Mass Balance
This document was uploaded by user and they confirmed that they have the permission to share it. If you are author or own the copyright of this book, please report to us by using this DMCA report form. Report DMCA
Overview
Download & View Mass Balance as PDF for free.
More details
- Words: 1,640
- Pages: 8
Material Balance Fundamentals Material balances (mass balances) are based on the fundamental “law of conservation of mass (not volume, not moles)”. In particular, chemical engineers are concerned with doing mass balances around chemical processes. Doing a ‘mass balance’ is similar in principle to accounting. In accounting, accountants do balances of what happens to a Company’s money. Chemical engineers do a mass balance to account for what happens to each of the chemicals that is used in a chemical process. Thus far, we have learned about the process variables that we need to describe the chemicals entering a process stream. Now, we must learn how to a) Specify a process stream b) Specify a process unit c) Do a mass balance on a process unit d) Do a mass balance on a sequence of process units.
Classification of Processes A.
B.
Based on how the process varies with time. a.
Steady-state process is one that does not change with time. Every time we take a snapshot, all the variables have the same values as in the first snapshot.
b.
Unsteady-state (Transient) process is one that changes with time. Every time we take a snapshot, many of the variables have different values than in the first snapshot.
Based on how the process was built to operate. a.
A Continuous process is a process that has the feed streams and product streams moving chemicals into and out of the process all the time. At every instant, the process is fed and product is produced. Examples are an oil refinery, a power grid and a steady salaried job.
b.
A Batch process is a process where the feed streams are fed to the process to get it started. The feed material is then processed through various process steps and the finished products are created during one or more of the steps. The process is fed and products result only at specific times. Examples are making a batch of a product, like soup or a specialty chemical.
c.
A Semi-batch process (also called semi-continuous) is a process that has some characteristics continuous and batch processes. Some chemicals in the process are handled batchwise. Some chemicals are processed continuously.
Types of Balances a.
Differential Balance is a balance taken at a specific instant in time. It is generally applied to a continuous process. If the process is at steady state, a differential balance applied at any time gives the same result. We will apply differential balances to steady-state continuous processes. Each term in a differential balance represents a process stream and the mass flow rate of the chemical(s) in that stream.
b.
Integral balance is a balance taken at two specific instants in time. It describes what has happened over the time period between the two points. An integral balance is generally applied to the beginning and the end of a batch process. It accounts for what happens to the batch of chemicals. We will apply integral balances to batch processes. Each term in an integral balance represents a process stream and the mass of the chemical(s) in that stream.
The Mass Balance Equation The law of ’conservation of mass’ states that mass cannot be created or destroyed. We will use this law in the form of a general mass balance equation to account for the total mass all of the chemicals that are involved in the process. The total mass balance equation can be written as INPUT − OUTPUT = ACCUMULATION I − O = A If the process is at steady-state, there is no accumulation of mass within the process. In CHEN 200, we will deal only with steady-state processes. Thus INPUT = OUTPUT I = O When we apply this equation to a process, it is best to write it as ΣMasses entering via feed streams = ΣMasses exiting via product streams We understand that we must include the mass of every chemical in every stream. The above equation can applied to batch and continuous processes as ΣMass in
=
ΣMass out
ΣMass in by flow
=
ΣMass out by flow
for a batch process, and for a continuous process.
If the process involves chemical reaction(s), we must account for the formation of product chemicals and the consumption of feed chemicals. We must remind ourselves that the law of conservation of mass means total mass. For this case, we must write a mass balance for each chemical and account its formation and consumption as follows ΣMass in + Mass formed by reaction = ΣMass out + Mass used by reaction
Or, written more simply as in + formed
=
out + consumed
What balances can one write? 1. 2.
A mass balance can be written using the total mass in each process stream. This is called a total balance. A separate mass balance can be written for each chemical component involved. These are called component balances.
Example: A process unit involves 3 chemical components. How many mass balances can be written? Solution: We can write 4 balances. We can write a total balance and 3 component balances. Independent balances: Not all balances are independent since the total balance in the sum of all of the component balances. Thus, the number of independent balances we can write = the number of components. Which of the following must be conserved in a chemical process? Total mass Mass of a chemical Total moles Moles of a chemical Mass of a specie (i.e. SO2−− ) Moles of a specie (i.e. SO2−− ) Mass of an element Moles of an element What’s next? You need to develop skill at using a systematic approach to solving mass balance problems. And later, skill at using a systematic approach to solving mass and energy balance problems.
Where am I? Where am I going ? How do I get there? To answer the first question, you need to 1. Read, study and understand the problem. 2. Draw a flow sheet for the process. 3. Label it with all given information, including symbols for the unknowns 4. Note any special relationships. To accomplish this step, you need to learn 1. The information needed to specify a stream. 2. How to use symbols to represent the required stream data. 3. How to determine the mass of each component in a stream (each mass will be a term in a mass balance) 1. 2. 3.
