Distributed Waste-to-Energy and

Renewable Organic Resources



January 2001

Organic products, bi-products and wastes of many sorts can be subjected to thermal, chemical, and/or biological degradation. Breaking the complex carbon-hydrogen bonds to release energy is the guiding thermodynamic principal of "bio-energy" generation. The inherent economic development potential has been called the “Carbohydrate Economy", recognizing benefits to be derived from turning waste carbon-hydrogen bonds into commodities. Conversion of organics through processing into fuels, and transformation of those fuels into power, can now be accomplished efficiently, cleanly and cost-effectively.

Lessons to be Learned

The technologies we hope to commercialize and deploy for distributed energy (DE) generation exhibit characteristic needs and barriers already recognized and met by other innovative technological advances. Looking to these progenitors for guidance is a worthy task. Resource recovery industrial development is a rich source of inspiration, particularly with the study of such recently commercialized commodities markets as that for recycled newsprint, and the diversification of industrial plastics and glass recovery.   

Aggregation and value-added processing of dispersed resources has always been critical for the recycling & resource recovery industries, just as this has been a key to economical fuel production for the petroleum industry. Ours is now a slightly different paradigm: add the value at the source and site of use through direct conversion to energy, rather than by attempting to transport materials to central processing stations. We still must understand the economics of aggregation, however, to really assess the avoided costs of on-site organics conversion DE. 

Some DE organic conversion system configurations are highly effective and well proven, and have been available for at least a decade (e.g., use of plug-flow and full-mix animal waste digesters, as methane generators). These may now be considered "known technologies", with accessible operations and maintenance (O&M) records. Similarly, landfill-gas fueled power generation and sewage treatment plant methane co-generation should both be recognized as important, long-standing examples of distributed waste-to-energy resources. These technologies should be promoted now as venues for retro-fit deployment of high-efficiency, low emissions bio-gas fueled converters of waste to electric power and heat (e.g., advanced micro-turbines and fuel cells). Wet-cell landfilling, designed and operated to maximize waste degradation and methane generation, is a sharp contrast to past "perpetual grave" landfilling practices; this biogas source has been repeatedly demonstrated as cost-effective, particularly when a full life-cycle assessment can recognize the deferred long-term management costs.  

New Tools, Old Problems

Advanced in-vessel anaerobic digestion systems capable of high-volume methane (and hydrogen) generation are being successfully demonstrated around the country and seem to hold great promise. Designs are quite scalable and are clearly past the "bench test" stage. Rapid global commercialization of these eloquent waste conversion technologies, with concomitant decrease in the costs brought about through large-scale manufacturing, promises to bring such forms of DE to many communities currently disenfranchised by their relative lack of quality low-cost power. Strategic business alliances that facilitate an infrastructure capable of global-scale distributed waste-to-energy conversion, the “surround” for systems such as the advanced biogas utilization generators, should be encouraged now at all industrial and institutional levels.  

Development of liquid bio-fuel has most commonly been represented by large-scale ethanol industrial efforts. Yet ethanol fermentation in and of itself is certainly not relegated to a particular scale. Again, the tenants of energy deregulation and deployment of distributed energy generation would argue for decentralization of both the actual ethanol generation industrial facility and of the infrastructure that it requires. Given an increasing market for industrial DE spurred by the economics of converting wastes and bi-products to commodities, today's bench-scale experimental unit may find very important market niches for highly customized demand-side waste conversion. The food processing industry is probably the most obvious target for on-site combined heat and power generation from their own waste streams. 

"Pyrolysis"; "Thermolysis"; "Incineration"; "Thermal Transformation": jargon for various forms of organic conversion technologies suitable to DE. There has been an amazing wealth of research and development in furnace design, properties of thermal decomposition, contaminant management and fuel conversion efficiencies. In the past, markets have been open only for massive centralized converters. This knowledge base now needs to be applied to two smaller-scale targets: (a) characterization of potential feedstock from: agricultural, silvicultural, industrial wood products waste management (and again, the food processing industries), and (b) optimization of scale, to find which elite thermal conversion mechanisms can be fired upon that demand-side, process- sustained feedstock generation. 

