Tactical Garbage to Energy (TGER)

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 isthe 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, C Springer Science+Business Media B.V. 2010



1 Introduction
The initial challenge was to mate the waste streams produced by smalltactical 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
TYPE WASTE Metal Glass HazMat Construction Plastics Cellulosic Biomass Other Food Carbohydrates 10 % 50 % NET POWER OUTPUT % Landfill Onsite Utilities NOT AUTHORITATIVE – Data from Open Source Publications 90 % 100 % Incineration SCWO Plasma Arc Pyrolysis Gasification Anaerobic Digestion Biocatalytic Hybrid Other factors – Time; Cost; EnvironmentalFig. 1 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 thecarbohydrates, 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
INPUT Dry Waste - Fiberboard - Paper - Plastic - Wood Wet Waste Food Waste Slop Food Raw Agri Liquid Waste BioPlastics BIOREFINERY BIOCATALYTIC Residual Prep Fermenter PRODUCER GAS Residues Water Source Ethanol Recovery Diesel Gen Set Ethanol Syn-Diesel Heat Exchanger Power Takeoff THERMOCHEMICAL OUTPUT

Feedstock Prep

Gasifier Electricity Heat Water or:

ETHANOL

- Thermal component provides heat and power to run biocatalytic - Residues from Bioreactor path are channeled to gasifier - System starts on diesel fuel; then create/introduces Producer Gas and Vaporous Ethanol to displace diesel to minimum drip for pilot ignition

- Petroleum based plastics recalcitrant until gasifier - Bioplastics can degrade immediately



J.J. Valdes and J.B. Warner

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 wateroccurs. 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.

2 Background Research
There were two key bodies of knowledge that defined our research and technology transition plan. First, was the development of an understanding of the military context in which the tactical biorefinery was to serve and, second, was the search of the available “solution space”, that is, the match of current and future technologies to requirements for energy generation and trash reduction. Within the military context, a number of science and technology variables were considered. These included the type of input biomass, the type or types of biomass processing to be used, the output energy stream that results, and the kinds of military applications that would be served. A graphic depicting our “solution space” is shown in Table 1. Table 2 illustrates the energy content of different fuels relative to diesel fuel [3–5]. The value of converting organic waste into ethanol is clearly shown. Ethanol
Table 1 Solution space for waste to energy Waste Food waste (starch) Food waste (oil, grease) Plastics
Petroleum Bio-based

TechnologyBioprocessing
Starch Cellulosic

Energy product Ethanol (fluid.69) Methanol (fluid 0.51) Bio-oil (fluid) Biodiesel (fluid 0.6) Methane (gas 0.97) Hydrogen (gas 0.2)

Military application served Liquid fuel for burners/generators (primary or fuel additive) Gaseous fuel for modified generators Fuel cells, PEMs generators Liquid fuel for advanced batteries Direct electricity to power grid Hot water for troop use

based

Paper (cellulosic) Fiber board (cellulosic) Locally agriculture
Form

Pyrolysis to bio-oil Gasification to energy Hybrid
Thermal Bioprocess

and energy per unit volume, Gasoline = 1.0


Tactical Garbage to Energy Refinery (TGER) Table 2 Relative energy content Energy product Diesel Gasoline Ethanol Producer gas
Diesel


Energy index 1.0 0.98 0.69 0.2

Energy per unit volume 138,000 BTU 48 MJ/kg 125,000 BTU 84,600 BTU 10 MJ/kg

= 1.0

has 69% of the energy content that the same volume of diesel fuel has, whereas synthetic gas has only 20% of the energy content of diesel fuel [6, 7]. Ignoring the potential energy contained within organic food and liquid wastes would result in a significant loss of energy and reduced diesel fuel savings.

