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How Can I Simulate Steam Generation From The Heat Released In A Reacto


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#1 Elmansi

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Posted 10 April 2020 - 06:26 AM

I am running a RSTOIC reactor whose product outlet stream temperature I want to be at 35, however upon doing this a significant amount of heat from the reactor is wasted and If I set the heat duty equal to zero, the product stream instead exits at 623 celsius, So I would like to make use of this heat to generate steam to heat other process streams. 
I set the heat duty to equal zero and connected the reactor outlet at 623 celsius through MHEATX to exchange heat with the cooling water I will use to generate steam, I don't know how much water I  must use . Secondly, at 623 celsius my product decomposes. If I thought of this heat exchanger as a temperature controller to keep the reactor operating temperature at 35, what should I choose as the valid phases in the specification?
If the reactor outlet is in liquid phase and the cooling water I will use to generate steam started as liquid and undergoes phase change into steam


#2 PingPong

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Posted 13 April 2020 - 05:20 AM

It is not clear what kind of process you are talking about.

You do not mention anything specific for your process.

 

In general: the operating temperature of a reactor is chosen on basis of kinetics, required conversion, optimal usage of reaction heat, et cetera. It is not just an arbitrary choice between either 35 or 623 degrees.

Obviously the lower the reactor temperature the bigger the reactor has to be, and more catalyst is required (if applicable).

However the higher the reactor temperature of an exothermic reaction the lower the equilibrium conversion, and the more expensive the metallurgy.

To remove the heat of reaction you could have multiple reactors in series with steam generators in between them to lower the process stream temperature to the next reactor.

Or you could have a reactor with steam generation piping inside it.



#3 Elmansi

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Posted 13 April 2020 - 12:16 PM

It is not clear what kind of process you are talking about.

You do not mention anything specific for your process.

 

In general: the operating temperature of a reactor is chosen on basis of kinetics, required conversion, optimal usage of reaction heat, et cetera. It is not just an arbitrary choice between either 35 or 623 degrees.

Obviously the lower the reactor temperature the bigger the reactor has to be, and more catalyst is required (if applicable).

However the higher the reactor temperature of an exothermic reaction the lower the equilibrium conversion, and the more expensive the metallurgy.

To remove the heat of reaction you could have multiple reactors in series with steam generators in between them to lower the process stream temperature to the next reactor.

Or you could have a reactor with steam generation piping inside it.

 I am designing a hybrid photo/thermochemical process to produce 1 kmol/s Hydrogen to shed light on the viability of the Cu2O/CuO subcycle using ASPEN PLUS?

These are the reactions for the complete cycle
H2O + 2 NH3 + SO2 --> (NH4)2SO3 (25 degrees celsius, chemical absorption)
(NH4)2SO3 + H2O--> (NH4)2SO4 + H2 (65 degrees celsius, solar photocatalytic step)
(NH4)2SO4 --> H2SO4 + 2 NH3 (250 degrees celsius, thermocatalysis)
H2SO4 --> SO3 + H2O (400 degrees celsius, thermocatalysis)
SO3 + Cu2O --> 2 CUO + SO2 (650 degrees celsius, thermocatalysis)
2 CUO --> Cu2O + 1/2 O2 (1050 degrees celsius, thermocatalysis)

 

My Problem

I want to circulate 15 kmol/sec to ensure liquid operation and that no precipitation of the ammonium sulfate and sulfite takes place.  In the Low temperature reactor ammonium sulfate decomposition takes place.  I have added a component separator to separate the gaseous mixture SO2, NH3 from the aqueous solution H2SO4. H2O serves no purpose and is considered a drawback because more heat duty is required to heat the feed streams (H2O+H2SO4 and SO3+H2O) to the respective temperatures (400 C and 650 C) and I cannot strip H2O from H2SO4. In the last reaction, I recycle Cu2O to the reactor with SO3+H2O. I used the exiting gaseous mixture (SO2+H2O) to exchange heat to minimize utility and heat the H2SO4+H2O to the reactor and (SO3+H2O) and recycled to the absorber. The (SO2+NH3) at 250 C  cannot raise any of the cold streams that require heating to above 10 degrees celsius  because of tits small flow rate . The reaction in the absorber takes place at 25, however the feed streams are at much higher temperatures as I mentioned is much higher so I want to utilize the significant amount of heat wasted to produce steam to heat the cold streams. 



#4 PingPong

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Posted 13 April 2020 - 01:05 PM

Please make a simplified flow diagram to indicate how the different reaction steps are connected, what inlet temperature is required for each reactor, what maximum outlet temperature is allowed for each reactor, et cetera. Include also recycle streams in the diagram.



#5 Elmansi

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Posted 13 April 2020 - 02:30 PM

Please make a simplified flow diagram to indicate how the different reaction steps are connected, what inlet temperature is required for each reactor, what maximum outlet temperature is allowed for each reactor, et cetera. Include also recycle streams in the diagram.

