**9. Cleaning of heat exchanger**

In order to maintain or restore efficiency of the heat exchanger, it is often necessary to clean the heat exchangers. Methods of cleaning may be classified into two groups: online and offline cleaning [38]. In some applications, the cleaning can be done online to maintain acceptable performance without interruption of operation. In other cases, offline cleaning must be used.

#### **9.1. Online cleaning**

Online cleaning generally utilizes a mechanical method designed for only tube side and requires no disassembly. The advantages of online cleaning are the continuity of service of the heat exchanger with the hope that no cleaning-mandated downtime will occur. However, it adds extra cost of a new heat exchanger installation or the large cost of retrofits and there is no assurance that all the tubes would be cleaned sufficiently.

**I.** Circulation of sponge rubber balls [39]

The technique is capable of preventing the accumulation of particulate matter, biofilm formation and scale and corrosion product deposition. It is only applicable to flow through the inside of tubes.

**II.** Two phases of the ferrous sulphate treatment

The first phase involves the initial laying down of the protective film. The second phase involves the maintenance of the film, which would be otherwise destroyed by the shear effects of flow.


High and low frequency sound emitters (horns) are used to relief fouling problems on heat exchangers. The use of sound is much less effective in sticky and tenacious deposits that are generally associated with slagging.

**VII.** Online chemical cleaning [46]

Injection of chemical solutions into the process streams for the cleaning purposes.

**VIII.** The use of radiation [47]

Radiation sterilization of microbial-laden water, the use of ultraviolet light and Gamma rays have been considered for a long time.

#### **9.2. Offline cleaning**

An alternative to online cleaning is to stop operation and clean the heat exchanger. Offline cleaning can be classified into offline chemically cleaning or by mechanical means. The cleaning method preferred without the need to dismantle the heat exchangers, but usually it is necessary to have access to the inside surfaces. It would be prudent to consider the installation of a "standby" heat exchanger, thereby providing the opportunity to clean the fouled heat exchanger while at the same time maintain the production.

#### *9.2.1. Offline mechanical cleaning*

**a.** Tube drilling and rodding [28]

Devices may be applied to the rotating shaft including drills, cutting and buffing tools and brushes that may be made from different materials, for example, steels or nylon, brasses depending on the tube material and the nature of the deposit.

**b.** Cleaning with explosives

Used of controlled explosions, where the energy to remove the deposits, is transmitted by a shock wave in the air adjacent to the surface to be cleaned or by the general vibration of tubes brought about the explosion. It is a relatively new innovation introduced in boiler plant cleaning. It is possible to begin the cleaning process, while the structure is still hot.

**c.** Thermal shock [48]

**II.** Two phases of the ferrous sulphate treatment

**III.** Chlorination used for combat bio-fouling [40]

deposits that are generally associated with slagging.

Gamma rays have been considered for a long time.

exchanger while at the same time maintain the production.

depending on the tube material and the nature of the deposit.

the shear effects of flow.

202 Heat Exchangers– Advanced Features and Applications

**IV.** Scale inhibitors [10, 41, 42]

**VI.** Sonic technology [45]

**V.** Magnetic devices [10, 43, 44]

**VII.** Online chemical cleaning [46]

**VIII.** The use of radiation [47]

*9.2.1. Offline mechanical cleaning*

**b.** Cleaning with explosives

**a.** Tube drilling and rodding [28]

**9.2. Offline cleaning**

The first phase involves the initial laying down of the protective film. The second phase involves the maintenance of the film, which would be otherwise destroyed by

High and low frequency sound emitters (horns) are used to relief fouling problems on heat exchangers. The use of sound is much less effective in sticky and tenacious

Injection of chemical solutions into the process streams for the cleaning purposes.

Radiation sterilization of microbial-laden water, the use of ultraviolet light and

An alternative to online cleaning is to stop operation and clean the heat exchanger. Offline cleaning can be classified into offline chemically cleaning or by mechanical means. The cleaning method preferred without the need to dismantle the heat exchangers, but usually it is necessary to have access to the inside surfaces. It would be prudent to consider the installation of a "standby" heat exchanger, thereby providing the opportunity to clean the fouled heat

Devices may be applied to the rotating shaft including drills, cutting and buffing tools and brushes that may be made from different materials, for example, steels or nylon, brasses

Used of controlled explosions, where the energy to remove the deposits, is transmitted by a shock wave in the air adjacent to the surface to be cleaned or by the general vibration of tubes brought about the explosion. It is a relatively new innovation introduced in boiler plant cleaning. It is possible to begin the cleaning process, while the structure is still hot. Changes in temperature particularly rapid changes, cause cracking of foulant layer with the possibility of flaking. This technique is similar to steam soaking. The water flushing carries away the dislodged material and it is repeated until clean surfaces are obtained.

#### *9.2.2. Offline chemical cleaning*

**a.** d. Inhibitor hydrofluoric, hydrochloric, citric, sulphuric acid or EDTA (chemical cleaning agent) for iron oxides, calcium/magnesium scales (foulant), etc. cleaning [49].

Inhibitor hydrofluoric acid is by far the most effective agent but cannot be used if deposits contain more that 1% w/v calcium.

