Cement is blown along inside a pipe!!! ■

Dear salam1409,

A pneumatic bulktruck unloading system could be as given here below:

Pressurized bulktruck :

tankvolume = 40 m3

cementvolume = 27.5 m3

cement content = 30.3 tons

screwcompressor 12 m3/min at 2.5 bar(o)

Outlet and pipe diameter 6 inches (150 mm)

horizontal length = 15 m

vertical length = 45 m

3 bends

The pneumatic conveying calculation is :

salam1405 sal d

Pressure discharge Cement

Convey length = 60 m

Nu of bends= 3

Pump vol = .2 + .2 m^3/s

q-convey = 0.20 m^3/s

Dia begin = 150 mm Dia end = 150 mm (6 inch pipeline)

Kettle volume = 40.0 m^3

Cement vol.= 27.5 m^3

C-Vessel = 500 tons/hr

Kettle Cement content = 30.3 tons

Pipevolume = 1.06 m^3

Press.- Pipeline Cap. - mu - Syst.Cap.- v-begin - v-end - kWh/ton - res.time

2.500 - 74 - 83 - 60 - 5.2 - 13.5 - 0.57 - 10.43

2.250 - 70 - 79 - 58 - 5.4 - 13.5 - 0.55 - 10.05

2.000 - 66 - 74 -55 - 5.7 - 13.5 - 0.53 - 9.66

1.750 - 61 - 69 -51 - 5.9 - 13.4 - 0.51 - 9.25

1.500 - 56 - 63 -48 - 6.2 - 13.4 - 0.49 - 8.77

1.250 - 50 - 56 - 43 - 6.5 - 13.4 - 0.47 - 8.31

1.000 - 43 - 49 -38 - 7.0 - 13.3 - 0.47 - 7.81

0.750 - 35 - 40 -32 - 7.8 - 13.3 - 0.47 - 7.24

0.500 - 25 - 29 -23 - 9.1 - 13.2 - 0.51 - 6.62

0.250 - 13 - 15 -13 - 10.9 - 13.3 - 0.73 - 5.94

Maximum system capacity : 60 t/hr 2.5 bar(o)

On top of the silo a filterunit has to be arranged as:

Filterarea = 30 m2 (2 to 2.5 times the air volume in m3/min)

Extraction fan = 60 m3/min at approx. 450 mmWC

Safety over- under pressure valve, set at -400 mmWC / +350 mmWC

If you want a higher capacity, a booster system with bigger pipes has to be considered, providing the bulktruck outlet is not the limiting factor.

success. ■

Please provide us your contact no.We will send our person from UAE to discuss and supply the system.

Anil

0091-0-9811055650 ■

Standard cement tanker is approx. 30 tons, rated at 2 barg and has a 4” outlet. Dense phase mode of conveying is used for cement unloading and standard compressor is rated at 2 barg, 7.5 m3/hr. At these conditions the tanker discharge time is less then 30 min for cement. So the flow rate are in the same region as you require.

20 m2 silo filter area is more then enough at these conditions and fan assistance is not essential but reverse jet is essential and also a suitable sized pressure relive valve on the silo. ■

my god john have they built that silo?,

I hope not . ■

Dear Mr Salam1409, Mr Mantoo,

Using a bulk truck (tanker) equipped with a 4 inch pipeline and a 7.5 m3/min compressor will bring 36.8 tons/hr on a 60m pipeline with an elevation of 45 m.

(if you are interested, I can also post the calculation)

This is not the 75 tons/hr which is requested.

Most of the tankers, I see around nowadays, have 10 m3/min and an outlet of 5 inches.

Some of them (the new ones) have 12 m3/min and a 6 inches outlet.

45 m is a rather high silo for a cement bulk tanker, which explains the rather low performance.

The filter size is chosen for the event that a tanker of air is released to purge the pipeline after unloading. The flow rate is under those circumstances rather high and the filter has to cope with that, in order to keep the overpressure in the silo within the allowable limits.

