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O2 Trim for Increased Boiler Efficiency & Emissions Compliance

Given today’s awareness to the advantages of minimizing energy usage and carbon footprint, boiler operators and plant managers are always on the lookout for ways to improve boiler efficiency and ensure emissions compliance. With improved efficiency, fuel usage is minimized which in turn reduces the carbon footprint (i.e. reduces CO2 emissions from the boiler) and reduces issues around emissions compliance. One way to increase boiler efficiency is to use oxygen trimming, or O2 Trim, at the stack.

A typical burner will operate from 3 to 4% O2 at 50% boiler load and higher. This stack O2 concentration corresponds to the amount of excess air at the burner, and excess air is required for burner operation to assure complete combustion of the fuel.  For example, for natural gas firing, 3% O2 corresponds to 15% excess air. During commissioning, the burner service engineer will set the fuel / air ratio so that there is always excess air over the firing range of the burner.  The service engineer must also keep in mind that ambient conditions (mainly air temperature changes) will affect air density which will affect the burner fan air flow output.  On cold days the fan will flow more air due to a higher air density, and on hotter days the flow will be less. Varying air flow conditions can adversely affect burner operation.

Boiler efficiency is affected by the excess air concentration in the flue gas. The rule of thumb is that for every 5% more excess air, boiler efficiency decreases by 0.5%. If not adjusted, the boiler stack can vary by at least 2% O2 (i.e., if normal operation is 3% O2, it can increase to 5% O2 on a cold day). That corresponds to about 1% boiler efficiency loss. Saving 1% efficiency over a year operation can save big on fuel costs. If the normal fuel bill is $10,000,000 per year, you would save $100,000. Adding an O2 Trim system would cost a fraction of that amount (assuming a 150,000 lb/hr steam boiler or smaller), providing a quick and worthwhile ROI. So, what exactly is an O2 Trim System?

Many burners use a control system where the fan air flow does not vary based on air temperature.  As explained above, the air flow can vary based on ambient conditions causing the stack O2 to vary; this can be solved by adding O2 Trim to the control system. O2 Trim is an air flow trimming system where stack O2 is measured (using an O2 probe) and the air flow is adjusted (trimmed) based on the reading. It’s a closed loop control system since changes in air flow will directly affect the stack O2 reading (assuming fuel flow is the same). By maintaining a consistent air flow rate, O2 trim reduces fuel usage in turn increasing boiler efficiency.

In addition to increased boiler efficiency, utilizing O2 Trim will ensure stable and safe O2 levels. On hot days with reduced fan air flow, the stack O2 level can drop to dangerously low levels and boiler emissions can go out of compliance. With O2 monitoring, alarms can be created to alert the boiler operator to either reduce fuel flow or increase air flow, to return to safe operating conditions.  

O2 Trim isn’t ideal for every boiler, though. Due to the residence time in the boiler and ducting, it takes time for the changes in burner fan flow to reach the stack. This causes a time delay with an O2 Trim system, which works well for boilers with slow load changes. However, for systems with rapid boiler load changes, the O2 Trim system typically can’t keep up easily and it is often “hunting” for the optimum air flow.

If you are interested in learning more about whether an O2 Trim System will benefit your operations, reach out to one of our qualified parts specialists or call 800-227-1966. Check out other articles on Nationwide’s Boiler Blog for more tips and tricks for improved boiler efficiency, routine maintenance, and more!

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Meeting Peak Season Demand with Rental Boiler Equipment

Tomato season is here, and we already have a 70,000 lb/hr, 400 psi design trailer-mounted rental boiler on location at one of our customer sites to support peak season steam demand. This boiler is rented annually in the Central Valley of California for three to four months during the tomato processor’s short but critical production season. To meet the requirement of 5 ppm NOx, the boiler is supplied with an ultra-low NOx CataStak SCR System. This solution allows the facility to operate their own boilers without overworking them, while complying with local air regulations and satisfying seasonal demand.

