Dear mr Kahn,

Trying to read your private message through the forum results in an error message that there is a problem with the database.

We will have to wait until that is fixed.

Selecting a vacuum pump (blower or screw compressor) is almost the last action in the design process of a pneumatic unloader.

Designing a pneumatic (vacuum) unloader starts with the desired specifications.

material(s)

material(s) properties

unloading rate of the (various) material(s)

ship size

dock situation

design suction pipe routing

calculate for the (various) material(s) the required air displacement and pressure drop

(do not forget the rotary lock air leakage)

select vacuum pump according the calculated requirements by consulting pump suppliers (f.i. Aerzen)

Asking a supplier for a quotation of an unloader is also a way to avoid inventing the wheel for the second time.

If you are not satisfied with the quotations and/or the vendor’s response, you can always decide to design and build your own machine, which means that you also have to design all the involved details. (a time consuming and expensive operation and possibly entering a learning curve)

success ■

I assume you are willing to pay for this consultancy service? ■

Dear mr Kahn,

As you informed us, that you want to unload 3-400 M/tons per hour with a blower of only 17.23 m3/min (30 kW) with a 8" suction and a 6" outlet on a 12" hose, I think this is way out of the physical possibilties.

Nature will not allow us this.

If you really want to have a pneumatic unloader, I strongly suggest to contact a manufacturer.

Their price will not be far off the cost you have to spend in case you are building this machine on your own steam.

best regards ■

Teus,

Could be a nice little earner for you :-)) ■

Dear Mr Kahn,

I am sorry that you feel disappointed, that is certainly not my intention.

Let us recapitulate what we have discussed sofar.

1)You have a Rootsblower of 17.23 m3/min 30 kW drive

6” inlet - 8”outlet

Pressure ?

You have tested this blower with a 12” suction pipe in wheat and achieved 7 tons/hr.

The 12”suction pipe has a cross area of 0.0706 m2

Combined with the 17.23 m3 # 0.287 m3/sec, the air velocity will be approx. 4.06 m/sec

As the suspension velocity of wheat is abt 8-9 m/sec, I am surprised that pneumatic conveying took place,

For an 8” suction pipe the air velocity would become 9.1 m/sec, which would be just the under limit for pneumatic conveying but any vacuum would bring the velocity under that limit.

That there was inefficient pneumatic conveying is also shown by the energy consumption of 30/7 = 4.3 kWh/ton, which is very high.

Regarding the inlet diameter and outlet diameter size;

As the blower is in fact a compressor, the gas volume at the inlet is more than at the outlet (compressed gas has a smaller volume). To maintain the same gas velocities at the inlet and the outlet, the outlet can be of smaller diameter then the inlet.

F.i. Inlet 8” and outlet 6” (The other way around would be illogical)

2)Using the Aerzen GMB 16.13 would result in:

Air displacement 140 m3/min = 2.333 m3/sec at 400 mbar vacuum – 120 kW

Maintaining approx 24 m/sec at the intake and at 0.5 bar vacuum, requires a pipe diameter of 0.2 m # 8”

To maintain the material in suspension further in the suction pipe and to keep the velocities at a not too high value, the pipe diameter should be increased further in the pipeline to 10”.

The capacity that can be reached depends on the suction length and elevation.

Assuming an energy consumption of 2 kWh/ton, would result in approx 60 tons/hr.

All these figures are (educated) estimates.

Outside this scope of estimates is the influence of the various intended materials with their different properties on an eventual design. That could lead to a much more complicated design, where blowers have to be switched on and off for different products.

although you mentioned in this forum that you will absorb the cost for an eventual consultancy, I must inform you that this forum is for the mutual benefit (and fun) of the participants and not for acquiring work that can also be performed by the sponsors of this website.

Moreover, I am not really interested in assignments.

Sorry.

best regards

teus ■

Dear Mr Kahn,

The GMB 16.13 is a blower with a pre inlet, which makes it suitable for high vacuums.

However, high vacuum installations only are feasible for powdery products s.a. cement.

In grains, only the normal rotary lobe vacuum pumps are used.

The required power of the GMb 16.13 is probably 220 kW

A GM 150S has the about the same air displacement as the GMb 16.13 VE and therefore will result in the same pipe diameter and performance.

