SYSTEM AND METHOD FOR PRODUCING CLEAN SYNGAS FROM BIOSOLID MATERIALS HAVING FLUOROCARBON MATERIALS THEREIN

Description

RELATED APPLICATIONS

This patent application claims the benefit under 35 U.S.C. § 119 (c) of U.S. Provisional Patent Application Ser. No. 63/677,565, entitled “Plasma/Ionic Reactor for Processing Biosolids Materials,” filed Jul. 31, 2024, and U.S. Provisional Patent Application Ser. No. 63/714,556, entitled “System and Method for Producing Clean Syngas from Biosolid Materials Having Fluorocarbon Materials Therein,” filed Oct. 31, 2024, the entire disclosures of each of which are hereby expressly incorporated by reference herein.

FIELD OF TECHNOLOGY

This patent relates generally to biosolid waste processing and synthesis gas (syngas) production, and more particularly to a system and method that uses plasma arc or ionic reactors and/or gasifier systems to produce syngas from biosolid or other waste or other having fluorocarbon materials, such as per- or polyfluoroalkyl substances (“PFAS”), therein.

DESCRIPTION OF RELATED ART

Biosolids management plays a crucial role in the sustainable handling of organic waste materials generated from wastewater treatment processes. Publicly Owned Treatment Works (POTWs) play a pivotal role in the management of biosolids, ensuring that wastewater is treated efficiently and safely before being released into the environment. The quantity of biosolids produced at POTWs is enormous. For example, 4.5 million metric tons of sewage sludge (biosolids) was generated in 2021. As central facilities in the wastewater treatment process, POTWs are responsible for the treatment and stabilization of biosolids. Through advanced treatment processes, POTWs are able to reduce the volume of waste and treat and eliminate some pathogens. By implementing rigorous treatment standards and innovative technologies, POTWs help to safeguard public health and protect water quality.

POTWs typically manage biosolids using a variety of methods, including application on agriculture lands, landfilling, incineration, and other disposal methods. An efficient and increasingly popular method of treatment includes performing advanced digestion techniques and thermal processes that enhance pathogen reduction and increase biogas production, which can be used for energy. However, public perception and regulatory uncertainty remain pressing challenges for the biosolids treatment industry. In response to both, the industry's future likely involves adopting enhanced treatment technologies to comply with tighter regulations, especially with respect to the treatment of Per- and Polyfluoroalkyl Substances (PFAS).

PFAS are a group of synthetic chemicals that emerged in the 1940s. Dubbed “forever chemicals,” PFAS are notoriously resistant to degradation due to their exceptionally strong carbon-fluorine bonds. PFAS were widely used across industry, from industrial to consumer-based products. Industrial applications include aerospace, automotive, electronics, and firefighting foams, among others, while consumer products range from non-stick cookware and food packaging to stain-resistant fabrics, water repellent clothing, and cosmetics. Though now phased out from production, due to the exceptionally strong bond and their ability to accumulate, PFAS are often persistent and ubiquitous in the environment including soil, water, food, and the human body.

As will be understood, the presence of PFAS in biosolids complicates management and beneficial reuse applications, prompting the need for more advanced technologies and stricter regulatory oversight to mitigate the impact of PFAS and to ensure the safe handling and application of biosolids including PFAS. Understanding the typical range of PFAS concentrations and annual production tonnage is vital, as total PFAS concentration at any particular waste processing plant can range dramatically. In fact, some studies have shown levels from 182-1,650 parts per billion at different waste processing plants.

Moreover, recent federal initiatives and regulatory advancements highlight an increased focus on managing PFAS, signaling an urgent need to develop effective treatment and destruction technologies for these chemicals. Generally, these regulations establish a framework for comprehensive PFAS management strategies. In addition to the noted regulations, the Environmental Protection Agency (EPA) is proposing revisions to existing regulations that govern the handling and disposal of PFAS. However, with PFAS as a category including thousands of compounds, various regulations are evaluating and targeting specific categories of substances within the PFAS family. In many cases, U.S. regulatory bodies are leveraging existing frameworks such as the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), the Resource Conservation and Recovery Act (RCRA), and the Solid Waste Disposal Act (SWDA) to promulgate new regulations. For example, proposed amendments to CERCLA aim to include PFAS, facilitating cleanups at contaminated sites and enabling cost recovery from responsible parties. Under RCRA, proposals seek to classify certain PFAS as hazardous constituents, thereby imposing stringent requirements for their treatment, storage, and disposal. Additionally, amendments to the SWDA are being considered to ensure that the disposal of solid and hazardous wastes containing PFAS does not lead to further environmental degradation.

Thus, in the realm of biosolids management, the emergence of Per- and Polyfluoroalkyl Substances (PFAS) presents and will continue to present significant challenges due to their persistence in the environment and potential health risks. The compounds have imposed a reevaluation of traditional treatment methods, emphasizing the need for innovative thermal technologies and processes to adequately manage the biosolids, while also addressing and destroying PFAS. Known technology categories used to treat biosolids with PFAS include oxidation, incineration, SCWO, plasma, pyrolysis and, notably, gasification. Each of these technologies is currently undergoing evaluation in efficacy for destroying PFAS, as well as with respect to the economic fitness and readiness for commercialization. However, ultra-high temperature gasification stands out as being most promising amongst the various technologies being considered in both its market readiness and PFAS destruction efficacy. PFAS destruction using an ultra-high temperature gasification unit is described in U.S. Patent Application Publication No. 2024/0165448. By effectively breaking down PFAS and other contaminants, this advanced solution not only enhances the safety and efficiency of biosolids processing, but also aligns with regulatory demands and sustainability goals, positioning the industry to better manage environmental and public health concerns.

While ultra-high temperature gasifiers work well to eliminate PFAS in materials, they work best on dried particulate material and are less effective when processing materials with a high liquid or moisture content. Unfortunately, biosolids, especially those produced by POTWs, have significant moisture or liquid content. Typically, POTWs process biosolid wastewater using one or more dewatering technologies to reduce the liquid or moisture content of the biosolid waste, to reduce odors, making it easier to dispose of, easier to further process the biosolid waste, etc. Various dewatering technologies may include the use of presses, belt systems, augers, centrifuges, etc. which operate to separate the liquids at least partially from the solids to form a wet biosolid cake. These biosolid cakes have anywhere from 5 percent to 30 percent or more dewatered solids (DS) therein. Thus, there is still a significant amount of liquid or moisture in these cakes, making it difficult to process this material in an ultra-high temperature gasifier, as doing so requires the use of more energy and longer residence times in the gasifier to eliminate or reduce the liquids or moisture.

SUMMARY

A biosolid processing system as described herein includes a low temperature conductive dryer which dries biosolids produced by, for example, a POTW, coupled to a high-temperature gasifier. The low temperature dryer further dries the dewatered biosolid cake produced by the POTW to produce a granular biosolid material comprising, for example, less than 1 percent moisture (or water or liquid), or in some cases less than 5 percent moisture (or water or liquid) or in other cases less than 10 percent moisture (or water or liquid). Thus, a preferrable target is 5-10 percent moisture in the dried product with a 1-5 percent moisture in the dried product being even more preferrable (resulting in a dried product having 90-99% dry solids (DS %), or greater). The granular biosolid material is then fed to and processed in the high temperature gasifier (e.g., an ultra-high temperature gasifier) which breaks the biosolid material into elemental parts to produce char and synthesis gas (syngas), which are both useful products. The syngas may be used to run a generator to produce electricity and waste heat. The waste heat may be used in the low temperature drier to dry the biosolid cake, and the electricity may be used to run the gasifier as well as for other beneficial uses.