Required Stream Information Stream name & symbol (1) Component masses/ stream composition (n) Stream temperature and pressure (these are needed only when an energy balance is being done, phase behavior is included or to specify chemical properties. How to represent the required information
1. Specify each stream and total mass --- Select a stream name & symbol a) Use a single Capital letter to represent the total mass( or mfr) of the stream. b) Select a stream name to clearly identify the stream, by the location or purpose of the stream on the flow sheet. c) Put the mass/mfr on the flow sheet using an equation symbol = value (if the mass is known) or symbol = ? (if the value is unknown) Example: The reactor is fed with 25 kg/s of a hot feed stream and a recycle stream. Label the reactor inputs.
Solution: The reactor has two input streams. We draw and label them as
Hot Reactor Feed, H =25 kg/s
Reactor Recycle, R=?
NOTE: The total mass balance will be written using the symbols selected for the stream names. Next we must learn how to represent the component masses so we can write the component balances. 2. Component masses/ stream composition A component mass can be represented directly, using a lower case letter and a subscript, or indirectly using the fractional composition times the stream total (use and reserve x,y,z for fractional composition). Note that a component mass can be calculated as the product of the total and the fractional composition. Example1: Stream F contains 500 kg of O2 and 700 kg of CH4. Label the stream. Solution: Note that the component masses must add to the total. The total mass in F is 1200 kg. Thus, Stream F F=1200 kg m O2 = 500 kg m CH4 = 700 kg
Example2: 1200 kg of a mixture of O2 , N2 and CH4 are fed to a process. The stream has 20% O2 by mass. Label the stream.
( Note the Mass of i in the stream is
F xi )
Solution: The composition is partially known. Note that the fractional compositions must add to 1.0. Thus, we can write two alternatives Using fractional composition
Feed Stream F, F=1200 kg xO2 = 0.2 xN2 = ? xCH4 = 1. – 0.2 - xN2 = 0.8 - xN2 or using component masses Feed Stream F, F=1200 kg mO2 = 240 kg mN2 = ? mCH4 = 1200 - 240 - mN2 = 960 - mN2 Some Suggestions for Component Labeling 1. If the stream composition is unknown (or if some of the component masses are known) represent the component masses directly and use a lower case letter for each chemical. Eg. If stream F contains chemicals a, b and c, label the flow rates as F, aF, bF and cF=F- aF - bF 2. If the stream composition is known from fractional compositions, represent the component masses directly and label as in 2. 3. If stream composition is partially known with fractional compositions and the total is known, represent the component masses indirectly and use lower case x,y,z for each fractional composition. 4. Avoid the creation of a product of two unknowns—this will result in a non-linear equation.
http://rapidshare.com/files/156063021/0849398479.zip http://rapidshare.com/files/14037980...ssing.rar.html Pass: tranvansang
http://rapidshare.com/files/30761111/HFBMT.rar http://rapidshare.com/files/13118039...ifications.pdf http://rapidshare.com/files/13577655..._2006.rar.html http://rapidshare.com/files/63729402/DF.zip http://rapidshare.com/files/68448283/Foad_the_2nd.rar http://rapidshare.com/files/71357786...527427.pdf.rar http://rapidshare.com/files/54306291/NFPT.rar.html http://rapidshare.com/files/12729078/FrMa.rar.html http://rs60tl2.rapidshare.com/files/...ntury.rar.html http://ifile.it/y98s17b/image_analysis_of_food_microstructure.rar http://rapidshare.com/files/9610406/WTFPI.rar.html http://ifile.it/onsijxv/starch_in_food.zip http://www.filefactory.com/file/752c2e/n/1855735431_zip http://rapidshare.com/files/3118518/..._._watson_.rar http://rapidshare.com/files/10102319....eBook-EEn.rar http://rapidshare.com/files/453450/P...Sanitation.rar http://rapidshare.com/files/12592065/pfscanv.rar.html
http://rapidshare.com/files/12567748/Characterization_of_cereals_an d_flours.rar http://rapidshare.com/files/9012793/AFE-FQQPC.rar http://rapidshare.com/files/18483349...g_Handbook.pdf http://rapidshare.com/files/25011577/FoPlDe.rar.html http://rapidshare.com/files/12602702/HFEP.rar.html http://rapidshare.com/files/170601407/0123742048.rar
http://rapidshare.com/files/54173293/Handbook_of_Food_and_Bever age_Fermentation_Technology.part1.rar http://rapidshare.com/files/54173591/Handbook_of_Food_and_Bever age_Fermentation_Technology.part2.rar http://rapidshare.com/files/194875671/berk_0123736609.rar http://rapidshare.com/files/13302360/Binder1.pdf.html
http://rapidshare.com/files/54173293/Handbook_of_Food_and_Bever age_Fermentation_Technology.part1.rar http://ifile.it/it4wae0/0824701054.zip http://rapidshare.com/files/86164138/HFPCRC.rar http://ifile.it/xqk17c8/0125953402.zip http://ifile.it/rlm4ex8/0824789083.zip
Classification of Processes A.
