Introduction

The hydrocyclone is very important in the separation industry. It is popular due to its simplicity in

design and effective operation. It was required that an investigation into the operation and design of

the hydrocyclone was performed. The necessary information that was obtained included the

theoretical background of the hydrocyclone as well as to how it should be designed. The

hydrocyclone uses centrifugal forces as a separation mechanism and during the separation process;

it produces an overflow and underflow stream. A mass and energy balance was required for a

hydrocyclone system so that it can be seen how the system works in terms of efficiency and

effectiveness in separation. Also it was necessary so that the control and safety factors of the

system can be implemented. The design of the system was undertaken to obtain the ranges and

capacities of the hydrocyclone. It can be seen that from the research and calculations preformed,

the hydrocyclone is reliable for separation of substances.

Hydrocyclone Theory:

Description

A hydrocyclone is a simple mechanical machine which contains no moving parts and uses centrifugal

forces to separate substances. It promotes separation of heavy components from light components.

It is also known as a static device. It is most popular in separating solid particles from liquid but it

can also be used for liquid-liquid separation and solid classification. However, it is not as effective

during liquid-liquid separation as it is for solid-liquid separation.

It is a closed vessel which consists of a cone body which is

also known as a vertical cylinder. It has a vortex finder,

orifice and an air core. The centrifugal force is induced by

the feed flow entering tangentially into the hydrocyclone.

The centrifugal force generated by the hydrocyclone is

mild. The feed flow usually consists of a slurry with small

particles. It is then divided into heavier and lighter

particles. The heavier parts are discharged out the

bottom which is known as underflow, while the lighter

particles discharge via the top of the hydrocyclone which is known as overflow. The extent of

separation depends on the particle size and density (3). The particles are thrown against the wall by

centrifugal forces and thereby fall into the outlet hopper.

Figure 1-Hydrocyclone (4)

The dimensions of individual cyclones range from 10mm to 2500mm and flow capacities can range

from 0.1 to 1000

. The particles that are separated could range from 10 to 500 micron. Operating

pressure will vary between 0.2 to 10 bars. The higher pressure is usually for smaller particle

separation. The underflow solid concentration will be between 40 to 60% by volume. It cannot be

higher otherwise the flow at the bottom shall be restricted. (1)

The hydrocyclone is the most cost effective method of separating substances (1). It doesnt require

maintenance because it contains no moving parts. It is simple in design and easy in operation. They

are excellent tools in reducing the load on the expensive filters and de-emulsification devices. They

protect and increase efficiency of other equipment such as the spray nozzles, heat exchanger and

pump seals (2).

Industrial uses of the Hydrocyclone

The alumina industry

Pulp and paper

Power plants

Industrial or Municipal wastewater treatment

Effluent treatment

They also form an integral part of the development loop in the following process industry

application:

Multiphase Reactor System

Fluidized Solid/Liquid

Contactor/Reactor System

Liquid/Liquid Extraction System

Limitation of the Hydrocyclone

They do not work of all separations.

They do not achieve perfect or complete separation.

There will be some heavy substances in the overflow and even some light substances in the

under flow.

They cannot handle variable flow rates because it causes the spin in the hydrocyclone to

vary. This means that if it is used in a process, the flow rate entering the hydrocyclone

should always be the same.

Material Balance Hydrocyclone

The circuit below shows the output from the Ball Mill and a Rod Mill going to a hydrocyclone with 2

products i.e. the underflow and overflow. The underflow product is recirculated to a ball mall to be

further ground. The initial hydrocyclone slurry density is 1140 kg/m3 and is sent for separation. It

produces an underflow slurry density of 1290 kg/m3 and an overflow slurry density of 1030 kg/m3.

The density of the dry solid is 3000 kg/m3. It takes 4 seconds for 3 litres of sample to reach

underflow.

Flow Diagram:

BALL MILL

OVERFLOW

ROD MILL

HYDROCYCLONE

UNDERFLOW

SOLIDS

MSR = 163.96

kg/hr

MTR = 3779.5 kg/hr

MWR = 3615.54kg/hr

MT = 3779.5 kg/hr

MTB = 3488.18 kg/hr

MUFT =3488.18 kg/hr MOFT =3779.5 kg/hr

CONCENTRATION

OF MINERAL

Percentage Solids in Feed:

Similarly: and

Dilution Ratio:

Similarly: and

Solids Flow rate for the UF:

By using the water balance:

Hence the solids balance:

Hence:

;

and

Using Dilution Ratios:

Hence Total Flows are:

Recirculation Ratio

Energy Losses Hydrocyclone

The balance for a cyclone without a pump is given by:

The following assumptions where made:

Level difference is negligible compared to other terms,

Kinetic energy of the exiting stream is negligible

Hence

Now from calculation of each term:

Choosing and the fluid inlet velocity calculated under design section. The second term is

calculated as 17.61.

