NESHAP and the Challenges with Baghouses
CEMENT: Will your Baghouse Help You Pass or Fail NESHAP Compliance Testing
New NESHAP (National Emission Standards for Hazardous Air Pollutants) have been in place since September 2015. Cement plants have to remain consistently in compliance with the new PM (Particulate Matter) standard of 0.07lb/t clinker using a combination of stack monitoring equipment and annual stack tests. If not attended to, baghouse operation will create compliance test situations that may put unintended operational constraints on the plant. Here is an example of how.
Background on the rule.
On an annual basis, the plant has to prove compliance with a Method 5 stack test. Three sets of tests have to be performed with mill on and mill off. Correlation of these stack tests must be made with a continuous parametric monitoring system (CPMS). The CPMS signal becomes the plant 30-day rolling average limit.
If a stack test is at or below 75% of the limit (0.07lb/t clinker) then the CPMS is scaled to 75% (0.052lb/t) of the emission limit. If this 30-day rolling average is exceeded, the plant has 48 hours to perform repairs and perform another Method 5 test within 45 days. This is not considered a violation.
A violation occurs if you exceed the 0.07lb/t limit or you exceed your CPMS limit (30-day rolling average) more than 4 times during a 1-year period (even if you never go above 0.07lb/t). Remedial action and retesting is also required.
Remember, after every stack test, you are establishing a new CPMS limit. Operation of the baghouse and reaction to problems can be different depending on the outcome of the test and how it sets your CPMS limit.
Quickly going from good to bad
ABC Cement Plant has a pulse jet baghouse that they recently replaced all the bags and cages, cleaned clean air plenums, replaced all non functioning solenoid valves on their cleaning systems and repaired any holes in the casing and hoppers.
They perform the compliance stack test. It comes in at 50% (0.035lb/t) of the PM standard limit so the CPMS is scaled for 0.052lb/t clinker (75% of the limit). All is good, as the plant™s 30-day rolling average has to operate below 0.052lb/t. No problem! The plant has lots of margin to work with.
Along comes year 2 and its time to perform your annual test. This time the test comes in right at 75% of the limit. The operating buffer that was there a year ago is no longer there! How did that happen? Maybe leaks have formed. Maybe the hopper system malfunctioned.
Then it gets worse. Any time the 30-day rolling average exceeds the current stack test level, you have to take remedial action. For purposes of this story, you have had 4 of them! Each time, you take action and retest. After each test, you reset your CPMS level. You cannot get ahead of it. Woops! You are now in violation.
Here are some things that would contribute to creating this scenario:
- Leaky compartment door seals
- Leaking tube sheets
- Excessive bag cleaning cycles
- Malfunctioning hopper systems
- Dust in the clean air plenum
- Leaking bag seams
- Poorly fit bags on cages
- Leaky poppet valves
What does this mean?
The constraints the compliance process puts on the plant puts emphasis on making sure you test as best as you can and you do not put undue constraints on the production process. You have to make sure the baghouse can consistently operate properly and is œtuned up so as not to create a higher than normal test. This is going to require a higher level of attention on the baghouse bags, cages, cleaning systems, dust removal and preventative maintenance.
To avoid these issues, plants should have properly developed and executed preventative maintenance plans. Monitoring of key operating metrics so that issues are identified and responded to before they result in exceeding the PM limit or its 30-day rolling average should be in place.
Neundorfer can help. We can assist in identifying the key risk factors, create best practices/procedures that are appropriate for maintaining continuous compliance and developing systems that are proactive in identifying issues before they become compliance problems.