Investigation on Self-binding Agent in Low Rank Coal during Low Temperature Binderless Briquetting Process

Investigation on Self-binding Agent in Low Rank Coal during Low Temperature Binderless Briquetting Process Toto Hardianto*, Adrian R Irhamna, Pandji Prawisudha, Aryadi Suwono Department of Mechanical Engineering Institut Teknologi Bandung Bandung, Indonesia *Email: toto@termo.pauir.itb.ac.id Abstract A novel technology to upgrade low rank coal into steam coal has been developed in Institut Teknologi Bandung, namely Coal Upgrading Technology (CUT). The product from this process is in dry powder form; therefore, additional agglomeration-compaction process is needed to improve the handling, storage and transport ability of the product. Briquetting process without the usage of binder (binderless briquetting) is chosen, but it usually requires high pressure and high temperature to produce a briquette with desirable mechanical strength. In this research, the potential of self-binding agent during the binderless briquetting process, especially in low temperature of less than C, was investigated. An axial hydraulic jack capable of compressing the briquette equal to 1500 bar was used with electric heated dies maintained at 50 C. The mechanical strength and reabsorptivity of the formed briquette was examined in drop test and natural drying experiments, and its physical composition was obtained using Thermogravimetric Analyzer. It was found that briquette with higher initial moisture content and light volatile matter has better strength and waterresistance, lead to a conclusion that moisture content and light volatile matter in the coal is regarded as self-binding agent in the low temperature binderless briquetting. Index Terms binderless briquetting, low temperature briquetting, self-binding agent, low rank coal upgrading I. BACKGROUND Coal resources in Indonesia is considerably high. According to the official data of Indonesian Ministry of Energy and Mineral Resources, coal resources in Indonesia is about 104 billion tons. Sadly, 30-40 % of total coal resources are identified as low rank coal [1]. Low rank coal is the youngest coal and has the lowest calorific value compared to that of medium or high rank coal. About 80 % of coal production in Indonesia is utilized as main fuel in power generation. The latest official data of Indonesian government says that 78 million ton of coal is consumed in one year only for power generation purposes [2]. However, only middle rank and high rank coals are usually exploited for power generation purposes, since low rank coal is not compatible with common burner installed in power generation facilities [3]. The wet properties and different ignition characteristics of low rank coals are the main factors why low rank coal cannot be utilized in common burner easily. Additional equipment might be required to burn low rank coal in such burner. Therefore, despite Indonesia has plenty of low rank coal resources, its exploration and exploitation are limited and tend to be set aside in Indonesia. To deal with that challenges, Thermodynamics Laboratory of ITB developed a novel technology namely Coal Upgrading Technology (CUT). This technology is developed to increase the quality of low rank coal [4][5]. In CUT process, low rank coal is dried using superheated steam to produce high calorie coal in powder form, since it is very practical for direct use purposes in which high calorie coal is burnt directly in common burner. However, in some cases, CUT products are preferred to be transferred from one place to another, and to be kept in storage before it is finally burned. In order to serve this option, the handling, transport, and storage ability of CUT product need to be improved. Analyzing these facts, an additional agglomeration-compaction process is considered to be obligatory for CUT products after the coal upgrading process. II. COAL BRIQUETTING PROCESS Briquetting is a common technique to obtain agglomeration-compaction process for powder material [6]. In the briquetting process, there are substances known as binder which provides adhesive properties among the briquetted particles. When particles are compacted in adequate pressure, binder will support the agglomeration process among the particles caused by mechanical interlocking. The mechanical interlocking itself is greatly affected by the deformation of coal particles, particle size, and compaction pressure [6]. Briquetting process is generally classified into conducted in two methods of briquetting with additional binding material and without any additional binding material (binderless briquetting). In briquetting with additional binding material, the agglomeration process is mainly produced by adhesive properties of binder material. However, in coal briquetting process, briquetting with additional binding material is not preferred. It is because the addition of binding material might change the produced briquette composition, which may affect

