Gasifiers demand oxygen, provided as air, pure oxygen, or combination of the two. The use of pure oxygen reduces the volume flows through the IGT gasifier and through downstream equipment, which reduces investment costs. Also the Autothermal Reformer (see below) is, for the same reason, preferably fired by oxygen. As the production of oxygen is expensive, there will likely be an eco­nomical optimum in oxygen purity. Oxygen-enriched air could be a compromise between a cheaper oxygen supply and a reduced downstream equipment size.

Cryogenic air separation is commonly applied when large amounts of O2 (over 1000 Nm3/h) are required. Since air is freely available, the costs for oxygen production are directly related to the costs for air compression and refrigeration, the main unit operations in an air separation plant. As a consequence, the oxygen price is mainly determined by the energy costs and plant investment costs (van Dijk et al. 1995; van Ree 1992).

The conventional air separation unit is both capital and energy intensive. A potential for cost reduction is the development of air separation units based on conductive ionic transfer membranes (ITM) that operate on the partial pressure differential of oxygen to passively produce pure oxygen. Research and develop­ment of the ITM are in the demonstration phase (DeLallo et al. 2000). Alternative options are membrane air separation, sorption technologies, and water decompo­sition, but these are less suitable for large-scale application (van Ree 1992).

At the end of fermentation, the beer contains 10% or more ethanol by volume. Separation of ethanol from the whole fermentation mixture begins with distilla­tion on a beer column [22]. Further removal of water is accomplished in subse­quent distillation steps using a rectifier and/or stripper. Conventional distilla — tion/rectification methods yield 95% pure ethanol, at which concentration of ethanol and water form an azeotrope. The remaining 5% water is removed by molecular sieves, which rely on size exclusion to separate the smaller ethanol molecules from water [23]. Finally, anhydrous (100% or 200 proof) ethanol is denatured, typically with 5% gasoline or with higher-chain alcohols formed in the fermentation, to exempt the ethanol from beverage alcohol taxes.

Stillage Processing and Feed Products

The slurry remaining after distillation of ethanol, known as stillage, is concen­trated by centrifugation. The solids cake is referred to as corn distillers grains. Up to one third of the liquid fraction, known as thin stillage, is recycled (backset) into the mash. The remaining liquid is concentrated by evaporation and mixed with the corn distillers grains. The mixture is either sold as wet distillers grains or dried to generate DDGS. The moisture content and correspondingly short shelf — life of wet distillers grains limit use of this feed product to the immediate vicinity of ethanol plants, though the shelf-life can be lengthened by adding organic acids as preservatives.

Fed-batch fermentation is a technique that is applied to processes in which a high substrate concentration is toxic to the culture. In such a case, the reactor is initiated in a batch mode with a low substrate concentration (usually 60-100 gL-1) and low fermentation medium volume, usually less than half the volume of the fermentor. The reactor is inoculated with the culture and the fermentation pro­ceeds. As the substrate is utilized by the culture, it is replaced by adding a concentrated substrate solution at a slow rate, thereby keeping the substrate concentration in the fermentor below the toxic level to the culture (Ezeji et al., 2004). When using this approach, the culture volume increases over time unless culture fluid is removed. The culture is harvested when the liquid volume is approximately 75% of the volume of reactor. Since butanol is toxic to C. aceto- butylicum and C. beijerinckii cells, the fed-batch fermentation technique cannot be applied in this case unless one of the novel simultaneous fermentation and product recovery techniques is applied. In a number of studies (Ezeji et al., 2004; Qureshi et al., 1992), this technique has been applied successfully to the ABE fermentation. In fed-batch fermentation, Ezeji et al. (2004) were able to utilize 500 g glucose in 1 L culture volume (500 gL-1) as compared to 60 gL-1 in a control batch process.

Qureshi et al. (1992) used a concentrated substrate of whey permeate (350 gL-1) to produce butanol in a fed-batch reactor of C. acetobutylicum. In this process, three different techniques of butanol separation were compared including perstraction, gas stripping, and pervaporation. In the three processes, 57.8, 69.1 and 42.0 gL-1 ABE were produced, respectively. ABE yield of 0.37, 0.38, and 0.34 were obtained, respectively. Overall, application of these three techniques suggested that fed-batch fermentation technique can be applied to the ABE fermentation provided ABE is removed from the culture broth simultaneously. In another study, Qureshi et al. (2001) produced ABE in a fed-batch fermentation of C. acetobutylicum and removed these solvents using a silicone-silicalite syn­thesized pervaporation membrane. The reactor was fed with 700 gL-1 glucose solution. In this system, 155 gL-1 ABE was produced with an average yield of 0.31-0.35 and productivities ranging from 0.13 to 0.26 gL-1h-1. Using the fed — batch technique, fermentation of more sugars (2-3 times) was possible when novel product removal techniques were applied to the process.

