U.S. patent application number 10/553243 was filed with the patent office on 2007-01-04 for integrated renewable energy system.
This patent application is currently assigned to H-EMPOWER CORP.. Invention is credited to John McNeil.
Application Number | 20070001462 10/553243 |
Document ID | / |
Family ID | 9956843 |
Filed Date | 2007-01-04 |
United States Patent
Application |
20070001462 |
Kind Code |
A1 |
McNeil; John |
January 4, 2007 |
Integrated renewable energy system
Abstract
A system and method are disclosed comprising coupling a
compression ignition engine (17) to an AC electrical generator (18)
and/or a DC hompolar generator (19), wherein the homopolar
generator (19) produces an electric current which is used to
electrolyse water into hydrogen and oxygen. The hydrogen from the
water electrolysis process may be used as a renewable fuel, either
in the form of a gaseous fuel or a reactant in a fuel cell. The
oxygen from the water electrolysis unit (23) may be used to produce
an oxygen enriched combustion atmosphere in the engine (17). The
oxygen may optionally be used as a reactant, along with the
hydrogen, in a fuel cell.
Inventors: |
McNeil; John; (Kent,
GB) |
Correspondence
Address: |
MCCORMICK, PAULDING & HUBER LLP
CITY PLACE II
185 ASYLUM STREET
HARTFORD
CT
06103
US
|
Assignee: |
H-EMPOWER CORP.
3RD FLOOR, TRADE WINDS BUILDING BAY STREET
NASSAU
BS
|
Family ID: |
9956843 |
Appl. No.: |
10/553243 |
Filed: |
April 8, 2004 |
PCT Filed: |
April 8, 2004 |
PCT NO: |
PCT/GB04/01561 |
371 Date: |
September 14, 2006 |
Current U.S.
Class: |
290/52 |
Current CPC
Class: |
F02M 25/12 20130101;
Y02P 20/133 20151101; Y02T 10/12 20130101; Y02E 60/36 20130101 |
Class at
Publication: |
290/052 |
International
Class: |
F01D 15/10 20060101
F01D015/10 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 15, 2003 |
GB |
0308729.3 |
Claims
1-29. (canceled)
30. A method of using an engine driven power generating process as
an integral part of a renewable energy system, wherein: a
compression ignition engine is used to generate either AC or DC
electric current by alternately coupling a drive shaft of the
engine, as and when appropriate, to either an AC electrical
generator or a DC homopolar generator; wherein DC electric current
from the generating process is supplied to an electrolysis unit
that converts water into hydrogen and oxygen; wherein the
compression ignition engine is fuelled by fuel that burns poorly in
an engine; wherein an enriched oxygen combustion atmosphere is
provided in the engine so as to enable the fuel to be combusted
more efficiently, and wherein the enriched oxygen atmosphere is
formed by mixing oxygen produced by the water electrolysis unit
with normal atmospheric air.
31. The method as claimed in claim 30, wherein the hydrogen
produced by the water electrolysis unit is packaged for use as a
renewable gaseous transport fuel or as a reactant in fuel
cells.
32. The method as claimed in claim 30, wherein surplus oxygen from
the water electrolysis unit is packaged for use as a reactant along
with hydrogen in fuel cells.
33. The method as claimed in claim 30, wherein the drive shaft of
the engine is arranged so that it can be readily engaged with or
disengaged from the AC generator or the DC generator, and in a
manner whereby the engine is only coupled to one generator at a
time.
34. The method as claimed in claim 30, wherein the fuel is a
renewable non-fossil biofuel or a petroleum fuel oil.
35. The method as claimed in claim 34, wherein the non-fossil
biofuel is vegetable oil, animal fat, fish oil, or natural alcohol
or mixtures thereof, or alternatively the non-fossil fuel is waste
biofuel such as waste vegetable oil, waste fish oil, waste alcohol,
or waste cooking oil or mixtures thereof.
36. The method as claimed in claim 34, wherein the fossil petroleum
fuel oil is heavy fuel oil, residual fuel oil, recovered fuel oil
or waste based mineral oil.
37. The method as claimed in claim 30, wherein AC electric current
from the generating process is supplied locally.
38. The method as claimed in claim 37, wherein the AC electric
current supplied locally is generated by burning renewable
non-fossil biofuel in the engine.
39. The method as claimed in claim 30, wherein the DC electric
current used to electrolyse water is generated by burning either
non-fossil biofuel or fossil petroleum fuel oil in the engine.
40. The method as claimed in claim 30, wherein the enriched oxygen
atmosphere inside the engine contains between 2% and 6% extra
oxygen, i.e. the combustion atmosphere has a composition of between
23% oxygen, 77% nitrogen and 27% oxygen, 73% nitrogen, depending on
the specification of the fuel being burned in the engine.
41. The method as claimed in claim 40, wherein the enriched oxygen
combustion atmosphere inside the engine contains more than 6%
oxygen.
42. The method as claimed in claim 30, wherein waste heat in
exhaust gas from the engine is recovered by raising steam in a
steam boiler and using the steam to drive a steam turbine to
produce more electricity.
43. The method as claimed in claim 30, wherein the homopolar
generator comprises an electromagnetic coil to produce an annular
toroidal magnetic field; means for positioning a conductive metal
disc in the toroidal magnetic field so that the disc is intersected
by both forward and return magnetic fields of the toroidal magnetic
field; means for connecting the conductive disc to a drive shaft
that is rotated by a compression ignition engine; and means for
collecting the electric current generated in the disc when it is
rotated through the toroidal magnetic field.
44. The method as claimed in claim 30, wherein the current from the
homopolar generator has a voltage of between 1 and 2 volts and a
current density of 5000 amps/m.sup.2 or more.
45. The method as claimed in claim 30, wherein the drive shaft of
the compression ignition engine drives a multiplicity of homopolar
generators connected together either in series and/or in
parallel.
46. The method as claimed in claim 30, wherein direct current
produced by the power generating process is connected by an
electrical circuit to either a single water electrolysis unit or to
a multiplicity of water electrolysis units connected together
either in series and/or in parallel.
