The following paper has NOT been altered whatsoever. Some notes a) A.E.S. stands for American Electroplating Society. b) the mention of l¼ million cfm is now incorrect as it is well over 3 million cfm c) The Grandview E.C.E. scrubber is a condensed name for Eliminate, Coalesce, Eliminate …. and this design is called by various names such as LMS …low micron scrubber and LMITS …low micron inertial type scrubber. d) the common scrubbing agent was always NaOH ….until the inertial blade type scrubbers appeared where by happen chance one found out that ordinary water was OK e) Bright Dip is the name given to a nitric phosphoric mix for cleaning aluminum, enormous ‘fumes’ are generated ! At STAYSA in Brantford I used to use an alkali to scrub the fumes using, like everyone else did, NaOH, as this plant was in a valley and the air monitoring people would check it out frequently … and then, during a visit, I checked the alkaline tank but the immigrant operator, whose English was poor, said … Only Aqua, aqua, aqua …. thereby indicating that the neutralizing liquid was NOT alkaline but just ordinary water. f) CFM stands for cubic feet per minute.e) italics stand for insertions and explanations as of July 2007 … 30 years hence.
The author, Freeman Newton, has held various papers on plastics in the past including “Ventilation and the possibility of Air Recycle” at the l976 A.E.S. conference. He has been deeply involved in eliminator concepts, imported the T-100 blades into North America and is the designer of the Grandview E.C.E. inertial scrubber.
THE PLATER AND AIR POLLUTION
Does the present dayplater have greater overheads than his predecessors ? Of course he does ! One of the main reasons lies in the increasing costs of pollution control. This article deals with exhaust air requirements, suggests some ways of reducing CFM, and reports on the importance of ‘Dry Scrubbers” why dry scrubbing techniques work and how they can be used.
No one likes a burocrat nor do we like to be told to do this or do that particularly as this and that involves not only a cash outlay but also recurring costs (eg. conventional scrubber operations) There are the Dept. of Labour (Ontario) requirements for a safe breathable in-plant environment. Having satisfied their standards, the exhausted air has then to meet the Ministry of the Environment (Ontario) air pollution standards. Should you politely ask the authorities what CFM you should exhaust, you might end up having an excellent exhaust system …but pay a fortune in heating costs. They will be or can be very helpful but their task is to try to ensure a safe environment, to vet designs, to set standards …but not to design ventilation equipment.
A very good book is INDUSTRIAL VENTILATION (Box 453, Lansing in Michigan, USA) . This is an excellent reference book whether you want to vent a tank or design a garage exhaust system. It shows fumehood designs and tables for calculating the amount of air (CFM) that a given process requires. If it errs it is because it uses inbuilt safety factors. Use it and the extraction will be very good – but again at a cost in BTUs.
In July 1977 the cost of one solitary CFM in terms of fuel required to heat the air to 65°F (24 hour operation) in the Toronto suburbs was 58¢ for oil and 36¢ gas per CFM per year. Can we save energy when we have got to exhaust some process? No. But you can design an extraction system that allows you to reduce the CFM and hence the fuel bill. In the case of some acids (eg sulphuric) or alkalines you could air recycle and save considerable fuel costs.
VENTILATION DESIGN - Caveat Emptor
You can pay initially less for a poorly designed ventilation system or one using incorrect materials (eg. galvanized steel for Chromic) but you will end up paying much more in the long run !
Maybe you should be a little suspicious of anyone trying to sell you an extract system. Is he just trying to make a sale? Does he take your problems to heart, does he know his materials, is he capable of proper design (if so, check out his past performance), does he use slot adjusters and/or dampers (an absolute must !), can he reduce your CFM ? Other considerations are the type of fan, will it or should it require vibration isolators – and especially will the final system meet existing pollution standards?
The name of the game is CONTROL. If you can capture the emissions at source: if you can reduce the “width or length” of your tanks, you will reduce not only your heating bill but then also negative air conditions.
One way is to regard your tanks as if they had tight fitting lids into which you had to cut a hole just big enough for your rack or whatever. Anyhow where feasible why not at least shroud the areas that the anodes or cathodes take up. This area only contributes to higher CFM costs.
Progressive Anodizing in Toronto came up with the idea of making up a simple narrow semi-immersed hoodlet to collect and vent off all the hydrogen bubbling up from the cathodes. Now there is much more to this idea than meets the eye. In this case (Sulphuric anodizing) the bubbles of hydrogen burst in a typical fashion as they hit the surface and form very small droplets of acid. In other words, theoretically, most of the exhaust requirements in this situation are due to this local electrolytic action. This means that the rest of their push-pull 50 foot ventilation system should be able to reduce CFM requirements way, way below the so-called standards. Intelligent thoughts, well executed, mean less precious fuel being consumed in wintertime.
