Compression & Conditioning
The machinery that turns a low-pressure gas into a dense fluid a pipeline can actually move, and the drying and clean-up that make the stream fit to put into somebody else's system.
Last updated 2026-09-06
Typical duration
Typically 12-20 months from foundation readiness to a proven train, with compressor manufacture usually the longest lead item on the entire project and often ordered before the rest of the design is finished.
What is Compression & Conditioning?
CO2 leaves a capture unit as a gas at not much above atmospheric pressure. In that state it is bulky, and moving useful quantities of it any distance would need a pipeline of absurd size. Compression fixes that. Raising the pressure makes the CO2 dramatically denser, until it stops behaving like a gas and starts behaving far more like a liquid - a fluid you can pump, meter and push down a pipe of sensible diameter at a sensible cost. The condition the stream is delivered in is set by the designer and by the transport and storage operator together, and it is the single decision that shapes the pipeline design, the pumping requirement and much of the operating cost of the chain.
Conditioning is the other half of the job and it is mostly about water. CO2 and water in company are aggressive towards ordinary carbon steel, and free water in the wrong conditions can also cause operating problems further down the line. So the stream is dried, and other impurities carried over from the capture unit are removed or reduced, until it meets the specification the transport and storage operator has set. That specification is a contract rather than a preference. The pipeline and the storage site were designed around a defined stream, the operator will measure what arrives, and an emitter that cannot meet the specification cannot inject. Conditioning equipment therefore gets designed to the entry conditions of a system somebody else owns.
On the ground this is a rotating machinery job and it feels different from the rest of the site. Grouted baseplates, precise alignment, lube oil systems that have to be surgically clean, coolers, seal systems, large drivers and a machine protection package. The trades are different too - millwrights, oil flushing crews, alignment and vibration specialists. It is usually the noisiest area on the plant, frequently the largest single electrical load, and almost always the item with the longest manufacturing lead time, which is why the compressor is often ordered before the rest of the design is anywhere near finished.
Compare the methods at a glance
When and why is Compression & Conditioning used?
Compression sits between the capture plant and the pipeline and it is the point where the chain changes character. Upstream of it, the project is a chemical plant handling a dilute gas. Downstream of it, the project is a transport system handling a dense fluid. Everything after this point - pipe wall, valve selection, material choices, venting arrangements, control philosophy, even how a maintenance isolation is planned - follows from what compression delivers. It is installed after the capture plant is standing because it needs the same crane access and because its interconnecting pipework runs to equipment that has to exist first, and it is commissioned before the pipeline can be filled, because the pipeline has nothing to receive until the machines run. The commercial logic is equally direct. Compression consumes a significant share of the energy the whole scheme uses, so its efficiency shows up in the operating cost every hour for decades, and the difference between a machine that runs and a machine that trips repeatedly is the difference between a project that meets its availability obligations and one that does not. That is why so much of the effort here goes into things that look like fuss - foundation stiffness, alignment, oil cleanliness, pipework that does not pull the machine out of line - and why the manufacturer's representative is on site for the installation rather than for the handover. There is also a safety reason to do it properly. Compression is where the process starts handling a fluid that is heavy, cold when it expands and capable of collecting in low ground if it escapes. Those hazards are managed by the designer through the layout, the relief and venting arrangements and the detection system, and by the operator through procedure and training. The construction team's job is to build that design exactly, prove it, and hand over the evidence.
Types of Compression & Conditioning
Explore each method in depth - benefits, limitations, plant and quality control on its own page.
Integrally geared centrifugal compression train
A compact multi-stage machine driven through a common gearbox, with cooling between the stages. Efficient, comparatively small in footprint and well suited to steady, continuous duty on a large emitter. Sensitive to foundation stiffness, alignment and the cleanliness of its oil and cooling systems, and normally the longest lead item on the whole project.
Explore this methodReciprocating compression
Positive displacement machines, generally chosen for smaller flows, wide operating ranges or duties where the flow varies a lot. More tolerant of turndown than a centrifugal machine, but heavier on maintenance and more demanding of the foundation because of the way the loads pulse. Frequently used on smaller emitters, on booster duties or as a later stage in a mixed arrangement.
Explore this methodCompression plus liquid pumping
The stream is compressed and cooled until it is dense enough to be pumped, then a pump does the remaining work. Pumping a dense fluid takes less energy than compressing a gas, so this arrangement can be attractive where a lot of pressure is needed, at the cost of a more complex plant and more equipment to maintain.
