The 13th International Exhibition of Oil, Gas and Petrochemical Industries and Products in Tehran in April is being used by Sandvik to highlight its project solutions for pastillation in general and sulphur in particular.
Since developing its Rotoform pastillation process in the early 1980s, the company has supplied more than 1400 units to customers across the world, for the chemical, food and oil and gas industries. While applications range from waxes and resins to chocolate, almost 30percent are used for the pastillation of sulphur.
Recognising the growing need for higher sulphur solidification capacities in refineries, Sandvik Process Systems made a significant breakthrough in 2005, with the development of the Rotoform HS system, a high-capacity version of the standard Rotoform offering double the throughput – plus a range of additional benefits, including easier and more economical servicing. Today, the RotoformHS system offers a solidification rate of 300t/d of sulphur pastilles.
While throughput capacity is substantially higher than the standard Rotoform, the basic principle remains the same (Fig.1).
A depositor – the Rotoformer itself – feeds precisely dosed droplets of the molten product onto a continuously running steel belt, which is cooled from the underside by water, sprayed through nozzles. The heat from the molten drops is transferred to the cooling water via the steel belt and by the time they reach the discharge end of the line they have been transformed into solid pastilles. This process delivers a uniform, premium-quality end product (to SUDIC specification) with free flowing, dust free characteristics plus low residual hydrogen sulphide and water content – ideal for subsequent handling, storage and transportation. It is also highly efficient, with the indirect heat transfer ensuring no contact between product and cooling media and delivering well defined cooling times for controlled crystallisation.
Another key benefit of the Rotoform system is its environmentally-friendly operation, with minimal air extraction required and that which does pass through the exhaust fulfilling all usual emission standards without any treatment.
Modifying mixing screws
Ajax Equipment is supplying vertical screw blenders to leading manufacturer of inorganic coagulants and water treatment polymers Kemira Water for use at its Bradford production facility in the UK.
Kemira Water manufactures water treatment solutions for industrial and municipal water treatment plants. Earlier last year, Ajax Equipment successfully designed, manufactured and installed replacement mixing screws of a modified design for two vertical screw blenders at the Bradford site.
As a result of the improved performance secured, the company was asked to provide four high capacity, vertical screw blenders as part of a further plant upgrade.
Ajax Equipment undertook powder testing to assess the polymer granules 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 and double outlets, ensuring the required mass flow of the polymer granules and rapid discharge.
The mixers have been designed for maximum capacity within a tight footprint and limited headroom, with a screw to provide a high re-circulation rate with mixing efficiency.
They use central ‘fountain’-type mixing augers featuring special taper design with increasing pitch and taper reducing centre cone. Lower sweep arms on the screws collect from the 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 a Bradford site expansion project, we identified the need to increase our dry blending capacity. We had previously worked with Ajax to improve the efficiency of two existing blender units and approached them to supply the new units. Our decision was based not only on the Ajax technical specification, but also their willingness to work closely with the customer to identify the right requirements for the application.”
No objective rules have yet been specified and adopted concerning the process of mixing concrete. A consensus exists, however, that a high specific input of energy into the mix is a crucial factor.
Concrete has been in use as a mass building material comprising just cement, aggregates and water for a very long time During the last 20–30years, however, the development and use of high-performance, speciality concretes has taken place alongside the continued use of mass concrete.
These newer concretes may contain up to six types of component, the established and essential three plus other solid and liquid additives and air. A great deal of R&D in technical institutions and universities throughout the world has been carried out.
Nevertheless it appears that no objective rules have yet been specified and adopted concerning the process of mixing concrete; it remains something of an art – so concretes, even high-grade materials, are still mixed according to ‘feel’. It is recognised that the satisfactory preparation of speciality and ultra high performance concretes is much more difficult than the 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 led the field in this respect for a considerable time. The company decided some time ago, therefore, to concentrate its development programme on mixers and procedures adapted to the production of the newer materials. The specific energy input achieved by the current models of Eirich mixer employing a drive power of 90kW is 3.75kW/100kg of hardened concrete. Comparable figures for other types of mixer commonly used in concrete mixing are: annular trough mixer; 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 energy input than any of the other types of mixer investigated. The comparison was arrived at using a mix of 1500litres (2400kg) of loose aggregates to produce 1.0m3 of hardened concrete in each case.
A reversible homogeniser
The Greerco reversible homogeniser from Chemineer can produce high quality shampoos, gels, creams, and lotions – without the need for vacuum processing vessels or in-line vacuum de-aeration devices.
Designed for in-tank atmospheric de-aeration and flow-direction control, the Greerco Homogeniser is effective across a wide viscosity range, including both liquid and powder components, and has the flexibility to consistently produce bubble-free end-products in different batch sizes
When the powder or liquid addition phase of the process is complete, the Homogeniser is switched to run briefly at full speed to fully homogenise the batch and completely disperse any remaining agglomerates
At this point in the manufacturing, when the deflector plate is located precisely at the surface level of the liquid-at-rest, de-aeration begins.
The operator adjusts the speed of the homogeniser to provide a smooth, laminar, non-splashing flow that moves 360° away from the circular deflector plate.
Entrained air bubbles are drawn up from the bottom of the batch and distributed gently at the surface of the liquid.
