Dear Mr. Bogdanov,

Please go back to your User Profile Field and register completely if you want to receive advice from our members.

Thank you.

The Adminstrator ■

Dear yury.bogdanov

Particle size and particle density are also important to know.

Then I can calculate the existing system and hopefully trace the possible areas of concern

Using a pressure transmitter on the tank is a good way to monitor the functioning of your system, but wait untill I made a calculation

Take care

Teus ■

Dear Yury.

Attached the calculations, based on your information.

The pneumatic conveying system is mainly for conveying air, as the Solid Loading Ratio (SLR) is only 1.3 (kg/sec material)/(kg/sec air)

The air pressure loss is 82% of the total pressure loss.

The reason is the far too high air volume of 30 m3/min (0.5 M3/sec), resulting in a very high energy consumption (18.5 kWh/ton)

Some improvement must be possible here.

Increasing this installation to 8000 kg/hr requires a completely new design.

I responded to your idea of installing pressure transmitters.

Have a nice day

Teus

Attachments

pvcpowdercalc (PDF)

■

Dear Yury,

I understand that you increased the pipediameters in the past, but that did not work out well.

An increased pipe diameter is indeed one of the options to improve the performance.

Obviously, you had the same opinion; otherwise it would not have been tried.

In what respect did the modification fail?

Capacity, stability?

In quoting performances, it is always very important to mention the respective pressure drop.

I assume that you still have the replacement pipes and I can recalculate for those pipes and find out the conveying difference.

Can you supply those pipe sizes?

A new design results in an optimum conveying installation with minimal energy consumption and can be based on low pressure and high volume or on high pressure at low volume.

Both systems with an almost equal power.

A new design does not mean necessarily a higher pressure.

Also, have a look at the following links:

Pneumatic conveying, Performance and Calculations:

https://news.bulk-online.com/?p=65

Dense phase- or dilute phase pneumatic conveying:

https://news.bulk-online.com/?p=238

Pneumatic conveying, turbo- or positive displacement air mover:

https://news.bulk-online.com/?p=309

Energy consumption per ton of a pneumatic conveying system:

https://news.bulk-online.com/?p=331

Pneumatic conveying, an unexpected relationship.

https://news.bulk-online.com/?p=445

Success

Teus ■

Dear Yury,

The calculation program, which I use is not available on the market.

I developed that myself over the last 28 years and it is still being developed.

Coming back on the first installation (the start of this thread)

A fluctuating feeding into the pipeline can cause a too high SLR and because of this, the pressure becomes too high and the safety valve of the blower opens and air is bypassed to the atmosphere. The SLR increases then even more and the conveying halts.

This can be detected by observation and (if mounted) a pressure sensor with a recording laptop.

The feeding control must then be improved.

I will study the second system for the same PVC powder.

What are the problems?

take care

Teus ■

Dear Yury,

Attached the calculation of the second installation.

The 2 installations can be compared as they have approx. the same sizes:

Installation 1

=============

Length 151 m

Diameter 102 – 114 – 127 mm

Bends 9

Air volume 0.5 m3/sec (30 m3/min)

Air velocity 41 m/sec

Capacity 3.25 tons/hr at 7590 mmWC

Capacity 8.1 tons/hr at 9500 mmWC (pressure drop/m = 62.9 mmWC/m)

Pressure drop/tom/m = 7.76 mmWC/(ton.m)

Energy consumption 18.62 kWh/ton

Installation 2

============

Length 148.5 m

Diameter 102 – 114 – 127 mm

Bends 12

Air volume 0.297 m3/sec (17.8 m3/min)

Air velocity 21 - 25 m/sec

Capacity 11.1 tons/hr at 9500 mmWC (pressure drop/m = 63.9 mmWC/m)

Pressure drop/tom/m = 5.76 mmWC/(ton.m)

Energy consumption 3.99 kWh/ton

Installation 2 is much more efficient than installation 1

(If the given data are correct)

Although the geometry of installation 2 is almost equal to geometry of installation 1, the capacity of installation 2 is 37% higher at almost half the velocity.

From the pressure readings follows a cycle time of approx 240 to 270 sec

Vessels of 0.35 tons gives a capacity of 3600/270*0.35 = 4.6 tons/hr (average)

However, the curves also show that the pressure is most of the time limited at 1 bar.

