DE102015005940B4 - Method for integrating regeneratively generated electricity into a power grid using carbon monoxide - Google Patents

Abstract

A method of integrating regeneratively generated electricity into a power grid, comprising combusting ground dried coal in a reactor into carbon monoxide to generate power in a gas turbine, storing in a liquid storage facility, or producing chemicals in downstream chemical plants, the plant generating high percentages Carbon monoxide pure oxygen in a reduced amount for partial oxidation, for the reaction C + 1 / 2O2 = CO, is supplied, and • wherein the ground, the dried dried coal is fed in a carbon dioxide stream to the endothermic reaction CO2 + C = 2CO reduce the temperature in the reactor, generating electricity by burning the high percentage carbon monoxide in a gas turbine with coupled generator and feeding the electricity into the power grid, • wherein the power generation by means of the gas turbine as well as the downstream chemical plants, with variations in electricity supply it or the demand for electricity can continue to operate with optimal efficiency, with an oversupply of regeneratively generated electricity in the power grid to reduce the production of electricity, only the gas turbine, not the reactor, is reduced and thereby liquefied a partial flow of the carbon monoxide produced in the reactor and in the Liquid storage is stored as chemical energy and is in the short and medium term in electrical energy shortage in the power network is converted by the gas turbine into electrical energy.

Description

Method for improving the integration of renewable energy sources into the existing energy system by converting electrical energy into chemical energy with intermediate storage of liquefied CO, thereby reducing CO2 emissions and promoting the further development of renewable energies.

State of the art

US 2006/0096298 A1 shows a method that is used taking into account a variable power requirement. One or more syngas streams are generated by gasification of carbonaceous materials and used to generate power to generate power during a period of peak power demand. Alternatively, the synthesis gas is used in chemical production plants to produce, for example, methanol. This is done especially during a period of low power consumption.

The publication DE 20 01 844 A shows a method and apparatus for producing carbon monoxide by reacting coke with oxygen and carbon dioxide.

The ever-increasing capacities of regenerative power generators cause local and temporal fluctuations in energy supply. In addition, there are of course day and seasonally fluctuating consumer demand. This can lead to overcapacity or shortage of electrical energy.

Obviously, in case of overcapacities, the electric energy should be stored.

However, it is not technically possible to store large amounts of electricity directly.

Now you can convert "excess" electrical energy by the electrolysis of water into hydrogen into chemical energy. Due to its physical properties, however, this can be poorly stored.

All efforts to this end have not been successful so far.

Therefore, for example, overcapacities coal plants have to be shut down.

If coal-fired power plants are operated in partial load operation, however, the electrical efficiency decreases. For the most modern coal-fired power plants, the efficiencies in full-load operation are around 45-47%. If these power plants are throttled to 50% power efficiency drops to 42-44%.

In other words, they emit more CO2 per kilowatt-hour generated than if they could run under optimal conditions.

This is of course counterproductive.

In addition, the power plants have to be designed for larger capacities in order to be able to cover the basic supply of electrical energy with natural reduced power of the regenerative power generator. This in turn means higher investment costs for the construction of these power plants.

It is certainly tempting to use the electricity generated by regenerative energy systems such as wind and solar power to generate hydrogen by means of electrolysis of water and then convert this to methane using the exhaust gases from CO2 emitters as raw material.

But what do you do when the regenerative energies "falter"? In nature this happens naturally.

You could implement the excess electrical energy in chemical energy and z. B. produce hydrogen. However, this encounters, as stated above, great technical and above all economic problems.

In order to keep downstream chemical plants, such as the production of methane, the electrolysers would have to be supplied with electricity from the grid to produce the hydrogen. With electricity that is anyway because of the failure of the regenerative sources already scarce and would be able to feed only by ramping up of plants from non-regenerative sources into the power grid.

However, a fast start-up of the base load-bearing conventional coal power plants is technically problematic. Alternatively, the methane production facilities could be shut down.

In such cases, a so-called GUD plant for power generation could be started up quickly enough. and provide the power needed to operate the plants.

With such combined cycle power plants is also a high efficiency, achieved by a combination of gas turbine with downstream steam turbine.

However, a GUD system requires gas (CH4) for operation. In addition, the facility for Such cases are interpreted as large, a large investment in case the wind does not blow.

Germany is almost completely dependent on imports for the energy resource gas.

This is not desirable in two respects. Once it increases the dependency on energy imports (gas) and then it is also not economical because financial resources are tied up as dead capital when the plants are running at a reduced load.

Funding that is not available for the expansion of regenerative energy generation, hinders therefore ultimately their expansion.

In order to find an improved energy conversion, since April 2014 developments in the so-called "Power to Gas" project HELMETH have been funded by the EU with 3.8 million euros. Hydrogen is to be generated there by means of steam electrolysis, whereby in a reverse conversion reaction the hydrogen is partly converted to CO 2 with H2 + CO2 = CO + H2O in CO.

