There can be a number of reasons for choking in the lance but you need to provide some more information i.e.

What is the particle size of the pet coke ? And also diameter of the lance?

Is the lance diameter smaller than the conveying pipe?

Is secondary air injected in the lance ?

Solid and air flows etc. Then a meaningful answer can be given. Picture is worth 1000 words in these cases. ■

There can be a number of reasons for choking in the lance but you need to provide some more information i.e.

What is the particle size of the pet coke ? And also diameter of the lance?

Is the lance diameter smaller than the conveying pipe?

Is secondary air injected in the lance ?

Solid and air flows etc. Then a meaningful answer can be given. Picture is worth 1000 words in these cases. ■

Dear justin,

This is a question referring to the chemical composition of the petcoke, which best can be answered by a chemical engineer or a petcoke supplier.

As Mantoo already stipulated, a number of reasons can be the cause.

You have already observed one correlation between the choking problem and the petcoke characteristics.

The particle size is 88 microns.

Is the petcoke sticky?

Is the pneumatic conveying installation working on the edge and the heavier petcoke over the edge?

Is the blower not worn out? It might be still capable of conveying the light petcoke, but not the heavier petcoke.

Without more detailed information about the installation, it is difficult to come up with ideas.

Some information can be obtained by the pressure of the blower under certain operational conditions.

If the pressure becomes too high and the pressure safety valve opens, then the petcoke is overfed or having a too high pneumatic conveying loss factor.

As soon as the pressure safety valve opens, the conveying air bleeds away and the pneumatic conveying stops.

have a nice day

Teus ■

Dear justin,

This is a question referring to the chemical composition of the petcoke, which best can be answered by a chemical engineer or a petcoke supplier.

As Mantoo already stipulated, a number of reasons can be the cause.

You have already observed one correlation between the choking problem and the petcoke characteristics.

The particle size is 88 microns.

Is the petcoke sticky?

Is the pneumatic conveying installation working on the edge and the heavier petcoke over the edge?

Is the blower not worn out? It might be still capable of conveying the light petcoke, but not the heavier petcoke.

Without more detailed information about the installation, it is difficult to come up with ideas.

Some information can be obtained by the pressure of the blower under certain operational conditions.

If the pressure becomes too high and the pressure safety valve opens, then the petcoke is overfed or having a too high pneumatic conveying loss factor.

As soon as the pressure safety valve opens, the conveying air bleeds away and the pneumatic conveying stops.

have a nice day

Teus ■

(i) Can the petcoke has high V.M. with high CV? how does this two being correlated?

Pet Coke will not have high V.M. Pet coke is a residual product after removal of all VM in the refining operation.

(ii) What are the possible causes of choked lance? Would it be due to clumping/agglomeration of the petcoke? If yes, why would it occur?

Pet coke has a lower softening point as compared to coal normally used for firing in rotary kilns. You can get softening point examined and check if temperature in the lance is exceeding this limit. (Pet is calcined in rotary kilns for making electrode grade carbon). ■

(i) Can the petcoke has high V.M. with high CV? how does this two being correlated?

Pet Coke will not have high V.M. Pet coke is a residual product after removal of all VM in the refining operation.

(ii) What are the possible causes of choked lance? Would it be due to clumping/agglomeration of the petcoke? If yes, why would it occur?

Pet coke has a lower softening point as compared to coal normally used for firing in rotary kilns. You can get softening point examined and check if temperature in the lance is exceeding this limit. (Pet is calcined in rotary kilns for making electrode grade carbon). ■

Dear justin,

If stickiness is the cause of choking (what is well possible), then the solution might be to increase the air flow.

The higher airflow causes a lower SLR and petcoke particles are conveyed at greater inter-particle distances, minimizing the possibility of forming bigger agglomerations.

The higher air velocity keeps the agglomerations, which have a higher suspension velocity, in suspension.

Assuming that the pneumatic conveying is already in the dilute mode, the conveying pressure will increase.

Success

Teus ■

Dear justin,

If stickiness is the cause of choking (what is well possible), then the solution might be to increase the air flow.

The higher airflow causes a lower SLR and petcoke particles are conveyed at greater inter-particle distances, minimizing the possibility of forming bigger agglomerations.

