Patent Application
20080006519
The detailed embodiments of the present invention are disclosed herein. It should be understood, however, that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, the details disclosed herein are not to be interpreted as limiting, but merely as the basis for the claims and as a basis for teaching one skilled in the art how to make and/or use the invention.
Referring to
The present system 10 employs a dryer 12 into which carbonaceous feedstock, such as biomass, for example, wood at 30% moisture content and having approximately 12.6 MBtu of available energy, is placed. In order for the present system 10 to work properly, the feedstock must be ground to a fine consistency and dried. As those skilled in the art will certainly appreciate, the equipment used in grinding and drying of the feedstock is readily available, and various known devices may be employed for this purpose.
From the dryer 12, which may be heated from waste heat from an associated reactor chamber 16 or from another source, the dried feedstock is forwarded to the reactor chamber 16 with the emissions from the dryer 12 forwarded to a cyclone and/or bag house 14 (or other suitable device which removes particulates from the emission stream). It is contemplated that where the drying of carbonaceous materials may generate other emissions, for example, volatile organic compounds (VOCs), the cyclone and/or bag house 14 may be replaced with a wet scrubber or other suitable device known to those skilled in the art for the control of emissions. The dried biomass, for example, the dried wood, is transferred to the reactor chamber 16 which operates at approximately 350° C. to approximately 560° C. While drying of the feedstock is disclosed in accordance with a preferred embodiment of the present invention, those skilled in the art will appreciate that drying is not always necessary as some feedstock arrives dry enough for processing and the drying step may be skipped.
Gas and vapor from the reactor chamber 16 is passed through a condenser system 72 as discussed below in greater detail and the vapor is condensed to recover the liquid product. This liquid product is known by several names including bio oil, pyrolysis oil, wood distillate, and other names, and is composed of water and numerous chemicals. Useful gas, for example, syngas, is collected as it exits the condenser system 72. The bio oil is collected for later use and the syngas is forwarded to a furnace 18, where it is combusted to provide at least part of the energy for the system 10. Alternatively, the syngas could be used to fuel an engine to generate heat and electricity for the system. As those skilled in the art will appreciate, syngas (or synthesis gas) is the non-condensable gas portion of the gas and vapor stream from the reactor chamber 16 and has energy value. The bio oil may be used as an energy source or a source of chemicals, or for other applications, in much the same manner as petroleum products.
The char, ash and heat carrier are transferred from the pyrolytic reactor 16 to the char separation and recovery system 20. The char separation and recovery system 20 separates the heat carrier (HC) 21, which is transferred to a heat exchanger 22 to be reheated and recirculated to the reactor chamber 16, and the char, which is collected and, to the extent necessary needed for process heat, burned in the furnace 18. Any char not needed for process heat becomes a byproduct. The hot heat carrier 21, when mixed with the feedstock in the reactor chamber 16, provides the thermal energy for pyrolysis to occur in the reactor chamber 16 without the introduction of oxygen into the reactor chamber 16.
With this in mind, and in accordance with a preferred embodiment of the present invention, the method is achieved by drying carbonaceous feedstock (if necessary), processing the dried carbonaceous feedstock and heat carrier 21 in a reactor chamber 16, separating char produced as a result of processing of feedstock within the reactor chamber 16 from heat carrier 21, separating and recovering liquid product and non-condensable gases from gas and vapor emitted by the reactor chamber 16, and burning the non-condensable gases and char as needed to provide energy for operation of the method.
The breakdown of biomass during the present process is shown in
Referring to
In accordance with this embodiment, and after drying as discussed above, the carbonaceous feedstock is fed into a storage hopper 112. The carbonaceous feedstock is directed from the storage hopper 112 by virtue of a feed mechanism, for example, and in accordance with a preferred embodiment, a rotating feed auger 126. In accordance with a preferred embodiment, the feedstock is fed to the reactor chamber 116 via a rotating feed auger 126 such as a conventional centerless auger (i.e., shaftless auger) in a tube or one or more side-by-side augers in a common trough. The use of the centerless or one or more side-by-side augers may facilitate feeding of particles that are irregular in shape or rod-shaped, such as short pieces of straw or grass. The distance is increased between the feed point and the reactor chamber 116 so as to reduce burn back and to form a better air seal, since it is necessary to maintain oxygen deleted conditions inside the reactor chamber 116. Where a single auger is used, a relief, such as, a raised ridge may be added to the inside of the end of the auger tube where the auger enters the reactor chamber 116 to increase the degree of feedstock compression and better facilitate the formation of an air seal. Although various auger systems are discussed above for feeding feedstock in accordance with a preferred embodiment of the present invention, other feed mechanisms may be employed without departing from the spirit of the present invention.
