RB-21 FACTORS TO CONSIDER WHEN USING LOW-SULPHUR FUEL OIL IN
This law implements the European Council Directive 1999/32/CE of 26 April 1999, regarding the reduction of the sulphur content of certain liquid fuels, in view of the fact that SO2 (sulphur dioxide) emissions directly affect human health and the environment, while contributing significantly to the problem of acidification in the European Community.
The planned reduction in the sulphur content of fuel oil will allow cogeneration plants to reduce considerably their emissions of SO2 and SO3 in exhaust gases, thereby contributing to fulfilling the objectives for human health and environment that the Directive and the Spanish legislation pursue.
A collateral aspect of the change of fuel Nº 1, currently containing 2.7% sulphur, to a fuel with 1% sulphur, is its influence on the operation of cogeneration plants with Diesel engines. Certain operational adjustments may be required to adapt to the new fuel oil. However, it must be stated from the outset that it is erroneous to suppose that the lower sulphur content in fuel oil should imply less corrosion at high temperatures on exhaust valves, turbochargers and other hot components of the exhaust gas circuit, since the level of corrosion will be similar to the present level, given that this type of corrosion basically depends on the presence of vanadium and sodium in the fuel oil, as explained below.
The consequences of the lower sulphur content in fuel oil will be limited, in practical terms, to the following aspects:
- Reduced SO2 emissions in exhaust gases (maximum 1,700 mg/Nm3 at 3% O2) in accordance with the Spanish Law R.D. 287/2001.
- Reduced corrosion at low temperatures in the areas of the exhaust gas circuit with temperatures lower than 150ºC (flues and chimneys), due to less condensation of sulphuric acid, as levels of SO2 and SO3 are reduced.
- The requirement for engine oil of lower TBN, due to the reduced presence of SO2 and SO3 in combustion, resulting in reduced formation of calcium sulphate. Although this substance is not corrosive, it nevertheless contributes to the accumulation of residues in the exhaust gas circuit. It will be necessary to change the type of engine oil to one with a lower TBN, while maintaining its detergency and dispersancy at the original level. This implies a reduction in the sulphated ash content of the oil.
We will now review the available options for obtaining fuel oil that is low in sulphur.
A) The Spanish market currently supplies “Fuel No. 1 BIA” (already used regularly in some co-generation plants) which complies with the requirement for maximum sulphur content of 1%, but whose physical and chemical characteristics are practically identical to those of the Fuel No. 1 currently used in the majority of plants running on fuel oil. The following main characteristics should be taken into account:
- Cinematic Viscosity (24-25 cSt at 100ºC in both cases)
- Carbon Residue (maximum 15% in both cases)
- Asphaltenes (approx. 1/3 of the total carbon residue)
- Vanadium (maximum 200 ppm in both cases)
- Sodium (maximum 50 ppm in both cases)
These parameters virtually coincide with the specifications for both ISO-F RME-25 and CIMAC E-25 Marine Fuel Oils, except in that the sulphur content is lower. (Both specifications stipulate a maximum of 5%, in comparison with 2.7% and 1% for Fuel No.1 and Fuel No.1 BIA respectively.)
Even though the type of Fuel No. 1 BIA currently supplied has a slightly lower level of impurities than Fuel No. 1, it has nevertheless caused corrosion problems in cogeneration plants where it has been used (see information below), except when treated with the additive “rb bertomeu” beco F1/ASF in order to minimise these problems.
B) Some suppliers of fuel oil in Spain are making preparations and initial proposals to cogeneration plants regarding the possible supply of a new fuel oil that complies with the specification of 1% sulphur, but which has a cinematic viscosity of between 35-37 cSt at 100ºC, while maintaining the maximum limits of impurities as stipulated for the current Fuel No. 1 and Fuel No. 2. This new low-sulphur fuel will therefore fall within the actual levels of impurities of fuels No.1 and No.2 when de-sulphured or obtained from crude oil with less sulphur. The maximum specifications would be those detailed in the table below, equivalent to ISO-F RME-25 or CIMAC E-25, de-sulphured but with the viscosity increased to the level of RMG-35 ISO-F specification or CIMAC G-35 (35 cSt at 100ºC)
- Cinematic Viscosity (35-37 cSt at 100ºC)
- Carbon Residue (maximum 15%)
- Asphaltenes (approx. 1/3 of the total carbon residue)
- Vanadium (maximum 200 ppm)
- Sodium (maximum 50 ppm)
This new low-sulphur fuel oil would be somewhat cheaper than the current Fuel No. 1 BIA, at the expense of creating additional operational difficulties in its utilisation, arising from its greater viscosity and possibly higher actual levels of impurities. In practice, its real content in metallic impurities (i.e. vanadium, sodium and others), carbonaceous residues and asphaltenes are certain to lie within the common values of Fuel Nº1 and Fuel Nº2. Therefore, the following immediate effects are to be expected:
b-1) Corrosion at high temperatures : at least to the extent found at present with Fuel-oil No. 1
b-2) Viscosity at atomisation : as it is more viscous, it will need to be heated more in order
to attain the same viscosity for atomisation.
