KLAREN Heat Exchanger Cleaning System
Solid particles circulate through a fluidised bed into the tubes of the vertical shell-and-tube heat exchanger, which can operate with a clean surface, whereas the tubes in conventional heat exchangers become heavily contaminated within weeks, days or even hours. These solid particles of glass, ceramic or metal (metallic wire) from 1.5 to 5 mm in diameter produce a gentle scouring action on the insides of the heat exchanger tubes. The cleaning effect that is produced by this process removes contaminant deposits from the insides of the tubes before they have had chance to accumulate and keeps the heat exchanger surfaces clean. This maintains a constant heat transfer coefficient. In addition to the cleaning effect, the particles improve heat transfer at low flow velocities and reduce pressure loss in comparison with conventional heat exchangers. Zero-fouling is guaranteed as long as the rate of fouling removal by the scouring action of the particles exceeds the rate of fouling precipitation.
The operating principle of self-cleaning fluidised bed heat exchangers is based on the circulation of solid particles through the tubes of a vertical shell-and-tube heat exchanger. The contaminated liquid is fed upwards through the heat exchanger’s pipe bundle that incorporates specially designed inlet and outlet channels. The solid particles are fed into the inlet using the company’s own flow distribution system which ensures that the particles are uniformly distributed around all the tubes.
The particles are fluidised by the upward flow of liquid through the tubes, where a gentle scouring effect is produced on the insides of the heat exchanger tubes. This removes any fouling deposits at an early stage before they have managed to accumulate. After the liquid has left the pipe bundle, the particles separate from the liquid inside the separator and are returned to the inlet channel through an external downcomer, and the cycle is repeated.
To control the number of particles fed into the inlet, part of the inlet flow to the heat exchanger is used to push the particles from the bottom corner into the inlet channel. The change in the number of particles is one of the parameters that influences the cleaning mechanism. Other parameters are particle size and material, and liquid velocity.
This self-cleaning heat exchanger effectively controls many types of deposits, whether hard or soft and whether they are derived from biological, crystallisation, chemical or particulate fouling mechanisms, or a combination of any of these factors. Many different types of liquids can be dealt with, from aqueous solutions to oils and sludge.
Improved Energy Performance
The pipes are kept clean in self-cleaning heat exchangers, ensuring that heat transfer remains constant which improves energy efficiency.
- When using a shell-and-tube heat exchanger to cool quench water, a 50% reduction in the heat transfer coefficient can be achieved within 20 days. The heat transfer coefficient remains constant in self-cleaning heat exchangers.
- Due to the lower flow velocities and the shorter tube lengths, the amount of pump capacity required is reduced in most applications. In the application outlined above, this amounts to a reduction of more than 50%.
- The use of self-cleaning fluidised bed technology on an evaporator, which concentrates wastewater, enables higher concentrations of solids to be produced in the circulatory flow without causing contamination problems when compared with falling film evaporators. This enables higher volumes of water to be recycled and dramatically reduces decomposition. If a spray dryer is added to achieve zero liquid discharge, the overall energy use of the self-cleaning unit combined with the spray dryer only amounts to 60% of the energy used by the falling film unit. The main reason for this is that KLAREN technology is able to further concentrate the waste water which results in lower flow rate because less energy is needed for spray drying.
- A shell-and-tube heat exchanger uses water to recover heat from an exothermic reaction. The heat is used at another stage in the process. Contamination on the chemical component side of the heat exchanger causes a reduction in the heat transfer coefficient which consequently decreases heat recovery capacity. If a fouling layer develops, higher amounts of additional steam need to be used to heat the process at a different point. In a self-cleaning heat exchanger, heat recovery from the exothermic reaction remains constant and steam does not need to be used.