MINISTRY OF HIGHER EDUCATION

UNIVERSITY TECHNOLOGY INSTITUTE

Dr. Federico Rivero Palacio
DEPARTMENT OF CHEMICAL PROCESSES
FIRST ROUTE
PRINCIPLES OF CHEMICAL PROCESSES

DIRECTED WORK
ENERGY BALANCE WITHOUT CHEMICAL REACTION

1. Write the energy balance equation for each of the following processes and
Determine whether the terms of heat and work, other than zero, are positive or
negativos

a) The contents of a closed container are heated using a burner from

25 °C to 80 °C.
b) The container from part a) is removed from the burner and cooled to 25 ºC.
A chemical reaction takes place in a perfectly insulated batch reactor.
thermally.
d) A reactor where the reaction occurs at a constant temperature and there is a
cooling jacket to remove heat from the reactor.
Steam enters a turbine and turns a shaft connected to a generator.
current. The inlet and outlet of the steam are at the same height. Part
energy is lost to the surroundings in the form of heat.
f) A process stream is heated from 25 ºC to 300 ºC; the speed
the fluid average is the same at the entrance and at the exit; there is no change in
elevation between these two points.
A chemical reaction occurs in a continuous reactor that does not contain parts.
mobile phones. The changes in kinetic and potential energy are neglected.

There is a turbine where 4000 kg/h of steam enters at 44 atm and 450 ºC at a
speed of 60 m/s. This steam exits the turbine from a point located 5 m by
below the entrance at a speed of 360 m/s and at atmospheric pressure. The turbine
delivers work at a rate of 600 Kw and the heat loss is 104Kcal/h.
Calculate the change in enthalpy that the steam undergoes as it passes through the turbine.
vapor

5m
vapor
Ws
3. Saturated steam at 7 bars is mixed with superheated steam at 10 bars and 300 ºC for
produce 200 kg/h of superheated steam at 250 ºC. The changes in kinetic energy and
potential are negligible.
a) Calculate the velocities of the two feed flows assuming that the
the process is adiabatic. Make any additional assumptions you consider
pertinent.
b) Calculate the flow velocities again assuming that the heat loss
the mixer is 3 kW.

4. Two streams of water are fed into a boiler with the aim of obtaining steam.
saturated at its operating pressure. Determine the required heat flow.
in the boiler (in Watts) disregarding the kinetic energies of the incoming flows.

Data: Operating pressure: 17 absolute bars

Internal diameter of the pipe: 6 cm

Input current Flow (kg/min) T ( °C ) State

1 120 30 Liquid
2 175 65 Liquid

5. It is desired to heat a gas stream that contains 60% by weight of ethane and 40% in
butane weight from 70 ºF to 220 ºF at a pressure of 30 psia. Calculate the
heat supply required per pound mass of mixture.

COMPONENT h (BTU/lbm)
70 °F 220 ºF
Ethane 453.9 522.3
Butane 164.9 277.5

300 l/h of a 20% molar mixture in C are mixed.3H8and 80% in C4H10at 0 ºC and 1.1
200 l/h of another 40% molar mixture in C3H8and 60% in C4H10at 25 ºC and 1.1
The ATM heats up to 227 ºC. Calculate the heat requirements in kJ/h. The enthalpies
propane and n-butane at 1.1 atm are presented in the following table:

T ( °C ) h (J/mol) C3H8 h (J/mol) C4H10

0 0 0
25 1772 2394
227 20685 27442
7. In the following liquid-liquid extraction tower, calculate the amount of heat that is
exchange through the walls of it. The indicated compositions in the
the diagram of molars.

E=? S = 2000 kgmol/h

xAE= 0.05 xs = 1

1000 kgmol/h R =?
xA=0.6 xAR= ?
xB=0.4 xSR= ?

kcal/kgmol
hA 100 - 35 30
hB 40 - 105 -
hS - 47.5 - 28

8. Saturated steam is used at 28 bar of absolute pressure to heat a

methanol vapor stream from 65 ºC to 260 ºC. To achieve this, a
heat exchanger that operates adiabatically. The water vapor condenses and
Exits the exchanger as liquid at 90 ºC and at the same pressure. The flow of methanol
it is 50 l/min under normal pressure and temperature conditions (CNPT) and can
assuming it behaves like an ideal gas.