From the gas mixture then hydrocarbons (Fischer Tropsch process) or in a Methanisierungsreaktion methane to be produced.

The methane could then be fed into the gas line system and eventually serve as a heating and power source to the consumer, implemented in a solid oxide fuel cell (SOFC).

The high temperature heat released in the exothermic process of methanation is to be used in the project to convert water to steam which is then fed to high temperature steam electrolysis to improve the energy balance of the hydrogen recovery process.

In the event of a failure of the regenerative energy sources, however, the hydrogen electrolysis and the downstream plants for conversion into chemical energy also have to be supplied with electricity from anthropogenic sources in this variant of the use of regeneratively obtained electrical energy.

In the so-called IGCC process, a synthesis gas is to be produced by gasifying a coal slurry (coal with water) with oxygen. However, the synthesis gas thus produced is not storable.

Unfortunately, this does not eliminate the difficulties of integrating renewable energy into the grid.

The object of the invention is therefore to integrate the regeneratively produced electrical energy into the existing energy system grid gas network advantageous, and thereby to support further expansion of these energies and to promote developments in the field of energy conversion, with the aim of reduced CO2 emissions with economic benefits connect to.

invention

The object is achieved by the features of the independent claim. The dependent claim shows advantageous embodiments of the invention.

If regenerative energy (such as wind) is to be used to an increasing extent, the energy systems must be able to be operated flexibly. On the one hand, renewable electricity is to be fed into the grid at any time and, on the other hand, sufficient energy can be generated if needed. In this case, as described in the prior art, various technical and economic problems. The problem is solved by the invention.

The basic idea is to use a coal power plant or an electrochemical apparatus as a producer of a chemical with chemical energy and to store this between, as well as the stored energy and the raw material, in a "weakening" of the regenerative energy, for a surplus of renewable energy to use the operation of downstream facilities for the production of fuel, methanation, etc. These systems can be operated continuously. This fulfills a basic requirement for an economical driving style.

According to the invention, not all of the power plant, but only a downstream gas turbine in your performance, is reduced in a large entry of renewable energy into the grid (for example, wind energy).

This can be done quickly in contrast to the down driving of the entire coal-fired power plant according to the requirements.

The effectiveness of power generation of the power plant is of course reduced. However, the liberated by the downgrade of the gas turbine gas stream is used as a chemical energy source.

The combustion of coal in the power plant is operated in this process for this purpose with pure oxygen but reduced amount of oxygen.

This mode of operation allows a very high concentration of CO gas to be generated and it also allows a modern method of fluidized bed technology.

The fuel used is dry coal.

The coal is fed into the reactor with a CO2 gas stream.

At the same time, the CO2 supplied serves to thermally control the combustion in order to prevent excessively high temperatures during combustion with pure oxygen.

The increased temperature in the combustion chamber through the conversion of the coal with pure oxygen is controlled by means of the endothermic reaction CO2 + C = 2CO.

By this combustion mode, a high concentration of the combustion gas is achieved at CO and thus facilitates the separation and storage of the CO.

From the heat released during combustion in the combustion chamber, steam is generated and electricity is generated in a steam turbine.

That cooled, high-percentage carbon monoxide (CO), however, is available as a chemical raw material or energy source in the event of a lack of energy in the electricity grid.

The purified CO gas can be burned in case of failure or lack of renewable energy for the electric energy production in a downstream gas turbine or just serve as a chemical energy source.

According to a partial stream of the CO gas of methane extraction or z. B. fed to the process according to Fischer Tropsch synthesis for fuel production. The hydrogen can be generated by a "shift reaction" to CO + H2O = H2 + CO2.

Another part of carbon monoxide (CO) is liquefied and stored in a liquid storage facility as chemical energy.

Although liquid CO does not have the very high energy content, such as gasoline or liquid methane, it does have as much liquid hydrogen, but it is much easier to liquefy and store.

Energy density MJ / L

• Liquid methane 24
• Gasoline 33
• liquid hydrogen 10
• liquid carbon monoxide 10.2

It is also advantageous that it can be generated in the generator, that is, it is at the front of the process chain.

The liquefaction of CO is also technically much easier to implement compared to hydrogen (comparable to oxygen). See also the in 4 ; 5 shown phase diagrams of hydrogen and carbon monoxide.

The very low boiling point of liquid hydrogen with Sp = -252.76 ° C also causes very large evaporation losses of hydrogen during its storage. Even with very good and therefore expensive isolation of the storage so the storage of liquid hydrogen is not economical.