47. The method as claimed in claim 30, wherein the water
electrolysis unit consists of a large number of electrolysis cells
typically containing a 25% solution of potassium hydroxide as an
electrolyte, and wherein the electrolysis unit operates at a
temperature of about 70.degree. C. and normal ambient atmospheric
pressure.
48. The method as claimed in claim 30, wherein renewable hydrogen
fuel is generated by burning a renewable liquid fuel, such as
vegetable oil, animal fat, fish oil or natural alcohol, in the
enriched oxygen combustion atmosphere to generate electricity, and
wherein direct electric current from the power generating process
is supplied to the water electrolysis unit to produce the
hydrogen.
49. The method as claimed in claim 30, wherein renewable hydrogen
fuel is generated by burning a fossil petroleum fuel oil, such as
heavy oil, residual fuel oil or recovered fuel oil, in the enriched
oxygen compression ignition engine to generate electricity, and
wherein direct electric current from the power generating process
is supplied to a water electrolysis unit to produce the
hydrogen.
50. The method as claimed in claim 30, wherein exhaust gas from the
engine is analysed for pollutants, and the exhaust gas is treated
in dependence of the analysis so that pollutants are abated to
acceptable environmental levels before the exhaust gas is released
into the atmosphere.
51. A homopolar electricity generating system comprising an
electromagnetic coil to produce an annular toroidal magnetic field;
a conductive metal disc positioned in the toroidal magnetic field
such that the disc intersects both forward and return magnetic
fields of the toroidal magnetic field; a drive shaft that is
connected to the conductive disc and is rotated by a compression
ignition engine; and means for collecting the electric current
generated in the disc when it is rotated through the toroidal
magnetic field.
52. The homopolar electricity generating system as claimed in claim
51, wherein the engine can drive a multiplicity of homopolar
generators that are connected together either in series and/or in
parallel.
53. The homopolar electricity generating system as claimed in claim
51, wherein electric current from the homopolar generator has a
voltage of between 1 and 2 volts and a current density of 5000
amps/m.sup.2 or more.
54. A power generating system that can produce either AC or DC
electric current comprising: a compression ignition engine; a
supply of oxygen enriched air to a combustion chamber of the
engine; a supply of poor burning fuel of fossil or non-fossil
origin to the combustion chamber of the engine; an AC generator;
and a homopolar electricity generating system having an
electromagnetic coil to produce an annular toroidal magnetic field;
a conductive metal disc positioned in the toroidal magnetic field
such that the disc intersects both forward and return magnetic
fields of the toroidal magnetic field; a drive shaft that is
connected to the conductive disc and is rotated by a compression
ignition engine; and means for collecting the electric current
generated in the disc when it is rotated through the toroidal
magnetic field; wherein the drive shaft of the engine is
alternately coupled, as and when appropriate, to the AC generator
or the DC homopolar generating system.
55. The water electrolysis system comprising a power generating
system as claimed in claim 54; a single electrolysis unit or a
multiplicity of electrolysis units connected together in series
and/or in parallel to electrolyse water into hydrogen and oxygen;
and an electrical circuit to supply direct current from the power
generating system to the electrolysis unit(s).
56. The water electrolysis system as claimed in claim 55, wherein
the water electrolysis unit is a low pressure, low temperature
system that operates at about 70.degree. C. and normal ambient
atmospheric pressure conditions, and wherein the water electrolysis
unit comprises a large plurality of electrolysis cells each
typically containing an electrolyte consisting of a 25% solution of
potassium hydroxide.
57. A hydrogen production system comprising the water electrolysis
system as claimed in claim 55; and means for packaging the hydrogen
produced by the water electrolysis unit so that the hydrogen is in
a suitable form for use as a renewable gaseous fuel in transport
applications or as a reactant in fuel cells.
58. An oxygen production system comprising the water electrolysis
system as claimed in claim 55; means for mixing oxygen produced by
the electrolysis system with normal atmospheric air to provide the
enriched oxygen combustion atmosphere for the engine; and means for
packaging surplus oxygen for use, for example, as a reactant with
hydrogen in fuel cells.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is entitled to the benefit of and
incorporates by reference essential subject matter disclosed in
International Patent Application No. PCT/GB2004/001561 filed on
Apr. 8, 2004 and Great Britain Patent Application No. 0308729.3
filed Apr. 15, 2003.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of using a
compression ignition engine in an integrated renewable energy
system, whereby the engine is used to drive either an AC electrical
generator to produce `green` electricity for local use or a DC
electrical generator to supply the electric current needed to
electrolyse water into hydrogen and oxygen.
BACKGROUND OF THE INVENTION
[0003] Compression ignition engines are fuel efficient and diesel
engines are therefore widely used for the generation of electricity
as well as for transport purposes. Because diesel engines are also
mechanically rugged and reliable, diesel engines are one of the
most common methods employed to generate local supplies of
electricity, particularly in remote, rural or island economies that
do not have access to grid supplies of electricity.
[0004] Compression ignition engines tend to be fuel specific
because they have primarily been designed to burn petroleum fuel
oils, such as diesel gas oil, medium fuel oil and heavy fuel oil,
which are specially formulated for this type of engine. A readily
available and plentiful supply of petroleum fuel oil is therefore
required if diesel engines are to be used for power generation
purposes. However, in developing countries and in remote locations,
such as rural and island economies, petroleum fuel oil can be a
relatively expensive commodity and the supply chain to such
locations may also be difficult.
[0005] Fossil based petroleum fuel oils are in any case finite
energy resources, and there is also increasing concern that the
emissions released into the atmosphere during the combustion of
petroleum fuel oils are causing serious damage to the
environment.
