Underground Coal Gasification - Experiment Report (Set-up, Igniting, Recording)

 General information of Coal Gasification

 

Coal gasification is the process of producing syngas—a mixture consisting primarily of carbon monoxide (CO), hydrogen (H₂), carbon dioxide (CO₂), natural gas (CH₄), and water vapour (H₂O)—from coal and water, air and/or oxygen.

Historically, coal was gasified to produce coal gas, also known as "town gas". Coal gas is combustible and was used for heating and municipal lighting, before the advent of large-scale production of natural gas from oil wells.

In current practice, large-scale coal gasification installations are primarily for electricity generation, or for production of chemical feedstocks. The hydrogen obtained from coal gasification can be used for various purposes such as making ammonia, powering a hydrogen economy, or upgrading fossil fuels.

Alternatively, coal-derived syngas can be converted into transportation fuels such as gasoline and diesel through additional treatment, or into methanol which itself can be used as transportation fuel or fuel additive, or which can be converted into gasoline.

Natural gas from coal gasification can be cooled until it liquifies for use as a fuel in the transport sector.

 Underground coal gasification (UCG) is an industrial gasification process, which is carried out in non-mined coal seams. It involves injection of a gaseous oxidizing agent, usually oxygen or air, and bringing the resulting product gas to the surface through production wells drilled from the surface. The product gas can be used as a chemical feedstock or as fuel for power generation. The technique can be applied to resources that are otherwise not economical to extract. It also offers an alternative to conventional coal mining methods. Compared to traditional coal mining and gasification, UCG has less environmental and social impact, though environmental concerns exist, including the potential for aquifer contamination.

 Source: https://en.wikipedia.org/wiki/Coal_gasification#:~:text=Coal%20gasification%20is%20the%20process,known%20as%20%22town%20gas%22.

 

Activities - Daily Account of experiment 

In this project of the Underground coal gasification simulation, it was done in a laboratory setting to analyze the potential of underground coal gasification for potential utilization of underground coal resources.  

Figure 1 : Schematic diagram of the coal gasification model at laboratory setting

The purpose of this project was to simulate the coal ignition to extract the Hydrogen and Carbon Dioxide gas and other important gases. Other uses of in-situ coal by coal gasification include the production of electricity, coal tar among others but in this case the coal tar is of insignificant and considered as waste with water.

The account of the activities conducted during the experiment are outlined below.

  Day 1

Set  up the experiment especially connecting the sensor cables from the coal seam model to the sensor measuring equipment. Two (2) drill holes were created and installed cracking sensors and cemented. crack sensor cables were channeled to detect crack location while burning. The closest crack returns the highest reading.

All the sensor cables were connected to the sensor reading equipment and calibrated based on calibration standards and trial/tests done to ensure all good to go. The sensors were to measure temperature, cracking of coal, flow rate of gas emitting under atmospheric pressure.

Oxygen was prepared to connect into the model so that it will aid burning coal under enclosed setting and help in getting out the resultant gas/products from the coal burning face.  LP gas was also used with a long copper tube and a ignition coil attached at the end of it for igniting the coal.  All other necessary pipes were connected and ready for experiment.

All the set up was done and ready for ignition  on the next day.

Figure 2 : Equipment set up completed and ready for measurement during coal burning

 Day 2

Ignition of coal started in the morning by burning the ignition coil attached to the copper tube with electricity which is connected to the LP gas. When the ignition coil was red hot, LP gas was opened, and it flowed through the copper tube and flame  burst. This set up was inserted into the coal seam and the coal seam was ignited in the model.

 As the coal seam was burning in the model and producing smoke, the ignition coil setup removed, and oxygen was supplied into the enclosed area to aid burning and closed the inlet/outlet pipe or the regulator pipe. Oxygen also help in getting the resultant gas and moisture out from the burning face.

Electric buster fan was used to suck smoke away from the working area. At the regulator pipe, the emitted gas during the burning of the coal is collected via metal pipe and monitored and recorded at the laptop inside the laboratory. Excessive gas emitted at two exit pipes above the building was then lighted up by gas burner to continue burning to prevent smoke.

 After some time, water is connected into the burning area via pipe to prevent excessive burning and protect non coal components of the model.

The gas produced from burning coal is a mixture of gas and moisture so there was a mixing chamber or collecting tank which was wrapped  with clear hose and frozen water pumped through and the moisture content got condense which also contain coal tar and is collected at the bottom/tip of the storage tank and further stored away in storage containers for disposal.

