Oil and Gas Plant Chemical Injection Systems

Oil and Gas Plants need Certain chemicals to be injected continuously or intermittently for Plant Safety, Reliability and to Increase Production or Production Quality.

Purpose

To provide a process description and describe the basic operation of the Chemical Injection System that is associated with an Oil and Gas Plant

Scope

This guideline applies to the Oil and Gas Plant Oil Treatment Facility.

Hazard Recognition and Other HES Considerations

Consideration must be given to the following hazards:

Potential for H₂S
Walking and Working Surfaces/Working from heights
Mechanical Energy
Body Strain
Pinch Points
High-Temperature Surfaces
High-Temperature Liquids
High-Temperature Vapors
Snakes and Scorpions
Rotating Machinery
Noise

Recommended controls for these hazards include:

Ensure all non-operations personnel working in the area have a valid ISSOW Permit.
Follow energy isolation requirements in accordance with ISSOW Procedure.
Ensure that any non-routine operating tasks conducted in the area are preceded by an appropriate risk assessment.
Follow procedures and utilize gas meter when entering enclosures and confined spaces.
Use proper body mechanics.
Keep eyes on work area and path.
Use appropriate tools.
Wear appropriate PPE (safety boots, hard hat, coveralls, safety glasses, rubber gloves, heat resistant gloves).
Follow housekeeping requirements and clean work area after job is completed.
Be alert, keep eyes on work area and walkways, and watch out for snakes and scorpions.
Conduct regular leak checks.

Introduction

Defoamer Injection Package

As outlined in the chart, Defoamer chemical is designed to be injected into the inlet lines of the Free Water Knockout vessels and to the inlet to the Degasser Boot. Foaming can cause poor oil/water separation and reduce the operating efficiency of the units, ultimately affecting the BS&W quality of the oil and the oil content of the produced water exiting the Dehydration tank. The Defoamer injection system consists of a dedicated skid complete with a storage tank and three diaphragm-type metering pumps to provide precise control of the amount of chemical added at each injection location. A simplified graphic of the system that has been excerpted from the HMI system is shown in Figure 1 below and Figure 2 following shows the general arrangement of the tank & metering pumps.

Figure 1: Schematic of Defoamer Injection Package

Figure 2: Defoamer Injection Package General Arrangement

The Defoamer chemical injection package consists of a storage tank and 3 electric-driven, chemical dosing pumps, all mounted on a self-contained skid. When tank charging is required, it is carried out by transferring the appropriate number of commercially prepared chemical drums via pneumatically operated barrel pumps into the storage tank. The storage tank has a dished bottom with a flat top and is constructed from SA-36 carbon steel. The tank has a maximum capacity of 750 gallons with a working volume of 607 gallons, which provides at least 7 days of supply of under normal operating conditions. The tank operates at atmospheric pressure and is provided with a goose-neck vent, complete with a bug screen attached. Level in the tank is monitored by a differential pressure type level transmitter which provides constant output to the HMI, complete with High and Low alarms. Local level indication is provided using a MAGNA-VOX magnetic level indicator. Nozzles provided on the tank are designed for 150# service and are listed as follows:

· 1 – 1 ½” chemical outlet.

· 1 – 1 ½” pressure relief valve return.

· 1 – 2” nozzle to attach the level transmitter.

· 1 – 1 ½” nozzle for the tank vent, flame arrestor and bug screen.

· 1 – 2” chemical inlet nozzle from the barrel pumps.

· 1 – 1 ½” nozzle to attach the level gauge.

· 1 – 2” bottom drain.

· 1 – 24” manway complete with cover and davit assembly.

The injection systems for all the other chemicals are arranged and equipped in a similar manner to the Defoamer system. Despite none of the systems are actually in service at this time, operators should ensure they are familiar with the layout of each injection package, the related distribution system and the hazards associated with handling the chemicals. Figure 3 provides a view of the entire chemical injection system. A brief description and simplified graphic for each system is shown below and additional, more detailed information is available in the referenced documents at the end of this document.

Figure 3: Chemical Injection Systems General Arrangement

Corrosion Inhibitor-1 Injection Package

The combined Corrosion Inhibitor-1 package (A, B) contains one 5000 gallon tank shared by two skids A and B. Each skid has 2 pumps (1 operating + 1 spare) with 44 gph as the rated capacity of each pump. Thus the combined package (A, B) has 4 dosing pumps, with only 2 pumps operating at one time. The chemical acts as an oxygen scavenger that may be required to prevent system corrosion at some point in the future, depending on changing conditions in the production field or with the processing equipment. The system is shown in the graphic in Figure 4 below.

