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Introduction

An efficient cleaning of metallurgical process and waste gas streams is very important for the economic operation of an integrated steel plant. In many cases due to stringent legislation (lower emission limits) plant operators have to make investments to fulfil environmental regulations for not being forced to reduce the production performance.

In the current project 1.5, the company partner is planning to transfer already known dry-based solutions (e.g. gas cleaning by means of fabric filters) into processes, which have so far installed wet-based scrubbing systems. Process gas cleaning systems for the BOF converter (BOF = Basic Oxygen Furnace), the blast furnace as well as direct reduction plants (COREX®, FINEX®) will be further developed. In this context, new solutions will be designed such as energy optimized BOF gas dedusting, and furthermore, already existing systems will be extended, whose concept development was started in prior K1-MET funding periods (blast furnace gas and sinter waste gas cleaning).

Huge amount of experience is existing concerning the wet-based separation of certain off-gas pollutants. In case of dry gas cleaning solutions insufficient information and knowledge is available. However, the replacement of wet gas cleaning solutions can lead to an enormous OPEX (Operational Expenditure) decrease with a simultaneous enhanced off-gas heat recovery.  

Objectives and Motivation

  • A concept of dry-based dedusting systems for plants from iron and steel industry
  • A compact design development of dry gas cooling systems with regard of an increased cooler performance Efficiency
  • The investigation of bag filter behaviour (mechanical filter deformation) during pulse jet cleaning for an increased separation efficiency

Methodology

Planned research methodology contain theoretical considerations and literature surveys, numerical calculations as well as lab-scale and large industrial measurement campaigns. The sinter gas cleaning system MEROS®, developed from a company project partner, will be extended with a catalytic sinter gas treatment step concerning a reduction of carbon monoxide (CO). With the help of a literature survey, suitable catalysts should be identified possessing a sufficient life time. Prior catalytic treatment investigations were not successful due to a considerable decrease of CO conversion after only a few operating hours. It was believed that specific waste gas components (sulphur components, coke formation at the catalyst surface) led to a blockage of the catalyst’s active surface.

The further development of dry gas cleaning solutions offers a simultaneous possibility for a further optimization of existing gas cooling systems. One partner in project 1.5, the department of Engineering / Environmental Sciences of the University of Applied Sciences Upper Austria (Wels), will perform CFD calculations (CFD = Computational Fluid Dynamics) for a cooler design optimization concerning a more effective gas flow control. The simulation results will be used from the involved company partner for an upgrade of their in-house gas cooling system design tools.

Beside the above mentioned theoretical and numerical considerations additional lab-scale measurement campaigns are necessary (test rigs for a research work evaluation by means of repeatable results in a stable technicum environment) as well as large scale measurement campaigns at already operating industrial plants. E.g. the development of a dry based BOF gas cleaning system is performed with the help of a test rig in the technicum of a company partner to investigate the suitability of a fabric filter for the BOF process. Furthermore, it is planned to continue the blast furnace gas dedusting development by means of measurement campaigns with a system, which was already taken into operation at a European steel plant. The main focus of the test series is on separation of specific off-gas pollutants (e.g. chlorides, sulphur components) in order to compare the results with prior measurement campaigns performed at wet-based scrubbing systems of blast furnace gas.

To complete the planned methodology in project 1.5 the cleaning step of fabric filters will be investigated by means experimental series at a test rig using the pulse jet cleaning technology. Periodic pressurized air pulses are used to remove dust particles from the filter surface. In the course of the experiments, a variation of different components and parameters will be realized such as bag filter geometry and length as well as explicit chosen system components (valves and nozzles) and specific operating conditions (pulse length and air flow rate). One partner in project 1.5, the Chair of Process Technology and Industrial Environmental Protection (Montanuniversität Leoben) possesses a high speed camera system and it is planned to visualize the mechanical bag filter deformation during the pulse jet impact.

Results and application

One advantage of dry-based solutions for cleaning of metallurgical process gases compared to wet scrubbing systems is a lower consumption of resources due to the absence of a scrubbing water cycle. Furthermore, a dry cleaned gas possesses a higher temperature, which leads to an increased energy output in case of a turbine being utilized after the cleaning step.

The expected research results in project 1.5 should be used for the realization of saleable industrial gas cleaning solutions ready for series as well as for a further upgrade of existing dry gas cooling systems. While the concept of the dry-based blast furnace gas cleaning process MERIM® is already at a quite advanced development stage, the realization of gas cleaning solutions for direct reduction plants is still at the beginning whereas theoretical concepts should be generated. In addition to this, a large scale implementation of the dry BOF gas dedusting system MERCON® should be another outcome of project 1.5 research results. Furthermore, the sinter gas cleaning process MEROS®, which is already implemented in large industrial scale at the steel plant of a company project partner, should be upgraded. In the course of this process revision, a catalytic gas treatment for a CO reduction should be implemented within MEROS® to fulfil environmental limits in case of growing stringent legislation.

Beside a safe bag filter operation during dedusting of metallurgical process gases, the cleaning step of the filter aggregate represents another main research topic in project 1.5. Appropriate pulse jet operating conditions during cleaning of the bag filters can help to prolong the filter material lifetime with a simultaneous increase of the separation efficiency.