Liquid Minerals Group Inc. - Magnesium Presentation

% Sulfur
IN FUEL

Excess
O₂ %

OIL FIRED UNITS
Sulfur Trioxide Expected in Gas
( ppm - parts per million )

LMGI Magnesium Presentation

I.   Introduction

       When boilers operated exclusively on coal they were very often inefficient. That didn't matter, the fuel was inexpensive and plentiful. Temperatures were relatively low. Heavy metal slags, when they formed, were an accepted part of burning coal. Boiler plume opacity was accepted. Maintenance costs were high, but the fuel was cheap so it didn't matter.

       With environmental concerns and the rising cost of coal, fuel oil became more preferred. With the use of oil, boiler temperatures rose to become more efficient. As the temperatures rose, slagging became more of a problem. As boilers became more efficient, temperatures continued to rise. As temperatures rose, corrosion became a concern. The community would no longer tolerate stack opacity.

       Initially oil boiler operators, many from the old coal school, accepted slag, corrosion, and opacity problems as part of the operation of the boiler. As operators became more aware of these problems and the need to operate their boilers more efficiently, many companies appeared proposing solutions to these problems. Magnesium was very often a part of these remedies. However, the crude forms of these magnesium products very often introduced more problems than they solved.

       This presentation will address the chemical causes of the problems found in today's modern boilers. We will discuss how these problems can be controlled using magnesium based products. We will discuss the various forms of magnesium products with particular emphasis on the benefits and disadvantages of each. We will discuss the LMGI magnesium product, at present and in the future. And finally we will discuss our preferred method of boiler testing.

II. Boiler Problems

Although there are many operational problems associated with running a boiler plant, we will concentrate only on the internal fireside problems that have chemistry as their origin.

A.   Hot Side Problems

       The two biggest problems encountered on the hot side - slag and corrosion - are both due primarily to the same causes: deposition of oxides and sulfates of vanadium and sodium.

       Vanadium and sodium are two chemical contaminants found in crude oil. They come from the organic materials that were laid down eons ago that ultimately formed petroleum. ALL crude oils (I know of only one that does not) contain vanadium and sodium. Crude oils from various regions of the world contain varying amounts of vanadium. Venezuelan crude oils contain some of the world's highest levels of vanadium. Sodium can also be added during the various transportation activities moving crude to the refinery and also during the refining process itself. As the crude oil goes through the refining process, these two elements and others that are present, are concentrated in the residual oils that typically become the fuels burned in boilers. Often the boiler fuel has a fairly high or no specification on vanadium.

       When these two elements are burned (as well as all other metallic elements) they combine with oxygen present to support combustion and with sulfur which is also present in the fuel to form oxides and sulfates. Vanadium oxide (normally present as the pentoxide) has a melting point of 675 °C. When combined with sodium sulfate a very low temperature melting point eutectic can be formed (as low as 525 °C). The graph below shows the temperatures where the various eutectics are "sticky." These temperatures can be at or below the operating temperatures of a boiler, especially in the superheater section.

1.   Slag

       Slag is the term applied to the metallic components that deposit on boiler tubes and surfaces. Temperatures inside the boiler are often higher than the melting point of the vanadium/sodium eutectics mentioned earlier. When the temperature is above the melting point, the oxides and sulfates are molten. When these materials are in the molten state, they are sticky. Putting this into terms that are more familiar, think of a glass of water. When the contents of a glass of water are thrown against a wall, the water coats the surface - it sticks to the wall. Now perform the same experiment with an ice cube. Very little of the ice will stick to the wall. This is the situation inside of the boiler. When sodium and vanadium are present they will form low melting- point compounds. When the temperature is high enough, these compounds will be molten and sticky. They deposit (stick) on the boiler surfaces.

       As the layers of metallic materials deposit on the tube surfaces, the outer layers insulate the inner layers from the heat of the flame. The inner layers cool and harden. But as the inner layers cool, they also insulate the outer layers from the cooling effects of the cooling water tubes. The outer layers get hotter still and more material will become molten and stick to these layers. This process repeats as long as the untreated boiler is in service. The layers of slag build up. As the slag builds on the tubes, the heat transfer into the water tubes is reduced. Often the boiler operator must increase fuel consumption to compensate for this loss of heat transfer. From theoretical calculations the following graph demonstrates the magnitude of the losses possible as slag thickness increases.