A 250 kW motor allows a delta(p) of 700 mbar in pressure mode but in vacuum mode, only 500 mbar is allowed.

All the remarks in my previous reply are still valid.

best regards ■

The price will depend on the rates chargeable by the consultant who offers his services. You just need to remember you need a consultant with a competancy in this subject otherwise you waste your money. ■

dear Mr Kahn,

Then I need the following information

material(s)

ship size

dock situation

have a nice day ■

Khan Sahab

Try this link

https://forum.bulk-online.com/showth...threadid=13854

This used conveyer might be something of interest to you. ■

Good Day

We are a pneumatic conveying consulting firm who design conveying systems for people on a regular basis.

Unlike Teus who gracioulsy offers his expertise and immense amout of experience on a free lance basis to the forum, our firm does the work and prepares the necessary specifications on a fee basis.

I have attached a profile of our capabilities and if you are interested in our submitting a proposal for your requirements, please send us a request to the email below and we'd be happy to do so.

If you have any drawings of the machine you have designed, please provide a copy as we will need to know suction lengths, etc.

As Teus has already mentined, your capacity requirements and the line size you would like to use are conflicting, but we can make the necessary calculations and tell you what the requirements would need to be once you have provided us with the full information.

Regards

Attachments

microsoft powerpoint - pneumaticconveyingconsultan (PDF)

■

Dear Mr Kahn,

400 tons/hr for wheat/sunflower/rapeseed for Panamax vessels will require an air flow in the region of 900 m3/min – approx 800 kW

Estimated weight of such a machine on tyres could be as much of 300 tons.

Consider Jack’s offer.

A rock phosphate unloader is a quite different machine.

best regards

teus ■

Dear Mr Kahn,

I doubt that the unloaders, you refer to are capable of unloading 60000 - 80000 dwt ships (Panamax(.

Have a look at

http://www.buhlergroup.com/32776EN.htm?grp=60

and you get an impression of such a unit.

all for now

teus ■

Hi guys,

The GLB16.13HV is not the correct machine for your application. The HV stands for High Vacuum and is typically used as a high vacuum booster in front of a vacuum pump in furnace, coating, and semiconductor applications. It sees a max delta p of 50 mBar and usually works in 10-3 vacuum.

The pre-inlet flanged GMB16F13m and GM150Sm can work with around 800mBar vacuum but do not possess the std. nominal flows of their std flanged sister models without the "m" (pre-inlet flange).

Tues' power guestimate is about correct, the GM150S will deliver 151 inlet m3/min at 173KW at 500mBar vacuum.

Start with your material and conveying specs, and then worry about the correct type and size blower you will need.

If you need more than 500mBar vacuum you may also want to consider a rotary screw machine such as our VML M series that usually saves around 20% power in comparison with roatry two or three lobe blowers. ■

Hello Ralf,

It always needs an insider to get to the point.

Thanks.

For the choice between high vacuum and low vacuum unloaders, it is important to evaluate the product.

Generally, you can say that powdery products (cement) can be unloaded with high vacuum systems and products with higher suspension velocities (cereals) are normally of the low vacuum systems.

But there is another issue to attend.

A screw compressor is more energy efficient above a certain load (vacuum).

In reality, an unloader is not always running at maximum vacuum.

Roughly, the clean up phase starts at the moment when half the total unloading time has passed.

From that moment on the average vacuum will be lower than the maximum (designed) vacuum and the consumed energy of a vacuum blower can become even less than that of the screw compressor,

The overall result can easily be, that the blower is more energy sufficient than a screw compressor.

(the advantage in the first half of the unloading is consumed in the second half).

In the 1980’s I was given a turbo compressor by your company and did a 6 month investigation on the performance and energy consumption in comparison with an identical blower installation. Being on the same unloader, this installation also unloaded exactly the same products.

It was then that I found out this difference (and others)

I must admit that a turbo is the worst machine in this application and that a screw compressor will perform better than a turbo.

have a nice day

teus ■

Hi Gukhan,

The HV series is not used in pneumatic conveying at all. It is designed for a completely different process and industry altogether.