DMFC electrocatalysts set the catalytic efficiency that dictates the DMFC per­formance and establish a large component of DMFC cost. Here, we discuss some recent developments in DMFC electrocatalysts and the materials used to support them.

Gonzalez et al. evaluated Pt and PtRu supported on single-wall carbon nano­tubes (SWNTs) and multiwall carbon nanotubes (MWNTs) as electrocatalysts [36]. The materials are integrated into electrodes and hot pressing with Nafion 115 to form MEAs. Half-cell experiments show the PtRu/C electrocatalysts have an earlier onset of methanol oxidation (i. e., lower potential) than the Pt/C coun­terparts. An MEA made with PtRu/MWNT showed the highest activity. When the electrocatalysts are evaluated in DMFCs, it was found the PtRu/C electrocat­alysts performed better than their Pt/C counterparts. The sequence of electroac­tivity being PtRu/MWNT > PtRu/C > PtRu/SWNT. Maximum power densities greater than 100 mW cm-2 are obtained with PtRu catalyst loadings of 0.4 mg cm-2.

A modified alcohol reduction method was used by Hwang et al. to produced nanosized PtRu/C electrocatalysts [53]. Various electrocatalyst preparations are compared to a commercial PtRu/C electrocatalyst, E-Tek 40 for morphology and effectiveness as an electrocatalyst. Transmission electron microscopy (TEM) show in-house preparations similarly well-dispersed as the commercial electro­catalyst. Metal particle size can be tailored by selection of the concentrations of preparation components. Activity of the electrocatalysts are compared under various methanol conditions in half-cell measurements made in a three-electrode cell. The results are mixed. Under realistic operating conditions (e. g., 40°C, 0.4 V, and [MeOH] ~ 15%) one of the in-house electrocatalysts outperforms the commercial catalyst. However, at higher potentials, the commercial catalyst per­forms better. This same trend holds true at [MeOH] = 35% and 50%, where the in-house catalyst performs better than the commercial at 0.4 V, but the commercial performs better at higher potentials. AC impedance data for this in-house catalyst suggest it has a lower resistance at all potentials and for all concentrations of methanol considered in the study.

An alternative to the costly Ru often employed in Pt-based bimetallic elec­trocatalysts of DMFCs may be Sn. The impact of introducing Sn to the Pt/C anode electrocatalyst of direct alcohol fuel cells (i. e., methanol and ethanol) was evaluated by Zhou et al. [47]. Cyclic voltammograms recorded vs. SCE showed the Sn-bearing electrocatalyst, PtSn/C, had a more favorable onset of oxidation potential (20 mV) than Pt/C (250 mV) and PtRu/C (110 mV), however, the peak oxidation potential of PtSn/C was intermediate (640 mV) to Pt/C (700) and PtRu/C (500 mV). For further comparison, three single-cell DMFCs were pre­pared. The maximum power densities of the three cell tracked with the peak oxidation potentials of the cyclic voltammetric experiments: PtRu/C (136 mW cm-2) > PtSn/C (55 mW cm-2) > Pt/C (17 mW cm-2). The work points to the possibility that adding relatively inexpensive Sn to the Pt/C anode may signifi­cantly improve DMFC catalysts. The effectiveness of this approach is difficult to assess as the performance of the Pt/C blank is so poor, however, the performance trends warrant further research.

One strategy to limit the effects of methanol crossover in DMFCs is to develop cathode electrocatalysts active toward the oxygen reduction reaction (ORR) but inactive toward the methanol oxidation reaction (MOR). Pt is active toward both reactions whereas Pd is active only toward ORR. In a short com­munication, Sun et al. use voltammetry and chronoamperometry to demonstrate a Pd:Pt alloy in the ratio of 3:1 supported on carbon is effective toward the ORR and ineffective toward the MOR [49]. The group goes on to compare the performance of DMFCs impregnated with either the Pd3Pt1/C electrocatalyst or Pt/C control in the cathode. The cell using the PdPt alloy had better overall performance with a maximum power density, ~40% higher than that of the Pt/C control. The authors think that once the ratio of Pd to Pt rises above a certain point, the active sites of the Pt become isolated and overall activity of the alloy toward MOR drops precipitously.

