BIOMASS ENERGY CONVERSION APPARATUS AND METHOD

Abstract

Method and apparatus are disclosed to utilize the energy in biomass (waste agricultural products). The inventive method and apparatus utilized heat and mass flow to efficiently generate a variety of products from biomass. In various embodiment, the invention may generate a liquid fuel (such as methanol or dimethyl ether), pure liquid CO2 (intended for CO2 sequestration), a soil enhancement product (intended to return to the agricultural site), process heat, and/or electricity. In one embodiment, the process requires no external energy inputs, and preserves a large percentage (ie. >50%) of the energy contained in the biomass. In another embodiment, the inventive method and apparatus can selectively be operated to produce electricity and or liquid fuels.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/952,506, filed Jul. 27, 2007, the entire contents of which are hereby incorporated by reference herein and made part of this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to the utilization of energy from biomass, and more particularly to a method and system that is capable of converting crop residues into one or more of a liquid fuel, electrical power or process heat.

2. Discussion of the Background

The prospect of converting biomass in the form of agricultural products and/or waste into fuels or energy is appealing, and is seen as a possible route to energy independence. Many such materials are considered to be waste or are disposed of in a manner that poses environmental problems. One such practice is the burning of agricultural waste, such as crop residues, in the field. Since the waste generally contains minerals taken up from the soil to the plant, this process is beneficial to the soil. However, burning these residues releases CO₂ and pollutants into the air, and is often prohibited. The term “crop residue” as used herein refers, without limitation, to materials left in the field after a crop has been harvested, or left after the processing of the crop into a usable resource.

While there is great interest in using crop residue for producing liquid fuels or power, there is as yet no generally useful or economic means for doing so. One problem with utilizing crop residue, is that the cellulosic materials in the residuals are notoriously difficult to refine into fuels. Thus, for example, many prior art reactors for converting biomass into fuels result in tar, ash, and soot. Tar can negatively effect the performance of the conversion and the reactors, and generally must be removed before fuel synthesis. Ash may form slag in the reactor, and must be purged and disposed of at temperatures below their melting point. Soot reduces the quantity of any gases produced in the reactor. In addition, other problems in converting biomass to fuels include the high energy input needed to produce synthesis gas of sufficient quality to be used for liquid fuel synthesis, and the high capital cost associated with production of O₂ gas, if it is to be used in the process.

Thus there is a need in the art for a method and apparatus that permits for the production of liquid fuels from crop residue. Such a method and apparatus should be cost efficient, energy efficient, and operable on a wide variety of feedstocks, including but not limited to crop and crop residue. The method and apparatus should also be exhibit of one or more of the following features: the removal of trapped atmospheric gases from the feedstock prior to processing; the separation of most or all of the carbon dioxide that is not formed into a liquid fuel; the easy removal of tars or other compounds from the apparatus; have low emissions of oxides of nitrogen and sulfur compounds; the ability to provide one or more of electric power, process heat, or liquid fuels; and utilize energy efficiently within the process.

BRIEF SUMMARY OF THE INVENTION

In certain embodiments, the disadvantages of prior art are overcome by a method or apparatus which may include one or more of the following features: 1) gasifying the feedstock sequentially at increasing temperatures; 2) forming process oxygen from ambient air; 3) reacting the feedstock with oxygen; 4) providing heat for feedstock gasification from a fuel synthesis process; 5) reacting the gasified feedstock with water to produce a favorable hydrogen-to-carbon monoxide ratio, and then removing the carbon dioxide and excess water to produce a mixture useful for a conversion to fuels; 6) combining the oxidizing gas with water and/or recirculating evolved gasses to achieve the proper stoichiometry for hydrogen rich synthesis gas; 7) producing an oxygen rich gas using surplus thermal energy from partial oxidation; 8) removing and sequestering or utilizing the carbon dioxide from the biomass; 9) a flash cooling step to prevent soot formation; 10) providing the heat required for air separation from a gas cooling process; and an efficient and cost effective method for disposal of agricultural waste.

In certain embodiments, a method is provided for operating a biomass energy conversion system. The method includes receiving a biomass, selectively generating output from the biomass energy conversion system, where the output is one or more of electric power or liquid fuel, and providing the output.

In certain other embodiments, an apparatus is provided for generating either electric power or liquid fuel from a biomass. The apparatus includes a biomass gasification unit to accept biomass and produce a gas stream, a generator to produce electric power from the gas stream, a synthesis unit to produce a liquid fuel from the gas stream, and one or more valves to selectively provide said gas stream to one or more of said generator or said synthesis unit. The one or more valves control the amount of electric power and the amount of liquid fuel provided from the biomass.

In certain embodiments, a method for utilizing biomass is provided. The method includes a torrefaction process, one or more additional processes, and providing heat from at least one of said one or more additional processes to said torrefaction process.