3 Materials and Methods
The TGER prototypes were fabricated and commissioned at Purdue University and conformed to the following selection criterion: a. Approach the problem as a “dual optimization” to develop a system which will simultaneously eliminate as much waste as possible while producing as much useful energy as possible. b. Design of the TGER must be “tuned” to the operationalcontext to ensure an easily available and reliable volume of military waste. c. The TGER should be designed to be contiguous with both the input source of wastes and the end user for the output energy product, avoiding any reprocessing or transport costs. d. The TGER must be operationally and tactically deployable via military airframe and able to be transported on the ground via standard military trailer. e. The TGER should not need additional manpower or machinery costs for waste separation. f. The process must minimize parasitic costs such as manpower, water, external energy, etc. g. The refining process should have minimal residual waste. h. Additional concerns of hazardous waste, safety, and troop use must be considered, and operation should be amenable to unskilled labor. The selection of gasification and biocatalytic fermentation has strategic value in that both methods are well-demonstrated technologies supported by high levels of research by the Department of Energy and, in the long course, are very likely to improve as new advances are achieved. Significant new advances in gasification include the introduction of integrated sensors and automated computerized control systems for the process. These recent




advances have resulted in gasification technologies with reliable and efficient conversion of waste to energy. Significant recent advances in biocatalytic fermentation include advances in genetically modified or modified via directed evolution enzymes and micro-organisms. Using methods developed at the Laboratory of RenewableResources Energy at Purdue University, several commercial entities have broken new thresholds in domestic ethanol production techniques by applying new biocatalysts and processes, the result being the economically viable production of ethanol for fuel [8]. Current advances in enzymatic design and development bode well for further methods to reduce what would normally be considered unusable biomass waste (e.g. paper fines from shredded cardboard and other cellulosic wastes) into usable energy, allowing more energy to be harnessed from the same waste stream. During the commissioning phase of the TGER, the system was able to deliver reliable power with very low parasitic costs required to operate the system internally. The core processes, gasification and fermentation for conversion of waste to energy, worked very well and the unique hybrid combination of thermochemical and biocatalytic technologies proved itself to be of considerable merit. These technologies could easily scale up to support military installations such as hospitals and major troop areas by converting waste into power, hot water, and usable fuel while eliminating costly waste removal expenses. Installation biorefineries could provide cost savings for US and overseas bases, reduce dependence on petroleum-based energy and support environmentally responsible initiatives, highlighting DoD’s support of renewable energy resource technologies.

3.1 TGER Retrofits
The first TGER prototype (Fig. 3) was built as a part of a Phase II STTR (Small business Technology Transfer Research) program and demonstrated proof ofprinciple

Fig. 3 Original TGER prototype before retrofit


Tactical Garbage to Energy Refinery (TGER)


Fig. 4 TGER after retrofit

but was not rugged enough to deploy to an OCONUS (outside the continental United States) site for field testing and validation. The initial function of the follow-on effort was to upgrade the existing prototype with better, more advanced equipment that could withstand the stresses of a three month OCONUS deployment in an operationally harsh environment (Fig. 4). Three of the key improvements identified during testing of the Phase II TGER and applied during the retrofit and fabrication are highlighted below. (1) First stage materials preparation (Industrial shredder and separations system). This component combines several key tasks which currently are done on the original prototype with separately acquired and integrated third-party components. Tasks include shredding, rinsing, auguring and compacting bioreactor residuals. The Industrial shredder performs these functions as a single component with half of the electrical power required by the original TGER. The new Industrial shredder was retrofitted onto the original prototype and included during fabrication of the second prototype. (2) Second stage pelletizer. Testing demonstrated that the size and shape of the pellets were the most critical qualities of gasifier feed-stock, followed by pellet density and then proportions of waste content (plastic vs. cellulosic, other). Our original view of the feedstock had focused on the latter, i.e. waste content proportions, and had used a lessexpensive compaction channel for gasifier pellets. Subsequent off-line testing with pellets made with equipment demonstrated a marked improvement in gasifier performance and subsequent engine output. The pelletizer, shown in Fig. 5, was included in the second TGER design and was a retrofitted improvement to the original prototype. (3) Stainless steel commercial grade distilling column. The stainless steel distilling column was upgraded from standard steel to stainless to prevent the introduction of rust into the distilling apparatus [9].




