ESP Technical Tip
Optimizing Your Precipitator: Performance Testing
In previous installments of this series on optimizing electrostatic precipitators, we examined the value of collecting data about your ESP's design, the importance of properly maintained internals, and the relationship between different power circuit components. Next we move on to performance testing, another tool for determining just how well the ESP is working and what modifications will result in the biggest bang for your buck.
The performance testing discussed here is sometimes referred to as "EPA Method 17." It involves inserting probes that contain filter into test ports while the ESP is running to measure gas dust loading. At the same time, flow, temperature and gas composition are determined. Testing is done at the inlet and at the outlet, and results are compared to determine overall collection efficiency.
The more representative data you can collect about how the ESP is operating today, the better off you'll be when it comes to correlating test results and determining what actions should be taken. Since the goal is to understand what's actually happening with the ESP, Method 17 typically involves 10-12 test runs (up to three runs per test condition) under varying conditions. For example, one run might be done at full load with normal load, another at normal load with no rapping, and another at 75% boiler load with no soot blowing and reduced ESP power input.
Method 17 testing provides a baseline picture of how well the ESP is running. For a more full picture of efficiency, it helps to simultaneously test fuel and ash samples, and collect other information such as primary/secondary current and voltage readings, CEMS data (Oxygen, NOx, opacity, etc.), and boiler O2%. All of this information can then be fed into a computer performance model to see the potential effect different modifications will have on collection efficiency.
Learn more about how to optimize your ESP: read Neundorfer's past Technical Tips, or give us a call anytime (440 942-8990) to ask for advice.
Baghouse Technical Tip
Debunking Common Baghouse Misconceptions
One of the most effective ways to extend the life of your baghouse is a return to the basics. Appropriate start-up procedures and a policy of cleaning based on differential set points, for example, are essentials that should be standard at every plant using a baghouse.
To grasp why such basics are so important, though, it helps to understand the essentials of how baghouses work. This article briefly debunks the three most common baghouse misconceptions. Get these points down, and you're well on your way to maximizing the lifespan and efficiency of your baghouse.
Please note: these misconceptions do not apply if you are using PTFE or Teflon-coated bags.
Misconception #1: Bags Filter
Fabric filter bags themselves do not perform the fine filtering of particles from the gas stream. Instead, it is the control layer of dust on the bags that does the filtering. Gas flows through the filter bags, and particles collect on the control dust layer. This is why proper start-up of new bags is so critical; without the control layer, particles get embedded in the fabric itself, eventually leading to prematurely blinded bags.
Misconception #2: Over-cleaning is Better Than Under-Cleaning
In most areas of our lives, the cleaner something is the better. Not so with fabric filter bags. When bags are cleaned excessively, the control layer of dust gets knocked off, and the fabric is left exposed. If a new control layer is not applied, fine dust particles get embedded in the fabric, leading to blinded bags. The decision about when to clean should always be based on differential pressure (DP) rather than time elapsed since the last cleaning. This saves bags and energy, and cuts down on emissions. (In a healthy baghouse, most emissions occur during cleaning.)
Misconception #3: Filtering Wears Out Bags
There's another reason not to clean fabric filter bags excessively: it is not filtering that wears out the fabric, but rather the cleaning process. Every time bags are cleaned, the fabric gets flexed; the indices open up, dust flows through, and some of that dust gets trapped. Excessive flexing also causes the fibers to break down. All bags eventually wear out, but they last a lot longer if cleaning is done only when necessary.
Learn more about how to care for your baghouse: read Neundorfer's past Technical Tips, or give us a call anytime (440 942-8990) to ask for advice.