+ q: is the conductive heat flux (SI unit: W/m2).
+ Q: is the heat source (or sink). Add one or several heat sources as separate physics features (W/m3)
+ keff : (SI unit: W/(m·K)) is the effective thermal conductivity (a scalar or a tensor if the thermal conductivity is anisotropic), defined by an averaging model to account for both solid matrix and fluid properties.
SITUATION OF RESEARCH
In Viet Nam.
Prof. Nguyen Thanh Son (Director of Vietnam National Coal - Mineral Industries Group - Vinacomin ) had research on Thermal Energy Magazine No. 105 of UCG in the Red River Delta. The authorgivenmathematicalmodel and calculated in the production.
In The world
Over 50 pilot UCG plants have been conducted worldwide since the 1930s. These developments have been concentrated in Union of Soviet Socialist Republic (USSR), Europe, USA and China. USSR may be considered the first nation to heavily engage in UCG. However, detail information on the UCG trials in USSR is scarcely available. These trials were conducted in different coal seams with different depths and thicknesses. Compare to US and USSR trials, most of the European trials have been performed in deeper coal seams ( Depth > 300 m ) of lower rank coals and few efforts for using highrank coals (anthartice and bituminous coals) were unsuccessful. In the following sub-sections, a brief review of important field trials and their findings are described based on their location.
Figure 4 summarizes all the UCG field trials performed worldwide in term of their depth and thickness of the coal seam. As can be seen, all of the trials except European efforts have been conducted in relatively shallow seams which are not currently targeted because shallow depth of seam limits the application of high operating pressures and increases the possibility of leakage.
Figure 4: The thickness and the depth of the test is performed all over the world (C.Pana, 2009)
Chinese studies have been mainly focused on the production of hydrogen-rich syngas from abandoned shallow coal mines (Depth <150 m). They followed a somehow different approach to achieve high concentrations of hydrogen. In this approach, they switched the injected gases between steam and oxygen in a cyclic manner. A long tunnel arrangement of wells was established as a result of these trials (Couch, 2009). It is shown that this method is capable of producing high quality syngas with a heating value of 12-14 MJ/m3
Figure 5: Long tunnel configuration in China (Couch (2009)) Yeary and Riggs (1987) calculated the growth for lignite and sub-bituminous coal. Recession rate of cavitysidewall has beenshown to have a strongdependenceon the flow rate and temperature of the injected gas. Lignite recession rate has been reported to begenerallylowercompared to sub- bituminous, while having a higher spalling rate (Yeary and
Riggs. 1987). These
observationsareconsistentwithweakmechanicalproperties of lignite and high reactivity of sub-bituminous coal. Also, ash has remainedintact in the sidewall for lignite coal, which can be attributed to higher ash content and stronger ash structure in lignite sample.
A series of experiments have been conducted in European Union, mostly Poland, to investigate the UCG behaviour in lignite coal seams. The mainobjective of thisongoingproject is to study the effect of variousparameters on hydrogenconcentration in syngas. Experiments wereconducted in a 2.5*0.7*0.7 m coal block with a 10 cmlinkbored in the block. Three distinctstages for the UCG process were observable in all of these experiments: ignition, combustion, and gasification with steam. As reported by Stańczyk etal. (2010), only 1 hr of stablesteamgasificationwasachieved in theirfirst experiments and further gasification was impossible due to low temperature of the coal block and fastdrop in temperature due to high moisturecontent of the experimented lignite (53%). To compensate this, the experiment was continued with high injectionrates of oxygen. Replacing oxygen with air was unfeasible due to rapiddecrease in temperature and termination of reactions (Stańczyk et al., 2011). Thus, oxygenrich air was used and optimum oxygen/air ratios for lignite and hard coal UCG were proposedaccordingly. Shorter ignition and combustion periods, higher
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temperatures and lower oxygen/air ratios were found to be attainable for hard coal due to its highercarbon content compared to lignite. In order to increase the extent of steam-gasification injection of pure oxygen was continued until high temperature of about 1100 to 1200 oC was reached in the reactionfront (Stańczyket al., 2012). Then, the inlet gas was switched to steam and the heating value of the