Patent Application
20150166914
The invention relates to processes that can be performed in plasma gasifiers (sometimes referred to herein as PGs and which may also be referred to as plasma gasification reactors or PGRs).
Extensive literature, both in patents and otherwise, deals with construction and operation of a plasma gasifier to process a feed material of various kinds, including, for example, waste materials such as municipal solid waste (MSW), to produce a synthesis gas, or syngas. Such technology can be of major benefit both in terms of waste disposal and, also, conversion of the disposed waste to form syngas for use as a fuel.
Some examples of techniques for such purposes are contained, or referred to, in US published patent application 20100199557, Aug. 12, 2010, by Dighe et al., assigned to Alter Nrg Corp., and in “Industrial Plasma Torch Systems”, Westinghouse Plasma Corporation, Descriptive Bulletin 27-501, published in or by 2005, and all such descriptions are incorporated by reference herein.
In the present description “plasma gasifier reactor” and “PGR” are intended to refer to reactors of the same general type whether applied for gasification or vitrification, or both. Unless the context indicates otherwise, terms such as “gasifier” or “gasification” used herein can be understood to apply alternatively or additionally to “vitrifier” or “vitrification”, and vice versa.
Prior practices have a degree of successful operation that is continually desirable to improve upon.
In a described embodiment, a process for gasification of solid feed material to produce a syngas includes: providing a plasma heated carbonaceous bed in a bottom section of a reactor vessel; feeding feed material into the reactor vessel to form a bed of deposited feed material on top of the carbonaceous bed in the bottom section; reacting the feed material with hot gases rising from the bottom section; forming, in a middle section of the reactor vessel, a syngas mixture containing a varying quantity of unreacted particles of the feed material; allowing the syngas mixture to rise into a top section of the reactor vessel toward one or more syngas outlets; maintaining conditions in the vessel such that unreacted particles from the middle section are subjected to further reactions in a first, lower, part of the top section; and at least partially quenching, by injecting a quench fluid including water, steam, or a mixture thereof, in a second, upper part of the top section, at least some of the unreacted particles sufficiently to reduce the number of unreacted particles exiting the reactor vessel that are likely to be deposited on walls of external ductwork.
The gasifier example of
The bottom section 12 contains a carbonaceous bed 13, one or more plasma torch tuyeres 14, a slag and molten metal tap hole 15 (there may be multiple tap holes), a lower start-up burner port (also serves as an emergency tap hole) 16, and one or more carbon bed tuyeres 17.
The carbonaceous bed 13 (sometimes referred to as the C bed) of the bottom section may be of metallurgical coke or other carbonaceous material derived from fossil fuel or from non-fossil sources (e.g., from biomass in various forms such as disclosed in the above-mentioned companion application). The plasma torch tuyeres 14 and the C bed tuyeres 17 in this example may each be six in number; they are arranged symmetrically about the bottom section's cylindrical wall 18, are angled down about 15% from horizontal and are aimed centrally into the C bed 13. The plasma torch tuyeres 14 are for plasma injection into the C bed 13. The C bed tuyeres 17 are additionally provided for optional use to introduce gas, such as air or oxygen, into the C bed 13. The lower burner port 16 can be used for heating, by a natural gas (or other fuel) burner, the refractory material along the wall of the reactor vessel to provide an internal vessel temperature above the autoignition temperature of combustibles such as carbon, hydrogen, CO and syngas introduced into the vessel. Then the supply of plasma, feed material and other reactants may occur with more safety and less risk of explosion.
The middle section 22 has one or more (such as three) feed ports 23 through the middle section's conical, upwardly expanding (helpful for more constant gas velocity) wall 24. The cylindrical wall 18 of the bottom section 12 and the middle section 14 conical wall 24 are joined at a detachable bottom flange joint 25. The feed ports 23 are angled up from horizontal by about 15° which helps minimize entry of moisture from wet feed material and can be favorable in other respects as described below. Horizontal or downward directed feed ports can also be acceptable in some embodiments. Feed material is supplied through the feed ports 23 from external feed supplies via mechanisms (not shown here) that desirably help achieve a substantially uniform and continuous feed rate, such as a compacting screw feeder which may be of a known commercial type. The introduced feed material forms a feed bed 26 in the middle section 22 above the C bed 13 of the bottom section 12. The middle section 22 also has a number (e.g., 12 to 24 each) of lower feed bed tuyeres 27 and upper feed bed tuyeres 28 that can be used to inject gases directly into the feed bed 26 as well as one or more gas space tuyeres 29 above the feed bed 26. Additionally shown in this example are a sight glass 30 for viewing within the feed bed 26 and an access door for personnel entry when the vessel (out of operation) needs internal inspection or maintenance.
