Patent Application
20130125455
Fuel cell systems (such as solid oxide fuel cell systems) use heat, oxygen, and fuel to generate electrical power. Fuel cell systems typically operate in sterile, controlled environments where purified, gaseous fuels are piped in. The environment is typically sealed so that gases or materials (e.g., other than the gaseous fuel and oxygen) do not contaminate the system and/or the flow rate of the gaseous fuel and/or oxygen introduced is carefully controlled (e.g., using valves). New fuel cell systems which are able to be used in a wider range of environments and/or conditions are being developed for campers, hunters, and others who do not have access to a power grid. These rugged fuel cell systems are designed to hold solid fuels (e.g., animal dung, biomass, agricultural waste, and/or wood chips). Accessories related to such new fuel cell systems would be desirable, for example which improve or optimize the power generation of these new fuel cell systems and decrease performance degradation over time.
Various embodiments of the invention are disclosed in the following detailed description and the accompanying drawings.
The invention can be implemented in numerous ways, including as a process; an apparatus; a system; and/or a composition of matter. In this specification, these implementations, or any other form that the invention may take, may be referred to as techniques. In general, the order of the steps of disclosed processes may be altered within the scope of the invention.
A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate the principles of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured.
A fuel block configured to be inserted into a fuel cell system is described herein. Such fuel blocks include biomass (e.g., plant material, vegetation, wood, forest and wood plant residuals, leaves, grasses, agricultural wastes, energy crops, algae, pits, shells, husks, rinds, agricultural or food processing byproducts, paper processing byproducts, animal waste, chemicals and/or material separated or extracted from biomass, etc.) and/or charcoal generated from pyrolyzing a biomass. Charcoal is the residue obtained by removing water and other volatile constituents from biomass and is obtained by pyrolysis. Pyrolysis is a thermochemical decomposition of matter at elevated temperatures without the participation of oxygen or with insufficient oxygen for complete combustion of the matter. Although some ingredients and/or manufacturing processes related to fuel blocks may be similar to those for charcoal briquettes (e.g., for barbequing), the fuel blocks described herein are different from barbeque charcoals in that fuel blocks are designed to optimize electrical power production and lifetime of a fuel cell system. This may include, for example, releasing one or more gaseous, electrochemically-active fuels (e.g., H2 and CO) during elevated temperature operation (e.g. greater than 550° C.-650° C.) which are used in the fuel cell system's electrochemical reaction to generate electrical power and/or releasing oxygen (also used in the electrochemical reaction). The fuel blocks described herein pyrolyze and release gaseous, electrochemically-active fuels in close proximity to a fuel cell system and may release undesirable compounds that degrade fuel cell power output and/or accelerate corrosion of metal components of the fuel cell system (e.g. stainless steel) thus decreasing useful life of the system. This degradation of the fuel cell and/or corrosion of metal components is a result of elements other than carbon, hydrogen, and oxygen in the fuel block, for example chlorine, and so the fuel block provided has a composition modified for improved gasification during operation and/or decreased fuel cell degradation and/or decreased metal corrosion. In contrast, barbeque charcoals are designed to ignite quickly, burn completely, and/or optimize heat release. Although a fuel cell system's electrochemical reaction requires heat, the fuel block recited herein is not intended to be the primary or main heat source for the electrochemical reaction. As such, different ingredients may be used and/or an ingredient may serve a different purpose.
Fuel cell system 102 and fuel block 112 are heated by heat source 106. Fuel cell system 102 provides a relatively small amount of power to, for example, operate an LED lamp, radio, a fan for a cookstove, or charge a cell phone battery. In this example, fuel cell system 102 is configured to sit at or near the bottom of container 104. One example of container 104 is a ceramic jiko stove common to East Africa. Other examples of container 104 include barbeque grills (e.g., Weber grills); high efficiency cookstoves; stone or clay fireplaces; 3-stone fires; or sand or dirt campfires.
In this example, fuel cell system 102 is configured to hold a single fuel block 112 in a single fuel chamber. In some other embodiments, multiple fuel blocks are able to be inserted into a single fuel chamber. For example, a company may make two models of fuel cell systems but sells fuel blocks in a single size. The larger fuel cell system may have a fuel chamber that can fit two, three, or more fuel blocks whereas the smaller fuel cell system has a fuel chamber that fits a single fuel block. In some embodiments, a fuel cell system has two or more fuel chambers. In some embodiments, a fuel block is inserted into each chamber. In other embodiments, a single fuel block is shaped such that it fills or partially fills multiple fuel chambers. Fuel cell system 102 is able to operate with biomass (e.g., wood and/or animal dung) or charcoal inserted into a fuel chamber, but electrical power production may not be as good as when fuel block 112 is used.
