Electrical heat tracing for waste incineration plant

Waste incineration plants are available for various applications and in a range of sizes and designs. Small waste incineration plants, for example, are often found in hospitals to dispose of bacterially contaminated waste on site. In large plants, the energy released during the process is often utilised in the form of district heating and/or for electricity generation.

In a waste incineration plant (also known as a waste-to-energy plant), a crane or grab transports the waste from the bunker via conveyor belts into a hopper, from where it slides directly onto the grates of the combustion chamber and is incinerated there at temperatures of 850–1200 °C. To optimise the combustion process and energy yield, care is taken to ensure that the calorific value remains as constant as possible.

The combustion process produces flue gases containing pollutants. A flue gas treatment plant is therefore used to remove pollutants from the flue gas in several stages, so that by the end of the process, mainly carbon dioxide and water vapour are emitted from the large chimneys. These emission levels are constantly monitored by the relevant authorities.

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Conveyor belt heating: Along the conveyor belts that transport waste from the bunker to the feed hopper, the main challenge in winter is to prevent damp or wet waste from freezing to the belt surface, the belt structure and the drive or idler rollers. Self-regulating heating cables are the preferred solution here: they automatically increase their heat output as temperatures fall and reduce it as temperatures rise – thus preventing both overheating of the belt materials and unnecessary energy consumption. The cables are typically laid on the underside of the belt trough and on exposed structural elements and rollers at risk of icing. The relevant temperature range for frost protection of the conveyor belt is approximately -25 °C to +5 °C ambient temperature. The heating system is designed to reliably maintain belt and waste temperatures above 0 °C. 

Feed hopper heating: The feed hopper is a particularly critical area, as waste that freezes to the sloping inner walls of the hopper can bridge the opening and completely block the flow of material into the combustion chamber. The hopper walls are typically heated using self-regulating heating cables or mineral-insulated heating cables. MI cables are robust, hermetically sealed against moisture and condensation, and resistant to the mechanically and chemically demanding environment immediately above the combustion chamber. They can be embedded within the hopper structure or welded onto it, and provide a precisely defined and uniform heat output per metre. The target holding temperature for hopper surfaces is generally between +5 °C and +15 °C – sufficient to prevent ice build-up and the freezing of condensate.

Ash hoppers: The ash hoppers located below the filter units collect the fine ash separated from the flue gas. If the hopper walls cool below the dew point of the flue gas – which contains not only moisture but also corrosive components such as sulphur dioxide and hydrogen chloride – condensation forms on the inner surfaces, causing the ash to clump together and solidify until the hopper outlet is completely blocked. Mineral-insulated (MI) heating cables are the preferred solution for this application: they withstand the corrosive atmosphere, the elevated ambient temperatures in flue gas treatment zones (often 40–80 °C) – even in winter – and abrasion from ash-laden surfaces. They can be welded or clamped directly onto the steel structure of the hopper and provide a precisely defined heat output. 

Sample gas line heating: For continuous emissions monitoring systems (CEMS), the sample gas must be transported from the sampling point on the flue gas duct to the analysis container without its composition changing. The critical threshold is the acid dew point of the flue gas, which typically lies between 120 °C and 180 °C, depending on the sulphur and chlorine content. Sample gas lines must therefore be maintained above this temperature along their entire length. For this purpose, heated analysis hoses from eltherm with integrated self-regulating or fixed-resistance heating elements are used. These hoses maintain a precisely controlled temperature profile from the probe connection to the analyser and reliably prevent the condensation of acidic components, water vapour and semi-volatile pollutants, which would otherwise distort measurement results or damage the measuring instrument.

However, eltherm not only supplies the necessary heating cables and analytical heating hoses, but also offers a complete solution package from a single source: Our application engineers develop the technically and economically optimal solution, our fitters are experts in the installation and commissioning of the trace heating system, and our service team is on hand to assist you with all subsequent maintenance work.