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Abstract
One of the safe and pressure
relieving systems in oil and gas refineries as well as petrochemical complexes,
is the relief header with the flare stack being the last component. In this
network all the excess gases are collected and sent to flare stack to be burnt.
A great amount of these gas mixtures has a high heating value and in some cases
it can even be used as the raw material forvarious units.
It is clear that burning
this gas mixture in flare stack causes environmental problems like air and
noise pollution and also is a financial waste. In this paper a step by step
approach and calculations are given to calculate and discuss flare gas recovery
benefits for refineries. The method contains data gathering of flare line’s
composition and other conditions, simulating of data and calculate financial
benefits for the case study by available equations. Therefore, Tabriz oil
refinery flaring system and available equation for flare system are used as a
case study.
Flare gas mixture in Tabriz
refinery consists of a wide spectrum of gases. After studying the methods for
flare gas recovery and economic analysis, a suitable method with a single stage
compressor is selected. The financial gain of this method is around 105,000 $
per year. Considering the implementation of Kyoto protocol in Iran, flare gas
recovery will be more economical.
Keyword: Flare gas recovery,
FGR, FGR calculations, FGR simulation
Introduction:
Even in most advanced
countries only a decade has passed from flare gas recovery technology, thus the
method is a new methods for application in refineries wastes. Of such countries
active in flare gas recovery are USA, Italy, the Netherlands, and Switzerland.
To recover flare gas, after
collecting from header and flare knock-out drum, flare gas passes through a
compressor. The compressor design and selection is the main part of the plan.
After gas compression based
on refinery structure or related unit, the gases used as a feed or fuel. If
required, to reach entrance gas temperature to flare gas recovery unit and
external gas temperature from this unit to an optional temperature, heat
exchangers are used.
To compress gases and to
design flare gas recovery unit, in general, liquid ring compressors or
reciprocating compressors are used. Advantage of first type is that gas is
cooled during compression by heat transfer of gas through water inside
compressor (usually water). It is possible to use amine instead of water in
such compressor to separate hydrogen sulfide from flare gases.
Reciprocating compressors
are purchased easily than the first type, also spare parts provision, repair
and maintenance is much easier. If using reciprocating compressors, please note
that it will explode if temperature exceeds over allowable limit.
