Quarry Southern Africa January 2017 | Page 26

10 %– 20 % saving on the 350 million tonnes of fuel the industry consumes per annum , the collective cost saving is vast .”
Fuel game-changer for European cement producers
Some cement kilns in Europe substitute 100 % of their fossil fuels with RDF , specifically during the substituting fossil fuels at the pre-calciner .
“ Examples exist where producers rely solely on alternative fuels as energy supply . This is indicative of the maturity of the mindset of the European recycling market , but also highlights the technological advancement of the cement plants .”
Cement kilns that aim to operate fully on alternative fuels need to undergo significant process conversions and systemic changes , which demand upfront capital investment .
Another legislative incentive — carbon taxes — makes it lucrative for European producers to invest this capital upfront . In South Africa , the green economy lags behind , with the carbon tax bill still in draft form .
In addition to capital outlay , a second consideration for cement producers is the metallurgical impact of RDF on clinker .
Standard to cement production , different types of fuel applications exist between the pre-calciner and main burner processes . The main burner uses a smaller-sized waste fraction because it has a shorter residence time as a result of higher temperatures . In the pre-calciner phase , temperatures are lower , the residence time longer , and the plant uses larger fuel particles . RDF is therefore more suitable for pre-calcising , however it can be shredded to the size fraction required for use in the main burner .
Processing impacts
From a process perspective , the use of a waste-generated fuel source adds alternative challenges and opportunities to clinker production .
“ Some studies have indicated the application of RDF as a better combustible material or fuel source than coal ,” says Young .
Controlling your RDF feed rate is critical for maintaining stable temperatures inside the kiln . Because RDF is a new fuel source with unpredictable combustion patterns — at least when compared to tried-and-tested coal — automated time adjustment of
A solid recovered fuel in the form of extruded logs .
Interwaste
Waste is now put to good use and used as a fuel in a number of cement kilns . dnrec . delaware . gov
24 _ QUARRY SA | JANUARY 2017