A new cationic emulsion transfer pump to move asphalt to storage drums for a company in the Caribbean 

In this case study, we are heading off to the Caribbean. This is where one of our pumps is being delivered, to help our client with the transfer of asphalt as a cationic emulsion from storage tanks located below ground into drums on the surface.

But first, what is an emulsion?

It is basically a mixture of two or more liquids that are normally unblendable, but have been mixed using an emulsifier. This is a substance that helps combine liquids that don't usually go together, like oil and water. 

In an emulsion, one liquid is mixed in with the other, with the dispersed liquid forming minute droplets within the base liquid. There are many types of emulsions such as:

• Oil in water (O/W)

An oil phase blended with an aqueous phase, for example, milk is an O/W emulsion

• Water in oil (W/O)

Conversely, this is an aqueous phase mixed with an oil phase - margarine is a W/O emulsion which is generally much fattier than a direct emulsion

Emulsions are part of many popular foods and drinks including:

•  Ice cream

Egg yolks have emulsifiers that keep ice crystals small and give a lovely creamy texture

• Mayonnaise

This is a fat-in-water emulsion containing egg yolk, vinegar or lemon juice, and occasionally mustard

• Ganache

An emulsion of cocoa fat and milk fat in a solution of water and sugar

• Espresso

Forcing water through coffee beans at high pressure makes the oil from the beans emulsify with the water

What is cationic emulsion?

A cationic emulsion is a type of bitumen emulsion where bitumen and water have been mixed by a cationic emulsifier. It is a chemical surface-active agent with a positive electrochemical charge. The bitumen is dispersed in the water as positively charged globules. 

Cationic emulsions are widely used in road construction, surfacing and cold mix asphalt. They are usually brown in colour and flow freely at normal temperatures. They have low viscosity, plus good penetration and spreading capacity. 

Cationic emulsions separate faster than anionic emulsions. They break up through the emulsifier acting as an adhesion additive, and through evaporation where the emulsion loses water. 

What is the difference between cationic and anionic emulsion?

The main difference between cationic and anionic bitumen emulsions is the electrical charge of the emulsifier.

In cationic emulsions, the surface charge is positive, while in anionic emulsions, the surface charge is negative. Almost all surfaces have a net negative charge which can be different from material to material. Because of this, anionic and cationic emulsions break down in different ways.  

With anionic emulsion, negatively charged drops of asphalt are added to a negatively charged surface. The components all repel each other and the only way the emulsion can break up is by losing water through evaporation. This makes it more difficult to create a uniform surface and produce enough adhesion.

In contrast, with cationic emulsion the bitumen drops are immediately attracted to the surface and begin to break. The emulsion also loses water by evaporation. This means that the cationic emulsion has two breaking mechanisms at work and will break faster and work more quickly than an anionic emulsion.

In short, this gives cationic systems a significant advantage over anionic emulsions.

What is the difference between cationic bitumen emulsion and bitumen?

As explained, cationic bitumen emulsion is the mix of water and bitumen dispersed by a cationic emulsifier, whereas bitumen is simply the residue from crude oil distillation.

As a bitumen emulsion, cationic bitumen emulsion has several advantages over traditional bitumen emulsions;

The benefits of cationic emulsions;

• They are easier to work with and are compatible with aggregates that have a negative charge

• They are less likely to become unstable

• They can be used across a wider range of temperatures

• They don’t need heating up to be applied

• They don't produce toxic fumes and have a much lower environmental impact

All in all, cationic emulsions can be used with a bigger range of aggregates, they can withstand more moisture and will break at a lower ambient temperature.

What did we specify for this project?

At North Ridge Pumps, we’re not restricted in the type of pumps we can specify.

As the UK’s largest pump supplier with over 25 years in the business, we are experts at selecting pumps for a vast range of applications. We use this specialist knowledge to deliver a well-engineered solution for each client, not a standard product straight off the shelf.

Most important of all, we specify the best pump for every project brief offering the lowest lifetime cost.

For this client, we specified a North Ridge FIG90 internal gear pump with 90° flange connections. This 2” self-priming internal gear pump is now being sent to our client in the Caribbean where it will be used to transfer asphalt as a cationic emulsion from storage tanks below ground to drums above ground.

Tailor-made pump design

In this case, our pump will be driven by a 4Kw ABB motor able to transfer the cationic emulsion mixture at around 80°C to 90°C at a flow rate of 50 gallons per minute.

In line with our client’s specification, we also designed the asphalt transfer pump to operate at less than 450rpm.  This ensured that the mixture remains homogenous and won’t be affected by shear. We also added an external heating jacket to the casing to make sure that the emulsion stayed warm within the pump.

We sealed the cationic emulsion transfer pump using packed gland. Also known as gland packing or stuffing box packing, this has a braided or twisted material wrapped around a pump shaft to stop fluid loss. The material is then compressed against the shaft by a gland - a mechanical seal that can be tightened to become leak-free.

Using a packed gland in bitumen transfer pumps also boosts seal longevity as it is less likely to be damaged on start-up than a mechanical seal, especially if the asphalt has solidified within the pump.

Perfect for this application

As positive displacement pumps, our FIG90 internal gear units are suitable for high pressure applications up to 14 bar and are specially designed to handle clean low to high viscosity lubricating fluids such as fuels, oils, greases, resins and adhesives.

The robust pumping action is carried out by the rotating intermeshing gears and a rotor which combine to push the fluid towards the outlet side of the pump. Due to the very tight clearances between the gears, these pumps are only designed for lubricating clean liquids.

Outstanding efficiency

In addition, this asphalt transfer pump offers incredibly high efficiency. This is thanks to our extremely simple design with just two moving components along with the exceptionally tight clearance within the internal moving parts.

In fact, there is almost zero slip while the pump is operating meaning that energy consumption is minimal. This makes our FIG90 internal gear pumps a great option for applications which demand continuous 24/7 operation.

We can supply our internal gear pumps with an external bypass valve and ATEX explosion-proof motors for use in hazardous non-safe environments and applications. ATEX is short for Atmospheres Explosibles, a set of EU regulations designed to ensure the safety of products and identify the level of protection provided by equipment used in potentially explosive situations.

Official ATEX documentation means that a piece of equipment has been tested and approved and is certified safe to use in explosive or hazardous environments.

If you need to pump sensitive fluids, solids or viscous materials, and aren’t sure which pump is the best for your application, speak to North Ridge Pumps today to see how we can help.