The deployment of Industry 4.0 technologies and smart grids is enabling the development of new ways to manage energy through energy flexibility mechanisms . This allows energy-intensive industries to optimize their energy use and reduce their carbon footprint and energy costs. It also contributes to improving the stability and reliability of the electricity grid as a whole.
Energy flexibility mechanisms are enabling more efficient adjustments to electricity supply and demand. By combining different sources of demand flexibility, various innovative solutions can be structured to allow flexible industries to optimize sector coupling with the help of intelligent equipment and control systems (e.g., electricity-heat, electricity-gas, smart electric vehicle charging, industrial and/or commercial demand response using IoT or IIoT).
Demand flexibility can be defined as a portion of demand, including that arising from the electrification of other energy sectors (e.g., heating or transport through sector coupling), that could be reduced, increased, or shifted over a specific period of time to:
- Facilitate the integration of Variable Renewable Energy (VRE) by reshaping load profiles to adapt them to VRE generation
- reduce peak loads and seasonality; and
- reduce electricity generation costs by shifting the load from periods with high supply prices to periods with lower prices.
Demand flexibility is already a reality and is being unlocked in many parts of the world.
Currently, a wide variety of real-world use cases for demand flexibility can be found in the industrial, commercial, and residential sectors. Below, I propose to analyze the cement industry as a practical case study.
By analyzing in detail the typical processes of any industry, it can be identified that the implementation of energy flexibility mechanisms could contribute significantly to a more sustainable industry , through the implementation of energy efficiency technologies, the integration of energy storage systems and the use of increasingly cleaner energy sources, such as natural gas and renewable energies.
CASE STUDY: CEMENT INDUSTRY
The cement industry is one of the world’s largest and most important industrial sectors , as cement is one of the most widely used building materials today. Its production is a very energy-intensive activity (in the form of heat or electricity), and energy costs represent a significant portion of its manufacturing costs (approximately 30%).
Unfortunately, cement production is also one of the industrial activities that produces the most carbon dioxide emissions , contributing significantly to global warming and climate change. Each ton of cement produced emits, on average, about one ton of carbon dioxide into the atmosphere.
In the cement production process [1] large amounts of thermal (heat) and electrical energy are used as energy sources for its production process and auxiliary areas.
Its manufacture begins with the extraction of raw materials such as limestone, clay, sand, and iron ore. These materials are ground and mixed in specific proportions to produce clinker, a granular material that is fired at high temperatures (~1,500°C) in a rotary kiln.
After firing, the clinker cools and is then conveyed to a system of conveyor belts that allow it to be mixed with other elements such as gypsum, limestone, pozzolan, and/or ash. This process is carefully controlled, as the proportion of each element determines its final application.
Once mixed, they go through a dry grinding process, where their main objective is to reach certain finenesses for subsequent storage in silos and dispatch in different forms, either as packaged cement and/or bulk cement.
In general, in the cement industry, the distribution of energy consumption is as follows: 80%-90% in the use of fuels for heat generation and 10%-20% in electricity.
Opportunities for Energy Efficiency and Flexibility
To design an optimal energy efficiency and flexibility strategy in an industry, a detailed knowledge of its processes, the technologies available for energy saving and operational flexibility, and the functioning of the electricity market (if the industry is interconnected to the electrical system) is required.
The most effective energy efficiency strategies in the cement industry [2] involve changes to fundamental equipment or processes in the production plant. Some of the most commonly identified opportunities in this industry are:
- Utilization of residual heat from processes (e.g., kiln, preheater and clinker cooler) to cogenerate electricity through a steam turbine, achieving efficiencies greater than 90%.
- Improvements in Process Control Systems. Mills operate most efficiently at their maximum capacity, so process control systems that maximize mill performance can reduce specific mill energy consumption. Implementing process control systems generally results in energy savings of up to 10%.
