Patent Application
20100008728
This application is based on the complete specification filed in relation to New Zealand Patent Application Number NZ544578, the entire contents of which are incorporated herein by reference.
The invention relates to a compactor and a method for compacting a landfill.
Landfills are an increasingly prevalent consequence of human development, urban expansion and the inexorable production of human refuse. Typical landfills are large recesses (either natural land contours or man-made excavations) in a designated site which are successively filled with refuse (predominantly organic or inorganic material), some of which may be subjected to pre-filtering or extraction of recyclable materials. The large land areas required, together with strict operating compliance requirements, mean landfills, and the operation thereof, can be extremely expensive. Furthermore, landfill sites require monitoring for dangerous settlement and any release of dangerous gases or leachate seepage for prolonged periods after the site is filled and sealed. Consequently, there is a strong incentive to maximise the efficiency of a landfill site and reduce the time period before the land may be used for beneficial purposes.
The variable composition of refuse however creates difficulties with the above aims; which are only partially addressed by prior art landfill construction, completion and management techniques.
A typical landfill site may be essentially considered as a fixed usable volume into which refuse may be placed before the site is sealed. Compaction of the refuse thus reduces the percentage of the landfill volume occupied by voids or ‘airspace’ and therefore increases the total amount of refuse that may be disposed of in the landfill. The increase in refuse density produced by mechanical compactors operating over the landfill surface is also complimented by the effect of refuse decomposition. As the organic matter in the waste rots further, voids are created in the landfill. The weight of the waste material itself can also cause a degree of compaction to voids in lower portions. A by-product of the organic matter decomposition is the production of methane gas, which may continue to be produced well after the landfill is full and sealed. Provisions must be made to cater for any methane gas production due to its flammable nature and potent greenhouse gas effect and may, depending on the volumes produced, warrant capturing the gas as stored energy.
Although the volume reduction caused by decomposition of the organic matter is affected by several factors; the predominant effect is moisture content. The type of refuse constituents, the permeability of the landfill (both during filling and after sealing), the rainfall conditions and the design of the landfill all affect the landfill moisture content. It is thus desirable to control the moisture content to facilitate the decomposition process and thereby liberate further volume in the landfill.
Consequently; to optimise the utilisation of limited landfill volumes by maximising the density of the landfill, and minimising air space, several techniques are known in the art.
At virtually all landfill sites, some form of mechanical compactor, bulldozer and roller compactor works the refuse surface, usually applying compacting pressure via rigid spiked wheels. Although typical landfill densities vary widely, they seldom exceed one tonne per cubic metre, even immediately after operation of such mechanical compactors. This is partly due to the constraints of operating a mobile compactor over the surface of variable density and integrity to ensure sufficient ground pressure is applied to achieve compaction; i.e. preventing the compactor from sinking into the surface to such a degree that movement is inhibited without requiring an uneconomically powerful engine.
The risk of a compactor capable of maintaining a good ground pressure becoming stuck may be mitigated by the use of widely separated compactor wheels. However, this has the drawback of creating a thin skin of harder material over the landfill surface and thus reducing the compaction effects on depths greater than about two metres. Considering the configuration of a typical large conventionally wheeled compactor with a wheel footprint of 1.4×0.4 m per wheel and a mass of 50,000 kg generates a resultant static ground pressure of 22,300 kg/m2. Even the largest bulldozer or roller compactors only achieve a ground pressure of around 20,000 kilograms per square metre. The ground pressure of a wheeled compactor is however increased by spikes on the wheels and the forward motion of the compactor achieving a ground pressure of approximately 30,000 kg/m2.
The degree of compaction possible by such vehicles is thus limited to the surface layer to a depth of approximately two metres.
Prior art compaction devices and techniques for landfill compaction fall into three categories:
U.S. Pat. No. 2,897,734 discloses a method for compacting a landfill which uses a heavy block lowered to the ground via an access aperture in the vehicle chassis. A vibration frequency of several, to several dozen Hertz is applied to the block. The combination of weight and vibration acts to increase density in the soil below the compactor.
However, the effects of this type of compaction are restricted to a shallow surface layer leaving the underlying landfill unaffected.
U.S. Pat. No. 5,244,311 discloses a landfill compaction method using a mass dropped by a crane. Control over the precise impact point is limited however, restricting the ability to compact the surface systematically.
Australian Patent No. 70488 discloses a method of compacting soil through repeated impacts of a dropped weight. The impacts create a momentary state of stress or strain within the soil so that excess pore water pressure in the soil reaches 50 to 80% of the value required to produce liquefaction and is followed by a rest phase during which the interstitial water is allowed to escape. The method therefore relates specifically to soil and its inherent characteristics and is thus not germane to landfill compaction.
Australian Patent Application No. 199715085 is a patent for a tracked vehicle for the compaction of soil. This vehicle utilises weights at both the front and rear of the vehicle which are capable of being raised and dropped repeatedly. However, the maximum height to which the weight may be elevated is restricted, limiting the impact energy attainable by the weights.
