Цементна промисловість

Alternative fuels that are too moist are not accepted by cement plants – or they lead to process problems in the rotary kiln: the flame temperature drops, clinker quality suffers, and the kiln becomes harder to control. A moisture upper limit of 20 to 25 % is typical for delivery; many plants require considerably less. Drying solves this problem directly: it increases the calorific value of the material, makes it reliably dosable in the process, and is what first enables the high thermal substitution rates of 60 to over 80 % that leading European cement plants achieve today.

Drying improves cost-efficiency on several levels simultaneously: the calorific value of the material rises, which enables higher revenue at the cement plant or avoids penalty costs for material that is too moist. The lower weight due to water removal directly reduces transport costs – less water means less tonnage. In addition, the storage stability of the material improves considerably, as biological activity and odor development are significantly reduced. For the cement plant itself, an in-house drying plant usually pays off through the saved primary-fuel costs and the increased substitution rate.

The requirements vary depending on the plant, the application and national regulations.
The calcination process usually allows higher material moisture levels, but these should also be well below 20 % residual moisture. The input materials here are mostly unsorted but pre-comminuted MSW/SSW materials.
At the main burner, the alternative fuels must reach much lower moisture levels to ensure optimal controllability of the combustion process. Material moisture levels of RDF and SRF below 10 % are the rule; below 3 % can be dried convectively in STELA dryers.
STELA designs the plant to the specifically agreed target values and ensures compliance through an automatic final-moisture control.

In addition to the process exhaust air of the clinker cooler, which is primarily used, cement plants have alternatively usable waste-heat sources: heat from ORC processes (Organic Rankine Cycle) or from combined heat and power. STELA belt dryers can also be operated as standard with thermal oil, saturated steam or already heated process air as the heating medium.
The connection to the existing infrastructure is designed on a project-specific basis. The result: the drying plant operates with “free” energy that would otherwise escape unused – the operating costs remain correspondingly low.

A blanket statement is not possible without specific plant data – the decisive factors are throughput, input moisture, available waste heat and the current market price for primary fuel, and above all CO₂ pricing plays a major role here.
As a guide: when using the plant’s own waste heat and a throughput of several tonnes per hour, typical payback times are between one and two years.

STELA belt dryers are designed for all common solid alternative fuels: RDF (Refuse Derived Fuel), SSW (Solid Shredded Waste), SRF (Solid Recovered Fuel), Fluff as well as accompanying fuels (BGBS). Since these materials can vary greatly in composition, moisture and flow behavior from batch to batch and depending on the season, an automatic final-moisture control is a standard component at STELA. Drying trials can be carried out in advance in the company’s own technical center to design the plant exactly for the respective material.

Drum dryers work with process temperatures of over 200 °C. For alternative fuels this has several disadvantages: plastic-containing fractions can decompose or stick together, volatile organic compounds (VOCs) are released and considerably increase the effort for exhaust-air cleaning, and the fire and explosion risk rises. STELA belt dryers, by contrast, work with temperatures in the range between 70 and 90 °C. Low-temperature belt dryers dry the material gently and can be operated directly with the plant’s own waste heat – which drum dryers frequently cannot do in practice.

Solid alternative fuels can generate dust particles during the drying process that are explosive under certain conditions. stela addresses this through appropriate design measures and monitoring systems and—where necessary—through a comprehensive explosion protection concept based on the CE risk assessment. The specific measures required depend on the product being dried, the dust characteristics, and local regulations, and are evaluated together with the customer early in the sales process.

The BT (belt widths 6,200 and 8,400 mm) is the high-performance dryer for cement plants with a large fuel demand – with throughputs of up to 60 t/h of drying product. The BTL (belt widths 2,000 and 3,000 mm) is suited to small to medium capacities or to getting started with alternative fuel drying. Both types work according to the same process-engineering principle and are individually configurable.

Yes. STELA drying plants are delivered as turnkey units and can be integrated into existing plant layouts – even in confined space conditions. The connection to existing conveying technology, heat supply and control systems is part of the standard scope of project planning. STELA accompanies the customer from the first design calculation through to commissioning.