- Savings from changes to more efficient equipment in raw material mills and grinding circuits (up to ~25 kWh/ton of cement), induced draft fans (up to ~10 kWh/ton of cement), compressed air systems (up to 33% of electricity consumption), conveying systems and silos, and through the conversion of processes in the kiln from wet to dry and semi-wet, being able to reduce fuel use by up to 50%, and increase the performance and lifespan of the kiln refractory.
Implementing energy flexibility strategies in an industry requires identifying critical and non-critical processes and loads in order to manage them optimally.
In the cement industry, electrical loads associated with the kiln system cannot be stopped or changed without product loss or damage to the kiln. This includes the drives for starting the kiln, the operation of the clinker cooler, material transport to and from the kiln, the induced-draft fans, and the filtration system that cleans the exhaust air to environmental standards before it is released into the atmosphere. However, as long as the pyroprocessing is not interrupted, significant electrical savings can be achieved without impacting plant operation.
On the other hand, operations related to the extraction and crushing of raw mix, fuel, and clinker, while critical, could be included in a flexible equipment (FE) scheme due to their intermittent nature. Critical loads such as raw and cement mills, and production process engines, can adopt a slightly different, event-based (opt-in) flexibility scheme. Another aspect to consider with this type of rotating equipment is that, for safety reasons, automatic start-ups and shutdowns are preferred.
For non-critical loads such as raw material storage, compressor operation, or lighting, fully automated FE schemes could be adopted . The interruptibility of these loads depends on the amount of storage present at various points in the cement process , the capacities of the mills compared to the kiln, and the types of mills used in grinding.
Plants with limited cement storage capacity lack the flexibility to shift the load across their finishing mills. If the cement mills or raw mills are undersized compared to the kiln, they may need to operate continuously during peak cement season to prevent bottlenecks throughout the cement manufacturing process, thus ruling out shutdown as a functional efficiency (FE) strategy. The technical capacity to implement a FE scheme depends on the level of controls and automation present at the cement plant .
Since cement plants are energy-intensive facilities, managing their energy demand is not a new issue. Through the implementation of flexibility strategies , cement plants have been able to modify their consumption patterns, allowing them to operate during periods of high electricity prices and peak demand with mills idle, resulting in savings of up to 30% in their energy costs.
Some of the most common energy efficiency (EF) strategies in industry are not new. Schemes such as [3] “Load Shifting, Load Scheduling, Load Shedding, and Fuel Switching” have been around for a long time . With the inclusion of sector coupling through the electrification of heat, hydrogen production and transport, and a greater level of sophistication in communication, monitoring, and control systems, industries are taking a more active role in managing their energy resources.
The following is a brief description of the most common FE strategies applicable to the Cement Industry :
1. Load Shifting and Load Scheduling Schemes
Material handling capabilities depend on the level of automation and programming, as well as the amount of storage at each stage of the cement manufacturing process. With proper automation, the plant’s operations can be programmed to respond to changes in dynamic electricity rates, allowing production to occur during off-peak hours.
Crushing clinker, fuel, and raw materials are energy-intensive processes that can be moved away from peak hours and higher electricity rates , provided there is sufficient storage to supply raw mix and fuel to the kiln and to store clinker during peak hours.
If the raw mix storage facilities are adequate, then the extraction, crushing, and homogenization of the raw materials can also be shifted to off-peak hours without interrupting plant operation.
With modern dispatch systems, cement shipping can be fully automated, providing the possibility of moving cement shipments outside of peak hours if truck or train scheduling is flexible.
2. Load Shedging Scheme
During periods when it is economically advantageous to reduce electricity consumption, numerous processes can be eliminated without interrupting the proper operation of the kiln, while maintaining necessary support processes. The raw material mill and the cement mill are the largest interruptible loads . If the raw material mill can be stopped, the rock crushers and quarry conveyors can also be shut down, as well as the raw material homogenization process, and the kiln can be fed with the raw mix from the storage silos. The cement mill can be shut down, and the clinker from the cooler will be stored.
