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Bag filters for gas fired melting furnaces

Odsávání spalin tavící pece

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The Gidly catalog includes baghouse units that are directly designed for use in applications of gas fired melting furnaces dedusting. We are offering 14 basic baghouse units for extraction of dust from gas fired melting furnaces, graded according to the required volumetric airflow.

Dust parameters

The dust resulted from gas fired melting furnaces is dry and made up of light particles. The exhaust gas temperature ranges from 300 ° C to 400 ° C depending on the furnace operating condition. The resulted exhaust is a product of gas combustion. The gas fired furnace increases the humidity of the extracted dust, and therefore poses a risk of vapour condensation inside the ducting and baghouse. The extraction technology has to be thermally insulated and its hopper heated. The dust from the furnace is very fine, dark, dry and slightly abrasive.

Dedusting of the gas fired melting furnace

The modern dedusting systems of gas fired melting furnaces are separated into two groups: raw flue gas extraction without dilution by coolant ambient air for cooling and to dust extraction from the filling lid above the furnace opening.

Flue gas extraction during the melting

The furnace manufacturer always provides the required ammount of vacuum and the amount of gas exhausted at a defined temperature. The function of the extraction system then directly affects the function of the furnace. The flue gas temperature is usually  about 400 ° C to 300 ° C when sucked into the extraction system. In practice, there are two ways to cool the flue gas for the baghouse filter operating temperature. The first option is to control the additional amount of extracted ambient air into the ducting and thereby regulate the temperature. The disadvantage of this solution is the growth in size, in electricity consumption and in investment costs of the whole dedusting technology.

Another option is to cool the extracted hot furnace gas before the baghouse with a heat exchanger. The gathered heat can then be use either for heating the air burned in the furnace or for heating the plant in winter seasons. With heat exchange, the extracted flue gas shrinks in volume and the baghouse can be smaller. The minimum temperature of air in the extraction ducting should not drop lower than 100°C (min 80°C) to prevent condensation of vapour. Please note that the flue gas includes a portion of HF and HCL acids, excluding the use of zinc coated steel. The zinc coated steel would last only a few days while used with a gas fired furnace. We recommend to dose Ca(OH)2 into the extraction ducting to lower the content of HF and HCl acid and improve the regenerativnes of the bag medium. The amount of gas extracted is reported by the furnace manufacturer, indicated either by QN [Nm3/h] at a specific temperature, or by QV [m3/h], also with conjuction to a specific operation temperature.

Extracting smoke from the furnace lid

The extraction hood in the furnace is placed right over the charging inlet. The extraction is neccessary only when the lid is open and the charging occurs. The extraction hood provides smoke extraction so that it does not extend into the workspace. Since the burner is not open when the lid is open, it is not a combustion that is dedusted but just the in the plant. The extration duct is therefore not to be insulated because the air is not extracted at a higher humidity than the surrounding environment and there is no risk of condensation inside the ducting or baghouse. We still dont advise to galvanize the ducting. We recommend applying a temperature-resistant and chemically resistant coating. The amount of exhaust air is given by the manufacturer but can also be determined empirically at a minimum of 4000 to 5000 m3 / h per 1m length of the suction hood.

Parameters of the baghouse for gas fired melting furnaces dedusting

Baghouse units in the GIDLY catalog are fabric filter units equipped with automatic regeneration of bags by a reverse pulse jet technology. From our experience of individual extraction applications, the lifetime of the filter media lasts for more than 20,000 hours without the need of any manual refinement. The filter media are flat smooth fabric sleeves made of non-woven fabric with an antistatic coating and an area mass of 600 grams per square meter and a temperature resistance for up to 200° Celsius.  The filter medium does not contain folds where the dust be sedimented and is very mechanically resistant to tearing or scraping.  The amount of residual dust particles ranges from 1 mg/m3 do 5 mg/m3, but the filtered air cannot be recirculated back into the plant because the flue gas contains CO, CO2, HF, HCl, NOx and other toxic substances. However, the heat from the filtered air can be recovered using special tube heat exchangers with heat exchange surface regeneration technology.

Recommended ducting solution

We recommend using Group III Ducting – a thick-walled, welded ducting. When extracting hot flue gas, it is neccesary to use stainless ducting with heat insulation, and with furnace lid extraction to use ducting  with a temperature-resistant and chemically resistant coating.

Bag filters for gas fired melting furnaces in the GIDLY Catalog

To find a specific assembly of the baghouse and fan, please go to the catalog and price list page. Select Baghouse units. From the list select „Gas fired melting furnaces“. Choose the required volumetric airflow value in the next step – marked in QV [m3/h] at t= 150°C . The result will be a set of components – baghouse + thermal insulation of the housing + thermal insulation and heating of the hopper + surface finish + stainless parts – fan – which all together result in the dedusting system. You can then insert the products in your costing.

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