WO2005035698A1

WO2005035698A1 - Method for treating coal piles, apparatus for applying said method and assembly of apparatus and a coal pile

Info

Publication number: WO2005035698A1
Application number: PCT/NL2003/000696
Authority: WO
Inventors: Horst Jürgen Josef TRESCHAN; Frank Cornelis Kiela
Original assignee: Ssp Bv
Current assignee: Ssp Bv
Priority date: 2003-10-15
Filing date: 2003-10-15
Publication date: 2005-04-21
Anticipated expiration: 2006-04-15
Also published as: AU2003304499A1

Abstract

The present invention relates to a method for treating coal piles, which aims to prevent spontaneous combustion or to stop possible smouldering fires in the pile. This method comprises injecting a gaseous medium in the coal pile at a depth below the surface of the coal pile. The gaseous medium can comprise an aerosol, that comprises a non combustible gas and a liquid or can comprise a non combustible gas. The invention furthermore relates to an apparatus arranged for applying this method to prevent spontaneous combustion of coal piles, which apparatus comprises at least one lance with outlets distributed over the surface of the lance, as well as an assembly of such an apparatus and a coal pile.

Description

Method for treating coal piles, apparatus for applying said method and assembly of apparatus and a coal pile.

The present invention relates to a method for treating of coal piles, which aims to prevent spontaneous combustion or to stop possible smouldering fires in the pile. The invention furthermore relates to an apparatus arranged for applying this method to prevent spontaneous combustion of coal piles. Spontaneous combustion is a serious problem associated with transportation and storage of coals. Fires due to spontaneous combustion may occur on transporting the coal or in storage piles of the coal and can be quite hazardous. Research has identified some of the important factors in spontaneous combustion as changes in the moisture content of the coal, air flow rate of the surrounding air, migration of combustible volatile matter such as hydrocarbons, coal particle size, temperature, pyrite content, geological factors, and mining practice. At present, however, there is no simple effective method to prevent spontaneous combustion. Prevention is normally based on suppressing these factors that favour spontaneous combustion. Control of spontaneous combustion is usually based on previous experience to reduce risk and to detect incipient combustion before a fire occurs. In US patent 4,331,445 a method for decreasing the spontaneous combustion tendency of coal is described, which method comprises contacting the coal with a composition of about 2 percent polyethylene oxide, the balance being water, and then drying the coal. The theory behind this method is that the composition provides the desired reduction in the spontaneous combustion tendency by sealing both the coal and the volatile hydrocarbons in the coal, thereby preventing oxidation thereof. A disadvantage of this method is that the surface of the coal pile is covered with a chemical substance which is unwanted by users of the coal. During use of the coal for combustion purposes these substances will be emitted to the environment. Other known prevention methods currently in use include; - compacting of coal piles by e.g. bulldozers to reduce the oxygen content in the space surrounding the coal particles; - storing the coal in sealed containers for protecting the coal from external oxygen. All these known methods have in common that they are quite laborious and expensive. The first method of compacting a coal pile has an additional disadvantage in the inevitable consequence of coal particles at the surface of the pile being fractured, and that as a consequence of this after some time smaller particles are washed down by rain. This leads to an increase in the space surrounding the coal particles at the surface of the pile, making it easier for ambient air to be blown or sucked into the pile. This effect of air penetrating in the larger holes or openings in the surface of a coal pile is sometimes referred to as 'chimney effect'. The present invention provides a simple, relatively inexpensive and yet effective method for treating of coal piles to prevent spontaneous combustion or to stop possible smouldering fires herein. This method comprises injecting a gaseous medium in the coal pile at a depth below the surface of the coal pile. The injected gaseous medium causes a protective intermediate layer in the coal pile from which virtually all oxygen has been expelled by replacement with the injected gaseous medium and which layer prevents, at least hinders, migration of oxygen and combustible hydrocarbons from both sides of the layer. Furthermore a decrease in temperature around the injected area can be obtained, especially when a cooled medium is used. A third important effect is that the injected gaseous medium causes an increase in pressure from within the coal pile, directly after injection. This increase in pressure compacts the coal pile from the inside and hinders oxygen from being sucked into the coal pile. In a preferred embodiment of the method for treating coal piles, the gaseous medium comprises an aerosol. More preferably the aerosol comprises a non combustible gas and a liquid. From experiments the application of an aerosol to prevent spontaneous combustion in coal piles has proven to be very successful. More in particular the aerosol is formed of small liquid parts dispersed in a gas. The liquid functions to extend the retention of the none combustible gas in the stockpile, to distribute the heat that is absorbed by the gas and moreover the liquid also withdraws heat from the stock pile through evaporation of the liquid. When injecting an aerosol it is preferred to use water as a liquid, due to its availability and the fact that water does not effect the quality of the coal. In another preferred embodiment of the invention the gaseous medium comprises a non combustible gas. More preferably the non combustible gas is supplied to the coal pile as a liquid gas. Injecting a non combustible gas in the coal pile provides a straightforward yet effective method to prevent spontaneous combustion. Supplying a liquid gas is advantageous with respect to the storage volume of the gas. Moreover the gas will be relatively cold upon injecting, thereby enhancing the cooling effect of the gaseous medium. According to the invention, the none combustible gas is preferably one of the group comprising nitrogen gas (N₂) or carbonacid gas (CO ). Both type of gasses are readily available. According to the invention it is advantageous, when the depth below the surface of the coal pile, at which the gaseous medium is injected, is 120 centimetres at maximum, preferably 100 centimetres at maximum. From practical experience it is known that below this depth less smouldering occurs. This because the weight of the top layer of about 120 centimetres compacts the coal pile in such an extent that less ambient oxygen will reach this depth. According to the invention it is advantageous that the depth below the surface of a coal pile, at which the gaseous medium is injected comprises a depth range. This range can be defined as a depth between X and Y, in which X preferably is between 5-

