Thermal Conversion Technologies have an Important Role to Play
SYDNEY,NSW — October 23, 2009 — With the passage of the Australian Federal Government's renewable energy target (RET) legislation through the senate in August, there has been renewed media, retail and institutional investor interest in renewable power technologies such as wind, solar, geothermal and wave.
However, the prospects from waste thermal conversion technologies (TCTs), which use heat to decompose waste, and has the capability to provide baseload power, significantly reduce waste to landfill and produce useful by-products, remain largely unnoticed.
TCTs are becoming an increasingly likely option to further reduce the residual post-recycled portion of municipal solid waste (MSW), construction & demolition (C&D) and commercial & industrial (C&I) waste streams to landfill in Australia.
Compared to energy sources such as wind and geo-thermal that have already attracted significant investment interest, TCT facilities can be located in relative close proximity to existing high voltage transmission lines or industrial end users, thereby minimising the distance power has to travel and hence transmission losses, making them an attractive renewable energy source.
Many municipalities in Europe, Japan and more recently the US have already or are increasingly looking at thermal and biological conversion technologies to process their MSW stream and generate renewable energy.
TCTs such as pyrolysis, gasification, pyrolysis gasification, and plasma gasification have shown to provide higher diversion rates from landfill and higher efficiency to generate electricity when compared to biological conversion technologies.
Both pyrolysis and gasification have been around since the 19th century, but were used for many other purposes than treating heterogeneous solid waste streams such as MSW. The production of syngas has been the main catalyst behind public and private large-scale investment in several facilities across large European cities and more recently in Japan.
Syngas can be used as fuel to generate electricity, produce a number of different chemicals or even liquid fuel. Ongoing research is also looking at syngas to be used for production of hydrogen for fuel cells and for production of ethanol.
New technologies used in TCTs continue to evolve. Some technology suppliers use emission control systems to clean syngas before combustion to generate electricity. Some high temperature gasification has also been designed to control metals, inorganic pollutants, and ash as usable by-products such as vitrified material, and metal alloys granules. The metals can be recycled and the vitrified materials can be refined further and used as substitutes for sand or gravel.
Because the pyrolysis process produces another valuable product, biochar (or carbon char), it is likely that if a carbon trading scheme is introduced, that recognises carbon sequestration benefits from products such as biochar, this will provide further impetus to invest in these types of technologies.
In Australia, changes are already underway to review the opportunities associated with such technologies, specifically in the area of gasification, pyrolysis, pyrolysis gasification and plasma gasification, which have already been introduced to MSW streams of major cities around the world today.
The challenge is to identify how these technologies might be applied locally, based on their environmental, economic and technical qualities, and from what has been learnt in other parts of the world.
The City of Los Angeles
During the 2009 Northern Hemisphere summer, a major milestone was reached for the City of Los Angeles in terms of its municipal waste management plans. Los Angeles is currently the leading waste recycler of all major US cities, and diverts approximately 60% of its MSW from landfill, which will be increased to 70% by 2013 under the City’s new waste management directives.
- Be capable of meeting a minimum 200 tonne per day throughput capacity;
- Were at a commercial or late emerging stage;
- Could produce marketable by-products that were compatible with post-source separated MSW; and
- Have the highest diversion rate.
Of the sixteen technologies, the following were selected for further evaluation: advanced thermal recycling, pyrolysis, pyrolysis gasification, gasification, plasma arc gasification, anaerobic digestion, and anaerobic digestion / composting. A life cycle analysis was performed to evaluate the ability of the alternative technologies to process post-source separated MSW from an environmental, technical and economic feasibility perspective.
Phase one of the project, involving the evaluation of alternative solid waste-processing technologies, concluded that thermal technologies rather than the alternative biological, chemical or physical processes, were best suited to process post-source separated MSW and achieve the City's objectives. The City is now reviewing a final shortlist of technologies, which includes a range of TCTs and Advanced Thermal Recycling options.
Scope for the Australian market In terms of the scope for these technologies in Australia, URS Asia Pacific has already begun to review a range of thermal conversion technologies, using a base case annual throughput capacity of around 50,000 to 100,000 tonnes per year of C&D, C&I and MSW combined waste streams.
Recent analysis of these technologies took into consideration costs and benefits generated by TCTs including revenue from selling renewable energy certificates (RECs) and selling power directly to the grid, capital and operating costs, diversion rates from landfill and reduction in greenhouse gas emissions.
Electricity generated by a thermal conversion facility processing MSW or mixed waste depends on the throughput of the facility (tonnes per year), heating value of the feedstock (kJ/kg) and the efficiency of the technology and electrical generation system used (boiler, generator etc). As a general indication based on a throughput of 150 tonnes/day of MSW and a heating value of 13,500 kJ/kg, TCTs can generate between 580 to 850 kWh per tonne of waste processed. It is noted that eligible renewable energy generators will receive one REC for each megawatt hour (MWh) of power produced, thereby providing an additional source of revenue.
In terms of capital costs, commercial facilities processing over 100 tonnes per day, have been established overseas within the prices range of AUD$30 to $90 million with operating costs of around AUD$3-6 million/year.
The results of several life cycle analyses performed indicate that greenhouse gas emissions of thermal conversion technologies are lower than most other alternative of MSW disposal options.
Diversion rates from landfill for the analysed TCTs (pyrolysis, gasification, pyrolysis gasification, and plasma gasification) ranged between 80% to 98%.
Conclusion Private industry and municipal governments around the world today are already committed to introducing thermal conversion technologies such as gasification, pyrolysis, pyrolysis gasification, and plasma gasification into management of their MSW, C&D and C&I waste streams.
Factors that influence decisions to invest have included the price paid for the amount of energy produced, and how this compares with the price to landfill. Other important factors include the importance of engaging communities early to ensure they can make informed decisions during public consultation processes where required.
Finally, the significant potential these technologies offer locally to reduce greenhouse gas emissions by producing renewable energy and sequester carbon, indicate Australia may not be far behind Europe, Japan and North America in introducing TCTs as part of an integrated waste management system.
Chani Lokuge MEngSc, MBA Senior Associate Solid Waste Management and Resource Recovery Engineer URS Australia
Dr Shapoor Hamid, PhD Senior Scientist URS Corporation USA