Introduction This invention relates to a furnace and a method for operating the furnace using de- aerated steam as a fuel.

High temperature gases are produced in a furnace for various applications, including waste material recycling and destruction, electricity generation, glass-making and many other uses. Conventionally, hot gas generation produces harmful gases that are exhausted to the environment, such as carbon dioxide (C0 ₂ ), nitrogen oxides (NOx), sulphur oxides (SOx), etc. Various apparatus and methods have been proposed to control or reduce the amount of these harmful gases discharged into atmosphere. Unfortunately, these have only had limited success. They tend to be very expensive and at best reduce, but do not eliminate, these harmful gases.

The present invention is directed towards overcoming these problems. Summary of the invention

According to the invention there is provided a furnace, including: a housing having a reactor chamber; a core element mounted within the reactor chamber a fuel-fired start-up burner mounted on the housing at the reactor chamber, said start-up burner operable to generate an operating temperature of at least 1500°C within the reactor chamber and the core element; and a de-aerated steam injector mounted on the housing at the reactor chamber for injection of de-aerated steam into the reactor chamber at the operating temperature to maintain said operating temperature within the reactor chamber when the start-up burner is switched off. ln another embodiment of the invention the steam injector is connected to a de- aerated steam generator. By using de-aerated steam this provides a complete absence of nitrogen within the reactor chamber. In another embodiment of the invention the furnace is operable to maintain a temperature in the range 1500°C to 3000°C within the reactor chamber.

In another embodiment of the invention the de-aerated steam generator comprises a water boiler having a water heating tank with a water inlet, a water outlet and a steam outlet, a pump for discharging water through the water outlet, and a heater mounted within the water heating tank.

In another embodiment of the invention a water tank is connected to the water heating tank, the pump having an outlet connected to an inlet of the water tank, an outlet of the water tank connected through a stop valve with the inlet of the water heating tank.

In another embodiment of the invention the core element comprises a high temperature fire brick construction.

In another embodiment of the invention the core comprises a porous matrix of high temperature fire brick.

In another embodiment of the invention the housing has a thermal treatment chamber above the reactor chamber and communicating with the reactor chamber.

In another aspect the invention provides a waste treatment system incorporating a furnace as previously described and including means for delivering waste material into the thermal treatment chamber.

In another aspect the invention provides a power generating system incorporating the furnace and an energy converter to convert heat generated within the furnace into electrical power. For example, the heat generated in the furnace may be used to generate steam to drive a steam turbine which is drivably connected to an electrical generator. In another aspect the invention provides apparatus for the production of de-aerated steam as described herein. In another aspect, the invention provides a method for maintaining a desired operating temperature of at least 1500°C in a reactor chamber of a furnace, including the steps: heating an interior of the reactor chamber to an operating temperature of at least 1500 °C by means of a fuel-fired start-up burner, and injecting steam into the reactor chamber when the reactor chamber is at the operating temperature to maintain the operating temperature within the reactor chamber with the fuel fired start-up burner switched off.

Brief Description off the Drawings

The invention will be more clearly understood by the following description of some embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic illustrating of a waste treatment plant incorporating a furnace according to the invention; and

Fig. 2 is a schematic illustration of a steam generator for use with the furnace of the invention.

Detailed Description of the Preferred Embodiments Referring to the drawings, there is illustrated a furnace according to the invention indicated generally by the reference numeral 1. In this case the furnace 1 is incorporated in a waste treatment system indicated generally by the reference numeral 2 which may, for example, be a dry distillation type incinerator of the type described in US 5,195,449.

The furnace 1 is formed in a housing 3 above a residue bunker 4 and beneath a thermal reaction area 5 which receives waste materials through a damper 6 at a top of the thermal reaction area 5 for distillation of the waste materials within the thermal reaction area 5.

The furnace 1 has a reactor chamber 7 formed within the housing 3. A fuel-fired primary, or start-up burner 8 is mounted at a side of the reactor chamber 7 and is operable to generate an operating temperature of at least 1500 °C within the reactor chamber 7. A steam injector 10 is mounted on the housing 3 at a side of the reactor chamber 7 and is operable for injecting de-aerated steam into the reactor chamber 7 at the operating temperature to maintain the operating temperature within the reactor chamber when the start-up burner 8 is switched off.

A core element 12 comprising a porous matrix of high temperature firebrick is mounted within the reactor chamber 7 to help maintain a steady operating temperature of between 1500 °C and 2000 °C within the reactor chamber 7. The core element can vary considerably in size depending on the size of the reactor chamber. An example of a typical core size is 100cm high (with 60 spaces) x 150cm wide (with 100 spaces) x 200cm long (with 200 spaces). The spaces are holes or gaps in the core element 12. For different applications the core element 12 size and shape will change. For example, a cubic, a cylindrical or a spherical core element 12 could be provided. Other core element shapes are possible also.

