Reference · Switzerland · 2020–21

SNCR system on an 8 MW biomass boiler – Switzerland

DeNOx SNCR system for a biomass plant fired with wood chips and bark: two injection lances in the boiler, automatic urea dilution by weight, dosing controlled on the NOx measured at the stack. The system is prepared for a second 8 MW boiler.

SNCR injection lances installed on the 8 MW biomass boiler, with urea and atomising air lines – Switzerland
8 MWThermal capacity
< 150mg/Nm³ NOx at stack
2Injection lances
2020–21Commissioning

The project

Ecotherm built the DeNOx SNCR system of a biomass plant in Switzerland, with an 8 MW boiler fired with natural wood chips and bark. The limit to be met was 150 mg/Nm³ of NOx, referred to 11% O₂, starting from boiler values up to 250 mg/Nm³: a reduction of around 40%, with residual ammonia (slip) below 30 mg/Nm³.

The system was designed from the start for two twin boilers: mixing tank, control panel and circuits are also sized for the second 8 MW line, which can be connected without rebuilding the plant. At commissioning the NOx limit was met.

How the system works

Injection into the boiler

Two atomising lances inject the urea solution into the post-combustion zone, within the temperature window in which the reaction with NOx is most effective. The lances work with compressed atomising air and are cooled by a dedicated blower, which extends their service life.

Dilution by weight

The 32.5% urea is diluted with demineralised water in a 2 m³ double-walled mixing tank mounted on load cells. The PLC doses the two liquids by weight, so the solution concentration stays constant with no operator intervention.

Dosing

Volumetric metering pumps with safety valves inject the flow calculated by the PLC. Each boiler has its own dosing line and can be enabled or excluded separately.

Control

The PLC panel receives the signal from the stack analyser and automatically adjusts the urea flow to stay below the set limit, avoiding reagent overdosing.

Scope of supply

  • Reagent feed: urea loading pump, demineralised water transfer pump, motorised valves
  • Mixing unit: 2 m³ double-walled tank on load cells, level control
  • Dosing unit: volumetric metering pumps with safety valves
  • Injection: atomising lances with pressure gauges and flow meters, cooling blowers
  • Control panel: PLC with operator panel and inverter, control on the stack NOx signal
  • Piping: urea, atomising air and cooling air circuits up to the lances
  • Installation, supervision and commissioning: with documentation in French and German

Plant photos

SNCR dosing skid installed in the plant room of the biomass plant, with metering pumps and cooling blowers – Switzerland
Dosing skid with metering pumps and lance cooling blowers.
SNCR PLC control panel with operator panel and stack NOx analyser – Switzerland
Control panel with PLC and operator panel; on the right, the stack NOx analyser.
SNCR plant room with dosing lines, pumps and urea mixing tank – biomass plant, Switzerland
Plant room: dosing lines and, on the right, the mixing tank on load cells.
PLC operator panel with SNCR process overview: NOx values per boiler, setpoints and mixing tank – Switzerland
The process overview on the operator panel: measured NOx and setpoint for each boiler, weight in the mixing tank.

Need to bring a biomass boiler within NOx limits?

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