Forced venting is installed to keep the internal pressure in the silo below ambient, in order to prevent dust coming out from possible openings and also buffer air flow surges.

best regards ■

Dr Mr Teus

30 ton cement tanker is easily offloaded in 4” inch line in less then 27 min taken from actual tanker unloading times. This gives about 65 tph since the height is bit higher then normal it will still be in excess of 55 tph. As far as bigger pipe size is concerned atleast in UK I have only seen 6” line on barges used for cement unloading not on road tankers.

As far as filter fan taking the surge from the tanker depressurization, according to HSE (UK) the air flow rate peaks at 13000 m3/hr. So the filter fan will be useless at these flow rates. Furthermore the DEFRA (UK) best practice for silo off loading states that the tanker should not be depressurized into the silo and should be depressurized from the on board tanker filter. Silo’s don’t leak and should not require negative pressure inside to prevent dust emissions.

Regards ■

Hi ,

we use Cement for Asbestos manufacturing and Cement is supplied by a nearby cement Plant . The present Compressor seems insufficient ( Model ZE - 55 ATLAS COPCO Make 2.5 bar Pressure)

Can anyone tell me how to Select an Oil-Free Screw Compressor ( HP , Pressure , FAD etc ) for a unloading of Cement from a Truck to Storage area ?

I can provide more information . Can anyone help with the type of information required ...

Chandan , Lagos, Nigeria ■

Dear Mr Chandan,

The compressor size for pneumatic conveying of cement is dependant on the pipe diameter used.

In combination with the pipe length and number of bends as well as the elevation to overcome, this results in a capacity at a certain pressure. To choose a compressor these input variables have to be known.

Are you really producing asbestos ?

(The asbestos, I think it is ?)

best regards

teus ■

Dear Mr. Teus,

Our requirement is to transport 30 tons cement from the cement tanker to the silo (at distance 20m horizontal, 20m vertical) in 20-30 minutes. Pipe size - 4 inches.

We need a screw compressor of capacity 720 m3 / hr @ 2.5 bar pr (as i was checking your previous replies).

The problem is that this size of compressor is not readily available, and our requirement is very urgent.

Can we select any other screw / reciprocating compressor using the formula "P1 x V1 = P2 x V2" ... Boyle's Law

e.g. 180 m3 / hr @ 10 bar capacity.

There is a pressure relief valve on the tanker. Is there any risk? What precautions to take?

Regards,

Tapas ■

Dear Mr Tapas,

For cement and a 4 inch pipeline, you absolutely need 10 to 12 m3/min (600 to 720 m3/hr) of free air delivery at 2.5 bar.

This is necessary to maintain the required minimum air velocity in the pipeline.

Any compressor with a lower free air delivery will cause a blocked pipeline.

But in case of urgency you can use a rented, oil filled, plant air screw compressor with an almost equal free air delivery in the following set up.

F.i. an Atlas Copco diesel driven portable screw compressor type XAHS 186 com3 or type XAHS 236.

On the outlet, mount a pressure reducer of sufficient size (approx. 15 m3/min) and set the reduced pressure at 2.5 bar.

Connect the reduced pressure outlet to the bulk truck tank with the ordinary hoses and hose connections of sufficient size, as used for pressurized air tools.

Then operate the bulk truck at approx 2.0 bar, as if the compressor belongs to the bulk truck itself.

The screw compressor will operate fully automatic on itself.

Contact the local office of Atlas Copco or another compressor supplier in Bahrain.

When the pressure in the tank rises above 2.5 bar, then the pressure reducer closes, limiting the tank pressure at 2.5 bar and the pressure relieve valve on the tank safeguards the pressure as well and is of sufficient size (>720 m3/hr)

This way of supplying air to a pneumatic conveying system is done before many times.

If you need further information please let us know.

Success ■

Dear Mr. Teus,

Thanks a lot for all the information. It was very clear.

Regards,

Tapas ■

Dear Mr. Jan Deysel,

Please contact Mr. Sergio Saraiva Pais of Atlas Copco, Antwerp, Belgium at sergio.pais@atlascopco.com

Sergio will then provide you the calculations and size the correct unit. ■

Dear dungnguyen,

A bulk truck of 1000m3 is really, really a big one.

To convey 300tph+ through a pipeline of 40 m horizontal an 20 m vertical requires a pipeline of 14” and a compressor of 1.5 m3/sec at 1.5 barg.