Figure 4: Corrosion Inhibitor-1 Injection Package Schematic

Corrosion Inhibitor-2 Injection Package

The combined Corrosion Inhibitor-2 package (A, B) contains one 5000 gallon tank shared by two skids A and B. Each skid has 2 pumps (1 operating + 1 spare) with 44 gph as the rated capacity of each pump. Thus the combined package (A, B) has 4 dosing pumps, with only 2 pumps operating at one time. The chemical acts as a filming biocide that may be required to prevent bacteriological growith at some point in the future, depending on changing conditions in the production field or with the processing equipment. The system is shown in the graphic in Figure 5 below.

Figure 5: Corrosion Inhibitor-2 Injection Package (61- A-00123) Schematic.

Demulsifier Injection Package

The Demulsifier injection package contains one 1655 gallon tank and 3 injection pumps (2 operating + 1 spare) with 5 gph as the rated capacity of each pump. The chemical acts to break water-in-oil emulsion and remove the thick film of emulsifying agents around the water droplets. Breaking the emulsion allows the water and oil separation process to be carried out more easily and improves the operating efficiency of the processing units. The system is shown in the graphic in Figure 6 below.

Figure 6: Demulsifier Injection Package Schematic

Scale Inhibitor Injection Package (61-T-00125)

The Scale Inhibitor injection package contains one 2550 gallon tank and 3 injection pumps (2 operating + 1 spare) with 4.17 gph as the rated capacity of each pump. The chemical acts to help prevent the formation of hard scales of calcium, magnesium and other salts that will reduce the thermal efficiency of system exchangers and prevent deposit formation in the piping systems. The system is shown in the graphic in Figure 7 below.

Figure 7: Scale Inhibitor Injection Package Schematic

Metering Pump Principle of Operation

The chemical injection pumps are a type of positive displacement metering pump that use the reciprocating action of a flexible Teflon diaphragm in combination with suction and discharge ball check valves to pump the Defoamer chemical. The reciprocating action is produced by the rotation of the electric drive motor being converted to reciprocating (back and forth) motion through a worm gear and crank system. The back-and-forth movement of the diaphragm produces volumetric positive displacement. When the diaphragm, which is attached to the plunger, is pulled inwards towards the crank pump chamber, volume increases, and pressure decreases. The suction ball check opens, the discharge ball check closes and chemical are drawn into the chamber. As the crankshaft turns into the second half of its cycle, the plunger and diaphragm begin to move outwards. The pump chamber pressure increases as the volume decreases. The suction ball check closes and the discharge ball check open causing the chemical previously drawn in to be forced out. Finally, the diaphragm flexes out once again and draws more chemical into the chamber, completing one stroke. The cycle is repeated 80 times per minute on these pumps.

The volume of chemical pumped per stroke can be changed by moving the stroke adjustment knob up or down. The stroke length of the crank shaft changes in proportion to the up and down movement of the sliding adjustment shaft. This movement changes the eccentricity of the crank which in turn reduces (or increases) the length of stroke of the hydraulic piston and changes distance travelled by the plunger and diaphragm, resulting is chemical being displaced per stroke. A break-away view showing typical pump internals is shown in Figure 8 below.

Figure 8: Cutaway view of metering pump and drive unit

Initial start-up

Position of Blinds and Valves

Prior to start-up it is essential that the operator checks the positioning of all valves and blinds:

For safe operation, the operator must confirm that all blinds are repositioned correctly, and all valves open to atmosphere are fitted with blind flanges.
Ensure that all the spectacle blinds on any lines are in the correct position for normal operation.
All the manual non-critical valves must be confirmed in the correct position.
Critical valves (CSO, LO, LC) must be confirmed in their desired position.

Purging

The following steps are provided as a guide only. Purging is only necessary if any portion of the piping system has been opened to the atmosphere. If such is the case, proceed as follows:

Prior to the introduction of hydrocarbons to any system, it is first necessary to purge all air from the system. This is normally achieved by purging with blanket gas.
In the event blanket gas is unavailable or purging needs are relatively small, bulk nitrogen containers can be brought onto the site for use during the purging operation. Alternatively, a mobile inert gas generator or liquid nitrogen trucks can be utilized.
The purge gas supply will have to be connected to a suitable point on the upstream side and a purge must be conducted in a logical and a sequential manner through the inlet and outlet in succession. All branch lines and attached equipment, including instrumentation that may have possibly been exposed to the atmosphere, must be confirmed clear of all traces oxygen.
This ‘pulse-purge’ procedure should be repeated a minimum of three times and the equipment should then be sampled for oxygen content. Should the oxygen content be above 2.0%, the purging operation will have to be repeated until an oxygen content reading of less than 2.0% is obtained.
Purging of the system would then proceed in a logical manner with the process flow in much the same manner until the entire system is confirmed with an oxygen content reading of less than 2.0%.