The incorporation of the oxygen storage material CeO2 into the carbon sup­ported Pt electrocatalysts of the cathode was found to enhance the performance of DMFCs when run on air [46]. The ceria compound is known to act as an oxygen storage buffer and helps to maintain the local oxygen pressure, but the effect only appears to be beneficial when using air. Yu et. al. found that when run on pure oxygen, the presence of ceria oxide in the cathode diminished the maximum power of a DMFC by ~20%. The most pronounced enhancements on performance are when operating the cell at low air-flow rates (250 sccm), but the effect becomes minimal at higher flow rates (1250 sccm). Impedance spectro­scopy was used to determine the polarization resistance of the ceria-doped and nondoped Pt/C cathodes under air and O2. The resistance of the ceria-doped cathode was lower than the control when under an air atmosphere, but the ceria — doped cathode had a higher resistance under O2. An optimized cathode compo­sition for use in air was found to be 1 wt % CeO2 and 40 wt % Pt/C.

The performance of PEFCs run on H2 and O2 has been shown to improve upon the incorporation of TiO2 into the carbon-supported Pt electrocatalyst layer [54]. Manthiram and Xiong tested the same modification of the DMFC electro­catalyst layer [48]. A number of deposition methods were tried as well as a series of heat treatments under a reducing atmosphere. The treatments result in an array of different sized particles (3.8 to 25.4 nm) that do not necessarily correlate with the electrochemically active surfaces areas (2.59 to 21.87 m2 g-1) of the particles. Some of the Pt/TiO2/C electrocatalysts showed higher activity toward ORR in sulfuric acid at room temperature than the Pt/C control. Also, a number of the TiO2-doped electrocatalysts have lower charge transfer resistances, as measured by AC impedance, than the Pt/C control. Cyclic voltammetry shows the hydrogen desorption potential decreases and the potential for reduction of platinum oxide increases in the presence of the added TiO2. When the performance parameters of the various Pt/TiO2/C electrocatalysts are compared, it is found the Pt/TiO2/C electrocatalyst prepared by depositing hydrated TiO2 onto a Pt/C substrate and subsequently heat treating at 500°C performed best. When integrated into the cathode of a DMFC, the TiO2 doped electrocatalyst shows higher tolerance to methanol crossover than the Pt/C control. The tolerance becomes more pro­nounced as the methanol concentration of the fuel stream is raised above 1.0 M. The performance of this TiO2-doped electrocatalyst, used either in the heat-treated
or as prepared form in the cathode of a DMFC was higher than an equivalent cell made with a Pt/C cathode.

There is independent evidence that MWNTs are a carbon support for DMFCs superior to the ubiquitous Vulcan XC-72, and that alloying Pt with other transition metals such as Ni, Fe, and Co produces catalysts with higher activity toward ORR than Pt alone. In a brief and preliminary paper, Li et al. bring these two notions together and test a PtFe alloy supported upon MWNTs for use as an electrocatalyst in DMFC cathodes [50]. A modified polyol strategy was used to prepare the electrocatalyst. Characterization of the material showed that the Pt:Fe ratio was ~1:1; however, the Pt and Fe did not form a stable alloy. The electro­chemical performance of the material was tested subsequent to introduction into the cathodes of DMFCs. It was found the mass activity (current per mg Pt) of the PtFe/MWNT cell held at 600 mV (the activation-controlled cell potential region) was ~40 % higher (4.7 vs. 3.3 mA mg-1 Pt) than the Pt/MWNT control cell. At a current density of 300 mA cm-2, the PtFe/MWNT cell held a cell potential of 210 mV versus 151 mV for the Pt/MWNT control. Though the mean particle size for Pt in the PtFe/MWNT material was larger than that of the Pt/MWNT material, the specific activity of the PtFe/MWNT electrocatalyst was more than 2-fold higher at 117 mA m-2 Pt versus 50 mA m-2 Pt for the Pt/MWNT control. The authors propose the presence of Fe in the material as being respon­sible for the enhanced ORR activity and DMFC performance and that detailed work be conducted to elucidate the Fe and Pt interaction resulting in the enhanced performance.

Two types of potential fuels (cardboard and wood) are presently a major part of the Municipal Solid Waste (MSW) stream, and comprise approximately 45.8% of all MSW composition (1). These green energy fuels are organic in origin and renewable in nature; therefore, they are carbon-cycle neutral, i. e., since they are composed of former living plant tissue, when used as fuel for heat or converted to alcohol fuel for electric generation, they do not add to greenhouse gasses or carcinogens to the environment. The carbon dioxide that is emitted is used by the next generation of growing plants to store energy; therefore, the carbon cycle is stabilized through their use. Petroleum fuels add carbon dioxide to the cycle, which has been sequestered and removed from the cycle for millennia.