The feed bed 26 is shown with upper and lower surface lines 26a and 26b, respectively, which are merely representative of the extent of the feed bed 26. In this example, the rate of supply of feed material and the rate of consumption of feed material in the feed bed 26 are regulated to an extent to keep the upper surface 26a below the feed ports 23 so the feed bed 26 does not interfere with the entry of feed material. (There may be provided feed bed level sensors as well as visual access to confirm no blockage occurs.) Otherwise, the feed ports 23 and the feed bed upper surface 26a are desirably proximate each other which promotes a longer residence time within the vessel 10 for particulates within the feed material that may be so light they do not descend onto the feed bed 26. A longer residence time in the vessel will enhance the probability of gasification of such particles in the middle section 22 above the feed bed 26 and in the top section 32. Heavier segments of the feed material fall immediately to form and to be reacted (gasified) in the feed bed 26. In general, in embodiments with middle section feed ports, the feed ports and the upper surface of the feed bed are desirably “proximate”, or close to, each other in the vertical direction as much as reasonably possible without encountering problems of feed port blockage or material in feed ports seeing radiation heating from the feed bed. The angling up of the feed ports in this example assists in the latter purpose). The middle section 22 may sometimes be referred to as having a lower part containing the feed bed 26 and an upper part with one or more feed ports 23 while still recognizing they are proximate to each other. This arrangement provides a greater distance between the feed ports and gas outlets, described below. Maximizing that distance can be favorable for gasification of fine particulates introduced in the feed material which may be of any of a wide variety of materials. For producing a syngas for use as a fuel, or fuel source, the feed material desirably includes some hydrocarbons; examples are MSW as well as biomass of various forms (and any mixtures thereof) that may include a large amount of fines that are better gasified by having a longer residence time for the reactor.
Still other embodiments, discussed below with reference to
Returning to
The illustrated configuration of wall parts 36 and 38 of the top section 32 facilitates construction of the vessel 10. In general, it is not necessary to vary the wall angle of the top section. For example, its entire extent could be substantially entirely conical. As explained in the above-mentioned published patent application, an expanding conical side wall can be favorable for maintaining gas flow at desirable levels. An expanding conical section reduces the gas velocity so it has a longer residence time; and it aids in having particulates settle out. The reactors of
instead, in the past, a roof would be located at the immediate top of the freeboard region and an exhaust port or ports would be through the roof on an upper part of the lateral wall of the freeboard region. As discussed below, there are instances in which some further gasification may occur in the quench zone 35a that can contribute to the quality of the output syngas.
The volume within the top section 32 designated the quench zone 35a is the volume of the top section penetrated by and affected by quench fluid while the volume below is here referred to as the freeboard region. For present purposes, the freeboard zone 35 and the quench zone 35a are generally regarded as two zones one above the other. Terminology applying the term “freeboard” to the total top section volume, but having a quench zone within the upper part of the freeboard is also applicable. In either case, the quench zone is an additional volume to that of otherwise similar prior reactors.
In the
The quench fluid inlets 42 are six in number in this example and make up a syngas quench system effective within the quench zone 35a in the upper part of the top section above the freeboard region 35. The quench zone 35a can be considered to be within about the top one-third of the top section 32 and is a region in which fluid (such as water, steam or a mix of water and steam, or possibly recycled syngas or an inert gas such as nitrogen) introduced through the inlets 42 provides an atomized mist that lowers the temperature in the quench zone 35a to make particulates rising with syngas into the quench zone less likely to exit through the outlets 41 in a molten (or soft) state and attach to, or condense on, the interior of external ductwork (not shown) from the outlets 41.
The quench zone 35a, where quenching by the inlets 42 occurs, is constructed with a volume to accommodate the injected fluid, which will thermally expand in the vessel, so as not to significantly affect the progress of syngas from the freeboard region 35 to the outlets 41. Some additional gasification may occur in the quench zone 35a but its added volume is primarily for the partial quenching function, as further described in
The top section 32 also has an upper start-up burner port 43 for use as described for the lower start-up burner port 16. Use of the two start-up burner ports 16 and 43 provides more uniform heating of the interior of the vessel with combustible gases eliminated before plasma pyrolysis commences.
