Fuel Oil Treatment[1]

8/7/2019 Fuel Oil Treatment[1]

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FUEL ADDI TIVES AND APPLICATIONS

Presented to: ASSOCIAT ION OF W AT ER T ECHNO LOGISTS

FALL CONVENTION - DECEMBER 6, 1991

ATLANTA, GEORGIA

Presented By: BRUCE T. KET RICK

GUARDIAN CHEMICAL SPECIALTIES CORP.


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FUEL ADDITIVES AND APPLICATIONS

By: Bruce Ketrick - Guardian Chemical Specialties Corporation

The use of fuel additives in the industrial market place has changed dramatically over the last twentyyears. In the 1970s, the use of a fuel additive was based on economics with only a small considerationto emissions. By the 1980s, the emissions of a boiler became very important, and today the use of afuel additive has become a multifaceted situation.

For a customer to use a fuel additive, there must first be a good economical reason for the customer torequire the additive compared with the same customer operating without the additive. After that needhas been filled, there has to be a consideration for how the additive will affect the emissions of theboiler. Once the economics and the emissions questions have been satisfied, you have to be able toprovide a service that your competitors do not have available. The sale of fuel additives is no longer theadd on sale of a magic quart of product which you have the customer add every time they get a fueldelivery, it is now a technical sale.

In order to review the more common types of fuels that are treated and the additives which can beadded to these fuels, this paper will be limited to the following:

FUELS: Natural Gas

Fuel Oil#2#6

Solid FuelsCoalWoodWaste Incineration

AREAS O F APPLICATI O N Transportation

PreburnerBurnerCombustion ZoneCold End

Page 2 FUEL ADDITIVES AND APPLICATIONS


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NAT URAL GAS:

Natural Gas is one of the most commonly used forms of fuel for the middle market boiler systems. Itis delivered to the boilers via a transmission pipe system from the gas fields and burns cleaner than anyof the other more commonly used fuels. As such, the additives that could be used in this case are verylimited.

Natural Gas is primarily methane with some ethane. The other hydrocarbons that are found in naturalgas as butane, hexane and octane are removed by the gas supplier in the compressor transmissionplants. They are removed because they are worth a great deal more as building blocks in chemicalsynthesis than they are as a fuel. Based on the market value of ethane for chemical synthesis inindustry, the natural gas may be almost pure methane. Methane has a BTU value of 980 BTU/cu. ft.whereas when the natural gas contains some ethane, the BTU value will increase to 1000 BTU/cu. ft..This is why there are some BTU value differences between gas users in each plant.

This natural gas does not by itself have a noticeable odor and can be very corrosive to the transmission

lines. The gas suppliers will then add mercaptan to the gas so that it will have that sulfur odor andcorrosion inhibitors to the gas to prevent line loss. These two materials can cause the most problem foryour boiler.

The corrosion inhibitor is a surface active agent which usually is never a consideration for the boiler.On occasion, it can drop out at the end of a line and slowly accumulate. If this does happen, you willexperience a slightly sticky liquid that restricts the burner and will not sustain combustion. Since gas ispure, where did this gunk come from is the usual concern of the boiler operator. You will have toexplain that it is a corrosion additive and that it will have to be mechanically removed.

The mercaptan that is added will usually only come into play when;

Boiler has been put on standbyBoiler is switching from oil to gasStack temperature is low

When a boiler is put on standby, the plant will usually treat the water side of the boiler to preventcorrosion. T hey do not however, do anything to the fireside. The fireside has air passing through it asthe natural draft pulls outside air through. This air will contain moisture, and if the gas has not beenburned properly and soot has been formed, the soot will absorb this moisture. Once absorbed, thesulfur in the mercaptan can react to form sulfuric acid, which will cause localized corrosion of theboiler tube metal. This is more prevalent in water tube boilers than in fire tube boilers, but it can occur

in both of them.


The means to prevent this possibility, is to either maintain the fire box so that it is too warm for


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moisture to collect, or to blow in an alkaline powder that will neutralize the sulfur, preventing sulfuricacid formation. This powder can be a fine grade of magnesium oxide, magnesium hydroxide ormagnesium carbonate. The smaller the micron size the more effective the product will be. Usually, thepowder is blown into the fire box with an educator while the boiler is on-line, and just prior to it beingtaken off of the line for an extended standby. The powder then adheres to the boiler internals much thesame way as talcum powder sticks to your body after a shower. W here it contacts any acids, theyneutralize each other out.

Where a water tube boiler is changing the fuel source from oil to gas, the usual consideration is that thecleaner burning gas will burn out all of the unburned carbon from burning the oil. This is not alwaysthe case and the soot in the boiler will act as a reaction zone for the corrosive mercaptan in the gas. Toprevent this problem, it is usually a good idea to place 100 lbs of fine magnesium hydroxide in the firebox. The draft of the boiler will take the powder to the points that need to be protected.