In certain other embodiments, an apparatus is provided for utilizing a biomass. The apparatus includes an oxygen separation unit to produce oxygen-enriched gases from air; a partial oxidation unit to accept a biomass stream and the oxygen-enriched gases; and a thermoelectric generator. The thermoelectric generator accepts heat from the partial oxidation unit and provides electricity for at least partially operating the oxygen separation unit.

Certain other embodiments of a biomass to fuel conversion system or process may include, but are not limited to, one or more of the following: 1) the production of oxygen; 2) energy recovery from the system to produce oxygen or nitrogen depleted air; 3) the use of oxygen, or nitrogen depleted air as the oxidizer; 4) the removal of trapped ambient nitrogen from the biomass; 5) effectively remove tars and other buildup from the system; 6) a system that facilitates sequestering or using the CO2 from the biomass; 7) utilizing several conversion steps, some of which are endothermic and some of which are exothermic, and efficiently using energy by transferring heat from exothermic to endothermic process steps; and 8) operating one of the conversion steps according to the following competing reactions by recirculating gases and/or adding water: a) C+CO₂→2 CO; b) C+H₂O→CO+H₂; c) C+2 H₂O→CO₂+2H₂; d) CO+H₂O→CO₂+H₂; e) CH₄+2H₂O→CO₂+4H₂; 9) prevention of soot formation from the unwanted reverse reaction of 8a) 2CO→C+CO₂.; 10) Mixing the oxidizer with steam and introducing this mixture as the oxidizer with the benefit of improved thermal uniformity in the partial oxidation reaction; 11) Mixing the oxidizer with steam and recirculated expressed hydrocarbon gasses, thus partially oxidizing these gases prior to introduction to the gassifier, resulting in improved thermal uniformity in the gassifier and improved synthesis gas composition; or 12) utilizing the ash content of the gasified biomass product as an inert, thermal transfer medium, and controlling the ash volume in the gassifier.

Advantages over the prior art may include, but are not limited to: a) integration of oxygen production from air with the system; 2) providing for carbon dioxide sequestration; 3) eliminating nitrogen and/or argon contamination from the system; 4) incorporation of a cleaning cycle; 5) providing a smaller scale process with good efficiency and economics; 6) increasing the carbon conversion efficiency and fuel output by effectively using heat generated in the process; 7) lowering the temperature required to achieve proper synthesis gas composition; 8) provide for opportunistic electrical generation; 9) provide process heat for general use, for instance in HVAC systems; 10) reducing the operating and maintenance costs; and 11) increasing the amount of biomass that may be processed and/or reducing the processing time.

In certain embodiments, the fuel produced is methanol. The methanol can be used, for example, as a transportation fuel or in hydrocarbon processing. The carbon dioxide from the system may be used to enhance oil recover or otherwise be sequestered or utilized

In certain other embodiments, the fuel produced is DME (dimethylether). The DME can be used, for example, as a transportation fuel or as a propellant. The carbon dioxide from the system may be used to enhance oil recover or otherwise be sequestered or utilized

In certain embodiments, the fuel is produced in conjunction with electricity. For instance, when fuel demand is low, electricity can be produced and sold. Alternatively, when consumer electricity demand is high, electrical production may have higher value. A real time electro-mechanical system to monitor and configure the optimum product mix reduces operating labor while optimizing the economic value. The carbon dioxide from the system may be used to enhance oil recover or otherwise be sequestered or utilized. In one embodiment, the relative output levels of fuel and electricity is monitored and the system is automatically configured to match the application needs.

These features together with the various ancillary provisions and features which will become apparent to those skilled in the art from the following detailed description, are attained by the method or apparatus of the present invention, preferred embodiments thereof being shown with reference to the accompanying drawings, by way of example only, wherein:

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a schematic diagram of the interaction of agriculture with the environment;

FIG. 2 is a schematic of a first embodiment biomass energy conversion apparatus;

FIG. 3 is a schematic of a first embodiment of a process for a biomass energy conversion apparatus;

FIG. 4 is a schematic of a second embodiment of a process for a biomass energy conversion apparatus;

FIG. 5 is a schematic of a third embodiment of a process for a biomass energy conversion apparatus;

FIG. 6 is a graph showing results of calculations of the process of FIG. 5 at a constant pressure and variable partial oxidation process temperature;

FIG. 7 is a schematic of a fourth embodiment of a process for a biomass energy conversion apparatus;

FIG. 8 is a graph showing results of calculations of the process of FIG. 7 at a constant pressure and variable partial oxidation process temperature; and

FIG. 9 is a schematic of a fifth embodiment of a process for a biomass energy conversion apparatus.