U.S. Pat. No. 6,499,542 discloses a device for ground compaction comprising essentially of a mass applied to the ground to achieve compaction through a system of rollers attached to a vehicle. Consequently, the compaction achieved is severely limited and fails to achieve deep soil compaction.
U.S. Pat. No. 6,505,998 discloses a ground treatment device dropped be a crane. The device essentially comprised of some form of pointed nose portion which widens above the tip, (e.g. a conical or frustro-conical section) up to a shoulder portion. The degree of penetration of the device is aided by the pointed nose, while over-penetration is prevented by the shoulder portion. The only means of varying the impact force of the device is to adjust the release height or to change the impact device for a different configuration. These options both provide a means of ensuring the impact forces generated when compacting surfaces of increased toughness (e.g. previously compacted areas) do not exceed any regulatory seismic limits. However, both options provide clear inefficiencies for landfill compaction by respectively reducing the degree of compaction possible from the reduced release height and lowering the rate of compaction due to the down-time in changing the impact device.
Patent application WO 2000/28154 discloses a trailer-mounted compactor intended for relatively small areas of soil compaction, in which the compactor is pivotally attached to the rear of a trailer to lie flat against the trailer for movement, and raised upright for compaction operations. There is however no disclosure how the device may be utilised for deep compaction of landfills or how the inherent difficulties in landfill compaction discussed herein may be addressed. The relatively small impact weight and associated mounting and lifting structure are unsuitable for up-scaling for deep compaction on an undulating landfill surface of variable consistency.
Patent application WO 2004/003301 by the same inventor discloses an extension to the compactor disclosed in WO 2000/28154 which utilises on-board monitoring means to measure feedback from the compaction impact to determine properties of the soil. However, it does not provide a means of monitoring the seismic effect of the impacts to maximise the compaction effects within regulatory vibration constraints.
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
It is acknowledged that the term ‘comprise’ may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term ‘comprise’ shall have an inclusive meaning—i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term ‘comprised’ or ‘comprising’ is used in relation to one or more steps in a method or process.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.
According to one aspect of the present invention there is provided a compactor including:
The impact tool is essentially a large mass used as a hammer/penetrator to crush refuse and the voids therein. The impact tool may take a variety of configurations though most preferably, is formed as a block (optionally elongated) or element with an impact face and lower tool tip shaped to penetrate uniformly into the refuse surface without being deflected or deviated from the vertical impact axis. Preferably, the tool tip is slightly tapered, to facilitate extraction of the tool after impact.
In one embodiment, the impact tool is provided with a laterally enlarged portion above the impact face. The enlarged portion or collar serves to prevent over-penetration into the refuse (which may make the impact tool unduly difficult to extract), and provides a visual indicator for the operator to maintain a uniform penetration depth.
The lifting mechanism may take any convenient form such as a pulley system, chain drive, ram drive (pneumatic, hydraulic or the like), a combination of same or any other sufficiently powerful means of reliably raising the impact tool to the raised position. Thus for example, the lifting mechanism may include a wire rope hoist configuration driven though multiple reduction sheaves via a hydraulic ram. The impact tool may be pulled from above (e.g. raised by pulley system attached to the upper portion of the support mast) or pushed from underneath, e.g., using one or more ram drive(s) acting on a lug projecting from the side of the impact tool.
In one embodiment, the impact tool is configured to travel inside the support mast, preferably attached to moveable guides adapted to slide along tracks, rails or similar. It will be readily appreciated the guides may be attached to the impact tool and the corresponding tracks located on the inside of the mast or vice-versa.
In an alternative embodiment, the impact tool is configured to be slideably coupled to an exterior longitudinal portion of the mast, capable of being lifted to the raised position and descending substantially parallel to, but exterior from the longitudinal axis of the mast.
In a yet further embodiment, the impact tool may be raised by the lifting mechanism and/or allowed to descend completely unrestrained by the support mast. It will be appreciated that in such a configuration, any movement of the compactor during raising or lowering of the impact tool may cause the impact tool to oscillate about its coupling to the lifting mechanism, causing potential instability and/or damage to the compactor. Moreover, such a system would be limited in its capacity to impact adjacent portions of the surface in an accurate systematic pattern unless the impact tool was stationary at the commencement of its descent and this in turn also depends on whether the compactor is stationary as the impact tool is raised.
To achieve compaction to a greater depth than conventional prior art compactors, the present invention employs a very substantial impact tool to achieve a high level of impact energy. The practicality of simply using a compactor with a significantly increased static weight is limited by the aforesaid difficulties in preventing such a massive compactor sinking into the refuse surface and the necessary motive power unit required for such a vehicle. Using a kinetic impact tool enables the total weight of the transporter to remain manageable whiles allowing high pressure levels to be applied. To optimise the benefits of such a configuration, the present invention utilises a substantially sized impact tool. While the specific size may naturally be varied without departing from the scope of the invention, an exemplary compactor configuration includes a 40,000 kg mass being lifted to a raised position 12 metres above the refuse surface.
