Distribution Of Methane Via Natural Gas Grid Environmental Sciences
The use of landfill in waste management has been known to be the best suitable method in UK for the past two to three centuries. Increasing use of landfill leads to increase use of land take which created adverse environmental impacts such as groundwater and air pollution as there have been significant leaks of leachate and biogas (methane - CH4 and Carbon dioxide - CO2) into the watercourse, and atmosphere. Continuous biogas leakage into the atmosphere results in increase of its concentration which in turn contributes to the global warming due to the biological activity of the degradation of the waste materials.
The advancement of technology has improved and helped in reduction of greenhouse gas emissions as the biogas released are collected and regenerated into energy providing electricity, heating and diverse supply of fuel. This report would be considering and comparing the advantages and disadvantages, cost, benefits and other factors involved in use of either spark ignition or distributing methane through the natural gas grid as alternative methods.2.0 Technical requirements between the uses of spark ignition and methane distribution via natural gas grid
In order to manage and reduce the escape of landfill gas the landfill Directive had set out clear obligations for this to be achieved in which have been implemented in the whole UK.
The distribution of biogas into the natural grid would entitle the displacement of use of natural gas for which it is treated up to the required standards, delivering 97% methane injected into the grid for usage. For this to be achieved, the use of a Pressure Swing Adsorption (PSA) technique would be used to eliminate non-methane gas such as carbon dioxide, oxygen and nitrogen from biogas stream. The gases are removed from the stream by their physical forces and size molecules using either carbon or zeolites catalysts as an activator. The following are the technical factors that limit the gas distribution:
The distance of grid is dependent on the cost of operation and maintenance
Dynamic parameters such as pressure, flow-rate and pressure drop are very important to consider as consumption may vary in temperature and seasonal changes e.g. summer and winter.
For the spark ignition, restrictions in use of fossil fuel may be as a result of wear, slagging and fouling, the efficiency of the boiler cleaning systems and the aging or deactivation of catalysts used (Francis Prince, 2000). However, the use of spark ignition provides high power, efficiency and reduces the emission of greenhouse gases. The engines are designed to operate for base load power generation under varying conditions which could be operated for long periods and at the same time ensures proper gas control as shown in fig. 1 below (SEPA 2003).
Figure 1: An example of injection point of the gas distributed into the gas grid (Claire, 2009).
The landfill gas is collected via two methods which are either vertically or horizontally. For the vertical method, the wells are sunk upright within the waste mass; the effective lengths of the wells are limited to the depth of the unsaturated zone due to the landfill cap below. Hence restricts the efficiency the wells performance which therefore requires several installations of the wells to maximise efficiency. As a result of using this method it could also lead to a weakness in the cap as it could damage the cap surface, disrupt the anaerobic processes in the landfill which could potentially result in wild fires or explosion of the gas within the gas extraction infrastructure, if it reaches a certain level of concentrations (Richard, B.et al). Another disadvantage of the use of vertical wells is that each pipe would require an extraction system in order to achieve control balance on the subsurface gas pressure as it could become a huge problem if contaminated (Richard, B.et al).
However, with the use of horizontal method to collect the gas would improve the efficiency of the landfill gas extraction systems as there are installed as vent trenches. This method has more advantage to the vertical wells as helps increase gas yield, few wells needed thus saves money, time and energy.(Richard, B.et al). Another technique that could be used is membrane and is a method for which methane gas are collected for treatment and at the same time providing high-pressure of methane-rich gas on the outside of the fibres and low pressure carbon dioxide enriched gas inside the fibres (SEPA 2003).
3.0 Practical Issues:
This section includes the economic implications and potential advantages of the fuel used in terms of cost of running, collection of biogas, treatment and transport. Energy retrieved from waste could lead to an opportunity which increases the UK market on renewable energy.
The clean-up options for the economics of the clean-up options are not really clear but reviews of the current practises and regulations could show that if the mass flow is minimised it could be of significant benefit in the operation and financial sector (SEPA. 2004). Analysis of cost benefits is much difficult as lack of performance data could be used for comparison and implementation of these clean-up technologies are required in a real life situation (SEPA, 2004). For this to be made accurate, the use of collating basic cost appraisal (CBA) provides information on the method of gas clean-up with the benefits on the environment and the tools used to understand the implementation are the assumed life of technology, capital cost, operating costs and revenues (SEPA, 2004).
The landfill gas released are used for different applications such as combined heat and power (CHP) plant for industrial facilities which involves use of brick and cement industry, spark ignition to produce electricity. The gas used to produce electricity is distributed in the main gas pipe for industrial and domestic purposes (SEPA 2003).
