Henry's Law and Its Application

Henry's Law:

Henry's law is one of the gas law. At a constant temperature, the amount of a given gas dissolved in a given volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
At a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.

An everyday example of Henry's law is given by carbonated soft drinks. Before the bottle or can is opened, the gas above the drink is almost pure carbon dioxide at a pressure slightly higher than atmospheric pressure. The drink itself contains dissolved carbon dioxide. When the bottle or can is opened, some of this gas escapes.Because the pressure above the liquid is now lower, some of the dissolved carbon dioxide comes out of solution as bubbles. If a glass of the drink is left in the open, the concentration of carbon dioxide in solution will come into equilibrium with the carbon dioxide in the air, and the drink will go "flat".

Formula and the Henry's law constant

Henry's law can be put into mathematical terms (at constant temperature) as

where p is the partial pressure of the solute in the gas above the solution, c is the concentration of the solute and k_H is a constant with the dimensions of pressure divided by concentration. The constant, known as the Henry's law constant, depends on the solute, the solvent and the temperature.

Some values for k_H for gases dissolved in water at 298 kelvins include:

oxygen (O₂)                    : 769.2 L·atm/mol

carbon dioxide (CO₂)      : 29.4 L·atm/mol

hydrogen (H₂)                  : 1282.1 L·atm/mol

An industrial example for Henry's Law is, Deaerator. A Deaerator is a device that is widely used for the removal of air and other dissolved gases from the feedwater to steam-generating boilers.

The removal of dissolved gases from boiler feedwater is an essential process in a steam system. The presence of dissolved oxygen in feedwater causes rapid localized corrosion in boiler tubes. Carbon dioxide will dissolve in water, resulting in low pH levels and the production of corrosive carbonic acid. Low pH levels in feedwater causes severe acid attack throughout the boiler system. While dissolved gases and low pH levels in the feedwater can be controlled or removed by the addition of chemicals, it is more economical and thermally efficient to remove these gases mechanically. This mechanical process is known as deaeration and will increase the life of a steam system dramatically. Deaeration is based on two scientific principles. The first principle can be described by Henry's Law. Henry's Law asserts that gas solubility in a solution decreases as the gas partial pressure above the solution decreases. The second scientific principle that governs deaeration is the relationship between gas solubility and temperature. Easily explained, gas solubility in a solution decreases as the temperature of the solution rises and approaches saturation temperature. A deaerator utilizes both of these natural processes to remove dissolved oxygen, carbon dioxide, and other non-condensable gases from boiler feedwater. The feedwater is sprayed in thin films into a steam atmosphere allowing it to become quickly heated to saturation. Spraying feedwater in thin films increases the surface area of the liquid in contact with the steam, which, in turn, provides more rapid oxygen removal and lower gas concentrations. This process reduces the solubility of all dissolved gases and removes it from the feedwater. The liberated gases are then vented from the deaerator. With these principles in mind, Sterling Deaerator Company employs a two-stage system of heating and deaerating feedwater. This system reduces dissolved oxygen concentration to less than 0.005 cc/liter (7 ppb), and completely eliminates the carbon dioxide concentration.

Crystallization

Find the page here to know about Crystallization process.

http://www.cheresources.com/cryst.shtml

Is anything there to replace the Heat Exchangers in Process Industry ?

Replacing of Heat Exchangers are possible in Process Industry. Any Process Industry greatly depends on heat exchangers for the recovery of energy through process fluid or utility fluid.

Why replace a heat exchanger?
Documented energy savings of up to 30% have been reported when replacing a shell-in-tube or plate and frame heat exchanger with a direct steam injection heater from Hydro-Thermal. Heat exchangers heat through a metal barrier which absorbs much of the steam's energy. Direct steam injection heaters, on the other hand, are your smart energy investment because they are more energy efficient by using all the industrial steam's energy to heat process fluids or utility water.

What is Direct Contact Steam Injection?

Direct steam injection transfers heat by precisely injecting metered amounts of steam into the process fluid, liquid or slurry. Injecting steam more rapidly and more efficiently transfers heat energy than indirect heat exchangers. Direct contact steam heating uses all of the sensible and latent energy in the steam, providing 100% thermal efficiency. Energy savings can be considerable reductions in the 20% - 30% are common.

Controlling Steam Flow

A Hydro-Thermal steam injection heater is an internally modulated mixing valve that controls both steam flow and mixing. Steam mixing is controlled by an internal stem plug that meters the amount of steam allowed to pass through the nozzle. Internal modulation eliminates the need for an external steam control valve.

Nozzle design ensures constant steam pressure and velocity at the point where steam contacts the liquid or slurry, eliminating the potential for pressure upsets and ensuring smooth heater operation. This feature provides tight temperature control to the process and extraordinary energy efficiency.

Low Maintenance Because of Self-Cleaning Design

The Hydroheater is cleaned by its own turbulent mixing action, so it does not foul or scale. Chemical clean-out is never needed for our heaters, so they save money and lower the environmental impact of harsh cleaning chemicals.  Maintenance time is also greatly reduced.
Thanks to the self-cleaning action these steam heaters have the flexibility to heat slurries containing a high concentration of solids or non-Newtonian liquids.

Compact Design

Hydroheaters and all accessories are compact and installed as part of the piping, requiring less space than heat exchangers or spargers.

Specifying a Direct Contact Steam Heater

To specify a Hydroheater, general information about the process and the fluid properties such as specific gravity, density, solids content, viscosity and whether any abrasive or corrosive products are present must be taken into consideration. Other information needed are flow rates and steam pressures.

More reasons to replace heat exchangers or spargers with a steam injection heater from Hydro-Thermal

• Less maintenance and more up time
  
• Exacting control of required process conditions and temperature
  
• Smaller foot-print
  
• Hydro-Thermal expertise, training, support services and warranty
  

Unlike heat exchangers or spargers, the Hydroheater is engineered specifically for your process conditions and unique application.

*** Application constraints are there.