Reference symbols are used in the Figures to indicate certain components, aspects or features shown therein, with reference symbols common to more than one Figure indicating like components, aspects or features shown therein.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be understood from a systems approach to agriculture, and in particular to FIG. 1, which is a schematic diagram showing the interaction of a prior art agricultural system 100 with the environment. Plants within system 100 utilize CO₂ from the air and nutrients from the soil, water from the environment and energy from the sun to produce O₂, crops, and non-crop residue. A simplified overall chemical balance may be written as:

6CO_2(gas)+12H₂O_(liquid)+photons→C₆H₁₂O_6(aqueous)+6O_2(gas)+6H₂O_(liquid)

The crop residue includes carbon compounds such as cellulose, hemicellulose, and lignin. Rice straw, for example, has a stoichiometry of CH_1.77 O_0.72. The crop residue typically has little or no nutritional value, and is either is burnt to fertilize the soil or is disposed of. Examples are presented herein with a crop residue of rice straw. These examples are for illustrative purposes only, and are not meant to be limiting of the scope of the present invention.

FIG. 2 is a schematic of a first embodiment biomass energy conversion apparatus 200. Apparatus 200 includes an oxygen production unit 210 and a thermochemical conversion unit 220. Also shown in FIG. 2 is the flow of air, water, and crop residue into apparatus 200, and the flow of nitrogen, argon, a fuel, carbon dioxide, and fertilizer from apparatus 200. Although FIG. 2 shows oxygen production unit 210 and thermochemical conversion unit 220, in certain embodiments, portions of the units are integrated or shared.

Biomass energy conversion apparatus 200 may work in conjunction with prior art agricultural process 100 to convert agricultural crop residue into useful products including, but not limited to, one or more of a fuel, electric power, fertilizer, or process heat. The fuel may be, for example and without limitation, a liquid fuel, such as methanol or dimethyl ether. In addition, apparatus 200 may also produce concentrated streams of nitrogen and/or carbon dioxide, which may be used for industrial purposes or, in the case of carbon dioxide, sequestered to remove it from the environment.

In one embodiment, one or more components of air are separated within oxygen production unit 210. Thus, for example, unit 210 accepts air from the environment and generates oxygen, or alternatively oxygen-enriched air, for use as an oxidizer in thermochemical conversion unit 220. The nitrogen may be a waste stream of unit 210 or, alternatively, some or all of the nitrogen may be provided to unit 220 for inclusion in a fertilizer.

Thermochemical conversion unit 220 accepts oxygen from unit 210, water, and crop residue (such as crop residue from prior art agricultural process 100) and produces three streams: a fuel, carbon dioxide, and fertilizer, which includes minerals from the crop residue. It is preferred, though not necessary, for the fuel to be transportable in a liquid state—that is it is predominantly liquid at ambient conditions or under easily achievable elevated pressures and/or reduced temperatures. In another embodiment, some or all of the fuel is consumed within unit 220 to generate electric power.

In one embodiment, oxygen production unit 210 and thermochemical conversion unit 220 are integrated, so that heat and/or work from thermochemical conversion process 220 drives some or all of the oxygen production unit 210. In another embodiment, grid electricity is used to power oxygen production unit 210 and thermochemical conversion unit 220 generates electricity which is returned to the electric grid. Alternatively, biomass energy conversion apparatus 200 operates independent of the electric grid.

In one embodiment, apparatus 200 converts crop residue, including but not limited to rice straw, to methanol or dimethyl ether, pure liquid CO₂, and a soil enhancement product formed by ash from the conversion process. In another embodiment, apparatus 200 requires no external energy inputs, and preserves a large percentage (i.e. ˜50%) of the energy contained in the biomass.

As an example of fuel synthesis reactions which may take place as part of thermochemical conversion unit 220, the overall reaction for the synthesis of methanol from glucose is the exothermic reaction:

C₆H₁₂O_6(solid)+3/2O_2(gas)→3CH₃OH_(liquid)+3 CO_2(gas); ΔH=−634.12 MJ/Kmol.

In this reaction, 50% of the carbon is converted to methanol. Approximately 78% of the energy content is retained in the methanol since the heat of combustion of glucose, given by

C₆H₁₂O_6(solid)+6O_2(gas)→6CO_2(gas))+6H₂O_(liquid)ΔH=−2,813.52 MJ/Kmol,

is approximately 78% of the the heat of combustion of methanol:

3CH₃OH_(liquid)+9/2O_2(gas)→3CO_2(gas)+6H₂O_(liquid)ΔH=−2,179.4 MJ/Kmol

In addition, the partial oxidation of the glucose can provides the energy to drive the conversion process.

For rice straw, the overall reaction is similar, but involves many sequential intermediate reactions. A chemical description of rice straw follows, and a process to economically convert rice straw to methanol and CO₂ will be described. Ideally this equipment will be located close (<30 miles) to the rice fields, to minimize transportation costs and losses.

Rice straw is a combination of cellulose, hemicellulose and lignin and mineral compounds (ash). As an example, 1 tonne of dry rice straw includes 70% hydrocarbons and 20% ash and 10% water. Thus a tonne of dry, ash free rice straw contains 28 kmol of elemental carbon. More specifically, the stoichiometry and mass fraction of ash free rice straw is given in Table I, and the energy content is calculated in Table II. The stoichiometry of rice straw may be represented as CH_1.77O_0.72(solid), and the energy content is 15.413 kJ/g.

