Non-polluting Steam Generator System

Abstract

A steam generating system comprising burning fuel which contains no sulphur or nitrogen in an atmosphere of pure oxygen to heat water in a heat exchanger for converting water to steam. Preferably, the fuel and oxygen are provided in liquid or gaseous form and are supplied under pressure to the combustion chamber, to provide more rapid combustion, and additional oxygen may be added to the burning gases as they are passed to the heat exchanger to further increase the temperature of the flame. In addition, the water to be converted into steam is maintained isolated from the products of combustion. Both method and apparatus are disclosed.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to steam generators and is particularly directed to compact, non-polluting steam generators which can be retrofit to replace conventional steam generators.

2. Prior Art

Steam generators have long been used to produce steam for heating, driving turbines and generators, providing motive power for locomotives and automobiles, and other purposes. However, the steam generators of the prior art have generally employed combustion chambers wherein fuel was burned in air at relatively low pressures of the order of 10 to 20 psia, and have required relatively massive heat exchange units or boilers, often 40 to 60 feet in length and 20 to 60 feet in diameter, to produce steam. However, steam generators often provide incomplete combustion of the fuel-air mixture and the products of such incomplete combustion have conventionally been released to pollute the atmosphere. Moreover, it has been customary, heretofore, to employ fuels which contain sulphur and nitrogen and to burn these fuels in air, which also contains nitrogen, with the result that the products of combustion have included noxious gases which were released to further pollute the atmosphere.

In recent years, such pollution has reached serious, and even dangerous proportions and it has been recognized that steps must be taken to reduce or eliminate such pollution. Numerous techniques have been proposed heretofore to reduce or eliminate this problem. However, none of the prior art techniques have been entirely satisfactory. Various types of filters, scrubbers, and the like have been employed for removing or neutralizing the noxious products and products of incomplete combustion. In addition, numerous techniques have been proposed for improving the efficiency of the combustion. However, the prior art devices and techniques have been only partially effective, at best, and add to the expense of the steam generator while decreasing its efficiency.

In submarines and the like, these problems have been overcome by employing a system wherein a hydrocarbon fuel is burned in an oxygen atmosphere and the products of combustion are used directly to drive a turbine or the like. However, these products of combustion include carbonic acid and other generally non-condensible gases such as hydrogen, carbon monoxide, and carbon dioxide, which, in gaseous form, are less efficient than steam in driving the turbine, tend to attack and corrode the turbine blades, and which cannot be recycled, as in the case of pure steam.

BRIEF SUMMARY AND OBJECTS OF INVENTION

These disadvantages of the prior art are overcome with the present invention and a steam generator is provided which is completely pollution-free, yet provides full efficiency, avoids turbine corrosion, and foreign gas condensation or disposal. In addition, the steam generator of the present invention is extremely compact and highly efficient. Moreover, the compact steam generator of the present invention requires little or no maintenance and minimizes down time and servicing costs. Furthermore, the steam generator of the present invention is compatible with conventional electrical generating system and, hence, can be retrofit into existing system with burned out or obsolete boilers.

The advantages of the present invention are preferably attained by providing a steam generator which employs separate heat producing and steam producing systems. In the heat producing system, air is excluded and liquid or gaseous oxygen is employed as an oxidizer for a fuel containing no sulphur or nitrogen, such as liquid natural gas. The liquid oxygen and fuel are raised to high pressure and vaporized into a gaseous state prior to combustion. The hot products of complete combustion are passed through a heat exchanger to convert water to steam in the separate steam producing system and may, then, be exhausted into the atmosphere without pollution. The products of this combustion will contain only water, carbon dioxide and carbonic acid, which quickly dissociates into water and carbon dioxide. Hence, the exhaust contains no pollutant material. At the same time, the separate water of the steam producing system is isolated from the carbonic acid and non-condensibles. Thus, the efficiency of the steam is preserved and the turbines are protected against corrosion. Moreover, the oxygen and fuel may be mixed and burned at pressures of up to several thousand pounds per square inch. This produces extremely rapid combustion which converts water to steam much more quickly and permits the size of the heat exchange unit to be vastly reduced which, in turn, greatly simplifies servicing and installation.

Accordingly, it is an object of the present invention to provide an improved steam generator.

Another object of the present invention is to provide an improved method of operating steam generators.

A further object of the present invention is to provide a steam generator which will not discharge pollutants into the atmosphere and yet will protect turbines, condensers, and the like against corrosion and non-condensibles.

An additional object of the present invention is to provide a steam generator which is extremely compact.

Another object of the present invention is to provide a steam generator which is simple to install and service.

