In an exhaust duct and a boiler, there are provided: a flue gas duct through which flue gases pass; a first hopper provided to the flue gas duct, the first hopper collecting PA in the flue gases; a low-repulsion section provided to the upstream side or the downstream side of the first hopper in the direction of flow of the flue gases, the low-repulsion section having a lower coefficient of repulsion than the inner wall surface of the flue gas duct; and a popcorn-ash-trapping section for trapping PA in the flue gases, the popcorn-ash-trapping section provided to the downstream side of the first hopper and the low-repulsion section in the direction of flow of the flue gases, whereby it is possible for solid particles in the flue gases to be properly trapped.

In an exhaust duct and a boiler, there are provided: a flue gas duct through which flue gases pass; a first hopper provided to the flue gas duct, the first hopper collecting PA in the flue gases; a low-repulsion section provided to the upstream side or the downstream side of the first hopper in the direction of flow of the flue gases, the low-repulsion section having a lower coefficient of repulsion than the inner wall surface of the flue gas duct; and a popcorn-ash-trapping section for trapping PA in the flue gases, the popcorn-ash-trapping section provided to the downstream side of the first hopper and the low-repulsion section in the direction of flow of the flue gases, whereby it is possible for solid particles in the flue gases to be properly trapped.

An improved method and system for treating flue gases from a natural gas furnace are provided. The method and system include an acidic gas trap (AGT) adsorber which enables the continuous adsorption and storage of SOx, NOx redox, and formic acid/CO/HC/CH.sub.4 oxidation, with a negligible pressure drop. The AGT adsorber includes a catalyst coating having a nanotube structure (e.g., a uniform nanostructure forest coating) or a uniform porous nanostructure of various low-cost oxides through scalable low temperature solution processes, including oxides of Ti, Cu, Ba, Mn, Zr, Zn, Sr, Ca, Li, K, Na, Al, or Ce.

An improved method and system for treating flue gases from a natural gas furnace are provided. The method and system include an acidic gas trap (AGT) adsorber which enables the continuous adsorption and storage of SOx, NOx redox, and formic acid/CO/HC/CH.sub.4 oxidation, with a negligible pressure drop. The AGT adsorber includes a catalyst coating having a nanotube structure (e.g., a uniform nanostructure forest coating) or a uniform porous nanostructure of various low-cost oxides through scalable low temperature solution processes, including oxides of Ti, Cu, Ba, Mn, Zr, Zn, Sr, Ca, Li, K, Na, Al, or Ce.

An improved method and system for treating flue gases from a natural gas furnace are provided. The method and system include an acidic gas trap (AGT) adsorber which enables the continuous adsorption and storage of SOx, NOx redox, and formic acid/CO/HC/CH.sub.4 oxidation, with a negligible pressure drop. The AGT adsorber includes a catalyst coating having a nanotube structure (e.g., a uniform nanostructure forest coating) or a uniform porous nanostructure of various low-cost oxides through scalable low temperature solution processes, including oxides of Ti, Cu, Ba, Mn, Zr, Zn, Sr, Ca, Li, K, Na, Al, or Ce.

An improved method and system for treating flue gases from a natural gas furnace are provided. The method and system include an acidic gas trap (AGT) adsorber which enables the continuous adsorption and storage of SOx, NOx redox, and formic acid/CO/HC/CH.sub.4 oxidation, with a negligible pressure drop. The AGT adsorber includes a catalyst coating having a nanotube structure (e.g., a uniform nanostructure forest coating) or a uniform porous nanostructure of various low-cost oxides through scalable low temperature solution processes, including oxides of Ti, Cu, Ba, Mn, Zr, Zn, Sr, Ca, Li, K, Na, Al, or Ce.

Provided is a duct wall surface structure which, in a flue of an iron-sheet duct with a hopper through which a solid-gas two-phase stream flows, can enhance the solid particle trapping efficiency of the hopper and reduce the outflow of the solid particles to the duct downstream side. The duct wall surface structure of a flue (10) through which a solid-gas two-phase stream containing large-diameter ash (50) flows includes a first hopper (20A) installed at the lower end of a first vertical flue section (12), installed in such a direction that the stream has a vertical component of velocity, to collect the large-diameter ash (50) from the stream, wherein a low-rebound part (60) having a lower coefficient of restitution than an iron sheet is provided on an inclined surface (21), with which the large-diameter ash (50) collides, on the upstream side in the flow direction from the first hopper (20A).

Provided is a duct wall surface structure which, in a flue of an iron-sheet duct with a hopper through which a solid-gas two-phase stream flows, can enhance the solid particle trapping efficiency of the hopper and reduce the outflow of the solid particles to the duct downstream side. The duct wall surface structure of a flue (10) through which a solid-gas two-phase stream containing large-diameter ash (50) flows includes a first hopper (20A) installed at the lower end of a first vertical flue section (12), installed in such a direction that the stream has a vertical component of velocity, to collect the large-diameter ash (50) from the stream, wherein a low-rebound part (60) having a lower coefficient of restitution than an iron sheet is provided on an inclined surface (21), with which the large-diameter ash (50) collides, on the upstream side in the flow direction from the first hopper (20A).

In an exhaust duct and a boiler, there are provided: a flue gas duct through which flue gases pass; a first hopper provided to the flue gas duct, the first hopper collecting PA in the flue gases; a low-repulsion section provided to the upstream side or the downstream side of the first hopper in the direction of flow of the flue gases, the low-repulsion section having a lower coefficient of repulsion than the inner wall surface of the flue gas duct; and a popcorn-ash-trapping section for trapping PA in the flue gases, the popcorn-ash-trapping section provided to the downstream side of the first hopper and the low-repulsion section in the direction of flow of the flue gases, whereby it is possible for solid particles in the flue gases to be properly trapped.

In an exhaust duct and a boiler, there are provided: a flue gas duct through which flue gases pass; a first hopper provided to the flue gas duct, the first hopper collecting PA in the flue gases; a low-repulsion section provided to the upstream side or the downstream side of the first hopper in the direction of flow of the flue gases, the low-repulsion section having a lower coefficient of repulsion than the inner wall surface of the flue gas duct; and a popcorn-ash-trapping section for trapping PA in the flue gases, the popcorn-ash-trapping section provided to the downstream side of the first hopper and the low-repulsion section in the direction of flow of the flue gases, whereby it is possible for solid particles in the flue gases to be properly trapped.