WO2011089169A2 - Method for using energy temporarily present in a power grid and exceeding the instantaneous power load - Google Patents

Abstract

The invention relates to a method for using energy temporarily present in a power grid and exceeding the instantaneous power load, wherein an air separation plant is operating using the excess energy, generating a fluid serving as an energy carrier and stored in a reservoir.

Description

description

Method for using surplus energy temporarily present in a power network in relation to the current power utilization

The invention relates to a method for the use of excess energy temporarily present in a power network in relation to the current power utilization.

Typically fluctuates over time in a power grid supply and demand of electric power, which that can not be assumed to be constantly available ste ^¬ Henden amount of electric power related. For example, at times, in particular for rege ^¬ nerative energy sources such. As wind power or photovoltaic systems are no takers for the bereitte te ^¬ te electric energy available when so-called base load power plants cover the currently required demand for electrical energy. In the opposite case, it may also be that renewable energy sources due to less favorable weather conditions ^¬ term can not feed power to the grid, although a need existed. Furthermore, it is known that the need for electrical energy at night is typically lower than during the day. In addition to these fluctuations up ^¬ seasonal variations occur in the amount of available regenerative electric energy. These circumstances necessitate the connection of peak-load power plants (such as gas and steam combined cycle power plants) at peak load times, while at low load times, excess electrical energy can not be used. This results in a need for energy saving, which in low-load periods store electrical energy and can emit at peak load times ^¬ again. Such energy stores are necessary in particular with regard to the expansion of the share of renewable energies in the ^{Stromerzeu ¬} supply, since these very energy sources are exposed by external, especially climatic circumstances strong fluctuations in energy production. Energy storage thus act to that not ver ^¬ falls to a usable energy and, secondly, that the stored energy can be fed back into the network in order in a possible elimination of z. As the increased regenerative share of the electricity mix to prevent in-stability of the network.

Energy storage for storing excess energy are known from the prior art in various embodiments. For example only mechanical energy storage, such. B. flywheels, compressed air storage or electrochemical energy storage, such. As redox cells, lithium batteries or electrolytic hydrogen production referenced. These methods are complicated, expensive and often ^¬ times have a low efficiency.

The present invention is therefore based on the problem of specifying an improved possibility of using excess energy.

The problem is solved by a method of the type mentioned, which is characterized in that an air separation plant is exaggerated loading with the excess energy which he witnesses a serving as an energy carrier fluid ^¬ which is stored in a memory.

The invention is based on the idea, a satisfactory stel ^¬ loin usage possibility of temporarily in a power grid of available excess energy, ie, energy, which for

Time of their emergence is not immediately needed to provide. According to the invention, the use of the excess energy is initially achieved by means of an air separation Anläge executed conversion of electrical surplus ^¬ energy into chemical energy.

Air separation plants cool air down to its condensation temperature, resulting in liquefaction of the air. As is known, gases can be liquefied only at temperature and pressure ratios below their respective critical point. The liquid air is further decomposed by distillation into individual fluid components, in particular oxygen and nitrogen. Here han ^¬ delt it is energy-rich fluids which are to be regarded as Energieträ ^¬ ger. These fluids are directed to a suitable memory and stored there. It is essential that this process takes place according to the invention increases when temporarily surplus ^¬ energy is present in a power grid. As described above, overcapacities or changes in network utilization, ie the amount of energy currently available, are dependent on a large number of factors and are therefore always recurring.

In particular, due to the steady expansion of the utilization of renewable or renewable energy sources can also with peak fluctuations in network utilization both low load times, in which low energy is consumed and fed into a power grid, thus surplus energy is generated, as well as peak load times, in which too little energy is available, which must therefore be purchased and / or must be generated by the connection of suitable for the dynamic operation see suitable power plants. The inventive method is where used herein, and the resulting in low demand periods via ^¬ excess energy for the operation of one or more Luftzerle ^¬ supply systems which the excess energy to liquefy the air, ie, for the production of fluids, in particular with a high energy density, according to the processes described above used. According to the invention, a conversion of electrical energy into a good one, ie as far as possible, takes place. loss-free, storable form of energy and storing the ^¬ ser.

Of course, in the inventive process a part of the excess energy for the operation of Luftzerle ^generating installation (n) itself, such as to generate the required refrigeration to liquefy the air, for compression of the fluid obtained is used or consumed and can not in width ^¬ ren get saved.

