Liquid nitrogen propulsion may also be incorporated in hybrid systems, e.g., battery electric propulsion and fuel tanks to recharge the batteries. This kind of system is called a hybrid liquid nitrogen-electric propulsion. Additionally, regenerative braking can also be used in conjunction with this system.
In June 2016 trials will begin in London, UK on supermarket J Sainsbury's fleet of food delivery vehicles: using a Dearman nitrogen engine to provide power for the cooling of food cargo when the vehicle is stationary and the main engine is off. Currently delivery lorries mostly have 2nd smaller diesel engines to power cooling when the main engine is off.
Description
Liquid nitrogen is generated by cryogenic or reversed Stirling engine coolers that liquefy the main component of air, nitrogen (N2). The cooler can be powered by electricity or through direct mechanical work from hydro or wind turbines. Liquid nitrogen is distributed and stored in insulated containers. The insulation reduces heat flow into the stored nitrogen; this is necessary because heat from the surrounding environment boils the liquid, which then transitions to a gaseous state. Reducing inflowing heat reduces the loss of liquid nitrogen in storage. The requirements of storage prevent the use of pipelines as a means of transport. Since long-distance pipelines would be costly due to the insulation requirements, it would be costly to use distant energy sources for production of liquid nitrogen. Petroleum reserves are typically a vast distance from consumption but can be transferred at ambient temperatures.
Liquid nitrogen consumption is in essence production in reverse. The Stirling engine or cryogenic heat engine offers a way to power vehicles and a means to generate electricity. Liquid nitrogen can also serve as a direct coolant for refrigerators, electrical equipment and air conditioning units. The consumption of liquid nitrogen is in effect boiling and returning the nitrogen to the atmosphere.
In the Dearman Engine the nitrogen is heated by combining it with the heat exchange fluid inside the cylinder of the engine.
Description and uses
Use in cryogenic
Currently liquid nitrogen is used in cryogenics, for example to cool superconducting magnets in nuclear magnetic resonance equipment, in the more sophisticated types of infrared sensor, in maglev maglev trains, in computer microchips that exploit the Josephson effect, and perhaps in the future in the superconducting magnets of the tokamak reactors, intended for nuclear fusion. It has also been proposed to use liquid nitrogen to cool superconductive ceramic sheets and thus to construct electric lines thousands of kilometers long, which would for example bring liquid nitrogen and electricity (without any resistance) for thousands of kilometers, from nuclear reactors in Arctic, up to northern cities such as Chicago or New York.
In medicine, direct use is made of cold in cryopreservation of cells such as spermatozoa and ova for artificial insemination or for in vitro fertilization. With the proliferation of pregnancies, the spread of cancer diseases that often require sterilizing therapies, and some fertilization techniques applied to women in their 60s, there is the possibility that many people may keep their gametes (or embryos) for decades, before starting pregnancy. Some people in Arizona, after death (or putting an end to their existence as suffering from incurable diseases), they have had their head or whole body frozen, with the remote hope, in a super-technological future, of being "thawed" with techniques futuristic, treated appropriately and subsequently revived and brought back to a new healthy life. You do not have the faintest idea if these attempts can succeed.
In the aerospace field, liquid nitrogen is used by NASA as a means to concentrate and store cold, safely, for long periods, which will be used (after the electrolysis of water) to bring the oxygen and water to the liquefaction temperature. hydrogen used in rocket propulsion like the Space Shuttle. An increase in the use of these fuels and / or of the oxidized oxygen comburent would inevitably lead to an increase in the consumption of liquid nitrogen. The use of liquid nitrogen in this role by NASA has already produced victims of asphyxiation,2, and since it is a completely odorless gas, the technicians who were next, suddenly breathed an atmosphere with a percentage oxygen content and absolute low (because at those temperatures a part of the oxygen condenses as liquid on the ground), comparable as absolute pressure of O 2 to that of the summit of Everest.