TABLE I
Composition of Rice Straw
						Fraction
						Dry
	Compound stoichiometry	C	H	O	N	Mass
	Cellulose	6	12	5	0	37%
	Hemi-cellulose	5	10	5	0	24%
	Lignin	10	12	3	0	14%
	Protein (less S, P)	11	18	4	3	5%
	Approximate error	1	−4	0	0	1%

TABLE II
Energy Content of Rice Straw
Energy (HHV) Value
Calculation
	C	0.3968 × 34.91 =	13.854
	H	0.0497 × 117.83 =	5.857
	O	0.3578 × −10.34 =	−3.700
	S	0.0040 × 10.05 =	0.040
	N	0.1600 × −1.51 =	−0.242
	ash	0.1878 × −2.11 =	−0.396
			15.413	kJ/g

FIG. 3 is a schematic of a first embodiment of a process 300 for a biomass energy conversion apparatus which may be, for example and without limitation, biomass energy conversion apparatus 200. Process 300 shows the energy and mass flow and includes an oxygen separation process 310 and a thermochemical conversion process 320. As described in further detail subsequently, process 320 converts biomass into a gas mixture of H₂ and CO having a molar ratio of 2:1 such that the methanol synthesis process 327 can generate methanol (CH₃OH).

Thermochemical conversion process 320 includes a biomass preparation process 321, a torrefaction process 322, a pyrolysis process 323, a partial oxidation process 324, a water shift process 325, a carbon dioxide removal process 326, and a methanol synthesis process 327. One or more of processes 310, 321, 322, 323, 324, 325, 326, and 327 may be carried in one or more individual apparatus, and/or one or more individual apparatus may carry out one or more of the processes. In one embodiment oxygen separation process 310 is carried out by oxygen separation unit 210 and thermochemical conversion process 320 is carried out by thermochemical conversion unit 220.

An indication of representative, though not limiting, materials flowing into and out of 310, 321, 322, 323, 324, 325, 326, and 327 are indicated in FIG. 3. The materials indicated are illustrative for biomass, and other components may be present.

Also shown of representative, though not limiting, energy or power flows are several additional arrows in FIG. 3. The flow of heat from methanol synthesis process 327 into torrefaction process 322 is indicated as Q1, and the flow of heat from partial oxidation process 324 into a pyrolysis process 323 is indicated as Q2. It is understood that there may be other heat flows into and out of the various processes in addition to Q1 and Q2, which are shown for the purposes of discussion of several aspects of the present invention.

Typically, processes 310, 321, 322, 323, and 326 are endothermic (requiring the input of energy to operate), and processes 324 and 325 are exothermic (generating excess heat). FIG. 3, 4, 5, 7, and 9, which each show processes, do not explicitly show all of the energy balances for each process. In general, the present invention includes the exchange of thermal or electric power between components to maximize the thermal efficiency of the overall process.

Biomass preparation process 321 prepares the biomass by drying and/or compressing the biomass prior to thermal conversion. In the embodiment in FIG. 3, biomass is heated and compressed in biomass preparation process 321, converting biomass to compressed biomass, at a low or slightly elevated temperature, T0. Compression reduces the volume of biomass and squeezes out any trapped air—specifically nitrogen gas which may interfere with process 320. In one embodiment, temperature T0, is greater than the ambient temperature. In another embodiment, temperature T0 is greater than 100° C., or is approximately 150° C. The elevated temperature evaporates the water, drying the biomass. The apparatus to carry out biomass preparation process 321 may include devices commonly used for solid handling applications in the food processing industry, or specialty devices developed for biomass power applications.

The compressed biomass undergoes torrefaction in torrefaction process 322 at low temperature, T1. In one embodiment, the equipment to operate torrefaction process 322 may be insulated pipe, or an insulated pipe with an internal auger to move material. The output of the torrefaction process 322 includes, in one embodiment, the torrefaction products of biomass, which may include torrefaction products of hemicellulose such as CO₂, H₂O and acetic acid, and de-polymerized solids such as cellulose and lignin, with some solids remaining. In one embodiment, T1 is between 200° C. and 300° C. In another embodiment, T1 is approximately 230° C. In another embodiment, the temperature T1 is maintained by heat transfer Q1 from methanol synthesis process 327, which, as described subsequently, may operate at a higher temperature T5.

The gas and solid products from torrefaction process 322 then undergo pyrolysis in pyrolysis process 324 at a temperature T2, which is greater than temperature T1. In one embodiment, during pyrolysis, de-polymerized cellulose and lignin are converted in torrefaction process 322 to C(s), CO, CO₂, H₂O, and hydrocarbon gases. In one embodiment, the temperature T1 is between approximately 400° C. and approximately 750° C. In another embodiment, the temperature T2 is maintained by heat transfer Q2 from partial oxidation process 324, which, as described subsequently, may operate at a higher temperature T3. In one embodiment, the equipment to operate the pyrolysis process 324 may be an insulated pipe with provision for gas exchange and counterflow.

