Enhancing the value of GGBS

Introduction:

We at Clair received a proposal for an installationof a new, Ground Granulated Blast Furnace Slag (GGBS) project with capacity of 2 lakhs per annum GGBS at Visakhapatnam, Andhra Pradesh state, India. This was an opportunity where we had to work with a cement manufacturer.

Here, the working setup is also discussed in detail:

• The Wet Granulated Blast Furnace Slag (GBS) is transported to the proposed plant site by 20T capacity tippers and stocked in GBS yard
• GBS is fed to slag hopper by JCB loader and transported to drier hopper through belt conveyors. GBS is extracted from hopper at a controlled rate, with weigh feeder and fed to flash drier for drying
• Coal is used as fuel in Hot Gas Generator for generation of the hot gas used for slag drying
• The dried slag is fed through rotary air lock and belt conveyor to close circuit ball mill with high efficiency separator to produce GGBS @ 4200 cm²/gm Blaine
• The ground GBS in the mill, is transported to separator for separation of product and coarse GBS. Coarse GBS is recycled back to the mill for further grinding and the product is collected in a bag filter & transported to GGBS storage silos
• The GGBS is extracted from silos and transported to packing plant for packing in jumbo bags of 1 or 1.5 t capacity or 50 kg bags as per customer’s requirement. The packed GGBS is stored in plant godown or at port godown

Data/ Table:

Table 1: Site Conditions

Observations:

Clair took up the challenge and observed that for the dust emission control;there were two types of sources identified:

1. Primary Sources included:-

• • Transportation of Slag from VSP to proposed plant is Primary source of dust generation. However, the input material, GBS having 12% moisture, dust generation may not occur during transportation by tippers
  • Primary dust source in a grinding unit is GBS mill and Separator. The mill will be provided with bag filter for effective venting of the mill and also for dust content in the exhaust. The separator will be provided with bag filter for effective venting of separator exit gases and also for dust content in the exhaust
  • Flash Drier is provided with cyclone. Dried GBS will be collected in cyclone and drier exit gases are vented through separator and separator bag filter.
  • Hence, dust generation may not occur during the manufacturing GGBS
  • For a Green field project, Dust emission (SPM) from stack shall be < 50 mg/ Nm³. (Norms during the installation of this Unit)

2. Secondary Sources include:-

• • All other dust sources are considered as secondary since they are not process implied. These dust sources occur wherever relatively dry or dusty material is handled, conveyed, pumped or extracted
  • Although, these dust emissions do not directly affect the process, it is desirable to keep the plant clean from the dust, which is not only a nuisance for the staff but harmful to the mechanical and electrical installations. As such, for all these places, wherever required high efficiency pulse jet type bag filter is considered
  • Dust emission from bag filters shall be < 50 mg/ Nm³
  • Ground Slag will be transported in packed jumbo bags, dust source may not occur during transportation

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