       As slag thickness increases and heat transfer into the desired activity of boiling water is reduced, the heat from combusting oil is lost into the back end of the boiler. Very often this heat is lost out the stack. It has been found that for each 55 °C increase in stack temperature, between 10 and 15 °C in steam temperature could be lost. These temperature changes in a boiler operation are useful indicators of a slag problem.

2.   Corrosion

       High temperature corrosion results from the deposition of the same metallic components - vanadium and sodium. For this problem, these compounds must remain molten.

       Most metals form a protective oxide layer to protect against corrosion. This layer is formed from the outermost layer of metal atoms. The metals used in boiler tubes do this too. While vanadium and sodium are in a molten state they cause destruction of this protective oxide layer. Vanadium oxide in particular dissolves this protective oxide coating. As this protective coating dissolves and is removed, a layer of the tube metal is removed. A fresh protective coating forms from the next layer of tube metal atoms, is subsequently dissolved, and a new layer forms. This process continues, much like the peeling of an onion until the tube thins to a critical thickness. When the tube is thinned sufficiently and if still in service, a blow-out can occur. The overall effect is called corrosion.

B.   Cold - End Problems

       Just as the high temperature problems are caused by chemical elements, so are most cold end problems caused by chemical elements. In the case of the cold-end the offending element is sulfur. Sulfur occurs naturally in the crude oils that are refined. The level of sulfur is concentrated into the residual fraction and finds its way into nearly all boiler fuels at varying levels. The level encountered is normally related to the specification level of the fuel purchase contracts.

       When sulfur is burned in the presence of oxygen (required to support combustion) it forms sulfur dioxide. Normally about 1 - 2% of the sulfur dioxide is further reacted with additional oxygen to form sulfur trioxide. More or less may be formed based upon the conditions found in the boiler. For example levels of excess air/oxygen (higher, more formed); vanadium, nickel or iron (higher, more formed); sulfur in the fuel (more present, more formed); size of boiler (larger, more formed); temperature of firebox (higher, less formed); and the residence time in the boiler (longer, more formed). All of these factors are competing at the same time making prediction of the actual amount of sulfur trioxide that will be formed difficult. The following table shows the expected amount of sulfur trioxide based upon excess oxygen and sulfur content.

ESTIMATE OF SULFUR TRIOXIDE IN COMBUSTION GAS

The chemical reactions forming these sulfur compounds
are represented as follows :

S + O₂ » SO₂	Sulfur Dioxide
2SO₂ + O₂ » 2SO₃	Sulfur Trioxide

One interesting note about the second reaction in particular is that the presence of hot iron surfaces and vanadium slags are requird to make the reaction go in the direction indicated. If there were no surfaces to actively catalyze this reaction, the temperatures found in boilers would effectively limit the formation of sulfur trioxide by forcing the reaction in the reverse direction.

1. Cold - End Corrosion

The formation of sulfur dioxide or trioxide is not a problem within the boiler (although this can be a problem outside the boiler when in the atmosphere - acid rain). The problem with sulfur trioxide is that it condenses with water vapor (formed from the combustion of hydrocarbons in the presence of oxygen) to form sulfuric acid according to the following reaction:

SO₃ + H₂O » H₂SO₄

Sulfuric Acid

(Sulfur dioxide has a similar reaction, but the resulting acid normally does not condense at boiler temperatures.)

       The formation of sulfuric acid is a problem because when temperatures are low enough, the acid can condense on metal surfaces causing a severe corrosion problem. This cold-end corrosion normally occurs in air preheaters where temperatures can be low enough - after heat is removed to warm incoming air - so that the acid condenses on the metal surfaces. Sulfuric acid corrosion can also occur on stack walls and particularly on any metal tops of stacks.

       The formation of acid in air preheater equipment - often black in color - can also act as a trap for fly ash. This leads to deposits that can interfere with the transfer of heat in the air preheater as well as a corrosion problem. Acid smuts that leave a stack are particles of fly ash with adsorbed acid on them. When these smuts float to the ground and deposit on automobiles, they can cause additional problems.

2.   Opacity and Acid Plumes

       Opacity has many causes from unburned fuel through dispersions of metal oxides that carry through the boiler and out the stack. The cause we are concerned with is due to the same condensation of sulfuric acid discussed above. Very fine droplets of acid form after the exhaust gases leave the stack and are cooled to the acid dew point. This leads to a visible plume often blue-white in color (can be reddish or yellow-brown depending on sun angle). The most obvious trait of this type plume is its persistence. An acid plume will carry a long way before dissipating.

