In combustion systems where the flue gases have a short residence time in the temperature window for SNCR reactions, SCR technology will have to be employed.
The chemical reactions utilised in the two plant types are basically the same, but in SCR systems, the catalyst allows them to commence fast enough at much lower temperatures – typically 200 – 420 °C.
SCR is a mature and well proven technology, but requires very precisely controlled process parameters to work efficiently. An even distribution of the flue gas flow over the cross section of the catalyst is crucial to avoid deposits or wear caused by dust, and the stratifications in NOx, NH3 and temperature must be kept within tight limits as well.
ScandeNOx’s founder got his first experience with the SCR technology from working with a demonstration plant connected to a Danish power plant. The demonstration plant had a main reactor equipped with catalyst from the Danish catalyst manufacturer Haldor Topsøe, 4 small side reactors for comparison with catalysts from other suppliers, and a rotary regenerative Ljungström Air Pre-Heater or Gas/Gas Heat exchanger that could be equipped with catalyst as well.
The demonstration plant could be operated in High Dust mode, Low Dust Mode and in Slip-Brake mode – and very clearly demonstrated the pros and cons of the different technologies.
The second SCR project conducted by ScandeNOx’s founder was a pre-project conducted for the Danish power plant Avedøreværket, unit #1 – in cooperation with Haldor Topsøe. Avedøreværket’s unit #1 is a is a coal fired power plant, producing app. 220 MW electricity + 350 MW district heating with a thermal efficiency of app. 91 %.
ScandeNOx has never supplied a full scale Low Dust SCR system, but we have a great deal of experience with various High Dust applications, Tail End applications – and the technologies employed to control the temperature for these.
High Dust SCR catalysts are normally placed between the Economiser and the Air Preheater, but in some cases constructional changes may have to be made to control the flue gas temperature.
In such cases the options are:
•Splitting up the economiser in two sections.
•ECO Umwaltz (water-side bypass of the economiser)
•Duct burner / heat exchanger
•Flue gas bypass of the economiser (normally not recommended)
The first of the above options is normally the most cost-effective for new boilers, but for retrofit SCR projects, the other options may have to be considered. ScandeNOx’s founder has the expertise and experience to help you select the best option for your system – from working 15 years in the boiler manufacturing business.
If there isn’t enough space available for retrofitting a High Dust SCR system – or if the High Dust flue gas is too aggressive for the catalyst, Tail End SCR systems (placed after deSOx- / de-dust equipment) can always be employed.
ScandeNOx has comprehensive experience with this technology, and partners / vendors with high degree of expertise and high quality products for such applications – that is catalyst, heat exchangers, cleaning systems etc.
Scope of supply:
Being a newly formed company, ScandeNOx does not yet have the capacity to undertake turn-key SCR supplies on our own.
So far we have to rely on partners to do the CFD- / physical modelling required for designing ducts, reactor, guide vanes and mixers, and for large scale systems, we’ll also have to rely on a partner for detailed design of the reactor and supporting structures.
We can however undertake consulting and project management of complete supplies, and we can supply small scale mixers and injection systems of our own make.
Further, we can undertake turn-key supply of complete systems of our own design for storage, handling and dosing of reagent – for even the largest SCR systems.
The first plant:
Demonstration plant for 10.000 Nm3/h of flue gas at power station Stigsnæsværket, Denmark, 1987.
High Dust SCR configuration / Slip-Brake configuration (through reactor bypass).
Low Dust SCR configuration with the APH used as GGH.
High Dust SCR:
Tail End SCR:
There is more to an SCR system than the catalyst. ScandeNOx focuses on the storage-, handling, dosing and injection equipment for the reagent, but for small scale plants, we can supply the complete package.
ScandeNOx has even developed a so-called Micro SNCR system, where all the required components for pumping, dosing, distribution and cleaning are assembled in a single cabinet. This system can also be employed as reagent handling and dosing system for SCR plants, and is particularly suitable for marine applications and similar projects with little available space for a deNOx system.