Fig. 5 Two high capacity laboratory pelletizers mounted on a single table with casters

3.2 Modifications of Second Prototype
Fabrication of the second TGER prototype began in early March 2008 and was completed in three weeks. During fabrication, additional modifications were applied to the second prototype that could not be applied to the first. These modifications are discussed in more detail below. a. Water circulation system. The material rinsing water was routed away from the main system through an intermediate sump pump and into a 500 gallon tank (see Fig. 6), and then routed back into the wash tank on the system using a sump pump. There were several reasons for this modification. First, the intermediate sump pump broke up any large debris (e.g. food slop and paper material) that passed through the sieve. This ensured that the re-circulated liquids would not cause any clogging of the plumbing. Using the large 500 gallon tank at ground level also made it easier and more efficient for the operators tomonitor the fermentation process and add the necessary biocatalysts. b. Rubber/flexible plumbing. The plumbing on the first TGER prototype was fabricated using standard two inch PVC pipe. When operating in freezing temperatures, water would collect in the pipes after operation, freeze overnight and cause the pipes to burst, causing significant delays in operation due to the time required to repair the pipes. The second TGER prototype therefore used a flexible rubber hose with quick disconnect fittings instead of pipes, allowing the water to be drained from the hoses after operation in order to prevent the pipes from freezing. Flexible hosing also eliminated the possibility of pipes breaking




Fig. 6 Material rinsing water routed off the main system through an intermediate sump pump and into a 500 gal tank

c.

d.

e.

f.

due to excessive vibration of the TGER either while in operation or during transport. Chiller. During testing of the first prototype, a chiller was needed to efficiently and quickly condense the distilled ethanol into a liquid state and collect it in the ethanol fuel tank. Due to design issues, the chiller could not be retrofitted on the first prototype but was included on the second. The chiller cooled a mixture of 50% water and 50% antifreeze and circulated it into a heat exchanger (condenser) where the ethanol vapor would condense into liquid ethanol, allowing the TGER to operate efficiently in hotter climates. Reflux valve. The reflux valve is a programmable valve that automatically redirectscondensed ethanol from the condenser to either the ethanol storage tank or back to the distillation column at a 5:2 time ratio. By redirecting condensed ethanol back into the distillation column at a 5:2 time ratio, the ethanol purity improved from 80% to 85%. Pellet auger/elevator. An external pellet elevator was purchased in order to automate the process of supplying waste-derived pellet fuel into the downdraft gasifier (Fig. 7). On the original prototype, a technician was required to climb onto the top of the TGER in order to pour waste pellets from a bucket into the gasifier, a time consuming and unsafe process. The pellet elevator allowed the technician to dump the pellets into a large collection bin at ground level and the pellet elevator would automatically deliver the correct quantity of pellets into the gasifer based on data received from an infrared sensor suspended over the gasification chamber. Centrifuge pump and basket filter configuration. On the original prototype, the centrifuge pump and basket filter had to be installed on their side. In order




Fig. 7 Pellet auger/elevator

to achieve optimal performance from the pump and filter it is necessary to install them upright. The frame on the second prototype was redesigned to accommodate an upright installation of both the pump and filter.