The higher air velocity keeps the agglomerations, which have a higher suspension velocity, in suspension.

Assuming that the pneumatic conveying is already in the dilute mode, the conveying pressure will increase.

Success

Teus ■

First of all high VM and CV will have nothing to do with lance blocking. Pet coke does not agglomerate during conveying on the contrary it is very abbrasive. Lances normally do nor protrude into the kiln so heat is not transferred back. Simple point is if heat can transfer back so can the flame!

It sounds like a conveying issue. I cannot comment on the system unless you give me some details. On the both materials and injection set up. Are you using a RV with fixed speed to inject into the kiln ?

Mr Teus

Kiln injection systems are always “very” lean phase as dense phase will not have a smooth fuel flow; hence flame stability issues which gives the kiln operator nightmares. Injection conveying has its own set of rules and the burner man is “The King” and gets to sets the rules we as conveying system designers follow there instruction.

The systems are always designed at a SLR of 1 - 5 with exit velocity of at least 25 m/s with max. of up to 40 m/s depending on the burner type and fuel etc. On bigger fluidised boilers systems massive ID fans are use to convey pulverised coal from the mills to the boiler in very large diameter pipe at very low conveying pressures and the SLR rarely exceeds 1 in these cases. ■

First of all high VM and CV will have nothing to do with lance blocking. Pet coke does not agglomerate during conveying on the contrary it is very abbrasive. Lances normally do nor protrude into the kiln so heat is not transferred back. Simple point is if heat can transfer back so can the flame!

It sounds like a conveying issue. I cannot comment on the system unless you give me some details. On the both materials and injection set up. Are you using a RV with fixed speed to inject into the kiln ?

Mr Teus

Kiln injection systems are always “very” lean phase as dense phase will not have a smooth fuel flow; hence flame stability issues which gives the kiln operator nightmares. Injection conveying has its own set of rules and the burner man is “The King” and gets to sets the rules we as conveying system designers follow there instruction.

The systems are always designed at a SLR of 1 - 5 with exit velocity of at least 25 m/s with max. of up to 40 m/s depending on the burner type and fuel etc. On bigger fluidised boilers systems massive ID fans are use to convey pulverised coal from the mills to the boiler in very large diameter pipe at very low conveying pressures and the SLR rarely exceeds 1 in these cases. ■

Mr Mantoo,

Thanks for the clear explanation of coal injection systems and the associated issues.

A pneumatic conveying problem under the prevailing circumstances as you indicate is hardly possible.

Nevertheless, Justin is facing this problem.

To Justin,

Did you examine the kind and composition of the clogged material?

If the pressure in a pneumatic conveying system increases, then the velocities decrease in the beginning of the pipeline and stay the same at the end of the pipeline.

As already said, higher density particles will travel more slowly and therefore closer together. However, at “very” low SLR, this effect should be negligible, unless the air velocity becomes too low for the heavier particles. Check the velocities. If they are in the order of 25 – 40 m/sec, as Mr Mantoo indicates, then there is no reason to believe that the blower is the cause.

You stated before that the choking problem started with a more dense petcoke.

Is the choking really at the lance OUTLET?

Success

Teus ■

Mr Mantoo,

Thanks for the clear explanation of coal injection systems and the associated issues.

A pneumatic conveying problem under the prevailing circumstances as you indicate is hardly possible.

Nevertheless, Justin is facing this problem.

To Justin,

Did you examine the kind and composition of the clogged material?

If the pressure in a pneumatic conveying system increases, then the velocities decrease in the beginning of the pipeline and stay the same at the end of the pipeline.

As already said, higher density particles will travel more slowly and therefore closer together. However, at “very” low SLR, this effect should be negligible, unless the air velocity becomes too low for the heavier particles. Check the velocities. If they are in the order of 25 – 40 m/sec, as Mr Mantoo indicates, then there is no reason to believe that the blower is the cause.

You stated before that the choking problem started with a more dense petcoke.

Is the choking really at the lance OUTLET?

Success

Teus ■

Since the density of the pet coke is higher and you are using a volumetric feeder the solid flow rate with pet coke increases. It is highly likely the your blower cannot handle the additional rate.

