Mass and Energy balance over the distillation column used for LPG separation
This task will be worth 40 marks and each individual will be required to produce their own report. The
report should be no more than 10 A4 pages including tabular output (this page count does not include
any front page, contents page or reference list, so is from Introduction to Conclusions). Hard copy to
be handed in to reception on Tuesday 15”‘ October, by 15:00 and electronic copy through Canvas.
The process flow diagram (figure 2.1 below) shows the preferred method of separating LPG into
butane and propane, chosen by the client.
Task 2.1 (80% of task 2)
Conduct a mass balance and energy balance across this process using the data constraints and
stream information outlined below. A molar balance is not required. Provide a concise report outlining
your methodology, assumptions made and your balance table/spreadsheet.
Table 2.1 – Component composition of the LPG stream
Component Composition (mass
Ethane 0.0005
Propane LightLP 0.4495
Propene 0.003
lButane l-leavyLF 0.039
Butane 0.355
lButene 0.035
1Butene 0.03
T2Butene 0.0415
C2Butene 0.0405
3M1 Butene 0.002
lPentane C 0.004
Table 2.2 – Feed properties of the LPG stream
Properties
19 «abs»
33 tonnes hr”
Task 2: Mass and Energy balance over the distillation column used for LPG
separation.
.
The process flow diagram (figure 2.1 below) shows the preferred method of separating LPG into
butane and propane, chosen by the client.
Task 2.1 (80% of task 2)
Conduct a mass balance and energy balance across this process using the data constraints and
stream information outlined below. A molar balance is not required. Provide a concise report outlining
your methodology, assumptions made and your balance table/spreadsheet.
Table 2.1 – Component composition of the LPG stream
Component Composition (mass %)
Ethane 0.0005
Propane Light LPG Product 0.4495
Propene 0.003
IButane Heavy LPG Product 0.039
Butane 0.355
IButene 0.035
1Butene 0.03
T2Butene 0.0415
C2Butene 0.0405
3M1Butene 0.002
IPentane 0.004
Table 2.2 – Feed properties of the LPG stream
Properties
o
Temperature 37.8 C
Pressure 19 bar (abs)
-1
Flow rate 33 tonnes hr
1
Task 2 Mini Design Project – to be handed in Tuesday 15th October by 15:00
In real distillation problems, the products will contain traces of impurities. As Table 2.1 indicates, the
light LPG product will contain propane and propene whilst the heavier product will contain Butane to
IPentane. The distillation column will be used to separate the products into light LPG and heavier
LPG. For the mass balance you should assume that the light LPG proportions of Propane and
Propene stay constant and the same can be assumed true of the heavier LPG (Butane to
3M1Butene). The bottom product contains 3% mass percent of light LPG whilst the top product
(stream 8) contains 95% mass light LPG. For the purposes of the mass balance calculations, you may
assume that all the Ethane entering leave in stream 5 and all the IPentane leave in stream 11.
Table 2.3 – Stream Information
Stream Number Comment
or Process Unit
o
1 The feed stream is first heated to 55.4 C by HE1, before it enters the column
(stream 2).
HE1 The hot water is available at a pressure of 4 bar (abs) and a temperature of 100
o
C. The heat exchanger has a heat transfer efficiency of 95%
D1 The distillation column will operate at a pressure of 17.5 bar (abs) with the top
o
stream (stream 3) operating at 47 C and the bottoms (Stream 10) leaving the
o
column at 102 C.
3 As the Light LPG is taken from the top of the column, it is cooled by an air cooler
o o
from 47 C to 38 C.
F1 Stream 4 enters the flash drum where the ethane and any vapour (if any) is
flashed off. The pressure in the drum is 15.5 bar (abs).
6 The column has a reflux ratio of 2. Stream 7 is returned to the distillation column
whilst stream 8 is taken as Light LPG product.
8 90 wt % of the Light LPG is sent for further processing in the refinery whilst 10 %
is sent to storage.
o o
10 Stream 10 leaves the column at 102 C and is cooled to 78.5 C by a water heat
exchanger.
o
HE2 The water used for this heat exchanger is available at 40 C and 5 bar (abs). The
heat exchanger has an efficiency of 95%
11 Stream 11 is cooled further by an air cooler which takes the heavy LPG fluid from
o o
78.5 C to 54.7 C.
12 Stream 12 is taken to further processing which is 95 wt % of the stream leaving
the air cooler. The further 5% is taken via stream 13 to storage.
o
A1 and A3 The air available for both of the air coolers is typically at 25 C and 1 atmosphere.
The air coolers are 80% efficient for heat exchange.
2
Task 2 Mini Design Project – to be handed in Tuesday 15th October by 15:00
You should explain any further assumptions made in the report and what effect they have on the
mass and energy balance. For the energy balance you will need to calculate the mass flowrate of
steam required (S1) and specify the outlet temperatures of the heating/cooling fluids in the heat
exchangers and air coolers. You should investigate what impact these specifications have on the
mass flow rates of the heating/cooling flow rates.
Task 2.2 (20% of task 2)
The plant has since been built and two years after start of production, the client is considering an
upgrade to increase the mass flow rate of the LPG feed into the distillation column by 20% by 2020 if
current economic trends continue. Unfortunately the air coolers (AC1 and AC2) are already running at
close to maximum capacity. Within your report, include a brief summary on the potential options
available to the client for increasing the capacity in the future.