Mills operate more efficiently during steady-state operation, so for the Load Shedding Scheme to be feasible, the incentives received for providing the Flexibility Service must outweigh the cost of stopping and starting up the processes.
If shutting down the cement mill completely is not feasible or desirable, cement can be ground from clinker with lower grinding energy requirements. If a plant manufactures several types of cement, grinding varieties with lower grinding energy requirements during peak hours can generate some energy savings without reducing mill output.
3. Fuel Switching
Within this scheme are solutions such as “Power to Heat”, “Hydrogen to Power” and Transport Electrification, which promote efficient electricity consumption.
3.1 “Power to Heat”
Solutions of this type are based on the integration of the heat and energy sectors through heat pumps, boilers and electric heaters, and energy storage. By converting electricity into heat, these technologies can provide demand-side flexibility through automation and intelligent management of their use.
Heat pumps are characterized by their high efficiency (one unit of electricity can produce four to five units of useful heat). Furthermore, some heat pumps are controllable, meaning their output can be varied. However, although their operating costs are decreasing, their capital costs remain high. Heat pumps are typically used to provide heating and cooling in industrial, commercial, and residential applications. They represent a viable option for displacing fossil fuels and promoting decarbonization.
Electric boilers or electric water heaters are devices that use electricity to heat water. In these devices, electricity flows through heating elements, which, due to their high ohmic resistance, produce heat according to Joule’s law. Their efficiency is much lower than that of heat pumps (typically 1 unit of electricity produces 1 unit of heat) but higher than that of conventional fossil fuel boilers. The capital costs of these devices are much lower, and therefore they are becoming increasingly common today.
Thermal energy storage is a type of energy storage system that can absorb and release heat (or cold) as needed. Thermal storage helps to balance the supply and demand for heating or cooling more efficiently.
3.2 «Natural Gas / Hydrogen to Power»
Cement kilns operate using coal or petroleum derivatives, but they often use other materials, usually waste and by-products from industrial processes – used tires, municipal waste, sewage sludge… – which depend on the location of the plants.
This scheme proposes the incorporation of natural gas and/or hydrogen into the fuel mixture that feeds cement kilns and mills , with the aim of improving combustion, replacing the use of polluting fuels, reducing CO2 emissions and optimizing energy requirements.
The use of natural gas in the cement industry has several advantages. First, it is a cleaner fuel than coal and oil, as it emits less carbon dioxide and other pollutants. This has led many cement companies to adopt natural gas as part of their sustainability and emissions reduction strategy.
Secondly, natural gas is a more efficient fuel than coal and oil. This means that less natural gas is needed to produce the same amount of energy as with other fuels. Therefore, its use can generate significant savings in production costs.
Third, natural gas is a safer fuel than other fossil fuels. As a mixture of gaseous hydrocarbons, natural gas is less flammable and explosive than other liquid fuels. This reduces the risk of accidents and increases worker safety in the industry.
On the other hand, there is hydrogen, an energy carrier like electricity, which is generating increasing interest in various countries and institutions worldwide. Hydrogen produced using renewable energy (Green Hydrogen) is identified as the potential missing link in the energy transition that could help to significantly decarbonize the industrial, commercial, and residential sectors. Hydrogen production from renewable energy is achieved through electrolyzers by coupling the energy and hydrogen sectors, also known as energy-to-hydrogen.
Electrolyzers are devices that use electricity to split water into hydrogen and oxygen. Electrolyzers can provide demand-side flexibility by adjusting hydrogen production to match wind and solar power generation patterns during periods of high resource availability (and therefore low electricity prices), and they can also provide grid balancing services.
3.3. Smart Charging of Electric Vehicles
The cement industry has already begun its transition to sustainable mobility. By using tractor-trailer trucks and concrete mixer trucks that operate entirely on electricity, they are reducing their fossil fuel consumption and carbon footprint in transportation. These electric trucks feature a completely silent motor , operate on 600-volt batteries, and have the capacity to transport four tons of cement per trip.
