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Lord Fin Tube-Heat recovery with steam

2020-02-12Leave a message

Heat recovery systems capture waste heat and repurpose it for useful applications, improving energy efficiency and reducing operational costs. In thermal processes, heat can be transferred using either liquid media or steam, each with distinct characteristics.

When transferring heat from a liquid medium (such as hot water or thermal oil), the sensible heat of the medium is utilized:

  • The liquid enters the heat exchanger at an elevated temperature
  • As it releases thermal energy, its temperature drops
  • The liquid exits the exchanger at a reduced temperature

Steam, as a heat transfer medium, exists in two primary forms:

  • Saturated (wet) steam - Water molecules remain in a gaseous state at a temperature corresponding to vapor pressure
  • Superheated (dry) steam - Steam heated beyond its saturation point, containing no liquid droplets

The vaporous nature of steam presents unique advantages and challenges in heat transfer processes compared to liquid-based systems.

 

How Steam Heat Recovery Works

In steam heat recovery systems, thermal energy that would normally be wasted is captured and put to productive use through these fundamental steps:

  1. Waste heat from industrial processes is captured and transferred to a steam generator
  2. The generated steam is distributed to various processes as a source of thermal energy
  3. This creates an eco-friendly and cost-effective solution for energy utilization

A key differentiator of steam systems is their ability to transfer heat at a constant temperature, unlike liquid-based systems where the temperature varies during heat transfer.

Components and Control Mechanisms

Effective steam heat recovery requires several critical components:

  • A control valve on the primary side adjusts heat input to maintain stable output temperatures
  • The system leverages latent heat released during condensation, which provides 2-5 times more energy than sensible heat from hot water systems
  • Condensate return systems ensure efficient reuse of water resources

Advantages of Steam Heat Recovery Systems

1. Superior Energy Efficiency

  • Steams latent heat of condensation provides significantly more usable energy than liquid-based systems
  • Natural circulation reduces pumping requirements, lowering electricity consumption
  • Energy recovery during phase change makes steam highly efficient

2. Precise Temperature Control

  • Steam enables isothermal heat transfer at constant temperature
  • Particularly beneficial for processes requiring uniform heating like press plates
  • Eliminates temperature gradients common in liquid systems

3. Reduced Mechanical Complexity

  • Steam moves via natural circulation (gravity or pressure differences)
  • Eliminates need for circulation pumps in many applications
  • Simplifies system design compared to forced-convection liquid systems

4. Rapid Heat Transfer

  • Condensation process ensures fast energy release
  • Improves overall process efficiency and responsiveness
  • Enables quicker heat-up times compared to liquid systems

Disadvantages of Steam Heat Recovery Systems

1. High-Pressure Requirements

  • At 300°C, steam requires >85 bar pressure
  • Thermal oil can transfer 400°C heat at atmospheric pressure
  • Pressure-rated equipment increases capital costs

2. Corrosion and Scaling Risks

  • Water impurities cause boiler scale and corrosion
  • Requires continuous water treatment (demineralization, deaeration)
  • Additional operational costs for chemicals and maintenance

3. Space and Installation Challenges

  • Steam generators need additional vapor space
  • Typically requires horizontal installation orientation
  • Ducting for gas heat recovery increases footprint

4. Operational and Safety Considerations

  • Steam hammering risks from improper condensate handling
  • Potential for water hammer damage in pipes and equipment
  • Requires skilled personnel for safe operation
  • Higher maintenance requirements than liquid systems

Industrial Applications of Steam Heat Recovery

1. Steam Jacketed Heating

  • Used in reactors, dryers, and process vessels
  • Provides precise temperature control
  • Direct steam injection ensures efficient energy transfer

2. Vacuum Steam Drying

  • Removes moisture from heat-sensitive materials

3. Humidification Systems

  • Maintains optimal humidity in HVAC and industrial spaces

4. Power Generation

  • Waste heat steam drives turbines for electricity

Steam heat recovery systems offer compelling advantages including high energy efficiency, precise temperature control, and rapid heat transfer. However, they require careful consideration of:

  • High-pressure system requirements
  • Water treatment needs
  • Space constraints
  • Operational expertise