safety design

Pada 23 Maret .2005 jam 1:20 siang, di BP Texas City refinery terjadi ledakan dan api yang mengakibatkan 15 orang meninggal dunia dan menciderai 180 orang dengan kerugian material melebihi $1.5 billion. Insiden terjadi ketika start-up isomerization unit, raffinate splitter tower meluap. Pressure relief device terbuka yang menyebabkan  flammable fluid keluar dari blowdown stack yang tidak dilengkapi dengan flare. Keluarnya fluid ini menyebabkan ledakan dan api. Fatality terjadi di kantor yang dekat lokasinya. 43.000 orang penduduk diperintahkan tetap didalam ruangan dan ledakan mengakibatkan rumah-rumah dalam radius ¾ mile dari refiney rusak.

Differential Pressure Level Transmitter Defect

Every liquid in storage tank will have hydrostatic pressure equal to the height of the liquid. With an assumption that the liquid has constant density. The DP level transmitter indication is a measure of the head pressure in the level of the tank whose level is to be detected. Head Pressure, DP, is calculated as DP = (Height).(Specific Gravity).

For example, let's say  50% level is displayed in the control room, the specified SG = 0.8. The DP transmitter is actually measure a differential pressure (50%)*(0.8) = 40 units of the differential pressure.

Gas Processing Unit Summary

Produced wellhead gas is wet, saturated with heavy hydrocarbons and contained with salt and sand.
Gas Conditioning Unit varies from a small station that handle 10 million SCFD to a big station that process 500 Million SCFD.

Wells scattered throughout the remote regions, and then carried by export line to the processing unit. Liquid are separated from gas. The liquids consist of salt water and condensate. The condensate is collected to oil refinery, where the condensate is blended into gasoline. The water is removed and then injected back into the ground in disposal wells.

The Logic Behind The Magic." Flash Gas Compression"

The condensate separated in the Liquid separator is stabilize by the condensate stabilization unit.
To recover the flash gas from the condensate stabilizer column and overhead of liquid separator, Flash gas compressor is installed for the compressing and recycling the gas to inlet of slug catcher.

Flash gas compressor is horizontal multistage cylinder balanced opposed type reciprocating compressor. These compressors are driven by 160 kW induction motor through a direct rigid coupling.

First, the gas flows to Flash Gas Compressor Scrubber to be scrubbed and condense any liquid from the gas stream.

The gas is then compressed by 1st stage flash gas compressor then the discharge gas cooled down from 116 deg C to 80 degC by 1st stage flash gas after cooler. After that condensed liquid is separated in the 2snd stage flash gas compressor suction scrubber prior compression by 2nd stage flash gas compressor to 48.5 barg. The compressed flash gas is cooled down to 90 degC by 2nd stage flash gas after cooler prior delivering to the slug catcher

The Logic Behind The Magic." Gas Dew Point Control and Metering 3".

Metering

The purpose of the flow metering system is to measure the gas flow for commercial purposes.
Sales gas metering package includes the dollowing:
- Flow Metering system
- Gas Chromatograph
- Miscellaneous component, like isolation valve, tube JB, etc.

One of the options is utilizing senior orifice meter. The flow meter is designed and constructed in accordance for AGA Report No 2. To compesate the flow readings, Pressure and Temperature transmitters are provided on each stream.

The Logic Behind The Magic." Gas Dew Point Control and Metering 3".

Gas Dew Point Control .

The Logic Behind The Magic." Gas Dew Point Control and Metering".

Dry gas from TEG overhead KO drum flows to Gas/Gas Exchanger where it is cooled by Low Temperature Separator overhead stream. The Gas/Gas Exchanger is a special Printed Circuit Heat Exchanger design. The exchanger is protected by strainers in order to avoid oversized particles entering Sales Gas Metering Skid.

The Logic Behind The Magic." Glycol Dehydration System 10"

Glycol Make Up System and Drain Vessel Control

The Logic Behind The Magic." Glycol Dehydration System 8"

TEG Vent Exchanger Outlet Temperature Control

The TEG Vent Exchanger outlet temperature is controlled by TC-FC cascade. The outlet temperature is influenced by Heating medium from TEG Reboiler

The Logic Behind The Magic." Glycol Dehydration System 7"

TEG Reboiler
Rich glycol from TEG Still column flows into the shell side of glycol  reboiler. Hotoil comes from hot oil supply header is used as heating medium in reboiler tube side. The renegerated flows by gravity across the length of the TEG reboiler and enters the Stripping gas column operate at 204.4 degC at atmospheric pressure. TEG loss is reduced by increasing the flow of the rich TEG through tube side of TEG reflux condenser.