By way of example, the process according to the invention described above is shown in a simplified flow diagram. 2

In the event that regenerative energy is not available, according to the invention, the entire CO gas from the combustion chamber of the power plant, after it was cooled by steam generation and then cleaned, fed to the downstream gas turbine and burned to CO2. The coupled generator thus supplies the power required in the power grid.

See 1

The gas turbine is now operated at full load. The achieved by a power plant of this type electrical efficiency of power generation then reaches its maximum value.

The CO is also burned in the gas turbine with pure oxygen.

This type of combustion achieves a high concentration of the combustion gas in CO2 and facilitates the separation and storage of the CO2.

A CO2 feed to the combustion gas avoids excessive temperature and thus damage to the turbine blades.

The raw material required for the downstream methanation or gasoline synthesis plants is taken from the CO storage tank in this case.

The use of the liquid CO storage allows according to the invention so the continuous operation of the downstream chemical plants.

The heat energy required for the evaporation of the stored liquid CO is available from the waste heat, for example from the steam turbine, since only a low temperature level is needed for the evaporation. Of course, the heat from other exothermic processes can also be used according to good engineering practice.

As a result of the method according to the invention, the power supplied by regenerative sources can thus be fed into the power grid without problems and thus made economically usable.

The process of energy supply and energy conversion of renewable energy sources into the grid or the conversion into chemical energy is made economically usable by the intermediate storage of CO as energy carrier and chemical raw material.

According to the invention, by this method, the supply of electricity from renewable sources in the network and the provision of the required electricity and the production of chemical energy in the form of methane or hydrocarbons or the production of NH3 and other chemicals secured and the regenerative energy also from an economic point of view advantageous.

Even with the so-called IGCC method can be produced according to the invention by gasification of coal with oxygen, a gas with a very high CO content. For this purpose, the coal is only partially burned by reduced oxygen supply according to the invention. The generated gas can also be partially liquefied and stored because of the high CO content. The missing in such a driving manner endothermic reaction H2O + CO = H2 + CO2 is thereby by the also endothermic reaction CO2 + C = 2CO replaced by the temperature in the reactor does not rise too high.

In a further development step of the method, according to the invention, the gas turbine of the coal-fired power station is replaced by a high-temperature fuel cell (SOFC).

Please refer 3 and 6 and 7

The overall efficiency of such a power plant is further increased because the energy conversion in the SOFC is not subject to the Carnot process as opposed to combustion in a gas turbine.

The electrochemical apparatus according to the invention should also be switched as high-temperature electro-pyrolysis cell in so-called. (Reverse operation) can be driven.

Since the expansion of regenerative energies is expected to result in greater fluctuations in the supply of energy, CO2 is reduced to CO in the event of an excess supply of electrical energy in this electrochemical aggregate. (see also 7 )

The CO formed is partially liquefied and stored as described above.

Another sub-stream is used for the production of synthetic fuels, methanation or ammonia synthesis.

The coupled in the electropyrolysis incurred oxygen is fed to the furnace of the power plant, whereby the plant for the production of oxygen can be made smaller.

In this case, then an O2 memory must be provided.

Description Fig. 1

Exemplary describes 1 sketchily the case that no or not enough regenerative energy is available, which can be fed into the power grid to meet the requirements. Regenerative energy is not available. This case is represented by RG = 0.

Nevertheless, to feed the required amount of electrical energy into the grid, therefore, a coal power plant described here is raised to maximum power. This is just one example. The required electrical energy could also be generated by another type of power plant, for example using the GUD technology or the IGCC process.

In the example sketched here, in the boiler coal (C) is burned by partial oxidation, preferably with oxygen to carbon monoxide (CO).

The resulting heat is evaporated in the heat exchanger by supplied water and transferred the superheated steam in a steam turbine into mechanical energy. The steam turbine (DT) is coupled to a generator that generates power that is delivered to the grid.

Generated carbon monoxide (CO) is burned after a gas purification stage (GR) in a gas turbine (GT). The gas turbine also generates power via a coupled generator which is delivered to the grid.

To counteract too high a temperature and thus protect the turbine blades, carbon dioxide (CO2) is added to the combustion gas (CO).

The overall efficiency of this type of combined power generation thus achieves the maximum efficiency of electric power generation.
RG = 0 entry of regenerative energy not available
DT = steam turbine
GR = gas cleaning
GT = gas turbine

Description Fig. 2

In the event of a surplus of regenerative energy, shown here with (RG = +), the power of the coal-fired power plant has to be reduced in order to be able to use the supply of electricity from the regenerative sources.

According to the invention, only the downstream gas turbine (GT) is driven back to generate electricity. In contrast to the return of the entire power plant, this process can be done quickly enough.

The released by the return of the gas turbine CO gas is partly directly in plants for conversion into methane, hydrocarbons or z. B. also guided NH3 and converted there into chemical energy. On the other hand, the gas is liquefied and stored and serves as a chemical energy storage.