Importantly, this new system responds to the pressing challenges posed by PFAS regulations and the limitations in traditional biosolids disposal methods by providing for up to 95% mass reduction with 90% carbon conversion of biosolids, depending on waste characterization, while concurrently generating two valuable resources including reusable char and clean renewable syngas for energy recovery. Still further, this system substantially reduces and, in some cases, eliminates PFAS within the biosolids, eliminating the need to dispose of contaminated by-products.

In one embodiment, a system for processing biosolids includes a dryer and a gasifier coupled to the dryer. The dryer includes a dryer input adapted to receive dewatered biosolids, a first section that stores heated dried biosolids, a second section coupled between the first section and a dryer output, wherein the second section receives heated dried biosolids from the first section and mixes the dewatered biosolids received at the dryer input with the heated dried biosolids from the first section to produce dried granulated biosolids at the dryer output. The gasifier includes a gasifier input adapted to receive the dried granulated biosolids from the dryer output and a reactor fluidly coupled between the gasifier input and a gasifier output to receive the dried granulated biosolids at the gasifier input, wherein the reactor subjects the dried granulated biosolids to heat and plasma to gasify the dried granulated biosolids to create syngas and char at a gasifier output.

In some cases, the system includes an electrical generator that receives at least a portion of the syngas and operates using the syngas as a fuel to generate electrical energy. The electrical generator may be electrically coupled to the gasifier and provide at least some of the generated electrical energy to the gasifier for use in creating heat within the reactor. Moreover, a first section of the dryer may include a heat exchanger which heats the dried biosolids within the first section of the dryer and the electrical generator may be fluidly coupled to the heat exchanger and indirectly heat the solids (mostly conductively) from the recovered heat from the gasifier via heating media circulating within the heat exchanger. The heat exchanger may include a set of pillow plates or pillow coils through which the heated gas flows to heat the dried biosolids within the first section of the dryer but may include other types of heat exchanger surfaces, such as tubular coil heat exchanger surfaces.

The dewatered biosolids may include one or more per- or polyfluoroalkyl substances (PFAS) and the gasifier operates to produce syngas and char that is substantially free of PFAS. If desired, the second section of the dryer may include one or more conveyors, wherein a first of the one or more conveyors includes a first input for receiving the heated dried biosolids from the first section, and a second input for receiving the dewatered biosolids, wherein the one or more conveyors are configured to mix the heated dried biosolids with the dewatered biosolids to produce the dried granulated biosolids. The first one of the one or more conveyors may include an auger for mixing the dewatered biosolids with the heated dried biosolids. Moreover, a positive displacement pump, such as a cavity or rotary lobe style progressive pump, may be used to inject the dewatered biosolids into the first one of the one or more conveyors. Still further, one or more conveyors may include a first conveyor output for providing a first portion of the dried granulated biosolids to an input of the first section and a second conveyor output coupled to the dryer output for providing another portion of the dried granulated biosolids to the gasifier. The system may further include a vacuum system coupled to the one or more conveyors to maintain a vacuum within the one or more conveyors and a condenser coupled to the vacuum system that condenses vapor flowing through the vacuum system.

In some cases, the reactor of the gasifier may include one or more sets of electrodes disposed around a reaction chamber, wherein the one or more sets of electrodes create arcs and heated plasma within the reaction chamber. The gasifier may be a high temperature gasifier that exposes material being processed to temperatures greater than 1,500, 2,000 or 2,500 degrees Celsius or an ultra-high temperature gasifier that exposes materials being processed to temperatures greater than 3,000 degrees Celsius. The gasifier may operate to produce temperatures between 3,000 and 10,000 degrees Celsius and may produce temperatures averaging about 5,000 degrees Celsius in the reaction chamber. Moreover, when the dewatered biosolids include one or more per- or polyfluoroalkyl substances (PFAS), the gasifier may destroy substantially all of the PFAS, such as at least 95 percent of the PFAS, at least 99 percent of the PFAS or in some cases at least 99.9 percent of the PFAS. The second section of the dryer may mix the heated dried biosolids and the dewatered biosolids at a ratio in the range of between 10:1 and 40:1 and some cases the ratio can be much higher such as 50:1 and even 200:1. The dewatered biosolids may be at least 5 percent dewatered solids, may be between 5 percent and 30 percent dewatered solids and higher or may be approximately 20 percent dewatered solids.

In another embodiment, a method of processing dewatered biosolids includes storing heated dried biosolids, mixing the dewatered biosolids with a portion of the heated dried biosolids to produce dried granulated biosolids and subjecting the dried granulated biosolids to heated plasma and electrical ares in a reaction chamber to gasify the dried granulated biosolids to produce syngas and char.

In still another embodiment, a system for removing per- or polyfluoroalkyl substances (PFAS) from a waste material including at least 5 percent dewatered solids includes a dryer having a heater for heating a dried waste material, and a mixer including a first input to receive the heated dried waste material, a second input to receive the waste material and a mixing apparatus that mixes the heated dried waste material with the waste material to produce a dried granulated waste material at a dryer output. The system also includes a gasifier coupled to the dryer. The gasifier includes a gasifier input adapted to receive the dried granulated waste material from the dryer output and a reactor fluidly coupled between the gasifier input and a gasifier output to receive the dried granulated waste material at the gasifier input, wherein the reactor subjects the dried granulated waste material to heat and plasma to gasify the dried granulated waste material to produce syngas and char and preferably, PFAS free syngas and char.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a combined dryer and gasifier capable of processing biosolids to produce substantially PFAS free char and syngas.

FIG. 2 is a detailed schematic diagram of an example dryer of FIG. 1 capable of operating on dewatered biosolids to produce granular biosolid materials.

FIG. 3 is a schematic diagram of an example ultra-high temperature gasifier of FIG. 1 that processes the granular biosolid material produced by the dryer of FIGS. 1 and 2 to produce char and clean syngas.

FIG. 4 is a selectively cross-sectioned top view of a plasma or ionic unit used in the exemplary embodiment of the plasma gasifier apparatus of FIG. 3.

FIG. 5 is a fragmented perspective view of an example plasma gasifier apparatus that can be used in the system of FIG. 3.

FIG. 6 is a perspective and partially cut-away view of a hybrid plasma or ionic reactor having a plasma reactor similar to that of the gasifier FIG. 3 and including a plasma torch disposed vertically at the top of the plasma reactor that can be used as the gasifier of FIG. 1.

FIG. 7 is a perspective view of a hybrid plasma or ionic reactor similar to that of FIG. 6 including three plasma torches, three electrode rings and a quenching section.

FIG. 8 is a diagram showing an example mass flow and processing capability of the combined dryer and gasifier system described herein.