III. Solutions to those Problems

There is one non-chemical method that can solve all these problems available to the boiler operator. That is to reduce the amount of excess air going to the boiler. Excess air is defined as the amount of air above that needed to exactly support combustion. This works by limiting the formation of vanadium oxides to those of a lower "valence" state. These compounds have higher melting points. Also since the formation of sulfur trioxide is dependent upon oxygen being present, by reducing the excess air to the absolute minimum, there is no oxygen present to form sulfur trioxide.

The reason this method becomes impossible to attain is long before this minimum excess air level can be reached, incomplete combustion would result in severe, unacceptable boiler smoke. However, reducing the excess air to as low a level as possible is always desirable for minimizing the formation of both hard slags and sulfur trioxide.

Experimentation on chemical means to solve these problems has been conducted since the 1950's. Early in this work magnesium was found to offer the most cost-effective method to control slag, high temperature corrosion, cold-end corrosion, and some opacity problems. And just as the problems are caused by chemical reactions, the solution of the problems using magnesium can be described by chemical reactions too.

A. Hot Side Problems

Magnesium combines with vanadium and sodium (chiefly vanadium) to form higher melting compounds. When magnesium is combusted in the presence of air, it forms magnesium oxide (MgO). The magnesium oxide combines with vanadium pentoxide to form among other compounds, magnesium orthovanadate.

3MgO + V₂O₅ » 3MgO • V₂O₅

Whereas vanadium pentoxide has a melting point from 675 °C and lower, magnesium orthovanadate has a melting point of 1243 °C. This temperature is well above the typical operating temperature of a boiler so the ash is no longer sticky.

1.   Slag

       When the melting points of any vanadium compounds formed are above the operating temperature of the boiler they will no longer be molten or sticky. If no longer sticky, there will be no build up on boiler surfaces and heat transfer will not be impeded.

2.   Corrosion

       Similarly, if the vanadium compounds formed are no longer molten, they will no longer dissolve the protective oxide coatings of the tube metal. If they no longer dissolve the oxide coatings, they will no longer cause corrosion.

B. Cold - End Problems

Magnesium is also used for eliminating or at least greatly reducing cold end problems. In this instance magnesium is used to coat the internal surfaces of the boiler. Recall that sulfur trioxide formation requires the catalyzation by hot iron surfaces or vanadium slags.

1. Cold - End Corrosion

When the catalytic surfaces are coated with the fine particles of magnesium oxide that result from the combustion of oil-soluble magnesium products, they are rendered passive. Magnesium orthovanadate does not catalyze the reaction of sulfur dioxide to sulfur trioxide. Thus the formation of sulfur trioxide is greatly reduced. Also, magnesium oxide acts to neutralize any acid or sulfur trioxide that may still form by the following reactions:

MgO + SO₃ » MgSO₄

MgO + H₂SO₄ » MgSO₄ + H₂O

Magnesium sulfate is not corrosive and water vapor already exists in the stack plume.

       By the coating action and neutralization, formation of sulfur trioxide can be substantially reduced or eliminated. This eliminates cold-end corrosion problems.

2.   Opacity

       Opacity that is the result of sulfuric acid formation in the plume can be controlled in the same manner with the use of magnesium additives. When sulfur trioxide is reduced or eliminated, sulfuric acid can no longer be formed so there is no acid plume.

C. Magnesium Products

Magnesium has been used because it has a relatively low atomic weight that means that more atoms of magnesium can be added to fuel for a given weight of additive. And since magnesium is relatively plentiful and easy to obtain from nature, the cost can be bearable for this application. ALL magnesium products will work to solve the problems discussed above. Magnesium is magnesium; the reactions discussed will occur no matter the source of the magnesium. What is different is the nature of the products, their reactivity and the manner in which the products are used. The following is a quick summary of the different types of magnesium products that have been used over the years.

1.   Powders

       Powders are typically magnesium oxide or hydroxide. Particle sizes range from a couple of microns up to tens of microns. The concentration of magnesium in powders is the highest of any magnesium products with magnesium oxide being 60% magnesium. Powders are very inexpensive. Handling problems make powders less than desirable to use. The inclusion of any moisture in a powder will cause clumping. For this reason it is necessary to keep sacks of powders dry. It may also be necessary to break up the powder particles before addition so their size is more uniform. Powders are often added to the back end of a boiler between the superheater and the economizer. They cannot be added to the fuel since they are insoluble and would separate from fuel if the fuel were not kept in motion. Erosion of valves and burner tips could also result if a powder were added to fuel. Magnesium hydroxide is more reactive than magnesium oxide. When the hydroxide is added to the hot furnace (or flame) it converts to magnesium oxide at that point and thus is more reactive. Many magnesium oxide powders are "dead-burned" which means they have been heated to high temperatures during drying so they are no longer reactive.

