Effect of the Heat Transfer Surface on Prevention of Spontaneous Combustion of Coal
Corresponding email: yulianto.nugroho@ui.ac.id
Published at : 25 Nov 2019
Volume : IJtech
Vol 10, No 6 (2019)
DOI : https://doi.org/10.14716/ijtech.v10i6.3620
Wicaksono, R.P.S., Fathia, S.H., Kolang, I.F., Riadi, A., Nirbito, W., Muharam, Y., Nugroho, Y.S., 2019. Effect of the Heat Transfer Surface on Prevention of Spontaneous Combustion of Coal. International Journal of Technology. Volume 10(6), pp. 1220-1227
| Ricky Putro Satrio Wicaksono | Department of Mechanical Engineering, Faculty of Engineering University of Indonesia, Depok 16424, Indonesia |
| Sofi Hesti Fathia | Department of Mechanical Engineering, Faculty of Engineering University of Indonesia, Depok 16424, Indonesia |
| Inkasandra Faranisa Kolang | Department of Mechanical Engineering, Faculty of Engineering University of Indonesia, Depok 16424, Indonesia |
| Achmad Riadi | Department of Mechanical Engineering, Faculty of Engineering University of Indonesia, Depok 16424, Indonesia |
| Wahyu Nirbito | Department of Mechanical Engineering, Faculty of Engineering University of Indonesia, Depok 16424, Indonesia |
| Yuswan Muharam | Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424,Indonesia. |
| Yulianto Sulistyo Nugroho | Department of Mechanical Engineering, Faculty of Engineering University of Indonesia, Depok 16424, Indonesia |
The increased use of coal for power
generation has increased the demand for low-rank coal, such as lignite and
sub-bituminous coal, and during its supply, it may need to be stored for long
periods. Because low-quality coal is more susceptible to spontaneous combustion
than high-quality coal, its storage could potentially cause work-related
accidents. One method being developed to control the temperature of stored coal
to prevent spontaneous combustion is the immersion of heat exchangers in coal
piles. This method can be used to control the temperature during both the
storage and transportation processes. The purpose of this study was to test
this method and, in particular, study the effect of changes in the
heat-exchange surface area on the effectiveness of temperature control. An
experiment was set up to control the temperature of a laboratory-scale coal
pile using a heat exchanger made from copper tubes. Coal samples were placed in
a cylindrical container with a spiral-shaped heat exchanger, placed in the
center of the cylindrical container, and cooled with ~27o seawater.
Tests were carried out using several configurations of heat exchanger
dimensions to determine the effect of changing the ratio of heat-exchange
surface area to volume of combustible material. The test results showed that
greater heat-exchange surface area produced a greater amount of cooling load
and temperature difference.
Coal; Heat exchanger; Heat transfer; Spontaneous combustion; Surface area ratio
Coal
is still used as a significant source of energy in most parts of the world
(Benalcazar et al., 2017), especially for electricity generation. The high demand
for coal worldwide has caused a shortage in the supply of high-quality coal.
This has resulted in the increased use of low-quality coals, such as
sub-bituminous coal and lignite, for combustion and gasification (Tristantini
et al., 2015). In the coal supply chain process, some regions of the world
still experience long storage times, whereby coal can remain stored in a ship for long
periods. Especially for low-rank coal, this tends to
lead to self-heating that can lead to spontaneous combustion, which has the
potential to cause accidents (Nugroho et al., 2000; Singh, 2012; Onifade &
Genc, 2018). Several methods have been used to reduce the spontaneous
combustion of coal, including the compaction of coal piles, direct spraying of
certain liquids onto the
coal, periodic temperature checks, volcano traps, and trenching (Wan-xing et
al., 2011).
Different approaches have also been explored using laboratory-scale
experiments, such as the use of water-sprays, mists, injections, showers, and
gases (Tuomisaari & Baroudi, 1998; Goransson &
Husted, 2007; Hadden & Rein, 2011). Each of these methods has advantages
and disadvantages in their practice; so further research is required to find
other methods that can more effectively prevent spontaneous combustion.