4 Current Outcome of Technical Implementation
Both TGER prototypes underwent a third party assessment conducted by the US Army Aberdeen Test Center. Three high risk and five medium risk hazards were identified on the TGERs. All risks weremitigated with minor hardware modifications, and sufficient safety devices and equipment were supplied as part of the basic issue items (BII). 007-DT-ATC-REFXX-D5104 Given that the mission of the Rapid Equipping Force is to quickly respond to field commanders’ requests by accelerating new technologies, the two first stage TGER prototypes were deployed by intent at what was considered to be the minimum technical readiness level for field evaluation. TGER assessment during the 90 day deployment to Victory Base Camp, Iraq met its objectives by identifying the key engineering challenges needed to advance from a first stage scientific prototype to an acquisition candidate system (Fig. 8). The Iraq deployment validated the utility of the TGER system as an efficient means to address a complex, mixed, wet and dry waste stream while producing power. The science and technology underlying the hybrid design of the TGER is unique and has considerable advantages over other unitary approaches. The engineering of the TGER system and, in particular, the difficulties which arose in having to modify third-party commercial off the shelf equipment to TGER purposes, were an expected and commensurate problem. Overall, the TGER performed well as a system for the first month of deployment. During the second month, unanticipated problems with the downdraft gasifier arose




which required considerable remedial attention by the technicians. With remote coordination with the manufacturer, many of these problems were quickly resolved, butthe overall reliability and performance of the downdraft gasifier was in general decline over the three months, resulting in considerable down-time during the deployment. Despite some initial tankage limitations (due to a delay in site prep by the Victory Base Camp DPW) and intermittent performance of the chiller system due to extremely high (120a—Š F) ambient temperatures, the bioreactor performed well during the first month. The chiller was eventually upgraded with one of greater capacity, but during the final month the system encountered a compromised heat exchanger, some pumping problems, and apparent loss of biocatalyst efficacy due to heat exposure. The technicians were able to bypass the failed heat exchanger, modify pump elevations and add fresh biocatalysts to recover system performance. About halfway through deployment, one of the two laboratory pelletizers became inoperative and could not be recovered. This resulted in a shift from a daily to an intermittent duty cycle (every other day) as the operators could not produce sufficient waste fuel pellets to keep the downdraft gasifier running continuously. The downdraft gasifier requires 60 lb/pellets/h and both pelletizers were needed to meet that throughput. Alternatively, the biggest issues anticipated prior to deployment, i.e., the viability of the waste processing equipment involving the shredder, material transport/feeding and generator flex-fuel control performed reliably and were generally trouble free. Our pre-deployment effort on these critical system tasks ensured the system performed reasonably well during thefirst month, and allowed the other engineering issues to emerge from the background for proper identification and characterization for remedy. Despite the mechanical issues, when the various elements of the TGER system were pulled together (routinely during the first month, then intermittently during the last two months) the system performed remarkably well. Field data demonstrated operations at or near 90% efficiency, with excellent throughput of both liquid and dry waste. The system generally conserved water at steady state and no environmental or safety problems emerged.



4.1 General TGER Parameters
Dimensions (L×W×H) Weight Waste residuals per day (Ash): Emissions Consumable electric power produced Water supply Manpower to operate 200”×88”×99” 10,000 lbs EPA compliant max 50 kW 600 gal is required to initially charge the system 1–2 operators

4.1.1 Consumables: Biological package, fuel, water, charcoal, and downdraft gasifier filter bags Lactrol (Antibiotic): 1 g/day ($0.26/g) Glucozyme (Enzyme): 50 g/day ($0.89/50 g) Amylase (Enzyme): 50 g/day ($2.05/50 g) Yeast: 200 g/day ($4.39/200 g) Total cost for biological package: $7.59/day Downdraft gasifier filter bags need to be replaced every 2 weeks 50 lbs of charcoal per month 4.1.2 Logistical Overhead: Set-up/breakdown time: three days total to operate the system through one full cycle 4.1.3 Safety and health risk: Received safety release from the Army Test and Evaluation Center for prototypes, certifying the prototypes safe for human use. TGER will require further safety evaluation tobe cleared for soldier operation 4.1.4 Target MTBEFF: TGER is composed of several subsystems, each with their own mean time between essential function failures (MTBEFF). The gasifier was the worst performer of the subsystems, with a MTBEFF of about 6 h. This has caused us to look at other gasification technologies to replace the current gasifier. The pelletizers in the material handling subsystem were the next worst performer. The pelletizers were undersized for the amount of throughput which caused some maintenance problems and breakdowns. The pelletizer MTBEFF was about 48 h. This problem should be resolved with pelletizers that have the right specifications. Applying the proper upgrades to the gasifier and replacing the pelletizers the target MTBEFF will be 1 month