When heat source 106 is ignited, fuel cell system 102 and fuel block 112 heat up. Air flows from the bottom or sides of container 104 and passes to the oxygen electrode (not shown) of the fuel cell(s). As fuel block 112 in the fuel chamber heats up, gaseous fuel species are released by fuel block 112 to the fuel cell(s), causing fuel cell system 102 to produce electrical power. The power is transferred out of the hot zone by power transfer leads 114 (e.g., to a rechargeable battery, a fan, an LED light, or a cell phone charger). If not replenished, the heat from heat source 106 will typically last from 30 minutes to several hours. Fuel cell system 102 produces power when the temperature is above approximately 550° C. with better power production occurring above 650-700° C. As such, the time that fuel cell system 102 is hot enough to produce power is generally shorter than the time during which heat source 106 is hot enough for cooking, space heating, etc., and may be as short as a few minutes. As heat source 106 heats fuel cell system 102 above about 550° C., electrical power is generated. As the temperature continues to rise, the power output increases. After some time, the temperature of heat source 106 and fuel cell system 102 begins to decrease and the power output also decreases. Thus, a typical session results in a “wave” of power generated. In some instances the session is short and fuel block 112 will not release all of the available fuel species and a portion of fuel block 112 will remain. Reusing the remaining portion of a previously used fuel block results in decreased power output and potentially causes damage to the fuel cell system. Techniques or features for distinguishing a new fuel block from a partially used fuel block ensures that an unskilled user does not reuse a fuel block. In other instances the session is long and most or all of the carbon or hydrocarbon content of the fuel block has been released. It is desirable that the remaining material, such as ash, not degrade the fuel cell or damage the fuel cell system.
Although fuel cell system 102 is able to use biomass in the fuel chamber, it is desirable to produce as much electrical power as possible. Fuel block 112, which includes biomass or charcoal generated from pyrolyzing a biomass, is designed to do this. For example, fuel block 112 is highly active in the production of gaseous electrochemically-active fuel species (e.g., H2 and CO) over a broad temperature range. This has the desirable result of increasing the instantaneous power output, as well as increasing the period of time (or, using another metric, increasing the range of temperatures) over which electrical power is produced. Since total energy is the integral of (e.g., instantaneous) power over time, total electrical energy production is improved (e.g., compared to fuels which may be found naturally at a camp site or other location, such as wood, charcoal, and/or animal dung). In some embodiments, fuel block 112 interacts with gaseous products from the fuel cell reactions (such as H2O and/or CO2) to generate more gaseous fuels (such as H2 and/or CO) for instance via reforming.
In contrast to other fuel cell systems employing purified gaseous fuels such as hydrogen or methane that are continuously piped in to generate electrical power, the solid oxide fuel cell system described herein (one embodiment of which is shown in
In some embodiments, compounds containing chlorine are minimized in fuel block 206, for example by selecting a low chlorine-content biomass or by removing chlorine compounds from the biomass and/or charcoal by rinsing with water (or, more generally, some liquid). In some embodiments, a chlorine removal process is not intended to remove all chlorine, but instead reduces (e.g., significantly) the amount of chlorine or chlorine compounds. It has been found that alkali and alkaline earth chlorides degrade the performance of a fuel cell system and reducing the chlorine content of a fuel block improves the lifetime of a fuel cell system. Common chlorides such as sodium chloride (NaCl), potassium chloride (KCl) and calcium chloride (CaCl2) have been found to be corrosion and degrade the performance of a fuel cell system.
In some embodiments, a finely divided biomass and/or charcoal derived from biomass has been compressed to form a fuel block configured to be inserted into a fuel cell system. A fuel block may be formed into a self-supporting object, such as a block, pill, sheet, pellet, or tablet. Compressing a fuel block increases the density and improves the handling and ease of insertion into the fuel chamber. Alternatively, other forming operations such as extrusion, tape-casting, tableting, etc. may be used to form the fuel block. A self-supporting object is easier to package and ship and the fuel block is preferably classified as non-hazardous for shipping by land, sea, and/or air.
In some embodiments, a fuel block has a wrapper. The following figure describes some example wrappers.
In various embodiments, wrapper 302 is impermeable or porous; clear, translucent or opaque; and/or loosely or tightly wrapped. Some example wrapper materials include paper, and polymer films such as acrylic, polyolefin, etc. In various embodiments, wrapper 302 is applied by wrapping, painting, spraying, dip-coating, shrink-wrapping or other means.
The following figures show some example performance graphs with wrappers made of various materials.
