Production and Use of Biogas in Landfills to Produce Energy

8/2/2019 Production and Use of Biogas in Landfills to Produce Energy

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Production and use of Biogas in Landfills to produce

Energy

Mario Heredia , Abdolrahman KhoshrouUniversidad de Aveiro, Aveiro, Portugal, 3810-366

Landfill gas is generated by the biological decomposition of wastes placed in a

landfill. The composition of landfill gas is highly variable and depends on a number of

site-specific conditions including solid waste composition, density, moisture content, and

age. The specific composition of landfill gas varies significantly from landfill to landfill

and even from place to place within a single landfill but in general we can say that are

composed by 50% of CO2 and 50% of methane CH4, the last one gives to the gas a

potential heating value that could be used in several ways whit an inherent economically

benefit, the environmental benefits are questionable and are linked to the technical and

efficient management of all process implicated, collect, filtration, dispose of

contaminants and burn to produce different kinds of energy.

Nomenclature

E th (MW): Thermal energy

ṁCH4: Flow rate of CH4 (m3 /h)

LHV CH4 : Lower heating value of CH4 (MJ/m3)

ℜ

: Recovery rate

E el (kWh) : Electrical energy

ηel : Electrical efficiency

I. Introduction

LL cities produce waste, the human activity uses a lot of disposable articles, and there is the need of processand disposal these waste. Usually the local governments, has a public or private collection service, that pick up the waste generated in homes and deposit it in a landfill.

At the beginning in a lot of countries in ways of developing a landfill is only a hole in the earth in orderto fill it whit waste an then when is full, cover it whit more earth.

This activity generates a lot of problems in the landfill situated local, bad smells, vegetation damage,mice and was founded that decomposition of waste generates a leachate, that contaminates the soil and if thereare ground water flows also contaminate it. Most of the time this ground water deposits feed water to the localtowns and cities.

Another problem that was founded is that the anaerobic decomposition of waste generates dangerousgases at the surface of the landfill, all of those are liberated to the atmosphere and this gas is hardly explosive.

So there is the need to have a technical plan in order to minimize the impacts of this landfills taking intoaccount that always the human activities will be producing more and more garbage.

II. Landfill Structure

The technical management of landfills suggests that we have to insulate the soil from the garbage and theexperience dictates that is more efficient and safe to have different levels of insulation.

A





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Table 1. Typical Landfill Gas Composition

Inorganic contaminants like mercury are also known to be present in landfill gas. Sometimes, evenradioactive contaminants such as tritium (radioactive hydrogen) have been found in landfill gas.NMOCs usually make up less than 1% of landfill gas. EPA identifies 94 NMOCs in their 1991 report, "AirEmissions from Municipal Solid Waste Landfills - Background Information for Proposed Standards andGuidelines." Many of these are toxic chemicals like benzene, toluene, chloroform, vinyl chloride, carbontetrachloride, and trichloroethane. At least 41 of these are halogenated compounds. Many others are non-halogenated toxic chemicals. More exhaustive test for contaminants in landfill gas has found hundreds of different NMOC contaminants.

There are some initiatives of landfill operators that are classifying the garbage, in order to have specific gasproduction landfills using only organic matter as waste, this improve the landfill gas final quality but don’t solvethe problem at all because was observed present of contaminants in the landfill gas composition that comes fromfertilizers using in agriculture.

IV. Landfill Gas Collection.

If we lead to gas migration off-site, it can cause explosions. The release of the methane creates some globalwarming problems (methane causes 21 times more global warming effects than CO2) and the release of toxiccontaminants can cause cancer and other health problems in local communities. A New York study of 38landfills found that women living near solid waste landfills where gas is escaping have a four-fold increasedchance of bladder cancer or leukemia so landfills should install gas collection systems to prevent the problemswith gas migration.

All landfills have a useful cycle of life, after that the landfill is closed and another geographical location ischosen to deposit the waste and begin another cycle; so be expected that the production of biogas also hascycles. Generally is consider only one cycle of gas production, but there is some investigations that shows theexistence of another cycle, whit the same characteristics of flow, that is produced when the landfill cover breaksdown and water penetrates the site, a second wave of gas will be produced and the landfill operator certainly

walked away untapped all the potential generated gas.

