James J. Valdes and Jerry B. Warner

Abstract An emerging concept is the convergence of “green practices” such as systemic sustainability and renewable resources with military operational needs. One example is developmental tactical refineries. These systems leverage advanced biotechnology and thermochemical processes for energy production and provide sustainability to military forward operating bases for tactical purposes.

Tactical refineries are designed to address two significant problems in an overseas crisis deployment. The first problem is access to dependable energy. Recent military operations in Southwest Asia have shown that, despite advanced logistics and host nation resources, access to fuel, particularly during the early months of a crisis, can be difficult. Further, even temporary loss of access to energy during military operations can have unacceptable consequences. The second problem is the cost and operational difficulties for waste disposal of materials created by military operations. Delivery of food, supplies, equipment and material to forward positions creates huge volumes of waste, and its removal inflicts a costly and complex logistics and security overhead on US forces.

As a simultaneous solution to both problems, deployable tactical refineries are being designed to convert military field waste such as paper, plastic and food waste into immediately usable energy at forward operating bases, on the battlefield or in a crisis area. These systems are completely novel and are only becoming feasible by taking advantage of recent advances in biotechnology and thermo-chemical science. In addition to providing operational benefits to US Forces, these systems will pro­vide significant cost savings by reducing the need for acquisition and distribution of liquid fuels via convoys which are vulnerable to attack. Tactical refineries would also serve a useful role in other military programs which support disaster relief or post-combat stabilization.

J. J. Valdes (B)

Department of the Army, Research, Development and Engineering Command, Aberdeen Proving Ground, MD 21010-5424, USA e-mail: james. valdes@us. army. mil

O. V. Singh, S. P. Harvey (eds.), Sustainable Biotechnology,

DOI 10.1007/978-90-481-3295-9_5, © Springer Science+Business Media B. V. 2010

Keywords Biofuel ■ Tactical energy ■ Synthetic gas ■ Fermentation ■ Downdraft gasifier

1 Introduction

The initial challenge was to mate the waste streams produced by small tactical units with technologies that were net energy positive at that scale. The TGER system was the result of a high level of optimization “from the trash up” and required a thorough scientific analysis and technology selection process with full consideration of the context within which it would be operating.

There are numerous waste to energy technologies, each with varying efficiencies and capabilities to digest complex waste streams [1]. Figure 1 breaks the problem set down to net power output (x axis) verses the type of waste (y axis), and shows the range of applications from landfill to onsite or tactical utilities. Incineration, for example, will handle all waste types including hazardous materials and metals, but has only 10% net power output at best and is most suited to large static operations such as landfills. By contrast, biocatalytic (i. e. enzymatic) approaches have much more limited ability to handle waste but are relatively efficient (~75%) in terms of net power output [2].

Biocatalytic approaches are therefore more suited to operations in which the waste stream is predominantly food waste and biomass. These two technologies occupy the extremes of this energy return spectrum.

WASTE TO ENERGY TECHNOLOGIES

The Tactical Garbage to Energy Refinery (TGER) design is a “hybrid” that uti­lizes both biocatalytic (fermentation) and thermochemical (gasification) subsystems in a complementary manner to optimize overall system performance and to address the broadest possible military waste stream. The hybrid design is based on detailed analysis of the waste stream combined with a modeling and simulation program unique to the TGER. Given the objective waste stream which includes both food and dry material wastes, a system which included a biocatalytic format for organic wastes such as food and juice materials, and a thermochemical format for solid wastes such as paper, plastic and Styrofoam, would have significant advantages over unitary approaches.

The Energy and Material Balance mathematical model showed that conversion of materials and kitchen wastes to syngas and ethanol would provide sufficient energy to drive a diesel engine and generate electricity. A downdraft gasifier was selected to produce syngas via thermal decomposition of solid wastes, and a bioreactor con­sisting of advanced fermentation and distillation was used to produce ethanol from liquid waste and the carbohydrates and starches found in food waste.

Both dry and wet field wastes (with the exception of metal and glass) are intro­duced into a single material reduction device which reduces both the wet and dry waste into a slurry. This slurry is then subjected to a “rapid pass” fermentation run which converts approximately 25% of the carbohydrates, sugars, starches and some cellulosic material into 85% hydrous ethanol. The remaining bioreactor mass is then processed into gasifier pellets which are then converted into producer gas, also known as “syngas”. The hydrous ethanol and syngas are then blended and fumigated into the diesel engine, gradually displacing the diesel fuel to an estimated 2% pilot drip. The design process model is shown in Fig. 2.

HYBRID TECHNOLOGY

IN- LINE BIOREFINERY DESIGN PROCESS MODEL

— Thermal component provides heat and power to run biocatalytic — Petroleum based plastics recalcitrant until gasifier

— Residues from Bioreactor path are channeled to gasifier — Bioplastics can degrade immediately

— System starts on diesel fuel; then create/introduces Producer Gas and Vaporous Ethanol to displace diesel to minimum drip for pilot ignition

Fig. 2 In-line biorefinery design process model

Adding the advanced fermentation process to the design of the TGER added no significant energy costs, as heat generated by the engine’s exhaust drives the distilla­tion, which is carried out in an 8-foot-high column packed with material over which fractionation of ethanol and water occurs. The additions of a few small pumps used to transport the ethanol solution from the fermentation tank to the distillation column and finally to the ethanol storage tank, were the only additional power requirements. The combination of the two waste-to-energy technologies allowed for the remedia­tion of a broader spectrum waste stream, both solid and liquid, the ability to extract much more energy from the waste, and operation of the generator at full power due to the anti-knock properties of the hydrous ethanol.