In current high- tonnage production of spray - dried detergents, continuous mixing of ingredients is used to form formulations that are spray dried in drying towers with nozzle atomization. Many spray towers have built-in flexibility of both co-current and counter - current air flows in order to handle special formulations and achieve specific bulk density.

The plant layout for detergent formulations consists of a feed-preparation section (automatic feeding, proportioning and mixing) feed pumping to the nozzle atomizer, dried- powder conveying and dosing, followed by thorough blending, screening and packaging.

Linear alkyl benzene sulphonate paste, is metered into a slurry preparation tank together with metered sodium silicate solution, and solid phosphates, sulphates and additives. The slurry preparation tank acts as a coarse mixer. Here lumps are broken down and air pockets are eliminated. Materials after blending are conveyed to an ageing vessel.

Mixing is carefully controlled to prevent aeration of the slurry. Feed slurry passes through a coarse filter, homogenizer (colloid mill) and fine filter. Deaeration of product is carried out if necessary. The slurry of constant solid content and viscosity is ready for spray drying. The handling of product in the feed treatment section plays a large role in the quality of the dried product (e.g. granulation, degree of fines, etc.)

The slurry (50 - 80°C, 120 - 180°F) is fed to the spray dryer by a high-pressure pump. Counter -current product-air flows are mainly used. A counter-current unit with multiple nozzles has been claimed to be of special merit, Counter -current systems give high product bulk densities 0.3 - 0.4 g/cm3 and moisture content 6 - 15%. Co-current systems give low bulk densities 0.1 - 0.3 g/cm3 with moisture content 3 - 8%.

The vast majority of powder leaves the base of the chamber. The entrained fines fraction is recovered from the exhaust air in cyclones or bag filters. These fines are reslurried.

The main product is belt conveyed to an air lift. Any after-drying dosing is carried out on the belt. This can be organic foam boosters (lauryl alcohol), enzymes (proteolytic) and sodium perborate. The air lift raises the powder to a storage hopper from where gravity feed takes the product through screens and a perfuming chamber to packing machines.