Converting Flue Gas Heat
Directly Into Vapour
Without the penalties of conventional systems — eliminating hot water loops, reducing footprint, and cutting auxiliary power consumption.
Why Most Plants Don't Recover Flue Gas Heat
| Factor | Impact |
|---|---|
| Low flue gas temperature | 100–180°C — too low for economical steam production |
| Very low energy density | Makes pressurised steam generation unviable |
| Additional fan power | Increased ID/booster fan load to overcome pressure drop |
| Large circulation systems | Hot water loops require significant pumping power |
Because of these constraints, producing pressurised steam from flue gas waste heat is typically uneconomical. Conventional systems therefore recover heat using hot water generators, which introduce additional energy and complexity penalties.
Limitations of Conventional Hot Water Generator Systems
- Bulky equipment — large hot water circulation loops and separate flash chambers
- Hydraulically inefficient — high pumping power for large circulation rates
- Parasitic power loads — additional electrical consumption on the host facility
- Complex interfaces — multiple equipment items between heat source and MED
Vacuum Vapour Generator (VVG)
The VVG directly converts low-grade waste heat into low-pressure water vapour under vacuum, eliminating intermediate loops and simplifying the heat recovery architecture.
Hot Water Generator System
Vacuum Vapour Generator
3-step process replaces 5-step conventional system. Single integrated device eliminates hot water loops, flash chambers, and circulation pumps entirely.
VVG Operating Principle
What Changes — and What Does Not
| Aspect | VVG Approach |
|---|---|
| What changes | Heat recovery front end — replaces hot water generator + flash chamber |
| What does not change | Downstream MED system and operating philosophy |
VVG vs Conventional Hot Water Generator
Typical performance improvements based on engineering analysis and project experience.
Process & Equipment
| Parameter | Hot water Generator | VVG | Improvement |
|---|---|---|---|
| Heat recovery approach | Heat recovery approach Sensible heat → hot water → flash vapour | Direct vapour generation | Simplified |
| Equipment items | Multiple | Single integrated device | Reduced complexity |
| Process-side flow rate | 1.0× | ~0.03× | ~97% reduction |
| Temperature driving force (LMTD) | 1.0× | ~1.9× | Higher |
| Heat exchanger surface | 1.0× | ~0.56× | Smaller |
| Equipment weight & footprint | 1.0× | ~0.56× | Reduced |
Power Consumption
| Component | HWG System | VVG System | Impact |
|---|---|---|---|
| Circulation pump | 1.0× | ~0.03× | Eliminated |
| Booster fan | 1.0× | ~0.57× | Reduced |
| Overall auxiliary power | 1.0× | ~0.52× | Lower |
Why the VVG Changes the Equation
Energy & Power
Equipment & Installation
Operations & Maintenance
Why This Matters
| Conventional Approach | VVG Approach |
|---|---|
| Recovers heat with high power cost | Recovers heat with minimal power penalty |
| Marginal economic viability | Clear operational benefit |
| Multi-equipment interface | Single integrated device |
The VVG enables recovery of low-grade waste heat without traditional power penalties, improving the practicality of thermal desalination from flue gas.
Sustainability & Circular Use of Heat
- enabling productive reuse of low-grade thermal energy
- reducing auxiliary electrical consumption
- improving water production efficiency in water-stressed regions
- converting unavoidable heat losses into useful resources
Application Envelope
| Application | Heat Source |
|---|---|
| Flue-gas-based thermal desalination | Power plant stack gas |
| Industrial evaporation systems | Cement, steel, glass process exhaust |
| Process concentration | Chemical and food processing waste heat |
| Engine heat recovery | Cogeneration exhaust |
| Refinery heat utilisation | Petrochemical low-grade streams |
Development Background
Operational challenges in conventional heat recovery systems — including equipment size, circulation power penalties, and gas-side pressure drop — informed the development of the VVG architecture.
The VVG represents a generalised engineering approach for converting low-grade heat into usable vapour for low-pressure thermal processes.
Turning Low-Grade Heat into Usable Vapour
The Vacuum Vapour Generator improves the efficiency of waste heat recovery by simplifying system architecture and reducing auxiliary power requirements
Interested in VVG for Your Facility?
If waste heat is available in the 100–180°C range, the VVG can enable freshwater production with minimal power penalty. Our team can assess your heat source and recommend the right configuration.