By way of further example, the gasifier embodiment of
Among other variations, (using reference numbers like the corresponding elements of
The quench system of quench zone 35a and inlets 42 may, for example, do a partial quench such as reducing the temperature of the syngas mixture that rises in the freeboard region at about 1000 to 1150° C. down to about 850° C. at the outlets 41 which can minimize sticking of molten or soft particles on the interior of ductwork from the outlets 41. Typical examples of suitable quenching are those that reduce the temperature of molten particulates rising from the freeboard region 35 by about 150 to 300° C. before they reach the outlets 41. Also, see the discussion below regarding
In embodiments with middle section feed ports 23 proximate the feed bed 26, it is not always required to have quench fluid inlets into a quench zone above a freeboard region. That is, advantage of the middle section feed ports can be taken even without the quench system. For example, quenching means may not be present or may occur only in the external ductwork from the syngas outlets. As disclosed in the above-mentioned companion patent application, an arrangement of feed ports proximate the feed bed can be favorable for minimizing carbon consumption in the C bed and that applies with or without a quench system or any particular form of quench system.
Additional points, for example, are that the feed material may, in addition to waste, such as MSW, to be processed, include, or be accompanied by, additional carbonaceous material (which may be retained and consumed in the feed bed or which may descend through the feed bed into the C bed 13 of the bottom section), and, also, flux to adjust the basicity, viscosity, and melting temperature of slag that forms and descends to the tap hole 15 in the bottom section. Also, any particulates that are carried out of the reactor with the outlet syngas may be captured externally and fed back in with the feed material.
The plasma torch tuyeres are provided with plasma torches of which an example is that commercially available as the MARC-11L™ plasma torch from Westinghouse Plasma Corporation. Such torches use a shroud gas in addition to a torch gas and oxygen or air may be used for those purposes, as well as other gases (see Dighe et al. U.S. Pat. No. 4,761,793 which is incorporated by reference herein for descriptions of plasma torch arrangements). The gas introduced by the torch can be superheated to a temperature in excess of 10,000° F. (about 5500° C.) that greatly exceeds conventional combustion temperatures.
The plasma torch tuyeres are sometimes referred to as primary tuyeres. The lower and upper tuyeres 27 and 28 of the middle section 22 are sometimes referred to as secondary and tertiary tuyeres, respectively. The tuyeres 27 and 28 can be used to deliver oxygen to further help control syngas temperature as well as possible other functions.
Chemical reactions are intended to occur, for example, as described in US Patent Application Publication No. 2010/0199557. The contents of the resulting syngas (including CO and H2 as well as possible others) and the consumption rates of the feed bed and the C bed are influenced by the oxygen (or air) and, possibly, steam introduced through tuyeres in the various sections.
Among variations that may optionally be employed together with the disclosed innovations are outlet ports for the syngas that have intruded ducts within the reactor vessel. Also, variations on the nature of feed ports may include feed port intrusions into the reactor vessel and/or mechanisms to vary the angle or distance feed material enters from the feed ports. The mentioned published patent application may be referred to for further information of such features.
In large part, many aspects of the total gasifier design and operation may be varied in accordance with past practices in plasma gasifiers and still incorporate innovations presented herein, such as, but not limited to, the top section quench system or the arrangement of one or more feed ports in the middle section proximate the feed bed.
Plasma gasifiers with a top section quench system are different than known PG practices that sometimes involve introducing a moderating gas directly into a freeboard region of a PG for purposes of stopping, or minimizing, gasification in the freeboard region. For example, in Dighe et al. U.S. Pat. No. 7,632,394, Dec. 15, 2009, there is disclosure of steam introduction into a freeboard region to reduce the temperature to about 450° C. or less to minimize further cracking of oil fractions in the process being performed of reducing heavy hydrocarbons.
In embodiments of the present invention, particularly aimed for use in processes for converting diverse waste to syngas (although not necessarily limited to such processes), the quench fluids are introduced into a quench zone that is in addition to and on top of the freeboard region where substantially complete gasification occurs. The quench zone here is, for example, to avoid exit of soft particles of fly ash containing such things as metal oxides that have melting points of about 900° C. or more. The quench system, as disclosed here, can reduce their temperature to about 850° C. The quench system is not needed, and usually would not be wanted, to cool the gases further. Some further gasification in the quench zone can be favorable;
where steam is included in the quench fluid that can be a plus as the steam can assist in cracking heavy hydrocarbons. But further gasification in the quench zone is generally not a main goal compared to that of minimizing the exiting of soft particles. A more important consideration is that the quench zone volume (additional to that of the freeboard region) accommodates all the expanding gases, from the introduced quench fluids, so the flow of syngas from the freeboard region to the outlets is smooth.
