WO2011128721A1

WO2011128721A1 - Green engine

Info

Publication number: WO2011128721A1
Application number: PCT/IB2010/051545
Authority: WO
Inventors: Donald J. Gariepy
Original assignee: Gariepy Donald J
Priority date: 2010-04-12
Filing date: 2010-04-12
Publication date: 2011-10-20

Abstract

A method and apparatus for converting heat energy from a plurality of heat sources having small temperature differences from one another into mechanical energy, said method using a volatile liquid to convert the temperature differences into vapor pressure differences in a 2-phase gas/liquid mixture, said mixture being mechanically confined in such manner to cause the vapor pressure differences to produce potential energy by elevating the liquid portion of the mixture and/or produce kinetic energy by imparting velocity to the liquid, said potential and/or kinetic energy of the liquid powering a waterwheel, hydraulic turbine or other hydraulic motor to generate electricity, propel a ship, operate industrial machines or other useful service.

Description

Title of Invention: Title: GREEN ENGINE Technical Field

[ 1 ] The GREEN ENGINE belongs to the field of heat engines, also to the field of heat exchangers, and also to the field of waterwheels & hudraulic turbines

Background Art

[2] BACKGROUND ART - HEAT ENGINES

[3] Heat engine development has concentrated on high temperature/high pressure

engines because they were observed to produce the greatest power and to make the most efficient use of fuel. Carnot's theorem of 1824 provided a theoretical basis for this observed result by showing the maximum possible efficiency of any heat engine to be determined solely by the high and low temperatures which drive the engine.

[4] Carnot maximum efficiency = (absolute hot temperature - absolute cold temperature)

/ (absolute hot temperature)

[5] An example of the Carnot efficiency limit is a coal burning power plant where the cold temperature is ambient water at 25 degrees Centigrade (C), and the hot temperature is burning coal at 565 C. Converting these to absolute temperatures, the cold temperature is 298 degrees Kelvin (K) and the hot temperature is 838 K. The Carnot efficiency is 64%. In actual practice the plant has a measured efficiency of 36%, the remaining 28 % being expended on internal inefficiences of the engine.

[6] The development of high temperature/high pressure engines peaked with Rudolph

Diesel's engine (DE patent 67207 of 1893) which still remains the most efficient heat engine today. Large marine diesels currently produce 75 megawatts (MW) to drive containerships with an efficiency slightly over 50%.

[7] Low temperature engine development began in 1881 when Jacques dArsonval

proposed a heat engine to generate electricity from the temperature difference in tropical oceans between the 25 C surface water and the 5 C deep water. This Ocean Thermal Energy Conversion (OTEC) is preferred over other naturally occuring temperature differences because it is large, stable, continuously renewed by the sun and usable in all seasons. On an average day, 60 million square kilometers of tropical seas receive solar radiation at 1366 watts per square meter, providing 8.196 x 10 ^Λ 16 watts of power, of which 15% is absorbed as heat. OTEC can provide 1.23 x 10 ^Λ 16 watts per day, which is 3 orders of magnitude greater than the average 1.504 x 10 ^Λ 13 watts per day consumed world wide for all purposes in 2008.

[8] Doctor dArsonval's engine does not cancel Carnot's theorem but it operates in an area where efficiency has a different importance because there is no fuel consumed. The thermodynamic efficiency remains very low. A heat engine with a cold tern- perature of 5 C and a hot temperature of 25 C has a maximum possible efficiency of 6.7%. And in real operating conditions some temperature is lost while pumping cold water up to the engine or lost in heat exchangers. The 20 C difference may reduce to only 5 C which reduces Carnot efficiency to 1.7 %, and quite possibly reduces engine output to less than what is needed to run the pumps and overcome internal friction. The importance of thermodynamic efficiency in the OTEC context is that it be high enough to achieve any operation at all.