4.2 Sub-system Specific Parameters Under Optimal Conditions Conus
Ethanol production and consumption Production Consumption Syngas production and consumption Production Consumption Pellet production and consumption Production Consumption Power efficiency Total power generated Parasitic power demand Total waste remediated per day Solid Liquid Diesel fuel consumption per day Diesel fuel saved per day

12 gal/day 1 gal/h 65 m3 /h 65 m3 /h 60 lbs/h 60 lbs/h 54 kW 14 kW 1,752 lbs 1,440 lbs 312 lbs average 24 gal average 86 gal

Although the TGER did not perform to its full potential during the 90 day assessment and validation, it did demonstrate its ability to convert waste to energy and reduce diesel fuel consumption in a harsh operating environment. Belowis the system level parameters recorded during live testing in Iraq. Due to equipment problems, the TGER was not able to demonstrate its ethanol production capabilities and provide enough data to statistically evaluate the bioreactor performance. The harsher conditions in Iraq also required more maintenance time for the pelletizer, thus reducing their pellet production capabilities. These issues and others contributed to the reduced fuel efficiency of the TGER while in operation in Iraq.
Ethanol production and consumption Production Consumption Syngas production and consumption Production Consumption Pellet production and consumption Production Consumption Power efficiency Total power generated Parasitic power demand Diesel fuel consumption per day Diesel fuel saved per day

Insufficient data Insufficient data 65 Nm3 /h 65 Nm3 /h 54 lbs/h 60 lbs/h 54 kW 14 kW average 48 gal average 62.4 gal

Below are specific data taken from various days when the TGER was operating at its best in Iraq. Figure 9 illustrates the ability of the TGER to conserve diesel



23 May 08 Off Board Power(KW) 60 50 40 30

J.J. Valdes and J.B. Warner

Diesel Flow (GPH) 3 2.5 2 1.5

1 20 0.5 10 0 0 – 0.5

Fig. 9 Example test data (fuel/power over time)

fuel when running at high loads. The specifications for the Kohler 60 kW generator used on the TGER rates the engine’s fuel consumption at 4.6 gallons per hour (gph) when less than 100% load. 100% load for the Kohler generator set using a 3-phase, 120/240 V 4P8 alternator at prime rating is 54 kW. The TGER maintained 50 kW of off boardpower (usable power) for approximately 2 h. During that same time the engine’s diesel fuel consumption was on average 1.5 gph, a diesel fuel savings of 2.76 gph. Figure 10 illustrates the power efficiency of the TGER. The yellow line represents all the power consumed by the TGER’s subsystems and is referred to as parasitic power. All remaining power generated by the TGER (50 kW) is available for use by the customer, and is represented by the light blue line. To determine the TGER’s power efficiency (pink line), we divided the power available to the customer (light blue line) by the total power generated (dark blue line). The TGER’s average power efficiency was approximately 77.37% during the recorded timeframe. Figure 11 illustrates the TGER’s ability to continue to conserve diesel fuel in adverse environmental conditions. The generator exceeded the recommended load of 54 kW and generated 55.5 kW of off board power while consuming only 2.5 gph of diesel fuel. The most likely cause of the increase in fuel consumption from 1.5 to 2.5 gph was due to foreign debris (i.e. sand and dust) entering the system and causing the gasifier filters to clog, thereby reducing the amount of syngas supplied to the engine. This forced the engine to compensate by supplying more diesel fuel into the engine in order to maintain 55.5 kW of off board power. Even under these sub-optimal conditions, the TGER was able to conserve 2.23 gph of diesel fuel. Table 3 shows data taken during field testing on 30 May 08 that was input into the TGER Energy Conversion Model. The model calculates the percentcontribution