Procedure

Wood and cardboard will be removed from the waste stream at the source. The project will utilize nonrecyclable cardboard and wood as direct combustible fuel. Compressed, baled, and placed on a pallet for ease of handling, nonrecyclable cardboard and other solid combustibles will be fed directly into a specially designed outdoor furnace that generates 1,000,000 BTUs per hour. Ash generated is rich in boron, an element normally deficient in New England soils. It will be incorporated into compost.

Potential Savings

As an example of the potential savings to be realized from utilizing these two forms of MSW, the BTUs in just one 500-pound bale of cardboard (at 8200 BTUs/lb) are equal to the BTUs in 29.7 gallons of #2 home heating oil (at 138,000 BTUs/gallon). Given the fact that one barrel (42 gallons) of crude oil only yields 9.2 gallons of home heating oil or diesel (2), the savings from using one ton of cardboard is the equivalent heating oil yield from 12.92 barrels of crude oil. There are approximately 7500 BTUs in one pound of wood. Given the above informa­tion, the project will be a net reducer of MSW that will contribute to the overall reduction of landfill mass.

Electricity Cogeneration by Combined Cycle

Unconverted synthesis gas that remains after the methanol production section can still contain a significant amount of chemical energy. These gas streams may be combusted in a gas turbine, although they generally have a much lower heating value (4-10 MJ/m3NTP) than natural gas or distillate fuel (35-40 MJ/m3NTP) for which most gas turbine combustors have been designed. When considering com­mercially available gas turbines for low calorific gas firing, the following items deserve special attention (Consonni et al. 1994; Rodrigues de Souza et al. 2000; van Ree et al. 1995): the combustion stability, the pressure loss through the fuel injection system, and the limits to the increasing mass flow through the turbine.

Different industrial and aeroderivative gas turbines have been operated suc­cessfully with low LHV gas, but on the condition that the hydrogen concentration in the gas is high enough to stabilize the flame. Up to 20% H2 is required at 2.9 MJ/m3NTP. Hydrogen has a high flame-propagation speed and thus decreases the risk of extinguishing the flame (Consonni et al. 1994).

Injecting a larger fuel volume into the combustor through a nozzle originally designed for a fuel with much higher energy density can lead to pressure losses, and thus to a decreased overall cycle efficiency. Minor modifications are sufficient for most existing turbines. In the longer term, new turbines optimised for low heating value gas might include a complete nozzle combustor redesign (Consonni et al. 1994).

The larger fuel flow rate also implies an increase in mass flow through the turbine expander, relative to natural gas firing. This can be accommodated partly by increasing the turbine inlet pressure, but this is limited by the compressor power available. At a certain moment, the compressor cannot match this increased pressure any more and goes into stall: the compressor blocks. To prevent stall, decreasing the combustion temperature is necessary; this is called derating. This will lower the efficiency of the turbine, though (Consonni et al. 1994; van Ree et al. 1995). Higher turbine capacity would normally give a higher efficiency, but as the derating penalty is also stronger, the efficiency gain is small (Rodrigues de Souza et al. 2000).

Due to the setup of the engine the compressor delivers a specific amount of air. However, to burn one m3NTP of fuel gas less compressed air is needed com­pared to firing natural gas. The surplus air can be bled from the compressor at different pressures and used elsewhere in the plant, e. g., for oxygen production (van Ree et al. 1995). If not, efficiency losses occur.

All the possible problems mentioned for the currently available gas turbines can be overcome when designing future gas turbines. Ongoing developments in gas turbine technology increase efficiency and lower the costs per installed kW over time (van Ree et al. 1995). Cooled interstages at the compressor will lower compressor work and produce heat, which can be used elsewhere in the system. Also gas turbine and steam turbine could be put on one axis, which saves out one generator and gives a somewhat higher efficiency.

Turbines set limits to the gas quality. The gas cleaning system needs to match particles and alkali requirements of the gas turbines. When these standards are exceeded, wearing becomes more severe and lifetime and efficiency will drop (van Ree et al. 1995). However, the synthesis gas that passed various catalysts prior to the gas turbine has to meet stricter demands. It is therefore expected that contaminants are not a real problem in gas turbines running on flue gas from methanol production.

