Podcast: Pumps, Flow and the Fight Against Wasted Energy

The Hidden Complexity of Bulk Solids

Our first piece comes from Amin Almasi, a mechanical consultant based in Sydney, Australia, writing in our Equipment Insights column. The article is titled "Bulk Solids and Powders: Flow, Storage and Conveyor Design in Chemical Plants," and it opens with a provocation that I think every engineer in this field should sit with: bulk materials are far more complex than they look.

We often assume that if you can weigh something and put it on a belt, you understand it. Almasi makes the case that this assumption costs plants real money.

Take density — something that sounds completely straightforward. Almasi explains that bulk density, the density of a material as it actually sits in your silo or rides your conveyor, is fundamentally different from particle density, the density of the individual grain or granule. And these numbers can diverge dramatically. Loose bulk density — meaning material that's flowing — can be as little as half the settled bulk density. If an engineer uses particle density when sizing a belt conveyor, Almasi warns the operational parameters could be off by 30 to 80 percent. That's not a rounding error. That's the kind of mistake that makes a system fail to perform from day one.

He also takes us through angles — specifically the angle of repose and the angle of surcharge. The angle of repose is the angle a naturally formed pile of material makes with a flat surface. The angle of surcharge is what you see on a moving conveyor belt, and it's typically 5 to 15 degrees less, because the motion and vibration of the belt flatten the pile. This gap matters enormously for conveyor design: it directly determines how much material you can safely carry and how steep an incline your system can handle. Free-flowing materials like dry chemical grains might allow inclines of only 10 degrees. Push past that, and you've got a stability problem.

Now, here's where it gets interesting for plant operators: these properties don't stay static. Almasi points out that raw materials arriving from different sources may have varying characteristics, and a thorough sensitivity analysis is essential to account for those variations. In other words, the material you designed for last year might not be the material you're running today.

The article also covers storage — hoppers, silos, bins, bunkers — and the failure modes that plague them. The three big ones are funnel flow, arching, and ratholing. In funnel flow, material moves only through a narrow central channel while stagnant material builds up at the sides. Ratholing happens when that stagnant material is cohesive enough to form a stable tunnel — and that means not only flow problems but degradation of the material sitting idle in the silo. Almasi's prescription for avoiding these problems: steep, smooth walls — typically 65 to 70 degrees or more — and outlets sized large enough to prevent arching.

And for cases where you're working with older, poorly designed equipment that can't be rebuilt? Flow-assisting devices. Almasi discusses vibrating hoppers — specifically gyrating and whirlpool devices — that can break up ratholes and bridges. He's candid that these are a workaround, not a first choice. The real preference is robust design that doesn't need mechanical intervention to keep material moving.

His closing thought is worth repeating: the gap between estimated and actual material behavior is where most bulk-handling failures begin. Real-world testing and sound design are not interchangeable. If you're in the early stages of specifying a bulk handling system, read this article before you finalize anything.

Heat Pumps and the Future of Distillation Energy

Our second piece takes us in a very different direction — from moving solids to moving heat. This article is from Thomas Kwan, Global Vice President of Strategic Innovation at Schneider Electric's Sustainability Research Institute and a contributor to our Energy Saver column. The title is "Heat Pumps Slash Waste in Distillation Operations."

Kwan opens by acknowledging something many of us already know: distillation is energy-intensive by design. You pump enormous amounts of heat into a reboiler, and then — frustratingly — most of that energy gets dumped right back out through the overhead condenser into a cooling tower. From a thermodynamic standpoint, Kwan calls it offensive. And he's right.

The fundamental proposition of his article is that industrial heat pumps offer a way to recapture that overhead heat and redirect it back to where you need it. Instead of treating condenser duty as waste, you compress it back up to a usable temperature and feed it to the reboiler. The result, Kwan says, is a 50 to 80 percent reduction in energy consumption compared to conventional steam reboilers. And he's careful to clarify: that's not a theoretical number. Even conservative implementations can hit 50 percent.

For evaporation and concentration operations specifically, mechanical vapor recompression — essentially a specialized type of heat pump — has a strong track record, routinely delivering north of 50 percent energy savings. Kwan cites a midsized chemical facility projecting over 5,500 megawatt-hours per year in annual savings from a heat pump deployment — numbers that get senior management's attention, as he puts it.

He introduces a key metric for evaluating these systems: the coefficient of performance, or COP. COP tells you how much heat energy you get out for every unit of electricity you put in. Well-designed industrial systems typically run between 3 and 8. A COP of 4 means you're getting four times the heating value of your electricity cost. That sounds excellent — but Kwan is honest about a complication: electricity generally costs more per unit energy than natural gas. The economics depend heavily on what he calls the "spark gap" — the ratio of electricity price to fuel price.

In the U.S., where that electricity-to-gas price ratio is unfavorable, heat pumps can struggle to break even on operating costs alone without additional incentives. European facilities have an edge because carbon pricing mechanisms — approaching 90 euros per ton of CO₂ — add meaningfully to natural gas costs and shift the math in heat pumps' favor.

