SOLID FUNDAMENTALS

Sizing of Fans and Blowers in Pneumatic Conveying and a mind'blowing' story from the early days!!

Bulkagram 9, January 21, 2021

Greetings and best wishes for the New Year! Hope all of you are well and safe amidst the dreaded 3rd wave of Covid!

Today’s blog will once again reiterate the importance of fundamentals in engineering and of experience in the powder handling field.

Sizing of centrifugal fans and positive displacement blowers-the workhorses of pneumatic conveying- is a critical factor in the design and engineering of dilute phase pneumatic conveying systems. Sizing these equipments for normal air or gas flow is empirical and follows well defined laws of physics. But once you introduce bulk powder or pellet into the airflow, empirical and theoretical equations often become only a guide. Actual pressure drops can vary widely depending on a number of factors of the conveying system from bulk density to particle size and characteristics to capacity to conveying distance to number of bends to number of diverters and on and on…

Many reputed vendors develop their own formulae to arrive at the correct conveying airflow. In our case we use a Product Factor multiple that is input in the calculation spreadsheet as a coefficient.

With more than 2000 installations running for more than 25 years we have finally cracked it!

Blower Room

Which brings me to an early and interesting incident when the Company began with me being the President and the Security Guard! A very venerable and reputed paints company of UK orgin had their headquarters in Calcutta-now Indianized to Kolkata- and got in touch with us for a pneumatic conveying requirement for polymer based pellets. They flew down an engineer to Bangalore to do a reconnaisance on us and once we sent in a bid (with great trepidation we drew up a Rs 3 lakh offer for the system) they asked me to come to Kolkata for finalization. I was very upbeat. There were many stalwart Companies in Kolkata in the field those days including Flakt India which later became SF India. So I was preening myself on this sudden honour from such a large Company. It was only when I met the team at Kolkata that I found that it was not because they found Scorpio the best Company in the world in the business but because a ship was sailing in with the product to be conveyed and was to reach their factory in 40 days. No one worth their mettle was willing to accept such short delivery and so voila! here was the proverbial sacrificial goat in front of them! In any case I accepted the delivery and got the order and started work. I was personally handling this (there was no one else) and moved heaven and earth to get the calculations done, drawings made and manufacure initiated. I managed to despatch in time and was all set for praise and bouquets from the customer. Instead I got a call from their Chief Engineer who made no bones in using very choice language to berate me on the supply - he said his engineers took a look at the fan that was supplied and told him it was grossly undersized and that the system would not perform. Period. The Chief Engineer was a colourful personality which included the shirts he wore. He gave me an ultimatum and said he wanted a re-sized fan in 4 days failing which he threatened to scuttle me and my fledgeling Company using his might. Duly chastened I looked through what went wrong.

Those days I was using Perry’s Chemical Engineers Handbook to do the fan calculations and Mr Perry did not factor in the product factor in the formula in the fan chapter. The fan I designed could only push air- it could not push air and product. I redid the calculations.

But how to deliver a new fan in 4 days? I located a contractor shop in Chennai who was idle and he jumped at this opportunity. So I placed on order on him and went to Chennai to sit with him on the shop floor . From supervising his cutting of the plates to the dynamic balancing of the impeller we spent 48 hours straight with very little sleep and airlifted the new fan to Kolkata. The Chief Engineer was pleased with this customer response (lesson to all Sales and Marketing engineers) and offered me free accommodation in his very British guest house at Rishra complete with complimentary whisky.

A nice end to what could have otherwise been the end of Scorpio Engineering!