So, the first issue is waste to energy (WTE), one possible way to turn municipal solid waste (MSW) to energy through some type of conversion technology.
We have heard many perspectives on WTE--from, "it's dirty, dangerous, unneeded, and way too expensive" to "with an aggressive Reduce/Re-use/Recycle campaign, there won't be enough MSW supply to feed the WTE technology, so what, then we import waste from other islands?" to "modern WTE technologies can turn waste into clean energy with only minimum impact on the environment--and that's a lot better than letting landfill gases escape--unflared!--into the atmosphere." And so on.
At the final "All Stakeholders" meeting, the SENTECH Hawaii Team asked the participants to address the WTE issue in the context of the energy sustainability plan that we're drafting. In this sense, waste can be seen as an energy resource--and without wanting to wade into the debate on whether or not waste is renewable, we (the Team) feel compelled to add some objective analysis to the issue so informed decisions can be made when it's time to make them. We do not intend to step on anyone's toes or take a position at this time--we just want to share some facts that we've gathered to date.
Mad props to our Technical Lead, Jill Sims, for doing some great research and analysis--see below--on Kauai's situation, WTE technologies, and potential issues related to WTE.
Please let us know your thoughts. Mahalo.
Doug Hinrichs, SENTECH Hawaii Team Lead
dhinrichs@sentech.org
301-219-7647
_________________________________________________________________
The Situation
The current waste diversion rate for the County of Kauai is approximately 25%, with over 250 tons per day (tpd) being sent to the Kekaha Landfill. Phase II of the Landfill has a capacity until May 2010, at which point a phased expansion would have to take place. The first phase is expected to expand capacity to October of 2013 at a cost of $12 million, the second phase would expand capacity until January 2017 at a cost of $9 million, and the third phase has a conceptual capacity of 5.4 years (until mid-2022) at a cost of $13-30 million.1
Kauai is also faced with volatile and rising energy costs. Utilizing municipal solid waste (MSW) to generate energy is one potential component of a local energy portfolio. The benefits of WTE include reduced landfilling (and potential reductions in landfill pollutants to Kauai's air, land, and water), reductions in Greenhouse Gas emissions, creation of a local energy resource, and potential useful products and by-products (reformation of syngas or biogas, slag, etc.). However, these benefits are balanced by the potential issues listed below.
About Waste to Energy (WTE) Technologies
1. Incineration
The most common WTE technology is incineration with energy recovery. Incineration is a waste treatment technology that involves the combustion of organic materials and/or substances. Incineration and other high temperature waste treatment systems (including gasification and plasma gasification) are described as "thermal treatment". Incineration of waste materials converts the waste into incinerator bottom ash, flue gases, particulates, and heat, which can in turn be used to generate electric power. The flue gases are cleaned of pollutants before they are dispersed in the atmosphere.
Incinerators reduce the volume of the original waste by approximately 70-90 %, depending upon composition and degree of recovery of materials such as metals from the ash for recycling. This means that while incineration does not completely replace landfilling, it reduces the necessary volume for disposal significantly.
WTE facilities can be a complimentary part of a modern MSW management program. Recyclable materials like glass and metal don't burn, so removing them from the waste stream feeding into the furnace makes the combustion process more efficient and reduces the amount of waste to be landfilled. This can be accomplished by integrating a modern Materials Recovery Facility (MRF) onto the front-end of a WTE facility.
2. Gasification
Gasification is a method for extracting energy from many different types of organic materials, relying on chemical processes at elevated temperatures greater than 700 °C. Gasification (and plasma gasification) can process many more types of waste and do not necessarily require pre-sorting. The product of gasification is synthesis gas, or syngas, which consists primarily of carbon monoxide and hydrogen. Gasification is potentially more efficient than direct combustion of the original fuel because the syngas product can be combusted at higher temperatures or utilized in fuel cells. The product syngas is normally used to fuel a combustion turbine power plant to generate electricity.