In oxygen separation process 310, air is separated into an oxygen fraction and an oxygen-depleted air fraction. In one embodiment, the energy for process 310 (not shown in FIG. 3) is obtained from exothermic reactions occurring in process 320, such as from the partial oxidation process 324. In another embodiment, an apparatus for carrying out oxygen separation process 310 may include cryogenic equipment, such as the Apsen 1000 manufactured by Cosmodyne, Inc. (Seal Beach, Calif.). In yet another embodiment, the oxygen separation process 310 may be accomplished by using a PSA (Pressure Swing Absorption) or VPSA (Vacuum Pressure Swing Absorption) plant, such as manufactured by Universal Industrial Gasses, Inc.

In partial oxidation process 324, the oxygen and the gas and solid products from pyrolysis process 323 are partially oxidized, producing ash and CO₂, CO, H₂O, and H₂. The ash is removed, producing a stream of CO₂, CO, H₂O, and H₂. The ash includes mineral content, as such may be useful for treating soil. In one embodiment, the equipment that operates partial oxidation process 324 may include a furnace, such as furnaces routinely manufactured for the coal power industry.

Water shift process 325 accepts gases from partial oxidation process 324 and water, and operates at a temperature T4. The water shift reaction is a well-known reaction that converts carbon monoxide and water to carbon dioxide and hydrogen through the reaction: CO+H₂O→CO₂+H₂. Preferably, the amount of water added to the water shift process 325 is sufficient to result in a H₂:CO ratio of 2:1, which is an advantageous proportion for use in methanol synthesis process 327. Specifically, the amount of H₂O added is selected to shift some of the CO to H₂, and give the 2:1 ratio of H₂ to CO.

In CO2 removal process 326, gases from water shift process 325 are compressed to a pressure of 50 bars, which liquefies the CO₂ for easy separation from the remaining H₂ and CO. In one embodiment, the energy required to operate CO2 removal process 326 is obtained from the exothermic partial oxidation process 324. The CO₂ thus removed may be used commercially or used to enhance oil recovery or otherwise sequestered. In one embodiment, the equipment to operate the CO2 removal process 326 may include a condenser and compressor.

Lastly, methanol synthesis process 327 accepts material from CO2 removal process 326 and produces methanol. Specifically, H₂ and CO undergo conversion to methanol at a temperature T5 according to the reaction:

CO_(gas)+2H_2(gas)→CH₃OH_(liquid).

In certain embodiments, the energy required to drive the endothermic processes (torrefaction process 322, pyrolysis process 323, Biomass preparation process 321, and oxygen separation process 310) may be obtained from the exothermic processes (partial oxidation process 324 and methanol synthesis process 327). In the previous discussion, energy from methanol synthesis process 327 is sufficient to operate torrefaction process 322, and energy from partial oxidation process 324 is sufficient to operate the pyrolysis process 323, the oxygen separation process 310, and the carbon dioxide removal process 326.

From an energy and mass balance of the system of FIG. 3, and it has been determined that process 300 achieves: 1) a 50% carbon to methanol conversion; 2) a 50% carbon to CO₂ conversion; 3) retention of 75% of the original biomass energy content in the methanol; and 4) the production of 565 liters of methanol for each dry tonne of rice straw.

FIG. 4 is a schematic of a second embodiment of a process 400 for a biomass energy conversion apparatus which may be, for example and without limitation, biomass energy conversion apparatus 200. Process 400 is generally similar to process 300, except as explicitly discussed below.

In process 400, oxygen from oxygen separation process 310 is provided to partial oxidation process 324 and a pyrolysis process 423. The energy to drive the pyrolysis reactions in pyrolysis process 323, which was, for example supplied by Q2 in processes 300, is supplied by exothermic reactions between oxygen and the other gases entering the pyrolysis. Thus, for example, the equipment to carry out pyrolysis process 432 includes a burner to combust oxygen to increase the temperature of the pyrolysis process to a value of T2.

Also in process 400, heat in the amount of Q3 is provided from partial oxidation process 324 to a thermal electric generator 401, which powers oxygen separation process 310. Some of the power from the thermal electric generator 401 may alternatively be provided to biomass preparation process 321.

FIG. 5 is a schematic of a third embodiment of a process 500 for a biomass energy conversion apparatus which may be, for example and without limitation, biomass energy conversion apparatus 200. Process 500 is generally similar to processes 300 and/or 400, and includes a thermochemical conversion process 520 which is generally similar to processes 320, except as explicitly discussed below. Specifically, process 500 has components that may be configured to achieve different outputs from a biomass stream and in which electricity is chosen as the primary output.

