Denitrification of steelmaking kilns

The SCR reactor and auxiliary systems consist of an ammonia injection system, SCR reactor, catalyst, soot blowing system, flue, etc.

The SCR reactor contains catalyst layers where, under the action of the catalyst, NH₃ reacts with NOx to remove NOx. The catalyst promotes the reaction between ammonia and NOx. At the top of the SCR reactor, there is a rectifying grid to ensure uniform distribution of the flue gas flow. The catalyst is installed in modular units for easy handling, installation, and replacement. Soot blowers are installed between the catalyst layers of the SCR reactor to remove dust and SCR reaction by-products deposited on the catalyst, thereby reducing the reactor pressure drop.

1) SCR Reactor

The reactor is equipped with optimized distribution devices and an ammonia injection grid. Catalyst beds are installed in the vertical section of the reactor, divided into two layers. The reactor adopts a fixed-bed parallel channel configuration.

2) Ammonia Injection System

To ensure uniform distribution of ammonia in the flue gas and facilitate adjustment of the NH₃/NOx molar ratio in the flue gas above the first catalyst layer in the reactor, ammonia injection ports are installed at appropriate locations in the inlet flue.

3) Heating System

Electric heating is used to raise the temperature of the raw flue gas (applied when necessary).

4) Soot Blower

The use of soot blowers ensures continuous cleaning of the catalyst, thorough dust removal without dead zones, maximizes the catalytic activity of the catalyst for denitrification reactions, extends the catalyst's service life, and reduces SCR maintenance costs. Each channel and each layer of the SCR denitrification system is equipped with a compressed air soot blowing system.

5) Catalyst

Currently, there are three mainstream types of SCR catalysts on the market: honeycomb, plate, and corrugated plate. Global SCR operational practices show that excellent system design and appropriate catalyst selection, based on actual design conditions, can ensure SCR system performance. Guangzhou Najie Company, based on catalyst usage and operational experience, as well as analysis of the design conditions of this project—including operating conditions, fuel, and fly ash properties—has comprehensively considered economic and safety factors and selected medium-low temperature honeycomb catalysts for this project. The reasons are as follows:

a) In terms of volume, as shown in the structural diagram above, the honeycomb type has a large contact area and requires nearly 30% less total volume compared to other catalysts under the same design conditions. Therefore, choosing honeycomb catalysts can reduce reactor size and lower the initial investment cost of the SCR system.

b) The flue gas temperature does not reach the active temperature range of high-temperature catalysts, so specialized medium-low temperature SCR honeycomb catalysts are used.

c) Specialized medium-low temperature SCR catalysts have a wide adaptation temperature range, typically 200-350°C.

d) The catalyst used is a specially developed medium-low temperature honeycomb catalyst with low SO₂ oxidation rate, designed for high-dust, high-sulfur, and high-NOx conditions. This catalyst has been applied in many building material kiln projects, demonstrating excellent anti-poisoning performance and efficiency.

f) Based on analysis of actual operating conditions, the ash content and properties, as well as flue gas parameters of this project, fall entirely within the experience database range of medium-low temperature honeycomb catalysts with low SO₂ oxidation rates. The catalyst manufacturer guarantees that the selected honeycomb catalyst is fully capable.

When the temperature is between 20°C and 150°C, the catalyst should be able to withstand a minimum temperature rise rate of 10°C/min.

When the temperature is between 150°C and 300°C, the catalyst should be able to withstand a minimum temperature rise rate of 50°C/min.

Ms. Fu 17324005195

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