Hydrothermal carbonisation, liquefaction and gasification plant

Abstract

The invention relates to a carbonisation, hydrothermal liquefaction and hydrothermal gasification plant incorporating a reactor (5) for the thermochemical conversion of wet organic waste into gases, a fluid and a solid waste, and comprising an energy recovery element (9), a heating system (14) with electrical resistors (28), a centrifuge (12), and a tank (13), wherein the energy recovery element (9) takes the form of a double-pipe coil (6) surrounding the reactor (5), comprising a first pipe (7), intended to receive the fluid of the reactor (5), which communicates the outlet of the reactor (5) with the inlet of the centrifuge (12), and a second pipe (8), in a closed circuit, comprising a fluid intended to exchange heat with the fluid of the reactor (5), such that the fluid exiting the reactor (5) has the function of heating the fluid entering the reactor (5).

Description

[0001] HYDROTHERMAL CARBONIZATION, LIQUEFACTION AND GASIFICATION PLANT

[0002] DESCRIPTION

[0003] OBJECT OF THE INVENTION

[0004] The present invention relates to a hydrothermal carbonization (HTC), hydrothermal liquefaction (HTL) and hydrothermal gasification (HTG) plant with reactor and energy recovery system optimized for the treatment of waste with high moisture and carbon content by thermochemical processes of carbonization, liquefaction and hydrothermal gasification.

[0005] The plant can operate within a wide temperature range (140 to 500°C) and pressure range (1 to 30 MPa). This allows for the valorization of organic waste with water content exceeding 70% and carbon content exceeding 25% through hydrothermal carbonization (HTC), hydrothermal liquefaction (HTL), and hydrothermal gasification (HTG). The innovative design of the reactor and energy recovery system reduces energy consumption compared to pyrolysis, while maximizing thermal efficiency and increasing the recovery of bio-oil and syngas.

[0006] BACKGROUND OF THE INVENTION

[0007] Hydrothermal liquefaction (HTL) is a thermochemical process that converts wet biomass into liquid biofuels (biocrude) using temperatures between 200-400 °C and pressures of 10-22 MPa, without the need for prior drying. Its ability to process waste with high water content (sewage sludge, slurry, algae, agricultural and urban waste) makes it an efficient alternative to technologies such as pyrolysis and gasification.

[0008] Hydrothermal carbonization (HTC) is a thermochemical process typically carried out between 180 and 250 °C and pressures of 1 to 4 MPa, applicable to the treatment of wet biomass to obtain a carbonaceous solid of the hydrochar type. This process allows obtaining products with high energy density and good workability, used as a solid biofuel or precursor of advanced adsorbents. Hydrothermal gasification (HTG) is also a thermochemical process that converts wet biomass into gases at temperatures between 400 °C and 500 °C and pressures of 22 to 30 MPa, without the need for prior drying.

[0009] Hydrothermal liquefaction (HTL) plants known in the prior art face several technical challenges that limit their efficiency and commercial viability. The main problems identified include:

[0010] - High energy consumption: Thermal losses in conversion systems reduce the overall efficiency of the process.

[0011] - Variable quality of the biocrude: The resulting biocrude has high levels of oxygen and nitrogen, which affects its stability and calorific value.

[0012] - Poor energy recovery: The reuse of heat generated in the process is not fully optimized.

[0013] - Inefficient management of the aqueous phase: Wastewater contains organic compounds that are difficult to treat, which increases treatment costs.

[0014] - Wear and tear on mechanical components: Traditional pumping systems suffer accelerated wear due to the composition of the processed biomass. - Non-linear flow of the suspension to be processed, which therefore presents pumping difficulties due to its non-Newtonian rheological behavior.

[0015] These problems prevent HTL from being a fully viable solution for the industrial production of biofuels and their integration into advanced biorefineries.

[0016] Next, a comparison of different alternative technologies is made to understand the advantages of HTL technology.

[0017] HTL vs. Pyrolysis.

[0018] - Lower energy consumption: HTL does not require pre-drying, whereas pyrolysis requires a moisture content of less than 10%, which increases energy costs.

