Heat Exchanger Problems

http://www.qvf.co.uk/files/heatexch.pdf shows a maximum differential pressure of about 2.5 barg for those sorts of temperature differences. The exchanger is operating above its design limit. It follows that an unacceptably high failure rate is not beyond expectation.

Which design limitations are you refering to since our operating temperature diff is 82 deg C (100-18 deg C, vapour and cooling water)and the cooling water supply pressure difference is approx 2 barg.

Well, that's different to the original poster's data.

The design limitations are shown graphically on page 5.4.

Per the design table that PW pointed out, the temperature differentials for the HEC450 are 85K at 4 bar and 98K at 0 bar, not 95K and 110K as originally posted (those values are for HEC200/HEC300). If your temperature differential (TD) is 82K then you are near the 4 bar limit for differential pressure (dP) between the coil and the shell.

You stated your cooling water dP is 2 barg - is this dP between the CW inlet and outlet or between the coil and the shell? It is not uncommon for closed loop CW pressure to be 5 to 6 barg, so if your CW does not have a point-of-use regulator you could be exceeding the ~4 bar dP design limit, depending on what your ruthenium vapor pressure is.

thanks for the correction, my mistake on design specs.

The cooling water supply is at 2 barg while the reactor is at -5kPa. we do have the the regulator on the cooiling water supply.

At which point the unit cracked? Tubes in the middle or tubes at the tube sheet joints? Does the tube arrangement have enough flexibility for the large dT? Was the vapour admitted before the cooling water was on? Is the heat exchanger vertical or horizontal? The pressure drop of 2bar on water side is very high. Normally it should be about 0.5bar. Probably the number of tubes is not adequate for the heat exchange area required.

You may check the requirement of impact testing of the materials used in the exchanger. If the rated MDMT is warmer critical exposure temperature of the equipment, then the material is to be impact tested. If the impact test energy resulted is less than minimum impact test energy as per UCS-66 figures then the material will crack in brittle fracture.

If this is the case then the material is changed with higher ne having more toghness then the previous one.

Best Regards

Ikram

The cracks were on the vapour inlet and oulet side (coils).

normally vapour is in the shell side and cooling water in the tube side. Your reference to coils in the inlet and outlet side is not clear. Pl clarify.

Inside the coils we have the coiling water running through. the shell side is the vapour coming from the reactor. so the crackes were at the side where there is first contact of the gas and the coilings and at the outlet of the cooiling water.

It would appear that the correct HE should be shell and tube type. Coil can not meet the dT properly. Further the vapour piping should be checked for flexibility.

Take a look at Tranter's Supermax shell & plate: http://tranter.com/pd/sm/dsn

The round plate and construction process allows extreme pressure and temp differentials. No square contact points to fatigue.

Hello this is miyova from coimbatore.I think the problem may be in the tolerable temperature range of the unit.the vapour from the distillation column may not constantly remain at 100 degrees.It may increase or decrease that depends on surrounding environment.so the withstandable temperature limit of HE should be increased.