Field of the Invention

The present invention relates to heat and electricity generating apparatus, in particular to a boiler unit suitable for use in a residential or small-scale building and arranged to generate electricity in addition to heat.

Background of the Invention

Boilers for use in residential or small-scale buildings are known. Typically, a boiler unit houses a burner assembly arranged to ignite and burn a liquid or gaseous fuel to generate heat, which is then transferred to a heat-conveying medium, such as water, through a heat exchanger. Water heated by a boiler may be circulated through radiators of a central heating system or made available for consumer usage. In a domestic or office environment, it is advantageous for a boiler unit to also generate electricity, for powering appliances or for sale to the mains electricity grid. Typically, the boiler unit itself will use electricity, to power such components as a fuel delivery pump, an igniter and system control circuitry.

Cogeneration or Combined Heat and Power (CHP) systems are known that are arranged to simultaneously generate heat and electricity. For example, it is known for heat emitted by a power station as a by-product of electricity generation to be used in a local or district heating system. This use of waste heat serves to increase the efficiency of the plant and reduce negative impact on the environment. It is also known for boilers to generate electricity as a by-product of producing heat.

International Patent Publication No. WO 99/23422 discloses a "Heating System Utilizing A Turbo-Machine For Self-Sustained Operation". The disclosed system uses the energy of the hot exhaust gas of a fuel after its combustion in a burner assembly to power a turbo-machine mounted on a shaft having a centrifugal air compressor that delivers a flow of air for sustaining combustion of the fuel. An electric motor-generator is coupled to the shaft of the turbo-machine for the purpose of starting the turbo-machine and bringing it up to speed for operation in a self-sustained mode. When the system has reached a self- sustaining operation, excess energy in the exhaust gas can be converted to electric energy by changing the motor-generator to act as a generator through the use of appropriate electronic controls. This electric power can be used for powering other electrical devices in the heating system, and for recharging the battery used for starting the heating system.

It is desirable to provide heat and electricity generating apparatus suitable for use in residential or small-scale buildings that, generates electricity as a by- product of providing heat, that offers higher efficiency and lower polluting emissions.

It is further desirable to provide heat and electricity generating apparatus suitable for use in residential or small-scale buildings of differing sizes. Summary of the Invention

According to a first aspect, there is provided heat and electricity generating apparatus, comprising: a centrifugal air compressor having an inlet and an outlet, a turbo-expander having an inlet and an outlet, an electric generator, a high- pressure combustor having an inlet and an outlet, a first heat exchanger having a first conduit and a second conduit, and a second heat exchanger having a first conduit and a second conduit; said air compressor, said turbo-expander and said electric generator are operatively connected by a rotatable drive shaft, the outlet of said centrifugal air compressor is in fluid communication with the first conduit of said first heat exchanger, the first conduit of said first heat exchanger inlet is in fluid communication with the inlet of said high-pressure combustor, and the outlet of said high-pressure combustor is in fluid communication with the inlet of said turbo-expander; the outlet of said turbo-expander is in fluid communication with the second conduit of said first heat exchanger, and the second conduit of said first heat exchanger is in fluid communication with the first conduit of said second heat exchanger, said second conduit of the second heat exchanger arranged to receive a heat-conveying fluid; wherein the outlet of said high-pressure combustor is in fluid communication with the second conduit of said first heat exchanger, and said heat and electricity generating apparatus further comprises a diverter gate operable to determine the proportion of combustion product gas issued by the high-pressure combustor that is delivered to the turbo-expander and the proportion of combustion product gas issued by the high-pressure combustor that is delivered directly to the second conduit of said first heat exchanger.

In an embodiment, the position of said diverter gate is manually adjustable and is also automatically adjustable by means of an actuator operating under the control of a control unit.

In an embodiment, the diverter gate is operable to divert between 0% and up to approximately 30% of the combustion product gas issued by the high-pressure combustor directly to the second conduit of said first heat exchanger instead of to the turbo-expander.

The heat-conveying fluid may be circulating fluid of a central-heating system or a hot water supply system.

According to a second aspect, there is provided a boiler system for use in a residential or small-scale building, comprising heat and electricity generating apparatus according to the first aspect.

