Waste heat is heat generated in a process by way of fuel combustion or chemical reaction,
which is then “dumped” into the environment and not reused for useful and economic
purposes. The essential fact is not the amount of heat, but rather its “value”. The mechanism
to recover the unused heat depends on the temperature of the waste heat gases and the
economics involved.

1. INTRODUCTION

This section briefly describes the main features of waste heat recovery.

Waste heat is heat generated in a process by way of fuel combustion or chemical reaction,
which is then “dumped” into the environment and not reused for useful and economic
purposes. The essential fact is not the amount of heat, but rather its “value”. The mechanism
to recover the unused heat depends on the temperature of the waste heat gases and the
economics involved.
Large quantities of hot flue gases are generated from boilers, kilns, ovens and furnaces. If
some of the waste heat could be recovered then a considerable amount of primary fuel could
be saved. The energy lost in waste gases cannot be fully recovered. However, much of the
heat could be recovered and adopting the following measures as outlined in this chapter can
minimize losses.

2. TYPES OF WASTE HEAT RECOVERY EQUIPMENT

Commercial equipment that can be used to recover waste heat and for other applications and uses.

2.1 Recuperators

In a recuperator, heat exchange takes place between the flue gases and the air through metallic or ceramic walls. Ducts or tubes carry the air for combustion to be preheated, the other side contains the waste heat stream. A recuperator for recovering waste heat from flue gases is shown in Figure 1.

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