In one embodiment, the impact tool descends from the raised position under gravitational force. However, in an alternative embodiment, the impact tool may be assisted during descent. The assistance may be provided by a number of means including biasing means (spring, buffers and the like), chain, belt or ram drives and/or any other suitable mechanism. It will be appreciated that by accelerating the impact tool to a super-gravitational descent rate, a lower impact tool mass may be used to produce the same impact energy as a larger mass falling under gravity alone. Equally, raising the impact tool to a greater height also provides a means for increasing the impact energy and/or decreasing the impact tool size.
Using the example configuration of a 40,000 kg mass with a 1 m2 area impact face falling under gravity for 12 m and coming to rest over 0.3 m, the impact pressure generated is 1,500,000 kg/m2 This equates to approximately 50 times the pressure of the largest wheeled compactors; or equivalent to the pressure exerted at the base of a landfill 1.5 kilometres deep. The high forces involved in raising and lowering such a large mass could create potential hazards for the stability of the compactor.
Thus, the present invention addresses the above complications of using such a large impact tool over the non-homogenous surface of a refuse site by use of the stabilising system which ensures the impact tool is free to descend without transmitting any lateral force to the support mast. It will be seen that due to the large kinetic energy levels involved, any misalignment of the support mast preventing the impact tool descending vertically would transmit a significant lateral force to the compactor which may cause damage and/or (in the case of large mast misalignments) possibly overturn the compactor.
Preferably, the stabilising system is also capable of maintaining the support mast in an orientation avoiding any lateral force on the impact tool during lifting to its raised position. The kinetic energy of the impact tool while being raised will be lower than that during descent, due to the lower velocities involved. Nevertheless, stabilisation of the mast (and thus the impact weight) during lifting of the impact tool enables the compactor to simultaneously move to its next location. This reduces the overall time cycle between successive impacts, thereby increasing efficiency.
The stabilisation system may be automatic, semi-automatic, or even manually operable. A fully automated system may be implemented in several configurations utilising some form of position sensors and actuators. The position sensors are used to detect the position of the support mast, absolutely and/or relative to the transporter. The sensor data is used by a stability control means to determine the orientation of the support mast and any deviation from a vertical position. The stability control means outputs control signals to actuators (e.g. electrical, hydraulic or pneumatic drives) capable of adjusting the mast orientation to correct any deviation detected. Such an automatic stabilisation system may perform corrections dynamically to ensure the mast is continuously aligned in a vertical orientation.
In addition to an impact crater and sub-surface compaction, the violent collision of a heavy mass with the refuse surface causes shock waves to radiate through the refuse. The goal of landfill compaction is to maximise the physical compression of the refuse material within any applicable environmental, practical and legislative constraints.
Given that most landfill sites have regulations governing the allowable ground vibration limits, it is desirable to achieve the maximum practicable compaction effect per impact of the mass without exceeding these seismic limits. The magnitude and propagation of the shock waves (or ‘seismic effect’) is dependant on numerous variables including the composition and structure of the refuse, the moisture content and the nature of the impact tool deceleration.
Considering a tool falling from a given height, the kinetic energy of the tool at the moment of impact will remain constant provided the mass remains constant. The impact force will be determined by the rate of declaration of the tool
A prolonged deceleration dissipates the kinetic energy of the impact tool over a longer period (i.e. a lower rate of change of momentum) thus applying a lower force impact to the surrounding material. Conversely, a rapid deceleration causes a high rate of momentum change producing a correspondingly higher impact force.
Thus, after an initial impact tool strike has been performed in a given area and the surface compacted to a degree, a subsequent tool impact in the same area would generate higher impact forces due to the more rapid deceleration generated by the hardened surface.
However, the rate of deceleration of a given mass also depends on the shape and surface area of the impact face and the consequential effect on the pressure applied by the tool impact face.
The present invention overcomes the problem of increased impact forces for areas of increased surface hardness by providing the compactor with a means of varying the pressure applied by the tool during impact and thereby maintaining a substantially constant seismic impact effect.
Thus, according to a further aspect, the present invention is configured such that the impact tool includes a variable area impact face.
The area of the impact face may be varied in a wide variety of means. According to one aspect, the impact tool includes a variable area impact face, said face including two or more portions, at least one portion being movable to either overlap with at least one other portion or be removed from the impact face. In one embodiment, at least one said impact face portion is detachable from the impact face, and preferably capable of being reattached to a separate portion of the impact tool to maintain a constant total impact tool mass.
In a further embodiment, at least one moveable portion is pivotally or slideably attached to allow variable overlap with at least one other impact face portion. In some embodiments, the impact face may include a fixed portion to provide greater strength; whilst in an alternative embodiment, the entire face may be composed of moveable portions which co-operatively overlap to a variable degree.
Preferably, the total weight of the impact tool remains substantially constant for any change in impact face area. Maintaining a constant weight for the impact tool means the resultant kinetic energy generated during each descent remains constant. Thus, as the surface becomes hardened and denser through previous impact tool strikes, the area of the impact face may be reduced to increase the impact pressure, causing greater penetration. As the tool deceleration occurs over a greater distance, the impact shock is reduced from that which would otherwise have been generated by the hardened surface. Thus an increased penetration may still be achieved in the pre-compacted surface without exceeding the impact force generated during the previous compacting of the area. As the impact area of each strike is reduced, the compactor is required to adjust the increments between strikes.