[0006] For example, the carbon element in petroleum fuel oils burns
to form carbon dioxide, a greenhouse gas, and it is now widely
accepted that the build-up of carbon dioxide in the atmosphere is
contributing towards global warming. In contrast, the hydrogen
element in hydrocarbon fuel oils is clean burning because water is
the only product produced by the combustion of hydrogen. This is
illustrated in the following combustion equation, which uses
pentane, an alkane hydrocarbon, as an example of petroleum fuel
oil. C5H12+8O2=5CO2+6H2O
[0007] Other environmental pollutants, including carbon monoxide,
volatile organic compounds and sooty particulates, are produced
when petroleum fuel oils burn incompletely in an engine, and these
substances can also damage the environment and harm human
health.
[0008] Acid gases, which cause environmental pollution and pose
risks to human health, can also be produced during combustion in an
engine. For example, nitrogen oxides (NOx) are produced by the
reaction of nitrogen and oxygen at high temperatures, and sulphur
dioxide (SO2) and hydrogen chloride (HCl) are produced by the
combustion of sulphur or chlorine compounds present in petroleum
fuel oils.
[0009] Attempts are being made to make petroleum fuel oils less
polluting by improving the specification of the oils. For example,
the quantity of sulphur permitted in petroleum fuel oils is
gradually being lowered in order to reduce the amount of SO2
released into the atmosphere from reciprocating engines.
[0010] Environmental regulations are also becoming more stringent
and exhaust gas abatement systems are now an essential element in
helping to reduce the release of pollutant emissions into the
environment. However, even with the introduction of improved fuel
quality and emission controls, the combustion of petroleum fuel
oils by reciprocating engines is still one of the major sources of
environmental pollution throughout the world.
BRIEF SUMMARY OF THE INVENTION
[0011] The present invention seeks to provide ways of using a
standard compression ignition engine as an integral part of a
renewable energy system, so that the benefits associated with a
diesel engine, i.e. its fuel efficiency and mechanical reliability,
can be fully exploited whilst simultaneously reducing environmental
pollution from the engine.
[0012] For example, if compression ignition engines were able to
efficiently burn non-fossil fuels, the carbon dioxide produced by
the combustion process would not directly contribute towards global
warming. Alternatively, if the power generated by a compression
ignition engine burning fossil fuel could be used to produce an
alternative renewable non-fossil fuel, then the subsequent clean
combustion of the renewable fuel would help to off-set the
emissions released from the engine when it had been burning the
fossil fuel.
[0013] By utilising a compression ignition engine in such a
flexible way, the engine could become an essential part of an
integrated low carbon renewable energy system. For example, the
engine could be used to generate `green` electricity from a
non-fossil fuel, or the engine could use either a fossil or a
non-fossil fuel to generate the power required to produce an
alternative clean burning renewable fuel. Preferably the
alternative renewable fuel should be capable of being used in the
integrated renewable energy system itself, either as a fuel for
local power generation or as a fuel for local transport
applications.
[0014] From a first broad aspect therefore the invention provides a
method of using a compression ignition engine in a renewable energy
system, whereby a diesel engine genset would be able to burn either
fossil or non-fossil liquid fuels in a clean and efficient manner,
and at least part of the electricity generated by the diesel engine
genset would then be used to produce an alternative form of
renewable non-fossil fuel that could also be used in the integrated
renewable energy system.
[0015] It is a well-established fact that non-fossil liquid fuels
burn poorly in standard compression ignition engines. For example,
non-fossil liquid biofuels tend to produce combustion deposits
inside the engine and the exhaust smoke emitted from the engine is
usually black and heavily polluted with carbon monoxide and sooty
particulates.
[0016] However, research by the applicant has shown that non-fossil
liquid biofuels, including vegetable oils, animal fats, fish oils,
natural alcohol and mixtures of such materials, can be burned
efficiently and cleanly in a standard compression ignition engine
by enriching the combustion atmosphere inside the combustion
chambers of the engine with oxygen.
[0017] Liquid biofuels are either derived directly from plants or
from animals that live on plants, and as plants absorb carbon
dioxide from the atmosphere during their natural growing cycle,
biofuels are a renewable and sustainable source of energy.
[0018] A further benefit of oxygen enrichment is that it
significantly improves the efficiency of the engine combustion
process and ensures that fuels are burned much more completely than
under normal naturally aspirated combustion conditions. The
emissions of pollutants that are produced by incomplete combustion,
i.e. carbon monoxide, volatile organic compounds and particulates,
are therefore much reduced under enriched oxygen combustion
conditions.
[0019] This is illustrated in Table 1, which compares the normal
naturally aspirated combustion of diesel gas oil in a compression
ignition engine with the enriched oxygen combustion of tallow
animal fat and a vegetable oil in the same engine. For ease of
comparison, the emissions in Table 1 are expressed as values
relative to those obtained during the normal combustion of diesel
gas oil.
[0020] As shown in Table 1, the emissions of carbon monoxide and
particulates are much reduced when an enriched oxygen atmosphere is
used in the engine; however, nitrogen oxide (NOx) emissions are
higher because of the greater concentration of oxygen in the
combustion chamber of the engine. Fortunately, NOx in the engine
exhaust gas is easily abated by means of catalytic reduction with
either ammonia or urea. TABLE-US-00001 TABLE 1 Combustion of diesel
gas oil, tallow and vegetable oil Relative exhaust gas emissions
Diesel Gas Oil Vegetable Oil Emission Naturally Tallow Animal Fat
Enriched Relative Values Aspirated Enriched Oxygen Oxygen Power 1.0
1.0 1.0 Carbon monoxide 1.0 0.23 0.32 NOx unabated 1.0 2.64 2.70
NOx abated 1.0 0.45 0.37 Particulates 1.0 <0.1 <0.1
[0021] Oxygen enrichment improves the combustion of all liquid
engine fuels, and fossil petroleum based fuel oils therefore also
burn much better in an enriched oxygen combustion atmosphere.
[0022] For example, enriched oxygen combustion would ensure that
petroleum fuel oils burned more efficiently and more completely in
an engine. Although the carbon dioxide released from the combustion
process would still have a greenhouse gas impact in the atmosphere,
because it had been derived from a fossil fuel, the emissions of
other combustion pollutants, such as carbon monoxide, volatile
organics and particulates, would be significantly reduced.
