Category Archives: Diesel blending

To make diesel fuel with high performance and optimal hydrocarbon content, modern methods of component content measurement are required.

It seems impossible to achieve without using additives. Additive efficiency depends to a large extent on the hydrocarbon composition of diesel. Additives for diesel fuel are mostly selected by trial and error. This stage is one of the most problematic for fuel producers. The main difficulty is combining surfactants of different nature and the consideration of susceptibility of fuel to additive packages.

It often happens that one additive improves a property and worsens another. For instance, a cetane improvement additive degrades lubricity, increases fuel density and viscosity. A lubricity additive reduces the susceptibility of the fuel to cetane improvement additives. Therefore, combining of these two types of additives requires increased concentrations. Using dispersers and pour point depressors can have a synergetic effect.

The current research is focused on selection and development of both multifunctional and individual additives. While the research is ongoing, there is a limitation: it is mostly performed on a specific type of diesel fuel. The composition of the product may vary even at one refinery. It is impossible to say that a fuel with good susceptibility to additives made by a certain manufacturer will be similarly susceptible to additives by another manufacturer. The problem can be solved by quickly adjusting the concentration of the additives or selecting more efficient additive concentrations.

The depressor and dispersion additives are the most sensitive to the hydrocarbon content variations of the fuel. An insignificant change of the n-alkane and amount and their molecular weight distribution reduces the low temperature properties of diesel fuel. Even stratification may occur in case of cold storage.

To sum it all up, knowing the hydrocarbon content of diesel fuel is a prerequisite to the production of high quality fuel and a basic tool for making the correct decision if the content of the fuel changes.

Diesel Fuel Production. Catalytic deparaffinization is increasingly used in oil refining due to its efficiency and technical simplicity. Experience shows that catalytic deparaffinization can be successfully integrated with deep hydrodesulfurization.

Let us briefly look at systems used for such processes. In 2003, hydrodewaxing equipment was first used. The equipment included a sulfur production section. The raw material for the process is a high paraffin content straight run diesel. The reactor section includes three reactors. In summer, when the demand for winter fuel is low, the second reactor can be stopped, excluding the process of dewaxing. The system is then set for diesel fuel hydrofining.

In 2005, a system for deep hydrofining of diesel fuel was developed. The general objective was achieved by using a multistage reactor system. Each reactor was equipped with a separate catalyst. In the first reactor, sulfur and nitrogen compounds were removed and olefins were saturated with hydrogen. The second reactor was designed for hydrodearomatization of hydrocarbons, and the third one for reduction of fuel pour point. This last reactor is mostly used in the cold season.

The catalytic hydrofining and dewaxing system was also implemented. The equipment allows the production of stable components, which can be used in production of high performance winter and summer fuels. The raw material is a mix of crude and gas condensate. The technology implemented in this system can produce winter and arctic diesel fuel with sulfur content below 50 ppm.

However, research is ongoing into increasing the efficiency of hydrofining to produce diesel fuels with low cloud point. The focus of this research is now the development of new catalytic systems.

Diesel Fuel Blends. Modern oil refining performs several important functions, among which improvement of the low temperature performance of diesel fuel performance and increased depth of hydrofining.

Until recently, the production of fuel with good low temperature performance was done by either reducing the end of fuel boiling from 360ºС to 340ºС (330ºС for arctic fuel), or by dilution with kerosene. In both cases, the economic viability was questionable. In many cases, diesel fuel performance suffered, with reduction of cetane number and lubricity.

Therefore, gradual implementation of modern catalytic hydrogenation processes into oil refining began: hydroisomerization and catalytic deparaffinization. The processes allow to change diesel fuel, optimizing their hydrocarbon composition.

Until recently, the phrase “diesel fuel for cars” could bring a smile to the faces of experienced drivers.  This is not surprising, because this oil was used mainly to fuel trucks and large special equipment.  But due to the significant progress in refining processes and engine manufacturing it has become possible to use diesel fuel in cars.

The issue which has always worried each driver is the quality of the fuel in the fuel tank.  A decisive role has been played by the ways to determine which petroleum product could be regarded as good, and which one – not so good.  It is more or less clear with gasoline, but how to determine the quality of diesel fuel?

What is the cetane number?

Among the most important qualities of diesel fuels, it is worth highlighting their ability of ignition and self-ignition.  This property is expressed as a numerical parameter, such as a cetane number.  By its physical nature, a cetane number is the time between the moment when fuel enters an engine cylinder and its combustion.  The higher the cetane number, the shorter the time interval, and the better is diesel fuel.  Running on fuel with a high cetane number is characterized by increased engine power, and at higher speed.

