Reducing emission of acid gases from pelletizing plant

CASE: LKAB pelletizing plant in Kiruna, SwedenBy installing the semi-dry flue gas cleaning system, FLS-GSA®, the emission of acid gases was reduced more than 99%.

Photo: LKAB

The objectiveLKAB decided to double its pellet production by installing a second pelletizing line with a capacity of 4 million tonnes per year.The building permits LKAB received from the Swedish authorities for the erection of a new steel sintering line included restrictions on emissions from SO², HCI, HF and dust. Emission from the acid gases in the flue gas had to be reduced by more than 95% at all times, and the dust emission had to be lower than 20 mg/Nm³ dry.

Defining the project The purpose of the pelletizing process is to transform iron ore into a composition suitable for steel production. LKAB’s pelletizing process consists of four steps: balling, drying/heating, sintering, and cooling. Moist magnetite balls are fed into the drying/preheating grate where they are dried and preheated with hot air. After reaching a temperature of app. 1000° C, the balls are sintered in a rotating kiln heated by a coal burner. The pellets are then cooled using atmospheric air as the cooling media. The outgoing air is used as the drying media in the first part of the drying grate, whereas off-gases from the sintering kiln are used for preheating the balls.

The flue gas leaving the preheating section at 350° C, is contami-nated with acid gases and dust. The gas is led to a heat exchanger for energy recuperation and is then cleaned in a gas suspension absorber installation supplied by FLSmidth before it is finally emitted into the atmosphere.

The solutionFLSmidth supplied LKAB with a semi-dry flue gas cleaning system. The GSA system, as illustrated in figure 1, is divided into two reactors and two Electrostatic Precipitators (ESP) for dust removal.

The time schedule from project start to erection and commercial operation was very tight. Further, the space available for the flue gas treatment plant was limited.

The final guarantee test was carried out 3½ years after the invita-tion to tender was received by FLSmidth, and LKAB’s time schedule was thus fulfilled.

Results Table 1 shows the design conditions for the flue gas cleaning system. The GSA system has been independently tested by the Swedish company, IMKAB. During the performance test and the daily operation of the flue gas cleaning system, the results shown in table 2 have been achieved. The availability of the flue gas cleaning system was guaranteed to be higher than 8.085 hours per year and this guarantee has been fulfilled. The installation has been running successfully for more than 10 years.

Figure 1. FLSmidth’s ESP at LKAB pelletizer plant in Kiruna

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Copyright © 2011 FLSmidth A/S. ALL RIGHTS RESERVED. FLSmidth is a (registered) trademark of FLSmidth A/S. This brochure makes no offers, representations or warranties (express or implied), and information and data contained in this brochure are for general reference only and may change at any time. C

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Component Unit Value

Gas flow Nm³/h wet 359,000

Gas Temp. °C 170

Water content Volume %, wet 2.4

Oxygen content Volume %, wet 14.0

SO² content mg/Nm³ dry, 11% O² 580

HCl content mg/Nm³ dry, 11% O² 230

HF content mg/Nm³ dry, 11% O² 194

Dust content mg/Nm³ dry, 11% O² 700

Component Guaranteed removal % Achieved removal %

SO² 95.0 99.1

HCl 95.0 >99.9

HF 95.0 >99.9

Dust 99.6 99.8

Table 1: Design conditions for the flue gas treatment.

Table 2: Removal efficiencies for the flue gas treatment.