In the slaughtering industry meat could be preserved, even for many years, this allows to keep the prices stable for many years (subtracting meat from the markets in periods of low consumption and putting it into the peaks) or to create strategic reserves to be used in the course of wars or catastrophes.
Use in environmental engineering
At the time of the Soviet Union, it was discovered that by spraying liquid nitrogen into the lower atmosphere, the mist could be precipitated by condensation or freezing of water vapor or microscopic droplets of mist water. This allowed, in windless days, to keep military airports open, creating a fog-free area around them.
Currently the same technique can be used to create areas of thinning fog, near airports, motorway junctions, or important monuments. As a deleterious effect there would be a slight drop in temperature in the immediate vicinity. In 1998, along the Trieste-Venice highway, the Russians demonstrated this procedure.
Other possible uses of liquid nitrogen concern the induction of rain (by spraying clouds with liquid nitrogen) or the deviation of hurricanes (by nebulizing it on marine areas), lowering the temperature and therefore the pressure, which would cause the disturbance to deviate towards the area of lower pressure, for example far from the mainland.
Use in transport
Currently, most road vehicles are propelled from the internal combustion engine that burns fossil fuel. If we assume that road transport must be sustainable in the very long term, current fuels must be replaced by something else that is produced by renewable energy. The substitute does not necessarily have to be a "tout court" energy source; but rather a means of transferring and concentrating energy, comparable to a sort of "energy currency".
Liquid nitrogen at low temperature, passing from a tube to a tube and expanding and absorbing the external heat of the environment into a ventilated grid, increases its pressure enormously and can move a turbine connected to an electric generator, which supplies electricity to electric motors that push the wheels. Various turbines put in series can develop current from the various temperature and pressure jumps, and finally, the emissions are made of low temperature nitrogen, 70% air component, and therefore the extent of the pollution is zero (even if it is not convenient to breathe directly from these cold exhaust pipes, because there is a risk of fainting and asphyxiation).
Currently, using similar principles, several prototypes of compressed air engines have been built, which in practice take heat from the surrounding environment and transform it into kinetic energy. These engines often get stuck due to excessive cold, and condense on their ice drains, even if their tanks (in kevlar) contain compressed air at temperatures equal to or higher than those of the surrounding environment. In fact, the air is made up of 78% molecular nitrogen.
Use in the distillation of seawater by condensation
Withdraw the relatively warm seawater (20-40 ° C) present in the bays and lagoons of the tropical atolls, heating it further with parabolic mirrors, or gas burners at about 60-80 ° C, and then making it "evaporate" in a container low pressure tin (at about 70-80% of atmospheric pressure), it can be condensed in a subsequent container at about 5-10 ° C, cooled inside a coaxial container with a non-toxic working liquid (like ethanol) and with a low melting point, which in turn is cooled by passing around a tank of liquid nitrogen. Connecting the evaporation tank to the condensation tank with a large pipe equipped with low pressure air turbines also generates electricity.
In the evaporation tank the salt concentration will increase considerably, and therefore the container must be emptied periodically. The hot residual water obtained, with a high salt concentration, can be placed in outdoor basins from where, after some time, the common cooking sea salt (NaCl) will be obtained by evaporation. The working fluid (for example ethanol), coming into contact with sea water, is brought to temperatures around 20-25 ° C which can be useful for air conditioning.
Nitrogen production (from air)
Liquid nitrogen is generated by cryogenic freezers and condensers or by the compression obtained by a refrigerated Stirling engine, bringing the common air to pressures and temperatures that can induce the main component of the air to change phase, in the liquid state. nitrogen (N 2, equal to 78% of the air we breathe). These cooling systems can be powered by renewable energy generating electricity or through the direct exploitation of mechanical work (with the Stirling engine) obtained from wind turbines or hydraulic turbines, better if located in cold climates.
