Disruptive substances and the burning behaviour of solid alternative fuels

1 Proportion of the thermal heat demand in % accounted for by the use of secondary fuels in the German cement industry (Source: VDZ 2009)

2 Clinker granule produced under reducing burning conditions(Foto: Baier 2003)

3 Phenomenological trial with solid alternative fuels for determining the distance of travel (Foto: Baier 2000)

4 Analytical classifier from Bückmann GmbH + Co. KG/Mönchengladbach

$5 Suspension fractionation by classification of solid recovered fuels (SRF) prepared out of an identical high-calorific fraction produced from a mechanical-biological treating [2]$

5 Suspension fractionation by classification of solid recovered fuels (SRF) prepared out of an identical high-calorific fraction produced from a mechanical-biological treating [2]

6 Mass distribution as a cumulative curve after classifying shredded and pelletized secondary fuel (SBS) [2]

7 Simplified sequence of the conversion of solid fuels with subsequent coke burnout [6].

8 Molar H/C and O/C ratios of fuels [6]

9 Grinding principle in the air-whirl-mill

10 Pressed biomass ground at about 200 °C (sample 1, TS 5 %) and about 80 °C (sample 2, TS 14 %), resulting in d₅₀ sample 1 < d₅₀ sample 2.

11 Biomass before (d₅₀: 3200 µm; left) and after (d₅₀: 200 µm) grinding (size reduction rate 16:1)

12 First test with hard pellets: It resulted in a mixture of finely divided and fluffy woolly pulverized alternative fuel.

13 Ignition delay of different materials according to Zelkowski [3]

14 Possible plant configuration for using solid alternative fuels
with and without air-whirl-mill (scheme for walking floor from
A.T. Tews)

Solid alternative fuel for the cement industry

Summary: The increasing requirement to use alternative fuels means that rotary cement kilns are being converted to the use of calciners and multi-fuel burners. However, the production of alternative fuels and the process technology must be matched even better to one another if the application rates are to be increased further without affecting the product or the emissions. This includes the fact that the alternative fuels must be characterized and appropriately processed not only chemically in accordance with the requirements of pollution control but also in accordance with the objectives of the thermal utilization process. This article describes the preliminary work and tests involved with the air-whirl-mill. Initial investigations into various pulverized alternative fuels have shown speeds of ignition and conversion that have previously been found only with pulverized coal and lignite.

1 Basic principles

Due to the continuing fluctuations in the price of energy and the debate on sustainable conservation of resources, the German cement industry has managed to decrease its overall energy demand continuously through technical optimization [1]. It has also increased the use of alternative fuels still further under pressure from German policy with the implementation of the ban on landfilling untreated waste (Technical Instructions) in 2005.

After the first oil crisis there was initially a changeover from oil to coal and, because of their high energy contents and relative ease of...

Disruptive substances and the burning behaviour of solid alternative fuels

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ZKG 06/2010

ZKG 06/2010

Related articles:

Proven experience with alternative fuels in the cement kiln process

Alternative fuels in the cement industry

Burn-out characteristics of lumpy secondary fuels and requirements for the design of calciners in the cement industry

Burn-out characteristics of lumpy secondary fuels and requirements for the design of calciners in the cement industry

PREPOL Step Combustor (SC) – a simple combustion system for solid alternative fuels

Burning alternative fuels in cement kilns