Tactical Garbage to Energy Refinery (TGER)
23 May 08 Total Power (KW) 90 80 70 2 60 1.5 1 0.5 20 10 0
7: Tim 47 e 7: :02 (s) 52 A 7: :54 M 58 A 8: :46 M 04 A 8: :39 M 10 A 8: :31 M 16 A 8: :23 M 22 A 8: :14 M 28 A 8: :05 M 33 A 8: :56 M 39 A 8: :47 M 45 A 8: :40 M 51 A 8: :34 M 57 A 9: :26 M 03 A 9: :10 M 09 A 9: :02 M 14 A 9: :55 M 20 A 9: :47 M 26 A 9: :40 M 32 A 9: :33 M 38 A 9: :25 M 44 A 9: :17 M 50 A 9: :10 M 5 10 6:0 AM :0 2 10 1:5 AM :0 5 10 7:4 AM :1 7 10 3:4 AM :1 0 10 9:3 AM :2 2 10 5:2 AM :3 5 10 1:1 AM :3 8 10 7:1 AM :4 1 10 3:0 AM :4 4 10 8:5 AM :5 7 A 4: M 51 AM



Fig. 10 Example test data (power components over tine)
Fuel Efficiency -28 May 08 Total Power (kW) 80 70 60 50 40 1.5 30 20 10 0 1 0.5 0
GPH

Diesel Flow (GPH) 3.5 3 2.5 2

Fig. 11 Fuel efficiency and power (28 May 08)

that diesel fuel versus biofuels has to generating electrical energy. The model calculated that, of the total energy produced, the biofuels contributed 77.26% of the required energy and diesel fuel contributed 22.74%. Figure 12 illustrates the effect of the introduction of ethanol on fuel consumption of the generator. Fuel consumption matches closely with the increase in power



J.J. Valdes and J.B. Warner Table 3 Data from TGER Energy Conversion Model

Feed materials (daily) -30 May 08 Garbage (gallons) Garbage (lbs) Food (gallons) Diesel (gallons)

70 20% paper, 50% cardboard, 30% plastic 399 40 9

Energy content of feed Total (lb) 2.0 279.3 59.9 59.9 62.8Heats of combustion (btu/lb) LHV 7200 8000 10250 17800 18397 Total Electrical energy production Total (kWh) Offboard (kWh) Total energy (BTU) 14394.24 2234400 613462.5 1065330 1155700 5083286 Total energy (kWhr) 4.21871 654.8654 179.7956 312.2304 338.7162 1489.826

Component Carbohydrates Paper/cardboard Plastic-polyethylene terephthalate Pastic-polystyrene Diesel (DF2)

343 230

Total thermal-to-electrical energy conversion efficiency (% of energy content of feed) 23.0% Offboard energy conversion efficiency (% of thermal energy content of feed) 15.4% Diesel fuel savings (gallons) 33 Energy delivery efficiency (% of electrical energy for offboard use) 67.1% %Contribution to feed energy 22.74% 77.26%

Diesel Biofuels

output until 1:30 pm, after which the fuel consumption drops off abruptly while the power output remains relatively steady. At 1:30 pm ethanol was introduced into the engine at rate of 0.5 gph causing the diesel fuel consumption rate to drop by more than 0.25 gph. Ethanol was supplied to the engine for approximately 30 min until mechanical difficulties with the ethanol pump began to occur and forced the operators to turn the pump off. When the ethanol pump is turned off the diesel fuel consumption gradually goes up while the power output remains relatively steady.