[0019] - Greater efficiency in energy recovery: HTL allows up to 55% of the energy contained in biomass to be recovered, compared to 35-40% in pyrolysis.

[0020] - Less solid waste formation: Pyrolysis generates more coke and tar, while HTL minimizes these byproducts. HTL vs. Gasification

[0021] - Fewer extreme conditions: HTL operates at temperatures below 400 °C, while gasification exceeds 800 °C.

[0022] - Larger fraction of liquid product: gasification predominantly produces synthesis gas, while HTL generates biocrude with high calorific value.

[0023] HTL vs. Anaerobic Digestion

[0024] - Higher carbon conversion: HTL converts up to 80% of organic carbon into biocrude, while anaerobic digestion only converts 30-50% into biogas. - Reduced residence time: HTL requires minutes instead of days or weeks for conversion.

[0025] The key parameters in HTL wet waste technology are as follows:

[0026] - Temperature: 250-370°C for standard HTL; 350-400°C under supercritical conditions.

[0027] - Pressure: 10-22 MPa, ensuring that the water remains in a liquid state. - Residence time: 14-60 minutes, depending on the type of biomass.

[0028] - Waste composition: HTL achieves efficient conversion into waste with more than 25% carbon.

[0029] On the other hand, HTL technology's greatest contribution lies in energy recovery and by-product management:

[0030] - Optimized heat exchangers can recover up to 80% of waste heat, reducing energy consumption.

[0031] - Use of the residual gas generated in HTL as an energy source for the same process.

[0032] - Reuse of the aqueous phase in anaerobic digestion for additional biogas production.

[0033] - Nutrient recovery (N, P) applicable in fertilizers.

[0034] The state of the art includes a number of documents that refer to HTL technology.

[0035] US2015362347 describes a process where hydrothermal liquefaction is performed on organic raw materials. The raw material is first subjected to hydrothermal carbonization, which converts it wholly or partially into a carbonized solid. The particle size of the carbonized solid is then reduced, and the reduced-size carbonized particles, including the remaining products of hydrothermal carbonization, are subjected to hydrothermal liquefaction.

[0036] US2024010919 discloses a system and method for producing synthesis gas and bio-oil from biomass. The method comprises producing synthesis gas from a carbonaceous feedstock in a gasification unit, optionally cooling the synthesis gas discharged from the gasification unit, piping the synthesis gas to a hydrothermal processing unit, wherein the hydrothermal processing unit is configured to process a biomass feedstock contained in a pressurized water stream, transferring heat from the synthesis gas to the biomass feedstock in the hydrothermal processing unit, and producing a hydrothermal product from the biomass feedstock in the pressurized water stream.

[0037] Document W02024081198A1 relates to systems and methods for producing biocrude oil. These include a well with a depth, an upper portion located at the surface, and a lower portion located underground. The well comprises a casing and tubing within it, forming an annulus. The casing and tubing define a hydrothermal liquefaction (HTL) reaction zone at the bottom of the well and a heat transfer and separation zone above the HTL reaction zone. The well includes a cable with an electric heating element located in the tubing of the HTL reaction zone, configured to transfer energy to the biomass slurry flowing through the tubing, converting a portion of it into biocrude oil via HTL.The depth of the well and the electric heating element are sized to generate the necessary temperature and pressure in the HTL reaction zone to form subcritical water and produce a product fluid composed of biocrude.

[0038] DESCRIPTION OF THE INVENTION

[0039] Despite the advances mentioned in the background section, current technologies still have limitations in terms of energy consumption, biocrude stability, and efficient management of byproducts generated during liquefaction. The present invention focuses on overcoming these limitations. To this end, it discloses a plant for hydrothermal carbonization, hydrothermal liquefaction, and hydrothermal gasification comprising an innovative reactor design and an improved energy recovery system. Key elements of this new invention include:

[0040] - a continuous multifunctional reactor, designed to operate under HTC, HTL and HTG conditions, maximizing process versatility and to process suspensions of solids in water with solid contents up to 30%, working in turbulent flow to improve residence times and heat transfer,

