Objective
The most common problem in heat exchangers is the so-called hard scale, caused by precipitation of inorganic salts. The precipitation forms crystalline build-up on the heat exchanger surfaces, which reduces continuously the heat transfer coefficient (K-value W/m²K) beginning at the first minute of the start up.
The aim of the project was to develop and implement a continuous self cleaning system for heat exchanger surfaces.L%
After start up the installation suffered from substantial operating problems caused by a quick reduction of the K-value.
After measures as :
- installation of more sieves to prevent clogging problems
- improvement of operating procedures to prevent thermal shocks which loose pieces of scale
- reducing of reactivity of the liquid by feeding it into a vessel to create residence time, we got promising results.
The K-value stays stable at 3000 W/m²K after 45 days of operation (instead a 12-day running time on the old system).
The idea was to feed cleaning particles into the process fluid creating scaling.
The cleaning particles should clean and polish the heat transfer surfaces continuously and keep the K-value on a high constant level.
The installation applies a self-cleaning heat exchanger with external circulation of the cleaning particles through one single external downcomer.
The heat exchanger has 151 tubes of O.D. 33 mm and a tube of length of 8 meters. The heat exchangers uses approx. 1700 kg of cleaning particles made of cut metal wire (14571) with a diameter of 1.5 mm. The cleaning particles are recovered from the process liquid in the separator and move as a packed bed through the downcomer into the control channel.
The flow of the (packed bed) particles in the downcomer can be measured from the outside of the downcomer, by a Sonar-Doppler-Shift velocity meter.
The flow of particles in the downcomer can be influenced by the control flow into the control channel, where the downcomer exits.
The packed bed flow of the particles in the downcomer can be activated, stimulated and even better controlled by the control flow, if vibrators are attached to the wall of the downcomer. New fascinating developments make it possible to prevent the various components of the installation from participating in the vibration.
There is always a possibility of solid material precipitating on the wall of the lines and/or storage vessel. During operation the precipitates material might come off the wall as flakes or other pieces of substantial dimensions and might be carried through the circulation pump into the heat exchanger. If no precautions are taken, these pieces might clogg the distribution of the cleaning particles over all tubes.
The distribution plate is prevented from clogging by smaller pieces of 'dirt' by installing a so-called distribution plate with non-clogging nozzle caps.This means that the nozzle caps can be lifted from their studs by a mechanism driven by a valve outside the inlet channel.
The installation also contains a particle storage vessel. A weight measuring system for this vessel and its contents should make it possible to distribute the cleaning particles in the right manner.
The system contains a second self cleaning heat exchanger.
Topic(s)
Call for proposal
Data not availableFunding Scheme
DEM - Demonstration contractsCoordinator
4054
Germany