 Readings of the temperature, flowrate, cracking are recorded hourly on prepared data sheet. Readings were also recorded continuously on the equipment and data is stored in memory disks. The recording of data is done hourly and 24 hours for 4 days.

Figure 3 : Water and coal tar mixture collected at the condenser tank

  Day 3

The hourly recording of temperature, cracking and flowrate under atmospheric condition continued.

The laboratory demonstrated and explained in simple terms the experiments to Junior High School Students. There were three set up on site at the research facility for students to observe:

1.      (a)The explanation of coal and demonstration of how coal and rock in terms of their physical properties. 

 (b) The coal and gravels were burned, and the results showed that gravels cannot burn but coal can burn when ignited.

(c) Another set up was that, coal was placed in a glass tube closed at the opening and a small L tube is connected. Using gas burner, the glass tube containing coal was burned and gas was produced and emitted through the L tube and finally lighted by gas lighter and it was burning and students were amazed with this experiment.

Figure 4 : Burning coal in the glass tube as a demonstration of coal gasification

2.  Explanation and demonstration of electricity generation by burning coal. Glass beaker was filled with water and firmly closed, and a tube connected via lid. This tube is then connected to a mini turbine with motor attached at the end and wiring was done to produce electricity and a light was produced.  By using gas burner, the beaker with water was heated and high pressure steam produced which is directed via the tube and into the turbine which turns the turbine and as the turbine rotates, it powers the motor which converts the mechanical energy to electrical energy.

Figure 5 : Demonstration of steam turning the turbine to power the motor and a red light given out.

 3.     The third set up was the explanation of the setting up of the underground coal gasification process and procedures and the explanation of the model being set up.

 

Figure 6 : Schematic Diagram used to explain the coal gasification set up at laboratory.

Day 4

The hourly recording of temperature, cracking and flowrate under atmospheric condition continued and Hosted the another group of Junior High School Students and conducted the same experiments and explanation on the previous day .

Figure 7 : Junior High School Student and technical team on site after completion of explanations.

 

Day 5

Continued with hourly recording of temperature, cracking and flowrate under atmospheric condition and removing wastewater from tank and poured into storage containers for treatment before disposal.

 Day 6

 Recording of readings or measurements stopped at 03:00 on the 6th Day. All the connections dismantled, and experiment was completed and ready for clean up the area. Most of the equipment were disconnected and removed.  

Another experiment at a small scale was prepared using small drums. 9 small drums were prepared by drilling the bottom at center and pipe inserted. Then poured mixed cement and let it dry.  Then coal seams measured their weights and placed in the drums and packed cement again at top. Then it was left to dry and packed in the laboratory for experiment in September 2020. Sensors will be installed in those drums and follow the same procedure and recording.  

Coal Samples

Drums ready for packing coal

Figure 8 & 9: Coal measured and ready for packing in drum as prepared on the next photo

Coal packed in drums

Coal packed and sealed with concrete

Figure 10 & 11 : Coal  packed in drums and finally covered with cement and ready for next experiment in a smaller scale.

 Day 6

 Finally, all sensor cables were removed and from the drill holes where the crack sensors were installed, the team poured white cement mixed with water until it filled up to brim. This was to determine extent or quantity of coal burnt during the experiment. Quantity of cement and water ratio mixed were recorded in the data sheet which also include the quantity of cement wasted.

Discussion and Conclusion

The data collected from this underground coal gasification would be analyzed with suitable software and results made known or published to stakeholders involved and the public once presented on publications.

Underground Coal gasification seems to be the effective way of extracting in-situ coal by way of burning and obtain the various desired products. Of course, there are economic and environmental challenges and consequences involved but needs careful consideration and management from feasibility to development to production to closure and post closure in such a project.

Disclaimer:

Some of the information provided here may not reflect the real intention of the experiment and detail information my not be provided. This article just a reported account of students who attend the experiment on internship purposes to broaden the knowledge and understand the concept of Under Ground coal gasification.

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Partial Assistance to Masters and PhD Candidates in filling Application Forms for Japanese Scholarships or Self Sponsor

This is a general announcement to keen researchers and potential researchers of the Earth Resources Engineering in Papua New Guinea and any other Pacific Island Nations.

If you are one of the interested or  potential research candidate (Master ,PhD, Post PhD etc) who are planning to apply for further studies through Japanese Government Scholarships or self sponsor or by any form of arrangements and need assistance in securing Supervisors/Professors from various Japanese Universities which is one of the requirements for the Scholarship Applications Forms, then we are more than willing to assist you in this regard. 