In some embodiments, a fuel block includes one or more binders. For example, if the fuel block uses solid fuel in the form of powder, dust, or pieces, a binder may be added to hold the fuel block together (e.g., for shipping, handling, and use by an end user). In one example, a binder is added to solid fuel in the form of powder. The mixture is then pressed, cast, extruded, rolled, tamped, and/or dried into the desired shape. Such processing may also compress the fuel powder, increasing the density of the fuel block. As a result, for a given fuel chamber size, more fuel can be inserted as a compressed fuel block, compared to loose powder. This results in higher power generation by the fuel cell during operation.
Some example binders include polymer binders (e.g., acrylic, polyethylene glycol, polyvinyl alcohol, hydroxypropylcellulose, paraffin, microcrystalline cellulose, lignin, sucrose, dextrin, lactose, and glycerin) and inorganic binders (e.g., such as clays, aluminosilicates, carbonate salts, and polyphosphates).
Various types of biomass may be pyrolyzed to obtain charcoal for use in a fuel block. In some embodiments chemicals and/or material separated or extracted from biomass or a specific portion of a biomass (e.g., heartwood, hemicellulose, lignin, bean, husk, etc.) may be pyrolyzed to obtain charcoal for a fuel block. The following figure shows example power performance using various types of biomass pyrolyzed to obtain charcoal for use in a fuel block. In some embodiments, biomass types having better/best performance (e.g., from the following figure) are used to create charcoal for use in fuel blocks.
In addition to biomass and/or charcoal generated from a pyrolyzed biomass, a fuel block may include an additive that improves the release of electrochemically-active fuel species from the fuel block. In some embodiments, an additive includes a potassium-containing compound. Potassium containing compounds include but are not limited to potassium oxide, potassium carbonate, potassium bicarbonate, potassium hydroxide, potassium nitrate, potassium phosphate, and potassium citrate. In some embodiments, a potassium-containing compound does not contain chlorine, for example potassium chloride (KCl) contains chlorine. In one example formulation, additives are 0-20 weight percent (wt %) of the fuel block. In some cases, less than 10 wt % is more attractive than 0-20 wt %. In some cases, 1-5 wt % is more attractive than less than 10 wt %. This may be because while in general increasing the amount of additive improves the release of electrochemically-active fuel species, some experiments have found that increasing the amount of potassium-containing compound additive beyond 10 wt % can increase degradation of the fuel cell system.
The following figure shows that in at least some embodiments, including a potassium-containing compound in a fuel block improves the performance of a fuel cell system. Some other additive examples include an alkali, an alkaline element, a hydrocarbon, a calcium-containing compound, a lithium-containing compound, an iron-containing compound, or a cobalt-containing compound.
A fuel cell system was loaded with approximately 15 g of fuel prepared by mixing mesquite charcoal powder with: nothing; 33% (by weight) oil; 10% (by weight) potassium compound; or 33% (by weight) oil and 10% (by weight) potassium compound. Various oils were experimented with, including: mineral oil, kerosene, candle wax, Crisco, and natural oils derived from olive, palm, soybean, and coconut. Various potassium-containing compounds were used, including: potassium carbonate, potassium bicarbonate, potash (the water soluble portion of charcoal ash). The power generated by the fuel cell operating with each fuel type was recorded during a thermal cycle of heating at 30° C./min to 750° C., holding the temperature for 10 minutes, and then cooling at 5° C./min to room temperature. Graph 700 shows the performance of the best performing mixtures from the experiment compared to pure charcoal. Charcoal alone (i.e., with no performance additive) is shown with an unbroken line; charcoal and mineral oil is shown with a dotted line; charcoal and potassium carbonate is shown with a dashed line; charcoal, mineral oil, and potassium carbonate is shown with a bold, dashed line.
The additives shown in graph 700 improve the peak power achieved during the hold at 750° C., as well as the power produced during heating and cooling. The total time of useful power production was increased with each of the additives. The addition of mineral oil and potassium carbonate provided the largest performance improvement.
In some embodiments, a potassium-containing compound (or other additive) is mixed together with a charcoal made from biomass. It was also determined during this experiment that potassium-containing compounds are most effective when they are mixed with the charcoal powder. Simply placing a potassium-containing compound inside the fuel chamber before or after loading the charcoal powder (i.e., without mixing the charcoal and potassium-containing compound together) did not result in a significant power improvement.
In some embodiments, a potassium-containing compound in a fuel block acts as a binder (e.g., to maintain the shape of a fuel block during shipping and handling).