Due to the future increase in the proportion of renewable energy in the power grid, it is preferred if at least part of the excess energy consists of energy generated from renewable energy sources. This includes, for example, energy generated by wind, sun or water, but also by ^¬ like regenerative concepts for energy production, such. B. generated from biomass energy. Often, these forms of energy are not always available in time and, to a limited extent, the supply of energy provided by them can only be foreseen, which can aggravate the aforementioned difference between guaranteed supply and demand. It might pronounced low-load and peak load occurring defects ^¬ th, which is why the future always a particularly large Be ^¬ may use respectively storing excess energy is present.

Particularly preferred as by the Luftzerlegungsanlage he ^¬ beguiled fluid is oxygen. Pure oxygen is an ener ^¬ giereicher substance that in many ways, such. B. in the (chemical) industry or in the power plant area in a variety of processes can be used. Of course, all other recoverable in the air separation plant fluids according to the invention can be used as an energy source. It is therefore expedient if the air separation installation and the storage are assigned to a consumer. Under

Consumers are understood to be any process or process or system that does so the air separation plant was created, as energy carrier can use the ^¬ nende fluid in any way. For the example of the Sauer ^¬ substance obtained by the air separation plant here in particular large-scale processes, such. For example, for the production of pig iron or steel as well as for the oxidation of various raw materials in the context of polymer synthesis. Oxygen is also required for the production of hydrogen and synthesis gas as well as for the production of sulfuric and nitric acid. Also, a use in glass manufacturers position is conceivable, the required for the high melting processes Tempe ^¬ temperatures can be achieved by the use of oxygen there. This list is merely illustrative and by no means exhaustive. A particularly preferred consumer in the context of the invention is a power plant in which the fluid is used as needed to operate a combustion process. Here, the energy stored in the memory is used for power generation. Particularly with respect to future Kraftwerkskon- concepts for the separation and storage of carbon dioxide, ^so-¬-called CCS (carbon capture and storage) power plants are by way of example two approaches where possible rei ^¬ ner oxygen is necessary given. One is the so-called pre-combustion separation. Here, in a gasifier, a solid or liquid fuel (eg coal, petcoke, heavy oil or chemical residues ^¬ , etc.) under reaction with oxygen and water in synthesis gas, ie a hydrogen-containing gas mixture, transferred. The synthesis gas is subsequently a so-called

Shift reaction, wherein carbon dioxide and water is generated essentially from carbon monoxide and water, subjected to carbon dioxide and hydrogen, and the resulting carbon dioxide by means of gas scrubbing ^¬ separated. The resulting, highly concentrated hydrogen, for example, can continue to be used as fuel gas in the gas turbine of a gas and steam power plant. On the other hand, the so-called oxyfuel combustion (oxyfuel combustion) to call, with coal is not burned as usual in steam power plants with air, but according to pure oxygen. The resulting exhaust gas contains essentially only water vapor and carbon dioxide (cf the nitrogen content of more than 60% in conventional processes). From the exhaust gases, the water can be condensed out at relatively low temperatures and so relatively pure carbon dioxide can be obtained.

The two concepts described thus require pure oxygen, which is why they can be advantageously assigned to a Luftzellegungsanlage for the production of oxygen, including an oxygen storage.

Regularly draw for the operation of air separation ^¬ legungsanlage necessary energy directly from their output ^¬ amount of energy from power plants, resulting in a reduction of net power and the efficiency of the power plant result.

By operating the air separation plant with excess ^¬ energy during off-peak times can according to the invention more oxygen than for the current operation of the power plant, is erfor ^¬ sary generated and stored in the memory. In peak load periods, the stored oxygen can be used, so that the operation of the air separation plant can be limited or even completely shut off, whereby the net output or the efficiency of the power plant is increased at the same gross power, since the power station side stream no share for the operation of the Air separation plant must be used and the stored oxygen for combustion can be used. If necessary, can be compensated and the additional start-operable dynamic power plants are avoided in a composite of several conceivable according connected to a Sau ^¬ erstoffSpeicher power plants in such a way a part of the missing to Spit ^¬ zenlastzeiten the net energy. These considerations also serve for so-called IGCC (Integrated Gasification Combined Cycle) power plants, whereby an air separation plant is also necessary for their operation, but in contrast to the above methods no separation of carbon dioxide takes place.

