Technical Manual
of Industrial Steam
General Table of Contents
- 1. Introduction: The Ultimate Thermal Vector
- 2. Fundamental Thermodynamics
- 3. The Pressure-Volume-Transport Relationship
- 4. Enemies of Efficiency: Air, Water, Scale
- 5. Steam Quality & Superheating Phenomena
- 6. Condensate Management & Flash Steam
- 7. The IoT Revolution: Wattnow Methodology
- 8. Appendices & Steam Tables
- 9. References & Sources
Foreword: This white paper is a technical extension of the guides from the National Agency for Energy Management (ANME). It aims to provide plant managers and maintenance supervisors with the theoretical and practical tools to understand their installation, combined with Wattnow's modern monitoring solutions.
Introduction: The Ultimate Thermal Vector
Steam has been used as an energy vector since the early days of the industrial revolution. Even today, it remains irreplaceable in process industries (food processing, chemicals, textiles, paper) and power generation.
Why does steam dominate industry?
Water is the most common fluid on Earth, chemically stable, non-toxic, and inexpensive. But it is its unique thermodynamic properties that make it the ideal heat transfer fluid:
- High energy density: Steam can transport a massive amount of energy in a small volume (thanks to latent heat), which allows for reducing installation sizes.
- Constant temperature transfer: Saturated steam condenses at a constant temperature, ensuring perfect uniformity in cooking or heating.
- High heat transfer coefficient: Condensation releases energy with heat transfer coefficients far superior to liquid convection.
- Ease of distribution: Steam moves under its own pressure, without circulation pumps.
The Wattnow Approach
If steam is a "perfect" vector in theory, its management is complex. Losses are invisible (leaking traps, failing insulation, overconsumption). Wattnow transforms this invisible fluid into tangible data to restore the theoretical efficiency of your installations.
Fundamental Thermodynamics
To master steam, one must master the concepts of energy, temperature, and pressure. Confusing these terms often leads to costly sizing errors.
2.1. Temperature Scales
Although industry commonly uses degrees Celsius (°C), thermodynamic calculations are based on the absolute Kelvin scale (°K).
2.2. Pressure: Absolute vs. Gauge
This is the number one source of error in the field. Industrial pressure gauges display gauge pressure (bar g), i.e., the pressure above atmospheric pressure.
2.3. Steam Energy: Enthalpy
Specific enthalpy (h) represents the energy contained in 1 kg of fluid. It breaks down into two critical phases during steam production:
Phase 1: Enthalpy of Water (hf) - Sensible Heat
This is the energy required to heat water from 0°C to its boiling point. This energy is "felt" because it raises the temperature.
Example (at atmospheric pressure): It takes 419 kJ to bring 1 kg of water from 0°C to 100°C.
Phase 2: Enthalpy of Evaporation (hfg) - Latent Heat
This is the magic energy of steam. Once boiling, water absorbs a massive amount of energy without changing temperature to change state (liquid → gas).
Example (at atmospheric pressure): It takes 2,257 kJ to transform 1 kg of water at 100°C into steam at 100°C.
Crucial Observation: At atmospheric pressure, the energy required to evaporate water (2,257 kJ) is more than 5 times greater than the energy to heat it (419 kJ). This is why steam is so powerful.
2.4. Enthalpy Table
| Pressure (bar g) | Temperature (°C) | Sensible Heat (hf) | Latent Heat (hfg) | Total Energy (hg) |
|---|---|---|---|---|
| 0 | 100 | 419 | 2,257 | 2,676 |
| 1 | 120 | 506 | 2,201 | 2,707 |
| 6 | 165 | 697 | 2,066 | 2,763 |
| 10 | 184 | 781 | 2,000 | 2,781 |
| 14 | 198 | 845 | 1,947 | 2,792 |
The Pressure-Volume-Transport Relationship
The previous table reveals a fundamental phenomenon: The enthalpy of evaporation (useful heat) decreases as pressure increases. So why do we produce steam at high pressure? The answer lies in Specific Volume.
