Natural gas and the environmental results of life cycle assessment

Natural gas and the environmental results of life cycle assessment

Energy 31 (2006) 138–148 www.elsevier.com/locate/energy Natural gas and the environmental results of life cycle assessment Angelo Riva*, Simona D’Ang...

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Energy 31 (2006) 138–148 www.elsevier.com/locate/energy

Natural gas and the environmental results of life cycle assessment Angelo Riva*, Simona D’Angelosante, Carla Trebeschi SNAM S.p.A, Piazza Vanoni, 1-20097, San Donato Milanese, Italy

Abstract Life cycle assessment (LCA) is a method aimed at identifying the environmental effects connected with a given product, process or activity along its life cycle. This paper presents results of the application of LCA method in order to evaluate the environmental advantages of natural gas over other fossil fuels and to have advanced techniques for analysing the environmental aspects of the gas industry. The evaluation of published studies and the application of the method to electricity production with fossil fuels, by using data from published databases and data collected by the gas industry, demonstrate the importance and difficulties of having reliable and updated data required for a significant LCA. Results show that the environmental advantages of natural gas over the other fossil fuels in the final use stage increase still further if the whole life cycle of the fuels, from production to final consumption, is taken into account. q 2004 Elsevier Ltd. All rights reserved.

1. Introduction All energy sources have impact on the environment through their life cycle from production to end use. Life cycle assessment (LCA) is a methodology to evaluate this impact and to identify the opportunity to improve environmental performances. According to the Society of Environmental Toxicology and Chemistry (SETAC) definition [1], LCA is a methodology ‘to evaluate the environmental burdens associated with a product, process or activity by identifying and quantifying energy and materials used and wastes released to the environment; to assess the impact of those energy

* Corresponding author. Fax: C39-025-203-8428. E-mail address: [email protected] (A. Riva). 0360-5442/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2004.04.057

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and material uses and releases to the environment; and to identify and evaluate opportunities to affect environmental improvements’. A LCA is made-up of the following stages: – Definition of objectives and boundaries of the assessment. – Inventory analysis, that involves the identification and measurement of the process impacts. – Impact assessment, that evaluates the significance of potential environmental impacts using the results of the inventory analysis. – Interpretation and improvement analysis, that identifies the opportunity to improve the environmental performances of each activity. The increasing attention for LCA derives from the increasing awareness that for environmental protection a global approach is required, considering all the environmental aspects related to a product or a service from cradle to grave. There are still many problems linked to the LCA methodology. The most relevant ones are: – Lack of reliable data for some steps of life cycle; in these phases rough data are used. – Homogeneity of bibliographic sources; in fact, ‘primary’ data collected inside each single industry are used with ‘secondary’ data, collected from bibliographic sources or databases that often ignore origin and methods used for the estimation. – Temporal homogeneity of data; literature data often refer to different time periods and this can cause inaccuracy in comparison among different technologies. – Choice and definition of environmental indicators used for classification and characterisation of impacts individuated by the environmental inventory. The results of a LCA may be used in various ways: to objectively identify the interactions of a product or service with the environment and to quantitatively analyse the environmental loads; to provide information to allow prioritisation of environmental improvements; to serve as a tool to evaluate the level of achieving target values and meeting regulations as part of company efforts for environmental protection; to communicate with consumers and customers on environmental quality of a product. In particular, Snam (the company in charge of the purchase, transmission, primary distribution and sale of natural gas in Italy) is studying the application of LCA in order to evaluate the environmental advantages of natural gas in comparison with other fossil fuels and to have advanced techniques for the assessment of its environmental performances. 2. Studies on LCA of energy systems Many studies on LCA have been carried out on energy processes for a variety of reasons. In recent times, when environmental issues have gained increasing priority with regard to the cost effectiveness of using one fuel rather than another, there is a constant interest to evaluate the environmental value of fuels considering their entire life cycle. LCA can also be applied to help focus industry attention on where the greatest impacts of a process arise. In the report of IGU ‘Environmental Care in the Gas Business’ [2] an overview of LCA studies which are most relevant to the gas industry is presented. While it is not possible to comprehensively review all