[0023] From a further aspect therefore the invention provides a
method of using a compression ignition engine as an integral part
of a renewable energy system, whereby an enriched oxygen combustion
atmosphere would be used in the combustion chambers of the engine
so that the engine had the capability of being able to burn either
fossil or non-fossil liquid fuels in a clean and efficient
manner.
[0024] The enriched oxygen air for the combustion process could,
for example, be produced by a gas separation membrane system, which
separates normal air into an oxygen rich fraction and nitrogen rich
fraction.
[0025] Alternatively, for some applications it may be more
convenient to produce the enriched oxygen atmosphere by adding pure
oxygen to normal air. Unfortunately, the pure oxygen supplied by
industrial gas manufacturers, either in the form of a compressed
gas or a liquid, is expensive and the high cost of the oxygen could
well influence the viability of the combustion process.
[0026] Oxygen can also be produced by various industrial processes,
including pressure swing absorption, vacuum swing absorption and
cryogenic systems; however, these methods of oxygen production are
both energy and capital intensive.
[0027] However, oxygen can also be produced by the electrolysis of
water, and in the context of an integrated renewable energy system,
water electrolysis is a particularly interesting process because it
also produces hydrogen, a clean burning, renewable and totally
sustainable source of energy, as well as oxygen.
[0028] For example, when hydrogen burns it recombines with oxygen
to form water, and hydrogen is therefore a unique energy resource
because, in theory, this cycle of converting water to hydrogen and
then combusting the hydrogen to form more water could be repeated
endlessly.
[0029] In contrast to fossil fuels, which always produce carbon
dioxide during their combustion, innocuous water is the only
product of combustion when hydrogen is burned. Hydrogen is
therefore an ideal sustainable fuel to use in a fully integrated
renewable energy system.
[0030] The water to hydrogen to water cycle is illustrated by the
following reactions: Electrolysis of water: 2H2O=2H2+O2 Combustion
of hydrogen: 2H2+O2=2H2O
[0031] Because hydrogen is an exceptionally clean burning fuel,
there is increasing interest in developing hydrogen as a potential
renewable energy resource, particularly for transport applications
where the environmental pollution from reciprocating engines
burning petroleum fuels is now causing worldwide concern.
[0032] The hydrogen and oxygen produced by the electrolysis of
water can also be utilised together as reactants in a fuel cell to
produce `green` electricity. Fuel cells convert chemical energy
into electrical energy, and unlike batteries, which only store
electricity and can run down, fuel cells will continue to operate
at a constant power output as long as there is a supply of hydrogen
and oxygen. Fuel cells have potential for transport applications as
well as for power generation, although the future use of fuel cells
on a large scale will be dependent on having a readily available,
cost effective supply of hydrogen and oxygen.
[0033] Hydrogen is therefore a unique energy resource because it
can be used in a number of different ways to power transport
vehicles. For example, hydrogen could be used as a compressed
gaseous fuel for an engine, or as a reactant, along with oxygen, in
fuel cells to power a vehicle by electricity, or as a fuel in
hybrid vehicles that combine both an engine and fuel cells.
Whichever way the hydrogen was used as a transport fuel, virtually
no pollutants would be released into the atmosphere from the
vehicle.
[0034] Water electrolysis is a well known process. For example,
when two oppositely charged electrodes are inserted into water and
a current is passed between them, electrons are transferred from
the anode to the cathode.
[0035] As the electric current passes through the water, the
chemical bond between hydrogen and oxygen breaks down to produce
two positively charged hydrogen ions and one negatively charged
oxygen ion. The negative oxygen ions then migrate to the positive
electrode (the anode) and the positive hydrogen ions are attracted
to the negative electrode (the cathode).
[0036] The smallest amount of energy needed to electrolyse one mole
of water into hydrogen and oxygen is 65.3 Wh at 25.degree. C., and
when hydrogen and oxygen recombine by combustion back into water
79.3 Wh of energy is released. 14 Wh more energy is therefore
released during the combustion of hydrogen than is needed to split
water into hydrogen and oxygen.
[0037] The electrical resistance of pure water is high at 100
ohm/cm, and to encourage electrolysis the electrical resistance is
usually lowered by the addition of heat; pressure; a salt to the
water; an acid to the water; an alkali to the water; or a suitable
combination of such variables. By way of example, a low pressure
commercial water electrolyser may well typically operate under
normal ambient atmospheric pressure and at a temperature of about
70.degree. C., and use an electrolyte consisting of 25% to 30%
potassium hydroxide solution.
[0038] An electrolysis cell primarily consists of a pair of
electrodes immersed into a container of electrolyte, and a water
electrolysis unit is composed of a large number of electrolysis
cells combined together, either in series and/or in parallel, to
provide a greater output of hydrogen and oxygen.
[0039] Water electrolysis is, however, an unusual electrical
process in so far as it requires a low voltage but very high direct
electric current. A voltage of only 1 to 2 volts is needed to
electrolyse water and depending on the efficiency of the
electrolysis system the energy input required to electrolyse water
is approximately 4 kWh/m.sup.3 of hydrogen produced.
[0040] Although the voltage required to effect water electrolysis
remains fairly constant, water will electrolyse under varying
levels of current. For example, commercially available electrolysis
units operate with currents varying from about 1500 amps/m.sup.2 up
to 5000 amps/m.sup.2 or more. The volume of hydrogen produced by
the electrolysis process is, however, related to the current, i.e.
the higher the current, the more efficient the electrolysis process
tends to be.
[0041] Although water itself is cheap, abundant and readily
available, the water electrolysis process is energy intensive and
also requires a specific supply of low voltage, high direct
current.
[0042] If conventional grid electricity is used to power a water
electrolysis process, the normal high voltage alternating grid
electric current has to be converted into low voltage direct
current, i.e. from AC to DC electricity.
