Issue 28/2014 - Analysis of the hazards and causes of low-quality marine residue fuel oil

Analysis of the hazards and causes of inferior marine residue fuel oil

□ Yantai China Combustion Marine Fuel Supply Co.
, Ltd.
Liu Guanghong

First, the polarization of standard "cleaning" and the deterioration of raw material
quality

In recent years, the quality of domestic trade marine residue fuel oil has shown two opposite trends: first, the standard has developed in the direction of "cleaning"; Second, the quality of harmonized raw materials tends to deteriorate
.

At present, China's quality requirements for domestic trade marine residue fuel oil are getting higher and higher
.
Table 1 shows the indicator changes of
180# fuel oil.
It can be seen from the table that the indicators of oil products are getting closer and closer to international standards, and the trend of national "clean" production requirements is very clear
.

Although the index requirements are becoming more and more stringent, the actual production of marine residue fuel oil blending in China is far from the same
.
With the increasingly fierce market competition, some producers one-sidedly pursue the maximization of profits, in the blending and production of marine residue fuel oil is widely the phenomenon of "wiping the edge", using some non-petroleum hydrocarbon chemical raw materials for blending, to produce inferior marine residue fuel oil
.
These inferior fuel oils can meet the technical requirements of the "table indicators" in the national standard, but in the requirements of blending raw materials, it greatly violates the two most basic principles
of the national standard "fuel should be a uniform mixture of hydrocarbons obtained from petroleum refining" and "the term petroleum includes tar sands oil and shale oil".
These inferior fuel oils are used in diesel engines, bringing more and more hazards
.

The production method of marine residue fuel oil in China's market has long been blended from the traditional straight distillation and vacuum distillation residue oil as the basic raw material, combined with the heavy diesel fraction on the production line, to the oil slurry and shale oil components as the main raw materials, a large amount of solvent oil, coal tar components, and even mixed with ethylene tar components
.
The basic properties, advantages and disadvantages of various blended raw materials are briefly described in Table 2
.

Table 1 Changes in the main indicators of the 180# fuel oil standard

Index Unit GB/T17411 GB/T17411 ISO-8217:2010Name -1998 -2012
RMG180
CCAI value No requirement Maximum 860 or 870 Maximum 870
acid value mgKOH/g No requirement Maximum 2.
5 Maximum 2.
5 sulfur content %(m/m) Maximum 5.
0 Maximum 3.
5
Regulatory requirements
Residual carbon %(m/m) Max.
20(RMF) Max.
18(RMG) Max.
18Vanadium
mg/kg Max.
200(RME), Max.
150(RME), Max.
350
500(RMF) 350(RMF)
Aluminum+silicon mg/kg Max.
80 Max.
60 Max.
60
Used lubricating oil No requirements Required There is a requirement
for calcium + phosphorus or calcium + zinc

Table 2 Basic properties, advantages and disadvantages of various blended raw materials

Raw material name Advantage Lack of
point oil slurry Low freezing point Poor ignition, large catalyst particles
, poor storage stability, viscosity cracking residue oil Good fluidity Poor storage stability, poor ignition
, poor thermal stability shale oil Good fluidity, low viscosity Contains more olefins, poor


oxidation stability coal tar Good fluidity, mainly Polycyclic aromatic hydrocarbons, Easy to further
aromatic hydrocarbons solvent-based strong oxidation condensation into sludge, poor ignition property
, low calorific value, heterocyclic and heterogeneous elements polyethylene
tar low viscosity, metal-free low calorific value, non-flammable, high asphaltene
content, easy coking, poor oxidation
stability

Second, the harm that inferior fuel oil may bring

1.
Flocculation occurs in the sedimentation tank Marine residue fuel oil directly flocculates when it encounters the original remaining oil in the sedimentation tank, and when the flocculation is serious, the oil cannot be pumped to the next stage for use
.
The investigation found that there was no problem with the blended fuel when used alone, the operation was normal before the tanker was refueled, and the flocculation problem was more common when
different batches of new and old fuel were mixed.

In order to find the cause of the problem, the ASTM-D7061(06) test method was further used to test the dissolution equilibrium state
of an oil sample in a case.
When the separation index of the two oils is determined separately, the separation index of the new oil of the oil supplier is 1.
058 and the separation index of the old oil of the receiving party is 1.
527, both of which are within the value range of safe use (the guiding value of international practice is that the separation index exceeds 5 is a bad state).

After mixing 90% of new oil with 10% old oil, the test separation index reached 5.
864, which was obviously incompatible
.
The test shows that although the surface index of the blended oil is qualified, due to the potential dissolution balance problem of its blended components, different blended components will be encountered at any time, forming incompatible group components, resulting in flocculation, which will bring problems
to the transmission of the diesel engine system.
In the follow-up investigation test, it was found that the sedimentation separation index in some sedimentation tanks reached 10.
952
.

The main cause of the dissolution balance problem is the change
of the blending raw material.
Before 2008, there was no problem of dissolution balance, and after 2008, when it encountered oil products blended with coal tar series raw materials, it brought about the problem
of dissolution balance.

2.
Clogging filters and oil separators When inferior marine residual fuel oil is transported to the primary and secondary filters and oil separators, dirty blockages such as serious blockage of the filter and even the blockage of the oil separator will
occur 。 There are many reasons for dirty blockage, and the main reasons related to oil factors are: (1) poor low temperature cleanliness index of oil products, such as excessive total sediment, directly blocking the filter; (2) Even if the total precipitate meets the standard, but the dissolution balance is uncertain, the flocculation filter blockage phenomenon may still occur; (3) Due to the uncertainty of coal tar series raw materials, in the process of continuous heating and transportation, the aromatic hydrocarbons, heterocyclic nitrogen, phenyl mercaptan, etc.
contained in the components will react and form sediment, which seriously affects the work of
the oil separator.