Other thing I would check will be the wear on the feeder pet coke is very abrasive and excessive wear can increase the air leakage and hence choking issues. ■

Since the density of the pet coke is higher and you are using a volumetric feeder the solid flow rate with pet coke increases. It is highly likely the your blower cannot handle the additional rate.

Other thing I would check will be the wear on the feeder pet coke is very abrasive and excessive wear can increase the air leakage and hence choking issues. ■

Dear Mantoo,

The volumetric feeder issue escaped my attention.

With a SLR of between 1 -5 and velocities between 25 to 40 m/sec, the pressure drop is only very slightly depending on the material flow.

A 20% higher throughput, increases the SLR to between 1.2 and 6.

As the throughput related pressure drops are maybe 20% of the total pressure drop, the increase in the total pressure drop is approx. 20% of 20% = 4%.

If that pressure increase causes the installation suddenly to choke, then the original design must have been or is operating on the edge.

I think this is unlikely (but can be true)

Have a nice day

Teus ■

Dear Mantoo,

The volumetric feeder issue escaped my attention.

With a SLR of between 1 -5 and velocities between 25 to 40 m/sec, the pressure drop is only very slightly depending on the material flow.

A 20% higher throughput, increases the SLR to between 1.2 and 6.

As the throughput related pressure drops are maybe 20% of the total pressure drop, the increase in the total pressure drop is approx. 20% of 20% = 4%.

If that pressure increase causes the installation suddenly to choke, then the original design must have been or is operating on the edge.

I think this is unlikely (but can be true)

Have a nice day

Teus ■

Dear Teus

Velocity is inversely related to SLR or Suspension density. In high velocity conveying systems, chocking occurs at very low loading values even though the conveying pressure is within the blower capacity. ■

Dear Teus

Velocity is inversely related to SLR or Suspension density. In high velocity conveying systems, chocking occurs at very low loading values even though the conveying pressure is within the blower capacity. ■

Dear Mantoo,

If high velocity, low SLR conveying systems are known to get choked, then the mechanism of choking must also be known.

Apparently we are here discussing a system consisting of one lance but regarding your reply to the thread - Pressure Drop in a t-Junction -, it could be well that only one lance chokes out of a series of parallel lances.

Justin,

We need more feedback.

Have a nice day

Teus ■

Dear Mantoo,

If high velocity, low SLR conveying systems are known to get choked, then the mechanism of choking must also be known.

Apparently we are here discussing a system consisting of one lance but regarding your reply to the thread - Pressure Drop in a t-Junction -, it could be well that only one lance chokes out of a series of parallel lances.

Justin,

We need more feedback.

Have a nice day

Teus ■

Dear Justin,

Can you explain how the - Rotary Piston Valve – works?

If it pushes the petcoke through a cylinder by a piston into the pneumatic conveying line, then a sticky material can form lumps in the rotary piston valve already.

Monitoring the blower pressure over a number of burning cycles can show the circumstances where choking occurs.

F.i. a gradual build up of increasing conveying pressure, indicating f.i. a decreasing pipe diameter due to a layer build up along the pipe wall.

In addition, information of the conveying installation itself will be helpful to get an idea of pressures and velocities.

Required data are:

-horizontal conveying length

-vertical conveying length

-number of bends

-pipe diameter(s)

-blower volume (or type and rpm or name plate data)

-blower pressure

-eventual backpressure at end of pipe

-installation altitude

-petcoke conveying capacity

take care

Teus ■

Dear Justin,

Can you explain how the - Rotary Piston Valve – works?

If it pushes the petcoke through a cylinder by a piston into the pneumatic conveying line, then a sticky material can form lumps in the rotary piston valve already.

Monitoring the blower pressure over a number of burning cycles can show the circumstances where choking occurs.

F.i. a gradual build up of increasing conveying pressure, indicating f.i. a decreasing pipe diameter due to a layer build up along the pipe wall.

In addition, information of the conveying installation itself will be helpful to get an idea of pressures and velocities.

Required data are:

-horizontal conveying length

-vertical conveying length

-number of bends

-pipe diameter(s)

-blower volume (or type and rpm or name plate data)

-blower pressure

-eventual backpressure at end of pipe

-installation altitude

-petcoke conveying capacity

take care

Teus ■

Dear Justin,

Thanks for the feedback. We would appreciate if more people would take the effort to do that.