What else does the cetane number value mean?

In addition to the ability of ignition and self-ignition, a cetane number also characterizes the degree of environmental friendliness of fuel.  The fact is that the ignition ability depends on the hydrocarbon composition of fuel.  Here is an example.  If paraffinic compounds dominate in oil, it ignites relatively easily.  When aromatic hydrocarbons dominate, the ignition occurs with a certain delay.

In the case of using diesel fuel with a cetane number below 40, it increases the risk of rough engine performance, which manifests itself in rapping at idle.  This results in deterioration of the engine performance, wearing on bearings and other critical components and parts of the fuel system.

Working conditions put forward certain demands to the cetane number of winter and summer diesel fuel.  In the former case this indicator should be higher than in the latter case.  Also, it should be understood that cetane number is different for engines operating on ships (20), trucks (40) and cars (55).

Cetane number measurement

For diesel fuels, the following method of cetane number determination is applicable.  First of all, the value is numerically equated to the percentage of cetane in its mixture with alpha-methylnaphthalene in fuel equivalent.  In further calculations the flammability of cetane is conventionally assumed to be 100%, and that of alpha- methylnaphthalene in fuel equivalent is 0%.  Then field trials are conducted, during which the time of fuel self-ignition is measured and compared with the figures for fuel equivalent.

Here is an example.  If it was determined that diesel fuel was ignited in a combustion chamber during the time equal to the time of ignition of a 30% cetane and alpha-methylnaphthalene mixture, it has a cetane number equal to 30.

Increasing cetane number

It should be noted that the quality of diesel fuel is determined not only by the value of its cetane number, but also by other factors, like oil contamination with mechanical impurities and the presence of water.  Nevertheless, the issue of increasing the cetane number to normalized values does not become less important.

Filtration and separation have almost no effect on the time of ignition and self-ignition of fuel.  They allow to clean fuel from water and mechanical impurities, but not more than that.

Special additives are used in practice to improve cetane number.  They are substances which are added to oil in a small amount in order to improve certain performance characteristics.  They compensate for the missing units of a cetane number of diesel fuel, normalizing the time of its ignition.

During industrial mixing of additives and petroleum products, it is necessary to ensure getting the most stable mixtures that would not break down for a long time.

Wyen using conventional mixing techniques, known today, fuel tends to break down when separate component parts are added to it.

The feature of USB-type plants produced by GlobeCore is the fact that using the injection method and hydrodynamic shock can increase cetane number of diesel fuel, while breaking down of the resulting product does not take place for at least 180 days.

Modern hydrodynamic (inline) mixing plants have proven themselves in industrial use as cost-effective, accurate and sustainable means of production of high-quality motor fuels with an optimal cost.  The achievable cost savings and improved profitability, compared to a conventional technology of components mixing in special vessels, can accelerate the return on investment up to 60% for one year and provide a return on the project for a period of one year or less.

Most frequently used diesel fuel production process includes several steps: treatment in distillation columns, cracking and compounding process.

Processing in distillation columns is the first step which is necessary for diesel fuel production.  Oil is heated at constant pressure up to the temperature of 180-360ºC.  This makes it possible to divide “black gold” into separate fractions.  The finished fuel outlet after processing in distillation columns is relatively small (about 20-25%).  The process features little expenditure in terms of time and money.

The process of cracking is required for long molecules breakdown.  It helps to obtain components that can be burned in diesel engines in large amounts.  There are several approaches to the process of cracking.  In thermal cracking oil is heated, while various catalysts are not used.  In hydrocracking oil reacts with hydrogen.  Catalytic cracking cannot be performed without metals, which act as catalysts.  Nickel, iron and platinum sponge are most frequently used.

After the second-stage, the output of diesel fuel can reach 70-80%.  But it is still not in a marketable condition, due to the presence of sulfur and other contaminants.

At the stage of compounding the products of cracking and direct distillation processes are mixed in the proportions specified with the process.  Additives are also added at this stage.  If the sulfur content does not exceed the permissible limits, diesel fuel can be shipped to the end user right after blending.  GlobeCore USB plants are used to mix all the individual components.  Through the use of hydrodynamic shock and injection method, this equipment allows to obtain high-quality diesel fuel, which does not break down for at least 180 days.

Today, three types of diesel fuel are available in the market: winter, summer, and Arctic. The main difference between, let’s say, winter and summer diesel fuel lies in their crystallization temperature and the temperature of complete solidification.   It depends on a method used for fuel production.

