Cyclone Sepertor Chokage in Spray Driers Application

Call the separator tech support people. The symptoms you describe aren't enough to go on.

Throughput, solids load, velocity and many other undefined factors that aren't known mean that this can't be diagnosed here.

If you have a process engineer ask him.

In my experience with cyclone filters, the customer usually doesn't understand how to use them and overwork them. I wasn't making coffee, but stripping resist off circuit boards.

Is it possible to fix vibrator(s) on the outer wall of separator? If not, a vibro-screen along the inner wall, such that the fines will not deposit on the inner wall. This would anyway call for extensive design change.

Possibly problem you are facing could be due to build up of static electricity.

To quote from http://www.swedishelectrostatics.com/leaflet_antistatic_electrostatic.html

"Equipment to eliminate static electricity, so called antistatic equipment, is being used in almost every branch of industry. Equipment can be subdivided into active and passive eliminators, where passive eliminators are e.g. carbon fibre brushes (often to be found in office machines), copper tinsel or old-fashioned Christmas tree glitter. The passive ionizer finds it's driving potential in the charged surface and is able to discharge as long as the potential is high enough.
Active eliminators, or ionizers, are producing ionized air, which constitutes the carrier of charge from the ionizer to the charged surface. Active ionizers are powered either by an electrical voltage source or by a radioactive source and are in a modern design touch proof. The active ionizer produces both positive and negative ions since the electrostatically charged surfaces adopt both positive and negative charge in an uncontrolled manner.
A charged surface attracts ions of the opposite polarity but repels ions with the same polarity. For this reason one can regard the whole thing as being a transport problem - it is all a matter of keeping a high enough ion concentration close to the actual surface for a time long enough so that the surface may be discharged. "

A good method to eliminate static electricity may be by employing air knife technology. The knife consists of a high intensity, uniform sheet of laminar airflow sometimes known as stremline flow Refer to

http://en.wikipedia.org/wiki/Air_knife:

You do not say if the build up is solid, which may be caused by inadequate drying, or powder not slipping down the walls which could be caused by too shallow a cone angle or a lack of smoothness of the internal walls (vibration will help if this is the case). Is this a new installation? Or has the problem developed on a previously healthy cyclone. If the system is new, it looks like you have a cyclone design problem. If the system is old, what has changed. More information please.

Without knowing a lot more about the process and product, there could be many factors affecting the operation. Also, it's not clear if you are using a tower or box dryer. Has this always been a problem or does it occur only some times?

1. Is this a seasonal effect (ie: does humidity increase in your location which could influence the drying characteristics of the coffee). This assumes you are not pre-conditioning the air to the dryer.

2. Have you changed the inlet slurry process conditions such as a difference in feed line psi (if pressure dryer) or rpm if centrifugal in-feed that is making the particle smaller.

3. Has air velocity through the dryer changed (faster velocity may create more smearing on the sidewalls of the cyclone).

4. Have you changed the temperature of the drying air to compensate for changing ambient conditions (reference 1 above).

5. Have any repairs been done recently to the system that required welding that may have left a ridge inside the dryer/cyclone that could act as an initiator for build-up.

6. Have you changed the operating parameters of the dryer (where zero pressure point is located) to compensate for varying ambient conditions or product characteristics.

7. Does it vary with the type of coffee dried (if more than one variety is being processed.

8. Are there cleaning procedures that are followed to periodically purge material from the dryer (either dry "scrubbing" or wet CIP process) and are they being followed.

9. Has the rotary airlock clearance changed due to wear. If this is separating a hot side from a cold conveying line operating at a different pressure, you could be getting moisture in the cyclone that is initiating a build-up.

In most cases, it could easily be a combination of these (and/or other factors that are causing this problem. As noted earlier, mechanical vibrators may help, just be careful that your cyclone metal thickness can handle the vibration without being damaged by the repeated stress. There are also sonic and subsonic horns available that I have seen and used to assist with removing build-up and that are less stressful to the dryer metal. Anyway, just some initial thoughts.

Dear Collegues.,

Thanks a lot for all your inputs., which was very useful. I have checked all the inputs and implemented some action points.

1.No chnages in proces paramters done recently.

2.No modifications done in drier

3.I have sealed all the joints in piping leading to cyclone to arrest possible air leak.

4.Rotary valve experts confirm the healthiness of rotary valve.

Irrespictive all the above actions taken there is no improvement.

5.DP across cyclone is around -215mmwc.Is this OK for a co-current drier

I am assuming that this process worked okay in the past and suddenly began to exhibit the buildup/plugging problems you described. If this is the case, something has changed. If this is a new process that has had problems from day #1, that's a whole different problem.

I guess I would start by going back and thoroughly examine the temperatures, pressures, flows, compositions, etc... and very carefully compare these process parameters from when it was running right to when you started having problems. Be careful not to mistake the symptoms from the probable causes. I would also ask the operators (in a respectful, sincere tone of voice) for their insights. It's surprising how often the guys who operate these processes day-in and day-out have some valid clues that they are reluctant to share because they don't want to be ridiculed.

As has been discussed static electricity could be the cause. To dissipate static elec an EARTH cable is usually fitted. Has this dropped off? Been cut off as it was in the way? Corroded at the terminal points? If the frame was the earth, has it been put on rubber feet to cut down noise? Has there been a long hot, dry spell and the ground isn't earthing as well as it was?

Simple to fix.

Jim

Thanks.let me check this also...