In 2021, WtE Buchs (belonging to VfA – Verein für Abfallbeseitigung) celebrates the sixtieth anniversary of its founding. Little remains of the original concept of waste disposal. Over the years, three modern ecologically operated incineration lines have been developed, using the recovered energy from waste to generate electrical power and to supply steam for industry, as well as an extensive district heating network, which extends into the neighboring Principality of Liechtenstein.
To improve the boiler cleaning, all three lines have been retrofitted with automatically operating Shock Pulse Generators (SPG) in 2018 and 2020. The operator is very satisfied with the reliability and quality of this boiler cleaning system.
At present, WtE Buchs (the Swiss plant name is KVA Buchs – Kehrichtverbrennungsanlage Buchs) operates three differently constructed incineration lines, which are equipped with different boiler concepts.
Line 1, the oldest one, is constructed of a three-pass vertical boiler. Since its commissioning in 1968, several rebuilds have been realized, but the concept is still original. Two vertical shott-type evaporators are installed in the second boiler pass, which are equipped with a rapping mechanism. Due to the stiffness of the tubes, the rapping system did not clean the shott evaporator sufficiently and the plant often had to be cleaned manually. Since the installation of an SPG between the two evaporator shotts, which is automatically activated with a pulse frequency of two hours, the heat transfer is always good. The third – the vertical boiler pass continues to be cleaned by shot cleaning. Therefore, an additional manual online blast cleaning is performed in the third pass every third week to ensure the required availability. The operator has been very satisfied with the cleaning effect and reliability of the SPG since its installation in 2018.
Line 2, built in 1994 has undergone extensive reconstruction. The classic four-pass boiler has been widened in the horizontal pass and is equipped with pneumatic rappers. Although these knock on both sides of the elastically designed tube bundles, the need for additional cleaning by SPG’s has arisen. The good experience with the SPG’s installed in the first incineration line in 2018 was decisive for upgrading of the line 2.
In 2020, therefore, one SPG each was installed upstream of the tube bundle of the evaporator and the first Eco’s. The vertical shott evaporator, which had similar cleaning problems as that of line 1, was as well equipped with an SPG already in 2018. Now the required cleaning quality of the entire boiler has been achieved. The operator’s statement «now the cleaning is optimal and the travel time has been extended» expresses his satisfaction.
In this incineration line, as well the pulse frequency is fully automated in a cascade from front to back by two hours each. The individual shot pulse, as such, remains for only few milliseconds. The tube bundles remain in a satisfactory condition during the entire travel time. See more in the following sketch:
Fig. 3: Condition before installation of the SPG
in the «Dirty» condition, [Photos WtE Buchs]
Fig. 4: Permanent «operating condition»
between the superheater and evaporator
with two hours pulse frequency each
Fig. 5: Permanent «operating condition»
between both Eco’s with two hours pulse frequency each
Line 3 from 1991 is designed as a two-pass boiler. All tube bundles are located in the second, the horizontal pass. To support the rappers, an SPG was installed between evaporator 2 and the final superheater in 2018. The hammer-rappers, together with the SPG can now keep the deposits permanently small, which behaves to satisfaction of the operator. The pulse frequency of two hours each has also proven itself in this line and the availability meets the operator’s expectations.
The gas supply to all SPGs is fully automated from the central, redundant gas storage system with two 12-cylinder batteries each and the DCS triggers the reordering in advance. All gases to the SPGs are led in well-engineered copper pipes.
The SPG type EG10XL was installed in all three lines. The annual maintenance is carried out by Explosion Power GmbH, which also provides for the necessary spare parts.
All three lines are equipped by a remote maintenance tool with ad-hock data transfer to the manufacturer.
The three SPGs, which were installed in 2018 report currently over 10’000 pulses per unit.
The operator is fully satisfied with the current development of boiler cleaning in all incineration lines and thinks that cleaning by means of SPG, which does not damage the boiler tubes, has brought a permanent optimization of the availability of the entire plant.