Liquid Fuels – Their Characteristics and Safety Requirements

Liquid Fuels – Their Characteristics and Safety Requirements

Liquid fuels are combustible or energy generating molecules that take the shape of their container. Most of the liquid fuels are derived from fossil fuels mainly from crude oil. Main liquid fuels used in iron and steel plant (Fig 1) are (i) furnace oil (FO), (ii) low sulphur heavy stock (LSHS), (iii) light diesel oil (LDO), and (iv) high speed diesel oil (HSD).  Coal tar fuel is a byproduct liquid fuel produced during the cleaning of the raw coke oven gas in the coke oven and byproduct plant. Liquid fuels are normally used in the steel plant for the production of steam for power generation, for heating purpose in various furnaces of the plant, for injection in blast furnace, and for the operation of locomotives and the mobile equipment.

Liquid fuels used in a steel plant

Fig 1 Liquid fuels used in a steel plant

Liquid fuels are chemically stable and incompatible with strong oxidizers. They do not react vigorously with common materials but can react with oxidizing agents.

Liquid fuels are stored in a dry cool, well – ventilated area away from heat and flame. They are also kept away oxidizing agents.

Furnace oil

Furnace oil is a fuel oil which is dark and viscous. It is a residual fuel oil which is obtained by blending residual products from various refining processes with suitable diluent usually middle distillates to obtain the required fuel oil grades. The fuel oil grades are similar in nature and are being marketed under different specifications in various countries.

Furnace oil is used mainly in different furnaces of the steel plant, in power plant boilers for raising steam and for injection in the blast furnace. It is also sometimes used in air preheaters.

Furnace oil is having flash point above 66 deg C. Since this is a residual fuel, there has to be gradual filtration system to prevent the choking of filter and fuel nozzles. Due to its viscous nature, it is normally to be heated to improve its flowability and to a proper temperature for proper atomization. Usually for furnace oil, gear pumps are preferred to avoid cavitation problems.

Typically the calorific value of the furnace oil is 10,500 kcal per kg. It is generally stored in vertical as well as horizontal tanks, above ground or even underground in some cases. The dimensions and capacities of these tanks are predefined and are to meet the statutory requirements for fuel storages.

For direct burning, furnace oil is viscous as well as not suitable for complete combustion. It is pre-heated to 55 deg C onwards, depending upon application. The flow increases with temperature and it improves the combustion also. A water based scrubber is used in the exhaust chimney of furnace, which arrests considerable amount of carbon soot and improves the emissions.

FO is a complex mixture of hydrocarbons. Its CAS number is 68476-33.5 and UN number is 1223. It has a colour ranging from brown to black with a diesel like smell. It is a flammable liquid. Its boiling point ranges from 185 deg C to 500 deg C. Its vapour density is 3.0 to 5.0 (air=1). It is insoluble in water and is also lighter than water. It is a neutral liquid (neither acidic nor basic).

Typical properties of furnace oil are at Tab 1.


Tab 1 Typical properties of furnace oil
Sl. No.PropertyValue
1Inorganic acidityNil
2Ash, % wt., max.0.1
3Gross calorific value, kcal/ kg10350Typical
4Net calorific value, kcal/ kg9600Typical
5Density at 15 deg C0.96Typical
6Flash point deg C , min.66
7Kinematic viscosity, cst at 50 deg C125-180
8Sediment, % wt., max.0.25
9Sulphur, total % wt., max.4
10Water content, % v/v, max.1
11Pour point, deg C+ 27
12Cleanliness, ASTM D 4740No. 1Typical
13Micro carbon residue (MCR), % mass16Typical
14Asphaltenes, % mass9Typical

Low sulphur heavy stock

Low sulphur heavy stock (LSHS) is a residual fuel processed from indigenous crude oil. This fuel is generally used in lieu of FO in the same applications where the FO is suitable.

The main difference with LSHS and FO is the higher pour point, higher calorific value and lower sulphur content in LSHS as compared to FO.

Since LSHS is having pour point higher than the ambient temperature, it needs specially designed oil handling systems such as steam traced or electrically traced storage tanks, pipelines, pumps and filters.

LSHS is handled hot at all stages and is maintained at 75 deg C. Special care is also taken so that no ‘boil over’ of LSHS takes place in the storage tank.

The main advantage in the use of LSHS lies is its low sulphur content. The life of equipment used is extended since the extent of corrosion both at high and at low temperature, is reduced very much. Low sulphur content also gives it advantage from the point of environmental pollution since it produces lesser quantity of sulphur dioxide.

LSHS is a complex mixture of hydrocarbons. It has a colour ranging from brown to black with a diesel like smell. It is a flammable liquid. Its boiling point ranges from 185 deg C to 500 deg C. Its vapour density is 3.0 to 5.0 (air=1). It is insoluble in water and is also lighter than water. It is a neutral liquid (neither acidic nor basic).

The gross calorific value of LSHS is slightly higher than that of FO. Also LSHS is a low viscosity fuel oil at handling temperature when compared with the FO. It is measured at 100 deg C.

Typical properties of LSHS are at Tab 2.


Tab 2 Typical properties of low sulphur heavy stock
Sl. No.PropertyValue
1Pour point, deg C, max.66
2Flash point deg C, min.76
3Kinematic viscosity at 100 deg C, cst, max.50
4Relative density at 15 deg C0.93Typical
5Gross calorific value kcal/kg10550Typical
6Acidity inorganic, mg KOH/gmNil
7Ash % by wt., max.0.1
8Sediment % wt., max.0.25
9Sulphur % wt. max.1
10Water content % v/v, max.1
11Accelerated dry sludge, % by mass, max.0.1
12Spot test for cleanliness, Rating, max.Number 2

Light diesel oil

Light diesel oil (LDO) is having flash point above 66 deg C. It is a blend of distillate components and a small amount of residual components. It is used as a fuel in certain boilers and furnaces.

