Don't Judge A Smokestack by its Plume!


Don't Judge A Smokestack by its Plume!

Anyone who gets out and about in this country has seen smokestacks of all sizes and shapes with their billowing plumes. Some people have a visceral reaction to what they see. They harken back to images from the 1920’s of Lackawanna and Pittsburgh when the steel mills filled the air with smoke so black the entire city was shrouded. Or they recall images from China before the Olympics where pollution was so thick that citizens had to wear masks just to walk in their own neighborhoods.

This is America, though, land of the Environmental Protection Agency (EPA). And, we have plenty of control over what comes out of smokestacks. What you see is not always what you think, and it’s important to know the difference and draw educated conclusions about what you see. If every time you see a smokestack plume, you think another company is polluting our atmosphere, there’s good news… It’s just not so. No country protects its people better.

Understanding Combustion

Let’s start at the beginning – combustion. It’s a dirty word, but one that is critical to the sustaining of our culture and lifestyle. It’s defined in Websters as “an act or instance of burning”. We utilize combustion in so many ways and so many facets of our lives - from our home stoves, furnaces, and water heaters that combust natural gas or oil to our wood fireplaces where we combust wood for heat and ambiance. Our cars, boats, ATV’s, motorcycles, and more combust gasoline, as do our snowblowers, lawnmowers, and weed whackers.

On a bigger scale, large manufacturers and power plants rely on combustion to exist.  Here are some everyday examples:

  • Power Plants: burn coal, natural gas, wood, garbage, yard waste, agricultural waste, tires, and more to create steam in large boilers, which drive large steam turbines, driving large generators to create electricity. Power plants also use oil and natural gas to run large gas turbines (much like an airplane engine), which spin huge generators to make electricity for this country’s power grid.

  • Cement Plants: burn natural gas and sometimes garbage in large kilns that are used in the process to create the cement.

  • Paper Plants: burn coal, wood waste, and natural gas in many different parts of the pulping process to allow for paper manufacturing. They also burn fossil fuels to create steam for heating needs in the paper-making process.

  • Ethanol Plants: burn natural gas in large boilers to create steam and heat used to turn corn into Ethanol.

  • Lumber Mills: burn wood waste from their sawmills to create steam that heats the kilns used to dry and season the wood. Excess steam can also drive steam turbine generators which supply electricity to the plant and even extra electricity to the nation’s grid.

  • Brick and Tile Plants: burn natural gas in the kilns and ovens used to dry and condition tiles and brick for the manufacturing process.

  • Food Manufacturers: burn natural gas in large boilers to make steam and hot water used in the sanitization and cooking processes. 

  • Universities: burn natural gas in large boilers to create steam for heating the campus and create hot water for use all over the campus.

Besides the above, there are many manufacturing operations all around the United States that burn some sort of fossil fuel to either make electricity to run their plants or make steam or hot water for use in their processes or to use directly in the plant. Without combustion, most of these plants and the products they produce would simply cease to be, and life as we know it would drastically change. 

The Byproducts of Combustion

Now let’s get back to combustion and those big plumes we see. We know that as a civilization, we rely on combustion. And we know that combustion creates byproducts that have been proven bad for our environment. Things like NOx (nitrogen oxides), SO2 (sulfur dioxide), CO (carbon monoxide), CO2 (carbon dioxide), HCl (hydrogen chloride), and Hg (mercury), for instance, are all byproducts of different combustion processes and nothing we want large quantities of in our atmosphere. But the important piece of information the layman is missing is how much the EPA controls what all these smokestacks are putting into our atmosphere.

When it comes to combustion, there is a range of how well it’s accomplished – and this is an important distinction. Efficient combustion produces much lower amounts of harmful pollutants than inefficient combustion. Think of it in terms of a campfire.

When your fire is rip-roaring, and the wood coals are all orange. If you look above the flames and barely see any smoke at all – that’s when it’s approaching complete combustion.  Now, if you throw a bunch of wet leaves in the fire, you’ll create a huge plume of white smoke – this is incomplete combustion where the moisture in the wood is not allowing for high enough heat to burn off everything before it enters the atmosphere.

If you throw a plastic bottle in the fire, you’ll create a plume of horrible black smoke. This is because the temperature at which the plastic is melting is not high enough to burn off all the chemicals in it. Both the leaves and the plastic in the campfire create different pollutants from incomplete combustion that are going into the atmosphere.

In older cars, you could see the results of poor combustion where oil was leaking and being burned in the engine causing huge amounts of white smoke. We’ve all seen diesel truck engines that spew massive amounts of smoke under stress while going uphill.  These are all examples of poor combustion, which leads to pollution. And the EPA is paying attention to all of it!

