MA0100: Filters & Centrifuges and Related Topics (Vocabulary)

Filters & Centrifuges

  • Chapter focus: common types of filters and strainers on board vessels; difference between filter and strainer; construction and maintenance of wire-mmesh filters and auto-klean filters; condition monitoring; brief on gravitational and centrifugal separation.
  • Keywords: Filter, strainer, filtration, gravitational separation, centrifugal separation, condition monitoring, simplex, duplex, priming, vent.
  • Objectives:
    • Outline the need for filters and the need for removing impurities from oils used on board ships.
    • List two types of filters used on board ships.
    • Describe construction and operating principles of different filter types with simple labeled diagrams.
    • Outline operating principle of a purifier.
    • Compare functions of a filter and a purifier.
  • On-board oil and filtration context:
    • Main oils: fuel oil (for engines) and lubricating oil (for lubrication and cooling).
    • Fuel oil stored in bunker tanks; lubricating oil in lubricating oil storage tanks.
    • Oil quality issues due to large daily consumption (roughly 20–30 t/day) necessitate cleaning; viscosity can be addressed by heating; contamination requires filtration.
    • Common impurities:
    • Fuel oils: ash, salts, water.
    • Lubricating oils: carbonaceous matter, metals, acids, water.
    • Purification aims: ensure proper combustion and lubrication with minimal wear and corrosion.
  • Filtration vs gravity vs centrifugal separation (overview):
    • Filtration: removes impurities by size exclusion through a filter element.
    • Gravity separation: relies on density differences to settle impurities over time.
    • Centrifugal separation: uses centrifugal force to separate immiscible liquids or solids based on density differences.
  • Common types of filters on ships:
    • Wire-mesh filters and strainers.
    • Auto-klean filters.
    • Purifiers (centrifugal separators) also called purifiers when used for cleaning/purifying oils.
  • Filtration basics (wire-mesh filters) – Fig.1 conceptually described:
    • Construction: cast cylindrical body, closed at one end, open at the other; a wire-mesh basket inside.
    • Inlet and outlet connections arranged so fluid enters the basket from the top and exits from the side.
    • Top closure with vent cock; bottom drain plug.
    • Typical arrangement includes inlet valve, pressure gauges, and duplex configuration to allow maintenance without shutdown.
    • Duplex arrangement: two filters connected so that one can be isolated and cleaned while the other remains in service.
  • Condition monitoring of wire-mesh filters:
    • Initially, inlet and outlet pressures are close; differential pressure is small.
    • Over time, as filter collects debris, differential pressure rises due to increased resistance.
    • When differential pressure reaches a preset value (per manual), cleaning/servicing is required.
    • Monitoring principle: pressure drop across the filter indicates dirt accumulation.
  • Wire-mesh filter – Fuel Oil Strainer (Fig.3 description):
    • Central concept: two-stage basket arrangement feeding the flow through the filter element.
    • Inlet at the bottom of the basket; outlet from the side; vent cock on the top; drain plug at bottom for maintenance.
  • Duplex wire-mesh filter arrangement (Fig.2) – maintenance-friendly: two filters in parallel so one can be cleaned while the other remains in service.
  • Auto-klean filter – Fig.4 (and related Fig.5/6 description):
    • Construction: cylindrical vessel with top cover; square cross-section spindle with hand-wheel passes through the cover.
    • Inside: a stack of metal discs with spacers; a square stationary spindle carries cleaning blades between discs.
    • Operation: when differential pressure rises, hand-wheel rotation rotates the central disc stack; cleaning blades remain stationary and peel off dirt from the periphery; dirt falls to the bottom while flow continues.
    • Advantages: faster servicing compared to wire-mesh filters; reduced mess; less downtime.
    • Duplex arrangement may also be used with auto-klean for maintenance without shutdown.
  • Gravity separation (Settling Tank) – principle and method:
    • Principle: immiscible liquids with different densities separate over time when allowed to stand; oil and water/solids separate due to density differences.
    • On ships, oil is stored in bunker/high tanks; daily usage requires smaller, stand-alone settling of impurities in a settling tank.
    • Method: oil is transferred to a settling tank for about 24 hours; heating may be used to lower viscosity and increase separation efficiency.
  • Disadvantages of filtration and gravity separation -> need for centrifugal separation:
    • Filtration and gravity separation primarily remove larger solids; small droplets or trace water remain problematic.
    • Centrifugal separation is effective for small contaminants and water content not removable by filters or gravity alone.
  • Centrifugal separation (Centrifuge / Purifier):
    • Principle: centrifugal force causes heavier liquid (water/solids) to move outward, lighter oil to occupy inner regions, enabling separation.
    • The purifier is a centrifuge used to clean/purify oils by removing water and impurities.
    • Visual representation (described): dirty oil enters the bowl, centrifugal forces separate water/impurities from oil, clean oil exits, separated water/impurities collect at the bottom.
    • Typical operating example: bowl rotates at around 8000 revolutions per minute (rpm).
  • Summary connections and practical relevance:
    • Filters remove larger contaminants; gravity separation helps with oil-water separation; centrifuges handle finer separation and emulsions.
    • Duplex and auto-klean designs reduce maintenance downtime and improve reliability for continuous operations.
    • Clean oil quality is vital for efficient engine operation and reduced wear.