Brief Description of the Drawings

For a better understanding of the invention and to show how the same may be carried into effect, there will now be described by way of example only, specific embodiments, methods and processes according to the present invention with reference to the accompanying drawings in which:

Figure 1 shows a boiler unit comprising heat and electricity generating apparatus;

Figure 2 is a schematic view of heat and electricity generating apparatus ; and

Figure 3 shows steps in an advantageous stage of heat transfer within of heat transfer within the operating process of heat and electricity generating apparatus according to the invention.

Figure 4 is a schematic view of an alternate embodiment of the heat and electricity generating apparatus wherein an additional diverter gate is employed to redirect some of the combustion product gas post-turbo expander directly to the second heat exchanger.

Figure 5 is a schematic view of an alternate embodiment of the heat and electricity generating apparatus wherein the first heat exchanger is eliminated completely.

Detailed Description

There will now be described by way of example a specific mode contemplated by the inventor. In the following description numerous specific details are set forth in order to provide a thorough understanding. It will be apparent however, to one skilled in the art, that the present invention may be practiced without limitation to these specific details. In other instances, well- known methods and structures have not been described in detail so as not to unnecessarily obscure the description.

Figure 1 A boiler unit 101 is shown in Figure 1 , in a domestic environment 102. The boiler unit 101 is arranged to provide heat for transfer to a water flow, the heated water then being circulated through radiators of a central heating system or supplied to a water tank to provide hot water for consumer usage. Advantageously, and as will be described in detail below, the boiler unit 101 comprises apparatus according to the present invention that is arranged to provide heat from high-pressure combustion and that is also arranged to generate electricity.

The provision of heat and electricity generating apparatus suitable for use in residential or small-scale buildings provides several benefits. The local production of electricity can replace electricity that would otherwise be drawn from the main electric power generation network (mains electricity grid). This serves to reduce consumer electricity usage charges, reduce maintenance costs of the mains electricity grid, and contribute resource to the overall electricity generation capability of an area.

The high-pressure combustion performed by the heat and electricity generating apparatus provides further advantages. Combustion under high pressure is thermodynamically more efficient than combustion under atmospheric pressure, requiring less fuel to be used in the combustion reaction. In turn, this increased fuel efficiency leads to fuel costs savings and reduced emissions of environmental pollutants, in particular carbon dioxide (CO ₂ ) and mono-nitrogen oxides (generally referred to as NO _x ) that are contributors to global-warming.

The heat and electricity generating apparatus of the boiler unit 101 is advantageously configured to provide a degree of control over the power to heat output ratio and operation during periods of transient operating conditions.

Figure 2

Figure 2 is a schematic view of heat and electricity generating apparatus 201 according to the present invention, shown in a heating system 202 suitable for a residential building. The heat and electricity generating apparatus 201 is arranged to provide heat from high-pressure combustion and also to be able to generate electricity.

The heat and electricity generating apparatus 201 comprises a centrifugal air compressor 203, a turbo-expander 204 and an electric generator 205, which are operatively connected by a rotatable drive shaft 206. The heat and electricity generating apparatus 201 further comprises a high-pressure combustor 207, a first heat exchanger 208 and a second heat exchanger 209.

The centrifugal air compressor 203 has an inlet for admitting air from the atmosphere, and an outlet for issuing compressed air. The first heat exchanger 208 has a first conduit 210 and a second conduit 21 1 . The outlet of the centrifugal air compressor 203 is in fluid communication with the first conduit 210 of the first heat exchanger 208.

The high-pressure combustor 207 has an inlet for admitting combustion air, a fuel port in fluid communication with a fuel source 212 for admitting a fuel, an igniter for igniting a fuel and combustion air mixture, and an outlet for issuing combustion product gas. Any suitable fuel may be used in the high-pressure combustor, such as natural gas, diesel or oil. The first conduit 210 of the first heat exchanger 208 inlet is in fluid communication with the inlet of the high-pressure combustor 207.