The 1.5 barg is because you are referencing to a bulk truck tanker. ■

Dear dungnguyen,

Choking is caused on higher conveying pressures rather than lower conveying pressures.

The 1.5 barg was chosen as a safe operating pressure for a bulktruck.

I know that the operating pressure of bulk trucks range from 1.5 to 2.0 barg.

You mentioned 3 barg

If you operate a 6”pipeline at 3.0 barg, the achieved capacity is calculated at 103 tph

You made a 6” installation at 2.0 barg (operating?) pressure for 100 tph (same length?)

Now you need an installation for 300 tph.

That is 3 times as big or 3 bulk trucks

If you select a 10” pipe with a 1.5 m3/sec screw compressor, the achieved calculated continuous capacity is approx. 275 tph at 3.0 barg (too high for a bulk truck) ■

Dear dungnguyen,

OK.

I noticed from your drawing that you are designing an inland self discharging cement carrier with 2 pressure tanks.

I am not sure that 2 big horizontal tanks with fluidization cloths is the most economical solution.

A big tank for 3.0 bar operating pressure require a big shell thickness and therefore heavy tanks.

However, it is your choice. ■

Dear dungnguyen,

Which model is best for you, I do not know.

Probably 10 pressure tanks @ 100 tons each, as a lot of cement tankers on the European inland waters are. ■

Teus

I think he is actually producing cement asbestos pipe.

Asbestos is a naturally occuring mined mineral like mercury etc

leon ■

Dear Leon,

You could be right, but it was the word “asbestos” that triggered my attention, because, in the Netherlands, it is a forbidden material.

( In the media we here of two old sea ships, that are facing problems with asbestos containing materials on board. One old ocean liner that cannnot be restored to its old glory and another freighter that is refused by the Turkish authorities for scrapping.

The principle :It is your problem, and they have a point)

When I “googled” this material, I found sites where the health dager is emphasized.

f.i www.osha.gov or www.en.wikipedia.org

I was surprised that, although the knowledge of today, there is still asbestos used.

good luck

teus ■

Thank you . Well the locals here still Call it ASBESTOS sheets. It is basically Non-Asbestos Cement Roofing Sheets !

Coming to the topic :

Pipe Size : 3 Inches

No. of bends : 2

Distance of Travel for Cement from Truck to Storage Silo : 15-20 Metres

Any Calculation to Calculate the Air Pressure / FAD of Compressor ? ■

Dear Mr Chandan,

It is a relief to learn that you are not using asbestos anymore for your products.

First step in this case is :

Pipe diameter = 3 inch = 0.075 m

Cross section pipe = 0.004418 m2

Choose terminal velocity of air at approx 15 m/sec for cement

The air volume is then approx. 15 * 0.004418 = 0.06627 m3/sec = approx 4 m3/min

Then your pipeline is modelled and a capacity calculation is made.

The system capacity is rather low compared to the pipeline capacity, due to the

long pressurizing time of a small compressor for a big tank (bulk truck)

Chandan ckg d 08-28-2006

Pressure discharge Cement

Convey length = 20 m

Nu of bends= 2

Pump vol = .06667 + .06667 m^3/s

q-convey = 0.07 m^3/s

Dia begin = 75 mm

Dia end = 75 mm

Kettle volume = 40.0 m^3

Cement vol.= 25.0 m^3

Kettle Cement content = 27.5 tons

Pipevolume = .08 m^3

-----------Pipeline------------- Syst

Press.----- Cap----- mu----- Cap.---v-begin----- v-end ------- kWh/ton------- res.time

2.500----- 59----- 199----- 36----- 6.4------------18.7----------0.24----------2.57

2.250 ----- 56----- 188----- 35----- 6.7 -----------18.6----------0.23---------- 2.51

2.000----- 52----- 176----- 34----- 7.1------------18.5---------- 0.22---------- 2.43

1.750----- 48----- 162----- 32----- 7.6------------18.4----------0.21----------2.35

1.500----- 44----- 147----- 30----- 8.2------------18.3----------0.21----------2.25

