Gravity Settling Chambers for controlling Air Pollution Presented by

Joy H Jones

Gravity Settling Chambers Gravity settling chambers are the oldest and

simplest means of removing suspended particles from a gas

In principle,pollutants are removed by reducing the velocity of the gas stream sufficiently to allow particles to settle out under the influence of gravity

The simplest chamber is merely a horizontal duct in which large particles settle out on the floor.

High-efficiency settling chambers are often fitted with baffles or deflectors to change the gas flow direction.

They are called precleaners This type of technology is a part of

the group of air pollution controls collectively referred to as "precleaners," because they are oftentimes used to reduce the inlet loading of particulate matter (PM) to downstream collection devices by removing larger, abrasive particles.

Settling chambers are also referred to as gravity settling chambers, gravity collectors, expansion chambers, and outfall chambers.

Multiple-tray settling chambers are also referred to as Howard settling chambers.

Simple Gravity Settling Chamber

. It is a long duct fitted with hoppers Figure 1, is a simplified

representation of a horizontal simple gravity settling chamber. It is a long duct fitted with hoppers on the floor to collect particulates. Physical dimensions are characterized by the ductwork above the collection hoppers: length = L, width = W, and height = H.

The length of the chamber determines the amount of time the particles remain at the reduced rate…. The primary section of the chamber is

characterized by its cross-sectional area (W x H) and by its length (L). The cross-sectional area is designed to be larger than the inlet and exit ducts in order to reduce substantially the gas stream's d inlet linear velocity. The length of the chamber determines the amount of time the particles remain at the reduced rate. This starving of the gas's forward motion allows the particles sufficient time to settle out into the hoppers.

collection efficiency

The collection efficiency of settling chambers varies as a function of particle size and settling chamber design. Settling chambers are most effective for large and/or dense particles.

Advantages of settling chambers include…… Low capital cost; Very low energy cost; No moving parts, therefore, few maintenance

requirements and low operating costs; Excellent reliability; Low pressure drop through device; Device not subject to abrasion due to low gas

velocity; Provide incidental cooling of gas stream;Temperature

and pressure limitations are only dependent on the materials of construction; and

Dry collection and disposal.

Disadvantages Relatively low PM collection efficiencies, particularly

for PM less than 50 micrometer in size; Unable to handle sticky or tacky materials; Large physical size; and Trays in multiple-tray settling chamber may warp

during high-temperature operations. The most common failure mode of settling chambers

is plugging of the chamber with collected dust. In expansion settling chambers the plugging can result from hopper bridging or hopper discharge seal failure.

Multiple-tray settling chambers may experience plugging of the individual gas passages.