http://www.environment.power.alstom....553051496.pdf ■

Multi-cyclones (small diameter, highest collecting efficiency) were typically used in cement plants until 30 years ago. They were good for high temperatures, up to 400 deg.C and high gas flows.

Their collecting efficiency is not good on particles below 10 microns so there are always visible emissions. Now they might be used as pre-collectors where the dust load is heavy, but will be followed up by a bagfilter or scrubber.

Bagfilters will collect sub-micron particles with no visible emissions. They are relatively insensitive to changes in dust loading or article size.

ESPs are good for fine particles, high gas flow but low dust load. ESPs are highly sensitive to the chemistry and electrical properties of the gas and the dust (including cement applications). This is the main reason they are no longer used in power station applications in Australia.

Michael Reid. ■

The selection of control equipment is going to be dependent on what kind of emission rate they have to meet, as well as the particle size distribution of the dust in the gas stream.

The cyclone is good on large particles, but requires very high pressure drops to drive the cut line down on the finer particles. Reasonable outlet emissions on particulate greater than 15 micron would be 25 mg/Ncm. Any size less would be much higher than 25.

ESP's are reasonable for some of the hot applications, but are poor on the high loading, fine particulate. Emissions will vary all over the map relative to application and loading. Will not meet the lower requirements we are now seeing.

Fabric filters appear to be the path that is being taken everywhere where emission limits are being lowered. Filters are constant outlet devices and can meet the lower emission rates with more conservative designs. ■

Suppose I was the manufacturer of Dyson Vacuum Cleaners(Bagless by definition & selling like every housewife wants pharmaceutical cleanliness) & prepared to delve into a less profitable heavy engineering enterprise.

"The hand that rocks the cradle rules the world." It seems to be just a matter of market size.

Cut off Tromping excuses seem to deride the public perception of the convenience gained by obviating dirty bag cleaning. Perhaps bag filters are living on borrowed time. ■

I'm sure James knows exactly where money is to be made, and it isn't selling kit to industry! ■

Actually it seems the opposite is true in the case of industrial filter bags. The EPA is taking a step forward and has actually certified filter medias that meet the U.S. EPA standards of PM 2.5. In fact the U.S. government is offering tax credits to companies that use those certified filter medias within their baghouse or dust collector. As a matter of fact Midwesco offers 5 of the 6 certified medias to their clients today.

See http://www.epa.gov/etv/vt-apc.html#bfp for more details. ■

In the Netherlands the emission level is now reduced to 5 mg/N.m3. This is also in the cement industry easely to reach with a wetfilter. Using such a system you having not the costs of filtermaterial changing and the usage of pressed air for cleaning the filters. In General the a wet filter is sheper as a bag-filter.

Ofcourse the cement is destroyed coming out of a wetfilter. Therefore very offen a cyclone is used in combination when the dust amount in the airstream is very high. ■

I've attached a page with a graph showing there is no comparison between cyclones and Fabric filter dust collectors (see graph curve after the filter has been coated during recommended start up run. As for e precipitators, I found this quote, Electrostatic Precipitators Also called electronic air cleaners or ESP, electrostatic dust collectors also collect fine particles.

As far as dust collection is concerned, ESP is pretty limited.

Electrostatic cells do well with smoke and mist, but will load up very quickly with any amount of dust greater than light atmospheric. Like HEPA, most ESP is best used for ambient air cleaners. Although, extremely large electrostatic precipitators are used in smoke stacks to remove fly ash.

Ron

Attachments

cyclone separator vs bag filter (PDF)

■

The attachment that you provided addresses the wood industry only, do you have any evidence that would support other industries, such as the cement, lime, metals, waste to energy, cogeneration, utiliity?

As mentioned before cyclones are very good at capturing large particulates in the air. Infact cyclones are used many times infront of the baghouse to capture the large particles/sparks in the gas stream. The filter bags/medias are used for capturing smaller particulate to reach the EPA's emmission requirements of PM2.5. Many times the porosity is reduced by using different fabric finishes such as ePTFE membrane. ■

The argument comes down to this: if you are collecting cement dust, use a bagfilter.

Michael Reid. ■

Mall,

it all depends on:

- dust particle size distribution

- system design

1. If you have, for example, sand and dust as your particulates, the cyclone will collect most of sand particles, while the baghouse will collect dust. So if your baghouse has an inlet baffle or tangential gas inlet, adding a cyclone will not save you much because bigger particles will not be collected on the filters anyways.

2. If you have dust (ultra fine, below 10 micron) then your cyclone will not probably collect much neither.

3. Another factor is cage/bag clearance. If the cages are properly sized, filter bags will not experience a lot of wear due to the flexing. Otherwise, that might also affect bag lifespan.

4. Assuming that your cyclone collects dust that would otherwise go to filters, reduced pulsing of the bags (let's say by half) would prolong filter bag life by 30-40 %.

Just wondering, what kind of high efficiency separator do you have upstream of your cyclone? This tells me that your cyclone must also be of high-efficiency type, able to further reduce dust load on the filters. ■

I want to know wat i can use to filter out fly ash from gases from a coal furnace at 700 C temperature , air flow will be 170 tons per hour ■

Originally Posted by prabuddha

We keep getting suggestions of using bag filters to trap cement dust. Are there specific reasons as to why bag filter is advised over cyclone or over e.precipitators

Dear Sir ,

How are you ?

I am Sunny from YKCSJ Filter Materials Co.,Ltd .We are the manufacturer of air filtration products ,such as fiberglass filter fabric,needle punched felt ,PTFE filter materials ,polyester filter materials ,nomex ,filter cages and dust collectors and so on .We can also provide fiberglass and PTFE sewing thread .

We hope that we can cooperate with your company in the air filtration field .Could you contact me if you are interested in our air filtration products ?

Thank you .

Best wishes

Sunny Zhao

Yingkou Chuangshiji Filter Materials Co.,Ltd

For more information, please visit:

https://edir.bulk-online.com/profile...-materials.htm ■

Bag filter i.e. fabric filter mfrs now gives gaurantee of 10 mg/Nm3 or even 5 mg/Nm3 at the outlet of the filter which is very very low in terms of pollution and dust vent to atmos. cost^^^^

whereas a static cyclone or cyclone cluster has a efficiency of max say 90-95% practically (95+% is only in theory) which means lot of dust will escape to atmos.

more fine the dust, more the probs. cyclone separator need a minimum particle weight to have the centrifuge effect. less size dust will always escape without collecting.

For max efficeincy use a good fabric filter with pre-separator entry type. to reduce the load (size/money) of that good fabric filter use a static cyclone separator before it. this will considerably reduce the op. cost but initial setup cost is high.

other things like ID FAN sizing and power consumption is a thing to watch for, layout constraints, space availablity to be checked for....

I dont have exp in ESPs, hence pardon me for not comparing with that. ■

Originally Posted by mall

hi to all

it is normal in today cement industry at finish grinding, use high efficiency separator and collecting bag filter.

but in case to reduce the load on the bag filter , we install static cyclone after high efficienct separator and follow by collecting bag filter.

how much does this type of arrangement save the maintenance and bag cost?

regards

Mall is correct

With today's standards you always need to finish with a baghouse. In cement the quantity of cement is extremely large so we use high eff separators (cyclones) to remove as much cement as possible prior to going on to the bag house. ■