Boiler Blog | Nationwide Boiler Inc.

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

Nationwide Boiler's Director of Environmental Solutions, Sean McMenamin, provided content for this month's issue of Process Heating Magazine. The topic of discussion this time around is reducing NOx emissions and improving overall boiler efficiency.

Sean has provided six tips to ensure the highest possible thermal efficiency, and lowest possible NOx output. This includes:

1. Reducing Stack Gas Temperature to Increase Efficiency
2. Managing Excess Air Levels for Optimum Performance
3. Utilizing Flue Gas Recirculation (FGR) to Reduce NOx Emissions
4. Selective Catalytic Reduction for Ultra-Low NOx Performance
5. Combining Economizers & SCR Systems for Emissions & Efficiency Gains
6. Monitoring Emissions & Efficiency Performance

For additional details related to these tips and tricks for reducing NOx and increasing efficiency, check out the full article in Process Heating's September 2018 issue!

With California having the most stringent emissions requirements in the country, it is important to be well versed on any and all rules and regulations when buying a new boiler or renting a temporary boiler. This is our final installment of the 3-part series on air permit compliance for boilers in California (be sure to check out part 1 and part 2 if you haven’t already).

Nationwide Boiler maintains a fleet of rental units that are sub-9 ppm NOx and pre-permitted for use in the SCAQMD. We take care of the bulk of the permit work saving our customers an exponential amount of time (no waiting for the application to be approved), and we pay for any processing fees. This allows for quick installation and start-up of a temporary boiler, which is extremely valuable in an emergency outage. The only requirement of our customer is the source testing of the equipment, if the source test is due. Most of these pre-permitted boilers require source testing on an annual basis, and the source test must be done at a job site within the county’s jurisdiction.

The SJVAPCD does not allow the pre-permitting of rental boilers, but they do have a program called the Temporary Replacement Emissions Unit (TREU) which can be utilized when a rental is needed  in a pinch. This program contains an application shield provision which allows renters to install a temporary boiler in place of an existing permitted boiler that is down for repairs without having to get a new permit for the rental boiler. In order to qualify for the TREU Program, the rental boiler being installed must have a heat input equal to or less than the unit it is replacing. Plus, it must not have the potential to produce more emissions than the current permit allows. There is a time limitation to this program; the temporary boiler can be on-site for a maximum of 180 days within a 12-month period.

If you are outside of the two territories listed above, don’t fret! Nationwide Boiler can assist with the permitting process as needed. In addition, utilizing a pre-permitted boiler in a location other than the SCAQMD does have its advantages and can help expedite the permitting process.

Within the RECLAIM standards, Rule 1146 outlines specific guidelines for boilers, steam generators, and process heaters that have a heat input of 5 mmBtu/hr or greater, that are utilized in all industrial, institutional, and commercial operations. This rule has changed several times, and at the end of 2018, another revision to the rule was adopted. All Group 1 units (>/= 75MMBTu/hr) as well as Group II units (20 - 75 MMBTu/hr) with an existing permit limit greater than 2 ppm must comply with a 5 ppm NOx limit. In addition, facilities that qualify must be in compliance by 2022 – 2023. The table below outlines all equipment and current limits based on category and heat input.

If your facility falls into the RECLAIM bubble, Nationwide Boiler can assist in bringing your stationary equipment up to current standards to comply with the latest rules and regulations. Our CataStak™ SCR system is proven to reduce NOx emissions to as low as 2.5 ppm on boilers, fired heaters, and other demanding applications. Imagine what we can do for your facility to get you in compliance with RECLAIM!

Stay tuned for part 2, where we will outline specific rules and regulations within the SJVAPCD.