Enhance EPDs with Burner Tech
BY Jim Feese
How to employ innovative burner systems, controls for optimum environmental efficiency
Your burner design can be conducive to saving energy, reducing CO2 emissions and improving your environmental product declarations (EPDs).
Aggregate dryer burner designs have evolved through the decades starting with many open-fired burner designs, which required the exhaust fan to induce combustion air into the flame/dryer, to more modern sealed-in burner designs with 100% air capability. The sealed-in designs have further evolved to improve energy footprint by way of reduced electrical energy consumption and British thermal units per pound (Btu/lb) of asphalt produced when operated with more sophisticated controls.
After over two years of intensive design and testing, Detroit Stoker Company Inc. (DSC), Monroe, Michigan, recently released the Detroit® HADES aggregate drying burner. The design capitalizes on DSC’s 30+ years of boiler burner design and application experience in addition to staff’s prior experience with a former aggregate drying burner OEM. The HADES design incorporates fast air/fuel mixing technology adopted from modern low NOx boiler burners with a rugged service duty and maintenance accessibility expected in the asphalt industry. More intense air/fuel mixing is achieved with the ability to shape the flame to obtain the necessary compact flame envelope to fit the dryer combustion zone with lower fan motor horsepower than previous designs. In addition, a control panel also designed by DSC provides air/fuel ratio control with additional features enabling plant hot-stops and light to waste oil fuel switch-on-the-fly capability, among others.
In the Field
A recent case study at Eureka Stone in Milford, Pennsylvania, now operating for over one year, demonstrates the energy savings potential of replacing an outdated burner design with this new technology. The plant is a 2-ton batch and produces approximately 120,000 tons per year of HMA. The dryer drum is approximately 8 feet in diameter by 30 feet long. The burner fires on either Compressed Natural Gas (CNG) or No. 2 fuel oil. The images on this page show the old open-fired burner replaced with a sealed-in Detroit HADES burner.
The open-fired burner utilized a high pressure 100-horsepower fan/motor whereas the new burner requires a 60-hp fan/motor and includes a variable frequency drive (VFD) for additional electrical energy savings. Furthermore, the single jackshaft arrangement (air and fuel damper/valve driven by a common actuator with mechanical linkage) was replaced with VFD only for airflow control and a direct coupled V-ball fuel flow control valve(s)/actuator(s) per fuel, which offer more precise flow control than the typical butterfly valves used on most gas burners. (See the “Electrical Energy Savings” sidebar for details.)
The payback on the burner VFD alone is less than six months. Depending on plant location, the utility may offer additional incentives through rebates and/or reduced peak load demand charges.
Fuel savings from installing a new burner and control system are difficult to accurately quantify with the many variables that contribute to fuel usage in the first place, including material mix and varying moisture levels from season to season. Industry experience has shown that switching from an open-fired burner system to a sealed-in burner system in conjunction with controls upgrades can readily yield 5-10% in fuel savings. Let’s look at the factors that make this possible.
First, the typical open-fired burner fan only provides about 30-50% of the stoichiometric combustion air required and relies on the plant exhaust fan to induce the balance. This can lead to inefficient air/fuel mixing and overall air/fuel ratio control; ultimately higher fuel consumption compared to a sealed-in burner with 100% total air fan. The sealed-in burner fully mixes 100% of the required combustion air intimately with the fuel at the burner nozzle(s) resulting in fast mixing, complete burn-out, and improved air/fuel ratio control. (See the “Fuel Savings With Natural Gas” sidebar for fuel information.)
Second, as already alluded to, the air/fuel control scheme can be much more precise with a sealed-in unit. In this case, we control 100% of the combustion air and can do so at any firing rate via a parallel position type control scheme. If your burner control system is not equipped with characterizable air/fuel curves as depicted in the screenshot of the HBC-1000 control panel, then your burner is likely running at non-optimal air/fuel ratio at multiple load points. The parallel position system is designed to operate with independent air/fuel ratio control [VFD for air and independent direct coupled fuel actuator(s)], with built-in safety limits to prevent operation beyond desired air/fuel ratios. Combined with the proper fuel flow control valves and precision actuators, this leads to very accurate air/fuel ratio control and eliminates slipping linkages and hysteresis common in mechanical linkages.
Another recent example from David A. Bramble, Wye Mills plant, involved a comprehensive plant upgrade complete with new dryer, exhaust ducting, baghouse, and exhaust fan (via Herman Grant Company Inc.) with new light and waste oil fired Detroit HADES burner and HBC burner control panel. The pictures on this page show the new equipment package versus the old unit as viewed from the burner end of the dryer. Burner equipment including fuel trains and safety limits are now more readily accessible, and easier to set-up, tune, and service. Wiring is clean and orderly, further improving safety and troubleshooting.
The new burner with 1,800 rpm fan with VFD is quieter than the old unit even though the old burner was enclosed to help reduce noise pollution. The lower speed fan also reduces fan vibration, improves fan life and minimizes long-term wear from typical quarry/gravel dust particles. Following the above calculations for a “typical” drum mix plant producing in the neighborhood of 200,000 tons per year or more of HMA results in substantially more cost savings and an even quicker payback on the controls and/or burner investment upgrade in addition to various benefits cited.
A new, properly tuned burner and control system providing energy savings in terms of KWh/ton and Btu/ton of asphalt produced in combination with avoided/reduced CO2 emissions is a positive step in improving an asphalt plant’s EPDs with many additional benefits.
Jim Feese, P.E., is director of the burner group at Detroit Stoker Company Inc. Jim has over 25 years of experience in burner design and development and holds several burner patents. He received his bachelor’s and master’s degrees in mechanical engineering from Pennsylvania State University. For more information, reach him at JFeese@detroitstoker.com.