Are Kilns Bad for the Environment? 3 Quick Facts

Are Kilns Bad for the Environment

published on November 19th, 2022

If you’ve ever used a kiln, you might have pondered about its environmental impact as it can reach temperatures of 1162-1240℃ (2124-2264℉) – a feat that requires a lot of energy. 

Kilns are bad for the environment because they are not always energy-efficient and give off high levels of pollutants.

Here’s everything you need to know about the environmental impact of kilns. 

1. How Do Kilns Affect the Environment?

There are different kinds of kilns, each with its own environmental impact.

They’re often used to make bricks and other building materials, art, or ceramic cutlery. 

They can be fired by wood, gas, or electricity. The exterior is usually made from brick, but you can also find metal kilns.

At a glance, you might think burning wood is more sustainable than using gas or electricity powered by fossil fuels. After all, trees are renewable.

With that said, trees take decades to mature, so although they are renewable, they are not easy to replenish.

Plus, since trees absorb carbon dioxide, they play a big role in the fight against climate change.

Cutting down and burning trees releases this CO2 back into the environment. 

Other kilns are powered by burning coal which is also non-renewable and releases CO2. 

Even more worrying, some kilns are even powered by burning discarded rubber tires.

While this sounds like a way to upcycle discarded tires, burning synthetic rubber is extremely detrimental to the environment. 

Research found that burning tires can potentially emit volatile organic compounds (VOCs), heavy metals, polycyclic aromatic hydrocarbons (PAHs), and particulate matter (PM).

VOCs are potent air polluters, while PAHs are toxic and carcinogenic. 

In the environment, PMs can cause acid rain, alter the pH of lakes and streams, and deplete soil nutrients. 

Emissions like this do not seem to be exclusive to kilns powered by burning tires. 

Research found that in order to manufacture approximately 3.5 billion bricks in Bangladesh every year, around 1.80 million tons of carbon dioxide is released.

These kilns also emit approximately 5.4 million kg of black carbon, 274 million kg of carbon monoxide, 14 million kg of sulfur dioxide, and 21 million kg of particulate matter.

Although black carbon does not remain in the atmosphere as long as CO2, it has a considerably higher warming effect, while sulfur dioxide can mix with other compounds in the air and create acid rain.

Aside from causing air pollution, these emissions can also negatively impact soil health, with the likes of heavy metals such as cadmium, arsenic, and lead being found. 

These substances are toxic. Some emissions from kilns, like formaldehyde, which is also toxic, are actually due to clay impurities.

While no kiln is free from emissions, it was noted that the most detrimental from an environmental standpoint were kilns fueled by rubber.

It was also found that contemporary brick kilns – which are technologically advanced – were less harmful than those fueled by coal. It is not clear what these kilns are being powered by.  

However, that does not mean they’re eco-friendly by any means. These kilns are not energy-efficient and still release emissions. 

On average, kilns seem to be only 50% energy-efficient, meaning it requires a lot of energy just to fulfill their function, as much is lost heating the kiln up or escaping. 

When it comes to being energy-efficient, the best choices seem to be vertical shaft brick kilns for small-scale production and the hybrid Hoffman kiln for bigger projects.

The Hoffman kilns save energy by transferring heat to adjacent tunnels. Vertical shaft brick kilns can reuse air as they face upward.

2. Are There Eco-Friendly Kilns?

There do not seem to be any truly eco-friendly kilns, but some types of kilns are more sustainable and less harmful to the environment than others.

As established earlier, relying on fossil fuels is not only unsustainable because they’re not renewable, but using gas or burning coal and tires releases harmful compounds and greenhouse gasses. 

Kilns powered by renewable energy would arguably be the greener choice.

Most energy use worldwide is still predominantly reliant on fossil fuels, so most electric kilns are not powered by renewables. 

As mentioned earlier, some of the emissions, such as formaldehyde and even greenhouse gasses like carbon dioxide, are the result of clay impurities, so even the most sustainable kiln will still likely have some negative environmental impact. 

When it came to CO2 emissions as well as PM and suspended particulate matter (SP,) research found vertical shaft brick kilns were the more sustainable, followed by zig-zag kilns and tunnel kilns. 

The difference in emissions was down to energy consumption, with the most energy-hungry kilns giving off the most emissions. 

So overall, the greener choice appears to be vertical shaft kilns and electric kilns powered by renewables. 

3. What Are Eco-Friendly Alternatives to Kilns?

There are not many eco-friendly alternatives to kilns.

Research found that compacting ceramics at room temperature using water and calcium carbonate nano powder is energy-efficient and does not cause as much pollution.

What’s more, the carbonate nano powder could be sourced from waste gasses from power stations or CO2 from the atmosphere, meaning this technology could potentially be carbon-neutral or even carbon-negative. 

However, these do not appear to be mainstream, so kilns appear to be the most popular method without a true alternative for the foreseeable future.

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