TEG Vent Exchanger
Water vapour from the shell side of the TEG reflux condenser passes through the shell side of an 8.36 kW double pipe type TEG Vent Exchanger before letting it go to the acid flare system. Water vapour is heated up to 150 degC by the hot oil passing through the tube side of the TEG vent exchanger for this purpose. The temperature of water vapor of the acid flare is controlled by an FC TC cascade control loop.

Stripping Gas Column

 The use of Stripping gas column is provided to reduce the water content of the regenerated glycol by counter current contact with hot fuel gas flowing upward through the stripping gas column. The stripping gas also reduces the partial pressure of the vapour in the TEG reboiler. Hence increasing the regeneration capability of the TEG reboiler. Regenerated glycol flows from the bottom of the stripping gas column by gravity into the hairpin type Hot Lean Rich TEG exchanger where it is cooled to approximately 124.8 degC and then goes into the other haipin type Cold Lean Rich TEG Exchanger where it is further cooled to approximately 85.55 degC.


TEG Accumulation Vessel
Lean glycol from Cold Lean/Rich TEG exchanger is sent to the TEG accumulator vessel. The TEG accumulator vessel is sized for a 22.3 minutes residence time between low-low liquid level and high-high liquid level, of lean glycol at pump maximum capacity (33 USgpm). The TEG accumulatoe vessel provides storage capacity for the TEG circulation pumps.

TEG Circulation Pumps
The TEG circulation pumps are rotary gear type pumps, operating at normal discharge pressure of approximately 52.06 Barg. The lean glycol from the discharge of the TEG circulation pumps is sent to the 235.8 kW TEG cooler,

TEG Cooler
The TEG coller is an air cooler where the lean glycol is cooled to 48.25 degC and sent to the TEG contactor for re-use. 2x5 kW fans are used to cool the lean TEG

The Logic Behind The Magic." Glycol Dehydration System 6"

TEG Regeneration Package Control


 

The Logic Behind The Magic." Glycol Dehydration System 5"

TEG Regeneration Package

TEG Reflux Condenser

TEG Reflux Condenser is located at the top of the TEG Still column and used to maintain the temperature of the steam leaving for condenser. Rich glycol flowing through the TEG reflux condenser coils is warmed to 49.48 degC by steam and glycol vapour present in the steam is condensed on the shell side.
  

The Logic Behind The Magic." Glycol Dehydration System 4"

TEG Overhead KO drum Control

TEG Overhead KO Drum Level Control

Gap Control is applied to the following level control.
On normal process valve, The control valve controlled normaly by level control. If the PV Rise Up Until Reach High Level Alarm. Controller   will send command to control valve for 100% open. If the PV decrease until reach low level alarm, controller will send command to control valve for 0% Close (Shut Off).
 

The Logic Behind The Magic." Glycol Dehydration System 3"

TEG Overhead Knock Out Drum

Dehydrated gas leaves the Glycol contactor and fed to TEG Overhead KO drum. The dehydrated gas leaving top of the TEG Overhead knock out drum passes through a Mist eliminator to remove entrained glycol. The TEG Overhead KO drum is designed to operate at 44.44.26 barg and 45.97 degC. Gas from the TEG Overhead knock out drum is sent to Gas/Gas Exchanger. TEG recovered in the KO drum is sent to the TEG Flash Drum in the outlet line of the KO drum is controlled by a LV which is operated by on-off configuration

The Logic Behind The Magic." Glycol Dehydration System 2"

Glycol Contactor Level Control

Gap Control is applied to the following level control.

On normal process valve, The control valve controlled normaly by level control. If the PV Rise Up Until Reach High Level Alarm. Controller   will send command to control valve for 100% open. If the PV decrease until reach low level alarm, controller will send command to control valve for 0% Close (Shut Off).

Instrument Control Function Detail

TEG Cooler

The different temperature between TEG contactor inlet and TEG cooler inlet is monitored by TDC. The different temperature will be calculated and use for controlling TEG cooler.

