Cutting Diesel Costs at Asphalt Plants: The Dual-Fuel Advantage

For asphalt producers, diesel fuel represents one of the largest variable costs in plant operations. Every gallon burned to power generators, dryers, and equipment eats into margins squeezed by competitive bidding and fluctuating material prices. The challenge has intensified as diesel prices climbed while natural gas prices trended lower. One solution gaining traction is dual-fuel generator technology, which allows existing diesel generators to burn natural gas alongside diesel, dramatically reducing fuel costs without sacrificing performance. Asphalt plant operators seeking to improve their bottom line should understand how this retrofit approach works, what real-world results look like, and what it means for operational budgets and environmental compliance. For a broader overview of safe and efficient plant operations, refer to our Asphalt Safety Comprehensive Guide to Hazard Management in hot mix asphalt operations.

The Rising Cost of Diesel for Asphalt Production

Asphalt plants are heavy consumers of diesel fuel. Generator sets powering conveyors, pumps, and control rooms run continuously during production hours. When diesel prices spike, every ton of hot mix asphalt becomes more expensive to produce, and those costs cannot always be passed on to customers in a competitive market.

The price volatility of diesel creates uncertainty in budgeting and bidding. A plant estimating fuel costs at one price per gallon may see margins destroyed when prices rise. This is particularly painful for asphalt producers who have locked in contract prices months in advance.

Why Diesel Dependency Is Costly

• Diesel prices are tied to global crude oil markets, subject to geopolitical instability and supply chain disruptions
• On-site diesel storage requires tanks, containment systems, and regular refueling logistics
• Diesel generator maintenance intervals are shorter due to carbon buildup and oil contamination from combustion byproducts
• Emissions from diesel combustion attract increasing regulatory scrutiny and compliance costs

Switching entirely to natural gas generators is one option, but the capital cost is prohibitive for many operators. A dedicated natural gas generator set costs two to three times more than a comparable diesel unit and requires a significantly larger footprint. That is where dual-fuel retrofit technology offers an attractive middle path.

How Dual-Fuel Generator Technology Works

Dual-fuel technology, also called bi-fuel technology, allows a standard diesel generator to burn both diesel and natural gas simultaneously. The diesel injection provides the ignition source through compression, while the natural gas contributes the majority of the fuel energy. The result is the same power output with substantially less diesel consumption.

The Core Components of a Dual-Fuel Retrofit

A dual-fuel retrofit kit typically includes three main subsystems:

1. Air-gas mixer: A custom-designed unit mounted between the air intake cleaner and the turbocharger. This mixer fumigates natural gas into the intake air stream, ensuring thorough mixing before the air-fuel charge enters the combustion chamber.
2. PLC controller: A programmable logic controller that monitors engine parameters in real time and adjusts the gas delivery rate dynamically. Key monitored parameters include engine vibration, exhaust gas temperature, electrical frequency, and electrical load.
3. Dynamic air-fuel ratio throttle: A fast-acting throttle valve that can open or close completely in 30 milliseconds, allowing the system to respond instantly to changing load demands.

How Combustion Works in Dual-Fuel Mode

In a standard diesel engine, compressed air in the cylinder reaches a temperature high enough to ignite diesel fuel when it is injected. In dual-fuel mode, the natural gas premixed with intake air is present in the cylinder before the diesel injection. The diesel injection still ignites first from compression heat, and that initial flame front ignites the surrounding natural gas-air mixture. The result is a more complete and homogeneous burn compared to pure diesel operation.

This cleaner combustion leads to several mechanical benefits:

• Engine operation is notably quieter with less vibration
• Oil contamination from incomplete combustion is reduced
• Engine maintenance intervals can be extended
• The generator set can instantly revert to 100% diesel operation if natural gas supply is interrupted

PLC Control and Safety Systems

A critical feature of modern dual-fuel systems is the speed and intelligence of the control system. The PLC has a reaction time of 10 to 20 milliseconds, and the air-fuel throttle valve can respond within 30 milliseconds. This allows the system to maintain the same governor speed control and power delivery as a generator running on 100% diesel.

If any parameter goes outside the calibrated range, such as an exhaust gas temperature spike, the system automatically reduces gas delivery until conditions normalize. No operator intervention is required. If a fault condition persists, the system safely reverts to 100% diesel operation and completely shuts off the gas supply. No modifications are made to the original OEM generator controller, preserving all factory safety and performance logic.

Real-World Results: Blalock’s Tennessee Asphalt Plants

The installation of dual-fuel generator systems at Blalock’s asphalt plants in Tennessee provides a powerful case study for the asphalt industry. Blalock operates multiple asphalt plants in eastern Tennessee and was looking for ways to reduce operating costs as diesel prices continued to climb.

In collaboration with the Sevier County Utility District (SCUD), which provided the natural gas supply, Blalock installed the Hythane OptiBlend dual-fuel system on their existing Caterpillar generators. The retrofit kits were installed over weekends, causing zero disruption to plant production schedules.

