Highly efficient and compact syngas generation system

A syngas generator has at least pyrolysis unit and a cracking unit which recycles treated input therein. The pyrolysis unit may recycle treated char to provide input heat for feedstock. The cracking unit may recycle syngas to assist in treating input gas/vapor mixture.

FIELD OF THE INVENTION

An object of the present invention is to potentially provide an efficient and/or compact system to convert organic material contained in organic waste, biomass, and/or other organic materials into a combustible, tar-reduced gas that may be utilized directly in such equipment an internal combustion machine or turbine for the generation of electricity, mechanical energy, and/or for other uses such as use in subsequent synthesis systems such as for the production of biodiesel, etc.

BACKGROUND OF THE INVENTION

A device for the pyrolysis and gasification of organic material such as organic household waste, wood waste, tires, plastics, or other hazardous organic components is commonly called a syngas generator. Syngas generators are used to provide a flammable gas/vapor mixture (syngas) for the direct generation of energy through such means as internal combustion machines or steam boilers, etc., for the synthesis of liquid hydrocarbons such as by the Fischer-Tropsch Synthesis or other techniques, and/or for other uses.

However, almost all of the organic materials suitable for the mentioned syngas generators have the following in common: they have a low energy density; and they are locally dispersed. This creates a challenge faced by this technology to either have a centralized large syngas plant where the organic material is transported to the plant from a large area or to have decentralized small syngas plants that are deployed in the area where the material is available in order to minimize transportation logistics.

While the specific investment costs as well the highest degree of utilization of the energy of a syngas system can be minimized by building centralized plants with a high capacity, the costs of the transportation of the feedstock increases since the materials will often need to be sourced from farther away. Because of the low energy density of the feedstock and the high transportation costs, economical reasons typically prohibit the realization of large centralized systems. Accordingly, there is a demand for smaller, decentralized syngas generators.

However, a disadvantage of smaller syngas generator units is the higher specific investment costs and lower energy efficiency. A challenge exists to find a suitable technology for decentralized units that may be balanced between investment costs and efficiency. The pyrolysis of organic material contains many chemical reactions that produce—besides the readily utilizable gaseous products—unwanted by products, especially large complex hydrocarbons commonly known as tars and soot, toxic components such as dioxins or organic acids. These byproducts prohibit the feedstock's direct utilization in an internal combustion machine because these byproducts cause early mechanical failure of the machine or in a downstream fuel synthesis plant.

The prior art of syngas generators has not yet made a commercially significant breakthrough mainly because of two reasons: (1) Low feedstock tolerance combined with a low throughput; and/or (2) Low syngas quality and the associated additional effort to clean the syngas prior to use in a subsequent process.

These two reasons lead to higher system cost due to increased size, inefficiencies, and additional process components, as well as higher maintenance and operational cost to obtain the desired product quality. The prior art syngas generators process the feed mainly by two different processes.

A first process is the Allothermal process. With the Allothermal process, the heat to maintain the pyrolysis is indirectly introduced to the product under the absence of oxygen. This process is typically a continuous process, accomplished through an indirectly heated auger reactor or an auger mixer that mixes a previously heated solid such as sand with the feedstock. The vapors of this process are predominantly used for the bio-oil production or direct combustion in a boiler. This principal has, due to the robustness of the auger, a very high feedstock tolerance towards humidity, particle size and melting behavior. Also, the principal does not generate high amounts of particles. When only the auger is heated from outside the heat transfer rate is low and hence the throughput is small, requiring large augers and surfaces to transfer the heat into product. The use of heat carriers such as sand requires a separate system for heating the sand and separating the sand from the char product; such a system significantly increases the complexity of the process and system cost. In practical applications such as for shredded wood particles, the particles are a mixture of fine and coarse particles. The larger particles in that mixture require a higher retention times for a complete pyrolysis in the reactor compared to the fines. The prior art addresses this issue by three measures: 1) Increasing the temperature which is limited by the materials of construction of the auger reactor or 2) By increasing the retention time which requires the reactor to be built longer which is limited by the cost and the size of the reactor. 3) Reducing the particle size to increase the heat transfer rates into the particles. On another aspect, with increasing throughput, the volume to surface ratio increases, which causes the reactor heat transfer into the particle to worsen due to the limited direct contact of the particles to the reactor. The prior art attempts to increase the throughput by using multiple small reactors or increase the residence time by using multiple reactors in series which complicates the system design and cost significantly with increasing throughput and particle diameter.