As shown
As mentioned above, and in accordance with a preferred embodiment, the feed auger 126 is split into first and second auger sections 128, 130 with an airlock 132 positioned there between. After passing through the first auger section 128, airlock 132 and second auger section 130, the carbonaceous feedstock enters the pyrolytic reactor chamber 116, which houses a rotating auger 134 or some other mixing device. The carbonaceous feedstock is formed into plugs as the feedstock is conveyed by the first and second auger sections 128, 130. The formation of plugs within the first and second auger sections 128, 130 in combination with the airlock 132 excludes air from the reactor chamber 116. Where burn-back is not a concern, the feeding system may consist simply of a single feed auger or multiple augers feeding into the reactor chamber or other feeding devices. In accordance with a preferred embodiment of the present invention, the heat carrier 121 is hot steel shot, although a variety of heat carriers may be utilized without departing from the spirit of the present invention.
In accordance with a preferred embodiment, the feedstock is injected into the bed of downwardly flowing heat carrier 121 or, alternatively, above the bed of downward flowing heat carrier 121. Char, ash and the heat carrier 121 exit the pyrolytic reactor chamber 116 via a separation and recovery mechanism 120 in which the heat carrier 121 is recovered for further use and separated from the char. Once the char and heat carrier 121 are separated, the char (which contains the feedstock ash) is passed to a char storage hopper 136 via an auger 137 (or some other conveying mechanism). From there, char product is removed and, as needed for process heat, a portion of the char is sent to a char/syngas burner (or furnace) 118. In particular, char is separated out from the heat carrier 121 by the separation and recovery mechanism 120, and conveyed via an auger 137 to a lock hopper 136 for storage.
As briefly mentioned above, the char and heat carrier mixture exiting the pyrolytic reactor chamber 116 are immediately separated. As those skilled in the art will appreciate, separation is impacted by the physical and chemical properties of the char and heat carrier 121. In accordance with a preferred embodiment, a stationary screen or moving screen (for example, including trommel or shaker screens) is used to separate the char and heat carrier 121 based upon relative particle size. With reference to
Oversize particles may pass the entire length of the cylinder 140 and drop off the exit end 148, where they are recovered separately. Screen opening size, speed of screen rotation, size of screen surface area, screen diameter, angle of screen inclination and other factors are some of the control parameters that may be adjusted to control screening effectiveness for separation of the char and heat carrier 121.
In accordance with an alternate embodiment, and with reference to
In accordance with yet a further separation technique, and with reference to
In accordance with an alternate embodiment, it is contemplated the magnets may be mounted stationary just beyond the surface of the rotating drum causing the heat carrier to be held against the rotating drum as it turns. Stationary magnets would only be positioned along a portion of the rotating drum's surface (reducing the number of magnets needed) and ending at the top of the drum, causing the heat carrier 121 to be released as the rotation of the drum carries the heat carrier 121 away from the influence of the magnets.
Referring to
Separation of the char and heat carrier may also be accomplished by using electrostatic charges to attract the char and thereby separate it from the heat carrier. The characteristics of the char particles, particularly size, versus the heat carrier, allow for separation of the char particles from the heat carrier. The collected char particles can then be periodically removed from the plates or surfaces by a number of means, such as rapping the plates, reversing the charges, and other means.
It is also contemplated, separation of the char and heat carrier may be accomplished by using a cyclone, typically oriented vertically, whereby the heat carrier and char are conveyed into the cyclone by a rapidly moving gas stream, or other means, and separated by density differences of the respective particles. Those skilled in the art will appreciate that these methods may be used separately or in combination with other methods.
By implementing the separation and recovery of the char as outlined above, the following improvements are noted. The excess char may be sold as a co-product. Char can have values of over $100 per ton and, for wood, can be in the range of 25% of the incoming dry weight of the wood. For poultry litter, it can be in the range of 45% of the incoming dry weight of poultry litter and can have values over $180 per ton. Thus, the separated and recovered char can represent a substantial revenue stream.
In addition, removal of the char allows for better process temperature control as the amount of char fuel can be precisely metered into a burner based upon process heat requirements. The removal of char also allows the char/syngas burner 118 to be placed outside the process loop and does not require the introduction of air into the process material flows or process loop. Therefore, the char/syngas burner 118 is not impacted by other process conditions and allows better control of combustion air since primary and secondary air can be introduced and controlled separately. Since the char/syngas burner 118 is separate from the process, it simplifies recovery of ash after combustion of the char. For example, one method is the use of a cyclone and/or a bag house in the burner stack emission stream. In fact, one design uses a burner that is also a cyclone so as the char is burned, the ash is automatically separated from the stack gases and recovered.