At that moment, the spring loaded relief valve is bleeding air and although the pressure is high the capacity can be low.

There is also a considerable period, in which the pressure does not reach the limit of 1bar.

This indicates that the line feeding is not consistent.

Resume:

A lot to figure out.

All for now

Teus

Attachments

pvcpowdercalcl2 (PDF)

■

Dear Yury,

The calculations of line 2 give no reason for expecting problems with choking pipelines.

The velocities are even still much higher than necessary.

In addition, you are referring to product velocities after the bend (11 m/sec) and these are also higher than necessary.

The air velocity of a pneumatic conveying system is chosen in relation to the suspension velocity of the material and the Re-number, which is a measure for the wall velocity.

Roughly, the air wall velocity is 1.5 times the local suspension velocity. This to prevent sedimentation.

Be skeptical about the table you use.

Increasing velocities in these 2 systems is the wrong way to go, as the velocities are very high already.

Checking the feeding stability of the systems at the location is the best way to proceed at this moment.

I will extend the calculations as indicated (also with the actual blower now)

If you have the pressure transmitter still in place, can you execute another measurement with a higher resolution ( 1 second readings for 1800 seconds).

Have a nice day

Teus ■

Dear Yury,

The pressure tank is filled, when a level switch is activated.

Checking the safety relief valve for bleeding air during conveying is OK. (Must be known by the operators already)

If you change the installation or installation settings, always do one change at a time and then do the observations. Otherwise it is later unclear, which effects were caused by which changes.

Sometimes one change has a counter effect on another change and the final result will be zero, leaving you with a wrong interpretation.

Moreover, the calculation program can predict consequences and makes it easier to observe the installation after the change has been made and generate more understanding.

We will wait for the pressure transmitter measurements.

Attached the calculations for the 2 installations, using the blower from the blower sheet.

In your own calculation, you used the “PRODUCT FRICTION FACTOR 2 (1-LOW, 8-HIGH)”. The value 2 seems arbitrary to me or is it based on actual measurements?

I used a friction factor of 3.2318*10^-11 (related to a formula in my program) based on some other data from existing installations from forum members.

After we have the pressure readings with the accompanying capacities, a more accurate product factor can be derived and calculations that are more accurate become possible.

All for now

Teus

Attachments

pvcpowdercalcline1_blower (PDF)

pvcpowdercalcline2_blower (PDF)

■

Dear Yury,

Compressor data are always related to intake conditions.

The inlet conditions are standardized and if the inlet conditions vary from those standard conditions, it is easy to correct for those.

Whatever the intake conditions are, they are considered to be constant in time.

However, the outlet conditions are depending on the delivered pressure, the outlet temperature (also depending on the pressure) and the internal leakage (also depending on the pressure).

The constant parameter is the internal displacement of the blower.

This internal displacement minus the internal leakage is the actual displaced volume.

The mentioned 12.05 m3/min is at a certain pressure and temperature and certainly not the displacement of the blower. The pressure and temperature are not mentioned.

In the calculation program, the air volume in the pipe is automatically calculated, depending on pressure, ambient temperature and material temperature. These conditions are recalculated every 0.001 second in the pipeline.

Attached the calculated blower performance table, based on the blower data curves.

You are correct about the slightly different particle sizes, not having a significant influence on the calculation results.

The SLR is defined as (kg material/sec)/(kg air/sec).

The kg air/sec can be considered almost constant (varies only slightly with pressure)

The kg material/sec is depending on the material outflow from the pressure vessel.

This outlet material flow is depending on the flow properties of the material in the pressure vessel during emptying and cannot be considered the same for every batch that is loaded.

There will always be fluctuations in the out flow rate and as a result of this, the SLR also fluctuates.

To control the feeding rate, a pressure controlled vessel by pass valve is installed.

In case the pressure is too high (too high SLR) then this valve opens and bypasses more air around the vessel. Then, less air is going through the vessel and less material is picked up, resulting in a lower SLR.

In case the pressure is too low (too low SLR), then this valve closes and bypasses less air around the vessel. Then, more air is going through the vessel and more material is picked up, resulting in a higher SLR.