One such method under
development for the indirect cooling of coal is the immersion of heat
exchangers in coal piles (Mikalsen et al., 2018; Zhafira et al., 2018; Nugroho
et al., 2019). This method can be used to control temperatures during both the
storage and transportation processes. The purpose of this study was to test
this method and determine the effect of the ratio of the heat-transfer surface
area to the volume of the combustible material for the effectiveness of
temperature control to prevent spontaneous combustion. Laboratory-scale tests
were carried out using a heat exchanger made of copper pipe. Coal samples were
placed in a cylindrical container and heated to certain temperatures in an
oven. After the coal reached a certain temperature, saltwater was then flowed
through the heat exchanger to maintain the temperature of the coal below a
critical temperature. Previous experiments have used this identical method
except for the method of water flow; Zhafira et al. (2018) and Nugroho et al.
(2019) manually used a water bag while in the current experiment, a pump was
used to automatically maintain a constant flow rate. Another similar experiment
to study spontaneous combustion used a hotplate heater that was then cooled by
flowing water after the sample reached a certain temperature (Mikalsen et al., 2018).
Previous research determined the characteristics of spontaneous combustion by
modeling heat distribution in heated coal (Saleh et al., 2017; Nugroho et al.,
2019).
The current
research explored this method because the transportation of coal by barges
introduces new problems mainly due to the frequent occurrence of spontaneous
combustion from coal being transported and the size of a heat exchanger impacts
ship design and stability; additions to ships greatly affect the load, which in
turn affects the stability of a vessel. Therefore, laboratory-scale experiments
to determine the optimum dimensions of a heat exchanger were undertaken to
ensure its effective use.
While
the effect of increasing a heat-exchanger surface area on heat transfer has
been generally examined, this study carried out an in-depth exploration
of a heat exchanger immersion method to control coal pile temperatures to avoid
spontaneous combustion. For the sub-bituminous coal used
in this experiment, the critical temperature was determined to be 122.5±5oC,
which was lower than the work undertaken by Nugroho et al. (2019) because of
the different coal samples used in the experiments. The spiral-shaped heat
exchanger used in this experiment was quite effective because of its small
impact on the coal loading volume compared with the additional heat-exchange
surface area. This eliminates reducing the volume of
coal that can be loaded onto barges that use heat exchangers, one of the
drawbacks of using immersion heat exchangers on coal barges. Spiral-shaped heat exchangers can reduce coal temperatures
to below critical spontaneous combustion temperatures. The experimental results showed that additional
heat-exchange surface area increased the heat loss and reduced the temperature
difference. All other similar, previous work has
reported the same results; immersed heat exchangers can effectively prevent the
spontaneous combustion of coal (Zhafira et al., 2018; Nugroho et al., 2019). However,
the current study did not determine an optimal value for the surface area ratio
for this method; it ranged between 0.118 to 0.205. The
results of this research can be combined with the distribution of coal
temperatures (Nugroho et al., 2019) to identify critical points of spontaneous
heating before continuing research on the implementation of this method for
coal barges. Therefore, further research related to this method must be
undertaken to discover other possibilities for optimal configurations.
The authors would like to thank the Ministry of
Research, Technology and Higher Education, Republic of Indonesia, for financial
assistance through the 2019 Penelitian
Dasar Unggulan Perguruan Tinggi (PDUPT) funding scheme with contract
numbers 1/E1/KP.PTNBH/2019, 234/PKS/R/UI/2019 and
NKB-1672/UN2.R3.1/HKP.05.00/2019.
| Filename | Description |
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| R1-ME-3620-20191101114258.png | Graphic1 |
| R1-ME-3620-20191101114309.png | Graphic2 |
| R1-ME-3620-20191101114318.png | Graphic3 |
| R1-ME-3620-20191101114325.png | Graphic4 |
| R1-ME-3620-20191101114334.png | Graphic5 |
| R1-ME-3620-20191101114346.png | Table1 |
| R1-ME-3620-20191101114355.png | Table2 |
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