When it is time to change out the filter bags in a boiler baghouse, also known as baghouse refurbishment, there are three distinct phases. The first phase is the pre-outage phase during which time preliminary preparations must be taken. The second phase is the outage itself during which time the replacement, cleaning, and maintenance is undertaken. The third phase is the post-outage phase during which time the flowrate is gradually increased, tests, samples, and monitoring are undertaken, and records are made. Each of these three phases includes a number of important steps which we will look at in more detail below.
The Pre-Outage Phase
The first phase is the pre-outage phase. In many ways this stage sets the tone for the entire process because it is during this part of the process that the majority of the planning, scheduling, and logistical steps are taken. Getting on track early and staying on task significantly improves the outcome of the outage.
- Material Procurement and Labor – Items like filter bags, cages, tensioning equipment, door seals, clamps, pulse valve parts, pre-coating, and leak detection materials need to be acquired. Depending on the site conditions additional equipment like air compressors, cranes, scaffolding, ventilation equipment, and welders may also be needed. Sufficient labor should be acquired and a plan should be developed to ensure that all parts, equipment, and labor are procured and scheduled before the refurbishment begins.
- Inspection – It is important to conduct pre-outage inspections to minimize the number of surprises and unknown variables as well as increasing speed and efficiency during the outage. A good inspection should identify problems such as corrosion between pipes or around the baghouse access doors, damage to tube sheets, stuck filter bags and the approximate volume of particulate accumulation. Other inspection discoveries include determining how many workers can fit in a compartment and what general work conditions will be.
- Staging – Staging refers to the laying out of needed parts, materials, and equipment prior to the onset of the outage. Proper staging will increase the speed and efficiency of workers and will help quickly identify any shortfalls or missing components.
- Scheduling – Establishing a proper outage schedule will help increase efficiency and track results and benchmarks as they occur. This will in turn help minimize cost and maximize the quality of the outcome.
The Outage Phase
It is during the second phase, the outage phase, that the actual bag replacement, cleaning, and maintenance takes place. This part of the process has the potential to escalate quickly in cost due to labor, downtime, and materials. It is imperative that this phase be performed as quickly as possible without sacrificing quality.
- Hopper Clean Out – The hopper, which collects the filtered ash, will need to be cleaned out. A proper disposal protocol and all necessary equipment should be in place.
- Filter Cage Removal – Prior to changing the filter bags, metal cages must be removed.
- Bag Disposal – Damaged or worn out bags will need to be disposed of. Once again a proper disposal protocol should be in place.
- New Bag Installation – Care should be taken while installing new bags to ensure that they are properly installed, fit well, and are not damaged.
- Tube Sheet Replacement – The tube sheet may not need to be replaced but if damage is extensive it can be replaced during the outage phase.
- Leak Testing – Once the new bags are in place and prior to ending the outage, the system should be tested for leaks. This is accomplished by running a powder through the baghouse which will fluoresce under a blacklight.
- Leak Inspection – Any areas that fluoresce under the blacklight expose a leak. This will need to be corrected before the outage ends.
The Post-Outage Phase
The post-outage phase is the final phase of the process and can be as the qualit assurance portion of the work. The biggest part of this phase involves on-going monitoring of the baghouse and its emissions levels. In many ways the post-outage phase doesn’t truly end until the next pre-outage phase begins.
- Pre-Coat – A precoat can be added to the bags prior to startup to increase efficiency and help protect the bags.
- Startup – Startup should be gradual to prevent shock to the system and damage to component parts. This can be done by preheating components and by initially restricting airflow.
- Inspections – Inspections of the baghouse compartment should be done on an on-going, routine basis to determine any changes or deterioration.
- Bag Testing – Damaged or worn out bags that were removed during the outage can be tested to gain valuable information about what caused the failure, such as whether or not it was due to mechanical, chemical, or thermal damage. Typical testing will analyze their permeability, burst strength, and flexural strength.
- Monitoring – Emissions levels for the entire system as well as individual compartments should be monitored. This will help determine absolute emission levels, any changes in emission levels over time, and variations that occurred in emissions during cleaning.
Together these three phases comprise the stages of a baghouse refurbishment or outage. The replacement of filter bags represents a major expense at industrial facilities. It is crucial that these refurbishment stages be performed carefully and efficiently to extend the life of the filterhouse bags and to minimize or eliminate all unnecessary costs.