DETAILED DESCRIPTION

FIG. 1 illustrates a biosolids processing system 10 including a dryer 12 and a gasifier 14, which is preferably a high-temperature gasifier (subjecting material to 1,500 or 2,000 degrees Celsius or higher), and most preferably an ultra-high temperature (subjecting material to about 3,000 degrees Celsius or higher) direct contact ionic gasifier. As will be understood, biosolids, in the form of dewatered biosolid cake (preferably around 20 percent DS but potentially ranging from 5 percent to 35 percent or greater DS) is provided via a storage container or tank 16 to an input of the dryer 12. The dryer 12, which is generally in the form of a low temperature, conductive heat dryer, dries the biosolid cake to produce a dried biosolid granular material that is then delivered to an input of the gasifier 14. As noted above, the gasifier 14 is preferably an ultra-high temperature, direct contact, ionic gasifier that exposes the granular biosolid material produced by the dryer 12 to extremely high temperatures, typically in the range of 3000 degrees Celsius (C) to 10,000 degrees C. In fact, the gasifier 14 may subject the granular biosolid material to at least 3,000 degrees C. and, in some cases, preferably subjects the granular biosolid material to at least 3,500 degrees C., at least 4,000 degrees C., at least 5,000 degrees C., at least 7,000 degrees C. and in some cases to at least 8,000 degrees C. However, the gasifier 14 may be a high temperature gasifier that subjects the granular biosolid material produced by the dryer 12 to high temperatures, typically at least 1,500 degrees C. or higher and preferably at least 2000 degrees C. or higher and even, in some cases, at least 2,500 degrees C. or higher. The operation of the gasifier 14 breaks the biosolid granular material down into constituent elements, mostly hydrogen, to produce synthesis gas (syngas) and char. The char may be delivered from the output of the gasifier 14 to a receptacle or container 20. The syngas may be captured and delivered via a suitable pathway (e.g., ductwork) to a generator or genset 22 which may burn the syngas to produce electrical energy and waste heat (in the form of heated gas), both of which may be used for various other purposes. In the example configuration illustrated in FIG. 1, the waste heat is provided from a liquid media which is used to recover heat from downstream syngas treatments after the gasifier 14, and then transfer the recovered heat back to the dryer 12 and is used therein as a low temperature conductive heat source to dry the biosolid materials therein. Likewise, in the example configuration illustrated in FIG. 1, the electrical energy is provided to the gasifier 14 and is used to energize electrodes or other elements in the gasifier 14 to produce the ultra-high temperatures produced therein to process the granular biosolid material.

In some embodiments, and depending on the make-up and quantity of the biosolids provided to and dried within the dryer 12, the gasifier 14 may produce enough syngas (which is burned in the generator 22) to produce enough waste heat to provide all of the conductive heat used in the dryer. In some cases, additional waste heat produced by the generator 22, over that needed by the dryer 12, may be siphoned off or delivered to other devices that may use the excess waste heat. In embodiments in which the generator 22 does not produce sufficient waste heat to run the dryer 12, an additional heat source (not shown) may be provided to make up the additional conductive heat needed in the dryer 12.

Likewise, in some embodiments, the gasifier 14 may produce enough syngas that, when burned in the generator 22, produces enough electrical energy to operate the gasifier 14 to process all of the granular biosolids produced by the dryer 12. In other cases, electrical energy produced by the generator 22 may be provided to and used to run other devices or provided (sold) to the electrical grid. In still other cases, a portion of the syngas produced by the gasifier 14 may be provided to the generator 22 and the rest of the produced syngas may be provided to other devices that use the syngas, or may be provided to and sold in the open market. In still other cases, additional electrical energy may be needed to be provided to the gasifier 14 to operate the gasifier 14 at the level needed to process the granular biosolids provided thereto. However, in at least some cases, it is contemplated that the dryer 12 and the gasifier 14 will be able to process all of the dewatered biosolid material provided to the dryer 12 using the waste heat and electrical energy produced by the generator 22 operating or running on the syngas created by the gasifier 14, thereby making it a self-sustaining system.

Importantly, the gasifier 14 operates to produce syngas that is relatively contaminant free, and in particular, that is substantially free of PFAS components, meaning that the gasifier 14 effectively destroys the contaminants and PFAS components present in the biosolids provided to the input of the dryer 12.

FIG. 2 illustrates an example of the dryer 30 which may be used as the dryer 12 of FIG. 1. In particular, the dryer 30 of FIG. 2 includes a storage tank 32 (which may be the storage tank 16 of FIG. 1) which receives, holds and disperses mechanically dewatered biosolids (DS) from one or more treatment plants or facilities. Typically the dewatered biosolids are around 20% DS, but can vary to as low as 5% DS or to as high as 30% or more DS, and may be received from, for example, a single POTW or from multiple plants (e.g., multiple POTWs). Generally, the received solids (biosolids in the form of a dewatered cake) are combined and treated in a process wherein most of the heat needed for fully drying the dewatered cake is transferred within the dryer 30 indirectly and conductively, versus the traditional approach that uses thermal drying technologies which mostly rely on convective heat transfer.

To perform the drying of the dewatered cake, the dryer 30 includes a vertical silo or tank 40 which includes or incorporates a conductive heat transfer mechanism or heat exchanger 42 fluidly connected to a source of heated gas or liquid 44. The heated gas or liquid from the source 44 flows through the conductive heat transfer mechanism 42 within the silo 40 to impart energy (heat) to the material in the silo 40. In one example, the heat transfer mechanism 42 may be or may include a set of pillow plates, pillow plate coils or tubular coils with flowing heating media (gas or liquid) which imparts all of the thermal energy needed in the downstream drying process. Of course, the heat transfer mechanism 42 could include or be made of other heat transfer mechanisms which allow a heated liquid or gas to flow next to the material within the tank 40 to be heated. Generally, the silo 40 starts with (is preloaded with) fully dried (granulated or granular) biosolids which are stored and pre-heated in the vertical silo 40. These granular materials may be small in size, and are typically in the range of 1 to 3, or in some cases higher, millimeters in diameter. These granular dried biosolids gravity flow out of through the tank 40 (from the top to the bottom of the tank 40) past the heat transfer mechanism 42 and are heated by the heated liquid or gas circulating within the heat transfer mechanism 42 until these dried biosolids reach a nozzle 46 at the bottom of the vessel 40. The nozzle 46 disperses or introduces the heated dried biosolids onto or into a first conveying/mixing section of a conveyor 50 which may be screw conveyor. Wet cake from the bottom cake bin or tank 32 is also injected into the first section of the conveyor 50 via, for example, a progressive cavity pump 52 which injects the wet cake through a series of ports 54 in the first section of the conveyor 50. The conveyor 50 operates to thoroughly mix and agglomerate the wet biosolids with the pre-heated granular biosolids from the silo or tank 40. The pump 52 may be operated so that the proportion of dry (granulated) biosolid material from the vessel or silo 40 to wet biosolid material from the tank 32 is typically high, ranging from, for example, 10:1 to 40:1, and in some cases at a much higher ratio. This ratio ensures that the wet biosolid cake always contacts dry particles and does not adhere to or agglomerate onto components of the mixing system including the walls of the conveyor 50. This ratio enables the dry material from the vessel 40 to fully contact and surround the wet material from the tank 32 and impart energy (heat) to the wet material to dry the wet material. This ratio results in the formation of more rounded and much higher density granulate at 45 to 58+lbs. per cubic foot, as compared to other drying methods. Still further, the use of significantly more dry material from the vessel 40 than the wet material from the tank 32 enables the material in the conveyor 50 to flow as granulated dry material, which enables the combined material in the conveyor 50 to provide pressure barriers between the two ends of the conveyor 50. The advantage of this configuration, i.e., mixing dry material with wet material in a conveyor in a manner to form a pressure barrier between the ends of a conveyor is described in detail in U.S. Pat. No. 11,439,961, which is hereby expressly incorporated by reference herein.

In any event, the drying process is mostly completed with the energy transfer and mixing that occurs in the conveyor 50. At the top of the conveyor 50, the mostly dried biosolids are directed into a second conveyor 60 (which may also be a screw conveyor) which then carries the mostly dried solids to the top of the silo 40, where they are returned to the silo 40 for re-heating using the thermal energy from the energy source 44. Further drying of the biosolids can also occur in the conveyor 60 prior to delivery back to the silo 40. A further vessel 62 may be disposed between the downstream (upper) end of the first conveyor 50 and the upstream (lower) end of the second conveyor 60 and may operate to direct the dried material within the first conveyor 50 to the second conveyor 60 while maintaining a preferred pressure, such as a vacuum, within the conveyors 50 and 60. A takeoff system 64 is positioned near the top of the second conveyor 60 and operates to draw off dried (granulated) biosolids at a rate equivalent to the amount of dried biosolids introduced with the wet cake at the input to the first conveyor 50. The output of the takeoff system 64 may be coupled to the input of the gasifier 14 of FIG. 1 and used as a raw material therein to produce syngas and char.

