The European Energy Research Alliance released a white paper on industrial heat storage technology research and development

Recently, the European Energy Research Alliance (EERA) Joint Research Program on Energy Efficiency of Industrial Processes (JP EEIP) released the white paper "Industrial Heat Storage: Supporting the Transformation to Decarbonized Industry", which puts forward the current status, challenges and research and development suggestions of industrial heat storage technology. The main points are as follows:

1. Potential applications of heat storage in industry

1. Industrial process heating or cooling

Depending on the climatic conditions, industrial solar heating systems can be combined with heat storage systems. Promising applications include: ① For high temperature process heat demand (400°C), electric heating combined with porous solid heat storage can be used; ② For medium temperature hot water and process steam demand (up to 200°C), there are multiple options, Including the combination of industrial heat pumps and heat storage, and the combination of solar heating systems and heat storage; ③For industrial cold storage (below 6°C), refrigeration systems (such as air coolers or air conditioners), sensible heat or phase change material heat storage systems can be provided Low-temperature energy to meet cold demand peaks at the start of a new refrigeration cycle and utilize low-cost renewable electricity.

2. Utilization of industrial waste heat

Promising applications include: ① Short-term heat storage, where the residual heat from batch processing is used to preheat the next batch to reduce energy input and improve energy efficiency, and the heat storage technology used depends on the available residual heat ( For example, exothermic processes in chemical industry that require sufficient starting temperature, such as polymerization or alkoxylation), short-term heat storage can also improve the potential of district heating using fluctuating industrial surplus heat; ② long-term heat storage, industrial production The remaining heat in the process is stored to provide space heating for the industrial base in winter, or output to the district heating network, which requires the heat storage temperature to be at 70-120°C, or to upgrade the stored low-temperature heat, and for low-temperature demand The heat users provide heat.

3. Industrial backup heat storage

Industrial backup thermal storage can be used as an uninterrupted thermal energy supply in case of emergencies, which requires fast response and high reliability. At present, the industry mostly relies on gas-fired boilers as a backup heat source, and the heat storage system can provide backup steam, avoiding the use of steam boilers. The products currently available in the market are steam accumulators, while phase change material heat storage and thermochemical heat storage solutions are the focus of future development. For higher temperature heat storage, porous solid heat storage can be used, and high temperature phase change materials and thermochemical heat storage can be developed in the future.

4. Industrial thermal power supply

In addition to batteries, heat storage can provide a low-cost solution to meet the future demand for high power, high capacity, and long-term energy storage. Industrial heat power supply needs to focus on the development of several technologies: ①High-temperature Carnot battery, using electricity Heating stores heat in porous solids up to 800°C; ②Medium-temperature Carnot battery, using a heat pump to convert electricity into heat, up to 200°C, in order to improve performance, industrial waste heat can be used as a heat source for the heat pump; ③Adiabatic compressed air system, Requires high temperature heat storage (often using ceramic porous solids).

2. Current status and challenges of industrial heat storage technology

1. Sensible heat storage

Sensible heat storage stores or releases heat by raising or lowering the temperature of materials. Typical heat storage materials include water, thermal oil, rock, sandstone, clay, brick, steel, concrete, and molten salt.

(1) The technical maturity level (TRL) of liquid-based sensible heat storage has reached level 9, and it is mainly used in situations where the cost is low and the space is not limited, and the heat storage period is several hours to several days. The main technical challenges faced by this type of technology are: ① increase volumetric energy density, thereby reducing space requirements; ② reduce temperature, pressure and slow down molten salt corrosion; ③ reduce heat loss due to lack of compactness.

(2) Solid-based sensible heat storage TRL reaches level 7, which is mainly used in situations where the cost is low and the space is not limited, and the heat storage period is several hours to several days. The main technical challenges faced by this type of technology are: ① reduce weight and increase volumetric energy density, thereby reducing space requirements and system weight; ② improve heat exchange process.

(3) Sensible heat storage TRL based on underground reservoirs such as aquifers reaches level 7, which is mainly used for large-scale seasonal heat storage below 90°C, and heat can also be used during charging. The main technical challenges faced by this type of technology are: ①reduce area requirements; ②reduce dependence on specific geological conditions; ③reduce high-temperature heat loss; ④reduce start-up time; ⑤increase temperature range.

(4) The mine-based sensible heat storage TRL reaches level 7, which is mainly used for large-scale heat storage in the temperature range of 60-80°C for several weeks to several months, and the heat can also be used during charging. The main technical challenges faced by this type of technology are: ①reduce the surface space requirement; ②improve the heat storage efficiency, and improve the influence of heat storage temperature level and stratification characteristics.