The pressure drop in a pneumatic conveying system (= compressor pressure) is depending on several parameters;

-Air pressure drop (1/2*air density*air velocity^2 and is pressure depending)

-Acceleration pressure drop (SLR*1/2*material density*material velocity^2 and is pressure depending)

-Suspension pressure drop (SLR and suspension velocity depending)

-Elevation pressure drop (SLR depending)

-Material velocity loss pressure drop (depending on SLR and turbulence and material properties)

From this summary, it can be concluded that the SLR and the material properties have a direct impact on the total pressure drop.

Higher SLR results in higher pressure drop.

In case of irregular feeding, the pressure drop is also irregular.

To keep the pressure fluctuations within the limits, it is necessary to keep the feeding under control.

The attachment is missing.

Probably, you have to convert the xls-file to a zip-file or a pdf-file.

All for now

Teus ■

Dear Yury,

Referring to the pressure transmitter curve; Is the range (f.i. 0 to 1 bar) limiting the measured values?

Make sure that the measuring range of the transducer is f.i. 2 times the highest expected measured value.

best regards

Teus ■

Dear Yury,

Increasing the blower speed will not decrease the pressure by itself.

The pressure is a result of the flow resistance in the pipeline.

The higer SLR will reduce the pressure drop, however, the increased velocities will increase the pressure drop at the same feeding rate.

The one of the two effects which will be the strongest determines the resulting pressure.

The electric motor of 45 kW limits the pressure at a lower value, when the rpm is increased.

For the time being, only measure and investigate

Cheers

Teus ■

Dear Yury,

The safety valve is located in your diagram between the exhaust silencer of the blower and the non-return valve to the tank.

It only serves as a protection against overloading the blower and should normally never open.

When it opens, the airflow through the pneumatic conveying system decreases and chokes.

There are 3 manual regulating valves:

1) Top air to the tank

2) Bottom air to the tank

The setting of these 2 valves is to control the mass flow in the tank in such a way that the flow is not too much and smooth.

One of these 2 valves must be fully open to avoid too much unessary pressure loss.

3) The tank by pass valve (V06) (Also known as “EXTRA AIR VALVE”)

This valves controls the average setting of the SLR as described in my earlier reply.

Parallel to V06, there is an automatic extra air valve, fine regulating the pressure at a constant value, which corresponds with a constant SLR (= Capacity)

I also described the functioning of this control in my previous reply.

The system is properly set up.

There is a possibility that the settings of the valves and the opening pressure are wrong.

It is certainly advisable to check these.

Success

Teus ■

Dear Yury,

Did you enjoy your stay at the plant?

It is there, that you learn to become an engineer.

For me, it was always the highlight of my work, cooperating and making fun with the operators.

Sometimes they have the most unbelievable humor.

Concerning line 1

The in line valve V06 is now switched as a shut off valve when pressurizing the tank. (Otherwise, the tank would never be pressurized)

Pressure regulation can now only be done by setting the 3 mentioned manual valves.

It is not an automatic system.

Pressurizing through Valve 04

Conveying starts with the opening of valve 06 and valve 02.

Having the pressure switch in the clean supply line is OK. It measures the same pressure as in the tank.

SLR sensors do not exist for industrial use.

If the motor of the line 2 blower is different from the motor of the line 1 blower, then it is necessary to check the nameplates of the blowers and motors and V-belt drives.

The diagram of Line 2 is a bit unclear.

It looks like a tank with a fluidized bottom with fluidizing air from below.

The material outlet is then from the top, but there is no internal pipe drawn.

In this case, there is also a short cut between the fluidizing air supply pipe and the conveying pipe.

Assuming the other way around (bottom pipe is material outlet) makes the fluidized bottom obsolete.

Functioning and build as drawn of this system must also be checked.

Checking the valve- and pressure settings for next week.

Have a nice weekend

Teus ■

Dear Yury,

Line 1:

The ball valve in series with V06 is a manual valve (extra air valve) for setting the SLR.

Opening this valve reduces the SLR and closing this valve increases the SLR.

Additional setting the SLR is done by the settings of the ball valves in the bottom- and top supply lines of the tank.

Open the extra air valve.

Start with open bottom valve and closed top valve.