b-3) Formation of fuel sludge : at least the quantities formed at present with Fuel-oil Nº 1
In any case, the fuel oil (with maximum 1% sulphur) to be used from the beginning of next year may be either the current Fuel No. 1 BIA or the new low-sulphur fuel oil with greater viscosity. Both fuels will invariably involve the familiar operational difficulties of the current Fuel No.1 and No.1 BIA, in terms of the consequences arising from their physical and chemical characteristics as well as their content in impurities. The only difference will be detectable in SO2 emissions and the resultant corrosion at low temperatures caused by SO2 and SO3 in the cold areas of the exhaust gas circuit (mainly flues and chimneys), as well as the amount of deposits of non-corrosive calcium sulphate in the exhaust gas circuit.
We will now review the series of problems that have been minimised in many plants by using the additive “rb bertomeu” beco F1/ASF.
CORROSION AT HIGH TEMPERATURES:
As is well known, corrosion at high temperatures in Diesel engines, occurring mainly on exhaust valves and turbochargers, are due to two main causes:
1- The formation of sodium vanadates with a low melting point, which are corrosive. These compounds will be formed with either of the two fuel oils that may be used (Fuel Nº 1 BIA or the new low-sulphur fuel oil) since both contain Vanadium (V) and Sodium (Na), although they will be formed in greater quantity if the new low-sulphur fuel oil with high viscosity is used (as it presumably contains more V and Na).
2- The formation of sodium sulphate, which is corrosive at high temperatures. This compound will continue to be formed, regardless of the sulphur content of the fuel oil, since the comparatively low sodium content in the fuel oil means that a sulphur content of less than the 0.1% is sufficient for this corrosive compound to be formed.
In order to prevent these corrosive effects on valves, turbos and other parts of the exhaust gas circuit that operate at high temperatures, the additive treatment currently employed should continue to be applied to the new fuel oil to be used from 01-01-03: the “rb bertomeu” beco F1/ASF additive.
Regarding a possible changeover to the currently available Fuel-oil Nº 1 BIA, experience has demonstrated that cogeneration plants that have used or that now use the current Fuel No.1 BIA have similar problems of corrosion at high temperatures as the plants that use Fuel No.1. In this respect, details are provided below of plants (all of them are clients of rb bertomeu S.L.) that can be consulted on their experience in the use of Fuel Nº1 BIA and Fuel No.1, either directly or in other plants belonging to the group.
MINERA DE SANTA MARTA – Belorado (Burgos) Spain
Contact: Mr. Juan A. Cejalvo – Plant Manager – Tel. 947 585 099
Deutz engines type BV 16 M 640
Fuel No. 1 BIA used previously; Fuel No. 1 currently used, treated with additives from “rb bertomeu”, except for certain periods without additive treatment, when the effects of corrosion were observed.
MINERIA Y TECNOLOGIA DE ARCILLAS – Orera (Zaragoza) Spain
Contact: Mr. Luis C. Dieste – Plant Manager – Tel. 976 892 250
Deutz engines, type TBD 645 L9
Fuel Nº 1 BIA used, treated with additives from “rb bertomeu”
COGENERACION APROFURSA (ABENER-ABENGOA) – Alcantarilla (Murcia) Spain
Contact: Mr. Jesús Moreno Vigara – Technical Coordinator of Operation and Maintenance – Tel. 954 937 176
Deutz engines type BV 16 M 640
Fuel Nº 1 BIA used, treated with additives from “rb bertomeu”, after having tried other brands of additives, which did not provide the desired results.
These plants have served to verify that the problems of corrosion at high temperatures in Diesel engines (mainly on valves and turbos) are similar when using either Fuel No.1 or Fuel No.1 BIA with their current specifications; in both cases, treating the fuel with the “rb bertomeu” beco F1/ASF additive will solve these problems.
If the changeover is made to the new low-sulphur fuel oil with high viscosity, the problems of corrosion at high temperatures will be at best equivalent to those involved with the current fuel oil No.1. Furthermore, these problems may be exacerbated if levels of metallic impurities are increased to the maximum limits specified by the supplier (as these metals act as a catalyst for corrosion at both high and low temperatures). In both cases, the additive for fuel oil “rb bertomeu” beco F1/ASF is effective in preventing this problem, which would undoubtedly reappear if the new fuel oil were not treated.
We have compiled ample data on the problems of corrosion at high temperatures that have been prevented or minimised in cogeneration plants with the use of the additive “rb bertomeu” beco F1/ASF.
It may therefore be concluded that, in order to prevent the problem of corrosion on exhaust valves and turbos, it is necessary to continue treating fuel oil with the additive “rb bertomeu” beco F1/ASF, whether changing over to the current Fuel Oil No. 1 BIA or to the new low-sulphur fuel oil with high viscosity.
HEATING THE FUEL OIL:
In cogeneration plants with Diesel engines running on fuel oil, the fuel is normally heated until it reaches a cinematic viscosity of 10 – 15 cSt before being injected in the engine.
