英文资料翻译原文Boiler management:General management principles and operating procedures are well known and must be always followed to avoid boiler mishap.With many small package boiler,the automatic control sequence usually ensures that the boiler fire is initially ignited from a diesel oil supply,and changed over to the usual source when ignition is completed.With good management ,to facilitate subsequent starting from cold,the fuel system of large boilers will have been flushed through with diesel oil when the boiler was on light duty immediately prior to being secured.When burning such diesel fuel it is essential for safety that only the correct(small) burner tip should be used.It should be kept in mind that if fire does not light,immediately shut off fuel and vent furance.Complete ignition of fuel in the furance is essential.The burner flame,the smoke indicator and the funnel should be frequently observed.With satisfactory combustion,the flame should appear incandescent with an orange shade at the flame tip,and a faint brownish haze should show at the funnel.If on fist ignition the flame is uncertain,badly shaped and separates from the primary swirler ,momentary opening or closing of air register may correct.The PH value of the boiler feed water should kept between 8 and 9 and the boiler density less than 300 ppm but,if water samples show a heavy concentration of suspended mater,short blow-downs of 20 seconds duration should be given until the sludge content is seen to be reduced.The boiler should be blown down when the oil burner is operating,the water level lowered and then restored to prove the functioning of the low water cut-out and the oil burner start-up equipment.the boiler scum valve should also be operated at this time to keep the water level clear floating scum.Fuel burner components and igniter electrodes should be cleaned weekly and the furance examined to ensure that there are no excess carbon deposits.Tubes in the exhaust gas section of the boiler should be brushed through at about six-monthly intervals,and those in the oil-burning section periodically examined and cleaned as necessary with a wire bristle brush.With correct feed water treatment,blow-down procedures and sludge contents in water samples at a stable level,it should not be necessary to wash out the water side of the boiler more than once every three or four months.Boiler fires may be out of for long periods when a ship is at sea and the boiler steaming maintained by heat input from waste heat recovery plant.This operation is free from hazard,but feed water and boiler water treatment must be maintained to prevent internal deterioration or scale formation.Water level controller must be kept operable to protect external steam-using plant from water “carry-over”danger.If a boiler is isolated from the steam-using system it must be kept either in closed dry storage with a suitable internal desiccant,or completely full of treated water,or under a low steam pressure preferably maintained by a steam-heated coil.Regular testing of boiler protective devices must be implemented.Frequent comparison of drum-mounted and remote reading water levelindicators:discrepancies between these have contributed to failures because of overheating through shortage of water,when a boiler was being oil-fired.If in doubt as to the true boiler water level,i.e.whether a water level indicator sightglass is completely full or empty,when a unit is being oil-fired the fire should be immediately extinguished until the true level is resolved.Procedures should be predetermined and followed in the event of shortage of water,bulging or fracture of plates or furance,or bursting of water tubes .In general,fires should be immediately extinguished by remote tripping of fuel supply valves;forced draught air pressure maintained if there is any risk of escaping steam entering the boiler room;stem pressure relieved if metallic fractures seem possible;and boiler water level maintained,where practicable,until the boiler begins to cool down. Regular operation of soot blowers,if there are fitted,when the boiler is on oil-fired operation.The steam supply line must be thoroughly warmed and drained before blowers are used,the air/fuel ratio increased throughout the action,and the blowers greased after use.Immediate investigation of any high salinity alarms in condensate system,and elimination of any salt water or oil contamination of boiler feed water system. Safety precautions taken before entering a boiler connected to another boiler under steam.Engine governor:A governor maintains the engine speed at the desired value no matter how much load is applied.It achieves this by adjustment of the fuel pump racks.Any change in load will produce a change in engine speed,which will cause the governor to initiate a fuel change.The governor is said to be speed sensing as a speed change has to take place before the governor can react to adjust the fuel setting.The sample mechanical governor employs rotating weights which move outward as the speed increases and inward as the speed reduces.This movement,acting through a system of linkages,can be used to regulate the fuel rack.Rather than having the rotating weights directly move the fuel linkage,hydraulic governor employ a servo system so the rotating weights only need to move a pilot valve in the hydraulic line.This makes the governor more ernors of this type require a speed change to tale place in order that they may initiate fuel rack adjustment.This is known