Extraction and Utilization of Landfill Gas – Independent Sector of World Industry

Gurvitch V.I, Lifshitz A.B

1. Introduction

The volume of world consumption that has been increasing last decades resulted in substantial growth of solid domestic waste collected over the world. Today, the mass of solid waste flow emitting to biosphere achieved almost geological-rated level and amounted to approximately 400 million tons per year. Solid domestic wastes tend to considerably affect the behavior of the global geochemical cycles of certain biophilic elements, particularly, organic carbon. The mass of this element to be naturally emitted in the environment makes up approximately 85 million tons per year, while the total volume of carbon to be collected in the planet soil cover is only 41.4 million tons per year.

One of the fundamental methods to be used for disposal of solid domestic wastes is the near-surface geological environment landfilling. In the conditions of these, the above wastes are exposed to intensive biochemical decomposition resulted in generation of landfill gas.

Landfill gas emitted in the environment induces the negative effects of both local and global nature. For this reason, a number of countries do their best to minimize landfill gas emissions. For the purpose of this, an independent sector of world industry including the branch of landfill gas extraction and utilization was established. This document covers the subject of the waste disposal sector activity, Russian industry development prospects, most promising technologies and a number of matters of ecological and techno-economic nature.

2. Gas generation processes

Different organic materials represent quite a considerable portion of solid domestic waste particles. Among the ones, food remains and paper may be specified as the main groups. Depending on the level of any country development, as well as on its geographic position and characteristics the ratio of the above materials may vary. But generally, the worldwide share of solid domestic waste organic fractions is subject to insignificant variations: from 56% in developed countries and to 62% in just developing countries. If to take the waste wood fractions into account, the very parameters shall be increased up to 61% and 69%.

In landfill conditions, with actually 80% of all waste products buried, some kind of anaerobic environment is generated, where organic substances are exposed to biological conversion under the influence of methane-genic community of microorganisms. As a result, biogas or so-called landfill gas consisting of macrocomponents methane (CH4) and carbon dioxide (CO2) is generated.

It may be proved that on average the process of gas generation terminates in 10-50 years and, in this case, the rate of gas specific output is valued as 120-200 m³ per each SDW ton. The rate of gas generation stoichiometry may be expressed by the following simplified reaction equation:

n C6H10O5 + n H2O -------> 3n CH4 + 3n CO2 (1)

Considerable variation of gas production and process rate is determined by the environmental conditions to be formed in a certain landfill mass. Such parameters as humidity, temperature, pH and organic fracrion composition may be considered as the ones controlling the process of bioconversion. Their combined influence is specified by the following first-order gas generation reaction kinetics equation (6):

Q=M*q*e^-kt (2), where:

Q – quantity of biogas (m³) generated within period t (years);

M – waste mass (t);

q – specific gas potential (m³/t);

k – gas generation reaction rate constant (1/year).

In practice, the rate of gas generation is specified by different formula modifications (2). Generally, they differ by quantity of solid domestic waste organic substance fractions being considered. As a rule, any organic substance consists of quick-, medium- and slow-decomposing materials to be distinguished by their physical-chemical properties and terms of biological decomposition. For example, any process of decomposition of “quick” fractions is terminated in 2-4 years, while the process of bioconversion of “slow” ones may run for decades. Depending on quantity of fractions specified in formula (2) the models forecasted might take the shape of single-, two- and three-phased ones.

Upon the long-term research held by company “Geopolis”, it was determined that the generalized two-phase model, where the reaction rate constants to be estimated on the basis of field observations are used, may be applied as the adequate landfill gas formation forecast method implemented in the conditions of Russia and Italy. The SDW specific gassing potential curve to be used for reproduction of the above model proves that the most intensive process occurs within the period of first 5 years with about 50% of total landfill gas reserve emitted.

 

3. Landfill gas composition and properties 

Landfill gas macrocomponents consist of methane (CH4) and carbon dioxide (CO2). The macrocomponent ratio may vary within the range of 40-60% to 30-60% respectively. Nitrogen (N2), oxygen (O2) and hydrogen (H2) are, as a rule, available in small concentrations (at minimum percentage level). As for its traces, landfill gas may contain a number of different organic compounds.

As per biogas composition, it is featured with some specific properties. First of all, landfill gas is of combustible nature and by its caloric factor it contents approximately 5500 kcal per m³. At certain level of concentration it gains toxic qualities. Certain toxic factors are determined by means of a number of such traces as hydrogen sulfide (Í2S). Ordinary, landfill gas is characterized with its specific pungent odor. Also, landfill gas pertains to so-called “greenhouse gas” and, therefore, it is subject to fixed world community attention.