In this day of efficient scavenging of flue gas BTU, we can bring the stack temperatures down below theacid dew point. At this point, the formation of acids can occur in the breaching, stack, economizer orair preheater. This is not very common when burning gas, and will usually only occur when the air/fuel

ratio is off. The fastest cure for this condition, is to have the boiler tuned up. Once the fuel efficiencyhas been improved, the problem will usually go away.

FUEL O ILS:

Fuel oils are No. 1, No. 2, No. 4, No. 5, and No. 6 on a broad basis with the A.P.I. gravitydetermining the grade that the oil falls into. Some general characteristics for these fuels are:


API Gravity Fuel Oils

GRADE OF OIL GRAVITY OF OIL

No. 1 Oil (Kerosene) 46 - 41 degreesNo. 2 Oil (Domestic Heating Oil) 39 - 30 degreesNo. 4 Oil 28 - 24 degreesNo. 5 Oil 22 - 19 degreesNo. 6 Oil (Bunker C) 17 - 9 degrees


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The most commonly used fuels are the No. 2 and the No. 6 oils. The No. 1 fuel is too expensive forcommon boiler use, and the No. 4 and the No. 5 fuels are used as blends of No. 6 and higher APIgravity oils where the convenience of the lower pour point, pumping temperature or atomizationtemperature is important to the plant.

At his point, we have the basic characteristics of the fuel oils used in industrial boilers, and should nowconsider how these different characteristics determine what problems can occur with the use of eachfuel and which additive program should be used.


In dealing with the fuel oils, remember, that the No. 5 oil can become a solvent for the No. 6 oil as ithas a higher API, the No. 4 becomes a solvent for the No. 5 and so on. Basically, the No.1 can be usedas a solvent for any of the other oils and aromatic naphtha becomes a solvent foe all of the oil grades

PROPERTIES OF FUEL OIL

GRADE No. 1 Oil No. 2 Oil No. 4 Oil No. 5 Oil No. 6 Oil

Type Distillate Distillate Very Light Light Residual Residual

Color Light Amber Black/Brown Black/Brown Black/Brown

API Gravity 40 32 21 17 12

S.G. 60/60 F 0.8251 0.8654 0.9279 0.9529 0.9861

Lb/US Gal, 60F 6.870 7.206 7.727 7.935 8.212

Visc. SSU. 100F 31 35 77 232 ------

Visc. SSF. 122F ---- ---- ---- ---- 170

Pour Point F Below Zero Below Zero 10 30 65

Pumping Temp. F Atmospheric Atmospheric 15 min. 35 min. 100 min.

Atomizing Temp.F Atmospheric Atmospheric 25 min. 130 200 *

Carbon Residue % Trace Trace 2.5 5.0 12.0 **

Sulfur % 0.1 0.4 - 0.7 0.4 - 1.5 2.0 max. 2.8 max.

Sediment & Water % Trace Trace 0.5 max. 1.0 max. 2.0 max.

Ash % Trace Trace Low 0.005 0.08

BTU/US Gal 137,000 141,000 146,000 148,000 150,000

* Actual atomization temperature will vary with the quality of the No. 6 fuel

** Residuals are based on complete combustion and are an average expected.

No. 6 Fuel Oil generally contains 85 - 86 % C, 10% H 2, 1% 02 + N2


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even No. 1. This is important when determining how to make up a fuel additive and how to solve thepreburner problems which we will address at this point.

DELIVERY AND STORAGE PROBLEMS:

The delivery of fuel oil can create its own problems for the plant. Number 2 oil can be delivered at anytemperature and still be ready to be burned. Number 4, 5, and 6 oils need to be heated when they aredelivered, or they will not be pumpable. They must also be heated while in storage, or else they willsolidify.

In the case of Number 2 oil, the only problems that are found with delivery and storage in the fuel oilstorage tank are biological fouling and moisture. Number 2 oil has a very low impurity level. It doesnot routinely contain vanadium, nickel or lead. it is not high in sulfur. It should only have a smallamount of sediment and water, and it does not need to be heated in order for it to be burned. For aboiler operator, short of using natural gas, this appears to be the ideal fuel oil. It is clean and has verylittle contamination.

As the fuel oil sits, it can take on moisture that forms from tank condensation. This moisture will thenseparate from the oil and create a water - oil interface much the same as we have sen with muchheavier oils. At this area, bacteria can begin to grow. If left alone, this bacteria growth will eventuallybreak free and carry into the preburner system. Once in this system, it will plug strainers and burnerswith a sludge like mass. In many cases, a delivery of contaminated oil can seed the storage tank and aproblem which has not occurred in the past will suddenly show up.

