PETROLEUM PLANT UTILITIES

o          Fuel Gas System

The primary source of fuel gas will be downstream of the expander compressor. For start-up purposes fuel gas will be taken from the two feed gas lines upstream of plant isolating valves and will tie-in to the main fuel-gas header upstream of the FG scrubber.

An orifice type meter shall be installed to measure overall plant gas consumption, which covers but is not necessary limited to, the following:

•           Fuel gas for gas turbine driven compressors and gas engine generators

•           Fuel gas for hot oil furnace heater

•           Purge gas

•           Pilot gas for flare and burn-pit ignition system

The Fuel Gas Package will comprise of the following:

•           Fuel Gas Scrubber (1 x 100 %)

•           Fuel Gas Filters (2 x 100 %)

•           Fuel Gas Heater (1 x 100 %)

The fuel gas off take is at 285 psig before let down into the fuel gas scrubber. The gas is totally dry for star-up, the gas taken from the pipelines will be water-saturated, so a fuel-gas heater is provided to elevate the gas temperatures.

o          Seal Gas System

The system will be designed and supplied by the selected Compressor VENDOR.

The seal gas system shall be able to handle the primary seal gas requirement of the selected gas compressors.

The Seal Gas Package might comprise of the following:

•           Seal Gas Scrubber (1 x 100 %)

•           Seal Gas Filter/Coalesces (2 x 100% )

•           Seal Gas Electrical Heaters (2 x 100%)

In addition, seal gas treatment and its control system shall be provided on the compressor skids.

o          Flare and Vent Systems

All hydrocarbon pressure relieving devices, with the exception of low temperature extraction section gases, will discharge to the high pressure flare header. This includes PSVs, rupture disks if approved for use, and emergency blowdown valves. To prevent any liquid entering the flare stack, a flare K.O. drum, and liquid removal pumps will be required. Downstream of the KO drum a water seal-drum shall be provided to prevent air from entering the flare header system.

The Flare Capacity shall be based on a worst-case scenario. The design shall be completed in detail engineering.

A flare header designed for the maximum plant throughput will pass 250 MMscfd under blocked outlet condition. The emergency blowdown rate will quickly reduce to below the normal maximum throughput of 250 MMscfd and is not the controlling case. If adequate protection against blocked discharge and failure of the protective systems cannot be economically achieved relative to the cost of a larger capacity flare system the system shall be sized for the maximum throughput. It is anticipated that an elevated flare system will be used.

In order to reduce the header size a maximum Mach number of 0.7 may be used for emergency discharge assuming the use of a conventional pipe flare. Consideration is also to be given to the use of a sonic flare tip operating at an elevated back pressure (approximately 30-50 psig at the tip inlet) which will considerably reduce radiation levels at and around the plant.

In addition to the HP flare a cold vent line shall be installed, which will be elevated and suspended from the HP flare stack. Some of the relief valve discharges and vents in the unit are at a very cold temperature and cannot be sent to the wet carbon steel flare system. These cold discharges would cause the formation of ice and hydrates with potential blockage of the free path to the flare. The cold temperature of these discharges are also too cold for the use of carbon steel material in the piping and flare. Therefore a separate cold flare system consisting of a stainless steel, (or other material suitable for the discharge condition), flare header shall be provided. Simulation indicates that cold liquid will not condense out during discharge, so a KO drum has not been indicated for the cold vent system. Bidders to confirm this fact or advise the installation of a SS KO-drum. Use of this separate line for the relatively low pressure De-C2 discharge allows a higher back pressure in the CS HP flare header thus reducing header size.

The radiation levels for personnel and equipment at the limit of the restriction zone resulting from the HP Flare shall not be more than the following:

(ref: API 520 Part II - Sizing, Selection and Installation of Pressure-Relieving Devices in Refineries):

•           Equipment Protection    5000     Btu / (hr.ft2)

•           Personnel, one minute exposure            1500     Btu / (hr.ft2)

•           Personnel, continuous exposure            500       Btu / (hr.ft2)

Liquids collecting in the Flare K.O. Drum are to be directed via the Flare K.O. pump to the Closed Drain Drum. The requirement for sizing of these pumps is removal of all liquid between LLH and LLL in 30 minutes.

The water seal drum will have a permanent water-line connection, level controlled to maintain a position seal in the drum. A water seal drum is not envisaged for the cold vent. This cold vent line will be fuel-gas purged only from its extreme upstream point. 

The flare system will comprise of:

•           HP flare header

•           HP flare stack

•           Cold vent header

•           HP flare tip

•           Flare ignition system

•           HP flare KO drum

•           HP flare KO drum pump

•           HP water seal drum

Individual atmospheric vents are to be used where possible with crossovers minimized and air-cooled exchanger fans used to assist dispersion. Flame arrestors shall be fitted at individual local atmospheric vents.

o          Instrument and Utility Air System

The Instrument and Utility Air System will comprise the following main components:

•           Instrument / Utility Air Compressors (2 x 100 %)

•           Instrument Air Drier (2 x 100 %)

•           Instrument / Air Receiver

•           Utility Air Receiver

•           Instrument and Utility Air Distribution Systems

Air Compressors and Air Dryers capacity is shown in Table-4.

The air receiver shall be sized for 30 minutes of air capacity from low pressure alarm down to low low pressure shutdown initiation.

o          Diesel Fuel System

The diesel storage facility with filter coalesces; loading facilities and transfer are to be provided. The storage tank shall be designed to accommodate the diesel fuel demand of diesel generator for 8 days in base load continuous operation condition, supply the diesel fire pumps and provide fuel for vehicle use through a day tank and vehicle fill hose.

The Diesel Fuel system comprises of:

•           Diesel Fuel Storage Tank

•           Diesel Fuel Daily Tank with fill hose

•           Diesel Fuel Loading Pump

•           Diesel Fuel Transfer Pump

•           Diesel Fuel Transfer Filter