By Bill Davis, President and CEO, Ze-gen
Each year Americans generate more than 400 million tons of municipal solid waste (MSW) and construction and demolition (C&D) waste. Of that, we recycle only a quarter, leaving 300 million tons of waste to dispose of as we wish. In the United States, this means that either we deliver our garbage to a landfill or incinerate it to reduce the volume and cull some energy in the process. These traditional methods have not been particularly adept at avoiding harm to the environment; landfills are the largest anthropogenic emitters of methane, which is a potent greenhouse gas, and incineration facilities produce mercury and dioxin emissions as well as toxic ash during the combustion process, which must eventually be landfilled.
Just as importantly, these two traditional disposal methods fail in their ability to tap the enormous energy potential locked in the waste streams. One pound of MSW has a heating value of roughly 4,000 Btus. The energy value of a pound of C&D waste is even higher: almost 7,000 Btus due to its high organic content. If there was a technology capable of culling all the energy available in C&D waste, for example, and converting it into useable power, one ton of C&D would generate more than 2 MWhrs of electricity. This is enough electricity to power 450 homes.
Since there currently exists no such technology, we dispose of what amounts to 600 million MWhrs of trash each year, and recover roughly 30 million MWhrs through incineration and landfill gas capture systems.
Luckily for us, a new form of waste disposal is on the horizon with the potential to solve many pressing issues surrounding municipal waste disposal. It is called waste gasification and it is gaining momentum in the United States.
The process of waste gasification involves converting the organic material within the waste into synthetic natural gas (syngas), which is a mixture of carbon monoxide and hydrogen gas. The syngas is used to produce electricity in the same way that natural gas is combusted for energy production-in combined-cycle mode-and the energy is delivered back to the grid. Municipalities that generate large amounts of waste also need large amounts of energy; both the waste and the resulting electricity, therefore, do not need to travel far to serve a large municipality’s needs. There are no byproducts formed in the gasification process that cannot be recycled and gasification technology operates at such high temperatures that harmful air emissions are not formed in the process.
Gasification’s potential upside is that the process solves two pressing problems at once: the problem of environmentally sensitive waste disposal and the challenge of clean energy generation. Waste gasification technologies hold the potential to accrue large amounts of both renewable energy credits in states that offer them (since waste is seen as a form of renewable fuel) and also carbon offset credits due to the large amount of landfill methane that is kept from forming by gasifying waste. As traditional energy companies are being forced to comply with increasingly stringent emissions limitations, they will take a greater interest in green power technologies such as gasification.
The question one inevitably asks, then, is why hasn’t gasification taken off as the dominant waste disposal method? Gasification, after all, is not a new idea. Around 100 facilities exist worldwide-most are found in Asia-that gasify various waste streams.
The reason is that existing gasification technologies are inefficient at producing power. The facilities in operation today are disposal methods for difficult-to-handle waste streams such as hazardous and medical wastes. Their objective is not to provide electricity; indeed, many of the facilities do not generate enough power to run their own operations, let alone sell power to the grid. The critical goal of mundane waste gasification is to generate high quantities of syngas capable of generating electricity in combined-cycle power mode. The technologies must approach 50 percent efficiency to produce syngas of high enough energy content to fuel a combined-cycle process, which is no small task. But power generation is the key economic driver of these systems. Without favorable economics, landfilling and incineration win out as cost-effective waste disposal alternatives.
Improved Outlook
In the last five years, much has changed to improve the potential for new technologies to participate in efficient waste gasification. Power generation equipment is becoming more fuel-flexible, gas scrubbing equipment is improving and material handling of mundane feedstocks such as C&D is now well practiced. Add on top of this regulatory tailwinds and financial incentives and it is easy to see why practical solutions may be just around the corner.
My firm, a company called Ze-gen Inc., is currently constructing an advanced waste gasification proof of concept facility in New Bedford, Mass. We predict that a full-scale facility, which is designed to accept 450 tons of mundane waste per day and generate a net output of 30 MW of renewable power, will have an average capital cost of $1,600/kW, which will allow Ze-gen to provide renewable electricity to the grid at a cost competitive with traditional fossil fuel facilities. The synthetic gas produced will have an energy value close to 350 Btus per pound and is expected to be clean enough to fuel a combined-cycle system with minimal gas clean-up at the back end of the system. The plant is expected to be operational in May 2007.