Explore this methodDehydration and impurity removal package
The conditioning half of the area - drying equipment plus whatever removal or polishing steps the entry specification demands. Usually supplied as a package by a specialist vendor and integrated between the compression stages. Its performance is measured continuously, because it is what proves the stream is fit to enter the transport system.
Explore this methodBest suited for
- Preparing a captured stream for pipeline transport at a scale a pipe can economically carry
- Meeting the entry specification set by a transport and storage operator the emitter does not control
- Emitters connecting into a shared cluster network with a defined common stream quality
- Projects where operating energy cost over decades justifies careful machine selection and installation
Compression & Conditioning: step by step
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Step 1: Prepare and grout the machine foundations
Rotating machinery is unforgiving about what it stands on, so the foundation is finished to the machinery supplier's requirements rather than to general civils standards. Concrete surfaces are prepared, anchor bolts and pockets checked, and the baseplate set, levelled and shimmed to the arrangement the supplier specifies. Grouting is a controlled operation with its own procedure covering surface preparation, materials, placement and curing, because a void or a poor bond under a baseplate will show up later as vibration nobody can explain. Levels are surveyed before and after. This step often gets treated as civils tidying-up and it is not - it is the foundation of the machine's whole operating life, and correcting it once the train is assembled means taking the train apart again.
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Step 2: Set the train and align it
The compressor, gearbox, driver and any coupled equipment are set on the baseplate and aligned to each other under the supplier's procedure and, on most projects, under the supplier's direct supervision. Alignment is checked cold, adjusted, and then checked again after the interconnecting pipework is connected, because pipework that has been pulled into place rather than fitted will drag the machine out of line the moment it is bolted up. Pipe strain checks are done for exactly that reason. Coupling installation, shaft end float and the fitting of guards and covers all follow the manufacturer's instructions. Everything is recorded as it is done. Alignment data taken at installation becomes the baseline that every later vibration investigation is measured against, so a set of readings nobody wrote down is a diagnostic tool thrown away.
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Step 3: Install the dehydration and conditioning package
The drying and clean-up equipment usually arrives as a vendor package, sometimes skid-mounted and sometimes as loose equipment, and it is set, connected and integrated into the compression train at the points the process design requires. Vessels, internals, media, valves, filters and the associated instrumentation all go in to the vendor's arrangement. The analysers that will demonstrate the stream meets the entry specification are installed here too, with their sample lines routed so they measure what is actually flowing rather than a stagnant pocket. Cleanliness matters through this whole package, because debris carried in during construction ends up in equipment it will be expensive to clean later. The vendor is normally present for installation and for the first operation of their equipment, and their sign-off is part of the completion evidence.
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Step 4: Install the coolers, lube oil, seal and utility systems
Around every compression train sits a set of systems it cannot run without. Coolers reject the heat that compression puts in, and they need their own foundations, cooling water or air-side connections and space for maintenance access. The lube oil system - reservoir, pumps, filters, coolers and the pipework between them - is safety-critical to the machine and demands a level of internal cleanliness that ordinary process pipework never sees. Seal systems, instrument air, nitrogen, drains and vents all connect in. Each of these gets installed to its own arrangement drawing and each gets tested and proved separately, because they are the systems that cause most early trips. The venting and relief arrangements are installed exactly as designed and to the positions shown, since where a discharge goes has been assessed rather than chosen.
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Step 5: Run the interconnecting pipework and the metering
Pipework between the capture plant, the compression stages, the conditioning package and the pipeline entry point is installed, supported and tested. The supports and guides matter more here than almost anywhere else on the site, both because the machine will not tolerate pipe strain and because thermal movement through the train is significant. Material selection is set by the designer to suit the stream once it has been dried, and the construction team builds to the specification rather than to what is available. Metering is installed at the boundary where custody of the stream passes from the emitter to the transport operator, and it is treated as a commercial instrument rather than a process one: its installation, straight lengths, calibration and verification are agreed with the parties on both sides of that boundary, because everything each of them gets paid or charged flows from what it reads.
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Step 6: Clean, flush and dry the systems
Before anything runs, the systems are cleaned out. Pipework is flushed, blown through or chemically cleaned as the design requires, temporary strainers go in ahead of the machines to catch what the cleaning missed, and the lube oil system is flushed to a defined cleanliness and proved by sampling rather than by inspection. Once the pressure testing is complete, the process systems are dried and purged, because water left in a system that will later carry CO2 is the one thing every material selection decision was made to avoid. This stage is genuinely tedious, it always takes longer than the programme allows, and it is skipped at the project's peril - the overwhelming majority of early machinery failures on new plant trace back to debris or water left in during construction.