3.1. Specific Volume (v)
Steam is a compressible gas. At low pressure, it occupies a huge volume. At high pressure, it is compressed.
- Steam at 1 bar g: 0.881 m³/kg
- Steam at 7 bar g: 0.240 m³/kg
Steam at 1 bar takes up almost 4 times more space than steam at 7 bar!
3.2. Piping Transport Capacity
Case Study: Transporting 100 kW of heat
Let's compare two DN25 pipes carrying steam at standard velocity, one at 2 bar, the other at 6 bar.
Case A: Steam at 2 bar g (hfg = 2163 kJ/kg, v = 0.603 m³/kg)Mass flow rate: 100 kW / 2163 = 0.046 kg/s
Volumetric flow rate: 0.046 × 0.603 = 0.028 m³/s
Velocity in DN25: 57 m/s (Too high! Noise, erosion, pressure drop).
Case B: Steam at 6 bar g (hfg = 2066 kJ/kg, v = 0.272 m³/kg)
Mass flow rate: 100 kW / 2066 = 0.048 kg/s
Volumetric flow rate: 0.048 × 0.272 = 0.013 m³/s
Velocity in DN25: 27 m/s (Perfect).
3.3. The Golden Rule of Efficiency
- Produce and Distribute at High Pressure: To minimize pipe sizes.
- Reduce Pressure to Low Pressure Before Use: Just before the heat exchanger, this increases the available enthalpy of evaporation.
Enemies of Efficiency: Air, Water and Scale
In an ideal heat exchanger, steam directly contacts the metal to release its heat. In reality, parasitic "films" form, creating formidable thermal barriers.
4.1. Air and Non-Condensable Gases
Air is the worst enemy of heat transfer. It comes from feedwater (dissolved O2 and N2) or air ingress during shutdowns.
Thermal Resistance Comparison
An air film 0.025 mm thick offers the same thermal resistance as a copper wall 380 mm thick!
Air is 1,500 times more insulating than copper.
4.2. The Water Film (Condensate)
Water conducts heat 60 times less effectively than steel. If steam traps do not evacuate condensate instantly, the heat exchanger becomes "waterlogged."
Wattnow Diagnosis
Wattnow monitors the Steam Consumption / Product Temperature Evolution ratio. If consumption remains stable but the product heats up less quickly, maintenance (descaling or trap repair) is required.
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Steam Quality & Superheating Phenomena
A standard industrial boiler does not produce "perfect" steam. Steam quality directly influences productivity and equipment longevity.
5.1. Steam Quality (x)
During boiling in the boiler, water droplets are carried along with the steam. This is called "wet steam."
- Dry Steam (x=1): 100% gas. Theoretical ideal.
- Standard Steam (x=0.95): 95% gas, 5% liquid water.
Economic Problem: Liquid water at 180°C contains 4 times less energy than steam. If you pay to produce 1 tonne of steam at quality 0.90, you pay for 100 kg of water that will provide no useful latent heat.
5.2. The Superheating Phenomenon
Superheated steam is steam heated beyond its saturation temperature (e.g., 6 bar at 200°C instead of 165°C).
Superheat Calculation
Expansion of dry steam from 6 bar to 1 bar.
- Upstream (6 bar): hg = 2764 kJ/kg.
- Downstream (1 bar, saturated): hg = 2707 kJ/kg.
- Excess energy: 57 kJ/kg.
Temp Rise = 57 / 2.06 ≈ 28°C.
Final temperature = 120°C (saturation) + 28°C = 148°C.
Although hotter (148°C vs 120°C), superheated steam behaves like a dry gas. Its heat transfer coefficient is very low. It must first cool down to saturation before it can condense.
Condensate Management & Flash Steam
Condensate is not waste; it is chemically treated water charged with energy (sensible heat). Its recovery is imperative.
6.1. Flash Steam
When hot condensate at high pressure is discharged to a low-pressure area (e.g., return to an atmospheric tank), it contains too much energy to remain liquid.
