RDF, SRF and TDF

RDF, SRF and TDF are waste-derived fuels used to replace part of the fossil fuel input in cement kilns, lime kilns, industrial boilers, and waste-to-energy plants.

RDF, refuse-derived fuel, is prepared from municipal or commercial waste after removing some recyclables and inert material. Quality can vary widely. SRF, solid recovered fuel, is a more specified recovered fuel, usually produced to tighter limits for calorific value, moisture, chlorine, ash, and particle size. TDF, tyre-derived fuel, is shredded or chipped tyre material used where the process can handle steel, zinc, and rubber-derived energy.

Process implications

Waste-derived fuels affect more than burner heat input. They change moisture, particle size, volatile content, ash chemistry, chlorine, sulphur, alkali, trace metals, and combustion stability. In cement kilns, these changes influence thermal substitution rate, preheater build-up, kiln inlet rings, bypass dust chemistry, clinker quality, and emissions control. In boilers, they influence slagging, fouling, corrosion, particulate loading, and air heater deposits.

Fuel preparation is therefore central. Oversized pieces can burn too slowly and land in the kiln or calciner. High moisture cools the flame and increases gas volume. High chlorine raises the risk of volatile cycles and sticky deposits. Variable calorific value makes stable control harder.

Environmental and safety context

Plants using RDF, SRF, or TDF need stronger receiving inspection, storage control, fire prevention, feed-rate control, and emissions monitoring than plants firing only conventional fuel. Odour, biological activity, self-heating, metal contamination, and foreign objects can all become operational issues before the fuel reaches the burner.

Acoustic cleaning context

Alternative fuels often increase deposit variability. Sonic horns can help keep preheater cyclones, riser ducts, baghouses, ESPs, and hoppers clear when the deposits remain dry and friable. They do not remove the need for fuel quality control. If chlorine, alkali, or incomplete combustion creates sticky or sintered deposits, the cleaning strategy must include chemistry control, bypass operation, combustion tuning, or outage cleaning.

Handling and combustion context

These fuels affect more than heat input. RDF and SRF can bring variable moisture, plastics, biomass, chlorine, metals, fines, and bulky pieces. TDF brings high heat value, steel wire, zinc, sulphur, and handling challenges. Plants evaluate them through calorific value, particle size, moisture, ash chemistry, chlorine, mercury, biomass fraction, storage stability, and the permitting limits that apply to the kiln, boiler, or incinerator.

Operational problems include feed bridging, chute fires, unstable flame shape, higher carbon monoxide, build-up in preheaters, corrosion, sticky ash, and more variable dust loading to filters or ESPs. Maintenance teams inspect dosing screws, weigh feeders, magnets, conveyors, fire detection, explosion isolation, and housekeeping around storage. Acoustic cleaning can be relevant downstream where fuel ash creates dry deposits in cyclones, ducts, hoppers, and gas-cleaning equipment, but it cannot correct poor fuel preparation or a feed system that delivers large slugs.

Monitoring and safety context

Alternative-fuel systems need strong housekeeping because the fuel can be biologically active, dusty, odorous, and sometimes self-heating. Plants monitor storage temperature, carbon monoxide, fire detection, belt condition, metal removal, shred size, and dosing stability. A fuel that meets average specification can still cause trouble if it arrives in wet pockets or with oversized pieces.

Downstream, the useful indicators are flame stability, oxygen, carbon monoxide, chloride input, dust loading, and deposit chemistry. Acoustic cleaning may reduce build-up caused by the changed ash stream, but fuel acceptance, preparation, and dosing remain the first control points. Safety reviews also cover fire, explosion isolation, vehicle traffic, and manual handling around receiving and storage.

Related terms

• Alternative fuel
• Thermal substitution rate
• Waste-to-energy