US20100300099A1

US20100300099A1 - Air-medium power system

Info

Publication number: US20100300099A1
Application number: US12/407,519
Authority: US
Inventors: Moxian Chen
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-05-27
Filing date: 2009-05-27
Publication date: 2010-12-02

Abstract

A system and method for generating power using air as the working medium. External air is compressed by an air compressor and heated by a heat exchanger and then used to cause rotation of an air turbine. The air is then mixed with fuel in a combustion chamber to allow for combustion. The resulting combustion gas is used by the heat exchanger to heat the incoming external air.

Description

FIELD OF THE INVENTION

This invention relates to a new thermo power generation system with air as the energy transfer medium, which could be applying for different fuel, saving water, and highly effective.

BACKGROUND OF THE INVENTION

Since the 1950s, with industrialization and an increase in the different modes of available transportation, global energy consumption has gone up significantly. It is projected that energy consumption will continue to increase with more development in developing countries and the increase in global population.
Increased fossil fuel usage and low energy efficiency cause significant environmental problems such as global warming, acid rain, and smog. Energy-efficient power plants will help to alleviate these environmental problems and improve the habitat.
Existing thermo power generation systems include internal combustion engines and external combustion engines. Examples of internal combustion engines include gasoline (Otto) engines, diesel engines, and gas (Stirling) engine. Examples of external combustion engines include gas turbines, steam turbines, and jet engines. Small power stations usually employ internal combustion engines while larger power plants usually employ external combustion engines.
Gasoline (Otto) engines take gasoline as the fuel and use electric ignition to ignite the fuel. The rotational speed of the engine generally is between 3000 and 6000 RPM, sometimes reaching as high as 10,000 RPM. Power capacity ranges from several hundreds watts to several hundred kilowatts. The maximum possible thermal efficiency for the engine is around 60%. Unfortunately, the emissions from gasoline engines can be very detrimental to the environment.
Diesel engines take diesel oil as the fuel, with the fuel being ignited by compressed air. Combustion occurs because of the high temperature of the compressed air. The rotational speed of a diesel engine is generally between 100 and 6000 RPM. The power capacity ranges from several kilowatts to several thousand kilowatts. The maximum possible thermal efficiency for diesel engines is around 63%.
Gas (Stirling) engines use coal gas, natural gas or some other combustible gases as the fuel. The Stirling engine uses electric ignition, or injects diesel oil for ignition by compression. The maximal possible thermal efficiency for the engine is around 58%.
Internal combustion engines like diesel engines or Otto engines have relatively higher energy efficiency and heat transfer efficiency, but they cannot combust with solid fuel.
The gas turbine is another mechanical system that produces power. The rotational speed of gas turbines may reach as high as several thousand RPM. Gas turbines may operate on an open cycle or on a closed cycle. The maximal possible thermal efficiency for the regenerative gas turbine is around 58%.
The steam turbine transforms heat energy in steam to mechanical energy. The steam turbine combined with a boiler and condenser is widely used in large-scale power plants because it can burn with solid fuel such as coal or firewood but its overall thermodynamic efficiency and heat transfer efficiency is low. The maximum possible thermal efficiency for the supercritical
Rankine cycle is around 50%. The thermodynamic cycle is dependent on water, or some other fluid, to operate
Therefore, an advanced thermo engine, which can combust all kinds of fuel with high energy efficiency, and under the thermodynamic cycle without other working medium participation, is needed.

