Cheap denitrification SCR/SNC: technologies and market? 

Cheap denitrification SCR/SNCR: technologies and market?

When people talk about cheap denitrification, many people immediately think about reducing CAPEX for catalysts or reactors. But real savings often lie elsewhere - in operating costs and, more importantly, in the correct choice of technology for a specific object. SCR, SNCR are not just abbreviations, but solutions that can either save the budget or lead to constant overruns due to incorrect initial data. The most common mistake is trying to use SNCR where SCR is needed, only because of its apparent simplicity and low initial price. Or vice versa.

Where does the cheapness really lie?

Let's start with the basics.SNCR technology- this is the injection of a reagent (most often urea or ammonia) into a high temperature zone (900-1100°C). Capital costs are indeed lower: there is no expensive catalyst or complex supply system. But the efficiency rarely exceeds 40-60%, and this is under ideal conditions. If the temperature in the boiler fluctuates, which often happens, especially under variable loads, efficiency drops to 20-30%, and ammonia emissions (slip) increase. It turns out that you pay for the reagent, but do not get the required NOx reduction. Cheap? Not really.

CSCR systemthe story is different. High efficiency (up to 90% and above), stability. But the price is not only the catalyst (which, by the way, becomes poisonous over time and requires replacement). This is also the heating of gases in front of the reactor, if we are talking about low temperatures (low-temperature SCR is a separate complex topic), this is energy consumption for the operation of smoke exhausters due to increased aerodynamic resistance. Cheap SCR denitrification is not about the cheapest catalyst on the market, but about optimizing the entire system: correct calculation of the catalyst layer, choice of its type (for example, honeycomb or plate) to minimize pressure losses.

I had experience at one thermal power plant - they wanted to save money, so they installed a thin layer of cheap catalyst. Six months later, the efficiency dropped, the pressure increased, and I had to change it. Saved on purchases, lost on downtime and replacement. Conclusion: cheap should be considered for the entire life cycle, and not at the stage of signing the contract.

Reagent market and pitfalls

The urea market for SNCR appears simple. But there are nuances here too. Not all technical urea is suitable. The concentration of biuret and impurity metals is important - they affect the kinetics of the reaction and can give additional emissions. Often customers buy the cheapest option, and then are surprised by low efficiency and clogged injectors. We have to explain that sometimes it is better to take a purer, albeit expensive, reagent - its consumption may be lower.

Ammonia for SCR is a different story. Aqueous ammonia, anhydrous, urea as a source of ammonia (in large plants). Anhydrous is more effective, but more dangerous, requires serious safety measures, which increases the cost of the facility. Water is simpler, but requires evaporators and requires more energy. The choice is always a compromise between security, CAPEX and OPEX. I have seen projects where, due to the desire to save on an anhydrous ammonia storage system, they ended up with a more expensive and cumbersome system for purifying emissions of ammonia itself.

And one more thing - logistics. If the site is remote, the cost of shipping and storing the reagent can eat up all the savings from choosing SNCR. This is often forgotten during the pre-project stage.

Practical experience: when SNCR works and when it doesn’t

Let me give you an example. Small coal boiler house, old boiler. The task is to meet the standards. The temperature profile in the firebox is more or less stable, there is a zone with the required 950-1050°C. We calculated and modeled - SNCR could provide the required 50%. They did. It has been working for three years without any complaints. The savings compared to SCR are several times. This is where cheap denitrification worked.

Counterexample: waste incineration plant. The temperature is unstable, the composition of gases changes. We tried to use SNCR - the efficiency jumped from 15% to 55%, the ammonia leakage went off scale. As a result, we modified it and added a precise temperature control system and additional tiers of nozzles. It turned out to be more expensive than if a hybrid system or compact SCR had been initially installed. An error in the original data was costly.

Hence the rule: before choosing a technology, you need to have a detailed temperature profile over the entire height of the boiler/furnace, not at one load, but at all modes. Without this, any calculations are fortune telling on coffee grounds.

Low-temperature SCR - panacea or complexity?

Nowadays there is a lot of talk about low-temperature SCR (operating at 150-300°C). This seems to be the solution for many sites where there are no high temperature gases. But here, too, not everything is so simple. Yes, you can put it after the electric precipitator and before the smoke exhauster without spending money on heating. But catalysts for such temperatures are different, often based on other active components (for example, manganese), they can be sensitive to SO2 in gases. If sulfur is present, it poisons the catalyst, dramatically reducing its service life.

There was a project for a cement kiln - gases after the raw mill, the temperature was about 200°C, but SO2 was present. They proposed low-temperature SCR, but with a mandatory desulfurization step. The customer initially refused desulfurization, deciding to take a risk. After 8 months, the activity of the catalyst dropped by half. We had to install a sorbent injection system to bind SO2, but this is an additional operating cost. It didn't come cheap.

Therefore, low temperature SCR is not just a replacement for hot SCR. This is a complex solution that requires careful analysis of the composition of flue gases throughout the entire service life of the installation.

The role of engineering and why ready-made solutions don’t always work

This is perhaps the most important thing. The market today offers many packaged solutions. But each object is unique: different fuel composition, different boiler geometry, different operating modes. A ready-made solution from the factory may not work. We need deep engineering, modeling (CFD), and sometimes pilot testing.

It is worth mentioning here companies that specialize in such complex solutions. For example,Chengdu Yizhi Technology Co. (https://www.yzkjhx.ru). This is not just a supplier of equipment, but a design institute created on the basis of a technology company. Their approach shows the depth of engineering: they will not sell you just a reactor, but will take into account your specific conditions - gas composition, temperature fields, required standards. This is important. Their experience, judging by the projects, just confirms the thesis that low cost is achieved by accurate calculations, and not by random selection of equipment. The authorized capital of 120 million yuan indicates serious opportunities for the implementation of large projects, where pre-project development is important.

In my experience, I came across situations where the same installations were purchased from different suppliers for similar boiler houses. For one it works, for the other it doesn’t. The difference was precisely in the adaptation: how the location of the injectors was calculated, how the injection control system was configured. Little things that make all the difference.

My bottom line is this: cheap denitrification is not a myth. It's achievable. But the path to it does not lie through searching for the cheapest equipment in the catalog, but through scrupulous analysis, the correct choice of technology (SCR/SNCR/hybrid) for the task and high-quality engineering at the design stage. You need to save on operation for 10-15 years, and not on the purchase price. Otherwise, it will turn out like in that saying: the miser pays twice. In our field, he pays constantly, for every extra kilogram of reagent, for every kilowatt to overcome resistance, for every hour of downtime due to a non-working system.