Another problem that arises from the growth of bacteria in the storage tank, is that it will have acidicexcretions. These excretions will act to start corrosion of the tank metal. This corrosion is at the waterphase of the tank which is unfortunately at the bottom. W ith the tight restrictions on fuel leaking from

underground storage tanks, the possibility of even a small leak from bacteria growth could prove to bea serious condition.

Buckman make MECT-5 which is Methylene bis(thiocyanate) 10% and 2 - (Thiocyanomethylthio)benzothiazole 10%. This is a wide spectrum biocide which when fed at 12 ounces for every 1000gallons of fuel oil, will kill the bacteria in the fuel storage tank. The material can be added straight orblended into a fuel additive product with certain solvents. The use of this type of product is veryinexpensive insurance for the prevention of potential biomass plugging and tank corrosion.

In the case of moisture build up, moisture can form sludge even with Number 2 oil, which willeventually cause preburner system plugging. If this is occurring, test the water level of the tank

Page 6 FUEL ADDITIVES AND APPLICATION

with any one of a number of water indicating pastes. If the water level is noticeable, have the waterpumped off mechanically. Then use a dispersing agent to break up the sludge that had formed in thetank. This in many case is the use of a multipurpose tank treatment product which was designed foruse in Number 6 oil. Again, even if this product used Number 1 as its base carrying agent, it is still alsolvent to the Number 2 oil.


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Another reason for periodic testing of the moisture level in the Number 2 tank is weather. The plant isusing Number 2 fuel oil because it does not have to be preheated to burn. They do not have anyheaters on the oil. Once the temperature has dropped below freezing, any moisture that is in the fuelcan freeze. If the moisture content is sufficient, the fuel lines can become blocked due to frozen water.This always happens at the wrong time when it is very cold and the plant goes into a panic. Thequickest way to break up this block is to heat it. However, as most fuel systems have lines runningunderground, you may not be able to get at the blockage with heat. in this case, a few gallons of alcoholpoured down the line will eventually work its way to the frozen water and cause it to thaw. This actsmuch the same way a drain cleaner goes to the clog and removes it. In an emergency, it is hard to getfuel oil treatment into the plant and a simple purchase of alcohol can solve the problem.

For the Number 4, 5 & 6 oils the delivery and storage problems are very much the same. As such, wewill address the Number 6 fuel primarily. In the delivery of these types of oil, both the amount ofbottom sediment & water and the impurities can come into play.

With pour points from 15 to 100 degrees Fahrenheit, the oil must be kept hot or it will not pump into

the fuel storage tank. The fuel must then be kept hot in the tank or it will not pump. This means that afuel heater must be in the tank or the plant could end up with a large chunk of asphalt in the tank. Thenext problem is that all of these forms of oil contain some degree of high ends. The higher the APIgravity, the greater the concentration of high ends. As you heat the fuel in the tank, these high ends arestripped and leave through the vent line. This gradually increases the viscosity of the fuel.

Where a storage tank of fuel is turned over on a regular basis, this loss of high ends is not too great of aproblem. Where the plant is holding a tank of Number 6 fuel oil as a back up for the normal naturalgas in case the gas supply is interrupted, then the plant will have extended periods of time where the oilis heated and high ends are lost. In this case, the Number 4 and Number 5 fuels will also tend tostratify into layers.

Number 4 and Number 5 fuel oil are blends of Number 6 and low grade Number 2 fuel oil. As theseoils are allowed to sit, the two different grades of oil will tend to split and a layering will occur. Whenthe tank is then brought on - line and used, you may find that the initial combustion is very easy withperiodic pops. This indicates that the fuel atomization temperature is too high and so the operatorreduces the fuel temperature. T hen as the fuel is burned, you start to get flame outs and comets, withnoticeable unburned hydrocarbons in the boiler. You have

Page 7FUEL ADDITIVES AND APPLICATIONS

now worked down to the level where the fuel is a mixture. The next level, the fuel may turn out to be allNumber 6 oil, and the plant is not set up to burn it. The result is a loss of a large portion of the fuel inthe tank and poor combustion.

To prevent these problems, the fuel oil tank needs to be periodically circulated during the period when


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it is not in use. The fuel needs to have a tank side treatment product added to it to help to keep thedifferent oil types in a homogeneous mixture. This product should be added every time that the tank isturned over or fuel is added to the storage tank.

In York, PA. during the Christmas season in 1989, the area experienced unusually low temperaturesfor an extended period of time. The industry in the area had not had to have the natural gas supplyinterrupted for the last five years and the alternate fuel users suddenly had four hours to convert to fueloil. Most of them had refused to use tank treatment during this time as it seemed to be a waste ofmoney for a fuel that would probably never be used. Those with Number 6 fuel as the alternate couldnot get the fuel to pump. Tank side additive had to be put into the tanks at ten times the normal feedrate and some Number 2 fuel had to dumped on top. Then the tanks were circulated for 12 hours andtwo days of adjusting fuel temperatures followed for those that actually ended up able to use thealternate fuel. The cost to the plants for gas charges, burner technician service charges and fuel oiltreatment was far in excess of what the simple use of additive and circulation would have been.

