Australian Biomass's regime has four basic phases:
A: Initially actively flowing leachates are tested along with some static gas sampling. If the indicators are promising then a series of three active phases are begun.
Deposition data and the mass/volume of the landfill are all determined from the clients' records in addition to the refuse mix.
If both the refuse mix and the tonnage of the landfill are suitable then the additional testing phases are implemented. A landfill requires a minimum 'critical mass' in order to be perceived as viable for development. It also requires that there is a sufficiently high level of organic matter in the deposited refuse mix and other properties which are all investigated and analyses as part of this passive phase.
One landfill gas well is drilled and fitted out as a normal production well. Its passive mass flow is measured with a standard apparatus.
B: The first active phase requires that a series of landfill gas wells be installed in selected parts of the landfill. This process is monitored for a series of indicators to see how stable the supply of the resource is.
Landfill gas is actively extracted and where its calorific value is high enough it is burnt through a flare. If its calorific value is not high enough then passive measures are recommended for its control or it is blended with a suitable fuel gas and burnt in an appropriate environment.
Along with this phase a further series of biochemical tests are conducted to observe how this aspect of the landfill behaves.
Where the landfill mass, volume and organics are well in excess of the critical mass ( generally seen as 1 million tonnes of refuse with at least 35% putrescible organics ) then the full well field can be installed. Provided there is a sufficiently high degree of confidence that this is 'wise'! This, though, is done only at the clients' request.
C: The second active phase requires a grid of landfill gas wells within the primary body of the landfill with a further series of monitoring regimes; while the landfill gas is flared. Both biochemical and gas composition stabilization parameters are plotted and analysed in accordance with Australian Biomass's empirically derived algorithms. The grid generally consists of 4 x 4 wells and a mixture of smaller grids, when applicable, across the landfills.
Australian Biomass does not use horizontal wells as these tend to work only near the suction end and fall off rapidly in their efficacy along the length of the well. Australian Biomass uses only vertical wells with diameters from a minimum of 900mm to the standard size of 1200mm and to the full depth of the landfill or to within 2 metres of the permanent water-table if such exists at a higher level than the base of the landfill body proper.
D: The third active phase is commenced only after there is a reasonable conviction from the analysis of the data compiled from the first three phases on what the workable landfill gas reserve of the landfill will be. The full well field is then installed and the void volume of the landfill flushed. For a period of time the full well field is operated at a 'maximum' load in a series of balanced mode cycles. This period can be as short as 3 to as long as 18 months ( generally from 2 - 4 months in over 98% of cases ) depending on the ability of critical parameters to stabilize. From here the final workable extractable volume of landfill gas is determined.
The Void Volume trap.
Some consultants advise clients that they need to know the 'void volume' of the landfill. Bunkum! Many professionals use hyperbole and obfuscatious language to bamboozle naive clients into regimes of unnecessary and expensive testing. Such testing contributes more to the consultants' doctorate or pocket than to the development of the resource.
Void volume is such an obfuscation. It is the interstitial space not occupied by refuse within the landfill body. It is impossible to know. And all tests deliver vague and baffling results. And if you did know the void volume exactly what is the point?
What is really necessary is to know the native production level of the landfill. This is what can be extracted and used. The void volume will act as a buffer irrespective of whether its volume is known or not. It is the balanced mode extraction capacity which is the most important aspect of extraction management.
THE MANAGEMENT OF THE EXTRACTION SYSTEM TO ENSURE UNINTERRUPTABLE SUPPLY FROM THE RESOURCE RESERVOIR.
Each well has its own native production level. Each landfill has its own native production level. To determine an individual wells native production level, different volumes of landfill gas are extracted at timed intervals, from that well only, while pressure ( vacuum ) differences are measured on surrounding wells. Gas composition variation is recorded both at the well head and the plant room. All these parameters are analysed on the basis of fluid migration through porous media. Once a stage D ( section 3 ) system and the reservoir void volume of the landfill is fully flushed then the native base methane percentile is read.