Leak Testing

Leak testing of all piping, the Chemical Injection Systems and all associated equipment/flanges etc. should be carried out with blanket gas or nitrogen/ inert gas. During the leak check, once the entire system is confirmed free of leaks at a pressure of 60 psi (g), the gas supply should be isolated, and the pressure monitored.
In the event the system pressure starts to fall, all flanges and other joints can be tested with a gas meter or soap solution, where bubbles would indicate the location of the leak.
If no leaks are evident, the pressure in the equipment under test should remain constant over a period of one hour.

Start-Up

Pre-Start

Following maintenance shutdown, there are number of tasks which must be completed prior to any hydrocarbons being introduced to the process piping systems. Plant maintenance often involves dismantling equipment, replacement of parts, introduction of air into piping and vessels which are normally filled completely with explosive gases or other hydrocarbons and the opening of vents and drains in literally hundreds of locations. Before a start-up can safely proceed, all equipment must be returned to the same status it was in prior to the shutdown and all equipment must be proven ready for service and purged free of air, with all normally closed drains and vents in the proper position. These steps to follow to ensure this is the case are as follows:

A system check has been completed where experienced personnel have walked through the entire system, using the latest revision of the P&IDs, to ensure all equipment is in functional order, valves are in their correct position, flanges are tight, control valves are all supplied with air and test operated. A punch list of any incomplete/ nonconforming points has been developed, attended to and completed.
If any piping repairs, replacements, or additions have been made or any equipment has been added to the system, confirmation must be obtained that it has been successfully hydro tested & pneumatically tested as applicable.
If applicable, any new sections of feed and outlet process piping must be confirmed flushed, cardboard blasted, chemically or cleaned as required.
All instruments are calibrated, installed, and confirmed operable.
All PLC system related interlocks are simulated as per the logic / C&E diagrams for the main process plant and any new equipment – as per the vendor packages.
Electric power is confirmed.
All electric tracing is checked for functionality and is operational.
All utilities systems are confirmed operable, including instrument air for UZV.
Ensure that all equipment, piping and the Chemical Injection Systems is completely dried and have undergone all pre-commissioning procedures.
Ensure all instrument isolation and bleed valves are in normal position.

Start-Up

The following steps assume that all the outlined pre-start checks have been completed for the system and that all vessels and equipment downstream from the Chemical Injection Systems has been prepared in a similar manner, are fully functional and ready to receive process flows. It is also assumed that the start-up of the Chemical Injection Systems will occur in concert with a start-up of the entire Oil Treatment system, as per the referenced guidelines at the end of this document. Confirm all instrumentation isolation valves and bypasses are in their correct positions and all instrument forces not required for the start-up have been removed.

Confirm that all drains and vents are closed and that all manual process valves are properly lubricated and in their correct operating position.
Confirm all instrumentation isolation valves and bypasses are in their correct positions and all instrument forces not required for start-up have been removed.
Confirm the electrical supply is energized for the injection pumps and that any alarms or trips for the pumps are functional and have been reset.
Closed Drain Vessel High-High level alarm 61-LAHH-00301 is not active.
Open Drain Drum High-High level alarm 61-LAHH-00270 is not active.
Operator selects the pump to start.
Motor status is “READY” on HMI.
Confirmed Fire or Gas ESD is reset.
CPF ESD is reset.
Field PB ESD is reset.
Power failure or Low-Low instrument air pressure alarm is not active.

The Defoamer Injection Pumps have MANUAL Start/Stop soft push buttons on the HMI, as well as MCC and field EMERGENCY STOP push buttons. A separate hardwired ESD panel is provided in the CPF Control Room with manual ESD pushbuttons for the pumps.

The pump motors have H-O-A (Hand/Off/Auto) switches in the MCC and selecting HAND will enable the motor to start from the MCC, without checking any process interlocks. Selecting OFF will not allow the motor to start either from MCC or HMI. Selecting AUTO will allow the motor to start or stop from the HMI. In the event of a power failure all outputs shall de-energize. When power is restored, all outputs shall remain de-energized until appropriate resets are initiated.

