Chiller System Analysis: Green Hydrogen Production

The Unseen Workhorse

Analyzing the Chiller’s Critical Role in Green Ammonia Synthesis

The Problem: Hot & Saturated Hydrogen

Hydrogen gas emerging from the electrolyser is not ready for ammonia synthesis. It’s saturated with water vapor—a potent poison to the expensive catalyst used in the next stage.

Inlet Gas Temperature

80°C

Extremely hot and humid

Process Flow Contamination Risk

💧

Electrolyser

Produces Hot, Wet H₂

→

☠️

Catalyst Poisoning

Water damages catalyst

→

🏭

Ammonia Plant

Production Halts

The Solution: Dehydration via Chilling

The chiller’s purpose is to drastically cool the hydrogen, forcing the problematic water vapor to condense into a liquid that can be safely removed.

Purified Process Flow

💧

Electrolyser

→

❄️

Chiller System

→

✅

Ammonia Plant

Outlet Gas Temperature

5°C

Cold and dry

What is COP and Its Purpose?

The Coefficient of Performance (COP) is a key measure of a chiller’s efficiency. Unlike a motor, a chiller’s COP is almost always greater than 1 because it’s moving heat, not creating cold.

The Bucket Brigade Analogy

bucket

Cooling Load (Heat Moved)

👟

Work Input (Energy Expended)

⚖️

COP (Buckets per Energy Unit)

The Technical Formula

COP =

Cooling Load (kW) Work Input (kW)

Deconstructing the Chiller’s Workload

The total cooling required (Heat Duty) is split into two jobs: cooling the gas temperature (Sensible Heat) and condensing water vapor (Latent Heat). The phase change consumes the vast majority of the energy.

The Energy-Water Relationship

Because condensing water (Latent Heat) is so energy-intensive, even a small increase in the initial gas temperature and humidity significantly raises the chiller’s power consumption.

The Power Equation

Power =

Heat Duty Efficiency (COP)

Power Use vs. Inlet Temperature

The Role of Electrolyser Pressure

Operating the electrolyser at a higher pressure is hugely beneficial, as it “squeezes” most of the water out of the gas stream before it reaches the chiller.

Feature	Low-Pressure Electrolyser (~1 bar)	High-Pressure Electrolyser (~30 bar)
Water Vapor in Gas	High (e.g., 31% by volume)	Low (e.g., 1% by volume)
Chiller Cooling Load	Very High (dominated by latent heat)	Low (dominated by sensible heat)
Chiller Size & CAPEX	Large & Expensive	Small & Cheaper
Chiller Power & OPEX	Very High	Low

How Vendors Design the Chiller System

The calculated values provide the critical specifications vendors use to size and build the chiller package’s main components.

Evaporator

Sized by:

Cooling Load

Compressor

Sized by:

Power Required

Condenser

Sized by:

Total Heat Dissipated

Consequences of Chiller Failure

If the chiller fails or is undersized, the effects are immediate, severe, and costly.

☠️
Catalyst Poisoning Wet hydrogen will irreversibly destroy the expensive iron catalyst in the ammonia synthesis loop.
❄️
Ice Formation Water entering the cold ammonia liquefaction section will freeze, potentially blocking pipes and causing a plant shutdown.
📉
Reduced Efficiency and Production Even small amounts of water can lead to unwanted side reactions, lowering the overall efficiency and output of the plant.