2.   Slurries

       Slurries are generally magnesium oxide or hydroxide powders dispersed in a light fuel oil (#2 or kerosene). A dispersing aid is included to stabilize the powder in the slurry. Particle size is generally down to around 1 micron. The smaller the particle size, the more expensive the slurry. Slurries are normally added to the fuel line just before the burners since they are not truly soluble in the fuel. This minimizes the chances they would settle from the fuel causing blockages. Slurry storage requires constant (or at least intermediate mixing) to keep the solids present in the slurry from settling. Drums of slurry very often need to be thoroughly mixed to resuspend the solids before the slurry can be removed from these drums. Even with caution, many slurry users report settling problems with slurry products. Slurries are still inexpensive, but cost more than powders. Magnesium concentration of slurries is typically between 28 and 35% magnesium. Many magnesium oxide slurries use "dead-burned" oxide, which means they have been heated to high temperatures during drying so they are no longer reactive.

3.   Water Based Products

       Water based products are often solutions of magnesium chloride, nitrate, acetate or sulfate. Water based products can be very inexpensive. However, they suffer the same disadvantages as slurries and powders in that they are not soluble in fuel. This requires them to be added to the flowing fuel stream just prior to the burners. They have another disadvantage too, magnesium concentrations cannot be very high (typically less than 10%) due to solubility limitations. Many of these compounds have reverse solubility, they are less soluble at higher temperatures so it becomes necessary to formulate even more dilute to avoid recrystallization. This could cause pump erosion and/or blockage. Because the water-based materials are in the molecular state when dissolved, they can be very effective additives if the handling difficulties can be overcome. Because they are water based, it is necessary to protect formulated containers from freezing in colder climates.

4.   Oil Soluble Products

       Oil soluble products offer the best technology. These products are typically magnesium sulfonates or carboxylates. Because they are oil soluble, they can be added at any location in a fuel system and will remain dissolved in the fuel. Because they have very small particle sizes in solution, they can be quite effective additives. They are stable in shipping containers and require no special handling precautions in use. Magnesium concentrations vary from about 13% up to about 30% magnesium. Oil soluble products often start from the same magnesium oxides used in the powders and slurries with additional processing required to make them oil soluble. The convenience of using oil soluble products often makes them the additive of choice. The higher cost is offset in large measure by the need to use less magnesium than is required with corresponding powders or slurries.

IV. LMGI Products

LMGI is an established company with a proven track record in boiler additive treating. Our technical staff has considerable experience. Unlike many of the other companies that provide boiler additives, our only business is magnesium additives for boilers. We have examined the other types of products that are currently available. We believe the oil soluble additive approach is the best and most logical method for treating these common boiler problems. We concentrate our efforts on providing all the benefits of oil soluble technology while minimizing cost.

A.   How They Work

       LMGI's oil soluble LMG-30^® product dissolves in the fuel. When the additive in the fuel passes through the flame very small particles of magnesium oxide are formed. These particles are activated at this point making them very reactive. T hey are able to then react with the vanadium present to form the high melting point compounds desired. Other particles of magnesium oxide coat the internal surfaces of the boiler passivating them against the formation of larger quantities of sulfur trioxide. Still other magnesium oxide particles carry into the back end of the boiler where they are able to neutralize any sulfuric acid that may still form.

       One requirement of an effective additive is a large number of particles available for reaction. This is achieved in the LMGI product - and other oil soluble products - through the presence of very small, highly reactive particles. The smaller the particle size of a given material, the greater the number of particles that can be packed into a given volume. For example a material with an average particle diameter of 10 microns could pack 1.9 x 1015 particles into a liter. But if the average particle size were reduced by a factor of 100 to only 0.1 microns, the number of particles available in a liter would increase by a factor of one million to 1.9 x 1021.

       As the number of particles increases, the opportunity for a particle of magnesium oxide to contact a particle of vanadium pentoxide increases. The reaction combining magnesium oxide with vanadium pentoxide must take place essentially in the space of the flame. With a typical slurry material this would be like throwing a soccer ball at another soccer ball at say 20 meters distance and expecting to hit it with each try. With an oil-soluble material with a substantially smaller particle size we would now have say half a million grapes to hit the soccer ball still just one time. From this simple analogy it is easy to see why oil soluble materials are more efficient at combining with vanadium.