Some years ago, the company identified a bottleneck in its evaporation system that hindered peak production capacities. The bottleneck was easily resolved; however, it would take more steam to fully realize the increase in production. Although the existing boilers were capable of running the newly found evaporation capacity, the increased production required the existing boilers to operate at 100% output continuously, leaving no room for margin and no buffer against any process anomalies. After evaluating the cost of investing in a new boiler, the detrimental effects of operating the existing boilers at 100 percent output, and the process vulnerabilities of having no excess steam capacity, the decision was made to rent a supplementary steam boiler on an annual basis.  

Many industries face periods of increased process steam requirements and to satisfy demand, steam can be supplemented with a temporary rental boiler. This practical solution allows facilities to maximize the resources needed to meet current, short-term and long-term steam needs. A short-term or long-term rental solution can save time, conserve capital, minimize risk and maximize available resources.

Check out our past article from Today’s Boiler Magazine to learn more about how temporary boilers can support seasonal steam demand, and contact us today if a rental boiler may be the solution to your peak season needs!

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Decarbonization: What Does it Mean for the Rental Boiler Industry?

Decarbonization relates to the reduction or ultimately the extinction of greenhouse gas emissions released into the atmosphere. According to the EPA, Carbon Monoxide (CO2) makes up the vast majority of greenhouse gases released during the combustion of fossil fuels. In addition to CO2, smaller amounts of methane (CH4) and nitrous oxide (N2O) are also emitted during the combustion process. With majority of rental boilers being natural gas or oil fired, what does this mean for the future of rental boilers?

With over fifty years in the industry, Nationwide Boiler has excelled through similar hurdles. In 1995, we became the first and only rental boiler company to convert our entire fleet of watertube boilers to low NOx levels of 30 ppm. In 2001, we started actively utilizing our CataStak™ SCR system on package watertube rental boilers for ultra low NOx compliance, and in 2011 we developed the product further announcing the ammonia-free / urea-based CataStak™ SCR. These and other initiatives were accomplished with sustainability and environmental improvements in mind.

While our CataStak™ and EconoStak fuel efficiency products help the environment by reducing tons of greenhouse gas emissions, we realize the need to consider an alternate non-fossil fuel with the potential to replace the “transitional” fuel of natural gas. Luckily there are some alternate energy solutions available today, including bio-fuels, hydrogen-fired, solar, hydro, and electric.

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Keeping up with the Compliance's

As much as we sometimes wish they would just go away, compliance regulations are here to stay.  Overall, regulations are put into place by local governing agencies for the health and safety of the public, environment and plant operations.  These are all items which we agree must be top priority. However, the most difficult part of regulations is interpreting, comprehending, and staying current with new rules, revisions, and updates.  Combine that with the fact that the applicability of regulations can also be daunting -- things just get harder and harder.  

When it comes to NOx compliance, Nationwide Boiler has you covered.  We have helped hundreds if not thousands of customers meet both local and national NOx compliance regulations ever since the Clean Air Act passed in the 1980’s.   Our boiler rental fleet is equipped with the most advanced burners the industry has to offer and our new and reconditioned boilers all include energy efficiency upgrade options and CataStak™ SCR System component add-ons, proven to reduce NOx to levels as low as 5 ppm.

Our most recent compliance success story is a project we recently completed with NRG Energy Center San Francisco.  Nationwide Boiler provided a single Ammonia-Free CataStak™ SCR System for two 55,000 lb/hr natural gas-fired boilers that were required to operate at 9 ppm NOx levels as governed by the Bay Area Air Quality Management District (BAAQMD).

Read more about this project and how it demonstrated a simple method of reducing greenhouse gas emissions without the use of a standard ammonia-based SCR in the fall edition of Today’s Boiler.

If you need help keeping up with compliance's, call us today at 510-490-7100.  We can help.

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