[0041] - Internal design of the continuous reactor using concentric baffle plates that allows working under turbulent flow conditions with variable residence times depending on the characteristics of the input material and the products to be obtained,

[0042] - a multi-stage helical energy recovery system that allows up to 80% of the heat generated in the process to be used, reducing energy consumption,

[0043] - advanced catalysts to improve the stability of the biocrude and reduce the formation of unwanted byproducts,

[0044] - a hydraulic system for optimizing biomass pumping: the improved hydraulic system reduces wear on mechanical components and improves heat transfer efficiency,

[0045] - a thermal pretreatment device to improve biomass conversion and optimize the quality of the resulting biocrude,

[0046] - Use of a triple crushing, filtering and colloidal grinding system that allows the non-linear flow of a solids suspension in water, capable of flowing through the piping system, reactor and heat exchanger without blockages, - Use of an auxiliary cleaning system by pumping a mixture of water and cleaning chemicals capable of removing scale and solid residues that may be adhered to the pipes,

[0047] - use of a system for separating polar and non-polar liquids at high temperature, by employing a centrifuge,

[0048] - a system for emptying inorganic ash from the bottom of the reactor by gravity. The elements mentioned allow for a more efficient and sustainable operation, overcoming the limitations of existing HTC, HTL and HTG plants.

[0049] The present invention offers a number of key advantages that significantly improve the performance and viability of HTC, HTL, and HTG technologies for biofuel production:

[0050] - Reduced energy consumption: Thanks to an optimized heat recovery system, the thermal efficiency of the process is improved.

[0051] - Greater stability of the biocrude: The use of catalysts and an integrated thermal pretreatment allows obtaining a biofuel of better quality and greater stability.

[0052] - Reduced generation of secondary waste: Reuse of the aqueous phase and efficient handling of by-products minimize environmental impacts.

[0053] - Increased component durability: Optimizing the pumping system reduces wear and maintenance of the equipment.

[0054] - Operational versatility: The ability to operate in both HTC and HTL and HTG allows for greater flexibility in biomass conversion and adaptation to different types of waste.

[0055] With these improvements, the present invention represents a significant advance in the optimization of hydrothermal liquefaction, allowing its integration into biofuel production systems in a more efficient and sustainable manner.

[0056] Industrial applications of the invention include:

[0057] - the treatment of organic waste with a high carbon content,

[0058] - the production of advanced biofuels with greater thermal efficiency, - the energy recovery of biomass without the need for prior drying.

[0059] Thus, one object of the invention is to develop a versatile plant capable of operating in HTC, HTL, or HTG mode, depending on the nature of the waste to be treated and the desired products. To this end, two key components have been optimized:

[0060] - the reactor, which has been adapted to operate under both HTC (180-250°C, 1-4 MPa) and HTL (275-370°C, 7-22 MPa) or HTG (400-500°C, 22-29 MPa) conditions, and - the energy recovery unit, which achieves up to 85% recovery of waste heat and a reduction in energy consumption.

[0061] As for the reactor, it has been specifically designed to allow triple use, meaning that with a single unit it can be operated in hydrothermal carbonization (HTC), hydrothermal liquefaction (HTL) or hydrothermal gasification (HTG) regimes, three processes that share characteristics, but differ significantly in their operating conditions and products obtained:

[0062] On the one hand, HTL operates between 275 and 370 °C and pressures of 7 to 22 MPa, and its objective is to produce bio-oil from wet waste without the need for prior drying.

[0063] On the other hand, HTC operates between 180 and 250 °C and pressures of 1 to 4 MPa, and its objective is to produce hydrochar from wet waste without the need for prior drying.

[0064] Finally, HTG, on the other hand, is carried out at higher temperatures, between 400 and 500 °C, and pressures of up to 29 MPa, generating mainly synthesis gas (mainly H2, CH4 and CO2), from wet waste without the need for prior drying.