Process 520 includes an electric generator 501, heat exchange processes 503 and 505, a condenser process 507 and a compression process 509. Process 520 converts biomass into electricity in electric generator 501, which requires an energy rich stream that does not have to have the specific concentrations required of a fuel synthesis reaction. Process 520 therefore does not require a water shift process to obtain specific molar ratios, as does methanol synthesis process 327

The input biomass flow is indicated in FIG. 5 as M₁, the prepared biomass as M₂, the torrifacted biomass as M′₁, the partially oxidized gases as M₃, the electric generator effluent as M₄. The heat flow from heat exchange processes 505 to biomass preparation process 321 is Q′1, the heat flow from heat exchange processes 505 to compression process 509 is Q4, and the external power into biomass preparation process is E_1e. The heat flow from heat exchange processes 503 to torrefaction process 322 is Q1. Electric generator 501 provides electric power E_3e to the oxygen separation process 310 and E_e as electric power production of process 500.

Oxygen is separated from air in oxygen separation process 310. In one embodiment, the separation is cryogenic, and the energy to run process 310 is obtained from electric power provided by electric generator 501. One example of such cryogenic equipment is the Apsen 1000 manufactured by Cosmodyne, Inc (Seal Beach, Calif.). The cryogenically produced oxygen and oxygen-depleted air are obtained at high pressure, and energy can be recovered from these streams in a turbine (not shown). This energy can be used, for instance, to cool the cold side of the electric generator 501. In a second embodiment, the energy required for selectively removing nitrogen from air, producing a gas essentially comprised of 95% O₂ and 5% Ar, at low pressure, is obtained from the electric generator 501. One example of a low-pressure system is a PSA (Pressure Swing Absorption) or VPSA (Vacuum Pressure Swing Absorption) plant, such as manufactured by Universal Industrial Gases, Inc. (Easton, Pa.).

The gases from partial oxidation process 324 are sent to the electric generator 501. In one embodiment, electric generator 501 operates according to an IGCC process (Chevron Corp, San Ramon, Calif.), and can provide very high efficiency (ie. 50%). In another embodiment, electric generator 501 is a steam generator, with the steam being heated by combustion of the partially oxidized gases. Electric generators are commonly available and the technology choice will be determined by the scale of the overall system. In either case, flue gases (stream M₄ in FIG. 5) will be generated by electric generator 501. The flue gases are then preferably cooled in heat exchange processes 503 and 505 and condenser process 507 and compressed compression process 509 to remove liquid CO₂ at a pressure of 10 bars, which liquefies the H₂O for easy separation from the remaining CO₂. In one embodiment, the energy required to operate the processes 507 and 509 is obtained from the electric generator 501. The CO₂ may be used commercially or used to enhance oil recovery or otherwise sequestered.

In certain embodiments, the energy required to drive the endothermic processes (torrefaction process 322, pyrolysis process 323, biomass preparation process 321, and oxygen separation process 310) may be obtained from the exothermic processes (partial oxidation process 324 and methanol synthesis process 327). In the previous discussion, energy from methanol synthesis process 327 is sufficient to operate torrefaction process 322, and energy from partial oxidation process 324 is sufficient to operate the pyrolysis process 323, the oxygen separation process 310, and the carbon dioxide removal process 326.

An energy and mass balance of the embodiment and configuration of FIG. 5 has determined that process 500 achieves: 1) a 100% carbon to CO₂ conversion; 2) conversion of 25% of the original biomass energy content into electricity.

FIG. 6 is a graph 600 showing results of equilibrium calculations corresponding to the process of FIG. 5. Specifically, graph 600 shows species fractions exiting partial oxidation process 324 at various temperatures T3 from 0 C to 1000 C, while the pressure is 1 bar.

Table III shows details of the results for the conversion of biomass (the “Input Species”) to gases exiting partial oxidation process 324 at a temperature T3 of 800 C, which the approximate temperature at which the gasses exiting partial oxidation process 324 contain no hydrocarbons.

TABLE III
Partial Oxidation Process Gases for Process 500 at a Partial Oxidation Temperature of
800 C.
	Temper.	Amount	Amount	Amount	Latent H	Total H
	° C.	kmol	kg	Nm3	MJ	MJ
INPUT SPECIES (1)
Formula
H2O (g)	120.000	1.110	19.997	24.879	3.57	−264.86
C6H10O4 (ADAg)	120.000	4.790	700.023	107.361	87.46	−4055.10
O2 (g)	25.000	9.580	306.549	218.339	0.00	0.00
OUTPUT SPECIES (1)
Formula
H2O (g)	800.000	4.905	88.365	109.939	142.75	−1043.41
CO2 (g)	800.000	5.861	257.941	133.579	219.30	−2087.03
CO (g)	800.000	22.803	638.721	519.708	550.35	−1970.32
H2 (g)	800.000	20.003	40.323	458.205	456.90	456.90
CH4 (g)	800.000	0.076	1.221	1.706	3.37	−2.31
		Kmol	kg	Nm3	MJ	MJ
BALANCE:		38.168	0.002	872.557	1281.64	−327.21

FIG. 7 is a schematic of a fourth embodiment of a process 700 for a biomass energy conversion apparatus which may be, for example and without limitation, biomass energy conversion apparatus 200. Process 700 is generally similar to processes 300, 400, and/or 500, and includes a thermochemical conversion process 720 which is generally similar to processes 320, except as explicitly discussed below.