SUMMARY OF THE INVENTION

The air medium power system of the present invention is a thermo engine that uses air as the working medium. Its thermodynamic efficiency is able to surpass those of other engines. In addition, the system can use solid, fluid, or gas fuel, and does not require water or other working substances to participate in the circulation. This system therefore has high efficiency, high fuel applicability, succinct structure, rapid start-up, and steady operation.
In one aspect, the invention comprises an air intake for introducing external air, an air compressor for compressing the external air to form compressed air, a heat exchanger for heating the compressed air to form compressed, heated air, an air turbine adapted to receive the compressed, heated air from the heat exchanger, and a combustion chamber adapted to receive air exiting from the air turbine and to combust the air with fuel to produce high-temperature gas. The high-temperature gas is then introduced into the heat exchanger for use in heating the compressed air. The expansion of the compressed, heated air in the air turbine causes the air turbine to rotate.
In another aspect, the air intake comprises an air filter.
In a more particular aspect, the air compressor is an axial-flow compressor. The axial-flow compressor may also comprise a compressor rotor.
In a further aspect, the air turbine comprises a turbine rotor, which may be mechanically connected to the compressor rotor. The air turbine may further comprise a spray nozzle.
In yet another aspect, the heat exchanger is a shell and tube heat exchanger comprising one or more tubes adapted to carry the compressed air. The one or more tubes may travel within the combustion chamber.
In another aspect, the system further comprises an electrical generator connected to the air turbine, wherein the electrical generator is adapted to convert rotation of the air turbine into electrical energy.
In a further aspect, the air turbine is connected to the air compressor, wherein the air compressor is driven by rotation of the air turbine.
In a more particular aspect, the invention further comprises a sensor and a controller connected to the sensor, wherein the controller is adapted to control one or more of the following: the flow of air entering from the air intake and the supply of fuel to the combustion chamber. The sensor may be adapted to monitor one or more of the following properties: the temperature of the air in the system, the pressure of the air in the system, and the flow of air in said system.
In yet another aspect, the invention comprises an air intake for introducing external air, an air compressor for compressing the external air, two or more intermediate sets, wherein each intermediate set comprises one heat exchanger connected to one air turbine, and wherein the first of the intermediate sets is connected to the air compressor and the next of the intermediate sets is connected to the air turbine of the preceding intermediate set, and a combustion chamber. The combustion chamber receives air exiting from the air turbine of the last of the intermediate sets and combusts the air with fuel to produce high-temperature gas, wherein the high-temperature gas is introduced into each of the heat exchangers for use in heating the compressed air.
In a further aspect, the invention comprises the steps of introducing external air through an air intake, compressing said external air with an air compressor to form compressed air, heating the compressed air with a heat exchanger to form compressed, heated air, allowing the compressed, heated air to expand in an air turbine, wherein expansion of the compressed, heated air causes the air turbine to rotate, combusting air exiting from the air turbine with fuel in a combustion chamber to produce high-temperature gas, and introducing the high-temperature gas into the heat exchanger to heat the compressed air.
In a more particular aspect, the step of introducing external air through the air intake further comprises filtering the external air.
In another aspect, the invention further comprises the step of converting rotation of the air turbine into electrical energy by an electrical generator.
The foregoing was intended as a broad summary only and of only some of the aspects of the invention. It was not intended to define the limits or requirements of the invention. Other aspects of the invention will be appreciated by reference to the detailed description of the preferred embodiment and to the claims.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be described by reference to the detailed description of the preferred embodiment and to the drawings thereof in which:

FIG. 1 is a diagram of an ideal single-class air-medium power system in accordance with the invention;

FIG. 2 is a diagram of an ideal dual-class air-medium power system in accordance with the invention;

FIG. 3 is the ideal constant pressure heat addition process diagram of the single-class air-medium power system in accordance with the invention; and

