Coal Carbonization Process

Coal carbonization include the reform process with the state of anaerobic (without oxygen) at low temperatures 459-700 Celsius and at high temperatures produces 900-12000 Celsius and porous solid materials which are residues carbonization process called coke or charcoal and volatile gases (Tsai, 1980 ).

In general, the solid material consists of semi-coke is formed from the coal that is not experiencing maturation and coke derived from coal that has undergone maturation.

During the carbonization of coal through several stages of physical and chemical changes. Physical changes of softening, the flow of material, and hardening of the merger, while the chemical changes of cracking polymerization and evaporation. The factors above may affect the quality of coal in terms of petrography composition.

Coal type is characterized by variation maceral and mineral content in coal (Cook, 1975; Stach, 1985). The formation of this type are controlled by various factors, including the spatial and temporal variation of the ancient climate, geological age, tectonic processes, the ecological conditions of sedimentation environment and the coal-forming plants in its community. Type of coal occurs in phase biochemistry.

 

Rank or rank of coal is the maturity level of organic material that starts from the lowest level of lignite, sub-bituminous, bituminous, semi-anthracite, anthracite to meta-anthracite. Carbonization stage is dominated by geochemical processes, so that the most important factor in the formation of coal rank is the temperature, pressure and time.

Observations by petrography in coal basically covers two things namely the identification maceral abundance and composition of maceral vitrinite, inertinite and liptinite. Coal with high inertinite composition and low vitrinite will tend to produce low-power one while if vitrinite high and low inertinite it will have the moderate-power, but coal with high strength obtained when the composition shows inertinite content and vitrinite was balanced. Strength of coal can also affect the rank of coal. Through petrography, coal rank can be known through its vitrinite reflectance value. The best range of vitrinite reflectance value is 1.2-1.4. The coal with good vitrinite value obviously can produce coal with high strength quality.

Tanjung Redeb, North East Borneo Geology

Structure and Tectonics

Structures found in the Tj Redeb consist of folds, normal faults, strike slip faults and lineaments. Faults trend NW-SE and SW-NE. Folds trend NW-SE and SW-NE forming anticlines and synclines. This are presumed to have four tectonic events. First event inferred during Late Cretaceous time or older. This event made the Bangara Fm. sediments into folding, faulting and low grade metamorphic rocks. Depositions of Early Eocene shallow marine sediment within the Sembakung Fm. (middle and western part of  area) was also formed Tabalar Fm. in the SE mapped in Eocene-Oligocene and followed by the second tectonic event. Deposition of the Bangara Fm. took place in the middle, east, south and west in the Oligo-Miocene where it is locally intruded by Andesitic rocks, which have been altered and mineralized. Oligo Miocene volcanic activity formed the Jelai Volcanic Rocks in the west. After deposition of the Birang Fm. the Latih Fm was deposited. The Latih Fm. sediments were formed surrounding Teluk Bayur during Late Early Miocene up to Middle Miocene.

The third tectonic event seems to have been occurred after the position of the Latih Fm. Deposition of the Labanan Fm. in the SW and Domaring Fm in the east occurred during the Late Miocene up to the Pliocene whereas the Late Miocene sediments of the Tabul Fm was formed in the north and deposition of the Sinjin Fm. (in SW and N of the sheet). After deposition of the Sinjin Fm. the Sajau Fm. was deposited in the Eastern portion of the sheet in the Plio-Pleistocene.

The Late Pleistocene, after deposition of the Sajau Fm. sediments, the fourth tectonic event was presumed to have occurred. This was showing folding and faulting sediments of the Sajau Fm. and older sediments on the lower part to form the recent topography and morphology.

Mineral and Energy Resources

Coal is one of natural resources having a good prospect in the studied area. The coal surveys were carried out since the Netherlands Indies Government and then continue investigating by the Indonesian Government. Coals are found within sediments of the Latih, Tabul, Labanan and Sajau Formations. The coal mining was formerly carried out by the NV Steenkolen Maatschappij Prapatan (SMP).

Previous geologists report 70 coal seams ranging from 20cm to 5.5 M in thickness. There are many varieties of coal grading from bituminous coal to brown coal. The bituminous and sub-bituminous coals have a quality of 6000 calories per gram. The Teluk Bayur coals have 7000 calories per gram. Building materials such as quartz sand and clays are widespread in Teluk Bayur and Labanan areas. Good quality limestone outcrops are found in Tanjung Selor but are limited in area. The limestone also crops out well in Siduung River upstream but it is hard to be mined because of bad transportation. Limited andesite outcrops were also found in the west and they were used by the logging company for building roads.