[9] Georges Claude constructed the first engine based on d'Arsonval's proposal in 1926

(US Patent 2006985 of 1935). This engine boils the surface water in a vacuum chamber at 25 C producing a low pressure vapor which drives a large turbine. The exhaust vapor is condensed by the cold deep water and the resulting liquid water is returned to the ocean. Internal engine losses include pumping the vacuum chamber, pumping the deep water, pumping the surface water. Heat energy is also lost in 3 temperature drops: warm surface water to vapor, exhaust vapor to cooling water, and deep water to cooling water. Professor Claude attempted three installations of this engine over a period of 26 years. None produced electricity.

[10] James Anderson's closed cycle engine (US Patent 3312054 of 1967) improved on Claude's engine. The closed cycle engine uses 2 heat exchangers, a boiler for the hot water and a condenser for the cold water. Only the heat energy from the sea water passes through the engine. Propane with a naturally low boiling temperature circulates through the boiler and condenser, producing a heavier vapor because it is gas under pressuure which powers a smaller turbine with greater efficiency and avoids salt water and contaminent gases. The closed cycle engine has only 2 temperature drops and the vacuum pump is eliminated.

[11] The first OTEC power generation was achieved in 1979 in a 3 million dollar joint venture led by Hawaii State. The OTEC demonstration plant was produced 53.6 kilowatts (KW) gross power, used 35.1 KW for the pumps, generated 18.5 KW of net power output at a capital cost of 162,000 $/KW, and remained in operation for 3 months.

[12] The US National Renewable Energy Laboratory defines the current state of the art as a 100 megawatt OTEC plant internally consuming 41 megawatts (MW) and providing 59 megawatts of useful power. This plant requires a 20 degree C temperature difference using water no more than 1000 meters deep. The depth is a limiting factor because the cold deep water is heavier than the warm surface water and requires 30% of the engine output to pump it up to the surface.

[13] BACKGROUND ART - HEAT EXCHANGERS

[14] Heat exchangers consist of a hot fluid providing heat to a cold fluid through a barrier, said barrier being normally copper or aluminum which are particularly good heat conductors. Heat exchangers require a temperature drop which reduces the temperature available to the engine. Heat exchangers are governed by the heat conductance equation:

[15] (heat flux) = k (temperature difference) (area) / (wall thickness)

[16] The constant k depends upon the metal used to make the exchanger. Using a closed cycle OTEC engine as an example of the effect of heat exchangers on low temperature engine performance, seawater provides a temperature difference of 20 C which allows a Carnot efficiency of 6.8%. If 20 megawatts (MW) of heat energy is pumped from the ocean then 6.8% eficiency allows a maximum output power of 1.36 MW. If the 20 MW of heat energy passes through an exchanger using copper tubes with a 1 mm wall and a total area of 10 square meters, copper having a k = 400, our equation becomes:

[17] 20 x 10^Λ6 = (400) (tl-t2) (10) / 10^Λ-3

[18] Which solves to a 5 C loss across each of 2 exchangers, or 10 C total loss. This loss reduces the Carnot efficiency from 6.8% down to 3.5 % and the possible output from the original 20 MW is reduced from 1.36 MW down to 0.7 MW.

[19] If aluminum heat exchangers of the same mechanical design are used, the temperature drop across the exchangers will double because aluminum has a k=200. Each exchanger will have a temperature drop of 10 C and the total temperature loss will become 20 C. The temperature differential available to the engine will reduce to 0 degrees C and the output power will be zero.

[20] This heat conductance equation appeared to be a fixed limit on heat flux until George Grover invented the heat pipe (US patent 3229759 of 1966). The heat pipe transfers heat by using a 2-phase liquid / gas mixture enclosed in a good heat conductor, normally copper or aluminum. A 2-phase mixture in a closed chamber maintains itself at "equilibrium vapor pressure" where the condensation is equal to the evaporation. This is a stable state so long as both gas and liquid are present. If heat is added then evaporation increases which increases the gas pressure and increases condensation until a new equilibrium is reached at a higher temperature and gas pressure where condensation is again equal to evaporation. Equilibrium vapor pressure maintains the 2-phase mixture exactly at the boiling point.

