Fouling effects on boiler

1) Padhiar Rushabh D. 1300101190612) Naik Harsh K. 1300101190593) Maharshi Soni H. 1300101190504) Mihir Dalwadi D. 130010119057

HEAT TRANSFER

PREPARED BY,

. TOPIC . EFFECT OF FOULING ON HEAT EXCHANGER

SUBMITTED TO :- PROF.ABHISHEK PANDEY

EFFECT OF FOULING ON HEAT EXCHANGER

Heat Exchanger Fouling

a. Types and Effectb. Facts and recent scenarioc. Design considerationsd. Economic importance of foulinge. Fouling control

CONTENTS

HEAT EXCHANGER

Heat exchangers are units designed to transfer heat from a hot flowing stream to a cold flowing stream.

Use :- Heat exchangers and heat recovery is

often used to improve process efficiency.

TYPES OF HEAT EXCHANGER

There are three broad categories:

The Recuperator, or through-the-wall non storing exchanger.

The Direct contact non storing exchanger

The Regenerator, accumulator, or heat storage exchanger

An interchangeable plate heat exchanger applied to the system of a swimming pool.

RECUPERATORS

The schematic of a shell-and-tube heat exchanger

RECUPERATORS

RECUPERATORS

Direct Contact

Regenerators

Applications of Heat Exchangers

Heat Exchangers prevent car engine

overheating and increase efficiency

Heat exchangers are used in Industry

for heat transfer

Heat exchangers are used in AC and

furnaces

Fouling, in technical language, it is the general term of unwanted material which is

accumulating on surfaces, such as inside pipes, machines or heat exchangers.

FOULING

Fouling occurs when any type of particles both organic or inorganic plug or plate out on heat transfer surfaces creating a resistance to transfer energy.

Examples of components that may be subject to fouling and the corresponding effects of fouling

Heat exchanger surfaces – reduces thermal efficiency, increases temperature on the hot side, decreases temperature on the cold side, corrosion, increases use of cooling water;

Piping, flow channels –reduces flow, increases pressure drop, increases energy expenditure, may cause flow oscillations, cavitation; may increase flow velocity elsewhere, may induce vibrations;

Ship hulls – increases fuel usage, reduces maximum speed;

Examples of components that may be subject to fouling and the corresponding effects of fouling

Turbines – reduces efficiency, increases probability of failure;

Solar panels –decreases the electrical power generated;

Electrical heating element – increases temperature of the element, increases corrosion, reduces lifespan;

Venturi tubes, orifice plates – inaccurate or incorrect measurement of flow rate;

Pitot tubes in airplanes – inaccurate or incorrect indication of airplane speed

TYPES OF FOULING

There are two broad categories :-

1. Macro fouling2. Micro fouling

Macro Fouling

Macro fouling is caused by coarse matter of either biological or inorganic origin, for example industrially produced refuse. Such matter enters into the cooling water circuit through the cooling water pumps from sources like the open sea, rivers or lakes.

Micro Fouling

As to micro fouling, distinctions are made between:

Scaling or precipitation fouling Chemical reaction foulingBio-foulingParticulate foulingCorrosion foulingSolidification foulingComposite fouling

Scaling or precipitation fouling

Scaling is the most common type of fouling and is commonly associated with inverse solubility salts such as calcium carbonate (CaCO3) found in water. Reverse solubility salts become less solute as the temperature increases and thus deposit on the heat exchanger surface. Scale is difficult to remove mechanically and chemical cleaning may be required.

Particulate/Sedimentation Fouling

Sedimentation occurs when particles (e.g. dirt, sand or rust) in the solution settle and deposit on the heat transfer surface. Like scale, these deposits may be difficult to remove mechanically depending on their nature.

Corrosion Fouling

Results from a chemical reaction which involves the heat exchanger surface material. Many metals such as copper and aluminum form adherent oxide coatings which serve to passivate the surface and prevent further corrosion. Metal oxides which are corrosion products exhibit quite a low thermal conductivity and even relatively thin coatings of oxides may significantly affect heat exchanger performance.

Chemical Fouling

Fouling from chemical reactions in the fluid stream which result in the deposition of material on the heat exchanger surface. This type of fouling is common for chemically sensitive materials when the fluid is heated to temperatures near its decomposition (degradation) temperature. Coking of hydrocarbon material on the heat transfer surface is also a common chemical fouling problem.

Corrosion Fouling

Chemical Fouling

Freezing Fouling

Occurs when a portion of the hot stream is cooled to near the freezing point of one of its components. An example in refineries is when paraffin solidifies from a cooled petroleum product. Another example is freezing of polymer products on the heat exchanger surface.