Therefore

The rate of mechanical energy that is lost from the system is given b the following equation:

Hence

These losses are made up by a pump in order to maintain flow through the system.

Design of a Hydrocyclone:

A hydrocyclone uses centrifugal forces to separate the solids from the liquids or one liquid from

another liquid. A centrifugal force (vortex motion) is produced by the liquid flow. When designing a

hydrocyclone, it is important to note the following:

The operating conditions i.e. the flow rate of the inlet stream as well as the bulk density of

this stream and viscosity

The particle size of solids

The d50 or cut size and/or the efficiency of the cyclone

Sizing of the hydrocyclone

There are many different methods that have been provided by engineers that are experts in this

field. The design method that was used for this assignment was given by Zanker (1977). Zankers

method is used as a preliminary design method using charts and equations. This method is

highlighted in Chemical Engineering Design, 4th edition (Coulson 1993).

The diagram below was used to calculate the cut size of the hydrocyclone. Particles of 100m were

used as the particle size of the design. The cyclone efficiency was calculated as shown:

Using the chosen particle size (100m) and the efficiency that was calculated above, the d50 was

found to be 71m.

The equation below was used to calculate the chamber

diameter of the hyrdocyclone and all other dimensions of

the hydrocyclone are ratios of the chamber diameter.

(Coulson 1993)

Where:

d50 particle size (m)

Dc diameter of the cyclone chamber (cm)

- viscosity of liquid (centipoise, mN.s/m2)

L Feed flow rate (l/min)

s density of solid (g/cm3)

L density of liquid (g/cm3)

, by substitution

Hence, and

The inlet velocity of the fluid can be calculated as follows:

Summary of the design

DIMENSIONS

Hydrocyclone diameter 0.204 m

Inlet pipe diameter 0.029 m

Overflow pipe diameter 0.041 m

Underflow pipe diameter 0.020 m

Wall thickness 3 mm

Inlet velocity of fluid uin * 2.68 m

All other dimensions of the hydrocyclone are ratios of the chamber diameter. All dimensions

are in mm and are represented in the sketches below.

Figure 2: Dimension ratios of a hydrocyclone Figure 2: Dimension ratios of a hydrocyclone (Coulson 1993)

Materials of construction:

The chosen material for this design in stainless steel. Stainless steel is suitable because:

It is suitable to be used in hot and cold conditions

It has a high tensile strength (>540 N/mm2) (Coulson 1993).

It is less susceptible to corrosion

It does not crack easily.

Although stainless steel is more expensive than most other materials, it requires less

maintenance so the cost balances out on a long term basis.

Mild steel can be used but it does not have a high tensile strength and since cyclones are

high pressure and high velocity vessels, a material with higher strength is more suitable.

To prevent damage to the steel wall, a lining can be placed on the inside of the wall of the cyclone.

Rubber can be used to line the cyclone. The only disadvantage of having a lining in a hydrocyclone is

that it requires constant inspection and maintenance and the lining can break off and disturb the

separation process.

Bibliography Coulson, J.M., Richardson, J.F. and Sinnott R.K. Chemical Engineering(Design). Vol. 6. Oxford: Elsevier

Butterworth-Heinemann, 1993.

L, Svarovsky. Solid-Liquid Separation. 4th Edition. Oxford: Butterworth-Heinemann, 2000.

REFERENCES 1. http://www.mamko.com/hydrocyclone.html MAMKO DESIGN AND ENGINEERING (1)

2. http://www.piiny.com/Krebs/krebs.htm Krebs Engineers

3. Coulson J.M, Richardson J.F, Chemical engineering design, volume six, 2003.

4. http://www.xkjxsb.com/Waterpower_Cyclone_Separator.htm-hyrdocyclone

5. http://www.hydrocyclone.com/faq.htm

http://www.mamko.com/hydrocyclone.htmlhttp://www.piiny.com/Krebs/krebs.htmhttp://www.xkjxsb.com/Waterpower_Cyclone_Separator.htm-hyrdocyclone