2. Latent heat storage

Latent heat storage utilizes the phase change of storage materials. Typical phase change materials include ice, paraffin, fatty acids, sugar alcohols, salt hydrates, inorganic salts, and metals. The TRL of this technology is 4-7, and it is mainly used in small heat storage devices, and the heat storage period is several hours to several days. The main technical challenges faced by this type of technology are: ① increase the heat transfer rate; ② improve the standardization and commercialization process of phase change materials; ③ improve the versatility of solutions; ④ improve the durability of phase change materials; ⑤ improve the purity of heat storage materials .

3. Adsorption heat storage

Adsorption heat storage is based on reversible gas-solid reactions between adsorbates (gases) and solid or liquid adsorbents, typically at temperatures below 200 °C. The heat of adsorption involved in this reversible adsorption/desorption process is usually greater than the sensible and latent heat storage, which has the advantage of being able to store heat for a long time with minimal heat loss. Typical solid sorbents include porous structured materials such as zeolites, silica gel, and activated alumina that can adsorb/desorb gases such as water or ammonia vapor; typical liquid sorbents are concentrated salt solutions such as lithium chloride, lithium bromide, and sodium hydroxide aqueous solution. The TRL of adsorption heat storage is 6-8, which is mainly used in the case of limited space, and the heat storage period is several hours to several months. The main technical challenges faced by this type of technology are: ① increase the commercial materials that can be used above 200 °C; ② use the generated cold energy to improve efficiency; ③ reduce the temperature difference between charging and discharging.

4. Thermochemical heat storage

Thermochemical heat storage is also based on reversible gas-solid reactions, similar to adsorption heat storage, and thus also has the advantage of small heat loss, but has higher heat storage density and lower cost. Its main difference from adsorption heat storage is that the gas is directly absorbed by the solid lattice, thereby changing the crystal structure. When the temperature is below 200°C, use solid inorganic salts and gases for thermochemical heat storage, such as calcium chloride and water vapor, or strontium chloride and ammonia vapor; in the temperature range of 250-600°C, use hydroxide to form (such as calcium oxide/calcium hydroxide) and carbonation reaction (such as calcium oxide/calcium carbonate) for heat storage; in the temperature range of 800-1800°C, oxidation reactions can be used for heat storage, such as barium peroxide/barium oxide or iron/ Iron oxide. The TRL of thermochemical heat storage is 4-6, which is mainly used in the case of limited space, and the heat storage period is several hours to several months. The main technical challenges faced by this type of technology are: ① improving the durability and stability of materials; ② eliminating the problem of agglomeration/agglomeration; ③ reducing the temperature difference between charging and discharging.

3. Emerging heat storage technology solutions

1. Solid sensible heat storage

Solid sensible heat storage systems provide a reliable and safe method for storing high-temperature heat, and recent emerging technologies include concrete heat storage and packed bed heat storage. Norway's EnergyNest company has developed and demonstrated a modular heat storage system based on highly conductive concrete, called Heatcrete®, which was recently applied to the steam pipe network of a chemical plant in Norway and will be used in the brick factory and the Senftenbacher company in Austria in the future Sloecentrale combined cycle power plant in the Netherlands. In Siemens Gamesa's Kano battery pilot plant, a 740°C basalt packed bed heat storage system with a heat storage capacity of 130 MWh is used; ArcelorMittal's steel recycling plant in Spain also uses packed bed heat storage waste heat recovery.

2. Phase change materials for heat storage

The new development of phase change materials for heat storage is high-temperature phase change heat storage materials, whose melting temperature exceeds 100°C, such as nitrate eutectic, dicarboxylic acid, sugar alcohol and even metal materials. In recent years, a lot of research has been carried out on improving the heat storage performance of phase change materials, such as enhancing the thermal conductivity by adding conductive fillers, thereby increasing the charge/discharge rate. By reducing the heat transfer surface area (such as metal fins), more compact and low-cost heat storage systems can be built. In addition, new high-temperature-resistant packaging materials are being developed to improve the application prospects of high-temperature phase-change heat storage materials.