[0043] Such radical current commutation requires expensive
transformers and rectifiers, and significant current losses can
also occur during the current conversion process. A further
disadvantage of using grid electricity to electrolyse water is that
a large part of the electricity supplied to many national grid
networks will probably have been generated from the combustion of
coal, the most polluting of the carbon based fossil fuels.
[0044] An alternative to transforming normal grid AC current to DC
current would be to use a DC generator to produce the low voltage,
high direct current needed to for water electrolysis, and such a
current can be produced by means of a homopolar generator.
[0045] From a further aspect, the invention uses an enriched oxygen
combustion atmosphere in a compression ignition engine, so that the
engine can burn either fossil or non-fossil liquid fuels in a clean
and efficient manner, and the engine is used in an integrated
renewable energy system to drive either an AC generator to produce
electricity for local use or a DC homopolar generator to produce
the direct current needed to electrolyse water into hydrogen and
oxygen. Hydrogen from the water electrolysis process is a valuable
renewable energy resource, whilst oxygen from the water
electrolysis process can be used to produce the enriched oxygen
atmosphere for the engine. Hydrogen and oxygen from the water
electrolysis process can also be utilised together as reactants in
fuel cells to produce electricity.
[0046] The principles of homopolar generation were originally
established by Faraday who found that when a conductive disc was
rotated through a magnetic field, a voltage was generated between
the centre of the disc and the outer rim of the disc.
[0047] Homopolar machines produce a unidirectional electromotive
force, and homopolar generators are unique in that they produce low
voltage but high direct current. Because the current produced by a
homopolar generator is low voltage, homopolar generation is also a
relatively safe method of generating and transmitting
electricity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] Now having described the invention in general terms,
embodiments of the invention shall be described in details with
reference to the drawings in which:
[0049] FIG. 1 is a schematic cross-section illustration of a simple
homopolar generator, based on the principles first described by
Faraday.
[0050] FIG. 2 is a schematic cross-sectional illustration of a
typical homopolar generator that has been designed to enable the
conductive disc to intersect both the forward and the return
magnetic fields produced by an electromagnetic coil.
[0051] FIG. 3 is schematic illustration of a diesel engine
generating system capable of producing either AC electricity for
local supply or DC electricity for a water electrolysis unit.
[0052] FIG. 4 is a schematic illustration of the exhaust gas
abatement system that may be required for an engine combusting a
variety of fossil and non-fossil fuels.
DETAILED DESCRIPTION OF THE INVENTION
[0053] In FIG. 1, a shaft 3 runs through the center of both poles
of a magnet 2, and in a manner whereby shaft 3 can freely rotate
within the magnet 2. A metal disc 1 is fixed to shaft 3 and is
spatially arranged so that the metal disc 1 is centrally located
between the north and south poles of the magnet 2.
[0054] Rotation of shaft 3, by the application of an external
rotating force, correspondingly rotates the metal disc 1 between
the poles of the magnet 2, so that the disc intersects the magnetic
field produced by the magnet.
[0055] Rotation of disc 1 in the magnetic field generates a voltage
between the center of the disc and the rim of the disc. An electric
charge, which can be collected by electrical contact brushes placed
at the rim and at the center of the disc, is produced in disc
1.
[0056] The efficiency of a homopolar generator is greatly improved
if an annular magnetic field, whose axis passes through the center
of the drive shaft, is used in the system. When an annular magnetic
field is used, the electromotive force developed in any ring is
constant so that all current paths in the disc are radially
orientated.
[0057] Improvements in the performance of homopolar generators have
tended to concentrate on utilizing as much of the available
magnetic field as possible. Particular emphasis has been placed on
the shape and position of the magnets used in homopolar machines
and also on the relative spatial arrangement of the magnets and the
conductive disc.
[0058] Another refinement to homopolar machines has involved the
use of superconducting electromagnetic coils. Superconducting coils
are able to produce high magnetic fields, which is beneficial for
efficient homopolar machine operation. However, to perform
effectively most superconducting materials have to be used at
extremely low temperatures, i.e. temperatures at or close to
cryogenic temperatures, and the need to maintain such low
temperature operating conditions does have an affect on the capital
and operating costs of the homopolar machine.
[0059] The magnetic field produced by an annular magnet or an
annular electromagnetic coil has an axis of rotational symmetry and
the field is toroidal in character. Lines of magnetic flux emanate
from the center of the magnet or coil and initially flow outwards
in a forward direction. The magnetic flux then moves in a circular
toroidal manner until the magnetic flux eventually returns back to
the rear of the magnet or coil.
[0060] Homopolar machines were originally designed with the
conductive disc positioned so that the disc only intersected the
magnetic field travelling in a forward direction, as illustrated in
the basic homopolar machine shown in FIG. 1. The performance of a
homopolar generator can be improved if both the forward and the
return magnetic fields produced by a magnet or a coil are utilized
to generate current in the disc.
[0061] In FIG. 2, the metal conductive disc 5, which is attached to
a drive shaft 6, and the annular electromagnetic coil 7 are
together referred to as the homopolar generator 4.
[0062] The annular electromagnetic coil 7 is composed of many turns
of either conducting material or more preferably superconducting
material. When a current passes through coil 7, a toroidal magnetic
field 12, comprising a forward field 10 and a return field 11, is
generated about an axis of rotational symmetry 9.
[0063] For ease of illustration, only one magnetic line of flux 12
with a forward field 10 and a return field 11 is shown in FIG. 2.
Diagrammatic lines of flux are a pictorial device used to
illustrate a magnetic field, and a true representation of the
magnetic field generated by coil 7 would entail an infinite number
of lines of flux completely surrounding the annular coil 7.
[0064] A thin and substantially flat conductive metal disc 5 is
connected centrally to a shaft 6 in a manner whereby rotation of
shaft 6, by an external rotary motive force, would also rotate disc
5 about a central axis that is perpendicular to the disc while
being simultaneously coincident with the central axis 9 of the
magnetic field. The disc 5 is positioned so that the bottom surface
of the disc is in close proximity to the annular coil 7.