Today winter diesel fuel can be produced by using two methods.  The first one is nearly the same as for summer fuel, but with lowering of carbonic fractions final boiling point to 20°C.  Also, winter diesel fuel can be obtained directly from summer fuel by adding special depressants that are able to lower its pour point.  At that, limiting filterability temperature remains unchanged.

Winter diesel fuel can also be obtained by adding kerosene to summer diesel fuel.  The lower the ambient temperature, the more kerosene is needed.  We should note that this method is not economical and the use of real winter diesel fuel in most cases is cheaper.

Rough running of an engine can be caused by different reasons.  The first one is injection timing control disturbance.  The second one is incorrect operation of the fuel equipment.  In both cases it is advisable to visit a service station and have the car examined by specialists.

Another possible reason of rough running is refueling with low-cetane fuel.  This parameter characterizes the ability of diesel fuel to combust.  In case of using low-cetane fuel, the time interval prior to ignition increases.  This will cause the greater part of diesel fuel to be in the combustion chamber before the ignition.  This results in flashing of combustible mixture throughout the combustion chamber volume, causing a sharp jump in pressure inside the cylinders, making the engine work roughly.

In order to understand how to deal with the problem, you must first identify its causes.  One of the reasons for fuel lower cetane number is its dilution with other petroleum products (kerosene, gasoline, etc.).  Most often it occurs in the cold season, when it is necessary to ensure the reduction of pour point.  And what happens if, for example, diesel fuel is diluted with engine oil?  In this case, the cetane number of diesel fuel increases.  If the softness of the engine running was the only issue, it would be possible to say that adding oil into fuel is justified.  But it is not so simple.

There is no agreement of opinion in this regard among the automotive industry experts.  The opponents of adding oil into fuel note that most modern fuel manufacturers exclude the possibility of dilution of their product at an early stage of production.  Be it an additive, gasoline, kerosene or oil.  Although sometimes they make exceptions for their own-produced additives.  This is understandable, since nobody wants to lose money on their products but earn as much as possible.  Another argument against the dilution of diesel fuel with engine oils is a discrepancy in amount of additives.  Typically, two-stroke engine oil originally contains fewer additives than diesel fuel.  The difference in operating temperatures leads to an increase in the intensity of soot formation and reduction of the speed of its burning out.  The products of incomplete burning of motor oil and ash clog the nozzles and accumulate on the surface of the turbocharger components, in the catalyst and in the particulate filter.

Furthermore, an excessive amount of oil added to diesel fuel will inevitably lead to unreasonably high cetane number, which is fraught with the drop in engine power, increase in fuel consumption and smoke emission.

But there is also the opposite point of view, which allows adding engine oil into diesel fuel.  But here, there are several alternatives.  Some experts admit the addition of oil into fuels for older engines with pintle-type nozzles, while such practices are not considered acceptable for diesel engines with multi-hole spray nozzles.  Some experts justify adding of oil only in the cold season, especially in the case of its previous dilution with gasoline, kerosene, etc.

The history of a diesel engine dates back to the previous century, when Rudolf Diesel proposed a fundamentally new design that converts fuel combustion energy into mechanical energy.  After many years, diesel engine has not lost its relevance and began to enjoy increasing popularity.  The reasons are obvious: the fuel for a diesel engine is relatively cheap and it is more environmentally friendly.

Moreover, modern diesel engines for passenger vehicles are highly competitive against gasoline engines.  Perhaps, a diesel engine is the only good option for large equipment.

Performance characteristics of a diesel engine are largely dependent on the quality of fuel used.  But it does not always have the necessary cetane number, sulfur content, etc.  The totality of these factors results in lower capacity, deterioration of environmental friendliness and economical efficiency, as well as reduction of serivce life.  Let’s consider possible solutions to these issues.

Increasing the Cetane Number

Today there are special additives produced to improve various consumer characteristics of diesel fuel.  Cetane number is no exception; it can be improved by adding specific substances to fuel.

Some additives can increase the cetane number by 5 units.  In addition, they improve fuel combustion properties and increase engine efficiency.  Typically, the concentration of cetane-enhancing additives is not more than 0.2-0.5%.  When making a choice in favor of such a solution, it should be understood that the cost of one liter of such fuel will slightly increase.

In recent years, an increasing number of smoke suppressant additives have been introduced to the market.  They have been seriously improved by the use of catalytic reagents.  Such additives are used to improve the combustion of diesel fuel, reduce exhaust smoke and carbon buildup.  Their concentration in fuel generally does not exceed 0.2%.  Due to this, diesel fuel is not that cheap any more, but not much more expensive either.