B.
Based on how the process varies with time. a.
Steady-state process is one that does not change with time. Every time we take a snapshot, all the variables have the same values as in the first snapshot.
b.
Unsteady-state (Transient) process is one that changes with time. Every time we take a snapshot, many of the variables have different values than in the first snapshot.
Based on how the process was built to operate. a.
A Continuous process is a process that has the feed streams and product streams moving chemicals into and out of the process all the time. At every instant, the process is fed and product is produced. Examples are an oil refinery, a power grid and a steady salaried job.
b.
A Batch process is a process where the feed streams are fed to the process to get it started. The feed material is then processed through various process steps and the finished products are created during one or more of the steps. The process is fed and products result only at specific times. Examples are making a batch of a product, like soup or a specialty chemical.
c.
A Semi-batch process (also called semi-continuous) is a process that has some characteristics continuous and batch processes. Some chemicals in the process are handled batchwise. Some chemicals are processed continuously.
Types of Balances a.
Differential Balance is a balance taken at a specific instant in time. It is generally applied to a continuous process. If the process is at steady state, a differential balance applied at any time gives the same result. We will apply differential balances to steady-state continuous processes. Each term in a differential balance represents a process stream and the mass flow rate of the chemical(s) in that stream.
b.
Integral balance is a balance taken at two specific instants in time. It describes what has happened over the time period between the two points. An integral balance is generally applied to the beginning and the end of a batch process. It accounts for what happens to the batch of chemicals. We will apply integral balances to batch processes. Each term in an integral balance represents a process stream and the mass of the chemical(s) in that stream.
The Mass Balance Equation The law of ’conservation of mass’ states that mass cannot be created or destroyed. We will use this law in the form of a general mass balance equation to account for the total mass all of the chemicals that are involved in the process. The total mass balance equation can be written as INPUT − OUTPUT = ACCUMULATION I − O = A If the process is at steady-state, there is no accumulation of mass within the process. In CHEN 200, we will deal only with steady-state processes. Thus INPUT = OUTPUT I = O When we apply this equation to a process, it is best to write it as ΣMasses entering via feed streams = ΣMasses exiting via product streams We understand that we must include the mass of every chemical in every stream. The above equation can applied to batch and continuous processes as ΣMass in
=
ΣMass out
ΣMass in by flow
=
ΣMass out by flow
for a batch process, and for a continuous process.
If the process involves chemical reaction(s), we must account for the formation of product chemicals and the consumption of feed chemicals. We must remind ourselves that the law of conservation of mass means total mass. For this case, we must write a mass balance for each chemical and account its formation and consumption as follows ΣMass in + Mass formed by reaction = ΣMass out + Mass used by reaction
Or, written more simply as in + formed
=
out + consumed
What balances can one write? 1. 2.
A mass balance can be written using the total mass in each process stream. This is called a total balance. A separate mass balance can be written for each chemical component involved. These are called component balances.
Example: A process unit involves 3 chemical components. How many mass balances can be written? Solution: We can write 4 balances. We can write a total balance and 3 component balances. Independent balances: Not all balances are independent since the total balance in the sum of all of the component balances. Thus, the number of independent balances we can write = the number of components. Which of the following must be conserved in a chemical process? Total mass Mass of a chemical Total moles Moles of a chemical Mass of a specie (i.e. SO2−− ) Moles of a specie (i.e. SO2−− ) Mass of an element Moles of an element What’s next? You need to develop skill at using a systematic approach to solving mass balance problems. And later, skill at using a systematic approach to solving mass and energy balance problems.
Where am I? Where am I going ? How do I get there? To answer the first question, you need to 1. Read, study and understand the problem. 2. Draw a flow sheet for the process. 3. Label it with all given information, including symbols for the unknowns 4. Note any special relationships. To accomplish this step, you need to learn 1. The information needed to specify a stream. 2. How to use symbols to represent the required stream data. 3. How to determine the mass of each component in a stream (each mass will be a term in a mass balance) 1. 2. 3.
Required Stream Information Stream name & symbol (1) Component masses/ stream composition (n) Stream temperature and pressure (these are needed only when an energy balance is being done, phase behavior is included or to specify chemical properties. How to represent the required information
1. Specify each stream and total mass --- Select a stream name & symbol a) Use a single Capital letter to represent the total mass( or mfr) of the stream. b) Select a stream name to clearly identify the stream, by the location or purpose of the stream on the flow sheet. c) Put the mass/mfr on the flow sheet using an equation symbol = value (if the mass is known) or symbol = ? (if the value is unknown) Example: The reactor is fed with 25 kg/s of a hot feed stream and a recycle stream. Label the reactor inputs.
