Jacket Temperature Control
Compact brazed heat exchangers helped a manufacturer of pharmaceutical ingredients and intermediates achieve tight temperature control of its reactors.
Keeping the temperature of chemical reactions at the right level is a delicate matter. Often, the reaction takes place in a reactor and is very sensitive to temperature changes. Thus, being able to influence the temperature is of utmost importance for chemical industries. Depending on which kind of chemical reaction occurs, adding or rejecting heat with some sort of heating or cooling medium is necessary. Often, quite complex systems are needed for tempering the reactor.
Procos produces synthetic pharmaceutical active ingredients and advanced intermediates. In its plant at Cameri outside of Milan, Italy, more than 35 large reactors are in process, all with a need for temperature regulation.
The Problem. When the reactors were designed, the cooling and heating fluids entered directly into the reactor jacket. No intermediate heat exchangers were used. This meant that the jacket had to be emptied of one fluid before the next could be let in. This was a very slow responding system. Furthermore, problems occurred because of mistakes being made when emptying and filling the jacket. This caused the wrong brine to end up in the wrong system -- for example, cooling tower water in the steam system -- with large maintenance costs as a result.
The Solution. The problem was solved by having intermediate heat exchangers for the four different flows. The brine that was heated or cooled with these intermediate heat exchangers could then circulate in the jacket independent of where the energy was taken from (i.e., steam, cooling water, etc). Compact brazed plate heat exchangers from Swep, Landskrona, Sweden, were chosen to act as a heat exchanger unit for the steam application. Four compact brazed heat exchangers in parallel were used in order to avoid problems with pressure regulations. Previously, gasketed heat exchangers were used. However, the steam pressure was increased to a level where gaskets melt; thus, the gasketed heat exchangers were replaced with compact brazed units.
After the retrofit, four flows, containing water and ethylene glycol at different temperatures, can be mixed in order to provide the jacket around the reactor with liquid of desired temperature. The different temperatures of the four flows are accomplished by exchanging heat in four different heat exchanger units:
The first heat exchanger unit cools the brine down to -4oF (-20oC) with another ethylene glycol brine from a chiller.
The second heat exchanger cools the brine to around 50oF (10oC) with city water.
Cooling tower is used in the third heat exchanger to produce a brine temperature of around 85oF (30oC).
The last unit consists of four compact brazed heat exchangers in parallel with steam connections on the front and water/glycol connections on back. The brine is heated to 280oF (138oC) by steam at 4 bar (284 to 302oF [140 to 150oC]).
The temperature of the flow entering the jacket is controlled by the stream -- whether it is the cooling-tower cooled stream or the city water cooled stream, for example -- and by the flow.