4. Scales of emission

Landfill gas global emission is the significant factor to be used for total estimation of the Earth climate forecasting models. Also, some developed countries make their national environmental strategy on account of estimation of dump methane flows. For example, after American analysts proved that any landfill may be considered as the main man-made source of methane, the law about all the USA polygons to be fit out with biogas extraction and utilization facilities came into force.

Initially, the global rate of landfill methane flow was studied last decade. In accordance with a certain reputed document analysis made in 1987 it was proved that the volume of CH4 global emission was achieved to 30-70 million tons per year or it was rated by 6-18% of its global flow. It was specified that the very value exceeded the mass of methane emitted by coalmines. On the basis of the preliminary research, it was proved that the volumes of SDW will grow and the next century all the dumps will become the major sources of methane global emissions.

In the mid of nineties, the committee experts of Intergovernmental Panel on Climate Change (IPCC) made assessment and came to conclusion that the level of landfill methane global emissions made up the rate of 40 million tons/year. Actually, the above committee confirmed the above assessment and entered methane in the global greenhouse gas register once and for all.

It should be noted that Russia makes its own contribution in the matter of global emission. As per the same IPCC’s assessments, the Russian dumps annually emit 1.1 million tons in atmosphere that may be specified in the ratio of 2.5% of all the planetary flow.

5. Description of landfill gas negative effect

With the landfill gas emitted, a number of its specific property negative effects, both of local and global nature, tend to be developed in the environment.

With the landfill gas collected, some explosive and fire conditions may be formed at the buildings positioned close to solid domestic waste landfill grounds. In case of illegal SDW disposal, the above events regularly occur in the dwelling sector. For example, a great number of objects, to have been built in Moscow last decade, are located at the areas of so-called “filled-up grounds” that really are nothing else than the gas-generating solid domestic wastes. Only some special-purpose safety projects made it possible to undertake respective activities for reconstruction of the above objects. Besides, sometimes the landfill gas collected within a building cellar resulted in its explosion. Some casualties had followed those kinds of incidents, particularly, in USA and England. Often due to spontaneous and uncontrolled spread of landfill gas, the polygons are fired.

Any amount of landfill gas collected in closed spaces is also toxically hazardous. There are a great number of fatal accidents related to intoxication that took place in the course of maintenance of any subsurface engineering facilities. Unfortunately, no open statistics of the fatal accident exist. Probably, old filled-up grounds generate the hazardous amount of such landfill gas.

The landfill gas is also hazardous for vegetation. The matter is that any vegetation being spread out around dumps is killed as a result of rootage asphyxia caused by the gas collected within the soil cover pore space.

Owing to free spread of landfill gas, any adjoining area atmosphere is also subject to contamination by toxic and stinking compounds. And finally, any amount of landfill gas is considered as greenhouse gas affecting the Earth environment as a whole.

The above list of the landfill gas negative factors proves that any level of gas emission should be prevented. In most of the developed countries some special laws, to have been adopted for the purpose of the polygon operators, regulate business activity for the purpose of preventing spontaneous spread of landfill gas. In terms of this matter, the main method is the one of landfill gas technological extraction and utilization.

6. Landfill gas extraction and utilization process

For the purpose of landfill gas extraction, the following technological process is principally used: the network of vertical gas drainage holes is connected to the gas pipelines that are joined to the compressor plant to be used for exhaustion of landfill gas and its conveying to the place of utilization. Utilization facilities are mounted at a special prepared place beyond the dump mass stock. The landfill gas collection system schematic flow diagram is specified in the following figure.

Each hole controls drainage functions of a certain solid domestic waste cylindrical block. Each drainage hole capacity depends on the flow rate that should not exceed the volume of newly generated landfill gas. The rate of current SDW mass efficiency subject to its assessment should be specified in the coarse of preliminary field gas-geochemical research.

Any gas drainage system may be constructed either over all the solid domestic waste polygon area (if the polygon is out of operation) or at certain sites of the polygon (depending on priority of their utilization). Also, it should be noted that at least 10 m of dump thickness might be considered as enough mass to be used for extraction of landfill gas. It is desirable, that the solid domestic waste polygon area to be scheduled for construction of landfill gas extraction system was put under revegetation (i.e. covered with soil of minimum 30-40 cm).

