欧宝热油锅炉系统说明

INTRODUCTIONTOTHERMAL FLUID SYSTEMS1INTRODUCTION (3)2BASIC THERMAL FLUID DIAGRAM (4)2.1M INIMUM FLOW (5)2.2C IRCULATION PUMP (5)2.3P IPING (6)2.4T HE EXPANSION TANK (6)2.5D E-AERATING PIPE (7)2.6T EMPERATURE BLOCKING PIPE (7)2.7D E-AERATOR (BOILING OUT PIPE) (8)2.8D OUBLE CIRCULATION PUMPS (8)2.9F ILLING PUMP, DRAIN- AND STORAGE TANK (9)3ECONOMISER (10)3.1D UMPCOOLER (10)3.2B YPASS DAMPER SECTION IN THE ECONOMISER (12)4BITUMEN TANKERS (15)5CHEMICAL TANKERS (15)5.1I NTER-MEDIUM HEATER (15)5.2T ANK-WASH (15)5.3A DDITIONAL STEAM FROM AN UNFIRED STEAM BOILER (16)1 INTRODUCTIONThis is a short introduction to our thermal fluid systems.We will start at the very basis of a heating a process and the technical level will bebuilt up slowly using diagram drawings of our systems with increasing complexity.We aim to tackle subjects like: constant flow, de-aerating pipe, de-aerator,expansion tank, drain tank, economisers with a double damper section anddumpcoolers.The description of more complex systems, like systems for chemical tankers, can becommunicated to you on request.Many technical processes require heating of a product to a temperature above theambient temperature.Essentially there are two ways to heat a product:•Direct heating: the product is mainly and directly heated from the outside bycombustion gases or electric heating elements•Indirect heating: a circulating heat transfer medium is used between heaterand heat consumer. Our thermal fluid systems are based on this principle.Fig 1.1 Difference between direct and indirect heatingIndirect heating is preferred above direct heating due to advantages like:avoiding local overheating;more accurate control of the product temperature;less explosion risk (consumer and heater are not situated near each other )2 BASIC THERMAL FLUID DIAGRAMBased on indirect heating, the most basic thermal fluid diagram is shown below.In this basic diagram the following components are present:HeaterCirculation pumpMinimum flow controlExpansion line between system and expansion tankExpansion tankPiping between the components.The fired heater heats up the fluid and the consumers cool down the fluid. The temperature difference between supply- and return temperature depends on the capacity of the heater and the necessary temperature accuracy.Most systems operate with a supply temperature between 180° and 280° Celsius anda return temperature of 40° to 60° Celsius lower.2.1 Minimum flowThe heater is built according the constant flow principle and the thermal fluid must circulate continuously to prevent the thermal fluid from overheating (cracking). When there is no heat demand from the consumers we still want to keep a constant flow through the heater to prevent the thermal fluid from heat damage. The minimum flow valve assures this sufficient constant flow. If the flow is too low, a flow alarm is generated (the burner will be switched off automatically).The (automatic) regulation of this minimum flow valve can be:Mechanical measuring the supply- and return pressure of the thermal fluid;Electrical measuring the (flow) differential pressure over an orifice;Pneumatic measuring the supply pressure in the thermal fluid line.2.2 Circulation pumpA circulation pump can be installed in the supply line or in the return line of a system. Our circulation pump is always situated in the return line of the system. This is done to reduce the risk of cavitation (pitting) caused by the lower return temperature (higher viscosity) and the pressure for the heat consumers is lower as well.The pressure on suction- and pressure side can be seen on the pressure indicators (PI) which are installed.The capacity of the pump must be sufficient to circulate the thermal fluid around in the system against a certain delivery head.The required capacity of the pump is according the formula: Q=m*c*∆T.For determining the delivery head of a pump we have to calculate the total pressure drop of the flow system, we estimate that the consumers have a totalpressure drop of maximum 20 m.l.c.2.3 PipingIt is normal that the thermal fluid flow is somewhat turbulent; when the velocity is increased the turbulence will also increase. The turbulence of the thermal fluid flow must not become too high otherwise it will cause excessive pressure losses in the pipingOn the pressure side of the system the velocity of the thermal fluid is approximately 2 m/s. On the suction side of the system the speed is lower to ensure