Beyond raw energy savings, Kwan lays out operational advantages that are sometimes underappreciated. Mechanical vapor recompression systems simplify the thermal architecture of distillation — fewer heat exchangers, less fouling, fewer cleaning cycles. And for heat-sensitive specialty chemicals, the tighter temperature control that heat pumps provide can actually improve product quality and reduce losses. In several projects Kwan references, those quality and yield improvements exceeded the direct energy savings in the economic evaluation.

He also highlights an emerging revenue angle: grid flexibility. Industrial heat pumps are controllable electrical loads, and as more renewables come online, grid operators increasingly value the ability to shift when large loads run. Demand-response programs can turn your heat pump into a modest revenue source on top of your energy savings.

Kwan closes with a practical implementation framework: start with distillation columns where the overhead-to-reboiler temperature difference is favorable — roughly anything under 80 degrees Celsius is worth evaluating. Deploy sequentially so you can demonstrate value before making facility-wide capital commitments. And he adds a note of urgency: the window to be an early adopter is closing. This will soon be standard practice.

If your plant runs distillation columns, evaporators, or concentration equipment, this is a technology to evaluate seriously — and soon.

Why That Pump Kept Shutting Off

Our third story is my favorite kind — a real-world troubleshooting mystery with a genuinely instructive answer. It comes from Andrew Sloley, our Contributing Editor and Plant InSites columnist. The article is titled "Why This Water Pump Kept Cycling Off."

Sloley starts with a scenario that will resonate with anyone who has dealt with small utility systems on a tight budget. A retired colleague is now serving on the board of a small municipal water utility, acting as the in-house technical resource. The system is simple: Pump P1 supplies water to a relatively small holding tank with about a 36-minute residence time between usable high and low levels. Pump P2 then takes water from that tank and sends it to a water tower. There's also a chlorination system around the tank, which means keeping P2 under positive suction is not optional — you don't want a chlorine release.

The problem: P2 keeps cycling rapidly on and off, eventually tripping the motor control circuit to protect the motor from damage. Maintenance arrives, finds nothing obviously wrong, resets the pump, and leaves. Then the cycle repeats.

The control logic protecting P2 is a level switch on the pump's suction piping — a simple on-off device with a very narrow dead band of just a few inches. When level drops too low, the switch cuts power to P2. When level rises, it brings P2 back online.

Here's the physics that nobody initially accounted for: Bernoulli's principle. When P2 is running, water is flowing through the suction pipe at a meaningful velocity — in this case, about 2.84 feet per second. That flowing water has velocity head, meaning some of its energy is in the form of kinetic energy rather than static pressure. When P2 shuts off and flow drops to zero, that kinetic energy converts back to static pressure. The level in the instrument well rises — not because more water arrived, but because the pressure conditions changed.

Sloley shows that at normal operating flow velocity, the velocity head conversion equates to about 1.5 inches of fluid. In most systems, that's negligible. But remember: the dead band on this level switch is only a few inches. So the sudden rise in apparent level caused by the pump shutting off is large enough to immediately retrigger the switch and turn the pump back on — before the tank level has had any real chance to recover. You get rapid cycling. Cycling stresses the motor. Motor control trips. Maintenance call. Repeat.

The fix is straightforward: replace the existing level instrument with one that allows a wider, deliberately programmed dead band. With appropriate hysteresis built into the control logic, the pump can stay off long enough for the tank to actually refill before P2 is called back into service. At the time the article was written, new instruments were being installed.

What I love about this story is the lesson beneath the lesson. The system was designed to be simple. But simplicity doesn't exempt a system from physics. Velocity head is a real phenomenon, and when your control dead band is narrow, even small pressure transients can become the dominant driver of system behavior. Choosing the right instruments — ones that allow appropriate control ranges — matters even in the most basic installations.

Sloley has covered related topics in previous Plant InSites columns, including inlet velocity in pumping systems and velocity head calculations, so if this sparked your interest, I'd recommend going back through the archive.

Three articles, three very different problems — and a common thread running through all of them: the gap between assumptions and reality is where plants get into trouble.

Amin Almasi reminds us that bulk material properties are not static, not obvious, and not interchangeable with particle properties. Get the density wrong, and your conveyor system is compromised from the start.

Thomas Kwan shows us that the energy waste built into conventional distillation isn't inevitable — heat pumps offer a real and increasingly proven path to dramatically lower operating costs and carbon emissions, if you do the economic homework for your specific site.

And Andrew Sloley demonstrates, through a small-scale but perfectly illustrative case, that instrument selection and control dead band width are not afterthoughts. Bernoulli doesn't care how small your system is.

All three of these articles are available in full at ChemicalProcessing.com. Links are in the show notes. I'm Traci Purdum — thanks for listening, and we'll see you next time.