[0065] The metal disc 5 and the annular coil 7 are spatially
arranged so that the forward magnetic field 10 passes through the
central portion of disc 5, while the return magnetic field 11
passes through the outer portion of disc 5. The central portion of
disc 5, which is subjected to the forward magnetic field 10, is
separated from the outer portion of disc 5, which is subjected to
the return magnetic field 11, by a ring of insulating material 13.
The ring of insulating material 13 runs radially around the disc 5
at a fixed distance from the center of the disc
[0066] When disc 5 is rotated through the toroidal magnetic field,
the currents generated in the inner and outer portions of the disc
5, which are subjected to the forward and reverse magnetic fields
respectively, flow in opposite directions in the two portions of
the disc.
[0067] In this particular embodiment of a homopolar generator, the
annular coil 7 is surrounded by a core 8 of highly permeable
magnetic material such as soft iron. The iron core 8 further
concentrates the return magnetic field 11 towards coil 7, so that
more of the return field passes through the outer region of disc 5,
thus allowing disc 5 to utilize more of the magnetic field produced
by the annular coil 7.
[0068] A slide arm mechanism 15 is fixed in position above the top
surface of the conductive disc 5, and in a manner whereby the slide
arm 15 extends from the center to the outside of the disc.
[0069] For example, the inner end of slide arm 15 is in close
proximity to drive shaft 6, while the outer end of slide arm 15
extends over the outer rim of disc 5. Electrical current contact
brushes 16, 18 and 19 are located on the underside of slide arm
15.
[0070] Brush 16 collects the current produced on the central
portion of disc 5. An interconnecting slide arrangement between arm
15 and brush 16 allows the position of brush 16, relative to the
top surface of disc 5, to be adjusted by sliding brush 16 along arm
15 until the brush is at the required position on the inner portion
of disc 5.
[0071] Brush 18 collects the current produced on the outer portion
of disc 5. An interconnecting slide arrangement between arm 15 and
brush 18 allows the position of brush 18, relative to the top
surface of disc 5, to be adjusted by sliding brush 18 along arm 15
until the brush is at the required position on the outer portion of
disc 5.
[0072] This arrangement allows fine adjustment of the contact
brushes 16 and 18, until the brushes are at the point of optimum
current on the inner and outer portions respectively of the
conductive disc 5. The contact brushes 16 and 18 can then be locked
in place on the slide arm 15 by using interlocking fixtures mounted
on the brushes and the slide arm respectively.
[0073] It is essential that brushes 16 and 18 make good contact
with the top surface of disc 5, in order to allow efficient
collection of the electric current generated by the homopolar
machine.
[0074] To help provide good conducting properties between the
contact brushes 16 and 18 and disc 5, a liquid metal contact
material could be used on the surface of the disc, and such liquid
metal conducting materials are described in U.S. Pat. No. 5,281,364
by the applicant.
[0075] Another current contact brush 14 makes contact with the
drive shaft 6, and a further contact brush 19 mounted under the
outer end of slide arm 15 makes contact with the outer rim of disc
5. Again it is essential that good electrical contact is made by
brushes 14 and 19 with the drive shaft and the outer rim of the
disc respectively.
[0076] Rotation of shaft 6 by an external motive force rotates disc
5 through the toroidal magnetic field produced by the annular coil
7. This in turn generates electric currents in the inner and outer
portions of disc 5, which are collected by contact brushes 16 and
18.
[0077] Brush 16 and brush 14 are connected to an electrical circuit
17, and brush 18 and brush 19 are connected to an electrical
circuit 20. The two circuits 17 and 20 are connected together,
either in series or in parallel, before the combined current is
finally transmitted from the homopolar generator to the water
electrolysis unit. Means to measure and control the current can be
included in the electric circuit that takes the current from the
homopolar generator to the water electrolysis unit.
[0078] Homopolar generators are compact machines and they can
easily be connected together in multiple combinations, either in
series and/or in parallel, to produce sufficient current to be able
to run similar multiple combinations of water electrolysis units,
which would also be connected together either in series and/or in
parallel.
[0079] Developments in the design of homopolar machines,
superconducting materials and current collection systems have
resulted in homopolar generators becoming much more efficient. For
example, it is not unknown for homopolar generators to have an
efficiency of over 99%.
[0080] A homopolar generator is therefore an effective method of
directly supplying the low voltage, high current needed to operate
a water electrolysis unit. Apart from relatively simple means to
measure and control the current, no other sophisticated commutation
equipment, such as expensive and inefficient transformers and
rectifiers, would be required to alter the current before it was
supplied to the water electrolysis unit.
[0081] Using an enriched oxygen compression ignition engine to
drive the homopolar generator also provides flexibility because
oxygen enrichment allows the engine to combust whatever liquid
fuels, of either fossil or non-fossil origin, are available
locally.
[0082] For example, oxygen enrichment would allow locally available
biofuels, such as vegetable oils, to be burned efficiently in an
engine, as well as petroleum fuel oils. In tropical countries this
would allow palm oil and coconut oil to be used as fuel, while
groundnut oil could be used in sub-tropical regions, and rapeseed
oil, sunflower oil and soybean oil could be used in temperate
zones. Animal fats and waste cooking oil could also be used as
biofuels in an enriched oxygen diesel engine, as could natural
alcohol fermented from locally grown sugar or starch producing
plants.
[0083] This provides a high degree of flexibility for the
integrated renewable energy system. For example, during the day the
engine could be run on say locally available non-fossil biofuels to
generate AC `green` electricity for local supply, while during the
night the engine could be run on either biofuel or petroleum fuel
oil to generate the DC electricity required for the electrolysis of
water.
[0084] When a non-fossil biofuel is used in the engine to produce
hydrogen by water electrolysis, the carbon dioxide released into
the atmosphere from the engine does not have a greenhouse gas
impact on the environment. In contrast, the most widely used
industrial method of manufacturing hydrogen, i.e. the steam
reforming of natural gas, uses a finite, fossil based raw material
and the process therefore produces greenhouse carbon dioxide.