FIG. 4 is the ideal constant pressure heat addition process diagram of the dual-class air-medium power system in accordance with the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Objectives of the present invention are to provide a power system that can use the chemical energy of fuel with high efficiency, surpass the thermodynamic efficiency of existing engines, save water, and provide a power system with high fuel applicability, succinct structure, rapid startup, and steady operation.
With reference to FIG. 1, the air medium power system comprises an air intake 1, an air compressor 2, a heat exchanger 3, an air turbine 4, a combustion chamber 5, and an electrical generator 7. The fresh air in turn flows through the air intake 1, the air compressor 2, the heat exchanger 3, the air turbine 4, and the combustion chamber 5.
Air enters through the air intake 1 and is delivered into the air compressor 2. The air compressor 2 increases the pressure of the air, which is then transferred into the heat exchanger 3. The air in the heat exchanger 3 absorbs energy (from the combustion chamber 5), thereby increasing the temperature of the air. The high-pressure, high-temperature air is then delivered into the air turbine 4, where it is released and in the process, causes the air turbine 4 to turn, which causes the electrical generator 7 to produce electricity. The resulting lower-pressure and lower-temperature air exits the air turbine 4 and enters the combustion chamber 5. The air mixes with fuel in the combustion chamber 5 for complete combustion and produces high-temperature gas. The high-temperature gas flows into the heat exchanger 3 and heats the air going through the heat exchanger 3. The low-temperature air then flows out from the heat exchanger 3 for discharge.
Preferably, the air intake 1 comprises an air filter to remove any particulates from the air before it enters the air compressor 2. In addition, the air compressor 2 of the invention is preferably an axial-flow compressor. After flowing through the air filter of the air intake 1, the pure air current flows into the air compressor 2 continuously. The air is compressed in the air compressor 2, causing the air pressure to increase. The air then flows continuously out from the air compressor 2.
The initial air pressure of the air before entering the air compressor 2 is denoted as p1 and its initial air temperature is denoted as T1. The air compressor 2 preferably comprises a feeder 21, a shrinkage 22, a set of inlet guide blades 23 and rows of stationary blades 26 (both fixed on the shell of the air compressor 2), a compressor rotor 24, rows of working blades 25 (fixed on the compressor rotor 24), and a diffuser 27. The air enters from the air intake 1 into the feeder 21 of the air compressor 2. The air then passes through the shrinkage 22, which causes the air current to even out and to obtain preliminary acceleration. The air flows through the flow channel through the set of inlet guide blades 23, which cause the air current to reorganize into an axial flow. The compressor rotor 24, with the attached working blades 25, rotates in high speed. The air current passes through alternating rows of working blades 25 and stationary blades 26. The rotation of the working blades 25 pushes the air current, causing it to accelerate enormously and transforming the mechanical energy of the spinning working blades 25 to rotational kinetic energy. The stationary blades 26 cause the rotational kinetic energy to be converted to static pressure.
A row of the working blades 25 and a row of the stationary blades 26 constitute a work stage. The air current flows through each work stage continuously and is progressively compressed to increase the air pressure. Finally, the air leaves the air compressor 2 through the diffuser 27, which raises the air pressure further by reducing the speed of air current.
Preferably, the compressor rotor 24 of the air compressor 2 is mechanically connected to a turbine rotor 43 of the air turbine 4. This allows for a reduction in the loss of energy and therefore, increased efficiency.
The pressure of the air leaving the air compressor 2 is denoted as p2, with its air temperature denoted as T2. The compressed air then enters into the heat exchanger 3.
The heat exchanger 3 is preferably a shell and tube heat exchanger comprising a series of arranged metal tubes 31. The exterior shell of the heat exchange 3 is preferably constructed with a heat insulating layer 32 and a protective layer 33. The compressed air from the air compressor 2 travels within the metal tubes 31 and absorbs energy from the hot combustion gas produced in the combustion chamber 5 and which flow over the metal tubs 31. This raises the temperature of the compressed air to a high level through adverse current heat transfer.
The high-temperature, high-pressure air from the heat exchanger 3 flows through a spray nozzle 41 of the air turbine 4, and the hot air current inflates in the spray nozzle 41 and accelerates, forming a high-velocity air current. The high-velocity air current impacts turbine blades 42 of the air turbine 4 and drives the turbine rotor 43. This rotation of the turbine rotor 43 is converted into electrical energy by the electrical generator 7. The air turbine 4 causes the compressed air to inflate stage by stage and output energy until the air pressure is equal to the internal pressure of the combustion chamber 5, which is where the air is discharged into. The air turbine 4 may use a small quantity of energy to drive the air compressor 2, with the remaining energy outputted to drive the electrical generator 7.
