Waste Not, Want Not

Turning waste into energy

People throw out a lot of garbage, but there are some places where waste is worth its weight in gold.

Houweling’s Tomatoes is a business that grows and sells greenhouse vegetables. Company chairman Casey Houweling runs the business. He has always been interested in making sure the company’s greenhouses really are “green” — meaning friendly to the environment. A green business may use fewer resources than similar businesses or make a very low level of carbon dioxide (CO2) and other air pollutants. These pollutants are sometimes called greenhouse gases because they trap warm air in Earth’s atmosphere like a roof traps warm air in a greenhouse. In recent years, Houweling’s took the “green” concept a step further, says David Bell, a spokesperson for the company.

Good Neighbors

The company decided to search for a new place to build a greenhouse that would let them capture and reuse industrial heat and CO2 waste to grow tomatoes year-round, he says. Mona, a small town in the central region of Utah, was exactly what the company was looking for. After three years of planning, Houweling’s built a greenhouse next door to a power plant.

The power plant creates electricity by burning natural gas. Besides electricity, the process produces heat and carbon dioxide. Before Houweling’s came to town, these were considered waste products. Houweling’s worked with the owner of the power plant, a company called Rocky Mountain Power, to funnel the extra heat and carbon dioxide into the greenhouse. The heat keeps the greenhouse toasty warm during cold Utah winters, and the tomatoes grow faster because the carbon dioxide helps fertilize them.

Rocky Mountain Power provides electricity for customers in Utah, Wyoming, and Idaho. The plant in Mona is what’s called a combined-cycle power plant. That means that it initially burns natural gas to turn two big turbines, which look like the fan in a jet engine. They’re connected to a generator. When the turbines turn, they create electricity through the generator. The exhaust from that process is sent to what’s known as a heat recovery steam generator, where the extra heat boils water to create steam. The steam turns another turbine, which produces electricity through the generator too.

Combined-cycle power plants can create up to 50 percent more electricity than simple-cycle power plants. In simple-cycle power plants, electricity is generated only by burning natural gas, without using the extra heat to boil water and produce more electricity with the steam. Combined-cycle power plants are also known to be reliable, an important quality for energy producers. Customers are counting on the lights turning on when they flip the switch!

“As customer needs increase, we have to increase our generation, and as customer needs decrease, at night, we have to decrease our output,” says Dave Eskelsen, a spokesperson for Rocky Mountain Power. “I like to say electricity is the only product that is manufactured and delivered in the same instant the customer asks for it.”

Eskelsen says the process of siphoning off the waste heat and carbon dioxide doesn’t affect the power plant at all, and the company’s leaders were happy to work with Houweling’s. Capturing the waste carbon dioxide and heat means that original material used by the power plant gets a third use.

“Our company has a long interest in environmental responsibility,” he says. “Our first and highest duty is to supply our customers with electricity, so we don’t do a lot of cutting-edge or experimental work in that area.” But when another company had an innovative, “green” idea, Rocky Mountain Power signed up.

Heat Plus Power

Reusing waste is a smart recycling practice in general. Using the leftover heat from a power generator has a term and history all its own: cogeneration, or combined heat and power (CHP). Although it’s uncommon in the U.S. today, it’s not a new idea. In 1882, American inventor Thomas Edison used the idea of CHP in the very first commercial power plant, Pearl Street Station in New York City. CHP works well when a power plant is near its customer for leftover heat, such as the Houweling’s greenhouse.

The idea stuck around through the early years of commercial electricity but grew less popular as consumers began to demand more and more power and companies started building larger, more centralized power plants to produce enough electricity to keep up. Because CHP plants tend to be more complex to build, simpler forms of power generation ruled.

Garbage to Burn

But in Europe, CHP is much more widely used, especially in Sweden. There, the fuel of choice is not natural gas, but garbage. People in this Scandinavian country recycle most of their household waste. Anything that can’t be reused or recycled is burned for heat and hot water for millions of people. In 2016 alone, the country burned nearly 2.3 million tons of household waste for energy. They’re so efficient with recycling or reusing waste that they sometimes don’t have enough of their own waste to burn and get more from other countries, which pay Sweden for the service. But all of this didn’t happen overnight.

Sweden started burning garbage for heat and energy in 1904. Through the 20th century, officials encouraged residents to separate recyclables. In the 1970s, 38 percent of household waste in Sweden was recycled. Today, more than 99 percent of Sweden’s waste is recycled or burned in power plants. By comparison, in 2018, the last year that data is available, Americans recycled just 32 percent of their household waste. Anna-Carin Gripwall, the communications director for Swedish Waste Management, says Sweden is so good at recycling in part because the government has worked hard to make recycling easy and to tell people why it’s important.

“If you can give them the reason why they should recycle, they’re more likely to do so,” Gripwell says. “When everyone communicates the same thing, it gives more impact.”

Recycled paper becomes new paper products. Recycled plastic becomes new plastic products. And recycled food scraps turn into compost and dirt. About half of household waste can’t be recycled into new things, so it’s burned for energy instead. The fires heat water, which generates electricity and also helps heat homes. Because burning is a dirty process, the smoke runs through a series of air filters before it escapes the plant.

Though some might think otherwise, Gripwell says, “Basically, what comes out of the chimney stacks is water.” The dirty air filters are even reused afterward. They help fill abandoned mines.

Worth a Second Look

The United States is far from Sweden’s rate of recycling and tends to use different fuel sources. But the efficient combined-cycle power plant is common here. And some American companies are looking at CHP again.

Houweling’s, the greenhouse attached to the power plant, expanded in size in recent years. As of 2021, it could grow 750 acres worth of tomatoes with a fraction of the resources. Bell says it is able to do more with the heat and carbon dioxide from the power plant. Turning greenhouse gases into greenhouse vegetables? Sounds like a pretty tasty plan.