A second process is an Autothermal process. With an Autothermal process: the heat to maintain the Pyrolysis process is normally introduced by an under-stoichiometric combustion of the feedstock. The Autothermal pyrolysis process normally is accomplished by blowing air or oxygen into a fixed bed or a fluidized-bed reactor. The pyrolysis heat is generated by the partial combustion of the feedstock with the available oxygen. The heat causes the non-combusted organic matter to disintegrate by pyrolysis which drives out the vapors from the feedstock. Due to high temperatures, the tars and other complex molecules are cracked into smaller fragments (gasification) so that the amount of tars is lower compared to the before mentioned Allothermic Pyrolysis. Some processes even add steam into the Autothermic process to facilitate the cracking reactions towards components such as Hydrogen and Methane. The feedstock tolerance with regards to humidity, size distribution, and melting behavior is lower due to e.g. channeling and clogging in fixed bed reactors or specific weight distribution in fluidized bed reactors. The dust generation in the Autothermal pyrolysis process is significant and must be removed from the vapor stream with cyclones and filters.

The prior art syngas generators produce a vapor/solid/gas mixture that also has unwanted byproducts such as tars, particulate matter, and toxic substances such as dioxins, besides the desired gaseous and vaporous fractions. Especially Autothermic processes are hard to control because the pyrolysis reaction kinetics is strongly dependent on the particle sizes, water content and other contaminants such as sand. If the reaction kinetics changes for instance upon feedstock quality fluctuations the reaction is prone to either cool down and starve or overheats, which causes an excessive energy consumption and a low caloric syngas. Remember, direct combustion in an internal combustion machine or the synthesis of hydrocarbons from the gasified feedstock normally requires a very clean synthesis gas within tight quality specifications. Accordingly, the prior art of syngas generators commonly require several cleaning steps such as scrubbing and filtering prior to introduction into an internal combustion machine or synthesis process. These cleaning processes increase the cost, maintenance, and operation effort that usually renders smaller systems economically unfeasible.

Alternatively, direct combustion of the syngas in a steam boiler can be performed. Since steam boilers have higher tolerances towards tars and particulate matter and the combustion process is better controllable, most current syngas processes operate on a steam system to generate electricity.

Steam systems, however, are typically more inefficient when compared to the direct utilization in an internal combustion machine. Furthermore, a steam system is often more expensive in investment, maintenance, and operation due to the additional piping, pressure vessels, turbines, condensate polishing, and handling systems.

Accordingly, there is a need in the prior art for a system that provides all of the benefits of a compact syngas generator system with a high feedstock tolerance combined with a high throughput that produces a syngas product quality suitable for the direct utilization in an internal combustion machine or other chemical processes that have low specific investment, maintenance, and operation cost preferably by avoiding syngas cleaning processes.

BRIEF SUMMARY OF THE INVENTION

In view of the foregoing disadvantages inherent in the known types of syngas generators for the disintegration and gasification of organic matter and the subsequent utilization of the pyrolysis gaseous and liquid products for the generation of energy or as a feedstock for creating chemical compounds now present in the prior art, many embodiments of the present invention provide a compact process unit for the disintegration and gasification of organic feedstock that directly generates a high quality syngas for the direct utilization in an internal combustion machine or other chemical processes through at least one of (a) recycling treated feedstock to heat incoming feedstock; and/or (b) recycling syngas to mix with incoming gas/vapor mixture.

DETAILED DESCRIPTION OF THE INVENTION

Referring now toFIG. 1there is shown the block flow diagram of the invention. The feedstock, or educt1, which may comprise any organic solid and/or pasty matter or mixtures of solid organic matter and/or liquid organic matter such as wood waste, plastics, organic household waste or tires is being disintegrated under heat and an oxygen deprived atmosphere in a pyrolysis unit13. Liquid matter may also be educt1for some embodiments. The pyrolysis unit13may be heated and may operate at a certain elevated temperature, such as from 200-1200 C or more preferably about 600 C (for at least some wood waste as educt1) to sustain a pyrolysis reaction. Products from the pyrolysis process of the treated educt1are: output char10and a gas/vapor mixture12.

