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Wednesday 30 September 2015

Air Cooled Heat Exchangers

Air cooled heat exchangers are only one of various kinds of heat exchanger. Heat exchangers are gadgets which are specially designed for aiding the transfer of heat from one fluid towards the other. For us to better understand, typical samples of devices that use heat exchangers include the air conditioners, refrigerators as well as space heaters.

But let us not dwell a lot of over the general heat exchanger rather let's now take a look at air cooled heat exchangers or ACHEs for short. It rejects heat from a hot fluid directly to fan-blowing ambient air. ACHEs are commonly utilized each time a procedure or set up creates heat that has to be removed and regrettably lacks local use. Your car's radiator is actually an example of ACHE device. The engine must be cooled to prevent overheating due to friction and combustion functions by the engine. The excess heat is taken away by the water or glycol coolant mix. Majority of the heat should be taken away, and the best way is as simple as supplying ambient air.

There are more functions for air cooled heat exchangers, including the upstream production, refineries and petrochemical facilities. It can also be used on conditions with high temperature, high pressure, corrosive fluids and environments. Moreover, air coolers is usually equipped and used in gas and oil refineries; compressor stations for oil pipelines; subsurface gas storage facilities; plants producing polychlorvinyl, polyethylene, glass fiber, biplastic; caustic soda plants; by-product coke plants and ammonia transportation and handling plants.

Besides learning the actual functions of ACHEs, we should have a view upon how it operates inside and its elements. Usually, air coolers for process application are composed of a finned-tube bundle with rectangular container headers on both ends of the tubes. Headers are boxers that dispense the fluid from the piping to the tubes. The other parts include one or more fans that give cooling air. The fans are generally powered by electric motors and are also accompanied by speed reduction devices. The fan drive assemblage is sustained by the metal mechanical drive support system. Generally, the air flows up-wards all the way through a horizontal tube bundle. The fans could be either forced or induced draft, dependant upon whether the air is pushed or pulled through the tube bundle. Forced draft unit enables a simple access for maintenance for the fans and the bundles. Furthermore, the fans stay in the cold ambient air. Whilst the induced draft unit provides a stable as well as strong thermal performance because of the protection of the finned surface against wind, rain, hail and snow by the plenum chamber. The induced draft also guarantees an improved air distribution, much less hot air recirculation, much less air-side fouling and lower noise levels at grade. Space in between the fans and the tube bundle is encircled by a plenum chamber, that directs the air. The full assembly is usually installed on legs or perhaps a pipe rack.

Understanding and knowing the inside and out of ACHEs is fairly difficult, especially for those who have no background in mechanical matters. And for this reason, let us once again move our attention on another subject matter, which is the "why" question. With regards to economy, air coolers are preferred due to the lower maintenance expenses. Some other benefits offered by air coolers are as follows: lack of the need for cooling water or other cooling media, no issue shall arise with regards to the thermal as well as chemical pollution of cooling fluids, and it quite fast to install by bolted assembly.

ACHEs are regarded as a "green" alternative because no chemical treatment methods are required to the water or fluid used by the assembly. And temperature is the only parameter that has to be considered whenever getting rid of the water used. Without a appropriate heat exchanger equipment, overheating will ruin your equipments and appliances, specially the parts subjected to heat. Out of all of the things that have been pointed out, if we are to consider the trend that the world is going, air cooled heat exchanger are the ideal choice for industrial plants and other plants if the environment is to be considered.

Tuesday 29 September 2015

How to install a heat exchanger?

Prior planning is very important before the installation of many types of heat exchangers.

- Adequate foundations and supports should be provided to bear the static weight of the exchanger unit, the weight of the units in it, and the dynamic loads due to wind, earthquake, etc. to make sure that the exchanger unit will not settle thus causing strains in piping and stresses in the unit.
- Leave enough space to be able to service the exchanger in a future, such as cleaning, repairs or replacement.
- Piping configuration should allow bypassing of the unit for inspection, cleaning, and repairs. Cooling water piping should be set to allow backflushing to remove deposits.
- Piping should be able to expand and contract freely. It should not transmit fluid pulsations and mechanical vibrations to the unit
- Provide necessary instruments to measure temperatures and pressure next to it.
- Do not pipe drain connections to a common closed manifold, as it makes it difficult to check if the unit has been thoroughly drained or not.
During actual installation of the unit on site take the following steps:
- On receipt of a heat exchanger inspect it for any damage in transit.
- Remove packing and preservative materials if it has been stored prior to installation.
- Set the unit square and level so that the piping connections can be made without forcing.
- Insulate the unit if very hot or cold compared to the ambient temperature.
- Pressure test the heat exchanger before starting operation.
What types of heat exchangers these installation recommendations can be used for?
These installation recommendations can be used for shell and tube, double pipe, finned coil, brazed plate heat exchangers, plate and frame type of exchangers, oil coolers and many other types.
These installation recommendations can be useful not only for industrial and / or commercial installations, but to home improvement installations of heat exchangers as well.
What other factors should be considered during selection and /or installation of the exchangers?
During selection and /or installation of the units another common factors to be considered are fouling, fluid viscosity, thermal performance, etc.
Most heat exchangers selected are thermally correct, but some constructions are not suitable for a specific application and can cause field problems. Constructions having a negative influence on plant operation, maintenance, metallurgy, requirements, cost, handling, shipping, freezing, recirculation, tolerances, manifolding, distribution, noise, availability, and pressure drop, etc. The effect of adjoining non-exchanger related constructions on performance should not be overlooked. The effects of filters, racks, screen rooms, packaging, heat sinks, hot spots, blowers, and ducting also have a great influence on performance of the heat exchangers.
We believe this information can be useful both for training engineering and non-engineering personell.