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Step 7: Complete the control, protection and monitoring systems
The compression area carries the densest instrumentation on the plant. Machine protection - vibration, temperature, position and the associated trips - is installed, connected, calibrated and functionally proved, with the trip settings coming from the machinery supplier and being verified rather than assumed. Process control loops are checked end to end from the field device to the operator screen. The safety instrumented functions and detection systems are tested individually, and the interfaces with the host plant's control room and with the transport operator's systems are agreed and demonstrated with both parties present. Condition monitoring is set up now rather than later, because the data recorded in the first weeks of operation becomes the healthy baseline against which every future problem is judged, and there is no way to go back and collect it.
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Step 8: Solo run, string test and performance proving
Commissioning of the area builds up in stages. Auxiliaries first, then the driver on its own, then the train uncoupled, then the complete string, each stage signed off before the next begins. Vibration, temperatures, oil condition and machine behaviour are watched continuously and compared against the factory test data and the installation baseline. Trips and protection functions are proved deliberately rather than discovered accidentally. Once the machine runs stably, performance is demonstrated against what was guaranteed, and the conditioning package is proved by measuring the stream against the entry specification the transport operator set. The machinery supplier is present throughout, the results are documented, and the area is handed over with a complete record - alignment, cleanliness, calibration, trip settings, baseline vibration - that the operator will still be referring to in twenty years.
Plant & equipment
- Mobile and crawler cranes for setting compressors, drivers, coolers and vessels
- Precision levelling, laser alignment and dial indicator equipment for the machine train
- Grouting equipment and controlled materials for baseplates and machinery bases
- Oil flushing rigs, filtration units and sampling equipment for lube oil cleanliness
- Pipework flushing, air blowing and chemical cleaning equipment
- Pressure testing, purging and drying equipment for the process systems
- Vibration analysis and condition monitoring instrumentation
- Calibration equipment for process, machine protection and custody metering instruments
Quality control & testing
- Baseplate levels and grout quality recorded before the machine is assembled on it
- Cold alignment recorded, then re-checked after pipework connection with pipe strain measured
- Lube oil cleanliness proved by sampling to the supplier's requirement, not by visual inspection
- Pipework flushing and cleaning certificates issued system by system
- Machine protection trip settings verified against the supplier's data and functionally tested
- Custody metering installed, calibrated and verified with both the emitter and the transport operator present
- Stream quality demonstrated against the transport operator's entry specification before acceptance
- Baseline vibration, temperature and performance data captured and retained for the operations team
Safety watchpoints
- Stored energy in rotating machinery, with isolation and lock-off discipline applied before any intervention
- High noise levels around the compression area during running, requiring controls and restricted access
- Large electrical loads and high-voltage supplies feeding the drivers
- Systems under pressure during testing and commissioning, with exclusion zones enforced
- CO2 released during venting or a leak is heavier than air and can collect in low or enclosed spaces; the designer controls this through layout, vent routing, detection and ventilation, and the operator through procedure
- Cold surfaces and cold discharge where the fluid expands, managed through the design and the operating instructions
- Chemicals used in cleaning, drying and the conditioning package, handled under the supplier's controls
- Working alongside the operating capture plant and the host facility under a shared permit system
Common defects to hunt
- Voids or poor bond under the baseplate grout, showing up as vibration nobody can diagnose
- Pipework pulled into place and bolted up, dragging the machine out of alignment
- Debris left in the system after inadequate flushing, wrecking seals and bearings in the first weeks
- Water left in a system that will later carry CO2, undoing every material decision the designer made
- Lube oil cleanliness signed off on paper rather than proved by sample
- Trip settings entered from a default list instead of the machinery supplier's data
- Custody metering installed without both parties agreeing the arrangement, leading to a commercial dispute
- No baseline data from installation and first running, leaving future problems with nothing to compare against
How long does Compression & Conditioning take?
Typical duration: Typically 12-20 months from foundation readiness to a proven train, with compressor manufacture usually the longest lead item on the entire project and often ordered before the rest of the design is finished..
Related processes
- Site Civils & Heavy Foundations
- Capture Plant Installation
- CO2 Transport Pipelines
- Injection Wells & Commissioning
- Integrally geared centrifugal compression train - method
- Reciprocating compression - method
- Compression plus liquid pumping - method
- Dehydration and impurity removal package - method
- Carbon Capture & Storage (CCUS) sector guide
- Utilities & Energy - group of sectors