DE2719889C2 - Method of withdrawing gas from a waste pit - Google Patents

Description

The invention relates to a method for drawing off gas from a waste pit according to the preamble of claim 1.

It is known that the breaking down of waste in a mine produces gas, the methane and contaminants contains. In some mines the concentration of methane is so sufficient that it can be used immediately can be. In some cases the methane is separated from the impurities in the gas by absorption, with suitable absorbent material, such as molecular sieves, serving to trap the contaminants absorb, and in others the methane becomes without removing impurities, / .. B. CO2, N, H, H2S etc. are used.

A source is lowered into the pit to extract the gas. The chemical reaction in the pit creates a pressure greater than atmospheric pressure so that the gas migrates into the source. To the To increase this natural flow, a pump can be used to reduce the pressure in the source will. One method of separating methane from the contaminants is from U.S. Patent 40 00 990 known.

From the point of view of the greatest gas generation, it is desirable to extract the gas from the source with maximum Subtract the speed at which the pump can be operated. However, this can be done through the surface Air can be drawn into the pit, which is very disruptive. When gas is extracted from the well air is not allowed to enter the pit because the oxygen is the microorganisms poisoned, which are important for the production of methane. Accordingly, the entry of air must be avoided will. If methane gas is produced in pits that is not to be used, it is used to avoid a dangerous, flammable atmosphere that develops on the surface of the pit, either flared or deducted.

One way to avoid Lul't entry is given by venting the gas and periodically analyzing the composition. If the gas is a Has a certain oxygen content, the withdrawal speed reduced in order to eliminate the oxygen in subsequently taken gas samples. The main problem here is that air entry is only indicated after air has entered and has flowed through parts of the pit to the source. So there is no display when the oxygen intoxication takes place. Between the corrective effect by reducing the take-off speed after There is a delay in detecting oxygen and cutting off air supply to the pit. That's why the analytical method is inexpedient.

A primary problem in the extraction of methane from manure pits is therefore the choice of the extraction speed, which is economically feasible and which avoids oxygen poisoning Another problem is the determination of the gap between neighboring sources in the pit. A correct distribution of the sources is important to ensure that all zones of the pit are exposed to the influence of the source with no air ingress are subject.

The invention is based on the object of continuing the known method described at the beginning form that the highest withdrawal speed is guaranteed without larger proportions of air in the Get to the pit.

This object is achieved according to the invention by the measures specified in the characterizing part of claim 1 solved.

jo This determination of the withdrawal speed takes place in a test phase that occurs before the source is used for production. The invention gives as Safety dimensioning an early warning system to determine the entry of air into the pit during production at. Thus, if air enters during production, it will be indicated early enough, before oxygen got through the pit to the source.

Without influencing the pit by devices such as pumps, the gas is at static pressure.

which is usually a little above atmospheric pressure. Tries to do this under static conditions Pressure differential between the pit and the atmosphere to allow the gas to escape to the atmosphere. The invention provides a test program in which the highest peeling speed is a function of those Abzichgeschwindigkcil is at which the pressure in a selected area in the pit is the atmospheric pressure approaching. As long as the pressure in the pit in the chosen area is not below atmospheric pressure decreases, there is no pressure differential that would allow air to enter the pit.

The test program according to the invention contains a method according to which the highest peeling speed before production is determined, which is the desired pressure ratio between a selected area of the Pit and the atmosphere is maintained. This happens, for example, through at least one source in the pit and then withdrawing the gas from the source with two withdrawal speeds during

bo two periods. The pressure in the chosen Ge ^Ki et in the pit is determined during both periods. Knowing the pressure and the haul-off speed, a general relationship between the pressure in the selected area and the haul-off speed can be established.

h ^r ) Hiekcil to be made. This relationship is used to determine the withdrawal rate that would produce near zero pressure in the area under study. This withdrawal speed is then the maximum

times permissible withdrawal speed for the source, which creates a pressure in the selected area, which is approximately equal to atmospheric pressure. The same speed can be used for other sources in the Pit may be used when the pit is considered to be relatively homogeneous. When crossing the maximum withdrawal speed would be the pressure in the selected area below atmospheric pressure fall and the dilTerential pressure on the surface of the pit would try to draw air into it.