Waste gasification has several advantages over incineration:
* The necessary extensive gas cleaning may be performed on the syngas instead of the much larger volume of flue gas after incineration.
* Electric power may be generated in engines and gas turbines, which are much cheaper and more efficient than the steam cycle used in incineration. Even fuel cells may potentially be used, but these have severe requirements regarding the purity of the gas.
* Chemical processing of the syngas may produce other synthetic fuels instead of electricity.
* Some gasification processes treat ash containing heavy metals at very high temperatures so that it is released in a glassy and chemically stable form.
A major challenge for waste gasification technologies is to reach an acceptable (positive) gross electric efficiency. The high efficiency of converting syngas to electric power is counteracted by significant power consumption in the waste preprocessing, the consumption of large amounts of pure oxygen (which is often used as gasification agent), and gas cleaning.
There are no current commercial installations of gasification or plasma gasification facilities processing MSW in the U.S. This presents a challenge for obtaining data on startup timeframe, emissions, O&M, reliability, etc. Plasco Energy Group has a MSW test facility in Ottawa, Canada called the Plasco Trail Road Demonstration Facility that makes public larger amounts of data and information than is available from other operations. The Partnership for a Zero-Waste Ottawa is a joint project between the City of Ottawa and Plasco Energy Group and, as such, makes progress reports, environmental performance reports, and other information publicly available.2
3. Plasma Arc Gasification
Plasma arc gasification (otherwise known as "PAG", "Plasma gasification" or "Plasma arc") is a waste treatment technology that uses electrical energy and the high temperatures created by an electrical arc gasifier. This arc breaks down waste primarily into elemental gas (syngas) and solid waste (slag), in a device called a plasma converter. The solid waste is a chemically inert, glass-like slag, resulting from a process called "vitrification". The process is intended to be a net generator of electricity, depending upon the composition of input wastes, and to reduce the volumes of waste being sent to landfill sites.
Plasma gasification operates at temperatures of up to approximately 14,000 °C. Certain metals, such as mercury, lead, zinc, and cadmium, may be volatilized, depending on the temperature in the reactor. That is, if the temperature is low, the metal will be melted and become part of the slag at the bottom of the reactor. If the temperature is high, the metal will be vaporized and rise with the gases out the top of the reactor. For example, lead volatilizes at 1737 °C. Below this temperature, the lead becomes part of the slag; above this temperature, it escapes with the gases and must be captured elsewhere in the system.3
4. Anaerobic Digestion
Anaerobic digestion (AD) is a series of processes in which microorganisms break down biodegradable material in the absence of oxygen. The MSW component for AD is source separated organics (SSOs). AD occurs in two phases: In the first phase a group of microorganisms referred to as “acid formers” breaks down complex materials in an acidic environment. In the second phase, a second group of microorganisms referred to as “methane formers” breaks down the output from the first phase and consume the organic material to form biogas.
Biogas from digesters is 55 to 60 percent methane; the remainder is mostly CO2. The biogas typically is used to generate heat or steam, through combustion in boilers, or it is used to generate electricity. Biogas generation varies by material. There is limited information on the comparative biogas generation of different materials in source separated organics or mixed waste streams. AD designers generally use their own proprietary data.
AD is particularly suited to wet organic material and is commonly used for effluent and sewage treatment. Until very recently, there were no anaerobic digestion facilities operating in the United States that processed MSW or source separated organic waste. In October 2006, Onsite Power Systems Inc., in association with the University of California Davis, launched their biogas energy project with the start-up of an anaerobic digester. This AD facility will initially process residential and restaurant waste from San Francisco, gradually increasing the amount to eight tons/day. Each ton of food waste is expected to generate enough bioenergy to power and heat 10 homes over a 24-hour period.