Combined Heat & Power (CHP) 

Thermal conversion alone is seldom sufficient to justify capital costs. The heat thus generated must be reclaimed and utilized. European “district heating” from biomass combustion is an example of the diversity and efficacy of small and mid-range thermal technologies. To date, tools to generate electric power from that heat resource have been relatively limited, consisting of a variety of (a) boilers, connected to (b) steam turbines. We are now witnessing the successful emergence of new power generation technologies at these smaller “community” scales, systems such as kinematic and non-kinematic externally-fired stirling-cycle engines. There is a great need for co-engineering heat exchange technologies, externally-fired power generators, and high-efficiency small furnaces, to match combined heat and power capabilities to sustainable feedstock generation rates and community energy profiles. 

Many of the developers of small scale renewable, biomass-driven combined heat and power units remain pre-commercial. A few globally are now becoming market ready. Others are relatively advanced after decades of trial and error, yet may carry legacies of missfires, contaminant wrecks, inelegant engineering and unstable business practices.  

Gasifiers fit this last profile, where past failures taint future possibilities: great technological strides are being made, yet agencies still  are reluctant to approve gasifier-based DE. The diverse and far-reaching arena of "Waste-to-Energy" itself remains an anathema, in the eyes of most state and federal agencies. Only thorough and objective scientific scrutiny can effectively counteract the clinging preconceptions accompanying early disaster to prove efficacy and credibility for new advances, given the weight of poor past performance. All the more reason to concentrate on standardized specifications, cross-technology comparison, outside engineering validation and closely-monitored demonstration.  

Distributed waste-to-energy as a concept is more comprehensible, easier to grasp, and may indeed have a better chance at overcoming public and agency angst than does the entrenched, centralized multi-megawatt waste-to-energy industry.

Economic Incentives for Environmental Remediation 

When we safely and economically offer "greener" alternatives to environmentally deleterious management practices, we may even turn environmental liabilities into economic commodities. The deferred dollar value of introducing DE as a Best Available Technology (BAT) for waste management can significantly aid commercial purchase amortization. Where DE systems can interject themselves into existing industrial process regimes without creating undue chaos while evincing a net economic improvement, on-site conversion for combined heat and power (CHP) may not need to depend on grid inter-connect and an equitable electric purchase/sale contract to be competitive. Perhaps most exciting: the capability to provide CHP from on-site produced feedstocks could actually make remote environmental remediation efforts economical. 

Total Systems Perspective

Often, the focus of Distributed Energy Resource discussion tends to be the final electricity-generating mechanisms in the path, and on the infrastructure necessary for grid inter-tie. Yet we recognize that there is much more than the last "black box" necessary to DE deployment. The importance of "front-end" infrastructure has been exemplified by the waste-to-commodity market structures now complimenting classic industries of waste management: source reduction, resource recovery, and environmental impact mitigation. 

A life-cycle approach to financial and environmental cost/benefit assessment is a critical step to DE commercialization and social acceptance. To facilitate this difficult process, all elements of the DE system must be characterized. How else can we hope to directly compare costs, efficiencies and contaminant management between a diesel-driven internal combustion engine, a natural gas-fueled turbine, a hydrogen fuel cell, and a bio-fueled stirling engine design? Further, life cycle assessment is becoming the global standard for any process analysis, and external engineering validation is the requisite for underwriting and "bankability".  

Broadening our life-cycle perspective to include all potential DE infrastructural components in the path to final utilization, we can better understand and compare the many emerging technological forms of distributed generation. Greater systems diversity translates into more thorough market penetration by the combined DE industries, and thence to broader market acceptance.

This article is copyrighted. You are free to reprint and use it as long as no changes are made to its content or references, and credit is given to the author.

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