Process 700 includes an oxidizer/steam mixing process 701, a flash cooler process 703 and heater 705, condensing process 707 and a first compression process 709 to remove carbon dioxide, a second compression process 711, and an optional DME synthesis process 713.

Oxygen produced by the oxygen separation process 310 is combined with a predetermined volume of steam in the oxidizer/steam mixing process 701 and then provided to the partial oxidation process 324. By combining H₂O and O₂ as an oxidizer, the ratio of CO:H₂ in the resulting synthesis gas can be optimized for methanol synthesis stoichiometry, eliminating the need for a water shift process as, for example, in process 300. Alternatively, process 700 may be run with no or minimal water entering the oxidizer mixing unit, and an water shift reaction processor such as process 325. In either case, adding the H₂O converts carbon monoxide and water to carbon dioxide and hydrogen through the reaction: CO+H₂O→CO₂+H₂. Preferably, the amount of water added to oxidizer/steam mixing processor 701 (water shift process 325) is sufficient to result in a H₂:CO ratio of 2:1, which will be needed in methanol synthesis process 327. In one embodiment, steam is added at approximately 400-600° C. This steam is generated in the heater 705, which has an input of recycled water, which is expressed and separated in the condensing process 707, and is approximately the proper volume to achieve the desired synthesis gas composition. The recycled H₂O stream is heated to produce steam by a counterflow heat exchanger coupling the H₂O stream to the POX output gas stream. It is important that this heat exchange process cool the synthesis gas sufficiently quickly to eliminate the formation of soot through the unwanted reaction 2CO→C(s)+CO₂.

The cooled gases from flash cooler 703 are then condensed (phase separating the H₂O) and compressed to 7-10 bars, which liquefies the CO₂ for easy separation from the remaining H₂ and CO. In one embodiment, the energy required to operate condensing process 707 is obtained from the exothermic partial oxidation process 324. In a second embodiment, the energy required is supplied from grid electricity. The CO₂ may be used commercially or used to enhance oil recovery or otherwise sequestered.

As an alternative embodiment, the methanol can be further processed to DME in the optional DME synthesis process 713 to provide a diesel alternative with a higher energy density than methanol, and which may also be more appropriate for farming equipment and trucking. This DME is produced according to the reaction:

2CH3₂OH_(liquids)→CH₃OCH_3(liquid)+H₂O_(liquid)

In one embodiment, the equipment to operate the DME synthesis process 713 may be a DME Reactor, such as manufactured for the coal-to-liquid industry.

Based on system simulations of the energy and mass balance of the system of FIG. 7, it has been determined that process 700 achieves: 1) ˜50% carbon to methanol conversion; 2) ˜50% carbon to CO2 conversion; 3) retention of 75% of the original biomass energy content in the fuel; and 4) the production of 565 liters of methanol for each dry tonne of rice straw.

FIG. 8 is a graph 800 showing results of equilibrium calculations corresponding to the process of FIG. 7. Specifically, graph 800 shows species fractions exiting partial oxidation process 324 at various temperatures T3 from 0 C to 1000 C, while the pressure is 1 bar, including steam provided from oxidizer/steam mixing process 701.

Table IV shows details of the results for the conversion of biomass (the “Input Species”) to gases exiting partial oxidation process 324 at a temperature T3 of 800 C, which the approximate temperature at which the gasses exiting partial oxidation process 324 contain no hydrocarbons.

TABLE IV
Results for Process 700 at a partial oxidation temperature of 800 C.
	Temper.	Amount	Amount	Amount	Latent H	Total H
	° C.	kmol	kg	Nm3	MJ	MJ
INPUT SPECIES (1)
Formula
H2O (g)	500.000	34.051	613.436	763.205	578.36	−7656.05
C6H10O4 (ADAg)	120.000	4.790	700.023	107.361	87.46	−4055.10
O2 (g)	25.000	9.580	306.549	218.339	0.00	0.00
OUTPUT SPECIES (1)
Formula
H2O (g)	800.000	29.000	522.441	649.994	843.96	−6168.98
CO2 (g)	800.000	14.700	646.944	335.031	550.04	−5234.48
CO (g)	800.000	14.000	392.146	319.077	337.89	−1209.69
H2 (g)	800.000	29.000	58.458	664.298	662.41	662.41
CH4 (g)	800.000	0.000	0.000	0.000	0.00	0.00
		kmol	kg	Nm3	MJ	MJ
BALANCE:		38.279	−0.018	879.494	1728.48	−239.60

In certain embodiments, the components of the various embodiments may be combined in a single device, and the selection of components for operation may be selected for specific outputs. Thus, for example, apparatus for carrying out process 500 provides for the production of electricity, and apparatus for carrying out process 300, 400, or 700 provides for the production of liquid fuels. In this way, a plant may be operated to economic advantage, such as by producing electricity at high electricity demand and producing liquid fuels ad low electricity demand.