Instrument Control Function Detail

Other controllers
The controller will used simple loop type with direct -reverse acting list as follows:

The Logic Behind The Magic." Glycol Dehydration System 1"

Sweet gas from Amine Overhead KO drum will flows to Triethylene Glycol Contactor where it will have its water contect reduced by contact with triethylene glycol solution. The Glycol unit consists of Glycol Contactor and Glycol Overhead Knock Out Drum.

Triethylene Glycol Contactor.
Sweet gas from Amine Overhead Gas Knock Out Drum is sent to the Glycol Contactor through the integral scrubber for removing free liquids, water and hydrocarbon condensate from the gas. Incoming gas is evenly distributed over the cross sectional area by an inlet distributor. In this distributor, inlet momentum of gas-liquid mixture is broken to enable disengagement of gas from liquid. The integral scrubber consists of mist eliminator to remove the free liquid present in the incoming gas. It is designed to operate at 45.16 barg at 43.85 - 444.25 degC. The hydrocarbon liquids from the separator leave from the bottom of the vessel. The flow is controlled by an LV

After the removal of free liquids, the gas enters the absorber section, Chimney trays are provided for proper distribution of the gas through the column. Dehydration of the gas takes place across height structured packing, against a counter current flow of lean Tri-Ethylene Glycol.

The dehydrated gas leaves to of the column passing through vane pack, mesh, and mist eliminator are provided to remove glycol before leaving the tower. The glycol is ditributed across the packing with high efficiency liquid distributor. As the glycol flows down the surface of the structured packing, it absorbs water from the gas. Rich glycol is collected on the top of the chimney tray and is discharged under level control valve LV to the TEG reflux condenser. Located in the TEG regeneration package.

The Logic Behind The Magic."H2S Removal system 7"

Amine Drain System.

 The drain system of amine unit is a closed system, where each drain line is tied into an underground pipe header, which flows into the Amine Drain Vessel. The system, from the piping, equipments and instrumentations, is hard piped and freely drained into Amine Drain Vessel.

The Amine Drain Vessel is located in the sump pit as the TEG Drain Vessel. The Amine Drain vessel is designed to store the entire liquid inventory of amine system. The vessel is constructed from CS lined with 3 layers epoxy lining and equipped with fireproofing insulation to anticipate pool fire condition in emergency case.

To prevent degradation of the solvent by air ingress, fuel gas blanketing is provided to drain vessel controlled by PCV-A, set at 0.27 barg and PCB-B set at 1.75 barg to release gas in case of built-up pressure at the vessel is maintained at about 0.1-0.3 Barg.

As the pit is open, rainwater could accumulate in the pit. Sum drain pumps are provided to pump the rain water out from the pit.

The drained solution is collected in the sumps provided at the following points where potential leakage or spillage is considered.

When amine solution liquid level is too high, the amine solution can be pumped back to the Amine Surge Vessle with the Amine Drain Vessel Pump.

The Logic Behind The Magic."H2S Removal system 6"

Amine Circulation System Control Narrative

The Amine Regenerator Overhead Cooler outlet temperature is controlled by TC. When outlet temperature of Amine Regenerator Overhead Cooler is decreases, VFD Speed Control is controlled by TC for preventing from more decreasing and increasing temperature.

 

Other controllers
The controller will used simple loop type with direct -reverse acting list as follows:

The Logic Behind The Magic."H2S Removal system 5"

Amine Circulating System.

The hot lean amine existing the amine regenerator flows into the lean side of lean/rich amine exchangers by means of heat lean amine pumps where heat is exchange with the cold rich amine from the flash drum. The cooler lean amine is further cooled to 45 degC in the lean amine air cooler. This is an air cooler utilizing stadard finned tubes and electric motor driven fans. Air cooler is equipped with bug screens and eazh bank includes one variable frequency drive (VFD) fan motor to assist in achieving close temperature control of the lean amine.

The Logic Behind The Magic."H2S Removal system 4"

Amine Regenerator Overhead Cooler Control Narrative

The Amine Regenerator Overhead Cooler outlet temperature is controlled by TC. When outlet temperature of Amine Regenerator Overhead Cooler is decreases, VFD Speed Control is controlled by TC for preventing from more decreasing and increasing temperature.

 

Other controllers
The controller will used simple loop type with direct -reverse acting list as follows: