If you’ve ever walked past a coal-fired power plant on a cool day and noticed thick plumes of steam rising from its smokestack, you’ve witnessed a small miracle of industrial engineering in action. That steam isn’t full of the harmful sulfur dioxide it once was—thanks to FGD, or Flue Gas Desulfurization, systems. And at the heart of every effective FGD system are FGD pumps, the unsung heroes that move the alkaline slurry needed to strip sulfur from flue gas. Today, I want to break down one of the most critical, yet often misunderstood, setups for these pumps: parallel operation. As someone who’s spent 12 years in the business as an FGD pump supplier, I’ve seen firsthand how getting this right can make or break a plant’s efficiency, compliance, and bottom line. FGD Pump
First, let’s start with the basics to make sure we’re all on the same page. FGD systems work by spraying a limestone slurry (a mix of crushed limestone and water) into a chamber where flue gas—rich in SO₂ from burning coal—passes through. The SO₂ reacts with the limestone to form gypsum, a solid byproduct that’s easy to dispose of or even sell for construction materials. FGD pumps are the workhorses that move this slurry from storage tanks to the spray nozzles, circulate it within the absorption tower, and transfer the finished gypsum slurry to dewatering equipment. Without these pumps, the FGD system is nothing more than an empty chamber.
Now, when a plant needs to move more slurry than a single pump can handle—whether because of a spike in flue gas flow, seasonal changes in fuel sulfur content, or planned maintenance on one pump—the go-to solution is parallel operation. Simply put, parallel operation means running two or more FGD pumps side by side, all connected to the same pipeline and feeding the same system. It sounds straightforward, but there’s a lot more to it than just flipping a switch and turning on extra pumps. Get it wrong, and you’ll end up with uneven flow, excessive wear on equipment, or even compliance issues from inconsistent SO₂ removal.
Let’s talk about why parallel operation is so popular in FGD applications, because it’s not just about handling high flow rates. For starters, it creates redundancy. FGD systems are required by environmental regulations to operate at peak efficiency almost 24/7, especially in the U.S. under EPA rules, or similar standards globally. If a single pump fails, your entire FGD system could shut down, leading to unplanned downtime, hefty fines, or even forced plant shutdowns. With parallel pumps, if one goes down, the others can pick up the load—though not perfectly, which is why we design systems to account for that.
Another big advantage is flexibility. Power plants don’t run at full capacity 100% of the time. During low-demand periods, like overnight or weekends, a single pump might be enough to handle the required flow. Running only one pump reduces energy costs, since pumps draw power in proportion to how much they’re moving. If you had to size a single pump to handle maximum flow, it would be oversized and inefficient when running at low load. Parallel operation lets you match the number of running pumps to your actual needs, cutting unnecessary energy waste.
But here’s where the challenges come in, and where my team at the FGD pump suppliers has spent years refining our designs. The biggest issue with parallel operation is flow imbalance. If two pumps aren’t identical—even a tiny difference in impeller size, wear, or motor speed—one will push more slurry than the other. That might not sound like a big deal, but in FGD, the absorption tower relies on uniform spray coverage to remove SO₂. If one pump is pushing 60% of the flow and the other 40%, you’ll get dead spots in the tower, where flue gas doesn’t get exposed to enough slurry. That leads to lower SO₂ removal efficiency, which can make you fall out of compliance with environmental regulations. Worse, the pump doing most of the work will wear out faster, since it’s handling more flow and pressure than it was designed for, leading to more frequent maintenance and replacement costs.
So how do we fix flow imbalance? It all starts with pump selection. We don’t just sell generic pumps for parallel FGD systems; we engineer them to match. First, we make sure all pumps in a parallel set are identical—same model, same impeller trim, same motor horsepower. But even identical pumps can imbalance if the system’s piping isn’t designed right. The suction and discharge headers (the big pipes that feed and receive flow from the pumps) have to be sized correctly to ensure equal pressure to each pump. If one pump’s suction line is longer or has more bends than the other, it will have higher friction loss, so it won’t move as much slurry. Our team works closely with plant engineers to design headers that minimize these differences, using equal-length runs and strategically placed valves to fine-tune flow.
Another tool we use to prevent imbalance is control systems. Modern FGD pumps come with variable frequency drives (VFDs), which let you adjust the pump’s speed to match demand. When running in parallel, we can program the VFDs to work in sync, so if one pump speeds up, the others adjust automatically to keep flow even. We also add flow meters on each pump’s discharge line, which send real-time data to the plant’s control system. If one pump’s flow deviates more than a set percentage from the others, the system can alert operators to adjust speeds or check for clogs—super important in FGD slurry, which is full of solids that can clog impellers or pipes.