3. Thermochemical and adsorption heat storage

Thermochemical and adsorption heat storage technologies are developing composite materials with high energy density and stability. The research and development department is exploring the composite material and its preparation technology of adding salt in the porous matrix, aiming to increase the energy storage density, enhance the stability of adsorption/reaction, and prolong the life at the same time. In addition, coating technologies have been developed to prevent caking or pulverization of thermochemical materials. The Swedish energy company SaltX Technology has confirmed the feasibility of this scheme. The company has developed a nano-coated salt for a thermochemical heat storage system called EnerStore, which has achieved multiple charging/discharging with low-cost materials. Circulation, a system based on a thermochemical reaction between calcium oxide and water/steam, has been piloted for Power-To-Heat at the Vattenfall CHP plant in Berlin and has been in operation since March 2019 use. Its heat storage capacity is 10 MWh, the total efficiency of electric heating is 72%-85%, and the theoretical maximum is 92%, which can control the heat release rate and level with high precision.

4. Advanced Simulation

The development of simulation models can effectively support the application of heat storage systems in integrated industrial energy systems, and can quickly design heat storage systems and conduct sensitivity analysis for innovative configurations. For example, a simulation-based performance evaluation of system designs has been newly developed in the field of latent heat storage. Especially for industrial thermochemical heat storage systems, the kinetics of thermochemical reactions in reactor and process design can be predicted by advanced nonparametric models. The efficiency of the overall system can be improved by changing the original adsorption unit to be part of a hybrid adsorption/compression cooler. The scheme increases the utilization of renewable energy by combining thermal and electrical energy, especially for low-temperature heat storage applications such as food processing.

4. Industrial heat storage system integration

1. Electric heating and power generation (Power-to-Heat-to-Power)

The electrification of industrial production has become the focus of research and application, but replacing industrial process fuel with electric energy will cause problems related to fluctuating power supply and grid capacity, which need to be solved by energy storage systems. So far, there is a lack of cost-effective energy storage systems that are not limited by geographical locations. Power-to-X-to-Power (PXP) is considered a promising solution, which will Electrical energy is converted to other forms of energy carrier and stored, reconverted to electrical energy when required. Electric heating power generation (Power-to-Heat-to-Power) is a low-cost option for PXP, also known as the Carnot battery solution. Siemens Gamesa has made a successful demonstration. Its Carnot battery storage in Hamburg The thermal power station was put into operation in the summer of 2019, using a basalt packed bed for heat storage and charging air through electric heaters and blowers. The system uses a steam Rankine cycle to convert stored heat into electrical energy with an electro-thermal-electric efficiency of 45% and a maximum power generation of 1.5 megawatts.

2. Renovation of existing power plants

Integrated heat storage systems can also help retrofit existing fossil fuel power plants, especially coal plants facing partial closure under CO2 reduction targets. For example, the German I-Tess project converts the surplus power of existing coal-fired power plants into heat, and uses the steam cycle of the power plant to convert heat energy when power is in short supply. The German Store To Power project is developing a thermal storage power generation pilot plant that combines an existing coal-fired power plant with high-temperature heat storage, including electric heating and a steam generator that can transport about 10% of the steam in the steam cycle of a coal-fired power plant. Siemens Gamesa is one of the leading companies dedicated to the transformation of coal-fired power plants. By integrating the heat storage system, it can provide electricity, heat or steam with the input of fluctuating renewable energy power. It has already carried out a 30 MW basalt heat storage system. demonstration.

5. Technical Action Suggestions

To facilitate the large-scale adoption of industrial heat storage, immediate technical action is required, especially for the pre-commercialization phase (Phase P) and the commercialization phase (Phase C), recommending:

(1) Carry out industrial heat storage research and development projects (P phase), focusing on the technical challenges mentioned above.

(2) Carry out technical and economic research on heat storage and its industrial application (P stage), including: ① Applying heat storage technology in renewable energy power-heat/cold-power generation, such as Carnot battery; ② In renewable energy Heat storage technology is used in electric heating/cooling to match fluctuating power supply with industrial heat demand; ③ Utilize geothermal energy and solar energy to meet heat demand; ④ Recovery, storage and utilization of industrial waste heat; ⑤ Heat storage in industrial refrigeration and cold chain applications; ⑥ use heat storage as a reliable backup system when other heating technologies fail.

(3) Identify and share applications where heat storage has economical, environmental, and operational advantages over other forms of energy storage (batteries or hydrogen) (Phase P).

(4) Develop and operate heat storage demonstration projects and provide open access results and data (Phase P).

(5) Actively share best practices and disseminate knowledge and data to industry, policy makers, and other stakeholders through publications, speeches, and other forms of media engagement (Phase P).

(6) Develop an accessible heat storage material database with unified key performance indicators (Phase C).

(7) Collaborate with regulators, professional bodies and industry to develop standardized heat storage systems (Phase C).