Vertical shell and tube heat exchangers applying a fluidized bed of solid particles in the tubes can operate with a clean surface where conventional heat exchangers may suffer from severe fouling in their tubes in a matter of weeks, days or even hours. These solid particles, made of either glass, ceramic or metal (cut metal wire) with diameters of 1.5 to 5 mm, create a mild scouring effect on the wall of the heat exchanger tubes. This scouring action removes the fouling deposits from the tube wall at an early stage of formation and keeps the heat transfer surface clean and thus a constant heat transfer coefficient is maintained. Besides the scouring effect, the particles enhance the heat transfer at lower liquid velocities and reduce pressure drop compared to conventional heat exchangers. Zero-fouling is guaranteed when the rate of removal of deposits by the particles exceeds the rate of precipitation of deposits.
The operating principle of the self-cleaning fluidized bed heat exchangers is based on the circulation of solid particles through the tubes of a vertical shell and tube heat exchanger. The fouling liquid flows upward through the tube bundle of the heat exchanger that incorporates specially designed inlet and outlet channels. In the inlet channel the solid particles are fed to the fluid using a proprietary distribution system to ensure a uniform division of particles over all the tubes. The particles are fluidized by the upward flow of liquid, where they create the mild scouring effect on the wall of the heat exchanger tubes, thereby removing any deposit at an early stage of fouling formation. After the tube bundle the particles disengage from the liquid in the separator and are returned to the inlet channel through an external down comer, and the cycle is repeated.
To control the amount of particles fed to the inlet, a part of the inlet flow to the heat exchanger is used to push the particles from the down comer into the inlet channel. Changing the amount of particles is one of the parameters to influence the cleaning mechanism. Other parameters are particle size and material and the fluid velocity.
With this self-cleaning heat exchanger many types of fouling deposits can be effectively handled, whether hard or soft, originating from biological, crystallization, chemical or particulate fouling mechanism, or a combination of these. A wide variety of fluids can be handled ranging from aqueous solutions, to oils and slurries.
Watch the video presentation about the operating principle of the self-cleaning heat exchanger.
In a self-cleaning heat exchanger the tubes remain clean and therefore the heat transfer can kept constant which improves the energy performance:
A self-cleaning heat exchanger needs not to be taken out of production for cleaning, therefore the capacity remains constant and in some cases the production yield can be increased, which enhances the productivity:
When using the self-cleaning heat exchanger technology chemicals are not required as online additives or needed for cleaning purposes. Therefore, there are no hazardous waste streams from cleaning which makes the heat exchanger more sustainable:
Because of a constant heat transfer in the self-cleaning heat exchanger, over dimensioning of the heat transfer surface is not required which results in a more compact design of the heat exchanger: