Method of stopping combustion in restrained combustion furnace in safety and combustion stop system therefor

Abstract: A method of stopping combustion in a restrained combustion furnace (1) in which waste to be incinerated is gasified and then burnt with an air amount lower than a theoretical combustion air amount, in case of emergency, comprises the steps of shutting off a combustion air supply line (7) connected to the restrained combustion furnace, simultaneously feeding inert gas from a source (12) to lower portions and an outlet side of the furnace, and opening a bypass line (15) connected to an upper portion of the furnace to pass gas in the furnace through a filter (10) to a waste gas stack (6). The combustion in the restrained combustion furnace can thus be stopped in safety in an emergency.

Description: The present invention relates to a method of safety stopping combustion in a restrained combustion furnace which is used, for example, for incinerating radioactive wastes, in case of emergency and to such a furnace having a system for stopping combustion. The restrained combustion furnace in which wastes to be incinerated are gasified and burnt with an air ratio lower than a theoretical combustion air amount, has been used as a furnace for incinerating general wastes since the waste gas from the furnace can be easily treated. Such a restrained combustion furnace is usually not provided with a system for stopping combustion in the furnace in case of emergency such as failure of an electric power source so that the combustion is naturally discontinued when the combustion air supplying blower is stopped. However it has recently been required to use the restrained combustion furnace for incinerating miscellaneous solid wastes or other matter contaminated by radioactivity generated from an atomic power plant. In this case, it is necessary that the combustion in the restrained combustion furnace is stopped in safety in an emergency without scattering of combustible gas and ashes contaminated by radioactivity into the air rather than waiting until the combustion in the furnace is naturally discontinued. The object of the invention is to provide a method and a system for stopping combustion in a restrained combustion furnace in safety in case of emergency such as failure of an electric power source while the combustible gas and ashes contaminated by radioactivity are prevented from scattering out of the furnace. There is now provided by the invention, a method of safety stopping combustion in a restrained combustion furnace as set out in claim 1. A restrained combustion furnace according to the invention is set out in claim 5. With the arrangement according to the invention, the combustion in the restrained combustion furnace in case of emergency can be stopped in safety without any leakage of radioactive gas or the like into the air. The accompanying drawing is a block diagram of an embodiment of a system according to the invention. The invention will be described in more detail in the following with reference to the accompanying drawing showing a preferred embodiment of the combustion stopping system according to the invention. A restrained combustion furnace shown in Fig. 1 comprises a furnace body 1 to which is connected a secondary combustion furnace 2 for combusting waste gas from the furnace body 1. The secondary combustion furnace 2 is communicated through a waste gas refining filter 3, a pressure control valve 4 and a waste gas blower 5 with a waste gas stack 6 by a waste gas conduit. In a normal running of the restrained combustion furnace, combustion air is supplied to the furnace body 1 by a combustion air supply line 7 in an amount less than a theoretical combustion air amount to gasify and then restrainedly burn wastes to be incinerated in the furnace body 1. Thus generated waste gas is discharged from the furnace body 1 through the stack 6 into the air. Incinerated ash is deposited in an ash removing box 8 and then removed for a further treatment. To the upper portion of the furnace body 1 is connected a relief duct provided with a safety valve 9 which relieves a gas from the furnace body to the stack 6 through a filter 10 by the relief duct when a pressure of gas in the furnace body is increased above a predetermined level. A combustion stop system embodying the present invention is arranged in the aforementioned restrained combustion furnace. Firstly, the combustion stop system includes a valve 11 provided at the combustion air supply conduit 7 for shutting off the combustion air supply conduit in case of emergency. Secondary, an inert gas source 12 is connected to the lower portion and the waste gas outlet of the furnace body 1 via valves 13 and 14, respectively for supplying inert gas such as CO₂, N₂ and the like to the furnace body in case of emergency. In a preferred embodiment, a CO₂ gas bomb may be used as the inert gas source. Thus, in case of emergency, the valves 13 and 14 are simultaneously opened to feed the inert gas from the gas bomb to the lower portion of the furnace body such as the combustion air supply conduit 7 and the ash removing box 8 and the other and the waste gas outlet connected to the secondary combustion furnace 2. Furthermore, a bypass line 15 is provided for bypassing the safety valve 9 at the upper portion of the furnace. The bypass line 15 is provided with a valve 16 which is opened in case of emergency to pass the gas from the furnace body through the filter 10 to the waste gas stack 6. The combustion stop system of the restrained combustion furnace according to the present invention arranged as mentioned above permits a restrained combustion by supplying air in an amount less than the theoretical combustion air amount from the combustion air supply line 7 during the normal running of the furnace, and supply of the waste gas from the furnace body 1 to the secondary combustion furnace 2 in which the waste gas is completely burnt. The burnt waste gas is sucked out the secondary combustion furnace 2 by the gas blower 5 and discharged through the waste gas stack 6 into the air. However, in case of emergency such as a failure of electric power source, the waste gas blower 5 is also stopped and therefore the waste gas is not smoothly treated at the downstream side of the secondary combustion furnace 2. According to the presentembodiment, in case of emergency, the valve 11 is simultaneously closed to shut off supply of air from the combustion air supply line 7 to the furnace body 1. At the same time, the valves 13 and 14 are opened to supply inert gas from an inert gas source 12 to the lower portion and outlet side of the furnace body 1. As the result, the combustion source which has not been burnt in the furnace body disappears and the combustion in the furnace body therefore is quickly discontinued, while a curtain of the inert gas is formed at the outlet side of the furnace body to prevent the gas from flowing out of the furnace body. In this embodiment, the inert gas is also simultaneously fed to the combustion air supply line 7. Furthermore, in this embodiment, in case of emergency, the valve 16 is simultaneously opened to communicate the upper portion of the furnace body through the bypass line 15 with the waste gas stack 6 to discharge gas generated in the furnace body through a filter 10 to the waste gas stack 6 until the combustion in the furnace body is stopped. Thus, according to the present invention, the combustion in the furnace body in case of emergency is quickly stopped and the gas in the furnace is prevented from leaking to secondary combustion furnace 2 and the downstream side thereof and permitted to pass through the filter 10 in the relief duct to the waste gas stack thereby stopping the restrained combustion furnace in safety.

