Heat exchangers separators/accumulators

The hot outlet stream from the process-to-process heat exchanger goes to a partial condenser and then to a vapor-liquid separator. The gas stream from the overhead of the separator recycles unconverted hydrogen plus methane back to the reactor via a compressor. Since methane enters as an impurity in the hydrogen feed stream and is further produced in the reactor, it will accumulate in the gas recycle loop. Hence a purge stream is required to remove methane from the process. Part of the liquid from the separator serves as the reactor quench stream. 

The deposits usually accumulate in the downstream separators, heat exchangers, and fractionating towers, and foul the transfer lines, eventually causing unit shutdown. Equipment fouling by the coke-like sediments formed in residual oil hydroconversion or the hydrocracking process can lead to enormous financial burdens in terms of increased costs of operation, maintenance, and shutdown. The refiners often use chemical and mechanical treatments to remove the deposits from the equipment Some refiners use antifoulant chemical additives to the feed to suppress the formation of sediments. 

Condensate purification In some boiler systems the condensate returning is retreated using ion exchange to minimise corrosion and deposit accumulation. This particularly applies to once-through boilers (mainly nuclear) where there may be no water/steam separator and perhaps limited facilities for blow-down. Additionally, some high heat-flux boilers (oil-fired) have been fitted with condensate polishing plant (CPP). 

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