1.250----- 39----- 131----- 27----- 8.9------------18.2----------0.20----------2.14

1.000----- 33----- 111----- 24----- 9.8------------18.0----------0.20----------2.02

0.750----- 26----- 89----- 20------ 11.0----------17.8----------0.21----------1.89

0.500----- 19----- 64----- 15------ 12.5----------17.7----------0.23----------1.73

0.250----- 10----- 34----- 9------- 14.6----------17.4----------0.32----------1.58

Maximum system capacity : 36 t/hr 2.5 bar(o)

As you see, all the variables have to be known or calculated before a decision can be taken.

best regards

teus ■

Dear Teus,

You are absolutely right that asbestos is forbidden material (even for asbestos based packing material) nowadays, but the term "asbestos roof" is still used widely, although the asbestos material have been replaced with other environmental friendly material (some use rags for replacement material).

Anyway, thank you for your calculations.

Rgds,

Leo ■

Dear Mr. Teus/ Everyone :

Thank you . The info was very Good. As a layman , I do not understand many of these :

Pump volume ( what is that ? ) - How do you calculate it ?

q-convey ?

Kettle Volume ?

res time

V-begin

V-end

May I also post scenario for other plant of ours ? Here also we use a Single ZE-55 , 2.0 bar Air Compressor , 55 KW . We presently use the system to unload Max of Two Trucks . When we Operate with One Truck , we need to Open & bleed Air from the Header . OTHERWISE , the Compressor loads / Unloads frequently & trips .When Two Trucks are operating there , the Compressor runs OK & operation is smooth. I as wondering if you can give an idea on the Correct Compressor Size for this application . I was thinking of a VSD ( Variable Speed Drive ) because one Compressor Will take care of Two Trucks - and Two trucks are not being unloaded simultaneously always .

This has :

9 bends

Length: 40 Metrers

Volume of each Tanker : 28 Cubic Meter

Pipe dia : 4 inches from Compressor to Header but we use a reducer to reduce to 3 inches before pipe entry into Truck

Operating Pressure : 15-2.0 bar

The truck has 28 Tons of Cement

Unloading present time for a Single Truck is approx : 1.5 hours

I was thinking VSD Compresor is best .

But as you are an expert on the subject , can you provide some insight ?

Regards

Chandan ■

Greetings Chandan,

compressors run either full on or they are off line so VFD is a no no.

Blowers are also run full on or off

Is it possible to remove all those bends and fly straight on with your pipe to the delivery point?

The reason being that every bend or incline is a huge energy drain as low pressure air is used to move product. you will have the same trouble with a compressor.

Is it possible to go up and over your obstructions in a straight line to storage?

Wih out a diagram its hard to see or visualise your situation.

pump volume is air flow ■

Dear Mr Chandan,

pump volume is free air delivery of compressor in m3/sec

Kettle volume is volume of cement tank in m3

res.time is residence time of a particle in the pipeline in seconds

v-begin is the air velocity at the beginning of the pipeline in m/sec

v-end is the air velocity at the end of the pipeline in m/sec

To complete a calculation for your scenario for other plant, I need the conveying pipe diameter.

I cannot find the data of the Atlas Copco ZE-55 compressor.

What is the free air delivery ?

55 kW at 2 barg indicates approx . 12 m3/min

I will wait for your info

have a nice day

teus ■

Thank you Mr Teus .

FAD is approx : 500 CFM

The Conveying Pipe is Rubber Hose Pipe of 3 inch Dia

Basically , it Will be interesting to Know , Correct Compressor Size for :

1 Truck alone

OR

2 Truck unloading simultaneously

Are you using some formulae or some software to size the Compressor Capacity ?

I look forward to your response.

Is Variable Speed Drive a Solution ?

Chandan ■

Mr. Teus :

What is q-convey & mu in your calculations ?

Chandan ■

An option is

1.Unload cement by gravity or smallpressure into a hopper under the tank truck unloading bay.

2. Move cement from the hopper by an airslide to a verticle screw conveyor / belt elevetor to the top of silo. Use airslides to move cement from top of vertical screw conveyor/belt elevator to the silo top opening.