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these studies, in this section some of the major studies are outlined with their conclusions and implications for the use of LCA within the gas industry. 2.1. Inventory analysis for energy systems [3] The main scope of this study is to provide environmental information on existing energy systems, which can then be used to describe the energy input to industrial and residential sub-systems, for life cycle analysis of products and for other environmental assessment studies. On the basis of consistent methodological approaches, emissions and resource utilisation levels are determined for the full life cycle of the energy systems from exploration to waste disposal and dismantling of infrastructures. The study stops short of classification and valuation of environmental impacts. However, when comparing natural gas with oil and coal, it can be stated that in many respects its environmental impact is more favourable than that of other fossil fuels. 2.2. Environmental aspects of energy supply: conventional and future options [4] The aim of the study is to provide an overview of the environmental impacts of conventional sources of energy. An extensive review of literature was carried out to define environmental burdens. The results are evaluated in terms of global warming potential (GWP), acidification potential (AP), fossil energy resources and solid waste production. Besides variations due to the composition of the fuels and the specifications of the technologies, the data used are somewhat uncertain. In order to take full account of this limitation it was decided to distinguish two cases per technology: Case L and Case H. The definition of Case L is that it estimates a low value of an indicator, while Case H estimates a high value of the indicator for a particular technology. This allows us to see how the variations in technology can alter the expected environmental impact. The results of the study are provided for each environmental indicator and for each energy source and are divided into a direct and indirect contribution. The direct contribution originates from the emissions and energy consumption during the consumption phase, such as combustion. The indirect contribution originates from the emissions and energy consumption in the phases before consumption such as production, processing and transport of the energy source. For example, Fig. 1 shows the relative contribution of combustion and precombustion for oil and gas used for domestic heating in terms of GWP expressed as kg of CO2 equivalent per functional unit of 1 GJ.

Fig. 1. Global warming potential for two technology cases applied to domestic heating.

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The analysis demonstrates that natural gas has the best environmental performances. The contribution relative to the final use is prevailing for natural gas and oil, while for coal an important contribution derives also from production and transport phases. 2.3. Life cycle analysis for Norwegian oil and gas [5] The study carried out by the Norwegian Institute of Technology has the objective to present environmental life cycle data for Norwegian oil and gas production. It identifies the main input resources required for the production of each tonne of oil and each cubic meter of natural gas from the Norwegian continental shelf, as well as the associated generation of waste, emissions to air and discharges to sea. The report is very precise with regard to its scope, limitations and definitions of various stages, however, it is weak with regard to estimating uncertainties and accuracy of the data used and the results produced. The application of LCA methodology in studies [6,7] used for comparison among biofuels and fossil fuels, has demonstrated that: – natural gas has the best environmental performances among fossil fuels; – in general, the greenhouse gas emissions produced by biofuels are lower than emissions caused by fossil fuels. Nevertheless, natural gas presents better environmental performances in terms of nongreenhouse effect in comparison with biofuels.

3. Life cycle inventory of natural gas system The life cycle of natural gas can be divided into the following stages: production, transmission, distribution and final use. In Table 1 the inventory of Italian gas industry atmospheric emissions and energy consumption collected by Snam for the year 1995 is presented [8].

Table 1 Inventory of Italian gas industry atmospheric emissions and energy consumption in 1995

Units Production Transmission Distribution Total a

Natural gas volume

Pipeline length

Energy consumptionC losses

Energy lossa

CH4

NOx

CO2

VOC

SOx

109 m3 20.0

km

106 GJ 13.1

(%) 1.70

(t) 7,000

(t) 1,017.0

(t) 472,000

(t) 644.0

(t) 743.0

54.7

27,659

15.3

0.73

31,600

4,035.0

683,200

117.0

98.5

27.2

159,250

12.9

1.24

209,000

106.4

92,800

13.6

80.6

247,600

5,158.4

1,248,000

774.6

922.1

Energy lossZ[(total consumptionCenergy lost)/(energy transmitted)]!100.

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The results show the extent to which the production, transmission and distribution of natural gas in Italy contribute to atmospheric emissions and energy consumption and they form the basis of the LCA of natural gas in Italy for the various types of final use. A database with a software called LICYA has been developed by Snam to prepare life cycle inventories of energy sources. This software collects and organises input/output data coming from available and reliable literature sources. Data from two important literature databases of energetic sources are considered: – ETH [9]. This database represents maybe the most comprehensive system, at present, available in the field of LCA, since data consider all the life cycle of the energetic sources (natural gas, oil, coal, nuclear, hydraulics) and include impacts from exploration and infrastructures. The database is related both to Swiss and other European scenarios. The emissions of several substances are considered in the process records and it is possible to determine the contribution of each phase of the cycle. – BUWAL250 [10]. This database is an elaboration of ETH second version, considering an average Western Europe scenario. The BUWAL database does not include the life cycle of the infrastructures and is limited to the electricity production from power plants and heat production from industrial boilers as final uses. The contribution of each life cycle phase cannot be evaluated. When data more reliable than those from literature are available, they can be included in the LICYA software and used for the life cycle inventory.