Absorber

H2O + 2 NH3 + SO2 --> (NH4)2SO3 (25 degrees celsius, chemical absorption) 

 

Inlet Streams:

SO2+NH3 from sep-01 at temperature 250

SO2+H2O exiting sep-02 at temperature 650

Outlet Streams 

(NH4)2SO4 + H2O at temperature 25 

 

Photoreactor 
(NH4)2SO3 + H2O--> (NH4)2SO4 + H2 (65 degrees celsius, solar photocatalytic step)

 

Inlet streams

(NH4)2SO3 + H2O at temperature 25 from Absorber

Outlet streams

(NH4)2SO4+H2+H2O + (unconverted NH4)2SO3) temperature 65

 

LTR
(NH4)2SO4 --> H2SO4 + 2 NH3 (250 degrees celsius, thermocatalysis)

(NH4)2SO3-->SO2+2NH3+H2O (250 degrees celsius, thermocatalysis)

 

 Inlet stream

(NH4)2SO4+H2O at temperature 65 from Photoreactor

Outlet stream 

H2SO4+H2O+SO2+NH3 at temperature 250

 

MTR
H2SO4 --> SO3 + H2O (400 degrees celsius, thermocatalysis)

 

Inlet Stream

H2SO4+H2O at temperature 250 from sep-01

Outlet Stream 

SO3+H2O at temperature 400

 

GTR
SO3 + Cu2O --> 2 CUO + SO2 (650 degrees celsius, thermocatalysis)

 

Inlet stream 

Cu2O at temperature 1050 from sep-03

SO3+H2O at temperature 400 from MTR

Outlet stream

CuO+ SO2 at temperature 650 

 

HTR
2 CUO --> Cu2O + 1/2 O2 (1050 degrees celsius, thermocatalysis)

 

Inlet stream 

CuO at temperature 650 from sep-02

Outlet stream 

Cu2O+O2 at temperature 1050

 

 

Attached Files


Edited by Elmansi, 13 April 2020 - 02:31 PM.


#6 PingPong

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Posted 15 April 2020 - 05:32 AM

In the mean time I noticed that you had already opened another topic on this subject in which you stated:

 


My Problem

I want to circulate 15 kmol/sec to ensure liquid operation and that no precipitation of the ammonium sulfate and sulfite takes place. Unfortunately, I think because of this, high heat duty is required in the Low temperature reactor where ammonium sulfate decomposition takes place. I have added a component separator to separate the gaseous mixture SO2, NH3 from the aqeous solution H2O. From this point in the process, H2O serves no purpose and is considered a drawback because more heat duty is required. How can we go about this problem of seperating H2SO4 from water without the addition of new chemicals.Cu2O exiting the reactor operating at 1050 is added directly to heat the SO3-H2O feed to the reactor (650), the gaseous mixture from this reactor is used to heat H2SO4 + SO3 + some of the ammonium sulfate, and finally returned to the absorber, significant heat is wasted. As a result, the calculated efficiency is not satisfying, 13 %. Also in one of the heat exchangers I am not sure whether at the specified outlet temperature the SO2-H2O will undergo phase change , so how can I account for the phase change if any in the specification of the MHeatx should I include in the phases vapor-liquid?

How can I input manually the heat capacities for the components of my system and allow aspen to heat based on these heat capacities.

https://www.cheresou...n-plant-design/

 

I never use Aspen Plus so I can not help you with the specific input options of that particular simulator.

Whether there is a phase change in a reactor or heat exchanger will be determined by the simulator based on your inputs.

 

From the above simulation scheme I get the impression that you use simple component separators for H2-sep, Sep-01 , Sep-02 and Sep-03 , however in the real world you have to take into account vapor/liquid equilibria and use Flash Separators in combination with a suitable Property Method.

 

For the absorber you also have to obey the laws of physics and thermodynamics. You can't add multiple streams and assume that all components end up in only one liquid outlet stream, unless maybe if you use sufficiently high absorber pressure. Or if it is not really an absorber but a mixer with possibly a mixed phase outlet stream.

 

Also for the reactors you have to use suitable property methods and thermodynamics.

 

It is not clear what is the phase of CuO and Cu2O containing streams. Are they slurry, or what?

 

Did you actually run this simulation, and if so, did you get a converged solution?

If so, indicate which reaction is endothermic and which is exothermic,

and what is the pressure, flowrate, composition and phase of each stream.


Edited by PingPong, 15 April 2020 - 05:33 AM.


#7 Elmansi

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Posted 15 April 2020 - 11:45 AM

In the mean time I noticed that you had already opened another topic on this subject in which you stated:

 


My Problem

I want to circulate 15 kmol/sec to ensure liquid operation and that no precipitation of the ammonium sulfate and sulfite takes place. Unfortunately, I think because of this, high heat duty is required in the Low temperature reactor where ammonium sulfate decomposition takes place. I have added a component separator to separate the gaseous mixture SO2, NH3 from the aqeous solution H2O. From this point in the process, H2O serves no purpose and is considered a drawback because more heat duty is required. How can we go about this problem of seperating H2SO4 from water without the addition of new chemicals.Cu2O exiting the reactor operating at 1050 is added directly to heat the SO3-H2O feed to the reactor (650), the gaseous mixture from this reactor is used to heat H2SO4 + SO3 + some of the ammonium sulfate, and finally returned to the absorber, significant heat is wasted. As a result, the calculated efficiency is not satisfying, 13 %. Also in one of the heat exchangers I am not sure whether at the specified outlet temperature the SO2-H2O will undergo phase change , so how can I account for the phase change if any in the specification of the MHeatx should I include in the phases vapor-liquid?