Steering Gear

  • Purpose: to steer a vessel by moving the rudder from the bridge through a control system.
  • Concept: steering gear consists of machinery to convert a steering command into rudder movement.
  • Simple 4-Ram steering gear system (MV Arcadia-style reference):
    • Four main parts (as per the diagram labels):
      1) Steering wheel unit with helm indicator (C)
      2) Control unit (G)
      3) Power unit (H)
      4) Hydraulic cylinders & rams (K) with transmission to the rudder (J) via tiller and rudder stock
    • Rudder angle feedback: signal (N) from rudder stock back to the control unit (G) and to the rudder angle indicator on the bridge (D).
    • Follow-up mode (FU): steering gear follows the helm indicator (C) until the rudder angle matches the helm signal; control unit stops the power unit when the desired rudder angle is reached.
    • Non-follow-up mode (NFU): the system continues moving in the commanded direction until NFU switch on the bridge is returned to neutral; used in emergencies if follow-up is not functioning.
    • Emergency control station (I): provided in the steering gear compartment for operation if FU/NFU on the bridge fail.
    • Power sources and redundancy:
    • One power unit normally active; the other on standby.
    • Power from main switchboard (E) or emergency switchboard (F) in case of power loss; ship can still steer via emergency power.
    • Performance requirement: rudder swing from -35° to +35° (one side to the other) at maximum speed; time limit to swing from 35° in one direction to 30° the other must not exceed 28 seconds.
    • Indicators and alarms (A): warn helmsman of system status.
    • Remote controls: remote start/stop and standby on the Navigation Bridge for No. 1 and No. 2 power units (B).
  • Exercise: Label the MV ARCADIA steering failure case study (referenced in the material) – practical application of FU/NFU, signals, and emergency controls.
  • Key concept connections:
    • Steering gear integrates bridge commands, control electronics, hydraulic power, and rudder actuation.
    • Redundancy and safety (emergency station, dual power units, alarms) are critical for safe ship handling, especially in confined waters or berthing.