With the use of heavier oil, the formation of sludge in the tank and water forming corrosive agentsbecomes more prevalent than with the lighter fuels. The emulsification of moisture with the oil forms

sludge. This builds up on the bottom of the tank to a point where it will then carry over into thepreburner system. In the preburner system, the strainers, fuel heaters and burner nozzles becomeclogged. In the burner tips, the clogging from sludge will cause an irregular flame pattern which resultsin the burner spitting oil and comets. This dramatically decreases the fuel economy. In the heater,sludge will form a varnish like deposit which prevents the transfer of heat from the heater to the oil. Asthe heater is forced to get hotter in order to bring the oil up to the proper temperature, the heater isover taxed and eventually fails. This is both a fuel loss and an expensive mechanical bill. A blockedstrainer means that the oil flow is restricted. This will cause the steam output of the boiler to bereduced as the fuel system can not deliver enough fuel to the burner nozzle.

At the water phase, much the same as with Number 2 oil, sulfuric acid is formed. In this case, since

there can be up to 2.8% sulfur in the fuel, the formation of sulfuric acid can become serious veryquickly. Again, the corrosion from this type of attack is at a point that is at the bottom of the tank. Onceit works its way through, there is a leak and the tank is lost. More important, you have an expensivefuel spill.


For a tank side treatment to keep the sludge down, stop corrosion, and keep the fuel in a homogeneousmixture, a tank side fuel treatment is needed. The product should contain;

A light aromatic or #1 Fuel carrying agentFuel Oil DispersantOil/Water Emulsifier

Filming Amine


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The product has a solvent base to help cut sludge and break down the oil. It contains a dispersant toprevent sludge formation, with an emulsifying agent for the homogeneous blending of the oils in thetank, and a filming amine which will coat the metal surfaces of the tank at the water phase to preventcorrosion.

If a low flash point aromatic naphtha is used as the base of the product, the solvency of the naphtha willclean up strainers and remove the varnish like deposits from the fuel heater. The product can also beused as a burner tip cleaner, as the aromatic naphtha will rapidly cut the carbon deposits on the burnertip. In addition, with the removal of the sludge in the tank and the cleaning up of the preburner system,the burner nozzle tip will remain cleaner longer. This will allow the tip to stay in longer and will allowan improved combustion efficiency.

BURNER:

There are a number of different types of burners for the combustion of fuel. When using Number 6

fuel oil, the use of an additive can make a difference. The abrasion from impurities can cause theburner nozzle to wear and yield an irregular flame pattern. Flame impingement will then cause tubefailure, refractory loss and throat spallation. The fluctuation of poorly blended fuels can result in flameout and nozzle wear.

Based on whether the burner is a pressure piston, steam atomizer or rotary cup; the better the qualityof the oils as it hits the burner, the more efficient the boiler will be.

You can view the boiler flame from the rear of most boilers. If you see sparklers or comets shootingout of the flame, it is a good indication of a poorly tuned boiler or of a worn burner nozzle. The finerthe atomization that the fuel droplet can achieve, the greater the efficiency of combustion, As a nozzle

orifice wears into a larger orifice, the oil droplet becomes larger and the oil is not properly burned.Recommend that the nozzle be replaced and look for sludge that will need to be treated. If the boiler isusing a slurry based fuel additive, the high solids content of this type of additive will erode the burnernozzle rapidly. Always keep track of this type of product.


If in a water tube boiler, the flame is contorted off to one side, this can cause the tubes and the brickwork to be over heated. The result is tube loss and possibly a flue gas leak as the brick work breaks

down. This is usually caused by a mechanical problem with either the burner impeller or the centeringsupport. Have these adjusted as soon as possible, or your fuel oil additive may get blamed for a purelymechanical problem.

When burning #6 fuel, low melting point impurities as vanadium, nickel and sodium can condensefrom a vapor form into a plasmatic onto the throat tiles and brick work around the throat. As they cool,these deposits expand and break the brick much in the same fashion as freezing and thawing ice breaksup a roadway. These impurities can combine with the silica in the brick and leach it out of the brick'slattice pattern. This causes the break down of the burner throat and the front end of the boiler. As this


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occurs, the flame pattern of the boiler is distorted. The treatment of these impurities usually requiresthe addition of fuel additives that combine with the impurities to form a higher melting point particlewhich then carries off with the flue gasses.