as speed drop and this is a definite speed for each load therefore the governor can not control to a single speed.A modification to the governor hydraulic system introduces a facility known as compensation which allows for further fuel adjustment after the main adjustment has taken place due to speed pensation restores the speed to its original desired value so the engine can operate at the same speed under all loads.Such a governor is said to be isochronous as the engine operates at a single speed.However,the governor is still speed sensing,so it is not ideal for all applications.Speed sensing governor:Where the engine drives an alternator any speed change results in a change in supply frequency.;Large changes in electrical supply frequency can have an adverse effect on sensitive electronic equipment connected to that supply.Where electrical generation is involved it is possible to monitor taking rotational speed as the control signal.Such governors are know as load sensing.It isextremely difficult to make a mechanical governor load sensing,even with a hydraulic system,but an electronic governor can take account of the electrical load applied to the engine and so can be considered “speed sensing”.Electronic governor:Electronic governors essentially comprise two parts,the digital control unit and the hydraulic actuator,which are interlinked but it is useful to consider them separately.Electronic governor controller: The digital control may be considered as a “black box” in which signals are processed to produce a control signal which is sent to the actuator.The controller may be programmed in order to sent points and parameters.The controller is a sensitive piece of electronic equipment and should not be mounted on the engine or in areas where it will be exposed to vibration,humidity or high temperatures.It should be ventilated in order to keep it cool and should be shielded from high-voltage or high-current devices which will cause electromagnetic interference.Similar restriction apply to the location of signal cables.Speed signals are taken from two speed transducers,one on each side of the flexible coupling which attaches the engine to the load.Failure of one transducer produces a minor alarm but allows continued operation with an electronic over speed value may be programmed into the controller in which case detection of over speed will cause the engine to be shut off.If the load is provided by an electrical machine the output from that machine provides a signal for load sharing.Should this transducer fail the load on the engine will be determined by the position of the governor actuator output.The controller can also receive signals from other transducers including in the engine’s air inlet pressure,which allows the fuel to be limited when starting.After processing input signals in accordance with programmed requirements an output signal will be sent to the governor actuator.Electronic governor actuator:The actuator is a hydraulic device which moves the fuel linkage in response to a signal from the digital controller.The operating mechanism is contained with an oil filled casing.Oil pressure is provided by a servomotor pump driven by a shaft connected to the engine camshaft.At the heart of the actuator is the torque motor beam is banlanced where the engine is operating at the desired speed.a.Consider a load increaseThe controller increases current to the torque motor which,in turn,causes the centre adjust end of the torque motor beam to be lowered.Oil flow through the nozzle is reduced ,which increases pressure on the top of the pilot valve plunger.This moves downward,unconering the port which allows pressure oil to the lower face of the power piston,which in turn moves upward, rotating the terminal shaft thereby increasing the fuel to the engine.As the terminal shaft rotates the torque motor beam is pulled upwards by increased tension in the feedback spring,increasing the clearance between the centers adjust and the nozzle.Leakage past the nozzle increases,reducing the pressure on the upper face of the pilot valve plunger and allowing the pilot valve to move upwards.This cuts off further oil to the power piston,and movement of the fuel control linkage ceases.Balance is restored to the torque motor beam with downward force from the feedback spring being matched by upwards force from oilleakage from the nozzle.The engine then operates at an increased fuel setting which matches the new load requirement at the set speed.B.consider a load reductionA decrease in load produces a reduction in current acting on the torque motor,which tends to turn the beam in an anti-clockwise direction about the torque motor pivot,resulting in an increased clearance between the centre adjust and the nozzle.Pressure reduces on the upper face of the pilot valve plunger and the pilot valve moves upwards,allowing the lower face of the power piston to connect with the geromotor pump suction.the power piston moves downwards ,rotating the terminal shaft which reduces fuel to the engine and tension in the feedback spring.The center adjust end of the torque motor beam is forced down,thereby reducing clearance between the centre adjust and the nozzle.Leakage past the nozzle reduces pressure on the upper face of the pilot valve increases and the pilot valve moves upwards,shuting off the connection between the lower face of the power piston and pump suction .The engine now operates with reduced load and reduced fuel,but at the same original speed.。