chapter - 1 introduction - Meghalaya State Pollution Control Board

Hills Cement Co. Limited.
8. Product & Feedstock Changes
Alkali Content
Reducing the alkali content from the cement is achieved by venting (called
the by-pass) hot gases and particulates from the plant, loaded with alkali
metals. The bypass also avoids plugging in the preheaters. This becomes
cement kiln dust (CKD). Many customers demand lower alkali content, as
it allows greater freedom in the choice of aggregates. The use of fly ash or
blast furnace slags as aggregates (or in the production of blended cement)
may reduce the need for low alkali cement. Low alkali cement production
leads to higher energy consumption. Savings of 2-5 Kcal/kg per percent
bypass are assumed. The lower figure is for precalciner kilns, while the
higher figure is for preheater kilns. Typically, the bypass takes 10-70% of
the kiln exhaust gases. Additionally, electricity is saved due to the
increased cement production, as the CKD would otherwise end up as
clinker.
There are no investments involved in this product change, although
cement users may need to change the type of aggregates used (which
may result in costs). Hence, this measure is most successfully
implemented in coordination with ready-mix producers and other large
cement users.
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