ChE 101.04ChE 101.04

MASS & ENERGY BALANCESMASS & ENERGY BALANCESPREPARATION & USEPREPARATION & USE

Dr. Abdulhadi Al-Juhani

Department of Chemical Engineering, King Fahd University of Petroleum & Minerals

4-12-07

MASS & ENERGY FLOW

Mass/Energy, Losses/Gains

- for mass loss/gain, do not forget unexpected things!

ChE 101.04 V (35)

Figure 3

Shedgum DGA Plant SimplifiedProcess Flow Diagram

Recycle & Purge Streams

ChE 101.04 V (36)

Boiler Blowdown Method

where: FBFW = Feedwater flow, lb/hr.FBD = Blowdown flow, lb/hr.FSTM = Steam flow, lb/hr.CBFW = Solids concentration in boiler feedwater, ppm.CBD = Solids concentration of blow down (circulating boiler water), ppm.X = Percent blowdown, percent of boiler feed water.

FSTM

FBFW

CBFW

FBD

C BD

BoilerDrum

FBFW

FBD

CBFW

X = (100)

FBFW = FBD C BD

CBFW FBD

FBFWC BD

X100= =

Recycle & Purge Streams

Recycle Streams

Hydrotreating Purge

ChE 101.04 V (37)

Treat Gas, TG

FEED F

Recycle, RPurge, P

Liquid Product L

Seperation Drum

Reactor

Figure 4

Recycle Streams

• Heat of Reaction

Chemical Reactions

· Overall Mass Balance Not Changed

· Mole Balance and Composition Change

· Reversible Reactions

· Irreversible Reactions

· Predict Reaction Products

Exercise 3

Directions:

Water is fed into a boiler from a demineralizer plant. There arespecifications on solids and chlorides in the boiler water. If thechloride specification is met, the solids specification isautomatically met, since demineralized water is good qualityboiler feedwater and the chloride specification is the harder ofthe two specifications to achieve.

The chloride content of the boiler water must be kept equal to orlower than 8 wppm (weight parts per million). The feedwater hasa chloride content of 0.2 wppm. The boiler raises 200,000 Ib/hr ofsteam. Calculate the boiler feedwater and blowdown rates.

Exercise 3, Cont’d

Answer:

( )100FFXBFW

BD

FBFW CBFW = FBD CBD

BFW

BD

BD

BFWFF025.0

82.0

CC

==⎟⎠⎞

⎜⎝⎛=

FBD = 0.025 (FBFW)FBFW = FStm + FBD

FBFW = FStm + .025 FBFW

0.975 FBFW = FStm = 200,000FBFW = 205,128 FBD = 5128

FBD

CBD

FBFW

CBFW

FSTM

X =

• Piping

Debottlenecking

• Towers

• Drums

• Exchangers

• Pumps

• Compressor

• Control Valves

2. How would you fix them?

Exercise 4

Introduction:

This Exercise will be worked on as a class discussion. In

Exercise 3 you prepared a mass and energy balance

around a C3/C4 splitter system. The owner of this

1. What would you do to find the bottlenecks?

Answer:

Exercise 4, Cont'd

1. Unless there are known limitations, a unit testwould be the first step. This would determine themajor limitations and uncover other areas that areclose to limiting. The class should suggestpossible areas at which to observe bottlenecks.

2. The instructor should propose bottlenecks and askthe class how they would find and solve them. A listof proposed bottlenecks should include:

First Step Unit Test• Tower flooding upper section• Tower flooding lower section• Overhead exchanger• Pumps

• Reboiler• Feed/effluent exchanger

tube leak • Control valve

Figu

re 8

C

3/C

4 Sp

litte

r

Computer Input/Outputs

Key Formulas

Summary

Evaluation

ChE 101.04 V (49)

Evaluation

Treat Gas

Reactor

Offgas

Product

Feed12,629 B/D

Evaluation, Cont'd

The refinery has 12,629 B/D of naphtha to hydrotreat. Theprocess licenser has the following process requirementsand data:• Treat gas rate must provide a minimum of 241 SCF

H2/bbl feed.

• The hydrogen partial pressure in the reactor must be aminimum of 56.6 psia.

• The hydrogen consumption is 5.83 SCF/bbl. Theconsumed hydrogen appears as H2S.

Evaluation, Cont'd

The refinery Information are as follows:

• Treat gas is 69.23 mole percent hydrogen. Theremainder is methane.

• The feed is totally vaporized in the reactor

• Feed information:moles per hour (mph)

iC5C5C6/310310/360360/395395/430430 +

MWsp. Gr.60

0.190.19

182.74223.52202.23166.67175.23950.76

152 0.785

Note that since there is insufficient time to run acomputer flash, assume a perfect split ofcomponents and that all the feed components leavein the product.

Evaluation, Cont'd

Calculate

1. The material balance around this unit.

2. The reactor pressure in psia.

Evaluation, Cont’d

Answer:

Feed rate:

( )( ) orhrlbs144518

hr24Dx

gallbs785.833x

Bgal42x

DB1629 =

950.76 mph x 152 mw = 144,515 lbs/hr

Hydrogen treat gas rate : 241 SCFH2/bbl feed.

22 Hmph6.334

SCF379molex

hrscf2.126816

hr24Dx

BHSCF241x

DB1629 ==

Evaluation, Cont'd

Total treat gas: Treat gas is 69.23 mole percent H2

0.6923 X = 334.6 mphX = 483.3 mph

Treat Gastotal treat gas ratehydrogen

methane

mph483.3-334.6

148.7 mph

Evaluation, Cont’d

Hydrogen consumed:

Consumption = 5.83 SCF/bbl feed

mph1.8SCF379

molexhr

SCF79.3067bbl

SCF83.5xhr24

DxDB1629 ==

• H2S created = H2 consumed =8.1 mph.

• Offgas composition (mph):

Treat Gas mph Consumed mph Offgas mph148.7 CH4 0 CH4 148.7 CH4

334.6 H2 8.1 H2 326.5 H2

483.3 8.1 8.1 H2S 483.3

E v a lu a tio n , C o n t’d

• M in im u m H 2 p a rt ia l p re s s u re = 5 6 .6 p s ia .T h is w ill o c c u r a t th e o u tle t w h e re th ep re s s u re a n d H 2 c o n te n t a re a t th em in im u m .

molestotalHmoles 2 x p re s s u re = 5 6 .5

76.9503.4835.326

+ x p re s s u re = 5 6 .5 =

0 .2 2 7 7 x p re s s u re

R e a c to r o u tle t p re s s u re = 2 4 8 .6 p s ia =2 3 3 .9 p s ig

ChE 101.04 V (57)

Evaluation, Cont’d

Feed

950 mph144,518 lbs/hr

Treat Gas

248.6 psia

Reactor

Offgas

Product950 mph144,258 lbs/hr

MW162

2379669

3048

lbs/hrmphCH4 148.7

H2 334.6483.3

CH4 148.7 H2 326.5

H2S 8.1483.3

mph16

234.1

MW2379653276

3308

lbs/hr

Evaluation; Cont'dEvaluation; Cont'd

Mass BalanceMass Balance

n

FeedTreat Gas

Ibs/hr

144,5183,048147,566

Out Ibs/hr Off gas 3,308Product 144.25(By difference)

147,566