QUESTION $1$

A triple effect forward feed evaporator concentrates a sugar solution from $8$ mass $\%$

to $35\%.$ The feed enters at $30000$ kg$/$h at $27$oC and the pressure in the vapour space

of the third effect is $16$ kPa. Fresh saturated steam is available at $205$ kPa. The liquid

heat capacity is given by Cp $=4\mathrm{.}192\mathrm{.}55$ x $($kJ$/$kg$.$K$)$ where x is the mass fraction of

sugar. It can be assumed that the BPR$$s can be neglected. The overall heat transfer

coefficients are: U$1=3\mathrm{.}123$; U$2=1\mathrm{.}987$ and U$3=1\mathrm{.}136$ kW$/$m$2$

$.$K$.$

Do only one iteration.

$1\mathrm{.}1.$ Draw a flowsheet for this process. $(3)$

$1\mathrm{.}2.$ Determine the flow rates of the vapour and liquid streams for each evaporator.

$(10)$

$1\mathrm{.}3.$ Calculate the Cp$$s in each effect. List all assumptions. $(4)$

$1\mathrm{.}4.$ Determine the heat balance around each evaporator. $(21)$

$[38$ marks$]$

QUESTION $2$

An effluent gas from a refinery with composition CH$4,$ C$2$H$6,$ C$3$H$8$ and C$4$H$10$ is fed into

an absorber to reduce the propane content of the effluent before recycling. The

absorber operated at $37$oC and $400$ kPa $($abs$).$ The entering oil and gas with its

composition is shown in the following table. The absorber has $4$ theoretical stages.

Table $1$: The entering oil and gas with its composition

Lo$,$ kmol$/$h VN$+1,$ kmol$/$h Ki

CH$41556\mathrm{.}65$

C$2$H$62981\mathrm{.}64$

C$3$H$82120\mathrm{.}584$

C$4$H$1020350\mathrm{.}195$

Oil $14000\mathrm{.}0001$

$4$

$2\mathrm{.}1.$ Do one iteration to determine the liquid and gas flow rates of all the

components. $(12)$

$2\mathrm{.}2.$ What is the total flow for both the liquid and gas outlet as per $2\mathrm{.}1?(2)$

$2\mathrm{.}3.$ Determine the percentage C$3$H$8($propane$)$ that is removed by the absorber

using the answer obtained in $2\mathrm{.}1.(2)$

$[16$ Marks$]$

QUESTION $3$

$100$ kg$/$s of solution containing $28$ mass$\%$ CuSO$4$ is cooled slowly to $10\backslash$deg C to form

crystals of CuSO$45$H$2$O$.$ The solubility of CuSO$4$ at $10\backslash$deg C is $9\mathrm{.}9$ kg$/100$ kg water. It is

estimated that $4\%$ of the water entering the crystallizer is lost by evaporation.

$3\mathrm{.}1.$ Draw a diagram of the crystallizer showing all streams around it and use the

yield method to calculate mass of crystals produced in the crystallizer. $(11)$

Additional information: Cu$=63\mathrm{.}5$ g$/$mol$,$ H$=1$ g$/$mol$,$ S$=32$ g$/$mol$,$ O$=16$ g$/$mol