WO2006027623A1

WO2006027623A1 - Combustion process, steam driven apparatus and method for imparting motion to an apparatus

Info

Publication number: WO2006027623A1
Application number: PCT/GB2005/003524
Authority: WO
Inventors: Donald James Highgate
Original assignee: Itm Fuel Cells Ltd.
Priority date: 2004-09-10
Filing date: 2005-09-12
Publication date: 2006-03-16
Also published as: GB0420119D0

Abstract

A process for the generation of high pressure steam, which comprises subjecting hydrogen and oxygen in a 2: 1 stoichiometic ratio to essentially continuous combustion, a steam-driven apparatus and a method for imparting motion to an apparatus.

Description

COMBUSTION PROCESS, STEAM DRIVEN APPARATUS AND METHOD FOR IMPARTING

MOTION TO AN APPARATUS

Field of the Invention

This invention relates to a combustion process, and in particular to a process that can utilise low/zero carbon footprint hydrogen as a secondary fuel. Background of the Invention

The combustion of hydrocarbon fuels using atmospheric oxygen in open cycle heat engines produces large amounts of atmospheric pollutants, principally carbon dioxide and oxides of nitrogen. This is the situation irrespective of the type of heat engine (internal combustion or external combustion), the type of thermodynamic cycle used or the standard of maintenance of the device.

It is now recognised that this situation is not acceptable if the quality of the environment is to be maintained, and significant effort is now being directed to the development of improved combustion systems and the replacement of high carbon fuels with hydrocarbons of lower carbon footprint. These developments are typified by the development of catalytic converters for automotive applications, sulphur removal from electric power stations and the replacement of coal and heavy oil fuels by light oils or gas (butane or propane) of reduced carbon footprint.

These methods have contributed to a significant reduction in the UK's carbon dioxide output. However, the reductions necessary to achieve long-term stability in the environment are considerably greater than can be achieved by the simple substitution of gas for heavy oil or coal and, for this reason, alternative energy systems are needed.

The generation of hydrogen by electrolysis, from low carbon footprint primary energy sources, wind power, wave power and nuclear energy is well known. A limitation is the cost and efficiency of the electrolysis plant.

It is normally stated that the efficiency of a fuel cell is significantly greater than that of a heat engine (typically 40-60% compared with 20-30%) and this is the justification for much research in fuel cells; however, if the heat engine can be designed to operate using oxy-hydrogen, the combustion temperature is approximately 3080^°K and the theoretical efficiency (the Carnot cycle efficiency) is then in excess of 85%, significantly greater than that available from any existing fuel cell. In addition, if the fuel gases are used in a stoichiometric ratio (as produced by the electrolysis process), the result is pure water.

For these reasons, it is desirable to develop improved means for the combustion of hydrogen and oxygen in heat engines. However, significant difficulties arise inter alia because of:

(i) the very wide combustion limits for hydrogen in oxygen which lie approximately in the region 4%H₂:96%0₂ and 95%H₂:5%0₂; (ii) the high flame front velocity in hydrogen air and hydrogen oxygen; and (iii) the high combustion temperature.

Item (i) above is reflected in the relative difficulty in achieving good charging of an internal combustion engine in which discrete charges of fuel- oxidant mixture must be introduced into a combustion chamber and then ignited. The wide combustion ratio results in pre-ignition in a spark ignition (Otto cycle) engine (simple oxy-hydrogen will not ignite due to compression heating alone, so a pure hydrogen diesel engine is not possible). In addition, the high flame front velocity makes complete combustion difficult, resulting in incomplete combustion of the charge in the cylinder.

For these reasons, engines which employ continuous combustion are simpler and easier to control. Continuous combustion may be employed in a piston engine such as the Stirling engine which is an external steady combustion system, but such devices have limited efficiency due to thermal conduction and heat transfer problems. Alternatively, continuous combustion may be used in gas turbine devices, but the high combustion temperature makes materials choice difficult, and catalytic combustion at reduced temperature is preferred.

