سیکلونها سیکلونها بر اساس نیروی گریز از مرکز جداسازی ذرات را انجام می دهند. سیکلونها قادرند ذراتی با قطر 5 میکرون را نیز به راحتی از هوا جدا سازند. سیکلونها نیز می توانند برای افزایش راندمان به صورت مرطوب نیز به کار گرفته شوند.

Cyclones Principle The particles are removed by the application of a centrifugal force. The polluted gas stream is forced into a vortex. the motion of the gas exerts a centrifugal force on the particles, and they get deposited on the inner surface of the cyclones

Collection Efficiency In order to calculate the efficiency, first the particle size with 50% collection efficiency (dp50%) as the baseline needs to be determined μ is dynamic viscosity of air (based on gas temperature) b is inlet width, Ne is the number of effective turns (number of turns the flow makes from the entrance to the midpoint of the core section) Vi is inlet velocity and ρp is particle density.

cyclone

Empirical Cyclone Collection Efficiency

Design factor having greatest effect on collection efficiency is cyclone diameter. Smaller dia, higher is efficiency, because centrifugal action increase with decreasing radius of rotation. Cyclone efficiencies > 90 % with particle dia of 10 μ > 95 % with particle dia 20 μ.

High efficiency- smaller body dia to create greater separating force. Increase collection efficiency, if increase in dust particle size, dust particle density, gas inlet velocity, inlet dust loading, cyclone body length Decrease collection efficiency due to increase in cyclone dia, gas outlet dia, inlet width, and inlet area

Problem A cyclone with a flow rate of 150 m3/min has an efficiency of 80%. Estimate the efficiency if the flow rate is doubled.

Solution Step 1 Q1 = 150 m3/min Q2 = 300 m3/min Pt1 = 100% - 80% = 20% Pt2/Pt1 = (Q1/Q2)0.5 Step 2 Final Efficiency = 1- Pt2 = 86%

Dimensions of a Standard Cyclone

Problem Design of Cyclone Body diameter = 0.75 m Flow rate = 2.75 m3/s ρp = 1600 kg/m3 ρg = 1.1 kg/m3 µ = 2.5*10-5 kg/m-s High throughput H = 0.8 * body diameter W = 0.35 * body diameter Lb = 1.7 * body diameter Lc = 2.0 * body diameter Calculate the diameter of particle with 50% efficiency

Solution Step 1: Inlet Velocity = Q/A = 17.46 m/s Step 2: Number of effective turns Ne = (Lb + Lc/2)/H Ne = 3.375 Step 3: Diameter of particle dpc = 10 µm

Operating problems Erosion Corrosion Material build up

Advantages of Cyclones Cyclones have a lost capital cost Reasonable high efficiency for specially designed cyclones. They can be used under almost any operating condition. Cyclones can be constructed of a wide variety of materials. There are no moving parts, so there are no maintenance requirements. Require less floor area. Simple construction and maintenance. Can handle large volume of gas at high temp.

Disadvantages of Cyclones They can not be used for small particles High pressure drops contribute to increased costs of operation. Requires large head room. Less efficiency for smaller particles (<10μm). Sensitive to variable dust load and flow rate.

Applications Control gas borne particulates from industries like cement, feed and grain processing, food and beverage processing, mineral processing, paper and textile industries and wood working industries. Used in recovery of catalyst ducts in petroleum industry and reduction of fly ash emission.