In a series of technical articles, we introduce you to the Nordsol technology for biogas liquefaction to bio-LNG. This third article discusses the operability and reliability of the installation.
Michiel van Aken
Technical Director & Partner
Nordsol’s technology explained: Operability and reliability
Dec 20 2024
Introduction
Summary video
Bio‑LNG production process
Bio-LNG is produced by liquefaction of biomethane extracted from biogas. The production of liquefaction-ready biomethane and the liquefaction itself are very different processes. This is why companies that manufacture process equipment focus on either gas treatment or liquefaction.
Why is this important? To realize a bio-LNG plant, EPC companies and system integrators must bring all the components for gas treatment and liquefaction together. To build a complete installation, the unit interfaces on these components must be matched. Also, for the installation to appear as one system to the operator requires a reliable PLC control and safeguarding system. This system communicates with all sensors and valve actuators, position feedback sensors, motor frequency drives, etc., while being compliant with safety standards.
Does that sound easy? It’s not. Energy-efficient and extremely reliable biomethane liquefaction is complex. At atmospheric pressure, biomethane becomes liquid at -162°C. Cooling the gas requires a process that includes different pressures, varying gas flows, and of course very low temperatures. It also requires ultra-pure biomethane, since other components in the gas, such as CO₂, heavier hydrocarbons (VOC’s) and water, will easily freeze and cause blockages and potential damage to the equipment. Therefore, the selection of process technology and equipment is decisive for the operability and energy consumption of a bio-LNG facility.
7 Reasons for on‑site bio‑LNG production now.
Learn how biogas producers significantly enhance both the ecological and economic value of their biogas through bio-LNG production, utilizing Nordsol’s innovative biogas liquefaction technology.
Unique design approach
Production of LNG is not new. For more than 30 years, natural gas has been liquefied to LNG in large industrial plants, capable of producing up to 15 Mtons LNG per year. Production of bio-LNG from biogas happens at a much smaller scale, typically 1,5 to 15 ktons per year. Some bio-LNG technology providers have therefore chosen to downscale existing LNG technologies. Nordsol has taken an entirely different approach. We have designed a production process that’s optimized for biogas. There were several reasons for this:
- Improve energy efficiency. In locations where fossil natural gas is liquefied to LNG, there is a surplus of cheap energy available for gas treatment and liquefaction. Therefore, energy efficiency is in these locations not the highest priority. In regions where biogas is produced, energy is valuable. This makes optimizing the bio-LNG production process for energy efficiency very important.
- Operability. Large LNG facilities employ a large number of specialized process engineers and operators who monitor and control the liquefaction process 24/7. For small-scale bio-LNG production to be viable, it is of critical importance that an installation can operate mostly unmanned, at full capacity, and without interruptions in the process.
- Reliability. Complex, large plants have redundant equipment to improve reliability. Redundancy would make small plants too expensive. A good alternative is to reduce the number of critical equipment to the bare minimum and select industry-standard, mass-produced components. Plant reliability is critical for a sound business case.
- Differences between biogas and natural gas. Biogas is much cleaner than natural gas. This makes gas treatment to produce liquefaction-ready gas a simpler and more efficient process. In addition, a bio-LNG installation needs to be adaptable to fluctuations in biogas flow and composition. The natural gas supply in a large-scale LNG installation is consistent in terms of flow and composition.
With this biogas liquefaction process design, we’ve put the interests of the plant owner and the operator first.
Operability
The design of Nordsol’s innovative process line-up and the selection of equipment played a key role in reaching a safe, reliable and very user-friendly production process. In this process, we fully integrated the biogas treatment and liquefaction steps. This is not only visible in the plant itself but also in the HMI system. This system, designed and developed by Nordsol, provides a single look and feel to all processes in the plant.
Full integration provides significant operational and economic benefits, in addition to energy efficiency. A stable and continuous plant operation means higher bio-LNG production volume and lower operational costs, as we currently experience every day at our bio-LNG plants in Amsterdam and Wilp.
The Nordsol design allows a safe and easy bio-LNG truck loading by unexperienced drivers. This is an unique feature. The semi-automated system guides the truck driver through a sequence of several steps, starting with connecting the earth cable and inerting the loading hoses. All actions are monitored and safeguarded by interlocks in the control system. During the last 3 years and hundreds of truck loadings, Nordsol has been able to make the truck-loading operations a safe and standard, well-controlled operation. Feedback from many truck drivers confirms the very user-friendly truck loading.
First plant at commercial scale
The production process was applied for the first time at a commercial scale in Nordsol’s own plant in Amsterdam. The realization of this plant, opened in 2021, was not only important to prove that the unique process works. It has also been critical in understanding what’s important in designing, owning, operating and maintaining a bio-LNG plant. We now know what it takes to produce bio-LNG efficiently, reliably and safely.
The first six months after commissioning were used to solve several challenging but common technical problems that arise when adopting a new technology. Most challenges were related to unstable flow dynamics, trip transients, vibrations and mechanical issues. This resulted in some control and hardware modifications. After these six months, the plant operated efficiently and reliably, 24/7, and unmanned outside office hours.
The design of Nordsol’s innovative process line-up and the selection of equipment played a key role in reaching a safe, reliable and very user-friendly production process.
Simulation and optimization
The detailed process simulation model in Unisim was the basis for all equipment design and shows a very close match with actual plant operation. It was also helpful in the optimization of the plant in the second and third year, achieving more energy efficiency and higher uptime.
Today, the plant in Amsterdam can operate for several months with interruption, unmanned, at 110% of design capacity. The process is very stable, highlighted by the fact that the deviation between the gas flow setpoint and measurement is max 1%. Also, cold restarts can be done in 1,5 hours, which further increases the uptime and yield of the plant.
Smooth commissioning at the 2nd and 3rd plant
The improvements made to the process and equipment at the Amsterdam plant are also applied in the design of new plants for our customers. The commissioning of the second and third plant, (at Attero in the Netherlands and at RenEco in the UK) went very well. Within a week, the biomethane liquefaction process was stable.
Michiel van Aken
Technical Director & Partner
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