Figure 2. Landfill gas production waves

EPA assumes that gas collection systems collect 75% of the gas, yet this is a best-case scenario. EPAassumes this is always the case, but on average, only about 50% of the gas is collected – and this is during only



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about 32% of the landfill's lifetime gas generation. Another 12% of the time, the collection rate is far lower,averaging around 25%. The rest of the time, no gas gets collected.

So as we mention in the first part, around the landfill we have a screening pipes grid, in order to pick upthe landfill gas generated by the anaerobic decomposition of waste.Fig. 3 shows a simplified cross section of a representative landfill used for LFG extraction and utilization. In the

drawing the following notation is used: (1) extracting pipe network; (2) control valves; (3) LFG collection wells;(4) liner of the landfill; and (5) low permeability capping layer, made from one or several different layers. Thepumping system, the LFG treatment system and the LFG utilization system are all represented as a box (6).This system is used by all landfill operators and presents some remarkable problems during collection due tovarious limitations inherent in gas collection systems. Gas collection wells cannot be placed too deeply in thelandfill, since they’d risk puncturing the bottom liner as the landfill settles over time.

Gas cannot be collected too close to the surface without the risk of drawing outside air into the system.Shallow landfills the decrease in methane production is mainly due to air ingress, since oxygen concentrationsequal or higher than 5% prevent the anaerobic digestion, and therefore the extraction of the LFG for energyutilization in such landfills may not to be economically viable also some gas gets caught in pockets that won’treach the collection wells and also gas collection systems can clog.

Usually an ‘Upper Oxygen Limit’ (UOL) is chosen in the pipe lines in the LFG extraction controlsystems [1]. This is often achieved through manually or automatically controlled regulation methods that aim to

keep the methane concentration constant in the LFG flow and equal to the value chosen as the ‘MethaneObjective Value’ (MOV) and the oxygen concentration below the UOL. The energy use intended for the LFGwill mark the lower limit for the MOV. The manually controlled LFG extraction normally requires weeklychecks for every extracting well. Nevertheless, the composition of the LFG should be monitored on a daily basisat the control station without the need for corrective action, unless strictly necessary.

It is recommended that the concentration of oxygen is monitored daily. Figures over 10% wouldnormally indicate a failure in the extracting network because of the penetration of air, and in such case theregulation station should be disconnected from the general system, for safety reasons.

Figure 3. Simplified cross-section of a simplified landfill design for LFG extraction and utilization

(Pat, atmospheric pressure).

Create an airtight capping for a landfill would be too expensive. There is a way to prevent air influx intolandfills even under high negative extracting pressures and still to keep the costs within acceptable level.

The design of the new landfill is shown in Fig. 4. The following notation is used: (1) extracting pipe network;(2) control valves; (3) LFG collection wells; (4) carbon dioxide injection pipe network; (5 and 6) low



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permeability capping layers, made from one or several different layers; (7) highly permeable layer; (8) thepumping system, the LFG treatment system and the LFG utilisation system; (9) control pipes; and (10) liner of the repository, made from one or several different layers.

Figure 4. Simplified sketch of the new repository design for LFG extraction and utilization (Pat,

atmospheric pressure).

A system for preventing a flow of gas from a gas-containing region to an adjacent region, comprising acomposite barrier and means to create a pressure differential across the permeable layer is not a new idea.However, in the past this idea has been mainly used in order to prevent the LFG from escaping outside thelandfill or to protect a building from volatile gases in the soil. In this case a similar idea is used in order toprevent the LFG from leaving the landfill, and air from entering the landfill.