The system can now be considered completely online, and start-up of the downstream piping systems and equipment can proceed as per normal procedure.

Normal Operation

During normal operation it should be ensured that all the drain points are closed and the lines going to closed drain system are closed.
During normal operation bypass line is closed.

Temporary Operation

In Temporary operation, the operator needs to refer to Management Of Change guidelines (MOC).

Emergency Operations (out of normal)

In emergency operation, the operator can refer to Consequences of deviation.

Normal Shutdown

The normal shutdown refers to the shutdown which is planned by the operator for an annual turnaround, maintenance of any equipment etc. The following reasons will justify the decision for a planned shutdown:

Preventive or periodic maintenance
Execution of modifications
Inspection by government authorities.
If the pumps are to be stopped – shutdown the pumps using the local emergency stop buttons to test function. Note that once the power has been locked out to the unit, a final check must be made to ensure the pumps will not start from the HMI (the emergency stop button is NOT to be considered sufficient means for locking the unit out electrically).

Emergency Shutdown

The ESD system for the project shall be a PLC based. It shall be designed to prevent the development of a hazardous condition that may lead to a process interruption, probably consequential property damage and / or personal injury (which may be caused by a process upset, machinery fault or an external event such as fire or gas detection) by providing adequate process control and ultimately safe emergency shutdown of all process equipment.

The ESDs initiated shall either be:

a) Process shutdown ESD / Inlet Shutdown.

This would involve shutting down the inlet ESD valve for individual trains, or isolating specific equipment only.

b) Plant shutdown ESD.

This would involve shutting down of the entire satellite or CPF facility including all the trains along with the associated utilities.

An Injection Pump will STOP under any of the following conditions:

Closed Drain Drum High-High level alarm becomes active.
Open Drain Drum High-High level alarm becomes active.
Flare Knockout Drum High-High level alarm becomes active.
Operator selects the pump to STOP at HMI.
Confirmed Fire or Gas ESD becomes active.
CPF Plant shutdown ESD button is pressed.
Pump Emergency stop push button is pressed in field.
Power failure or Low-Low instrument air pressure alarm becomes active.

Considering that as the total production flow drops following an initiated shutdown, the Chemical Injection Systems should be shutdown in the following manner:

Confirm that all chemical injection points are properly isolated.
Confirm that all water flow exiting the tank has ceased and that all equipment and vessels feeding to those systems is shutdown and depressurized. Confirm also that Chemical Injection Systems systems have been shutdown as per the referenced guidelines at the end of this document before proceeding with the next steps.
if maintenance is planned on the Chemical Injection Systems or the associated piping, the system can either be bypassed using the isolation valves and line or the system can be completely isolated, using the following steps.
The Chemical Injection Systems is now completely shutdown and the other PW Coolers can be shutdown in the same manner.

Start-up following maintenance/emergency shutdown

The permissives for the Defoamer Injection Pumps to START are:

Closed Drain Vessel High-High level alarm is not active.
Open Drain Drum High-High level alarm is not active.
Operator selects the pump to start.
Motor status is “READY” on HMI.
Confirmed Fire or Gas ESD is reset.
CPF ESD is reset.
Field PB ESD is reset.
Power failure or Low-Low instrument air pressure alarm is not active.

Troubleshooting Criteria

Successful Troubleshooting requires a combination of the following tools:

A basic knowledge of the entire Oil Treatment system, including any ancillary systems such as the instrument air and flare systems.
Operational knowledge of the components within these systems.
A sound understanding of how each component interacts in the overall operational sequence of the Oil Treatment system.
A logical and analytical approach to fault diagnosis.

Figure 3 below outlines a suggested process flowchart that outlines a methodology for undertaking and troubleshooting a specific problem with the Water Aerial Cooler.

Figure 3: Troubleshooting Flowchart

The following table offers a list of problems that could be associated with operation of the Chemical Injection System, along with the possible causes and suggested remedial actions.

