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7

Flare Process

Lawrence K. Wang, Clint Williford, and Wei-Yin Chen

CONTENTS
INTRODUCTION AND PROCESS DESCRIPTION
PRETREATMENT AND ENGINEERING CONSIDERATIONS
ENGINEERING DESIGN
MANAGEMENT
DESIGN EXAMPLES
NOMENCLATURE
REFERENCES

1. INTRODUCTION AND PROCESS DESCRIPTION

“Flares” are open flames used for disposing of waste gases during normal operations
and emergencies (1–8). Flares are an open combustion process in which surrounding air
supplies oxygen to the flame. They are operated either at ground level (usually with
enclosed multiple burner heads) or at elevated positions. Elevated flares use steam
injection to improve combustion by increasing mixing or turbulence and pulling in addi-
tional combustion air. Properly operated flares can achieve destruction efficiencies of at
least 98%. Figure 1 is a schematic of the components of a flare system (9–11). Flares
are typically used when the heating value of the waste gases cannot be recovered eco-
nomically because of intermittent or uncertain flow or when the value of the recovered
product is low. In some cases, flares are operated in conjunction with baseload gas
recovery systems (e.g., condensers). Flares handle process upset and emergency gas
releases that the baseload system is not designed to recover.
Several types of flare exist. The most common are the steam assisted, air assisted, and
pressure head flares. Typical flare operations can be classified as “smokeless,” “non-
smokeless,” and “fired” or “endothermic.” For smokeless operation, flares use outside
momentum sources (usually steam or air) to provide efficient gas–air mixing and turbu-
lence for complete combustion. Smokeless flaring is required for the destruction of
organics heavier than methane. Nonsmokeless operation is used for organic or other vapor
streams that burn readily and do not produce smoke. Fired or endothermic flaring requires
additional energy in order to ensure complete oxidation of the waste streams, such as for
sulfur tail gas and ammonia waste streams. The US Environmental Protection Agency

From: Handbook of Environmental Engineering, Volume 1: Air Pollution Control Engineering
Edited by: L. K. Wang, N. C. Pereira, and Y.-T. Hung © Humana Press Inc., Totowa, NJ
329