COMBUSTIO N ZONE:

In the combustion zone most of the deposit formation and slagging occurs. In a water tube boiler, theareas of concern include; high temperature corrosion, slagging and convection section screen tubefouling.

The temperatures of a water tube boiler by section are:


In that the slag forming components formed in the boiler have ash fusion points from 1155 to 2055degrees fahrenheit, it is obvious that many different types of fouling problems can occur.

Most high temperature corrosion in the boiler is caused by vanadium. vanadium forms vanadiumpentoxide in the furnace. The melting point of vanadium pentoxide is 1274 degrees fahrenheit. This isvery close to the actual metal temperature in the furnace, which means that the V2O5 will remain on thetubes in a semiliquid state. This allows the vanadium compound to wet the metal surface. As it doesthis, the boiler metal is oxidized, as vanadium pentoxide is an excellent oxidation catalyst. The ironoxide protective film on the boiler metal is then dissolved into the pyroplastic or liquid vanadates. Thiscauses the metal to corrode. The vanadium pentoxide will then take oxygen from the flue gasses andcontinue the cycle of corrosion.

BO ILER FIRESIDE T EMPERAT URES AND PROBLEMS

GAS OUT ER METAL DEPOSITLO CAT ION T EMP.F T EMP. F T EMP. F PROBLEMFLAME 2500 - 3100 Combustion

FURN ACE 2000 2800 800 2000-2500 High temp. corrosion; slag;

spalling

SUPERH EAT ERS 1200 - 2000 1000 1000-2000 High temp. corrosion; slag; & REHEAT ERS

fouling

CON VECT ION 900 - 1200 500 - 900 1000 Fouling

ECON OM IZER 600 - 1200 200 - 600 fouling Low temp. corrosion;

AIR HEA TER 300 - 600 200 - 500 fouling Low temp. corrosion;


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The reduction of excess air to the point that the vanadium is only able to form vanadium trioxide cansolve most vanadium based problems. Vanadium trioxide has a melting point of 3570 degreesfahrenheit, which then allows it to pass through the boiler with the flue gasses as ash. When thereduction of excess air is a problem, the use of magnesium salts has been seen to be a help. Themagnesium salts will react to form a high melting point particle which can pass through the boilerwithout dropping out plasmatically. Metal oxides can also act as combustion catalysts and allowreduction of excess air to a point where vanadium trioxide is formed. So, it becomes critical for thecontrol of vanadium based deposits to carefully control excess air and to use metal oxides to improvecombustion efficiency.

Copper, calcium, barium, cobalt, manganese, and iron have all been used as combustion catalysts.These metals are blended into a carrying oil or fired into the boiler as a powder. They were originallyused as soot preventatives. As a soot remover, they allowed unburned carbon to be burned, improvedcombustion and allowed the trimming of excess air. The end result was that the excess air level waslowered, which allowed the reduction in both vanadium and sulfur compounds dropping out in theboiler.

The use of organo manganese blended into a tankside treatment, has been found to help in thereduction of excess air in the flue gasses. The manganese assists combustion as it acts as a catalyst. Theimproved reaction towards combustion allows the air to be trimmed in the boiler. The reduction from7% excess air to 1 - 2% excess air will dramatically reduce the formation of deposits in the boiler. Anexcellent means to get the organo manganese into the boiler, is to take the tankside treatment productand blend in approximately 5% organo manganese by weight to the product. This is then acombination product which is both a tankside treatment product and a combustion catalyst.

One other problem that is being seen in the boiler today is the rise of "sintering". This is where youstart to see a build up in the rear of the furnace box near the turn into the screen tubes of a heavy ash.

This ash restrict flue gas flow and can cause heat transfer problems. The ash is an aluminum baseddeposit. In the past, aluminum was added with magnesium to help form a high


temperature ash with vanadium which would carry out of the boiler as a solid. It was also effective inthe neutralization of sulfuric acid in the cold end. Now, it is turning up as a deposit. The reason is thatmore and more of the fuel oil that is being sold today is either visbottoms or decant. These are fuels

which are what is left over after all of the useful hydrocarbons have been removed. They contain higherthan normal levels of aluminum which is leached into the oil in the catalytic crackers.

This "sintering: is also abrasive and can cause metal wear as it impinges on the rear section of theboiler. The means to remove the problem is to feed a magnesium oxide in a fine micron size to thecombustion zone. This then reacts with the aluminum to form a magnesium aluminum complex whichis of a higher melting temperature, and as such, can carry with the flue gas out of the boiler. Again, addthe magnesium to the tank side treatment. In a powdered form, you may need to use a heavy oil tosuspend the magnesium, which now brings you into slurry technology. On the other hand, the use of an


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organo magnesium will allow you to blend the magnesium into the tankside treatment at a ratio of 2:1with the organo magnesium up to approximately 20% as organo magnesium based on the base solventused in the product.

