What filter fabrics suitable for sugar industries?
The general issues and precautions for the use and maintenance of pulse jet bag filter will contain three aspects: First, discharge excessive dust pollutions;
Second, the pressure of filter is much higher then normal one;
Third, the service time of the filter bags is much shorter than usual.
There are some relationships exist among the three of them, which will explain as following:
I. Discharge excessive dust pollutions.
1. The dust collecting layer on the surface of the filter bags is not enough.
If discharge excessive dust pollutions, the pressure for the bag filter house is lower then designed, the problems may be that the dust collect layer on the surface of the bags is not good, the reason may be:
The over estimate of filter speed;
The period for the cleaning of the bags is not long enough; The pressure for the compressed air is too high, the loading of the dust is reduce.
Research has shown:
Over estimate of filter speed, the dust discharging will increase, much higher the wind speed will break the dust collecting layer and the bags will crushed buy dust lead to the broken of the bags. If purgying the bags at this time or with a high clean frequency which will lead to the fabrics loosen and discharge excessive dust pollutions.
We should design the longest pulse cleans period for the filter bags under the precondition of stable operating pressure, and the pulse cleaning time is better short under the precondition that dust collect layer on the surface won’t drop. If the dust collect layer on the surface is not thick enough, we can prolong the cleaning period to make it up.
If it discharges excessive dust pollution just after the bag cleaning, we only have to check whether the air pressure for the pulse is extremely high.
The loading rate of the dust is low may due to reduce of the productivity or bag filter systems mending, etc, the solutions are: reduce the pressure or pre-load the dust.
2. Filter bags broken. (Abrasion, burning, corroding)
The filter bags using will take up most of the maintenance cost, even up to 70%. The bags broken mainly own to the reason of abrasion, burning, corroding and so on, the solution can be taken as following:
Extortionate wind speed will increase the impingement of the dust, which will break the filter bags.
Solutions: adjust inlet wind volume, keep a stable pressure.
If inlet air volume is uneven will easy lead to the exhaust gas hit the filter bags directly and perforate the filter bags nearby air inlet.
Solutions: install the air distribution board in the air inlet or change the special which abrasion resistant filter bags.
The distance between the filter bags too little, the crooked filter cages will lead to the bags abrasion, such as the fiber glass filter bags which is sensitive for the abrasion, so we have to choose the better filter components.
The diameter difference between the filter bags and the cage is very important; the better distance is the filter bags’ perimeter will 10~20mm more than the cages. If the distance too little, the dust release will not be so good; on the contrary, the abrasion will increase between the filter bags and the cages. So we must concern about this problems very much.
The burr exist at the weld point at the filter cages will accelerate the abrasion of the filter bags.
If the seal is not good between the filter bags and bag plate will lead to the head of the bags abrasion, so it’s better to adopt the spring top ring with the correct size.
Venturi tube or pulse tube is not fix good will easy to cause the abrasion of the filter bags.
The filter bags’ clean is too much times will cause the filter bag’s abrasion.
The dust content exceed the estimate will accelerate the abrasion of the bags.
Flue dust retainer stored too much dust will accelerate the abrasion of the bags.
All of the reason above will cause the discharge excessive dust pollution, and will reduce the using time of the filter components; we should take much attention on these problems.
ii. Burning of the bags.
The reason for the burning of the bas is due to the high temperature of the exhaust gas.
If the temperature in the bags house high than the estimate for a long time which will lead to the bags become shrink, turning hard or melt, and the glow particle also will burn the filter bags, so choose a right material of the filter bags is crucial.
On condition that the cooling system is needed, so we have to concern much on the humidity on the cooled air, whether there are acid or alkali included, at the same time we have to try to guarantee the temperature of the exhaust the air high them their dew point, in case the liquid percolate through the filter bags.
The solutions may adopt to avoid glow particle slide into the bag house and burn the filter bags:
Coating some protection layer on the surface of the bags, such as the kaolin, limestone powder, etc, at the same time, we have to protest the unburned carbon material is on fire again.
The general reason for the corrosion is there are acid, alkali included in the exhaust gas, along with the density of the corrosive material higher and higher, if the temperature in the bag filter house is lower than the dew point, the SO2, H2SO4, etc will come into being, so the bags will be corroded.
Solution: adopt the alkali and acid resistance filter bags; keep the temperature stay above the dew point.
3. The components for the filter bags are inferior.
II. over resistance.
The resistance for the dust remover was decided when they are designed, if there are any resistance increase sharply which will means some problems occur, the mend and adjust required.
The possible reasons:
1. The resistance increase sharply immediately when open.
2. The resistance increase sharply in the middle of the working time.
If the filter designing is not good, the first situation may occur.
The second situation will due to the wrong operating or maintenance, main reason:
Bad cleaning of the filter bags, the filter bags blocked, the air distribution is uneven.
i. clean system is not good.
Check the content of the impress air to seem whether the water and the oil are existing.
Check the inlet air pipe to avoid is blocked.
Check the solenoid valve to see whether it’s working normally, any loose on the Bolton, any loose on the solenoid coil, whether the spool valve be locked, etc.
ii. Filter bags blocked.
The reason for the filter bags’ blocked: the filer speed is too fast, diameter of the particle is tiny, the dust is adhesive, clean system is not good, and the filter bags are damped.
If the filter speed is too fast and over the estimate when design which will easy to make dust locked in the middle of the filter cloth and blocked the filter bags.
As for the solutions the membrane and coated with protect layer seems the better choices.
For the adhesive dust, we’d better to down the filter speed, increase the pressure of the compress air, offline cleaning, but best solution is increase the filter area so as to down the filter speed, prolong the bags’ life.
The clean system is not goods include the cleaning time is too many, the time is too long, which will lead the dust block the bags and also will drop the dust collect layer on the surface.
If the cleaning time is short, the filter bags will working before be cleaned, so the dust will accumulated on the surface of the bags which will block the filter bags, we can test run and choose the best operating data.
Why the bags easy damp? Possible reason: the bags filter house is not seal tightly and the water coming to the filter house, the pulse jet air is not clean which may include the water and oil.
So as to avoid the filter bags damp, in the cold area, we have to clean the impress air and increase the exhaust gas, and we’d better clean the bags 10~20 minutes after close the filter.
The water is the biggest problem for blocking, why the moisture exist? The reason is moisture will become dew point in the low temperature, special deal with the burning or high temperature fume remove, the solutions may take are:
i).Avoid wrong operating.
ii).Avoid runs the filter when the resistance is much higher.
iii). Avoid runs the filter under the temperature of the dew point.
III. Shorter life of the filter bags.
The factors which related with the bags life are:
Kind of the filter bags, quality of the bags, filter speed, dust content, clean method, times of the clean on the fix time, times of running and closing the filters, etc.