Chocolate Getting You Down?

So you want to pump chocolate, but it's giving you headaches. Or perhaps you know someone who does, and you want to help them maximize their pumping equipment life-cycle costs. Or maybe, you simply have a burning curiosity that can only be sated with boring articles. Well, you’re in luck, because I’ve written a handy guide and I’m giving it to you for "free."

Let's just dive right in - we all have work to do. There are many factors involved and I'll try to cover the basics here. By all means, feel free to angrily comment if you disagree - but also if you have anything to add or just want to compliment my excellent writing. I welcome it (mostly the compliments). So let’s get started . . .

Temperature Control:

Constant and accurate monitoring and control of chocolate temperature can be critical to the success of the operation. As anyone who deals with chocolate knows, different types require different temperatures, and often, a pretty tight range. Some chocolate formulas are more susceptible than others but for the purposes of this article, we’ll discuss it as though we are dealing with a delicate flower.

The mixture must be kept moving through the pump/system. The cocoa can burn and ruin the taste - even if you are maintaining the proper temperature downstream/upstream – if it is allowed to stay in the pump too long and absorb heat.?Additionally, it can lump up, caramelized or congealed due to high temperature. This has a snowball effect, causing more heat, more damage to the cocoa and eventually, loss of equipment usefulness.

Conversely, it’s critical to keep in mind that if the product is allowed to solidify in the pump during shutdown, it must be gently and completely warmed back to flow-able temperatures before restarting to avoid severe damage to the pump. Generally I would advise a pump with a steam jacket be used, allowing hot water or steam to flow through (without coming into contact with the product) to facilitate delicate reheating of the product.

The importance of precise control of temperature cannot be emphasized enough.

The importance of precise control of temperature cannot be emphasized enough.

Yes. I said that twice.

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Speed, Pressure and Shear Sensitivity:

A good rule of thumb is to keep your discharge pressure <100psi and pump speed <300rpm. The reason for this is two-fold; chocolate can be very viscous and time must be allowed in order for the product to enter the suction of the pump. Another reason you’d want to keep the flow and pressure down low is that many ingredients (cocoa butter, sugars, etc.) can be abrasive, and I don’t need to explain the harms of that here, to the pump and to the entire system.

Additionally, higher velocities and/or pressures above 100psi can cause ingredients to separate in chocolate production due to its shear sensitivity. This can cause burned chocolate and possible blockage.

It should be noted here that chocolate viscosity can vary widely by formula and temperature, if allowed to reach room temperature, it could thicken to 50,000cp or more, where ideally, it should be half of that. A temperature of 50°C can achieve this in many cases. Again, I want to emphasize the importance of temperature control. Have I said that enough times?

Best Equipment for Pumping:

Due to the above-mentioned factors, viscosity, shear-sensitivity, etc., a positive displacement pump would offer the best product results and lowest LCC (Life Cycle Cost) when all application factors are considered.

Operating at low speeds and pressures, a PD pump is optimal. As the name “positive displacement” implies, these pumps will displace a positive amount of fluid with each rotation. In an ideal installation, flow is very reliable and is directly proportional to speed and can easily be throttled with speed variations (reminder – keep it under 300rpm). Gear pumps are generally chosen due to their single shaft, for ease of maintenance. But other commonly used types of pumps would be rotary lobe or circumferential piston style. These will have two shafts, and thus, two seals and are often overlooked in this application for that exact reason. But I would suggest a serious look at them, for superior solids handling capability and clean-ability. Another overlooked technology is the rotary sliding vane pump; self-priming, more efficient than gear pumps and will typically last forever (Note: nothing lasts forever, but I have customer units in place that have been in operation since the early 1980s).

I would be remiss if I didn't mention the eccentric disk pump. It offers self-priming and a seal-less design that eliminates the persistent headache of leaky pumps - and that can be a pretty big deal. But also, under the right conditions, the eccentric disk can provide a speedy ROI; their unique downstream line stripping capabilities can result product recovery rates up to 90%. No pig system needed!