30 centimetres and in which Y preferably is between 180-270 centimetres. Injecting the aerosol in a depth-range will be more effective with respect to the establishment of a protective layer, as has been described before. More in particular according to the invention the depth range is between 10 centimetres and 250 centimetres. This range has proven to be effective in preventing spontaneous combustion of a coal pile. According to an aspect of the invention, the method of treating coal piles comprises an additional step of determining a hot spot in the coal pile. Upon determining the hot spots in the coal pile first, one can inject the gaseous medium at the most appropriate locations. One can for example determine the hot spots by using an infrared camera. According to another aspect of the invention, the method of treating coal piles comprises injecting the gaseous medium at at least three locations around the hot spot. In this way the hot spot can be protected from spontaneous combustion more effectively. According to yet another aspect of the invention the temperature of a hot spot in a coal pile before injecting is above 50° C. At these temperature it is known, that an increased risk exists for spontaneous combustion. The invention furthermore relates to an apparatus arranged for applying the method, as it is described above, which apparatus comprises at least one lance having outlets distributed over the surface of the lance. According to a preferred embodiment the apparatus comprises three or more lances. Analogously to the injection at three locations such an embodiment will be more effective in treating the hot spots in a coal pile. According to another preferred embodiment the apparatus comprises at least one storage tank for an none combustible gas and supply means for a liquid. In this embodiment it is advantageous according to the invention when the storage tank comprises a none combustible gas, such as one of the group comprising N or CO₂. Furthermore it is advantageous when the liquid supply means comprise a storage tank containing liquid such as water. According to yet another preferred embodiment of the apparatus, the lance comprises at least one inlet for a liquid and at least one inlet for a none combustible gas, the liquid inlet being arranged downstream of the gas inlet. The advantage of this embodiment is that the inlets are arranged such that an aerosol can be created by applying the appropriate flow of liquid and gas in the respective supply lines. The invention finally also relates to an assembly comprising an apparatus for treating coal piles and a coal pile, at least one lance being inserted in the coal pile. The method and corresponding apparatus of treating coal piles according to the invention will now be illustrated with reference to the accompanying drawings, in which; Figure 1 schematically depicts three layers in a coal pile with different risks to spontaneous combustion; Figure 2 schematically depicts a cross section of an upper part of a coal pile, in which two lances are inserted; Figure 3 schematically depicts a possible embodiment of the apparatus. Like reference numbers refer to like parts throughout the drawings. One can distinguish three layers in a coal pile 1 in figure 1 ; - top layer 30 with a high risk to spontaneous combustion: next to a relatively large amount of oxygen inherent to large interstitial spaces in a coal pile, here there is also a relatively large amount of oxygen arising from the air ambient to the coal pile;