Our team has been approached by several Professors of the Department of Earth Resources Engineering in Kyushu University Under the Faculty of Engineering to connect any interested research candidate (Master ,PhD, Post PhD etc) who may be interested to study in Japan through either scholarships or by various  sponsorship arrangements.

Kyushu University's Department of Earth Resources Engineering  aims at equipping students with professional-level knowledge in the field of earth resources as well as a grounding in a wide range of engineering fields, the Division of Earth System Engineering provides lectures, lab sessions and practical training as follows:

Economic Geology	Resource Geology I & II Mineral Engineering Mineral Engineering Experimentation I & II
Exploration Geophysics	Geo-Information Science I, II & III Geo-Information Science Experimentation I & II
Geothermics	Geothermics Geothemal Engineering Geothermal System Modeling Geothermal Engineering Experimentation I & II
Resources Production and Safety Engineering	Resources Development and Environment Resources Production Systems Safety Engineering Safety Engineering Experimentation Resources Production Experimentation
Rock Engineering and Mining Machinery	Rock Engineering I & II Mining Machinery System Engineering Rock Engineering Experimentation I & II
Mineral Processing, Recycling and Environmental Remediation	Mineral Processing Engineering I, II and III Mineral Processing Engineering Experimentation I & II
Energy Resources Engineering	Energy Engineering Reservoir Engineering Mass Transfer Engineering Energy Resources Engineering Experimentation I & II

 Source: https://www.eng.kyushu-u.ac.jp/e/g_earth.html 

If you are interested or need guidance in this regard then feel free to contact us through the contact form on our website.

The requirements and steps are:

1. Topic of Research

2. Your Scope of Study or Study Plan is basically the brief of what you intend to do under your topic selected. i.e. Introduction, Objective, Methodology etc.. Have a clear idea on the topic.

3. State Clearly which Laboratory you would like to apply to do your research. The Laboratory of your choice can either be related to your topic.

4. Provide you contact information especially e-mail. 

5. We will introduce your topic and your contact to the Professors concern.

6. The Professors will then contact you for further discussions regarding your topic and research plan and further provide direction for actions at your end including the entry requirements and applications.

Kasuga Gold Mine in Kagoshima, Japan

DISCLAIMER

To avoid doubt, this is not a scholarship information and we do not provide scholarship Application Forms either. It is just an announcement offering assistance to those who are in need. Helping others progress in Earth Resources Engineering.

We help to connect interested researchers to Researchers.

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Slope Stability Analysis of Hamata Tailings Dam, Hidden Valley Mine, Papua New Guinea

 ABSTRACT

Construction and management of Tailing dams in Papua New Guinea (PNG) is faced with many challenges such as high altitude with high rainfall (2000-5000 mm/yr), high seismicity and structurally controlled zones which pose threat to the slope stability of tailings dams. Therefore, slope stability analysis is necessary to give confidence to some extent to the stakeholders. The location for this study is at Hamata Tailings (dam) Storage Facility (TSF) at Hidden Valley Mine in PNG which has two rock/earth filled embankments, the main dam and the saddle dam with downstream construction method. Currently the TSF owner is planning to raise the dam height from RL 2000 to RL 2015 with extra 15 Mt storage capacity as the pond water approaching its designed capacity at RL 2000. The objective of this study is to analyse the slope stability of Hamata TSF using phase 2 based on the design basics for the crest expansion from RL 2000 to RL 2015 and beyond and recommend an ideal slope stability under various conditions in terms of shear strength reduction factor ((SSRF). The results obtained in this study is useful for PNG Mining Regulators in comparing company results in the appraisals for tailings dam development proposals and, it will be useful to future researchers in PNG and other similar tropical regions.

 Keywords: Tailings dam, slope stability analysis, Hamata TSF crest expansion, embankment, Shear Strength Reduction Factor, RL-Reduced Level(m).

 INTRODUCTION

Tailing dam construction in PNG are faced with natural factors such as high altitude with high rainfall (2000-5000 mm) coupled with high seismicity zones and geological/geotechnical conditions which pose threat to the stability of tailing dams. One of the learned experience is the case of Ok Tedi tailings dam failure in 1984 (Griffiths et al. 2004). After this incident, the PNG government allowed mining companies to discharge tailings into the river systems and on to the sea floor (deep-sea tailings placement (DSTP)) which pollutes the riverine and ecology within the vicinity of the mine impacted natural environment and communities downstream and the marine lives respectively.  However, the PNG Government amended the Environment Act to abolish riverine tailings discharge and encourage tailings dam construction in PNG.