[21] When equilibrium vapor pressure exists, any heat added or subtracted from the fluid immediately evaporates or condenses gas rather than heating or cooling the liquid. Thermal flux increases significantly because the "latent heat of evaporation" necessary to turn liquid into gas is much greater than the heat required to change liquid temperature. The heat pipe performance is described by Los Alamos National Laboratory at:

[22] www.lanl.gov/news/releases/archive/00-064.shtml

[23] "A lithium heat pipe developed at Los Alamos in the mid-1980s transferred heat energy at a power density of 23 kilowatts per square centimeter. To put this figure in perspective, heat is emitted from the sun's surface at a mere six kilowatts per square centimeter. We now routinely build heat pipes with similar capability."

[24] This principle of operating with volatile liquids at equilibrium vapor pressure does not automatically apply to all heat exchangers. Many exchangers carry liquids at temperatures and pressures determined by an industrial process. The exchangers may also have structural limitations on high pressure operation. Equilibrium vapor pressures for practical 2-phase fluids are over 10 bars and require pipes rated for the high pressures involved. The principle of the heat pipe can be applied to heat exchangers intended to evaporate gas from liguid or to condense gas into liquid.

[25] BACKGROUND ART - WATERWHEELS AND HYDRAULIC TURBINES

[26] Waterwheels and hydraulic turbines are gravity driven engines which achieve high efficiency at low pressures and no temperature change. They are not heat engines and are not subject to Carnot limits. They convert liquid potential and/or kinetic energy into mechanical energy. Hydraulic engineering rates these engines by water head which is a measure of pressure based on the weight of water, 1 bar being approximately equal to 10 meters of water head.

[27] Traditional waterwheels achieve 40% to 70% efficiency, depending upon details of construction. The current state of the art is the Kerby waterwheel (US patent 4,023,915 of 1977) which achieves 90% efficiency down to a waterhead of 1 meter and will operate below that at a reduced efficiency. Hydraulic turbines also achieve 90% efficiency but are more specific to how much waterhead and how much volume is required. The Kaplan turbine is appropriate from 2 to 40 meters, the Francis turbine from 10 to 350 meters and the Pelton turbine from 50 to 1300 meters.

[28] Both the turbine and the waterwheel are scalable for various design power levels.

The waterwheel is more flexible, is operable at lower speeds and lower power levels and it can be built with less technology. The hydraulic turbines produce much greater power for a given physical size but have a more narrow operating range and require better technology to manufacture.

Disclosure of Invention

Technical Problem

[29] The technical problem in the current art of low temperature engines is the efficiency of the gas turbine. The problems preventing commercial use of the low temperature engine are effects of this basic problem.

[30] The theoretical 100 MW power plant of the present art requires a deepwater pipe 1000 meters long and 11 meters in diameter which is exposed to wave, current, wind and storm damage. This pipe is difficult to construct and to maintain and it greatly limits the location of the power plant. Failures in deepwater pipe construction and operation have terminated most OTEC projects. Gas turbine efficiency controls the length of the pipe because 1000 meters is required to reach the 5 C water which the gas turbine needs to operate. Gas turbine efficiency also controls the diameter of the pipe. An overall engine efficiency of 5% requires an input of 2000 MW of heat energy to produce a 100 MW output. In physical terms this means that 200 cubic meters per second of 5 C water is required and the pipe must be wide enough to prevent excessive friction loss or the energy required to pump this water will consume the entire output of the turbine.

[31] The deepwater pipe also causes a developmental problem. It can not be scaled to a shorter length and still preserve the required 20C temperature differential. It is therefore not possible to build small OTEC systems which would allow practical use and experimental development of this concept, leading to progressive construction of larger installations based on predictable costs and reliable performance. The 100 MW OTEC plant envisioned by the US National Renewable Energy Laboratory remains a theory because 162,000 $/KW is not reasonably close to other available options such as Diesel-electric at 350 $/KW, hydoelectric at 2000 $/KW, wind turbines at 5000 $/KW, photovoltaic at 12000 $/KW.

