you have neglected to explain whether the system is suction/vacuum based or pressured discharge!!!!!!!!!!!!!!!!!!

You have answered your own problem simply due to the fact that your batch size is increased- try putting a ball valve in to reduce flow to pre increase levels and that should solve it.

Elbows equal restrictions period and require much more energy to move material from a to b.

By installing collectors all you doing is adding sn escape point for dust and usable pressures HG or manomometer; by adding cleanouts all your going to do is add more work possible leaks and a definite probability that dust will block even more as any fugitive dust is lazy just like water and electrcity.

You will be better off replacing the elbows with sweep fitings to reduce the angle of resistance to flow in either case- have you taken a manomometer reading while the system is working if pressure based or used a milkhouse vacuum gauge to measure vacuum pressure HG.

Did the system get sized properly in relation to altitude and atmosperic pressure at your location?

How often do you change the filter bags?, do you look at the restriction indicator for the red zone and reset it see if it goes back to green and if not do you change the bags or reverse airflow to clean the bags?

Do you clean the housings/frames of the filters and inspect the gaskets or clamps? how often are the bags replaced?, do you glue in new gaskets when needed?!!

Changing the elbow with cleanouts does not solve the problem one bit-you power source may be undersized for your application and the method of suction or pressure discharge may be entirely wrong for your application.

If the seller of the system is still around which I doubt ask them to come in and explain why it is doing what it is doing!!!!!!!!!!

I am sure my dear friend teus will have more to add if I missed something.

leonZ ■

You have increased batch size from 1000 kg to 1400 kg. The fumes and dust load in exhaust gases would have also gone up by 40%. If you have not increased the exhaust system and fan capacity, system is now overloaded and the dust is settling in elbows.

Do you have long horizontal ducts at the end of elbows. If you have, please replace them with inverted V shaped ducting. Dust will not settle in horizontal portions of ducting near elbows.

In a laundry, exhaust air will be moist and if you have sulfur oxide in fumes, there may be corrosion problem also. ■

Hi Ham,

It sounds like you are working with a Baghouse dust collection system. You say you have increased the dustload by 40%.

1 - because you have increased dust load that does not mean you need to suck more air through the duct system. It just means you need 40% more filter cloth area at the Baghouse - i.e. a second Baghouse.

2 - With the existing Baghouse your bags get clogged that much faster. When that happens your pressure drop increases through the filter bags and you end up pulling less air. This reduces velocity in the ducts and at the bends. That causes the dust particles to drop out at the bends and to block up.

SOLUTION

(I) - Add a second baghouse.

(II) - Cut a cleanout door at each elbow.

We provided critical elbows with clean out doors because we were running with a Dirty Duct system - due to insufficient filter area (inefficient). We added some compressed air nozzles inside the bends so we could manually blow the dust away.

You say that - [Dusts collected are hygroscopic powders with fumes of sulfuric acid, surfactant and water vapor. These occur during neutralization of our powders with acids]. That means your dusts tend to cake. Compressed air would only work on dust which has not caked yet [if you are desperate you could put a timer on the compressed air nozzles to blow out every few hours. Sub-optimum solution, but better than a Shut-Down due to blocked ducts].

Regards - Sgt John.Rz

www.latviantourists.com.au ■

You haven't given enough information to allow a proper analysis. What is the gasflow, humidity and temperature? Is the ducting all one size or many branches? What is the radius of the 'elbows'? A radius of at least twice the duct diameter is prefered in this situation.

If the lack of airflow is because of clogging filter bags, can the baghouse be replaced by a wet scrubber?

One solution would be to insulate the baghouse and trace heat the hopper to keep the gases above dew point. Trace heating and insulating the ducting might be needed as well.

Michael Reid. ■

The suggestion is to make the centreline radius of the bends equivalent to two duct diameters, not increase the duct diameter.

Keep the ducting temp. above the acid dew point. Insulate the ducting and elbows and trace heat them. At the same time, keep the velocity in the ducts above 18 or 20 m/s.

Michael Reid. ■

Ham,

I am not sure that we are addressing the root cause of your problem here. This is a complex problem involving a baghouse, the system design and most importantly, the process.

To answer your question. There is no rule of thumb for selection of insulation thickness. To start, you must know the dew point temperature of your gas. The presence of acid gases lowers the "normal" dew point temp. of moist gas or air.

You can calculate this temp. if you know the chemical composition of the gas, or you can measure it by sampling. A fair degree of skill is required.

Knowing the temperature gradient, from inside to outside of the duct, you can easily select an appropriate insulation material and thickness from the manufacturer's catalogue.

Good luck,

Michael Reid. ■