A specific object of the present invention is to provide a steam generator comprising a source of an oxidizer containing no nitrogen, a source of fuel containing no sulphur or nitrogen, a combustion chamber, a closed system for deliverying said oxidizer and said fuel to said combustion chamber, a source of water connected to supply water to said heat exchanger, and output means for delivering steam from said heat exchanger to a utilizing device.

These and other objects and features of the present invention will be apparent from the following detailed description, taken with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

The FIGURE is a diagrammatic representation of a steam generating system embodying the present invention.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENT

In that form of the present invention chosen for purposes of illustration in the drawing, the FIGURE shows a steam generator, indicated generally at 2, having a combustion chamber 4 and a heat exchanger 6. A pair of storage tanks 8 and 10 are provided and tank 8 is filled with a liquid oxidizer, such as oxygen (O, O.sub.2, O.sub.3) or hydrogen peroxide, while tank 10 is filled with fuel. Virtually any type of fuel may be employed However, it is imperative that the fuel contains no sulphur or nitrogen. Thus, liquefied methane natural gas is a preferred fuel, although other fuels such as hydrogen, ethane, propane, alcohol, etc., may be used. From the storage tanks 8 and 10, the oxygen and fuel are conducted to the combustion chamber 4 by a delivery system indicated generally at 12, which is closed to prevent air from contaminating the fuel or oxygen. Thus, the liquid oxygen is drawn from the storage tank 8, through a suitable flow control device 14, by a pump 16 and is passed to a vaporizer 18, where the liquid oxygen is expanded to a gaseous state. The gaseous oxygen is then conducted through conduit 20 and flow control device 22 to a pressure regulator 24 and is passed through an additional flow control device 26, such as a sonic or cavitating fluid venturi nozzle, to the combustion chamber 4. Similarly, the liquid fuel is drawn from storage tank 10, through a suitable flow control device 28, by pump 30 and is passed to vaporizer 32, where it is expanded to a gaseous state. The gaseous fuel is then conducted through conduit 34 and flow control device 36 to a temperature controller 38 and is passed through an additional flow control device 40 to the combustion chamber 4. Preferably, pressure sensing transducers 42 and 44 are connected to the respective conduits; as shown, and supply signals, indicative of the respective pressures, to a differential pressure controller 46 which compares these signals and serves to control the pressure regulator 24 to automatically maintain the desired pressure ratio between the fuel and oxygen.

Within the pre-combustion chamber 4 or the main combustion chamber 58 the oxygen and fuel are ignited by a suitable igniter, as seen at 48, and the burning gases are passed through the central circular tube or other geometric gas passage 50 of heat exchanger 6. If desired, additional oxygen may be passed through conduit 52, flow control device 54, and manifold 56, and introduced to the burning gases at 58, adjacent the entry to tube or passage 50 of the heat exchanger 6 to increase the temperature of the gases. Alternatively, if desired, the initial combustion of the oxygen-fuel mixture may occur at 58. To produce steam, secondary fluid, such as water from a suitable source, not shown, is supplied through pipe 60 and inlet manifold 62 to the jacket 64 of the heat exchanger 6 and is conducted in heat exchanging relation with hot gases in the central gas passage 50, the water being converted into steam by the time it passes out through outlet manifold 66. Steam then passes through conduit 68 to a utilizing device, not shown, such as a turbine other suitable means. Preferably, the water supplied to pipe 60 is first passed through an exhaust condenser 70 from inlet 61 in heat exchanging relation with the exhaust gases from the central tube 50 of the heat exchanger 6. This serves, simultaneously to cool the exhaust gases from the heat exchanger 6, to improve efficiency, and to preheat the water supplied to the pipe 60. With this arrangement, it is found that the overall recovery of combustion gas enthalpy can be of the order of 4,000 Btu per pound, or greater.

The combustion chamber 4 and heat exchanger 6 may be formed of conventional high temperature metals, such as steel alloyed with nickel, chromium, cobalt, or nickel or copper alloys such as BeCu, Cu, Ag-Cu, or a combination of these, or can be lined with a conventional refractory material, such as molybdenum, tungsten, tantalum, or the like, for high steam temperatures. In addition, the configuration and relationship of the combustion chamber 4 and heat exchanger 6 may be made substantially as desired, provided that the ratio of the combustion gas passage length to the hydraulic diameter (gas flow area to wetted perimeter rates, multiplied by four) is large, preferably greater than 100 and less than 1000, on the gas side. Similarly, the flow direction of the secondary fluid may be substantially as desired and will be determined by the specific use of each installation.

