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.

Fail Safe Design Maintainability In Remote Platform?

Shutdown platform occurred during my site trip last year in one of the remote offshore wellhead platform. ESD alarm on the operating console showed that the shutdown is triggered  by one of the push button on the cellar-deck.


The the problem comes, every time the operator wants to reset the ESD logic. The push button fail safe  mode which in de-energized status keep sending shutdown command and it cannot be re-setted.
Since the override command is only accessible to authorised maintenance personnel. the operator cannot access the overrides command and he started to panic

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:

The Logic Behind The Magic."H2S Removal system 3"

Amine Regeneration System.

The rich amine solvent from the contactor bottom flows to the Amine Flash Drum through level control valve. This level will let the rich amine pressure down from 46.3 to 5.5 barg. This is where the first stage of degassing of the solvent takes place. The drum is designed to allow the break out of the H2S and CO2. The drum is designed for liquid removal efficiency of 99% or greater for liquid droplet size of less then 70 micron, limiting the liquid carryover in the gas to be less than 0.1 gal.MMSCF, maximum oil carryover in the outlet water is 1% weight and maximum water carryover in the outlet oil is 1% weight.

Rich amine solution from the flash drum, at 31 degC flows into the lean/ rich amine exchangers and  is heated to about 93.5 degC. Proir entering the exchanger; the rich amine is filtered at the rich filter to removed any contaminant particles.

The Logic Behind The Magic."H2S Removal system 2"

Amine contactor System Control Narrative

Amine Contactor Inlet KO Drum level controller

Gap Control is applied to the inlet KO Drum level control. On normal process valve, the control valve controlled normally by level control. If PV decrease untuil reach low level alarm the controller will send command for 0% close to control valve, and if PV increase until high level alarm. The controller will send command for 100% open.

The Logic Behind The Magic."H2S Removal system 1"

The H2S removal system is usually utilizes Methyl Diethanolamine (Ucarsol) solvent to absorb content in the gas stream and reduce H2S concentration to 10 ppmv to meet sales gas specification.

 Ucarsol solvent is formulated to operate at a 15 +/- 5 % wt. Operating above this concentration range can lead to viscosity related problems such as in efficient acid gas absorption, hydrocarbon entraintment, poor heat transfer efficiency and higher pumping requirement. Operating below this will result in increase circulation rate and higher reboiler duty requirement. The system also includes regeneration of Ucarsol solvent to strip H2S gas and H2S tail gas is further treated in the thermal oxidizer prior disposal.

The Logic Behind The Magic."Liquid Separator and condensate coalescer package"

Separator
The separation of water and hydrocarbon liquids takes place in the liquid separator. The separated water is routed to the condensate stabilization unit via condensate coalescer package.

The liquid separator is basically a three phase separator that has specific internals to allow good performance in oil-water-gas separation. Baffle distribution and plate pack are provided for oil-water separation and vane pack mist eliminator is enable for gas liquids separation.

The Logic Behind The Magic."Slug catcher and Inlet Separator".

The fluids at receiving facility flow to slug catcher, where gas and liquid are separated. The feed gas line is also equipped with a connection and injection quill for methanol injection to prevent hydrate formation.

The separation of gas from the liquid is occur in the slug catcher.in this case finger type slug catcher is usually used.

The Logic Behind The Magic."Onshore Processing Facility"

Wellhead fluids are routed to onshore processing facilities through the export pipeline. Onshore processing facilities will processes fluids from wellhead. The onshore processing facilities usually comprises of the following facilities:

The Logic Behind The Magic."Seal Gas System"

Seal gas will be provided to each turbine driven compressor as a barrier between the process gas lift and the dry gas seals. The primary source of seal gas is from  the discharge of the 2^nd stage gas lift compressor. The gas is regulated by inlet control valves (2x100% configuration) to maintain the pressure at 95 barg.

The seal gas scrubber will remove any entrained liquid from the supply gas. The filter coalescer is provided to removed 99.9% any liquid / solid particle greater than equal to 2 micron.  Liquid drop is removed in the seal gas scrubber located immediately downstream of the pressure control valve. 

Invert, always invert

If f and f⁻¹ are inverses, then the graph of the function

is the same as the graph of the equation

  the solution of many hard problems can be clarified by re-expressing them in inverse form.

"Invert, always invert",Carl Gustav Jacob Jacobi 

The Logic Behind The Magic."Fuel Gas System"

Fuel Gas is normally supplied from the Compressor discharge with back-up take-off from MP separator gas outlet header. At start-up, the gas wells should be run first to provide fuel gas. Alternatively, gas may be sourced from Separator.

The Logic Behind The Magic."Open Drain System"

The Open Drain System is intended to collect and process atmospheric pressure drains from equipment or from deck drainage prior discharge to the environtment. This includes any liquids such as process drain, spill, and overflows.

There are two sub system to the open drain system. one is received drains from hazardoud area and the other receives drains from non hazardous areas. Drains from both systems are routed to the open drain tank which is overflow weir type separator. The overflow water will flow to the open drain caisson while the oil will flow to the internal oil compartment within the tank. The recovered oil will be pumped to the LP flare KO drum via open drain pump.