The turbo-expander 204 has an inlet for admitting gas and an outlet for admitting expanded gas. The inlet of the turbo-expander 204 receives combustion product gas issued by the high-pressure combustor 207. The outlet of the turbo-expander 204 is in fluid communication with the second conduit 21 1 of the first heat exchanger 208.

The second heat exchanger 209 has a first conduit 213 and a second conduit 214. The second conduit 21 1 of the first heat exchanger 208 is in fluid communication with the first conduit 213 of the second heat exchanger 209. The second conduit 214 of the second heat exchanger 209 is arranged to receive a heat-conveying fluid. In the shown heating system 202, the heat-conveying fluid is circulating fluid of a hot water system 215. The circulating fluid may be water, oil, helium or any other fluid of a hot water system or central heating system. The first conduit 213 of the second heat exchanger 209 is in fluid communication with an exhaust to atmosphere. The hot water system 215 is fluidly connected to a water tank 216 and/or central-heating system 217.

The electric generator 205 is electrically connected to interface circuitry 218, which is electrically connected to a rechargeable electricity storage cell 219 and/or the mains electricity grid 220. The electric generator 205 is arranged to convert mechanical power generated by the rotation of the turbo-expander 204 into electrical power. The electric generator 205 is also preferably arranged to provide start-up power for initial operation of the heat and electricity generating process.

The rotatable drive shaft 206 is provided with bearings, indicated at 221 , to facilitate smooth and balanced rotation. The rotatable drive shaft 206 may be provided with any of the following bearing types: hydrodynamic, air, magnetic, ball. In the shown arrangement, the electric generator 205 is located between the centrifugal air compressor 203 and the turbo-expander 204. It is found that locating the electric generator 205 in the middle of the centrifugal air compressor 203 and the turbo-expander 204 provides superior rotor dynamic behaviour and reduces the number of bearings 221 required when compared to alternative arrangements.

Advantageously, the heat and electricity generating apparatus 201 is arranged such that, in operation, combustion product gas received and subsequently issued by the turbo-expander 204 passes through the first heat exchanger 208, to heat compressed air issued by the centrifugal air compressor 203 prior to entry into the high-pressure combustor 207, and then passes through the second heat exchanger 209, to heat the fluid of the hot water system 215. In this way, the hot combustion product gas is firstly used to transfer heat to the combustion air prior to entry into the high-pressure combustor and then subsequently used to transfer to a heat-conveying fluid. Using the hot combustion product gas from the high-pressure combustor to pre-heat the combustion air increases the efficiency of the combustion. This leads to a reduction in the fuel used in the combustor and, in turn, a reduction in undesirable post-combustion emissions. Beneficially, the heat and electricity generating apparatus 201 comprises a diverter gate 222 arranged to receive the combustion product gas issued by the high-pressure combustor 207. The diverter gate 222 is operable to deliver the combustion product gas issued by the high-pressure combustor 207 to either the inlet of the turbo-expander 204 or to the second conduit 21 1 of the first heat exchanger 208. The diverter gate 222 allows the power to heat ratio of the heat and electricity generating apparatus 201 to be controlled. To achieve a higher power to heat ratio, the diverter gate 222 is positioned to deliver the combustion product gas issued by the high-pressure combustor 207 to the inlet of the turbo- expander 204. To achieve a lower power to heat ratio the diverter gate 222 is positioned to deliver combustion product gas issued by the high-pressure combustor 207 to the second conduit 21 1 of the first heat exchanger 208.

The functionality of the diverter gate 222 advantageously allows the heat and electricity generating apparatus 201 to be installed within residences or buildings of different sizes. For example, the same heat and electricity generating apparatus 201 can be suitable for installation within a 2-bedroomed residential building (with a lesser heat output requirement) or within a 5-bedroomed residential building (with a greater heat output requirement); the diverter gate 222 is set at the time of installation of the heat and electricity generating apparatus 201 within the home to determine the proportion of combustion product gas issued by the high-pressure combustor 207 that is diverted away from the turbo-expander 204 to the second conduit 21 1 of the first heat exchanger 208 as appropriate for the size of the residential building. The diverter gate 222 may be configured for manual operation, for initial set up.

