Page 277 - Mechanical Engineers' Handbook (Volume 4)

266 Furnaces

Figure 43 Combustion control diagram for recuperative furnace. 1

standards for air quality. Designs for furnaces to be built in the immediate future should
anticipate a probable increase in restrictions of air pollution in coming years.
Toxic contaminants include sulfur and chlorine compounds, nitrogen oxides, carbon
monoxide, and radioactive wastes. The epidermic of ‘‘acid rain’’ in areas downwind from
large coal-burning facilities is an example.
Combustible contaminants include unburned fuel, soot, and organic particulates from
incinerators, and the visible constituents of smoke, except for steam. Other particulates in-
clude suspended ash and suspended solids from calcination processes.
Types of control equipment include

1. Bag filters or ceramic fiber filters to remove suspended solids. Filters require periodic
cleaning or replacement, and add to the pressure drop in flue gases leaving the
system.
2. Electrostatic filters, in which suspended particles pass through a grid to be electrically
charged, and are collected on another grid or on spaced plates with the opposite