4. LCA of natural gas for electricity production The analysis has considered the following steps of life cycle of natural gas:

At first, the analysis has been conducted by considering literature data with three different cases: – Natural gas produced in Russia and transported to Italy where it is used. Data from ETH database have been employed (Case: ETH Russia). – Natural gas produced in the Netherlands and transported to Italy where it is used. Data from ETH database have been employed (Case: ETH Netherlands). – Natural gas produced, transported and used in Western Europe. Data from BUWAL database have been employed (Case: BUWAL). Atmospheric emissions as the most relevant environmental impacts of fossil fuels cycles have been considered. The results referred to the production of 1 kW h of electricity are presented in Table 2. The differences demonstrate the importance of the study boundaries and of data considered, showing that the environmental burdens for gas produced in Russia are higher than those from gas produced in the Netherlands.

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Table 2 Atmospheric emissions of natural gas cycle for electricity production with literature data Emissions

Unit

ETH Russia

ETH Netherlands

BUWAL

NOx SO2 CO2 CH4

g/kW h g/kW h g/kW h g/kW h

1.24 0.35 742 4.07

0.88 0.009 644 0.46

1.49 0.27 767 1.76

To evaluate the effects of technology for electricity production and to take into account the emissions limits established by Italian legislation, literature data for the phase of electricity production have been replaced by the emissions resulting from the real energy efficiency and the application of emission limits established by the Italian Ministerial Decree 8.5.89 for new large combustion plants higher than 300 MW presented in Table 3. For gas turbines in combined cycles a NOx emission limit of 60 mg/m3 (15% O2) has been assumed according to permits released by authorities. In particular, the following two cases have been considered: – Natural gas produced in Russia and transported to Italy where it is used in a steam plant. Data from ETH for production and transmission phases and emission factors based on emission limits and energy efficiency for an Italian steam plant have been used (Case: Legislation Steam Plant). – Natural gas produced in Russia and transported to Italy where it is used in a combined cycle plant. Data from ETH for production and transmission phases and emission factors based on emission limits and energy efficiency for an Italian combined cycle plant have been used (Case: Legislation Combined Cycle). From the results presented in Table 4, and compared with the case ‘ETH Russia’ previously analysed, it can be seen that, when the energy efficiency and emissions of real new power plants instead of general and probably old literature data are considered, there is a significant reduction of environmental burdens for the whole life cycle, in particular with gas combined cycle. The results of five cases analysed can be aggregated and evaluated with impact categories such as GWP and AP as shown in Fig. 2. The GWP aggregates the emissions of carbon dioxide and methane expressed as CO2 equivalent (1 kg CH4Z21 kg CO2eq). The AP aggregates the emissions of SO2 and NOx expressed as SO2 equivalent (1 kg NOxZ0.7 kg SO2eq). The total values are formed by two contributions: the combustion phase that takes into account the emissions of power plants for electricity production and the precombustion phase that takes into account the emissions from production and transmission of natural gas. Table 3 Emission limits for new large combustion plants (PO300 MW t) Fuel

NOx (mg/m3)a

SO2 (mg/m3)

Dust (mg/m3)

Solid Liquid Gaseous

200 200 200

400 400 35

50 50 5

a

Referred to 6% oxygen content in the flue gases for solid fuels and to 3% oxygen content for liquid and gaseous fuels.

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Table 4 Atmospheric emissions of natural gas cycle for electricity production with emission limits of Italian Legislation Emissions

Unit

ETH Russiaa

Legislation Steam Plant

Legislation Combined Cycle

NOx SO2 CO2 CH4

g/kW h g/kW h g/kW h g/kW h

1.24 0.35 742 4.07

0.96 0.33 635 3.87

0.61 0.22 427 2.6

a

Case: ‘ETH Russia’ for comparison.

In the BUWAL case only total values are presented because the separate contributions for combustion and precombustion phases are not available. It can be seen that the use of gas from the Netherlands and the electricity production with combined cycle, having a high efficiency and requiring less fuel consumption, significantly reduce the GWP and AP, both in combustion and precombustion phases. The values of emissions presented in international databases regarding the natural gas cycle are often not updated and based on estimates. To improve the reliability of LCA, an application has been conducted by substituting data from databases for production and transmission of natural gas with data collected by the gas industry. In particular the following cases have been considered: – Natural gas produced in Russia and transported to Italy where it is used in a combined cycle. Data from Ref. [11] and collected by Snam have been employed for production and transmission phases. In electricity production, emission factors based on emission limits and energy efficiency for an Italian combined cycle have been employed (Case: Gas Russia). – Natural gas produced and used in a combined cycle in Italy. Data collected by Snam for the Italian natural gas cycle and presented in its Health, Safety and Environment Report [8] have been employed

Fig. 2. Global warming potential and acidification potential of natural gas cycle for electricity production.

