Created by: Glen Zhu | Updated Date: November 21st, 2023
In contemporary biogas facilities, a diverse range of organic materials, including agricultural residues, plant matter, food scraps, and by-products from the production of sugar, wine, and beer, are processed in anaerobic digesters. The materials undergo fermentation within sealed containers where specialized bacteria thrive in the absence of oxygen. During the fermentation process, biogas is produced as a result of organic components breaking down. Biogas, a renewable source primarily composed of methane, is harnessed to provide a sustainable energy source – heat and electricity for various applications. The entire procedure occurs within a fully operational biogas plant.
The Figure illustrates the fundamental concept behind a biogas plant. Facilities typically encompass input systems for solids or liquid substrates, one or multiple heated fermenters, a storage tank, and possibly a post-fermenter, gas tank, and gas treatment unit.
The core component, known as a combined heat and power station (CHP), includes a gas engine with a heat exchanger and an attached generator. Depending on the energy content of biogas, A combined heat and power (CHP) system can attain an electrical generation efficiency of approximately 30% and a heat generation efficiency of around 60%. The generated electricity is integrated into the public power grid, while some of the produced heat is utilized to maintain the fermenter’s temperature. Additionally, the surplus heat finds applications in heating residential and agricultural buildings, maximizing the overall energy utilization of the biogas plant.
Figure 1 – System overview of biogas plant
Lightning Protection Systems (LPS) and surge protection structures are not optional, but essential demands mandated by various regulations and safety standards globally that emphasize the critical need to safeguard lives, property, and electronic equipment from the devastating impact of lightning strikes and voltage spikes.
Adhering to international standards, for instance: IEC 62305 in Europe, Lightning Protection System is not just a legal obligation but a fundamental responsibility. Compliance with these standards ensures that structures are equipped with certified Lightning Protection Systems and surge protective devices, providing comprehensive protection from structural damage, electronic equipment failure, and lightning-induced fires.
According to the Institute of Electrical and Electronics Engineers (IEEE) Standard 142, lightning-induced surges and electromagnetic fields can cause significant harm to sensitive equipment and devices. The induced surges can lead to voltage transients, damaging circuitry and disrupting operations. In addition, the National Fire Protection Association (NFPA) 780 standard highlights the risk of fire caused by lightning strikes. Lightning-induced fires can occur in various settings, including residential, commercial, and industrial areas. The extreme heat generated during a lightning strike can ignite flammable materials, leading to destructive fires that endanger lives and property.
For instance, in a lightning strike, the voltage can surge to levels as high as 300 kV per meter, and the current can spike to tens of thousands of amperes within microseconds. The rapid surge of voltage and current can induce powerful electromagnetic fields, leading to voltage transients in nearby conductive systems. In the absence of proper lightning protection, sensitive electronic equipment in biogas plants can experience voltage spikes of several thousand volts, well beyond their tolerance levels, causing irreparable damage.
Biogas safety primarily involves safeguarding the anaerobic digestion building, fermenter facilities, and other related structures. Lightning strikes can carry extremely high voltages, reaching up to 100 million volts, and current intensities of 30,000 to 50,000 amps. These immense electrical discharges can cause devastating damage to any structure or system in its path.
To counter risks, external lightning protection devices, notably lightning rods, and air-termination systems, play a pivotal role. Strategically positioned on elevated points, lightning rods intercept lightning strikes, channeling the electrical energy safely to the ground through a well-designed grounding system. By absorbing and dissipating excess energy, it helps devices shield critical components from damage, ensuring uninterrupted plant operations. Lightning protection devices act as a reliable barrier, preserving the integrity of components housing precise electrical equipment within a biogas plant such as fermenters, anaerobic digesters, and electronic control systems.
Fermenters in modern biogas plants are frequently roofed with foil due to their inherent advantages. Foil roofs, which are durable and weather-resistant, capable of withstanding UV radiation and moisture, ensure long-term reliability and create an airtight enclosure crucial for controlled anaerobic digestion in foil-roofed fermenters. Maintaining precise internal conditions enhances the fermentation process, maximizing biogas yields. Some foil materials also enable natural light transmission, reducing the need for artificial lighting and promoting energy efficiency.
To safeguard fermenters with foil roofs from direct lightning strikes, two effective methods are employed. One approach involves the installation of steel telescopic lightning protection masts, as depicted in Figure 3. The masts can be adapted for natural soil and ground foundations, reaching impressive heights of over 25 meters in customized versions.