How the EPA Manages Combustion

Complete and efficient combustion is EVERYTHING! The EPA spends a lot of time and money making sure plants are directed and incentivized to achieve the best combustion possible. Large and small plants spend millions of dollars to ensure their combustion is complete and that pollutants created are removed from the exhaust stream before they enter the atmosphere. 

In many cases, what’s coming out of a smokestack at a single plant is cleaner and contains less pollution a year than a single farmer who burns a huge pile of scrap wood and vegetation in his open field. It can be cleaner than what a small army of gas-powered weed whackers, or a single house fire put out in terms of pollution. 

So why should that smokestack not keep you up at night? First of all, any plant, anywhere in the US, that has a large combustion process that will put exhaust into the atmosphere has to get an Air Permit from either the EPA or their local or State air agency. This permit will spell out exactly how much of each pollutant they can put into the atmosphere each year. The EPA tracks all the pollutants going into our atmosphere, and you can bet that it’s a far cry less than it was when a Lackawanna Steel Mill was belching black smoke in the 1920’s.

Once a plant has an air permit, the equipment must be designed to stay with the prescribed limits. Equipment manufacturers (boilers, turbines, burners, incinerators, and more) have gone to great lengths to make their combustion more and more efficient. 

Additionally, plants install pollution control devices after combustion that clean a great deal of the pollutants out of the exhaust before it goes to the atmosphere. There are “scrubbers” that use chemicals and media to remove SO2 and Mercury. There are baghouses that remove and collect those pesky particles of ash (even the tiny ones). There are SCR devices (selective catalytic reduction) that operate much like the catalytic converter in your car that removes NOx, and more.

So how does the EPA make sure their air permit limits are enforced? Several ways:

  1. After a new plant is built and started up, it must demonstrate through testing that the combustion from the exhaust is within the allowable limits. In many cases, a Continuous Emissions Monitoring System is brought to the plant, and direct measurements are made to demonstrate compliance.

  2.  In thousands of plants across the US, air permits require that Continuous Emissions Monitoring Systems (CEMS) are installed on the combustion source. This Continuous Emissions Monitoring System is an expensive piece of instrumentation ($100-200K) that constantly pulls a sample from the stack (after any pollution control devices and right before it exits into the atmosphere) and measures specific gases of interest (like NOx, SO2, CO2, CO, Hg, HCl and more). The information is compiled in a database, and reports are generated quarterly, which are sent to the applicable air agency (EPA, State, or local agency). If a limit is exceeded (NOx, for instance), an alarm is sounded, and the upset condition has to be immediately corrected. In some cases, the plant will need to be shut down until it’s corrected. In the event the problem is not fixed, the EPA can levy fines in the 10’s or 100’s of thousands of dollars (something every plant wants to avoid). Continuous Emissions Monitoring Systems are kept in check themselves with extensive requirements (all guided by the EPA) for daily, quarterly and annual testing. It is pretty safe to assume that the Continuous Emissions Monitoring Systems and the information from them are valid. The plant is remaining in compliance with its air permit limits/requirements. The air is safer because of them.

  3. For plants that don’t have a Continuous Emissions Monitoring System, annual testing may be required to show compliance. There are also requirements on fuel testing and other process restrictions that help ensure less pollution.

So now we know that the EPA is on our side and helping to ensure that the manufacturers we rely on are doing their best to reduce and control pollution. The United States has the most stringent rules compared to a large percentage of the world and is doing a huge part to control global pollution. 

Why Smokestacks Are Safer Than You Think

One more thing about smokestacks – and that’s smoke versus steam. We all know that when it’s cold outside, and we breathe out, condensation comes out of our mouths. This is the moisture in the warm air in our breath hitting the colder air and condensing. It’s the same for smokestacks. All combustion processes are “hot and wet”. Gases coming out of a smokestack are in the neighborhood typically of 200-400 degrees F. When this air hits our atmosphere, it condenses and can cause what looks like a huge cloud. In fact, this is just moisture… water… H2O – not pollution, and no cause for concern. It’s a naturally occurring condensation. 

If you’ve ever seen the large towers in pictures of a nuclear plant, you’ve seen the huge plumes pouring out of them. Those upside-down funnel shape towers are cooling towers, and what’s coming out of them is not even smoke or a product of combustion. It’s condensation from the process of cooling hot water.

So next time your blood pressure rises because you pass a smokestack and see a plume, remember that it’s not all bad. We rely on these plants to maintain our way of life, and what’s coming out is much less harmful than we may have thought, and there are plenty of safeguards and an entire government agency looking over them for us to keep us safer and safer.


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