How an Oil-Lubricated Compressor Destroyed a Hot Extractive System and FID at an Oil Refinery: Why Air of the First Purity Class Is Not a Whim but a Necessity

In this article, I want to share a case that vividly demonstrates how even a perfectly designed and installed gas analytical system can fail in the shortest possible time due to a seemingly secondary component — the air supply compressor. The situation unfolded at a major oil refinery where industrial safety and environmental control are taken with the utmost seriousness. The project was executed competently, albeit with minor remarks, and the equipment was selected in accordance with process requirements. However, one detail left without due attention led to a serious failure, a complete shutdown of the monitoring system, and costly repairs that were, moreover, deemed out-of-warranty.

What Was Installed: A Hot Extractive System with FID

A modern continuous emission monitoring system was installed at the refinery. It included two key components:

• A hot extractive system — a multi-component analyzer operating on the "hot-wet" principle. The sampling probe, heated line, and measurement cell are maintained at a temperature above the dew point, which prevents condensation of aggressive components and ensures reliable measurement of SO₂, NOₓ, CO, CO₂, and other gases. The cell temperature was 180 °C.

• An additional FID module — a flame ionization detector configured to measure TOC (Total Organic Carbon) in emissions. The FID operates by combusting the sample in a hydrogen flame and requires a constant supply of clean air to sustain combustion and ensure correct operation of its pneumatic components.

The installation point was chosen in compliance with all standards, mounting was carried out according to the manufacturer's recommendations, and the design documentation passed all necessary approvals. It seemed the system was destined for long and trouble-free operation.

The "Weak Link": A Standard Oil-Lubricated Compressor Instead of a Specialized One

The equipment of the hot extractive system and the FID module requires a constant supply of compressed air of a specific quality. This is not simply "air from the plant's utility line" but air of the first purity class — strictly regulated in terms of solid particle content, moisture, and, critically in this case, oil.

The integration partner responsible for supplying auxiliary equipment decided to cut corners or perhaps simply did not attach importance to this. Instead of a specialized oil-free compressor with a multi-stage filtration and drying system, a standard reciprocating compressor with an oil sump and a simple moisture separator filter at the outlet was installed. Such a compressor, even when brand new, inevitably allows microscopic oil droplets to pass into the pneumatic line — this is a feature of its design, not a defect.

Chronicle of Failure: How Oil Killed the Analytics

The system was put into operation and initially ran smoothly. However, after just a few weeks, problems began to surface.

The FID module was the first to suffer. Inside the FID analyzer is a complex pneumatic block responsible for the precise metering of gases — hydrogen, air, and sample. This block contains extremely fine capillaries through which the combustion air passes. The oil mist carried with the compressed air began to condense and deposit on the walls of these capillaries. The cross-section gradually narrowed, the air flow rate decreased, and the flame in the detector became unstable. Soon the capillaries were completely clogged with an oily deposit, making further operation of the FID impossible.

But the problems did not end there. Some of the oil aerosol, having passed through the pneumatic system, entered the measurement cell of the hot analyzer. Small oily specks appeared on the optical windows of the cell. A continuous film did not form, but even these point contaminations on the windows led to local scattering and attenuation of the optical signal. The signal intensity dropped, the automatic gain control system exhausted its reserve, and the analyzer stopped producing reliable data.

Consequences: Repair, Downtime, and an Out-of-Warranty Case

Diagnostics quickly identified the cause of the failure, but rectifying the consequences required significant effort and time:

• The hot analyzer was dismantled, and its measurement cell was sent for overhaul. The problem was solved by replacing the optical windows on which the oily specks had appeared. A complete disassembly and cleaning of the entire cell were not required, but replacing the windows and subsequent alignment took time.

• The FID module required the replacement of the pneumatic block with the capillaries. Cleaning oil-clogged capillaries is impossible or impractical, so the block was replaced with a new one, followed by recalibration of the entire module.

During all this time, the emission monitoring system was non-operational. Data was not transmitted to the state environmental system, which for an enterprise of this level is a serious violation fraught with fines and injunctions.

When the refinery contacted the analytical equipment supplier for warranty repair, the case was deemed out-of-warranty. The reason is clear: the manufacturer of the analytical system explicitly stated in the documentation the requirements for the quality of the supplied air — air of the first purity class. Using an oil-lubricated compressor with simple filtration is a direct violation of these requirements. All responsibility for the consequences fell on the enterprise and the integration partner.

The Moral: Follow the Manufacturer's Recommendations Implicitly

This case is a vivid example of how saving on auxiliary equipment can lead to the failure of the main, far more expensive system. The cost of an oil-free compressor with a high-quality air preparation system is incomparable to the expense of replacing the FID pneumatic block, replacing the measurement cell windows, and, more importantly, the losses from monitoring system downtime and reputational risks.

Key Lessons from This Story:

1. Always strictly adhere to the manufacturer's requirements for auxiliary media quality. If the documentation states "air of the first purity class," it is not a recommendation but a mandatory condition of operation.

2. Do not skimp on compressor equipment. To supply analytical systems, especially those containing precision pneumatic components (FID, chemiluminescence analyzers, NDIR modulators), only oil-free compressors with multi-stage filtration, drying, and, if necessary, adsorption purification from residual oil vapors are permissible.

3. Be aware of out-of-warranty risks. Equipment failure due to non-compliance with operating conditions results in a 100% denial of warranty repair. All costs will be borne by the equipment owner.

4. Verify the work of integrators. If you entrust installation and commissioning to a third-party organization, ensure they are competent in the specifics of gas analytical equipment and do not attempt to "simplify" the solution at the expense of reliability.

I hope this experience helps you avoid similar mistakes. Remember: in gas analytics, there are no minor details. Sometimes it is precisely "just a compressor" that determines whether a system will operate for years or fail a month after startup.