Unit production system disadvantages

Unit-dose systems offer the easiest technical solution to this problem, but have the disadvantages of higher cost of manufacture and of not being as compact as a multidose product containing equivalent doses. Unit-dose products are usually made of low-density polyethylene (LDPE), with the formulated sterile solution being without a preservative, and sealed using the form-fill-seal process. 

It should be noted that the operating parameters of the unit can be adjusted to suit the client s needs. These particular operating conditions were an attempt to maximise productivity (i.e. minimise capital cost) and minimise the waste volume. While the NaCl recovery efficiency is about 96%, the brine purity is not exceptionally good (43.4% sulphate removal). This is not considered a disadvantage, however, since the low removal efficiency can be compensated for by increasing the flow of feed that is treated by the system. If necessary, removal efficiencies of over 95 % can be obtained. 

The near completely random motion of the catalyst bed virtually ensures an isothermal operation, but the efficiency of the hydrodesulfurization reaction tends to suffer because of the back mixing of the product and feedstock. Hence, to effect sulfur removal at over 75% efficiency, it may be necessary to operate with two or more reactors in series. The need for two or more of these units to effectively desulfurize a feedstock may be cited as a disadvantage of the reactor, but the ability of the reactor to operate under isothermal conditions as well as the onstream catalyst addition-withdrawal system and the fact that the reactor size required for an expanded catalyst bed is often smaller than that required for a fixed bed can be cited in support of such a unit. 

The important advantage of this strategy is that the reactor behaves as decoupled from the rest of the plant The production is manipulated indirectly, by changing the recycle flows, which could be seen as a disadvantage. However, it handles nonlinear phenomena better, such as for example the snowball effect or state multiplicity. Additionally, this strategy guarantees the stability of the whole recycle system if the individual units are stable or stabilized by local control. 

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