Solid fuel firing plants are suited to burn all different solid fuels to generate thermal energy. maxxtec heat recovery systems recuperate the energy in the hot exhaust gases and transfer it to an organic fluid. The thermal fluid allows high temperatures with low pressures in the system and heat consumers.


The main component of the maxxtec heat recovery system is the gas heater. The thermal energy in the hot exhaust gases from the firing plant is transferred here to the heat transfer fluid. Contrary to fuel oil or gas, solid biomass fuels have varying properties. The humidity content and heating values of the fuel can change. The presence of sand, soil or other contaminations have an impact on the fuel properties.


Two-pass heat recovery systemBecause of these varying properties demands on firing plants to achieve a clean and efficient combustion of different materials are strict, but also the gas heater must meet specific requirements in order to achieve a cost-efficient and environmental friendly operation of the Thermal power plant 14800 M.


To burn clean natural fuels the compact gas heater is a very good solution. Convection and radiant heater are integrated in one common sheet. This allows a compact and cost-efficient heat recovery system design.


Since many years industry has been using the heat recovery systems in 3-pass design to generate process heat. However, changing and increasing demands, such as the continuous full load operation required in biomass fired CHP plants, uncovered the disadvantages of traditional heat recovery systems in 3-pass design.


To meet all operational requirements of a continuous full load modus and to increase operational safety, maxxtec developed the new heat recovery stystem in 2-pass design. This design is an improvement on the traditional heat recovery stystems in 3-pass design and offers decisive advantages.



In the traditional heat recovery systems in 3-pass design a separation must be installed between the first and third exhaust gas pass. This involves also a gasket between heater coil and heater cover. Different thermal expansion, or faulty installation of the gasket after servicing, often caused exhaust gas leakages between the passes which could finally effect the overheating of the heater sheet and the gasket frame. Because the gasket frame is usually welded onto the heater coil, deformations of the gasket frame will cause tensions which may result in leakages at the heater coil.  


The new maxxtec heat recovery system in 2-pass design does not need any gaskets between the exhaust gas passes. Damages caused by overheating through a gas leakage are avoided.


The heat recovery systems in 3-pass design requires an exhaust gas turning chamber between 1st and 2nd pass. At this stage the exhaust gas temperatures are still relatively high. Since the turning chamber has no cooling possibilities, the heater sheet may be overheated if the exhaust gases are not cooled down enough in the first and second pass. This occurs when the heating surfaces are fouled.



In modern maxxtec heat recovery system in 2-pass design the heater sheet is cooled by the outer coil. Only at the exhaust gas outlet the heater sheet is exposed to the exhaust gases and there they are already cooled down sufficiently to prevent damages. Furthermore exhaust gas temperature is monitored by a safety temperature limiter. In this way overheating of the heater sheet is surely prevented.


In heat recovery systems in 3-pass design the exhaust gases must pass 3 passes connected in series. Furthermore the exhaust gases have to be reversed twice within the heater. This design results in high exhaust gas pressure drops, resulting in a high power consumption of the fans. The thermal oil heater coils in the heat recovery systems in 3-pass design are connected in series: the thermal oil needs to flow through all the entire heater coils. The result is a high oil pressure drop, also effecting a high power consumption of the pumps.


In maxxtec heat recovery system in 2-pass design the exhaust gases are reversed only once.  In the convection section the exhaust gas flows parallel. The thermal oil heater coils are also connected in parallel. In this way high pressure drops are avoided. The design reduces pressure losses both on the exhaust gas side and on the thermal oil side considerably. Reduced power consumption of exhaust gas fan and circulation pumps reduces operational costs.


Cleaning of traditional heat recovery stystems in 3-pass design is only possible for the convection heating surfaces with fixed cleaning nozzles installed on top of the heater and at the lower part of the heater. The pressurized air needs to be transported to two locations on the heater, which increases installation efforts. Static cleaning nozzles blow the pressurized air with high velocities onto the heating surfaces on the same place repeatedly. Depending on the fuel these places may corrode or erode and this will result in damages on the heating surfaces or even in leakages. Adequate and extensive inspection and maintenance on the heater is vital for the operational safety and must be carried out thoroughly and with short intervals. Static cleaning nozzles must be sufficiently powerful to clean a greater part of the heater. Therefore pressurized air consumption will be very high.


Maxxtec heat recovery systems in 2-pass design are cleaned solely from the top down. The heating surfaces are cleaned with the "airmaxx4" - a boiler cleaning system for heating surfaces specially developed for this heater design. The pressurized air is lead close to the soiling of the heating surface. Damages caused by repeatedly blasting on the same place are avoided. Cleaning and pressurized air consumption are reduced considerably.








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