[0085] A further benefit of the proposed system is that when a
fossil fuel, such as petroleum fuel oil, is used in the engine, it
provides a method of converting the hydrocarbon based fuel oil into
valuable hydrogen and oxygen on a scale that is not only practical
but also specifically related to local requirements for renewable
energy.
[0086] Both the oxygen and the hydrogen from the water electrolysis
process would have applications in the integrated renewable energy
system. The oxygen could be used to produce the enriched oxygen
combustion atmosphere for the engine, while hydrogen could be used
as either a clean burning renewable gaseous fuel or as a reactant,
along with oxygen, in fuel cells to produce `green`
electricity.
[0087] The integrated renewable energy system will now be described
with reference to illustrations given in FIGS. 3 and 4.
[0088] In FIG. 3, a compression ignition engine 34 has a drive
shaft coupled to both an AC electrical generator 35 and a DC
homopolar generator 36. In practice the homopolar generator 36
would consist of a multiple combination of homopolar generators,
connected together either in series and/or in parallel, to produce
sufficient current to be able to run a similar multiple combination
of water electrolysis units.
[0089] Liquid fuels for the compression ignition engine would be
stored in a number of fuel storage tanks 20, although only one fuel
tank is shown in FIG. 3. The fuels could be either fossil fuel
oils, such as petroleum fuel oils and waste mineral oils, or
non-fossil biofuels, such as vegetable oils, animal fats, fish
oils, natural alcohol, waste biofuels, waste cooking oil and
mixtures of such materials.
[0090] Fuel from storage tank 20 would be heated and filtered, as
necessary, before being transferred to the fuel injectors of engine
34. The fuel injectors would inject fuel at the appropriate time
into the combustion chambers of the engine.
[0091] The oxygen rich air that comprises the combustion atmosphere
of the engine would be prepared by mixing pure oxygen from storage
tank 21 with normal atmospheric air, using a mixing valve 22 that
would also continually analyse the composition of the enriched
oxygen air.
[0092] For example, the enriched oxygen air would usually contain
between 2% and 6% extra oxygen, i.e. the enriched oxygen air would
typically have a composition of between 23% oxygen, 77% nitrogen
and 27% oxygen, 73% nitrogen, depending on how difficult the fuel
was to burn in a compression ignition engine. Fuels that are very
difficult to burn in an engine may well need even more than 6%
extra oxygen in the combustion atmosphere of the engine.
[0093] The oxygen rich air would be introduced into a cylinder
inside the engine through the air inlet valve, and the air would
then be compressed by a piston travelling up the cylinder. A fuel
injector would inject fuel into the combustion chamber of the
cylinder, and the fuel would ignite by the heat of compression. The
piston would then be forced back down cylinder.
[0094] The motion of the pistons up and down the cylinders in the
engine would be transferred as a rotary motion to the drive shaft
of the engine, and the drive shaft would be coupled to both an AC
generator 35 and a homopolar generator 36. The drive shaft would be
capable of being readily engaged to or disengaged from the AC
generator 35 and the DC homopolar generator 36 respectively, so
that the drive shaft would only be coupled to one generator at a
time.
[0095] When driving the AC generator 35, the AC electricity
produced by the genset would be supplied to an electric circuit
that would distribute the electricity to meet local demands.
Preferably a non-fossil biofuel would be used when generating the
AC electricity so that `green` electricity was produced for local
use.
[0096] When driving the homopolar generator 36, the DC electricity
produced by the genset would be supplied by an electric circuit to
a water electrolysis unit 23. Either non-fossil biofuel or fossil
petroleum fuel could be used to generate the DC electricity.
[0097] The current from a single homopolar generator would
typically have a voltage of about 2 volts and a power density of
about 5000 amps/m.sup.2 or more, whilst the energy consumption of a
typical electrolysis unit would be about 4 kWh/m.sup.3 of hydrogen
produced.
[0098] For ease of illustration, the water electrolysis unit 23 in
FIG. 3 consists of only four electrolysis cells. In practice, a
commercial electrolysis unit may well contain several hundred
electrolysis cells, and a typical electrolysis unit could have an
hourly output of over 400 m.sup.3 of hydrogen and over 200 m.sup.3
of oxygen.
[0099] By combining a number of homopolar generators together, in
series and/or in parallel as appropriate, sufficient current could
be produced to be able to operate a similar multiple combination of
electrolysis units, also connected together either in series and/or
in parallel, in order to meet the specific demands for hydrogen and
oxygen.
[0100] The electrolysis unit illustrated in FIG. 3 is a schematic
representation of a typical low temperature, low pressure
electrolysis system, of the type manufactured, for example, by
Norske Hydro.
[0101] Each cell would have a cathode 24, made from say low carbon
steel, and an anode 25, made from say nickel plated low carbon
steel.
[0102] The electrolyte in each cell would typically be a 25%
solution of potassium hydroxide, and there would be means to
continually replenish the cells with fresh water. Application of
the electric current produced by the homopolar generator 36 to the
electrolysis cells produces hydrogen at the cathodes of the cells
and oxygen at the anodes.
[0103] In order to keep the hydrogen and oxygen separate from each
other, each cell would include a separator 26 manufactured, for
example, from woven asbestos cloth.
[0104] Hydrogen from the cathodes of the cells is collected in a
discharge tube, which would deliver the hydrogen to a packaging
plant (not shown in FIG. 3) where the hydrogen would either be
compressed and packed into cylinders or be liquefied and packed
into tanks.
[0105] Oxygen from the anodes is collected in a separate discharge
tube 30 and the oxygen is delivered to storage tanks 21, although
only one storage tank is illustrated in FIG. 3.
[0106] The oxygen cycle in the integrated energy system would then
be complete, because oxygen from tank 21 would be used to produce
the enriched oxygen combustion atmosphere for the engine 34 that
powers the system. Excess oxygen in tanks 21 would be delivered to
a packaging plant (not shown in FIG. 3) where the oxygen would
either be compressed and packed into cylinders or be liquefied and
packed into tanks.