The reactor is only partially shown in
A few additional comments on aspects of side entry, multiple, feed ports are the following and can pertain to reactors generally even without a quench zone, although that combination would be often desirable. It is known that the porosity of a feed bed (such as 26) is normally higher along or near the side walls when feed material comes in from the top. If lateral feed ports are used, more material is deposited near the walls because of proximity to the feed ports. This results in more resistance to gas flow along the walls. Gas is also, at least sometimes, injected through the walls (e.g., by tuyeres 33 and 34). The side feed ports make it less likely for gases rising from the C bed to be channeled along the wall without reacting with feed materials because of bypassing the bed. Now, with side entry feed ports, any such tendency is minimized and more gas is forced towards the center of the vessel. Consequently, this can sometimes be an additional favorable aspect of lower side entry feed ports with feed bed buildup at the vessel walls more than in the center. So while it is generally the case that a substantially uniform feed bed mass is desirable across the middle section 22, the extent to which the feed ports 23 result in a greater build up of feed material at the wall 24 is not a severe detriment and is preferable to having a greater buildup of feed material in the center of the vessel.
The angling up of feed ports 23 in
Regarding the quench system, in some applications, there may be processes with feed material that is high in complex hydrocarbons and concerns can arise about undesirable tar formation. However, the quench system, when water and/or steam is included in the injected fluid, will aid in conversion of any polycyclic aromatic hydrocarbons (PAHs) rising from the freeboard region into the quench zone to CO, CO2, H2 and H2O. Multiple phase fluids (e.g., water and steam together) can work well as a quench fluid. Steam can serve as a motive gas to atomize water better than just having a water spray. Water, H2O in either form, (water, when injected, will quickly turn to steam) offers an advantage of allowing use of a smaller mass of fluid, compared to some other gas that may be cooler when injected, because of its latent heat of vaporization. Also, it may be noted that the volume of the quench zone in the reactor can be a function of the droplet size of fluid droplets injected or formed in the quench zone. Finer water droplets will evaporate more quickly and descend less distance in the vessel than larger droplets.
Quenching is often best if regulated in relation to the rate in which feed material is introduced. The system can be designed so that a lowering of the feed rate results in a lowering of the rate of quench fluid injected in order to control the gas temperature.
Reactors of interest can have any number of outlet ducts located anywhere in the roof or upper side wall. But two or more ducts can be favorable in the respect that temperature monitoring in the ducts can indicate temperature differences that can be used to adjust quench fluid flow through the respective nozzles to help make the ducts output more uniform if preferential flow is established in one duct.
Multiple feed ports, as in the example discussed, can be run at individually different rates to adjust for changes in the feed bed that may occur across the bed.
Among the potential variations of the foregoing examples that are within the broader aspects of the present inventions are embodiments in which one or more middle section feed ports are located, through the side wall below the upper surface (26a of
Extra-low, or underfeeding, feed ports, such as those of
Such extra-low feed ports may either be the only feed ports into the reactor vessel or they may be additional to one or more other feed ports, which may be like the feed ports 23 or otherwise. Equipment can be arranged with the extra-low feed ports so feed material can be effectively forced into the feed bed.
Extra-low feed ports can be provided in a reactor vessel for use as desired. An example of their use can be where the feed material contains a relatively large amount of fine particulates. By having such material submerged in the feed bed it will be entrained by rising hot gases initially in the feed bed for more thorough gasification which may occur either in the feed bed itself or above the feed bed.
An additional aspect of some suitable embodiments is to separate fines, or particulates in general, from syngas that exits through the outlets and recycle them into the reactor through any one or more feed ports or tuyeres including those that feed into the C bed or directly into the feed bed (by extra-low feed ports) or above the feed bed.
The disclosed embodiments include innovations for improved performance in enabling one or both of (1) more thorough gasification of particulate feed material and (2) minimization of the occurrence of unreacted molten particles of feed material exiting a reactor vessel along with syngas and being deposited on an inner wall of external ductwork from a vessel outlet.
While it is generally the case that PGRs can take advantage of the described features individually, there can be a preference for their use in combination. Particularly when used in combination, opportunities for greater output of syngas with good qualities from a wider variety of feed material compositions can be enhanced.
