Fremont Industries - Water Management Solutions

Boilers, cooling towers and heat exchangers are notoriously susceptible to deposit formation due to the presence of  a variety    of impurities in the process water.  Deposit formation in this equipment may result in:

• A decrease in heat transfer.
• Loss in system’s energy efficiency.
• Unplanned down-time/loss of production.
• Increased fuel or energy costs.
• Increased maintenance expenses.
• Component failure and/or premature replacement.
• Dangerous system operating conditions.
• Increased insurance costs. 

An understanding of deposits and the prevention of their formation may result in:

• Cleaner heat transfer surfaces.
• Increased system efficiency.
• Maximized economy of operation.
• System maintenance cost savings.
• Greater system life.
• Safer working conditions.

CLASSIFICATION OF DEPOSITS

Deposits found in steam generation and related equipment fall into three primary groups; true scale deposits, scale like deposits, and sludge or sedimentary deposits.

True Scale

By definition, a true scale deposit  is a macrocrystalline growth held together by intercrystalline bonding forces.   True scale may be either crystalline or amorphous (possessing no definite crystalline structure).  True scales are the result of dissolved substances from a supersaturated solution.  The formation of true scale deposits is relative to physical and chemical system variables.

Scale-Like Deposits

Scale-like deposits may be crystalline or amorphous, in structure.

These scale-like deposits form by the deposition of precipitated suspended solids from the bulk water solution.  Typically, scale-like deposits are bonded by ionic or static charges existing between the individual particles of the deposit.  Most frequently, the formation of scale-like deposits is relative  to the agglomeration of suspended solids at a point of evaporation, low flow velocity area or dehydration.

Sedimentary or Sludge Deposits

Sedimentary or sludge deposits are formed by the agglomeration of suspended matter present in the bulk water.  Sludges differ from true scale and scale-like deposits in that their formation is primarily affected by the physical (as opposed to the chemical) characteristics of the system.  Sludges are typically comprised of contaminants present in the make-up water, process contaminants, and by-products of corrosion processes.  These deposits influence the formation of true scale and scale-like deposits. 

Examples
Boiler Scale	Boiler Sludge	Oxygen Attack on Boiler Metal

DEPOSIT CONSTITUENTS, CAUSES AND PREVENTION - BOILER SYSTEMS

DEPOSIT SAMPLING TECHNIQUES

The first step in gathering useful information from a deposit analysis is the careful collection of a truly representative sample of the deposit.  Deposit samples should be forwarded to the laboratory with attention paid to the following: 

• Every effort should be made to remove the deposit in its natural state.  Do not crush, dry, treat or otherwise alter the deposit sample prior to forwarding to the laboratory.
   
• Caution must be taken so as not to remove under-deposit materials such as base metals, plastics, or wood.
   
• If deposit analysis trend data is to be valid, deposit sample must be removed from the same locations over a predetermined period of time.
   
• As much accompanying data as can be gathered should be forwarded with the deposit sample (location, products in use, system condition, etc.).  Excessive data is never a hindrance; insufficient data can be.
   
• The deposit samples should be sent to the laboratory for analysis as soon as possible following the removal.   Timeliness is extremely crucial in cases where biological fouling is suspected.

SCALE REMOVAL OPTIONS

Alkalinity Treatments
Alkaline treatments are typically used to remove gases, oils, and organic contaminants.  Alkaline treatments are of particular value in the preoperational cleaning of new systems.

Acidic Descalers (Off Line) 
Acidic treatments are effective in the removal of carbonate scales and corrosion by-product deposits.  The acids most commonly used include hydrochloric (muriatic), sulfuric, citric and sulfamic; often containing a corrosion inhibitor.

In-Service Deposit Removal Treatments
In-service treatments offer a non-acid option for the removal of inorganic salts.  Deposit cleaning during system operation is particularly advantageous in situations involving systems which cannot be shut down for acid or alkaline cleaning procedures.