Natural gas vs. Coal – a positive impact on the environment

Global energy demand is growing. Energy needs rise more slowly than in the past but still are expected to expand by 30% between today and 2040. This is the equivalent of adding another China and India to today’s global demand. A global economy growing at an average rate of 3.4% per year, a population that expands from 7.4 billion today to more than 9 billion in 2040, and a process of urbanisation that adds a city the size of Shanghai to the world’s urban population every four months are key forces that underpin International Energy Agency projections.

All this puts a lot of pressure on our planet’s ecosystem. The current levels of atmospheric concentrations of greenhouse gases (GHGs) are unprecedented in the last 800,000 years.

The energy generation sector (electrical and heat) is the largest source of GHGs, accounting for more than 60% of all GHG emissions (electricity production – 28.4%; industry – 22%; commercial and residential – 11%) which primarily come from burning fossil fuels for energy (source: Report by the US Environmental Protection Agency – EPA).

The role that natural gas can play in the future of global energy is inextricably linked to its ability to help address environmental problems. With concerns about air quality and climate change looming large, natural gas offers many potential benefits if it displaces more polluting fuels. This is especially true given limits to how quickly renewable energy options can be scaled up and that cost-effective zero-carbon options can be harder to find in some parts of the energy system. The flexibility that natural gas brings to an energy system can also make it a good fit for the rise of variable renewables such as wind and solar PV.

Natural gas is a fossil fuel, though the global warming emissions from its combustion are much lower than those from coal or oil. Natural gas emits 50 to 60 percent less carbon dioxide (CO₂) when combusted in a new, efficient natural gas-power plant compared with emissions from a typical new coal plant.

The amount of CO₂ produced when a fuel is burned is a function of the carbon content of the fuel. The heat content, or the amount of energy produced when a fuel is burned, is mainly determined by the carbon (C) and hydrogen (H) content of the fuel. Heat is produced when C and H combine with oxygen (O) during combustion. Natural gas is primarily methane (CH₄), which has a higher energy content relative to other fuels, and thus, it has a relatively lower CO₂-to-energy content. Water and various other elements, such as sulfur and noncombustible elements in some fuels, reduce their heating values and increase their CO₂-to-heat contents. That’s the reason why different fuels emit different amounts of CO₂ in relation to the energy they produce when burned.

Table 1: Pounds of CO₂ emitted per million British thermal units (Btu) of energy for various fuels. 

Source: US Energy Information Administration

Coal-fired plants emit not only carbon dioxide. There are also other toxins that have an immediate and direct impact on people’s health such as mercury. Avoiding coal burning would save hundreds million $ a year in health-care costs by avoiding illnesses caused by pollutants, such as asthma attacks, heart attacks and deaths linked to the coal-fired plants’ emissions.

Cleaner burning than other fossil fuels, the combustion of natural gas produces negligible amounts of sulfur, mercury, and particulates. In transportation, burning natural gas does produce some nitrogen oxides (NO_x), which are precursors to smog, but at much lower levels than gasoline and diesel used for motor vehicles. Analyses by the US Department of Energy indicate that every 10,000 U.S. homes powered with natural gas instead of coal avoid the annual emissions of 1,900 tons of NO_x, 3,900 tons of SO₂, and 5,200 tons of particulates. Reductions in these emissions translate into public health benefits, as these pollutants have been linked to problems such as asthma, bronchitis, lung cancer, and heart disease for hundreds of thousands of people.

Each fossil fuel has a different life cycle. The extraction/production; refining/conditioning; transportation/storage; and combustion of each fossil fuel is different. And, each fossil fuel contributes greenhouse gases at different stages of its life cycle. Likewise, at different stages, every fossil fuel contributes to global warming to a different degree.

The total environmental impact of coal is greater than that of any other fossil fuel. Especially with respect to open-pit coal mining, the environmental impact of coal cannot be overstated. From the destruction of forests, devastation of water quality, and the irreversible changing of landscape, coal mining has a massive impact on the environment.

With respect to carbon emissions, coal mining and the burning of coal account for a greater sum than any other fuel.

Coal, unlike gas fuels and oil, does not emit carbons into the air in its natural state. However, during the mining of coal, methane is released into the air. Tremendous amounts of methane (CH₄) are released into the air in fact. Each year, in the U.S. alone, coal mining releases an estimated 61 million metric tons of carbon dioxide equivalent (MMTC02E) tons of methane into the air.

Coal combustion produces more greenhouse gases than the combustion of any other fossil fuel. There are a handful of coal types, but almost all contribute substantially more CO₂ into the air than other fossil fuels upon combustion.

We have to mention that there is a lot of methane released into the atmosphere during oil and natural gas production too. Therefore, the technology developed by the GASVESSEL project that allows utilizing natural gas currently burned or released into the air is contributing to global GHG reduction efforts.