Extraction holes

The amount of SDW polygon landfill gas can be extracted by means of vertical drainage holes. Ordinary, the ones are arranged uniformly over the area of the dump mass stock at 50 – 100 m pitch. The above holes diameter is rated within the range of 200 – 600 mm and their depth is determined by the dump mass thickness that may vary up to dozens of meters. The holes may be bored both, by standard boring equipment and by special-purpose machines to be applied for digging of large diameter holes. Any type of the above equipment shall be stipulated by its economic reasonability.

In Russian environmental conditions the holes are preferable to be bored by the method of auger drilling. This method of boring is comparatively cost effective and easily accessible, for it is widely applied in such activities as geological engineering survey. With the very method used, the maximum diameter of holes may achieve to 0.5 m. But in Russian environmental conditions, the landfill mass used to be filled with quite an amount of foreign inclusions (metal and concrete structures, equipment and mechanism remains etc.) resulted in hard boring and frequent failures of tools. As per our experience, the holes that have the diameter of 250 - 300 m are quite enough to be used for landfill gas extraction.

Each hole is arranged in several phases. At the first stage, any perforated steel or plastic pipe plugged at its bottom and flanged at its mouth is dipped in the hole. Then, some amount of porous material (e.g. gravel) is filled in the tube space and compacted in layers up to the level rated of 3-4 m from the hole-mouth. At the last stage, the clay-made locking device with its thickness of 3-4 m to be used for protection against aeration is constructed.

Upon constructing the hole-head is installed. The hole-head is a metal cylinder fit out with gas shut-off valves to be used for adjustment of hole flow rate and for control of landfill gas compound level, as well as with a pipe branch to be used for connection with any gas pipeline.

At last, the hole-head is fit with metal or plastic box to be used for preventing of unauthorized access to the hole.

Landfill gas conveying pipelines

Within the waste mass the rate of landfill gas temperature may be increased up to 40-50 °Ñ and the rate of moisture content may amount to 5-7%. Upon extraction of landfill gas out of the dump mass stock and its conveying into gas pipeline, the rate of temperature abruptly drops resulting in generation of quite an amount of condensate. With landfill gas extracted in amount of approximately 100 m³/hour, the daily volume of generated condensate makes up about 1 m³. Therefore, the matter of condensate evacuation by means of special-purpose devices is the one of primary importance, as the amount of condensate being collected in the pipeline may affect the rate of landfill gas extraction.

For the purpose of specifying of pipe diameter per each dumping site, some specific hydraulic characteristics shall be analyzed.

For gas conveying, as a rule, two types of pipes are applied: plastic and steel pipes. The above pipes shall be compared in accordance with the following criteria:

·  Mechanical strength;

·  Corrosion resistance;

·  Usability in filler soils.

Steel pipes can be differed by their mechanical strength and are quite popular at the Russian gas pipeline sector. As for the plastic pipes, their high corrosion resistance and plasticity may be taken as the preferable factors. In view of high solid domestic waste subsidence capacity and landfill gas corrosion activity, it is recommended to use the gas pipeline made of low-pressure plastic (polyethylene) pipes. As compared to metal pipes, the polyethylene pipes are light by weight, durable, flexible and corrosion-resistant. Besides, the plastic pipes are perfectly welded. Such gas pipelines do not need electrochemical protection. With any gas pipeline being constructed the rate of labor productivity is increased by 2.5 times. With the polyethylene gas pipeline commissioned the maintenance documents as per SNiP 2.04.08-87 and SNiP 3.05.02-88 should be available.

If required, you may apply steel pipes. Due to high rate of any landfill stock corrosive medium all the steel pipes must be insulated with protective reinforced coating to be specified in accordance with technical regulations: bituminous-polymeric, bituminous-mineral and polymeric materials (as per GOST 15836-79).

Gas pipeline should be laid in trenches at the depth that is required for preventing freezing of pipes in winter seasons. If any gas pipeline is constructed for the purpose of condensate, the requirements for gradients and moisture evacuation extractors should be followed.

Condensate extractor comprises steel welded container to be used for drainage of condensate and hydraulic lock assembly.

The gas pipeline operation is adjusted by means of biogas corrosion resistant shutoff valves (stopcock, slide valves and gates). The above shutoff valves should ensure reliable and safe operation of gas piping line with minimum hydraulic losses.

Landfill gas is delivered to the collecting station via the pipeline system.

Landfill gas collecting station

The gas collecting station is intended for forced extraction of landfill gas out of the dump mass. For the purpose of collection, just a low rate of discharge (about 100 mbar) is generated in the gas pipeline system by means of special electric fan.