To optimise the compaction potential of the present invention, the compactor ideally needs to accurately know the compactor location (to plot the position of successive tool strikes) and the amount of seismic effect generated per strike. Thus, according to a further embodiment, the present invention further includes a position location system and/or a seismic sensing system
In one embodiment, at least one seismic sensor is located remotely from the compactor and/or on the compactor, wherein seismic measurement data is transmitted from the sensors to an impact control means. The impact control means incorporates logical processing capability, associated circuitry and interconnects, and may also serve to provide other logical control functions associated with the compactor, such as stabilisation control. Thus, in one embodiment, the stability control means and impact control means are provided by a common control system. Moreover, it will be understood to one skilled in the art that the logical control means is not to be interpreted in a restrictive sense as being a single unit or device, but alternatively subsist in a two or more computing devices operatively interfaced or networked together, located onboard, or remote from the compactor. Remotely positioned sensors and/or control means may communicate with the compactor via any convenient known means including wireless communications.
The impact control means may be used to monitor the seismic effect of each impact and alert the operator to vibration levels approaching a predetermined threshold and/or (in a fully automated embodiment) activate corrective action between subsequent tool strikes. The corrective action may range from a reduction in the area of the tool impact face, or even reducing the release height of the tool. Adjustments to the tool impact face area may be made be an operator or, in some embodiments, automatically according to control signals from the control means.
Convenient position location systems include the global positioning system (GPS) which can provide very high level of three-dimensional positional accuracy. Thus, a GPS-based system may be used to determine the elevation of the compactor on the landfill surface in addition to its horizontal position. Naturally, alternative location sensor systems may be employed, including radio triangulation, radar, microwave and the like. The use of accurate position measurement of the compactor, and the position of tool impacts, enables a systematic compaction of the landfill to be performed. The position of successive strikes may be performed in an incremental sequence of overlapping, contiguous, or closely spaced strikes.
It will also be appreciated that control of the compactor movements and impact tool strikes may be performed remotely from the compactor. Such remote control allows the mitigation of operator exposure to operational hazards such as noise, vibration, and surface gas emission.
The physical configuration of the transporter, support mast and impact tool may also take several forms.
Spreading the weight of the compactor over a wide area is one means of reducing the risk of the compactor getting stuck. The transporter may include caterpillar tracks, wheels, skids or a combination of same. Tracks offer the greatest resistance to becoming stuck; may be configured to be self-propelled, and are reliable. The entire mast, tool and lifting mechanism assembly may be carried on a transporter with a single pair of tracks. However, placing the mast, impact tool and lifting mechanism on a bridge portion spanning separate tracks, is a preferable configuration due to:
The compactor transporter may include a symmetrical configuration with two substantially identical, preferably tracked, drive units separated by the bridge portion. Alternatively, the transporter may include a powered base with a pair of tracks connected by the bridge portion to a simplified single drive outrigger unit. In both such configurations, the support mast, impact tool and lifting mechanism is preferably positioned on the bridge spanning the tracked units, ideally such that ground pressures under the tracks are equalised. Although any appropriate type of drive may be employed such as toothed wheels, half track s and the like, for the sake of clarity, the present invention is henceforth described with reference to tracked drives, though this should not be seen as limiting. As used herein, the term drive unit also included powered and un-powered, freewheeling drives
In preferred embodiments, a bridge portion is pivotally or articulately coupled to the separate tracked units, enabling the separate tracked units to operate at different elevations. This is a significant advantage in a systematic compaction process by enabling one of the tracked units to run in the compacted lower ground after an initial series of tool strikes has formed a compacted trench or plateau. The difference in height between the tracked units requires the stabilisation system to make corresponding corrections to maintain a vertical orientation of the support mast and impact tool. However, the inclination of the bridge portion between tracked units at different heights may be reduced by providing the lower unit with an elevating mechanism to raise the bridge portion attachment point. It will be appreciated that an elevating/lowering mechanism may be incorporated into both drive units (enabling the compactor to traverse a bench layout in either direction) or restricted to one of the units, which has sufficient range to maintain the bridge substantially on the level whether the drive unit is in a trench or on a plateau.
It will also be appreciated the above referenced stabilisation system may also be extended to other facets of an embodiment with a bridge portion and two or more drive units. Stabilisation applied between the support mast and the compactor transporter may be subdivided into stabilising actions performed by actuators operating between the;
In a yet further embodiment, the stabilisation system includes actuators operable between a drive unit and said elevation mechanisms. In each instance, the stabilisation system applies inputs to the stabilisation actuators to ensure the alignment of the support mast remains substantially vertical to ensure the impact tool is able to descend vertically without applying any lateral force to the support mast.
Stabilisation between the transporter and the adjacent terrain is implemented by actuators acting on support legs deployed from the compactor. Such stabilising support legs are commonly utilised in many forms of lifting and earth working machinery, mobile cranes, diggers, cherry pickers and the like. However, in such applications, the support legs are lowered into contact with the ground and braced before any destabilising forces are applied to the vehicle. However, in the present invention, the large mass of the impact tool, particularly in its raised position, may cause stability problems for the compactor as the compactor traverses the undulating and variable density refuse surface. In instances of such sudden instability, due to the movement of the compactor, there may be insufficient time for the support legs to deploy before the compactor pitches over or damage occurs.
