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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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New 250HP Package Boiler Achieves 5 ppm NOx - And the Outlook for a 2.5 ppm Solution is Bright

Promoting a sustainable future is the focus now more than ever in the boiler industry, and Nationwide Boiler has been at the forefront of identifying and supplying reliable ultra-low NOx solutions to industry for more than three decades. Today, we can proudly state that we have achieved 5 ppm NOx performance with a recent ultra-low NOx burner/boiler package - and the outlook is bright for this ultra low NOx burner. 

With half of the state covered in forests, it is no surprise that Washington is one of the country's largest lumber and plywood producers. Exterior Wood is a leader in the industry for pressure treated wood products and is in the same business park as Nationwide Control Solutions, a division of Nationwide Boiler Inc. Facing operational issues with their existing 700 HP CB boiler, Exterior Wood consulted Nationwide Control Solutions to evaluate their system and recommend the best solution to address each of the problem areas.

The problem areas that were identified included: (1) the burner head assembly constantly getting burnt out and replaced, (2) the combustion air fan motor which was rebuilt many times without a like-in-kind replacement option, and (3) stack temperatures at low fire were so low that the stack gases would condense in the stack and rain down corrosive condensate on the boiler tubes. Plus, the boiler tuning was becoming increasingly difficult to meet their local emissions requirements due to the age and condition of the existing burner controls. After a thorough review of existing equipment, site conditions, and natural gas usage reports, we concluded that the boiler was greatly oversized and that continuing to replace and rebuild components was not a viable solution for the longevity of the system.

Based on these results, our team offered a new 250 HP Superior package firetube boiler with an Oilon LN30 ultra-low NOx burner that was capable of not just meeting but exceeding their NOx emissions requirements of 12 ppm. Upon start-up and source testing, the ultra-low NOx capabilities of the Oilon burner were proven with the impressive results of 5 ppm NOx and 0 ppm CO output. Plus, the LN30 recently completed additional testing on a boiler from Nationwide's stock inventory, with results that prove it to be a reliable 2.5 ppm option.

Built upon cutting-edge technology, this new Superior Boiler/Oilon burner package will provide Taiga / Exterior Wood with many years of low maintenance and reliable operation. And, with a commitment to sustainability and efficiency, this solution ensures future emissions compliance to help minimize environmental impact.

Check out Nationwide Boiler's recent press release for additional information. If you would like to learn more about how you can achieve ultra-low emissions requirements, contact us or call 1-800-227-1966.

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Best Performance Standards (BPS) Boiler

Are you looking for a boiler that offers the latest boiler technology in emissions and efficiency? Does your boiler need to meet an upcoming compliance deadline date and you are not sure what to do? If so, you have come to the right place.

Nationwide Boiler continually seeks technology that offers the maximum emission reductions and the highest thermal efficiency that may provide valuable emission credits and energy rebates. Our Best Performance Standards Boiler keeps this tradition alive and is equipped with the latest technology to ensure you are operating with the greatest efficiency possible.

The BPS boiler is designed with the latest efficiency upgrades (high turndown controls, O2 trim, VFDs, and extended surface economizers) and includes the CataStak SCR System for 2.5 ppm NOx.  Nationwide's patent pending NOx reduction control system is also included for precise ammonia flow control.

The yearly efficiency savings and emission reductions that are quickly achieved with a BPS boiler provide a greater return on investment and most importantly, peace of mind with compliance assurance for years to come.

Call us today to obtain a free product bulletin and to learn more about our BPS solution.

BPS

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