- intermediate layer 40 with an intermediate risk to spontaneous combustion; here less oxygen will be present compared to the top layer due to the compacting function of the weight of the top layer and the larger transportation distance of the air ambient to the coal pile;

- inner-layer 50 or core of the coal pile with a low risk to spontaneous combustion; here virtually no oxygen is present or at least in concentrations that are low enough to prevent spontaneous combustion, due to the large compacting forces of the top layer 30 and the intermediate-layer 40. Typical estimated layer thicknesses are approximately 5-10 meters from the top layer 30, approximately 3-7 meters for the intermediate layer 40 and approximately 8-12 meters for the inner layer 50 (top to bottom), respectively. A typical diameter of a stored coal pile measured at the bottom of the pile is approximately 40-50 meters. Fig. 2 depicts a part of the upper layer 30 of a coal pile 1 with a hot spot 2 located in the top layer, in which pile two lances 3, 4 have been inserted. Here the lances 3, 4 are connected both to supply pipes 5, 6 for supply of a liquid and connected to supply pipes 7, 8 for supply of a none combustible gas. The appropriate location for the insertion of the lances 3, 4 is determined first by determining the location of the hot spots in the coal pile. Typical temperatures of a hot spot before injecting are above 50° C. At normal use lances 3, 4 will be inserted in a coal pile to dispose all outlets 9 under the surface. Under some conditions of a smouldering coal pile it is conceivable that the upper outlets are located just above the coal pile surface. When liquid is supplied, the supply of the liquid has been deliberately arranged downstream of the supply of the gas. In combination with appropriate flow through the respective supply pipes 5, 6, 7, 8, it is obtained that an aerosol is injected. The aerosol or non combustible gas in case no liquid is supplied will be injected in the coal pile through outlets 9 (see figure 3) which are distributed over the surface of the lance 3, 4. Regarding the distribution of outlets 9, the gaseous medium will be injected in various directions 10, 11, 12, 13. Immediately after injection of the aerosol a cylindrical shaped area will exist in the coal pile, indicated with lines A, B, C, D in fig. 1, which area comprises a gas or an aerosol. Upon a careful selection of the locations for insertion of the respective lances these areas will form an intermediate protective layer within the coal pile. In practice injection will take place by means of inserting three of more lances at the same time. This protective layer will protect the hot spot in different ways;

- the layer will absorb heat and energy from the hot spot; - the layer will prevent, at least reduce ambient oxygen transport from outside the stock pile to the oxidizing or smoulding part of the stock pile;

- the layer will prevent, at least reduce transport of volatile hydrocarbons from the coal pile to the outside;

- the layer creates an internal pressure in the coal pile, which pressure compacts the pile and thereby hinders supply of oxygen. On storage of large amount of coals, one will determine the hot spots on a regular base. As soon as a hot spot is detected, with a typical temperature above 50° C one will (re)insert the lances in the coal pile and (re)inject a gaseous medium.