In order to achieve the maximum methane production, the withdrawal speed should be the same as the maximum allowed value. Using a lower speed results in a safety factor but the gas generation is reduced.

The area in which the pressure is detected is preferably near the surface of the pit and isl also permitted for areas that are removed from the mine surface, which are so long at pressures below atmospheric pressure lie, as there is a layer at the top of the pit, which is at least at atmospheric pressure lies. To use the lowest possible pressures in the pit and therefore the highest To achieve withdrawal speed, the selected area is preferably directly under the covering material, which is applied to the surface of the waste of the pit. In this arrangement, the upper edge area represents of the waste in the pit creates a pressure barrier that separates the inner areas of the pit from the atmosphere isolated.

The selected area should be horizontally next to or close to the source because the zone of the pit surface usually has the lowest pressure immediately next to the source. If the chosen area is in substantial horizontal distance from the source and maintained at zero pressure, so can, if the pressure barrier is not over the whole area of the pit, the pressure just below that Masking material close to the source, below atmospheric pressure.

The different withdrawal speeds do not have to be determined in one and the same area. In addition, the surveyed area may contain several different zones in which pressures are read can be. For example, the pressure readings can be taken for various depths of the pit, where the accuracy of the pressure information can be checked.

In order to obtain further analytical data regarding the gas composition in the mine, it is often desirable to a second source in the pit, preferably at some distance from the first one. The probes are then in the desired pattern and in set up the desired depths between the two sources. The described measures to determine the maximum permissible withdrawal speed can also be used for the second source.

A second phase of the testing process determines the distance between the sources for a given production speed For this purpose, the pressure in the pit is distributed in distributed areas during the two withdrawal periods determined, preferably directly under the cover material of the pit, with for determining the pressures can be read off from the distance between the sources. Those noted during the first period Pressures are then used to explore the point closest to the source where a static Pressure exists during this first period. The pressures observed during the second period will be used in the same way to determine the location closest to the source, the during static pressures occur during this period. These defined points and the pull-off speeds are then used to build a relationship between the shortest distance from the source to the static Pressure and the peeling speed. For greater accuracy, it is preferable to determine

Ki three such points. The resulting curve shows the Zone of influence of the source for a certain withdrawal speed. The influence zone and the source distance are used to determine the maximum possible withdrawal speed.

If the two sources have mutually exclusive zones of influence or do not work simultaneously, each can be operated up to the maximum permissible pull-off speed. However, if the sources are operated at the same time and have overlapping zones of influence, appropriate settings can be made take place. For example, an empirical setting can be made which is the highest permissible For a given source distance.

After the test procedures have been carried out, the pit is used for production. As a security measure the pressure in a selected area in the pit can be monitored during production can take place continuously or intermittently. if

jo the pressure in the pit below atmospheric pressure decreases, the withdrawal speed can be reduced, which can increase the pressure in the source, in order to build up the pressure in the selected area that ensures that the pressure limit is restored. When using this system, the print size in the source can correspond to the print in the selected one Area to be regulated. The area for pressure measurement is preferably the same or similar the one in which the determination of the maximum permissible peeling speed success.

The invention is described with reference to the drawings. It shows

Fig. 1 is a plan view of a manure pit from which gas, which contains methane, can be deducted:

F i g. 2 shows a section along line 2-2 in FIG. 1 ;

Figure 3 is a sectional view of a preferred form of source;

Figure 4 is a plan view of a preferred probe construction;

F i g. 5 shows a section along line 5-5 in FIG. 4, with a preferred probe arrangement;

F i g. Figure 6 is a graph of average probe pressure versus peel speed;

F i g. 7 is a graph of average cover probe pressure versus distance from source for different peel speeds, and

F i g. 8 is a graph of source spacing versus production speed for both single-source and also for double source production,

bo Figs. 1 and 2 /. own a manure pit 11 in which anaerobic decomposition produces a gas containing methane. The pit 11 is usually formed by the deposition of waste 13 in a cavity 15 in the soil 17 and also has a layer of covering material 19, 7- B. soil which has been brought over the surface 2t of the waste 13. Although the waste 13 in Fig .2 is represented homogeneously, this is usually not the case and there can be several layers of earth between the upper

surface 21 and the bottom 23 of the pit 11 included. The test program according to the invention can be used for cavity pit 11 as well as for other green shapes be applied.

