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.

Rule of Thumb

Rule of thumb basically means the experience on doing any particular job by applying the standard or reference. The variety of rule of thumb is varies among different people according to their experience. Different discipline engineers will have different rules of thumb that applicable to their work. For example, chemical engineers might have their rules of thumb when designing any process equipment. Piping engineers might have their own when routing the piping. The application of applying this rule of thumb mainly in engineering design work can shorten the time required to design.

This rules of thumb is mainly comes from research done by any institute such as American Petroleum Institute (API), Tubular Exchanger Manufacturer Associates (TEMA), etc. In addition to this, there are also from experience of the engineer him/her self all this while doing the design work. For example, pressure drop across the shell and tube heat exchanger is roughly about 0.7bar which typical value is allowed when designing it. This is purposely made so that the pumps that pumping upstream of the heat exchanger can cater the required pressure drop. There are no specific standards telling so, but from experience of people designing heat exchanger. Some people might say 1.0bar also can be considered. Some people might give more stringent value which is 0.3bar. So, if there is argument in deciding the value, it’s better to refer to the design basis that agreed by the team for that particular project.

The rule of thumb is basically would give some flavor of the rightness when getting the result. It is not only giving the standard to be used but when converting from one unit to another unit. For example, natural gas that having molecular weight 19-22kgmole/kg will give 1mmscfd equal to 1000kg/hr. Again this type of rule of thumb can be cross checked with simulation data to verify it. However, as we all doing the work with simulation interference, this can be on our finger tips.

Finally, this rule of thumb can be used to design any new equipment if you are referring very established sources such as TEMA, API, etc. That rule of thumb from your experience can be used to quick check of the calculation.

MAN Turbo to Supply Compressors to Abu Dhabi

MAN Turbo AG of Oberhausen (Germany) has been awarded a contract for the supply of nine compressors to the value of around €60 million to the emirate of Abu Dhabi for the expansion of the Thamama-B oil field. The purchaser is the Abu Dhabi Company for Onshore Oil Operations (ADCO). The contract forms part of an overall project awarded by ADCO to SK Engineering and Construction (SKEC) of Seoul as the general contractor.

The contract that has now been signed relates to the ‘Bab Gas Compression Project’ and focuses on the expansion of Thamama-B, one of the five most important oil fields in Abu Dhabi. ADCO thereby aims to increase its production from the existing field considerably, thus further helping to safeguard the country’s energy supply. Over 94% of the United Arab Emirates’ total oil and gas reserves can be found in Abu Dhabi. The emirate has the world’s tenth-largest gas reserves.

In addition to the tendered compressor technology, the short delivery times agreed were a key factor in the award of this contract to MAN Turbo. ADCO, the biggest oil and gas producer in the United Arab Emirates, wants to commission the installation as a whole by 2011 and increase its yield from the existing field substantially by the year 2030.

The compressor trains manufactured by MAN Turbo at its Berlin plant are used in so-called gas collecting stations. Three compressor trains operate in each of the three stations. The incoming gas is conducted there to the compressor trains, which increase its pressure. The gas is then transported via pipeline to the Gasco refinery in Habshan for further processing.

For MAN Turbo and SKEC, this is the first order for ADCO. The two companies have successfully handled a similar contract in Kuwait in the past. “We are supplying compressor technology to Abu Dhabi for ADCO for the first time. This gives us a good foothold for further activities in this region. The Middle East with its emergent economy and its important oil and gas industry is of great strategic importance for our company,” said Dr Gerhard Reiff, a member of the MAN Turbo executive board.

Source: www.gulfoilandgas.com 7/27/2009, Location: Middle East