a pressure-bearing housing;

a combustion chamber arranged in the pressure-bearing housing;

a heat-exchange furnace arranged in the pressure-bearing housing communicating with the heat-exchange furnace; and

cooling tube groups fixed in the heat-exchange furnace;

wherein

the pressure-bearing housing is provided with a flue gas outlet pipe, a heat-exchange medium inlet and a heat-exchange medium outlet, wherein the flue gas outlet pipe is configured to communicate with the heat-exchange furnace;

heat-exchange medium flows upward in the pressure-bearing housing and in the cooling tube groups, and exchanges heat with high-temperature flue gas flowing downward in the heat-exchange furnace, thereby achieving a counterflow heat exchanging;

the heat-exchange furnace comprises a multi-stage heat-exchange chamber that includes heat-exchange chambers with each heat-exchange chamber being cylindrical, two adjacent heat-exchange chambers are configured to communicate with each other through a flue gas turning channel, and each heat-exchange chamber comprises a cooling tube group of the cooling tube groups vertically arranged within;

the heat-exchange chambers are arranged one upon another from top to bottom, such that the high-temperature flue gas diffuses from a center part of a heat-exchange chamber to a periphery of the heat-exchange chamber and gathers from a periphery of an adjacent heat-exchange chamber of the heat-exchange chamber to a center part of the adjacent heat-exchange chamber, the adjacent heat-exchange chamber being under the heat-exchange chamber, and in each heat-exchange chamber, the high-temperature flue gas laterally scouring the cooling tube group arranged in each heat-exchange chamber;

the heat-exchange medium is driven upward to enter each cooling tube group in a heat-exchange chamber and exchange heat with the high-temperature flue gas in the heat-exchange chamber, and to discharge from an upper part of each cooling tube group and mix with the heat-exchange medium that in the pressure-bearing housing and outside the heat-exchange chambers;

each heat-exchange chamber comprises a cylindrical peripheral wall, an upper tube plate and a lower tube plate, wherein the upper tube plate and the lower tube plate are hermetically connected with the peripheral wall, thereby enclosing an inner cavity of each heat-exchange chamber;

the upper tube plate is provided with a flue gas inlet, and the lower tube plate is provided with a flue gas outlet;

the flue gas outlet of a bottom-most heat-exchange chamber of the multi-stage heat-exchange chamber is arranged at the peripheral wall of the bottom-most heat-exchange chamber, and is configured to communicate with the flue gas outlet pipe;

a first heat-exchange chamber of the multi-stage heat-exchange chamber is configured to communicate with the combustion chamber, and a second heat-exchange chamber of the multi-stage heat-exchange chamber is configured to communicate with the first heat-exchange chamber;

the flue gas inlet of the first heat-exchange chamber is a first flue gas inlet arranged in a center part of the upper tube plate of the first heat-exchange chamber, and the flue gas outlet of the first heat-exchange chamber is a first flue gas outlet arranged close to a peripheral wall of the first heat-exchange chamber;

the flue gas inlet of the second heat-exchange chamber is a second flue gas inlet corresponding to the first flue gas outlet, and the flue gas outlet of the second heat-exchange chamber is a second flue gas outlet arranged in a center part of the lower tube plate of the second heat-exchange chamber;

the second flue gas outlet is used to communicate with a third heat-exchange chamber or communicate with the flue gas outlet pipe provided on the pressure-bearing housing; and

the high-temperature flue gas enters the first heat-exchange chamber from a center part of the first heat-exchange chamber and diffuses to a periphery of the first heat-exchange chamber, the high-temperature flue gas enters the second heat-exchange chamber from a periphery of the second heat-exchange chamber and gathers to the second flue gas outlet arranged at the center part of the lower tube plate of the second heat-exchange chamber, thereby laterally scouring the cooling tube group in the second heat-exchange chamber.