# US 11,999,921 B2 · Hydrothermal carbonization of sludge including recycling of a wet-oxidized fraction > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,999,921 B2 - Document ID: US11999921B2 - Status: Granted - Kind: B2 - Application number: 16/954,288 - Filed: 2018-12-11 - Published: 2021-03-25 - Granted: 2024-06-04 - Earliest claimed: 2017-12-21 - Assignees: C-Green AB - Applicants: C-Green AB - Inventors: Fredrik Lundqvist; Erik Oden; Fredrik Ohman - Web page: https://patentgrep.com/patent/US11999921B2 ## CPC - C10L 9/086: {Hydrothermal carbonization} - C02F 11/08: Wet air oxidation - C10L 5/46: on sewage, house, or town refuse {(C10L5/403, C10L5/406 take precedence)} - C02F 11/13: by heating - C02F 11/18: by thermal conditioning (by pyrolysis C02F11/10) - C02F 2103/34: from industrial activities not provided for in groups C02F2103/12 - C02F2103/32 - C02F 2209/08: Chemical Oxygen Demand [COD]; Biological Oxygen Demand [BOD] - C10L 2290/06: Heat exchange, direct or indirect - C10L 2290/10: Recycling of a stream within the process or apparatus to reuse elsewhere therein - C10L 2290/24: Mixing, stirring of fuel components - C10L 2290/54: Specific separation steps for separating fractions, components or impurities during preparation or upgrading of a fuel - Y02E 50/10: Biofuels, e.g. bio-diesel - Y02E 50/30: Fuel from waste, e.g. synthetic alcohol or diesel - C10L: FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G OR C10K; LIQUIFIED PETROLEUM GAS; USE OF ADDITIVES TO FUELS OR FIRES; FIRE-LIGHTERS - C02F: TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE (separation in general B01D; special arrangements on waterborne vessels of installations for treating water, waste water or sewage, e.g. for producing fresh water, B63J; adding materials to water to prevent corrosion C23F; treating radioactively-contaminated liquids G21F9/04; regeneration of reactants for recirculation into processes, see the relevant places for the processes) - Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION ## Abstract There is provided a method of hydrothermal carbonization of a sludge, comprising the steps of: preheating the sludge to obtain a preheated sludge; mixing the preheated sludge with a wet-oxidized fraction to obtain a reaction mixture; subjecting the reaction mixture to hydrothermal carbonization (HTC) in a reactor to obtain a HTC-treated sludge; separating a fraction from the HTC-treated sludge; and mixing the fraction with an oxidizing agent, such as oxygen gas, to obtain the wet-oxidized fraction, wherein the temperature of the fraction before the wet oxidation is at least 15° C. higher than the temperature of the preheated sludge. A corresponding system is also provided. ## Claims ### Claim 1 A method of hydrothermal carbonization of a sludge, comprising the steps of: preheating the sludge to obtain a preheated sludge; mixing the preheated sludge with a recirculated wet-oxidized fraction to obtain a reaction mixture; subjecting the reaction mixture to hydrothermal carbonization (HTC) in a reactor to obtain an HTC-treated sludge; separating the HTC-treated sludge into first and second HTC-treated sludge fractions; mixing the separated first HTC-treated sludge fraction with an oxidizing agent to obtain a wet-oxidized fraction; and recirculating the wet-oxidized fraction to be mixed with the preheated sludge; wherein a temperature of the first HTC-treated sludge fraction before the wet oxidation is at least 15° C. higher than the temperature of the preheated sludge. ### Claim 2 (depends on 1) The method according to claim 1, further comprising subjecting the second fraction to flashing to obtain at least one steam fraction and a cooled fraction, wherein the at least one steam fraction is recirculated for use in the preheating step. ### Claim 3 (depends on 1) The method according to claim 1, wherein the sludge is a municipal or industrial sludge from a wastewater treatment plant. ### Claim 4 (depends on 1) The method according to claim 1, wherein the temperature of the HTC-treated sludge is 180-250° C. ### Claim 5 (depends on 1) The method according to claim 1, wherein the temperature of the HTC-treated sludge is at least 20° C. higher than the temperature of the preheated sludge prior to it being mixed with the wet-oxidized fraction. ### Claim 6 (depends on 1) The method according to claim 1, wherein the average retention time in the reactor is 0.25-8 h. ### Claim 7 (depends on 1) The method according to claim 1, wherein the volumetric flow rate of the first fraction is 10-50% of the volumetric flow rate of the preheated sludge. ### Claim 8 (depends on 1) The method according to claim 1, wherein the chemical oxygen demand (COD) of the first fraction is at least 15 g/l. ### Claim 9 (depends on 1) The method according to claim 1, wherein preheated sludge is mixed with the wet-oxidized fraction in the reactor. ### Claim 10 (depends on 1) The method according to claim 1, wherein preheated sludge is mixed with the wet-oxidized fraction in a position upstream the reactor. ### Claim 11 (depends on 1) The method according to claim 1, wherein the temperature of the first fraction before the wet oxidation is at least 20° C. higher than the temperature of the preheated sludge. ### Claim 12 (depends on 1) The method according to claim 1, wherein the amount of oxidizing agent is such that wet oxidation reactions reduces the higher heating value (HHV) of the sludge by 5-49%. ### Claim 13 (depends on 1) The method of claim 1, wherein the oxidizing agent is oxygen gas.