Use of Alonised Tubes and Candle Demisters

The return gases from IPAT are heated again to ignition temperature of the catalyst in the subsequent pass. The heat required for this was generally obtained from the 

This often reduced the rate of heat transfer or even punctured the tubes, causing process upsets. Hence the tubes were alloyed with aluminum to minimize corrosion which could overcome the process difficulties to a considerable extent. 

Stainless steel demister pads were installed after the IPAT in the path of the return gases to arrest the acidic mist particles, but these were not sufficiently efficient. 

Later developments of very efficient candle type demisters installed in the IPAT itself enabled use of steel tubes again because the acid mist particles were separated with 99.5-99.9% efficiency. 

These however increased the resistance to gas flow, resulting in somewhat more power consumption by the air blower. This disadvantage was offset by the higher sustained heat transfer in the gas-to-gas heat exchangers and the performance of the catalyst in the later passes which is very essential to achieve an overall higher degree of conversion. 

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