Technical Solution

[32] Maximize heat exchanger performance and use an engine that is efficient at low temperature and pressure. .

[33] The heat exchangers of a closed cycle low temperature engine convert liquid into gas and gas into liquid, making them a possible application for 2-phase gas/liquid mixtures at equilibrium vapor pressure. Working fluids appropriate for the temperature range of 0 C to 30 C include, but are not limited to, propane, ammonia and methyl chloride. If propane is used, 25 C on the hot exchanger will produce an equilibrium vapor pressure of 9.2 bars. While 5 C on the cold exchanger will produce an equilibrium vapor pressure of 5.2 bars. The pressure difference of 4 bars or 40 meters of water head is far in excess of what is needed for 90% efficiency using hydraulic engines.

[34] Designing for the lowest water head that will permit 90% efficient operation at the lowest possible temperature difference will reduce the capital cost of the deep water pipe and also increase the power output for a given quantity of water pumped.

Operating the hot exchanger at the same 25 C produces the same 9.2 bars. Using 20 C water on the cold exchanger produces equilibrium pressure of 8.2 bars. The temperature difference of 5 degrees C produces a pressure difference of 1 bar or 10 meters of water head. Further reducing the temperature differential to a 1 C difference still provides the 2 meters of water head required for 90 % efficient operation of either the Kaplan turbine or the Kerry waterwheel. Advantageous Effects

[35] The ability to operate at 1 or 2 degrees of temperature difference greatly reduces the deep water pipe requirements because the ocean temperature change with depth is not a linear function. According to the "Temperature at Depth" graph on page 3 of:

[36] www.msc.ucla.edu/oceanglobe/pdf/thermo_plot_lab.pdf

[37] The tropical ocean temperature drops about 10 degrees in the first 100 meters and 10 degrees more in the next 900 meters. An engine that operates on less than 5 C of temperature difference has a deepwater pipe length requirement less than 50 meters. The required pipe is short enough to be streamlined and attached to a moving vessel. A 100 MW OTEC generator of the present invention can provide the 75 MW (100,000 horsepower) required by a large containership. Marine propulsion is a particularly de- sireable OTEC application because the power produced is locally used which eliminates transmission losses.

[38] The reduced differential temperature requirements of this invention permit use of heat derived from ground water, ambient air, geothermal, solar heat, industrial waste heat or any other source of temperature difference.

[39] Small systems are practical and cost/performance data can be developed to permit the predictable construction of larger installations.

Mode for Invention

[40] One embodiment of this invention uses a stationary housing which surrounds the engine and contains fluid. Said housing is divided into a hot chamber and a cold chamber by an insulated barrier in the center of the housing. Two hoses connected to the hot chamber provide for the circulation of fluid to and from a hot source. Two other hoses connected to the cold chamber provide for circulation of fluid to and from a cold source. Each of the two chambers contains a heat exchanger. The fluid circulated through the hot chamber maintains the hot chamber, the hot exchanger and all other engine parts contained within the hot chamber at the temperature of the hot source. The fluid circulated through the cold chamber maintains the cold chamber, the cold exchanger and all engine parts contained within the cold chamber at the temperature of the cold source. The circulating fluid serves only to bring heat energy into the engine, it does not mix with the working fluid inside the heat exchangers. The heat energy of the circulating fluid is transferred to the working fluid inside the two heat exchangers through the metal tubes of the heat exchangers.

[41] The circulating fluid which fills the hot and cold chambers will be water at ambient pressure in many cases. The working fluid will normally be propane, ammonia, butane or similar volatile chemical at high pressure. Said working fluid being selected to match the temperature range which will drive the engine in each specific application. The heat exchangers are partially filled with the working fluid so a 2-phase gas/liquid mixture will exist at equilibrium vapor pressure. By the laws of vapor pressure, the pressure within the hot exchanger will be higher than the pressure within the cold exchanger.