Start conveying. (The convey pressure should be low under there conditions)

Open the top valve gradually and monitor the conveying pressure. (Should increase step by step)

When the top valve is fully open and if the pressure is then still not high enough, then starts closing the extra air valve in small steps, while monitoring the conveying pressure.

Then, when the conveying pressure is approx. 90% of the maximum allowable pressure, the settings are reached.

By closing the top valve and opening the extra air valve again, conveying stability can be influenced.

Line 2:

It is hard to believe that the drawing of line 2 is in conformity with the as-build situation.

-Pipe 100-TN2505 (on the right of the drawing) short cuts the airflow into the conveying pipe. The function of this pipe is not clear.

-The extra air valve is located in the drawing above ZSH2242 and is followed by a non-return valve in the wrong direction.

-In the tank is a fluidized bottom. The tank-air supply pipe in the side should be under the fluidizing pads. This is an efficient way to fluidize the material properly and generate a smooth and stable material flow.

Setting the conveying pressure for line 2 is done similar to the setting for line 1.

Success

Teus ■

Dear Yury,

The setting procedure can be executed while conveying.

No dismantling is necessary. (Manual valves)

However, you are interupting the material flow for a while.

Coordinate this with the operators.

Success

Teus ■

Dear Yury,

Line 2:

The suspected “coil” represents a flexible rubber sleeve in the pipeline, which is clearly shown on the picture in line 100-TN2501 (not 100-TN2505)

The functioning of pipe 100-TN2505 is still unclear. There is an actuated butterfly in that line.

The PLC- program determines the action of that valve and can show the purpose.

I do not think you need flow meters right now, as the conveying pressure is the main information of the performance of the systems.

Blower pressure or tank pressure meters/sensors are therefore important.

Further:

In line 1 is a cooler (SC) installed after the blower and a water drain is foreseen.

This device cools and dries the conveying air.

Is cooling not necessary to protect the resin from too high temperatures?

have a nice day

Teus ■

Dear Yury,

Indeed, the presuure curve tells a lot about the pneumatic conveying system performance.

I will study the graphset diagram

Have a nice day

teus ■

Dear Yury,

The graphset is describing the sequence of filling, discharging and switching.

When the tank is filled, detected by the high-level tester (LSH) or a timer, then the discharge cycle begins without pressurizing before the outlet valve opens.

The by pass valve V06 (=CV6924) is then closed.

It seems that, if the tank pressure becomes too high (PSH) then the discharge process is aborted by the condition “PSH IS ACTIVE”.

The discharging is stopped by opening the bypass valve (CV6924), closing the pressurizing valve (CV6925) and closing the discharge valve (CV6921).

The tank is then shut off, most likely with material and pressure inside.

The condition “not LSL” (Low-level tester not active) and “not PSL" (tank pressure < PSL) are not fulfilled and halt the next step (see START) and the system is hang up.

I think it is time now to go on side and do the fieldwork based on the gathered information and knowledge.

Success

Teus ■

Dear Yury,

As far as I could follow your calculations, I would say that the math is Ok.

However, you must have made other calculations or measured data too.

If you have calculated the airflow, capacity, and pressure drop, it is not necessary to calculate the SLR separately, because that value is used in your calculations.

Therefore, I assume that you have measured values from an existing installation.

A time efficiency of 55% for a blow tank system must be a single vessel system.

Then you want to increase the capacity of the same (?) system to 8000 kgs/hr, by proportionally increasing the airflow and keeping the SLR and the pressure constant.

This is not allowed in pneumatic conveying, because everything else changes too.

Actually, you created a new installation.

Velocity increases, because the airflow increases and therefore the air pressure drop increases too.

The pressure drop for product collision losses increases also, because of the increased velocities. (SLR = constant).

The pressure drop for keeping the resin in suspension decreases because of the higher velocity (the time that the resin is kept in suspension is shorter).

Pressure drop for elevation stays the same.

The pressure drop for acceleration increases, because of the increased velocity.

The sum of the changed pressure drops is not zero and therefore the calculation is not valid.

This is the reason why the calculation of pneumatic conveying installations is such a complex iterative process that always starts with a starting value. (A guess)

Best wishes

Teus ■