Re: Temperature Effect On Saturated Carrying Capacity
Dear parikshitshastri,
Which temperature are you talking about?
- Conveying gas temperature?
- cement temperature?
- Cement/gas mixture temperature?
Pneumatic conveying is a technology whereby the internal energy of a gas is used to move a material from a high pressure zone to a low pressure zone, whereby the internal gas energy is exhausted.
As the internal energy of a gas is given by its volume, pressure and temperature, temperature is important. ■
Teus
Re: Temperature Effect On Saturated Carrying Capacity
Hello Sir,
Thanks for reply.
I have multiple temperature sensors that basically measure the temperature of gas through the calciner.
To be precise, I am conveying cement raw material (Calcium Carbonate). My aim is to determine the saturated carrying capacity of the combustion gas.
I have learnt that saturated carrying capacity corresponds to the mass flux at lowest point on curve in Zenz diagram.
The lowest point in the diagram (pressure gradient versus superficial gas velocity) usually occurs at Type A chocking velocity and at this velocity the mass flux (kg/m.s) is the saturated carrying capacity (kg/m.s).
Question: Initial Gas Temperature Ti=600°C)
100 kg/hr of raw material (Initial temperature 20°C) was introduced and in the upward flowing combustion gases with superficial gas velocity (us=4 m/s).
Steady state is achieved and my gas temperature is T=400°C. (Heat lost as wall heat losses, preheating raw material, etc)
Now,
Step-1: I reduce the superficial gas velocity gradually (For example us=3.5 m/s..3 m/s...2.5 m/s), and at each velocity allow the steady state to be achieved at same ram material rate (100 kg/hr).
Step-2: At each steady state, I will get a pressure grradient and thus I am tracing Zenz diagram curve.
BUT! Velocity of gas reduced (by reducing the volume flow rate), means less heat of gas coming in contact with same amount of solids means more cooling of gas.
So the graph I am tracing is at variable temperature. I am doubtful about how can I explain this result.
Decreasing pressure gradient with decreasing velocity (dilute phase transport) at constant mass flux makes sense; but I feel temperature should also be constant.
In major literature [Rhodes et al., Bi et al.] everyone explain about the Zenz diagram. Howver no one takes about if the temperature is same or not. Others just explain it for air.
I would really appreciate your thoughts on this.
Thanks. ■
Re: Temperature Effect On Saturated Carrying Capacity
Dear parikshitshastri,
[quote]100 kg/hr of raw material (Initial temperature 20°C) was introduced and in the upward flowing combustion gases with superficial gas velocity (us=4 m/s).[unquote]
[quote]Initial Gas Temperature Ti=600°C).[unquote]
The mixture conveying temperature is formed by the stored heat in the material and the stored heat in the gas.
Normally the resulting mixture temperature is close to the material temperature, as the heat content of the conveyed material is high in relation to the heat content of the conveying gas.
In addition, the mixture temperature changes along the pipeline by cooling or heating, depending on the surrounding temperature.
Also the conveying air cools down along the pipeline, due to expansion, which is equalized with the temperature of the material.
By using less conveying air, the resulting mixture temperature should be closer to the material temperature, providing that the material flow is constant (Required for a Zenz diagram)
In your example is the material temperature constant 20 degrC and the gas is at 600 degrc.
That means that the mixture temperature should decrease a little towards the material temperature.
As soon as the mixture temperature is cooled down below the surrounding temperature (surrounding pipe cooling, gas expansion) the material keeps the mixture at a temperature that is compensated by heat loss from the material.
Another issue could be that approaching the lowest pressure drop towards the lowest point of the Zenz diagram, the compression temperature also drops.
Nevertheless, the heat content of the material and thereby the material temperature is normally dominant in the mixture temperature (depends on the solid loading ratio) ■
Teus
Re: Temperature Effect On Saturated Carrying Capacity
Dear Mr. Tuinenburg
I totally acknowledge your thoughts on heat-transfer that will take place in the vertical transport line (Calciner).
In my case, this line is connected with combustion chamber. So, the system is able to achieve stable state (even after raw material introduction at 100 kg/hr) at around 400°C (mixture temperature)
This means there is approximately temperature difference of 200°C.
Now mixture temperature is 400°C (Stable state).
If I reduce velocity by reducing the volumetric flowrate of gas, the system temperature will reduce further.
Main Question:
Is it acceptable that the temperature along the curve in Zenz diagram changes? ■
Re: Temperature Effect On Saturated Carrying Capacity
Dear parikshitshastri,
I understand
- You are calculating a Zenz diagram of a pneumatic conveying system.
- You understand the heat exchanges during pneumatic conveying.
A lower gas flow results in a mixture temperature closer to the material temperature.
You also stated, that you ignore the calcination process.
Whether this is acceptable or not, is for you to decide. (Calcination is endotherm, thus heat is involved)
If the calculated mixture temperature is not what you expected, then you must look into your software, how the temperature is calculated and decide whether the used formulas are correct.
A Zenz diagram is always valid for the calculated, complete installation and therefore including the different temperatures at different locations at the curve.
Your question seems more a heat balance problem than a pneumatic conveying problem. ■
Teus
Temperature effect on Saturated Carrying Capacity
Hello everyone,
Currently, I am working on a developmental project about cement conveying in vertical pipes (calciner).
Here, I tried to replicate the Zenz diagram - found the boundary between dense and dilute phase transport regime.
My conveying gas is combustion product of natural gas combustion. (Basically combustion gas)
Question: Suppose transport tube temperature is 600°C (Ignore calcination)
Now when I try to decrease superficial gas, the pressure gradient should decrease unit I reach the minimum point of the Zenz curve.
However, in doing so, the temperature also decrease. Temperature decrease is obvious because lower combustion gases- lower heating.
At a constant solid flux, the pressure gradient decrease and follows the Zenz pattern - BUT the temperature is not constant!
I cannot just neglect the effect of temperature on pressure gradient.
Is this the correct way to interpret the results? In the Zenz diagram do we ignore the temperature effect in the transport line? ■