Pyrolysis Boiler

Abstract

Heat and power engineering, specifically being heating devices includes a pyrolysis boiler, in which, wood is subjected to high-temperature gasification and pyrolysis with subsequent burning off of pyrolysis gases. A stable and controllable gasification of wood with a natural high moisture content is achieved, and at the same time, a highly efficient transfer of combustion heat to a liquid heat-transfer agent is obtained. A gasification chamber is positioned between two compartments of a pyrolysis gas combustion chamber of the pyrolysis boiler, while the external wall of the combustion chamber is used as a heat-transfer surface, and at the same time, neither the fuel bunker nor the gasification chamber are in contact with water.

Claims

1. A pyrolysis boiler comprising: a single vertical housing comprising within a rectangular hopper for solid fuel and a gasification chamber below the rectangular hopper, which has an internal heat-resistant thermal insulation coating, and an outlet window with a grate whereby pyrolysis gases can exit; a pyrolysis gas combustion chamber in the form of two symmetrical, parallel, horizontal compartments; primary and secondary air supply ducts supplying primary and secondary air and a pressure fan installed outside the housing; a double-walled water cavity surrounding the pyrolysis gas combustion chamber, in such a way, that an outer wall of the combustion chamber is also an inner wall of the water cavity, wherein the gasification chamber is placed with no gap between the two compartments of the pyrolysis gas combustion chamber, and the horizontal slots are located into side surfaces of the compartments of the combustion chamber facing the gasification chamber, which ensure that flow of the pyrolysis gas passes from the outlet window of the gasification chamber to the combustion chamber with the flow turning 90 degrees left and right.

2. The pyrolysis boiler of claim 1, wherein the primary and secondary air supply ducts are made in the form of flat ducts and installed on the side surfaces of the combustion chamber compartments facing the gasification chamber, while these ducts cover only a part of the side surface area of the combustion chamber compartments.

3. The pyrolysis boiler of claim 1, wherein the primary and secondary air supply ducts are made in the form of a flat grid of circular or rectangular pipes and installed on the side surfaces of the combustion chamber compartments facing the gasification chamber, and wherein the pipes cover only a part of the side surface area of the combustion chamber compartments.

4. The pyrolysis boiler of claim 1, wherein nozzles for supplying secondary air are placed in the secondary air supply ducts, in such a way, that the flow of secondary air coming from them, moves at a speed of about 10-20 m/s parallel to, in the same direction as, and in close proximity to the flow of the pyrolysis gas entering through the above horizontal slots into the combustion chamber compartments.

5. The pyrolysis boiler of claim 1, wherein the horizontal slots of the pyrolysis gas inlet are 2-3 times shorter than the length of the combustion chamber compartment and are located at the front end of the combustion chamber compartments.

6. The pyrolysis boiler of claim 1, wherein a figured insert made of heat-resistant insulating material is installed in each compartment of the combustion chamber opposite the horizontal slots of the pyrolysis gas inlet, covering at least two surfaces of the combustion chamber, being i.e., the bottom and side wall opposite the horizontal slots.

7. The pyrolysis boiler of claim 1, wherein each compartment of the combustion chamber is equipped with a longitudinal horizontal partition, the length of which, is less than the length of the compartment, wherein the partition without a gap is in contact with the front end of the combustion chamber compartment.

8. The pyrolysis boiler of claim 7, wherein the longitudinal horizontal partition has a form of a flat box, with the air flow moving inside it, and the outer surface of the box containing nozzle openings for supplying secondary air into the combustion chamber,

9. The pyrolysis boiler of claim 1, wherein the water cavity contains a fire-tube heat exchanger, the inlet of which, is connected to an outlet of the combustion chamber compartments by means of a gas flue, and the exit of which, is connected to a smoke flue opening to the atmosphere by means of the gas flue.

10. The pyrolysis boiler of claim 2, wherein nozzles for supplying secondary air are placed in the secondary air supply ducts, in such a way, that the flow of secondary air coming from them, moves at a speed of about 10-20 m/s parallel to, in the same direction as, and in close proximity to the flow of the pyrolysis gas entering through the horizontal slots into the combustion chamber compartments.