The system relies on availability of gas, which would be more suitable for pumping in the permeablelayer than air. The most suitable gas would be CO2, as it does not affect the anaerobic digestion, and it is alreadypresent in the LFG, therefore injecting CO2 would not increase the costs of LFG treatment. Also, when LFG istreated for pipeline quality gas, CO2 is separated and the quality of this CO2 is normally such that it can only beused for industrial purposes (e.g. oil recovery). The new system would provide good use of the separated CO2.In the present system, in the layer 7 a sufficient supply of carbon dioxide is pumped in through the injectionsystem 4 to keep the pressure of the gas in the permeable layer above atmospheric. In this way flow of carbondioxide is provided from the permeable layer through the two barrier layers 5 and 6 into the atmosphere and therepository, respectively.

As a result of this flow a decrease of influx of air into the repository as well as decrease of escape of LFG from the site is expected. This can be understood if one takes into account that the carbon dioxide willescape from the layer 7 mainly through the routes that air would use to flow into the repository, as these routes(mainly faults in the capping system) represent the lowest resistance for the flow of gases. Therefore, the airwould flow in the opposite direction to the flow of carbon dioxide when entering layer 7 and the flow of airwould be only due to diffusion, as the pressure driven flow is in the direction layer 7/air.

The flow of air from layer 7 into the repository would be in the same direction as the flow of carbondioxide, and would be due to both, the concentration and pressure gradients.

However, the presence of air in layer 7 would be largely reduced for three reasons: there would be freshsupplies of carbon dioxide in the permeable layer that would dilute the air; part of the air, which entered layer 7will flow back in the atmosphere due to the bulk flow since the pressure in the layer 7 is higher thanatmospheric; and finally, the mechanism by which air enters the permeable layer 7 is only due to diffusion.

Therefore, from the fluid mechanics point of view, it can be concluded that the new type of repositorywould reduce the ingress of air into the repository, and also would reduce the escape of LFG from the landfill.



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The reduction of LFG escape is not explained explicitly, but the argument follows the same logic as for thereduction of air ingress

Note.- It is important to add that the right way to treat the components trapped by the filters, is to disposal inspecial containers, and isolate from the natural ambient. There are some researches that are looking for achemical process that can neutralize the toxics by converting the halogens to relatively harmless chemicals like

salts. We mention this because generally the landfill operators burn this contaminants and this don’t solve theproblem.

V. Landfill usage

There are different options to landfill gas applications, usually there is a torch and the gas is conducted to itand burned, generally the landfill operators collect the gas but forget to filter and treat them.

This is the worst way to do whit gas because when halogenated chemicals (chlorine, fluorine, or bromine)are combusted in the presence of hydrocarbons, they can recombine into highly toxic compounds such asdioxins and furans, the most toxic chemicals ever studied. Burning at high temperatures doesn't solve theproblem as dioxins are formed at low temperatures and can be formed as the gases are cooling down after thecombustion process.

Throughout EPA's reports on landfill gas utilization, they refer to the destruction efficiency of various

landfill gas combustion technologies. They usually assume it's about 98% or more. In other words, they pretendthat these halogenated non-methane organic compounds simply go away. There is almost no talk about whathappens to the chlorine, fluorine and bromine atoms that go into the burner.Mercury and tritium cannot be destroyed through combustion and no efforts have been made to prevent theirrelease into the environment when landfill gas is collected and burned.

Nowadays are discussed another uses because the landfill gas has an inherent heating value that couldbe used in order to produce energy or vapor and if it is properly treated and filtered we could avoid someenvironmental issues.

These applications make necessary the addition of other devices at the end of the chain previouslyexposed, like engines, gas turbines, boilers, etc. There are some issues reported whit the use of these devices andwe will discuss it.

Flares

As we mention generally the landfill gas is conduced to a candle flare or a shrouded flare. A candleflare is an open air flame. With such, there is no reliable means to monitor for dioxins or other toxic emissions.

A few tests shows that, for the most part, flares produce more dioxin than internal combustion enginesor boiler mufflers

If we just flare the gas we are wasting all the heating value that is content in the gas, so it is not thebetter way to destroy and eliminate the contamination.

Note.- we have to take in count most of the times the gas production exceeds the amount of gas that theburn device could use, in this case we can’t liberate the gas to the ambient, so a candle flare in order to burn anygas excess is always needed.

