METHOD FOR STORING AND LATER RECOVERING ELECTRIC ENERGY

Description

[0001] The invention relates to a method for storing and later recovering electrical energy from a wood processing plant.

[0002] With the global shift away from fossil fuels, the energy sector is undergoing a transformation. Renewable energies—hydropower, biomass, sunlight, and wind power—are primarily converted into electrical energy, which must be stored in a suitable form.

[0003] There are various ways to store and subsequently recover electrical energy. Pumped-storage hydroelectric plants are probably the most frequently used large-scale energy storage systems. Pumped-storage technology has proven to be the most technically successful. In this process, water is pumped from a lower reservoir to a higher reservoir and stored there. The electrical energy is stored as the potential energy of the water. When energy is needed, the water is released through a turbine, and a generator is used to recover the electrical energy. Pumped-storage hydroelectric plants operate with an efficiency of between 70 and 80%. The difference in elevation between the two reservoirs is crucial for the energy density.

[0004] Pumped-storage power plants are very complex in design and expensive to manufacture. Furthermore, they have a significant impact on the environment, the extent of which depends on the size of the reservoirs. Due to their size and cost, pumped-storage power plants are more suitable for municipal utilities than for industrial plants.

[0005] Based on the theory that current can flow indefinitely in a superconducting circuit without any further energy input, superconducting magnetic energy storage devices were developed. In this system, a direct current from a rectifier flows through a coil made of superconducting material, generating a magnetic field in which the energy is stored. Once charging is complete, the current supply is interrupted. To discharge the stored energy, the circuit is reconnected to the inverter, converting the direct current into alternating current. Such a storage device is well-suited for industrial applications, but it is also structurally complex and expensive to manufacture.Aside from its use in electromobility, electrical energy storage makes sense when demand is low but the energy generation facility needs to operate continuously. Then, when demand for electricity rises again, the storage unit is discharged and the electricity fed into the grid. Such storage is also useful within industrial plants.

[0006] Many industrial companies generate the electricity they need for their operations in their own power plants. When a plant is decommissioned, it must either be shut down or the excess electricity produced must be fed into the public grid. Starting up and shutting down a power plant is not only delayed in relation to energy demand, but also significantly reduces its efficiency. The electricity fed into the public grid is "lost" to the company. During peak electricity demand that cannot be met by the company's own power plant, or not quickly enough, the company has to purchase electricity at a higher price than it was paid for feeding into the grid.

[0007] The use of renewable energies for electricity generation brings further challenges regarding the supply of electricity to the population and industries. When there is sufficient wind and sunlight, a correspondingly large amount of electricity can be generated with wind turbines and solar panels. However, when there is no wind and it is dark, little or, in the worst case, no electricity can be generated with wind turbines and solar panels. Since the price of electricity is also determined by supply and demand, the price is low when the wind is strong and high when it is weak. It is therefore advisable to store electricity when the price is low and to supplement the supply with this stored energy when the price rises.

[0008] In general, it is known, for example from EP 2 657 469 A1 or US 2011 / 0259250 A1, to produce dust from a biomass and to store this dust in order to burn the dust when needed and to convert the thermal energy obtained into electrical energy.

[0009] Based on this, the invention aims to provide a method for storing and subsequently recovering electrical energy, which is particularly suitable for use in industrial plants, but can also be used on a large scale.

[0010] To solve the problem, a method according to the invention is characterized by the following steps: a) Calculating the plant's energy requirements in advance, b) Setting an energy demand limit, which is undercut when electricity from a grid has a lower price than electricity produced in the wood processing plant, and which is exceeded when electricity from the grid has a higher price than electricity produced in the wood processing plant, c) Generating dust using an electrically driven device when the energy demand limit is undercut due to decreasing production and thus decreasing electricity demand from the wood processing plant, d) Storing the dust in a dust bunker, e) Releasing at least some of the dust from the dust bunker when there is a demand for electrical energy, f) Burning the dust to generate thermal energy.If the energy demand limit is exceeded due to increasing production and thus increasing electricity demand of the wood processing plant, g) conversion of thermal energy into electrical energy.

[0011] The advantage of this process is that all process steps represent established technology and can be easily implemented. The dust is poured onto long piles and can be handled automatically using a claimer / reclaimer system. Large quantities of dust can be stored.

[0012] It is economically advantageous to generate and store the dust when electricity prices are low, and to offload the dust, incinerate it, and convert the thermal energy into electrical energy when electricity prices are high. If the costs associated with carrying out steps c) and d) are lower than those associated with carrying out steps e) to g), the operator of the respective plant will make a profit, with the margin depending on supply and demand.

[0013] Dust can be generated by grinding or machining, particularly by grinding, a material. Storing the dust in bunkers is a known technique. In the simplest case, the dust can be burned using conventional gas burners that are fueled with dust instead of combustible gas. A continuous dust explosion then occurs at the burner outlet, burning the emerging dust cloud. Dust burners are also known. Converting the resulting thermal energy into electrical energy in a steam turbine, which drives a generator, is also a well-established process.

[0014] The dust is preferably produced from dried wood chips or dry wood recyclate. The wood chips can be produced from roundwood and, if necessary, temporarily stored before and / or after drying. This technique is used, for example, in the production of particleboard. The wood chips can be dried using combined heat and power (CHP), which is particularly advantageous when electricity prices are high because demand exceeds supply. Processing the wood chips into dust is preferably carried out when electricity prices are low, when supply exceeds demand.

[0015] The dried wood chips can then be stored and, when needed, retrieved from storage and ground into dust in a mill. A refiner used in the wood processing industry can also be used as a mill.

[0016] The handling of the dust can be automated, from its generation to its further removal from the dust bunker (disembarkation).

