Monday, November 17, 2014

Flare Gas Recovery (FGR) to Minimize Wastes and Economical Benefits

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

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.

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