4.0 Current and Future Policy on renewable:
A policy for renewable energy replacing the Non-Fossil Fuel Obligation (NFFO) framework established as part of the Electricity Act 1989 was recently introduced in England by the government. This new policy ensures that renewable energy sources could compete in the open market. The renewable obligation stated that power suppliers had to deduce certain amount of electricity supplied to customers from renewable resources (SEPA. 2003). This approach was used to create a strong financial incentive for suppliers to be able to fulfil the Renewables Obligation through Renewable Obligation Certificates (ROCs) (SEPA. 2003). Table 1 below provides the percentage trade of renewable sources from year 2002 to 2010 and the value for 2010 been fixed for the next 17 years.
Percentage of total sales of electricity from renewable sources
Table 1: Total electricity sales for each year with 2010 value maintained until 2027, (SEPA 2003)
An energy source such as solar energy replaces itself after usage is termed as a renewable energy, but scientifically, there are rising concerns about the implementation of renewable energies. Recently the interest in the renewable energy market has excited a number of scientists hence resulting in a possible search of infinitely renewable energy; the search of this energy that never runs out leads to a research in the different technologies and energy sources (IEA CADDET Centre, 2000).
Methane gas extracted from landfill could be harnessed and seen as a renewable energy as there is a tendency for the gas to escape to the atmosphere due to degradation of waste (IEA CADDET Centre, 2000). This process does not require use of energy as the methane gas are collected and transferred into the natural gas grid which could be used as fuel or electricity.
5.0 Potential Climate Change Benefits:
The gas liberated from landfill sites are astonishingly in large volumes over a period of time. This could create long-term nature of source and the large volumes of gas involved could cause potential adverse effects on human health and the environment, particularly at locations close to landfill gas vents (Elizabeth S.1997).
The European Union (EU) set out policies in relation to waste disposal and recovery. The strategy identifies the type of waste collected or treated, technical requirements and quantity, the origin of waste recovered and disposed. In UK, the strategy for sustainable waste management developed into a concept of hierarchy which is reduce, reuse, recover and dispose (with disposal as the least option and reduction as the main focus.
Monitoring the impact of emissions of local air quality and global atmosphere would require improved sampling, use of analytical techniques which when modelled would permit to access the impact of landfill gas emissions on the local environment from the vents and flares to be appraised and systematically assessed. Hence, the use of risk assessment would be necessary as it provides the authorities information of the potential negative impacts and ensure that these are not ignored (Elizabeth Simmons. 1997). The assessment identifies and describes the direct and indirect effects on human health and the environment. For instance, a large scale waste treatment and disposal on municipal solid waste would require assessment of a wide range of criteria such as, visual impact, air emissions, water discharges, human health, traffic, habitats and biodiversity, socio-economic impacts and site operations. The benefits would be that there would be low greenhouse gas emissions with the use of bio-fuels and use of sophisticated exhaust gas treatment e.g. selective catalytic reduction system which allows low emissions that meets up to the standards (Fiskum, R, 1998).
During clean up, the use of pre-combustion gas clean-up technologies would be essential has it would help reduce the damages to the engines therefore, resulting in low maintenance cost of the engine during operation. The clean-up processes are justified by ensuring that the environmental impacts are carefully considered via the use of risk assessment of emissions and the Pollution Prevention and Control (PPC) that helps balance out the cost, different technologies used and the savings for repair and maintenance due to failure of plant by contaminants in the gas supply (SEPA. 2003).
The following assumptions are based on the findings of distributing methane via the natural gas grid are;
It is assumed that with the use of methane as a renewable source of energy would lead to a decrease in the use of fossil fuels as a source of energy.
Methane is assumed to have a low heating value
Improvements in efficiency as a substantial amount of emissions are burned into the atmosphere, helps in reducing the amount of greenhouse gases released to the atmosphere from the usage.
It is taken that the landfill gas could vary from between sites due to certain factors such as site characteristics, moisture content, waste type, pH, age of the waste, temperature and management of the gases released.
Risk assessments are carried out on sites prior to design in order to consider the risks on air pollution, health and noise.
All necessary approvals have been obtained via passing all criteria from environmental assessment.
Regular checks of the gas pipelines are carried out during collection, treatment and distribution of methane gas.
The assumed life of the clean-up option is based on the life span of the asset.
For achieving the potential environmental benefits, the use of cost benefit analysis would be appropriate as it provides the information on the best suitable method on treating and supply of the methane gas which would help reduce gas emissions on supply to the gas grid or from the engines into the atmosphere. Also, balancing cost benefits and environmental factors could become a problem to the operator and technology industries in terms of the financial issues if the maintenance cost is not reduced.
The technical requirements would require taking careful considerations on the distance of grid as it is dependent on the cost of operation and maintenance as well as understanding the as pressure, flow-rate and pressure drop of the gas as there may vary in temperature due to geographical locations.
With the new policies enabling renewable energy to compete in the market has led to potential benefits in a reduction of greenhouse gas emissions with the use of biofuels (methane) through the use of appropriate gas treatment to meet the required standards; thus proves that the use of methane distribution in the natural gas grid is viable, economic and possible if based on the above assumptions.
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