An ammonia stripper does not always have to deliver a polished effluent. If the aim is a bulk reduction of a very strong ammonia stream, with the rest handled elsewhere, a simpler, more compact stripper can do the job. This post looks at a 300 m³/day stripper designed to take ammonia from up to 7,000 mg/l down to roughly 1,750 mg/l, a 75% reduction, with an option to recover the stripped ammonia as ammonium sulphate.

The challenge: very high ammonia, remote location

The client was looking at a high-strength ammonia wastewater, with up to 7,000 mg/l in the inlet, at a flow of 300 m³/day. Two features of the enquiry shaped the design:

• The unit was expected to suit remote locations or sites with limited supervisory support, so it had to need little operator attention.
• The unit was expected to be readily mobile, so it could be moved between sites.

Heat was understood to be available on site in the form of a steam feed, so the design could use thermal conversion of ammonium ions to ammonia gas without adding chemicals.

The approach: a compact, packing-free stripper

What the unit is, and what it is not

The proposal was explicit about its limits. It provides a bulk reduction in ammonia but is not designed to reach very low concentrations. That honesty matters, because it tells the buyer that downstream treatment will still be needed if a tight discharge limit applies.

The main components

• Dual stripper and cooling-tower column. The column uses packing-free vortex scrubber technology, so there is no packing to clean. A single tower combines the stripping function with cooling of the exit liquid and pre-heating of the incoming air, which reduces process complexity and footprint.
• Dual-path feed filtration. Both filters are sized for the full flow and have pressure gauges to show when they need attention.
• Stripping air blower. It is rated at 6,000 Nm³/h, with a direct-drive arrangement to avoid belt changes and downtime, and a variable speed controller to tune airflow and the exit ammonia concentration.
• Feed heater. A steam-heated unit brings the incoming liquid to process temperature.
• Instrumentation. Level monitoring on the stripper and cooling liquids, and a pressure switch on the blower outlet to detect loss of stripping air.

Everything is mounted on hot-dip galvanised skids. Pipework is galvanised, MDPE or 304 stainless steel depending on its duty, and the control panel is weatherproofed to IP65. Because the unit has two columns it is not fully transportable as built, so some dismantling and re-erection would be needed when it moves.

Optional ammonia recovery

The exhaust air can be bubbled through a sulphuric acid absorber to remove the ammonia as ammonium sulphate. That turns the stripped ammonia from a disposal problem into a product, and it avoids releasing ammonia in the exhaust air.

Why it works

The design trades polish for simplicity. Because it uses heat rather than chemical addition (other than perhaps some anti-foam, depending on the organic content of the feed), the operating inputs are steam, power and air. Because it is packing-free, the main routine task of cleaning packing disappears. And because it is skid-mounted, it can be installed with limited site work.

Sludge is handled separately. The design provides a flanged access point for sludge removal and a separate flanged connection for a progressive cavity sludge pump. Electrical equipment was to conform to BS 5345, the code for electrical equipment in hazardous areas, and the unit was expected to be installed in the open air in a compound.

What was left to the client

Civil works, steam raising equipment, electrical supply, water supplies for steam raising, signal cabling for SCADA or telemetry, and sludge handling facilities were excluded.

What to consider for your own project

1. Be clear about the target. A bulk reduction stripper is not a polishing step. Plan what follows it.
2. Confirm your heat source. Steam availability is central to this design.
3. Consider ammonia recovery. An acid absorber can convert ammonia to ammonium sulphate, subject to a market or disposal route.
4. Plan for sludge. Precipitated solids need a removal route. Specify it at the outset.
5. Check the discharge route. Residual ammonia may need further treatment before discharge. See the Environment Agency’s permit guidance.

FAQ

What does bulk reduction mean?

It means removing most of the ammonia without trying to reach a very low concentration. Here, from up to 7,000 mg/l to about 1,750 mg/l.

Do I need chemicals to strip ammonia?

This design used heat instead of chemical dosing, other than possibly a little anti-foam.

What is ammonium sulphate recovery?

Bubbling the exhaust air through sulphuric acid captures the ammonia as ammonium sulphate.

Can the unit be moved?

It was designed to be readily mobile, though with two columns it needs some dismantling for transport.

Dealing with strong ammonia liquors?

Tell us your flow, ammonia strength and available steam and we will outline a stripping route. For larger plants and process comparisons, read our post on three ways to meet an ammonia stripping specification.