3.
High-pressure nozzle plunger sintering, blockage There are four reasons for the sintering and blockage of high-pressure nozzle plunger: (1) The viscosity of 180# fuel oil blended by coal tar, solvent oil, etc.
(high aromatics, high solubility) is often too low, such as 50 °C viscosity is lower than 50cSt, so that its normal heating (about 120 °C) through the high-pressure nozzle plunger, due to too low viscosity or no viscosity (often lower than 8cSt) and dry friction, friction wear makes the nozzle and plunger need to be replaced frequently
。 (2) If the oil has oxidized and coked at the temperature of the high-pressure nozzle, it will directly block the nozzle
.
(3) When the viscosity temperature characteristics of the blended oil product do not conform to the law of petroleum hydrocarbons, the viscosity is as high as 30~40cSt at high temperature, and the nozzle is directly blocked; Or due to excessive viscosity and poor atomization, the diesel engine burns poorly, and large particles of oil accumulate near the nozzle, which also causes the blockage
of the nozzle.
(4) The oil itself has poor compatibility with the raw materials, is seriously layered in the daily oil tank, does not match the transportation combustion process with heating, or the local viscosity is too large, and can not form effective atomization particles, resulting in local blockage, or even blocking to the plunger or nozzle
.

4.
Poor fire, poor combustion, blocked exhaust valve, black smoke, etc.
In addition to mechanical problems, the lag period is prolonged due to poor combustibility, poor ignition or poor atomization effect of the oil, resulting in aftercombustion, blocked exhaust valve and black smoke
.
Practice has proved that the carbon aroma index CCAI value of oil is an effective index to measure the ignition quality of marine residue fuel oil, and its effect is equivalent to the cetane number
in diesel.
International studies have shown that when the CCAI value is below 850 (the current index is below 860 or 870), the fuel oil matches the lag period of the low-speed diesel engine well, and the combustion tends to be complete
.
When the CCAI value is about 850 in practical experience, the corresponding cetane number is 29~31; When the CCAI value is about 875, the cetane value is 18~20
.
A high CCAI value indicates a high aromatic content, which means a low cetane number and poor
ignitability.
It can be seen that those marine residue fuel oils with high density and low viscosity do not meet the highest standards of CCAI value, which will inevitably cause poor combustion, aftercombustion, blocked exhaust valves, black smoke and other phenomena
.
If the CCAI value exceeds 880, it may not catch fire
.

In addition, if there are defects in other aspects of the oil index, there is also a hazard
.
Defects in the low temperature cleaning performance of oil products such as total sediment, moisture, metal content, medium and low temperature direct filtration will directly affect whether the oil can be transported smoothly, and may cause downtime, poor working conditions, power degradation or friction and wear
due to blockage.
For example, the high temperature cleanliness of oil products such as residual carbon, ash and other indicators exceed the requirements, which brings direct problems such as
more carbon formation, hard carbon formation, high probability of blockage, ash accumulation in the exhaust valve, and affecting the transmission of combustion airflow.

3.
Opinions and suggestions on eliminating harm

1.
Control the viscosity-temperature characteristics of fuel oil According to the heating procedure of the diesel engine and the normal entry temperature, two viscosities of 50 °C and 100 °C are set up to ensure the basic requirements of the viscosity-temperature characteristics, and the viscosity-temperature characteristics of qualified oils do not change abruptly, and the viscosity changes
within the allowable range.
It is best for oil blending enterprises to configure high-temperature viscosity experimental equipment that can detect 110~150 °C per interval of 5 °C, and test the viscosity range of oil products when the diesel engine enters the temperature, in general, the medium and low speed diesel engines are controlled at 9~16cSt, and the ultra-low speed is controlled at 12~24cSt
.

2.
Extended investigation of the compatibility of fuel oil Timely sampling of different batches of fuel oil, and tracking of customized samples of different proportions to investigate compatibility
.
The inspection of layered density, moisture or spot test, effective special test, etc.
is taken to exclude the incompatible and unstable situation of
oil.
Test the separation index if necessary to confirm the dissolution equilibrium state
.

3.
Medium and low temperature simulation test for blended products The main purpose of the test is to understand the properties of unstable components in blended raw materials, and master the temperature conditions for their formation of flocculation or blockage and the temperature conditions
for the formation of impurities.

4.
Control the calorific value of residual marine fuel oil Ensuring the calorific value level of fuel is a necessary condition
to ensure the combustion performance of oil.
The general control value
of the Shanghai Fuel Oil Futures Exchange is usually used.
By controlling the calorific value, the composition of the raw material can be traced backwards at the same time, unless mineral oil components and other undesirable components are involved
.

5.
Emphasize the control of the CCAI value of fuel oil Blending fuel oil requires full attention to the C aroma index
.
The world has been accustomed to using this indicator to measure the quality of fuel oil, and controlling this value can ensure the content
of hydrocarbon mixtures or combustion better components in the oil from the side.

6.
Investigate the correspondence between high temperature friction and high temperature corrosion The main purpose is to obtain the influence of metals, impurities, acids and alkaline substances in fuel oil on the stability of oil through experiments, so as to further take corresponding filtration measures to reduce the harm
of bad components to oil quality and diesel engine use.