Dye dosing systems
Dye dosing systems design depend on sorts of dyes used on particular paper machines. Systems preparing solutions from powder products or systems dosing ready-made liquid dyes and proportionally dissolving them before dosing can be used.
If the dyes are prepared from powder products, e.g in case of preparing FeOx slurries (iron oxide pigments used for dying decor papers), the powder product is purchased in 20 kg sacks or in 450 - 650 - 1,000 kg Big-Bags. In both cases the systems are similar.
The equipment consists of a standard 430 litres hopper containing hundreds kgs of the product (depending on its specific weight). For a higher demand silos for 1 to 2 m3 are used.
The Big-Bag systems are delivered either together with apropriate lifting towers or suitable existing customer's devices can be utilised. The powder material is poured out to the hopper and from there it is delivered in defined mode to a dissolving batch by means of a screw conveyer. The screw conveyer drive is controlled by a frequency converter so that a high dosing accuracy is achieved. A quantity of the product delivered to the dissolving batch is measured by means of a strain-gauge weighing apparatus installed in the batch legs. The batch lid holds a high performance disperging agitator with a motor the input of which is designed depending on the dissolved material and its final concentration. The agitator work element is a Z-disc. The agitator is driven directly. Its motor is controlled by a frequency converter thus increasing the system variability with regards to the operation conditions. The dissolving batches include systems of measuring water, high pressure walls and agitator sprinklers, systems of filtering air during pouring material and measuring and control (M&C) elements (sensors of level, temperature, on demand sensors of viscosity M&C). The solution is pumped out either with diaphragm pumps driven by pressurised air (with a high capacity and a long lifetime period) or with screw (Mohno) pumps either with controlled or with uncontrolled performance or with centrifugal pumps. The solution is pumped to a storage tank with a volume designed for the given conditions. The tank volumes are in a very wide range of 3 to 100 m3. They are equipped with agitators to homogenise the solution or the slurry, with level sensors and emergency level detectors. The dosing stations are designed for required performances of tens to thousand litres per hour. Electric diaphragm pumps or screw (Mohno) pumps are always driven with frequency convertors. The solution or slurry flow rate is measured either with inductive or for higher demands with mass flowmeters. The dosing stations are designed with regards to the performance and they include either one or more pumps with needful fittings and M&C elements. They are usually designed as compact units to be connected to input/output pipelines by means of standard flanges. Connections to signal and power cabling are solved as per the on-site situation. Switchboxes or switchboards can be used or the M&C elements are connected directly to the mill control systems.
Materials: The system can be made from plastics (PP, PE) or from AISI 304/316 stainless steel. The tanks are either delivered mounted (standing on legs and anchored to concrete foundations by means of anchoring screws) or welded on site (and in such a case the tank bottom is embedded in concrete).
Systems for purchased liquid raw materials include suitable pumps to deliver liquid dyes from 1000 kg IBCs to suitable storage tanks volumes of which are 3 to 100 m3. Most of all there are utilised diaphragm pumps driven by pressurised air, screw (Mohno) or centrifugal pumps. The pump choice depends on the raw material features. The storage tanks are equipped with agitators to permanently homogenise the solution or the slurry. The dosing stations are designed the same way like for the powder products.
The equipment as described above is used also for preparing and dosing other slurries like china clay, calcite, itanium white etc. The plants are commonly identical, they differ in performances for various purposes.