TECHNOLOGICAL ASPECTS CONCERNING DIMINISH OF DUST CONTENT IN WASTE GASES RESULTED IN STEELMAKING PROCESESS

Costica T. Mustata1, Elena Ionela Chitovet2

1UZINSIDER Bucharest, 2Politehnica University Bucharest

Key words: steelmaking plant, dedusting, dry purification, bags filter, electric arc furnace.

Abstract: The paper presents technological aspects related to modernization of the dedusting equipment for waste gases resulted in steelmaking proceses at Resita Metallurcical Complex. It designed an installation that collect and purify the raw waste gas from electric arc furnace and ladle furnace both 100 tonnes capacity.

1. INTRODUCTION

            With the increasing industrialization of the planet. ambient pollution has become one of the most important issues, related to the evolution of life on earth. In this context, international bodies and organizations have initiated and implemented several environmental projects, and forced world governments to issue specific laws in this respect . The most important project in this category is "Kyoto Protocol" signed by most countries that sets out milestones to be pursued in view to improving the planet’s life. Romania is also a signatory to this Protocol and elaborated the legislation which requires to polluters operators , environmental protection measures.

In this frame, UZINSIDER, IPROMET and Resita Steelmaking Plant, [CSR] designed, manufactured and put into operation at the electric steelmaking plant of the last one, a dedusting system of waste gas resulted in steelmaking process.

2. CURRENT SITUATION

Existing dedusting system at the Resita Steelmakling Plant for capture and purification of gases from an Electric Arc Furnace [EAF] of 100 tons capacity, includes only the aspiration through the hole capture located in the furnace cap and wet cleaning system. This capture system has several disadvantages such as:

Inability capture the entire amount of gas released during both melting and especially in the tilted vault phase;

The Wet separation system of dust from gases not fully ensure its retention and, most of it crosses all systems capture and flue it to the chimney, dust which it release into the atmosphere;

Although wet separation system retains some of the dust, it pollutes the water, which is still needed capturing dust in settling ponds.

3. PROPOSED TECHNOLOGY

It was concluded that the wet treatment should be replaced with a dry cleaning, more effective, thus

suggesting a separation of dust from waste gas in the battery bag filters with pulse-jet bag desilting or reverse air blow.

To capture the entire amount of waste gas in all of all steelmaking technological phases it was included a secondary circuit, consisting in a hood located under the roof of steelworks, above EAF. This will takeover surplus of gas resulted during melting, as well as those that arise during tilted vault of the furnace.

4. DESCRIPTION OF THE CAPTURE AND FILTRATION SYSTEM. PRINCIPLE OF OPERATION

The system was designed to retrieve all waste gases quantities resulted both EAF and installation adjacent, namely LF, both with a capacity of 100 tons.

System structure consists of two circuits namely; primary, for gas suction through capture cap hole of EAF and secondary circuit for suction of waste gas through hood on the roof and dry cleaning facility.

That was dimensioned so to ensure treatment of whole quantity of gas for both circuits, and includes assembly plant to ensure thorough mixing, filtration, circulation and evacuation undertaken by them.

Figure # 1 is shown a section through electric steelmaking plant, where can see the entire set of capture and circuit of gases to filtration system and then to the chimney, and Figure # 2, an exterior view of filtration plant.

Figure # 1 - CSR Electric Steelmaking Plant – section

The Dedusting Insalation is composed by: Afterburner chamber; Cooling pipes' pipe in pipe "; Cooler air; Spark Retention and Mixing Chamber, with the

purpose to retain, by gravimetric separation, sparks or solid particles who were involved in the secondary circuit capture, and did not stop along the way, sparks should not get into the filter bag that can burn.

Figure # 2 – Bags Filter - outdoor baths

Bags Filter is main cleaning machine, the dust in raw gas is kept at passing a special canvas bags. The gas passes through, but dust can not cross, and thus deposited on the incident side. The cleaning of bags being performed by a special fan, or blowing with compressed air.

waste gas chimney.

In Figure. # 3 and 4, it can see a typical section through a bags filter where is seen a filtering bags battery and the organization of it [1].

Flue gas circulation through the installation is provided by two exhausters, located between the bags filter and chimney , with dampers and start devices on the suction pipes.

Figure # 3 Structure of bags filter

Waste gas from EAF and LF are captured at the vault level and directed to filtration and dedusting installation.

Figure # 4. Section through the Bags Filter Module

For the determination and computation of the filter bags is use specialized software programs, as Fluent and Gambit. As a first approximation it is considered that the flue gas behaves ideally. In this case, equations describing the gas flow, and which is used in mathematical modeling are:

Flow equation;

 

Continuity equation;

Momentum Equation ;

+

Based on these equations it was calculated the gas stream through the filter circuit. Similar researches were made at Intensive-Filter GmbH & Co. KG [1] which highlighted several advantages of using CFD method in designing of bags filters. A simulation of gas flow into the filter bag is shown in Figure # 5

Figure # 5. The gas streams into filter module

5. RESULTS

In Table # 1 are showing the main data on the waste gas resulted in steelmaking process.

Tabelul 1Nr. Denomination UM Value

crt.1 Total gas quantity c.m./h 1,000,0002 Total filtration surface sq.m. 8,561

3 Dust content in gas gr./c.m. 2.54 Gas temperature degrees 130

5 Depressure in filter mm CA 120

6 Filters material density gr./sq.m. 600

7 Bag sizes diameter mm. 140

length mm. 5,2008 Number of modules pcs. 12

9 No. of bags per module

pcs. 312

10 No. of rows per module

pcs. 24

11 No. of bags per rows pcs. 13

12 Dust in filtered waste mg./q.m. 10

The Graphs in Figure # 6 and # 7 highlight the evolution of the waste gas volume, respectively the dust quantity in steelmaking period.

Figure # 6. Variation of waste gas emission

Figure # 7. Variation of the dust quantity in the waste gas.

6. CONCLUSIONS:

Commissioning of the dedusting installation at Resita Steelmaking Plant solved one of the most acute environmental problems in the area. Steelmaking Plant from CSR equipped with EAF and LF, produces approx. 400,000 tonnes of liquid steel per annum.

Before commissioning of dedusting plant, factory emits into the atmosphere about 2.0 tons of dust each hour of operation in the melting regime. New technology, have reduced the amount of dust in the waste gas to 10 kg. per hour.

In accordance with the Romanian laws, but also with European Union Directives, the dust content in exhausted gases in the atmosphere should not exceed 50 mg / c.m.As such, dedusting installation made by UZINSIDER, IPROMET and CSR has achieved its goal.

REFERENCES:

1. Knop, K., Koger, A., Schrooten, T. – CFD for Filters – Global Cement Magazune, June, 2010;2. FabriClean Design Principles – www.flsmidth.com3. Rimini, B., Ferretti, G., Bartolomasi, M. – Sizing of Dedusting System, World Cement, June, 1997.4. Swar, A.K., Meikap, B.C., - Role of Particle Capture Velocity to Control Fugitive Dust Emission by Bag Filter System, South Africa Journal of Chemical Engineering, Vol. 16, no.1,2010.