A biomass may be pyrolyzed at a variety of temperatures when creating charcoal. The following figure shows some performance values for charcoal pyrolyzed at various temperatures. In some embodiments, charcoal is pyrolyzed at the temperature(s) having better or best performance as shown below.
In some embodiments, a moist inert gas is used during pyrolyzation. In one experiment, mesquite heartwood was pyrolyzed according to the procedure described above at 400° C. for 3 hours. Two batches were produced: one with dry argon flowing during pyrolysis, and one with moist argon flowing during pyrolysis. The argon was moistened by bubbling argon gas through a water bath at room temperature, resulting in a mixture of approximately 97% Ar and 3% water. The resulting charcoals were used to fuel a fuel cell system held at 0.65V at either 650° C. or 800° C. for 2 hours. At 650° C., the charcoal pyrolyzed in moist argon produced 1.9 times more charge than that pyrolyzed in dry argon. No significant difference was observed at 800° C. It is believed that the addition of water creates hydrogenated charcoal species during pyrolysis, and these species release hydrogen-rich gaseous fuel species during operation. It is further believed that these species are completely released at temperatures below 800° C., so they did not contribute to power generation at 800° C.
In some embodiments, a lid which is included with a fuel block is sticky or tacky where it comes into contact with fuel chamber 904 (e.g., the lid has a layer of adhesive, such as wax and the lip of the fuel chamber is pressed into the wax, connecting the lid and the fuel chamber). Alternatively, a portion of the fuel block (with or without a lid) is sticky or tacky. In some applications, this is attractive because it permits a lid to be used no matter the shape of a fuel chamber. Over time, fuel chambers may warp (e.g., because of the extreme heat from a fire) or bend (e.g., from being dropped or stepped on). A lid which is used over and over may become misaligned with the fuel chamber over time and it may be difficult to close or seal the reused lid. In other applications, the is attractive because it permits fuel blocks to be loaded into the bottom or side of the fuel chamber and prevent them from falling out during subsequent placement of the fuel cell system near the heat source.
Another advantage of having an integrated lid is that it may be easier to remove a spent fuel block and insert a new fuel block when a fuel cell system is still hot and/or in a hot zone. For example, a camper may have an abundant supply of firewood and is able to keep a campfire lit. The camper may wish to remove a spent fuel block while the fuel cell system remains in the campfire. Using tongs, the camper grabs on to the lid and pulls out the spent fuel block and inserts a new fuel block (e.g., again using tongs and grabbing the lid). In contrast, a reusable lid which must be buckled, clipped, or screwed on to a fuel chamber would require fine motor skills which would be difficult to perform while the fuel cell system is still hot and/or in a hot zone.
In some embodiments, a fuel block has some sensory indication (e.g., a visual or tactile indication) which enables a user to monitor the consumption of the solid fuel and/or decide when to replace a fuel block (e.g., when looking through opening 1004). In some embodiments, a fuel block includes a volatile binder, where the binding of fuel block is relatively weak and falls apart after use. In some embodiments, certain types of biomass or charcoals are included where such biomass or charcoals produce enough ash during use to effect a visible color change.
In some embodiments, a fuel block includes one or more indicator ingredients which changes color after use to clearly distinguish an unused fuel block from a used fuel block. Some example indicator ingredients include transition metal oxides, metallic flakes, dyes, and colored polymers. The indicator can be a change in color, surface finish (shiny to rough), reflective particles (sparkles), etc. In one example, fuel blocks were prepared by pressing charcoal powder and a binder. The fuel blocks were then painted with a mixture of acrylic emulsion and red/orange iron oxide (Fe3O4). The fuel blocks were then used in a fuel chamber placed in a ceramic jiko stove for one cooking session. After cooling, the fuel blocks were removed from the fuel chamber. The iron oxide had turned dark black from reduction (e.g., to FeO or Fe2O3). In some embodiments, an indicator ingredient may be contained only in the wrapper, dispersed throughout the solid fuel itself, etc.
Fuel block 1006 additionally includes mesh 1002. Mesh 1002 keeps the remnants of the solid fuel together so that if a fuel block is removed from a fuel chamber, all of the remnants of the solid fuel are removed from the fuel chamber. This enables a new fuel block to be inserted without being blocked by remnants from previously used fuel blocks. In some embodiments, mesh 1002 is made of metal wire.
Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed embodiments are illustrative and not restrictive.
This application claims priority to U.S. Provisional Patent Application No. 61/551,086 (Attorney Docket No. PSPIP005+) entitled FUEL BLOCK FOR HIGH TEMPERATURE ELECTROCHEMICAL DEVICE filed Oct. 25, 2011 which is incorporated herein by reference for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 61551086 | Oct 2011 | US |