The arrangement of the diverter gate 222 within the heat and electricity generating apparatus 201 beneficially allows for the air mass flow through the turbo-expander 204 at any moment in time to be adjusted. To ensure self- sustaining operation of the heat and electricity generating apparatus 201 , the flow through the centrifugal air compressor 203 and the turbo-expander 204 should match. During periods of transient operating conditions, such as during start-up of the heat and electricity generating apparatus 201 , the diverter gate 222 can be operated to prevent undesirable occurrences, such as choking or surging of the centrifugal air compressor 203 that can occur when the flow through the centrifugal air compressor 203 and the flow through the turbo-expander 204 are mismatched. The diverter gate 222 may be configured for automatic operation, for adjustment during use.

In an embodiment, the mechanical diverter gate 222 is manually adjustable, for setting the power to heat ratio of the heat and electricity generating apparatus 201 , and is also automatically adjustable by means of an actuator operating under the control of a control unit, for the purpose of transient control of the turbo- expander 204. The diverter gate 222 may be mechanically linked to the housing of the turbo-expander, with an adjustment element provided that extends from the turbo-expander housing and is manually operable to adjust the position of the diverter gate 222. The actuator may be a pneumatic operated actuator, an electrically operated actuator or a hydraulically operated actuator. The control unit is configured to adjust the position of the diverter gate 222 during periods of transient operating conditions and during off-grid usage. The control unit is programmed with control logic relating to the following aspects of the heat and electricity generating apparatus:

- Electric power requirement of the centrifugal air compressor and excess torque requirement during start-up. The control unit is programmed to adjust the diverter gate towards providing optimal conditions during the start-up period.

- Electric power generation during off-grid operation. The control unit is programmed to adjust the diverter gate towards matching the electric power generated to the consumer power demand without drawing power from the mains electricity grid.

- Maintaining optimal operation of turbo-expander. The control unit is programmed to adjust the diverter gate towards achieving the optimal mass flow rate through the turbo-expander for the speed of the turbo-expander.

The diverter gate 222 is set at a default position during the installation of the heat and electricity generating apparatus 201 . When the boiler unit is switched on, the diverter gate 22 becomes operational under the control of the control unit. In an embodiment, the diverter gate 222 is operable to adjust up to approximately 30% of the mass flow rate through the turbo-expander 204. Such as O, 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28 or 29%.

In an embodiment, the diverter gate 222 allows the heat and electricity generating apparatus 201 to provide a power output range from zero (providing heat only) to approximately 120% of the rated power setting.

Features of an example will now be described. The centrifugal air compressor has a mass flow rate in the range 0.01 -0.2 kg/s, an outlet air temperature in the range 400-600 K, and an outlet air pressure in the range 2-6 bar. The inlet temperature of the first conduit of the first heat exchanger (receiving air from the centrifugal air compressor) is in the range 400-600 K, and the inlet temperature of the second conduit of the first heat exchanger (receiving combustion product gas from the turbo-expander) is in the range 800-900 K. The pressure loss within the first heat exchanger is approximately 5%. The outlet temperature of the first conduit of the first heat exchanger (issuing combustion inlet air to the high-pressure combustor) is in the range 450-800 K, and the outlet temperature of the second conduit of the first heat exchanger (issuing combustion product gas to the first conduit of the second heat exchanger) is in the range 550- 700 K. The high-pressure combustor has a combustion air inlet temperature in the range 450-800K and a combustion product gas outlet temperature in the range 900-1300 K. The inlet temperature of the turbo-expander is in the range 900-1300 K, and the outlet temperature of the turbo-expander (issuing combustion product gas to the second conduit of the first heat exchanger) is in the range 800- 900 K and the outlet pressure is in the range 1 -1 .5 bar. The inlet temperature of the first conduit of the second heat exchanger (receiving air from the centrifugal air compressor) is in the range 550-700 K, and the outlet temperature of the first conduit of the second heat exchanger (exhaust to atmosphere) is approximately 350 K. The rotational speed of the turbo-expander, centrifugal air compressor, rotatable drive shaft and electric generator is in the range 50,000-250,000 RPM. Features of an example illustrating the effect of operation of the diverter gate will now be described. When the unit mass flow through the turbo-expander at full operating speed is 0.1 kg/s, and the diverter gate is so open as to divert 0.03 kg/s of the combustion product gas issued by the high-pressure combustor to the second conduit of the first heat exchanger instead of being delivered to the turbo- expander, the heat and electricity generating apparatus is producing zero electricity output but is self-sustaining to provide heat only. When the unit mass flow through the turbo-expander at full operating speed is 0.1 kg/s, and the diverter gate is so fully closed as to divert 0.00 kg/s of the combustion product gas issued by the high-pressure combustor to the second conduit of the first heat exchanger instead of being delivered to the turbo-expander, the heat and electricity generating apparatus is producing maximum electricity output.

