Patent Application
20110220846
The present invention relates to a method and apparatus for gathering and converting biomass to syngas. Specifically, non-densified agricultural by-products (such as straw and chaff) are used as a feedstock material for a modified countercurrent gasifier. The modified countercurrent gasifier converts the feedstock materials into a syngas and char.
Multiple processes currently exist for converting various plant-based materials into energy. Most of the current gasification processes have shown the greatest utility with wood and various compacted or densified materials. Many of the previous gasification technologies that have proven useful for high alkali, high silicon containing biomass like straw have been based on designs that include a “fluidized bed” configuration that requires (among other things) the utilization of sand or other solid materials to create a uniform and consistent heat gradient within the gasifier. Other biomass gasification reactors utilize “updraft” or “downdraft” designs. However, many of these processes specifically prohibit the use of grass and cereal straws as feedstock because at high operating temperatures (generally required for the gasification of wood), the burning of straws results in the formation of glass-like slag. The formation of slag is due to high concentrations of silicon and alkalis that are present in cereal and grass straws. The slag disrupts the gasification process and decreases the efficiency and net energy yield of the process. The modified countercurrent gasifier process of the current invention does not utilize fluidized bed technology.
Other recycling processes that use straw require transportation of the straw to a bio-refinery or to a recycling facility. However, transportation costs reduce the net benefits of the bio-energy generation process and in some cases may exceed the revenues generated by the process.
Although straw is among the most plentiful of agricultural by-product resources, there are a very limited number of applications in which straw can be profitably utilized and exploited. The need exists for an energy generating means that allows farmers and producers to directly convert straw into usable energy with minimal processing and transportation costs. The current invention discloses a method and apparatus that allows straw to be directly converted into syngas and char. The energy generation process of the current invention is relatively simple and can operate on a single-farm scale so that transportation costs are minimized and the energy generated from the process is usable on the farm where the straw is produced.
The current invention is directed to a syngas production system. The syngas production system comprises a modified countercurrent gasifier. The modified countercurrent gasifier includes a fuel gas inlet, a feedstock inlet that is above the fuel gas inlet, a production outlet that is above the feedstock inlet, and a recirculation tube that has an inlet above the feedstock inlet, and an outlet below the feedstock inlet.
In operation, as the feedstock is metered into the gasifier through the feedstock inlet, the gasifier converts the feedstock into syngas and char, and produces the syngas and char through the production outlet. In the preferred embodiment, the syngas is separated from the char by a cyclone separator. The syngas is then used to power a generator at the facility where the syngas is produced.
The current invention is also directed to a method of producing syngas. The method includes the steps of providing a modified countercurrent gasifier and metering a non-densified straw feedstock into the gasifier. Char and syngas are then produced from an upper portion of the gasifier.
The present invention comprises a method and apparatus for collecting non-densified biomass and converting the biomass to syngas and char that can be used at a facility where the biomass is generated. Although the preferred embodiment of the current invention is directed to the use of grass and cereal straws, other types of straw as well as cellulosic and non-cellulosic biomass should be considered within the scope of the current invention.
In the first step of the current process, non-densified biomass materials are gathered. This process is represented as the “Collect” step 20 shown in
In the preferred embodiment, at the conclusion of a growing season, wheat (for example) is harvested in a conventional manner and the straw is combined and compiled into a windrow. A self-propelled chopper picks up the windrow, “processes” the straw, and blows the straw into a truck so that the truck transports a load of processed straw (i.e. non-densified cellulosic biomass) to a holding/storage area. In the holding area, the straw is combined with chaff and other similar cellulosic agricultural by-products that have also been processed or otherwise reduced to a similar state as the straw.
In the preferred embodiment, the straw is “processed” by cutting the straw during a field chopping operation into lengths of approximately two inches so that the straw has a form that is usable as feedstock for the current invention. In alternative embodiments, the straw/feedstock may be processed into lengths of greater or less than two inches based on the nature of the feedstock and the capability of the hopper and/or feedstock conveyance system. The amount and type of “processing” required is dependent upon the nature of the straw or other cellulosic biomass gathered. The reduction of the straw and other agricultural by-products into a feedstock form is represented as the “Process” step 22 shown in
From the holding area, the processed biomass is directed into the syngas production system 40 (see
Through the gasification process, the biomass feedstock is converted into syngas and char. The process of producing syngas from the gasified feedstock is represented by the “Produce Syngas” step 28 shown in
The syngas production system 40 generally shown in
As noted supra and generally shown in
In the preferred embodiment, the feedstock conveyance system 43 comprises an auger 44 which continuously moves the feedstock into the body of the gasifier 46. In alternative embodiments, the feedstock may be continuously moved into the gasifier 46 by any means known in the art consistent with the process of metering the feedstock into the gasifier 46.
As shown in
In a modified countercurrent gasifier 46 system, oxygen and fuel gas are initially ignited within the gasifier 46 to bring the gasifier 46 to operating temperature. Biomass feedstock is then fed into the gasifier 46. After feedstock ignition occurs, the supply of fuel gas is discontinued and combustion within the gasifier 46 is self-sustaining as a result of the continuous ignition of the biomass. Feedstock is directed into the modified countercurrent gasifier 46 through an intermediate port 50 above the lower inlet 48. A recirculation tube 49 recycles a portion of the syngas and entrained char from an area above the intermediate port 50 to an area below the intermediate port 50.
In the preferred embodiment, air (that includes oxygen) may be used in combination with the fuel gas. The operating temperature in the area of the gasifier 46 adjacent to the intermediate port 50 is near the maximum temperature achieved by the burning of the fuel gas. Cellulosic feedstock combined with the air and propane (the fuel gas) combusts in a gasifier combustion zone 52 above the intermediate feedstock inlet port 50.
The recirculation tube 49 re-circulates a portion of the syngas with entrained char from an upper recirculation port 51 to a lower recirculation port 53. Recycling the syngas and entrained char improves the efficiency of the conversion of biomass carbon into combustible components of syngas and char. As discussed supra, the remaining syngas with entrained char is produced from an upper production outlet port 54 of the gasifier 46 in the direction of the arrow 57.
The modified countercurrent gasifier 46 of the current invention is distinguishable from prior art gasifiers because (among other things) the modified countercurrent gasifier 46 does not utilize a fluidized bed or additional complicating elements. The modified countercurrent gasifier 46 of the current invention functions most efficiently and effectively when a relatively homogenous and combustible processed cellulosic feedstock (like straw which includes chaff) is used. Using this type of feedstock, the gasifier 46 is able to operate at temperatures that are generally below 1400° F., and thereby avoid the formation of glass-like slag (discussed supra) that is generally associated with cereal grass feedstocks.
As shown in
The syngas is then directed out of the cyclone separation apparatus 58 in the direction of the arrow 62 to be used in any means known in the art. In the preferred embodiment, a blower motor 64 propels the syngas in the direction of the arrow 66 to an electrical generator which produces electrical power to be used at the facility where the biomass originates.
For the foregoing reasons, it is clear that the invention provides an innovative method and apparatus for the gasification of biomass to produce syngas and char that have utility in downstream processes. The invention may be modified in multiple ways and applied in various technological applications. The current invention may be customized as required by a specific operation or application, and the individual components may be modified and defined, as required, to achieve a desired result. Although the materials of construction are not described, they may include a variety of compositions consistent with the function of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