Preferably, the drying process implemented by the dryer 30 of FIG. 2 is carried out under a vacuum (i.e., lower than atmospheric pressure) and preferably a high vacuum (e.g., as low as 14.1 psi below atmospheric pressure [−14.1 psi], or approximately 0.6 psi absolute). However, in at least one embodiment, the vacuum is preferably kept between below −9 and −14 psi (that is, below atmospheric pressure) or between approximately 0.7 and 5.7 psi absolute. This vacuum may be maintained in the first and second conveyors 50 and 60, in the transfer tank 62 and in the silo 40. The heating method and the low pressure in the system enables the system to operate without the use of outside or “drying” air.

A treatment system 70 is coupled to the conveyors 50 and 60 and may include a condenser circuit and a vacuum system and operates to maintain the vacuum in the loop comprising the conveyors 50 and 60, the transfer tank 62 and the silo 40 as well as to draw off water vapor and a small amount of volatile organic compounds (VOCs) and trace contaminants, if present in the wet cake. In particular, vapor ports 72 may be disposed at, for example, the top or upper ends (downstream ends) of the conveyors 50 and 60 or at other desired locations, and these vapor ports 72 are fluidly connected via appropriate flow passages to a condenser 74 which removes the evaporated water. VOCs, together with any infiltration air and trace contaminants, are collected or drawn off out of the condenser 74 and may be injected into the vacuum system (not shown) allowing for treatment of the VOCs in an odor control system, or may be blended in with makeup air to the downstream power generator 22 of FIG. 1 which utilizes syngas from the gasifier to generate power, wherein the VOCs may be destroyed by the combustion process within the generator 22. As illustrated in FIG. 2, condensate may be removed via a lower or bottom port from the condenser 74 and may be disposed of in any known or desired manner. If this condensate includes PFAS, this condensate may be treated, for example, with a resin in an ion exchange process to capture the PFAS, and then disposed of in a safe manner. A cooling circuit 76 having one or more heat exchangers therein may provide external cooling (e.g., using external or ambient air) to cool the condensate and provide cooling fluids to the condenser 74.

Advantageously, the dryer 30 of FIG. 2 can be used to process (dry or granulate) a wide spectrum of dewatered sludges, such as digested, undigested, waste-activated, or primary sludges, separately or in combination. This versatility makes the dryer 30 extremely useful in processing different biosolids from different treatment plants or other sources to produce granulated biosolids to be processed in the gasifier 14 of FIG. 1.

The combination of indirect and conductive heating, the blending of the wet biosolid cake with a high proportion of already dry solids, and the use of very low operating pressures result in several beneficial aspects to the overall approach, including achieving very high thermal efficiencies, with low operating temperatures, minimal off gas and emissions, the capability to work with a wide range of heat sources which in many cases cannot otherwise be utilized, maximum level of inherent safety and reliability, all within a small footprint.

FIG. 3 illustrates an example gasifier 100 that may be used as the gasifier 14 of FIG. 1. In particular, the gasifier 100 may be constructed using any of the principles and structures disclosed in U.S. Patent Application Publication No. 2024/0165448, which is hereby expressly incorporated by reference herein. Generally speaking the gasifier 100 is a plasma or ionic reactor that implements an ultra-high temperature ionic gasification process that can be used in an environmentally friendly manner to dispose of dried biosolids from, for example, wastewater treatment plants as well other waste feed stocks such as municipal solid waste (MSW) to produce, for example, renewable syngas that can be used to provide heat, power, renewable fuels, renewable hydrogen, and/or renewable chemical production. The gasifier 100 does so by generating electrical arcs across the interior of the gasifier reaction chamber creating a localized, controlled temperature well in excess of 3,000 degrees Celsius along with ionic gas or particles (plasma). This ultra-high temperature gasification zone and active ionic environment combine to very effectively and efficiently break down molecules into their constituent atoms and ions, in a process called complete molecular dissociation and ionization. This ultra-high temperature ionic zone also rapidly decomposes impurities in the feed stock such as microplastics, PFAS (Per- and/or Polyfluorinated Substance or Substances), and other fluorocarbon materials. Moreover, the gasifier 100 may be very compact, modular, and transportable, allowing it to address a broad range of applications, to be located close to a treatment facility, etc. More particularly, the gasifier 100 implements an ultra-high temperature ionic gasification process that operates between 3,000 and 10,000° C., efficiently and thoroughly destroying stable molecular bonds characteristic of PFAS compounds. The gasifier 100 is a direct-contact ionic gasifier, differentiated from typical commercial gasifiers which produce a plasma jet that burns at high temperatures, but that typically can only reach temperatures around 1,500° C. As will be understood, the plasma ionic gasifier 100 utilizes (energizes) multiple pairs of opposing electrodes simultaneously to form a large, conjoined electrically or field active plasma region where waste materials are dissociated at extremely high temperatures as they fall directly through a reaction zone. As an ionic gasification technology, feedstock ionization results from plasma energy transfer by particle collisions. Ionic species exit the reactor and rapidly cool, yielding high quality, clean, tar-free syngas, which reduces post-gas treatment costs. The system utilizes multiple plasma arcs controlled within the ionic reactor to generate an ultra-high temperature electrically active processing zone, allowing for the complete dissociation of complex waste molecules without the production of harmful byproducts like tars, oils, or even acid gases.

More particularly, as illustrated in FIG. 3, the gasifier 100 processes an input material 112 introduced at an input 113 of the gasifier 100 to produce an output material 114 emitted from an output 115 of the gasifier 100. The output material 114 may be, for example, a synthesis gas and/or other materials as described herein, including char. As illustrated in FIG. 3, the plasma gasifier 100 contains one or more circular plasma units 116 that are stacked in tandem with respect to one another (i.e., aligned along a longitudinal axis through the center of each unit 116), with each plasma unit 116 being formed from a circularly (in cross section) shaped outer ring with a cylindrical interior space defined in the middle of the outer ring. This interior space makes up a plasma or reaction zone 118 within the gasifier 100. Still further, each plasma unit 116 has one or more sets of electrode assemblies 120 extending through the outer wall thereof and into the reaction chamber 118. Each set of electrode assemblies 120 includes an anode electrode and a cathode electrode that extend radially towards the center of the plasma unit 116. Each set of electrodes associated with a set of electrode assemblies 120 is coupled to a working gas supply 122, a coolant supply 124 and a power supply 126 by various applicable conductors or electrical connectors. Generally speaking, the working gas supply 122 provides a working gas to each electrode assembly 120, and this gas is transported through and emitted from the electrode of the assembly 120 into the reaction chamber 118. This working gas helps cool the electrode tips of the electrodes and, additionally, is subject to high electric fields and arcing created by the electrodes within the reaction chamber 118 and, as a result, ionizes to create plasma within the reaction chamber 118. The coolant supply 124 provides coolant to the electrode assemblies 120 to help assist in keeping the electrodes (which may be made of tungsten, for example) from overheating during use. This coolant may be recycled and cooled in the coolant supply 124 to create a closed coolant loop. Additionally, the coolant for each electrode assembly 120 may be supplied via a high-pressure pump. After cooling the electrode or an electrode tip, the coolant exits the electrode assembly 120 and may be stored in a reservoir, not shown. When fresh water is available, the coolant in the reservoir may be kept cold by a cooling unit, not shown, such as a portable water heat exchanger. In another embodiment, when fresh water is not available, the cooling unit can be a chemical based chiller or any other cooling unit. In other embodiments, the electrode assemblies 120 may include electrodes made of an expendable material, such as graphite, which crodes or is consumed during use. In this case, the electrode assembly 120 may include a mechanism to move the associated electrode of the electrode assembly 120 radially into the reaction chamber 118 as the electrode or the electrode tip is consumed during use.