GAS STREAMS DO NOT EXIST!
Nearly all ambient temperature emissions of acids or alkalines are NOT gas streams. The term “gas stream” is a vague definition so often repeated that it is accepted as a fact.
The great majority of environmentally hazardous acid or alkali fumes at ambient temperature emissions consist of invisible to the eye droplets of liquid in an airstream are in the 2µm to 40µm range.
This phenomena is not generally realized by most engineers or chemists – and therefore they are blissfully unaware that inertial devices (especially the very high efficiency horixontal eliminators) can be just as effective as wet packed tower scrubbers in some cases – and yet operate ‘dry’, hence virtual collection of all the acid fumes and no demand for alkali scrubbing liquors.
In the plating industry this is definitely the case with Chromic … or Sulphuric … or Phosphoric etc … and to a lesser extent with Hydrochloric but only to a minor extent with pure Nitric.
The worst of the common acids is Nitric and the associated thoughts of NOX and brown plumes. Mixed with HF, Hydrofluoric, the most dangerous acid as far as skin contact is concerned, you have a very potent mix. Nitric acid fumes contain NHO3 droplets plus NO, N2O4, N2O3 as well as NO, the cause of the brown plume.
NO2 PLUME REMOVAL
NO2 brown plumes are not easy to remove as many a plant engineer may bear witness. The reddish brown plume is bad for three reasons. Firstly it is an eyesore (and many a complaint to the authorities is based on a visible plume). Secondly, it probably masks other emissions. Lastly, it eventually combines with the air moisture and sunlight to reform Nitric acid as do also the other NOX components.
Even to-day some people or Companies have not been able to remove it. So there is a certain amount of negative it-can’t-be-done feeling based on solid fact ….but fact based on conventional methods.
There are, in the ambient temperature spectrum, two types of NO2 plumes (EPA, please note !). The dry condition and the wetted plume where other chemicals are also vented in a common system containing the nitric fumes. The dry emission is much more difficult to conquer as the brown plume is a pure gas. The solution ? So far inertial separation can be made to work for the wetted airstream but the dry plume must somehow be moisturized and then removed intertially.
WHERE ANGELS FEAR TO TREAD
My thanks go to the manager of a large Ontario plating plant (Kuntz Electroplating) who was venting a hot nickel strip tank (concentrated nitric). He said he was sure that his brown plume was wet. At that time we had serious reservations about nitric plumes (which is another way of saying that we were scared witless).but based on what he had said, we felt sure we could remove hit wet brown plume. It turned out hat we were both quite wrong.
The apparent wetness of his plume was due to droplets of pure nitric. The first attempts of removing the plume itself failed, a few modifications later and the plume disappeared. Had we both known the true facts beforehand we probably would never have used the inertial approach. There will be disbelievers but you cannot knock success even if it is arrived at by roundabout means.
THE INERTIAL APPROACH
viz.. the capture by inertial deflection and consequent impaction of droplets onto a mist eliminator profile.
Grandview have been airflow engineering and making mist eliminators using sine-curve vane profiles for over five years. Well over l¼ million CFM of dry scrubbers has been made in its Mississauga plant Toronto plant involving, in most cases, virtual total acid recovery and therefore amortization of equipment costs to the end user.
The so-called T-120/2 ( 2 banks of T-100 blades @ 20 mm centres) goes down to 10 micron capture, the recent Grandview, my, invention of the E.C.E. inertial scrubber goes down to the 2 or 3 micron range – with one Company reporting 0.5 micron acid capture using reagents. The E.C.E. being particularly suitable for NO2 plume removal in such operations as Brightdip etc. Actual tests by INCO # 2 RESEARCH indicated removal of 0.2 to 0.8 microns at 86% efficiency. This was in a sulphuric airstream.
This technology has helped Grandview considerably to export their products – technology gained by theory and then experimentation. However to many people, the word ‘mist eliminator’ is synonymous with many relatively crude droplet devices. Droplet capture from a generating device such as a packed tower, wetted cyclone etc is fairly simple to achieve. But to produce a sophisticated eliminator (eg. dry scrubber) requires careful airflow engineering of all the components ! (ie. inlet transition angle, sump depth, blade overlapping)
The failure rate has been surprisingly low – on the other hand it was initially extremely difficult to persuade customers that the high velocity inertial route would work and solve their problems particularly as in those earlier years we could not draw on anyone else’s experience in this field. In retrospect it appears that Grandview was the first Company (in North America) and maybe in the world to very successfully remove various acid emissions, recycle the chemicals, meet pollution standards – and yet thereby often permit the end user too amortize his investment by acid recovery.
Remember, within the previously mentioned stipulation, GAS STREAMS DO NOT EXIST ….. and if they do not exist, just what is the point (and cost) of using a packed tower scrubber when inertial capture may work?