Teus explained correctly that your decision between a blower and compressor is related to your vacuum level and how long you operate at that value. Our GM90Sm and GM150Sm pre-inlet vacuum three lobe blowers have been extensively used in this application. The majority of other global manufacturers also use three lobe blowers as well. Especially the exhaust noise can be treated much better with a three lobe blower. Power savings with a VML m series compressor kick in when you operate at 70% vacuum most of the time. Jack can probably tell you what air flow rate and vacuum you will end up needing. I am sure there are turn key system options, or you need to get RFQ's for your blowers yourself. Good luck from here. ■

Hi there,

The standard GM150S would provide you with either 1000mBar pressure, or it can be used in vacuum service up to 500mBar.

I would not attempt a budgetary quotation attempt without knowing that this is really what you need. I will steer you in the right direction once you have flow, pressure, and site conditions (ambient temp, inlet temp, elevation above sea level etc.) I hope this will work for you for now.

Let me know when you have the above information. Good luck and have a great week. ■

Hi Ghazanfar,

Well that was fast. We would still need inlet pressure (operating and design condition); I am assuming you will vent to atmosphere and you are trying to use this machine in vacuum service.

Have a great day. ■

ralf

yes - vacuum service

inlet vacuum is 13" Hg

discharge to atmosphere

regards ■

Hello Jack,

Thank you very much for the information! ■

If the operating vacuum is increased to 15" Hg, the conveying rate will be increased but the blower volume must also be increased to compensate for the higher inlet vacuum.

Regards ■

Hi Gukhan,

I saw what you asked Jack to calculate the 15"Hg flow. If you gave him a material flow rate resulting in the 13"hg vacuum level and respective air flow rate, then going to 15"Hg and more air flow also must mean significant changes to the system layout such as pipes etc., but most importantly your material feed rate will also change. Considering the size and expense of this exquipment you should consider making sure you narrow down your basic material flow requirements since with any change your total equipment cost and size dramatically (not mentioning the overall power consumption. I took Jack's 13"Hg to mean the operating condition with the design condition 15"Hg which with a positive displacement blower means that you will lose a little air volume but not much. Either way the blower can handle both conditions. Please let me if you really want to re-size your system.

Customarily centrifugal machines are not used in this type application at the vaccua mentioned above. The limiting factor is their bell curve flow versus RPM characteristics, which narrow the bandwidth where they will work most effectively. They work very effective within in this range. That is not the case in vacuum unloading. In pneumatic conveying - especially vacuum unloading - your vacuum varies significantly during the conveying process. Diffent operators influence the vacuum level significantly by how they move the inlet nozzle through the bulk material. ■

Dear Gukhan, Jack, Ralf,

Changing 1 of the conveying installation parameters causes also changes of other derived parameters.

In this case (a vacuum unloading) the increase of the vacuum above the designed vacuum causes a decrease in the air mass flow.

This decreases the air velocity at the intake and while the air velocity at the end can be considered almost constant, a decrease of the air density.

The lower velocities lead to a longer residence time of the particles and thereby to an increased pressure drop for suspension.

The lower air mass flow lead to a higher SLR and therefore the energy demand for product losses is also increased.

The lower velocities lead to lower pressure drop for kinetic energy

Air friction loss pressure drop decreases

The pressure drop for lifting stays the same.

Adding all these energy losses leaves us with a positive or negative value.

That means that the outcome of a change can be positive or negative, depending on the working point of the design.

In other words, your estimate or guess can be right or can be wrong.

Therefore recalculation is always necessary.

Changing the vacuum might ask for changing pipe diameters or increasing air flows with influence on other installation components s.a. filters.

A pneumatic conveying system operates normally at the best energetic efficiency at a pressure ratio around 2.

take care

teus ■

Based on operating at 15" hg in the Filter / Receiver, which now raises the actual vacuum at the inlet to the vacuum pump to a higher level, the new air flow requirements can be estimated as follows

18" pipe -- 278 m3/min -- ~ 235 mtph

20" pipe -- 340 m3/min -- ~ 293 mtph

24" pipe -- 490 m3/min -- ~ 432 mtph

Please note that the volumes specified are at atmospheric condtions -- IE - inlet to the conveying system -- not inlet to the blower which will be significantly higher.

Jack ■