According to a further aspect of the present invention, said stabilisation system further includes support legs deployable from the compactor to an adjacent terrain surface, wherein the support legs are configured to trail over the terrain surface in an un-locked mode, unless an activation signal is received from said stability control means indicating the orientation of support mast deviates from the vertical by more than a predetermined angle, whereupon at least one support leg is locked to prevent further angular deviation and preferably, apply corrective movement to re-align the support mast vertically.
Thus, by allowing the support legs to remain in a continual standby position of instant readiness, the stabilisation system may act rapidly to prevent a roll-over or other instability. Allowing the support legs (typically powered by hydraulic rams) to trail over the landfill surface in the condition known as ‘float’ (i.e. the actuator ram that raises and lowers the support leg is configured with all the valve ports open, preventing any force being exerted on the support leg), there is no delay in bringing the support leg in contact with the refuse surface. To avoid excessive drag caused by the trailing support legs, the underside of the contact portion of each support leg is contoured to slide over the surface. As soon as the impact tool is being dropped, or (optionally) lifted and the activation signal is received, the ram valve locks, locking the stabilizer to the ground to provide more stability. If the roll rate of the whole compactor exceeds a certain value during movement over the landfill site, or if the whole machine inclines past a predetermined angle, then the support legs may also be configured to lock.
The above-described compactor provides numerous efficiency improvements in the compaction of landfills and may be employed on existing landfill sites with or without implementing all the various features described above. The present invention also provides for advantageous methods of constructing, filling, compacting and managing a landfill site using the above described compactor, and in some embodiments, prior art compactors.
More specifically, the present invention provides a method of landfill compaction of a landfill tract composed of a plurality of strips utilising a compactor substantially as hereinbefore described, said method including the steps:
Preferably, adjacent locations are contiguous, closely-spaced or at least partially overlapping. Preferably, adjacent strips are substantially parallel. In a preferred embodiment the transporter drive is capable of indexed movement, whereby each impact tool raise and descent cycle is indexed to a fixed distance movement of the drives.
Thus, a uniform, continuous and systematic compaction may be applied to any portion or tract of the landfill surface.
According to a further embodiment, said compaction method utilises seismic data feedback from one or more seismic sensors, said method including the steps of:
The present invention also provides an enhanced method of constructing and operating a landfill for collection of landfill generated gas (particularly methane), said method including the steps of
Applying differing degrees of compaction to differing regions, areas of greatest compaction will become more impermeable to gas and to moisture which is key to decomposition of the organic material in the refuse. Thus, by selective application of the increased levels of compaction, the relatively uncompacted areas become focal points for the production and collection of methane and other gases. Thus, gas collection means such as perforated conduit and the like inserted through the refuse layers may collect a far higher proportion of the generated gas than would otherwise be possible in a homogenously compacted landfill.
Over time, the collection of gas from a designated area and the consequential reduction in refuse density due to the decomposed material will cause the overlying refuse to crush the voids generated. The gas collection means may then be re-located to other regions which have become (or been made) comparatively more permeable and less dense. Thus, the gas collection sites may be systematically relocated over the lifetime of the landfill to ensure maximum gas collection in conjunction with selective compaction to produce density and/or permeability gradients between different regions.
According to a further embodiment the impact tool includes at least one penetrator e.g. a spike, pin, pipe or the like for penetrative impact with the landfill. In use, driving the penetrator into the landfill and subsequently withdrawing provides an elongated aperture into the landfill. The aperture may be used to tap gas pockets in the landfill or promote decomposition by permitting air to permeate through the aperture and to collect gas generated by the decomposing landfill. In the prior art, gas collection has typically been performed on uncompacted, or ‘conventionally’ compacted (by existing compaction techniques) sites which are thus prone to significant settling as the organic landfill matter decomposes and settles. Consequently, the gas collection holes formed in the relatively ‘soft’ material require ‘sleeving’ to ensure the aperture avoids collapse. Furthermore, typical prior art apparatus required to form apertures for gas reticulation collection in landfills generally comprise a drilling rig or the like and thereby require a considerably longer period of time to drill to depth than a single impact device such as the present invention as aforementioned.
In contrast, the present invention is able to significantly enhance the effectiveness of such gas collection by utilisation of two, above-described, features, i.e. the penetrator and the systematic method of compaction.
Where the landfill has been compacted to the enhanced levels capable using the present invention, the apertures formed by the penetrator may be utilised without sleeving due to the enhanced structural integrity of the compacted material surrounding the hole. Thus, according to a preferred embodiment, the present invention provides a method of operating a landfill for collection of landfill generated gas substantially as hereinbefore described, said method further including the steps of:
Preferably, said landfill aperture is capped by a sealable extraction conduit placed in the aperture and extending to the surface. Thus, only a relatively small and inexpensive device, e.g. capping pipe, is required for each hole, in contrast to prior art systems which require considerable lengths of ‘sleeving’ which must be withdrawn or left in the landfill upon further compaction or addition of landfill material. Consequently, the present invention enables a large number of such landfill apertures to be formed quickly, and without the costs associated with individually sleeving each aperture.