Tactical Garbage to Energy Refinery (TGER
Fuel Efficiency - 1 AUG 08 Off Board Power 60 50 40 1.5 30 1 20 10 0 0.5
GPH kW


Fig. 12 Fuel efficiency and power (1 August 08)

Table 4 shows the use of the TGER Energy Conversion Model to analyzethe performance of the TGER on 1 August 08. Biofuels contributed 92.92% of the required energy to generate electricity and diesel fuel contributed 7.08%. This shows that the TGER can run almost entirely on biofuels, although the increase in biofuel contribution did have a negative affect on the thermal to electrical conversion efficiency. The increase in the contribution of energy from biofuels lowered the thermal to electrical conversion efficiency from 23% on 30 May 08 to 16.8% on 1 August 08, which is attributable to the fact that the Kohler generator was specifically designed to run on diesel, rather than biofuels.

5 Expert Commentary and Five Year View
The Tactical Garbage to Energy Refinery (TGER) is a trailerable, skid-mounted device capable of converting waste products (paper, plastic, packaging and food waste) into electricity via a standard 60 kW diesel generator. Additionally, the system can utilize available local biomass as a feedstock. Waste materials are converted into bio-energetics which displaces the diesel fuel used to power the generator set. The system also co-produces excess thermal energy which can be further utilized via a “plug and play” heat exchanger to drive field sanitation, shower, laundry or cooling devices. With additional engineering, the TGER could include a small subsystem to recover water introduced with the wet waste and produce potable water to further reduce logistics overhead. The system requires a small “laundry packet” of enzymes, yeasts and industrial antibiotics to support the biocatalytic subsystem.


J.J. Valdes andJ.B. Warner Table 4 Additional data from the TGER Energy Conversion Model

Feed materials (daily)-01 Aug 08 Garbage (gallons) Garbage (lbs) Food (gallons) Diesel (gallons)

90 20% paper, 50% cardboard, 30% plastic 513 58 3

Energy content of feed Total (lb) 2.9 359.1 77.0 77.0 20.9 Heats of comustion (btu/lb) LHV 7200 8000 10250 17800 18397 Total Electrical energy production Total (kWh) Offboard (kWh) Total energy (BTU) 20871.65 2872800 788737.5 1369710 385233.2 5437352 Total energy (kWhr) 6.11713 841.9695 231.1657 410.439 112.9054 1593.597

Component Carbohydrates Paper/cardboard Plastic-polyethylene terephthalate Pastic-polystyrene Diesel (DF2)

267.5 221.2

Total thermal-to-electrical energy conversion efficiency (% of energy content of feed) 16.8% Offboard energy conversion efficiency (% of thermal energy content of feed) 13.9% Diesel fuel savings (gallons) 27 Energy delivery efficiency (% of electrical energy for offboard use) 82.7% % Contribution to feed energy 7.08% 92.92%

Diesel Biofuels

The residuals from waste conversion are environmentally benign including simple ash, which can be added to improve soil for agriculture, and carbon dioxide. The TGER will deploy on a XM 1048 5-ton trailer and is designed to support a 550 man Force Provider Unit (FPU), which produces approximately 2,200 pounds of waste daily. On a daily operational basis, this would conserve approximately 100 gal of diesel. The capability for such conversion would provide