The liquefaction of the carbon monoxide is less technically complicated than the liquefaction of hydrogen. See also the 4 and 5 ,

When there is a lack of renewable energy, the gas turbine, using carbon monoxide gas, has to generate more electrical power to meet the demand for electric energy.

Now the downstream chemical plants would have to be reduced or even switched off.

On the one hand, this would cause great technical difficulties, on the other hand, the plants could not be operated economically.

According to the invention, the continuous operation is provided by the provision of the basic base material and energy carrier CO [evaporation] in the short to medium term from the CO liquid storage, but secured.
GT = gas turbine

Description FIG. 3

If it comes through the producers of renewable energy (here simplified as wind energy RE = max shown) to a "surplus" of electrical energy, the gas turbine of a coal power plant would have (see also description to 2 ) be reduced accordingly.

According to the invention, the gas turbine is to be replaced in the future by a SOFC which can be used in so-called. (Reverse operation) as SOEP [solid oxide electro pyrolysis cell].

This electrochemical cell converts CO2 into CO. In this case, unneeded power is used in the network for the operation of the cell and thereby causes a reduction of the CO2 emission.

The oxygen produced concurrently in the cell during the reaction is used in a power plant instead of the atmospheric oxygen. In the event of an energy deficit in the power grid due to reduced input of renewable energy, the oxygen must be stored.

This procedure facilitates the separation of CO and CO2 from the power plant exhaust without the use of an air separation plant.

However, the type of electrochemical apparatus of this type is currently not mature for large-scale use.

Based on the findings in the development of high-temperature water electrolysis, however, is expected in the medium term.
REmax = Regenerative energy in excess
SOFC = Solid Oxide Fuel Cell
SOEP = Solid Oxide Electropyrolysis Cell

Description Fig. 6

The 6 Sketchy describes the work of a high-temperature fuel cell in which CO is burned to CO2 under generation of electric current.

In the electrolytic cell, cathodes and anode space are separated by a membrane of oxidic material. The membrane is conductive at temperatures of 600-800 ° C for oxygen ions. The two surfaces of the membrane are coated with catalytically active metal oxides and electronically conductive. The catalytic metal oxides cause the conversion of oxygen into oxygen ions and, on the other hand, the oxidation of CO to CO2.

The heating and cooling of the gas streams is regenerative (not shown).
SO = solid oxide membrane
K = cathode
A = anode

Description Fig. 7

In the 7 sketched the electrolytic reduction of CO2 to CO.

In the electrolytic cell, cathodes and anode space are also separated by a membrane of oxidic material. The membrane is conductive at temperatures of 600-800 ° C for oxygen ions. The two surfaces of the membrane are coated with catalytically active metal oxides and electronically conductive.

The very low concentration of oxygen ions on the cathode side is pumped by the externally applied DC voltage from the cathode side to the anode side of the membrane.

The electronic pumping process is carried out against the partial pressure of oxygen in the anode compartment of the cell.

The necessary pumping voltage can therefore be reduced by a reduced pressure on the anode side. This is technically difficult. According to the invention, it is better to lower the oxygen partial pressure and thus the pumping voltage by lowering the partial pressure of the oxygen by feeding another gas, preferably by CO 2, into the anode compartment.

The CO2 addition is in the 7 shown in parentheses.

Claims (2)

Method for integrating regeneratively generated electricity into a power grid, comprising Burning grounded dried coal in a reactor to carbon monoxide to generate electricity in a gas turbine, for storage in a liquid storage facility or for producing chemicals in downstream chemical plants, Wherein the reactor for generating high-percentage carbon monoxide pure oxygen in a reduced amount for partial oxidation, for the reaction C + 1 / 2O2 = CO, is supplied, and Wherein the ground pulverized coal is fed to the reactor in a carbon dioxide stream to reduce the temperature in the reactor with the endothermic reaction CO2 + C = 2CO, Generating electricity by burning the high-percentage carbon monoxide in a gas turbine with a coupled generator and feeding the electricity into the power grid, • whereby the power generation by means of the gas turbine as well as the downstream chemical plants, with variations of electricity supply or electricity demand can continue to operate with optimum efficiency, with an oversupply of regeneratively generated electricity in the grid for reduced generation of electricity, only the gas turbine, not the Reactor, is driven back and thereby a partial flow of the carbon monoxide produced in the reactor liquefied and stored in the liquid storage as chemical energy and short and medium term in electrical energy shortage in the power grid is converted by the gas turbine into electrical energy. The method of claim 1, wherein according to the entry of renewable electricity in the power grid, another partial stream of carbon monoxide as a chemical energy source and raw material for downstream chemical plants of methane production, gasoline synthesis (Fischer Tropsch method) or the NH3 synthesis is available and these plants is supplied.

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