To review why we try to use magnesium, calcium and aluminum in the prevention of furnacecorrosion, slagging, and general deposit build up, below is a reference table of ash, slag and additives.

Page 12 FUELADDITIVES AND APPLICAT IO NS

In that the temperature at the flame is 3100 degrees F. or lower, if we can maintain an ash that is above3100 degrees F. in melting point, then we should be able to carry the ash out of the boiler as a lightfriable ash.

In the case then of fouling in the high temperature zones of a boiler, we find that we have a material that

begins to build between the tubes, restricting the flue gas flow. As this builds up, the flue gasses willmove more rapidly through this section, which prevents the boiler from properly pulling the BTUvalue out of the flue gas. This causes a tremendous loss of efficiency. It also causes slagging to occur,as the flue gas temperatures start to rise in the fouled zone. In that corrosion becomes more severeonce slagging occurs, we find that fouling will lead to slagging which in turn leads to increasedcorrosion. Again, the answer is to promote low excess oxygen and friable ash with the use of eithermagnesium or calcium salts.

In that the sodium vanadyl vanadate and the nickel orthovanadtae are two of the most corrosive

NONSLAG FORMING ASH ASH FUSION TEMP. F

Aluminum Oxide (Al2O3) 3686

Calcium Oxide (CaO) 4658

Nickel Oxide (NiO) 3794

Vanadium Tetraoxide (V2O5) 3572

Vanadium Trioxide (V2O3) 3572

SLAG FORMING ASH COMPONENTS ASH FUSION

TEMP. F

Magnesium Sulfate (MgSO4) 2055

Vanadium Pentoxide (V2O5) 1274

Sodium Sulfate (Na2SO4) 1630

Nickel Sulfate (NiSO4) 1545

Sodium Metavanadate (Na2O.V2O5) 1165

Sodium Pyrovanadate (2Na2O.V2O5) 1210

Sodium Orthovanadate (3Na2O.V2O5) 1590

Nickel Orthovanadate (3NiO.V2O5) 1650

Sodium Vanadyl Vanadate 1155

(Na2O.V2O4.5V2O5)

FUEL OIL ADDITIVES ASH FUSION TEMP. F

Magnesium Oxide (MgO) 5072

Aluminum Oxide (Al2O3) 3686

Calcium Oxide (CaO) 4658

Magnesium Aluminate (MgAl2O4) 3875

Manganese Oxide (MnO2) 3000

FUSION TEMPERATURE OF OIL ADDITIVES AND COMPOUNDS


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vanadium based deposits in the boiler, we must treat them first. The means to determine the properfeed rate of Magnesium Oxide for this is done as:

Measure ppm of Vanadium in oilMultiply V by 1.785 to get Vanadium Pentoxide valueUse MgO 1:1 on a weight basis

In that the combination of magnesium oxide with vanadium pentoxide is not 100% complete, this isbasically an under feed, but a good starting point for the feed rate of magnesium oxide to formmagnesium oxide orthovanadate (3MgO.V2O 5). Now based on whether you are using a powderedproduct, or a liquid product, you take the value of ppm vanadium X 1.785 X % active MgO.

Carefully check the aluminum oxide level in the fuel before you start to determine that you are going tohave in your fuel additive. W ith today's oils, as we have discussed, you should not use the magnesiumalumina type of product if the aluminum oxide content is over 100 ppm.

COLD END CORROSION:

The problem with the cold end section of the boiler is usually corrosion from either fouling or directacid contact. The fouling is due to unburned hydrocarbons and wet ash, while the acid attack can comefrom the flue gas temperature being below dew point for sulfuric acid formation, or in the case wherethe oil has originated from over seas, chloride forming hydrochloric acid due to salt water washing ofthe fuel to remove excess sulfur from the fuel.

The problems therefore, with the cold end always start with the combustion section of the boiler. Thenext area of concern is the stack temperature, or where you have either an economizer or


an air preheater, the flue gas temperature in these areas. Control of the potential for corrosion beginswith control of excess air. If your additive program is allowing the excess air to be trimmed to 1% - 2%,then the corrosion rate on carbon steel will be below 10 mpy where he flue gas temperature is as low as150 degrees F. Above 2% excess air, the corrosion rate on carbon steel rises dramatically. It is safe toconsider that the flue gas temperature should not fall below 275 degrees F. in any section of the coldend if the excess air is above 2%, or the corrosion rate can go up to as high as 60 mpy. Reference thecharts at the back of this report to see "AIR HEATERS AND ECONOMIZERS - COLD END

PROBLEMS" to see where the problem with flue gas can occur.

