Over the last 30 years, the European Union has periodically tightened the air emission regulations and particularly the NOx (Nitrogen Oxide) emissions for power plants. Existing and pending NOx regulations in Europe currently impose NOx emission limits in the 50-175 mg/Nm3 range for large coal fired power plants.
It is probably safe to say that all industrial and utility power plants in the EU area already have different types of NOx reduction technology in place. However, the trend towards lower and lower emission limits continues and energy producers are therefore obliged to constantly make decisions to invest in expensive emission control equipment.
Installing and operating low-NOx technology has different initial and operational costs
Emission reduction technology has been developed since early 1990’s and there are several principal ways to reduce the NOx emission of industrial and utility boilers. We can distinguish between so-called primary (LNBs, OFA) and secondary methods (SCR, SNCR) and the techniques can be used alone or in combination with one another to achieve specific levels of NOx reduction.
Depending on the chosen methods, installing and operating the technology has different initial costs (CAPEX) and different operational costs (OPEX) and also their potential to reduce emissions varies. To optimize plant value, asset owners should consider using best available technology that can provide substantial NOx reduction at lower total life time cost.
The so called secondary methods, i.e. reducing the NOx compounds that are already formed in the combustion process, are verifiably effective NOx reduction tools. In SCR systems, NOx emission reductions over 90% efficiency are achieved. NOx reduction potential of SNCR technology is limited to up to 60% at the maximum, which alone is in many cases not sufficient to reach the desired level in the EU.
While these technologies alone can provide the necessary reductions, the overall costs are very high, as both require a reagent to reduce the nitrogen oxides. In addition to the initial investment cost of installing the system, the operational expenses of running the boiler will also increase due to constant need of urea or ammonium.
Primary methods are the most cost effective way to achieve significant NOx emission reductions
Low-NOx technology based on primary methods reduces emissions effectively by staging and optimizing the combustion process, thus eliminating of NOx formation at its source. Although CAPEX is obviously required, implementing primary methods typically will not increase OPEX, as no additional operational substances are involved.
Fortum eNext has been a forerunner and developed its own low-NOx solution based on primary methods even before the first European emission limits came into force in the mid-1990’s. Our solution consists of modifying the existing burners to low-NOx type of burners or replacing them with new low-NOx burners (LNB), combined with Over Fire Air (OFA) system. By using modified burners or new LNBs in conjunction with carefully designed OFA nozzles, the NOx emissions in power production can be reduced to a level below 300 mg/Nm3. Typical NOx reduction with low-NOx burners and OFA systems has been 40–80 %.
Our experience has confirmed that by combining our state-of-art low-NOx combustion technology with a secondary NOx reduction system, substantial NOx emission reductions can be achieved in an economical way. Compared to alternative solutions, there is a minimum need for new equipment, no auxiliary power consumption, no water consumption, and no ammonia or urea consumption thus no by-products for disposal.
Altogether Fortum has supplied more than 1 000 low-NOx burners in more than 50 international projects globally. Our low-NOx solution is designed to fit any original equipment manufacturer’s (OEM) technology. We can guarantee that the desired emission levels are met, regardless of the current set up at the site.
Investing into primary methods is wise, irrespective of the current set-up
Many energy producers already have very effective SCR based technology in place. What often is not that well recognized, however, is that an investment additionally into primary methods is always an economical way to cut down operational costs in the long run, irrespective of the current set-up at the boiler. A solution based on primary methods provides one-off CAPEX investment for the customers without additional OPEX required and is therefore very cost-effective.
The table below shows a comparison of alternative NOx reduction technologies and solutions to reach 300 mg/Nm3 at all times. Our 40 years of experience in delivering low-NOx combustion solutions for different types of boilers and fuels gives us the required expertise to consider all relevant aspects and thereby the ability to conduct reliable simulation.
*Setup: 500MWe coal fired power plant, Full load, 8000 h/a
We have estimated that for a 500MWe coal fired power plant the life-cycle cost for the first five years of our low-NOx implementation would be around 5 MEUR compared to a selective non-catalytic reduction (SNCR) being almost 30 MEUR. The technologies involving a catalyst, in this case selective catalytic reduction (SCR), is an extremely expensive option, where operational costs amount to 40–45 MEUR after first five years.
Also the initial investment cost of installing the emission control system, shown on the second row in the table, are considerably lower for primary methods. Further to this, primary methods require no additional maintenance whereas SNCR poses a high risk of NH3 slip in fly ash or flue gases and SCR requires frequent regeneration and catalyst replacement.
Achieving required NOx reductions and enhancing plant performance in a cost efficient way
As a conclusion, it is always less costly to prevent the formation of NOx than it is to eliminate NOx later on. Implementing primary NOx reduction methods entail lower operating and maintenance costs as compared to secondary methods, thereby ensuring that overall life-cycle costs are kept at minimum. Moreover, primary methods not only reduces emissions, but simultaneously enables to enhance plant performance through optimization of boiler operations.
Statistics show that hundreds of coal-fired power plants will need to go through technological upgradation to meet the stringent emission norms allowed by the latest EU regulation. Plant owners would do wise to examine primary methods as a way to invest in the most cost-efficient solution to reduce emissions.