A first, often a primary, pyrolysis reactor32may be fed with a stream30, which may preferably be a mixture of the educt1, received at inlet101, and a portion of hot, recycled char106from return auger31. The recycled char106is believed to increase the average retention time of the educt1inside the primary auger32(and/or pyrolysis unit13) for a higher conversion of the educt1and/or recycled char10into a gas/vapor mixture12as well as for an increase of the heat exchange rate into the feedstock or educt1that allows the reactor system32pyrolysis unit13and/or system100to be built more compact. Approximately 0 to 100 percent of treated char24(and preferably, 5-70 percent, 10-55 percent, 20-50 percent, 30-45 percent or about 38 percent) may be provided as recycled char106as opposed to output char10for at least some embodiments.

The char/educt mixture or stream30decomposes through introduced heat such as by one or more heaters104,105within heat chamber11such as with the primary auger32and/or return auger31into volatile liquid and/or gaseous products appearing as a gas/vapor mixture12that may be fed into a cracking reactor21and treated char24that may be fed into the return auger31. The return auger31preferably recycles a portion of the treated char24back to the inlet of the primary auger32as return char106while another portion of the char24can be removed from the process as output char10at outlet102. Alternatively, a certain particle size of the char from the primary auger32can be separated in a sieve117that can be placed in the receiver box6and fed to the Return Auger31. This allows to selectively return only larger particles that require a higher retention time in the primary reactor32. For wood as a feedstock approximately particle sizes of the treated char24larger than 4 millimeter (and preferably larger than 16 millimeter) may be provided as recycled char106as opposed to output char10for at least some embodiments. Return auger31preferably directs recycled char106in an opposite direction from primary auger32to be able to provide stream30when combined. Primary auger32may move educt1linearly (or not). Return Auger31may move recycled char106upwardly as well as rearwardly relative to a direction of motion of primary auger32so as to potentially provide a loop like system while removing gas/vapor mixture12and output char10from the loop.

A steam and/or cracking reactor21cracks higher hydrocarbons such as tars and other long chained or complex hydrocarbons as well as toxic components such as dioxins and furans into basic, gaseous components from the gas/vapor mixture12. The cracking reactor21may be designed as a plug flow reactor with a loop where syngas25may be recycled back into the feed of the cracking reactor21, possibly in a loop manner, as will be explained in further detail below. This may increase the average retention time of the syngas25in the system, which is believed to have the following advantages towards a plug flow reactor without recycling: (1) the system may be built more compact; (2) the system may provide a higher degree of unwanted byproduct conversion into syngas; and/or (3) the system may be operated at low temperatures to reduce unwanted carbon formation.

The cracking reactor21preferably operates at least at the temperatures of the pyrolysis auger reactor32for many embodiments. For the illustrated embodiment, temperature can be closer to 800 C, which can often be maintained by the partial combustion reaction occurring in the steam based cracking reactor21by injecting oxygen107and/or steam108as mixture19. The steam108in the mixture19may be added to the cracking reactor21to ensure an excess of hydrogen radicals to assist in shifting the reactions taking place in the cracking reactor21towards gaseous components. The cracking products, also called syngas22, leave the cracking reactor21for further use as will be explained below. Oxygen107and/or steam108injection as mixture or stream19may be introduced to maintain a cracking temperature and a steam cracking reaction in the cracking reactor21. Stream19may also serve as a driving injector gas to maintain the recirculation and mixing of the gas/vapor mixture12with recycled gas14. To maintain a constant recirculation in the cracking reactor21and when the reactor temperature is high enough so that the demand for stream19is too low to maintain a sufficient circulation in the cracking reactor21, a portion of the syngas22may be recycled back as recycled syngas27into the cracking reactor21.

The cracking reactor21may have a main reaction chamber29and a gas injector28. The main reaction chamber29may preferably be formed as a single long pipe or multiple pipes in parallel that may include static mixing elements such as baffle plates and may be operated under a lower pressure than the pyrolysis reactor13. The lower pressure may assist in directing a flow of the gas/vapor mixture12into the inlet109of the cracking reactor29.

The gas/vapor mixture12may be mixed with hot recycled gas14at the inlet of the main reaction chamber29to potentially support the cracking reaction to occur in the cracking reactor21, possibly in the reaction chamber. Towards an outlet110of the cracking reactor29, a portion of the reaction products25may be introduced into the gas injector28to be mixed with stream26previously mixed with the oxygen/steam mixture19and/or possibly recycled syngas27as a propellant, to then be directed back into the reaction chamber29(possibly in a loop-like manner). Approximately 0 to 100 percent (and preferably 0-50 percent, 10-30 percent or about 22 percent) of the reaction products25may be combined with gas/vapor mixture12to provide mixture113for at least some embodiments.

