WHY AND HOW SHOULD BAGFILTERS BE AUDITED?
As equipments that come last in line, after the entire line of process equipment/s Bagfilters and Baghouses are actually the most neglected areas of any dust handling plant. They instantly attract the highest concern when an emission problem crops up, and such dust collectors become the center of attraction. The users have mixed feelings and confused objectives as to what solution should be implemented once the dust collector begins to misbehave.
Bagfilters do not explode with performance problems overnight. They keep showing signs well before the problem actually manifests. It is hence prudent to get your Bagfilters auditing on a regular basis, to catch the concern area before it blows out of proportion and causes a financial dent. Regular checks and audits help in good mantainence and improving the overall performance of the Bagfilters. Unfortunately, since these equipments are grossly ignored and unkempt, it is only when the stack vents columns of dust smoke does the Auditors get a panic call.
Misaligned holes for purging the compressed air from the blowpipe will result in compressed air hitting the ventury walls instead of reaching the bottom of the bag, hence inefficient cleaning of the bags and blinding.
Also, marks of compressed air hits are seen on the ventury walls indicating that the blowpipe is fixed in twisted orientation.
A comprehensive audit is not a fault finding mission of where the mantainence team has failed, but is a detailed assessment of various aspects- design, operational, mechanical and electrical, constructional as well as mantainence of the Bagfilters. The exercise will not just be a stich in time, but will also benefits to
Increase reliability of performance
Substantially bring down outages due to mantainence issues
Curb fugitive emission largely a well as
Bring to light, reasons for any upgrades required
Be a part of continual improvement for air pollution control systems in the plant.
At the working level an all-inclusive audit should ideally cover various important areas to yield an inference aligned with the overall performance improvement and providing concrete technical solutions for the problems faced. Hence, the objectives should be clearly defined before the start of this activity which can be
1. Checking the adequacy of the Bagfilters in terms of capacity, Air to cloth ratio
available filtration area etc..
2. Improve life of the filter bags and the Cages
3. Improve the performance of the Bagfilters and reduce fugitive emissions
4. Reduce reasons for breakdowns, failures and forced outages
5. Offer Hands-on training to the concerned staff on troubleshooting, good
Maintenance and theory and technology updates.
Banana clump formation – due to sag in the tube sheet and twisted cages. The clustering of bags takes place which causes friction between two adjacent bags, restricting the inter-bag gas distribution this leads to high ACR & higher CAN velocity.
A standard assessment methodology for every Bagfilter will include the following activities for checks for its adequacy with regards to following
a. Application, location w.r.t other process equipment and maintenance records
b. Duct Work and hoods, associated structures and its layouts
c. Balancing of the pressure of inlet ducting in case of multiple pickup points
d. Assessment of discharge capacity / downstream material handling systems
e. ACR as well as Can Velocity w.r.t application, dust characteristics
f. Adequacy of header capacity, solenoid valves, air purging system
g. General practices followed for monitoring the performance
h Fan & its inlet-outlet ducting, as well as the stack height, design and geometry
i. Allied monitoring and other instruments & their functions
j. Possibility to save compressed air by optimizing the cleaning cycle.
k. Suggest modifications to the equipment / instruments to optimize power
consumption, replacement cost & maintenance frequency.
Hydra formation, horizontal ducting pitting and holing leading to static pressure loss, duct blockage, improper flow & pressure balancing between the header and branch ducts. Holing & pitting lead to entry of false air.
Once the data and photos are collected by the Auditor, he will organise the same and analyse it, conduct a design based review for equipment adequacy and derive inferences that will lead to some results. These findings are converted into engineering solutions and presented to the Customer giving details of modifications required, their costs for engineering and fabrication (if any) and implementation in toto, in form of a Report. The Report should be based on the principle below.
Every dust collector is like an individual. Although they have a GA diagram and documented process parameters, they seem to have their own mind and logic to operate. But when you delve in to understand the logic behind their ailment, they begin to respond to the treatment. It is just for this reason that technical expertise and experience, both qualifications count when selecting an Auditor for your Bagfilters.
The assessing party should ideally be a
a) A Consultant – who will identify, assesses problems, analyze data and derive improvement or upgrade schemes
b) An Equipment Supplier – who can supply you the equipment/s within budget, as per requirement
c) A Contractor – who will supervise work at site for erection and commissioning, and
d) A Supplier of Spares/ replacement parts
They should be well equipped with qualifications, capability and infrastructure to not just report reasons for shortfall of performance or identify brewing problems, but should also be in a position to supply appropriate equipment parts, as well as design and engineer improvement solutions, implement the same and offer guarantees of performance improvement after implementation and execution.