For various reasons, clinkers may sometimes be formed in the process or foreign objects may be introduced into the system. The use of a char/heat carrier separation system allows the removal of these oversize or foreign particles before they cause a problem. More particularly, and with reference to the trommel screen separation and recovery mechanism 138 discussed above, the screen 144 of the separation and recovery mechanism 138 is constructed with a fine mesh screen along the first section 144a at the initial length of the screen 144 to remove fine char particles. The fine mesh screen is followed by a coarser screen along the second section 144b at the final length of the screen 144 with openings just large enough for the heat carrier to pass therethrough. The clinkers (as well as stones, tramp metal, and other large particles) drop off the exit end 148 of the screen 144 where they may be recovered and removed by various means.
As discussed above, the char and heat carrier 121 are separated. Once the char has been separated from the heat carrier 121, the separated heat carrier 121 is transferred to and readily reheated in a heat exchanger 122 associated with the pyrolytic reactor chamber 116 and the char/syngas burner 118. Char acts as an insulator and, since it typically has particle sizes smaller than the heat carrier 121, it tends to fill the voids between the heat carrier 121 particles thus effectively insulating the heat carrier 121 particles. Char can also tend to act as a “flowable fill” when mixed with the heat carrier 121, which may then cause the char/heat carrier mixture to set up when a conveying auger is stopped. By separating the heat carrier 121 and char, especially if performed as soon as possible after the reactor chamber 116, this inefficiency is eliminated and the heat carrier 121 may be reheated in a much more efficient manner.
As such, the heat carrier 121 is coupled with a heat exchanger 122 that is heated by the separately controlled char/syngas burner 118 as previously described. The heating of the heat carrier 121 can, therefore, be better controlled. For example, and with reference to
As those skilled in the art will certainly appreciate, the heat exchanger 122 may be formed as part of the heat carrier recirculation loop, thus combining the function of the heat exchanger 122 so that it can be both a heat exchanger and a conveyor (see
Gas and vapor depart the pyrolytic reactor chamber 116 via a tube 114 and may be directed to a condenser system 172 or, alternatively, the gas and vapor—comprising a syngas—may be used for energy directly without a condensing system. Condensed liquids, for example, bio oil, are collected by virtue of a liquid transfer pump or pumps.
The gas and vapor is directed out of the pyrolytic reactor chamber 116 via an exit tube 114. Prior to entering the condenser system 172, the gas and vapor may be cleansed by passing it through a char trap 178 and a tar trap 180, as well as other suitable cleansing devices. Vapor and gaseous material depart the pyrolytic reactor chamber 116 via the gas exit chamber 114 and are ultimately directed to a condenser system 172. Condensed liquids (for example, including bio oil) from the condenser system 172 are transferred to storage tanks 182 by gravity or by virtue of one or more liquid transfer pumps.
The uncondensed gases, which can contain considerable energy value (for example in the form of syngas), are also collected and used for energy by directing them to the char/syngas burner 118 or for applications independent of the pyrolysis process. The uncondensed gases may be used for energy by using the uncondensed gases to fuel an engine (for example, reciprocating internal combustion engine, combustion turbine, or Stirling engine) to provide mechanical and/or electrical power and heat for the process. Depending upon the type of feedstock and the feedstock moisture content, there can be enough energy in the uncondensed gas to supply all the electrical and/or heat requirements of the present system 100. The use of the uncondensed gas can thus minimize or eliminate the need for external fuel sources which reduces operating expense and may allow the units to be operated in remote areas (for example, military camps and/or logging camps).
Conventional condenser designs subject vapors exiting the reactor chamber to either a cold surface or a cold liquid stream (which may be bio oil, water, or another suitable liquid stream) to cause the vapors to condense to create a single liquid product that is a mixture of many chemicals. Due to the physical and chemical characteristics of the liquid product generated, the resulting liquid pyrolysis oil product using these methods may have limited uses and thereby limitations in value.
In accordance with a preferred embodiment, and with reference to
More particularly, the condensation column 300 has internal packing, or, more typically, horizontal plates 302a-i (for example, sieve trays) similar to a distillation tower to create points for condensation of the vapors to occur as the vapors pass through the previously condensed liquids with some reflux liquid returned to the highest plate. The temperature inside the condensation column 300 will decrease as the vapors flow upward and the composition of the liquids on the plates 302a-i will reflect the boiling point of the liquid as in a similar fractional distillation column. Additionally, if needed, the internal temperature of the condensation column 300 can be controlled by heating or cooling systems placed around the condensation column 300 at different heights. Thus, the liquid on each plate 302a-i will have a different chemical composition as reflected by the boiling point of the liquid. Liquids from the different plates 302a-i may be extracted continuously as the reactor 116 is fed feedstock continuously and gas and vapor is produced and fed continuously to the condensation column. The upward flow of gas and vapor from the reactor 116 may be aided by a recycling stream consisting of the non-condensable gas from the process or by another suitable gas.