Sevierville Plant: First Installation

In August 2011, Blalock installed their first OptiBlend system at the Sevierville, Tennessee plant on a Caterpillar C32 generator set. The results were impressive from the start. At the middle of the electrical load range, the system reduced diesel usage by up to 70%. Across the full normal range of plant operations, Blalock averaged a 50% reduction in diesel consumption, which translated into a 35% reduction in overall power costs.

Kodak Plant: Second Installation

Building on the success of the first installation, Blalock installed a second OptiBlend system in March 2012 at their Kodak, Tennessee plant. This unit was installed on a Caterpillar 3412 generator set. At the Kodak plant, the system reduced diesel usage by up to 65% across the generator’s load range, with operational savings exceeding 35%.

Return on Investment

The financial case for dual-fuel retrofitting is compelling. The Kodak plant achieved a return on investment of less than one year based on fuel savings alone. By retrofitting existing generator sets rather than purchasing new dedicated natural gas units, Blalock avoided the large capital costs of equipment replacement. William Smith, asphalt manager for Blalock, noted that the systems have been highly beneficial because they reduced operating costs without sacrificing performance.

The following table summarizes the performance data from both installations:

The installation process itself was remarkably efficient. The modification to the existing diesel generator required only one to two days. Because the work was completed over a weekend, there was no impact on the plant’s production schedule. This minimal downtime is a significant advantage over installing a dedicated natural gas system, which would require removing the existing diesel generator and setting up new equipment.

For more on the equipment used in asphalt production, see our article on Asphalt Plants and Pavement Construction Equipment a Complete guide to hot mix asphalt production plants.

Environmental and Operational Benefits of Dual-Fuel Systems

Beyond direct cost savings, dual-fuel generator technology delivers meaningful environmental and operational advantages that align with the growing emphasis on sustainable construction practices.

Emissions Reductions

The environmental benefits of dual-fuel operation are substantial. When running in dual-fuel mode, the key emissions from a diesel generator set are significantly reduced:

• NOx reduction of approximately 50%: Nitrogen oxides are a primary component in the formation of ground-level ozone and smog. Cutting NOx emissions by half represents a major improvement in local air quality around asphalt plant sites.
• Particulate matter reduction of approximately 50%: Diesel particulate matter is a known respiratory hazard. Reducing PM emissions improves working conditions for plant personnel and reduces the plant’s environmental footprint in surrounding communities.
• CO2 reduction of approximately 10%: Carbon dioxide emissions, a primary greenhouse gas associated with climate change, are also reduced. While 10% may seem modest, for a plant running a large generator set for hundreds of hours per production season, the cumulative reduction is significant.

These emissions reductions come from the more complete and homogeneous combustion that natural gas provides. Natural gas burns more cleanly than diesel, producing fewer byproducts of incomplete combustion.

Energy Independence and Fuel Security

Dual-fuel systems also contribute to energy security at both the plant and national levels. By using domestically produced natural gas in place of imported diesel fuel, asphalt producers help decrease dependence on foreign oil. The United States has abundant natural gas reserves, and the pricing advantage over diesel has been sustained and significant.

At the plant level, dual-fuel operation provides fuel security that a dedicated natural gas system cannot match. If the natural gas supply is interrupted for any reason, the generator set automatically returns to 100% diesel operation with no interruption in power. The plant always has diesel fuel stored on-site as backup, while capturing the cost savings of natural gas during normal operation.

Operational Advantages for Asphalt Producers

1. Minimal capital investment: Retrofitting existing generators costs a fraction of purchasing new dedicated natural gas units, which are two to three times more expensive than diesel generators.
2. No production downtime: Installation is completed over a weekend, with no impact on plant operations.
3. Reduced maintenance costs: Cleaner combustion reduces oil contamination and extends engine maintenance intervals.
4. Quieter operation: Natural gas combustion produces noticeably less engine noise and vibration, improving working conditions.
5. Fuel flexibility: The plant can take advantage of whichever fuel offers the best economics at any given time.

The impact of well-maintained paving operations extends beyond the plant. Quality asphalt production supports long-lasting pavement performance. Read about High Performance Pavement How a Process Driven Business paradigm is reshaping asphalt repair and road durability.

While dual-fuel technology has existed since the early days of the diesel engine, its application to asphalt manufacturing plant generators is a relatively new development. The success at Blalock’s plants demonstrates that off-the-shelf dual-fuel retrofit systems can deliver immediate, measurable cost savings and environmental benefits. For asphalt producers watching their fuel costs rise, this technology offers a practical path forward that does not require a complete overhaul of existing equipment.

As natural gas prices remain low relative to diesel and emissions regulations continue to tighten, the economic case for dual-fuel systems will only strengthen. Producers who act now to retrofit their generator sets can lock in the dual advantage of lower operating costs and a reduced environmental footprint for years to come. For facility managers looking at broader site improvements, our guide to Jointless Concrete Floors With Type K Cement a high performance solution for modern facilities offers complementary insights into durable infrastructure.