Chemical mixing machine design

1Document Information31.1Document Purpose31.2Document Status32Key Design Features32.1Vessel Design32.2Recirculation Pump32.3Recirculation Line Raw Material Addition32.4Mixing42.5Cooling42.6Storage/Recirculation42.7Materials/Standards43Typical Batch Sequence44Washing and Sterilisation4

Main Mixer and Recirculation Design & Operational Philosophy

1 Document Information 3

1.1 Document Purpose 3

1.2 Document Status 3

2 Key Design Features 3

2.1 Vessel Design 3

2.2 Recirculation Pump 3

2.3 Recirculation Line Raw Material Addition 3

2.4 Mixing 4

2.5 Cooling 4

2.6 Storage/Recirculation 4

2.7 Materials/Standards 4

3 Typical Batch Sequence 4

4 Washing and Sterilisation 4

1 Document Information

1.1 Document Purpose

This is a Level 2 document and has been written to highlight the main design features and purposes of the standard Unilever Liquids Main Mixer and Recirculation system

The document will describe the standard designs used, options where necessary and the reasons for the options may be used

Reference should be made to the Level 2 PFD when reading this document

1.2 Document Status

Revision Issued Status

A 18.11.09 Issued for Comments

2.1 Vessel Design

Blending of the raw materials into the finished product is achieved using a simple, welded cylindrical vessel with standard dished ends The vessel is made from stainless steel and usually suspended from a floor or platform (usually the first floor of the making plant) so that the top is easily accessible and the bulk hangs below Loadcells are incorporated in the vessel supports in order to weigh main additions during manufacture The vessel sizes are standardised into 5 m³, 10 m³ and 15 m³ working volume

Raw materials are mainly added into the top of the vessel in liquid form, but several methods exist For details on this refer to the Raw Materials Addition information

The top of the vessel also houses a manway (for inspection of the contents, minor additions and maintenance access), a vent connection, three washing connections and an agitator mounting Details of the vent connection can be found in the Ventilation information – note these vents can tend to be large There are three 360º sprayballs arrange 120º apart for vessel washing These are connected to the CIP system which supplies hot water The agitator motor

is mounted vertically directly on top of the vessel The agitator shaft hangs down into the vessel supporting the agitator blades Four baffles are mounted at 90º from each other inside the vessel, to aid the action of the agitator Much work has been done on the actual design of the agitator blades and baffles For details on this refer to the Agitator information

2.2 Recirculation Pump

The outlet from the vessel is located at the bottom of the tank in the centre of the dished end Flow then passes to a recirculation pump, usually located directly below the main mixer, on the ground floor The recirculation pump delivers product through the recirculation line at a rate of five times the vessel working volume per hour, i.e 25 m³/h, 50 m³/h or 75 m³/h The pump is a lobe pump with electric drive as this copes best with the range of duties required and the media

to be pumped A pressure-relief bypass from the pump discharge to the suction side is required

to prevent the pump over-pressurising and damaging itself or the line

2.3 Recirculation Line Raw Material Addition

Depending on the product being made some raw materials are best added into the fast-moving recirculation line rather than the main mixer When this is the case, these materials are added here, just after the pump but before the mixer For details on this refer to the Raw Materials Addition information

2.4 Mixing

Depending on the product being made, a static mixer or a powered high-sheer mixer can be installed on the pump discharge side Refer to actual Product information for details of mixing requirements The mixer is usually installed on the ground floor alongside the recirculation pump There is usually a bypass around the mixer for those batches that do not need mixing

2.5 Cooling

Product usually needs cooling before passing to storage The most efficient way to cool the product (in terms of energy use and foot-print) is a plate heat-exchanger in the recirculation line (this is known as side-arm cooling) The heat-exchanger is usually installed on the ground floor next to the recirculation pump There is usually a bypass around the heat exchanger for those occasions cooling is not required A cooling water system is required for this exchanger The exchanger design is based on cooling the contents of the vessel 1ºC per minute

2.6 Storage/Recirculation

After the heat exchanger, the recirculation line splits Finished product is delivered to buffer storage or further additions (enzymes or post-dosing) through one outlet, the other outlet returns flow to the vessel, usually through a hygienic manifold and dip-pipe

2.7 Materials/Standards

The recirculation line is made from fully welded stainless steel, to help meet hygienic criteria Where connections cannot be avoided, hygienic couplings are used The valves and equipment

in the lines are all certified hygienic

Typically, a batch sequence will be as follows,

• Vessel is clean and empty

• The first additions are made, usually water and bulks from a tank farm Once the level

is sufficient to cover the bottom blade of the agitator, the agitator will start

• Minors are added to the batch, either from IBCs, pre-mixers, big-bags (powders) or manually (through the manway)

• Recirculation begins to cool and shear (with the mixer) the product until product specification is met

• Bypasses activated and product diverted to buffer storage

• As level falls, agitator and pump are stopped appropriately, to prevent damage

• Once vessel is empty, a wash cycle or the next batch begins Washings diverted to a suitable washings tanks for re-use in the next compatible batch

• Vessel is clean and empty

When washing a vessel, around a tonne of water is used Hot water is added to the vessel through the sprayballs, to wash the vessel The pump is activated and hot water through the recirculation line passed for several minutes The washings are then transferred to the washings tanks by the recirculation pump Some residue will be left on the walls of the vessel and the pipes, but this is very dilute and will not affect the next batch

Periodically, the equipment must be sterilised This is accomplished in the same way, but the vessel and pipes are held at a higher temperature for an extended period to eliminate bacterial growth