California Emissions Standards Met With Oven Retrofit
Ball Corp. supplies metal and plastic packaging to the beverage and food industry. The company also provides aerospace and other high technology products and services to governmental and commercial customers through its subsidiary, Ball Aerospace & Technologies Corp., Boulder, Colo.
Meeting emission standards after Ball entered a joint venture with Con Agra Foods at its Oakdale, Calif., can manufacturing plant proved to be its biggest challenge yet. The San Joaquin Unified Air Pollution Control District requirements for this facility called for some of the lowest emissions ever specified by a governmental agency.
Ball Corp. called on International Thermal Systems (ITS), Milwaukee, and Maxon Corp., Muncie, Ind., to hit these low emission specifications on three 1940s vintage wicket ovens at the Oakdale plant.
ITS, with its years of oven experience as OSI and IHEI, teamed with Maxon, a long-time provider of low emission technology, to put together a cost-effective package to re-trofit the ovens. The team analyzed the application and considered several issues to develop the best solution for Ball Corp.
Emissions Crash CourseThe key pollutant that the regulations are targeting to reduce is NOX. This is a generic term for oxides of nitrogen such as NO and NO2. To a lesser degree, they are also concerned with carbon monoxide (CO). These are the same pollutants that the government is forcing automakers to reduce in mobile source emitters. There also is increasing pressure to reduce these pollutants in fixed source emitters, or manufacturing facilities, that use heat in their processes, such as Ball's wicket ovens.
When regulatory agencies specify emissions levels, they use either units of pounds per million BTUs (#/MMBTUs) which is a mass measurement, or parts per million corrected to 3 percent oxygen concentration (ppm corrected to 3 percent O2), which is a concentration measurement. It always is necessary to specify an oxygen concentration, especially when using ppm units.
In ovens that have a fair amount of fresh air being drawn into the oven, either through the ends or the makeup air ports, the emissions are heavily diluted. Consequently, the oxygen concentration has a large effect on the concentration of emissions. The oven design, amount of recirculation, and process will allow for a steady-state oxygen concentration in industrial ovens that can range from 16 percent O2 to just more than 20 percent O2 and even beyond. For reference, the air that we breathe has an oxygen concentration of 20.9 percent O2.
An "as measured" reading of 3.3 ppm NOX with 19 percent O2 in the oven is equivalent to 30 ppm NOX corrected to 3 percent O2. If the oxygen in the oven was 20 percent O2 with a 3.3 ppm as measured reading, the new corrected number would be almost 60 ppm NOX when corrected to 3 percent O2. The corrected number does not always double with a 1 percent change in oxygen concentration, but the example proves that emissions are significantly affected by different oxygen concentrations and should be corrected for comparison. The easiest way to compare is to always correct to 3 percent O2. For the rest of this article, NOX will be expressed by simply stating "NOX corrected."
Factors Affecting EmissionsThe first and most important step in controlling emissions is to use the latest low emission technology. Low emission burners control the air-fuel mixture and flame temperature better than traditional burners that have been on the market for the last 30 years. Traditional oven burners typically produce emissions on the order of 100 ppm NOX corrected. Newer technology burners can reduce the emission rates to 25 ppm NOX corrected and lower.
The second important step is evaluating the application and the environment in which combustion will occur. The chamber temperature is critical to make any emissions guarantee. NOX is formed more easily at higher temperatures, especially above 1,000oF (538oC). Most oven applications are in the range of 300 to 500oF (149 to 260oC), making it easier to control NOX than in a high temperature application.
Other factors to consider are cross velocity and fuel type. Cross velocity can have a large impact on CO generation. In some applications, the flame must be protected from a high cross velocity to keep the perpendicular airflow from cooling the flame too much. Fuel type can affect emissions as well. Generally, propane gives higher numbers than natural gas.
Emissions Turndown vs. Thermal TurndownEmissions turndown also is a concern as emissions turndown can be different from the thermal turndown of a burner. In some applications, it can be difficult to maintain low emissions throughout the firing rate. For example, a burner may produce low emissions right up to low fire. At low fire, the emissions may be difficult to control due to chamber conditions or other factors. High pressure drops across shut-off valves or high pressure droops through a main gas regulator can cause poorer emissions rates at low fire.
Despite these low fire issues, high fire of any burner is still considered the worst case scenario for regulatory agencies because this condition generates the largest quantity, or mass, of emissions (#/MMBTU).
If a burner has a thermal turndown of 15:1, it may have an emissions turndown of 15:1 under good conditions or 10:1 under poor conditions. Any formal guarantee is made on a case-by-case basis. Every situation -- application, type of burner and emissions turndown -- is different. For these reasons, low emissions cannot be easily summed up as one magic, low number. In the process heating world, you are not dealing with the constant chamber conditions of a boiler.
Ball Corp.'s SolutionBall Corp. considered several different types of burners that utilize low NOX technology, including:
- Gun-style, low NOX Cyclomax packaged oven burners.
- In-duct, low NOX Crossfire line burners.
- High temperature, high output, low NOX Kinedizer burners.
Traditional oven burners have higher thermal turndowns than low emission oven burners. Because of this, low NOX oven burners should never be oversized. In the past, a larger-than-necessary burner may have been used without concern for overheating the oven at low fire. Now it is recommended that engineers look closer at an oven's heat balance, especially at low fire. In short, use the smallest low NOX burner possible for any application below about 5 million BTU/hr. In applications above 5 million BTU/hr, consider a burner with thermal turndowns up to 40:1.
After considering the many variables associated with the retrofit at Ball Corp.'s Oakdale plant, ITS and Maxon decided on Maxon's second generation packaged Cyclomax low NOX burner. This burner offered many advantages for this application, including:
- A range of BTU inputs, ensuring no zone would be oversized.
- Almost all of the flame is contained in the combustion sleeve, so flame length was not a concern in the small heater houses.
- A formal guarantee of emissions at the lowest NOX level ever specified by a governmental agency for such an application.
ResultsAn independent certified source tester conducted all tests. After performing three tests each on all three ovens, the average emissions rate for the nine tests was 7.8 ppm NOX corrected to 3 percent O2. With an oven oxygen concentration of 19 percent on average, this amounted to less than 1.0 ppm NOX as measured. One particular test produced rates at 4.1 ppm NOX corrected. These numbers were met over a wide emissions turndown. Ball Corp.'s principal environmental engineer, Bob Hall, says that the company is pleased with these emission rates. The Oakdale plant now boasts of some of the lowest emitting ovens in the country.
The team effort by Ball Corp., ITS and Maxon proved successful. Though every application is different and may not produce emission rates this low, every application also has the opportunity to beat these rates.
Matt Brueck is sales engineer at Maxon Corp., Muncie, Ind. For more information about Maxon's low emission burners or ITS's ovens and retrofitting capabilities: