Posted on: 09. 15. 26
Ensuring natural gas flows freely through production equipment is vital to plant uptime. Differential pressure in gas processing matters most to engineers because it illustrates baseline resistance through piping networks. Drastic changes to differential pressure gas processing profiles signal restricted flow, reduce liquid recovery, and trigger higher compression costs.
Why should you care about system friction loss? Maintaining detailed data on pressure drops across vessels helps technicians identify unexpected process upsets before they knock critical compressors offline. This article helps Technical Project Engineers and Operations Managers better understand what causes disruptions to expected pressure drops across equipment internals.
Let’s walk through hydrocarbon liquid knockouts so we can keep those barrels recoverable!
Gas Processing Basics
Raw natural gas exits wellsheads as a mixture of methane gas, heavier hydrocarbons, water vapor, and suspended solids. Separators, amine treating units, glycol dehydrators, and filter vessels slow down this fluid mixture due to intrinsic surface friction.
Too much resistance equals low plant efficiency. The ability to discern between good vessel resistance and harmful restriction ensures operators avoid unscheduled downtime.
How Differential Pressure Gas Processing Impacts Production
Monitoring differential pressure gas processing allows operators to easily benchmark:
- energy losses due to friction factors
- natural gas velocity through vessels
- hydrocarbon liquids knock out restrictions
Operators review these monitored values over time to establish equipment health trends and predict failures before liquid carryover or gas bypass occurs.
Ideal versus Actual Process Conditions
Ideal conditions assume no valves or bends disturb gas flow in piping networks. In actuality, processing plants operate in relative steady-state. Events like amine flooding, feed tank drawdowns, or sudden upticks in production cause momentary flux in overall system pressure.
Common Gas Processing Pressure Drop Values
| Pressure Drop | Asset Example |
| 3 to 7 PSI | Inlet Slug Catcher |
| 2 to 5 PSI | Particulate Coalescer |
| 4 to 8 PSI | Amine Contactor Tower |
| 2 to 6 PSI | TEG Dehydration Unit |
| 5 to 12 PSI | Molecular Sieve Bed |
Establishing a pressure drop baseline assists teams in maintaining consistent equipment performance while preventing unnecessary isolation events.
Why Establish a Baseline Gas Pressure Drop Profile
Pressure drops should always increase with rising throughput. Reviewing normal ΔP ranges against live production data helps engineers quickly identify trouble spots. Perhaps compression levels match previous slows, but pressure drop readings fall far outside of this established curve.
Operators can assume process upsets occur when there is no historic baseline gas pressure drop profile to reference against. Gas processing units receive gas at fluctuating inlet pressures based on changes to wellhead supply. A high pressure drop suddenly appearing in the system could be the result of increased throughput versus process equipment failures.
One method of developing a true baseline pressure drop is capturing readings during initial startup trends and creating normalized curves.
- Take differential pressure measurements across every vessel at 50%, 75%, and 100% of nameplate flow.
- Record temperature, gas gravity, and entrance pressures for each data point.
- Normalize collected measurements to establish baseline performance curves.
Operators should investigate when live readings deviate from these normalized pressure drop curves if production levels remain unchanged.
How Hydrocarbon Liquids Knockout Affects Vessel Pressure
Hydrocarbon liquids knockout occurs when flowing natural gas reduces in velocity, allowing heavy liquids to separate from the vapor phase. Adequate hydrocarbon liquids knockout prevents solids from building up inside process equipment and stabilizes tray differential pressure. This avoids harmful liquid draws into compressors, which may cause costly downtime.
Incoming natural gas streams entering an inlet vapor separator need sufficient freeboard for liquids to settle by gravity. Equipment such as mist eliminators, vane packs, and cyclone separators aid in this separation process. As shown in the image below, excess buildup of liquids within these internals drastically reduces the open area allowing gas to pass.
Reduced flow area causes fluid velocity to increase as the same volume of gas attempts to move through a smaller opening. As velocities rise inside the vessel, so does the baseline ΔP measured across the asset.