Typical properties of LDO are at Tab 3.


Tab 3 Typical properties of light diesel oil
Sl. No.PropertyValue
1Acidity, inorganic, mg KOH /gmNil
2Ash, percent by mass, max.0.02
3Ramsbottom carbon residue, % by mass, max.1.5
4Pour point , max.
a. winter12 deg C
b. summer21 deg C
5Copper strip corrosion for 3 hrs at 100 deg CNot worse than no.2
6Flash point, 0 deg C, min.66
7Kinematic viscosity, cst at 400  deg C2.5 to 15.7
8Sediment, percent by mass, max0.1
9Density at 15 deg C, kg/cum855Typical
10Total sulphur, percent by mass, max1.8
11Water content, percent by volume, max1
12Gross calorific value, kcal/kg10300Typical

High speed diesel oil

HSD oil is a complex mixture of hydro carbons. It is a brown coloured oily liquid with pungent smell. It has a pungent smell. Its vapour density is 3.0 to 5.0 (air=1). It is insoluble in water. Its specific gravity is in the range of 0.81 to 0.91 (water=1). It is a neutral liquid (neither acidic nor basic). HSD is flammable with a flash point ranging from 32 deg C to 96 deg C. Its auto ignition temperature is 256.6 deg C.

It is used in diesel engines of mobile equipment, diesel- generator sets, and locomotives.  It is the prime mover in a wide range of power generation and pumping applications. The diesel engines are usually of high compression and self-ignition engines. Fuel is ignited by the heat of high compression. HSD is normally used as a fuel in medium and high speed compression ignition engines (operating above 750 rpm).

Typical properties of high speed diesel are at Tab 4.


Tab 4 Typical properties of high speed diesel
Sl. No.PropertiesBharat stage 3 (Euro 3)Bharat stage 4 (Euro 4)
1Inorganic, mg KOH/gmNilNil
2Acidity total mg of KOH/gm max.0.20.05 (Typical)
3Ash % by mass, max.0.010.01
4Carbon residue(Ramsbottom) on 10 % residue percent by mass, max0.30.3
5Cetane number min.5151
6Cetane index min.4646
7Pour point, deg C, max.
a.  winter33
b.  summer1515
8Copper strip corrosion for 3 hrs. at 100 deg CNot worse than No. 1Not worse than No. 1
9Distillation % v/v recovered
a.  at 360 deg C min.9595
b.  at 370 deg C min.
10Flash Point
a.  Abel, deg C, min.3535
11Kinematic viscosity, cst at 40 deg C2.0 to 4.52.0 to 4.5
12Sediment, % by mass, max.0.05
13Total contamination, mg/cum, max.2424
14Density at 15 deg C kg/cum820 – 845820 – 845
15Total sulphur, mg /kg, max.35050
16Water content, % v/v, ISO 3675 or 12185
17Water content, mg/kg, max., ISO 14596 or 8754200200
18Cold filter plugging point (CFPP), max.
a.  Winter, deg C66
a.  Summer, deg C1818
19Total sediment, mg per 100 ml, max.1.51.5
20Oxidation stability gm/cum max.2525
21Polycyclic Aromatic Hydrocarbon (PAH), % by mass, max.1111
22Lubricity corrected wear scar diameter (wsd 1.4) at 600 deg C, microns, max.460460
23Oxygen content,% by volume, max0.60.6

Typical gross calorific value of diesel oil is around 10,800 kcal per kg.

Health hazard and safety issues with liquid fuels 

The combustion products (carbon mono oxide, carbon di oxide, and sulphur di oxide) of liquid fuels are hazardous in nature.

Routes of entry may be through inhalation, ingestion, skin, eye contact and mucous membrane. Effects of exposure and symptoms include dizziness, headache, spontaneous vomiting, irritation of mouth, gastro-intestinal effect, and oil acne.

Permissible exposure limit is 5 mg/cum while threshold limit value is 10 mg/ppm.

In case of inhalation, the affected person is removed to fresh air and artificial respiration is given if necessary. In case of ingestion, vomiting is not to be induced. The contaminated clothing is to be removed and all affected skin is to be washed thoroughly with soap and water. In case of eye contact, eyes are to be irrigated with copious amounts of water.

Liquid fuels are to be stored at cool, ventilated and specified area. During handling and storage, contact with liquid or vapours is to be avoided. Gumboots are to be used while handling the product. In case of spillage, the fuel is not to be pushed to drainage but it is to be recovered by using absorbent materials such as saw dust, sand and land fill etc.

The firefighting media to be used is foam, dry chemical powder (DCP) and CO2. Water spray is to be used to cool the containers if exposed to fire.

The following are the dos and don’ts in case of liquid fuel leaks and fires.

  • In case of leaks monitor % LEL, restrict ignition sources. Stop traffic/vehicular movements and dilute vapour cloud with water spray.
  • Look for wind direction.
  • Approach from upwind side.
  • If caught on downwind, move perpendicular to wind direction and assemble at nearest safe assembly point.
  • Cordon off the area.
  • Use self-contained breathing apparatus (SCBA) set in case of fire.
  • Contain leaking liquid on sand or earth.
  • Do not panic.
  • Do not enter without knowing the wind direction.
  • Do not approach leaking / affected area without proper respiratory protection.
  • Do not approach from downwind direction
  • Do not run.
  • Do not move along or opposite to the direction of wind.
  • Do not allow unauthorized personnel.

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