The power supply 126 provides electrical power to the electrodes of the electrode assemblies 120 at sufficient power (e.g., voltage and current) to create arcing between the anode and cathode of each electrode pair 120. The power supply 126 may be an AC power supply which may provide, for example, one phase or three phase AC power to the electrodes 120, or may be a DC power supply. A separate power supply 126 may be provided for each set or pair of electrode assemblies 120 or a combined power supply may provide power to multiple electrode pairs of a set of electrode assemblies 120. However, the power signal sent to each pair of electrodes or each set of electrode assemblies 120 may be electrically isolated from the power signals sent to the other pairs or sets of electrodes of other electrode assemblies 120. Furthermore, the electrode assemblies 120 may be connected to the power supply 126 through water-cooled cables, which provide both the cooling and current paths for the electrode assemblies 120.

Although one plasma unit 116 can be used, performance may be optimized through the use of a plurality of plasma units 116 stacked on top of or next to one another so that the outer walls or rings align longitudinally. For example, in FIG. 3, the plasma gasifier 100 is illustrated as including four stacked plasma units 116 creating an elongated tubular or cylindrical reaction zone 118. It should be understood, however, that the plasma gasifier 100 can have any number or plurality of stacked plasma units 116, including only one. By stacking the plasma units 116, the plasma or reaction zone 118 is lengthened along the longitudinal axis of the gasifier 100, and this elongated space or reaction chamber 118 enables the processing time for the incoming material 112 introduced into the reaction chamber 118 of the plasma gasifier 100 to be extended or increased, as the incoming material 112 flows in sequence through each of the different plasma units 116 when traveling from the input 113 to the output 115 of the gasifier 100. Moreover, the modular configuration created by stacking multiple plasma units 116 next to (e.g., on top of) one another enables an operator to manipulate the power settings in each of the plasma units 116, e.g., in the electrodes 120, separately to achieve an overall temperature profile for the plasma gasifier 100. An operator or designer can also add or subtract modular plasma units 116 to achieve the desired residence time for complete gasification of a particular class of incoming material 112.

As illustrated more clearly in FIG. 4, which depicts a longitudinal view of one of the plasma units 116 of FIG. 3, each plasma unit 116 has an annular body 128 with an inner wall 130 and an outer wall 132. The inner wall 130 defines a central plasma zone or reaction chamber 134 (e.g., making up part of the reaction chamber 118 of FIG. 3). The inner wall 130 is refractory and so is capable of containing the heat of the plasma without significant degradation. A preferred material for the inner wall 130 is graphite. However, certain refractory ceramics can also be used. A gap space 136 exists between the inner wall 130 and the outer wall 132. The gap space 136 is packed with insulation 138, such as high temperature ceramic fibers. In one embodiment, the insulation 138 (e.g., the ceramic fibers) may be, but is not limited to, Zirconia fibers. Alternatively and/or additionally, granulated sand and/or granulated oxide materials can be used as the insulation 138. Ceramic fibers or granulated oxide materials have significant advantages over conventional solid high-density blocky oxide insulations as granulated oxides and/or ceramic fiber blankets make up very low-density packing materials having significant voids therein. These voids have very low thermal conductivity and have excellent thermal insulation properties. Very low-density thermal insulation materials also reduce the overall weight of the gasifier 100.

In any event, the annular bodies 128 and the central plasma zones 134 concentrically align when the plasma units 116 are stacked. Moreover, the central plasma zone 134 of each plasma unit 116 is accessible through a plurality of access ports 140. Preferably, each plasma unit 116 contains at least eight access ports 140 but any other number of access ports could be used including more or less access ports 140. Each of the access ports 140 is lined with a sleeve of refractory material, such as a ceramic material, which can maintain integrity in the heat field of plasma created in the reaction chamber 134. Moreover, each access port 140 may be used to insert or hold an electrode assembly 142 therein. As such, it is preferable to have at least two access ports 140 in each plasma unit 116 and to provide for an even number of access ports 140, although this is not strictly necessary. Moreover, one or more of the access ports 140 may be used to store or insert a sensor of some sort to provide measurements or viewing of the reactions within the reaction chamber 134.

Most of the access ports 140 in each of the plasma units 116 receive electrodes or electrodes assemblies 142. Each of the electrode assemblies 142 is surrounded by an insulator that is sized to pass into the access ports 140 with tight tolerances. The tolerances prevent any significant gaps from existing between the insulator and the interior of the access port 140 that can leak plasma out of the plasma gasifier 100. Each of the electrode assemblies 142 includes an electrode tip 146 and a gas conduit 147 (illustrated in dotted relief in one electrode 142 of FIG. 4). The electrode tip 146 extends into the central plasma zone 134 and creates an arc with another electrode tip 146 during operation. The gas conduit 147 introduces a working gas from the working gas supply 122 of FIG. 3 into the plasma or reaction zone 134, which working gas is converted into plasma by the arc created between the tips 146 of two electrodes. Each of the electrode assemblies 142 is cooled by a coolant from the coolant supply 124 of FIG. 3. Moreover, it will be understood that each of the electrode assemblies 142 is coupled to the power supply 126 of FIG. 3 to receive electrical power (voltage and current).

Generally speaking, each plasma unit 116 receives the electrode assemblies 142 in sets of two. As such, each plasma unit 116 can receive two, four, six, eight or more of the electrode assemblies 142, depending upon the number of access ports 140 present. The electrodes of a first set of electrode assemblies 142 are set at a first position P1 and a second position P2 on opposite sides of the central plasma zone or reaction chamber 134. Likewise, the electrodes of a second set of electrode assemblies 142 are set at positions P3 and P4 and the electrodes of a third set of electrode assemblies 142 are set at positions P5 and P6. Accordingly, in the example of FIG. 4, there are three sets of electrode assemblies 142 and each of the set of electrode assemblies 142 includes one anode electrode and one cathode electrode. However, any other number of sets of electrode assemblies 142 could be used on each plasma unit 116, including one set, two sets, four sets, etc., and the electrodes of each electrode assembly 142 need not be spaced apart from each other at 180 degrees around walls 130, 132.

Moreover, the positions P1, P2 of the first set of electrode assemblies 142 are disposed radially or circumferentially with respect to the positions P3, P4 of the second set of electrode assemblies 142 and with respect to the positions P5, P6 of the third set of electrode assemblies 142 within each plasma unit 116. The angle of separation between the electrode assemblies 142 of the second set and the electrode assemblies 142 of the third set of electrode assemblies 142 is illustrated in FIGS. 3 and 4 as being 90 degrees. The angle of separation between the electrode assemblies 142 of the first set and the electrode assemblies 142 of the second set is illustrated as 45 degrees. Moreover, the angle of separation between the electrode assemblies 142 of the first set and the third set is also 45 degrees. However, these are but examples and other angles of separation between different sets of electrode assemblies could be used.

FIG. 5 illustrates one example of the configuration of the electrode assemblies 142 connected to mechanical motivators or actuators for reciprocally moving the electrodes of the electrode assemblies 142 or the electrode tips 146 of the electrode assemblies 142 radially into and out of the reaction chamber 134 while the electrode assemblies 142 are disposed in the access ports 140. The reciprocal movements are controlled by a corresponding linear actuator 148 that attaches to each of the electrode assemblies 142. Each set of electrode assemblies 142 can be moved synchronously to or independently of each other. In a single plasma unit 116, the separation (arc gap) between any set of electrode assemblies 142 can be adjusted by moving those electrode assemblies 142 into, or out of, the access ports 140.