The de-aerated steam injector 10 connects via a de-aerated steam feed line 14 with a de-aerated steam generator indicated generally by the reference numeral 16. The de-aerated steam generator 16 has a water boiler 17 having a water heating tank 18 with a water inlet 19, a water outlet 20 and a de-aerated steam outlet 21. A water inlet valve 22 is mounted at the water inlet 19. A steam outlet valve 23 is mounted at the de-aerated steam outlet 21. As the water heating tank 18 operates under a vacuum, de-aerated steam is generated at a relatively low temperature.

A water tank 25 is mounted directly above the water heating tank 18 and connects thereto, a water outlet 26 communicating through the water inlet valve 22 with the water inlet 19 of the water heating tank 18. A water feed pipe 28 communicates between the water outlet 20 of the water heating tank 18 and a water inlet 29 of the water tank 25. A pump 30 in the water feed pipe 28 is operable to feed water from the water heating tank 18 to the water tank 25. The water is circulated through a three-way filling valve 32 which also connects via a water filling line 33 with a water supply which may be a water reservoir, or a mains water supply. The de-aerated steam feed line 14 also connects through a valve 35 with the water tank 25. A heating coil 36 is mounted within the water heating tank 18. The de-aerated steam generator 16 is operable to generate de-aerated steam devoid of any air. The water heating tank 18 is filled completely with water to remove all air. This water is then pumped by means of the pump 30 into the water tank 25, thus creating a vacuum within the water heating tank 18. The water heating tank 18 is then partially filled with water from the water tank 25 delivered through the water inlet valve 22. Operation of the heating coil 36 then heats the water within the water heating tank 18 to generate low pressure de-aerated steam, devoid of air, which is delivered through the de-aerated steam feed line 14 to the steam injector 10 for combustion within the reactor chamber 7. In use, the start-up burner 8 is operated using a hydrocarbon fuel to generate an operating temperature of at least 1500 °C, and preferably about 1500°C to 1600 °C, within the reactor chamber 7. Over a period of about 20 minutes the core element 12 is heated up to this temperature. When the desired operating temperature has been reached de-aerated steam is delivered into the reactor chamber 7 by the steam injector 10 to maintain the operating temperature within the reactor chamber 7 when the start-up burner 8 is turned off. De-aerated steam injected into the reactor chamber 7 is split into hydrogen and oxygen which combust within the reactor chamber 7 to produce high temperature gases which migrate into the thermal reaction area for use in the distillation of the waste materials. The de- aeration of the steam prior to injection into the reactor chamber 7 advantageously helps to eliminate nitrogen from the reactor chamber 7.

It will be noted that the core element 12 within the reactor chamber 7 is constructed from high temperature firebrick and is constructed in a design that allows the core 12 to maintain a temperature of 1500 °C to 2000 °C constantly by the combustion of the de-aerated steam (H ₂ 0). Combustion of de-aerated steam (H ₂ 0) within the reactor chamber 7 maintains a constant temperature of up to 2000 °C using de- aerated steam (H ₂ 0) only. Any over temperature can be controlled by allowing some air into the reactor chamber 7 which reduces the rate of combustion.

Carbon dioxide produced during operation of the furnace 1 is converted into carbon monoxide. At the operating temperature pure carbon dust/powder is injected into the high temperature gases within the reactor chamber 7 which results in a chemical reaction whereby the added carbon bonds with the high temperature carbon dioxide converting it to carbon monoxide. The reaction is as follows:

Various gases generated in the distillation process within the thermal reaction area are treated or neutralised in a gas treatment section of the plant by condensing, washing or conversion. Hydrogen and carbon gases are condensed into fuel oils and energy. No plumes or harmful gases are exhausted into the atmosphere, so there is no necessity for a chimney or smoke stack in this system. The gases in the reactor chamber 7 are mainly carbon dioxide, hydrogen and water. These will react as follows.'

It will be appreciated that as air and hydrocarbon fuel is excluded from the reactor chamber (other than at start-up) the NOx and SOx gases normally produced as a by-product of hydrocarbon fuel combustion are not generated. The combustion of de-aerated steam in the reactor chamber generates cleanly the required heat for the distillation and chemical conversion of waste material in the thermal reaction area 5.

The invention advantageously saves energy and maximises output using water as a fuel. A further advantage of the invention is the conversion of carbon dioxide into carbon monoxide which is then converted into methane and water as indicated above, thus eliminating carbon dioxide emissions.

The invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail within the scope of the appended claims.