In an alternative embodiment, the metal tubes 31 in the heat exchanger 3 may be a part of the combustion chamber 5. The combustion chamber 5 may also burn with different types of fuel (i.e. solid, liquid, or gas). There is no need for water or other substances to participate in the thermo circulation.
A controller 6 may also form part of the system. A sensor 61 connected to the controller 6 collects air temperature, air pressure, and airflow readings and transmits the information to a PLC (programmable logic controller) 62 in the controller 6. The PLC 62 calculates and sends signals to actuators 63 to control the incoming airflow and the supply of fuel.
With reference to the FIG. 2, the present invention may also use a two-stage system wherein a second air turbine 11 and a second heat exchanger 10 are added. In such an embodiment, the air exiting from the air turbine 4 is introduced into the second heat exchanger 10. This heated air is then introduced into the second air turbine 11. After the air has exited the second air turbine 11, it is then mixed with fuel 51 in the combustion chamber 5 for combustion. The resulting high-temperature gas from the combustion is used by the heat exchanger 3 and the second heat exchanger 10 to transfer heat to the air flowing through them. The generator 7 is able to take advantage of both the air turbine 4 and the second air turbine 11 to generate electricity. In addition to having a second air turbine 11 and a second heat exchanger 10, further multi-stage systems are also possible wherein multiple sets of air turbines and heat exchangers are added. These systems achieve further energy balance between the released energy of the burning fuel and the absorbed energy of the hot air.
The work principle of the present invention is that the air flows (in sequence) through the air intake 1, the air compressor 2, the heat exchanger 3, the air turbine 4, and the combustion chamber 5. After flowing through the air intake 1, the air may be filtered by an air filter before being delivered to the air compressor 2. The air compressor 2 increases the air pressure, and pushes the air into the heat exchanger 3. The air in the heat exchanger 3 absorbs energy, thereby elevating the temperature of the air. Then the high-pressure, high-temperature air is delivered to the air turbine 4. The air inflates in the air turbine 4 to the internal pressure in the combustion chamber 5. The inflation of the air moves the turbine rotor 43, allowing the electrical generator 7 to produce electricity. The low-pressure and low-temperature air then enters the combustion chamber 5 and mixes with fuel 51 for complete combustion, producing high-temperature gas. The high-temperature gas flows through the heat exchanger 3 and releases energy to the air in the heat exchanger 3 in air adverse current exothermic. Finally, the low-temperature gas flows out from the heat exchanger 3 for cleaning and discharge.
Because no combustion gas enters into the air compressor 2 and the air turbine 4, internal liquid droplets and solid particles from combustion gas cannot affect the operation of the air compressor 2 and the air turbine 4. Therefore, the present invention can use any type of solid, liquid, or gaseous fuel.
Although the temperature of air discharged from the air turbine 4 after inflation is high, this high-temperature air enters the combustion chamber 5 and is able to increase the fuel gas foundation temperature. This results in a higher combustion gas temperature and a greater heat transfer temperature difference. Therefore, the chemical energy of the fuel 51 can be used effectively and fully. This system is also advantageous in being able to complete the combustion process in low-grade fuel.
Regardless of whether solid, liquid, or gaseous fuel is burned in the combustion chamber 5, the working substance that passes through the air compressor 2 and the air turbine 4 is pure air. The pure air enters into the air turbine 4 after absorbing heat energy in the heat exchanger 3 and inflates in the air turbine 4. This relatively higher temperature air then enters into the combustion chamber 4, where it can increase the fuel gas foundation temperature and obtain a higher combustion gas temperature, thereby obtaining a greater heat transfer temperature difference. The chemical energy of fuel can be used effectively and fully. The present invention also has the advantage of being able to complete the combustion of low-grade fuel.
The present invention's principle of work, under ideal conditions, is based on the following assumptions: the system radiation loss is zero and the friction loss and pressure loss of air is zero when the air passes through the heat exchanger 3. Then, the process in the air compressor 2 of the present invention is an isentropic compression process, the process in the heat exchanger 3 is a constant pressure heat addition process, and the process in the air turbine 4 is an isentropic expansion process.
The isentropic compression process is as below:
