# US 10,309,649 B2 · Exhaust duct > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,309,649 B2 - Document ID: US10309649B2 - Status: Granted - Kind: B2 - Application number: 15/591,193 - Filed: 2017-05-10 - Published: 2017-11-30 - Granted: 2019-06-04 - Earliest claimed: 2016-05-24 - Assignees: Rinnai Corporation - Applicants: Rinnai Corporation - Inventors: Takahiro Ono - Web page: https://patentgrep.com/patent/US10309649B2 ## CPC - F23M 20/005: {Noise absorbing means} - F23C 9/00: Combustion apparatus characterised by arrangements for returning combustion products or flue gases to the combustion chamber (fluidised bed combustion apparatus with means for recirculation of particles entrained from the bed F23C10/02; fluidised bed combustion apparatus with devices for removal and partial reintroduction of material from the bed F23C10/26) - F23R 2900/00014: Reducing thermo-acoustic vibrations by passive means, e.g. by Helmholtz resonators - F24H 1/40: with water tube or tubes - F24H 8/00: Fluid heaters characterised by means for extracting latent heat from flue gases by means of condensation - F24H 9/1836: using fluid fuel - Y02B 30/00: Energy efficient heating, ventilation or air conditioning [HVAC] - F23M: CASINGS, LININGS, WALLS OR DOORS SPECIALLY ADAPTED FOR COMBUSTION CHAMBERS, e.g. FIREBRIDGES; DEVICES FOR DEFLECTING AIR, FLAMES OR COMBUSTION PRODUCTS IN COMBUSTION CHAMBERS; SAFETY ARRANGEMENTS SPECIALLY ADAPTED FOR COMBUSTION APPARATUS; DETAILS OF COMBUSTION CHAMBERS, NOT OTHERWISE PROVIDED FOR - F23C: METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN {A CARRIER GAS OR} AIR (burners F23D) - F23R: GENERATING COMBUSTION PRODUCTS OF HIGH PRESSURE OR HIGH VELOCITY, e.g. GAS-TURBINE COMBUSTION CHAMBERS (fluidised bed combustion apparatus specially adapted for operation at superatmospheric pressures F23C10/16) - F24H: FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL (steam generation F22) - Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS ## Abstract [Problems to be Solved] An exhaust duct (4) for assembly into a combustion apparatus has: a burner (1) to eject air-fuel mixture downward; and a combustion box (3) disposed on a lower side of the burner (1). The exhaust duct includes: a riser duct section (42) elongated in a vertical direction and having, at a lower portion thereof, an inlet port (41) connected to an exhaust port (35) for combustion gas which is opened in a lower portion of the combustion box (3); and a flat horizontal duct section (43) bent at an upper end of the riser duct section (42) so as to be elongated forward. By restraining the resonance of an upper wall part (431) and a lower wall part (432) of the horizontal duct section (43), noises due to resonance sounds are reduced. [Solving Means] The natural frequencies in an upper wall part (431) and the lower wall part (432) of the horizontal duct section (43) are varied from each other. For example, the lower wall part (432) is fixed to a burner body (11) in order to vary the natural frequencies of the upper wall part (431) and of the lower wall part (432) from each other. ## Claims ### Claim 1 An exhaust duct for assembly into a combustion apparatus, said combustion apparatus comprising: a burner to eject air-fuel mixture downward for combustion; and a combustion box which is disposed on a lower side of the burner and which houses therein a heat exchanger to be heated by combustion gas, said exhaust duct comprising: a riser duct section elongated in a vertical direction and having, at a lower portion thereof, an inlet port which is connected to an exhaust port for combustion gas and which is opened in a lower portion of the combustion box; and a flat horizontal duct section bent at an upper end of the riser duct section so as to be elongated forward, wherein natural frequencies in an upper wall part and in a lower wall part of the horizontal duct section are varied from each other. ### Claim 2 (depends on 1) The exhaust duct according to claim 1, wherein one of the upper wall part and the lower wall part of the horizontal duct section is fixed to another constituent element in order to vary the natural frequencies in the upper wall part and in the lower wall part from each other. ### Claim 3 (depends on 1) The exhaust duct according to claim 1, wherein one of the upper wall part and the lower wall part of the horizontal duct section is provided with a reinforcing rib in order to vary the natural frequencies in the upper wall part and in the lower wall part from each other. ### Claim 4 (depends on 1) The exhaust duct according to claim 1, wherein the upper wall part and the lower wall part of the horizontal duct section are made of materials of different specific gravities in order to vary the natural frequencies in the upper wall part and in the lower wall part from each other. ### Claim 5 An exhaust duct for assembly into a combustion apparatus, said combustion apparatus comprising: a burner to eject air-fuel mixture downward for combustion; and a combustion box which is disposed on a lower side of the burner and which houses therein a heat exchanger to be heated by combustion gas, said exhaust duct comprising: a riser duct section elongated in a vertical direction and having, at a lower portion thereof, an inlet port which is connected to an exhaust port for combustion gas which is opened in a lower portion of the combustion box; and a flat horizontal duct section bent at an upper end of the riser duct section so as to be elongated forward, wherein: the horizontal duct section is divided into a plurality of segments, said plurality of segments being grouped into segments of a first group and segments of a second group such that segments of respective groups are free from being mutually adjacent to each other, and; in order to vary natural frequencies in the first segment and in the second segment of an upper wall part and of a lower wall part, respectively, of the horizontal duct section, the first segment has a reinforcing rib formed in the upper wall part, and the second segment has a reinforcing rib formed in the lower wall part.