China: ammonia desulfurization - technologies and products? 

When people talk about ammonia desulfurization in China, many people immediately imagine giant installations at thermal power plants. But reality, as usual, is more complex and interesting. What is often overlooked is that the key challenge is not so much the technology itself, but rather adaptation to the specific fuel and, more importantly, the effective management of the by-product ammonium sulfate. This is where the difference between theory and practice is visible.

From theory to “dirty hands”: where the catch lies

In textbooks, the process looks straightforward: absorption of SO2 by an ammonia solution, oxidation, crystallization. In fact, the first problem is the quality of ammonia. If you use liquid ammonia, you need serious safety measures, storage, and logistics. When you switch to ammonia water, you have different equipment and different evaporation standards. And if the facility has access to industrial waste containing ammonia, then the task changes completely; we are no longer talking about pure chemistry, but about engineering “according to circumstances?”.

The second point that beginners often underestimate is the influence of the composition of the flue gases. Chinese coal fuel is a different story. Fluctuations in SO2 concentration, the presence of dust, heavy metal vapors, chlorides - all this is not just “background noise”, but factors that can damage the injectors or clog mass transfer in the absorber in just a week. You have to constantly keep your finger on the pulse and adjust the modes. This is not “set it and forget it”.

And the third pitfall is precisely that same ammonium sulfate. Getting it is half the battle. You need to get a marketable product that can be sold. This means stable crystal size, low moisture content, and minimal impurities. If the crystals are small and stick together, then in the warehouse they will turn into a monolith that is then impossible to cope with. Have you seen such “surprises”? at one of the early installations in Shanxi province - then they broke this block of stone for six months.

Evolution of technology: not only absorbers

If ten years ago the focus was on basic schemes such as the ammonia-cyclic process, now everything has shifted towards optimization and hybrid solutions. For example, a combination of wet ammonia desulfurization with a pre-dry or semi-dry stage for gases with very high SO2 concentrations. This allows you to reduce the load on the main absorber and, critically, reduce the volume of liquid waste.

A separate story is the fight against the removal of droplets of ammonia fog. Standard dampers (mist eliminators) sometimes fail, especially at peak loads. We have to experiment with multi-stage systems, including fiber filters. This increases capital costs, but it ensures that no “smoke” comes out of the pipe. with the smell of ammonia, which is fraught with complaints from the population and fines.

Digitalization is also slowly but surely penetrating this area. We are not talking about “industry 4.0”, but about simple systems for monitoring key parameters in real time: pH of the circulating solution, suspension density, outlet temperature. This allows the operator not to constantly run around with test tubes, but to see trends and predict problems, for example, the onset of uncontrolled crystallization in the heat exchanger tubes.

Product range: from fertilizer to niche applications

The main product is, of course,ammonium sulfateas a nitrogen-sulfur fertilizer. But the fertilizer market in China is cyclical and very competitive. Therefore, the profitability of the entire installation is tied to the stability of sales and price. Smart players try not just to produce a standard product, but to work on its quality in order to receive a premium. For example, for use in the production of complex fertilizers or even in the food industry (after deep purification), crystals of special purity are required.

There are also lesser-known but promising areas. Purified high-quality ammonium sulfate can be used in fire retardants and in ore flotation processes. But this already requires deep cooperation with the consumer and understanding of their technical process. The most interesting case that I came across was the use of a desulfurization by-product at one chemical plant as a raw material for the production of potassium sulfate using the Mannheim method. The result is an almost waste-free cycle.

But attempts to produce pure sulfuric acid or elemental sulfur from it in China, as far as I know, are more experimental in nature. The economy has not yet converged, energy costs are high. Although, in the context of tightening emission standards and rising sulfur prices, such projects may receive a second wind.

Experience and mistakes: a look from the inside

One of the most indicative projects that I have seen is associated with the companyChengdu Yizhi Technology Co.(their website ishttps://www.yzkjhx.ru). It is a design institute established by Chengdu Huaxi Chemical Technology Co., Ltd., with serious registered capital. Their approach has always been distinguished not just by the sale of equipment, but by complex “turnkey” design, taking into account subsequent operation. For example, they were one of the first in China to actively introduce systems for automatically washing nozzles in absorbers without stopping the installation - a small thing, but which greatly increases the overhaul mileage.

But not everything was smooth for them either. I remember that at one of their first installations for a small boiler house there were problems with corrosion in the area where the gas temperature was on the border of the dew point. The material chosen seemed to be correct - duplex steel, but the welds became a source of corrosion. We had to change the seam post-processing technology on the fly and install additional gas heating chambers at the inlet. It was an expensive lesson, but it later became part of their standard protocols.

Another common mistake at many facilities is the underestimation of the ammonium sulfate packaging and storage system. They set up regular packaging lines, and then it turns out that in the high humidity conditions in southern China, the product in bags cakes in a couple of weeks. It is necessary to retrofit warehouses with air drying systems, which leads to unplanned expenses. It’s better to put this into the project right away.

What's ahead: not only ecology, but also economics

The driver for the development of ammonia desulfurization in China is now not only and not so much strict environmental standards (they already exist), but the search for economic sustainability. The installation must not only comply with regulations, but also make a profit from the sale of ammonium sulfate or, at a minimum, significantly reduce operating costs compared to using limestone (where the problem is gypsum dumps).

There is a trend towards creating more compact, modular installations for medium and even small emission sources - not only in the energy sector, but also in metallurgy and the chemical industry. The key here is not maximum cleaning efficiency (although that is important), but ease of maintenance and all-season reliability. In winter in northern China, with systems where there is a lot of fluid, there is always a headache.

And, of course, there remains the challenge of integrating with purification systems for other pollutants - nitrogen oxides (NOx) and dust. Combined technologies, for example, based on ammonia for simultaneous desulfurization and denitrification (SNCR/SCR type process), require a delicate balance. Excessive consumption of ammonia - and you get a "slip" unreacted ammonia, poor supply - efficiency decreases. This is an area for fine tuning and constant search for compromise, where there are no ready-made recipes, each object is unique. It is in this “kitchen” and real experience is born, and not in ideal schemes from catalogs.