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Reference Number DTI/CC/133
Title Optimisation of Furnace Design for In-Furnace NOx Reduction
Status Completed
Energy Categories FOSSIL FUELS: OIL, GAS and COAL(Coal, Coal combustion) 80%;
OTHER POWER and STORAGE TECHNOLOGIES(Electric power conversion) 20%;
Research Types Applied Research and Development 100%
Science and Technology Fields ENGINEERING AND TECHNOLOGY 100%
UKERC Cross Cutting Characterisation Not Cross-cutting 100%
Principal Investigator Mr GJ Hesselmann
No email address given
Technology Centre
Babcock International Group plc
Award Type 3
Funding Source DTI
Start Date 01 January 2000
End Date 01 December 2001
Duration 23 months
Total Grant Value £126,780
Industrial Sectors
Region London
Programme
 
Investigators Principal Investigator Mr GJ Hesselmann , Technology Centre, Babcock International Group plc (99.999%)
  Other Investigator Project Contact , University of Edinburgh (0.001%)
Web Site
Objectives
  • To determine the optimum burner size relative to furnace dimensions
  • To determine the minimum acceptable pitch between adjacent burners and between the wing burners and furnace side walls
  • To investigate the effect of interleaving the burner pitches in opposed wall fired plant in order to increase furnace utilisation and improve the turndown characteristics of the plant
  • To investigate whether biasing of fuel or air across a burner row offers significant improvements in NOx levels without adversely affecting carbon burnout
Abstract

Retrofit installations of low NOx systems are often constrained to some extent by the configuration of the existing plant. These practical constraints can be avoided in the design process for new plant. Factors such as the size, number and pitching of burners are selected to optimise furnace performance in terms of heat input, residence time, corrosion, pollutant formation and economics. The identification of optimum burner size and pitch with particular regard to NOxemissions and carbon burnout is
of significant interest.

The complex process of coal combustion can be simulated with some degree of accuracy by means of Computational Fluid Dynamics (CFD) modelling. This represents a valuable technique for the analysis of the effect of various factors on combustion performance and pollutant (NOx) formation.

A review of existing front and opposed wall furnace designs found that for furnace sizes of 300 and 500 MWe, the typical thermal ratings of the burners employed are between 40 and 60 MWth. A non-dimensionalised horizontal, vertical and wall clearance pitch value of around 2.75d (2.75 x throat diameter) was representative of the units examined, with a number of units featuring burners having considerably tighter pitches (around 2d). The review also allowed the specification of the dimensions of generic furnaces for modelling purposes.

Physical modelling of utility furnaces can be undertaken to obtain accurateflow measurement data. Data was obtained from a 1/10th scale perspex model of a generic front wall fired furnace. The measured data was used to validate the use of CFD techniques to investigate the effect of changes to furnace configuration.

The effect of the variation of the number and size of burners was investigated in a front and an opposed wall fired furnace. Results established that fewer large burners are preferable to a larger number of smaller burners in terms of lower NOx (fuel and thermal) and plant economics, without adversely affecting carbon in ash (CIA). The predictions were consistent with previous studies of the effect of scaling criteria. Air biasing or off-stoichiometric firing was also investigated. NOx reductions predicted were poor, in line with plant experience.

As pitch was reduced in a generic opposed wall fired furnace, flames became narrower, with a merging of tertiary air streams, a lessening in strength of the internal recirculation zone and a flaring out of flow to occupy available volume. Although fuel NOx showed little variation with reducing pitch, thermal NOx and CIA increased. The minimum acceptable pitch was identified. An additional study showed the sensitivity of fuel NOx to excess air level, and predictions from the CFD model were consistent with plant experience.

The novel technique of burner interleaving in opposed wall fired furnaces was e valuated.Significant NOx reductions were gained through vertical interleaving but at the expense of higher CIA. The analysis of the design of the OFA systems applied to the front and opposed wall fired furnaces gave reductions in NOx comparable with expectations. Little or no NOx reduction benefit can be expected to accrue from the use of interleaving on opposed wall fired furnaces with deeply staged OFA systems, as staging becomes the limiting factor for NOx generation.

Publications DTI (2002). Optimisation of Furnace Design for In-Furnace NOx Reduction: Project Summary 229. DTI Cleaner Coal Technology Programme, URN 02/1022, DTI, UK (PDF 545 KB)
Final Report (none)
Added to Database 01/01/07