Reducing Emissions in Plant Flaring Operations Figure 1: Demountable Flare System Figure 2: Flare System in Operation
Figure 3: Startup of Flare Gas Recovery System
improving the resistance of the internal tubes to collapse, the design eliminates the introduction of the air deep inside the flare, which could have otherwise resulted in internal burning, thermal stress and ultimately, flare destruction. Cracking of the flare burner shell – a common failure in conventional flare design – typically propagates from fillet welds on brackets and attachments joined to the flare tip. To eliminate the stress riser and the resulting crack, the new flare burner uses a circular, plug-welded design, which helps to optimise flare burner service life.
The flare tips use high-stability, low-consumption pilots to reduce the amount of natural gas that is required for operation. The Callidus pilots consume half the natural gas of conventional pilots, saving nearly US$20,000 per year on natural gas costs. The pilot design is extremely stable and can survive winds of more than 160mph and rainfall of over 12 inches per hour. The pilot system incorporates a windshield, strainer and a true premix burner capable of firing in 0% oxygen environments at the pilot tip. This makes the pilot operation extremely stable. The pilot gas tip, flame shield and thermocouple mounting are all investment castings of CK-20 to ensure long life. The placement of the thermocouples is designed to maximise response to all weather conditions and minimise exposure to direct flame. Figure 2 shows the flare system in operation.
Flare Gas Recovery In keeping with their corporate objectives of achieving zero flaring and reducing fuel costs, visible flame, odours and the auxiliary flare utilities,
44
such as steam, the plant also purchased two FGRSs to complete the flare systems. Numerous studies completed since 2000 have proven that recovering hydrocarbon gases that are normally discharged to the flare is the most cost-effective investment a refinery can make.4
Each FGRS for the Dushanzi plant was designed to recover 60 million British thermal units per hour (MMBTU/hr) of flare gas (see Figure 3). The FGRS is a skid-mounted packaged system located downstream of the knockout drum since all the flare gases are available at this single point. Compressors take suction from the flare gas header and compress and cool it for reuse in the refinery fuel gas system. As flare gas flows through the flare header, it is diverted to the FGRS downstream of the knockout drum by a liquid seal vessel and enters the compressor. Typically, a liquid ring compressor is used because the design of the compressor can process two-phase flow that commonly exists in flare headers. The compressed gas is then discharged into a mixed phase separator. The liquid is pumped through a heat exchanger and back to the service liquid inlet on the compressor as shown in Figure 4. The compressed gas is separated from the liquid and is piped to the plant fuel gas header, or other appropriate location.
The compressor recycle valve is regulated with control signals based on the inlet flare gas pressure. This ensures that the flare header is under positive pressure at all times. In the event that the flow capacity of the FGRS is exceeded, the liquid seal vessel will allow the excess waste gas to go to the flare where it is safely burned.
H Y D R O C A R B O N WO R L D – V O L UME 6 I S S U E 1
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84