its quality as fuel. Besides, the briquette may be sticky and cause difficulties during its handling. Furthermore, the price of additional binding material is quite expensive [6]. In binderless briquetting process, agglomeration is mainly affected by self-binding agent enclosed in coal raw material. Because the binding material in coal briquetting is coming from the coal itself, binderless briquetting will not alter the quality of coal. Therefore, binderless briquetting method is the favored method to conduct the agglomeration-compaction process for coal particles. Binderless briquetting can be conducted both in high temperature, -200 C, and low temperature, < C. Experiment of binderless briquetting in high temperature and low temperature, has been conducted in Thermodynamics Lab in ITB [7][8]. In high temperature binderless briquetting of 200 C, tar located in the coal matrix, is considered as the self-binding agent [7]. The heating process during the briquetting will soften the tar on the coal surface, and when adequate pressure is exerted into the stack of coal, the agglomeration process will be occured. From this information, temperature and pressure of briquetting are considered as two main parameter of the hot binderless briquetting [5][7]. As the result, the coal briquette is formed in high temperature binderless briquetting as shown in Fig.1. coal tar initial void coal particle Therefore, this research is focused on the investigation of selfbinding agent in low temperature binderless briquetting. III. INVESTIGATIONS ON SELF-BINDING AGENT Investigation on self-binding agent was started from identifying the composition of several types of low rank coals, then producing briquette in several condition, and will be ended with investigations of briquette products. A. Analysis of Low Rank Coal Composition The research is started by analyzing several types of Indonesian low rank coal to obtain the detail of coal composition supposed as self-binding agent. To know the effect of self-binding agent distinctly, the coal which is going to be used in this research need to be different in both of the composition and characteristic, especially in the light volatile matter and moisture content. The analysis is carried out on the 4 types of Indonesian low rank coal, namely Coal P, Coal Q, Coal R, and Coal S, based on ASTM D3173 for moisture content analysis and ASTM D7582. Table 1 and Figure 2 shown below are the result of coal composition analysis on 4 different low rank coals. TABLE 1 Proximate Analysis on 4 different Indonesian low rank coals Coal Total FC (%) VM (%) Ash (%) Type MC (%) P 18.70 30.82 47.89 2.59 Q 47.30 14.03 36.84 1.83 R 34.00 20.75 43.53 1.72 S 18.00 24.76 52.93 4.31 dry pore Before briquetting binder After briquetting yield mass (%) Fig 1. Coal particles before and after binderless briquetting process [7] In low temperature binderless briquetting of < C, unlike hot binderless briquetting which use tar as its binder, moisture content is considered to be the self-binding agent. In this case, due to its adhesives properties, the moisture content among coal particles supports the agglomeration process when adequate pressure is exerted. Moreover, due to its low temperature operation, moisture content of the produced briquette is still considerably high [8]. Maintaining low temperature operation during the briquetting process is also expected to soften light tar as the additional self-binding agent in the agglomeration process. However, according to the last experiment, the distinction of self-binding agent effect is not clear [8]. So far, only the percentage of moisture content has major impact as selfbinding agent. Further investigations are needed for selfbinding agent in low temperature binderless briquetting. 80 150 200 250 300 Temperature ( C) P Q R S Fig 2. Thermogravimetry analysis on 4 types of low rank coals between - 300 C From proximate analysis result in Table 1, it is shown that 4 types of Indonesian low rank coal has different composition. The differences is occurred especially in both moisture content and volatile matter. From thermogravimetry analyzer, volatile matter of each coal can be identified further based on its decomposition temperature as shown in Fig 2. Fig 2 shows that Coal S has the highest composition of light volatile matter due to larger decomposition in the temperature range of -400 C. Meanwhile Coal Q and Coal R have medium composition of light volatile matter and Coal P coal has the lowest composition of light volatile matter compared to the other coal

types. Based on this findings, these 4 types of Indonesian low rank coal are able to be used in investigation research. B. Briquettes Production After obtaining its composition, each coal types are then used as raw material in briquetting process. Briquetting process is conducted in the piston-cylinder system powered by hydraulic By applying this hydraulic power, the piston-cylinder system can exert pressure up to 2500 bar. The piston-cylinder system is also equipped by electric heater to maintain the briquetting process occurs at temperature of 50 C. Before coal fines is compacted in piston-cylinder system, the particle size of raw coal need to be conditioned into certain size and dried into the desired moisture content. The whole briquetting process is conducted by following the procedures on [8]. However, in this time, the briquetting process is only conducted at briquetting pressures, 2500 bar and 1250 bar. C. Investigations of Briquette Products Produced briquettes are then investigated to obtain its characteristics. Several characteristics of briquette has to be identified because it is strongly