The added oxygen107may react with a portion of the recycled syngas25and/or27. A heat of reaction preferably provides the necessary temperature increase to sustain the cracking reaction in the reactor29although heater(s)111may be useful (at least at startup).

Referring now toFIG. 2: A more detailed description of the pyrolysis reactor13is shown inFIG. 2. The feedstock, or educt1, may be introduced at an inlet101such as through a valve2such as an air tight gate such as a rotary gate valve and introduced into a receiver3. Receiver3may be a portion of primary reactor32or of the return reactor31where the feedstock may be mixed with a portion of the hot or treated char24that was transported by the return auger7driven by motor8through a receiver box6located at the distal end of the primary auger reactor32.

The reactor(s)31,32are preferably operated under a slightly lower pressure than the surrounding environment. The mixture30of treated char106and educt1may be introduced in the primary reactor32at inlet30. The primary reactor32may have a main auger5which can be a single, double or multiple auger combination with an inlet30and outlet24. The return auger31may be designed to consist of multiple single return augers to increase the heat transfer surface between the auger wall towards the returned particles106and the heating chamber11and/or heating element105. The main auger5may be driven by an electric motor4. The primary reactor32may be at least partially externally heated by being situated inside a heating chamber11with heater(s)104and/or105. The heating chamber11may operate at a certain elevated temperature(s), such as from 200-1200 C or more preferably about 500 C for wood waste as educt1to sustain a pyrolysis reaction along the main auger5.

The primary auger5preferably conveys the mixture30through the heated chamber11where the pyrolysis reaction preferably takes place. The mixture30may emit under the heated environment a gas/vapor mixture12that may be drawn out of the primary reactor32from outlet103. The remainder may be treated char24that may be released from toward or at the distal end112of the primary reactor32. The treated char24may fall into a receiver box6where the material may be screened by sieve117and a portion of the screened material char10may leave the pyrolysis reactor13through a gate valve9or other device at outlet102, if not recycled as explained above.

A more detailed description of the cracking reactor21is shown inFIG. 3. The cracking reactor21may be operated under a lower pressure by means of compressor16than the connected pyrolysis reactor13. The gas/vapor mixture12from the outlet103pyrolysis reactor13flows into the main reaction chamber29from the inlet109of the cracking reactor21where it preferably mixes with the hot recycled gas14.

The temperature of the vapor/gas mixture113is between 500 C-1200 C, preferably it has about or even the same temperature as the operating temperature of the pyrolysis reactor13. The elevated temperature of the mixture113preferably initiates the cracking process of the gas/vapor mixture12. At the distal end of the cracking reactor29a portion of the cracked gas (syngas)22preferably flows through a cooler15. The cooled gas23may be compressed by a compressor16. A portion of the compressed syngas17may leave the reactor21for the direct use in any subsequent process such as an internal combustion machine114or other chemical synthesis processes such as the production of fuel, plastics, and/or other process. A control valve18may control a flow of recycled syngas27. A control valve20may control the mixture19, which may comprise a mixture of oxygen107and/or steam108and/or evaporated or gaseous combustible agent116with a flame point below 600 C (preferably below 300 C), such as hydrocarbons, such as Diesel oil to support the initial ignition of the cracking reaction and/or inert gas such as nitrogen115or other gas when air is used as an oxygen carrier. The two streams27and/or19may be mixed to form the input26that may be introduced into the gas injector28, possibly as a propellant.

The bypass stream25in the injector28may heat up the input26. Once the injected gas mixture input26reaches a sufficiently high temperature, the available oxygen in the injector28may react with the combustible syngas25. The released energy of the oxidation reaction preferably provides the energy (and heat) required to sustain the endothermic cracking process in the cracking reactor21. The cracking reactor21(such as the main reaction chamber29and the gas injector28) are preferably lined with high temperature resisting materials such as ceramics. Presently preferred ceramic liners can be made from A1202, Silicon Carbide, Si02, and/or Fire Clay with very low iron contents, such as lower than about 0.1%.

Numerous alterations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that the present disclosure relates to the preferred embodiment of the invention which is for purposes of illustration only and not to be construed as a limitation of the invention.