Solution: The reactor has two input streams. We draw and label them as
Hot Reactor Feed, H =25 kg/s
Reactor Recycle, R=?
NOTE: The total mass balance will be written using the symbols selected for the stream names. Next we must learn how to represent the component masses so we can write the component balances. 2. Component masses/ stream composition A component mass can be represented directly, using a lower case letter and a subscript, or indirectly using the fractional composition times the stream total (use and reserve x,y,z for fractional composition). Note that a component mass can be calculated as the product of the total and the fractional composition. Example1: Stream F contains 500 kg of O2 and 700 kg of CH4. Label the stream. Solution: Note that the component masses must add to the total. The total mass in F is 1200 kg. Thus, Stream F F=1200 kg m O2 = 500 kg m CH4 = 700 kg
Example2: 1200 kg of a mixture of O2 , N2 and CH4 are fed to a process. The stream has 20% O2 by mass. Label the stream.
( Note the Mass of i in the stream is
F xi )
Solution: The composition is partially known. Note that the fractional compositions must add to 1.0. Thus, we can write two alternatives Using fractional composition
Feed Stream F, F=1200 kg xO2 = 0.2 xN2 = ? xCH4 = 1. – 0.2 - xN2 = 0.8 - xN2 or using component masses Feed Stream F, F=1200 kg mO2 = 240 kg mN2 = ? mCH4 = 1200 - 240 - mN2 = 960 - mN2 Some Suggestions for Component Labeling 1. If the stream composition is unknown (or if some of the component masses are known) represent the component masses directly and use a lower case letter for each chemical. Eg. If stream F contains chemicals a, b and c, label the flow rates as F, aF, bF and cF=F- aF - bF 2. If the stream composition is known from fractional compositions, represent the component masses directly and label as in 2. 3. If stream composition is partially known with fractional compositions and the total is known, represent the component masses indirectly and use lower case x,y,z for each fractional composition. 4. Avoid the creation of a product of two unknowns—this will result in a non-linear equation.
http://rapidshare.com/files/156063021/0849398479.zip http://rapidshare.com/files/14037980...ssing.rar.html Pass: tranvansang
http://rapidshare.com/files/30761111/HFBMT.rar http://rapidshare.com/files/13118039...ifications.pdf http://rapidshare.com/files/13577655..._2006.rar.html http://rapidshare.com/files/63729402/DF.zip http://rapidshare.com/files/68448283/Foad_the_2nd.rar http://rapidshare.com/files/71357786...527427.pdf.rar http://rapidshare.com/files/54306291/NFPT.rar.html http://rapidshare.com/files/12729078/FrMa.rar.html http://rs60tl2.rapidshare.com/files/...ntury.rar.html http://ifile.it/y98s17b/image_analysis_of_food_microstructure.rar http://rapidshare.com/files/9610406/WTFPI.rar.html http://ifile.it/onsijxv/starch_in_food.zip http://www.filefactory.com/file/752c2e/n/1855735431_zip http://rapidshare.com/files/3118518/..._._watson_.rar http://rapidshare.com/files/10102319....eBook-EEn.rar http://rapidshare.com/files/453450/P...Sanitation.rar http://rapidshare.com/files/12592065/pfscanv.rar.html
http://rapidshare.com/files/12567748/Characterization_of_cereals_an d_flours.rar http://rapidshare.com/files/9012793/AFE-FQQPC.rar http://rapidshare.com/files/18483349...g_Handbook.pdf http://rapidshare.com/files/25011577/FoPlDe.rar.html http://rapidshare.com/files/12602702/HFEP.rar.html http://rapidshare.com/files/170601407/0123742048.rar
http://rapidshare.com/files/54173293/Handbook_of_Food_and_Bever age_Fermentation_Technology.part1.rar http://rapidshare.com/files/54173591/Handbook_of_Food_and_Bever age_Fermentation_Technology.part2.rar http://rapidshare.com/files/194875671/berk_0123736609.rar http://rapidshare.com/files/13302360/Binder1.pdf.html
http://rapidshare.com/files/54173293/Handbook_of_Food_and_Bever age_Fermentation_Technology.part1.rar http://ifile.it/it4wae0/0824701054.zip http://rapidshare.com/files/86164138/HFPCRC.rar http://ifile.it/xqk17c8/0125953402.zip http://ifile.it/rlm4ex8/0824789083.zip
Related Documents
Mass Balance
December 2019 21
Mass Balance
May 2020 7
285000187-mass-balance-pdf.pdf
April 2020 12
Kelompok 4 Mass Balance
October 2019 22
Ammonia Mass Balance
June 2020 6