The economy, growing public concerns, and tighter regulations have put pressure on the industry to develop solutions for a decarbonized world. This has driven new innovation in air emission control and energy conservation technologies. Many industries are facing tough engineering challenges. However, SMART SOLUTIONS are available and continue to be the focus of NESTEC’s quest to achieve the best and most economical APC solutions.
Oxidation has proven to be a very effective approach for removing Volatile Organic Compounds (VOC), Hazardous Air Pollutants (HAPs), and odors from process exhaust streams. The effectiveness of the oxidation system depends on several factors, but the combustion process is a primary element. It is directly related to the three (3) “T’s” and Destruction Removal Efficiency (DRE). Oxygen content, equipment design, and proven experience are also key features necessary to achieve the best and most economical air emission control system while reducing CO2 emissions.
- AVAILABLE OXYGEN
- EQUIPMENT DESIGN
- PROVEN EXPERIENCE
When a hydrocarbon or organic vapor is burned, it must be held at a specified temperature for a sufficient time to ensure that the hydrocarbons are completely oxidized. If the retention time at purification temperature in an RTO/RCO is less than one second, the DRE will be reduced. On the other hand, if it remains for a time longer than necessary at = > 1500 oF, additional auxiliary fuel will be increased, adding both capital and operating costs to the process. Thus, time plays a critical role in the overall DRE.
Uniform air flow and temperature through the combustion zone is also a key factor. NESTEC has incorporated unique design features to ensure maximum flow and temperature uniformity in the purification combustion zone.
The DRE will have a direct linear relation to the retention time (increasing the retention time will increase the DRE linearly).
Turbulence ensures a thorough mixing of the oxygen and the hydrocarbons as well achieving temperature uniformity. If turbulence is not maintained, certain part of the fuel will have excess oxygen available for the combustion while the remaining having too little. This will result in incomplete combustion of carbon forming carbon monoxide instead achieving the maximum DRE. If proper turbulence is not maintained, some part of the hydrocarbons will be exhausted without getting oxidized, which will decrease the DRE.
The DRE will vary based on the turbulence factor, increasing turbulence will increase the DRE to the second power.
During the combustion process, if the purification temperature is not sufficiently high, hydrocarbons with longer ignition lag time will require additional retention time for maximum DRE. Hence, it is very important to maintain a uniform correct temperature to ensure complete combustion of the hydrocarbons.
Increasing the purification temperature offers the most potent avenue for improving DRE and typically increases it to the fourth power.
Sufficient oxygen is a necessary part of the process of combustion. The higher the oxygen content, the greater the combustion of the hydrocarbon. It is essential both the oxygen and hydrocarbons are thoroughly mixed for combustion.
If your oxidation system is coming up short in achieving the required DRE for your permit requirements, and you want to find the best corrective solution, contact NESTEC.
NESTEC Inc. continues its quest to reduce CO2 emissions from the utilization of fossil-based fuels at all of our air pollution control (APC) installations. Maximizing thermal efficiency, including recirculation and/or cascading, and secondary heat recovery, all contribute to substantial reductions in CO2 emissions.
For example, NESTEC’s APC installation at a Wood Pellet facility reduced the potential CO2 emissions by 1,500 lbs per hour or 6,000 tons per year in addition to reducing the operating costs with a savings of $600,000 per year.
NESTEC has designed several RTO/RCO systems with enhanced features to improve thermal efficiency and DRE, as well as reduce the CO2 emissions.
- MEDIA: selection of multiple layers and types to maximize TER and DRE for the specific application based on actual experience.
- THERMAL ALIGNMENT: automatic control to maximize mass balance flow through the heat exchange chambers.
- FAN: selection of forced vs. induced draft
- UNIFORM: air flow distribution through the RTO/RCO
- MULTIPLE: burner selection and placement
- VARIABLE: energy recovery system from 2 to 20% LEL
Those are just some of the factors we control to optimize for efficiency and effectiveness. NESTEC also deploys many other features to enhance the performance of RTOs and RCOs.
Multiple NESTEC installations are operating with greater performance and efficiency than other RTO/RCO designs. For example, examine the following NESTEC wood industry RTO/RCO’s actual performance over an extended period:
HM: 1783-1267 = 516
A 110,000 SCFM wet NESTEC unit operating with only 0.56 MMBtu/hr of burner fuel input.
PM: 3029-2282= 747
A 160,000 SCFM wet NESTEC unit operating with only 0.82 MMBtu/hr of burner fuel input.
NESTEC’s enhanced features minimize the mass unbalance due to the burner combustion products that are added to the exhaust flow of the RTO/RCO. Self-sustaining RTO/RCO operations provide the highest TER operation, as the burner input increases the thermal efficiency decreases.
Many RTO/RCO are sold as 95% or 96% thermal energy recovery (TER)**units, but in fact are operating at substantially less efficiency. A 95% TER unit operating at 92.7 or 96% TER operating at 94.1% TER increases the fuel consumption and operating cost as well as the CO2 emissions.
- The increased exhaust temperature increases fuel consumption.
- The higher exhaust temperature decreased the available energy and also increased the fuel consumption.
- The higher exhaust temperature also increases the radiation losses and the fuel consumption (Cost).
A true RTO/RCO TER should be based on temperature to establish the actual fuel consumption and cost:
A 95% TER design purification temperature (1500) – exhaust temperature (202) = 1298 purification temperature (1500) – inlet temperature (100) = 1400 = 0.927/100
or 92.7% TER
If you would like an energy analysis of your existing or potential new RTO/RCO application, please contact NESTEC.
For assistance with any air emission control application from our extensive industry experience, call or email NESTEC Inc. (Office: 610-323-7670) for a free evaluation of your VOC control equipment needs.
Jim Nester, firstname.lastname@example.org (Sales)
Jaymie Deemer, email@example.com (Sales)
William Holden, firstname.lastname@example.org (Service/Aftermarket)