FIG. 9 is a schematic of a fifth embodiment of a process 900 for a biomass energy conversion apparatus which may be, for example and without limitation, biomass energy conversion apparatus 200. Process 900 is generally similar to processes 300, 400, 500 and/or 700, except as explicitly discussed below.

Process 900 includes a includes a thermochemical conversion process 920 that further includes a biomass-to-gas generation process 921, a fuel synthesis process 923, and an electric generation process 925. Oxygen from oxygen separation process 310 and biomass are provided to biomass-generation process 921. The flow of material from process 921 is then controlled by valves V1 and V2 to flow to one or more of fuel synthesis process 923 or electric generation process 925. As shown in FIG. 9, heat Q from electric generation process 925 may flow to fuel synthesis process 923. This heat flow may maintain the fuel synthesis components at a temperature necessary to produce fuel the instant the flow diverts gas through fuel synthesis process 923.

In one embodiment, biomass-generation process 921 includes biomass preparation process 321, torrefaction process 322, pyrolysis process 323, and partial oxidation process 324. In another embodiment, biomass-generation process 921 includes thermal generator process 401.

In one embodiment, fuel synthesis process 923 includes water shift process 325, carbon dioxide removal process 326, methanol synthesis process 327, as in FIG. 3, and optionally DMI synthesis process 713. In another embodiment, fuel synthesis process 923 includes oxidizer/steam mixing process 701, flash cooler process 703 and heater 705, condensing process 707 and first compression process 709, second compression process 711, and an optional DME synthesis process 713, as in FIG. 7.

In one embodiment, electric generation process 925 includes electric generator 501, heat exchange processes 503 and 505, condenser process 507 and compression process 509 as in FIG. 5.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

Similarly, it should be appreciated that in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this invention.

Thus, while there has been described what is believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such changes and modifications as fall within the scope of the invention. For example, any formulas given above are merely representative of procedures that may be used. Functionality may be added or deleted from the block diagrams and operations may be interchanged among functional blocks. Steps may be added or deleted to methods described within the scope of the present invention.

Claims

1. A method of operating a biomass energy conversion system, said method comprising:

receiving a biomass;

selectively generating output from the biomass energy conversion system, where said output is one or more of electric power or liquid fuel; and

providing said output.

2. The method of claim 1, where said biomass energy conversion system includes a biomass gasification unit to accept a biomass and produce a gas, an electric power generator and a fuel synthesis reactor, and where said selectively generating includes selectively providing said gas to said electric power generator or said fuel synthesis reactor.

3. The method of claim 2, where said method includes exchanging heat from said electric power generator to at least a portion of said fuel synthesis reactor.

4. The method of claim 2, where said method further includes generating products of biomass gasification by thermally reacting said biomass.

5. The method of claim 4, where said generating further includes pyrolyzing the biomass.

6. The method of claim 5, where said generating further includes partially oxidizing the pyrolyzed biomass.

7. The method of claim 3, where said method further includes exchanging heat from said electric power generator or said fuel synthesis reactor to heat the biomass.

8. The method of claim 1, where said biomass is rice straw.

9. An apparatus for generating either electric power or liquid fuel from a biomass, said apparatus comprising:

a biomass gasification unit to accept biomass and produce a gas stream;

a generator to produce electric power from said gas stream;

a synthesis unit to produce a liquid fuel from said gas stream; and

one or more valves to selectively provide said gas stream to one or more of said generator or said synthesis unit,

where said one or more valves controls the amount of electric power and the amount of liquid fuel provided from the biomass.

10. The apparatus of claim 9, further comprising a heat exchanger to provide thermal energy from said generator to said synthesis unit.

11. The apparatus of claim 9, where said gasification unit includes a torrefaction unit, and where said apparatus further includes a heat exchanger to provide thermal energy from said generator or said synthesis unit to said torrefaction unit.

12. A method for utilizing biomass, said method comprising:

a torrefaction process;

one or more additional processes; and

providing heat from at least one of said one or more additional processes to said torrefaction process.

13. The method of claim 12, where said method produces a synthetic fuel, and where said one or more additional process is a fuel synthesis process.

14. An apparatus for utilizing a biomass comprising:

an oxygen separation unit to produce oxygen-enriched gases from air;

a partial oxidation unit to accept a biomass stream and said oxygen-enriched gases; and

a thermoelectric generator,

where said thermoelectric generator accepts heat from said partial oxidation unit and provides electricity for at least partially operating said oxygen separation unit.