When the pit H has a sufficient amount of meihan contains, which makes a deduction appear economical, the 'fixed program / order will determine various Factors such as the maximum allowable withdrawal speed and the appropriate land between the production sources. The first step in The test program is the definition of the test area 25, which has the shape of a circle, for example, and from the edge 27 of the pit 11 has a certain distance. For example, the Tcstgebiel 25 can have a diameter of 150 meters and at least 75 meters be away from the edge 27. If the pit 11 is too small for these dimensions, the diameter of the Test area 25 and the free space between the test area and the edge 27 can be reduced accordingly. For example, the diameter of the test area could be 25 to 120 meters and the free space accordingly 60 meters can be decreased. Other dimensions can also be used. The specified parameters are only those that have been determined to be sufficient.

Production sources 29 and 31 are inserted into the pit 11 at opposite points on the circumference of the test area 25, as in the example described 150 meters apart and set up identically are.

F i g. 3 shows exactly the structure of the source as an example 29, because the sources are structured identically.

The source 29 includes a bore 33, with a diameter of 58 to 87 cm, which for example Bottom 23 of the pit can lead. The bore 33 preferably extends almost to the bottom 23 of the Manure pit. In the bore 33 there is a corresponding number of pipe sections 35, which through Coupling mats 37 are connected to one another. The lowermost pipe section 35 is through a flexible connector 41 coupled to a perforated pipe section 39, which allows axial movement between the perforated pipe section 39 and the lowermost pipe section 35 allows. The connector 41 can be of common construction. The perforated pipe section 39 has a series of perforations 43 and is in of the bore 33 centered by centric devices 45, which on the perforated pipe section 39 in a corresponding Way, e.g. B. by clamps attached. The bottom of the perforated pipe section 39 is through a cap 49 closed, which lies on a layer of gravel 51 at the bottom of the bore 33. The pipe sections 35 and 39 can for example consist of plastic such as polyvinyl chloride.

In the bore 33, most of the length of the perforated section is packed with gravel 53. Next to the The upper end of the perforated section 39 is a seal 55 around the perforations 43 against the upper Shield areas of the hole 33. In the example shown, the seal consists of a layer of earth 57 and a concrete layer 59. Above the seal 55 in the bore 33 there is a filling of unused soil 61. The uppermost drilling section 35 is connected to a pump 63 via a throttle valve 65 and a Tube 67 closed. A flow indicator 68 with a suction pipe can be located in between.

Between the sources 29 and 31 are four rows 69, 71, 73 and 75 of probes 69a, 71a. 73a and 75, -i, whose number and depth, and their arrangement may feed varied according to the desired results within wide limits and in the illustrated ^r, Example uniformly, for example 3 meters are apart. The probes 69.). 71.). 73.) and 75.) of the corresponding rows 69, 71, 73 and 75 are closest to the source 29 and result in a transverse row. The other probes are similar

to the four rows arranged in transverse rows. In the exemplary embodiment, the probes 69a, 71a, 73, -j and 75a at a distance of 3 meters from a reference line 77 which passes through the source 29 and affects the scope of the test area 25. For example, the next four rows of probes from the Reference line 77 at a distance of 7.5 m, 15 m, 30 m or 75 m away. These distances are not critical and are only intended to represent a suitable probe arrangement.

2 (i The probes 69b, 716, 73i> are located in a similar manner and 75i> closest to source 31. The distances between the reference line 79, which is tangent to the circumference of the test area 25 at the source 31, and the four rows of probes which are closest to the source 31 can be identical, so that the description here too for source 29 applies.

The probes are preferably located at different depths in the pit. Like F i g. 5 shows the probes are 69a up to 75a arranged in progressively lower layers.

jo Although various arrangements are possible, the cross-section according to FIG. 5 is assumed to be typical of the exemplary embodiment, i. H. all probes of the Row 69 are at the same depth, all wells in row 71 are at the same depth, and so on. All wells are

J5 have the same structure, except for their lengths, therefore, only the probe 69a will be described in detail.