Example: Condensate at 4 bar g (152°C, hf=641 kJ/kg) discharged to atmosphere (hf=419 kJ/kg, hfg=2257 kJ/kg).
% Flash = (641 - 419) / 2257 = 0.098 or 9.8%.
6.2. Economic Implications
At a plant consuming 10 tonnes/hour of steam at 4 bar:
- 1 tonne of steam is lost as a "white plume" from trap discharges if not recovered.
- This is a loss of water, chemicals, and energy.
Optimized Solution
This "Flash Steam" is free steam! Instead of letting it escape, it should be collected in a flash vessel and injected into a low-pressure network. Wattnow quantifies this wasted energy source by measuring condensate return temperatures.
The IoT Revolution: Wattnow Methodology
Thermodynamics dictates the rules, but IoT allows us to verify they are followed. An unmonitored steam installation naturally drifts towards inefficiency.
7.1. Monitoring Architecture
- Steam Meters (Vortex/Orifice): Measure mass flow rates corrected for Pressure/Temperature.
- Temperature Sensors (Wireless): Placed at heat exchanger inlets/outlets and on condensate returns.
- Pressure Sensors: To verify network stability.
7.2. Dashboards & KPIs
| Indicator (KPI) | Physical Meaning | Corrective Action |
|---|---|---|
| Steam/Product Ratio | Kg of steam to produce 1 tonne of product. | If increases: Leaks or drop in heat exchanger efficiency. |
| Pressure Stability | Pressure variations at the point of use. | If unstable: Undersized boiler or poorly managed load peaks. |
| Steam Quality | Proximity to the saturation curve. | If T° > T°sat: Unnecessary superheat. If T° < T°sat: Presence of air. |
| Night/Weekend Flow | Consumption when the plant is idle. | This is the direct measurement of static leaks. |
Case Study: Food Processing Industry
Context: Tomato processing plant. High theoretical consumption.
Wattnow Diagnosis: Sensors revealed that at night, while production was stopped, the boiler maintained a flow of 800 kg/h.
Cause: A bypass valve on a large exchanger was left slightly open, and 4 thermodynamic steam traps were stuck open.
Result: Immediate repair. Savings of 40,000 TND / year with a 3-month ROI on the IoT solution.
Saturated Steam Tables
Quick reference for your daily calculations.
| Pressure (Bar Abs) | Temperature (°C) | Specific Vol. Gas (m³/kg) | Latent Enthalpy (kJ/kg) |
|---|---|---|---|
| 1 | 99.6 | 1.694 | 2258 |
| 2 | 120.2 | 0.885 | 2201 |
| 3 | 133.5 | 0.606 | 2163 |
| 4 | 143.6 | 0.462 | 2133 |
| 5 | 151.8 | 0.375 | 2108 |
| 6 | 158.8 | 0.315 | 2086 |
| 7 | 165.0 | 0.272 | 2066 |
| 8 | 170.4 | 0.240 | 2048 |
| 10 | 179.9 | 0.194 | 2015 |
| 15 | 198.3 | 0.132 | 1947 |
| 20 | 212.4 | 0.099 | 1890 |
| 25 | 223.0 | 0.080 | 1835 |
Data from ANME Guide and NIST tables
Bibliographic Sources
This white paper was written by energy efficiency experts at Wattnow, based on national and international technical standards.
Main Sources
- ANME: Steam Guide - Volume 1: Physical principles of steam. Energy Efficiency Program in the Industrial Sector.
- IAPWS: IAPWS-IF97 Formulation for the Thermodynamic Properties of Water and Steam.
- Spirax Sarco: Steam Engineering Handbook, 2022.
Associated Standards
- ISO 50001: Energy management systems.
- ISO 50015: Measurement and verification of energy performance.
About Wattnow
Wattnow is an IoT energy management solution that helps industrial companies visualize, analyze, and optimize their energy consumption in real-time. Our technology combines hardware (smart sensors) and software (analytics platform) to make invisible waste visible.
Disclaimer: The information contained in this document is provided for informational purposes only. We make no representations or warranties regarding the completeness, accuracy, or reliability of the content.
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