In use, the liquid fuel and oxygen, from storage tanks 8 and 10, are raised to high pressure states and are supplied to the combustion chamber 4, where they are ignited at 48, or at 58. Preferably, the gaseous fuel and oxygen are supplied to the combustion chamber 4 under pressure since it has been found that this results in more rapid combustion when the gases are ignited. This provides for more efficient conversion of water to steam, and, hence, permits the size of the heat exchanger to be reduced. Obviously, the greater the pressure of the gases at ignition, the more this result will be obtained. After ignition, the burning gases are passed through the heat exchanger 6 and additional oxygen can be added to further increase the temperature of the flame.

As an example, it has been found that when the gaseous fuel (1.97 lb./sec.) and oxygen (7.89 lb./sec.) are supplied to the combustion chamber 4 at a pressure of approximately 460 psi, ignition of the gases will produce a flame having a temperature of the order of 1,200.degree.F. Pressures within the combustion chamber may range from 150 psia to 400 psia. Moreover, when additional oxygen is added at point 58, as the flame enters the heat exchanger 6, the temperature of the flame in the central tube 50 of heat exchanger 6 will be increased to approximately 6000.degree. F. With these temperatures, the water in the jacket 64 of the heat exchanger 6, flowing at a rate of 36.6 lb./sec., is rapidly converted to 36.6 lb./sec. steam at 375 psi and 600.degree. F, with 160.degree. F superheat, and it is found that the size of the heat exchanger can be significantly reduced. In fact, it has been found that, with the aforementioned pressures and temperatures, a heat exchanger unit having a combustion gas length of about 100 inches and a fluid hydraulic diameter of approximately one-half inch is entirely adequate to convert the water to steam. It will be seen that a heat exchanger of this length can be moved for servicing by a fork-lift, or even manually, whereas it has been necessary heretofore to employ heavy duty cranes or special equipment for moving conventional heat exchangers Furthermore, the compact size and non-polluting character of the steam generating system of the present invention make possible use of the system for aircraft power plants and weapons, on ships, busses, and in mines, and even in portable power plants.

As noted above, the fuel must not contain sulphur or nitrogen, as it is these elements which combine with other elements in the exhaust to produce pollutants. Moreover, by using pure oxygen with this fuel in a closed delivery system, the nitrogen contained in atmospheric air is excluded. As a result, the exhaust from the steam generating system of the present invention will consist only of water, carbon dioxide and carbonic acid, which rapidly dissociates into water and carbon dioxide. At the same time, by keeping the water of the steam producing systems isolated from the products of combustion of the heat producing system, the efficiency of the steam is preserved and the carbonic acid and non-condensible carbon dioxide are kept out of the steam and, hence, cannot attack and corrode turbine blades and the like.

Obviously, if desired, the fuel and oxygen could be stored in gaseous, rather than liquid form. Moreover, solid fuels could be employed, provided they contain no sulphur or nitrogen and are stored and delivered to the combustion chamber in a manner which excludes air. Furthermore, where desired, other secondary heat exchanging fluids, such as liquid metal, organic fluid, carbon dioxide, mercury, or the like, may be employed as intermediate heat exchanging fluids between the hot combustion gases and the water. In addition, numerous other variations and modifications may be made without departing from the present invention described above and shown in the accompanying drawing, which is illustrative only and is not intended to limit the scope of the invention.

Claims

What is claimed is:

1. A steam generating system comprising:

a source of an oxidizer containing no nitrogen,

a source of fuel containing no appreciable sulfur or nitrogen,

a combustion chamber,

a closed delivery system connected to deliver said oxidizer and said fuel to said combustion chamber under pressure,

a heat exchanger connected to receive heat from said combustion chamber on one side of a heat exchanger wall,

a source of water connected to supply water to an opposite side of said heat exchanger wall in heat exchanging relation to said combustion chamber heat, said heat exchanger having a ratio of the gas passage length to the hydraulic diameter on the gas side greater than 100, and

output means for delivering steam resultant from vaporization of said water from said heat exchanger to a utilizing device.

2. The system of claim 1 wherein said oxidizer is oxygen.

3. The system of claim 1 wherein said oxidizer is stored in said source in liquid form.

4. The system of claim 1 wherein said fuel is a hydrocarbon fuel.

5. The system of claim 1 wherein said fuel is stored in said source in liquid form.

6. The system of claim 1 wherein said fuel is natural gas.

7. The system of claim 1 further comprising:

delivery means connected to deliver additional oxidizer adjacent said one side of the heat exchanger wall, together with combustion products from said combustion chamber.

8. The method of generating steam comprising the steps of:

burning a fuel containing no appreciable sulfur or nitrogen in a pressurized oxidizing atmosphere containing no nitrogen to produce heat, and

passing said heat in heat exchanging relation with water to convert said water to steam while maintaining said water isolated from the products of combustion and maintaining the ratio of the gas passage length to the hydraulic diameter on the gas side greater than 100.

9. The method of claim 8 wherein said fuel is a hydrocarbon fuel.