Landfill gas utilization

The methods of landfill gas utilization used to be applied in the world are as follows:

·  Flame burning: suppression of odor nuisance and decrease of fire hazards within the area of SDW polygon. In this case, the landfill gas power potential is not subject to utilization;

·  Landfill gas direct burning: production of heat energy;

·  Utilization of landfill gas, as gas engine fuel for the purpose of electric and heat energy;

·  Utilization of landfill gas, as gas turbine fuel for the purpose of electric and heat energy;

·  Gaining the content of landfill methane (enrichment) up to 94-95% with its following utilization in communal gas networks.

Expediency of a certain landfill gas utilization method depends on economical activity conditions occurred at the SDW polygon and is determined by availability of any solvent power resource consumer. In a dozen of developed countries special laws regulate this kind of activity. For example, in a number of EEC countries and in the USA there the laws binding the consumers to purchase alternative energy are adopted. Besides, this type of energy has a prize that is ordinary 2 – 2.5 times higher than the one of the energy provided by traditional power sources (natural gas, oil products etc.).

In Russia no similar legal base is available. Owing to the low rate of landfill gas energy sales the national economy gets in disadvantage. The very situation obstructs any activity directed to technology development. At the best, landfill gas may be efficiently utilized for needs of solid domestic waste polygon or local consumer.

7. Scope of world landfill gas extraction

In a number of different countries, including USA, Germany, Great Britain, Netherlands, France, Italy and Denmark, biogas is extracted and utilized in great volumes. The rates of annual gas-extraction output volumes are specified in Table 1. As follows from the table, the volumes of utilized landfill gas makes up approximately 1.2 billion m³ per year to be equivalent to 429 thousand tons of methane or to 1% of the gas global emission. As well as you can see, the volumes of the gas extracted are minimum to the one being generated. Thus, the biogas extraction sector has quite a large potential for its development.

 

 

 

 

 

Table 1. – Annual gas extraction output volumes

Country	Landfill gas output, million m3/ year
USA	500
Germany	400
Great Britain	200
Netherlands	50
France	40
Italy	35
Denmark	5
Total:	1230

 

8. Landfill gas extraction and utilization projects to be developed in Russia

For the purpose of estimation of promising technological projects to be implemented in Russia, some special engineering and economic factors of potential typical landfill gas extraction and utilization facilities were estimated. Some results of the pilot projects implemented by company “Geopolis” in Moscow region were used as the source information. One of the above projects realized in Serpukhov is described in this document in details. The standard object typical life was projected for 10 years.

It must be pointed out that with gas extraction profits calculated the prices were specified as per the ones available in the energy source market (i.e. 180 rubles for 1 m³ of landfill gas and 250 rubles for 1 kW/h).

Two variants of gas utilization schemes were considered. The first one was related to power generation and the second one – to supply of crude landfill gas to a consumer. As per the evaluated results (Tables 2 and 3), the following conditions may be stated:

·  Electric power generating facilities need an amount of investments and may be considered as quite profitable by their total gains;

·  With the landfill mass increased, the facility technical and economical output rates are advanced proportionally;

·  All the variants considered are economically efficient

But it should be noted that any estimation results are of limited nature. The matters of taxation and inflation effect are not taken into account. Probably, the ones to be introduced in calculation algorithm will force the promising expectations to decrease considerably.

 

Table 2. Standard landfill gas power generation facilities engineering and economical performance

Landfill mass (million tons)	Object capacity (MW)	Investment + operating costs (million rubles)	Profit accumulation (million rubles)
≥2.5	≥2.6	≥12300	≥25000
2.5-1.0	2.60-1.04	12300-10350	25000-10000
1.0-0.5	1.04-0.52	10350-5200	10000-5000
≤0.5	≤0.52	≤5200	≤5000

 

The rate of profit is specified without taxation and discounting coefficient.

Whereas this analysis was held accounting for the conditions of stiff competitiveness with landfill gas energy being delivered by cost to be less than the conventional one, any technology being projected within the area of Russia should be considered for its efficiency. No doubt, the very process should be stimulated by arrangement of the most favorable financial-and-legal conditions, as it principally depends on its ecological aspects that were not stated in this document.

Prior to estimation of landfill gas extraction and utilization Russian potential, all the current Russian dumps (Table 4) were preliminary classified. As per the data classified, at least several hundred objects available for implementation of economically efficient landfill gas projects may be specified. Thus, the potential to be available is quite great.