Claims: A method of safely stopping combustion in a restrained combustion furnace (1) in which in normal operation wastes to be incinerated are gasified and then burnt with combustion air supplied by a combustion air supply line (7) in an air amount lower than a theoretical combustion air amount, the combustion gases are passed towards a waste gas stack (6) via an outlet of said furnace (1), said method of stopping combustion in case of emergency comprising the steps of shutting off the combustion air supply line (7) connected to the restrained combustion furnace (1), simultaneously feeding inert gas to a lower portion and said outlet of the furnace to stop combustion in the furnace, and opening a bypass line (15) connected to an upper portion of the furnace to pass gas in the furnace through a filter (10) to said waste gas stack (6). The method claimed in claim 1, wherein the inert gas is CO₂, N₂ or the like. The method claimed in claim 1 or claim 2, wherein the restrained combustion furnace includes an incinerated ash removing box (8) connected to a furnace body of the furnace (1) and said inert gas is fed to a lower portion of the ash removing box (8). The method claimed in any one of claims 1 to 3, wherein the inert gas is fed to the furnace via a length of the combustion air supply line (7). A restrained combustion furnace (1) in which in normal operation wastes to be incinerated are gasified and then burnt with combustion air supplied by a combustion air line (7) in an air amount lower than a theoretical combustion air amount, said furnace having an outlet for combustion gases for passing said gases to a waste gas stack (6), said furnace further having a system for safely stopping combustion in the furnace (1) in case of emergency, comprising a shut-off valve (11) adapted to be actuated in the emergency and provided in the combustion air supply line (7), an inert gas source (12) adapted for feeding inert gas into a lower portion of the furnace and said outlet of the furnace in the emergency, and a bypass line (15) connected to an upper portion of the furnace and adapted for passing gas in the furnace through a second filter (10) to said waste gas stack (6). The furnace claimed in claim 5, wherein the inert gas source (12) is a gas bomb containing CO₂, N₂ or the like. The furnace claimed in claim 5 or claim 6, wherein the restrained combustion furnace includes an incinerated ash removing box (8). The furnace claimed in claim 7 wherein the inert gas source (12) is connected to the combustion air supply line (7) and a lower portion of the incinerated ash removing box (8) through respective valves (13,14) which are opened in case of emergency. The furnace claimed in any one of claims 5 to 8, wherein said outlet is connected to said waste gas stack (6) through a secondary combustion furnace (2), a waste gas refining filter (3), a pressure control valve (4) and a waste gas blower (5). The furnace claimed in any one of claims 5 to 9, wherein the combustion air supply line (7) is connected to a lower portion of the furnace (1).

Inventors: KAWAI HIROAKI GLORIOUS HEIGHTS, KAWAI, HIROAKI, 701 GLORIOUS HEIGHTS KASUGAI
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1990
Main classification: F23G5
IPC codes: G21F9, F23G5, F23N5