Your Guide to Green Boiler Technology

Many companies are looking to become more environmentally friendly whether it’s due to new regulations or wanting to reduce their carbon footprint. For some aspects of a business, this is fairly straightforward. Looking into green boiler technology, however, can be complicated. This guide is intended to introduce you to the factors that determine an “eco-friendly boiler,” as well as the types of industrial boilers that have a reduced carbon footprint.

What Determines a Green Boiler?

The first question most people have is “what makes a boiler eco-friendly, anyway?” There are two main factors that go into determining just how green a boiler is: energy efficiency and clean emissions.

Energy Efficiency

Boilers, at their core, are energy transfer devices that convert the energy stored in gas, fuel, or electricity to useful heat energy. The overall efficiency of a boiler system is the percent of useful energy transferred into the boiler export medium (steam, hot water, etc) to the input energy (from combustion source or electricity).

Typically, steam boilers are around 80 - 85% efficient but there are a plethora of heat recovery devices available to capture more of that lost energy. Hot water boilers are able to use condensing and other technologies to achieve 90 - 98% efficiency. This kind of extreme efficiency reduces the carbon footprint of the boiler, making operations considerably greener.

Clean Emissions

The next aspect of a green boiler is the emissions output by the boiler. There are many components to boiler exhaust but the typical items of regulation are:

CO: Carbon Monoxide

Newer burner designs account for CO creation by limiting unburnt fuel, utilizing FGR, and having proper combustion design. Under 100 ppm is typically acceptable but should be reduced as much as possible, depending on local authority.

NOx: Nitrogen Compounds

Typically consisting of nitric oxide (NO) and Nitrogen Dioxide (NO2). Most regulations call for NOx emissions to be less than 30 ppm. Some stricter regulations are seen, especially in California, with < 9 ppm or < 5 ppm.

SOx: Sulfur Compounds

Typically consistent of sulfur dioxide (SO2) and sulfur trioxide (SO3). Formed by the combustion of fuels containing sulfur. Utilizing ultra low sulfur fuels is the primary method of SOx emission reduction.

Particulate Matter

Consisting of many different types of compounds, broken down into two categories PM and PM10. PM10 being the emissions with a diameter less than 10 microns. Using clean fuels reduces PM/PM10 substantially. Larger boilers utilize emission control devices to lower levels such as: precipitators, scrubbers, and baghouses.

Types of Green Boilers

Now that we know what exactly a green boiler is, let’s go over the different types of boiler systems that are considered green or more eco-friendly. Each type of boiler has its own advantages and drawbacks. However, to find the right one for you will always be dependent on your priorities and circumstances.

Condensing Boilers

Condensing boilers are very popular in the hot water boiler market. The extra energy is extracted from the flue gas being brought below its dew point and condensing. Typically the flue gas is routed through the colder return water connection to ensure maximum condensing of the gas (since it is interacting with the coldest water in the system). This condensation releases energy into the boiler and greatly reduces the wasted heat energy from escaping out the exhaust stack.

Due to the nature of steam boilers, this can only be accomplished by a condensing economizer. The biggest benefit is seen when the water being heated is well below the dew point of the flue gas.

The other benefits of a condensing boiler are very high energy efficiency and the fact that they are readily available in the hot water boiler market. There are a few drawbacks to the condensing boiler though. Namely, more expensive maintenance and the complexities of utilizing it in a steam system.

Electric Boilers

Instead of burning fuel or gas, an electric boiler uses electricity to power heating elements inside of the boiler to transfer energy. Because electricity does not need to be generated with fossil fuels and can be created with renewable energy, it can be more carbon-neutral than fuel or gas boilers. Additionally, electric boilers have zero emissions, making them much cleaner than other boiler systems.

The advantages of electric boilers include quick and accurate controls and the lack of complex combustion equipment. The disadvantage of electric boilers is the high electric demand, which can make running the boiler too expensive for some companies.

Biomass Boilers

Biomass boilers use agricultural byproducts as fuel, a really interesting solution to making a more eco-friendly boiler system. Anything from wood, bark, agave fiber, rice husk, chicken manure, sugar cane bagasse, king grass, MSW, construction debris, nuts, shells, husks, paper, card/board products, hog fuel, sawdust, shavings, or sludge can be used to generate power for the boiler.

Not only are they considered carbon neutral, but also biomass boilers are a great way to dispose of wood and other types of agricultural waste. There are a few drawbacks as well. Biomass boilers are much larger than other types of boilers, and they can be more expensive upfront to purchase. However, it’s likely that they will save you money in the long run on fuel costs, as gas and oil prices rise.

How to Reduce Boiler Emissions

If you’re not ready to replace your entire industrial boiler system right now with a more environmentally friendly boiler, there are other options to make your system greener without such a large upfront cost.

Selective catalytic reduction (SCR) can be added to your boiler to reduce emissions. SCR utilizes ammonia injected into the flue gas stream as a reducing agent which then comes in contact with a catalyst to turn the NOx into N2 and H2O.

Ammonia typically is available in 3 different ways:

  1. Anhydrous Ammonia is the easiest to use in the SCR system, but the most difficult to handle.
  2. Aqueous Ammonia requires storage and vaporization equipment but is easier and safer to handle than anhydrous.
  3. Urea is the easiest to handle but the least effective type of ammonia.

In addition, ultra-low NOx burners can be outfitted onto your boiler system. This is a new technology and is currently very expensive, but they are very effective at reducing emissions and increasing energy efficiency.

All in all, there are green boiler solutions for every circumstance and setup. While converting your boiler system can come with a large upfront cost, depending on the solution you choose, you can save money in the long term with a more energy-efficient system while preparing for increased or existing government regulations on emissions.

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