A newer trend in Europe is to market anaerobic digestion as one component of an integrated Mechanical Biological Treatment (MBT) system. MBT systems typically have a sorting component similar to a MRF. Traditional AD vendors have begun to partner with larger MSW processors who already have composting technologies or facilities, as well as transfer stations and/or landfills. The advantage of MBT for many communities is that organics do not have to be source separated by residents.4
Potential Issues
1. Process Emissions and Products
As part of the 1990 Clean Air Act mandates, the U.S. Environmental Protection Agency (EPA) promulgated new air pollution control standards for municipal waste combustors, including WTE facilities. These standards also require facilities to use the "maximum achievable control technology," and therefore are referred to as the MACT standards. No new facilities can be built unless they can demonstrate that they can meet the strict new standards.
Incineration and Gasification: The EPA also established the TCLP test (Toxicity Characteristic Leaching Procedure) for determining whether the ash from WTE facilities is hazardous. This ash must routinely be tested before it leaves the facility to insure that it is not hazardous. The ash exhibits concrete-like properties causing it to harden once it is placed and compacted in a landfill. This reduces the potential for rainwater to leach contaminants in landfills into the ground. Ash landfill studies conducted over the past decade show that leachate is like salty water with a metals content at about the same level as the standards set for drinking water. In some states, waste ash is used as a substitute for aggregate in road bed materials.
AD: There are three principal products of anaerobic digestion: biogas, digestate and water. Biogas is mostly methane and carbon dioxide, with a small amount hydrogen and trace hydrogen sulfide. As with syngas, it may require treatment or 'scrubbing' to refine it for use as a fuel. Digestate is the solid remnants of the original input material to the digesters that the microbes cannot use. A maturation or composting stage may be employed after digestion, making the digestate more suitable as a soil improver. Further treatment of the wastewater is often required. This treatment will typically be an oxidation stage where air is passed through the water in a sequencing batch reactors or reverse osmosis unit.
2. Greenhouse Gas (GHG) Emissions
In thermal WTE technologies, nearly all of the carbon content in the waste is emitted as carbon dioxide (CO2) to the atmosphere (when including final combustion of the products from gasification and plasma gasification). MSW contains approximately the same mass fraction of carbon as CO2 itself (27%), so treatment of 1 metric ton of MSW produce approximately 1 metric ton of CO2. In the event that the waste was landfilled, 1 metric ton of MSW would produce approximately 62 cubic meters of methane via the anaerobic decomposition of the biodegradable part of the waste. This amount of methane has more than twice the global warming potential than the 1 metric ton of CO2.
The methane in biogas can be burned to produce both heat and electricity. Biogas does not contribute to increasing atmospheric carbon dioxide concentrations because the gas is not released directly into the atmosphere and the carbon dioxide comes from an organic source with a short carbon cycle.
3. Cost
Incineration: The ISWMP estimates the cost of a proposed WTE facility at $46-52 million, with an operating cost of $8-9 million/year. The facility would process 40,500 tons of MSW in 2013, or approximately 110 tons per day. The anticipated energy produced is 18,200-20,200 MWh. 5
Gasification and Plasma Gasification: The capital and operations cost of gasification WTE can be extremely high. A cost/benefit analysis will have to be performed to compare WTE to source reduction and diversion efforts, and the benefits of WTE will likely have to be significant to balance the cost differential.
There are no current commercial installations of AD, gasification or plasma gasification facilities processing MSW in the U.S., which presents a challenge when verifying capital cost and operational cost estimates provided by companies. Project costs for all WTE technologies will also be site-specific.
4. Verification of Cost and Performance Estimates
Many proposals come from new companies or vendors promoting new technologies. This presents significant issues regarding the reliability and economic viability of technologies or businesses without a proven track record.