The first heat exchanger (combustion air pre-heater) transfers heat from the hot combustion product gas to the combustion air. The second heat exchanger (water system heater) transfers heat from the hot combustion product gas to water. The electric generator is electrically connected to an electric rectifier and then to a grid interactive inverter (grid-tie inverter), to prepare the generated electricity for local use or supply to the mains electricity grid. The electric generator can also generate power for electrically-powered elements of the system.

Figure 3

Figure 3 shows steps in an advantageous method of heat transfer 301 performed during operation of heat and electricity generating apparatus according to the invention.

At step 302, combustion product gas issued from a high-pressure combustor is passed to a diverter gate, the position of which determines the proportion (some or all) of the combustion product gas that will be passed to a turbo-expander and the proportion (some or none) of the combustion product gas that will be passed directly to a first (air-to-air) heat exchanger. At step 303, combustion product gas is passed to the turbo-expander, and the combustion product gas issued from the turbo-expander is then passed to the first (air-to-air) heat exchanger. At step 302, if it is determined by the position of the diverter gate that some of the combustion product gas issued from the high-pressure combustor is to bypass the turbo- expander, then a proportion of the combustion product gas is passed directly to the first (air-to-air) heat exchanger. At step 304 the combustion gas is passed through the first (air-to-air) heat exchanger, to elevate the temperature of combustion air before entry into the high-pressure combustor. Thus, the combustion product gas issued from a high-pressure combustor is passed through the first (air-to-air) heat exchanger, whether delivered via the turbo- expander or delivered directly thereto.

At step 305, combustion product gas issued from the first air-to-air heat exchanger is passed through a second (air-to-fluid) heat exchanger, to heat a heat-conveying fluid. This method of transferring heat using the hot combustion product gas improves the overall efficiency of the heat and electricity generating apparatus.

Figure 4

Figure 4 is a schematic view of heat and electricity generating apparatus 201 according to the present invention, similar to that shown in Figure 2, shown in a heating system 202 suitable for a residential building. For consistency, numerals remain the same throughout.

In this embodiment the heat and electricity generating apparatus comprises an additional diverter gate (412) located after the turbo-expander (204). The purpose of the additional diverter gate is to redirect a portion of the combustion product gas directly to the second (air-to-fluid) heat exchanger.

In one embodiment the additional diverter gate is operable to divert 0 to 30% of the combustion product gas to the first conduit of the second heat exchanger. Such as 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28 or 29%.

Advantageously, redirecting a portion of the combustion product gas directly to the second heat exchanger provides a more efficient apparatus. Advantageously, inclusion of the additional diverter gate provides apparatus that use less energy. The additional diverter gate thus provides a more efficient method of transferring heat within a heating system. Figure 5

Figure 5 is a schematic view of heat and electricity generating apparatus 201 according to the present invention, similar to that shown in Figure 2, shown in a heating system 202 suitable for a residential building. For consistency, numerals remain the same throughout.

In this embodiment the first (air-to-air) heat exchanger is eliminated. The combustion product gas from the diverter gate is either directed directly into the first conduit of the second (air-to-fluid) heat exchanger or to the turbo-expander (204) and then to the first conduit of the second heat exchanger.

Furthermore, because the first heat exchanger is eliminated, air from the compressor is fed directly into the combustor without passing through a heat exchanger.

Advantageously eliminating the first heat exchanger provides a more efficient apparatus and a more efficient method of transferring heat within a heating system.