Marine Diesel Engines

  • Lesson focus: working principle of internal combustion engines with emphasis on marine diesel oil engines; two main cycles: four-stroke and two-stroke; timing diagrams; essential terminology; constructional differences; operational differences.
  • Key definitions:
    • Internal combustion engine: combustion occurs inside the cylinder; ignition achieved by compression (compression ignition) in diesel engines.
    • External combustion engine: combustion occurs outside the cylinder (e.g., steam engine).
    • Compression ignition engine: fuel ignites due to high temperature air in the cylinder (diesel engine).
  • Basic components needed in a diesel engine:
    • Cylinder with close-fitting piston, crank mechanism, connecting rod, and crankshaft to convert reciprocating to rotary motion.
    • Valves or ports for air intake and exhaust; fuel injector for delivering fuel oil as a fine spray.
    • Purpose of the crank mechanism: converts piston motion into crankshaft rotation; power is taken off the crankshaft via transmission.
  • Two-cycle vs four-cycle concepts:
    • Four-stroke cycle requires four piston strokes (induction, compression, power, exhaust) per cycle, i.e., two revolutions of the crankshaft.
    • Two-stroke cycle requires two strokes (compression and power, with scavenging occurring concurrently) per cycle.
  • The four-stroke cycle (Fig. 2 description):
    • Induction stroke: piston moves down; induction air valve opens; air drawn in; induction valve closes near end of stroke.
    • Compression stroke: piston moves up; induction and exhaust valves closed; air compressed to ~90 bar with end-temperature ~550°C.
    • Power stroke: near TDC, fuel injected; combustion raises pressure; piston pushed down; gases expand; temperature increases; near end of stroke, exhaust valve opens.
    • Exhaust stroke: piston moves up; exhaust valve opens and expels gases; cycle repeats with induction valve opening.
    • End-of-compression pressure typically around 90 bar and end-of-combustion pressure can reach ~130 bar; end-of-combustion temperature around 550°C (examples vary with engine design).
  • The two-stroke cycle (Fig.3 description):
    • Compression: piston moves up; scavenge and exhaust ports are covered; air previously taken into the cylinder is compressed to ~90 bar and ~550°C; piston reaches TDC.
    • Power: fuel is injected as piston reaches TDC; hot compressed air ignites fuel; rapid pressure rise drives piston down.
    • Blowdown: exhaust gases rush out as exhaust valve opens; pressure falls toward atmospheric.
    • Scavenge: scavenge air is introduced at higher pressure (approximately 1.2–1.5 bar) through scavenge ports to sweep remaining exhaust gases out; swirl is created by tangential port design; as piston uncovers ports, fresh air fills the cylinder; once at BDC, piston moves up to close ports and begin compression for the next cycle.
    • Turbocharger: rotary air compressor (driven by gas turbine in some designs) provides the scavenger air.
    • Cylinder head in two-stroke engines often simpler than four-stroke due to integrated scavenging design.
  • Flywheel: stores kinetic energy to keep crankshaft turning between power strokes; smooths operation since power strokes are intermittent.
  • Compression ratio: fundamental attribute of diesel engines; defined as the ratio of the total cylinder volume to the clearance (minimum) volume just before combustion.
    • Example: If the whole cylinder volume is 160 cm
      times 3 (assuming a given example) and the least cylinder volume is 10 cm extsuperscript{3}, then the compression ratio is
    • CR = rac{V{ ext{whole}}}{V{ ext{least}}} = rac{160}{10} = 16.
  • Key operational notes:
    • End-compression pressure and end-compression temperature are critical for reliable ignition in compression-ignition engines.
    • The two-stroke engine uses scavenging air to push out exhaust and fill the cylinder with a clean charge, enabling a higher power-to-weight ratio but requiring careful timing and port design.
  • Visual aids referenced in course materials:
    • Diagrams illustrating four-stroke cycle (air induction, compression, combustion/power, exhaust) and two-stroke cycle (compression, power, blowdown, scavenging).
    • Flywheel and crank mechanism illustrations; basic cylinder components; fuel injector placement; intake/exhaust valves or ports.
  • Real-world relevance:
    • Understanding cycle differences informs maintenance strategies, fuel efficiency, and emissions.
    • Combustion characteristics (pressure and temperature) determine lubrication needs, wear, and component design.

Environmental Pollution

  • Scope: oceans pollution from ships; main sources include accidental discharges, cargo operations, machinery spaces discharges, sewage, garbage, air pollution, ballast water, and ship bottom paints.
  • Oil pollution specifics:
    • Discharge pathways include cargo tank washings, accidental spills during loading/discharging, bilge discharges, and oily water separator inefficiencies.
    • Preventive measures include segregated ballast arrangements, clean ballast, slop tanks, Crude Oil Washing (COW), oily water separators, and oil content monitors.
  • Ballast Water Management (BWM):
    • Ballast water moves around the world with ships, carrying aquatic organisms that may become invasive species in new ecosystems.
    • Management options:
      1) Ballast water exchange mid-ocean.
      2) Ballast water minimization and non-release strategies.
      3) Discharge to reception facilities at ports.
      4) Emerging technologies to treat ballast water and kill invasive species prior to de-ballasting.
  • Double hulls and regulatory responses:
    • After major spills (e.g., Exxon Valdez), regulation favored double-hull tankers with space (about 6 feet) between oil tanks and the outer hull to reduce spill risk.
  • Crude Oil Washing (COW):
    • COW circulates cargo through fixed tank-cleaning equipment to remove waxy deposits; more effective than water washing as oil acts to disperse sediments and can restore cargo to its loaded condition.
    • Inert gas systems are required during COW for safety.
  • Ship bottom paints and antifouling:
    • Historically, Tributyl tin (TBT) was used to prevent barnacles but is highly toxic to aquatic life and poses human health risks.
    • IMO ban on TBT paints (effective 2003; overlay coatings allowed to prevent discharge by 2008).
    • Tin-free (TF) self-polishing antifouling paints are now used to improve fuel efficiency by maintaining smooth hull surfaces and reducing drag.
  • Sewage treatment and disposal:
    • Raw sewage can reduce dissolved oxygen in water and harm aquatic life; E. coli indicator used for sewage presence.
    • Treatment options: chemical vs biological.
    • Biological treatment uses aerobic bacteria to break down sewage into sludge; extended aeration systems support bacterial growth; continuous sludge recycling requires periodic partial removal.
    • Discharged effluent is treated to meet regulatory standards; sludge is disposed of ashore or incinerated.
  • Incineration of waste:
    • Incinerators burn solid waste and sludge; primary and secondary combustion chambers ensure complete combustion and destruction of hydrocarbons.
    • Typical combustion temperatures range from 850–950 °C; high-temperature alarm at 1050 °C.
    • The primary chamber dries waste and starts burning; hydrocarbon gases may burn in the secondary chamber.
    • Incineration reduces solid waste while controlling emissions.
  • Ballast water management regulatory context and environmental risk emphasis:
    • Invasive species risk, ecological disruption, and potential disease transmission.
    • Ship operators must implement BWM measures to minimize environmental impact.