Situmorang, R.L. and Burhan, G., 1995

Regional Stratigraphy

• Qa – Quaternary alluvium, Mud, silt, sand, cobbles, pebbles and peat, grey to blackish colors, Unit thicknesses up to 40M..
• Ql – QUATERNARY REEF LIMESTONE, Reefal, coralline and brecciated corals, white to grey, brown, crystalline, hollows, containing corals, locally brecciated, deposited in shallow marine environment.
• TQps – SAJAU Fm. Alternations of claystone, siltstone, sandstone, conglomerate, intercalations of coal seams, contains molluscs, quartzite and micas. Shows cross bedding and lamination. Coal seams 20-100CM thick, black to brown. Unit thickness about 775M deposited in fluviatile and delta environments..
• Tps – SINJIN Fm. Alternations of tuff, agglomerate, lapilli, pyroxene andesite lava, silicified tuff, tuffaceous claystone and kaolin. Contains lignite, quartz, feldspar and black minerals. Unit thickness up to 500M.
• Tmpd – DOMARING Fm. Coralline limestone, chalky limestone, intercalations of marl and lignite; deposited in swampy-littoral environment, thickness is about 1000M. Of Late Miocene-Pliocene Age.
• Tmpl – LABANAN Fm. Alternating polymic conglomerate, sandstone, siltstone, and claystone, intercalations of limestone and coal seams (20-150CM thick) deposited in fluvial environment. Thickness is about 450M. Late Miocene-Pliocene age.
• Tmt – TABUL Fm. Consisting of sandstone, claystone, conglomerate and coal seam intercalations. Contains Operculina sp. Unit thickness about 1050M. Deposited in delta, regressive environment. Late Miocene age.
• Tml – LATIH Fm. Quartz sandstone, claystone, siltstone and coal in the upper part. Intercalations of sandy shale and limestone in the lower part. Black and brown coal seams 0.2 to 5.5M thick. Deposited in estuary, delta and shallow marine environments. Unit thickness is about 800M. Early Miocene to Late Miocene age.
• Tomj – JELAI VOLCANICS, Volcanic breccia, tuffaceous sandstone and tuff. Locally intercalated with coal seams, shows graded bedding and cross bedding structures. Andesite cleave intrusive. Unit thickness reached 200M. Oligocene to Miocene age.
• Tomb – BIRANG Fm. Alternations of marl, limestone and tuff in the upper part. Alternations of marl, chert, conglomerate, quartz sandstone and limestone in the lower part. Thickness is about 1100M. Fossils content: Lepidocyclina ephicides, Spiroclypeus sp., Miogypsina sp., Marginopora vertebralis, Operculina sp., Globigerina tripartite Koch, Globigerinita altispira, Globorotalina mayeri Cushman and Ellisor, Globorotalia peripheronda, Globigerinoides immaturus, Globigerinoides sacculifer, Pre-Orbulina transitoria, Uvigerina sp., and Cassidulina sp. Fossils range Oligocene-Miocene Age.
• Teot – TABALAR Fm. Lower part consist of grey marl, sandstone, shale and intercalations of limestone and basal conglomerate. Upper part consists of dolomite and calcarenite and marl intercalations. Deposited in fluvial-shallow marine environment. Thickness is about 1000M. Eocene to Oligocene age.
• Tes –SEMBAKUNG Fm. Claystone, siltstone and sandstone in the lower part. Quartz sandstone, sandy limestone, chert and tuff in the upper part. Contains fossils: Nummulites sp., Discocyclina sp. Operculina sp. Globigerina sp. Reusella sp. Nodosaria sp., Planulina sp., Amphistegina sp., and Borelis sp., Unit thickness up to 1000M. Deposited in marine environment. Eocene age.
• Kbs – BANGARA Fm. Alternations of metamorphic claystone, silicified claystone, black claystone and shale intercalated with laminated tuffs containing radiolaria. Flysch deposit.
• Tomi – INTRUSIVE ROCKS, Andesite, consisting of vitrophyre, prophyllitic andesite and pyroxene andesite lavas.

Karbonisasi

Karbonisasi meliputi proses perombakan batubara dengan keadaan anaerob (tanpa oksigen) pada temperatur rendah 459-700⁰ C dan pada temperatur tinggi 900-1200⁰ C menghasilkan material padat dan berpori yang merupakan residu proses karbonisasi disebut kokas atau arang serta gas yang mudah menguap (Tsai, 1980).

Pada umumnya material padat terdiri atas semi kokas yang terbentuk dari batubara yang yang tidak mengalami pematangan dan kokas yang berasal dari batubara yang telah mengalami pematangan.

Selama karbonisasi batubara mengalami beberapa tahap perubahan fisika dan kimia. Perubahan fisika terdiri atas pelunakan, aliran material, penggabungan dan pengerasan, sedangkan perubahan kimia terdiri atas perekahan polimerisasi dan penguapan. Faktor-faktor di atas dapat mempengaruhi kualitas dari batubara dalam hal komposisi petrografinya.

Type batubara dicirikan oleh variasi maseral dan kandungan mineral dalam batubara (Cook, 1975; Stach, 1985). Pembentukan type ini sangat dikontrol oleh berbagai faktor, diantaranya oleh variasi spatial dan temporal dari iklim purba, umur geologi, proses tektonik, kondisi ekologi lingkungan pengendapan tumbuhan pembentuk batubara dan komunitas tumbuhannya. Type batubara terjadi pada fase biokimia.

Rank atau peringkat batubara adalah tingkat kematangan material organik yang dimulai dari tingkat paling rendah berupa lignit, sub-bituminus, bituminus, semi antrasit, antrasit hingga meta antrasit. Tahap karbonisasi ini didominasi oleh proses geokimia, sehingga faktor terpenting dalam pembentukan peringkat batubara ini adalah temperatur, tekanan dan waktu.

Pengamatan petrografi batubara pada dasarnya mencakup dua hal yaitu identifikasi kelimpahan serta komposisi maseral yaitu maseral vitrinit, inertinit dan liptinit (Tabel 1). Batubara dengan komposisi inertinit tinggi dan vitrinit rendah akan cenderung menghasilkan batubara berkekuatan rendah sedangkan apabila vitrinit yang tinggi dan inertinit yang rendah batubara tersebut akan memiliki kekuatan sedang. Namun batubara dengan kekuatan yang tinggi akan didapatkan apabila komposisi batubara menunjukkan kandungan vitrinit dan inertinit yang berimbang. Kekuatan batubara dapat pula mempengaruhi peringkat batubara, melalui petrografi dapat diketahui peringkat batubara melalui reflaktansi vitrinit. Batubara dengan reflaktansi vitrinit bernilai 1,2-1,4 dapat menghasilkan batubara dengan kekuatan yang tinggi.