A further advantage is that the apparatus is cheaper to manufacture and smaller due to it comprising fewer parts.

The skilled person will appreciate that features of the embodiment described herein can be combined without deviating from the spirit of the invention.

A boiler system comprising the heat and electricity generating apparatus described herein is suitable for use in a residential or small-scale building and provides several advantages, including reduced electricity bills and reduced harmful emissions. The heat and electricity generating apparatus described herein is adaptable to buildings of different sizes and has improved operational features. In one embodiment the first heat exchanger is an air-to-air heat exchanger. That is, it uses air or gas in a first conduit to transfer heat to second conduit of air or gas.

In one embodiment the second heat exchanger is an air-to-fluid heat exchanger. That is, it uses air or gas in a first conduit to transfer heat to a second conduit of fluid.

In the context of this specification "comprising" is to be interpreted as "including".

Aspects of the invention comprising certain elements are also intended to extend to alternative embodiments "consisting" or "consisting essentially" of the relevant elements.

Where technically appropriate, embodiments of the invention may be combined.

Embodiments are described herein as comprising certain features/elements. The disclosure also extends to separate embodiments consisting or consisting essentially of said features/elements.

Technical references such as patents and applications are incorporated herein by reference.

Any embodiments specifically and explicitly recited herein may form the basis of a disclaimer either alone or in combination with one or more further embodiments.

PARAGRAPHS

1 . Heat and electricity generating apparatus, comprising:

a centrifugal air compressor having an inlet and an outlet,

a turbo-expander having an inlet and an outlet,

an electric generator,

a high-pressure combustor having an inlet and an outlet,

a second heat exchanger having a first conduit and a second conduit;

said air compressor, said turbo-expander and said electric generator are operatively connected by a rotatable drive shaft, the outlet of said centrifugal air compressor is in fluid communication with the inlet of said high-pressure combustor, and

the outlet of said high-pressure combustor is in fluid communication with the inlet of said turbo-expander;

the outlet of said turbo-expander is in fluid communication with the first conduit of said second heat exchanger, said second conduit of the second heat exchanger arranged to receive a heat-conveying fluid;

wherein the outlet of said high-pressure combustor is in fluid communication with the first conduit of said second heat exchanger, and said heat and electricity generating apparatus further comprises a diverter gate operable to determine the proportion of combustion product gas issued by the high-pressure combustor that is delivered to the turbo-expander and the proportion of combustion product gas issued by the high-pressure combustor that is delivered directly to the first conduit of said second heat exchanger.

2. Heat and electricity generating apparatus as described in paragraph 1 , wherein the position of said diverter gate is manually adjustable.

3. Heat and electricity generating apparatus as described in paragraph 1 or paragraph 2, wherein the position of said diverter gate is automatically adjustable by means of an actuator operating under the control of a control unit.

4. Heat and electricity generating apparatus as described in paragraph 3, wherein the actuator is one of: a pneumatic operated actuator, an electrically operated actuator, a hydraulically operated actuator.

5. Heat and electricity generating apparatus as described in any preceding paragraph, wherein the diverter gate is operable to divert between 0% and up to approximately 30% of the combustion product gas issued by the high- pressure combustor directly to the second conduit of said first heat exchanger instead of to the turbo-expander. Heat and electricity generating apparatus as described in paragraph 1 , wherein said heat-conveying fluid is circulating fluid of a central-heating system or a hot water supply system. Heat and electricity generating apparatus as described in any preceding paragraph, wherein said high-pressure combustor has a fuel port in fluid communication with one of: a gas fuel source, a liquid fuel source. Heat and electricity generating apparatus as described in any preceding paragraph, wherein said rotatable drive shaft is provided with one of the following bearing types: hydrodynamic, air, magnetic, ball. Heat and electricity generating apparatus as described in paragraph 1 , wherein said electric generator is electrically connected to a mains electricity grid. . Heat and electricity generating apparatus as described in any preceding paragraph, wherein said electric generator is electrically connected to a rechargeable electricity storage cell. . A boiler system for use in a residential or small-scale building, comprising heat and electricity generating apparatus as described in paragraph 1 .