[42] A rotating shaft extends through both chambers of the housing, passing through a hole in the insulated barrier. Said shaft is supported by bearings at the opposite ends of the housing. The shaft may optionally extend through a rotary seal in the wall of the housing to drive an external load. All moving parts of the engine are mounted on this shaft and rotate as a unit. The shaft is a hollow pipe so that hoses interconnecting the hot and cold exchangers can be run through the center of the shaft and pass through the stationary insulated barrier without special provision.

[43] It is an object of this construction to avoid friction losses in high pressure rotary couplings. It is also an object of this construction that the high absolute pressure of the working fluid be balanced between all parts of the engine in such manner that only the small pressure differences between the hot exchanger and the cold exchangers are able to act upon the engine.

[44] The circulating fluid from the hot and the cold sources will be impelled to rotate with the shaft and working parts of the engine by means of blades attached to the rotating heat exchangers. In this way the engine pumps the circulating fluid from the hot and cold sources by direct mechanical force, eliminating the 5% conversion loss inherent in the current art where all mechanical energy produced by the engine goes through a 98 % efficient alternator to become electricity and 40% of this resulting electricity then operates 90% efficient electric motors to produce mechanical energy to drive the pumps that move the circulating fluid.

[45] The hot exchanger of this embodiment functions similar to a water wheel to drive this engine. Said hot exchanger is made of copper or other heat conductive material and it consists of tubes containing the working fluid. The tubes of the hot exchanger are mounted parallel to the rotating shaft and are extended on radial arms from the shaft so that gravity acting upon the fluid contained in a tube will have the extension of the radial arm to generate the torque which rotates the shaft. The tubes act in opposite pairs so that one tube reaches top dead center at the same time that the opposite tube reaches bottom dead center. The opposite tubes are connected together by a hose, pipe or other connecting means and have enough fluid to fill only one tube at a time. The hose connecting the tube pairs is connected to the bottom of the lower tube so that the liquid which stays at the bottom of the lower tube by gravity will be forced into the hose by the pressure of the vapor which remains in the top portion of the lower tube. The other end of the connecting hose is connected to the top of the upper tube. When the full tube reaches bottom dead center and the empty tube reaches top dead center, a controlled valve, operated by cam, electronic or other control means, opens to connect the upper tube momentarily through a hose or other connecting means to the low pressure of the cold heat exchanger. The low pressure in the upper tube of the hot exchanger allows the high pressure vapor in the top of the lower tube to pump the fluid from the lower tube to the upper tube. The upper tube becomes the full tube which then rotates by gravity to become the lower tube, imparting its potential energy as torque to the shaft and the cycle is repeated. A plurality of tube pairs may be used to provide even torque and smooth operation.

[46] The cold exchanger of this embodiment is a tube of heat conductive material which is aranged in a spiral around the shaft within the cold chamber. When the controlled valve of the upper tube in the hot exchanger opens, hot vapor enters the cold exchanger where it condenses into liquid. The spiral shape of the cold exchanger acts as an Archimedes screw to pump the condensed liquid to the opposite end of the cold exchanger where the collected condensate enters a hose which returns the condensate to the hot exchanger through the shaft. The condensate flows into the upper tube through a one-way valve when the controlled valve connecting to the cold exchanger opens and momentarily reduces the high pressure in the upper tube to the lower pressure of the cold exchanger. This eliminates the need for a pressure pump to restore liquid at low pressure from the cold exchanger into the higher pressure of the hot exchanger.

Industrial Applicability

[47] The GREEN ENGINE may be used in, but is not limited to, electric generation, marine propulsion, pumping water, or recovery of industrial waste heat.

Claims

[Claim 1] A method for converting heat energy from a plurality of heat sources having small temperature differences from one another into mechanical energy, said method using a volatile liquid to convert the temperature differences into vapor pressure differences in a 2-phase gas/liquid mixture, said mixture being mechanically confined in such manner to cause the vapor pressure differences to produce potential energy by elevating the liquid portion of the mixture and/or produce kinetic energy by imparting velocity to the liquid, said potential and/or kinetic energy of the liquid powering a waterwheel, hydraulic turbine or other hydraulic motor to generate electricity, propel a ship, operate industrial machines or other useful service.