 

Table 3. Standard landfill gas extraction facilities engineering and economical performance

Landfill mass (million tons)	Object capacity (m3/h)	Investment + operating costs (million rubles)	Profit accumulation (million rubles)
≥2.5	≥2000	≥12300	≥12000
2.5-1.0	2000-800	8400-4000	12000-6000
1.0-0.5	800-400	4000-2000	6000-3000
≤0.5	≤400	≤2000	≤3000

 

The rate of profit is specified without taxation and discounting coefficient.

Prior to estimation of landfill gas extraction and utilization Russian potential, all the current Russian dumps (Table 4) were preliminary classified. As per the data classified, at least several hundred objects available for implementation of economically efficient landfill gas projects may be specified. Thus, the potential to be available is quite great.

Table 4. Classification of Russian Federation landfilling areas

Landfill mass (million tons)	Number of objects in Russia
≥2.5	≥20
2.5-1.0	90
1.0-0.5	400
≤0.5	800

 

9. Moscow region polygon landfill gas extraction and utilization pilot project

Project “Sanitary landfilling along with power recuperation within the area of Moscow region” was initiated in January 1994 and was held for the period of two and a half years.

On of the main aims of the project is directed to demonstration in Russia the potential of biogas technological process – the element of solid domestic waste polygon sanitary landfilling to be widely used in the world.

Biogas is the product of microbial decay of certain waste fractions buried in a polygon. The waste disposed may include plant and animal remains, paper and timber. The rates of bioinversion, the above materials are subject to, vary and depend not only on types of wastes, but also on physical and chemical conditions formed in any landfill mass (humidity, temperature, pH etc.).

Biogas is of combustible nature and consists of 50-60% of methane and 40-50% of carbon dioxide; its heat value is approximately two times lower than the one of the nature gas and makes up about 4500-5000 Kcal/m³.

The amount of biogas subject to extraction and utilization at any solid domestic waste polygon is determined in direct proportion to the waste mass.

At Moscow region two typical polygons “Dashkovka” (Serpukhov district) and “Kargashino” (Mytishchi district) were nominated for demonstration of biogas technology potentialities.

Some preoperational research procedures held at the above polygons included the following kinds of activity:

·             Field gas-geochemical research for the purpose of determination of landfill layer efficiency;

·             Exploratory boring for the purpose of determination of landfill mass capacity and its parameterization;

·             1:500 topographic mapping

Upon investigating the projected area such characteristics as biogas potentialities, rates of its generation and promising gas-extraction performance were estimated. Due to the data received, the last parameter was rated for the purpose of typical Moscow region polygon (area: 5-7 ha and average waste layer thickness: 10-12 m). In compliance with the below figure, any amount of biogas generated within the area of any Moscow region polygon is ordinary featured with its release rate of 600-800 m³ per hour, while about 50% of the emitted volume may be utilized as alternative energy source.

At solid domestic waste Moscow pilot polygons the method of biogas utilization in the form of power generation was taken for priority. For this purpose the gas-extracting systems consisting of gas holes, pipelines and compressor stations to be used for delivery of gas to motor-generator sets disposed in close proximity to the solid domestic waste polygons were constructed within the area of polygons. The new compressing equipment and power generating plants supplied by Holland Company “Grondmai” within the bounds of Moscow region engineering support program were used in the project.

In 1995 the first biogas plant was commissioned. Quite an amount of detailed information about areas used for gathering of biogas via a single extracting hole, about the ground shield waste covering efficiency and about the modes to be applied in different weather conditions.

Today, the both plants (Serpukhov and Mytishchi) are operated in their pilot mode, with each one generating by 80 kW/h. In terms of experience, the volume of 1 m³ of gas may be used for electric power production within the range of 1.3 – 1.5 kW. It means that, with any polygon biogas stock being totally utilized, the range of 260 to 300 kW per hour (2500 MW per year respectively) may be produced.

To account for today energy costs, the rate of potential return gained with just a single biogas plant operated at any typical Moscow region polygon may amount to approximately 1.2 billion rubles. But the situation to occur at the financial sector and energy distribution monopolistic business activity are the very events that make a doubt about possibility of searching for a certain solvent consumer. Therefore, it is better to utilize the energy generated partially for solid waste polygon auxiliaries and partially for production of energy-consuming products (e.g. hothouse flowers or vegetation). Due to reduction of costs, the product gets competitive.

This kind of experience gained after implementation of project may be applied for the following introduction of the given technological process at the Russian polygons.