Ultra-Low NOx Burner Upgrade at Ferrybridge, UK

The Challenge

Units 3 and 4 of SSE Ferrybridge C power station (both superheated front-wall fired radiant steam boilers rated at 500 MWe) had already been fitted with Doosan Babcock Mark III low NOx burners to meet a NOx limit of 650mg/Nm³. When a further NOx reduction down to 500mg/Nm³ was introduced, the plant opted for a BOFA system to achieve this, rather than a more costly SCR or SNCR system. However, with this set-up, the plant was not operating efficiently and was experiencing long flames, unacceptably high levels of Carbon in Ash (CiA) and CO, as well as overly high temperatures in the superheater and reheater areas which were causing expensive tube failures and unplanned outages. To resolve these issues, the plant operators called in RJM to identify the root causes and propose a solution.

RJM Solution

In order to fully understand the burner and boiler dynamics, RJM undertook three separate CFD models. A single boiler model for comparative burner performance with its own RJM ultra-low NOx burner; a full furnace model to review furnace combustion and thirdly; a full furnace model including the superheater and the reheater convective heat exchangers to better understand the elevated metal temperatures in those areas. Having reviewed all the data, RJM drew four key conclusions: it could deliver lower CO by optimising the dynamics of the burner; deliver considerably reduced and compliant NOx levels; produce power with a much lower”carbon” loading at the BOFA ports and raise burner O₂ and thus reduce the BOFA air flow.

Results

Having completed the full furnace CFD, the plant operators at Ferrybridge ordered a full refit for 48 RJM ultra-low NOx burners to be installed in Unit 3 with some additional work to be carried out on the BOFA nozzles. Following the RJM upgrade, the plant was no longer experiencing high metal temperatures in the convective section and the furnace remained stable with excellent emissions performance in terms of NOx, CO and dust. In fact, with NOx emissions reduced by 50% following the RJM upgrade, meant the plant could look forward to the forthcoming NOx limit of  200mg/Nm³ with confidence instead of having to consider an additional SCR system at a cost of between £50m – £100m.

Read the full article published in Power Engineering International here:

MKT-DOC-009 PEI May 2012 (Ferrybridge)