Finding the best solution for your fluid handling needs

Suzanne Gill looks at a variety of different pumping solutions which have been specified for handling abrasive fluids.

Movement of abrasive fluids demands careful pump specification to ensure the best solution to transport the medium efficiently, while minimising pump wear, maintenance costs and downtime.

Operating conditions should always be taken into account as this will have a significant effect on the service life of a pump system. Transferring fluids at lower speeds, for example will reduce any abrasive effect, so a common solution when pumping abrasive fluids is to overspecify the pump to allow it to be operated at lower speeds and differential pressures.

Careful pump specification can offer other benefits, as one glass manufacturer has found out. By rethinking its pump requirements, the company has overcome the problems associated with pumping abrasive fluids and has also benefitted from some impressive energy savings.

For many years the glass manufacturer had relied on four split-case centrifugal pumps for the supply and circulation of process water around its plant. Excessive wear, caused by the level of work demanded of the pumps, resulted in signs of declining performance.

The Omega’s axially-split case pump simplifies maintenance procedures, enabling ready access to all parts for thorough cleaning.

Numerous repairs and overhauls of the pump system had been undertaken over the years, but, following one inspection by Industrial Pumps Ltd (IPL), it became clear that further repair work was going to be uneconomic, and the decision was made to look at replacement pumps.

Based on the application details provided by the plant’s pump engineer and a review of the nature of the wear on the pumps, IPL recommended replacing all four existing pumps with two KSB Omega pumps.

The water used in the plant is drawn from two large lagoons and pumped around the site to the production areas. After passing through filtering weirs, it is returned to the lagoon.

Commenting on the challenges of the application, David Silverwood, IPL technical sales engineer, said: “The pumped water contains quantities of glass, sand and various other solids and the cumulative effect these aggressive particulates had on the pump casings and other key components meant that it became uneconomical to effect repairs. In addition, it was becoming harder to source spare parts from the original equipment manufacturer. A further consideration was the running costs of the pumps, which had escalated over time.”

“The pumped water contains quantities of glass, sand and various other solids.”

The task facing IPL was to replace the four pumps with new units that would provide greater resistance to wear, deliver optimum performance at all timesand reduce running costs. Following discussions with KSB UK, it was decided that the best solution would be the installation of two KSB Omega 200-250 AGBV1s in a duty/standby configuration. This would allow the customer to have total control over the pumps at all times in order to adjust flow levels following production requirements. The pumps are monitored 24/7, and if there is a power cut or loss of pressure in the operating pump, there is an immediate switch-over to the duty standby pump.

With corrosion resistance and energy savings high on the customer’s agenda, the Omega was a natural fit as the corrosion and abrasion-resistant materials used in the pump contribute to long service life by protecting key components. Further, being an axiallysplit case pump simplifies maintenance procedures, enabling easy access to all parts for thorough cleaning. The interior of the pump is designed to transport water with the minimum of flow resistance, a factor that also contributes to its energy savings and reduced life-cycle costs.

IPL was able to convince its customer that two Omega 200-250 AGBV1s, each delivering flows of 700m³/hr at a head of 90m and power absorption of 206.7kw running at 1490rpm, would be more than adequate to replace the existing four pumps. They would also be far more economical to run, with a reduction in the absorbed power being over 50%.

“As with any project, capital investment costs were closely examined,” concluded Silverwood. “After just 12 months of continuous operation, the new pumps have provided power savings of 80kw/hr which translates into a £49,000 reduction in the running costs of pumping water around the plant.”

A HORIZONTAL SOLUTION

To efficiently pump liquids with abrasive solids in suspension, Goulds Pumps, a division of ITT Industries, can offer a single-stage, enclosed-impeller, back pullout process pump. The model CW/CWX horizontal pumps have wear parts made of HC600 chrome iron to ensure a long service life in all types of slurry applications.

The pumps are designed with only three power ends for maximum interchangeability of parts and reduced spare parts inventory. Rugged casings are made with abrasion-resistant HC600 with extra-thick metal sections for maximum operating life.

The patented Shearpeller design feature of the CWX non-clogging pump ensures it can handle large, stringy or fibrous solids in suspension, entrained air in water, viscous materials, plus many other hard-to-pump slurries. The Shearpeller’s radial vanes narrow as they approach the eye to allow large or stringy solids to enter. This way, almost anything that enters the impeller can be pumped. The vanes widen toward the OD of the impeller to provide a positive pumping action and higher heads than fully recessed impeller pumps.

HOSE PUMPS

RVA specialises in the recovery and recycling of salt slag – a by-product of aluminium smelting which contains around 5% residual aluminium metal and various metal oxides, mainly aluminium oxide.

Pumping this slurry is a particularly harsh application, for which the company specified Bredel hose pumps from Watson-Marlow Fluid Technology Group (WMFTG) to safely transfer this abrasive fluid around a plant. Salt slag is considered hazardous waste, so the recycling operation relies on a closed-loop process that makes minimal demands on the environment.

The recovery process first sees the salt slag milled with optional recirculation to liberate aluminium using an eddy current separator, and iron via a magnet. Next, the remaining salty material is introduced to a dissolution section where it is mixed with water which is recovered later in the process. The brine-laden water is transferred by two high-flow Bredel 100 pumps into pressurised reaction vessels, before Bredel 65 and 40 pumps transfer aluminium oxide as aslurry to the reactors. It is here that the aluminium oxide is very abrasive and at a high temperature.

“After just 12 months the new pumps have provided power savings of 80kw/hr which translates into a £49,000 saving.”

Residue from the reaction phase is then conveyed to a belt filter where brine and water are pumped out under vacuum using a Bredel 80, leaving a solid residue known as Valoxy. Clean water – along with water removed at the dissolution stage – is then used to wash the solids.

In the final stage of the process, the effluent brine continues to the crystallisation section. Sodium chloride and potassium chloride are crystallised out of solution, and an in-line decanter increases the concentration of solids in the slurry, facilitating higher salt recovery.

The hose pump is well suited to use in this application as it has no valves or seals to clog or replace and the pump hose is designed to handle abrasive slurries with up to 80% solids in suspension.

A low maintenance chocolate pumping solution

KINNERTON CONFECTIONERY IS A UK-BASED manufacturer of chocolate and novelty confectionery. The company recently decided to convert its entire pump range to DESMI ROTAN pumps. Lee Hunt, engineering manager at Kinnerton Confection, explained why: “One of the main reasons for the conversion was due to the low maintenance demands of these pumps. Traditionally we have done six-monthly pump checks and often needed to do a full repair. With the DESMI ROTAN pumps installed, so far we have done a yearly check and have only had to replace the packing on a few pumps.”

When pumping such a difficult fluid as chocolate, the pumps’ internal parts often get blocked due to a temperature increase in the pump caramelising the chocolate which congeals as a result. As more chocolate congeals the internal friction in the pump increases, and ultimately the pump can become blocked entirely.

To overcome this issue, the internal tolerances in the ROTAN pump have been designed to ensure that new chocolate is always added to the areas around the rotating parts of the pump, and in particular around the pivot of the star wheel and bushings. This reduces or eliminates the tendency for the chocolate to caramelise on the back of the rotor and at the bearing of the star wheel, helping to prevent the pump from blocking. The pumps are also equipped with a heating jacket on the front and rear end.

ROTAN pumps are also well suited to applications where the media must be handled delicately because the internal toothing of the gear pump results in almost no change in the flow direction through the pump, translating into gentle fluid transfer.