Biological Fouling:

Occurs when biological organisms grow on heat transfer surfaces. It is a common fouling mechanism where untreated water is used as the coolant. Problems range from algae to other microbes such as barnacles and zebra mussels. During seasons when these microbes are said to bloom, colonies several millimeters deep may grow across the surface within hours, impeding circulation near the surface wall and impacting heat transfer.

Macro-fouling Micro-fouling

Sand Silt Scale Rust Mineral deposits Ex. Calcium Carbonate

Biological growth Algae Bacteria Mussels

Micro-fouling is controlled by water treatment.

Macro vs Micro

CaCO3 + Sand = Concrete

Many contaminants mix together to form larger deposits

Example- CaCO3 mixed with sand makes concrete.

It is these large particles that create problems

Shell and Tube Heat Exchanger• Prone to fouling

especially during low flow or downturn.

• Particles tend to settle with laminar flow.

Typically no, as they do not precipitate out of solution until they reach 120F, or if the ph. is out of balance.

The Bigger the Particle….The Bigger the Problem

Are dissolved solids and particles under 40 micron a problem?

FoulingParticle Size vs. Volume with 1 Trillion Particles

Size of Particle Quantity of Particles Volume Volume % Volume

5um 212.5 Billion 14.58cm³ 14580mm³  

3um 212.5 Billion 3.11cm³ 3110mm³  

1um 212.5 Billion 0.11cm³ 110mm³  

0.45um 212.5 Billion 0.0098cm³ 9.8mm³  

Sub Total: 850 Billion 17.83cm³ 17809mm³ 1%

10um 37.5 Billion 21.30cm³ 21300mm³  

25um 37.5 Billion 303.16cm³ 303160mm³  

50um 37.5 Billion 2459.70cm³ 2459700mm³  

75um 37.5 Billion 8260.72cm³ 8260720mm³  

Sub Total: 150 Billion Particles 11044.88cm³ 11044880mm³ 99%

Fouling on Mars

NASA Mars Exploration Rovers experienced Abiotic fouling of solar panels by

dust particles from the Martian atmosphere.

Some of the deposits subsequently cleaned off.

This illustrates the universal nature of the fouling

phenomena.

DESIGN CONSIDERATIONS

It is important to consider fouling in the design of a heat exchanger. There are different methods to provide the added heat transfer area

needed to account for the expected fouling and maximize runtime between cleaning.

For shell and tube heat exchanger, the common method is to

use fouling factors. For other types of heat exchangers, excess heat transfer area is often used. However, fouling is a self-fulfilling prophecy and the selection of fouling factors or excess area must be done carefully.

Fouling FactorThe performance of heat exchangers usually deteriorates

with time as a result of accumulation of deposits on heat transfer surfaces.

The layer of deposits represents additional resistance to heat transfer and causes the rate of heat transfer in a heat exchanger to decrease.

The net effect of these accumulations on heat transfer is represented by a fouling factor (Rf), which is a measure of the thermal resistance introduced by fouling.

The fouling factor depends on the operating temperature and the velocity of the fluids, as well as the length of service.

Fouling increases with increasing temperature and decreasing velocity.

For an unfinned shell-and-tube heat exchanger :

Rf, i and Rf, o are the fouling factors

Fouling Factor

Representative fouling factors (thermal resistance due to fouling for a unit surface area)

Economic and environmental importance of fouling

Fouling is ubiquitous and generates tremendous operational losses, not unlike corrosion. For example, one estimate puts the losses due to fouling of heat exchangers in industrialized nations to be about 0.25% of their GDP.

Another analysis estimated the economical loss due to boiler and turbine fouling in China utilities at 4.68 billion dollars, which is about 0.169% the country GDP .

FOULING CONTROL

Plate and frame heat exchangers can be disassembled and cleaned periodically. Tubular heat exchangers can be cleaned by such methods as acid cleaning, sandblasting, high-pressure water jet, bullet cleaning, or drill rods.

In large-scale cooling water systems for heat exchangers, water treatment such as purification, addition of chemicals, and testing, is

used to minimize fouling of the heat exchange equipment. Other water treatment is also used in steam systems for power plants, etc. to minimize fouling and corrosion of the heat exchange and other equipment.

A variety of companies have started using water borne oscillations technology to prevent biofouling. Without the use of chemicals, this type of technology has helped in providing a low-pressure drop in heat exchangers.

CONCLUSION

MAINTENANCE IS NOT

AN OPTION IT IS MUST!!!

REFERENCES

https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CBwQFjAAahUKEwitl5HD7KjIAhXJBY4KHd-KDmA&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FFouling&usg=AFQjCNFOt2WzgJxRkxrld33MOYTZOIi7Vg

Heat and Mass Transfer book by R.K.Rajput.

Principles of Heat and Mass Transfer, 7th Edition By Dewitt and Incropera.

THANK YOU…