In compliance with the PNG government’s intention, the Hidden Valley mine and the K92 mine have constructed tailings dams respectively and store their tailings in the facilities overcoming all odds. However, management of the tailings dam under challenging environment is one of the key concerns of the dam owners to make sure the dam is stable throughout the operation till closure and post closure. On the other hand, the mining regulators and the impacted communities downstream also concern about the stability of the dam as it will affect their livelihood in an unlikely event of failure.

 In this study, it is proposed to review and assume Hamata Tailings Dam designs and embankment material properties to evaluate the slope stability conditions of the TSF under various geotechnical/soil parameters.

 Study Location – Hidden Valley Mine

The Hidden Valley(HV) Mine (coordinates: 7⁰27’17” S,146⁰40’24” E) in PNG operates the Hamata Tailings dam.  Hidden Valle Mine is an Open pit gold-silver mine located in Morobe Province, about 210 km North West (NW) of Port Moresby. The Mining Lease was Granted in 2005 for 20 years and renewal upon expiry. The Lease holder is Harmony Gold Ltd. Mine development Construction started in 2007 and commercial production began in September 2010.

 Figure 1 PNG map (Courtesy of Mineral Resources Authority) showing location of Hidden Valley Mine (Circled).

 Mine Layout

The mining lease area has two main mine pits which are about 6 km apart and mining at three main ore bodies which are named as Hidden Valley- Kaveroi(HVK) and Hamata epithermal gold and silver deposits.  The Hidden Valley and Keveroi Ore deposits are close to each other while the Hamata ore body is on its own. Ore mined from HVK is transported via belt conveyor to the processing plant near Hamata pit. 

The mine has a total mineral resources of 68.776 Mt at Hidden Valley Kaveroi deposits with a metal content of 3.307 Moz Au and 57.270 Moz Ag while the Hamata deposit has a total mineral resource of 2.216 Mt ore with metal content of 0.133 Moz Au as of June 2019 (HV Annual Report-2020).

 Figure 2 Hidden Valley Mine Plan (Rynhoud et al ,2017)

 Hamata Tailings (Dam) Storage Facility (TSF)

The Hamata Tailings (Dam) Storage Facility is constructed using the downstream method with two earth and rock filled embankments, the saddle dam and the main dam. The dam Construction commenced in June 2007 and the starter embankment construction was completed in February 2009 (Rynhoud et al, 2017). The embankments are constructed using the waste rock/materials from the two mine pits at HVK and Hamata.

Klohn Crippen Berger Ltd (KCB) is the design engineer for the Hamata TSF, (Rynhoud et al, 2017). The main dam and the saddle dam is designed to a maximum crest elevation of RL 2000 with a storage capacity of about 40 Mt of tailings with a mill throughput of 4.2 Mtpa (Rynhoud et al, 2017). The height of the dam from the main dam is about 145 m at the RL 2000 crest.

Figure 3 Hamata Tailings Dam, Main dam at NW and Saddle dam at SE (Google Image-7°25'36.6"S146°38'32.0"E)

 Problem Statement

Tailings deposition and sedimentation at Hamata TSF result in ponded water approaching dam crest elevation at RL 2000, the miner proposed to raise the dam height to RL 2015 with extra 15 Mt tailings storage capacity.

The foundation of expansion (RL 2015) embankment is likely to begin at RL1960 to RL 1970 of the RL 2000 design. With the pond water seeping through the embankments coupled with high rainfall, the geotechnical parameters are altered over time and displacement of embankment is anticipated under wet conditions and/or seismic conditions and potential dam slope failure is anticipated in a worse case scenario.

The focus of this study is to review available options to minimize significant displacement of embankment under various stress conditions.

 Significance of Study and Research Advancement

Related literatures of slope stability analysis of tailings dam in PNG is rarely available online except the design basics of dam published by Rynhoud et al 2017 and Murray et al 2010. There are also publications of tailings dam about Frieda River Mining Project and Ok Tedi Mine of which most of the data from this study is obtained from all these publications.

Further research can be done beyond this study in terms of slop stability analysis of tailings dam under various geotechnical and seismic conditions in similar tropical regions.

