China: How to dispose of VOC tail gas? 

To be honest, when you hear about recyclingtail gas VOCin China, the first thing that comes to mind is catalytic afterburning or carbon adsorption. But in practice, especially at chemical plants in Sichuan or Shandong, everything often comes down not to the choice of technology, but to how to squeeze it into existing production, which cannot be stopped. I have seen many times how projects, beautiful on paper, stumble due to a banal lack of space for installation or fluctuations in gas composition. This is what I want to talk about.

Where the dog is buried: gas composition and paper standards

The main mistake is to start designing with only passport data or outdated measurements.Volatile organic compounds- the concept is flexible. At one paint and varnish production it can be aromatic hydrocarbons, at another - esters, and somewhere - all together, and even with impurities of sulfur or organosilicon. The latter, by the way, are a killer for most catalysts. There was a case at a plant in Fuzhou: they installed an RTO (regenerative thermal oxidizer), and six months later the efficiency dropped by 40% due to silicon, which was modestly kept silent about in the initial data.

Emissions regulations are becoming stricter, yes. But often local environmental inspectors look less at subtle grams per cubic meter than at visible smoke and odor. Therefore, sometimes a customer is willing to put up with a system efficiency of 90% if it is guaranteed to remove odor, instead of chasing 99% using expensive technology. It's a matter of economics and practical compromise.

And one more nuance - concentration. Theoretically, thermal methods require a certain calorific value of the gas for the process to be autothermal. In practice, the flow is often unstable: during the day there is one composition, at night - another, when a batch of raw materials is changed - a third. If you design a system for peak values, it will come out golden. If under medium, during periods of low concentration it will consume a lot of fuel to maintain the temperature. So you have to spin around, sometimes adding buffer tanks or admixture systems.

Technologies in the field: what works and what collects dust in the warehouse

Adsorption on activated carbon is a classic of the genre. Cheap to purchase and relatively easy to install. But this is a double-edged sword. Regeneration of coal is a different story with steam or hot nitrogen, and then somewhere else to dispose of this condensate, which in itself is hazardous waste. I saw installations where carbon cartridges were changed like filters in a vacuum cleaner, and the old coal was simply sent to a landfill - what kind of ecology is that? For low concentrations and small flows it’s all right, but for serious production it’s a half-measure.

Catalytic oxidation (CO) is my favorite topic of debate. In theory, it is effective; the operating temperature is lower than that of purely thermal methods, which means savings on energy resources. But the Chinese market is flooded with catalysts of varying quality. Good, resistant to poisoning, with the right carrier - expensive. And often they put something cheaper, and then they wonder why after a year or two activity decreases. The key point is the preliminary purification of gas from dust and catalyst poisons. This is often neglected.

But RTO and RCO (regenerative oxidizers) are already heavy artillery. Efficiency of 95-99% is a reality. But! These are huge installations, expensive to install and requiring highly qualified maintenance. They are installed in large petrochemical or pharmaceutical plants. I remember a project for a tire factory in Shandong: an RCO installation the size of a three-story house. The difficulty was not even in itself, but in the system for collecting and transporting gas from dozens of emission points throughout the plant. Pipelines, fans, explosion protection - the cost of this piping is sometimes comparable to the cost of the oxidizer itself.

Unobvious pitfalls: energy, space and people

Often it all comes down to energy. Thermal methods are gluttonous. In regions where there are problems with electricity or gas, the project may become unprofitable even at the stage of calculating the payback. Sometimes it is more profitable not to recycle, but to capture and return it to the process, if this is technologically possible. For example, solvent recovery using deep-cooling condensation. But this is also not a panacea - the equipment is capricious and requires a stable vapor composition.

Space is the bane of old factories. They were built at a time when the environment was the last thing they thought about. There is simply nowhere to put a new installation. We have to resort to tricks: placing equipment on roofs, moving it outside the perimeter, which lengthens communications and increases losses. And also approvals, inspections of firefighters... Bureaucracy can delay implementation for months.

And most importantly - personnel. You can install the most modern German installation, but if there is no engineer at the plant who understands the principle of its operation, and the operators see it as a burden, then everything will quickly fall into disrepair. Staff training is not an item on the budget, but a prerequisite for success. Often failures occur not because of poor technology, but because of the human factor: they changed the filter at the wrong time, missed a technical inspection, or responded incorrectly to an emergency signal.

Experience from the project: case with Chengdu Yizhi Technology

For example, I worked with designers fromChengdu Yizhi Technology Co.(their website, by the way,https://www.yzkjhx.ru). This is their parent company, Huaxi Technology, which has been in the chemical industry for a long time. Their approach is often practical: do not impose the most expensive, but first conduct a detailed audit. I remember their project for a polymer plant in Chengdu. The task was to utilize gases from reactors, a complex mixture with variable flow rates.

They proposed a hybrid scheme: first, condensation to capture the most valuable components (returned to the cycle, which saved on raw materials), and the remaining low-concentrated stream was sent to a catalytic oxidation unit. But not the standard one, but with a customized catalyst that is more resistant to possible impurities. The trick was in the control system, which monitored the temperature on the catalyst bed in real time and adjusted the heating. This made it possible to reduce energy consumption during periods of low load.

There were difficulties during commissioning. We did not take into account the vibration from the neighboring compressor - the fastenings of the gas lines had to be modified. And the local electricians mixed up the phases when connecting the main fan... Little things, but because of them the deadlines were delayed. As a result, the system works and the customer is satisfied. But the main conclusion I made from looking at this and other projectsChengdu Yizhi Technology: success depends on the depth of immersion in the technology of the source plant itself. Without this, any, even the best, recycling system is just an expensive toy.

Instead of a conclusion: thinking out loud about the future

Where is everything going? It seems to me that the future lies not in one super technology, but in a smart combination of methods. First, cut off as much as possible and return to the process what is of value. Then - to destroy what could not be preserved, with minimal energy consumption. And all this is under the control of sensors and algorithms that adapt to changes. The ideal is a closed cycle, zero emissions. But we are far from this yet.

Nowadays there is a lot of noise around membrane technologies and concentration methods, but they are still rare guests in large-scale chemistry. Expensive. And in China, with all the strictness of the regulations, the issue of price is often decisive. Therefore, when choosing a recycling technologytail gas VOC, you need to face the truth: what the plant can afford here and now, what will pay off, and what will turn into a museum exhibit that is turned on only before inspection. Sometimes it is better to make a simple but reliable system that actually works every day than a complex and expensive monster that is idle due to a lack of specialists or money to maintain it. It all comes down to common sense and detailed knowledge of your production. Without this, no technology will help.