[0065] Furthermore, the reactor features a vertical, continuous design incorporating concentric baffle plates to induce turbulent flow and controllable residence times. This allows for optimized biomass conversion based on the specific process and waste being treated. Additionally, the reactor is built to withstand extreme pressures and temperatures, making it versatile and durable, capable of operating with dense solids suspensions of up to 30%.

[0066] This modular and adaptable approach allows:

[0067] - Maximize yield according to the raw material and the desired product.

[0068] - Reduce reaction times and improve heat transfer.

[0069] - To make the switch between hydrochar production (HTC), liquid biofuels (HTL) and gaseous biofuels (HTG) more flexible.

[0070] Regarding the energy recovery unit, it incorporates a double-pipe helical heat exchanger, designed to maximize the thermal efficiency of the process. The characteristics of this energy recovery unit are:

[0071] - It operates by countercurrent heat exchange, where the hot fluid exiting the reactor transfers its heat to the incoming biomass stream. - It consists of a system of concentric tubes arranged in a spiral, which increases the contact surface area and improves heat transfer.

[0072] - It is fully thermally insulated to prevent heat loss to the environment.

[0073] In this way, with the energy recovery system:

[0074] - Up to 80-85% of the heat that would otherwise be dissipated is recovered, significantly reducing the overall energy consumption of the system.

[0075] - The incoming substrate is preheated, which accelerates its conversion upon reaching the reactor. - The sustainability of the process is improved, bringing the system closer to energy self-sufficiency through the use of its own thermal waste.

[0076] Together, the combination of reactor and recovery unit allows for increased overall process efficiency, reduced operating costs, and progress towards a competitive waste valorization technology.

[0077] In summary, the invention relates to a hydrothermal carbonization (HTC), hydrothermal liquefaction (HTL), and hydrothermal gasification (HTG) plant, comprising a reactor for the thermochemical conversion of wet organic waste into gases, a fluid, and a solid residue.

[0078] The plant additionally comprises:

[0079] - an energy recovery system,

[0080] - a heating system comprising electric resistors,

[0081] - a centrifuge, and

[0082] - a deposit,

[0083] The energy recovery unit consists of a double-tube coil that surrounds the reactor. The coil also comprises:

[0084] - a first tube, intended to receive the fluid from the reactor that connects the reactor outlet with the centrifuge inlet, and

[0085] - a second tube in a closed circuit, comprising a fluid intended to exchange heat with the reactor fluid. In this way, the fluid leaving the reactor has the function of heating the fluid entering the reactor.

[0086] The reactor is configured to withstand temperatures up to 500 °C and pressures up to 30 MPa.

[0087] Inside the reactor, the thermochemical conversion is preferably carried out at a temperature above 330 °C.

[0088] In one embodiment, the plant comprises a wet organic waste receiving tank, a crusher, and a colloidal mill that treats the material before it is sent to the reactor.

[0089] In another embodiment, the coil tubes are corrugated so that they can expand thermally.

[0090] DESCRIPTION OF THE DRAWINGS

[0091] To complement the description being made and in order to help a better understanding of the characteristics of the invention, according to a preferred embodiment thereof, a set of drawings is included as an integral part of said description, in which, for illustrative and non-limiting purposes, the following has been represented:

[0092] Figure 1.- Shows a simplified diagram describing the material flow in the pilot plant for hydrothermal liquefaction and gasification

[0093] Figure 2.- Shows an elevation view of the reactor with the energy recuperator and an electrical resistor in a semi-transparent mode, so that the concentric configuration of the recuperator can be seen.

[0094] Below is a list of the different elements represented in the figures with their associated numerical references: 1. Receiving tank.

[0095] 2. Crusher.

[0096] 3. Mill.

[0097] 4. High pressure pump.

[0098] 5. Pressure reactor.

[0099] 6. Serpentine.

[0100] 7. First tube.

[0101] 8. Second tube.

[0102] 9. Energy recovery unit.

[0103] 10. Ash tank.

[0104] 11. Pressure reducer.

[0105] 12. Centrifuge.

[0106] 13. Deposit.

[0107] 14. Heating system.