The penetrator may be formed integrally with the impact tool, and move in unison therewith. Alternatively, the penetrator may be formed as a discrete element of a minority mass detached from, or slideably attached to, the remainder of the impact tool having a majority mass, the penetrator being configured to receive impacts in use from the majority mass to form said apertures. The specific ratio of mass between the minority mass of the penetrator and the majority mass of the main impact tool body may be selected according to the particular constraints of the compactor and its intended application. It is however self-evident to one skilled in the art it is desirable that the penetrator be lighter (preferably substantially lighter) than the remainder of the impact mass. Not only does this more efficiently transfer momentum of the impact into penetration of the landfill surface, it also facilitates the ease of removal of the embedded penetrator from the landfill.
The optimal depth of an aperture to effectively tap landfill-generated gas may exceed the stroke length of the impact tool. Consequently, the penetrator may be composed of a plurality of sections, in a comparable configuration to a drill string, fed sequentially into the aperture. The maximum number of penetrator sections that may be effectively employed is determined by the extracting power of the compactor and the frictional properties of the landfill material bounding the aperture.
Thus, according to a yet further embodiment, said penetrator includes a plurality of connectable sections capable of being sequentially attached and driven into a common aperture.
According to a further aspect, the present invention provides a method of constructing and/or operating a landfill for collection of landfill generated gas using the compactor including said penetrator substantially as hereinbefore described, said method including the steps of
As previously referred to, moisture is also a key factor in the decomposition of organic matter in the landfill. Whilst moisture levels between 20-70% are suitable for decomposition, moisture values outside these limits pose difficulties.
A significantly dry landfill may only be subjected to limited compression due to the small quantity of decomposition that can occur. The lack of moisture may be due to climatic conditions, the landfill capping layer being too tightly sealed with no access for moisture ingress, or the leachate either not recycled or not present.
Excessively high moisture levels may also cause problems due to the potential for impact tool strikes to cause liquefaction of the landfill surface, while the excess water may prevent displacement of the voids in the landfill and thus hinder compaction. Thus, excessively moist landfills may require dewatering of all or part of the landfill immediately prior to the compaction process.
Thus, according to a further aspect, the present invention includes a method of managing landfill moisture content, said method including the steps of
The decomposition accelerants make take any convenient form including drilling, or otherwise aperturing (e.g. using the above-described penetrator) the refuse surface to increase the permeability to moisture or configuring the contours of the landfill surface to increase natural water flow over the surface. In areas of low rainfall, decomposition acceleration may be achieved by pumping water into the landfill through the drill sites.
It can be thus seen that the present invention provides a particularly advantageous compactor and means of landfill compaction, capable of increasing landfill efficiency and reducing the time before the completed landfill site is usable for further purposes.
Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:
a-d show a series of front elevation views of the compactor shown in
a shows a front elevation of the first embodiment of an impact tool with a variable area impact face for use with the compactor of the present invention;
b-d show side elevations of the impact tool shown in
a-f show further embodiments of impact tools with a variable area impact face;
a-b show a side section elevation of a landfill compactor with a penetrator attached;
The present invention utilises a compactor specifically adapted for use on landfill refuse sites and the like.
The transporter further comprises a bridge portion (6) which joins both drive units (4) in a transverse arrangement such that both drive units (4) are able to move substantially parallel to each other. The bridge portion (6) is also pivotally coupled to the support mast (2) at the centre point of the bridge portion (6), equidistantly between the drive units (4). The support mast (2) is a substantially elongated frame capable of a variable orientation with respect to the bridge portion (6) (shown by the dotted lines in
Control over the support mast (2) orientation is effected by a mast stabilising system including a plurality of mast actuators (7) and bridge portion/drive unit stabilising actuators (8) (shown in
As the impact tool (10) is typically made as a substantially massive block (e.g. approximately 40,000 Kg), any misalignment of the support mast (2) from the correct vertical orientation during raising or lowering of the impact tool (10) may cause the impact tool (10) to apply pressure laterally against the support mast (2) potentially causing serious instability and/or damage to the compactor (1).
With respect to
In the embodiments shown in the drawings, the impact tool (10) is configured to slide within the support mast (2), guided by rails (not shown) on an interior portion of the support mast (2). It will be appreciated however that the impact tool (10) need not be internally constrained within the support mast (2) and may be coupled to slide parallel, though externally to, the support mast (2). In further embodiments (not shown), the impact tool (10) may be completely unrestrained by the support mast (2) and coupled to the compactor (1) solely via the lifting mechanism (9). In such a configuration where the impact tool (10) is essentially allowed to swing free under its own weight. It will be appreciated that the support mast (2) requires accurate stabilisation to ensure the impact tool (10) does not swing into the support mast or any other portion of the compactor (1).
