On-line cleaning solutions for heat exchangers and condensers compared

Brushes versus Sponge Balls

On-line cleaning solutions for heat exchangers and condensers compared

After you’ve decided that on-line cleaning is the right solution to maintain efficiency and to extend bot service time between turnarounds and equipment lifespan, the following question presents itself: Which on-line cleaning approach is the best for your project?

In this article, we look at the different options available. Obviously, as a supplier of brush cleaning systems, we cannot be completely unbiased. However, we do try to present the facts from a neutral standpoint.

Brush or Ball cleaning: 2 workable approaches

Germany’s MAN Turbine Manufacturing initiated the development of on-line or continuous cleaning systems for heat exchangers and condensers in the last century. The company asked its two senior engineers (Hermann Heeren and Josef Taprogge) independently to come up with a solution for efficiency loss due to fouling.

Hermann and Josef retreated to their design benches to wrack their brains for the best solution. Inspiration struck both individually, so today there are two on-line cleaning systems on the market. The solutions they devised are as follows.

Brush cleaning by Hermann

  • Nestle brushes in catch baskets at the end of each tube.
  • Place a flow reversal valve between the cooling tower and the condenser.
  • Propel the brushes through the tubes at regular intervals by reversing water flow in the condenser for a short period. The brushes remove all sediment and fouling during the cleaning cycles.

Sponge ball cleaning by Josef

  • Inject sponge balls into the cold-water pipe from the cooling tower.
  • The balls travel through the condenser tubes and remove fouling on the way.
  • After the condenser, trap the balls in a strainer and keep them in a ball reservoir until the next cycle.

Both systems proved workable, although Hermann jokingly asked Joseph if he would also recommend using sponges as a tool to avoid scaling in dental hygiene strategy.

But seriously, let’s have a closer look at these two systems. We’ll do so by pointing out the disadvantages of one approach in comparison to the other (click “+” for details).

Disadvantages of brush cleaning

Installation

The installation of the reversal valve in the piping between the condenser and cooling tower needs to be done by a qualified contractor and may be challenging or even impossible in specific projects.

Possible bypass in traditional design reversing valve

Some valve designs (swing pipe or plug valve) have a high internal bypass, which means cold water flows to the warm water side of the valve. The lack of cold water supply during peak loads may cause the chiller to trip.
Modern (swing box) valve designs have addressed this issue and come with zero bypass.

Pipe diameter limitation

Water forces in pipe diameters above 600 mm are too high for reversal valve operations. Other solutions are available via tailored engineering.

Disadvantages of ball cleaning

Irregular cleaning of tubes outside main stream area

The flow speed in the center of the condenser is higher than those in the periphery, and therefore, the tubes in the center receive more cleanings. Eventually, the sponge balls may get stuck and block the outside tubes that were subject to fouling buildup, which can prove very counterproductive.

Ball wear and tear

Balls suffer from wear and tear or may get lost in the system when they pass the strainer and end up in the cooling tower fill or basin. This may affect the effectiveness of the system.

Operational cost

The balls (as many as one-third of the number of tubes) have an average lifespan of around 1,000 chiller running hours. Considering the price of the balls, this can double the cost of ownership over a functional system lifespan of 10 years. Brushes have an average lifespan of 20,000 chiller hours.

Conclusion

We can conclude that both systems are effective in avoiding fouling that decreases the condenser’s efficiency and while doing so, minimizing electricity waste from the compressor. As a supplier of continuous tube brushing systems, however, we like to highlight the fact that brushing allows worry-free operation with minimal need for checking and the lowest operating cost.

Example comparison Operating cost

A hotel chiller (450 RT) runs with a 270 kW compressor motor with 600 tubes. The compressor running time is 5,000 hrs. per year over a period of 10 years. Total running time 50,000 hrs.
Over the functional lifespan, an easy 1,000 MWh can be saved on electricity (based on 10% waste) which in most countries is around US$ 100,000.
For comparison, the typical Capex of this chiller is also around US$ 100,000 (US$ 200-300 per RT).

We can conclude that chillers with continuous cleaning system save as much on electricity over their functional lifespan as the investment in the next chiller will be. The system pays for your next chiller, therefore.

SystemBrushBall
Useable600 brushes200 balls
ReplacementEvery 20,000 running hoursEvery 1,000 running hours
Replacement & inspection frequencyEvery 48 monthsEvery 2.4 months
Value per unitUS$ 2.00US$ 2.00
Total useable units (10 yrs-50,000 hrs)1,200 brushes10,000 balls
Cost of useable
(first set included in initial set-up)
US$ 2,400US$ 20,000

 

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