The probe 69a is accommodated in a bore 81 which passes through the cover material 19 and has a bottom 83 which can lie, for example, 60 cm below the covering material 19. The probe 69i) contains a tube 85 with a cap 87 at the upper end, which extends over the cover material 19 to the bottom 83 leads. The part of the tube 85 under the masking material

4 ^r > 19 contains several perforations 89. The part of the tube 85 which has the perforations 89 is preferably relatively short, for example 60 cm long, in order to isolate the vertical point at which the pressure can be read. The area of the bore 81 is covered under the covering material 19 around the pipe 85 with a material, e.g. B. filled up gravel. The upper region of the bore 81 is supported by a plate 93, e.g. B. made of concrete, sealed. The tube 85 can be small in diameter and made of a plastic such as polyvinyl chloride.

The probe 69a is a covering probe because it connects to the area of the pit 11 immediately under the covering material 19 communicates. With the tube 85, a pressure indicator 94, e.g. B. Manometer, be connected,

bo that the pressure of the mine gas immediately below the Indicates cover material 19 next to the probe 69a.

The probe 71a is no longer than the probe 69a. For example, the probe 71a can extend to a depth which is equal to 20% of the depth of the sources 29. The probes 73a and 75a can reach 50% and 70% of the depth, respectively the source 29 reach. Each probe is housed in its own borehole 81. The length of the pipe 85 with the perforations 89 can be identical for each probe

be.

The sources 29 and 31 and the probes can be in any sequence can be installed, with the static pressures indicated by display devices 94 in all probes and in the sources 29 and 31 are continuously or intermittently determined for a sufficient duration to the determine static pressure for sources 29 and 31 and for each probe with sufficient accuracy. For example, the pressures on the indicators 94 may be within a 24 hour period with an interval of four Hours can be read. In addition to determining the pressure, the temperature in the probes and in the sources as well as the atmospheric pressure and the outside temperature can be read.

Then the take-off speeds are chosen empirically. For example, the withdrawal speeds 2.83 m '/ min, 8.50 m' / min and 14.16 mVmin. The pump 63 for the source 29 is cranked and operated at a rate of 2.83 mVmin to supply the gas from source 29 draw. The pump of the source 31 is switched off during the entire test of the source 29. The pumping of the spring 29 continuously reduces the pressure in the probes. Eventually the pressures in the probes stabilize, d. H. the pressure does not vary significantly during the venting. The gas comes out at a speed of 2.83 m-Vmin subtracted after pressure stabilization in the probes. The pressures in all probes that displayed by the display devices 94 are either continuous or intermittent both before as well as after pressure stabilization. The speed of the pump is set manually.

Of particular importance is the pressure in the cover probe 69a after pressure stabilization, since after this determines the stable average pressure for the cover probe 69a. This happens for example by averaging the readings for the pressure after pressure stabilization has taken place.

The pressure at the covering probe 69a is particularly important, since air mostly enters here first, because this covering probe is arranged closest to the perforations 43 of the source 29. For this reason, during the operation of the source 29 and the pump 63, the covering probe 69a is better at a lower pressure than one of the other covering probes 69, because these are offset from the perforations 43 by a greater distance. However, if for any reason one of the other cover probes 69 is at a lower pressure than cover probe 69a, that other probe would be selected as the critical cover probe and its mean pressure determined and used as described auiwciSi, b <j can the pit also have a relatively flow-free channel to this probe. In some cases this channel can be destroyed so that the cover probe 69a has the lowest pressure of the cover probes 69.

After a stable mean pressure has been determined for the critical cover probe at a withdrawal speed of 2.83m ^J / min (here this should be probe 69a), the pump 63 is switched off and the pit 11 can return to its static pressures, which were before the passed the first time the pump was used. This can e.g. B. take 48 hours.

Upon return of the pit 11 to static pressure, the pump is at a withdrawal speed operated by 8.50 mVmin. Thereafter, the pit 11 can return to static pressure and after the pump has been operated at a withdrawal speed of 14.16 mVmin, the process is started repeated.

Using the data obtained, the diagram of FIG. 6 can be set up. There the points A. and Cilen represent the stable average pressure in the covering probe 69a at speeds of 2.83 mVmin, 8.50 mVmin and 14.16 m '/ min and serve to establish a relationship between the pressure at the Cover probe 69a and the withdrawal speed. This relationship is then used to establish the withdrawal speed at which the pressure at probe 69a becomes zero. ie is equal to atmospheric pressure. In the case of the FIG. 6, the pressure at the probe 69a would be Nu !! will. This withdrawal speed is then the maximum permissible speed in this example, because higher wedges of wind produce a negative pressure at the cover probe 69a which is lower than the atmospheric pressure and thus a pressure difference! arises trying to draw air into the pit 11, while at zero pressure there is no pressure differential.