One example is to provide an arrangement of quench fluid inlets in an upper part (such as the roof) of a top section of the reactor vessel and injecting a fluid such as, but not limited to, water, steam, or a mix of water and steam, to cool soft or molten bits of unreacted feed material sufficiently to minimize the number of them exiting the reactor vessel that are likely to be deposited on the inside of external ductwork. The arrangement of quench fluid inlets (sometimes referred to herein as a quench system (or partial quench system)) is best combined with a reactor vessel having an additional volume (referred as a quench zone) that allows for the volume of expanding fluids from the quench fluid inlets so as to minimize any adverse effects on flow of syngas from a freeboard region below the quench zone to syngas outlets. In prior practices, the ductwork from syngas outlets has often been subject to a build up of deposited material and a quench system with good performance inside a duct is difficult to build.
Another technique, an embodiment of which (without a quench system) is also disclosed in the aforementioned companion patent application, is to provide a reactor vessel with a bottom section, for containing a carbonaceous bed, a middle section, for containing a bed of deposited feed material, and a top section including a freeboard region and a roof over the freeboard region and having one or more feed ports through the lateral wall of the middle section, above and proximate to the upper surface of the bed of feed material or into the bed itself This enables the feed material to be (a) for heavier segments, deposited quickly and directly on the feed bed for reaction and (b) for lighter particles (or “floaters”) that are kept above the feed bed by rising hot gases, to have a long residence time within the vessel that promotes more complete reaction (gasification) of the particles. Feed ports into the bed itself, sometimes referred to as underfeeding, can substantially prevent floaters. The companion application also explains how such an arrangement can contribute to less carbon usage in the carbonaceous bed of the bottom section. This arrangement contrasts from some prior practices of PGRs with one or more feed ports located only in a top section well above the feed bed. Here, embodiments are included that make the distance between feed ports and gas outlets large by the location of feed ports no higher than only a short distance above the feed bed while the gas outlets in the top section are remote from the feed bed.
Merely by way of example, the referred to sections of the reactor vessel, particularly the middle and top sections, may include truncated inverse conical shapes, wider at their upper ends, which contribute to achievement of substantially constant gas velocity for the increasing quantity of gas rising within the vessel. (See the above-mentioned published patent application as to such conical configurations.) The top section conical wall may have less of an angle to the center axis of the reactor vessel than the middle section conical wall; and the top section has an additional upper volume, referred to as the quench zone, where quench fluid inlets are effective, that is, in one illustrative example, within a cylindrical part above the conical part of the top section.
Specific, but not the only, embodiments may combine, in a reactor vessel having the above-mentioned conical characteristics, a bottom section (which may be cylindrical) with a carbonaceous bed (of coke or as presented in the companion application) and plasma nozzles, a middle section (conical) with a plurality (e.g., two or three) of lateral feed ports to feed process material onto or just above the carbonaceous bed with good distribution over the interior of the middle section, a top section above the middle section that has both a freeboard region (with a conical configuration that may be less angular than the middle section) and, above the freeboard region, a quench zone (that may have a cylindrical configuration) in which injected fluid at least partially quenches (i.e., hardens or makes less soft) solid bits of matter rising with gaseous reaction products from below to one or more outlet ports at or near the top of the quench zone.
Multiple syngas outlets are better than a single, central, gas outlet in the respect that the outlets away from the roof center cause gas flow toward the lateral walls of the vessel and prevent funneling or core flow being established, resulting in better use of the reactor volume.
This application is a divisional application of U.S. patent application Ser. No. 13/199,813, filed Sep. 9, 2011, and titled “Enhanced Plasma Gasifiers For Producing Syngas”, which claims the benefit of U.S. Provisional Application No. 61/462,601, filed Feb. 5, 2011. These applications are hereby incorporated by reference. A companion application (U.S. patent application Ser. No. 13/199,814, filed Sep. 9, 2011, entitled “Plasma Gasification Reactors with Modified Carbon Beds and Reduced Coke Requirements”, US Patent Application Publication No. 2012/0061618) filed on the same date as the U.S. patent application Ser. No. 13/199,813, includes descriptions related to plasma gasifiers and their operation that may be combined with the subject matter of U.S. patent application Ser. No. 13/199,813, and said companion application is hereby incorporated by reference for such descriptions.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13199813 | Sep 2011 | US |
| Child | 14631214 | US |