Usually, the use of organo manganese in a blended fuel additive is used to enhance combustion andthen reduce the potential for acid formation in the cold end. In cases where the sulfur trioxide contentis still a problem, an alkaline product can be introduced to the flue gas or to the flame zone to keep thepotential for corrosion down. In this case, magnesium hydroxide can be blended into a fuel oiltreatment product and injected into the boiler. This will tend to neutralize the acid by forming amagnesium sulfate. Calcium can also be used in this situation, and ammonia has ben used in utilitysystems for the neutralization of acid forming agents and for the enhancement of the electrostatic


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precipitators to remove opacity.

Back to the boiler, if the ash is being treated properly and a soft friable ash has been formed, then sootblowing becomes very important. Regular soot blowing will prevent the boiler from fouling, which inturn can prevent the build up of ash in the cold end. The ash can form a conglomerate of other solidswhich become sticky. Once sticky, they attract other ash, foul flue gas passages, reduce heat transferefficiency in the economizers and air preheaters, and generally prevent the proper operation of theboiler's combustion system. This ash as it is allowed to collect and absorb moisture becomes thereaction zone for the formation of sulfuric acid. O nce formed, this acid becomes the major problemwith cold end corrosion.

The control of excess oxygen, maintaining the proper flue gas temperature (above dew point) and theuse of an alkaline additive can reduce the problems usually found in cold end corrosion. One problemwhich is physical, is that when an additive program is used either as a slag modifier in the combustionzone, or as a cold end corrosion control agent, the amount of particulate matter that comes out of theboiler is increased. Usually, this particulate matter increase is 100% of the particulate matter that wasusually found coming out of the system. This condition requires the use of stack emission control

systems in many cases. It also requires that you increase the capacity of the scrubbers or bag housewhere they are in use.

Keep in mind, that the acid will condense out in the cold end at a temperature that is slightly less thanthe actual dew point for the particular section of the cold end. Also, that this acid will vary inconcentration based on temperature. As the temperature of the particular section of the cold enddecreases while still being below the dew point, the strength of the acid will also decrease. Thus, therewill be a variation of acid strengths and corrosion rates across the cold end.


TROUBLE SHO OT ING - FUEL COMPO NENTS

OIL COMPONEN T PROBLEMS ADDITI VE COMPO NENT MECHANISM

VISCOSITY Difficult to pump Dispersant Heat + dispersant, viscosity control

Poor atomization Aromatic Solvent Better atomization

Carbon deposits - tip Less burner tip cleaning

Poor oil flow Temperature Control Fouling, more complete combustion

Incomplete combustion

Smoke & carbon deposits

B.S. & W. Line, strainer & nozzle blockage Dispersant Disperse metal salts, penetrate silt

Aromatic Solvent

Corrosion, flame failure Corrosion Inhibitors Form film from filming amine

Poor combustion Oil/water emulsifier Emulsify for more complete burn

SLUDGE Slow turnover = Sludge Dispersant Disperse, emulsify and condition

Heating coil leaks Solvents tank, strainer, oil heaters, burners,


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Condensation, drainage Filming Amine solvent/dispersant to stop plugging

ASH Unburned Hydrocarbons Combustion catalyst Minimize carbon ash particulate

Manganese

SULFUR Corrosion - tanks & lines Corrosion Inhibitor Film protection, less excess air,

High Temp. corrosion Combustion catalyst (Mn) High melting point eutectic,

Cold End corrosion Magnesium compound SO3 neutralization

VANADIUM, SOD IUM, Slag, Gas pass plugging Magnesium compounds Elevate eutectic, make ash more

NICKEL Spalling, Low melting point friable, larger voids, easily removed

eutectic. Corrosion catalyst by soot blowing

Impact ash

ALUMINUM, SILICA, Low sulfur fuels, catalyze fines Magnesium compound More friable, larger voids, easily

NICKEL Al, AL2O3 plugging in package removed by gas velocity or soot

boilers blowing

SOLID FUELS

The solid fuels that would most likely be encountered, are coal, wood and waste. Coal is starting tomake a come back, wood is used where it is an excess fuel and waste is basically garbage and red bagwaste, which is on a rise at this time.


COAL:

EXCESS AIRFUEL TYPE OF FURNACE OR BURNER % BY WEIGH T

Pulverized Coal Completely Water Cooled 15 - 20 %Furnace for slag tap ordry ash removal

Crushed Coal Cyclone Furnace 10 - 15 %

Pressure or suction

Coal Spreader stoker 30 - 60 %

COAL CLASS FIXED CARBON VOLATILE % BTU/PO UND

ANTHRACITE 92 - 98% 2 - 8% --


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BITUMINOUS 70 - 86% 14 - 30% 10,500 - 14,000

SUB-BITUMINOUS 9,500 - 11,000

LIGNITE 6,300 - 8,300

The two tables above demonstrate that there are number of different types of systems to burn coal andthat there are also a number of different types of coal. Therefore, rather than dwell on all the types ofcoal, we will look into soot, ash, slag and corrosion in general.