The Logic Behind The Magic."Flare System "

High Pressure (HP) and Low Pressure (LP) flare system are provided to safely dispose of gas relief valve, starting gas, and blowdown from vessel. Each system consists of a gathering header, KO drum, a flare tip and ignition system, During normal operation, the flare system should only have a small purge gas flow, The HP and LP KO drums separate liquid and gas from the flared gas system.

HP Flare System
The HP Flare KO drum is designed to handle the capacity of flare system and accommodate the liquid knockout under the maximum relieving scenario. i.e. during emergency total platform blowdown

The Logic Behind The Magic."Reject Oil Tank and pumps

The reject oil vessel receives recovered oil from the produced water hydrocyclone and vessel. Reject oil  pump is provided to transfer oil from the reject oil collection vessel back to the separator. The pump speed is regulated to maintain oil level in the vessel.

The Logic Behind The Magic."Gas Turbine Compressor 2"

Compressor Surge Detection and Avoidance

The surge condition occurs when the compressor does not have enough flow to produce sufficient head and the gas in the discharge line will flows back into the compressor. This cycle of flow is called surge.
An anti surge valve is designed for surge control by recycling the flow to the suction line of  compressor.
The  input to the anti surge control are flow differential pressure across the flow meter, compressor suction and discharge pressures (Ps, Pd), temperatures,  and the anti surge valve position feedback.

The surge detector monitors flow differential pressure pulses across the flow meter. Flow pulse may indicate a compressor surge event. When a flow pulse occurs, the ASC step changes the command to the Anti surge valve to 15% more open to increase the flow into the compressor to prevent any possible surge. If the ASC detects 5 pulses within 10 second the train is cooldown shutdown.

The surge avoidance fuction is based on the reduced head vs. reduced flow factor.

The surge margin takes input of pressure, temperature and flow to calculate compressor surge margin which is defined to be distance from the operating reduced flow factor to the reduced flow factor at the surge limit line as a percentage.  The ASC compares the operating flow factor to keep the compressor operating a safe distance away from surge.
The ASC will begin to open the Anti surge valve if the surge margin drop below 10%.
PI algorithm is used to close and open the valve. One set of gains is used to slowly close the anti surge valve and another set to quickly close the anti surge valve. If the surge margin drops below 10% the ASC override manual modes.

 

The Logic Behind The Magic."Gas Turbine Compressor 1"

Compressor
Compressor is used to flow gas from a lower pressure to a higher pressure system. Compressor are used to compress the gas for sale or on long pipelines to restore pressure drop lost to friction.

Usually the compressor is centrifugal compressor which takes gas from the suction scrubber out oulet and compress is to adjustable pressure. usually  the compressor is driven by gas turbine. Suction pressure controller within the package unit control panel will maintain the pressure at suction scrubber by regulating the compressor turbine speed control.

 Typical gas turbine cycle

 

The Logic Behind The Magic. “1st Stage Compressor Suction Scrubber"

The purpose of suction scrubber is to remove liquid prior to feeding gas into the 1st Stage compressor. Collected liquid is routed to HP flare KO drum, The liquid level in the scrubber is controlled using GAP control by opening/ closing the liquid outlet control valve

The Logic Behind The Magic."Produce water treater vessel and injection pump"

The separated produced water from the hydrocyclone is routed to the Produced Water Treater Vessel to further enhance oil and water separation, The Primary function of treater vessel is to degas the produced water. As the pressure is reduced from the hydrocyclones, the gas bubles that are liberated rise within the water in the degasser and capture and separate the small, finely dispersed oil droplets. Larger oil droplets are removed by internal weir.

After treatment, produced water is re-injected back into reservoir via the Produced Water Injection Pumps. produced water treater process schematic is shown as following:

The Logic Behind The Magic."Produce water Hydrocyclones"

The purpose of the Produced water treatment is to de-oil the produced water before injection back to reservoir. Produced water treatment is designed to achieve the discharge oil-in water to meet the specification (e.g. 25 mg/L (ppmV). A common oil in water analyzer is usually installed for monitoring and recording of oil content in water from Produced oil water treater vessels
Under normal operating condition, produced water from the MP separators flows into hydrocyclones and the produced water flow is regulated by the interface level controller in the Separators. 

The hydrocyclone is operated under differential pressure ratio controller i.e the ratio of  (hydrocyclone inlet pressure minus reject oil stream pressure) to ( hydrocyclone inlet pressure minus hydrocyclone water outler pressure).  The DPR controller is set at adjusted value and will continuously adjust the hydrocyclone reject oil control valves to achieve the DPR set point.

The Logic Behind The Magic."Separators Operational and Control Philosophy"

The Separators are designed to operate in parallel with a flooded weir. The normal liquid level is maintained above the weir by a level controller. The oil-water interface level is maintained by the interface level controller. The separated gas is used for for gas lift and fuel gas with the balance to the compressors. Oil from the separator is delivered to the Separator oil pumps and combined with the compressed gas. Water is sent to Produced water treatment package.

The Logic Behind The Magic."Basic System Configuration"

 Typical Oil and Gas Production Process