It can also be seen in
In order to minimize the necessary travel for the mast stabilising actuator (7) to maintain the support mast (2) in vertical alignment, the support drive unit (4a) is provided with an elevation mechanism (20) capable of varying the height of the support drive unit (4a) attachment to the bridge portion (6). The elevation mechanism (20) may be formed from any convenient configuration such as telescopic struts, scissor linkages, hydraulic rams and the like.
d illustrates an unfavourable position for forming a second compacted trench (18) in which both the main drive unit (4) and the support drive unit (4a) are positioned on the same uncompacted surface (19) resulting in the support unit (4a) travelling adjacent to the uncompacted edge of the previous trench (18) which is likely to be unstable for such weight bearing applications. The compacting methods shown in
Landfill sites are typically subject to impact vibration restrictions governed by regulatory or local authorities' requirements. To maximize the efficiency of landfill compaction within such constraints, the compactor (1) is able to utilise input from seismic sensors (not shown) which may be located on the compactor (1) and/or at remote locations about the landfill site and which transmit seismic data to an impact control means (not shown).
The impact control means may be a discrete unit or form part of other logical processing systems and associated communication means located on the compactor (1) or remotely and may be programmed to control the impact magnitude of the strikes. The impact force caused by its strike may be varied by adjusting the height of the impact tool (10) before release and/or by varying the area of the impact face (17) of the impact tool (10), as described more fully below.
It will be seen therefore that in
a-f show further embodiments of impact tools (10) with their variable area impact face (17).
Each moveable portion (22a) is formed as a complimentary elongated substantially cuboid element with facing side open. Foot portions (26) on each movable portion (22a) at least partially overlap the impact face (17) of the fixed blade (24) and (according to the degree of separation of the two moveable portions (22a)) are capable of interlocking with each other. This has the resulting effect of varying the exposed lower surface area of the two moveable portions (26, 22a) and the fixed portion (24) forming the impact face (17).
c shows a variant of that shown in
d shows a further variant to that shown in
e shows a variant of the embodiment in
f shows a yet further embodiment of the impact tool (10) shown in plan view in which the moveable portions (22c) are attached to an adjacent moveable portion (22c) on an opposing longitudinal edge at a hinged point (28). Thus, the entire assembly may be concatenated or expanded by laterally separating the moveable panels between the non hinged edges.
a-d also show the lifting points (25) to which the wire (13) (not shown in
The maximum achievable compression in any given layer is approximately 40% and any excess compaction is transmitted through to underlying layers. Thus, the second and third layers (32, 33) are compacted to a lesser degree, i.e. 30% and 20% respectively, while the lower two layers (34, 35) are only compressed by 10% and 0% respectively. The second and third strikes of the impact tool (10b, 10c) penetrate less into the surface as the upper layers become more compacted resulting in the compaction effect being transmitted deeper into the refuse pile. It will be appreciated that by varying the area of the impact face (17), the impact tool (10) would be able to penetrate further into the refuse further increasing compaction whilst avoiding an increase in the impact force.
b shows stage two in which some of the refuse from stage one (39) rots and loses density due to the release of methane gas (40) which escapes through a second layer of refuse (41) laid over the first layer (39). The second layer (41) is again compacted using conventional roller compactors.
The density of the stage one refuse (39) decreases to approximately 0.6 to 0.8 tonnes per cubic metre due to the released gas.
c shows stage three in which a further layer of refuse (42) is laid down and is compacted as per the previous stages one and two. Typically, the landfill (37) is now full though the permeability of the refuse layers (39, 41, 42) still allows methane gas (40) to still be released. The stage two refuse (41) also rots giving off further methane gas (40) with a decrease in the resulting density to approximately 0.6-0.8 tonnes per cubic metre.
d shows the landfill (37) after a capping layer (43) is applied over the landfill surface. The capping layer (43) is of a low permeability material, constraining the methane gas being produced by the refuse layers (39, 41, 42) to be restricted from escaping through the entire landfill (37) surface. Collection pipes (44) are inserted through the capping layer (43) and through the refuse layers (39, 41, 42) to concentrate collection of the methane gas (40).
e shows stage five in which the landfill (37) has been closed for a period of time and settlement due to the release of the methane gas (40) has occurred. The capping layer (43) has thus become displaced in a lower position from the original volume boundary position (45) at the original time of closing the landfill (37).
Considering an example volume of landfill being 100,000 cubic metres, the average density of the landfill at the point of closure in stage four (
The present invention provides an improved means landfill construction and operation over the above prior art method. Firstly, the landfill (37) efficiency defined as the percentage of airspace in the landfill may be improved simply by use of the compactor (1) as hereinbefore described due to its superior compaction abilities. The following landfill construction and operation method preferably utilises such a compactor (1), though it should be understood prior art compactors may be used, albeit with reduced effectiveness. The following example is thus based on using a conventional toothed roller compactor to illustrate the advantages of the method over the prior art.
a shows stage one of filling an equivalent landfill site (37) to that represented in
Stage two, illustrated in
c shows stage three in which the centre portion (48) of the landfill (37) is further compacted to a density of 1.3-1.4 tonnes per cubic metre. The edge portions (41) of the landfill (37) are not compacted beyond the effects of stage two to avoid any damage to the liner (38).
d shows stage four in which further refuse portions (49) laid down over the centre portion (48) are subjected to a repeated cycle of refuse filling and compaction to produce approximately the same density as of the centre portion (48). As the lower layers rot, the high density of the upper layers (49) crushes the lower layers maintaining the density. The remaining area (50) of landfill above the centre portions (37) is filled with further refuse layers though compacted to a lesser extent. Thus a density gradient is formed between the upper landfill areas (49, 50) with a commensurate effect on permeability. Thus, the methane gas generated from the rotting refuse is naturally channelled from areas of low permeability (i.e. the highly compacted area (49)) to areas of high permeability (the less compacted area (50). Placing gas collection pipes (44) in the high permeability areas thus enables the volume of collected methane (40) to be optimised.
