Residual fuels

Question 1

residual fuel oil is

Answer 1

the third most important petroleum product after gasolines and gas oils

Question 2

Material remaining after maximizing light and middle distillate production (i.e., atmospheric or vacuum resids) are blended with

Answer 2

a minimum amount of distillates to produce salable

fuel oils.

Question 3

Refineries generally aim at minimizing the production of fuel oil, the lowest valued petroleum product,

Answer 3

to maximize their refining margins.

Question 4

Fluid catalytic cracking units

Answer 4

FCCUs

Question 5

The average refinery production of fuel oil has come

down from 20 vol % (percentage by volume) of the crude oil 20 years ago to

Answer 5

approximately 14 vol %

at present

Question 6

Residual fuel oil is

Answer 6

a bottom-of-the-barrel product blended from the vacuum residue of crude oil distillation, and the residual products from various refining processes, to make cheapest possible fuel.

Question 7

Viscosity ranges from

Answer 7

450 cSt to 180 cSt at 120F.

Question 8

The flash point is typically

Answer 8

above 150F.

Question 9

Since residual fuel oil is thick and viscous

Answer 9

it must be heated before use to reduce its viscosity for easy combustion

Question 10

Residual fuels are widely used in

Answer 10

industrial applications requiring heat generation

for steam generation in power plants and in the boiler “lighting up” facility in every coal-fired power plant where they initiate the combustion process. Among other uses are open hearth furnaces, soaking pits in the iron and steel industry, rotary kilns in cement and lime industry, and for firing heaters for petroleum refining and the manufacture of petrochemicals.

Question 11

A petroleum refinery may consume

Answer 11

8 to 10 percent of its throughput as liquid refinery fuel depending on the complexity of the process

Question 12

Residual fuel oils are used in industries such as

Answer 12

cement, glass, and paper. It is used as a feedstock in fertilizer manufacture where it generates hydrogen by a partial oxidation process.

Question 13

The marine industry is

Answer 13

the largest single consumer of residual fuels (bunker C fuel), consuming almost 33 percent of the world’s total residual fuel oil production

Most of the fuel oil used by the world’s merchant fleet and other naval ships is residual fuel oil

Question 14

DIESEL ENGINES

Answer 14

The shipping industry generally uses residual fuel oil for economic reasons. The world’s shipping fleet is powered mainly by slow and medium-speed diesel engines. A smaller percentage use marine diesel.

Question 15

DIESEL ENGINES 2

Answer 15

It is estimated that more than 95 percent of the world’s shipping fleet is powered by slow speed (less than 300 r/min) and medium speed (300 to 1000 r/min) diesel engines. Unlike high speed (more than 1000 r/min) diesel engines that use automotive diesel as fuel, low and medium-speed diesel engines use residual fuel oils.

Question 16

A large merchant ship powered by diesel engines may consume

Answer 16

150 tons/day heavy fuel oil and may typically carry 3000 to 4000 ton of fuel oil in tanks

Question 17

Two-stroke low-speed diesel engines are capable

Answer 17

of burning the lowest and cheapest quality commercially available residual fuels.

Question 18

Reducing the speed of an engine to half is known to

Answer 18

increase engine life four times

Slow-speed diesel engines are
capable of attaining efficiencies of more than 50 percent.

Question 19

STEAM BOILERS

Answer 19

Residual fuels are widely used both in stationary and mobile steam boilers of all sizes. No particular
problem is encountered in its burning. However, in high-pressure steam boilers that also operate at
high temperatures, the fouling of boiler tubes may be encountered due to the presence of vanadium
and other metallic compounds in the fuel oil ash

Power generation companies use slow-speed diesel
engines in preference to medium-speed diesel engines and steam turbines because of their better
efficiencies and longer engine life.

Question 20

GAS TURBINES

Answer 20

A gas turbine extracts energy from the flow of hot gases produced by the combustion of gas or fuel
oil.

It has an upstream air compressor coupled to a downstream turbine and a combustion chamber
in between.

Question 21

GAS TURBINES 2

Answer 21

Compressed air is mixed with fuel and ignited in the combustion chamber. The resulting
gases pass over the turbine blades, spinning the turbine and mechanically powering the compressor.

Question 22

GAS TURBINES 3

Answer 22

Finally, gases pass through the nozzle, generating additional thrust, and pass to the atmosphere. Gas
turbines are used on high-speed naval boats, ships, locomotives, and in small power plants.

