SWEATT (Solid Waste to Energy by Advanced Thermal Technologies)

Abstract

Solid waste (SW), from mostly forest, agricultural residuals and potential energy crops on otherwise unused lands as well as selective institutional and municipal waste could fuel much more of U.S. and global energy needs than they currently do while creating good local jobs and industries. Previous versions of this SWEATT study stressed the advantages of replacing scarce, high-cost premium fossil fuels by carbon-neutral biomass and selected low- or negative-cost SW. However, natural gas (NG) supplies and prices have changed considerably due to intensified use of hydraulic or fracking and horizontal drilling into gas shale formations. In this update, we seek the best current ways of maximizing SWEATT benefits and in particular examine fracking’s impact on a number of our prior proposals for co-use of biomass and natural gas (BANG). Among a number of possibilities, the use of NG to facilitate pyrolysis of SW in modes that yield valuable products appears to provide promising ways of mitigating major national security, energy, environmental, and economic (SEEE) problems. Pyrolysis, the breakdown of organic material into volatiles and char by indirect heating to high temperatures without oxygen, has important advantages with respect to other thermal technologies like direct combustion or air- or oxygen‐blown partial combustion gasification. We examine the economic impact of current low NG prices using an analytical cost estimation (ACE) model that can separately relate the cost of electricity (COE) to the cost of fuel (COF) and the cost of capital, operation, and maintenance for diverse electrical generating technologies, including SWEATT systems. We also use an analytical semiempirical model (ASEM) of pyrolysis products developed in an effort to find patterns in the hundreds of molecular products from pyrolysis systems and feedstock that could be helpful in maximizing yields of high-value products. The pyrolysis approach can also yield environmental externality benefits from soil applications of biochar, an important feature of the pyrolysis approach. High transportation costs due to the low energy densities of biomass and SW, compared to petroleum or coal, suggest that installing SWEATT systems close to the SW sources would have cost and environmental advantages. Our final conclusions are based largely on our prior research and development work on co-use of domestic fuels (CDF) particularly using NG to enhance combustion efficiency and reduce harmful emissions. This work has suggested a number of strategies in which inexpensive gas can substantially enhance the economic benefits of SWEATT systems.