High Pressure Drop Causes Gas Line Restrictions
Now we know how liquid holds up influence overall system resistance, but what causes high pressure drop gas line restrictions to develop? Most common root causes include:
- hydrate formation
- spout adhesion
- accumulation of solids on filter elements
- gasket failure or displaced packing material
You should always be proactive when discovering unexpected pressure drops. Higher than normal resistance wastes compressor horsepower and diminishes returns on downstream processing units. Troubleshooting steps include:
Gas Processing Troubleshooting Checklist
- Hydrate Formation: Occurs when system temperature drops below its freezing point at a given operating pressure. Water molecules bond with hydrocarbons, creating ice-like blocks that adhere to the inside of pipelines.
- Solid Objects: Rust, minerals, and debris collect on filter elements over time. This trapped accumulation rapidly increases filter differential pressure.
- Paraffin/Wax: Heavier hydrocarbon components chill then adhere to cooler pipe walls. Think of how these high pressure drops cause gas line contractions and slow operations.
- Equipment Failures: Loss of support structures inside processing equipment causes flow paths to narrow. Broken filter cloths, displaced packing, and valve seats dropping into the liquid space are all examples.
A quick method of identifying what high pressure drop causes gas line problems is measuring surface temperatures along the line. Cooling largely occurs right before a restriction due to the Joule-Thomson effect, a principle leveraged in JT skids for gas conditioning.
Natural Gas Plant Efficiency Loss
Operators witness natural gas plant efficiency loss whenever excess system restrictions force compression units to inject more fuel gas in order to maintain design discharge pressures. Shutdowns occur as unused compression capacity becomes dedicated to pushing gas through newly restricted lines.
Unplanned downtime equals lost production. Losing one compressor to tray damage costs plant managers dearly, not only due to repair bills but lost gas throughput as well.
Mathematically, think about how pressure loss equals money loss. Field compressors require extra input power to overcome any resistance inside piping networks.
Less Common Gas Pressure Drop Causes
In addition to the previously mentioned issues, here are some unique situations that can increase your pressure drop.
- Vapor Binding: Cooling coils used to chill incoming natural gas streams can cause liquids to condense out upstream of processing equipment. Common causes for vapor binding include hydrate formations and hydrocarbon condensation.
- Air Ingress: Higher than normal ΔP may be from leakage of air into your system. Just like hydrate formation, air can bind to hydrocarbons and cause high pressure drop across equipment.
- Nitrogen Dilution: Nitrogen injections help control volume depletion and styrene polymerization. Sometimes, excess nitrogen can build up inside systems and cause high pressure drops similar to vapor binding.
Track Your Pressure Drop Trends
Pressure drop monitoring doesn’t have to be difficult. By knowing what common issues cause sudden shifts in baseline pressure drop data, field technicians can target remedial efforts before severe problems occur.
Pro-Gas Can Help
If your current system is suffering high-frequency failures due to poor filtration or process inefficiencies, speak to an engineer today. Pro-Gas specializes in custom fuel gas conditioning, portable NGL storage, liquid separator, and filtration solutions designed with the toughest field conditions in mind.
Learn how we helped one of our customers improve operations. Review our case study and see how Pro-Gas helped a customer improve operational efficiency by reducing pressure drops across gas processing equipment.
Reach out to our group of Pro-Gas engineers tomorrow to see how we can help optimize your current plant hydraulics.
Frequently Asked Questions
What can cause the sudden changes in pressure drop?
Valves introduce changes in pressure. Before and after pressure points are used to measure pressure drop across vessels. Any unwanted change in pressure can be classified as a pressure drop.
What causes differential pressure to change?
Common process upsets that cause gradual changes to differential pressure in gas processing include pump failures, unexpected process upsets, line breaks, or feed tank failures. Gradual decreases in DP can stem from leak paths within pipes.
Will reducing pressure drop increase efficiency?
Reducing pressure drop will decrease your utilities bill. Utility costs increase with higher ΔP demands. When friction losses decrease inside vessels, compressors don’t need to work as hard to boost gas to the desired outlet pressures.
Does pressure drop cause low production?
Restrictive pressure drop causes low production. Gas processing plants take gas at one pressure and increase that pressure, sending gas downstream at elevated pressures. Something causing pressure drop somewhere in the system is stealing your production.
