KangCy
Chemical
- Jun 23, 2022
- 10
Hello,
I have a mixing tank 1.7 m3 half covered with plain cooling jacket (heat transfer area 2.44 m2).
I tend to use the mixing tank for a reaction that is exothermic (ca -10kW), for that reason I want to check if cooling duty of chiller and jacket is sufficient.
We carried out some tests and the results showed that jacket had a cooling rate of 2.3 oC/h dropping temperatures of the reactor content (400L) from 15 to -10oC in 11hours. That seems extremely slow.
Notes:
[ul]
[li]Reactor content: 400L of 30% IPA[/li]
[li]Reactor size 1.7 m3 and filled to 0.4 m3.[/li]
[li]Tank contents were mixed during cooling and process was batch.[/li]
[li]Jacket was insulated, pipes of 4 m were not insulated.[/li]
[li]Coolant: 50% glycol[/li]
[li]Coolant rate 38 m3/h[/li]
[li]Coolant initial temperature -2 oC and cooled down down to -20 oC.[/li]
[li]Coolant buffer 1 m3 was used. The coolant was circulated from buffer to chiller to jacket and back to buffer.[/li]
[li]Jacket coolant velocity is 0.2 m/s (seems low).[/li]
[li]We found out that chiller has a cooling duty of 12 kW at temperatures input of 15oC and drops to 5 kW at temperatures input around -5 oC. It showed that cooling duty decreases as temperature input to chiller decreases. Kind of makes sense.[/li]
[/ul]
Then we tested the cooling efficiency of the jacket, showing very bad results, of cooling duty ranging from 2 kW (at temperatures around 15 oC) to 0.3kW at temperatures below 0 oC. This duty was calculated measuring the temperature content of the reactor over time, taking into account the mass and specific heat capacity of reactor content.
The temperatures input and output to the jacket were measures but due to calibration errors they were not showing any reasonable temperature difference to be used to calculate duty. In order to get such a low cooling duty the temperature difference should be around 0.01 oC.
In order to understand if this is reasonable, I calculated the U-value of the cooling jacket. I used the following tool: CheCalc ‐ Jacketed Vessel Heat Transfer and I came up with a U of 140W/m2 K (quite reasonable for a cooling jacket).
The effective heat transfer area of the jacket was measured to be 2.44 m2 (the liquid in the reactor was touching half of the cooling jacket. With an estimated LMDT of 10-12 oC (that is the difference throught the tests between cpolant input temperature and reactor temperature), the estimated duty was calculated at 3.42 kW. So I don't understand why in reality the cooling of mixing reactor is a lot less efficient.
My questions are:
[ul]
[li][/li]
[li]What do you think are the reasons of this inneficiency and how can I improve it on an existing plant without changing the design.[/li]
[li]Is the LMΔΤ for jacket of a batch reactor correctly assumed that is the difference of inlet temperature to reactor content temperature?[/li]
[li]To me it seems that bigger chiller won't make any difference. What do you think?[/li]
[li]Do you think that low coolant velocity in the jacket is affecting this? Higher flow though won't give higher DT because it's already too small difference.[/li]
[/ul]
I have a mixing tank 1.7 m3 half covered with plain cooling jacket (heat transfer area 2.44 m2).
I tend to use the mixing tank for a reaction that is exothermic (ca -10kW), for that reason I want to check if cooling duty of chiller and jacket is sufficient.
We carried out some tests and the results showed that jacket had a cooling rate of 2.3 oC/h dropping temperatures of the reactor content (400L) from 15 to -10oC in 11hours. That seems extremely slow.
Notes:
[ul]
[li]Reactor content: 400L of 30% IPA[/li]
[li]Reactor size 1.7 m3 and filled to 0.4 m3.[/li]
[li]Tank contents were mixed during cooling and process was batch.[/li]
[li]Jacket was insulated, pipes of 4 m were not insulated.[/li]
[li]Coolant: 50% glycol[/li]
[li]Coolant rate 38 m3/h[/li]
[li]Coolant initial temperature -2 oC and cooled down down to -20 oC.[/li]
[li]Coolant buffer 1 m3 was used. The coolant was circulated from buffer to chiller to jacket and back to buffer.[/li]
[li]Jacket coolant velocity is 0.2 m/s (seems low).[/li]
[li]We found out that chiller has a cooling duty of 12 kW at temperatures input of 15oC and drops to 5 kW at temperatures input around -5 oC. It showed that cooling duty decreases as temperature input to chiller decreases. Kind of makes sense.[/li]
[/ul]
Then we tested the cooling efficiency of the jacket, showing very bad results, of cooling duty ranging from 2 kW (at temperatures around 15 oC) to 0.3kW at temperatures below 0 oC. This duty was calculated measuring the temperature content of the reactor over time, taking into account the mass and specific heat capacity of reactor content.
The temperatures input and output to the jacket were measures but due to calibration errors they were not showing any reasonable temperature difference to be used to calculate duty. In order to get such a low cooling duty the temperature difference should be around 0.01 oC.
In order to understand if this is reasonable, I calculated the U-value of the cooling jacket. I used the following tool: CheCalc ‐ Jacketed Vessel Heat Transfer and I came up with a U of 140W/m2 K (quite reasonable for a cooling jacket).
The effective heat transfer area of the jacket was measured to be 2.44 m2 (the liquid in the reactor was touching half of the cooling jacket. With an estimated LMDT of 10-12 oC (that is the difference throught the tests between cpolant input temperature and reactor temperature), the estimated duty was calculated at 3.42 kW. So I don't understand why in reality the cooling of mixing reactor is a lot less efficient.
My questions are:
[ul]
[li][/li]
[li]What do you think are the reasons of this inneficiency and how can I improve it on an existing plant without changing the design.[/li]
[li]Is the LMΔΤ for jacket of a batch reactor correctly assumed that is the difference of inlet temperature to reactor content temperature?[/li]
[li]To me it seems that bigger chiller won't make any difference. What do you think?[/li]
[li]Do you think that low coolant velocity in the jacket is affecting this? Higher flow though won't give higher DT because it's already too small difference.[/li]
[/ul]
