Water-in-oil emulsions have existed since the turn of the century. However, only recently have companies such as Water Services Ltd been able to control the stability and quality of the emulsion to make it advantageous for industrial and power-generating uses.

Water Services Ltd's water-in-oil emulsion system and products are now used in a variety of boilers and furnaces.

The emulsions are engineered to provide reduced carbon particulate, lower opacity and lower nitrogen oxide levels. In many cases, increased thermal efficiency, as well as reduced fireside fouling result.

By understanding how this technology works the advantages of our WSF E-2650 are exposed.

WSF E-2650 emulsion is a water-in-oil emulsion fuel consisting of from 5 percent to 15 percent water dispersed as droplets in a continuous oil phase. The key to achieving maximum combustion with this fuel is producing water droplets in the range of 5 microns to 20 microns in diameter within the oil. This is accomplished by introducing a small amount of WSF E-2650 .

to control water droplet size and prevent coalescence. Proper mixing and proportioning of the water, oil and WSF E-2650 creates a very stable emulsion that is ready to burn. Figure I compares the size of a typical fuel oil droplet sprayed into the combustion chamber with a WSF E-2650 emulsified fuel droplet containing many water droplets of 5 microns to 20 microns in size.

A typical burner atomizer produces a spray of fuel oil droplets around 100 microns to 200 microns in diameter, depending on fuel quality and atomizer design. Typically, the larger fuel droplets do not completely burn, leaving unburned carbon to collect on heat transfer surfaces and escape as particulate matter in the exhaust gases. This reduces overall thermal efficiency.

In the combustion of a water-in-oil emulsion, the primary spray fuel droplets are further divided as a result of the explosive vaporization caused by rapid heating of the water dispersed within the individual fuel droplets. The internal water droplets undergo spontaneous nucleation of steam bubbles at a temperature well above 212 F, causing a violent conversion of the water droplet to steam.

The vaporization, in turn, produces a rapid expansion of the surrounding oil droplets, fragmenting the oil into a vast number of smaller fuel droplets.

The name for this process is secondary atomization. A National Science Foundation (NSF) Study at Adelphi University verified this phenomenon with high speed cinematography analysis. The pictures show that droplets of emulsified fuel, 200 microns in size, fragmented into a multitude of 1 to 10 micron-sized fuel droplets.

In order for secondary atomization to be most effective in a combustion process, very small droplets with a well-controlled size distribution are necessary. If the number of water droplets is too small (1 micron or less), insufficient energy will be produced to cause secondary atomization. On the other hand, larger droplets (10 microns or larger) reduce the number of droplets for explosion and tend to produce less violent explosions within the oil droplets because of nucleation taking place at lower temperatures.

Water Services Ltd's WSF E-2650 emulsion fuel was developed to meet these important requirements. The product is recognized for its ability to produce properly sized and uniformly distributed water-in-oil droplets with unusual stability.

The following iso concentration infrared scanning photographs show the effect of secondary atomization in a boiler.

The coordinates of the graphs are distance from the burner tip in meters, while the color index represents the area temperature in Kelvin grades X 100.

This process greatly increases the number and surface area of the fuel droplets in the flame zone.

Since the combustion of fuel is a surface reaction, the greater the surface area, the less time it takes to burn out the carbon.

This results in overall shorter flame length which reduces the possibility of flame impinging on the back wall of the boiler.

This shorter flame length most likely creates the condition favorable to reduced fireside fouling, as the vanadium/sodium/magnesium complexes formed in the combustion process go through a "tacky" state as they cool.

If they are at or above this tacky state temperature, the complexes will adhere to boiler surfaces upon impingement. Shorter flame length allows for a radiant "cool down" period prior to impingement on boiler surfaces, and therefore, theoretically, less adherence. Improved atomization creates smaller particle size complexes which in turn improves the radiant cooling capability.

Over the past 15 years, emulsified fuel oil has been shown to significantly reduce unburned.

In one test, Water Services Ltd's WSF E-2650 emulsion system was measured against M-3500” fuel oil and was shown to reduce total particulate by a remarkable 69 percent.

Other potential benefits of emulsified fuel are:

• Elimination of high cost fireside additives
• Reduction in nitrogen oxide due to reduced excess air and lower peak flame temperature
• Increase in thermal efficiency and heat rate due to reduced fireside deposits and excess air
• Improved opacity
• An increase in the range of fuel options

In summary, emulsified fuels solve a major problem confronting utilities today--the need to reduce unburned carbon and to produce more complete combustion minimizing particulate emissions and fireside fouling.

Each of these benefits has potential economic savings. However, a specific cost savings picture cannot be calculated without thorough research and analysis of equipment. Cost benefits are proportional to the severity of problems found in the existing equipment.