Marine Engineering I

Marine Engineering I Attendance Course Outline 2 Hour Examinations – 40 % (20 % each) Laboratories – 15 % ** ** All labs are mandatory and include STCW content. Missed labs will not be made up during the term and will result in a “F” for the course.

Marine Engineering I Homework – 10 % Class Participation & Quizzes – 5 % Final Exam – 30 % * * In order to pass the course with a grade of “D” or better, Midshipman must have an examination average of 60 % or better.

Marine Engineering I What happens inside a Steam Generator? A fuel (Oil, Coal, Natural Gas, Wood and other fuels) (Chemical Energy). Mixes with the O2 in air and undergoes combustion. From combustion heat is generated (Thermal Energy).

Marine Engineering I The heat is transferred to the water and steam in the boiler which raises it temperature and changes its phase.

Marine Engineering I Heat Transfer is accomplished in three different modes. Conduction – which is heat transfer thru a solid. Convection – which is heat transfer thru a fluid (liquid and/or vapor). Natural convection – Convection due to a density difference. Forced convection – Convection by the use of a mechanical means (fan, blower, etc.)

Marine Engineering I Radiation – Heat transfer thru electromagnetic wave lengths Conduction (Q) = KA(Δt/Δx) Convection (Q) = hA(t1 – t2) Radiation (Q) = εσA(T14 – T24) All three modes of heat transfer have what in common?

Heat Energy Required Superheater outlet conditions 600 PSIA 800 °F h = 1407.9 BTU/lbm

Heat Energy Required Feedwater entering Boiler 700 psia 300 °F h = 269.7 BTU/lbm

Heat Energy Required Energy required to raise temperature of boiler water to where boiling take place?

Heat Energy Required Since boiler pressure is 600 psia, the corresponding saturation temperature is 486.25 °F h 600 psia = 471.7 BTU/lbm Energy Required to heat water to its boiling point is h 600 – h 300 471.7 BTU/lbm – 269.7 BTU/lbm 202.0 BTU/lbm

Heat Energy Required Energy required to change phase is 732.0 BTU/lbm Energy required to change water at 600 psia to 100% steam at 600 psia. hf = 471.7 BTU/lbm hg = 1203.7 BTU/lbm hfg = 732.0 BTU/lbm Energy required to change phase is 732.0 BTU/lbm

Heat Energy Required Energy needed to superheat steam from saturated conditions to boiler outlet conditions. hg = 1203.7 BTU/lbm Superheater outlet conditions are 600 psia and 800 °F, hSH = 1408.3 BTU/lbm Energy required to superheat steam is hSH – hg 1408.3 – 1203.7 = 204.6 BTU/lbm

Heat Energy Required Total energy required is: 202.0 BTU/lbm (Sensible Heat Energy) 732.0 BTU/lbm (Latent Heat Energy) 204.6 BTU/lbm (Sensible Heat Energy) Total Energy Required is 1138.6 BTU/lbm

QIn Work QOut

Marine Boilers Fire Tube Boilers (Scotch Boiler) Water Tube Boilers

Firetube Boilers The fire or hot gases from the burner is channeled through tubes that are surrounded by the fluid to be heated. The body of the boiler is the pressure vessel that contains the fluid. In most cases the fluid is water that will be circulated for heating purposes or converting to steam.

Firetube Boilers Every set of tubes that the flue gas travels through, before it makes a turn is considered a “pass”. A three pass boiler will have three sets of tubes with the stack outlet located on the rear of the boiler. A four pass boiler will have four sets and the stack outlet at the front of the boiler.