The choking mechanism could be as follows.

-The moisture and oil residue causes the petcoke to be sticky.

-The stickiness of the petcoke causes particle agglomerations with a higher suspension velocity.

-Due to the higher suspension velocity, some agglomerations are not kept in suspension and form deposits in the pipe.

-The effective conveying pipe diameter decreases and the conveying pressure will increase.

-At certain locations (f.i. bends), the petcoke deposit will continue to grow by the impact of the sticky petcoke on an already formed bed. This event can use some time.

-The reduced effective conveying diameter can eventually block the material flow and the system is chocked.

I experienced a similar problem with the conveying of sticky cement. Choking did not occur, because the formed deposit in the pipeline increased the velocity enough to keep the conveying going at a lower rate and the same (regulated) pressure.

Applying a booster, to increase the air velocity solved the problem.

Have a nice day

Teus ■

Dear Justin,

Thanks for the feedback. We would appreciate if more people would take the effort to do that.

The choking mechanism could be as follows.

-The moisture and oil residue causes the petcoke to be sticky.

-The stickiness of the petcoke causes particle agglomerations with a higher suspension velocity.

-Due to the higher suspension velocity, some agglomerations are not kept in suspension and form deposits in the pipe.

-The effective conveying pipe diameter decreases and the conveying pressure will increase.

-At certain locations (f.i. bends), the petcoke deposit will continue to grow by the impact of the sticky petcoke on an already formed bed. This event can use some time.

-The reduced effective conveying diameter can eventually block the material flow and the system is chocked.

I experienced a similar problem with the conveying of sticky cement. Choking did not occur, because the formed deposit in the pipeline increased the velocity enough to keep the conveying going at a lower rate and the same (regulated) pressure.

Applying a booster, to increase the air velocity solved the problem.

Have a nice day

Teus ■

Dear justin2004,

The mechanism of forming agglomerations in a bulk solid caused by liquids is explained in:

http://en.wikipedia.org/wiki/Dispersiveadhesion

Depending on the pressures and temperatures in the conveying pipe, condensation can occur.

The condensed water then can adhere to the particles and through the dispersive adhesion forces, the particles can form agglomerations.

The condensation is most likely always at the same location in the pipeline and the condensed water with particles can also adhere to the wall at always the same location, building up a scale.

The occurrence of condensation depends on:

Air intake conditions: Temperature, pressure and RH

Local conveying air conditions: Mixture temperature, pressure

Material: temperature, hygroscopic, react with water.

Pipe line environment: temperature

Pipeline: heat conduction (insulation), heat radiation

This can be calculated at any position in the pipeline.

Have a nice day

Teus ■

Dear justin2004,

The mechanism of forming agglomerations in a bulk solid caused by liquids is explained in:

http://en.wikipedia.org/wiki/Dispersiveadhesion

Depending on the pressures and temperatures in the conveying pipe, condensation can occur.

The condensed water then can adhere to the particles and through the dispersive adhesion forces, the particles can form agglomerations.

The condensation is most likely always at the same location in the pipeline and the condensed water with particles can also adhere to the wall at always the same location, building up a scale.

The occurrence of condensation depends on:

Air intake conditions: Temperature, pressure and RH

Local conveying air conditions: Mixture temperature, pressure

Material: temperature, hygroscopic, react with water.

Pipe line environment: temperature

Pipeline: heat conduction (insulation), heat radiation

This can be calculated at any position in the pipeline.

Have a nice day

Teus ■

Hi Kit Joy,

That pet coke with a lower oil residue prevents choking is valuable information for the forum members. Thanks for sharing.

A lower particle size (<170 mesh # <88 micron) should be no problem.

Probably the air flow rate can be reduced then as well, which saves energy.

The moisture content of the pet coke must be as low as possible (<0.5% ?).

At least lower than the moisture content of the presently conveyed pet coke.

Moisture condensation can be prevented by proper cooling and drying of the convey air.

The compressor choice influences this parameter.

A recalculation of your existing installation will show the effects to be expected.

Have a nice day

Teus ■