Since the pit responds relatively slowly to low pressure differentials and the highest permissible Withdrawal speed based on the mean pressure, the choice of the maximum allowable withdrawal speed as described above, definitely

jo sufficient.

In the embodiment described, the relationship between the take-off speed and the pressure at the probe 69a is shown in a diagram as a line 95. This relationship can too

J5 can be determined without recording the same. The withdrawal speed, at which the pressure at probe 69a is approximately zero. can through trial and error procedures or by a combination of sample and error and interpolation, the results of which are determined.

The stable average pressure at other probes can also be entered in the diagram according to FIG. 6. For example, it can be useful to show the stable average pressures in the probes 71a in FIG. b, even if one of the items A. B and C in Fig. 6 is wrong. The deeper probes 73 and 75 are used to determine the zone of influence of the source 29 at different withdrawal speeds.

In order to display the zone of influence and

to enable the source distance, the creation of the F i g. 7 take place. This figure shows the average cover probe pressure, i.e. h, the one at the probes 69 versus the distance from the source for three positive pull-out gaps. nüuCruCm shows F i g. 7 shows the static pressure on the probe 69 at various distances from the source 29, ie from the reference line 77. The three velocity curves intersect the line of the static pressure at points D, E and F.

F i g. 8 is a diagram of the source spacing across

M) the withdrawal speeds. The points D, E and F of FIG. 7 are taken over into FIG. 8 in order to produce a relationship in the form of a line 97 between the sources and the withdrawal speed.

If the sources 29 and 31 are operated simultaneously and their zones of influence overlap, the maximum permissible take-off speed for a given source distance can be reduced by the Interactions between neighboring sources too

11th

compensate. This is done by using the relationship according to line 99 in Figure 8. In particular, the withdrawal speed was reduced by 25% when the sources were operated at the same time, which is indicated by the line 99 in FIG. 8 is shown. This reduction factor is regarded as sufficient. When using line 99 for the maximum permissible withdrawal speed of 13.03 mVmin, the sources should be at least 95 meters apart. The test method described can, if desired, be repeated for the source 31 while the pump 63 for the source 29 is switched off. This would result in the entries in FIGS. 6 to 8 for source 31. In this case, the figures can höchstzulässi- i ^r> ge-off speed for the sources 29 and 31 are also used, and for the other drilled into the pit sources for these two sources for the determination of Quellcnabstands and.

After the end of the test program, the Qucl'cn 29 and 31 are used to produce gas. aside from that other wells can be drilled into the pit. It can be assumed that the test results, d. H. the maximum withdrawal speeds and the distance between the sources 29 and 31 also for others Sources in the pit can be used.

The sources that are operated at production areas, found by the method of the present invention have no problem with entry of air through the cover material 19 into the pit It. The invention includes an early warning system for air ingress. It does this by monitoring the Pressure in the cover ends 69 adjacent to one or more powered sources. For example, the Pressure in the cover probes 69 and especially in the cover probe 69;) during the production of the source s> 29 are monitored. In the event of a pressure drop at one of the cover probes 69 below zero for a given line or The take-off speed can be reduced accordingly by a given value in order to achieve the To eliminate pressure differential across the cover material 19 that tries to force air into the pit. Thus would very low or low negative pressures in the cover probes 69, which last only a short time, because of the slow response of the air and the pit 11 to pressure differentials of this type, no air entry cause. The speed of the pump 63 can be manually or automatically according to the Pressure ratios in the cover probe 69 are regulated.

For example, the pump speed should correspond to the pressure in the cover probe 69a at Decrease by a given value of e.g. B. 6.35 mm HjO column under atmospheric pressure for 48 hours be reduced.