Shipboard Machinery & Piping Systems

  • Bilge System and Oily Water Separator (OWS):
    • Engine room bilges collect dirty oily water from machinery spaces; regulations prohibit discharging oil-contaminated water directly overboard.
    • Oily Water Separator (OWS) separates oil from bilge water; oil is routed to a sludge tank; clean water (oil content < 15 ppm) is discharged overboard.
    • The oily water mixture is pumped through the separator unit where oil, being lighter than water, tends to rise and be collected separately.
    • The remaining water passes through a fine separation stage and is discharged after meeting the 15 ppm standard.
    • An automatic valve directs separated oil to a storage sludge tank and discharges clean water overboard via a controlled path.
  • Bilge pumps and servicing:
    • Bilge pumps draw from multiple suction points (Port Forward, Starboard Forward, Aft Engine Room) to prevent loss of suction if one point is empty.
    • Bilge well diagrams show non-return valves and strainers to prevent air entry and maintain prime.
  • OWS operation steps:
    • Pre-start: ensure suction valves are shut; verify overboard discharge valve is open; start the bilge pump; verify oil content monitor and discharge pressure.
    • Discharge monitoring ensures operation within regulatory limits; stop discharge when no more discharge is detected.
  • OWS cross-reference and indicators:
    • The system includes sample ports, oil content monitoring devices, and a multi-valve arrangement to manage discharge streams.
  • Sewage and waste processing (contextual):
    • Sewage treatment and incineration are separate but related environmental systems on ships, designed to minimize pollution and comply with MARPOL and local regulations.

Sewage Treatment and Waste Management (Environmental Pollution section)

  • Basic biology and chemistry overview:
    • Untreated sewage contains suspended solids and bacteria; oxygen depletion can harm aquatic life.
    • E. coli and other bacteria serve as indicators of sewage presence.
  • Treatment approaches:
    • Chemical treatment: storage tanks that hold solids for disposal or shore facilities; limited treatment of liquids.
    • Biological treatment: aerobic bacteria break down organics; extended aeration processes support biological digestion; sludge formation and recycling occur within the treatment tank.
    • Chlorine contact stage: disinfects water prior to discharge.
  • Incineration and grounding: incinerators manage solid waste and oily residues not suitable for discharge.

Ballast Water Management (BWMS) and Environmental Pollution – Ballast Water Handling

  • Ballast water risks: introduces non-native species across oceans, potentially causing ecological and economic harm.
  • Management strategies:
    • Ballast water exchange mid-ocean to reduce the number of organisms in ballast tanks.
    • Non-release or minimal-release strategies to minimize ballast water discharge.
    • Shore reception facilities for ballast water disposal.
    • Development and adoption of new technologies to treat ballast water before discharge.
  • Ballast cycles (illustrative):
    • At source port: ballast water loaded into ballast tanks.
    • During voyage: ballast tanks may contain local species; ballast management seeks to minimize spread.
    • At destination port: ballast water discharge aligns with regulatory requirements.