Question 23

GAS TURBINES 4

Answer 23

Gas turbines
have very high power-to-weight ratio compared with reciprocating engines but have a high initial
cost. The inherent simplicity of gas turbines makes this type of power plant attractive for many
applications.

Question 24

GAS TURBINES 5

Answer 24

A simple cycle gas turbine for power generation requires a smaller capital investment
and actual construction can take as little as a few weeks, compared with years for base power plants.
Gas turbines can be turned off and on within minutes, supplying power during peak demand.
However, simple cycle gas turbines are less efficient than combined cycle turbines; they are generally
used as peaking power plants.

Question 25

RESIDUAL FUEL OIL SPECIFICATIONS

Answer 25

Marketing specifications have been established by a number of agencies to assure the satisfactory operation of industrial and marine equipment utilizing heavy fuel oils. These specifications include ISO-8217, ASTM D-396, BS 2869, and CIMAC (Conseil International des Machine a Combutiou).

Question 26

Marine Fuel Oils

Answer 26

There are two basic types of fuel oils; distillate and residual. A third type of fuel oil is a mixture of the two basic types, commonly known as “intermediate” (Table 6-2). Distillate fuel oils are made of diesel fractions of crude oil fractionation, whereas residuals are blended from distillation residue such as atmospheric or vacuum bottoms with diesel boiling range cutter stock to reduce their viscosity to specification.

Question 27

In marine industry, distillate fuels are called gas oil or marine gas oil. For example, as per ISO 8217 specifications, marine fuel grades

Answer 27

DMX, DMA, DMB, DMC are marine gas oils.

Question 28

Residual fuels are called marine fuel oils or residual fuel oils (Table 6-1). Specifications for marine fuels use the first letter “D,” signifying or “R,”

Answer 28

“distillate fuel,” signifying “residual fuels.”

Question 29

Residual fuels | are designated by letters A to H, K and L, and a number signifying

Answer 29

viscosity limit

Question 30

For example, | RMA -30

Answer 30

is “Residual Marine Fuel A” with a maximum viscosity of 30 cSt at 50C.

Question 31

One important difference between land-based distillate fuels and marine fuels from an environmental perspective is sulfur content.

Answer 31

Land-based fuels are generally required by environmental regulations to have lower sulfur levels than equivalent marine fuels.

Question 32

DMA is a common fuel for

Answer 32

tugboats, fishing boats, crew boats, drilling rugs, and ferry boats. Oceangoing ships that take residual fuel oil bunker also take distillate fuels for use in auxiliary engines and sometimes in port areas. The most common residual fuels are grades with a kinematic viscosity of 180 and 380 cSt at 122F. All marine fuels for safety and insurance reasons are required to have a minimum flash of 140F (60C).

Question 33

Ash Content

Answer 33

Compared with coal, residual fuel oils have a very low ash content and no ash-handling equipment is required. However, certain elements present in fuel oil ash may cause problems in furnaces where very high temperatures are encountered.

Question 34

Ash Content 2

Answer 34

Sodium and vanadium are particularly troublesome. The vanadium concentration of residual fuels varies quite widely. Vanadium comes from the vacuum resid component of fuel oil.

Question 35

Ash Content 3

Answer 35

Sodium can be removed by water washing and centrifuging of fuel oil. Vanadium and sodium can cause corrosion and fouling of superheater tubes in highpressure boilers, with high operating temperatures of 1200F or above. Similarly, excessive corrosion and fouling of gas turbine blades may be encountered at temperatures of more than 1200F. At a temperature below the fusion point of ash, there is relatively little corrosion in either boilers or gas turbines

Question 36

Ash Content 4

Answer 36

Severe metallurgical attack as temperature is elevated. • Refractory attack through formation of eutectic (a low melting inorganic compound) on the surface of refractory, which at a critical temperature can destroy refractory. • Because V2O5 is a catalyst for the conversion of SO2 to SO3, it can greatly increase the concentration of SO3 in the stack gases, thus increasing sulfuric corrosion.

Question 37

Aluminum and Silicon

Answer 37

Residual fuel oils blending use heavy aromatic cutters such as light and heavy cycle oils, decant oil ex fluid catalytic cracker unit. These cutters may contain suspended catalyst fines. Catalysts used in FCCUs and other cracking units are aluminum and silicon zeolites. The measurement of aluminum and silicon content of fuel oil provides an indication of the catalyst fines in fuel oil. In residual fuel oil, catalyst fines can cause significant abrasive wear of engine components such as fuel pumps, injectors, cylinders, and pistons. The centrifuging of marine residual fuel reduces catalyst fines to a safe levels before use in marine engines.