Waste to Energy

As a boiler fuel, biomass has shown great promise while suffering from a slow development history. One factor limiting its use has been the combustion system. For the most part, conventional grate-fired boilers have been the only option. Today, the most efficient approach to burning biomass to produce electricity and steam is fluidized bed combustion (FBC). Whether you choose FBC or grate, biomass presents unique challenges to control system designers.

Most countries are trying to increase the percentage of their electricity supply that comes from renewable sources. But because capital costs for renewable generation still, in most cases, are higher per kilowatt-hour than for fossil-fueled power, governments are looking at all options for encouraging the development of greater renewable capacity. Feed-in tariffs (FITs) are one policy tool that has been used, most notably in Europe. Now North America is testing FITs as well.

Power plant operators, especially those located in countries with enforceable carbon emissions standards, are concerned about their CO₂ emissions. But for Helsingin Energia—which provides power, heating, and cooling for Helsinki, Finland’s 300,000 residents—the main concern is local warming, not global warming. In Helsinki, temperatures on midsummer afternoons only reach an average 21C, and for half the year daytime temperatures are below 10C.

An Australian sewage plant this April began using treated wastewater falling down a 60-meter (m) shaft to produce its own power.

When it is completed, later this summer, the UK’s Drax Power Station biomass facility will become the largest dedicated cofiring project of its kind in the world. As U.S. coal-fired generators come under increasing pressure to cut emissions and take advantage of incentives to promote power generation from renewables, Drax offers an example of what is possible.

As U.S. utilities increase the percentage of renewable energy in their generation portfolio, they must deal with a number of key issues related to selecting specific technologies. Additionally, they must figure out what it will take to make renewables emerge as a mainstream generating option in the future.

It is clear that energy use will expand in the future as our population and society’s standard of living increase. Meanwhile, the push toward a sustainable lifestyle requires that all resources be utilized efficiently and sparingly. The National Academy of Sciences has identified paradigm shifts from current processes to an ideal vision centered on renewable energy and an atom economy—defined as maximum incorporation of starting materials into final products. These seemingly disparate paths converge if one considers energy production from municipal solid waste (MSW).

In response to Ontario’s provincial regulatory mandates to phase out the use of coal by the end of 2014, Ontario Power Generation (OPG) is exploring its capability to employ biomass feedstocks to displace coal in some units within the OPG thermal fleet. The primary fuels employed during the respective trials at its Nanticoke and Atikokan Generating Stations have been agricultural by-products and commercial grade wood pellets. The Canadian utility has learned valuable lessons about fuel supply and logistics, and the technical challenges of safely handling and firing high levels of biomass.

The race is on to claim the title of "most efficient coal-fired power plant" on the planet. However, it’s tricky identifying finalists because of the widespread misuse of the term "efficiency" and all those nagging assumptions. Let’s first establish clear definitions and then identify the title contenders.

"It’s déjà vu all over again," said Yogi Berra. The Hall of Fame catcher could easily have been predicting the coming resurgence of natural gas – fired generation. Yes, a few more coal plants will be completed this year, but don’t expect any new plant announcements. A couple of nuclear plants may actually break ground, but don’t hold your breath. Many more wind turbines will dot the landscape as renewable portfolio standards dictate resource planning, but their peak generation contribution will be small. The dash for gas in the U.S. has begun, again.