Advances in mixing and blending improves efficiency

Tag : powder blenders

Since developing its Rotoform pastillation process in the early1980s, the company has supplied more than 1400 units to customersacross the world, for the chemical, food and oil and gasindustries. While applications range from waxes and resins tochocolate, almost 30percent are used for the pastillation ofsulphur.
Recognising the growing need for higher sulphur solidificationcapacities in refineries, Sandvik Process Systems made asignificant breakthrough in 2005, with the development of theRotoform HS system, a high-capacity version of the standardRotoform offering double the throughput – plus a range ofadditional benefits, including easier and more economicalservicing. Today, the RotoformHS system offers a solidificationrate of 300t/d of sulphur pastilles.
While throughput capacity is substantially higher than the standardRotoform, the basic principle remains the same (Fig.1).
A depositor – the Rotoformer itself – feeds preciselydosed droplets of the molten product onto a continuously runningsteel belt, which is cooled from the underside by water, sprayedthrough nozzles. The heat from the molten drops is transferred tothe cooling water via the steel belt and by the time they reach thedischarge end of the line they have been transformed into solidpastilles. This process delivers a uniform, premium-quality endproduct (to SUDIC specification) with free flowing, dust freecharacteristics plus low residual hydrogen sulphide and watercontent – ideal for subsequent handling, storage andtransportation. It is also highly efficient, with the indirect heattransfer ensuring no contact between product and cooling media anddelivering well defined cooling times for controlledcrystallisation.
Another key benefit of the Rotoform system is itsenvironmentally-friendly operation, with minimal air extractionrequired and that which does pass through the exhaust fulfillingall usual emission standards without any treatment.
Modifying mixing screws
Ajax Equipment is supplying vertical screw blenders to leadingmanufacturer of inorganic coagulants and water treatment polymersKemira Water for use at its Bradford production facility in the UK.
Kemira Water manufactures water treatment solutions for industrialand municipal water treatment plants. Earlier last year, AjaxEquipment successfully designed, manufactured and installedreplacement mixing screws of a modified design for two verticalscrew blenders at the Bradford site.
As a result of the improved performance secured,
the company was asked to provide four high capacity, vertical screwblenders as part of a further plant upgrade.
Ajax Equipment undertook powder testing to assess the polymergranules bulk flow characteristics by measuring the bulk density,wall friction and shear strength of the polymer granules.
The results were used to design the blender base geometry anddouble outlets, ensuring the required mass flow of the polymergranules and rapid discharge.
The mixers have been designed for maximum capacity within a tightfootprint and limited headroom, with a screw to provide a highre-circulation rate with mixing efficiency.
They use central ‘fountain’-type mixing augersfeaturing special taper design with increasing pitch and taperreducing centre cone. Lower sweep arms on the screws collect fromthe base of the blenders to provide rapid discharge.
David Barron, global project engineer for polymers at Kemira Water,summarised the Ajax input to the project: “As part of aBradford site expansion project, we identified the need to increaseour dry blending capacity. We had previously worked with Ajax toimprove the efficiency of two existing blender units and approachedthem to supply the new units. Our decision was based not only onthe Ajax technical specification, but also their willingness towork closely with the customer to identify the right requirementsfor the application.”
No objective rules have yet been specified and adopted concerningthe process of mixing concrete. A consensus exists, however, that ahigh specific input of energy into the mix is a crucial factor.
Concrete has been in use as a mass building material comprisingjust cement, aggregates and water for a very long time During thelast 20–30years, however, the development and use ofhigh-performance, speciality concretes has taken place alongsidethe continued use of mass concrete.
These newer concretes may contain up to six types of component, theestablished and essential three plus other solid and liquidadditives and air. A great deal of R&D in technicalinstitutions and universities throughout the world has been carriedout.
Nevertheless it appears that no objective rules have yet beenspecified and adopted concerning the process of mixing concrete; itremains something of an art – so concretes, even high-gradematerials, are still mixed according to ‘feel’.
It is recognised that the satisfactory preparation of specialityand ultra high performance concretes is much more difficult thanthe preparation of mass concrete and demands, amongst other things,a particularly high specific energy input.
Gustav Eirich of Hardheim, Germany, claims that its mixers have ledthe field in this respect for a considerable time. The companydecided some time ago, therefore, to concentrate its developmentprogramme on mixers and procedures adapted to the production of thenewer materials. The specific energy input achieved by the currentmodels of Eirich mixer employing a drive power of 90kW is3.75kW/100kg of hardened concrete. Comparable figures for othertypes of mixer commonly used in concrete mixing are: annular troughmixer; 37kW and 1.54kW/100kg: annular trough mixer with agitators;37+22kW and 2.46kW/100kg: planetary mixer; 44kW and 1.83kW/100kg.
So Eirich machines achieve a considerably higher specific energyinput than any of the other types of mixer investigated. Thecomparison was arrived at using a mix of 1500litres (2400kg) ofloose aggregates to produce 1.0m3 of hardened concrete in eachcase.
A reversible homogeniser
The Greerco reversible homogeniser from Chemineer can produce highquality shampoos, gels, creams, and lotions – without theneed for vacuum processing vessels or in-line vacuum de-aerationdevices.
Designed for in-tank atmospheric de-aeration and flow-directioncontrol, the Greerco Homogeniser is effective across a wideviscosity range, including both liquid and powder components, andhas the flexibility to consistently produce bubble-freeend-products in different batch sizes
When the powder or liquid addition phase of the process iscomplete, the Homogeniser is switched to run briefly at full speedto fully homogenise the batch and completely disperse any remainingagglomerates
At this point in the manufacturing, when the deflector plate islocated precisely at the surface level of the liquid-at-rest,de-aeration begins.
The operator adjusts the speed of the homogeniser to provide asmooth, laminar, non-splashing flow that moves 360° away fromthe circular deflector plate.
Entrained air bubbles are drawn up from the bottom of the batch anddistributed gently at the surface of the liquid.