[0108] 15. Cleaning pump.

[0109] 21. First duct.

[0110] 22. Second conduit.

[0111] 23. Third conduit.

[0112] 24. Fourth conduit.

[0113] 25. Fifth conduit.

[0114] 26. Sixth conduit.

[0115] 27. Recirculation duct.

[0116] 28. Electrical resistors.

[0117] PREFERRED EMBODIMENT OF THE INVENTION

[0118] A preferred embodiment of the hydrothermal liquefaction and gasification plant according to the present invention is described below with the help of figures.

[0119] As can be seen in Figure 1, the process begins with the reception of wet organic waste (e.g., sewage sludge, food waste, digestate) in a receiving tank (1), where it is temporarily stored and homogenized before processing. From this tank (1), the waste is conveyed to a mechanical preparation stage. First, the waste passes through a shredder (2), which reduces its size to facilitate handling and improve heat transfer in subsequent stages.

[0120] Next, the crushed material is processed by a turbofilter or colloidal mill (3), which performs a finer disintegration of the particles, generating a homogeneous and fluid slurry suitable for thermochemical treatment.

[0121] This slurry is subsequently pumped by a high-pressure pump (4), through a first conduit (21) to a pressurised reactor (5), the core of the system, designed to withstand temperature conditions between 180 and 500 °C and pressures of 10 to 30 MPa. In this unit, hydrothermal carbonization (HTC), hydrothermal liquefaction (HTL), or, if operating under supercritical conditions, hydrothermal gasification (HTG) takes place.

[0122] The reactor (5) has the capacity to maintain the optimal reaction conditions for the minimum time necessary for the reaction to occur with the highest quality, i.e., with a transformation yield of organic matter close to 100%.

[0123] The main factors that help to meet this requirement are:

[0124] - a reaction start temperature above 330 °C, and

[0125] - heating by means of auxiliary electrical resistors (28) to reach 380 °C.

[0126] The reactor (5) incorporates an internal circuit formed by two concentric cylinders that force the fluid to travel through three perfectly defined phases.

[0127] In the first phase, the organic matter is heated to the reaction temperature, at which the polarity of the water changes, dissolving all the organic matter and separating the inorganic matter.

[0128] In a second phase, the inorganics are decanted, thanks to the change in water polarity, with a final calming and separation zone to a lower zone, to proceed with the purging of these inorganic solids. In a third phase, the total separation of the organics is carried out and the reactions of the products to be extracted are completed.

[0129] To make the most of the residual energy from the process, a high-performance energy recovery unit (9) has been provided with a double-tube coil (6), a first tube (7) and a second tube (8) concentric to the first.

[0130] Figure 2 shows the energy recovery unit (9) located around the reactor (5) with electrical resistors (28).

[0131] The first tube (7) is intended for the circulation of fluid from the reactor (5).

[0132] The second tube (8) is intended to receive heat energy from the first tube (7), for which it contains a heat transfer fluid, such as thermal oil, and operates in a closed circuit.

[0133] The entire assembly is made of steel suitable for withstanding all the requirements of the process, while infinitesimal calculations will be performed to analyze its behavior during the process.

[0134] In addition, the material used for the two tubes (7, 8) of the coil (6) is seamless high pressure pipe steel ASTM Schedule 80S.

[0135] The two tubes (7, 8) are highly efficient at heat exchange and are corrugated to allow for adequate thermal expansion due to contact with the fluids they carry.

[0136] The temperature of the fluid at the reactor outlet, before entering the energy recovery unit (9) is at least 350 °C, while the temperature at the reactor outlet, after passing through the recovery unit (9), is no more than 80 °C.

[0137] The main objective of heat recovery is to heat the reactor fluid (5) so that the temperature at the reactor inlet (5) is at least 300 °C. The difficulty of this recovery is that the pressures of the two circuits, that of the first tube (7) and that of the second tube (8), although similar, are very high.

[0138] However, the expansion of the first tube (7) due to the need for an expansion bellows makes operation with a single heat exchange circuit unfeasible.