In that the excess air has to be so high for the burning of coal, the formation of sulfur compounds andslag is a very real problem. Coal can be washed to remove much of the sulfur. Washing will lead to ahigh moisture content, which is a problem in both burning and in storage. If the moisture content of thecoal is too high, it will cause incomplete combustion which will lead to soot formation and slag buildup. In the winter, a high moisture content in an outside hopper can cause freezing, which stops the coal

from moving. The coal should be stored so as to allow the moisture to drain off of it, and givenventilation to allow moisture content to drop. For the storage of outside coal piles, spraying the pilewith a sodium polyacrylate will leave a water barrier film on the surface of the coal. This will determoisture pick up by the coal and can reduce coal pile erosion.

Once soot has formed, a powdered form of sodium chloride, iron oxide, zinc oxide and either


copper sulfate or magnesium oxide can be added to the boiler by blowing the powder in. Care shouldbe taken as the chloride ion can become very corrosive if it is overfed. A good rule of thumb is towatch the speed at which the soot is removed, and if it is very noticeable and rapid, the chloride ion isprobably too high and corrosion is possible.

For the control of sulfur trioxide, calcium as both the oxide and the carbonate have been used toabsorb the sulfur compound. As with fuel oil, magnesium salts are also very effective for theneutralization of sulfur in the flue gas.

The control of slagging can be approached by using a barrier ash concept. This blows in magnesiumoxide into the boiler at the area of the combustion make up air entrance into the boiler. The powder

will spread and adhere to the walls of the furnace. As the slag begins to form, the area in which it wouldnormally attach to boiler internals, is attached to the magnesium salt, this allows neutralization at thepoint of ash impact and allows the slag that forms to drop harmlessly to the furnace floor formechanical removal during boiler shut down. This approach requires that the powder be renewed on aregular basis. Therefore, the powder must be fed everyday to every shift to maintain that propercontrol of slagging. It is very important to start this type of program with a boiler that is as clean aspossible. The cleaner the boiler is when it starts, the more effective the barrier ash will prove to be.

Emission from a coal burning system are usually very visible. A combustion catalyst as manganese,


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calcium or magnesium can be fed to the coal as it is being fed to the boiler to improve combustion,which will reduce opacity. Care must be used here, as this will dramatically increase the particulatecontent of the flue gas and it is important to use some type of scrubber or bag system to remove theparticulate prior to it exiting to the open air.

W O O D :

Wood is used as a waste fuel in most cases, in wood burning boilers. Where the wood comes fromfurniture scrap which for the most part if seasoned hard wood, as long as the fuel to air ratio is proper,there is very little that will need to be done. You should inspect the system for soot build up, whichcould lead to a combustion catalyst, but in most cases, adjustment of the excess air will solve theproblem.

Where the wood is bark, or scrap from wood processing and it contains some natural moisture, youwill find potential for slag formation. This is not a sulfur yielding fuel, so cold end corrosion is notusually a severe problem. However, the wood will yield silica, calcium and sodium. These can

combine to form hard insulative deposits which will restrict flue gas passage and create high heat zonesin the boiler. At the same time, the build up of the slag can be so severe as to cause the plant to shutdown for mechanical cleaning every few weeks. The approach in this case is to watch the furnacetemperature and to try to control the temperature below 2000 degrees F.


Then to feed magnesium as a salt to the flame. The complex will have a higher melting point than thesilica, and it will pass out of the boiler as a solid ash. Complete combustion is the other area that isimportant, as well as, soot removal. Soot removal is corrected by proper air adjustment mechanically,and by the use of sodium chloride based soot removers as used with the coal. To completecombustion, the feeding of organo manganese to the boiler will improve the wood's ability to burnmore completely.

Again, the temperature of the furnace is very important. If it is to high, the silica complex will still meltand the boiler will foul quickly.

W ASTE BURNING:

Waste is burnable garbage and red bag waste from hospitals. In both cases, the variance of the fuelsource makes it difficult to be treat and a sampling of the ash may have to be performed in order todetermine the proper blending of the additives. In both of these cases, silica again becomes a culprit. Itis one of the lowest melting point contaminants and as such has to be treated for. The temperature ofthe flame zone should be under 2000 degrees F as with the wood burner, and a blended powderconsisting of calcium, magnesium and other metals should be fed to the fuel source on a continuous


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feed basis.

This area is growing very fast and has a number of different variables. The use of an additive mustrequire some analysis of the fuel source and the ash content. It can have a high level of aluminum,which would require the magnesium oxide percentage in the product to be higher, it could havecontamination that would require special additive blending. In any case, the primary slag buildingparticulate is silica, followed by just about anything.

Documents

Fuel Oil Treatment[1]