Fueling asphalt production with LNG and CNG

Asphalt companies without a readily-available pipeline are turning to LNG and CNG.

By Gas Technology September 26, 2019

The asphalt industry might not seem very competitive. However, the companies involved in the business are like any other. They’re trying to reduce costs any way they can while not skimping on quality or worker safety. They also must abide by current and future standards.

The process for making asphalt is not something many consider. When drivers are on the road, the only thought on their mind is when the trip will be done so they don’t have to drive on uneven, bumpy roads. However, it is a very intricate process. The work requires a great deal of precision.

Wolf Paving, a Wisconsin-based company that specializes in asphalt pavement installation for commercial, residential and municipal locations, highlights a seven-step process for making asphalt:

1. Demolition and removal, which is completed using heavy machinery such as forklifts, loaders and large dump trucks.

2. Grading and sloping, which involves ensuring water will run off because that’s a major cause of asphalt damage.

3. Preparing the sub base, which provides the stable surface to support the new asphalt pavement.

4. Proof roll and undercutting, which helps ensure the sub base is secure and does not have anything that could compromise the structure.

5. Binder and surface course, which is a large aggregate layer mixed with oil.

6. Installing the asphalt surface, which is the end result people see. The surface is a mix of small aggregate, sand and oil.

7. Butt joints and transitions, which is where the asphalt connects to existing driveways, roadways or parking lots and making sure the process goes smoothly.

It is a long, involved process, but it is more involved than paving and cutting. Keeping operations sustainable for a long period of time is just as important as the asphalt production process. If the asphalt plant isn’t reliable, it’s going to be a long time before drivers are going to have a smooth ride.

The asphalt plant is responsible for the site work required to make their yard able to accept trailers, bring communications, electricity and a new low-pressure gas pipe to the decompression station. A second burner is recommended to attain dual-fuel capability. Dual-fuel capability facilitates supply redundancy and protects against price swings.

LNG and asphalt

Asphalt plants typically are located close to the paving project site to maintain quality. However, these plants often are not located near a natural gas pipeline. This means a greater reliance on fuel sources, which may be more expensive – not just for the fuel, but for secondary costs such as equipment maintenance.

Many asphalt manufacturers have found a solution to address these challenges by using liquefied natural gas (LNG) to fuel their stationary and temporary asphalt production facilities. These manufacturers are finding LNG to be more sustainable in terms of cost and safer than the fuels used to produce asphalt.

LNG is a clear non-toxic liquid that forms when natural gas is cooled to -162 C. According to the U.S. Energy Information Administration (EIA), the cooling process shrinks the volume of the gas about 600 times. This makes it easier and safer to store and ship and will not ignite in its liquid state. When LNG reaches its destination, it is turned back into a gas at regasification plants. It also is environmentally safe. It does not emit soot, dust or fumes and does not require any remediation of soil, groundwater or surface waters like traditional oils would.

LNG is stored in double-walled, vacuum-insulated pressure vessels and is denser than compressed natural gas (CNG), which means more energy can be stored by volume in a given tank. This is helpful for asphalt manufacturers, who may have to expend more energy in peak summer months when the daily temperature reaches its apex.

However, the upfront costs for aspects like transportation and cryogenic make the initial process quite expensive for companies involved. Also, LNG doesn’t have an unlimited shelf life and cannot remain in a liquefied state forever. If a company is going to use LNG, they have to use it quickly. Given the pressing needs of an asphalt project, these are challenges that can be overcome.

LNG is a safe option for asphalt manufacturers

Another important aspect for asphalt manufacturers is what happens if there’s a spill. LNG is lighter than helium and quickly dissipates into the atmosphere if there’s a spill.

This is in contrast to spills involving propane and diesel. For example, when propane, a heavy fuel, is spilled, it is extremely hazardous until fully mixed with surrounding air. In the interim, the combination of an ignition source and the presence of propane in a low area or corner of an asphalt plant can create an extremely hazardous situation for employees, first responders and others at the scene.

Diesel fuel spills are another major concern. Depending on the amount spilled, they could require a HAZMAT response team and could contaminate the ground, requiring a costly removal and cleanup process.

LNG, because of its gaseous state, does not have these potential drawbacks and is, overall, a safer option for asphalt manufacturers.

LNG is a cleaner energy option

An important reason for the growing use of LNG in asphalt plants is its widespread utility. Any stationary or temporary plant currently operating on recycled fuel oil (RFO) or waste oil is an ideal candidate to convert to LNG.

RFO is a low-cost heavy oil that contains large amounts of sulfur, nitrogen and heavy metals and is hazardous for the environment and for people in close proximity to the production. Asphalt plants that burn RFO have increased plant maintenance and downtime.

LNG, however, is environmentally safe. It does not emit soot, dust or fumes and does not require any remediation of soil, groundwater or surface waters like traditional oils would.

CNG benefits for asphalt manufacturers

CNG is a flexible, low-cost and clean-burning fuel used to complement pipeline natural gas to provide dynamic supplies of heat and electricity that respond to erratic temperatures and uncertain flows. During peak summer and winter months, when heating and electricity demands are highest, the supply of natural gas can be constrained.

In addition, it can be costly to switch to a backup fuel, which causes lost revenue when the price of electricity is high during the peak months. CNG also is useful because seasonal weather can be unpredictable. By using peaking supply, power producers can receive supplemental supply only when it is most economical.

CNG, unlike LNG, doesn’t require new technological development to implement, which makes it a viable alternative in terms of upfront costs.

To maintain the temperature and consistency of the finished products, asphalt plants typically are located close to the paving project site. In many cases, these plants are not located near a natural gas pipeline, which means reliance on other sources of fuel that may be more expensive, demand greater amounts of equipment maintenance, or emit greater CO2 emissions. A competitor located on a pipeline may be able to underbid the facility not on a pipeline.

CNG is stored on the vehicle in high-pressure tanks – (3,000 to 3,600 psi). Natural gas consists mostly of methane and is drawn from gas wells or in conjunction with crude oil production. As delivered through the pipeline system, it also contains hydrocarbons such as ethane and propane as well as other gases such as nitrogen, helium, carbon dioxide, sulfur compounds and water vapor. A sulfur-based odorant is normally added to CNG to facilitate leak detection. Natural gas is lighter than air and normally will dissipate in the case of a leak.

At first glance, LNG and CNG might not seem like a natural fit for asphalt manufacturers. While there are some up-front challenges with costs, the long-term benefits from energy savings and worker safety make them viable alternatives for companies that don’t have ready access to pipelines.

– This article appeared in the Gas Technology supplement.