Thursday, August 27, 2009

HX Design - BEU and BFU

It’s very hard to see design of heat exchanger with configuration of BFU in the industry. Whereby this configuration or F-shell has its own advantage when using compared to BEU configuration. It’s again because the designer, client, owner, and whoever in the position deciding the configuration has a tendency to choose BEU. Usually when deciding on choosing the configuration, the process stream properties will be considered such as temperature approach, fouling resistance, fluid phases, etc. Issue on temperature approach will be discussed in detail here since BFU has its own beneficial to get desired temperature even the temperature approach is very low and sometime even the temperature cross happens. The TEMA configuration for BEU and BFU is shown:-

Usually when temperature cross happens, BEU configuration will be used in series to cater issue of very low temperature approach or temperature cross. This is very common to happen because the designer or the decision making authority more convenient to use series of BEU heat exchanger. There is no any other engineering reason but only based on their experience. So, if thorough engineering study is conducted some other alternative might be able to be considered such as by using BFU configuration. The only different is that the longitudinal baffle that separating the shell into two sections which is ultimately separating the inlet and outlet of shell side fluid.

Some people might say that issue on temperature cross can be resolved if the flow is counter current. However, the true counter current is not achieved in E shells if the tubeside pass is only one pass but again not to be forgotten that pressure drop across the tube should be utilized to increase the velocity of the tube side which eventually enhance the heat transfer coefficient of tube side. So, by considering the minimum number of passes as two passes, the true counter current cannot be achieved if there is no any device separating the fluids between tube and shell meeting as co-current. Here is typical configuration of BEU heat exchanger with its flow as shown:-

So, it’s again very important to consider BFU configuration which actually might give lot of impact to economic of the heat exchanger to be purchased or fabricated. It’s not that BEU in series cannot be used but on apply existing shell type not fully utilized when some circumstances such as very low temperature approach or temperature cross persist.

No comments:

Post a Comment