In the exemplary embodiment of FIGS. 3-5, three sets of electrode assemblies 142 are inserted into each plasma unit 116 through the access ports 140. Preferably, in this case, one or both of the remaining access ports 140 are used for observations of the plasma gasifier 100 in operation, such as to hold sensors of some kind or another (e.g., temperature sensors, pressure sensors, video cameras, etc.). Of course, the electrode assemblies 142 attach to (are inserted into) the access ports 140 that are not being used for observation. Moreover, as illustrated in FIG. 5, each of the electrode assemblies 142 has the linear actuator 148 that controls the movements of the electrode assemblies 142 into and out of the access ports 140 and each linear actuator 148 may be connected to a control mechanism or controller that enables a user to control the movement of the electrode assemblies 142 during use. The mechanical or linear actuators 148 may be electrical actuators, hydraulic actuators, or any other desired type of mechanical or linear actuators.

During operation, one or more arcs can be ignited between the cathode and the anode of each pair of electrodes by (i) a high voltage discharge, (ii) a high frequency discharge, or by (iii) touching and withdrawing one electrode set from each other or by (iv) plasma energy from another module or by (v) a plasma torch such as that illustrated in FIGS. 6 and 7. When a high voltage or high frequency discharge is used to ignite an arc, the electrode tips 146 of the electrodes of a set of electrode assemblies 142 are brought in close proximity to each other such as by operation of the actuators 148. After the power supply 126 that supports the electrode assembly 142 in question is energized, a high voltage or high frequency discharge is applied across the central plasma zone 134 between electrode tips 146, which ignites an arc.

In a touch and withdrawal method of igniting an arc, the anode and cathode electrode tips 146 from a particular set of electrode assemblies 142 are brought into contact with each other momentarily after the associated power supply 126 is energized. As soon as a spark is generated, the electrode assemblies 142 are drawn apart quickly and an arc is ignited. Moreover, after a first arc is ignited, a second set of electrode assemblies 142 may be moved into the first arc region for ignition. The second set of electrode assemblies 142 may require thermal conditioning for a few seconds in the arc before it is self-ignited. In particular, thermal conditioning may be required to heat the electrode tips 146 to a sufficient temperature for thermionic emission of electrons to occur. Different plasma units 116 in the same plasma gasifier 100 can be used to form a combined arc system. In this configuration, arc systems complement each other in heating the combined plasma to achieve a much higher energy state than is possible using a single plasma unit 116. Additional plasma units 116 in the plasma gasifier 100 can be ignited in the same way.

As will be understood, the use of a plasma gasifier 100 with two or more plasma units 116 can generate very large and significantly high temperature arcs within the common plasma zone or reaction chamber 134 using relatively low input power from each participating plasma unit 116. Moreover, the plasma units 116 can be duplicated and stacked onto one other. In this manner, when one or more upper plasma units 116 sustain arcs, there is a field free (absence of current and voltage) high-energy plasma tail flame that can flow into other lower plasma units 116. In this case, the electrode assemblies 142 in the other plasma units 116 superimpose discharges in the tail flame and reignite it back into an arc state so that the stacked plasma units 116 produce a very large plasma column with very significant energy content. The modular stacking configuration of plasma units 116 can operate so that a “field free” (current and voltage free) plasma flame from the upstream unit is reheated to a “field active” (current and voltage active) arc state by superimposing an electric discharge in the downstream plasma units 116. The net plasma energy flow from one plasma unit 116 to another is called “energy cascading,” which adds energy to the downstream plasma units 116 and allows the downstream plasma units 116 to operate with a lower energy requirement.

FIG. 6 depicts another example gasifier 220, referred to herein as a hybrid gasifier, which could be used as the gasifier 14 of FIG. 1. The hybrid gasifier 220 is illustrated in FIG. 6 in a perspective, partially cut-away view and includes a vertically disposed plasma torch 204 in addition to three plasma units 116. The hybrid gasifier 220 is essentially the gasifier 100 of FIG. 3 modified to include three plasma units 116 (or rings) and to include a vertically mounted plasma torch 204. The same or similar reference numbers are used in FIG. 6 as are used in FIGS. 3-5 to indicate the same or similar components. As illustrated in FIG. 6, the hybrid gasifier 220 includes multiple plasma units 116 (in this case, three) stacked vertically on top of one another with electrode assembles 120 (FIG. 3) or 142 (FIGS. 4-5) mounted in the ports 140 so that the anode and the cathode of a particular set of electrode assemblies 142 are disposed on opposite sides of the unit 116, i.e., 180 degrees around the unit 116 in which the electrodes are disposed, and so that the electrodes 142 extend radially into the reaction chamber 134. While the hybrid gasifier 220 of FIG. 6 is illustrated as including three plasma units 116 each with three sets of electrodes 142, more or less plasma units 116 could be used and more or less sets of electrode assemblies 142 could be disposed in each plasma unit 116. Still further, while the sets of electrode assemblies 142 and the electrodes therein within adjacent plasma units 116 are illustrated as being mounted in a vertical line with respect to one another, the various electrodes 142 of different plasma units 116 could be offset from the electrodes in adjacent plasma units 116 by any desired angle (e.g., by 15 degrees, 20 degrees, 30 degrees, etc.).

As illustrated in FIG. 6, a plasma torch 204 is mounted on the top of the hybrid gasifier 220 and has an output 222 that extends into or that is disposed at the top of the reaction chamber 134 above or higher than the uppermost plasma unit 116. The plasma torch 204 is connected to a source of working gas and receives the working gas. As is typical, the plasma torch 204 (also referred to as a plasma jet generator or creator), creates or generates an arc between a cathode electrode and an anode electrode that are positioned close together inside the body of the torch 204 (not shown in FIG. 6). The working gas is then passed through the arc, therein creating a tongue of plasma which is then emitted from the output 222 of the plasma torch 204 as a stream of hot plasma 208 into a reaction chamber 134. Here, depending on the flow of the working gas into the plasma torch 204, the stream of hot plasma 208 may travel down through the center of the reaction chamber 134 (i.e., longitudinally or along a longitudinal axis of the plasma units 116) and intersect the reaction zones of one or more of the plasma units 116, thereby providing additional plasma or ionic material in the reaction chamber 134 to process material therein.

As illustrated in FIG. 6, the material to be processed may be introduced into the reaction chamber 134 via one or more openings or inputs 224 disposed in the top of the gasifier 220 around or near the plasma torch 204. However, the processing material input(s) 224 of the hybrid gasifier 220 may be located at one or more other locations on the gasifier 220, such as on the side of the gasifier 220 above the first (uppermost) plasma unit 116. The material to be processed, once introduced via an input 224, is gravity fed and flows down through the reaction chamber 134 through each of the stacked plasma units 116. Of course, this material contacts or interacts with the ionic gas produced by the plasma torch 204, especially near the inputs 224, and also interacts with the electrical arcs (shown in some cases in FIG. 6) that emanate from or that form between the electrode tips of the anode and cathode electrodes of the various pairs of electrode assemblies 142 extending into the reaction chamber 134. In the case in which the electrode assemblies 142 also provide a working gas within the chamber 134, which also becomes ionized (i.e., forms plasma), the material to be processed additionally interacts with this plasma, all of which helps heat and break down the material. Thus, as will be understood, the plasma from the plasma torch 204 provides additional heating and ionized gases which interact with and break down the material being processed. Likewise, the plasma stream 208 generated by the plasma torch 204 may be used to ignite one or more of the electrodes of the sets of electrode assemblies 142 during start up by providing plasma and heat and ionizing sources in the chamber 134. This operation may reduce or eliminate the need to cause the anode and cathode electrodes of a pair of electrode assemblies to be moved together or to touch to start the arcing activity. This operation may also reduce or eliminate the need to provide working gas into the reaction chamber 134 via the electrode assemblies 142. In any event, after the material being processed travels generally vertically through (from top to bottom) the reaction chamber 134 and is subjected to the plasma generated by the plasma torch 204 and the plasma and arcs generated by the various pairs of electrode assemblies 142 in each of the plasma units 116, the processed material leaves the reaction chamber 134 via one or more outputs 115 at the bottom (lower vertical end) of the gasifier 220. While the plasma torch 204 is illustrated in FIG. 6 as being disposed near the inputs 224, it could be disposed near the output 115 and extend longitudinally into the reaction chamber 134 from the bottom, expelling or emitting plasma (e.g., a plasma plume or flame) directed upwards through the center of the reaction chamber 134. In cases where the feed or input material and/or the product or processed material includes solids, the plasma torch 204 is suitably positioned longitudinally to direct the plasma plume 208 downward or otherwise co-currently with the flow of material through the reactor or gasifier 220. In other cases, the plasma torch 204 could be mounted so as to direct the plasma plume 108 radially inward from one of or between different ones of the plasma units 116.