Removal of deposits

In order to clean an engine’s fuel system, a special method is used worldwide.  In essence, this is how it works.  An engine is running on special solvent instead of fuel for some time (usually no longer than an hour).  It cleans fuel pump and fuel lines from deposit builup and restores normal operation of nozzles.  This effect is achieved due to the fact that solvent contains surfactants which are capable of catalyzing the oxidation of hydrocarbon compounds at high temperatures, when the engine is running under load.  Interestingly, the washout is carried out immediately after treatment with solvent.  The builup residue burns away during the next 16-20 hours.  Automobile industry experts suggest that the use of this technology during every scheduled maintenance will increase service life of diesel engines.

Removing water

Beside the presence of buildup and low cetane number, the quality of diesel fuel is also reduced by water. Water in the fuel adversely affects fuel equipment.  The greatest harm is caused to the high-precision plunger pairs of fuel pumps and injectors, which are subject to corrosion.

There are several ways for water to get inside diesel fuel.  Most often it can condense out of the air into fuel tanks of vehicles.  Sometimes refueling at unreliable gas stations is to blame.

In this case, there are also special additives that can remove water from fuel tanks and protect fuel equipment against corrosion.  The concentration of these additives does not exceed 0.5%, and they are usually used every 5-10 thousand kilometers.

Protecting fuel from sulfur

Sulphur is a very interesting component of diesel fuel.  On the one hand it contributes to the appearance of acidic compounds under certain engine operating conditions, and on the other hand it improves lubricating properties of diesel fuel. Therefore it is very important to refuel with petroleum product containing the optimum amount of sulfur, which will minimize its harmful impact and maximize the benefits.

Fighting deterioration of diesel fuel quality as a result of long-term storage

Very often, in order to insure themselves against seasonal price variations, owners of large vehicle fleets buy diesel fuel in bulk.  As a result of long-term storage, fuel can oxidize, darken and become contaminated with mechanical impurities.  In such case, it cannot be used.  Therefore, to restore normal performance, special equipment should be used – UVR type plants by GlobeCore.

They allow to remove hydrogen sulfide and unsaturated hydrocarbons from oxidized diesel fuel after long-term storage and reduce sulfur concentration and wax content. After processing with UVR plants, diesel fuel is clarified and does not re-oxidize or darken.

Diesel fuel is produced in refineries using special technological processes: primary and secondary processing of oil, as well as compounding (blending).

Primary processing is required to separate oil into individual fractions that have different boiling points.

Technically, this process is performed in special distillation columns.  One of the results of primary distillation are diesel fractions that are then used in diesel fuel production.

Secondary distillation is necessary to change the structure of hydrocarbons and chemical composition of oil.  Cracking is the main method which is the basis of secondary distillation. It allows to split large molecules into smaller molecules.  There is thermal cracking, catalytic cracking and hydrocracking.

In thermal cracking, molecule breakdown occurs under the influence of high temperature without the use of catalysts. Implementation of catalytic cracking requires catalysts, hydrocracking requires catalysts and hydrogen.

The resulting oil contains a lot of sulfur, which is removed by hydrotreatment.

Comparison of primary and secondary processing shows that secondary processing is characterized by a more complex and lengthy process, as well as higher cost.  But it is impossible to give up these processes, as they not only increase the yield of commercial fuel, but also significantly improve its quality.

The next stage of diesel fuel production is compounding. It is the mixing of the products obtained in the previous stages with additives.  Compounding is the final step in the production of diesel fuel, and it forms the quality of the final product which goes to the consumer.  GlobeCore USB-type plants are used for compounding.

When using ordinary methods of blending, fuel tends to break down into separate component.

The feature of the proposed equipment is that the use of injection method and hydrodynamic shock can increase cetane number of diesel fuel.  Also, separation of the product does not occur for at least 180 days.

Modern hydrodynamic (inline) mixing plants have proven themselves in industrial use as cost-effective, accurate and sustainable means of production of high-quality diesel fuel with optimum cost.

The achievable cost savings and improvement of profitability, compared to conventional technology of components mixing in blender tanks, can accelerate the return on investment up to 60% per year and provide a return on a project for a period of one year or less.

Hydrodynamic mixer uses the mixing process which allows to simultaneously feed all the components in a predetermined ratio to a common mixing header, which supplies the finished product to a storage tank.

The advantages of this technology include precise control of each component dispensing, significant reduction in mixing cycle duration and avoiding the use of mixing tanks to ensure homogenization of the final product.

During the mixing process in an inline mixer, the flow rate of each component is continuously adjusted to ensure that the final product that comes out of a mixing header has stable quality indicators according to a predetermined formulation.

