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Ultra Low Sulfur Diesel (ULSD): the Good, the Bad, and the Rusty

Posted July 18, 2018 by Caleb Courville

You have probably heard mixed reviews about ultra low sulfur diesel (ULSD). Some say it is great for the environment while others claim it causes more problems than it solves. If you are looking for an unbiased take on the ins and outs of ultra low sulfur diesel, you are in the right place.

Below we cover why ultra low sulfur diesel exists, its benefits and disadvantages vs. traditional diesel, and what you can do to protect your equipment from any negative effects of ULSD.

Why Does Ultra Low Sulfur Diesel Exist?

Ultra low sulfur diesel (ULSD) was created in response to a number of regulatory actions aimed at reducing diesel fuel emissions.

Clean Air Act Amendment (1990):

In 1970, Congress passed the Clean Air Act as a means to reduce harmful emissions from automobiles. The Clean Air Act was later amended in 1990, requiring stricter emission reductions of hydrocarbons, carbon monoxide, nitrogen oxides, and particulate matter.

Icon set displaying the harmful emissions associated with burning diesel fuel such as hydrocarbons, sulfur oxides, carbon monoxide, nitrogen oxides, and particulate matter.

Concurrently, the EPA started imposing sulfur content limits on diesel fuel in an effort to help buses and trucks become compliant with other emission standards coming into effect that year.

The primary motivator for reducing overall emissions was to mitigate the harmful health and environmental effects caused by fossil fuel emissions.

Highway Diesel Program (2001):

In 2001, the EPA finalized a federally-mandated program called the 2007 Heavy-Duty Highway Diesel Program. This program was established to further decrease emissions by enabling the use of advanced emission control technologies for highway diesel engines. Although effective, these technologies were found to be easily damaged by sulfur, requiring serious sulfur reductions in the fuel in order for them to be used. Effective June 2006, the maximum sulfur limit in diesel was slashed from 500 to 15 parts per million (ppm).

Chart of sulfur content (ppm) in on-road diesel overtime

This reduction officially marked the switch from Low Sulfur Diesel (500 ppm) to Ultra Low Sulfur Diesel (15 ppm).

Clean Air Off-Road Diesel Rule (2007):

Shortly after the highway diesel program’s inception, the EPA issued the Clean Air Non-Road Diesel – Tier 4 Final Rule. This rule mandated sulfur reductions for off-road diesel engines, effective 2007.

Chart of sulfur content (ppm) in off-road diesel overtime

As a result, the maximum sulfur limit in off-road diesel fuel dropped from 3,000 to 500 ppm in 2007 and later 500 to 15 ppm in 2010.

The Pros & Cons of Ultra Low Sulfur Diesel

Emission Reductions

Since the 1990s, the EPA has mandated a 99.7% reduction in fuel sulfur content in order to reduce sulfur emissions from diesel fuel. Sulfur oxides (SOx), specifically SO2, have been determined to be a serious threat to public health and the environment.

sulfur oxides and the threat to public health

Health concerns related to exposure to SOx include respiratory problems and lung damage. SOx has also been found to cause environmental harm in the form of tree, plant, and stone damage, acid rain, and reduced visibility (haze). The less sulfur content in the fuel, the less polluting SOx emissions released. This has proven to be the major benefit of ultra low sulfur diesel.

Changes in Fuel Chemistry

Removing sulfur contents from the fuel has been shown to greatly alter the lubricity and overall chemical composition of diesel fuel. Refineries use severe hydrotreating to remove sulfur from diesel which, in addition to removing the sulfur, it also removes natural lubricity compounds, lowers the fuel's aromatic contents, conductivity, and energy density (fuel economy), and increases cetain levels and production costs.

Icon set displaying changes that occur to diesel when it is converted to ultra low sulfur diesel such as removing sulfur and natural lubricity compounds, lowering aromatic content, conductivity, energy density, and fuel economy, and increasing cetane levels and production costs.

While some of these side effects to hydrotreating are positive, a majority of them are not. Fuel economy of ultra low sulfur diesel is decreased by an estimate of 1% and, according to the EPA, severe hydrotreating also increases fuel production costs by 5 to 7 cents per gallon. However, these costs may be significantly higher depending on market, distribution, and other production factors.

Corrosive Effects of ULSD

Same Tank, Different Fuels

In 2007, pollution awareness and prevention was on the rise as emission mandates came into full effect. Since then, fuel tank corrosion damage has hit an all-time high in both gasoline and diesel fuel tanks.

ULSD fuel tankers labeled with ULSD and ethanol describing switch loading

This is because fuel hauling tanker trucks participate in something called switch loading. For example, a truck could be hauling ethanol-based gasoline one day and ULSD the next.

ULSD causes fuel tanks to rust because of the increased water content and retention

This due to ULSD having a higher affinity to water than traditional diesel. Water is essential for microbial growth. However, as the EPA has confirmed, accelerated tank corrosion occurs when ULSD blends with small quantities of biofuel. Therefore, when ULSD combines with ethanol, or other types of biofuel, even in small quantities, a problematic chain reaction occurs that not only accelerates tank corrosion but can also pose a risk to backup power systems:

ULSD problem flow chart that come from the increased microbial growth and sludge from using ULSD

Preventing Problems Caused by ULSD

Addressing Low Sulfur

To combat problems with ULSD effectively, including decreased lubricity, energy density, and fuel economy, use of broad spectrum fuel additive  is considered best practice. A fuel additive can restore many of the lost properties of diesel while continually reducing emissions. This is achieved through a fuel catalyst which allows for a more complete combustion of the fuel. Benefits of using a fuel additive can include:

Preventing Corrosion & Downtime

As previously discussed, tanks containing ULSD have corrosion problems. If ULSD mixed with biofuel during transportation, those problems will manifest at an accelerated rate. To combat these issues, along with the formation of sludge, clogged filters, and downtime, you have to look at the chain of events that lead to these outcomes. In this particular case, everything traces back to microbial growth. Microbes that proliferate in diesel fuel love areas where water and fuel meet.

ULSD microbial growth from fuel contamination image

If you remove water, you effectively halt microbial growth along with the development of previously mentioned problems. So how do you remove water?

You have two options:

#1 Hire a mobile fuel polishing company

A mobile fuel polishing company will bring specialized equipment to your location and filter out water, particulate, and sludge from your fuel.

Note: Without a permanent installation, like a fuel maintenance system, it is recommended you test your fuel regularly to prevent future contamination due to condensation of new water or introduction of new fuel to the tank.

#2 Invest in a fuel maintenance system

A fuel maintenance system is a permanent installation that regularly maintains the fuel by removing water and other contaminants. These solutions run automatically.

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