Modelling ( Oh! ) the measured parameters enables a clear picture of how the various regions of the landfill perform for the production process. This varies continuously. Initially daily monitoring followed by weekly readings from each well enable optimum control on the extraction process ensuring minimum oxygen infusion and maximum quality of calorific value of the extracted landfill gas.
THE APPROPRIATE EXTRACTION TECHNOLOGY REQUIRED TO MAINTAIN LONG TERM RELIABLE TROUBLE FREE EXTRACTION OF THE RESOURCE.
My preference is for Centrifugal fans with statics of 40Kpa. The extraction volume capacity generally twice the maximum estimated landfill gas reserve.
The Extraction compressor should be as close to the final usage point as possible. Installing fans up to hundreds of metres from their end usage will result in the pressure pipe drowning in condensate of compression unless the condensate is removed immediately with a refrigerated drier.
Pall type filters for extraction of carried over detrital matter and residual condensate should be used on the pressure side of the extraction compressor after the flow has passed through a refrigerated drier.
Vane, turbine, piston, screw compressors and rootes type blowers are all suitable for the extraction of the landfill gas resource. I prefer fans.
ASSISTANCE WITH THE END USAGE OF THE RESOURCE FROM USING IT IN AN UNPROCESSED MANNER FOR HEATING OF BRICK-KILNS, ELECTRICITY GENERATION TO PURIFICATION FOR MUNICIPAL RETICULATION.
The best end usage for landfill gas is to burn it. In a brick kiln, in a boiler, a greenhouse, supplementary fuel for cement production or in a drier.
(The two preferred end uses being either the brick kiln or the cement production kiln or high temperature MHD power generation. Only these three environments provide for retention times in the domain of seconds and with sufficiently high temperatures to totally destroy all the VOC's and other contaminants within the gas-stream).
One of the most common uses of landfill gas is the production of electricity; generally from stationary piston engines. The least amount of processing of the resource the lower the amount of capital that is required for its development and the greater the financial return. The more complicated the end use components the greater the maintenance costs. Large stationary engines i.e. Waukesha or Rushton etc are best suited for the process of generating electricity from the landfill gas resource. Selection of final end use is governed by the availability of local industries that can use the resource raw. Otherwise power generation is the best other option.
( As long as the landfill gas is combusted in one way or another it is still better, though some combusting methods are less efficient than others, to burn the landfill gas than to allow it to migrate into the atmosphere raw ).
The worst possible end use of landfill gas is to purify it and use the purified resource for domestic reticulation. There are too many VOC's in the raw resource for this to be done safely. To supply the purified resource for industrial uses is a tad defeatist. It can be supplied raw with scrubbers removing much of the VOC's but the scrubbers need their own regime of chemicals and this further adds to the waste problem which led to the landfill gas in the first place.
Though initially I supported the use of steam turbine power plant for the generation of electricity on closer inspection of such a plant its efficiency was no better or worse than a standard stationary piston engine but its technological infrastructure proved far too complex when compared to a stationary piston engine type of plant. Other cleaner systems for the production of electricity also exist.
Where modified gas turbines are used heat recovery from the exhaust ( and from the cooling water of the piston engines ) is suitable for low grade heating applications: Swimming pools, greenhouses, central heating etc... .
Liquefaction is definitely not an option that should be considered due primarily to the heterogeneous nature of the gas.
DESIGN OF THE LANDFILL FOR THE MAXIMISATION OF LANDFILL GAS PRODUCTION.
As easy as it may seem the best management policy for maximizing the production of landfill gas from a landfill is to shred everything. Isolate all large non recyclable products to a specific area of the landfill so that they do not interfere with the drilling of wells when they are needed and build the landfill forward from its full height as quickly as possible.
With the first full height section reached commence the installation of the landfill gas extraction system.
Moisture is the fuel of the anaerobic process. Leachate collected in perimeter drains and recirculated through surface trenches assists the anaerobic process. The fill content ( non organic ) of the landfill filters out heavy metals and other toxins dissolved in the leachate over time. Thus while there is active methanogenesis within the landfill the recirculation of the leachate aids this and the inert content of the landfill traps the solutes within the leachate.