[0107] In the integrated renewable energy system illustrated in
FIG. 3, oxygen enrichment would enable the compression ignition
engine 34 to burn a variety of fossil and non-fossil fuel oils. The
exhaust gas from the engine would therefore need to be cleaned to
an appropriate degree before the exhaust gas was released to the
atmosphere, and the abatement required would mainly be dependent on
the type of fuel being burned in the engine.
[0108] A typical engine abatement system is described in FIG. 4. In
FIG. 4, the compression ignition engine 34 is again coupled to the
AC generator 35 and the DC homopolar generator 36. Fuels are stored
in fuel tanks 37, although only one tank is shown in FIG. 4, and an
enriched oxygen combustion atmosphere is supplied to the
engine.
[0109] The condition of the exhaust gas emitted from engine 34 will
be dependent on the particular fuel being burned in the engine.
[0110] For example, the exhaust gas from the enriched oxygen
combustion of either a good quality low sulphur petroleum gas oil
or a virgin non-fossil biofuel would contain very little carbon
monoxide, volatile organic compounds, sulphur dioxide, heavy metals
or particulates. In this instance, NOx abatement with urea by a
catalytic reduction unit 27 would probably be the only treatment
required before the exhaust gas was in a suitable state to be
released to the atmosphere through the chimney 33.
[0111] Other petroleum based fuel oils, such as medium and heavy
fuel oils, can contain sulphur and particulate material, and these
particular fuel oils are also more difficult to burn than gas oil,
even with oxygen enrichment. The exhaust gas from the enriched
oxygen combustion of medium/heavy fuel oil would therefore
definitely need NOx abatement in catalytic reduction unit 27 and
probably filtration in filter 32 to remove particulates.
[0112] Further abatement will depend on an analysis of the exhaust
gas, and could possibly include catalytic oxidation in unit 28, to
reduce carbon monoxide and volatile organic compounds, and acid gas
neutralisation in unit 31.
[0113] The combustion of waste based fuels, including waste mineral
oil and waste cooking oil, is becoming much more strictly
controlled, and very stringent emissions limits are being imposed
on waste combustion processes under regulations such as the EU
Waste Incineration Directive. When burning waste based fuels, and
particularly waste mineral oils, the exhaust gas from the engine
would probably therefore need full emission abatement, i.e. de-NOx
in unit 27, catalytic oxidation in unit 28, neutralisation in unit
31 and filtration in unit 32.
[0114] The engine combustion system illustrated in FIG. 4 is a
combined heat and power (CHP) process where the exhaust gas passes
through a boiler 29 in order to recover the waste heat in the
exhaust gas. The steam from boiler 29 could be used to drive a
steam turbine 38, which would produce more AC electricity for local
use, and/or the steam could be used for local heating. The size of
the compression engine, and hence the amount of heat available in
the engine exhaust, would determine whether or not a steam boiler
in the exhaust would be a practical proposition. Heat is also
available from the engine cooling system and this source of waste
heat can also be used for local heating purposes.
[0115] The integrated renewable energy system illustrated in FIGS.
3 and 4, which is based on using a compression ignition engine to
generate heat and power for local needs and also to supply the
specific current required by a water electrolysis process, can be
used in a number of different ways, depending on the fuels
available locally.
[0116] Because the engine incorporates an enriched oxygen
combustion atmosphere, the engine is able to efficiently and
cleanly burn locally available fuels of either fossil or non-fossil
origin.
[0117] For example, when burning non-fossil biofuels, the engine
can be used to drive an AC electrical generator to produce `green`
electricity for local needs, and the waste heat from the combustion
process can also be recovered for local use.
[0118] When burning fossil petroleum fuel oils, the engine can be
used to drive a DC homopolar generator to produce the current
required for the water electrolysis process, whilst the heat
produced from the combustion of the petroleum fuel oil can still be
recovered for local use.
[0119] With full exhaust gas abatement, the system can even be used
to safely incinerate waste oils. For example, when burning waste
mineral oil the engine can drive the homopolar generator to produce
the current required to electrolyse water. The system then acts as
a method of converting potentially polluted waste mineral oil into
clean burning, renewable hydrogen fuel, whilst the heat from the
combustion process can still be recovered for local use.
[0120] The integrated energy system can therefore produce a number
of valuable product streams, including a supply of `green`
electricity from the AC generator when non-fossil biofuels are
combusted in the engine, a supply of valuable hydrogen and oxygen
from the water electrolysis process, and a supply of heat from the
engine combustion process.
[0121] Both the hydrogen and the oxygen produced by the
electrolysis of water are valuable products that have potential
applications in a variety of end uses. For example, hydrogen is a
unique energy resource with particular potential as a clean burning
transport fuel, while oxygen is already used in a number of
industrial applications including combustion processes, chemical
processes, aerobic fermentation, water purification and medical
uses. Hydrogen and oxygen can also be used together as the
reactants in a fuel cell to produce clean, `green` electricity.
[0122] The proposed integrated energy system is especially aimed at
supplying local heat and power requirements in a low carbon, energy
efficient manner. Because the integrated energy system is based on
being able to burn different fuels of either fossil or non-fossil
origin, the system could be of particular benefit for remote
locations, such as rural or island economies, as they would no
longer need to solely rely on petroleum fuel oils for their local
energy requirements.
[0123] Transport applications for the hydrogen produced from the
system would similarly be aimed at locally based transport systems
that could, for example, use specially adapted vehicles for short
distance operations, such as local public transport or local
distribution services. The vehicles could then be supplied with
hydrogen fuel from specialised locally based storage depots.
[0124] While the present invention has been illustrated and
described with respect to a particular embodiment thereof, it
should be appreciated by those of ordinary skill in the art that
various modifications to this invention may be made without
departing from the spirit and scope of the present invention.
* * * * *