 Objective Of The Study

The objective of this study is to analyze the slope stability of the Hamata Tailings dam construction and operation of crest expansion from RL 2000 to RL 2015 and recommend an ideal risk factor of safety under various stress conditions. The study adopts Finite Element Analysis in Phase2 software to analyze the slope stability conditions of the dam for RL 2015 based on the design basics and material properties of the dam embankment. Design basics are modified for the purpose of modelling and may not represent construction design specifications.

Slope Stability conditions are expressed in terms of Shear Strength Reduction Factor (SSRF or SRF) and the corresponding displacement under stress conditions.

 METHODOLOGY

Study methodology is designed in a way to review related literatures of the past and collect field data including design parameters and proceed with modelling. Results from the model are interpreted to make conclusion and necessary recommendation is anticipated.

In the case of field research which is impossible at hand, related data from other projects in both PNG and abroad are borrowed for the purpose of modelling in this study.

General information regarding mining in PNG are reviewed and adopted some scripts in this paper. Most of the data at hand is obtained from both unpublished and published literatures related to the Mining in PNG and off-course Hamata TSF.

Most of the material property data is expected to be borrowed from Frieda River Mining Project and other publications and reports which are referenced in this paper.

 Design Basics

The design basics are adopted from the published papers by Murray et al, 2010 and Rynhoud et al, 2017 for RL 2000 and assumptions are made for RL 2015 in terms of construction methodology. A combination of upstream, centerline and downstream method of construction is assumed to analyze the slope stability condition of the dam using the phase 2 software. The maiden modified design in the model is shown in Figure 4.

Figure 4 Proposed expansion design (model-cross section, main dam) for RL 2015 (modified from Murray et al, 2010)

 The foundation of expansion embankment is at RL 1960 and RL 1970 in the model design. The expansion (RL 2015) design for the model is modified from the RL 2000 design published by Murray et al, 2010.  

This study adopted material property data from the proposed Frieda River Tailings Dam in PNG which has similar embankment fill materials to that of Hamata TSF. 

 Modeling And Results

Based on the borrowed embankment material property/parameters and design basics data, a maiden model was built in Phase2 and computed to observe the behavior of the TSF embankment. The material strength parameters used in the model are shown in the Table 1. Mohr-Coulomb failure criteria is used for all plastic materials type computed in the model.

 Table 1 Material strength parameters

Material	Unit Weight (MN/m3)	Cohesion  (MPa)	Friction angle(o)
Bedrock	0.02	0.25	45
Boulder Colluvium	0.018	0	30
Lacustrine(clay-assume)	0.02	0.03	20
Alluvium(Organic)	0.018	0	15
Oxide	0.018	0	25
Random Fill (Oxide)	0.018	0	25
Fresh rock fill	0.023	0.6	25
Gravel filter drain	0.021	0	35
Tailings	0.02	0.001	34

 The results obtained from the maiden model shows that potential failure is anticipated. At the critical SRF of 1.4, the total displacement is 0.153 m at the embankment. Ground water conditions and permeability are not computed in the maiden model but will consider in the preceding models.

  

Figure 5(a) Shear Strain, underground water seepage flow rate at main dam embankment in model. (b) Total Total Displacement. (c) Shear Strength Reduction Curve.

Figure 6 Model Results at various SRF in terms of Shear Strain and Displacement Progression at increasing SRF.

 DISCUSSION and CONCLUSION

Results indicate that shear strain is concentrated along the chimney drain and almost steady at all stages of SRF. Displacement is significant and vary at all stages.  At Critical SRF of 0.48, Maximum Displacement is 0.251m.   Maximum displacement is observed at the foundation of RL2015 expansion.  The    Toe of TSF has insignificant shear strain and is stable but weight of displaced materials can induce stress at the toe to be unstable over time. Thus, it requires more attention in this regard.

The Weight of RL2015 foundation cause the maximum shear strain at the chimney drain/ channel in the model and thus displacement at the crest of RL 2015 and along the slope of the downstream embankment.  Seepage water might cause the saturation of embankment materials and failure is anticipated during wet conditions and/or seismic activity.

Therefore there following measures will be taken in the next phase of this study:

q  Model

ü  Variation of model parameters and input data

ü  Analyze other Sections of the TSF.

q  Review Counter Measures to stabilize the unstable slope conditions:

ü  Construction Method

ü  Fill material variations

ü  Geotechnical support systems –i.e. geogrid

ü  Design parameter variations etc..

 

Note:

 This publication is a work in progress and several articles will be published in the future. If you want full paper of this publication and the advanced information regarding Slope Stability Analysis of  Tailings dam then contact  us via contact form.

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