immediate and responsive energy requirements forexpeditionary operations as well as yielding estimated cost savings of $2,905/day [10]. A projected fielding plan for the TGER involves identification of current Modified Table of Organization and Equipment (MTO&E) trailers associated with FPU kitchen support which would then be modified to include the waste conversion technology. This would avoid any changes to the MTO&E or prime mover designation. Estimations indicate that the additional tasks associated with maintenance support for the operator and mechanic would not exceed those standards for the assigned Military Occupational Specialty and Generator Mechanic. Higher order support may follow a Contractor Logistics Support or low density support plan similar to that for the reverse osmosis purification unit equipment. Anticipated field employment of the system is such that the TGER would be pulled by the assigned 5-ton family of medium tactical vehicles assigned to accompany the FPU Containerized Kitchen. Upon occupation of the FPU site, the TGER would start up initially on diesel fuel alone. This would provide immediate power to the kitchen and begin to heat up/power the system components. As waste is developed from the kitchen, it will be introduced to the TGER and the two energetic materials (synthetic gas and ethanol) will begin to displace the diesel fuel. By six to twelve hours (depending on the waste stream), the TGER will run on 98% waste energetics and is capable of running for 12 h with a one hour maintenance shut-down intervening. Improvements for future models revolve around three subsystems: the gasifier, bioreactorand materials handling. The current downdraft gasifier equipment is too complicated and unreliable under desert conditions. However, modifications to the current design could reduce the complexity of the system and, with a thorough inspection, repair and evaluation by the manufacturer, we believe a number of alterations to the downdraft gasifier would mitigate its reliability problems. Ultimately, it would be advantageous to consider alternative thermo-chemical approaches. The issues with the bioreactor are much less complex and more easily addressed, as the system was custom built by Purdue University and several supporting subcontractors. Repairing and upgrading this system will primarily involve replacing and upgrading the two heat exchangers, modifying the system software to accommodate the changed thermo-dynamics and thermal management, and adjusting the “plumbing” of the ethanol collection and delivery system. During the intervening 18 months since the TGER fabrication, the commercial field of biomass fuel processing has greatly expanded. There are a number of new options for third party equipment such as improved shredders, pelletizers and pellet drying systems which did not exist previously.

6 Conclusion
Throughout the course of the 15 month program the TGER underwent testing in a variety of conditions and environments. Performance characteristics of the TGER varied in each environment and provided valuable information as to how to improve



J.J. Valdes and J.B. Warner Table 5 Theoretical/optimal TGER performance data

Diesel consumpPower Power tionoutput efficiency rate 54 kW 90% 1 gph

Ethanol consump- Ethanol tion production rate rate 1 gph 1 gph

Solid waste processing rate (pellet production) 60 lb/h

Liquid waste Total waste processing processing Diesel rate rate Savings 13 lb/h 1,752 lb/day 3.6 gph

Table 6 Power vs. Fuel Consumption Table Recorded at Purdue University Power Fuel Diesel Fuel gas Ethanol Idle 100% 0 scmh 0 gph 25 kW 1.3 gph 57 scmh 0 gph 35 kW 1.0 gph 65 scmh 0 gph 45 kW 1.2 gph 60 scmh 0.5 gph 55 kW 1.0 gph 65 scmh 1 gph

Table 7 TGER performance data set recorded at VBC Average TGER performance data at victory base camp Solid waste processing Diesel Pellet (pellet consumption consumption production) 2 gal/h 60 lb/h 54 lb/h

Power efficiency ~80%

Liquid waste Total waste processing processing 13 lb/h

Diesel saved

1,752 lb/day 2.6 lb/h

the overall design of the TGER in order to achieve what we believe to be the optimal theoretical performance characteristics shown in Table 5. Prior to the deployment to Victory Base Camp, the TGER underwent testing in a controlled environment at Purdue University. The fuel consumption of all three fuels (syngas, ethanol and diesel) was measured at varying loads using digital flow rate sensors as seen in Table 6. Although the TGER did not perform as well in Iraq as it had when in a controlled environment at Purdue University, it did demonstrate the ability to conserve fuel and remediate waste in a forward deployed operational environment. Table 7 shows the TGER’s performance characteristics when it was running under optimal conditions atVictory Base Camp. With improved engineering and further development all of these performance characteristics can be improved, maximizing the TGER’s potential as a viable portable power generation system.
Acknowledgements The authors gratefully acknowledge the funding support of the US Army’s Rapid Equipping Force, the Small Business Technology Transfer Research program and the Research Development and Engineering Command. We also thank the many forward deployed personnel at Victory Base Camp, Iraq for their support on the ground. Special thanks to Ms. Donna




Hoffman for pre-deployment and deployment support and for extensive editing and preparation of the manuscript.

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