“Cold saccharification” technology allows enzymatic release of glucose from starch without liquefaction (e. g., jet-cooking) with steam. Laboratory-scale alcohol fermentation of ground rice without cooking was reported in 1963 [39] and an industrial-scale fermentation was reported in 1982 [40]. Use of very high solid concentrations improved productivity and yielded high concentrations of ethanol. In 2004, commercial technologies for direct conversion of raw starch to ethanol were developed for use in modern dry-grind ethanol fermentation facil­ities [41, 42]. A key to cold-process technology is the development of robust and efficient conversion enzymes [43]. The benefits of a no-cook process include reduced energy, water, and waste costs, reduced capital and related maintenance expenses, improved conversion efficiency resulting in increased ethanol yield, and increased protein content and quality of feed coproducts. Possible drawbacks to the technology include the cost and amount of enzyme required for the process and an increased chance for microbial contamination and corresponding loss of yield, because heating to partially pasteurize the mash does not occur. Heating that occurs in the standard dry-grind ethanol process also aids release of starch that is bound to fiber or protein, and inactivates some toxins that may be present in the grain. The no-cook method must manage these issues by means of alternate technologies [44]. Widespread adoption of cold-hydrolysis technology stands to greatly impact the productivity and profitability of the ethanol industry.

The major engine operation issues with alcohol-blended fuels are fuel quality, volatility, octane number, enleanment, cold start, hot operation, and fuel con­sumption. The physical properties of the blended fuels compared to pure gasoline are shown in Table 7.3. Octane numbers determined by the usual ASTM proce­dures indicate that alcohol-blended gasoline increases fuel octane over the base

Source: Guerrieri, D. A., Caffrey, P. J. and Rao, V, Investigation into the Vehicle Exhaust Emissions of High Percentage Ethanol Blends, SAE Technical Paper Series, #950777, 1995.

gasoline (23-28). Fuel consumption increases when oxygenates are blended with gasoline due to the lower energy content of the oxygenated fuel. Table 7.4 shows that fuel economy decreases with ethanol concentration. The theoretical increase in fuel consuption is 3% for E10 and 6% for E20 (29).

Corrosion of metallic fuel system components is generally not an issue with E10 (28). Researchers have also shown that E20 blends do not appear to affect fuel-system operation (8). Elastomeric and plastic components of new engines are compatible with E10, but many older engines are not (28). Evidence reported has shown that ethanol blends offer less lubrication than pure gasoline (29);

however, that has not been a noticeable issue in terms of wear or engine life over the last 20 years. Over the last few years, Brazil has shown that conventional catalysts used in U. S. vehicles can operate on 10% and neat (100% ethanol) (30). Ref. 8 states that higher ethanol blends show higher catalytic efficiency, because there is a smaller concentration of sulfur species. Barnes (1999), from Ref. 8, says that the increase in catalytic efficiency could be as large as 24%. Guerrieri, Caffrey, and Rao 1995 from Ref. 8 show that volatility decreases with higher ethanol blends. The highest volatility is around 5% ethanol (31). Carbon mon­oxide emissions are lower for ethanol blends (32-35). E10 can be employed in vehicles without equipment changes and without violating manufacturer’s war­ranties (4).

Enleanment is defined as an excess of oxygen compared to the ideal air/fuel ratio. Common problems of enleanment are loss of power and engine misfires (8). Both problems increase emissions. Finland has shown that E15 vehicles can operate with stock carburetors and that 80% of vehicles running on E15 show less wear compared to pure gasoline. Fluorinated polymers have good resistance to both gasoline and ethanol (36). Nylon-coated nitrile rubber has also shown resistance to both gasoline and ethanol (37). Overall, engine operation and life (wear) are not affected by small (10-20%) concentration of ethanol blended with unleaded gasoline.

Solid oxide fuel cells are very promising energy conversion systems that can generate electricity at high efficiencies using not only hydrogen but also alcohol and hydrocarbon fuels. Further progress on the development of fuel cell materials, particularly the electrodes, which prevents carbon deposition and sulfur-resis­tance, will play a key role to achieve a stable operation of direct-alcohol SOFCs with high power densities. In contrast to double-chamber SOFCs, the single­chamber solid-oxide fuel cells offer a simple design that are not affected by the challenges of high temperature sealing and may be a cost-effective alternative

with a mechanically more robust structure. Recent developments in single-cham­ber SOFCs show promising results toward achieving significantly high power densities using hydrocarbon fuel gases mixed with air.

The fish sold will be processed into fillets to increase consumer sales appeal, although the project has potential customers presently who wish to purchase live fish. The project will process the fish in a specially designed portable unit. Processing will be done by special equipment that strips off all the scales from the fish and automatically fillets them. The equipment is very fast, using no more than a few seconds to process each fish. All waste from this processing is saved and made into fish meal, another very important feed ingredient making the project just that much more efficient. The need for marine, or salt water, fish meal is thereby eliminated and the protein signature of the meal is identical to the requirements of the fish being raised.