For this purpose 4 sheets of drawings

bO

Claims (14)

Patent claims: 1. Method of withdrawing gas from a waste pit without introducing air into it in such quantities occurs that the methane is destroyed in the Pit is created, characterized in that at least one source (29, 31) in the pit (11) is provided, from which the gas is withdrawn at a first pressure which is so low that it does Gas can flow from the pit into the source that the pressure setting in at least one selected The area in the pit that is outside the source is monitored and that the size of the first pressure according to the pressure that is set in this selected area that the prevention of air entry into the pit is largely guaranteed. 2. The method according to claims 1, characterized in that that the pit (11) contains a layer of covering material (19) to prevent the ingress of air, and at least one covering probe (69a, 71a, 73a, 75a; in the pit (11) next to the source (29, 31) is used, which serves as a monitoring element, and that the selected area is that of the Includes pit next to the probe and next to the cover material. 3. The method according to the preceding claims for creating the maximum production quantity, characterized in that the pressure is in at least one area of the pit (11) and outside the one source (29,31) during a first period, with the gas from the source being monitored during a second period is deducted and then the pressure in at least an area inside the pit and outside the spring was determined in this second period will, that a relationship is established between the withdrawal speed and the two pressures observed will, and that the maximum production quantity as well as the maximum take-off speed are generated, which latter would exist according to this relationship at gauge pressures of approximately zero. 4. The method according to claim 3, characterized in that the pit (11) with cover material (19) covered and a cover probe (69a; in the pit next to the source, and that the pressure at that probe was determined during the first period will. 5. The method according to claim 3, characterized in that the pressure during the first period is determined to obtain an average pressure for part of that period. 6. The method according to claim 5, characterized in that by withdrawing the gas during During the first period, the pressure determined is progressively reduced to a relatively stable value becomes, and that this part of the first period is relatively stable after reaching this Value occurs. 7. The method according to claim 3, characterized in that that the pressure found in a given area during the second period M has been decreased during the first period. and that / intervene in the two periods the interval is so long that the pressure in the area in which it was measured during the second period is practically reduced to static pressure. 8. The method according to claim 3, characterized in that the gas from a point in the pit deducted during the production period at no more than approximately the maximum production quantity thereby practically eliminating the possibility of air entering the pit. 9. The method according to claim 8, characterized in that the pressure in a selected area next to this point is monitored during at least part of the production period and the withdrawal speed is controlled according to the pressure in the area next to this point during the production period so that the entry of air into the pit is largely prevented during the production period. 10. The method according to claim 9, characterized in that that the pit (11) is covered with a layer, and that next to this point the withdrawal speed of the source (29,31) is regulated so, that the pressure in the area adjacent to the cover does not fall below atmospheric pressure. 11. The method according to the preceding claims, characterized in that several probes (69a, 71a, 73a, 75a ^ in a pattern Ln of the pit are arranged that withdrawn gas in a first period and the pressure in at least a first Group of probes is found to have a maximum withdrawal speed for the first source using these pressures it is determined that this speed is practically the highest speed represents in which the gas is largely withdrawn without air entering the pit and that the withdrawal of gas from the first source occurs at a rate which is not higher than the highest take-off speed. 12. The method according to claim 12, characterized in that when arranging a plurality of probes the first group of these probes is provided at a depth in the pit that a second group of probes are deeper in the pit than the first group and a third is deeper than the second, and that the gas pressure is measured in the second and in the third probe group. 13. The method according to claim 12, characterized in that that the gas is withdrawn from the first source (29) during a second period and the pressure is detected in at least some of the probes during the second period, and that using the determined pressures, the maximum permissible withdrawal speed as that is built up, in which the pressure at at least one probe is approximately equal to atmospheric pressure is. 14. The method according to the preceding claims, characterized in that the static Pressure in the pit (11) at several distances from the source (29, 31) is found that the gas is withdrawn at two different speeds during the two periods that the Pressure in several areas of the pit (11) during both periods in at least two areas is found that are at different distances from the source (29,31) that the during part of the first period observed in these areas Pressures are used to determine the shortest distance from the source (29, 31) for the first withdrawal speed at which static pressure prevails during part of the first period that the pressure determined in this area during part of the second period also serves to determine the shortest distance from the source (29,31) at the second withdrawal speed at which there is a static pressure during this part of the second period that a relationship is established between the shortest distances and the withdrawal speeds, by means of which the source distance for different flow velocities can be determined, that at least one other source (3i) is provided in the pit (11), that the maximum permissible withdrawal speed of the sources, which can be used without large air entry into the pit, is built up, and that gas from the sources is withdrawn at a speed no greater than the withdrawal speed that you The relationship described is established and the maximum permissible withdrawal speed is.