The electrification of transport through the use of electric vehicles demonstrates a demand-side flexibility scheme . Electric vehicles can employ different charging strategies. The simplest is generally known as uncontrolled charging, meaning that electric vehicles will charge to maximum power as soon as they connect to the grid. This charging strategy is inflexible and can pose a challenge to electrical systems if the number of connected electric vehicles is high, increasing peak load and ramp requirements and presenting additional flexibility issues for the system. However, with the use of smart charging strategies, the charging process can be optimized according to the limitations of the distribution and/or transmission network, the local availability of renewable energy sources, charging price signals, and customer preferences.
4. «Combined Heat & Power Modulation (“CHP”)»
Cement manufacturing is an energy-intensive industrial process, but it also has significant thermal surpluses, despite the thermal integrations used in it. This means that the cement industry has a high potential for generating electricity from the waste heat of the process.
Traditionally, combined heat and power (CHP) systems have been sized to meet the specific energy needs of each industrial facility. However, with a relatively modest investment, these systems could be redesigned with sufficient additional generation capacity to support the electrical grid.
Because CHP units located in industries generally operate continuously, they can respond quickly when grid services or additional power are needed.
The additional revenue from grid services could significantly enhance the profitability of a cogeneration system, transforming it into a revenue generator. There are examples of industrial users participating in Reliability Markets through their CHP systems , obtaining a substantial additional source of income to offset the investment costs of these systems.
“CHP” systems offer multiple benefits and advantages compared to conventional power production, including:
- Greater efficiency: produces electricity and heat needed for industrial processes with less fuel use
- Reduced emissions: due to lower fuel consumption, they contribute to reducing greenhouse gas emissions and other air pollutants.
- Reduced costs: CHP efficiency reduces operating costs and can provide protection against increases in electricity costs.
- Reliability: “CHP” systems are on-site generation plants, which reduces dependence on the energy grid and can offer greater energy security and reliability in electricity production even in the event of a disaster or grid interruption.
5. «Solar PV/ BESS»
Solutions that integrate photovoltaic solar energy and battery energy storage systems (“BESS”) allow you to harness and capture all the solar energy generated to use it and/or send it to the grid when needed , avoiding the loss of resources or economic losses due to under-dimensioning (non-optimal) “behind-the-meter (BTM)” solutions.
BESS systems, when combined with local thermal or renewable generation, can smooth variability, improve operational efficiency, and store excess energy for later use, resulting in a more cost-effective and resilient microgrid.
With the electrification of processes, the use of fossil fuels is expected to be displaced for energy solutions, with storage or storage + renewable energies playing a leading role in providing a flexible and environmentally friendly supply.
Energy storage allows renewable energy sources to be used for more hours of the day and enables projects to be sized with better financial performance metrics. Storage also allows on-site thermal generation to operate more efficiently and with less variability, reducing emissions and associated costs. Energy storage systems (ESS) can operate to respond to the internal needs of industry and the grid through the use of advanced control and analytics systems.
6. By-Product Optimization
The use of recycled materials is one of the seven principles of sustainable construction. Recycled materials, such as recycled concrete aggregate, contribute to reducing the use of primary raw materials in cement and concrete production.
Recycled cement and concrete are mainly used for road construction, and smaller quantities are also used in the production of new cement and concrete with mixes reaching up to 20%.
The use of recycled concrete aggregates is a clear and obvious example of the circular economy at play and has benefits that include reduced use of natural resources and less landfill waste. It provides a significant opportunity for the concrete industry to contribute to the sustainability of the modern built environment.
Digitalization of the Cement Industry
Unlike many other industries, the cement industry has not yet embarked on its comprehensive journey to digital transformation. Of the 54 manufacturing plants designated as leaders in the use of Industry 4.0 technologies according to McKinsey & Associates , none are cement plants.
The cement industry must evolve into a self-organizing sector within a “smart ecosystem.” Linear processes and isolated functions must be transformed into interconnected clusters that exchange information in real time.