I’ve seen a few mistakes that plants make when setting up parallel FGD pumps, so let me share those lessons here. The first is cutting corners on piping design. A plant once tried to save money by using a single suction header that split into two smaller lines for two pumps. The result? One pump drew more air from the suction line, causing cavitation—when low pressure makes bubbles form in the slurry, which implode and damage the pump’s impeller. That pump failed six months early, costing them tens of thousands of dollars in repairs and downtime. We now educate every client on why equal suction piping is non-negotiable, not an optional upgrade.
Another mistake is not accounting for pump wear over time. FGD slurry is abrasive—limestone particles and gypsum are hard on pump components like impellers and casings. As a pump wears, its performance drops, so even identical pumps will start to imbalance after a few years. That’s why we offer wear-resistant materials, like high-chrome impellers and rubber-lined casings, and we also recommend a regular maintenance schedule where pumps are inspected and replaced in pairs, not individually. If you replace one pump and leave the old, worn one in the parallel set, you’ll end up with even worse imbalance than before.
Let’s also talk about when parallel operation is the right choice, versus other setups like series. Series operation is when pumps are connected end to end, so flow goes through one then the next, to build higher pressure. That’s useful if you need to push slurry over a very long distance, but for most FGD applications, parallel is better because it’s more flexible and reliable. I’ve only recommended series a handful of times in my career—usually for plants with absorption towers that are much taller than average, where high pressure is non-negotiable. For 90% of FGD systems, though, parallel is the way to go.
Now, let’s get real about performance. A well-designed parallel FGD pump setup can boost a plant’s SO₂ removal efficiency by up to 5%, according to the data we’ve gathered from our clients. That might not sound like a lot, but when you’re dealing with millions of tons of flue gas a day, 5% translates to thousands of tons less SO₂ released into the atmosphere. It also cuts energy costs by 10-15%, since you’re not running oversized pumps at low load. And the redundancy means you’re far less likely to face unplanned downtime—something that’s critical for plants that risk large fines for missed compliance deadlines.
As a supplier, our role doesn’t end at selling the pumps. We provide full support for parallel setups, from initial design consultation to installation supervision and ongoing maintenance training. We recently worked with a power plant in the Midwest that was struggling with frequent pump failures and low FGD efficiency. Their old setup had two mismatched pumps running in parallel, leading to 12% flow imbalance and a 92% SO₂ removal rate—just barely meeting the 95% minimum required by their permit. We replaced their pumps with three identical, VFD-equipped models, redesigned the piping headers, and set up a sync control system. Within six months, their flow imbalance was under 2%, their SO₂ removal rate jumped to 97%, and they saved over $120,000 a year in energy and maintenance costs. That’s the kind of impact parallel operation can have when done right.
I know some plant operators might be wary of adding more pumps to their system—more equipment means more parts to maintain, right? But the key is to design the parallel setup for reliability, not just flow. Our pumps are built with heavy-duty, corrosion-resistant materials that stand up to the harsh FGD environment, and we offer extended warranties to give peace of mind. Also, with modern VFD controls, operators don’t have to manually adjust pumps— the system does it automatically, so it’s less work for the plant’s staff.
If you’re evaluating your FGD system’s pump setup, ask yourself a few questions: Are your pumps matching each other in performance? Is your piping causing flow imbalance? Are you accounting for wear over time? If any of those answers are no, parallel operation might be the fix you need to boost efficiency and avoid costly issues.
At the end of the day, FGD systems are all about balance—balance between performance, cost, and compliance. Parallel operation of FGD pumps is a core part of that balance, when done right. It’s not just about moving more slurry; it’s about moving it evenly, reliably, and efficiently, to keep the air clean and your plant running smoothly.
If you’re looking to optimize your FGD pump setup, troubleshoot flow issues, or learn more about how parallel operation can benefit your facility, I’m here to help. We’ve worked with plants of all sizes, from small municipal facilities to large utility-scale power plants, and we tailor every solution to your specific needs.
Sand Pump References
- “Flue Gas Desulfurization (FGD) Systems: Design and Operation,” Power Engineering Magazine, 2021.
- Pump Handbook, 5th Edition, McGraw-Hill, 2020.
- “Parallel Operation of Centrifugal Pumps in Industrial Applications,” American Society of Mechanical Engineers (ASME) Paper, 2019.
- EPA Regulations for Flue Gas Desulfurization, U.S. Environmental Protection Agency, 2022.
- “Abrasion Resistance of Pump Materials for FGD Slurry,” Journal of Industrial Water Treatment, 2021.
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