3. The system will require far less power to operate, will be easier to maintain and will have much smaller dedusting units on top of silo as well as feed end of the vertical screw / belt elevator.

Vinayak V. Sathe

15, Rangavi Estate, Dabolim Airport,403801, Goa, India

Tel: +91 832 2538294. email: vinayak.sathe@gmail.com ■

Dear Mr Chandan,

q-convey is equal to the pump volume minus air loss through a rotary lock.

(The air volume of the compressor is not always the same as the convey air volume through the pipe.)

mu is the loading ratio in (kg material per sec) / (kg of air per sec)

The calculation results for one tanker are:

Chandan chan d 09-01-2006

Pressure discharge Cement

Convey length = 40 m

Nu of bends= 9

Pump vol = .236 + .236 m^3/s

q-convey = 0.236 m^3/s

Dia begin = 75 mm Dia end = 75 mm

Kettle volume = 28.0 m^3

Cement vol.= 25.5 m^3

Kettle Cement content = 28.0 tons

Pipevolume = 0.17 m^3

-----------Pipeline------------ Syst.

Press.----- Cap.------mu------Cap------ v-begin------ v-end------ kWh/ton----res.time

2.000------- 28-------26-------18 ----------23.0---------57.3---------1.49---------1.51

1.750-------25-------24-------16 ----------25.0---------57.6---------1.47---------1.42

1.500-------22-------21-------14 ----------27.5---------57.8---------1.46---------1.30

1.250-------19-------18-------12 ----------30.5---------58.1---------1.49---------1.20

1.000-------15-------14-------10 ----------34.3---------58.2 ---------1.57---------1.08

Using the ZE-55 compressor for one pipeline of 3 inches results in very high air velocities

and therefore inefficient conveying (low capacity against high energy demand per ton)

The unloading time of 1.5 hr per 28 tons gives 18.6 tons/hr

In my calculation, this would require approx 2 bar.

Running with this compressor on one truck, a slight increase of cement rate, increases the pressure immediately above the maximum pressure setting of the compressor. (overload)

When you bleed off air, you reduce the amount of convey air making the pneumatic conveying less sensible for cement rate (loading ratio) variations.

When you unload 2 trucks at the same time with this compressor, each truck should get half the amount of air, creating the same circumstances as if you are unloading one truck, while bleeding air off.

The calculation results for unloading a truck with half the amount of air are:

Chandan chan d 09-01-2006

Pressure discharge Cement

Convey length = 40 m

Nu of bends= 9

Pump vol = .118 + .118 m^3/s

q-convey = 0.12 m^3/s

Dia begin = 75 mm Dia end = 75 mm

Kettle volume = 28.0 m^3

Cement vol.= 25.5 m^3

Kettle Cement content = 28.0 tons

Pipevolume = .17 m^3

-----------Pipeline------- Syst

Press-----Cap----mu -----Cap-------v-begin------- v-end------- kWh/ton------ res.time

2.000------35----68-------22 --------11.5 -----------30.7-----------0.58 ----------- 3.01

1.750------32----62-------20 --------12.5 -----------30.7-----------0.56 -----------2.83

1.500------29----56-------18 --------13.6----------- 30.7-----------0.55-----------2.63

1.250------26----50-------16 --------15.0-----------30.7-----------0.54-----------2.43

1.000------22----43-------14 --------16.8-----------30.6-----------0.53-----------2.22

0.750------18----35-------12 --------19.1-----------30.5-----------0.53-----------2.01

0.500------13-----25--------8 --------22.1---------- 30.4-----------0.59-----------1.81

0.250--------6----11--------4 --------25.9----------30.3----------- 0.96----------- 1.61

Unloading two trucks at the same time should take 1hr and 16 minutes at 2 bar.

Using a VSD drive, you can reduce the delivered air volume of the compressor.

But, whether the compressor can cope with 2 bar at half speed needs to be verified with the manufacturer.

The volumetric efficiency reduces leading to higher temperatures and the lubrication also changes.

Increasing your pipe diameters can also be an economic option, but have to be calculated again.

The program. that I use for these calculations, is a result of many years of study and field testing.

The program is also based on a mathematical analysis of the physics of pneumatic conveying.

best regards

teus ■