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Table 5 Atmospheric emissions of natural gas cycle for electricity production with gas industry data Emissions

Unit

Legislation Combined Cyclea

Gas Russia

Gas Italy

NOx SO2 CO2 CH4

g/kW h g/kW h g/kW h g/kW h

0.61 0.22 427 2.6

0.39 0.04 383 1.39

0.34 0.007 356 0.17

a

Case: ‘Legislation Combined Cycle’ for comparison.

for production and transmission phases. In electricity production, emission factors based on emission limits and energy efficiency for an Italian combined cycle have been employed (Case: Gas Italy). The results presented in Table 5, and compared with the results of the case ‘Legislation Combined Cycle’ previously analysed, confirm the importance of the study boundaries showing that the emissions for the entire life cycle for gas produced in Italy are lower than those from gas produced in Russia. Moreover, it can be observed that in international databases (Case: Legislation Combined Cycle) there is an overestimate of the emissions, in comparison with data collected by the gas industry. Fig. 3 shows the contribution of gas production, gas transmission and power generation phases to total GWP and AP. The main contributions derive from power generation, except for the case ‘Legislation Combined Cycle’ for which the contribution to AP from gas production and gas transmission is significant.

5. LCA of fossil fuels for electricity production An application of LCA has been developed to evaluate environmental aspects of life cycles of different fossil fuels for electricity production. The following cases have been considered:

Fig. 3. Global warming potential and acidification potential of single phases of natural gas cycle for electricity production.

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Table 6 Atmospheric emissions of fossil fuel cycles for electricity production Emissions

Unit

Coal

Oil

Legislation gas combined cycle

Gas Russia

Gas Italy

NOx SO2 CO2 CH4

g/kW h g/kW h g/kW h g/kW h

1.44 2.52 989 1.67

1.27 2.31 886 1.08

0.61 0.22 427 2.6

0.39 0.04 383 1.39

0.34 0.007 356 0.17

– Coal produced in South Africa and transported to Italy where it is used in a steam plant. Data from ETH for production, treatment and transport phases, and emission factors based on emission limits and energy efficiency for an Italian coal steam plant have been employed; – Oil produced in Middle East and transported to Italy where it is used in a steam plant. Data from ETH for production, treatment and transport phases and emission factors based on emission limits and energy efficiency for an Italian oil steam plant have been employed. The results obtained and compared with those for three different cases of natural gas cycle ‘Legislation gas combined cycle’, ‘Gas Russia’, ‘Gas Italy’, previously analysed are presented in Table 6. Though more expensive abatement plants are required to comply with the emission limits for power plants fuelled with coal and fuel oil, natural gas maintains significant environmental advantages, not only for the lower atmospheric pollutant emissions, but also for the other environmental impacts, as the absence of large amounts of waste produced by abatement plants required for coal and oil power plants. The GWP and AP, split up into precombustion and combustion contributions, for the analysed cases, are presented in Fig. 4. The major contribution to GWP is due to combustion for all fossil fuels, while an important contribution to AP derives also from precombustion phases. Among fossil fuels for electricity production, the natural gas cycle has the best environmental performances. In comparison with the coal cycle there is reduction of GWP of 53–65% and of AP of 81–93%. In comparison with the oil cycle there is a reduction of GWP of 47–60% and of AP of 79–92%. The ranges of reduction depend on the gas cycle boundaries and source of data considered.

Fig. 4. Global warming potential and acidification potential of fossil fuel cycles for electricity production.

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6. Conclusions All energy sources have impacts on the environment throughout their life cycle stages from production to end use. Many studies on the application of LCA methodology have been carried out to evaluate the environmental value of fuels and to have advanced techniques for the assessment of environmental performances of energy industry considering the complete life cycle of fuels. The evaluation of published studies indicates that, although there are still many problems related to the LCA methodology, including the availability of reliable and complete data for environmental inventories yet, natural gas shows best environmental performances among fossil fuels. The application of LCA methodology to natural gas system for electricity production, by using data from published databases and data collected by the gas industry, demonstrates that the results depend on system boundaries, source of data and technology adopted. The environmental burdens associated with the cycle of gas produced in Russia are higher than those from gas produced in the Netherlands and Italy. When energy efficiency and emission limits of real new power plants are considered, instead of general and probably old literature data, there is a significant reduction of environmental impacts. In international databases there is an overestimate of the emissions in comparison with data collected by the gas industry. In the natural gas cycle, the prevailing contribution to emissions and energy consumption derives from the electricity production phase, however, the gas industry has a constant attention to evaluate and to constantly improve its environmental performance in gas production and gas transmission phases. The application of LCA to coal, oil and natural gas cycles for electricity production, with the evaluation of their GWP and AP, demonstrates that the environmental advantages of natural gas over the other fossil fuels in the final use stage, increase still further, if the whole fuel cycles, from production to final consumption, are taken into account.

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