Cooling system maintenance |
Offline cleaning of heat exchangers: methods compared
Deposits in cooling systems are a real problem, with a significant impact on thermodynamic efficiency and power plant performance. In open cooling systems using surface water as their water source, condensers are often subject to accelerated fouling and deposit build up. When the speed of deposit build-up is high, off-line cleaning methods should be considered. This article discusses various off-line cleaning methods with a focus on foam cleaning
Dr Frank Udo Leidich Lead Expert in Power Plant Chemistry, Germany; Jacek Sadowski Director for International Business Development, Ecol Sp. z.o.o., Poland; and Wojciech Majka CEO, Ecol Sp. z.o.o., Poland
Huge efforts go into improving the efficiency of fossil fuelled power plants by increasing main steam temperatures and pressures. This naturally leads to limitations imposed by the available and affordable materials. Optimisation at the lower temperatures at which steam condensation occurs is often neglected, even though it is just as important for plant efficiency as the live steam parameters.
Deposits in the condensers of fossil fired power plants have a major impact on thermodynamic efficiency and performance. Even thin deposits on condenser tubes can lead to a dramatic deterioration in heat exchange with the cooling water. This increases the condensation temperature and thus also the exhaust steam pressure (see Figure 1). The different kinds of deposits in condenser tubes (Figure 2) form through the following
mechanisms: ● sedimentation and deposition of suspended solids (microfouling);
● colonisation of surfaces by micro- and macro- organisms;
● formation of biofilms through the deposition of metabolic products from microorganisms, mostly slime-forming bacteria (biofouling);
● crystallisation of dissolved water constituents (scaling); and
● corrosion products.
The direct influence of fouling on the Carnot efficiency (C
It is determined by the upper (TH temperature (TC
): C = 1 - TC /TH
An increase in the condensation temperature by 1-2°C or, respectively, in the condensation pressure reduces efficiency by up to 0.3% (see Figure 3).
In addition, deposits and scale increase the risk of under-deposit and standstill corrosion, which ultimately leads to the risk of cooling water intrusion into the water–steam cycle. In a nutshell: the cleanliness of condenser
) of the cycle is obvious. ) and lower
Condensing steam Condensing steam
Figure 1. Deposits on tubes impair heat transfer
internal surfaces is one of the most important factors in achieving reliable, trouble-free operation of steam power plants at optimal thermal efficiency.
In open cooling systems using surface water as the water source, condensers are often subject to accelerated fouling and deposit build up. When speed of deposits build-up is high, in particular in once-through cooling systems, where dosing of conditioning chemicals like scale inhibitors, dispersants, and biocides is not permitted, a continuously operated sponge ball cleaning system might not be efficient enough to fully avoid or control scale built-up. In such cases, the application of off-line cleaning, either event driven or at regular intervals, should be considered. Below we discuss the various off-line cleaning methods, with a focus on foam cleaning, a highly effective process that can be used not only for scale removal but also for disinfection of heat exchanger water boxes before visual inspection of the heat exchangers.
Offline methods for removing scale and deposits from condenser tubes
Common offline cleaning methods are: ● high pressure water jet blasting; ● water gun with projectiles;
22 | March 2026 |
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● mechanical cleaning (with brushes, drills, etc); ● chemical cleaning; and ● foam cleaning.
The pros and cons of the methods are discussed hereunder.
High pressure water jet blasting High pressure water jet blasting is a powerful and effective method to remove scale, deposits and debris from condenser tubes. Even the toughest deposits can be removed. Because of the high water pressure, addition of chemicals like cleaning additives is not necessary. However, the process is very time consuming as it requires cleaning tube-by- tube with a water jet lance (see Figure 4). Because of the high pressure applied (typically 1200-1500 bar), there are EHS (environmental, health, and safety) concerns and the operators accordingly need to be protected against the high pressure water jet, which impedes freedom of handling and movement.
There is also a risk of damaging the tubes when using high water pressure. The method requires powerful high-pressure pumps and consumes large volumes of water, which results in a large amount of waste water that may need treatment before release into rivers or sewage systems.
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