       And just as there are many magnesium oxide particles available to react with vanadium, an oil soluble material also provides trillions of particles to coat the internal surfaces of the boiler to interfere with the reaction of sulfur dioxide to sulfur trioxide. And because the particles formed from an oil soluble material are so small, they are able to migrate throughout the boiler to neutralize any sulfuric acid that may still form.

B.   Where We Are Today

       Because LMGI is a new company in boiler treating, we have not produced the wide range of products available from other companies. We have decided to be the best at one thing before we move to anything else, at that is providing the best magnesium oil soluable additive available. Because we believe passionately in our approach, we want to provide oil soluble technology to as many customers as possible as soon as possible. We want to begin to provide the benefits of an oil soluble product today, we will however, continue to develop other products in this field.

C.   Where We Will Be In The Near Future

       We have recently added a world class chemist to our staff who brings over 26 years of magnesium chemistry knowledge and boiler and turbine treating experience to our company.

V.   Test Protocol

       In order to demonstrate unequivocal results that are easy to interpret we prefer to test on a clean boiler. To allow LMGI to make a computer generated starting dosage recommendation we will require information about the boiler and the fuel in use. The starting dosage will by necessity be higher than we expect the post test treatment to be. This is because we do not want to lose time by making an economically attractive recommendation just to learn we need to treat at a higher, unacceptable rate following the test. It is better to begin at a level that is higher than you will need to ever treat so your costs are known and suitable budgets can be established. Essentially it is better to have an expensive success than a cheap failure.

       If you believe your worst problem is slag and/or corrosion in the hot section, a suitable test would require up to six months unless adequate historical data is available to compare the test period against. This should include comparable boiler loads, a similar fuel, and other parameters. Temperature changes of the various locations in the boiler and the stack can be examined to note any variations indicating boiler behavior.

       If you believe your worst problem is cold-end corrosion and an acid plume testing can proceed much faster. Often, especially with an acid plume, it is obvious within a day or two of starting treatment that the treatment is effective. If a dew point meter is available we can use it to determine the reduction in dew point with treatment.

A.   What You Need To Provide

       A willingness to work with us. If we have not used LMG-30^® at any other locations, then some experimentation will be required. There will be no risk to your equipment, magnesium additives work.

       In order to make the initial recommendation and determine where we should begin treatment, we will require the following information:
Superheater temperature, fuel vanadium content, sodium, potassium, lead, sulfur, nickel, specific gravity, excess air/oxygen level and approximate boiler size (in MW).

       A location to store drums. Preferably this location should provide some cover from the weather, especially if in a damp climate.

       You will also need to provide a suitable chemical feed pump to deliver the additive into the fuel. Because oil soluble chemicals require no special equipment, any pump that can deliver a relatively small quantity of additive per hour against the back pressure in the fuel line is adequate.

       We will require, and we believe you will want, your own personnel to tap into your fuel line where the additive should be added. Because oil soluble additives can be added at any convenient location in the fuel system, normally we can utilize an existing valve location. One requirement is that the location selected is outside of the recycle loop to avoid retreating the same fuel.

B.   What We Will Provide

       LMGI will provide a world class magnesium additive and be happy to provide testing in some type of arrangement. We will provide technical support and expertise to oversee the trial. We will assist in the evaluation process both before and after the test. Before the test begins - and hopefully before the boiler is cleaned - we would like to take photos of the untreated condition. We would also like several representative boiler deposit samples as well as one or two representative fuel samples. If you already have analyses of any of these we would be able to use those otherwise we will have our own analyses performed.

       At the conclusion of the trial we would like to reinspect the boiler with photos again. We would also like several deposit samples from the same locations sampled before the trial began.

       Following the development of the photos and sample analyses, we will provide a detailed report outlining the improvements in boiler operation and cleanliness. This report will include any other information that is deemed important as the trial proceeds.

VI. Next Steps

We are ready to start. What more do you need from us?

A.   Let's Start A Test

       Magnesium is magnesium, no matter the source. As indicated in the section on different types of additives, ALL magnesium additives will work for this purpose. They differ in the amounts needed to provide benefit and their cost. We have removed the cost barrier for this initial test period.

B.   How Will This Benefit You

       You will receive all the benefits of using a magnesium additive: substantially less slag, corrosion control in the hot section, reduction in sulfur trioxide formation (less acid rain), controlled cold end corrosion, a boiler that can be more efficiently operated, and finally a boiler that will be easier and faster to clean.

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