Liquid nitrogen is produced and stored in special insulated containers: the isolation, minimizing the heat flow towards the inside of the container, reduces the loss of nitrogen due to evaporation and re-transformation into gas. Storage requirements prevent the distribution of nitrogen through pipes: it would be uneconomical to keep the entire pipeline at the required temperature.
Using the Stirling engine in reverse
The consumption of liquid nitrogen would be nothing more than the inverse of its production: the same Stirling engine that made liquid nitrogen re-transform it into gas, recovering the energy spent in the liquefaction process and providing a source of power for motor vehicles and electric generators. It would also be possible to directly use liquid nitrogen as refrigerant for refrigerators and air conditioners, then allowing the resulting gas nitrogen to return to the atmosphere from which it was extracted.
Advantages
Liquid nitrogen vehicles are comparable in many ways to electric vehicles, but use liquid nitrogen to store the energy instead of batteries. Their potential advantages over other vehicles include:
Much like electrical vehicles, liquid nitrogen vehicles would ultimately be powered through the electrical grid, which makes it easier to focus on reducing pollution from one source, as opposed to the millions of vehicles on the road.
Transportation of the fuel would not be required due to drawing power off the electrical grid. This presents significant cost benefits. Pollution created during fuel transportation would be eliminated.
Lower maintenance costs
Liquid nitrogen tanks can be disposed of or recycled with less pollution than batteries.
Liquid nitrogen vehicles are unconstrained by the degradation problems associated with current battery systems.
The tank may be able to be refilled more often and in less time than batteries can be recharged, with re-fueling rates comparable to liquid fuels.
It can work as part of a combined cycle powertrain in conjunction with a petrol or diesel engine, using the waste heat from one to run the other in a turbocompound system. It can even run as a hybrid system.
Disadvantages
The principal disadvantage is the inefficient use of primary energy. Energy is used to liquefy nitrogen, which in turn provides the energy to run the motor. Any conversion of energy has losses. For liquid nitrogen cars, electrical energy is lost during the liquefication process of nitrogen.
Liquid nitrogen is not available in public refueling stations; however, there are distribution systems in place at most welding gas suppliers and liquid nitrogen is an abundant by-product of liquid oxygen production.
Other Uses
In 2008, the US Patent Office granted a patent on a liquid nitrogen powered turbine engine. The turbine flash-expands liquid nitrogen that is sprayed into the high-pressure section of the turbine, and the expanding gas is combined with incoming pressurized air to produce a high-velocity stream of gas that is ejected from the back of the turbine. The resulting gas stream can be used to drive generators or other devices. The system has not been demonstrated to power electric generators of greater than 1 kW, however higher output may possible.
Political arguments
The possibility of making the current thermal engines adaptable to liquid nitrogen and the achievement of different means of production could probably lead to the diversification, localization and stability of the energy market. [ without source ]
One possibility of energy diversification includes hydrogen economy, photovoltaics and biofuels alternatives.
The dependence on the oil economy [ broken link ] has a dramatic global influence. Oil reserves, wells and oil fields are authentic " assets " of current political and monetary power, which governs and monopolizes information. Moreover, according to the theory of peak oil, by 2015 oil consumption will exceed the maximum production capacity, leading to a further surge in prices.
Currently large economic investments, and considerable political and military efforts are aimed at ensuring the long-term stability of coal, oil and gas supplies, and this urgent necessity shapes the policies and military actions of many countries, which to secure energy supplies. they often renounce the struggle for human rights.
From an environmental point of view, the impact generated by the carbon dioxide produced by fossil fuels is (together with deforestation) one of the main causes of the greenhouse effect. Other collateral damage produced by fossil fuels is acid rain, devastation of the landscape, pollution of the aquifer and the seas. It is vital to find alternatives to fossil fuels that allow long-distance storage and transport of energy.
Criticisms
Cost of production
Liquid nitrogen production is an energy-intensive process. Currently practical refrigeration plants producing a few tons/day of liquid nitrogen operate at about 50% of Carnot efficiency. Currently surplus liquid nitrogen is produced as a byproduct in the production of liquid oxygen.