Ship Bottom Paints and Hull Coatings

  • Historical use: Tributy tin (TBT) used as anti-fouling biocide to prevent barnacles and marine growth; also served as a fungicide.
  • Environmental and regulatory action:
    • IMO ban on TBT paints effective January 2003; as of January 2008, overlay coatings were required to prevent TBT discharge.
  • Current alternatives:
    • Tin-free (TF) self-polishing antifouling paints that reduce hull roughness and improve fuel efficiency by maintaining smooth hull surfaces.

Marine Auxiliary Steam Boiler

  • General purpose of a marine auxiliary steam boiler:

    • A closed pressure vessel that generates steam by burning fuel; used to drive pumps, heating, or to supply steam for other systems.

  • Typical layout and components (Fig. features described):

    • Miura-style boiler shown; donut-shaped steam drum and water drum connected by multiple water tubes.
    • Fuel oil is heated and sprayed by a burner; air is supplied via forced-draft fan.
    • Heat transfer through radiation, conduction, and convection to water tubes; steam/ flue gases flow through tubes and are exhausted.
    • Normal working pressure around 7 bar.

  • Boiler mountings (overview of common fittings):

    • 1) Lower inspection port (hand hole) for cleaning/inspection below the water space.
    • 2) Main feed check valve (screw-down non-return type) regulated by the feed-water regulator.
    • 3) Water level gauge with steam, water, and drain cocks; glass shows water level half-full when working.
    • 4) Safety valves: spring-loaded; lift to release pressure when above normal.
    • 5) Main steam stop valve: isolates boiler from main steam line.
    • 6) Air valve: allows air escape when raising steam from cold conditions.
    • 7) Upper inspection port: access for cleaning/inspection.
    • 8) Pressure gauge with valve: reading boiler pressure.
    • 9) Scum valve: allows skimmed impurities to be drained.
    • 10) Salinometer valve: sample testing port for boiler water.
    • 11) Blowdown valve: bottom-of-boiler discharge valve for cleaning and maintenance.

  • Safety devices and alarms:

    • Low-low water level cutout (burner shut off if water level dangerously low).
    • High water level alarm.
    • High steam pressure alarm.
    • Flame failure cutout (shutdown if flame fails).
    • High fuel temperature alarm; low fuel pressure alarm (affects atomization and flame stability).

  • Exhaust gas boiler usage (heat recovery):

    • Exhaust gas boiler recovers heat from main engine exhaust to generate steam for auxiliary uses or to drive a steam turbine for electrical generation.
    • Master-slave arrangement: auxiliary boilers, turbine, and feed water system.

  • In port operation:

    • When the main engine is not in operation, auxiliary boilers supply saturated steam; in port, exhaust gas boilers may be idle.

  • Purpose of saturated vs superheated steam:

    • Saturated steam is used for heating tasks; superheated steam can drive turbines for electrical power generation.

  • Connections to earlier chapters and real-world relevance:

    • Filtration, lubrication, and filtration-based maintenance directly support diesel engine reliability and environmental compliance (e.g., cleanliness of oil and oil-contaminated effluent).
    • Steering gear reliability and redundancy tie into overall vessel safety and maneuverability in constrained waters.
    • Environmental protection measures (pollution control, ballast water management, incineration, and wastewater treatment) are essential for compliant and sustainable ship operation.

  • Key formulas and quantitative references to remember:

    • Internal combustion compression-ignition basics: ignition temperature of fuel, compression pressure values, and end-of-compression temperatures (typical end of compression around ~550°C with pressures around 90 bar; modern engines may reach ~130 bar).
    • Four-stroke cycle timing: Induction, Compression, Power, Exhaust – two crankshaft revolutions per cycle.
    • Two-stroke cycle timing: Compression, Power, Blowdown, Scavenge – with crank-driven scavenging and port-based intake.
    • Compression ratio: CR = rac{V{ ext{whole}}}{V{ ext{least}}} where Vwhole is the total cylinder volume and Vleast is the clearance volume at TDC.
    • Oily water separator standard for discharging bilge water: oil content in discharged water must be less than 15 ext{ ppm}.
    • COW and ballast management involve multiple regulatory limits and processes to minimize environmental impact.

  • References to common engine theory and marine engineering texts in the transcript:

    • General Engineering Knowledge for Engineers, Vol. 8 (Jackson & Morton)
    • Marine Auxiliary Machinery (Smith)
    • Marine Auxiliary Machinery (Souchotte)
    • Other textbook references and video resources noted in the transcript.