	Problem	Possible Causes	Actions
1.	High produced water temperature at outlet of cooler.	Fans tripped Broken fan belt Faulty temperature transmitter/controller High produced water flow Fouled exchanger tubing. VSD malfunction.	Check/reset fans as required. Replace broken belts. Check/recalibrate/repair or replace transmitter/controller as required. Reduce PW flow Check differential pressure/clean exchanger as required. Check/repair VSD operation.
2.	High differential pressure across cooler.	Outlet block valve restricted. Exchanger fouling. Faulty transmitter.	Check valve and open/clear obstruction as required. Confirm high differential and clean exchanger as required. Check/Repair transmitter as required.
3.	Fan or motor vibration	Motor & fan out of alignment Fan blade damaged Slipping or broken drive belt. Obstruction inside fan cowling.	Check/adjust alignment as required. Replace damaged fan blade as required. Replace/tighten belt as required. Remove obstruction/check for damage

Isolation for Maintenance

If the produced water system is to be left in service during the cooler isolation, flow should be diverted around the cooler using the bypass line (open the block valve slowly to minimize flow disruption). One the bypass valve is fully open, isolation of the cooler can proceed as follows.\
Arrange for I/E to lock out power to the fan motors (remember to reset the emergency stop and attempt to start the pump after the power supply has been locked out).
Close the 6” inlet block valve, downstream from the bypass line branch.
Close the 6” outlet block valve, downstream from the bypass line tie-in.
Once all the block valves are confirmed closed, the 2” on both the inlet and outlet lines on the cooler side of the closed block valves can be cracked open to the closed drain system open drain system – to confirm a tight shut-off, in preparation for swinging the spectacle blinds.
Finally, the 2” vent to atmosphere on the inlet header can be cracked open to break the vacuum and help drain liquid from the system.
Once all liquids have drained from the lines, the unit can be prepared for maintenance, all closed block valves should be locked and tagged as per procedure and all three spectacle blinds (suction, discharge & recycle) should be swung to the closed position. All open drains and vents should be tagged in the open position.
The differential pressure transmitter can be left unblocked to accommodate calibration during the cooler isolation.

The Dehydration Water Aerial Cooler can now be considered completely isolated and empty and preparations can be made for issuing a WCC Permit as per ISSOW Procedure for maintenance as required.

This concludes the CPF Phase 2 Chemical Injection Systems process description Guideline. For more specific details of system operation or information about the system components or operation, consult the referenced documents at the end of this document.

Ø 12.0 Variance

If a variance is required for this guideline, it shall be approved by the Team Lead in accordance with the Policy, Standard, Procedure, Guideline (PSPG) Variance.

Glossary

Ambient Conditions – A term used to describe the prevailing, surrounding atmospheric conditions of temperature, pressure and atmospheric components in which a piece of equipment operates

Baffle – A plate or barrier that is deliberately placed in the normal path of a liquid or gas stream to deflect it and change direction, normally to aid in liquids removal.

Central Processing Facility (CPF) – The central oil processing and treating facility comprised of several crude oil treating trains, four de-oiling trains, and common systems including utilities, tank storage and metering/custody transfer facilities.

Check Valve –A mechanical device installed in a piping system which allows fluid to flow in one direction only and prevents reverse flow.

Closed Drain – A drain system connected directly to pressure vessels. Liquids in a closed drain system can become pressurized and may contain dissolved gases that flash in the drain system.

Demulsifier – a chemical used to displace the compounds that stabilize the oil/water interface so that droplets in the emulsion can coalesce to form bigger droplets and make separation easier.

Emulsion – a stable dispersion of one liquid in another, in this case oil and water.

Flare – An elevated vertical stack or chimney used for burning excess gases or flammable gas and liquids released by pressure relief valves during unplanned over-pressuring of plant equipment.

Guideline – An outline or indication of policy. Establishes acceptable best practice to achieve a goal that is consistent with policies and procedures. Guidelines are intended to provide users the latitude and deviation to regulate their actions or decisions in a manner that reflects good judgment and remains consistent with policy and procedure.

Integrated Safe System of Work (ISSOW) – It is an electronic system for work control, risk assessment and isolation management. It is a very important part of our Company Safety Management System. Operators should be familiar with ISSOW procedures and guidelines and they should be certified by PTW coordinator.

ISSOW Permits– ISSOW Permits are controlled documents which are used to identify Hazards & co-ordinate, communicate, control & record work activities. ISSOW Permits will be required for all work activities and are issued from the Permit Office.

Responsibility

Team Leader – is responsible for approval and dissemination of this guideline and supporting Operations on issues regarding the application of this guideline.

Supervisor – is responsible for the development and maintenance of this guideline. They are also responsible for developing and maintaining work site employee awareness of and compliance with this guideline.

Employees – are responsible for compliance with this guideline.