FIG. 7 illustrates a further example of a hybrid gasifier or ionic reactor 300 similar to that of FIG. 6, which may be used as the gasifier 14 of FIG. 1. The hybrid gasifier 300 is similar to the gasifier 220 of FIG. 6 and the gasifier 100 of FIG. 3 modified to include three plasma units 116 (or rings) and to include three generally vertically mounted plasma torches 204. The same or similar reference numbers are used in FIG. 7 as are used in FIGS. 3-6 to indicate the same or similar components. The hybrid gasifier 300 is illustrated in FIG. 7 in a perspective view and as noted above includes three generally vertically disposed plasma torches 204 mounted on the top of the gasifier 300 which produce a plasma flame in an initial reaction chamber within the interior of the gasifier 300 defined by a region or section 305. The three plasma units 116 or plasma rings 116 are disposed below the section 305 and the plasma torches 204 and the plasma units 116 form a reaction chamber such as the reaction chamber 134 of FIGS. 4 and 6 (but not specifically shown in FIG. 7). The rings 116 are stacked vertically on top of one another with electrode assembles 120 (FIG. 3) or 142 (FIGS. 4-5) mounted in the ports 140 so that the anode and the cathode of a particular set of electrode assemblies 142 are disposed at an angle of offset of 135 degrees around the reaction chamber 134 (instead of being on the opposite sides of the unit 116), and so that the electrodes 142 extend radially into the reaction chamber (not shown in FIG. 7). The electrode assemblies 142 are not completely illustrated in FIG. 7, but it is to be understood that they may include the elements illustrated and described with respect to FIGS. 3-6. While the hybrid gasifier 300 of FIG. 7 is described as including three plasma units 116 each with three sets of electrodes 142, more or less plasma units 116 could be used and more or less sets of electrodes 142 could be disposed in each plasma unit 116. Still further, while the sets of electrodes 142 in adjacent plasma units 116 are illustrated as being mounted radially offset from one another, they could be mounted in a vertical line with respect to one another. Moreover, the various electrodes 142 of different plasma units 116 could be offset from the electrodes in adjacent plasma units 116 by any desired angle (e.g., by 15 degrees, 20 degrees, 30 degrees, etc.). Still further, the anode and cathode electrodes of a particular pair or set of electrodes 142 may be offset from one another by other desired angles including, for example, 180 degrees (i.e., directly opposite each other around the reaction chamber), 90 degrees, 45 degrees, etc.

As illustrated in FIG. 7, the three plasma torches 204 are mounted on the top of the hybrid gasifier 300 and each has an output that extends into or that is disposed in the initial reaction zone 305 above or on top of the reaction chamber 134 formed by the rings or units 116. The plasma torches 204 are connected to a source of working gas (not shown) and receive the working gas therefrom. As is typical, each of the plasma torches 204 (also referred to as a plasma jet generator), creates or generates an arc between a cathode electrode and an anode electrode that are positioned close together inside the body of the torch 204 (not shown in FIG. 7). The working gas is then passed through the arc, therein creating a tongue of plasma which is then emitted from the output of the plasma torch 204 as a stream of hot plasma into the reaction chamber formed by the annular space in the region 305 as well as, in some cases, into the reaction chamber 134 formed by the upper most ring or plasma unit 116. Here, depending on the flow of the working gas into the plasma torches 204, the stream of hot plasma may travel down through the center of the initial reaction chamber or zone 305 (i.e., generally longitudinally or along a longitudinal axis of the plasma units 116) and intersect the reaction zones 134 of one or more of the plasma units 116, thereby providing additional plasma or ionic material in the reaction chamber 134 to process material therein.

As illustrated in FIG. 7, the material to be processed may be introduced into the initial reaction chamber 305 via one or more openings or inputs 324 disposed in the top center of the gasifier 300 near or between the plasma torches 204. However, the processing material input(s) 324 of the hybrid gasifier 300 may be located at one or more other locations on the gasifier 300, such as on the side of the gasifier 300 above the first (uppermost) plasma unit 116, e.g., in the region 305. The material to be processed, once introduced via the input 324, is gravity fed and flows down through the initial reaction chamber 305 and thereafter through each of the stacked plasma units 116. Of course, this material contacts or interacts with the ionic gas produced by the plasma torches 204 in the initial reaction region or zone 305, especially near the input 324, and also interacts with the electrical arcs that emanate from or that form between the electrode tips of the anode and cathode electrodes of the various pairs of electrode assemblies 142 extending into the reaction chamber 134 formed by the plasma rings 116. In the case in which the electrode assemblies 142 also provide a working gas within the reaction chamber 134, which also becomes ionized (i.e., forms plasma), the material to be processed additionally interacts with this plasma, all of which helps heat and break down the material. Thus, as will be understood, the plasma from the plasma torches 204 provides additional heating and ionized gases which interact with and break down the material being processed. Likewise, the plasma stream generated by the plasma torches 204 may be used to ignite one or more of the sets of electrodes 142 disposed in the plasma rings 116 during start up by providing plasma and heat in the chamber 134. This operation may reduce or eliminate the need to cause the anode and cathode electrodes of a pair of electrode assemblies within one of the rings 116 to be moved together or to touch to start the arcing activity. This operation may also reduce or eliminate the need to provide working gas into the reaction chamber 134 via the electrode assemblies 142. A viewing port 330 may be disposed in the top of the gasifier 300 to enable a view into the initial reaction zone 305 and into the reaction chamber 134 formed by the plasma rings 116. This viewing port 330 may be made of a clear substance to enable visual inspection of the reactions occurring within the gasifier 300 and/or may enable various sensors (e.g., cameras, temperature sensors, flow sensors, spectral analyzers, etc.) to be mounted therein for taking various measurements during the operation of the gasifier 300.

As noted above, in the reaction chamber 134 formed by the rings 116, the material being processed undergoes intense heat (e.g., at temperatures ranging from 1,500 or 3,000 degrees Celsius and 10,000 degrees Celsius, and averaging around 5,000 degrees Celsius) and undergoes molecular dissociation in a low oxygen environment causing atoms and ions thereof to reform into elemental particles, i.e., these atoms and ions reform into low molecular weight species.