Figure 2 – Lightning surge protection system used to protect a fermenter with foil roof
Figure 3 – Protection of a fermenter with a foil roof by means of telescopic lightning protection masts
Alternatively, the use of conductors offers another viable solution. High-voltage-resistant conductors, insulated and equipped with a unique outer sheath, function as insulated down conductors, complying with IEC 62305-3 (EN 62305-3) standards. To ensure compliance with the required separation distance, the separation distance is calculated according to the standards and verified against the equivalent separation distance of the conductor.
In Solution 1, air-termination masts with pre-assembled conductors are internally installed, as depicted in Figure. The total length of the air-termination system from the equipotential bonding level to the air-termination tip is limited to 15.5 meters (for LPS II class). Due to mechanical constraints, the free length above the fermenter’s top edge should not exceed 8.5 meters.
For Solution 2, air-termination masts with pre-assembled power conductors are internally installed. The total length of the air-termination system from the equipotential bonding level to the air-termination tip is restricted to 18 meters (for LPS II class). Similar to Solution 1, the maximum free length above the fermenter’s top edge remains at 8.5 meters.
Figure 4 – Protection of a fermenter by means of air-termination masts, isolated by means of a conductor
Figure 5 – Protection of a fermenter by means of air-termination masts, isolated by means of a conductor
Metal sheets are an excellent choice for fermenters due to their outstanding conductivity, strength, durability, uniformity, and ease of installation. As regulated in Table 3 of IEC 62305-3 (EN 62305-3), ranging in thickness from 0.7 mm to 1.2 mm, strike a balance between strength and flexibility, ensuring durability and compliance with safety standards during lightning strikes.
Adequate conductivity is crucial for facilitating the efficient dissipation of electrical charges, significantly mitigating the risk of lightning-induced damage. It is imperative to ensure that metal sheets used in fermenters meet stringent electrical conductivity standards outlined in regulations like IEC 62305-3 (EN 62305-3). Adequate conductivity is vital for efficiently dissipating electrical charges, substantially reducing the risk of lightning-induced damage.
Inadequate conductivity can lead to the generation of excessive heat, melting, or even ignition at the point of impact during a lightning strike. Such scenarios pose a substantial risk of fire, explosion, or structural damage within both the fermenter and the broader biogas plant.
The Figure illustrates a biogas tank surrounded by completely welded steel sheets, with a focus on lightning protection. Compliance with Annex D of IEC 62305-3 (EN 62305-3) is imperative for the lightning protection systems, which provides essential supplementary information tailored specifically for lightning protection systems (LPS) in structures vulnerable to explosion risks. Notably, if the explosion risk zones associated with exhaust openings fall within the protected area safeguarded by the enclosure’s lightning current-carrying metal components, the installation of additional air-termination systems is unnecessary. However, if the alignment is not met, the implementation of supplementary air-termination systems becomes necessary. The systems are vital in shielding the exhaust openings from direct lightning strikes.
Furthermore, the integration of extra lightning protection systems demands meticulous connection to the container’s enclosure without disrupting the existing anti-corrosion measures. In scenarios where seamless integration proves challenging, an isolated lightning protection system, such as the conductor, should be considered. This approach ensures comprehensive lightning protection while maintaining the integrity of the biogas tank’s structural and anti-corrosion measures, promoting the development of green energy.
When lightning occurs and tension increases, a well-established earthing-termination system in a biogas plant serves multiple crucial functions and it as a part integrates a complete grounding system. It ensures the safety of personnel working within the facility, providing a secure pathway for fault currents to dissipate harmlessly into the ground. Simultaneously. The structure significantly reduces the risk of electric shocks, creating a secure environment for workers. In parallel, the earthing system is critical in safeguarding the plant’s electrical equipment by redirecting fault currents away from sensitive devices like control panels and motors.
Figure 6 – Earthing system within a biogas plant
In addition to the earthing system, equipotential bonding is another required element of the grounding infrastructure, seamlessly integrating into the complete Lightning Protection System. Equipotential bonding aims to eliminate potential differences between conductive parts, ensuring they remain at the same electrical potential. The system prevents electrical shocks and reduces the risk of sparks in case of a fault. In a biogas plant, various metallic structures, pipelines, and equipment are bonded together to maintain uniform voltage levels.
The generated biogas is commonly utilized in gas or pilot injection engines to produce both electricity and heat. These engines are designated as combined heat and power plants (CHP). The CHP facilities are situated within a distinct operational structure. Within this building, the electrical equipment, switchgear cabinets, and control cabinets are either co-located in the same room or housed separately. The electricity generated by CHPs is integrated into the public grid system.
