ABSTRACT The benefit of gasification channel availability in an underground coal gasification experiment is investigated in laboratory. The experiment is conducted using a simulation rectangular reactor made of steel. There are two experiments conducted in this study: the first experiment is without gasification channel and the second experiment with a gasification channel inside the reactor. The result of the experiments shows that the amount of CO2 gas is in the range of (4,6-11,4)% and (11,6-14,4)%; CO gas is in the range of (0,3-4,0)% and (1,2-6,8)%; H2 gas is in the range of (0,1-2,5)% and (1,6-3,2)%; C3H8 gas is in the range of (0,0-0,6)% and (0,2-0,9)%; CH4 gas in the range of (0,0-2,2)% and (0,4-3,0)%, CnHm gas in the range of (0,0-0,0)% and (0,0-0,4)% for the first and the second experiment respectively. The caloric value of gas is in the range of (81-343)kcal/m3 and (263-516)kcal/m3 respectively. The range of temperature development during the gasification process shows that: in the first experiment, the range of gasification temperature T1 is (335-565)oC; and T2 is in the range of (110-240)oC. On the other hand, T1 from the second experiment is in the range of (550-705)oC and T2 is in the range of (160-628)oC. Besides that in the first experiment, the pattern of T1 and T2 changing has a decreasing tendency, while in the second experiment, it has an increasing tendency in relation with the progress of gasification process. It can be concluded that the availability of gasification channel in the second experiment allows the gasification reactions occur more efficiently compared with the reactions in the first experiment without the channel inside.
Key word : Underground gasification, coal, channel, reactor, gas composition
Underground coal gasification is not a new idea, it was first suggested by Siemens in 1868 for the gasification of coal left in place after mining. Underground coal gasification is a method of converting unworked coal, deep underground, into a combustible gas, which can be used for industrial heating, power generation or the manufacture of hydrogen, synthetic natural gas or other chemicals.
Basically, this method allows us to eliminate the need for mining especially for the coal which is considered uneconomical to mine, due to several reasons for example the coal seam which locates very deep underground. Edgar (1974) mentioned that this underground coal gasification method was the most economical method to convert the solid coal to gas. Besides that, this method is able to reduce the risk of mining and minimize the environmental destruction related with the mining activities (Schrider & Whieldon, 1977).
The basic concept of underground coal gasification is illustrated in Figure 1. Two boreholes, or wells, are drilled to the bottom of the coal seam to be gasified. Normally the natural permeability of the coal bed is not high enough nor the fissures large enough to permit gas percolation through the seam, so it is necessary to enhance the permeability. This is called “linking” of the wells or in other word it can be mentioned as the gasification channel forming, in which narrow linear channel of high permeability are formed without increasing the permeability of the bulk of the coal seam. There are three parameters affects the underground gasification process. The first parameter is the geological parameter such as coal seam thickness, type of overburden; country rocks; and water table. The second group of parameters is the characteristics of coal such as moisture and ash contents; caking ability etc. The third group is the operasional parameters of gasification such as airflow rate; gasification channel; oxygen rate, pressure, the length of gasification zone etc. The knowledge and understanding of those parameters are very important and very helpful in planning the equipments related with the operation and interpretation of the result of underground coal gasification. The geological parameters and characteristics of coal are the most important and closely related. The operasional parameters are used to eliminate or at least to reduce the negative effect of geological parameter and characteristics of coal in this underground coal gasification. The effective combination of these parameters can support the successive progress of an underground coal gasification either from quantity or quality of gas product or from the efficiency point of view of this gasification process (Gunn, 1978). For more Info: See: http://dspace.ipk.lipi.go.id/dspace/
The result of the experiment show that in an underground coal gasification conducted in laboratory using a simulation reactor, a gasification channel is a rate limiting factor. This gasification channel affects the production of gases and also its quality. The result shows that the first reactor without a channel inside produces less amount of gases (CO2; CnHm; CO; H2; C3H8 and CH4 ) compared the gases from the second reactor which has a channel inside. The gasification process in the first experiment is not as effective as the gasification process in the second experiment. It is indicated by the calorific value of product gas from the first experiment which is in the range of (81-343)kcal/NM3, while the calorific value of gas from the second experiment is in the range of (263-516)kcal/NM3.
This is also supported by the temperature of the experiment. T1 in the first experiment is in the range of (335-565)oC; and T2 is in the range of (110-240)oC. On the other hand, T1 of the second experiment is in the range of (550-705)oC; while T2 is in the range of (160-628)oC. Besides that, the pattern of temperature changing from the experiment is different. For the first experiment, the pattern of T1 has a decreasing tendency during the gasification progressing. The same pattern also occures for T2. On the other hand, the pattern of T1 and T2 in the second experiment has an increasing tendency in relation with the progress of the gasification.
It can be concluded that the success of the underground coal gasification depends on the gasification channel foming during the run of the gasification. The channel gasification is one of the main parameter and becomes rate limiting factor in this underground coal gasification although there are numerous other factors can affect the gasification process such as coal type, seam thickness, gas input volume, type of gas input etc. Further experiment is suggested to examine the effect of these other factors to the gasification.
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