Good performance of diesel engines requires high quality fuels.  But in practice, it is not so simple to find it.  The purchased fuel may be inadequate in terms of cetane number, may be contaminated and unadapted for use at different periods of the year.  In the case of use of low-quality diesel fuel, the condition of engine can deteriorate, which may lead to its failure over time.

To prevent such consequences, special additives have been developed that can perform different functions: increase cetane number, reduce the intensity of oxidation and corrosion processes, and reduce smoke content in exhaust gases.

Additives are differentiated by the way of addition: those that are added directly to the tank, and those that are added in the injection system and are not mixed with fuel.  Their effectiveness is somewhat different.  While the first type of additives cleans the entire fuel system, the second type restores only injection system.

Antigel

Increased wax content in diesel fuel leads to its high self-ignition capacity in summer, and thickening in winter as the temperature decreases.  Paraffin molecules begin to stick together, and it simply can’t pass through a fine filter.  The filtering device is clogged and does not let diesel fuel pass into the engine, which is highly undesirable.  Therefore, special additives, antigels, are added to fuel.  They prevent the formation of paraffin agglomerates and improve the properties of diesel fuel.

How to properly use additives?

It should be noted that the introduction of additives to diesel fuel is only possible if the fuel is in a liquid state.  In the case when fuel has already turned into a gel, it is not possible to restore it with additives.  It is recommended to carry out the mixing of additives at a temperature which is 10 °C higher than the pour point.

It is worth remembering that the effective concentration of an additive is always indicated on its package, and its increase will not lead to a further improvement of diesel fuel properties.

The effectiveness of additives also depends on the initial quality of diesel fuel.  That is why it is recommended to buy fuel only on approved gas stations.

Before adding several additives it is necessary to study carefully both their composition and characteristics of their action.  The fact is that you can purchase incompatible additives that could cause engine to seize.

Today there is a lot of controversy around additives for diesel fuel, and there is no general opinion on their effectiveness.  Therefore, the use of this method of improving diesel fuel is an entirely private matter of each car user.

Quality mixing of additives with diesel fuels

Industrial mixing of additives with diesel fuel requires special equipment.  Existing technologies are not able to fully ensure the quality of mixing, therefore, diesel fuel breakdown into individual components occurs in time.  Given this fact, GlobeCore company began the development of new equipment, which would be devoid of this shortcoming.  The scientific research of the company’s engineering department resulted in market appearance of USB-type plants.  The advantage of this equipment is that the use of injection method and hydrodynamic shock can increase the cetane number of fuel, and the breakdown of the resulting product does not occur for at least 180 days.

When selecting fuel for your car you should in the first place pay attention to its quality.  Perhaps the most significant of these indicators is its cetane number.  This parameter characterizes the ability of diesel fuels to ignite. In fact, it is the time required for combustion initiation from the moment of fuel injection into a cylinder.  The higher the cetane number, the smaller the time interval, and the higher engine power.

To some extent, cetane number can characterize ecological compatibility of diesel fuel because its combustibility depends on the hydrocarbon content.    For example, paraffin compounds ignite fairly rapidly, whereas aromatic hydrocarbons have the opposite property.

The use of diesel fuel with cetane number of less than 40 will result in the engine being more rough at idle.  This situation is fraught with rapid wear of bearings and other components, which emit the characteristic knocking sound during engine operation.

Determination of cetane number is based on its value equal to the percentage of cetane in the mixture thereof with alpha-methyl naphthalene in a fuel equivalent.  When calculating, the flammability of cetane is assumed to be 100%, and that of alpha-methyl naphthalene is 0%.  In the course of the tests the time of self-ignition of fuel is compared to that of the fuel equivalent.  Here is an example.  If the time of diesel fuel ignition in the combustion chamber is equal to ignition time of 40% mixture of alpha-methyl naphthalene with cetane, the cetane number of the tested fuel will be equal to 40.

Now the question arises:  what to do if the values do not meet the requirements?  Is it possible to increase cetane number?  The answer is definite:  yes, surely.

For this purpose, special additives are added to diesel fuel.  To obtain a homogeneous and nonvolatile product, a GlobeCore USB plants for mixing fuel and additives can be used.  This equipment is designed for mixing from two to five separate components, in particular poor quality diesel fuel with additives.

When using conventional methods of blending known today, fuel tends to break down when separate components are added to it.

The advantage of the unit is that the use of injection method and hydrodynamic shock can increase the cetane number of fuel, and the breakdown of the resulting product does not occur for at least 180 days.