China: LNG liquefaction technology, description? 

When people talk about Chinese liquefaction technologies, many people immediately think of giant turnkey plants. or about borrowing Western licenses. But this is just the tip of the iceberg. In fact, over the past ten years, a whole layer of engineering competencies has been formed, where the key is adaptation, integration and, importantly, reducing the cost of processes for specific, often non-ideal conditions. It’s about this, about that very “kitchen” that is not always visible in glossy press releases, that I want to speculate.

From license to adaptation: evolution of the approach

It all started, of course, with licenses. Technologies from Air Products, Linde, Shell - they became the basis. But copying blindly is expensive and often ineffective. The Chinese market required solutions for smaller capacities, for gases with unstable composition (the same associated petroleum gas or coal mine methane), for locations with logistics and water restrictions. And this is where the real work began.

Design institutes appeared that took on not just drawings, but the revision of technological chains. A striking example -Chengdu Yizhi Technology Co.(a subsidiary of Huaxi Technology). They initially grew out of chemical technological engineering, which means that in their DNA there is a deep understanding of heat and mass transfer, separation, and cryogenics. Their websiteyzkjhx.ru- this is not just a business card, it shows an evolution: from standard installations to modular solutions and technologies for high-nitrogen gas.

The main shift, in my opinion, has occurred in mentality. We stopped trying to do “like theirs”, and started looking for “what’s best for this particular case?” For example, the classic liquefaction scheme with a turboexpander is effective, but difficult to maintain for a remote station. We took the path of optimizing mixed refrigerants (MRC) and cascade cycles to increase flexibility and lower the entry barrier for small investors.

Key nodes and “sore spots” process

If you take it apart, the heart of any installation is the heat exchanger. China has made a big bet on spiral wound heat exchangers of its own production. Yes, the first samples lagged behind in efficiency, there were problems with the uniformity of refrigerant flow. But now a number of manufacturers, including those who collaborate with institutes such as Yizhi Technology, have reached a completely competitive level. Their advantage is cost and speed of delivery.

Another critical point is gas pre-treatment. Chinese raw materials can be very “dirty”. It is necessary to strengthen the removal units for CO2, mercaptans, and mercury. Hybrid solutions are often used here: adsorption + membrane separation. I won’t say that this is always ideal; at some facilities there were problems with rapid contamination of membranes, but engineers learn from these mistakes and constantly update regeneration cycles.

And, of course, refrigerants. Working with propane, ethane, and ethylene in mixtures is always a balance between safety and efficiency. On one of the projects where we participated in commissioning, there was a serious problem with “runaway?” mixture composition with a sharp drop in inlet pressure. We had to improve the online analysis and automatic topping system. Such nuances are never described in textbooks, this is pure practice.

Modularity as a response to challenges

A trend that cannot be avoided is modular (block) construction. Chinese companies includingChengdu Yizhi Technology Co., Ltd., promote it very actively. The point is not just to assemble a plant at a shipyard and deliver it. The point is the deep standardization of technological modules for different capacities: 50, 100, 500 thousand tons per year.

This results in a fantastic reduction in construction time on site. But it also adds headaches. Docking modules along pipelines, electrical, instrumentation and control systems is a jeweler's work. The slightest mistake in interface design can result in months of delays on site. By the way, their company has a whole digital twin department specifically for working out these connections virtually, before sending the module. It doesn't always work perfectly, but the approach is correct.

For the customer this is often a double-edged sword. On the one hand, it’s faster and sometimes cheaper. On the other hand, there is less flexibility for changes already in progress. I have seen projects where the customer, having received the modules, still made a lot of changes “on the spot”, which negated all the advantages. So modularity is not a panacea, but a tool that requires a very disciplined approach from all participants.

Focus on specific gases and niche markets

While big players are fighting for megaprojects, such engineering companies have found their niche. This is, for example,biogas liquefactionfrom landfills or wastewater treatment plants. Or the utilization of APG in small oil fields, where the gas was simply flared. Here we need completely different solutions - compact, mobile, resistant to fluctuations in composition.

One of the most interesting cases that I came across was a plant for liquefying coal mine methane with a high content of nitrogen and oxygen. The problem is that when cooled, oxygen can condense, creating an explosive mixture. The solution that the engineers proposed was multi-stage separation with cryogenic rectification and strict control of concentrations at each stage. The installation turned out to be not the most efficient in terms of energy consumption, but it solved the main problem - safety and the transformation of problematic gas into a marketable product.

It was in such complex, non-standard projects that practical experience was forged. This is not about pretty pictures, but about the daily struggle with the physics and chemistry of the process.

Looking forward: challenges and growth points

Where is everything going? It is clear that the trend towards energy efficiency and reducing the carbon footprint is here to stay. There is now a lot of talk in China about using renewable energy to power liquefaction plants. Technically this is possible, but the question is economics and, most importantly, the stability of the energy supply. Solar panels and wind turbines do not provide an even load, and the liquefaction process does not like this very much. For now these are more pilot projects.

Another direction is intelligent control systems and predictive analytics. Implementation of IoT sensors to monitor vibration of turbines, the condition of catalysts, and microleaks in heat exchangers. Chinese companies are actively experimenting here, collecting huge amounts of data from operating installations. True, the depth of analytics is often lacking - the data is there, but it is not always possible to extract practical benefits from it for optimization. We need closer connections between technologists and data scientists.

And, of course, the footage. Experienced cryogenic engineers who have gone from start-up to long-term operation and have seen all the “childhood diseases” installations are still not enough. Knowledge gained from projects like those led byChengdu Yizhi Technology Co.- this is the main asset. But they need to be systematized and transferred, and not stored in the heads of a few key specialists. This is perhaps one of the main challenges for the entire industry in China - to move from accumulated experience to creating a sustainable knowledge system.