Figure 7 – AC lines of main low-voltage distribution borad of the consumer installation
As previously indicated, it is imperative to establish equipotential bonding following established standards and protocols for all conductive systems entering the building.
Surge protective devices (SPDs) are essential electrical components designed to safeguard electronic equipment and appliances from voltage spikes or surges. Surges can result from lightning strikes, power grid fluctuations, or switching operations within the electrical system. When the voltage across an MOV exceeds a specific threshold, typically known as the “clamping voltage,” the MOV begins to conduct electrical current.
A type 1 surge protective device is installed at the main electrical incoming 230/400 AC lines of the low-voltage distribution board. For instance, FLP25-275, renowned for its robust capabilities, is a pluggable type 1 AC Surge Protective Device that can withstand an impulse current of up to 25kA (10/350 μs). Thanks to its unique design, it can effectively solve the isolation and extinguishing arc, greatly mitigating risk of causing fires. SLP40-275/4S type 2 Surge protective device, mounted in the sub-distribution boards located downstream. Having received certifications from TUV and CB, it is notably proficient in discharging transient currents of up to 40 kA (8/20 μs).
At the distribution board of the CHP, a modular multipole combined surge protective device is installed to withstand exceeding current. Installing SPDs within a proximity of 5 meters to the loads requires extra protection for terminal equipment.
Modern biogas facilities comprise a diverse array of precise components intricately designed to collaborate seamlessly, facilitating the cohesive execution of the production process. Managing these complexities can be challenging. Therefore, the implementation of remote monitoring systems is essential. Remote monitoring not only enhances the efficiency of the production process but also streamlines management by providing real-time insights, enabling proactive decision-making, and securing prompt issue resolution, thereby optimizing overall plant performance.
The remote monitoring using advanced sensors and interfaces like Ethernet or RS 485, crucial data such as temperature and gas production rates are transmitted in real-time to a centralized system. This technology enables remote access for operators and service staff via computers and modems. Immediate issue resolution is possible, minimizing downtime and ensuring uninterrupted biogas production. Additionally, predictive analytics identify potential problems before they occur, optimizing maintenance schedules and reducing costs. By closely monitoring production trends, operators can make data-driven decisions, enhancing overall efficiency. The communication interface is protected by a combined surge protective device.
Coaxial Surge Protection COAX-BNC/FM
The figure is an example of how a CCTV system is protected using surge protective devices. Camera system architectures exhibit diverse configurations. Video transmission commonly employs a coaxial cable with a BNC plug connection or a twisted pair cable. If the camera incorporates a control unit, data transmission occurs through a serial RS485 interface using a twisted pair cable, while a two-pole cable serves as the power supply. FLP25-DC75 along with patch cables, safeguards the data network – Ethernet, while the FRD4-24 arrester is utilized when a coaxial cable is employed for video transmission.
In contrast, modern cameras, known as IP cameras, feature a single RJ45 connection. The connection handles both data and video signals, as well as power supply through Power over Ethernet (PoE) technology.
Figure 8 – Surge protection for the installations of information technology systems
In biogas systems, a sophisticated process control network ensures seamless operation by capturing real-time data, including temperature, pressure, gas composition, and volume. The captured information will be analyzed promptly, allowing the system to autonomously adjust parameters and optimize microbial digestion conditions for maximum gas production. Predictive analysis identifies potential issues in advance, enabling proactive maintenance and minimizing downtime. The vigilant process control system manages data volume efficiently, contributing significantly to sustainability goals and energy conservation efforts.
Surges resulting from power grid fluctuations, equipment malfunctions, or device switching pose a significant threat to the stability of process control systems within biogas facilities. When surges disrupt the control mechanisms, the intricate production processes come to a halt. The complexity of the whole system magnifies the impact, causing prolonged interruptions and unscheduled downtime. The downtime not only disrupts the biogas production but also triggers a chain reaction of complications.
Resolving these issues and restoring the system to normal operation can be time-consuming, leading to significant delays and potential financial losses for the plant operators. Frequency converters and actuators require protection by FLP25-275 series surge protection device as near as feasible to the building’s entry point. It is advisable to install a type 1 surge protective device that aligns with the maximum continuous operating voltage, nominal discharge current, and impulse current specifications of the workplace and the type of signal transmission.
LSP’s reliable surge protection devices (SPDs) are designed to meet the protection needs of installations against lightning and surges. Contact our Experts!
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