With reference to FIG. 3, suppose that the air initial temperature entering into the air compressor 2 of the present invention is T₁, the initial pressure is P₁, the compression ratio is r, and the specific heat ratio is k (this stage is denoted as S₁).
After an isentropic compression (i.e. after the air leaves the air compressor 2, or stage S₂), the air temperature T₂would be:
T ₂ =r ^(k-1) *T ₁
The air pressure P₂would be:
P ₂ =r ^k *P ₁
After a constant pressure heat addition (i.e. after the air leaves the heat exchanger 3, or stage S₃), the air pressure P₃would be:
P₃=P₂
The air temperature would be T₃.
After an isentropic expansion (i.e. after the air leaves the air turbine 4, or stage S₄), the air pressure P₄would be:
P₄=P₁
The air temperature T₄would then be:
$\begin{matrix} T_{4} = {(P_{4} / P_{3})}^{(k - 1) / k} * T_{3} \\ = {(P_{4} / (r^{k} * P_{1}))}^{((k - 1) / k)} * T_{3} \\ = r^{(1 - k)} * T_{3} \end{matrix}$
Again with reference to FIG. 3, suppose that the air volume after the constant pressure heat addition (i.e. after the air leaves the heat exchanger 3) is V₃, the air volume after the isentropic expansion (i.e. after the air leaves the air turbine 4) is V₄. The isentropic expansion ratio E would therefore be:
$\begin{matrix} E = V_{4} / V_{3} \\ = {(P_{3} / P_{4})}^{(1 / k)} \\ = {((r^{k} * P_{1}) / P_{1})}^{(1 / k)} \\ = r \end{matrix}$
Further suppose that the air volume after the isentropic compression process (i.e. after the air leaves the air compressor 2) is V₂. The constant pressure expansion ratio Y would therefore be:
$\begin{matrix} Y = V_{3} / V_{2} \\ = T_{3} / T_{2} \\ = T_{3} / (r^{(k - 1)} * T_{1}) \end{matrix}$
Suppose that the constant-pressure specific heat is C_p. Then the total constant-pressure heat addition quantity Q₁would be:
Q ₁ =C _p*(T ₃ −T ₂)
The total constant-pressure exothermic quantity Q₂would be:
Q ₂ =C _p*(T ₄ −T ₁)
which returns into the combustion chamber 5 to participate in the constant pressure heat addition process.
The output energy W is:
W=Q ₁ −Q ₂
The hot combustion gas exchanges heat energy with fresh air via countercurrent flow in the heat exchanger 3. Under ideal conditions, the temperature of the combustion gas as it exits the heat exchanger 3 would be the temperature T₂of the air entering the heat exchanger 3. Therefore, the heat content Q₃of the discharged combustion gas from the heat exchanger 3 would be:
Q ₃ =C _p*(T ₂ −T ₁)
Therefore, the actual energy Q released from combustion in the combustion chamber 5 would be:
$\begin{matrix} Q = W + Q_{3} \\ = Q_{1} - Q_{2} + Q_{3} \end{matrix}$
The thermal efficiency η would be:
$\begin{matrix} η = W / Q \\ = (Q_{1} - Q_{2}) / (Q_{1} - Q_{2} + Q_{3}) \\ = (C_{p} * (T_{3} - T_{2}) - C_{p} * (T_{4} - T_{1})) / \\ (C_{p} * (T_{3} - T_{2}) + C_{p} * (T_{2} - T_{1}) - C_{p} * (T_{4} - T_{1})) \\ = (T_{3} - T_{4}) - (T_{2} - T_{1})) / (T_{3} - T_{4}) \\ = 1 - (T_{2} - T_{1}) / (T_{3} - T_{4}) \\ = 1 - ((r^{(k - 1)} - 1) * T_{1} / ((1 - r^{(1 - k)}) * T_{3}) \\ = 1 - r^{(k - 1)} * T_{1} / T_{3} \end{matrix}$
The thermal energy consummation μ would be:
$\begin{matrix} μ = η / (1 - (T_{1} / T_{3})) \\ = (1 - r^{(k - 1)} * T_{1} / T_{3}) / (1 - T_{1} / T_{3})) \end{matrix}$
From
6η/6r ^(k-1) =T ₁ /T ₃,
we know that as the value r gets larger, the value η gets smaller; when the value r gets closer to 1, the value η increases.
Therefore,
$\lim_{r \to 1} η = \lim_{r \to 1} (1 - r^{(k - 1)} * T_{1} / T_{3}) = 1 - T_{1} / T_{3}$ $and$ $\lim_{r \to 1} μ = \lim_{r \to 1} η / (1 - T_{1} / T_{3}) = 1$
From
6η/6T ₃ =r ^(k-1) *T ₁ /T ₃ ²>0,
we know that, as the air temperature T₃after the constant pressure heat addition, which is limited by the heat resistance performance of the material, gets larger, the thermal efficiency η also increases, and has
$\lim_{T_{3} \to r^{(k - 1)} * T_{1}} η = \lim_{T} (1 - r^{(k - 1)} * T_{1} / T_{3}) = 0$
Suppose that the air specific heat ratio k=1.4, the isentropic compression ratio r=2, the air initial temperature T₁=293.15 K, and the air temperature after the constant pressure heat addition process T₃=1473.15 K, then the thermal efficiency η and the thermal energy consummation μ is calculated as follows:
η=1−2^(1.4-1)*293.15/1473.15=73.7%
μ=73.7%/(1−(293.15/1473.15))=92%
Obviously, the ideal thermal efficiency of the present invention is already greater than the ideal thermal efficiency Otto engine, diesel engine, gas turbine cycle or steam turbine cycle.
A similar analysis can be done in a system with a second air turbine 11 and a second heat exchanger 10, as shown in FIG. 4. In such a system, stage 5 (denoted by the subscript 5) would correspond to the stage characterized by the air exiting from the second heat exchanger 10, and stage 6 (denoted by the subscript 6) would correspond to the stage characterized by the air exiting from the second air turbine 11.
The present invention can also be applied to other thermodynamic cycles. Its main characteristic is that the high-temperature air after the expansion process enters into the combustion chamber 5 and can be reused in the thermal process, resulting in a much higher thermal efficiency and improved thermal energy consummation, depending on the specific application.
Although the preferred embodiment and alternative embodiments have been described herein, it will be appreciated that the scope of the invention is not intended to be restricted thereby, such scope instead being discerned from a combination of such disclosure and the claims that follow.