In any event, after the material being processed travels generally vertically through (from top to bottom) the reaction chamber 134 formed by the rings 116 and is subjected to the plasma generated by the plasma torches 204 and the plasma and arcs generated by the various pairs of electrode assemblies 142 in each of the plasma units 116, the processed material enters a quenching zone or chamber 340 formed by one or more rings disposed below the lower most plasma ring 116. In the quenching chamber 340, particles rapidly cool to their lowest energy state in the form of hydrogen (H₂) and carbon monoxide (CO) gas. These particles emerge as a tar free and PFAS free syngas, which can be converted to other fuels, separated to capture the gases (carbon monoxide and hydrogen) or used in a generator to generate electricity.

In cases where the feed or input material and/or the product or processed material includes solids, the plasma torches 204 are suitably positioned mostly longitudinally (vertically) to direct the plasma plume downward or otherwise co-currently with the flow of material through the reactor or gasifier 300. In other cases, the plasma torches 204 can be mounted so as to direct the plasma plume 108 radially inwardly from one of or between different ones of the plasma units 116 or from below the plasma units 116. In the case illustrated in FIG. 7, the plasma torches 204 are disposed at a slight angle to the top of the chamber so as to direct plasma flames into the top of the chamber 305 at a slight angle to the longitudinal axis of the chamber 305. Moreover, the inner wall of the chamber 305 may be tapered so as to decrease from the top to the bottom to direct hot plasma gas and material to the center of the chamber 134 within the rings 116 as well as to provide for more reaction space or volume in the initial reaction section 305 then in the chambers formed by the rings 116.

The gasifier 300 of FIG. 7 additionally includes a first output 350 for providing syngas created therein to, for example, a generator or other device which may convert the syngas for other uses. Likewise, the gasifier 300 includes a second output 352 for collecting char produced in the gasifier 300. The second output 352 may allow the char to fall through to the bottom of the unit 300 and be collected at convenient times or to be collected in a collection tank disposed below the unit 330.

In any event, a system using any of the dryers 12, 30 of FIGS. 1 and 2 in combination with any of the gasifiers 14, 100, 220, 300 of FIGS. 1, 3-7, provides for effective and highly efficient treatment of wastewater residual solids resulting in volume and mass reduction, contaminant destruction and energy recovery, as well providing a platform for creating high value byproducts such as hydrogen (syngas) and fine carbon products (e.g., char).

FIG. 8 illustrates, as one example, material flow in such a system. In particular, a combined dryer and gasifier system 400 is illustrated as including the dryer 30 of FIG. 2 and one or more gasifiers constructed in accordance with the principles described with respect to the gasifier 300 of FIG. 6, wherein the gasifiers 300 includes three plasma units, each including three sets of electrodes. As illustrated in FIG. 8, 50 tons of dewatered biosolids (having 20 percent solids) is provided to and processed in the dryer 30 according to the principles described herein resulting in the creation of 11 tons of dried biosolids, which amounts to a 78 percent reduction in mass. The 11 tons of dried biosolids are then processed in the gasifier 300 to produce tar-free or contaminate free syngas and 2 tons of char, which is a 96 percent reduction in mass. As illustrated in FIG. 8, at least some of the syngas is used to power one or more generators 22 which produce and provide 700 kilowatts of power to the gasifier 300 used to process the 11 tons of dried biosolids. Waste heat is collected from the generator(s) 22, e.g., from the generator exhaust gas, to provide heating energy and to act as a heat energy source for the dryer 30, and the cooled exhaust from the generator(s) 22 is expelled to the atmosphere. Likewise, the condensate from the dryer 30 is provided to a wastewater treatment plant (WWTP) for processing if needed.

Here it should be noted that the syngas produced by the gasifier 300 is relatively free of contaminants, including PFAS. As an explanation, the gasifier 300 achieves temperatures between 3,000° C. and 10,000° C. throughout the reactor's entire plasma field. Exceeding temperatures of the sun, this ionic gasification far outperforms other thermal solids destruction technologies, fully destroying PFAS compounds at unprecedented reaction rates. Biosolids freefall through the gasifier reactor 300 with gas residence times measured in less than a second. High operating temperatures generated through direct contact with the plasma field within the gasifier reactor 300 result in assured PFAS destruction, even with relatively short residence times. Additionally, ultra rapid cooling from reaction temperature leads to stable product formation of pure hydrogen and CO (syngas) while dissociated fluorine mineralizes to fluoride salts (MgF₂ and CaF₂) versus HF when there is a high concentration of alkaline and alkaline earth elements, which are both present in biosolids.

Empirical data confirms that contact with temperatures above 2,000K (1,720° C.) results in high decomposition rates at sub millisecond residence times for PFES, a short chain molecule representative of a broad spectrum of PFAS compounds. This evidence reinforces the technical ability of the gasifier 300 as described herein to meet and exceed regulatory requirements for PFAS destruction. Moreover, several analytical processes were used for targeted analysis and the study of mass balance across both the syngas and char streams of one or more experimental systems implementing the combined drying and gasification process described herein. In particular, the analytical methodology of EPA Method 537 modified and Method 1633 were used to analyze the biosolids, while the EPA Method 537 modified and draft method OTM-45 were used to analyze the syngas, and EPA Method 537 modified and Method 1633 were used to analyze the char.

Preliminary testing at a pilot scale unit demonstrated the promising destruction capabilities of the system described herein, with the testing demonstrating near complete PFAS destruction on the artificially spiked biosolids. Initial testing was conducted using a pilot configuration of a gasifier as described herein, operating at a loading rate of 0.25 ton per day of dried biosolids. Feedstock for the testing included AFFF-spiked biosolids measured at approximately 200 ppm total PFAS. A mass balance was performed on the system, inclusive of biosolids feed, AFFF, syngas, and char to track the fate of PFAS throughout the process. The table below illustrates the results of this pilot testing.

Moreover, a second phase of testing was performed on a commercial full-scale gasifier reactor as described herein, sized with a biosolids processing rate of 1 ton per day (wherein, the system was capable of 3.5 tons per day). Feedstock for the test was locally sourced Tennessee dried biosolids. Method 537 modified was used to test char samples for PFAS, with results indicating non-detection for all 39 compounds tested. Out of the conducted tests, this solids test proved most impacted by higher detection limits and blank contamination associated with Method 537 test methodologies described above.

A third phase of testing included performing additional PFAS testing on the biosolids, char, and syngas as well as performing FTIR syngas testing. Preliminary analysis results indicated no trace of acid gases (HF, H₂S, & HCl) or of fluorinated compounds (CF₄ C₂F₆ or SF₆), while final analysis found trace amounts of some of these compounds, inferring that the ionic gasification performed by the gasifier was not simply decomposing long PFAS compounds into shorter chain compounds, but in fact breaking up the compounds into element constituents. Preliminary results of this testing are presented in the table below.

Still further, a mass balance analysis was performed to understand the amount of PFAS volatilization in the syngas and the resulting vapor phase destruction. Syngas samples were collected from 3 separate runs and tested using a combination of method OTM-45 and method 537 Modified. The following (11) compounds, listed in the table below, observed over 99.87% destruction, which was achieved in the vapor phase. The additional compounds targeted in the full analysis identified data quality concerns, indicated with “B” tag (sample and blank contamination). Additionally other compounds indicated “J” tag (amount of that analyte was below the minimum for accurate measurement).

As a result, low temperature drying paired with ultra-high temperature gasification as performed by the system described herein represents a paradigm shift in PFAS destruction technology for biosolids. With its proven efficacy, versatility, and alignment with environmental and regulatory demands, it offers a reliable forward-looking solution to the global PFAS challenge at a realistic economic and commercial readiness level.

Although the presently described systems can be embodied in many ways, only some exemplary embodiments have been selected for the purposes of illustration and discussion. Moreover, it will be understood that the embodiments of the present invention that are illustrated and described herein are merely exemplary and that a person skilled in the art can make many variations to those embodiments. All such embodiments are intended to be included within the scope of the present invention as defined by the claims.