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In February of this year, the Boiler MACT rule was published in the Federal Register, causing the Environmental Protection Agency (EPA) to propose new regulations calling for system upgrades on boilers and auxiliary equipment in many plants. The costs associated with these upgrades can reach up to $35 billion according to the EPA, but because the costs will be specific to each individual plant, no one will know the real costs until the boiler equipment is evaluated to comply with new and future regulations. Boiler operators are hesitant to spend the money due to the uncertainty of regulations, but eventually something will need to be done.
There are resources available, and the U.S. boiler and combustion equipment industry is readily able to meet the demand for these system upgrades. Randy Rawson, President of the American Boiler Manufacturer’s Association (ABMA), said, “We have the workforce resources to meet the needs of our customers, as long as our customers don’t push compliance go the last minute.”
The largest air districts in California have passed rules that require NOx compliance as low as 5 ppm by the year 2015. Few burner manufacturers have been successful with developing new ultra low NOx (ULN) burner technology that easily and safely performs at 9 - 7 ppm NOx. Many users that have tried ULN burners suffer the consequences of high FGR or excess air rates that compromise not only efficiency, but also the operational limits of boiler equipment, resulting in limited turndown capabilities, flame pulsations and unstable operation.
Today, selective catalytic reduction (SCR) technology has taken over as the best available control technology for complying with ultra low NOx emission requirements. Nationwide Boiler, having invested in SCR technology for our rental fleet over the last ten years, has both the experience as an user and a supplier of the CataStak™ SCR system. Our SCR systems have met or exceeded emission requirements for over one hundred boilers, steam generators and gas turbines installations.
The Nationwide Boiler CataStak™ SCR system is proven to decrease emissions, increase energy efficiency, reduce fan horsepower and provide greenhouse gas / carbon reductions. Typical users can save significant energy costs by reducing flue gas recirculation which substantially reduces fan horsepower (HP) and when compared with a typical 9 ppm burner, fan HP can be reduced by as much as half.
If you are concerned or have questions about how your facility is planning to comply with local air quality regulations, send am email to firstname.lastname@example.org and together we can come up with a solution that can perform as low as 2.5 ppm NOx and pass any current air regulation with the lowest carbon footprint.
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