Applications
Operating installations
Total number of self-cleaning heat exchangers designed, installed and put into operation under the supervision of Dr. Ir. Dick Klaren, the President of KLAREN BV, amounts to more than 80, totaling over 10,000 m² heat transfer surface.
Treatable fouling services
Fouling services which can be treated with the KLAREN self-cleaning exchangers are the following:
- Forced circulation evaporators and reboilers.
- Chemical processes where heating and cooling causes polymerization fouling or resinous deposits.
- Heat recovery from hard scaling and/or biologically fouled waste waters.
- Concentration of waste waters by evaporation.
- Cooling and evaporative cooling crystallization.
- White-water and black-liquor heating in pulp and paper industries.
- Heating of slurries in mining industries.
- Raw juice heating in food processing.
- District heating and/or power generation with geothermal brines.
- Brackish water and seawater desalination.
- Production of medium and high pressure steam from severely fouling chemically untreated waters.
- Self-cleaning lube oil chillers to replace scraped surfaces.
- Crude oil preheater.
The demand for self-cleaning heat exchangers is increasing. Figure 1 gives an impression of a number of installations equipped with self-cleaning heat exchangers. Amongst them:
 A Multi-Stage Flash / Fluidized Bed Evaporator (MSF/FBE) for the desalination of seawater on the Isle of Texel, the Netherlands, with a production capacity of 500 tonne/day. This installation operated on chemically untreated seawater at a maximum temperature of 115 °C.
A forced circulation evaporator for a food processing plant in Japan. Conventional exchangers were never considered because the severely fouling process liquid would cause a blockage in just a few hours.
A forced circulation evaporator for the concentration of waste water from a Medium Density Fibre-board (MDF) plant in Belgium while producing steam of 200 °C and 14 barg. This steam is used in the process for preheating wood chips. At this high temperature level, the concentration of this severely fouling waste water by evaporation would cause severe fouling and blockage problems in any conventional heat exchanger.
A forced circulation reboiler for the production of a proprietary chemical, replacing conventional heat exchangers which required cleanings every 4 to 5 days, has been put into operation at a chemical plant in Houston, Texas in 1991. At this very moment, 18 years later, this exchanger, although employing a design which today can be considered as fully obsolete, is still in operation to full satisfaction of the operators and only opened once a year for inspection.
An application for very large self-cleaning heat exchangers catching worldwide attention refers to a chemical plant in the United States which cooled large quench water flows from a proprietary process in open cooling towers. This quench water released volatile organic compounds (VOC’s) into the atmosphere. As a consequence, environmental regulations required the quench water cycle to be closed by installing heat exchangers between the quench water and the cooling water from the cooling towers. After considering other solutions, plant management decided to carry out a test with a small, self-cleaning heat exchanger so that its performance could be compared with a conventional shell and tube exchanger. Figure 1 shows the results of this test, while figure 2 compares the design consequences for the self-cleaning heat exchangers and the conventional shell and tube heat exchangers.
Figure 1: Installations equipped with self-cleaning heat exchangers.
Plant management decided in favour of the self-cleaning technology because of the above results and the substantial savings on investment cost. In March 1998, they ordered four self-cleaning heat exchangers, each with a shell diameter of 1.2 m, a total height of 20 m and a surface of 1,150 m² (12,500 ft²). Each exchanger uses 9,000 kg cut metal wire with a diameter of 1.6 mm as cleaning particles. After 30 months of continuous operation with non-declining heat transfer coefficients, the exchangers have been opened for the first time for an inspection.
The heat transfer surfaces proved to be clean and even shiny, although the surface and internals did not show any measurable indication of wear as a result of the cleaning action by the particles. Figure 3 shows the four selfcleaning heat exchangers at the plant site. Similar applications are being considered.
Improved thermal seawater desalination technology
Developments in the past 25 years have contributed to a number of improvements which have upgraded the ideas behind the MSF/FBE already mentioned above into a truly
revolutionary thermal seawater desalination technology.
The advantages of this unique seawater evaporator with fluidised bed condensers can be best summarized as follows:
- No chemicals are required for scale control in spite of maximum temperatures of the seawater far exceeding 100 °C
- In combination with the higher temperatures, gain-ratios of 30 or even 40 may come within reach.
- No wire-mesh demisters are used.
- Complete flash-off of the brine in the flash chambers.
- Compact design due to high vapour space loadings.
- Distillate production can be varied between 0 and 100 % in only 30 minutes, maintaining excellent distillate quality.
- Excellent brine level control in all flash chambers for all operating conditions.
This MSF/FBE can be built as new very compact and energyefficient installations, but any existing conventional multi-stage flash evaporator can also be expanded or revamped with an MSF/FBE at the high-temperature front-end of the plant. This makes it possible to increase the distillate production of the existing plant by a factor 2 and also reduce the specific heat consumption by a factor 2, or sometimes even better.
Compact self-cleaning heat exchangers
KLAREN engineers have discovered the methods to use rather large diameter cleaning particles in smaller diameter tubes. For more than 30 years, for stainless steel particles, the ratio inner diameter tube Di/ particle diameter (dp) had to exceed 15. Today we can use much smaller diameter tubes with Di/ dp ratio’s less than 8 and combine the tube-side design with the very best shell-side baffle configurations. The consequences of this new development
is that now self-cleaning heat exchangers can be designed with the same characteristics as plate heat exchangers, i.e.:
- Small hydraulic diameters,
- thin tube wall,
- high degree of turbulence,
- low liquid velocities, and
- excellent film coefficients for heat transfer resulting in overall heat transfer coefficients or k-values of ≥ 4000 W/(m²·K).
This new development has stirred an enormous interest and it is very likely that these exchangers will be very competitive with plate exchangers in severely fouling applications. Oil and gas producing companies recognise that this new development can replace many voluminous and heavy air coolers on offshore platforms by direct seawater cooled compact self-cleaning heat exchangers.
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