When the permeability of the collection area (50) drops below an adjacent area (49), the area may then be highly compacted (to 1.3-1.4 tonnes per cubic metre) and the gas collection points (44) moved to the adjacent area.
e) shows stage five in which the landfill is sealed with a capping layer (43) as per the prior art method. Comparing a numerical example with the prior art method described above for a landfill volume of 100,000 cubic metres, the average density of the total landfill (37) at the instance of sealing would be approximately 40% at 1.3 tonnes per cubic metre and 60% at 1.1 tonnes per cubic metre. This gives a total mass of 118,000 tonnes and a generated gas volume of approximately 20,000 tonnes at the time of sealing.
Assuming an annual input rate of 10,000 tonnes, the lifespan of the landfill is thus 13.8 years. Furthermore, gas generation after closure will be approximately a further 15% or 18,000 tonnes.
The rotting of the organic portions of the refuse is thus a useful side effect in terms of liberating additional landfill volume and also for producing methane gas. However, degradation of the organic material is highly dependant on the moisture content and is proportional to moisture content between values of approximately 20% moisture content to 90% saturation.
As discussed above, it is desirable to decompose as much of the organic material as rapidly as possible to recoup landfill volume and reduce the period after sealing of the landfill before the land can be used for alternative purposes.
Furthermore, un-decomposed organic matter creates a long-term liability as eventually decomposition will occur, up to hundreds of years later. This is particularly likely if the landfill has low moisture content (either due to environmental/climatic conditions and/or the landfill cap is well sealed) and breaks down over an extended period. Buildings may have been erected over the old landfill or in close proximity which may be in jeopardy from possible subsidence and toxic gas emission. Although the landfill operator is responsible for stabilization and remediation, this period typically extends only for 30 years at which time some of the above problems may not yet have manifested. However, if the landfill can be decomposed as rapidly as possible the liability is mitigated and the land can be used safely for other purposes.
The rate of methane gas generation determines the viability of capturing the gas for power generation.
Currently, low uneconomic gas yields per cubic metre of landfill are flared or just left to vent to atmosphere. Clearly, neither is environmentally beneficial.
Landfills are typically filled to a volume limit and then sealed, irrespective of the organic content, density, moisture content or final settlement after the time of closure. Commonly this size limit is reached when the majority of the landfill volume comprises low density un-rotted organic material. Thus, any decomposition that can be achieved in the landfill allows more material in before closure.
Consequently, the moisture content of the landfill is an import factor in landfill compaction. Depending on several environmental factors, the moisture content may vary resulting in the following conditions:
Thus, in further embodiments (not shown), the present invention includes a method of managing the moisture content of the landfill.
If, after the moisture levels have been determined, insufficient moisture is present for decomposition, one or more localised decomposition-accelerants may be inserted into the landfill. The accelerants make take any convenient form including simply drilling the refuse surface to increase the permeability to moisture. In areas of low rainfall, the decomposition accelerates may include pumping water into the landfill through the drill sites.
In landfills with excess water, moisture management techniques may include
According to one embodiment, in use, the impact tool (10) is raised and spike (51) placed against the surface of the landfill (shown in
In the prior art, gas collection has typically been performed on uncompacted, or ‘conventionally’ compacted (by existing compaction techniques) sites which are thus prone to significant settling as the organic landfill matter decomposes and settles. The gas collection holes formed in such ‘soft’ material required sleeving to ensure the apertures avoid collapse. The use of the compactor (1) with the spike (51) in compacted landfills avoids the need for such burdensome infrastructure, in addition to the manifold decrease in the total time required to create and utilise each landfill aperture.
Variations in landfill configurations and compositions may require landfill apertures of different lengths and widths to be formed. However, the optimal landfill aperture depth may exceed the stroke length of the impact tool (10). Consequently, (as shown in
The simplicity of the gas reticulation infrastructure associated with the present embodiment provides a significant economic and operational improvement over the prior art. In the absences of any time consuming drilling and sleeving of landfill apertures (52), gas may simply be collected by a capping pipe (53) (shown in
In use, a conduit (not shown) may be attached to the outlet (54) of each capping pipe (53) to convey the gas to a suitable collection reservoir (not shown). It will be appreciated that the capping pipe may include a valve (55), vents or the like to alter the rate of gas egression or to release pressure. In the embodiment shown in
Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 544578 | Apr 2006 | NZ | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/NZ07/00081 | 4/13/2007 | WO | 00 | 9/29/2009 |
