Cleaning Method in a Critical Process Environment

Heat exchangers play a decisive role in many industrial processes, being responsible for transferring thermal energy between various media. Over time, however, deposits of flue‑gas residues, dust or chemical particles can accumulate on the heat‑exchanger surfaces. As a result, the efficiency and performance of the plant drop significantly. It is in this context that high‑frequency impactors of the NHK series from NetterVibration come into play. These devices tackle firmly adhering material effectively and provide continuous cleaning of heat exchangers. This, in turn, reduces downtime, boosts boiler efficiency and lowers maintenance costs.

Construction and Mode of Operation of the NHK

In the NHK high‑frequency impactor, a freely oscillating, self‑regulating piston generates sinusoidal, linear vibrations. The piston drives a heavy mass, which delivers up to 50 impact blows per second onto the component. As a result, the surface is cleaned particularly thoroughly. In contrast to conventional impactors of the PKL series, the NHK uses lower impact energy but strikes far more frequently. While a PKL delivers one single robust blow, the NHK applies many lighter blows per second. The outcome: gentler on the component but still effective in cleaning. 

The striking frequency can be adjusted steplessly via a pressure regulator. One further advantage is the NHK’s versatility: depending on the pressure setting it can either vibrate or impact. In use, it lifts off the component slightly and then returns, thereby generating highly effective cleaning results depending on the application. 

Particularly Suitable for Use on Heat Exchangers

A key feature of the NHK is its robust construction, developed specifically for use in process‑critical environments. The overall design is geared toward corrosive conditions involving flue gases and elevated temperatures. The NHK can be deployed across a variety of heat‑exchanger installations, with its placement determined on a case‑by‑case basis by NetterVibration’s application engineers. Typically, the NHK is mounted at critical points—such as on shell‑and‑tube or plate heat exchangers—where deposits restrict heat transfer and conventional cleaning methods like chemical flushing or manual intervention are not feasible or efficient.

Cleaning with an NHK causes minimal wear, requires little maintenance and thanks to its unique combination of vibrating and impacting, is particularly flexible. Thorough cleaning with less stress on the components increases service life and improves plant availability. Deposits and crusts are reliably removed without damaging the heat‑exchanger structure. Importantly, cleaning takes place during ongoing operation, thereby minimising downtime. Revision costs can be reduced substantially. 

Practical Applications

In a number of incineration plants producing process or district heat, customers of NetterVibration use the NHK on heat exchangers. At the beginning of the process, for example, waste wood, recycled wood or refuse is combusted. In the flue‑gas stream a closed heat‑exchanger—often a tubular system (bundles or cylindrical with baskets)—is installed, facilitating heat transfer between the flue‑gas and the heat‑exchanger medium (frequently thermal oil). Over time, gases, dust, lime etc. deposit on the heat‑exchanger surface. As a consequence, the gas bypasses the exchange surface unused, less heat is transferred and system energy efficiency falls sharply. 

To prevent this, the tubes of the heat exchanger are subjected to high‑frequency vibration via the NHK and, as required, also to impacts, which frees up or prevents adherence of deposits. As a result, heat exchange remains unaffected and the overall throughput time—the interval between two shutdowns and revisions—is noticeably increased. The NHK is calibrated on‑site by NetterVibration staff prior to commissioning and configured to suit the local process; this, naturally, should be checked at each overhaul. Typically a mix of vibration and impacts is configured to achieve the best possible result. 

Side Note: Versatile Use of the NHK

Foundries use vibration technology, among other things, for de‑moulding cast parts and compacting moulding sand during the manufacture of castings. The NHK high‑frequency impactor is installed beneath a vibration table for these purposes. Via the vibration the moulding sand is better distributed in very short time and especially highly compacted; air inclusions are minimised, which in sum leads to higher precision and surface quality of the castings.

Due to its robust and durable build, the NHK is also used for vibration tables when freeing sintered‑metal parts from moulds, for permanent mould casting, and for compacting rammed masses for industrial furnaces.

Read the full article here (in German, published in Schüttgut & Prozess 4/2025).

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