Energy density of liquid nitrogen
Any process that relies on a phase-change of a substance will have much lower energy densities than processes involving a chemical reaction in a substance, which in turn have lower energy densities than nuclear reactions. Liquid nitrogen as an energy store has a low energy density. Liquid hydrocarbon fuels, by comparison, have a high energy density. A high energy density makes the logistics of transport and storage more convenient. Convenience is an important factor in consumer acceptance. The convenient storage of petroleum fuels combined with its low cost has led to an unrivaled success. In addition, a petroleum fuel is a primary energy source, not just an energy storage and transport medium.
The energy density — derived from nitrogen's isobaric heat of vaporization and specific heat in gaseous state — that can be realised from liquid nitrogen at atmospheric pressure and zero degrees Celsius ambient temperature is about 97 watt-hours per kilogram (W•h/kg). This compares with 100-250 W•h/kg for a lithium-ion battery and 3,000 W•h/kg for a gasoline combustion engine running at 28% thermal efficiency, 30 times the density of liquid nitrogen used at the Carnot efficiency.
For an isothermal expansion engine to have a range comparable to an internal combustion engine, a 350-litre (92 US gal) insulated onboard storage vessel is required. A practical volume, but a noticeable increase over the typical 50-litre (13 US gal) gasoline tank. The addition of more complex power cycles would reduce this requirement and help enable frost free operation. However, no commercially practical instances of liquid nitrogen use for vehicle propulsion exist.
Frost formation
Unlike internal combustion engines, using a cryogenic working fluid requires heat exchangers to warm and cool the working fluid. In a humid environment, frost formation will prevent heat flow and thus represents an engineering challenge. To prevent frost build up, multiple working fluids can be used. This adds topping cycles to ensure the heat exchanger does not fall below freezing. Additional heat exchangers, weight, complexity, efficiency loss, and expense, would be required to enable frost free operation.
Safety
However efficient the insulation on the nitrogen fuel tank, there will inevitably be losses by evaporation to the atmosphere. If a vehicle is stored in a poorly ventilated space, there is some risk that leaking nitrogen could reduce the oxygen concentration in the air and cause asphyxiation. Since nitrogen is a colorless and odourless gas that already makes up 78% of air, such a change would be difficult to detect.
Cryogenic liquids are hazardous if spilled. Liquid nitrogen can cause frostbite and can make some materials extremely brittle.
As liquid N2 is colder than 90.2K, oxygen from the atmosphere can condense. Liquid oxygen can spontaneously and violently react with organic chemicals, including petroleum products like asphalt.
Since the liquid to gas expansion ratio of this substance is 1:694, a tremendous amount of force can be generated if liquid nitrogen is rapidly vaporized. In an incident in 2006 at Texas A&M University, the pressure-relief devices of a tank of liquid nitrogen were sealed with brass plugs. As a result, the tank failed catastrophically, and exploded.
Tanks
The tanks must be designed to safety standards appropriate for a pressure vessel, such as ISO 11439.
The storage tank may be made of:
Steel
Aluminium
Carbon fiber
Kevlar
other materials, or combinations of the above.
The fiber materials are considerably lighter than metals but generally more expensive. Metal tanks can withstand a large number of pressure cycles, but must be checked for corrosion periodically. Liquid nitrogen, LN2, is commonly transported in insulated tanks, up to 50 litres, at atmospheric pressure. These tanks, being non-pressurized tanks, are not subject to inspection. Very large tanks for LN2 are sometimes pressurized to less than 25 psi to aid in transferring the liquid at point of use.
Emission output
Like other non-combustion energy storage technologies, a liquid nitrogen vehicle displaces the emission source from the vehicle's tail pipe to the central electrical generating plant. Where emissions-free sources are available, net production of pollutants can be reduced. Emission control measures at a central generating plant may be more effective and less costly than treating the emissions of widely dispersed vehicles.
Source from Wikipedia
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