Pressure increase when flow stops 1

[ThijsM]

Hello,

I am looking for a solution for the fact that we had a power failure yesterday and all pumps stopped operation in the plat. One of the pumps is used to sent mash to a cooler and when the flow stopped, we found a temperature increase of 0.5 degrees Celsius in 2 minutes and then the temperature was constant.
What caused this increase?
- The mash was reacting further and that increased the temperature? (But why did it stop after 2 minutes?)
- The heat transfer of a flowing liquid is different then that of a stagnant liquid and in this case +/- half a degree?
- or is there another solution?

Thanks in advance,

Thijs

 

[ThijsM]

Damn, "pressure" in the title should be "temperature" of course!

 

[eadwine]

Where was the temp. rise? In the mash loop or the coolant loop? Also, where are the temp. sensors located within the loops?

 

[ThijsM]

The temperature I am talking about is in the mash-loop on the outlet of the fermenter (suction of the mash cooler pump), before the cooler.
Another temperature sensor is located in the outlet of the cooler, also in the mash loop. Because of the power failure, the mash cooler pump stopped and the product stood still in the line. There is a difference in temperature profile between the 2 sensors which I can not explain jet. But this can also be caused by the fact that the valve positions of the mash flow to the cooler can not be found anymore in our system.

 

[eadwine]

So this comes out of the Fermenter, through the mash pump, into the cooler and then out. The Temp. sensors are located on the outlet of the Fermenter and on the outlet of the cooler. After the elec.failure all flow stopped. Temp. rise occured in the Fermenter outlet line and then stabilised over time.

Sounds like there might be a slight exotherm occuring in the Fermenter. The reaction still occurs even if there is a power failure and by convection through the mash the temp rise is transmitted to the sensor. And or, the mash is picking up heat from the environment via conduction through the pipe walls due to flow stoppage. When temp. equilibrium is reached, the temp. will then remain constant.

Make sense?

 

[Compositepro]

Is your final temperature your room temperature?

 

[Latexman]

I'm curious, why worry about only a 0.5 [sup]o[/sup] C rise in this stream?

Good luck,
Latexman

 

[ThijsM]

Hello, thanks for your thoughts.

Eadwine, your description of the proces is right, and the reaction is exotherm, but why did that cause an increase in only the first 2 minutes of half a degree? I would expect a longer period. When the flow is brought back, the temperature decreases to the original value. There is no heat coming from the environment because the ambient temperature is +/- 30 degrees lower (and the pipe is insulated and the change went very fast), and why is the temperature decreasing immediately when the flow is back if the reaction still occured?

The fact that we are looking at this point is that I am working on a plant that is under construction and now I am learning the process in a sister plant and there we faced the power failure. A nice learning event for me, and therefore I was looking at the data for the cooling of the fermenters and I found this.

I agree that it is not a big issue, but maybe somebody might know the answer.

Regards,

Thijs

 

[Latexman]

Describe the temperature measurement. RTD, thermocouple, filled system? Point measurement, averaging measurement? Fast response, slow response?

What is this leading to? Let's say you have a slow response time (minutes) on your temperature measurement. The temperature of the fluid going by may vary +/- 1-2[sup]o[/sup] C when measured with the fluid flowing using a temperatre measurement with a fast response time (seconds). It is a victim of process and control variablities upstream. With a slow response time, you don't see this, because your slow response device reports a moving average temperature that is dependent on it's time constant. Now, consider the power failure, and let's say the fluid that stopped in the volume immediately surrounding your temperature element is 0.6 [sup]o[/sup] C above the moving average temperature being reported at that time. The fluid surrounding the temperature element heats the element and the element cools the surrounding fluid such that the resulting temperatrure of the two is 0.5 [sup]o[/sup] C higher than two minutes before.

I had a production unit many years ago that had three different temperature elements with three vastly different response times in the same gas stream downstream of a furnace. The slow one (filled system with an averaging tube) deviated +/- 1-2 [sup]o[/sup] C. The medium one (RTD is a thermowell) deviated +/- 5-10 [sup]o[/sup] C. The fast one (bare thermocouple) deviated +/- 20-40 [sup]o[/sup] C. Neat, huh?

Good luck,
Latexman

 

[eadwine]

Ah yes... variation in sensor sensitivity, and repeatability.
Let's not go there, yet.

 

[Latexman]

Well, let's combine them. Mearurement varibility plus some fermentation would easily explain the little kick they saw. Agree?

Good luck,
Latexman

 

[curtis2004]

"ThijsM (Chemical) 28 Jan 10 4:32
Hello, thanks for your thoughts. Eadwine, your description of the proces is right, and the reaction is exotherm, but why did that cause an increase in only the first 2 minutes of half a degree? I would expect a longer period. When the flow is brought back, the temperature decreases to the original value. There is no heat coming from the environment because the ambient temperature is +/- 30 degrees lower (and the pipe is insulated and the change went very fast), and why is the temperature decreasing immediately when the flow is back if the reaction still occured?The fact that we are looking at this point is that I am working on a plant that is under construction and now I am learning the process in a sister plant and there we faced the power failure. A nice learning event for me, and therefore I was looking at the data for the cooling of the fermenters and I found this.I agree that it is not a big issue, but maybe somebody might know the answer.Regards,Thijs"

Thijs,
You've already spent a lot of your valuable time for a nonsence (0.5 degree C is nothing). I think, it is better to investigate why power failure occured and what could be done in order to avoid this in future. This is much more important than 0.5 C increase in temperature during power failure, in terms of process, relaibility, profitability of plant.
Regards,
Curtis

 

[dvd]

Pipe frictional losses will result in the pipe wall being at a higher temperature than the fluid while the fluid is flowing, since this is an insulated line.

When the fluid is not flowing the pipe wall and fluid reach an equilibrium temperature that is higher than the fluid temperature.