Claims

1. A system for generating power, said system comprising:

an air intake for introducing external air into said system;

an air compressor for compressing said external air to form compressed air;

a heat exchanger for heating said compressed air to form compressed, heated air;

an air turbine, wherein said air turbine is adapted to receive said compressed, heated air from said heat exchanger and wherein expansion of said compressed, heated air causes said air turbine to rotate; and

a combustion chamber, wherein said combustion chamber is adapted to receive air exiting from said air turbine and to combust said air with fuel to produce high-temperature gas;

and wherein said high-temperature gas is introduced into said heat exchanger for use in heating said compressed air.

2. The system of claim 1, wherein said air intake comprises an air filter.

3. The system of claim 1, wherein said air compressor is an axial-flow compressor.

4. The system of claim 3, wherein said axial-flow compressor comprises a compressor rotor.

5. The system of claim 4, wherein said air turbine comprises a turbine rotor.

6. The system of claim 5, wherein said compressor rotor is mechanically connected to said turbine rotor.

7. The system of claim 1, wherein said heat exchanger is a shell and tube heat exchanger comprising one or more tubes adapted to carry said compressed air.

8. The system of claim 7, wherein said one or more tubes travel within said combustion chamber.

9. The system of claim 1, wherein said air turbine further comprises a spray nozzle.

10. The system of claim 1, further comprising an electrical generator connected to said air turbine, wherein said electrical generator is adapted to convert rotation of said air turbine into electrical energy.

11. The system of claim 1, wherein said air turbine is connected to said air compressor, wherein said air compressor is driven by rotation of said air turbine.

12. The system of claim 1, further comprising:

a sensor;

a controller connected to said sensor, wherein said controller is adapted to control one or more of the following: the flow of air entering from said air intake and the supply of said fuel to said combustion chamber.

13. The system of claim 12, wherein said sensor is adapted to monitor one or more of the following properties: the temperature of the air in said system, the pressure of the air in said system, and the flow of air in said system.

14. A system for generating power, said system comprising:

an air intake for introducing external air into said system;

an air compressor for compressing said external air;

two or more intermediate sets, wherein each intermediate set comprises one heat exchanger connected to one air turbine, and wherein the first of said intermediate sets is connected to said air compressor and the next of said intermediate sets is connected to the air turbine of the preceding intermediate set;

a combustion chamber, wherein said combustion chamber receives air exiting from the air turbine of the last of said intermediate sets and combusts said air with fuel to produce high-temperature gas;

and wherein said high-temperature gas is introduced into each of said heat exchangers for use in heating said compressed air.

15. A method for generating power, said method comprising the steps of

introducing external air through an air intake;

compressing said external air with an air compressor to form compressed air;

heating said compressed air with a heat exchanger to form compressed, heated air;

allowing said compressed, heated air to expand in an air turbine, wherein expansion of said compressed, heated air causes said air turbine to rotate; and

combusting air exiting from said air turbine with fuel in a combustion chamber to produce high-temperature gas; and

introducing said high-temperature gas into said heat exchanger to heat said compressed air.

16. The method of claim 15, wherein the step of introducing external air through said air intake further comprises filtering said external air.

17. The method of claim 15, further comprising the step of converting rotation of said air turbine into electrical energy by an electrical generator.