US 4,347,155 AGranted

Energy efficient perlite expansion process

AssigneeManville Service Corporation

InventorKenneth L. Jenkins

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Abstract

A thermally efficient process for the expansion of perlite ore is described. The inlet port and burner of a perlite expansion chamber (preferably a vertical expander) are enclosed such that no ambient air can enter the chamber. Air and fuel are metered to the burner with the amount of air being controlled such that the fuel/air premix contains at least enough air to start and maintain minimum combustion, but not enough to provide stoichiometric combustion. At a point immediately above the burner, additional air is metered into an insulated enclosure surrounding the expansion chamber where it is preheated by the heat passing through the chamber walls. This preheated additional air is then circulated back to the burner where it provides the remainder of the air needed for combustion, normally full combustion. Flow of the burner fuel/air premix and the preheated additional air is controlled so as to maintain a long luminous flame throughout a substantial portion of the expansion chamber and also to form a moving laminar layer of air on the inner surface of the expansion chamber. Preferably the burner is a delayed mixing gas burner which materially aids in the generation of the long luminous flame. The long luminous flame and the laminar layer of air at the chamber wall eliminate hot spots in the expansion chamber, result in relatively low and uniform temperature gradients across the chamber, significantly reduce the amount of fuel consumed per unit of perlite expanded, increase the yield of expanded perlite and prevent the formation of a layer of perlite sinter on the walls of the chamber.

In a perlite expansion process wherein perlite ore is charged to a flame zone in an expansion chamber where it is rapidly heated and expands, and is thereafter transported out of the flame zone by entrainment in the exhaust gas stream of the flame zone, and wherein said expansion chamber has an inlet port at one end and an outlet port at the other end and burner means for creating said flame zone is disposed directly in proximity to the inlet port;

an improvement whereby the thermal energy consumed is efficiently utilized to expand perlite ore, sintering is minimized, improved perlite ore expansion is obtained, and equipment service life is extended, which improvement comprises:
(a) enclosing said inlet port and a delayed mixing gas burner in a first enclosure which is closed to the ambient atmosphere;
(b) providing said first enclosure with a cross-sectional area substantially greater than the cross-sectional area of said delayed mixing gas burner;
(c) providing a supply of air and a supply of fuel for combustion;
(d) separating the supply of air into a first air stream and a second air stream;
(e) mixing said first air stream with said supply of fuel and passing the resultant fuel/air mixture to said delayed mixing gas burner;
(f) controlling the relative proportions of air in said first stream and said second air stream such that the amount of air in said first air stream is that quantity which is at least sufficient to initiate and maintain minimal combustion of said fuel, but less than the amount which is required to obtain stoichiometric combustion of the fuel;
(g) passing said second air stream into a second enclosure which surrounds at least a portion of the wall of said expansion chamber and wherein said second air stream is heated by the heat passing through said wall of said chamber;
(h) passing the heated second air stream from said second enclosure through a conduit into said first enclosure;
(i) controlling the total amount of air provided such that the quantity of air is at least the amount necessary to obtain significant combustion of said fuel;
and
(j) controlling the flow rate and ratio of said fuel and air such that a long luminous flame having a diameter substantially less than the diameter of said expansion chamber is produced throughout at least half the axial dimension of said expansion chamber, a moving laminar layer of air is created along the inner surface of said wall of said expansion chamber, and the length of the flame path and temperature of the flame zone are suited to the characteristics of the perlite ore feed.

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Abstract

Claims8