Reducing energy consumption and heat exchanger network

In summary, adding a preheater before the reactor and a cooler for acetone production can improve the energy efficiency of this process.
  • #1
gfd43tg
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Homework Statement


If you are allowed to make changes of column pressure and temperature, stream preheating or cooling temperature, please propose a process change that can significantly reduce the energy consumption at DTmin of 10°C. The modified process should maintain the product quality and production rate unchanged.
upload_2015-5-2_23-12-56.png
Utility Information

Low pressure steam (LP, 140°C) = 0.03 $/kWh = 240 $/kW-Yr

Medium pressure steam (MP, 170°C) = 0.05 $/kWh = 400 $/kW-Yr

High pressure steam (HP, 200°C) = 0.07 $/kWh = 560 $/kW-Yr

Hot Oil (HO, supply 450°C – return ≥ 300°C) = 0.15 $/kWh= 1200 $/kW-Yr

Electricity = 0.1 $/kWh = 800 $/kW-Yr

Cooling water (CW, 30°C) = 0.005 $/kWh = 40 $/kW-Yr

Chilled Water (ChW, 5°C) = 0.05 $/kWh = 400 $/kW-Yr

Refrigeration

(R-10, -10°C) = 0.1 $/kWh = 800 $/kW-Yr

(R-50, -50°C) = 0.3 $/kWh = 2400 $/kW-Yr

(R-100, -100°C) = 1 $/kWh = 8000 $/kW-Yr

(R-200, -200°C) = 5 $/kWh = 40000 $/kW-Yr

Homework Equations

The Attempt at a Solution


This is my converged aspen simulation of a process to produce acetone (AC) from isopropyl alcohol (IP). I used a heat exchanger simulation software and here are my streams
upload_2015-5-2_23-11-57.png

Basically just inputting the heat duties of all the units. I just do a heat curve analysis and when the heat capacity changes I add a separate cooler, which is why there are blank rows in "Name", because the specific heat capacity is assumed to be constant only in one phase.

This is my composite curve
upload_2015-5-2_23-15-22.png


This is my heat exchanger network
upload_2015-5-2_23-15-49.png


I'm wondering what I could do to improve the efficiency of this process? Or at least places I could start looking and what I should look for.
 
Last edited:
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  • #2
Some new idea, I decided to add a heater before the reactor in order to preheat the IP, since I can use low pressure steam which is cheaper than hot oil for the reactor. However, for some reason the Aspen file will not converge when I add this heater. The amount of IP being fed is changed, even though I specify the amount. In the OP the mass flow rate is 19483 kg/hr, now its 21123 kg/hr. It is quite strange.

upload_2015-5-4_16-16-19.png

The Energy report from SPRINT
upload_2015-5-4_16-20-35.png


This is my original energy report from the previous iteration
upload_2015-5-4_16-22-11.png
 
  • #3
Wouldn't trust any answer at all from a non-converged A+ simulation.
I have preciously little to go by, but my advice is to check the pressure drop in the feed preheater. T1 has trouble now (offgas flow disproportional) and then T2 crashes.
Good luck !
 
  • #4
If you wish, I can send you the Aspen file, but in the mean time I will try your suggestion
 
  • #5
Either that or increase the feed pressure.
Something else that came to mind: does the reactor do the same thing with a feed of 25 degrees as it does with a feed of 140 degrees ?
 
  • #6
As far as I know there is no difference
 
  • #7
If there are no temperature dependencies in the reactor, then it must be the pressure ...
 
  • #8
Ah yes, I forgot that the pressure in the preheater should be 2 atm.
 
  • #9
Okay, so I added a preheater before the reactor to IP, and a cooler for the AC.

upload_2015-5-6_20-57-55.png


This is my grand composite curve, and I should somehow use it to improve my energy efficiency. I know the flat blue lines are the utilities that I need, but I am unsure how to translate this curve into my process so that I know where I should put heaters/coolers.

upload_2015-5-6_20-59-24.png


And here is my utilities cost (this one is higher because DTmin is 20 C), but I have improved it with what I have done so far

upload_2015-5-6_21-8-12.png
 
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FAQ: Reducing energy consumption and heat exchanger network

1. How can heat exchanger networks help reduce energy consumption?

Heat exchanger networks are designed to optimize the transfer of heat between different streams of fluids, such as water or air. By implementing a heat exchanger network, the energy used to heat or cool a fluid can be transferred to another fluid that requires heating or cooling, thus reducing the overall energy consumption.

2. What factors should be considered when designing a heat exchanger network?

When designing a heat exchanger network, factors such as the type of fluids being used, their flow rates, temperature differences, and the desired heat transfer rates must be taken into account. The layout and arrangement of the network must also be carefully planned to ensure efficient heat transfer and minimal energy loss.

3. Can heat exchanger networks be applied to all types of industries?

Yes, heat exchanger networks can be applied to various industries, including chemical, petrochemical, food processing, and HVAC systems. Any industry that requires heating or cooling of fluids can benefit from implementing a heat exchanger network to reduce energy consumption.

4. What are the advantages of reducing energy consumption through heat exchanger networks?

Reducing energy consumption through heat exchanger networks not only helps to reduce operating costs, but it also has a positive impact on the environment. By using less energy, there is a decrease in greenhouse gas emissions, leading to a more sustainable and eco-friendly operation.

5. Are there any challenges or limitations to implementing a heat exchanger network?

Some challenges or limitations to implementing a heat exchanger network may include the initial cost of installation and maintenance, as well as the potential for fouling or corrosion within the network. However, these challenges can be mitigated through proper design and regular maintenance of the network.

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