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Chemistry

High-efficiency Selective Non-catalyst Reduction (SNCR) System for Municipal Waste Incinerator

Selective non-catalyst reduction (SNCR) removes nitrogen oxides (NOx) using ammonia (NH3) injected into a combustion chamber heated to 800° - 900°C. Whereas conventional SNCR systems deliver a maximum NOx removal efficiency of around 30%, the newly developed SCNR system from Hitachi Zosen boasts NOx removal of up to 60% - 70% without catalysts, thanks to significant performance improvements.
Temperature distribution inside an incinerator fluctuates in line with waste composition. The new SNCR system features three sets of NH3 injection nozzles to ensure a continuous supply of NH3 regulated to the optimum temperature position (see Figure 1). This enables the system to achieve a maximum NOx concentration of 40 ppm at boiler outlet (Figure 2).
The SNCR process boasts a significantly lower life cycle cost compared to selective catalytic reduction. It will be used as one of the NOx reduction technologies offered by Hitz in the application of new incinerator and the replacement of existing incinerator facilities.

<Environmental Systems & Plant Laboratory>


Figure 1 Overview of high-efficiency SNCR system


Figure 2 NOx concentration (at 12% oxygen, 1atm, 273.15K) at SNCR inlet/outlet

Numerical Prediction of a Wet Scrubber

A wet scrubber with alkaline aqueous solution is an acid gas removal device in flue gas, and the device has high acid gas removal performance. There are two types of devices, one is a device having a combined cooling zone and absorption zone, and the other is a device having a separated cooling zone and absorption zone.
We developed a technique for numerical prediction of vaporization behavior of water sprayed in the cooling zone of two wet scrubbers. The numerical prediction results are shown in Figs.2-4.
We establish optimum design guidelines from our experience and developed technique, and achieve reliability improvement, prevention of the device trouble, and cost reduction.

<Environmental Solution Technology Group, Technical Research Institute>

Schematic diagrams of two types of wet scrubbers

Fig.1 Schematic diagrams of two types of wet scrubbers
: The left figure is a device having a combined cooling zone and absorption zone, the right figure is a device having a separated cooling zone and absorption zone.

The temperature profile

Fig.2 The temperature profile on the center-plane section in the cooling zone of the device having a combined cooling zone and absorption zone.

The H2O concentration profile

Fig.3 The H2O concentration profile on the center-plane section in the cooling zone of the device having a combined cooling zone and absorption zone.

The wall temperature profile in the cooling zone of the device having a combined cooling zone and absorption zone

Fig.4 The wall temperature profile in the cooling zone of the device having a combined cooling zone and absorption zone.

RESEARCH & DEVELOPMENT