Calculate the mass flow rate in kg/h of steam required for this exchange.

data
V = 22.4 l/mol (CNPT)
Cpmethanol7.29 kJ/kg °C between 65 °C and 260 °C
Cpwater= 75.4 J/mol ºC for liquid between 0 ºC and 100 ºC

A mixture that contains 65% mole in acetone and the rest in acetic acid is separated.
through continuous distillation at 1 atm of pressure. The following presents the
flowchart of the process:
 T = 63 C

Condenser

D=?
98% acetone
T = 58 °C
F = 100 moles/h
65% acetone
T = 68 C

Calderin

W=?
15.5% acetone
T = 98 C

The column top product is a vapor that passes through a condenser.

The condensed liquid is divided into two streams: one is separated as distillate D and the
another returns to the column like reflux L0.

The bottom current is a liquid that partially vaporizes in a boiler;

liquid fraction is separated as bottom product (residue) while the vapor is
return to the column. The thermodynamic data for each is presented below
current

T (°C) Enthalpy of steam ( cal/mol)

CURRENT Acetone Acid Acetone Acid
acetic acetic
Distilled D 58 0 0 - -
Top column 63 - - 7322 6807
Nutrition F 68 354 335 - -
Waste W 98 1385 1312 - -

The specific enthalpy of the mixture in the different streams will be calculated as:
 hM xi hi ximolar fraction of the compound
hispecific enthalpy of the compound

a) Calculate the net heat quantity in kcal/h involved in the process

b) Calculate the amount of heat in kcal/h that is exchanged in the condenser for a
L0/D = 1.
c) Calculate the amount of heat in kcal/h that is supplied in the boiler.
d) Knowing that saturated steam at 102 C is available which can be used in the
boiler, calculate the mass flow in moles/h of steam needed to carry out the
exchange considering that the water will come out as saturated liquid.

10. The flowchart of a feed mixer is presented below.

a reactor:

Reagent A
hA= 5 KJ/kg
mA= 100 kg/min Feeding at
reactor
hF= 8 KJ/kg
Reagent B F= ?

hB= 3 KJ/kg
mB70 kg/min Q

a) Calculate H for this process.

b) In what case does the value calculated in part a) equal the heat flow?

11. From a synthesis unit, methanol vapor comes out at a temperature

from 800 ºF and passes through a boiler where it is cooled, this process generates
saturated vapor at 70 psia. The water feed to the boiler enters at 70 ºF and 70 psia.
If the ratio between the molar feed of water and methanol is 0.2 and the boiler
operates adiabatically, calculate the outlet temperature of the methanol.

hwater(70 ºF and 70 psia) = 38.05 BTU/lbm

Cpmethanol= 10.54 + 9.2 10-3T T in ºF

12. An equimolar mixture of benzene and toluene at 10 ºC feeds

continuously a container where the mixture is heated to 50 °C. the liquid product
contains 40% by mol of benzene and the vapor product 68.4% by mol of benzene.
Calculate the amount of heat that must be transferred to the mixture per mole of feed.
13. Benzene vapor is cooled to 1000 ºF and changes state at 75 ºF.
a continuous condenser. The condensate is poured into 55-gallon barrels and takes 2 minutes.
fill each of them. Calculate the heat flow that is extracted from the condenser in
BTU/h.

14. Saturated steam at 29.8 psig is used to heat a flow of ethane.

at constant pressure. Ethane enters the heat exchanger at 60 ºF and 20 psia, at a
flow of 27890 ft3and it heats up to 200 ºF. The steam condenses and exits from the
exchanger as liquid at 80 ºF. The specific enthalpies of ethane at 20 psia are
450 BTU/lbm at 60 ºF and 513 BTU/lbm at 200 ºF.

a) Calculate the amount of heat (BTU/min) that needs to be supplied to heat

ethane from 60 ºF to 200 ºF.
b) Calculate the volumetric flow rate (ft3/min) of vapor that must be supplied to the
exchanger.
c) Indicate whether the flows in the heat exchanger should be placed in the same
direction or in opposite directions. (Remember that heat always flows
from a higher temperature to a lower temperature

15. There are 75 liters of ethanol at 70 ºC and 65 liters of water at 25 ºC; we

they are mixed in a closed and well-insulated container. Neglecting evaporation and the
mixing heat, calculate the final temperature of the mixture.

16. A flow containing propane gas enters the interior of a pipe.

a double pipe heat exchanger at 40 ºC and 250 kPa, and exits at 240 ºC at the same
pressure. Superheated steam at 300 ºC and 5 enters through the outer tube (annular space)
bars flowing in the opposite direction to the propane current and exiting as vapor
saturated at the same pressure. Calculate the ratio m3steam-powered 3propane
supplied. Consider the thermal losses to the environment negligible.

TDBEsinReaccPBIQ08
April 2008/U.M