In addition, there is a need for transport engines to exhibit high torque at low rates of rotation, such as can be achieved in conventional steam engines or electric motors. Summary of the Invention The present invention is based on an appreciation of the fact that the use of electrolysis (specifically by means of a solid polymer electrolyte electrolyser) results in the production of high purity hydrogen (>99.99% purity) and oxygen in precisely stoichiometric ratios. The hydrogen can be reconverted to useful energy either by the use of a fuel cell or by combustion in a heat engine; in either case, if the oxygen which results from the electrolytic production process is employed, the only resulting by-product is water.

According to the present invention, a steam-generating system, effectively a very low thermal mass high response rate boiler, comprises combusting H and O in stoichiometric ratio (2:1 as produced directly from an electrolyser), to produce high temperature steam with no other products of combustion. Description of the Drawing

The accompanying drawing is a schematic representation of a device that can be used in this invention. Description of the Invention

In one embodiment of a system of the present invention, it may be used directly if appropriate, controlling the fuel feed rate (smoothly and continuously) as necessary to match the input energy generation rate to the output demand. In this case, the operating conditions, principally pressure, temperature and energy production rate, may be varied continuously. Such a simple steam-raising device is shown in the drawing. Because of the relative simplicity of the device, the high operating temperature of oxy-hydrogen may allow the structure to be constructed using ceramic materials (there being no valves or other moving parts).

If necessary or desired, a catalytic combustion process may be employed to reduce the effective burning temperature of the hydrogen-oxygen fuel, although this would reduce the maximum efficiency possible. In another ambodiment of the invention, using continuous hydrogen- oxygen combustion, a valved steam-raising chamber (as shown in the drawing but with a suitable valve in the exit port at point A) may be combined inter alia with a piston and cylinder engine to achieve the advantages of continuous combustion and the simplicity of a piston engine but one in which the torque is not dependent upon the explosive combustion of a fuel charge as in an Otto cycle or Diesel cycle engine. In this application, the combustion rate may be continuous and the fuel feed rate controlled smoothly to achieve the time average energy output required of the system, but the combustion chamber may be valved so that the pressure may change discontinuously as required during any one 'cycle' of the piston engine to which it is attached.

In this case, the fuel feed and combustion are continuous, but the steam- generating chamber is valved and the pressure is allowed to fluctuate in order that there can be an exhaust cycle from the piston/cylinder system.

The cycle may involve a long charge phase during which the steam pressure increases in the cylinder pushing upon the piston, increasing the effective torque of the engine until rotation occurs. The piston then moves down and begins the return stroke, at which point the exhaust valve opens and the steam inlet valve shuts; during this phase the pressure in the steam raising chamber increases. The duration of the exhaust cycle can be reduced by the introduction of, for example, an additional gas cylinder into the primary piston/connecting rod. This device allows the duration of the 'inlet' and 'exhaust' cycles to be controlled to reduce the pressure changes which would otherwise occur in the fuel combustion chamber. An alternative way of operating the engine is to make it a multi-cylinder device in which the duration of the inlet/exhaust phases can be controlled.

Claims

1. A process for the generation of high pressure steam, which comprises subjecting hydrogen and oxygen in a 2:1 stoichiometic ratio to essentially continuous combustion.

2. A process according to claim 1 , in which the hydrogen and oxygen are produced by an electrolyser from input electricity of low carbon footprint.

3. A process according to claim 1 or claim 2, which is conducted in the presence of a catalyst, whereby the combustion temperature is controlled and lowered.

4. A process according to any preceding claim, in which the combustion is conducted within a valved chamber.

5. A method for imparting motion to apparatus, e.g. a piston engine, driven by high pressure steam, in which the steam is generated by a process according to any preceding claim, i

6. Steam-driven apparatus comprising a combustion chamber supplied by an electrolyser supplying hydrogen and oxygen in a 2:1 stoichiometic ratio.

7. Apparatus according to claim 6, wherein the combustion chamber is valved.

8. Apparatus according to claim 6 or claim 7, which is a piston engine.

9. Apparatus according to claim 8, which additionally comprises a sealed gas chamber in the primary piston-connecting rod, thereby allowing the use of combustion in conjuction with a piston engine cycle.