connected with the existence of self-binding agent like briquette strength and briquettes water resistance. Two main test utilized in this investigations are Drop Test, to know the strength of the briquette, and Reabsorptivity Test, to know water resistance of briquettes. Both test procedures are conducted by also referring [8]. IV. RESULT AND DISCUSSIONS A. Briquette Strength Formed briquetted are investigated for its strength by drop test method. Shown Fig 3 and Fig 4 are the result of drop test conducted on briquettes of 4 different low rank coals. From the pictures, overall drop test result shows that produced briquettes of 4 different low rank coals have briquettes endurance more than 80%. Briquettes with 20% moisture content of raw material has briquettes endurance between - %, meanwhile briquettes with 10% moisture content of raw material has briquettes endurance about % above. BRIQUETTE ENDURANCE (%) 0 1250 2500 BRIQUETTING PRESSURES (BAR) Fig 3. Briquettes strength of 4 low rank coal types with 20% moisture content raw coal BRIQUETTE ENDURANCE (%) 0 1250 2500 BRIQUETTING PRESSURE (BAR) Fig 4. Briquettes strength of 4 low rank coal types with 10% moisture content raw coal For briquettes of 4 different low rank coals with 20% moisture content of raw material, the difference of briquetting pressure between 1250 and 2500 bar does not create major impact on briquette endurance. Briquette endurance is relatively similar between 1250 and 2500 bar briquetting pressure for briquettes with 20% moisture content of raw materials. However, in this condition, the effect of low rank coal composition difference cannot be seen because of every coal types show relatively similar briquette endurance. Slight distinction happened for Coal P briquettes at 2500 bar briquetting pressure might be caused by poor repeatability data measurement. Additional identical test might be needed to emphasize the precise value of the Coal P briquettes endurance. On the other hand, drop test conducted on briquettes of 4 different low rank coals with 10% moisture content of raw material shows interesting outcome. Briquette with 10% moisture content of raw material shows differences on briquette endurance for different briquetting pressures. From shown Fig. 5, briquette produced at 2500 bar has better in strength than briquette produced at 1250 bar. It happens for most of coal types briquettes, except briquettes of Coal P which tends to be constant, no change, in respect with the change of briquetting pressure. Unlike the briquettes with 20% moisture content of raw material, this time, the difference of briquette strength at certain briquetting pressures can be identified among briquettes produced from 4 different low rank coals. In general, at the same briquetting pressure, briquettes of Coal Q have the highest briquette endurance, followed by briquettes of Coal R and Coal P respectively, and briquettes of Coal S have the lowest briquette endurance among 4 different low rank coal. The significant difference of briquette strength between briquettes with 10 and 20 % moisture content of raw material, is the evidence that the presence of moisture content has major roles as self-binding agent in low temperature binderless briquetting. Coal with higher percentage of moisture content will produce briquette with better strength than coal with lesser moisture content. After moisture content, the coal composition is another factor considered as the self-binding agent in low temperature binderless briquetting. Coal Q which has the highest moisture content than the others, 47% moisture, will provides higher porosity due to its drying process to set its moisture to 10 or 20 % before it is then compacted. Porosity provides many edges on coal fines that will be very useful in mechanical interlocking mechanism when compaction force is applied to the coal fines. Based on this reason, therefore,

briquettes of Coal Q is the strongest briquettes, followed by briquettes Coal R (35% of initial moisture) and Coal P (19% of initial moisture) respectively, and briquettes of Coal S is the weakest among briquettes produced from these 4 low rank coals. However, effect of light volatile matter or light tar could not be identified in this test condition. It might need another test condition to prove the effect of light tar in low temperature binderless briquetting. B. Water Resistance of Briquette The result of reabsorptivity test in this research are shown in Fig 5 and Fig 6 below. As shown in [8] before, the effect of the briquetting pressure difference is not significant compared to the percentage of moisture content. Therefore, in Fig 5 and Fig 6, shown reabsorptivity tests are only provided at 2500 bar briquetting pressure as maximum briquetting pressure references. Fig 5 shows that all of briquettes are absorbing about 8-13 % water during reabsorptivity test and need around 24-48 hours to return to its initial moisture. In this reabsorptivity test, the drying curve of every coal briquettes only have small differences. However, further in Fig 5, it can be seen that the gradient of moisture content drying is steeper for briquette of Coal X and Coal R than briquette of Coal P and Coal S. However, the difference among the gradient curve is not so large so it cannot be concluded immediately. In Fig 6, generally moisture