Reference · Italy · 2015–16

SNCR system on a 6.5 MW biomass boiler – Cosio Valtellino, Italy

DeNOx SNCR system for a woodchip-fired biomass plant: urea diluted by weight with demineralised water, two injection lances in the duct between combustion chamber and boiler, dosing controlled on the NOx measured at the stack.

SNCR injection lance installed on the duct between combustion chamber and boiler, with urea and air lines – 6.5 MW biomass boiler, Cosio Valtellino, Italy

6.5 MWThermal output

150 mg/Nm³NOx limit met

2 + 2Lances and spare positions

2015–16Commissioning

The project

Ecotherm built the DeNOx SNCR system for a biomass plant in Cosio Valtellino, in the province of Sondrio (northern Italy), with a 6.5 MW boiler fired with wood chips. The limit to meet was 150 mg/Nm³ of NOx, referred to 11% O₂, starting from estimated values of around 300 mg/Nm³: a reduction of about 50%, with residual ammonia (slip) below 5 mg/Nm³.

The system was built together with the plant in 2015 and commissioned in early 2016. At start-up both the NOx limit and the residual ammonia limit were met.

How the system works

Storage on two levels

The 32.5% urea tank is on the ground floor. The solution flows by gravity into the mixing tank on the basement level, with no transfer pumps, and the amount loaded is controlled by weight.

Dilution by weight

In the basement, two tanks on load cells hold the demineralised water and the ready solution. The PLC doses urea and water by weight and prepares a highly diluted solution, which spreads better in the flue gas and reduces the risk of overdosing.

Injection in the duct

Two atomising lances inject the solution into the duct connecting the combustion chamber to the boiler, where the flue gas is within the temperature window useful for the reaction. Two more positions are prepared on the duct, with guide pipes and blind flanges, for additional lances if needed.

Dosing and control

Two metering pumps, one on standby, inject the flow calculated by the PLC from the stack NOx analyser signal. Dedicated blowers cool the lances and protect them even when dosing is stopped.

Scope of supply

Urea storage: insulated fibreglass tank with level control and alarms
Solution preparation: tanks for demineralised water and diluted solution on load cells, pneumatic valves, transfer and recirculation pumps
Dosing: two metering pumps, one on standby, with safety valves and pulsation dampers
Injection: 2 atomising lances with pressure gauges and flow meters, 2 spare positions prepared
Lance cooling: dedicated blowers
Control panel: PLC with operator panel, control on the stack NOx signal
Installation, start-up and staff training: with documentation in Italian and English

Plant data

Technical data

Sector	Biomass plant
Country	ItalyCosio Valtellino, province of Sondrio
Technology	SNCR – selective non-catalytic reduction
Thermal output	6.5 MW
Fuel	Wood chips
Flue gas flow	about 17,000 Nm³/hdesign value
Inlet NOx	about 300 mg/Nm³11% O₂ – design value
Stack NOx limit	150 mg/Nm³11% O₂ – met
Residual ammonia	< 5 mg/Nm³met
Injection points	2 lancesplus 2 spare positions
Reagent	32.5% ureadiluted by weight with demineralised water
Commissioning	2015–16

Did you know?

Why dilute the urea

Commercial 32.5% urea is stable and easy to store, but injected at that concentration it spreads poorly in the flue gas. Diluted with demineralised water it reaches the whole section better, and residual ammonia stays under control.

Dosing by weight instead of by volume keeps the concentration constant, with no operator intervention.

Plant photos

SNCR injection lance above the boiler duct, ready to be inserted into the guide pipe – Cosio Valtellino, Italy — Lance ready to be inserted into the guide pipe, with urea and air lines.

SNCR atomising lance assembled with flange, pressure gauges and urea and air fittings, before installation — The lance assembled on site, before installation on the boiler.

Metering pumps of the SNCR system with safety valves and pulsation dampers – Cosio Valtellino, Italy — Metering pumps, one in service and one on standby.

PLC operator panel with SNCR process overview: tanks, weights, stack NOx and ammonia — The process overview on the operator panel: tanks with weights, NOx and ammonia measured at the stack.

Fibreglass storage tank for 32.5% urea – SNCR system, Cosio Valtellino, Italy — Urea storage tank on the ground floor.

Demineralised water and urea solution tanks on load cells in the basement – SNCR system, Cosio Valtellino, Italy — Basement: the tanks on load cells for dilution by weight.

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