PETROSYSTEM Srl Via Gaspare Spontini, 29/4 - 00043 Ciampino (Roma) – Italy Tel:+39 06 7932.1621 Fax:+39 06 7932.1160 Email: [email protected] web: petrosystem.it VGRS - VENT GAS RECOVERY SYSTEM System Description Previously the vent gas from the Still Vapour Condenser was vented to the atmosphere via the LP vent system. These vapours contain Natural Gas, BTEX, water and inerts (Nitrogen, Carbon dioxide). As a result of a separate project large amounts of stripping gas were also introduced into the glycol regenerator, which would lead to additional gas being vented. In order to prevent this large emission to atmosphere a Vent Gas Recovery System was introduced. The Vent Gas Recovery System was built as one skid SK-1000 and was located on the cellar deck. A total of five skids have been supplied so far. The vent gas from the Still Vapour Condenser is released at a temperature of approximately 40 deg.C and is saturated. The condensate formed is drained to a holding tank. In this tank the Hydro Carbon phase and the Water phase are separated and brought via separate lines to the sump The vapour is extracted via the existing LP vent line. This line contains a number of bends which collect condensed liquids and prevent liquid entrainment. This vent line is continuously drained to the holding tank. After the drain point at the top of the line a tie-in point is made to the VGRS. This line has to be process traced and kept at a minimum of 30 deg.C in winter to prevent additional condensation. In summer this temperature will be higher as the tracing releases a constant heat. In the Vent Gas Recovery Skid the vapour is compressed to 1.8 barA, then cooled to approx. 5 deg.C and reheated to approx. 30 deg.C. During the cooling a large part of the vapours are condensed. The condensed liquid is discharged to the holding tank. Since the water content of the gas is significantly reduced it can be re-used as stripping gas. Also a significant amount of the BTEX is condensed and this reduces the heating value (calorific value) of the gas to the same level as the production gas of the platform. Re-heating the gas is necessary to prevent condensation in the downstream system. All downstream pipe work is also trace heated for this reason. Objectives & Benefits • Comply with the latest environmental legislation regarding emissions from offshore platforms. • Avoid penalties from central government where emissions persist past 2002. • Maximise the waste gas to aid the Glycol Generator and service local burners and generators. • Due to its stand alone function the skids can be installed and commissioned with little or no process down time. Compressor skid of a similar design is used for VGRS assemblies