By coupling the reactor chamber with a fractional condensation system as described above, a simplified, continuous method of recovering various chemicals from condensed liquid is achieved. This minimizes or eliminates the need for additional processing of the liquid (which requires additional equipment, energy and cost) in order to recover chemicals from the liquid product. It also reduces cost since an additional extraction, upgrading, separation, and/or other system is not necessary to recover the chemicals and multiple, individual condensers are not required.
As discussed above, a char/syngas burner 118 is utilized in burning the separated and gathered char for use in heating the heat carrier 121 and thereby the pyrolytic reactor 116. The char is combusted in a combustion device that is outside the process loop. Referring to
By utilizing a better designed char/syngas burner 118, better efficiency in using the char is provided and process heat for the plant is provided. Both types of systems provide for very rapid burning response because only a very small amount of fuel is in the burner 118 at any one time. The fluidized bed system also has the distinction of infinite turndown since one can stop feeding fuel to it for a period of time and, so long as enough heat is retained in the refractory insulation and bed material to ignite incoming fuel, can start up automatically when fuel is again fed into the burner. As those skilled in the art will certainly appreciate, a variety of burner configurations are commercially available. However, in accordance with a preferred embodiment some or all of the char is burned outside the process loop to provide some or all of the process heat.
As discussed above, a pyrolytic reactor chamber 116 is utilized in accordance with the present invention. In accordance with the present reactor design, the biomass is conveyed into the reactor chamber 116 with an auger or some other feed mechanism 126. The heat carrier 121 enters the reactor chamber 116 above the biomass so as to sweep the lighter biomass particles into the vapor/gas stream downward with it. Alternatively, the biomass may be fed directly into a bed in the reactor chamber 116 consisting of the heated heat carrier 121. The reactor chamber 116 throat cross sectional area may be increased in size to decrease the velocity of the vapor/gas so as to minimize the particulate carryover. The inside of the reactor chamber 116 may be lined with refractory material to increase its efficiency and the inside of the reactor chamber 116 is designed to be free of protrusions which may impede flow of materials or form a basis for buildup of slag.
Various methods of mixing the biomass and the heat carrier 121 in the reactor chamber 116 can be used as a replacement for a traditional horizontal auger configuration. For example, a stirred tank reactor 116′ may be utilized or a rotating cylinder 116″ may be utilized (see
In addition, the char/heat carrier/oversized particle screening system can be incorporated into the reactor design in several ways. This eliminates the need to have a separate screening system and thus simplifies construction. For example, if the reactor consists of a single auger in a trough or tube, the later part of the trough or tube can be a screen that can be of different size openings to accommodate the separation of fine char particles, heat carrier particles and oversized particles. Alternatively, the screen could be a trommel screen on a common shaft with the horizontal mixing auger in the reactor.
The present reactor design allows for quick vaporization of very small sized feedstock particles upon their entry into the reactor. The resulting very small char particles may be swept upward by the flow of gas and vapor and may form deposits on the ducting and condenser surfaces that cause plugging of passages. They may also contaminate the bio oil. By injecting the biomass beneath the heat carrier or into a heat carrier bed within the reactor chamber, these particles are swept downward by flow of the heat carrier. The reactor throat cross sectional area may also be increased in size to decrease gas and vapor flow rates from the reactor and thereby decrease the amount of particulate carryover in the gas and vapor stream. The inside of the reactor may be lined with refractory to provide better insulation and a hotter, more even temperature environment for the reactor. The inside of the reactor throat is smooth so that falling biomass does not become hung up on it in any manner. If, the screen and reactor are a common system, the need for separate screening system is eliminated and construction of the plant is simplified.
With regard to the condenser, a settling chamber or cyclone may be added between the reactor and the condenser to remove particulates out of the gas/vapor stream before they reach the condenser system. A heat transfer fluid may be used for controlling the condenser temperature. This heat transfer fluid may be used as a direct contact condenser or in an indirect contact condenser such as a shell and tube condenser. Finally, the condenser may utilize non-stick surfaces to minimize or prevent tar/char build up.
The settling chamber of the condenser minimizes the amount of char the gets into the bio oil. The use of the heat transfer fluid simplifies the control of the condenser system since one can obtain heat transfer control fluids that go up to several hundred degrees Fahrenheit without boiling or cracking. By using proportional controls, one can control the oil temperature, and hence condenser temperature, very precisely. Finally, by using non-stick materials or coatings, the formation of tar build up and subsequent plugging can be minimized or eliminated.
While various preferred embodiments have been shown and described, it will be understood that there is no intent to limit the invention by such disclosure, but rather, is intended to cover all modifications and alternate constructions falling within the spirit and scope of the invention as defined in the appended claims.