Both the current Fuel No. 1 and the current Fuel No. 1 BIA have a cinematic viscosity of 24-25 cSt at 100 ºC, and should therefore be heated to a temperature of between 133 and 117 ºC approximately. (Tables of Viscosity of fuel oil according to temperature.)
Therefore, a changeover from the Fuel No. 1 currently used to Fuel Nº 1 BIA at its current specification will not involve any change in the requirements of warming up the fuel so that it reaches the desired degree of atomisation.
On the other hand, a changeover from the Fuel No. 1 currently used to the new low-sulphur fuel oil with greater viscosity (35-37 cSt at 100ºC), would indeed have significant effects on the heating equipment and the requirement for heating.
By way of an example, the new low-sulphur fuel oil with a cinematic viscosity of 35 cSt at 100ºC, should be heated to a temperature of between 149 and 133ºC in order to achieve a viscosity of 10-15 cSt. (Tables of Viscosity of Fuel Oil according to Temperature.) In contrast with the current situation with Fuel No.1 or Fuel No.1 BIA (both having 24-25 cSt), this involves analysing the following series of problems:
a) The heating capacity of the current heating system, given that it will be necessary to increase the temperature by 16ºC on average when heating the fuel oil.
b) The series of problems arising from the accelerated formation of residues due to the rapid ageing of the fuel oil at temperatures close to 150-152ºC. (These temperatures may be reached sporadically, or they may actually be necessary if the viscosity surpasses 35 cSt even slightly.)
b-1) Increased wear on injectors and pump components.
b-2) Increased levels of incrusted residues on the heating system itself, leading to a progressive reduction in its heating capacity.
When evaluating the utilisation of the new low-sulphur fuel oil with greater viscosity it is important to take into account the new specifications of that fuel oil, in terms of its heating, as well as the operation of injection pumps so as to obtain good atomisation of the fuel. These questions raise the following significant points:
1- Cinematic viscosity
2- The content in asphaltenes
In any case, the use of the additive “rb bertomeu” beco F1/ASF, which already produces good results with the specifications of the current Fuel oil No.1, will be even more critical in proportion to the increase in both the aforementioned parameters, because it homogenises the fuel and helps to obtain optimum levels of fluidity and atomisation, thereby improving combustion.
In view of the fact that the series of problems involved in the use of the current Fuel oil No.1 in co-generation plants will not be remedied by changing over to either of the two types of low-sulphur fuel oil soon to be available (either the current Fuel oil No.1 BIA or the new low-sulphur fuel oil), on the contrary, these problems will remain or be exacerbated if the second alternative is chosen, we therefore believe it is apt to recall the financial benefits currently obtained with the use of the additive for fuel oil “rb bertomeu” beco F1/ASF, in the co-generation plants where it is employed:
· Reduced fuel oil sludge (average 70%)
· Reduced fuel consumption (minimum 1.5%)
· Reduced costs of replacing exhaust valves (between 69% and 88%)
· Reduced exhaust valve blowouts (average 80%)
· Reduced repair costs for turbochargers
· Increased TBO for exhaust valve maintenance (between 50% and 100%)
· Increased TBO for cleaning turbochargers (between 50% and 100%)
· Increased operational life for exhaust valves and turbochargers by preventing corrosion (minimum 100%)
· Reduced requirements of cleaning for filters, depuration systems and pipes.
· Reduced wear on components of the injection system and extra fuel savings (between 0.9% and 1.2%)
All the aforementioned benefits are highly significant when the plant is in operation for around 4,000 hours per year as is currently the case. However, if an operational schedule of 8,000 hours per year is required, it is necessary to add the benefits derived from fewer stoppages due to breakdowns, cleaning and non-scheduled maintenance.
In fact, when the plant operates for 4,000 hours per year, the tasks of cleaning and repair are carried out at weekends and/or on days when the plant is not required to be in operation. However, when continuous operation (8,000 hours per year) is required, as scheduled in the majority of plants, any unscheduled stoppage, whether due to breakdown, blowouts or cleaning, causes a reduction in the service factor, and consequently, a reduction in the annual production of energy. This leads to financial losses, which could be considerable if there is the obligation to pay some sort of penalty to the electrical company supplied by the plant, in addition to the loss of energy production.
In summary, there are two hypotheses regarding the fuel to be used from 01/01/2003 in relation to the additive treatment of the fuel oil. In both scenarios, the same additive treatment should be maintained in order to prevent the problems of corrosion at high temperatures, to minimise fuel oil sludge, to save fuel, to avoid breakdowns and stoppages, etc.
A) If it is decided to use the current Fuel No. 1 BIA with a viscosity of 24-25 cSt, it will be necessary to continue the additive treatment with the “rb bertomeu” beco F1/ASF additive.
B) If it is decided to use the new low-sulphur fuel oil with a viscosity of 35-37 cSt and a higher content in impurities, this should also be treated with the “rb bertomeu” beco F1/ASF additive, as the active ingredients are sufficient for the maximum content in V and Na as specified by both ISO-F RME-25 and CIMAC E-25.
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