Condensate trapped in on site condensate traps is best suited to being returned into the landfill for this purpose. As automatically happens with the barometric drip legs.
DESIGN OF APPROPRIATE MANAGEMENT PRACTICES FOR BOTH THE MANAGEMENT OF THE WASTE-STREAM AND THE LANDFILL FOR BOTH THE MAXIMISATION OF LANDFILL GAS PRODUCTION AND MAXIMUM RECOVERY OF RECYCLABLE GOODS.
This equates to the ultimate landfill waste-management facility. (ULWMF) Sanitary landfills designed with impermeable liners ( really they leak but very very slowly 1 litre per hectare or less ) onsite recycling recovery and reprocessing, shredding everything that goes into the landfill and even routeing organics to large cell digesters to accelerate their decomposition and recycling the digested products for agricultural non food plants.
AUSTRALIAN BIOMASS OFFERS THE ONLY BALANCED MODE EXTRACTION SYSTEM WHICH WORKS IN CONCERT WITH THE NATIVE LANDFILL GAS PRODUCTION LEVEL OF THE LANDFILL FOR THE MINIMISATION OF AIR INFUSION INTO THE LANDFILL DURING EXPLOITATION OF THE RESOURCE. THUS MINIMISING THE MIGRATION OF THE AEROBIC BOUNDARY LAYER INTO THE BODY OF THE LANDFILL PROPER.
Balanced mode extraction, though self explanatory, involves rigorous field testing to be properly implemented. A landfill gas extraction system operating in balanced mode operation will have minimal air infusion and maximum methane recovery of its resource.
It involves balancing all wells and groups of wells and the entire well field such that the landfills' native production level is extracted in balance with its production.
Oversuction of the resource, will in the short term, appear to yield more joules. But what it also does is draw the aerobic boundary deeper into the body of the landfill. It also draws more nitrogen into the slipstream and this adds an unnecessary amount of NxOx to the exhaust pollution from power stations and other applications where the landfill gas is being burnt. It also destroys the anaerobic process and once the amount of joules begins to fall and measures are being taken to boost production it can take up to 18 months for the anaerobic process to recommence once a volume of refuse has been subjected to prolonged periods of aerobic activity.
IN SUMMARY: THE DESIGN, INSTALLATION, COMMISSIONING AND CONTINUED MAINTENANCE OF THE LANDFILL GAS RESOURCE ALONG WITH THE DESIGN AND MANAGEMENT OF APPROPRIATE WASTE-STREAM PROCESSES TO CLIENT REQUIREMENTS.
A balanced mode installation once installed can be operated either automatically or manually as already discussed earlier. My own preference is to have personnel who physically inspect the well field if not every day at least once or twice a week.
Data manually collected can be relayed anywhere in the world for analysis and evaluation. Tweaking corrections can be relayed in seconds to return instantly. Australian Biomass offers such a service not only for its own installations but also for existing and new installations.
A mass flow apparatus does not have to have butterfly valves in order to have its data analysed. Australian Biomass already services some remote clients and their mass flow is all done with orifice plates. ( Mass flow calculated using AGA-3 ).
There is greater consumer co-operation in the domain of waste recycling. Specialized collection bins for specific waste products is making the process easier. Political initiatives need to be implemented to facilitate such processes more broadly and effectively. Couple this with the correct collection and reprocessing infrastructure and the need for landfills will diminish and fewer and fewer will be required.
The few that are to be used can be increasingly located in more remote
locations and have less and less if not nil toxic products deposited within.
There should not be any toxic products deposited in landfills at all and
any landfill contractor that accepts toxic substances should not be allowed
to manage landfills. The deposition of toxic substances continues. It should
be stopped and penalties for offenders should be very very severe. Any
residue from the (ULWMF) should be blended into an insoluble matrix before
being deposited within the landfill.
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