Boilers

Boilers are among the cheapest options. They produce heat, not electricity. Boilers are generally lesssensitive to landfill gas contaminants and therefore require less cleanup than other alternatives. Boilers have thelowest NOx and carbon monoxide emissions of the combustion technologies.

Landfill gas used in boilers brings in the issue of piping the gas to local industries. While boilersthemselves may not require much cleanup of the gas, the pipelines do require some cleanup, since corrosivecompounds in the gas (particularly the acids and hydrogen sulfide - H2S) can damage the pipelines. There havebeen many concerns associated with landfill gas pipelines brought out by environmentalists living near landfillsconsidering this use. Among the concerns are the integrity of the pipeline (at least one proposal involves lateralseams), liability issues, and the economic support of neighboring polluting industries which might use the gas.



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Internal Combustion Engines

Internal combustion engines (ICE) are the dirtiest technology for burning landfill gas (regardlessflares). They emit most carbon monoxide CO and NOx and they may be the largest dioxin source of theavailable technologies.

In addition the engine need a dry landfill gas, it seems that no vapor or water steam is desired, because

this hinders the operation of the engine and corrodes the internal components, like valves, valve seats, pistonrings, etc. Is usually reported problems whit the gasket of the cylinder cover caused by corrosion.

There is an advantage that generally the generator set is cheap, and its maintenance does not requirevery specialized knowledge.

Gas Turbines

Theoretically gas turbines are somewhere in the middle in terms of carbon monoxide and NOx emissions. There isn't enough data about feed landfill gas to burn in a turbine to provide any sort of comparison.

Conversion to Methanol and/or Dry Ice

There is an option, converting methane from landfills into methyl alcohol or methanol. However, the

halogenated organics theoretically have to be filter out and isolated from environment, we mention this becausethe usual practice is sent it to a flare and this has a negative impact on the atmosphere like is mentioned before.

Other companies have expressed interest in converting the carbon dioxide in landfill gas to dry ice forsale to industry. They have claimed that the carbon dioxide in landfill gas is actually more profitable to recoverthan the methane, but nowadays there isn’t a representative market to consume this produced dry ice.

Cleaning up the Gas to Pipeline Quality

Since natural gas prices are so low, this is not expected to be economical anytime soon. It also requiresa high degree of cleaning and filtering the gas, table 2 shows the typical required composition for a pipeline gas.To the extent that the gas is not adequately filtered, then the landfill gas will be degrading the quality of thenatural gas by adding more contaminants to the system.

These contaminants could seriously damage the pipelines; the sulfur content is potentially dangerous

because in combination with water vapor will produce sulfuric acids that will corrode the pipelines causingdangerous gas leakages that could damage the people by eventually explosions and also causes a seriouslyenvironment damage if the pipelines are underground.

Table 2. Typical natural gas pipeline specifications

Cleaning LFG to use as a transportation fuel

The collected LFG can be treated and the obtained gas used as fuel. When purifying LFG for fuel, theLFG must be of higher CH4 content in order to have feasible fuel production. The presence of air in the LFGincreases the costs of LFG treatment due to N2 injection is needed.

Fuel cells

Some scientist have shown their interest in recuperate only the hydrogen for the landfill gas, to use in fuel cellapplications to produce energy, but this is actually in study and there is not enough information about theprocesses involved yet.



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VI. Important Issues

Burning landfill gas is dirtier than burning natural gas. Whether using an internal combustion engine or agas turbine, burning landfill gas to produce energy emits more pollution per kilowatt hour than natural gas, so inthis way the affirmation of that energy produce based in landfill gas is green or renewable is questionable.

Generally attempts to justify the burn of landfill gas saying that is more contaminant than CO2, and that the

CO2 causes global warming but we see that if the landfill operator don’t have an adequate filtrate process inorder to get out the contaminants present in the landfill gas in the form of NMOC’s and inorganics, and burn it,the problem is worse than liberate the landfill gas to the ambient. So is also important to say the burn landfill gasto produce energy is less contaminant than burn coal.