In the cement plant of the future, flexibility is the key approach. Real-time, data-driven decision-making will be the norm, and continuous adjustments will account for the ecosystem’s variability.
The digital revolution in the cement industry must be accompanied by a large number of very rapid changes, which will be supported by six core technologies of Industry 4.0 :
- Artificial intelligence and robotics
- Internet of Things
- Digital Twins
- Autonomous vehicles
- Blockchain
- 3D printing
There are different efforts underway across the cement industry and different paths to achieving digitalization. Oficemen , in partnership with Siemens, proposes following the “5 values – 5 pillars – 12 digital portfolio components” method :
The 5 Pillars of Digitalization
The pillars refer to the set of investments that companies must undertake to fully develop their potential and to occupy a strategic market position above their competitors. These five pillars are:
- Intelligent equipment: These are fixed assets of the manufacturing process, autonomous and capable of interacting with their environment, often with the help of sensors that trigger response actions.
- Networking and connectivity: are based on decentralized ICT systems that cover all aspects of production, form the habitat of an ecosystem for the integration of new applications and equipment and can create a virtual view of production.
- Value chain integration will result from the integration of ICT systems. Daily operations within a company will be better coordinated once the value chain has been integrated into the set of decision-making methods and variables, and this integration occurs in an optimized, often automated, manner. The complete, real-time connection of all links in the chain, facilitated by value clusters and automation, will be the integrating factors for the entire value chain. In this way, changes in supply and demand are automatically and directly fed into the production process, allowing for a rapid and efficient response to periods of greater market volatility. This enables companies to become more agile and evolve towards dynamic, market-oriented models.
- Data analysis: To fully leverage digitalization, data analysis tools must be developed or acquired. Applying statistical algorithms to multidimensional time series data obtained in real time allows for maximizing the benefits of the vast amounts of data generated by digitalization. The advantages of data analysis range from cost savings through predictive maintenance and reduced spare parts inventory to the optimization of production-related assets and the improvement of business strategy.
- Smart products: These are products that can interact with customers and provide benefits and services beyond their immediate function. These products allow companies to identify new business opportunities they don’t currently offer.
The 12 Components of the Digital Wallet
To support the implementation of the five pillars mentioned above, Oficemen/Siemens propose to support the transformation of the industry with the following digital portfolio:
- Reliable automation of the cement manufacturing process.
- Systematic energy saving.
- Advanced process control.
- Information and network security.
- Industry Information Structure (IT).
- Sensor technology and smart equipment.
- Status monitoring and diagnosis.
- Smart manufacturing management.
- Digital twin and simulation.
- “MindSphere” analysis of factory data.
- Factory life cycle design.
- Autonomous operation.
The implementation of these advanced technologies will allow the cement industry to optimize its energy use , putting it on the path to energy savings and thus contributing to a more sustainable and energy-efficient industry.
This case study is a clear example of the importance, for the energy transition, of incentivizing the development of smart industries and the use of energy flexibility mechanisms.
Implementing advanced technologies in industry can significantly reduce the carbon footprint and contribute to the stability and reliability of the electrical grid as a whole. Furthermore, by utilizing energy flexibility in production processes, load profiles can be adapted and energy use optimized, enabling more efficient integration of variable renewable energy sources. All of this is essential for reducing greenhouse gas emissions and achieving the emissions reduction targets set in international agreements.
[1] Cement is a composite material mainly made up of clinker, gypsum and additives, which is used as a binder in the construction of buildings, roads, bridges, dams and other infrastructure projects.
[3] In Europe, demand response programs have been minimal due to many barriers, such as the lack of adequate price signals or a regulatory framework that would allow business models to flourish. In the United States, such schemes have been in operation since the early 1970s, and since the early 2000s, many independent system operators have implemented demand response programs (e.g., ERCOT, NYISO) enabling industrial demand participation in ancillary services markets or the Demand Response Program.