Depending on the specific storage conditions, one can also decide to keep the lances within the coal pile. The apparatus 20 arranged for applying the method for treating coal piles as it is described above, is depicted in more detail in figure 3. This figure illustrates a preferred embodiment of the lance 3, 4, which is provided with an inlet 14 for a liquid and an inlet 16 for a non combustible gas. The inlet for the liquid 14 is arranged downstream of the gas inlet 16 in order to have a mixture of a non combustible gas and a liquid in the form of an aerosol. Other configurations, for example two liquids inlet and one gas inlet, are also conceivable. The liquid inlet 14 is connected to liquid supply means, which in this embodiment comprises a storage tank 17. This storage tank 17 normally will contain plain water possibly comprising special additives. In practice the liquid supply means can also comprise a connection to the public water net. At the upper part of the lance 3, 4 in figure 3 a handle 15 is disposed which facilitates the manipulation and insertion of the lance. The gas inlet 16 is connected to a storage tank 18 through supply pipes 7, 8.

Preferably this storage tank for the gas contains nitrogen gas without oxygen or carbon acid gas without oxygen. In practice the storage tank 18 will be of a type that can contain liquid gas under pressure. At the insertion end of the lance 9, the lance is cone-shaped in order to facilitate insertion. After the possible withdrawal of the lances from the coal pile it is preferred that the holes that have been created by the lances are closed, e.g. by using a shovel, in order to prevent oxygen from migrating into the coal pile ('chimney effect').

Claims

1. Method for treating coal piles (1), which method comprises injecting a gaseous medium in the coal pile (1) at a depth below the surface of the coal pile.

2. Method for treating coal piles (1) according to claim 1, wherein the gaseous medium comprises an aerosol.

3. Method for treating coal piles (1) according to claim 2, wherein the aerosol comprises a non combustible gas and a liquid.

4. Method for treating coal piles (1) according to claim 3, wherein the liquid comprises water.

5. Method for treating coal piles (1) according to claim 1, wherein the gaseous medium comprises a non combustible gas.

6. Method for treating coal piles (1) according to claim 5, wherein the non combustible gas is supplied to the coal pile as a liquid gas.

7. Method for treating coal piles (1) according to anyone of the claims 3-6, wherein the none combustible gas is one of the group comprising N₂ or CO .

8. Method for treating coal piles (1) according to anyone of the preceding claims, wherein the depth below the surface is 120 centimetres at maximum, preferably 100 centimetres at maximum.

9. Method for treating coal piles (1) according to anyone of the preceding claims, wherein the depth below the surface comprises a depth range.

10. Method for treating coal piles (1) according to claim 9, wherein the depth range is between 10 centimetres and 250 centimetres.

11. Method for treating coal piles (1) according to anyone of the preceding claims, wherein the method comprises an additional step of determining a hot spot (2) in the coal pile.

12. Method for treating coal piles (1) according to claim 11, which method comprises injecting the gaseous medium at at least three locations around the hot spot.

13. Method for treating coal piles (1) according to claim 11 or 12, wherein the temperature of the hot spot (2) before injecting is above 50 °C.

14. Apparatus (20) arranged for applying the method according anyone of the preceding claims comprising at least one lance (3, 4) having outlets (9) distributed over the surface of the lance.

15. Apparatus (20) comprising three or more lances (34) according to claim 14.

16. Apparatus (20) according to claim 14 or 15, comprising at least one storage tank (18) for a none combustible gas and supply means (17) for a liquid.

17. Apparatus (20) according to claim 16, wherein the storage tank (18) comprises a none combustible gas, such as one of the group comprising N₂ or CO ₂.

18. Apparatus (20) according to claim 16, wherein the liquid supply means (17) comprises a storage tank containing liquid such as water.

19. Apparatus (20) for treating coal piles according to anyone of the claims 14-18, wherein the lance (3, 4) comprises at least one inlet for a liquid (14) and at least one inlet (16) for a non combustible gas, the liquid inlet being arranged downstream of the gas inlet.

0. Assembly comprising an apparatus (20) for treating coal piles (1) according to anyone of the claims 14-19 and a coal pile (1), at least one lance (3, 4) being inserted in the coal pile.