Firetube Boilers Firetubes Stay Rods Firetubes Stays Furnace Furnace Source: www.steamesteam.com Combustions Chamber

Firetube Boilers Source: www.steamesteam.com

Exhaust Out Steam Out

Scotch Boiler Consists of a horizontal cylindrical shell closed a each end. Inside the shell were mounted the following: Mounted corrugated metal furnaces Combustion chamber(s) Fire tubes Structural support members called stays

Fire Tube Boiler Size The amount of heating surface needed to provide the required rate of evaporation and steam pressure The type of fuel being used (Coal, Oil, Gas) Method of firing

Furnaces Space provided within or as a part of boiler construction for the burning of fuel The furnaces were constructed of a corrugated design for the following advantages 1. Greater Strength 2. Increase surface area for heat transfer 3. Allow for expansion and contraction

Combustion Chambers Is an enclosed space constructed of steel, provided for the completion of combustion which was started in the furnace. The combustion chamber was located in the rear of the scotch boiler shell and also acts to redirect gases of combustion and also serves as part of the heating surface of the boiler.

Combustion Chambers Types of combustion chambers 1. Dry back combustion chamber with single or multiple furnaces. 2. Wet back combustion chamber with single or multiple furnaces.

Uptakes Uptakes are generally constructed of steel and are used to serve as a retainer for the exhaust gases of combustion flowing from the front head to the boiler stack Uptakes are provided with inspection doors and are insulated to prevent personnel injury and excessive heat from radiating into the fire room

Fire Tubes Fire tubes are small cylindrical shells or pipes that make up the greatest surface area for heat transfer The rear ends of the fire tubes are connected to the front face of the combustion chamber (know as the tube sheet) The front ends of the tubes are connected to the front head of the boiler shell.

Stay Tubes In a fire tube boiler the products of combustion pass through the fire tubes which are surrounded by water Stay tubes are thicker tubes and are used not only as a heating surface, but also structurally support the tube sheet of the combustion chamber(s) to the front head of the boiler.

Mountings and Fittings Internal feed line – This line is a continuation of the feed pipe within the boiler and is used to distribute the feed water evenly along the length of the shell Scum pan – Is located at the normal water level of the boiler and is used to collect floating impurities on the water surface and lead them to the surface blow connection

Mountings and Fittings Dry pipe – This pipe is located near the top of the shell and runs almost the full length of the shell, It is used to collect steam for removal from the boiler and to minimize moisture carryover Fusible plug – The fusible plug is a device installed in the center of the crown sheet of the combustion chamber to warn the operator in the event of low water level

Advantages of Scotch Boiler Low cost Easy accessibility for maintenance Less radiation losses (fires and gases of combustion are surrounded by water) Capability of using relatively impure water without causing serious damage Less skilled operators required because of the large quantity of water present Steadier steam pressures

Disadvantages of Scotch Boilers Susceptibility to explosions that would result in hot water dumping into the fire room, flashing into steam, and injuring engineroom personnel. Thick boiler plating requirements for high pressures making the boiler weight prohibitive for most high pressure applications Relative long warm up period (minimum time 12 to 24 hours)

Disadvantages of Scotch Boilers Weakened structural integrity of the ship (Scotch boilers are usually delivered completely assembled which requires large openings in the fire room for installation and when filled with water offer large concentrations of weight to some structural members of the ship Incapability of rapid changes in steaming rates for maneuvering purposes

Disadvantages of Scotch Boilers Sluggishness for long maneuvering periods requiring frequent changes in steam demand (caused by large volume of water in the boiler) Incapability of rapid changes in steaming rates for maneuvering purposes

Firetube Boilers Source: Cleaver-Brooks

Cleaver – Brooks Boiler Dryback Style 15 – 80 Horsepower Heating or processing Steam (15-250 psi) or Hot Water (30 psi) Oil, Natural Gas or combination Alternate fuel capability Low NOx capability

Firetube Boilers Source: www.energyinc.com

Firetube Boilers Source: www.energyinc.com

Firetube Boilers Source: Babcock & Wanson

Firetube Boilers Source: Babcock & Wanson

Firetube Boilers Advantages Relatively inexpensive Easy to clean Compact in size Available in sizes from 600,000 BTU/hr to 50,000,000 BTU/hr. Easy to replace tubes Well suited for space heating and industrial process applications Very easy to automate

Firetube boiler Disadvantages Not suitable for high pressure applications of 250 psig and above. Limitation of high capacity steam generation.

Firetube Boilers