By Julio César Centeno
Venezuelan public officials frequently refer to electricity generated with natural gas as clean, green, non-polluting energy. An assessment in conflict with the evidence.
When natural gas is used as fuel in a thermoelectric plant, an average of 530 kilograms of CO2 is emitted per megawatt-hour (Mwh) of energy generated, half of what is emitted using mineral coal and two-thirds of what is emitted using diesel or fuel oil.
It is not true that natural gas is a clean, non-polluting fuel, a fuel " green"Its combustion in thermoelectric plants emits significant amounts of carbon dioxide (CO2). Only these emissions are lower than those from the consumption of mineral coal or petroleum derivatives to generate the same amount of electricity.
This comparison corresponds only to emissions from the direct combustion of the products mentioned. However, the carbon footprint of electricity also includes emissions from previous activities: exploitation, processing, transportation, storage and distribution. Taking into account the life cycle from exploitation to combustion, the average carbon footprint of gas-based electricity in Venezuela is 685 kilograms equivalent of CO2 per Mwh, and that from oil derivatives 990 kg / Mwh.
In 2012, 127,610 Gwh were generated in Venezuela ( gigawatt hours) Of electricity. 64% from water sources, 16% from natural gas, 13% from diesel and 7% from fuel oil. Less than a fifth of the thermal generation came from combined cycle plants, whose efficiency can be 40 to 50% higher than that of conventional plants. This implies that they generate between 40 and 50% more electricity per unit of fuel used.
Taking into consideration the life cycle from exploitation to combustion, thermal plants emitted 40 million tons of CO2 equivalent in 2012, of which 14 Millions originated from natural gas-fired plants.
However, in the case of natural gas, two additional and determining factors must also be included: fugitive emissions and burns in lighters or flares.
Gas CC = combined cycle Gas TG-TV = Turbo gas - Turbo steam
Natural gas is on average 85% composed of methane ( CH4). In the short term, each ton of methane that is emitted directly into the atmosphere traps heat radiation equivalent to 85 tons of CO2. In technical jargon it is stated that the Global Warming Power (GWP) of methane is 85. This is the value established in the most recent report of the Intergovernmental Panel of Experts on Climate Change which will be published later this year ( IPCC AR5).
However, the effective half-life of methane is around 12 years; it is destroyed by solar radiation. Consequently, the global warming potential in the long term it is reduced from 85 to 30 compared to CO2, a gas that remains active for centuries in the atmosphere ( IPCC-AR5).
In the production of natural gas, leaks occur at different stages of the process: at the exploitation, during processing, in the transport pipes, in the storage tanks, when it is distributed or when it is used. The amount of gas that escapes varies from 2% on average in the United States to 10% in other countries. Due to the high value of its global warming power (30), fugitive methane emissions tend to rapidly erode the advantage of gas-fired thermoelectric plants relative to those using coal or petroleum derivatives.
When one kilogram of methane (CH4) is consumed, 2.75 kgs of CO2 are produced. This is due to the significantly higher molecular weight of oxygen (16) relative to hydrogen (1). The global warming power of this CO2 is 2.75. If that same kilogram of methane escapes into the atmosphere, its long-term global warming power is equivalent to 30 kg of CO2. Consequently, the carbon footprint corresponding to the direct broadcast of methane to the atmosphere is 11 times higher to the one that is generated if it burns. From the point of view of global warming, it is preferable to avoid fugitive methane, even through its combustion in lighters (fires). It is clear that the most beneficial alternative is to avoid leaks.
The greater the methane leak, the smaller the difference in CO2 equivalent emissions compared to those from coal-based or petroleum-based thermoelectric plants. In Venezuela, a diesel or fuel oil-based thermoelectric plant emits on average 45% more CO2 per unit of electricity produced than a gas-based plant. This comparative advantage is nullified if fugitive methane emissions reach 4% of the gas consumed in that plant. In consecuense, Fugitive methane emissions above 4% imply that CO2 emissions from gas-based thermoelectric plants exceed those from diesel or fuel oil-based plants.
The climate benefit
Natural gas-based electricity production can generate a climate benefit depending on the magnitude of fugitive emissions. With fugitive gas emissions in Venezuela exceeding 6%, natural gas-based plants emit 13% more CO2-equivalent than plants that use petroleum derivatives.
The carbon footprint of a gas-fired thermoelectric plant can be equivalent to half the footprint of a coal-fired plant, or two thirds of the footprint of a diesel-fired thermoelectric plant, only if fugitive methane emissions are zero.