By way of example, some of the possible types of storage of the fluid serving as energy carrier within the scope of the invention are again given by way of the example of the oxygen. The simplest variant provides, the gaseous oxygen expediently under elevated pressure, d. H. the pressure is higher than needed in the power station to store between. In this way, the recycling process can be facilitated and a higher energy density can be achieved during storage.

In continuation of this variant, starting z. B. from a spherical tank for storing the oxygen with a diameter of 20 m at a pressure between 50 and 75 bar in this at 50 bar about 280 tons and at 75 bar corresponding to 420 tons of gaseous oxygen. It follows that in a power plant, which for process control z. B. 50 bar, 140 tonnes of gaseous oxygen are contained in the memory, if the pressure is not lowered below 50 bar (this is the difference of the amounts of stored gaseous oxygen). With this amount, the oxygen demand of a 850 MW power plant, depending on the type of power plant, could be covered for about half an hour to an entire hour, as simulation calculations have shown.

In a second example, the oxygen is stored in a cavern with a volume of 300,000 m ³ , the pressure levels should correspond to the above example. The capacity is almost two orders of magnitude higher so that an amount of oxygen corresponding to the needs of a power plant of several days can be stored. In a third example, a cryogenic storage of the fluid, in this case the oxygen, is proposed. In the spherical tank with a diameter of 20 m known from the first example, about 4,700 tons of liquid oxygen could be stored in this way. With this amount could be one

Supply 850 MW power plant with oxygen for about one day.

The examples illustrate that by cryogenic spoke ^¬ tion, can be realized an extremely high energy density of the stored fluid, here the oxygen. This Varian ^¬ te is advantageous in that is obtained in the case of a motor ^¬ work with existing air separation plant of this already liquid oxygen. Further advantages, features and details of the invention will become apparent from the ^exemplary embodiment described below and from the drawings. Showing:

Fig. 1 is a diagram showing the course of the power fed into a power grid over time and

Fig. 2 by way of exporting method ^¬ approximately embodiment of the present invention. Fig. 1 shows a diagram for illustrating the course of the power fed into a power grid over time. The ordinate describes the power fed into the grid and the abscissa the time. It can be seen from graph 1 that the power fed into a power grid is not constant over time but fluctuates. The graph 1 passes in the diagram by broken lines respectively three separate areas 2, 3 and 4, wherein Be ^¬ rich 2 represents an initial state in which an electrical ^¬ specific power Po is fed into the power grid. Area 3 represents the power fed into a power grid at low load, which is obviously below Po. Region 4 provides a peak load represents time in which the power fed into the electricity network ^¬ power Po is located above. The inventive method is in the range of 3, which is a low-load time is available in a power supply system so tem ^¬ answer service excess energy. With the excess energy an air separation plant is operated, the one serving as an energy carrier fluid, in particular oxygen, he witnesses ^¬ which is stored in a memory. Memory and Luftzerlegungsanlage are preferably a consumer ^¬ cher, such. As a power plant (see Fig .. 2) or other large-scale plant, which can use the fluid generated by the air separation plant in any way assigned.

The excess energy consists at least proportionally of regenerative energy sources such. B. generated by solar, wind or hydropower energy. Due to external circumstances, and in particular their dependence on climatic conditions, these renewable energy sources are subject to greater fluctuations in their electricity generation (quantity, time). By way of example, a stormy night is mentioned in which wind turbines generate a large amount of energy, for which, however, if necessary, no customer can be found. On the other hand, it may be possible that energy would be needed on a comparatively wind- ^styling day, but the wind power plants can not generate this. This problem will become ever more present due to the future increase in the share of renewable energies in the electricity mix. Especially the use of the surplus electricity generated during off-peak hours or the surplus ^¬ energy is not satisfactorily resolved to date.

According to the invention it is now proposed to convert the electrical contact ^¬ excess energy over the operation of an air separation plant primarily to chemical energy in the form of serving as Energieträ ^¬ ger fluid, as it can be better stored in comparison to the electrical energy. Of course, part of the excess energy for the operation of the air separation plant or, if appropriate, terer funding of serving as energy carrier fluid in one or more memory, consumed.

The store (s) are thus filled by the operation of the air separation plant at low load times and preferably emptied at peak load times. In this case, it may be that the stored in the memory, serving as energy Flu ^¬ id, for example, for the operation of a power plant, in particular in its combustion processes or gasification processes, is used and thus increases the efficiency, ie the net ^¬ performance of the power plant. Another aspect is ever ^¬ but also only operate the air separation plant if surplus energy is available, as may be more favorable in these off-peak hours of electricity price.