Furthermore, sell of energy produced by landfill gas burn don’t solve the problem that the industry is usinga lot of contaminants in the production process of food for example, and more away there are another bigproblem that is not looking, the consumerism, that is generating thousands of tons of garbage that we are unableto recycle, somehow we are blocking the development of an recycle culture& industry and we are hiding theconsumerism problem that are ending the natural resources of the planet.

Also we have to take in count that the use of this type of energy is blocking the development of anothertypes of true green and renewable energy, like wind or solar for example.

Based in these things we could say that energy produced by landfill gas burn is not green, and is notrenewable but nowadays is the best use that we could make of it.

VII. Landfill gas flow estimation

When we are trying to develop a landfill gas recuperation project, having in count the exposed issuesand recommendations the next step to take is to calculate the estimate the amount of gas production in orderto know the capacity of electricity production (it this is the chosen alternative).

So there are some practical structures designed to estimate the flow rate in a landfill facility, likeshowed in figure 5.

Figure 5. Landfill flow rate estimation structure

These kind of systems, imply the need of a drill machine to place the wells, valves to control de flow, a blowerto create a vacuum and extract the gas, and necessarily a flare for security reasons. Also is needed some measuredevices (manometers and flow meters).According to this structure we can make an in situ measure, and whit an equation model has a real estimate of gas production.Also we can use some software that help us to estimate the gas production, next we will analyze a supposed caseto have a better idea of the economic performance of a landfill gas recuperation and utilization process.



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VIII. Technical - Economical Analysis

However, landfill gas is typically comprised of methane and carbon dioxide, approximately 50 percent eachby volume, with trace quantities of other compounds. Methane is the primary component of landfill gas thatcontributes to the gas's heating value. The heating value of methane is typically defined on a volume basis.

The methane generation potential per ton of waste, Lo, depends on the fraction of organic matter present in

the refuse. It could be estimated using the stoichiometric and the biodegradability methods or the IPCC(Intergovernmental Panel on Climate Change) 2006 guidelines. The stoichiometric and the biodegradabilitymethods are perfect biological systems whereby all the degradable organic materials are assumed to beconverted to carbon dioxide and methane.

However, in practice not all the organic carbon present in the waste biodegrade to produce landfill gas. Theresistant materials (such as lignin) present in the waste and plastics materials retained in plastic bags, forinstance, are less prone to biodegradation. Therefore the IPCC method, which gives a much realistic estimate,was used to estimate the methane generation potential. According to the IPCC guidelines (2006), the valueof Lo ranges from 100 to over 200 m3 methane/ton waste. This shows that the estimated value of Lo is

within acceptable range.It is very important to have a good estimation of rate constant, k value, as the estimation of methane

production from the landfill is extremely sensitive to it. The k value can either be taken from IPCC 2006Guidelines as default value or estimated by calculation. The k value in this study was determined usingRETSCREEN program. The rate constant was found to be 0.05.There are numerous models available for estimating rates of landfill gas generation, however accepted industrystandard models are generally first order kinetic models that rely on a number of basic assumptions. Thesemodels are used to predict the variation of landfill gas generation rates with time for a typical unit mass of solidwaste. This generation rate curve is then applied to records, or projections, of solid waste filling at a site toproduce an estimate of the site's landfill gas generation over time.In the following pages we try to analyze the economic and environmental features of a sample landfill, using theRETSCREEN software. The landfill was opened in 1970 and is expected to be used for 60 years. Wastes aremoderately decomposable; site precipitation is about 750 mm/yr. The moisture content of the waste within alandfill is one of the most important parameters affecting the landfill gas generation rate. Primarily theinfiltration of precipitation through the landfill cover, the initial moisture content of the waste, the design of theleachate` collection system, and the depth of waste in the site influence the moisture content of waste within alandfill waste disposal at the landfill was initially 100.000 t/yr and is expected to reach 300.000 t/yr during thefinal year of use.

As an example, we assume there is a 6 MW Reciprocating engine power plant which has to be fuelledby the gas from a nearby landfill.