5. Size
According to Kauai's draft Integrated Solid Waste Management Plan (ISWMP), in 2005 the Kekaha landfill received 89,156 tons of municipal solid waste (MSW), for an average of 244 tpd. A total of 27,223 tons of MSW were recycled, for a total waste generation of 116,379 tons or 319 tpd. Based on 2005 resident and tourist population of 85,806 persons, the per capita generation rate per day is 7.43 lbs, which is consistent with tourist destinations. The draft ISWMP projects a 2009 total daily de facto population of 91,900 persons with a generation of 134,670 tons, or 369 tpd.5
Many WTE technologies must take advantage of economies of scale to be cost effective, meaning that they need to process 500-1000 tpd or more of MSW. This is significantly more waste than Kauai currently produces. One solution could be to bring MSW from other islands to support a WTE facility.
Many of the AD facilities currently in operation, particularly those with operational experience of greater than five years, have capacities smaller than 20,000 metric tpy, although there is a trend to build larger anaerobic digestion facilities because of economies of scale.
6. Siting
There are significant environmental issues that may be raised by national advocacy groups such as the Sierra Club & the Global Alliance for Incinerator Alternatives (GAIA). Opposition by local residents could be a significant issue when siting a project. Environmental reviews and permitting requirements could be significant. Having a WTE facility approved successfully will require an upfront analysis of inputs/outputs, including emissions, and a comparison of these with more conventional waste management strategies such as landfills.
Most of the WTE facilities in the U.S. became operational between 1980 and 1996. Only three new plants have come on line since 1996 (2 in 1997 and 1 in 2000).6 The primary reason for the slow-down in new WTE plants is the environmental concern involving existing plants. Most of these plants were installed without adequately addressing the environmental issues. The WTE industry is currently in the middle of an $800 million plant upgrade to install adequate air quality control systems that will allow the facilities to meet current EPA standards. Because of their historical emission problems, the WTE combustion plants have received and continue to receive significant resistance from environmental groups and negative reviews in the press. Groups such as GAIA and Greenaction have called alternative WTE technologies (gasification and plasma gasification) "Incinerators in Disguise" due to the combustion of product syngas to produce electrical power.
7. Odor
Modern WTE facilities are built so that a constant negative air pressure is always drawing air from the refuse pit (where incoming waste is dumped) into the furnace where the waste is combusted. At the temperatures encountered in a modern combustion system all smells/odors associated with waste are eliminated. This insures that no odor will be detected around or downwind of the facility.
8. Timeframe
The lifetime of many WTE plants is 25-30 years or more. Such long-term contracts may be inadvisable for communities and waste generators as they may stifle better options that may become available in the shorter term. Many alternative technologies such as gasification and plasma gasification remain under development and significant advances could emerge sooner than 25 years.
References
- County of Kauai Department of Public Works, “Public Informational Meeting: MSW Landfill Issues, www.kauai.gov/LinkClick.aspx?fileticket=3P1sSc3vtDQ=&tabid=238
- Plasco Energy Group, "A Partnership for a Zero-Waste Ottawa", http://www.zerowasteottawa.com/en/
- R.W. Beck, "City of
- Kelleher, Maria, “Anaerobic Digestion Outlook for MSW Streams”, BioCycle, August 2007, http://www.jgpress.com/archives/_free/001406.html
- County of Kauai Department of Public Works, “Integrated Solid Waste Management Plan”, draft 3/2009, http://www.kauai.gov/
- Recovered Energy, Inc., http://www.recoveredenergy.com/d_wte.html
- HPower, http://www.honoluluhpower.com/
- Oahu City Department of Environmental Services, "City to Brief Council on Plasma Arc Recommendations for Landfill Reduction Press Release", March 30,2004, http://www.honolulu.gov/refs/csd/publiccom/honnews04/plasmaarcrecommendations.htm
Acronyms AD – Anaerobic Digestion
EPA - Environmental Protection Agency
ISWMP - Integrated Solid Waste Management Plan
MACT - Maximum Achievable Control Technology
MBT – Mechanical Biological Treatment
MRF - Materials Recovery Facility
MSW - Municipal Solid Waste
PAG - Plasma Arc Gasification
TCLP - Toxicity Characteristic Leaching Procedure
Tpd - Tons per day
Tpy – Tons per year
WTE - Waste to Energy
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