If the diagram shown in FIG. 1 relates to the power fed into a power network from a single power plant, the area 2 represents the conventional operating state of the power plant. According to the invention, the power plant is associated with an air separation plant including a storage facility, wherein in the conventional operating state the air separation plant as for the loading ^¬ operating the power plant, in particular a continuously produced much oxygen, this associated combustion process is required. Neither oxygen is stored here, nor even in that case

Memory used existing oxygen. The net electrical output, which results from the power fed into the power grid, remains constant in time, it is a pure base load power plant.

In off-peak periods, as represented by the area 3, characterized by the presence of temporal About ^¬ excess energy, the power delivered to the power supply capacity of the power plant more oxygen is lowered and instead purification system by means of the air separation generated. This is stored in the spe ^¬ essential dedicated memory. The amount of oxygen stored at low load times is determined by the Area between the dashed line and the graph 1 given.

The method according to the invention makes it possible to avoid the connection of peak-load power plants. During peak load periods of the operation of the air separation plant is gedros ^¬ rare and this off completely. Thus, the electrical power consumption of the power plant is lowered and increases the net electrical ^¬ performance and the efficiency of the power plant. The corresponding increase of the graph 1 in the region 4 of the slide ^¬ program is thus a measure of the performance of the air separation plant or their consumption in the conventional operating state of the power plant. The area B extending in the area 4 between the dashed line and the graph 1 is related to the amount of stored oxygen.

FIG. 2 shows the method according to the invention on the basis of an ^exemplary embodiment. A power plant 5 here is a Luftzerle ^¬ supply system 6 and a memory 7 assigned. A line 8 represents a direct connection of the air separation plant 6 with the power plant 5, via which the power plant 5 constantly the fluids generated by the air separation plant 6, in particular ^¬ special oxygen, are supplied. The power plant 5 outputs the energy generated to a power grid 9. The amount of energy required to operate the air separation plant 6 is withdrawn directly from the output of the power plant 5 via a supply line 12.

In off-peak hours, ie in the presence of excess energy, the air separation plant 6 via the line 10 fills the storage 7 with the generated by this, serving as an energy carrier fluid (oxygen). The Speichervolu ^¬ men of the memory 7 is, of course, on the one hand by the dimensions of the memory 7 itself, the se beispielswei- may be formed as a tank or cavern limited, but on the other hand it is also possible, the storage volume through a cryogenic storage, ie storage at low Temperatures in which the fluid generated by the Luftzerlegungsanlage 6 is liquid, increase.

In peak hours is preferred, operation of the air separation legungsanlage throttled 6 and it is switched off completely, so that it supplies the power plant 5 via line 8 a redu ^¬ ed to no amount of oxygen. The 5 amount required for loading ^¬ operating the power plant of oxygen is now obtained from the memory 7 through the line. 11 By switching off or throttling the air separation plant 6, the net output of the power plant 5 increases.

As mentioned above, the air separation plant 6 and the storage 7 can also be assigned to a consumer other than a power plant 5, for example, different systems of the chemical industry being considered here. Likewise, the inventive method results in a cost advantage by throttling or switching off the air separation plant at peak load times, in which the price of electricity is particularly high. At peak load times required for the respective process substance or fluid can be removed from the store, so this be emptied. A refilling of the storage by the air separation plant he ^¬ preferred only in low load periods, where the electricity price is regularly low.

Claims

claims 1. A method for utilizing relative to the instantaneous current utilization temporary excess energy in a power supply system existing overpressure, characterized in that is operated at the over ^¬ excess energy an air separation unit (6) which generates a serving as an energy carrier fluid which (in a memory 7) is stored. 2. The method according to claim 1, characterized in that the excess energy at least partially consists of regenerati ^¬ ven energy sources generated energy. 3. The method according to claim 1 or 2, characterized in that the fluid is oxygen. 4. The method according to any one of the preceding claims, characterized in that the Luftzerlegungsanlage (6) and the memory (7) are associated with a consumer. 5. The method according to claim 4, characterized in that the consumer is a power plant (5), in which the fluid is used when needed for operating a combustion process or Verga ^¬ sungsprozesses. 6. The method according to any one of the preceding claims, characterized in that the fluid is stored cryogenically ^¬ ge in the memory. 7. The method according to any one of the preceding claims, characterized in that the memory (7) is designed as a tank or cavern.