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Understanding PPMVD and O2 Level Requirements

Have you ever wondered what ppmvd (ref. 3% O2) means? This term is often seen in air permits and is referenced as the emission unit for pollutants such as NOx from boilers.

PPMVD stands for “parts per million by volume, dry”.  For example, “9 ppmvd” refers to (9 / 1,000,000) x 100 = 0.0009% of the volume of flue gas. The reason they stipulate “dry” is because when the emission is measured, the instrument typically removes all moisture (water) from the sample. The “ref. 3% O2” is required as a benchmark for the oxygen content in the flue gas. This is because the boiler will operate at various O2 levels, and the air district needs to normalize the measurements.

Sometimes, emission limits are referenced with different O2 levels for equipment in the same plant.  For example, on a boiler application, NOx may be listed as 9 ppmvd (ref. 3% O2) whereas for a gas turbine it might be 9 ppmvd (ref. 15% O2).  What does it mean when the O2 levels are different?

The difference in the example above is that O2 is referenced at 3% and 15%. Looking at actual numbers will help explain the difference. Let's say a boiler or gas turbine is firing natural gas and the heat input is 100 million Btu/hr. The fuel flow is the same for each case, about 4500 lb/hr. The air flow, however, will be different. 

For boilers, the burner typically runs at about 15% excess air (this is 15% extra air flow above the stoichiometric requirement). In other words, 15% of the air flow passes through the system without being oxidized. This is why the stack O2 (O2 is the extra oxygen in the boiler flue gas flow) is about 3% on a dry basis. This also explains why the 3% O2 benchmark is typically used.Based on the 100 million Btu/hr input and 15% excess air, the boiler air flow is about 81,000 lb/hr. 

On the other hand, gas turbines typically run at higher excess air levels as compared to boilers. To get 15% O2, dry in the stack, the excess air works out to about 230%. The air flow would be about 233,000 lb/hr with the gas turbine application. Stack flow, or the sum of fuel and air, differs in boilers vs. gas turbines:

Boiler stack flow:                            4500 + 81,000 = 85,500 lb/hr
Turbine stack flow:                         4500 + 240,000 = 244,500 lb/hr

You can see that for the same heat input of 100 million Btu/hr, the stack flow will be quite different for these two applications. This also explains why the O2 benchmark is different for these two cases. When comparing the NOx values in lb/mmbtu, we have:

9 ppmvd (ref. 3% O2) NOx firing natural gas is equivalent to 0.011 lb/mmbtu
9 ppmvd (ref. 15% O2) NOx firing natural gas is equivalent to 0.032 lb/mmbtu

This means that even though both 9 ppmvd volumetric numbers are the same, the numbers are actually different on a weight basis (i.e. lb/mmbtu).

Nationwide Boiler provides temporary and permanent solutions with our CataStak SCR System for boilers, gas turbines, and other demanding applications, to meet the most stringent emissions requirements. Contact us today for more infromation. 1-800-227-1966

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EPA Announces New Ozone Standard

Ground level ozone, which is created by combining the emissions of nitrogen oxides and volatile organic compounds in the presence of sunlight, can cause respiratory health issues and has been on the radar for decades. Since 1980, substantial progress has been made on ozone reduction and levels have fallen 33% while the economy continues to grow. Most recently, the Obama Administration and the Environmental Protection Agency (EPA) were evaluating the current ozone standard and proposed earlier this year a new decreased standard of 65 to 70 parts per billion (ppb). The current standard of 75 ppb was set in March of 2008, and some counties are still not in compliance.

The long awaited decision on the National Ambient Air Quality Standards was announced by the EPA yesterday, and the standard was reduced from 75 ppb to 70 ppb for ground-level ozone, produced by emissions released into the air from industrial plants, utilities, and vehicles. The EPA states that the public health benefits resulting from this new rule are an estimated annual savings of $2.9 to $5.9 billion in health care costs by 2025.

The EPA doesn’t expect states to comply to the new standard right away, and depending on the severity of the specific state’s ozone problem, the majority of states will have until between 2020 and 2025 to meet the standards. California, however, will have a longer period of time to comply, through 2037, due to its decades-long air pollution issues. Although fewer counties are in violation of the new standard than if they had lowered it to 65 ppb, 241 counties will be nonattainment for the 70 ppb standard, and it is estimated that 14 counties outside of California will not meet their deadlines.

States will be required to submit a state implementation plan (SIP) to the EPA for any designated nonattainment areas. The plans will outline how the State will attain and maintain the standard, and will contain control measures and strategies to reduce emissions. Plants that fall under the rule will likely be required to upgrade pollution equipment and monitoring systems to meet the new standard.

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CIBO's Emissions Control Conference

Representatives from Nationwide Boiler & Nationwide Environmental Solutions are headed to Portland, ME to attend CIBO's Industrial Emissions Control Technology Conference next week.

The EPA has been cracking down on boiler owners with multiple new rules and regulations to aid in the effort of lowering overall greenhouse gas emissions. In fact, this October a decision will be made by the EPA on new rules which may cause a drastic increase in non-attainment areas. This conference will help users understand (1) the current situation, (2) the potential rules and regulations and their timing, (3) the applicability, operation capabilities, and limitations of control technologies, and (4) the alternative compliance possibilities.

Visit Sean McMenamin and Bill Testa at booth #10 to learn how Nationwide's CataStak SCR system can be utilized in many demanding applications to lower NOx emissions and comply with the new standards.

We hope to see you there!

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Did You Know: Innovation with the CataStak SCR System

In 1999 we saw the first demonstration project of an SCR system for ultra low NOx performance and in 2001 Nationwide Boiler announced the CataStak SCR System, proven to reduce NOx emissions by as much as 90%.

The CataStak is a portable, low-temperature selective catalytic reduction (SCR) system consisting of a single-reactor housing with low temperature catalyst and an ammonia (aqueous or anhydrous) or urea (diesel exhaust fluid) injection option. This technology not only meets 5 ppm NOx, but outperforms burner technology and provides emissions reductions as low as 2 ½ ppm NOx. Advantages of the system include:

  • Easy field retrofit – no burner or fan changes required
  • Ammonia-free option – no special permits required
  • Low operating cost • Stand-alone operation – minimum operator intervention
  • Dramatic reduction in stack emissions – NOx, VOC & CO

In over 100 installations, the Nationwide Boiler CataStak SCR System has never failed a third-party compliance test and has provided peace of mind for plant owners knowing that their system will remain in compliance year-after-year, well past any current AQMD requirements.

Contact Nationwide Boiler today to learn how you can decrease your facility’s operating costs and lower your carbon footprint with a CataStak SCR System.

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