uptake in this test is higher than shown in Fig 5. It can be seen that the highest moisture uptake is hold by briquette of Coal S and followed by briquette of Coal P and Coal R respectively, and briquette of Coal X has the least amount of moisture uptake, about 15 %, compared to other types of briquette coal. Further in Fig 7, reabsorptivity test of briquette with 10% moisture content of raw material cannot return to its initial moisture. Moisture absorbed is trapped inside the briquette. This finding is exactly the same result shown in previous reabsorptivity test for briquette with 10% moisture content of raw material in [8]. In the end of reabsorptivity test the briquette of Coal P contains the highest moisture uptake, followed by briquette of Coal S and Coal R respectively, and briquette of Coal Q has the least moisture uptake. Apparently, all these discovered phenomena are strongly related to the presence of the self-binding agent inside briquette. Briquette with 20% moisture content of raw material have better in agglomeration than briquette with 10% moisture content of raw material. Better agglomeration gives better water resistance. However, water is not hydrophobic so reabsorptivity test of briquette produced at low temperature takes longer time to return to its initial moisture than reabsorptivity test of briquette produced in high temperature [9]. 15 MOISTURE UPTAKE (%) 10 5 0-5 0 24 48 72 96 120 144 168-10 HOURS Fig 5. Result of 24 hours reabsorptivity test result of briquettes produced at 2500 bar with 20% moisture content raw material

35 30 MOISTURE UPTAKE (%) 25 20 15 10 5 0 0 24 48 72 96 120 144 168 HOURS Fig 6. Result of 24 hours reabsorptivity test result of briquettes produced at 2500 bar with 10% moisture content raw material As for effect of coal composition, porosity created among coal fines due to moisture content drying, also has important roles in reabsorptivity test as shown in drop test before. As mentioned before, porosity among coal fines will enhance the probability of mechanical interlocking among coal fines that will gives better agglomeration. Because of Coal Q is dried from 47% to 10 and 20% moisture content before it is compacted, Coal Q has the largest porosity compared to the other coal types. This is why briquette of Coal P always has the least moisture uptake compare to the other type of coal briquettes. On the other hand, the effect of light tar in coal composition cannot be identified. The trapped moisture inside of briquettes with 10% moisture content of raw material is the proof that there is no/ only few hydrophobicity properties in the briquettes. It means, no light tar was soften in this operating condition during low temperature binderless briquetting process. V. CONCLUSIONS Moisture content has important roles in low temperature binderless briquetting as the main selfbinding agent The porosity created due to moisture content drying enhance the possibility of mechanical interlocking mechanism in low temperature binderless briquetting. Light tar cannot be soften in this operating condition of low temperature binderless briquetting. Different operating condition of low temperature binderless briquetting (in slightly higher temperature) might be approached in order to prove this deduction. Dalam Negeri Tahun 2014, Kementrian Energi dan Sumber Daya Mineral, Indonesia, 2013. [3] Central Research Institute of Electric Power Industry. Improvement of Pulverized Coal Combustion Technology for Power Generation, Yokosuka Research Laboratory. Kanagawa, Japan, 2002. [4] T. Hardianto, A. Jauhary, P. Prawisudha, A. Suwono, Development of Seven Ton per Hour Coal Upgrading Pilot Plant Based on CUT Process, Preprints of International Conference on Fluid and Thermal Energy Conversion 2006, Jakarta, Indonesia, December 10 14, 2006. [5] T. Hardianto, A. Suwono, W. Ardiansyah, N.P. Tandian, W. Lawrence, Analisis Tentang Temperatur Pengeringan Untuk Mendapatkan Hasil Terbaik Dalam Proses Coal Upgrading Technology (CUT), Proceeding pada Seminar Nasional Tahunan Teknik Mesin XI (SNTTM XI) & Thermofluid IV, Yogyakarta, 16-17 Oktober, 2012. [6] Komarek, R.K., Binderless Briquetting of Peat, Lignite, Subbitunimous and Bitunimous Coal in Roll Press, Komarek Co. Technical Paper [7] T. Hardianto, P. Prawisudha, T. Novera, A. Suwono, Experimental Study on Hot Binderless Briquetting of Indonesian Low Rank Coal, Proceedings of the International Conference on Fluid and Thermal Energy Conversion. Jakarta, Indonesia. December 10-14, 2006. [8] A. Irhamna, P. Prawisudha, T. Hardianto, A. Suwono, Proses Pembriketan Binderless Temperatur Rendah pada Batubara Muda Indonesia, Proceedings pada Seminar Nasional Tahunan Teknik Mesin XIII (SNTTM XIII), Depok, Indonesia, 2014. [9] T. Hardianto, P. Prawisudha, A. R. Irhamna, A. Suwono, Briquetting Method Development of Coal Upgrading Product from Indonesian Low Rank Coal, Proceedings on AUN/SEED- Net Regional Conference on Mechanical and Manufacturing Engineering (RCMME), Hanoi, Vietnam, October 9-10, 2014. REFERENCES [1] Pusat Sumber Daya Geologi, Potensi Sumber Daya Batubara Indonesia, Kementrian Energi dan Sumber Daya Mineral, 2009, Indonesia [2] Keputusan Menteri Energi dan Sumber Daya Mineral Nomor 21 K/30/MEM/2013 tentang Penetapan Kebutuhan dan Persentase Minimal Penjualan Batubara untuk Kepentingan