Filtration

Principles and Practices, Second Edition, Revised and Expanded

Michael J. Matteson, Clyde Orr

• Publisher: Routledge
• Year: 2017
• ISBN:
  9781351448758
• Edition: 2
• Topic: Physical Sciences
• Subtopic: Chemistry
• Index: Chemistry

Completely revised and updated, this Second Edition of the critically acclaimed referenceprovides the very latest theoretical and practical data on filtration of gases and liquids.Filtration: Principles and Practices, Second Edition, Revised and Expanded features severalall-new chapters which detail filtration in the mineral industry, high-efficiency air filtration, cartridge filters, and ultrafiltration.The most authoritative and comprehensive guide to essential, state-of-the-art data, Filtration: Principles and Practices, Second Edition, Revised and Expanded is an indispensable referencefor industrial process and chemical engineers and scientists engaged in research, development, and production in the chemical, mineral, food, beverage, and pharmaceutical industries. Itis also a valuable reference for upper-level undergraduate and graduate students in chemicalengineering courses in unit operations.

1

Gas Filtration Theory

JOSEF PICH

The J. Heyrovsky Institute of Physical Chemistry and Electrochemistry Czechoslovak Academy of Sciences Prague, Czechoslovakia

I. INTRODUCTION

Filtration can be defined as the process of separating dispersed particles from a dispersing fluid by means of porous media. The dispersing medium can be a gas (or gas mixture, most frequently air) or a liquid. With regard to the type of the medium, this process can be divided into the filtration of aerosols and lyosols. In this chapter attention is focused on aerosol filtration although there are several common features in filtration of both types of disperse systems. From a phenomenological point of view, the filtration process can be characterized by several parameters.

The pressure drop of a filter Δp is defined by

$\text{Δp}={\text{p}}_1-{\text{p}}_2$

(1)

where p₁ is the gas pressure before the filter and p₂ that behind the filter. This quantity is dependent only on the properties of the fluid and on the proprties of a porous substance used as the filter in the case of a clean filter. As filtration proceeds the pressure drop also becomes dependent on the properties of particles deposited in or on the filter.

If G₁ is the flux of particles into the filter, G₂ the flux of particles from the filter, and G₃ the quantity of particles retained by the filter in unit time, G₁ = G₂ + G₃ from the law of conservation. For a monodisperse system of particles, the filter efficiency E is then defined by

$\text{E}=\frac{{\text{G}}_3}{{\text{G}}_1}=\frac{{\text{G}}_1-{\text{G}}_2}{{\text{G}}_1}=\frac{{\text{G}}_3}{{\text{G}}_3+{\text{G}}_2}$

(2)

The first equality in Eq. (2) defines E in terms of captured and incoming particles, the second in terms of incoming and outgoing particles, and the third in terms of captured and outgoing particles. The quantities G₁, G₂, and G₃ can be expressed in terms of number, weight, activity, etc. The related quantity is the penetration of the filter P, defined by

$\text{E}+\text{P}=\text{1}$

(3)

Sometimes the coefficient P* = P⁻¹ = (1 − E)⁻¹ is used, describing the lowering of the particle concentration after passage through the filter. For example, E = 0.99999 may be expressed as P = 10⁻⁵ and P* = 10⁵, indicating that the particle concentration after a passage through this filter will decrease 10⁵ times.

Filter capacity is defined as a quantity of deposited particles (usually expressed in grams or kilograms) which the filter is capable of accumulating before reaching a certain pressure drop. The filter capacity is approximately equal to a quantity of particles accumulated on the filter between two subsequent operations of filter regeneration. The capacity of the same filter for small particles is always smaller than for large particles. Hence, the filter capacity should be specified for particles of a given size.

Economic indexes include the cost of the filter device, the consumption of energy and material (consumption of energy for overcoming the filter resistance, filter cleaning, and regeneration), and the cost of the gas cleaning (usually expressed as a cost of cleaning to a given degree of 1000 m³ of gas per hour).

There are, of course, further important factors such as the chemical composition of the filter and its physical and chemical properties. For a comparison of different filters a quantity Q*, called the filter quality, is used; this is defined by

${\text{Q}}^{*}=\frac{-ln\text{P}}{\text{Δp}}$

(4)

so that the better filter is characterized by a higher value of Q*. A certain disadvantage of the definition of filter quality given by Eq....

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface to the Second Edition
• Preface to the First Edition
• Contributors
• 1 Gas Filtration Theory
• 2 Liquid Filtration Theory
• 3 Filter Media
• 4 Industrial Gas Filtration
• 5 Filtration Pretreatment
• 6 Filtration in the Chemical Process Industry
• 7 Ultrafiltration
• 8 Filtration in the Mineral Industry
• 9 Filtration in Heating, Ventilating, and Air Conditioning
• 10 Cartridge Filtration
• 11 High-Efficiency Air Filtration
• 12 Analytical Applications of Filtration
• 13 Filter Evaluation and Testing
• Index