We have the following assumptions & parameters:[6]

The cost of installation : $3,000/kWThe rate of electricity which can be sold to the grid : $0.1/kWhEstimated amount of inert materials in waste: %10The project life: 25 yrsOperating costs: $ 750,000 /yrInflation rate: % 2

Debt ratio: % 70Debt interest rate: %7Debt term: 10 yr

Applying the RETSCREEN software we have the following results:

Electricity exported to grid:49.932 MWhHeat rate:12.000 kJ/kWhElectricity export rate:100,00 $/MWhInitial costs: 18.000.000 $Debt payment in 10 yrs: 1.793.957Electricity export income: 4.993.200

Figure 6, shows the cumulative cash flow graph, the negative part is the amount of money that we haveto spend as initial and annual costs and the positive side is the amount of money that we earn and save by sellingthe electricity to grid. As we can see in the graph, the payback time will be around 2 years and after that we start



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saving money. After 10 years, by paying back the entire loan the slope increase and we have a rapid growth inthe graph.

Figure 6. Cumulative cash flows graph

A projection of the LFG generation up to 2050 was done for the above mentioned landfill as well.Figure 7 shows the landfill gas production profile up to the year 2050.The graph showed that the amount of landfill gas would keep on increasing until it reached a maximum in 2035 where 4.500 m 3 /h

methane would

be produced and 9.000 m 3 /h LFG gas would be generated. After 2035, no more waste would be placed in the

present available space, however, the landfill gas would continue to produce but at a lower rate. We can see thatthe annual average required fuel 68.4 GJ/h, and the LFG fuel potential meet that demand. It should be noted thatusually about 50% of the LFG is methane and recovery rate is about 75% we took around 10% of the solidwaste as inert materials. An inert waste is one that does not contain an appreciable quantity of organic orbiodegradable material, e.g., construction and demolition wastes.

Figure 7. Landfill gas generation graph



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IX. Power Generation

The use of LFG for generating electricity is a promising approach both in terms of conserving energy andalso for reducing air pollution if the landfill gas is correctly filtered and the dangerous components are correctlydisposed and isolated. Energy recovery from waste represents an important way to reduce the amount of electricenergy to be produced using fossil fuels, that is, non-renewable sources of energy but also we have to take in

count that landfill gas also is not really a renewable energy.There are many incentives in using LFG in waste to energy conversion systems [5]. In addition to conserve

valuable alternative energy resources, direct LFG utilization results in reduced greenhouse gas emissions.The amount of thermal energy generated from the landfill gas could be found using equation below.

Thermal energy: E th (MW)= ṁ CH4 × LHV

CH4 × ℜ

WhereṁCH4 - flow rate of CH4 (m3 /h)

LHV CH4 - lower heating value of CH4 (MJ/m3)ℜ

- recovery rate

The amount of power could be computed using the electrical conversion efficiency using theequation below.

Electrical energy, E el (kWh) =ṁ CH 4 × LHV CH 4 × ℜ ×ηel

Where ηel : electrical efficiency

In time and beyond the closure of the landfill, the amount of gas generated will be insufficient forviable electricity operations. At this time, the power station would be removed and any remaining gas generatedwould be flared using the existing facility, or in some cases, where gas has declined considerably, with a newsmaller flare. The cycle of gas production varies during the life of the landfill with it increasing whilst landfilling continues. Should the life of the site be less than ten years, it will peak at closure and then decline steadily

thereafter (Fig8). If the landfill operates for more than ten years the gas production will reach its maximumabout ten years after opening and will remain at the same level until the closure of the landfill.

Figure 8. Electricity generation vs time



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Based on the gas flow from the landfill, it is possible to superimpose the generation potential of the siteover its life. Engine/gensets are added and later removed as the gas flow increases during active landfillingoperations and then as gas flows decline post closure respectively.

There are several facilities using landfill gas for the production of power that are in operationworldwide utilizing gas engines. The gas engine had an advantage over the other facilities in the sense that itproduced less waste heat if we collect the remain thermal potential of the exhaust gases, therefore, increasing its

efficiency. The amount of landfill gas forecasted was used to estimate the amount of power that could begenerated from the landfill gas. A 6MW gas engine is used to burn the landfill gas and estimate the powerproduced on site. The different parameters used to input in the models are shown in Table 1.

