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How Clean is Natural Gas? Greenhouse Gas Emissions by the Numbers

3
By Clean Energy Compression

This is the first article in a series of three articles that explore the role of natural gas in the race to reduce greenhouse gas emissions.

The question was raised at a recent forum on the future of energy, “How clean is natural gas?”

With so much riding on the topic, understanding how natural gas stacks up to diesel by the numbers has never been more important.

Special interest groups have been putting considerable effort behind heavily publicizing the fact that natural gas does in fact produce greenhouse gas emissions, not only from carbon dioxide (CO2) at tailpipe but from escaped methane (CH4) during extraction, transport and fueling. All of this is true, but the question is how much greenhouse gas? If a developing nation replaces diesel fleets, coal & bunker fuel based power plants today with natural gas are they reducing greenhouse gas emissions?

Full Scope Emissions – Getting the Whole Picture

Emissions don’t just happen at the tailpipe. Getting the whole story for any fuel source means following it from “well to wheels.” All good scientific analysis will examine what is often called “full scope emissions” – in other words how much greenhouse gas emissions were generated in the extraction, refining, transport and end-use of the fuel.

The sources all agree, the answers are clear: all the studies find that well-to-wheels, natural gas fuel emits significantly less greenhouse gas and other pollutants than diesel, coal or gasoline at the tailpipe, but how much greenhouse gas emissions are generated from wellhead to the application?

Making Things Equal

In the past, in-part because of very motivated competition among the petroleum producers, rumours were circulating that natural gas’ footprint during production, transportation and storage were higher than crude. Natural gas is primarily methane (CH4), a greenhouse gas that is 21 times as impactful as CO2 by volume and does escape in small quantities during development. With the GHG impact order of magnitude being significantly higher, it was easy to convince the masses that Natural Gas is not as green as once thought. However examining full-scope emissions with a conversion of methane emissions to “CO2 equivalent units” we are able to compare atmospheric impacts versus petroleum products from well-to-wheels.

Natural Gas Does have Higher GHG Emissions During Transportation & Storage, but that’s Where the Story Ends

Current scientific studies do highlight distribution emissions have been measured to be 55g CO2 equivalent/ km emissions compared with only 6g for diesel. This is where the story ends however. Overall, natural gas extraction and processing combined use 119g CO2 equivalent / km of energy while diesel production uses over 280 CO2 / km.

(See First 3 Columns of Figure 1 below which evaluates well-to-wheels emissions on a Cummins diesel versus similar the similarly powered Cummins Westport natural gas engine with CNG fueling system).

Figure 1 –

Well to Wheels emissions comparisons natural gas to diesel

The True Benefit of using Natural Gas is that it Reduces GHG Emissions by Approximately 30% Compared to Diesel

Current studies show full scope emissions are heavily in favour of natural gas when compared to diesel when used for transport trucks, transit buses and fleet vehicles. When comparing transport trucks, well-to-wheels modelling shown in figure 1 illustrates diesel emissions are 34% higher than natural gas emissions over the total life cycle, from the fuel’s extraction to processing, storage, transportation and including its end use. When used for power generation, compared with coal or bunker fuels, natural gas can reduce emissions by more than 40%.

An Even Greener Outlook for Natural Gas

The numbers are clearly in favour of natural gas by indications are the gap will widen in the future. As a result of stringent regulations, continual improvements in processing, and shipping technology reducing escaped natural gas, emissions will continue to drop. Unfortunately for diesel and gasoline the full-scope emissions for crude oil are likely being under-estimated and are growing due to the vast increases in drilling depths and the distances from refineries to market. Most notably, the production of tar sands oil involves using significantly dirty heat and energy for processing, which can double or triple CO2 emissions over conventional extraction.

Pollutant and Greenhouse Gas Emission Reductions by the Numbers

Air Pollution by Fuel Solid comparing Diesel and Natural Gas Emissions

Compared to diesel, natural gas emits:

•     99% less sulphur oxide (0.005% of diesel)

•     80% less nitrogen oxide (18% of diesel)

•     40% less CO2

•     No heavy metals

•     No soot particles

Figure 2

Natural Gas in Power Generation:

Burning natural gas produces fewer greenhouse gas emissions

  • 40% lower per unit of generated electricity than coal
  • And 25% better than diesel

Natural Gas is a Realistic Solution for GHG Reductions Now Because it Costs Less.

Although there has been great talk of meeting the COP21 climate conference targets, developing nations have a whopping 2,400 coal-fired power plants planned (Figure 4). China alone opens a new plant every 13 days on average. The growth of developing nations depends on adding cheap energy and lots of it.

If the economics aren’t there, the process of reducing greenhouse gas emissions will not happen on a large enough scale. In an increasingly competitive world, low energy costs are not only pursued by developing nations, but also by developed nations. Cheap energy is the goal of virtually all countries, regardless of the long-term impact.

What just might save us from constant acceleration of global warming is the fact that natural gas is also supported by economics.

Natural Gas Can Be Implemented Now, with Existing Infrastructure

In order to succeed, we need to reduce emissions quickly without incurring trillions in capital expense – trucks, trains, boats and power plants can all be easily retrofitted to replace fuel sources with natural gas, in many cases at a cost savings over diesel. Our addiction to cheap but incredibly dirty coal and bunker fuel may require increasing levels of legislation or taxation.

Abundant & Affordable Supply for All Global Markets

Natural gas is the cleanest fuel readily available worldwide. It is the best available solution to cost-effectively replace coal, oil and diesel by converting existing engines and infrastructure to make real reductions in emissions.

Natural Gas Supports Renewable Development

Natural Gas is the bridge to the successful implementation of 100% renewable fuels, it supports wind power when the wind isn’t blowing, and solar when the sun isn’t shining. Wider adoption of natural gas could easily support the next decade’s global targets for greenhouse gas emissions; combined with solar and wind, reduction targets could be exceeded quicker, not to mention it would help millions breathe easier.

 

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