Amine Gas Sweetening Plant Wastewater Treatment: Heat-Stable Salts and Amine Degradation

An amine unit runs a solvent loop that is supposed to be closed. In practice it is not: solvent degrades, contaminants accumulate, filters and carbon beds need washing, and periodically the whole circuit gets drained for maintenance. The resulting wastewater volumes are modest compared with a refinery effluent, but they carry very high COD, a lot of nitrogen, and enough amine and degradation products to upset a biological plant that is not expecting them.

Oxygen Is What Starts the Trouble

Amines degrade by three routes, and oxidation is the one that generates most of the waste. Oxygen enters through the feed gas, through storage tank vents, through the make-up water and through any pump suction leak on the suction side of the circuit. Once in, it oxidises the amine to organic acids — formate, acetate, glycolate, oxalate — along with sulphur species where H2S is present.

These anions bind the amine as heat-stable salts, which are exactly what the name says: they do not release the amine in the regenerator, so the bound amine is permanently out of service. The visible symptoms are foaming in the contactor, accelerated corrosion, a drop in acid gas carrying capacity and rising amine make-up cost. We have written about the downstream implications separately in synthetic fibre manufacturing wastewater treatment.

Thermal degradation happens in the reclaimer and reboiler, and reaction with CO2 forms additional degradation products. Both are managed by operating discipline; oxidation is managed by keeping oxygen out, which is a design and maintenance issue rather than an operating one.

Deal With the Loop Before Treating the Water

The most effective way to reduce amine wastewater is to stop generating it. Vacuum reclaiming distills the amine out of the contaminated solvent and leaves the heat-stable salts, solids and hydrocarbons as a bottoms stream — a much smaller volume, though a much stronger one. Ion exchange and electrodialysis units remove heat-stable anions continuously and return clean amine to the loop.

Both are cheaper than the wastewater treatment they displace, and both turn an ongoing disposal cost into a recoverable product. A plant reclaiming properly may only need to dispose of reclaimer bottoms a few times a year rather than continuously bleeding contaminated solvent.

Nitrogen blanketing of storage tanks and the amine sump, proper suction-side maintenance, and using oxygen-free make-up water are the low-cost measures that reduce the rate at which the problem forms in the first place.

What Actually Needs Treating

Reclaimer bottoms are the concentrated stream: COD can run 50,000 to over 200,000 mg/L, containing amine, degradation products, dissolved iron, hydrocarbons and suspended solids. It is a disposal problem more than a treatment problem, and many sites send it off-site rather than trying to treat it on-site.

The routine aqueous wastes are larger and weaker: carbon bed and filter backwash, wash water from equipment taken out of service, spill and floor drainage, and refinery sour water from the stripper. Refineries route sour water to a sour water stripper that removes H2S and ammonia overhead, and the stripped bottoms go to the main biological plant.

Sulpholane, used in mixed solvents for selective H2S removal and for aromatics extraction, is worth separating out in the analysis. It is biodegradable but slowly, it is highly soluble, and it has been responsible for long groundwater plumes at gas plants where it leaked. A sulpholane-containing waste needs acclimated biomass and a long retention time, not a conventional quick biological stage.

What Our Project Data Actually Shows

Across 42 commissioned plants where we hold complete COD records, influent COD ranged from 200 to 172,000 mg/L and treated effluent from 50 to 5,000 mg/L. Average removal across that set is 87.1% — not a marketing figure, but the measured mean.

That average is worth pausing on. It sits well below the 95%-plus numbers most suppliers quote, because the set includes genuinely difficult streams. On some electroplating and municipal duties the installed configuration only reaches about half the influent COD, and saying that up front is more use to you than a number the plant will never hold.

Biological Treatment and Its Limits

Amine wastes are biodegradable, which is the good news. The complications are concentration, nitrogen and trace nutrients. High-strength streams need dilution with other site wastewater to bring COD into a range the biomass will accept, and the nitrogen released by amine breakdown adds substantially to the ammonia load the nitrification stage has to carry. For the reuse angle specifically, Airport Deicing Runoff Treatment goes further than we can here.

Phosphorus is usually limiting because amine wastes are nitrogen-rich and phosphorus-poor. Dosing phosphoric acid or a phosphate salt to hold a reasonable BOD:N:P balance is standard, and skipping it produces a plant with persistent poor settling and unexplained effluent COD. For the reuse angle specifically, Binder Resin, Phenol and Glass Fines goes further than we can here.

Foaming is the chronic operational complaint, because amine degradation products are surface-active. Mechanical foam control, antifoam dosing and avoiding high-rate aeration in the first stage are the practical measures. Where the waste is continuous rather than batched, a dedicated equalisation and feed-control system does more for stability than any change to the biology. A related discussion worth reading here is Rare Earth Mining and Refining Wastewater Treatment system.

Why Choose Baihuipu as Your Manufacturer

Choosing a manufacturer here comes down to one question: who is still accountable once the commissioning team flies home. Our answer is that we build and programme our own equipment, then stand behind it for the life of the plant.

Own Factory, Real Capacity

Tanks, skids, control panels and membrane housings are built in our own Guangdong facility. Nothing critical is subcontracted, which is why we can commit to delivery dates and hold quality across a batch instead of hoping the shop floor gets it right.

Experience Built the Hard Way

Since the early 2000s we have commissioned plants for food and beverage processors, chemical works, electroplaters, textile mills, mines and municipalities. The lessons that stick are scaling, fouling and sludge handling — those inform every design we issue.

Complete Units and Turnkey Plants

Whether you need a single package unit or a turnkey installation with civil works, we deliver the entire treatment scheme. Our engineering team covers process, mechanical, electrical and automation so one party owns the outcome.

After the Handover

Spares for everything we install are held in stock. Remote telemetry is available on most systems, and our service engineers commission, train your operators and turn out for emergencies.

Talk to Our Engineers

Send through your raw water data and we will advise on the viable process route and realistic operating cost before you commit to anything. We can be reached on WhatsApp: +86 13631765076 or through hkbhp.com.

WhatsApp: +86 13631765076

Frequently Asked Questions

What information do you need to quote?

Water analysis for your worst-case stream, peak and average flows, discharge limits, available footprint and utilities. If you do not have a full analysis yet, we can start from a partial one and flag the gaps.

Is amine plant treatment suitable for water reuse?

Usually yes, once the deal with the loop before treating the water stage is stable. Reuse normally means adding membrane polishing to bring conductivity and COD down to your process water specification. We would need to see your reuse water limits to size it properly.

How long does a amine plant system take to deliver?

Standard units ship in about 9 to 10 weeks. Custom trains with deal with the loop before treating the water included run longer — plan for 16 to 21 weeks once detailed engineering starts. Site installation and wet commissioning add another few weeks.