Ecologically Sound, Cost-Effective Energy

Waste to energy (WtE) is a vital part of a strong and sustainable waste management chain. Fully complementary to recycling, it is an economically and ecologically sound way to provide a renewable source for energy while diverting waste from landfills. 

A WtE plant converts solid waste into electricity and/or heat - an ecological, cost-effective way of energy recovery.
 
A waste-to-energy (or energy-from-waste) plant converts municipal and industrial solid waste into electricity and/or heat for industrial processing and for district heating systems – an ecologically sound, cost-effective means of energy recovery. The energy plant works by burning waste at high temperatures and using the heat to make steam. The steam then drives a turbine that creates electricity.

Recover valuable resources
 
Energy from waste (EfW) isn’t just a trash disposal method. It’s a way to recover valuable resources.

Today, it is possible to reuse 90% of the metals contained in the bottom ash. And the remaining clinker can be reused as road material. 

The results and benefits are proven:

• Avoids methane emissions from landfills
• Offsets greenhouse gas (GHG) emissions from fossil fuel electrical production
• Recovers/recycles valuable resources, such as metals
• Produces clean, reliable base-loaded energy and steam
• Uses less land per megawatt than other renewable energy sources
• Sustainable and steady renewable fuel source (compared to wind and solar)
• Destroys chemical waste / conventional HAPs
• Results in low emission levels, typically well below permitted levels
• Catalytically destroys NOx, dioxins and furans using an SCR
  

High efficiency and low emissions

Waste to energy is one of the most robust and effective alternative energy options to reduce CO₂ emissions and replace fossil fuels.

Approximately 2/3 of household waste is categorized as biomass. Therefore, we can recover 2/3 as CO₂-neutral energy and reduce our dependence on fossil fuels.

In Europe, 50 million tons of waste is converted into valuable energy through WtE technology, supplying 27 million Europeans with electricity. Still, 50% of municipal solid waste becomes landfill. This releases greenhouse gasses like methane which is more than 20 times more powerful than CO₂. Our WtE technology eliminates these emissions.

Our goals are two-fold: to maximize production and efficiency to meet energy needs, and to reduce our environmental footprint. 

Waste facts

• 4 tons of waste equals 1 ton of oil
• 2 tons of waste equals 1 ton of coal

As urbanization and spending on consumables increases, more solid waste is generated. The amount of solid waste has grown over the last century to more than 3 million tons now generated per day globally, and the number is expected to double by 2025 (Organization for Economic Cooperation and Development).

Solid waste management is often one of the greatest costs to municipal budgets. Increasing the amount of municipal solid waste in landfills translates to increases in greenhouse gas (GHG) emissions, air and odor pollution, and soil and water contamination.

Sustainable waste management

To reduce the size, cost and environmental impacts of landfills, many regions are shifting from a linear economy (make-use-dispose) to a more circular economy model, where materials are made, used and reused to their fullest extent. Complementary to recycling, WtE plants extend the useful life of the solid waste, converting it into electricity and/or heat for industrial processing and district heating systems, filtering out harmful substances and recovering metals and other material for reuse. WtE is one of the most robust and effective energy options to produce power while treating waste and reducing emissions as an alternative to fossil fuels.

Mass-Burn or Refuse-Derived Fuel (RDF)

B&W provides two boiler options when using waste as a combustion fuel. Mass burning municipal solid waste uses the refuse in its as-received, unprepared state. The second technique uses prepared refuse, or refuse-derived fuel (RDF), where the as-received refuse is first separated, classified and reclaimed in various ways to yield salable or otherwise recyclable products. The remaining material is prepared for firing in the boiler.

Boiler Designs

Mass burning is the most common refuse combustion technology worldwide. Three major designs are used in modern mass burn power plants: 1) single-pass furnace, 2) multi-pass furnace with vertical convection pass, and 3) multi-pass furnace with a horizontal convection pass.

B&W has proven experience with designing and building all three variations, with the choice of design determined by the application. All three designs feature a furnace that is strategically arranged over the grate to control gas flow and maximize heat absorption, and thus, maximize efficiency. B&W designs the flue gas flow path to provide reasonably uniform cross-section flow and temperature distributions by using physical and/or numerical computational fluid dynamics (CFD) modeling, and empirical data. A short summary of each follows:

Single Pass Furnace

B&W’s single-pass furnace is a top-supported design that features a single vertical shaft for the rising combustion gases from the grate, with enough residence time and temperature to burn the fuel completely and cool the flue gas to the required furnace exit gas temperature before entering the superheater. The flue gas then turns 90 degrees around a furnace arch to pass through the horizontal crossflow top-supported superheater before turning downward to flow through the longflow steam generating bank. The flue gas then passes vertically over the crossflow economizer and exits the boiler enclosure.

Multiple Pass Furnace with Vertical Convection Pass

B&W’s multipass furnace with vertical convection pass locates the steam generating bank and superheater in the vertical third pass, and the economizer in the fourth pass. In this design, furnace gases pass upwards through the radiative section then makes a 180-degree turn and flows downward through a second vertical radiation pass. The gas then makes another 180-degree turn and flows up through the third pass where the superheater and generating bank are located. Finally, the flue gas is directed downward through the fourth pass which contains the crossflow economizer. While this design minimizes the larger footprint of the three-pass furnace, accessing the superheater in the vertical gas path for maintenance is more difficult.

Multiple Pass Furnace with Horizontal Convection Pass

The combustion gases of B&W’s multipass furnace with horizontal convection pass leave the grate and lower furnace and pass upward through the first open furnace pass and then downward through the second open pass. A portion of the first pass may be covered with specialized materials to reduce heat absorption and permit the flue gas to maintain a suitable temperature for complete combustion of the fuel in smaller boilers, and at lower loads in larger units. At the bottom of the second open pass, the flue gas turns 180 degrees to pass upward through the third pass to cool the flue gas to the required gas temperature before entering the horizontal convection pass.

Combustion Grates 

B&W combustion grates provide waste flow that ensures drying, ignition, combustion, energy release and complete burn-out before the bottom ash outlet.

In a waste-to-energy plant, the grate is where waste is converted into energy – the heart of the system. As such, grates are a significant focus area for us. Over the past 80 years we have supplied more than 500 combustion grates worldwide. Many of our older grates are still in operation, running efficiently and living up to current environmental standards.

B&W offers two combustion grates: the DynaGrate^® technology and Vølund combustion grates. Each grate is available in both water-cooled and air-cooled designs. The DynaGrate and the Vølund grates were developed to provide reliable transport of waste through the furnace.