[0017] Even after the dust has been removed from the dust bunker, it can be handled automatically until it is burned.

[0018] This process is used in a wood processing plant. The process is particularly well-suited for the use of renewable energies, as the yield is subject to particularly strong fluctuations in this context.

[0019] If the wood processing plant includes a facility for the production of wood-based panels, equipment for producing wood chips from round timber, drying them, and storing them is present. The dust generated during the cutting (sawing) of the wood-based panels can also be stored.

[0020] The energy requirements of a wood processing plant can be calculated in advance. If this calculation is performed regularly, electrical energy can be stored or recovered when a predefined energy demand limit is reached. For example, if production needs to be reduced due to falling demand, the available electrical energy can be used to generate dust instead of producing particleboard. If the plant's energy demand increases due to rising demand, the dust can be burned, and some of the energy stored in it can be recovered and fed back into the plant's electrical grid.

[0021] An automated process is feasible in which the potential shift between surplus and demand is determined at regular intervals, for example, by software. This creates an effective way to balance grid fluctuations, which are essential for ensuring a reliable electricity supply to society. This applies to both municipal power suppliers and individual companies of any size.

[0022] Since virtually no lead time is required for the process, a rapid switchover from production operation to storage operation and vice versa is possible.

[0023] An embodiment of the invention will be explained below with the aid of a sketch.

[0024] The diagram shows a simplified representation of the energy storage and recovery process. The plant is supplied with electricity via supply line 20. From there, supply lines 21, 22, and 23 provide electricity to a wood chipper 3, a preheater 4, and a refiner 5. Wood chips 3.1, such as those required for the production of engineered wood panels, are produced in the wood chipper 3 from roundwood 1 or recycled wood 2. The wood chips 3.1 are dried in the preheater 4, and the dried wood chips 3.1 can then be mechanically fiberized in a refiner 5. The fiberized wood chips can then be ground into dust in a mill (not shown in detail here) and stored in the dust bunker 6. Alternatively, the wood chips could be ground directly after drying, rather than being fiberized in a refiner 5 first.The round timber 1 or the wood recycled material 2 can also be machined, in particular sanded, to generate the dust.

[0025] The electrical energy used to generate dust from the roundwood 1 or the wood recycling 2 is largely stored in the dust. If electrical energy is required because the energy demand limit is exceeded, the dust is extracted from the dust bunker 6 and burned in a burner 7. The fact that dust can spontaneously ignite (dust explosion) can be utilized in this process. The thermal energy generated during combustion powers a steam generator 8. The steam produced in the steam generator 8 is used to drive a steam turbine 9, which is connected to a generator 10. This generator produces electrical energy and feeds it into the supply line 20 via the supply line 24.

[0026] The power plant described above is an on-site power plant used in a wood processing plant that already has a chipper 3, preheater 4, and refiner 5 when producing wood-based panels, so only a mill for dust generation would need to be added. If the grinding discs of refiner 5 are designed accordingly, dust can also be produced directly with the refiner instead of fibers. When energy demand decreases (for example, at night), no wood-based panels are produced; instead, dust is generated. When energy demand increases again (during the day), the previously generated dust is burned, the thermal energy is converted into electrical energy, and then fed back into the power grid that supplies the machines for manufacturing the wood-based panels.

[0027] The dust bunker(s) can be built in various locations. Their size is adapted to the surroundings, and their number is determined by the amount of dust required for energy storage. The dust does not have to be wood-based; the use of any type of dust or dust mixture is conceivable.

Claims

1. A method for storing and later recovering electrical energy of a wood processing plant with the following steps: a) calculating the energy required by the plant in advance, b) determining an energy requirement limit which is not met when power from a supply network is cheaper than the power generated in the wood processing plant and which is exceeded when power from the supply network is more expensive than the power generated in the wood processing plant, c) generating a dust by means of an electrically driven device when the energy requirement limit is not met when production and therefore the demand for power of the wood processing plant decreases, d) storing the dust in a dust bunker, e) evacuating at least some of the dust from the dust bunker if there is a need for electrical energy, f) burning the dust to generate thermal energy when the energy requirement limit is exceeded when production and therefore the demand for power of the wood processing plant increases, g) converting the thermal energy into electrical energy.

2. The method according to claim 1, characterized in that the dust is generated by milling a material.

3. The method according to claim 1, characterized in that the dust is generated by machining a material.

4. The method according to claim 3, characterized in that the dust is generated by grinding a material.

5. The method according to claim 2 or 3, characterized in that the dust is made from dried wood chips.

6. The method according to claim 2 or 3, characterized in that the dust is made from dry recycled wood.

7. The method according to claim 5, characterized in that the wood chips are made of round timber and are intermediately stored before drying.

8. The method according to claim 7, characterized in that the dried wood chips are stored.

9. The method according to claim 7 or 8, characterized in that the wood chips are collected from storage and ground to dust in a mill when needed.

10. The method according to one of the preceding claims, characterized in that the handling of the dust, from generation to release, is automated.

11. The method according to one of the claims 1 to 6, characterized in that the handling of the dust, from generation to burning, is automated.

12. The method according to one of the preceding claims, characterized in that the dust is burned by way of spontaneous combustion as a dust cloud.

13. The method according to claim 1, characterized in that the plant comprises an installation for producing wood-based material panels.

14. The method according to claim 1 or 13, characterized in that the electrical energy required by the plant is regularly calculated and then, if the previously defined energy requirement limit is reached, electrical energy is stored or recovered.

15. The method according to claim 14, characterized in that the energy requirement is continually calculated.

16. The method according to one of the preceding claims, characterized in that the burning of the dust serves to generate steam, which drives a steam turbine coupled with a generator.