How can I input manually the heat capacities for the components of my system and allow aspen to heat based on these heat capacities.

https://www.cheresou...n-plant-design/

 

I never use Aspen Plus so I can not help you with the specific input options of that particular simulator.

Whether there is a phase change in a reactor or heat exchanger will be determined by the simulator based on your inputs.

 

From the above simulation scheme I get the impression that you use simple component separators for H2-sep, Sep-01 , Sep-02 and Sep-03 , however in the real world you have to take into account vapor/liquid equilibria and use Flash Separators in combination with a suitable Property Method.

 

For the absorber you also have to obey the laws of physics and thermodynamics. You can't add multiple streams and assume that all components end up in only one liquid outlet stream, unless maybe if you use sufficiently high absorber pressure. Or if it is not really an absorber but a mixer with possibly a mixed phase outlet stream.

 

Also for the reactors you have to use suitable property methods and thermodynamics.

 

It is not clear what is the phase of CuO and Cu2O containing streams. Are they slurry, or what?

 

Did you actually run this simulation, and if so, did you get a converged solution?

If so, indicate which reaction is endothermic and which is exothermic,

and what is the pressure, flowrate, composition and phase of each stream.

 

I employed component seperator because in this process H2 is generated from the (NH4)2SO4 aqueous solution and no separation is required. NH3 and SO2 gas can be separated from H2SO4 aqueous solution. SO2+H2O can be automatically separated from solid product CuO ( I cannot simulate solid-gas separation using a flash separator)
 
Multiple inlet streams from the Sep-01, Sep-02 are connected to the absorber, in addition to Freshwater, to form aqueous ammonium sulfite. That's also what my supervisor suggested to operate the absorber at high pressure (>9 bar), the outlet stream which is also a tear stream, I have defined to exit at 25 C and 9 bar with a mole flow rate of 15 kmol/s H2O and 1.05263157895 kmol/s (NH4)2SO3 respectively. 
 
I have used a Rgibbs reactor model to estimate the likelihood of forming the products I have specified, ignoring the kinetics. 
 
CuO and Cu2O are in solid phase. Cu2O exiting Sep-03 is another tear stream exiting at 1050 C, 9 bar, and its flow rate is 1 kmol/s
 
I ran the simulation, and it converged. All reactions are endothermic except the reaction taking place in the absorber. 


#8 Elmansi

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Posted 18 April 2020 - 03:43 AM

I am not permitted to upload apw or tmp files. 

In the mean time I noticed that you had already opened another topic on this subject in which you stated:

 


My Problem

I want to circulate 15 kmol/sec to ensure liquid operation and that no precipitation of the ammonium sulfate and sulfite takes place. Unfortunately, I think because of this, high heat duty is required in the Low temperature reactor where ammonium sulfate decomposition takes place. I have added a component separator to separate the gaseous mixture SO2, NH3 from the aqeous solution H2O. From this point in the process, H2O serves no purpose and is considered a drawback because more heat duty is required. How can we go about this problem of seperating H2SO4 from water without the addition of new chemicals.Cu2O exiting the reactor operating at 1050 is added directly to heat the SO3-H2O feed to the reactor (650), the gaseous mixture from this reactor is used to heat H2SO4 + SO3 + some of the ammonium sulfate, and finally returned to the absorber, significant heat is wasted. As a result, the calculated efficiency is not satisfying, 13 %. Also in one of the heat exchangers I am not sure whether at the specified outlet temperature the SO2-H2O will undergo phase change , so how can I account for the phase change if any in the specification of the MHeatx should I include in the phases vapor-liquid?

How can I input manually the heat capacities for the components of my system and allow aspen to heat based on these heat capacities.

https://www.cheresou...n-plant-design/

 

I never use Aspen Plus so I can not help you with the specific input options of that particular simulator.

Whether there is a phase change in a reactor or heat exchanger will be determined by the simulator based on your inputs.

 

From the above simulation scheme I get the impression that you use simple component separators for H2-sep, Sep-01 , Sep-02 and Sep-03 , however in the real world you have to take into account vapor/liquid equilibria and use Flash Separators in combination with a suitable Property Method.

 

For the absorber you also have to obey the laws of physics and thermodynamics. You can't add multiple streams and assume that all components end up in only one liquid outlet stream, unless maybe if you use sufficiently high absorber pressure. Or if it is not really an absorber but a mixer with possibly a mixed phase outlet stream.

 

Also for the reactors you have to use suitable property methods and thermodynamics.

 

It is not clear what is the phase of CuO and Cu2O containing streams. Are they slurry, or what?

 

Did you actually run this simulation, and if so, did you get a converged solution?

If so, indicate which reaction is endothermic and which is exothermic,

and what is the pressure, flowrate, composition and phase of each stream.

 






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