Natural gas consumption in Venezuela reached 77.6 billion cubic meters in 2012, of which 2 billion m3 were imported from Colombia. That same year, fugitive emissions of natural gas reached 6% of production: 4,500 million cubic meters per year. In 2012, 2,000 million m3 of gas were imported from Colombia, while 4,500 million m3 of gas was allowed to escape into the atmosphere.
The oil industry absorbs two thirds of the national gas consumption. It reinjects 44% of the production in oil wells and uses an additional 23% in combustion and processing activities.
According to OPEC, in 2012 11,350 million cubic meters were burned in flames, 15% of production ( OPEC: Annual Statistical Bulletin 2013). That same year the corresponding figure for Algeria: 2%, Qatar: 1%, the average of the OPEC countries: 5%. The figures published by OPEC are supplied by the countries.
If the corresponding proportion of emissions from burning in flames according to OPEC is included, the carbon footprint of electricity generated with natural gas in 2012 is 20% higher than that from plants powered by petroleum derivatives.
If gas re-injected into oil wells, leaks and gas burned by flares are discounted, the net consumption of natural gas drops to 28.4 billion m3 in 2012 ( Energy Information Administration 2012), equivalent to 26 million tons of oil.
Venezuela has the second proven natural gas reserve in the Western Hemisphere: 5,600 Giga M3 (billions), 74% of the proven reserves of all of Latin America ( BP Statistical Review 2013); mostly associated with oil. Both the potential and the need to significantly increase production are evident. Such a condition magnifies the need to minimize the gigantic levels of waste that are currently registered, not only for obvious economic reasons, but to minimize greenhouse gas emissions and the carbon footprint of the national electricity sector.
Economic and environmental liabilities
The price of imported gas from Colombia is indexed to the market in the terminal Henry Hub from Louisiana, USA. In 2012, it averaged US $ 2.75 per million Btu, equivalent to US $ 0.1 / m3 of gas. The import of gas from Colombia cost the country 200 million dollars in 2012. While l fugitive emissions (4,500 million m3) implied the loss of 450 million dollars that same year.
Additionally, the burning in flames reported by the Organization of Petroleum Exporting Countries for 2012, 11,350 million m3, implies the burning of 1,100 million dollars annually at current prices.
It is urgent to minimize the gigantic losses of natural gas in production processes. Based on 2012 values, reducing gas leakage from 6% to 2% and burning in flares from 15% to 5%, would make it possible to take advantage of an additional 10,500 million m3, which in turn would allow to more than replace the current consumption of diesel and diesel in electricity generation. At least 130,000 barrels of diesel would be released per day (2 billion gallons / year) whose value in the international market exceeds 6 billion dollars per year at the average price of 2012. This substitution would also reduce CO2 equivalent emissions by 8 million tons per year.
In Venezuela, both the use of natural gas and the generation of electricity are responsibilities of the state. It thus corresponds to the national government, through Ministry of Popular Power for Electric Energy:
· Reformulate the information campaign on the presumed green, clean, non-polluting nature of the energy currently generated by natural gas.
· Monitor and inform the population about the magnitude of the natural gas leak in the different stages of the industrial process: exploitation, processing, transportation, storage, distribution and use. This information should be audited by independent entities, such as universities and research centers.
· Monitor and inform the population about the magnitude of natural gas burning in flames, and implement the necessary measures to protect both the populations and the affected ecosystems. The official figures released by OPEC are alarming.
· Define and execute a national strategy to reduce both leakage and burning in flares to a maximum of 2% of national production in each case, using available technologies with proven profitability. A policy of this nature is not only justified in economic terms. It is also a necessity to effectively take advantage of the advantages that gas offers to generate electricity with less CO2 emissions per unit of electricity than those derived from oil.
· Replace the consumption of diesel and fuel oil in thermoelectric plants with natural gas, not only to release these products to other markets and optimize profitability, but also to ensure an effective reduction of the carbon footprint of the Venezuelan electricity sector.
· Prioritize the installation of combined cycle thermoelectric plants, since their efficiency can be 40 to 50% higher than that of conventional plants. This implies that between 40 and 50% more electricity is generated per unit of fuel used, reducing costs and emissions of gases into the atmosphere.
Design a strategy to mitigate part of the carbon footprint of electricity generated by thermoelectric plants through the reforestation of deteriorated hydrographic basins, using mixtures of native species of each area, with the purpose of protecting and stabilizing water sources for future generations and at the same time offset part of the greenhouse gas emissions into the atmosphere.
Julius Caesar Centeno
University of the Andes
Merida - Venezuela