Another option can be to use air-operated double-diaphragm pumps. They are very versatile, robust and also seal-less. One must be aware that the acceleration in certain areas internal to those pumps can cause shear, but this varies depending on your operation and particular chocolate formula. If that isn't an issue for you, the AODD can be an excellent choice.

Best Pump Materials:

Given that chocolate does not promote bacterial growth, it is often handled with cast iron pumps. But don't take my word for it - by the time you read this, the FDA could change the rules. Cast iron is less expensive, can be detected with x-ray or removed with magnets in case of contamination, and offers superior heat conduction (temperature control!) over stainless steel. Items such as seals, gaskets and packing that come in contact with the chocolate should be FDA food-grade approved. When dairy products are present, such as in the making of milk chocolate, stricter standards may be required. It is not the intention of this author to get into specifics on FDA regulations, but to give a general idea of why a chocolate pump can be held to a more lenient standard than some other food-grade pumps.

Seals:

Now we come to the question, what is the best seal? How can we keep the chocolate from leaking all over the floor?

The simplest sealing method is a food-grade packing. It's also one of the oldest methods, evolving from stuffing rags into the pump "stuffing box." One should keep in mind that packing is designed to leak for proper lubrication and should be loose enough to allow about one drip per second to escape. That seems like a lot, and would require a method of collection (drip pan is very common). Further, an operator with a wrench and a bit of knowledge (a dangerous combination) may feel that the pump shouldn’t leak at all, and tighten the packing until the leak stops. When that happens, the packing can cause mayhem - from damaging the shaft to product burning to locking up the pump (but does not cause dogs to marry cats, as some have reported). If your operator has a wrench, make sure they understand this.

A dynamic O-ring seal is sometimes used, and it’s generally reliable and more easily conforms to food-grade standards. It’s commonly used on rotary lobe or circumferential piston style pumps and is used in a single or double O-ring configuration.

A triple-lip seal can be utilized as well. Triple lip seals offer superior sealing and can result in 3X the life of a double O-ring seal, but are expensive to replace. One must insure that it will handle warmer temperatures as well. Note that I do not advise using a single lip seal as it is not nearly as effective or reliable and far more susceptible to early failure/replacement.

In some cases, a food grease barrier is used. It's not as gross as it sounds.

Lastly, one could use a mechanical seal, but it is listed last here as the most complex solution. If using a seal, I would suggest a double mechanical seal with a food-grade fluid barrier. With this you would need a pressure pot configuration. Expensive, yes. But if you have pressurized nitrogen available (for that pressure pot) and a competent maintenance staff and good PM, it could be a reliable option for you.

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General Practices:

I can’t write about an application without reminding the reader that good installation practices are always essential. The first thing I would advise would be to read the operation and maintenance manual from cover to cover. Monitoring upstream and downstream pressures and temperatures is essential, so sensors/gauges should be put in place. Minimizing pipe strain is critical, with whatever method you choose. A good rule of thumb is that the piping should remain in place, moving no more than a thickness of a gasket, whether the pump is installed or not. I would further suggest that with warmer fluids - where thermal expansion could occur - to install expansion joints on the inlet and outlet where possible. A solid foundation is important as well, with precise pump and motor alignment when long coupling and vibration mitigation such as grouting the base-plate. Last but not least, a good preventative maintenance schedule is critical, and will be detailed in any good O&M manual, but you will likely need to adjust that for your particular application. Obviously you want optimal suction and discharge conditions, taking into account the demands of the pump as well as the application fluid – adequate NPSHA, pipe sizing and inline components, including proper selection of valves, elbows strainer/filters and reducer.

There you have it, you are now an "expert." If you'd like to know more about any pumping application (liquid or vacuum) or filtration, hose, general process equipment, etc., check out Anderson Process. Schedule a visit with your regional rep today.