Parameters Unit

Input

Mass flow rate of methane 19.7 Mm

3 / r

LHV of methane 37.5 MJ/kg

Methane generation from waste (L0) 170tons/m

3

Methane generation constant (k) 0,05

Efficiency of LFG collection 75 %

Output

LFG fuel potential 68,4 GJ/h

Table 3. Parameters used as input in the model

X. Conclusion

The actual lifestyle of our society implies two principal things, energy consumption and waste generation.Particularly these two things have a point in common, greenhouse gases emission. The concentration of thesegases in our atmosphere has an impact in all human activities and become a threat for the environment.

Today much of the scientific community has turned their efforts in order to find more efficient processes that let

us manage and mitigate this danger, and a lot of professionals are looking for sustainable ways to develop ouractivities.

Is not a discovery that anaerobically decomposition of organic matter generates methane and carbon dioxide, theway to manage this natural process actually find a new options to develop, because whit limited energyresources and increased prices of it, all that has an inherent heating value take relevance in order to produceenergy. In this way around the world some countries are implementing systems that use the methane content inthe landfill gas to produce value-added.

The major technical drawback related to the landfill gases collect and storage system is the entry of air in thelandfill, this prevents the anaerobic decomposition and therefore methane formation, so the total yield of theproject decrease caused the energy decreased production, there are some initiatives to solve this problem buttheir effect are discussable by their complexity and intensive energy use.

Another problem is the combustion device to use in order to recuperate the heat value in the landfill gas and thepost combustion gases generated, this is caused by the extremely variable landfill gas composition that causesissues in the internal components and when combusted tend to form dioxins and furans.

Energy production via landfill gas recuperation is generally called green or renewable energy, but if we make adetailed analysis we could find that these definitions are not appropriate. A green or renewable energy does notproduce CO2 emission during operation, and energy production by landfill gas recuperation necessarily impliescombustion gas and atmosphere emissions of combustion products throughout combustion device used to heator power production. Some estimation shows that the inorganic content in the landfill gas liberated to theatmosphere after combustion process could be more dangerous for the environment than other produced gasesby another energy production sources.Attending to that some filtration processes are developed in order to separate these dangerous components andsome scientific investigations are focused to find effective filtering procedures and disposition of these

pollutants.



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Having in count these technical recommendations the energy production by landfill gas combustion areeconomically attractive, and can be a promising approach both in terms of conserving energy and also forreducing air pollution.In the analyzed case at the end of this document was found that, the amount of energy produced in 2010 was68.4 GJ/h and it could be seen from the graph that it would reach a peak power in 2035with more than 120GJ/h. It would be worth pointing out that both the landfill gas production and power produced reached a peak

value in 2035. At commercial electricity rates the amount of energy produced can offer an interesting payback period, so the investment in this kind of projects can be remarkable for local governments.

References

1 Vicktor Popov., “A new landfill system for cheaper landfill gas purification,” Renewable Energy, Elsevier

Ltd., Volume 1021-1029, Number 30. 2005.

2 VS.O. Bade Shresta, G. Narayanan ., “Landfill gas whit Hydrogen addition – a fuel for SI engines,” RenewableEnergy, Elsevier Ltd., Volume 3616-3626, Number 87. 2008.

3 Mike Ewall., “Landfill Gas,” Journal Energy Justice, Volume 215-743. 2008.

4 Virginia A. Malik, Steven L. Lerner and Donald L. MacLean, “Electricity, methane and liquid carbondioxide production from landfill gas,” BOC Group, Inc., Butterworth Et Co, Volume 0950-4214, Number 87.

1987.

5 “2nd International Conference on Environmental Engineering and Applications,” IPCBEE., IACSIT Press,

Singapore, Volume 17. 2011

6 URL: http:// www.retscreen.com

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URL: http:// http://www.epa.gov/

Documents

Production and Use of Biogas in Landfills to Produce Energy