[Claim 2] The method of claim 1 mounting all engine parts on a single rotating shaft so that the high absolute pressure of the volatile liquid has no effect on the operation and only the small differences in pressure between the hot and cold heat exchangers act upon the engine to produce energy.

[Claim 3] The method of claim 1 with a method of injecting the condensate into the hot engine at the time in the operating cycle when the pressure difference is momentarily zero with the object that additional pumps are not required to move the condensate from the low pressure portion of the engine to the high pressure portion of the engine.

[Claim 4] An apparatus for converting heat energy from a plurality of heat

sources having small temperature differences into mechanical energy comprising,

A. an insulated housing capable of containing fluid, said housing being divided into a hot and cold chamber by an insulated barrier,

B. a means to circulate fluid from an external hot and cold source with the object that all engine parts in the hot chamber remain essentially at the temperature of the external hot source and all engine parts in the cold chamber remain essentially at the temperature of the cold source,

C. a rotating shaft extending through the hot and cold chambers, and through a hole in the center of the insulated barrier, said shaft being supported on bearings to provide free rotation, said shaft being hollow to permit passage of hoses or pipes or other connecting means,

D. a hot exchanger mounted on the rotating shaft within the hot chamber and a cold exchanger mounted on the rotating shaft within the cold chamber, the exchangers being normally separate but posessing controllable means of connection, both heat exchangers being partially filled with a volatile working fluid, thereby producing a high vapor pressure within the hot exchanger and a low vapor pressure within the cold exchanger,

E. the hot exchanger being composed of at least 2 tubes, said tubes being made of heat conducting material, said tubes being mounted parallel to the shaft on radial arms extending from the shaft, such that one tube is at top dead center of the shaft rotation when the other tube is at bottom dead center,

F. the opposite tubes being connected together as a pair by a hose or pipe or other connecting means to function as a single reservoir of volatile liquid, said connecting means being attached to the side of each tube which is opposite to the shaft, the object being that the bottom connecting means accepts liquid from the bottom of the lower tube and delivers the liquid to the top of the upper tube, the quantity of volatile liquid being such that only one tube may be filled with liquid at a given time, the other tube of the pair being filled with vapor,

G. each tube having a controlled valve connecting the tube to the cold exchanger, said valve being controlled by cam or electronic or other control means, said valve being briefly opened when the tube reaches top dead center, allowing the high vapor pressure in the tube at bottom dead center to pump the volatile fluid up into the tube at top dead center, the upper tube then becoming the full or heavy tube and the lower tube having only vapor, the upper tube then rotating by gravity to become the lower tube and the cycle repeating,

H. the cold exchanger being a tube made of heat conducting material which spirals around the rotating shaft, and is separated from the shaft by radial arms,

G. the vapor entering the cold exchanger from the tubes of the hot exchanger condensing by the low pressure and cold temperature of the cold exchanger, the condensate being pumped to the opposite end of the cold exchanger by the rotating spiral acting as an archimedes screw, said condensate returning to the hot exchanger by a hose or pipe or other connecting means, said condensate then entering the hot tube through a one-way valve at top dead center when the controlled valve connecting the hot tube to the cold exchanger is open and the pressure within the hot tube momentarily equalizes with the lower pressure of the cold exchanger.

The apparatus of claim 4 where the shaft is extended outside the the housing to operate an electric generator, ship propellor, industrial machine or other useful load.

The apparatus of claim 4 where there is a plurality of tube pairs.

The apparatus of claim 4 using auxiliary pumps.

The apparatus of claim 4 where fins are attached to the rotating heat exchangers to pump the circulating fluid and/or be pumped by the circulating fluid as the application may require.

The apparatus of claim 4 where there is no housing, the hot exchanger being extended on a rotating shaft so that the hot exchanger is within the hot source, and the cold exchanger being extended on the rotating shaft so that the cold exchanger is within the cold source.