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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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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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White House Executive Order Supports Combined Heat & Power Initiative

Last week the White House announced an executive order supporting Combined Heat & Power (CHP) and industrial energy efficiency.  The order calls for a national combined heat and power deployment goal of an additional 40 GW by 2020.

CHP systems can reach efficiencies above eighty percent (80%) and currently supply twelve percent (12%) of U.S. energy capacity. There is approximately 82 GW of CHP installed in the U.S. and industry estimates indicate the technical potential for additional CHP at existing sites in the U.S. is approximately 130 GW (plus an additional 10 GW of waste heat recovery CHP).

Investments in industrial energy efficiency, including combined heat and power, offer significant benefits to manufacturers, utilities and communities across the country, including:

    •    - Manufacturers could save at least $100 billion in energy costs over the next decade, improving U.S. manufacturing competitiveness

   - Meeting the 2020 goal could mean $40 to $80 billion of new capital investment in American manufacturing facilities and helps to create jobs

   - Offering a low-cost approach to new electricity generation capacity to meet current and future demand:  Investments in IEE, including CHP, cost as much as 50% less than traditional forms of delivered new baseload power

    •    - Significantly lowers emissions:  Improved efficiency can reduce nationwide GHG emissions and other criteria pollutants.

USCHPA Executive Director, Jessica Bridges, said "CHP technology can be deployed quickly, cost-effectively and with few geographic restrictions. Establishing this national goal toward greater CHP deployment will significantly advance cleaner energy generation in the U.S., benefit the environment, and help create much-needed manufacturing and industrial jobs. I applaud the White House for its efforts to support clean power generation through CHP and pledge the combined heat and power industry's support to help achieve this goal."

USCHPA is a trade association whose membership includes manufacturers, suppliers, and developers of combined heat and power (CHP) systems.  CHP lowers demand on the electricity delivery system, reduces reliance on traditional energy supplies, makes businesses more competitive by lowering their energy costs, reduces greenhouse gas and criteria pollutant emissions, and refocuses infrastructure investments toward next-generation energy systems. CHP is a proven and effective energy resource that can be immediately deployed to help address current and future global energy needs by incorporating commercially available and domestically produced technology.  For more information, visit www.uschpa.org.

In support of the Executive Order, the Department of Energy and the Environmental Protection Agency released a new report Combined Heat and Power: A Clean Energy Solution  that provides a foundation for national discussions on effective ways to achieve 40 GW of new, cost-effective CHP by 2020, and includes an overview of the key issues currently impacting CHP deployment and the factors that need to be considered by stakeholders involved in the dialogue.

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Boiler Basics 101: Economizers for Increased Efficiency

The price of fuel is constantly fluctuating and with it comes creative ways to be more economical. Finding methods to be more energy efficient is never a waste of time. In the boiler room, efficiency improvements can be found by many sources, however, a common option for energy savings includes the use of an economizer. What is an economizer? The economizer is a fabricated assembly of finned tubing that captures waste heat extracted from the boiler’s stack flue gases; the exhaust that leaves the boiler stack (or “flue”).

It’s all about the principle of Heat Transfer. While low temperature water, or feedwater, enters a boiler system, high temperature flue gas exits. An economizer captures heat from the flue gas that would typically go to waste, and utilizes it to preheat the feedwater. By doing this, an economizer is able to increase thermal efficiency by decreasing the energy required to heat the water to steam. This will typically result in a reduction of 1% in fuel cost per 10 degree rise in feedwater temperature. Overall, an economizer can be a major cost savings for boiler owners and will easily provide a quick return on investment.

The economizers’ simple technology and static parts provide longevity and low maintenance, and they are available in multiple designs and configurations. Conventional economizers are cylindrical or rectangular and come in a range of sizes for both firetube and watertube boilers. Rectangular designs are more commonly used for larger industrial watertube boilers, and can be configured for vertical or horizontal gas flows, finned or bare tube design, and other additional options if needed. A condensing economizer can improve waste heat recovery even further by cooling the flue gas below its dew point, reclaiming both sensible heat from the flue gas and latent heat by condensing the flue gas water vapor.

BOILER EFFICIENCY COMPARISON
  Combustion Efficiency at
4% Excess Oxygen
Stack Gas
Temperature
 Boiler  78% to 83% 350F to 355F
 Boiler with Standard Economizer  84% to 86%  250F to 300F
 Boiler with Condensing Economizer  92% to 95%  80F to 150F


When determining whether an economizer is ideal for your boiler equipment, the location of the economizer into stack is important. To ensure the most thermal recovery during the process, you need to make sure the economizer is installed as close to the furnace breach as possible. This will help avoid thermal loss and cooling.

At Nationwide Boiler, we offer our EconoStak economizer as an optional addition (or a standard addition in some cases) on our fleet of watertube rental boilers. The EconoStak consists of the economizer as well as all of the associated piping and structural supports required for very efficient and safe operation. In addition, we are a West Coast representative for E-Tech Heat Recovery Systems, a leading provider of economizers for new, replacement, and retrofit applications.

Contact Nationwide Boiler today to see if an economizer is the right option for you, and be sure to check out our previous Boiler Basics 101 blogs. We review various topics each month, so stay tuned for the next edition!

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Monday, 09 December 2019 08:15
Guest — Emma
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Tuesday, 10 March 2020 08:02
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