11. The pyrolysis boiler of claim 3, wherein nozzles for supplying secondary air are placed in the flat grid, in such a way, that the flow of secondary air coming from them, moves at a speed of about 10-20 m/s parallel to, in the same direction as, and in close proximity to the flow of the pyrolysis gas entering through the horizontal slots into the combustion chamber compartments.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The arrangement of the pyrolysis boiler is illustrated by drawings. FIG. 1 shows a cross section of the device; FIG. 2 shows a longitudinal section of the device in the embodiment with flame tubes and nozzle openings for supplying additional secondary air.

DETAILED DESCRIPTION OF THE INVENTION

[0029] The pyrolysis boiler contains a hopper for solid fuel 1, a gasification chamber 2 with a heat-resistant thermal insulation coating 3 and a pyrolysis gas exit window with a grate 4, two compartments of the pyrolysis gas combustion chamber 5 with horizontal slots 6 and figured heat-resistant inserts 7, a cavity with water 8 surrounding the combustion chamber, air ducts 9 made in the form of flat ducts with nozzle openings for supplying primary air 10 and secondary air 11 installed in the form of a longitudinal horizontal partition in the compartments of the combustion chamber, flat box-shaped air ducts 12 with nozzle openings for supplying additional secondary air 13, gas flue 14, flame tubes 15, smoke pipe 16, ash collection box 17 installed below the grate.

[0030] The pyrolysis boiler works as follows: Solid fuel (for example, firewood or wood chips with a natural moisture content) is loaded into the hopper 1. Due to gravity, wood fuel goes down, successively passing through the drying zone (upper part of the hopper), dry distillation zone (lower part of the hopper) and entering the gasification chamber 2.

[0031] The air blown by the external fan (not shown) to the box-shaped air duct 9 is heated through the walls of the duct by the flame in the combustion chamber 5 and is forwarded at high speed to the upper part of the gasification chamber through the nozzle openings 10, where the process of incomplete combustion (smouldering) of wood fuel takes place. Wood fuel is gasified under the influence of the heat from smouldering, as well as from being heated by the hot walls of the combustion chamber compartments, and the pyrolysis gas formed during this process moves through a layer of hot coal to the exit window 4 located at the bottom of the gasification chamber, and then, turning 90 degrees left and right through the slots 6, enters the compartments of the combustion chamber. The heat-resistant thermal insulation of the internal walls of the gasification chamber protects the metal surfaces from burning out (thermal erosion) and, due to its heat capacity, smoothes random temperature fluctuations inside the gasification chamber.

[0032] The flow of hot secondary air exiting the box-shaped air duct 9 through the nozzle openings 11 at high speed (10-20 m/s) carries with it the flow of pyrolysis gas, mixes with it, and the resulting gas mixture ignites. Due to its high heat capacity and low thermal conductivity, the figured heat-resistant insert 7 maintains a stable high temperature in the ignition zone, and its shape contributes to the vortex motion of the gas mixture, which provides high-quality mixing of the fuel (pyrolysis gas) and the oxidant (air). To ensure optimal combustion conditions, secondary air is supplied in two zones: through the openings 11 at the entrance to the combustion chamber and through the openings 13 along the flame flow.

[0033] The stream of hot combustion products moves to the opposite end of the combustion chamber compartment, turns 180 degrees and comes back, moving above the horizontal partition 12; such movement scheme of the combustion products provides intensive heating of the gasification chamber along its entire height. Thereafter, the combustion products move through the gas flue 14 into flame tubes 15, and upon exiting, the gas flow is released into the atmosphere through the smoke pipe 16.

[0034] The optimal temperature of the side walls of the gasification chamber for gasifying moist wood fuel is achieved by adjusting the speed of the air flow moving through the box-shaped air duct 9, selecting the appropriate surface area of the box-shaped air duct or by replacing the solid box with a flat grid of individual tubes; thus, the design allows to achieve a stable and controlled gasification of wood fuel.

[0035] Heat transfer to the heat-transfer fluid (water) circulating in the cavity 8 is carried out in two zones: on the surface of the external walls of the combustion chamber 5 compartments and through the flame tubes 15; in the first zone, convective heat transfer from combustion gases to the wall of the combustion chamber is complemented by powerful heat radiation from a high-temperature (more than 1000 C.) flame. Thus, the claimed design maintains the main advantage of the traditional scheme (effective heat transfer from the heated walls to the water jacket), while being free from the main disadvantage of the traditional scheme, since in the claimed design, the heat transfer fluid does not contact the gasification chamber at any point and therefore does not cool it.