[0139] Therefore, an intermediate heating fluid (such as thermal oil) is required to absorb energy from the reactor fluid (5) at the outlet and transfer it to the fluid at the reactor inlet (5) via an additional circuit. This is where the double-tube coil (6) comes in, allowing fluid from the reactor (5) to enter through the first tube (7) to transfer thermal energy to the oil in the second tube (8), and exit the reactor (5) at a much lower temperature.

[0140] Therefore, the recovery of process energy, essential for process efficiency, necessitates two combined exchanger systems.

[0141] This explains the existence of a system of smooth, concentric tubes coiled in a spring-like spiral, which, in addition to meeting all the process requirements, allows for free and balanced expansion of the tubes. Inside the pressurized reactor (5), the thermochemical conversion of biomass into biocrude takes place, also generating gases, a liquid fraction mixed with solid matter, and a solid fraction consisting of ash and hydrochar.

[0142] The gases produced, mainly CO2, (with traces of CH4, H2, etc.), are extracted through a second conduit (22), which connects to the reactor (5) at the top, to be directed towards treatment or energy utilization systems such as, for example, a heating system (14) comprising electrical resistors (28) connected to a power source.

[0143] Simultaneously, the liquid outlet flow from the reactor (5) is channeled to the first tube (7) of the coil (6) of the helical energy recovery unit (9), where the heat from the hot fluid is transferred to the inlet stream, through the intermediation of the oil in the second tube (8), thus maximizing the energy efficiency of the process by means of countercurrent heat exchange. The ash and inorganic solids leave the reactor (5) through a third pipe (23), this material reaching an ash tank (10), where they are separated and stored, allowing for their eventual recovery or safe disposal.

[0144] For its part, the liquid fraction, rich in biocrude, after having passed through the coil (6) of the recuperator (9), is conducted through a fourth conduit (24) that incorporates a pressure reducer (11), towards a centrifuge (12), where the separation between the recoverable biocrude and the aqueous phase is carried out.

[0145] The biocrude can be stored as a final product in a tank (13) accessed from the centrifuge (12) via a fifth pipe (25) or sent to upgrading processes, while the aqueous fraction can be extracted from the centrifuge (12) through a recirculation pipe (27) for reuse. Alternatively, it can also undergo further treatment, such as anaerobic digestion or nutrient recovery.

[0146] The plant is also equipped with a closed-loop cleaning-in-place (CIP) system, comprising a cleaning pump (15) in a sixth conduit (26), through which it connects to the system, and which allows automatic cleaning of the reactor (5) and the conduits under high pressure and temperature conditions, ensuring operational continuity and hygienic safety of the process.

Claims

CLAIMS 1. A hydrothermal carbonization (HTC), hydrothermal liquefaction (HTL), and hydrothermal gasification (HTG) plant, comprising a reactor (5) for the thermochemical conversion of wet organic waste into gases, a fluid, and a solid residue, being characterized in that it further comprises: - an energy recovery unit (9), - a heating system (14) comprising electrical resistors (28), - a centrifuge (12), and - a deposit (13), where: - the energy recuperator (9) is configured by a double-tube coil (6) that encircles the reactor (5), - the coil (6) comprises: - a first tube (7), intended to receive the fluid from the reactor (5) that connects the outlet of the reactor (5) with the inlet to the centrifuge (12), and - a second tube (8) in a closed circuit, comprising a fluid intended to exchange heat with the reactor fluid (5). so that the fluid leaving the reactor (5) has the function of heating the fluid entering the reactor (5).

2. The plant of claim 1, wherein the reactor (5) is configured to withstand temperatures up to 500 °C and pressures up to 30 MPa.

3. The plant of claim 1, wherein the thermochemical conversion is carried out at a temperature above 330 °C.

4. The plant of claim 1, comprising a wet organic waste receiving tank (1), a crusher (2) and a colloidal mill (3) that treats the material before it is sent to the reactor (5).

5. The plant of claim 1, wherein the tubes (7, 8) of the coil (6) are corrugated, so that they can expand thermally.

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