Chinese desulfurization technology: how does it work? 

To be honest, when you hear about “Chinese desulfurization technologies,” the first thing that comes to mind is huge absorbers at thermal power plants somewhere near Shanghai. But the point, of course, is not the scale, but how the process is approached. Many people mistakenly believe that it is simply a matter of purchasing a license and installing it. In reality, it is a constant adaptation, often by trial and error, to a specific fuel and specific, sometimes very stringent, environmental standards. I’ll try to sort it out on the shelves, as it is seen from the inside, without gloss.

Not just a scrubber: the basis is the chemistry of the process

Most modern Chinese installations are based on the wet lime/limestone method. It would seem like a classic, described in any textbook. But the whole point is in the implementation details. It is not enough to simply feed the suspension into the gas stream. The key parameter is spray dispersion. Drops that are too large—poor contact; drops that are too small—entrainment. At one of the early installations near Chengdu, they encountered fog eliminators clogging due to non-optimal spray. I had to sort out the injectors and adjust the pressure.

And here it is not so much the hardware that is important, but the preparation of the sorbent itself. The quality of the limestone is a huge variable. In Sichuan Province, for example, local stone often has high magnesium content, which affects the reactivity and structure of gypsum. You have to constantly adjust the grinding fineness and density of the suspension. These are not theoretical calculations, but daily operational practice.

Another nuance is oxidation. In order for calcium sulfite to fully transform into gypsum, an effective oxygen supply is needed. Some schemes use forced oxidation with air, while others rely on natural suction. The second option is cheaper, but more capricious. I saw a case when, due to a change in the load on the boiler and, as a consequence, the gas temperature, the natural oxidation “choked”, and a viscous mass of sulfite began to grow in the absorber, which led to a drop in efficiency and the risk of shutdown. We tried to increase the air supply to the pool, but this is an additional cost.

Automation and control: where the real efficiency lies

You can assemble a system from the best pumps and pipes, but without a smart control system it will work at half capacity or in reserve. Chinese engineering companies, especially those that have grown out of practices likeChengdu Yizhi Technology Co.(their website, by the way,https://www.yzkjhx.ru), place great emphasis on adaptive control algorithms. It's not just about maintaining pH in the absorber.

The system must respond in real time to changes in the SO2 content at the inlet, which depends on the coal (and its quality, alas, can “dance?”) and the boiler load. I saw how operators at one station manually “pulled” supply of limestone according to the schedule. The result is excessive reagent consumption and unstable emissions. After implementing a system with feedback and a predictive model, costs fell by 8-10%, and stability reached a new level.

But this is not without problems. Sensors, especially pH meters and slurry density sensors in harsh environments, are a weak link. Their contamination and drift of readings is a headache. It is often necessary to duplicate measurements or build indirect control models. This is the same “practical reliability” that cannot always be described in a beautiful prospectus.

By-product: gypsum is not always a commodity

The ideal picture: flue gases are purified, and the output is commercial gypsum for the construction industry. The reality is more complicated. The quality of gypsum directly depends on the purity of the limestone and on the effectiveness of desliming and washing in the system. If there are a lot of chlorides or fluorides in the gas (and when burning some coals this is the case), they go into suspension and then into gypsum.

There was an experience at a station where gypsum, due to the high content of water-soluble chlorides, was not accepted by any local plasterboard production plant. It had to be stored, which negated part of the project's economics. A solution was sought in installing an additional stage for washing the gypsum pulp, but this again was capital and operating costs. Institutes like the one mentionedChengdu Yizhi Technology Co., Ltd., which was created as a design division of Huaxi Technology, often solves such non-standard problems by selecting the chemical composition of the flush.

Therefore, now, when designing, deep cleaning of gypsum is increasingly included, even if this increases the cost of the project initially. Because problems with waste disposal end up costing more. This is a lesson learned in practice.

Integration into an existing farm: the main headache

New stations are being built from scratch? taking into account cleaning systems. But the lion's share of the work is the modernization of existing facilities. And this is where the fun begins. Often there is no room for a perfectly compact layout. The chimneys are old, the foundations are not designed for additional loads, and the space for placing the absorber and oxidation pools is limited.

We have to make compromises. For example, use compact disc absorbers instead of spray absorbers, although their hydraulic resistance may be higher. Or place equipment in tiers. I remember a project where, in order to supply limestone suspension to a height of 40 meters, it was necessary to install not one, but two cascades of pumps, because one could not cope, and this gave rise to problems with reliability and vibration. Trifle? No, this is exactly what determines whether the system will work without stopping.

Another point is the effect on the operation of electric precipitators or bag filters located in front of the scrubber. Increased humidity of gas after wet cleaning, if proper heating is not provided before release, can lead to condensation in the pipes and corrosion. This is also taken into account at the design stage, but is fully manifested only in operation, especially in winter.

Looking ahead: more than just limestone

Although the wet method is dominant, there is experimentation with other approaches. Semi-dry methods with a spray dryer are interesting for medium-sized facilities where the issue of liquid waste is important. But there is its own difficulty - accurately maintaining the temperature at the dew point. for maximum capture and avoidance of sticking in the device.

They are also trying combined schemes, for example, pre-adsorption with activated carbon or injection of sorbent into the firebox. But this is rather for specific cases with special requirements or for post-treatment. It has not yet become a mass solution - it is more expensive and more difficult to manage.

The main trend that I see is not the search for some revolutionary technology, but a deep optimization of the existing one. Smarter control systems, more resistant materials for components subject to abrasion and corrosion (nozzles, mixers), and an integrated approach to by-products. The goal is not just to meet the standard, but to make the process as economical and waste-free as possible under the specific conditions of the plant. And this, perhaps, is the essence of what is now understood as wasteChinese desulfurization technology- not blind copying, but pragmatic engineering, honed on many real objects, with all their imperfections.