a good flow to the circulation pump.2.4 The expansion tankThe expansion tank is in open connection with the atmosphere. The expansion tank is used as a gravity tank; so the bottom of the expansion tank should be installed above the highest point in the thermal fluid system. This will provide sufficient pressure to the suction side of the circulation pumps.The height of the expansion tank varies between 1,500 mm and 6,000 mm.A number of level switches (LA) are installed on the expansion tank, which are activated in case of high, low or too low level of thermal fluid in the tank.The variation in thermal fluid contents, present in the expansion tank, can be seen on the level indicator (LI).When heating up the (mineral) thermal fluid, the fluid will give an expansion in volume of approximately 7% per 100° Celsius. This expansion must be absorbed by the expansion tank via the expansion line.With this basic diagram we have an “air” problem. Vapours can never leave the system. Therefore we have added some system pipes to the system.There are three system pipes necessary in this system:de-aerating pipe;temperature blocking pipe;de-aerator.During operation of the system light fractions or vapours can develop. These vapours will cause cavitation (pitting) of the circulation pump. To give the gases the opportunity to escape to the atmosphere and eliminate the cavitation problem, a de-aerating pipe is installed in return line of the heat consumers. The bottom side of this pipe is connected to the suction side of the circulation pumps.The velocity of the thermal fluid is reduced in the de-aerating pipe to ensure optimal and continuous de-aerating. The return line of the heat consumers is connected with the de-aerating pipe from which the top is connected with the top of the expansion tank via the de-aerating line.2.6 Temperature blocking pipeThe lifetime of thermal fluid will be reduced (“aged”) in case the thermal fluid in the expansion tank is in contact with oxygen (air) at high temperature. Whenever possible the temperature in the expansion tank should be kept below 70° Celsius to reduce the ageing of the oil.Therefore the expansion line of the system to the expansion tank is connected to a temperature blocking pipe so that always the coolest thermal fluid is pressed to theexpansion tank.2.7 De-aerator (boiling out pipe)Most light fractions and vapours will develop by heating the fluid during the first start up. Furthermore it can happen that some water is in the installation, which will evaporate in the heater. To give the steam and light gases the opportunity to leave the installation as soon as possible, a de-aerator is mounted directly behind the heater. On the de-aerator a boiling out pipe is mounted. This boiling out pipe is provided with a valve, which is connected to the top of the expansion tank.It is important, for an extended durability of the thermal fluid that it is only allowed to open the boiling out valve during the first start-up period, until all the gases have escaped. To prevent oxidation of the oil in the expansion tank, the valve must be closed directly after the boiling out procedure.2.8 Double circulation pumpsFor marine purposes all classification societies demand a double execution, if the heating is used for essential services.Double circulation pumps are also required in case the system is executed with an economiser(s).The standby circulation pump takes over in case of breakdown of the pump inservice by means of a pressure controller (PC).2.9 Filling pump, drain- and storage tankThe system is provided with a drain/storage tank. You are able to fill the system with an electrical driven filling pump.The filling pump is connected in such a way that you have following possibilities: - To fill the installation from the storage tank (via the expansion tank).- To empty the storage tank outside of the ship.- To empty the installation outside of the ship.There is also an overflow line connection between the expansion tank and the drain/storage tank in (emergency) case the expansion tank cannot absorb the necessary expansion. A (manual hand) pump must be installed to remove condensate/water from the drain/storage tank.The quick opening valve (XA) in the drain line near the expansion tank can be opened in case of an emergency. If opened the thermal fluid in the expansion tank will flow to the drain tank.The size of the drain/storage tank must be sufficient to collect the biggest drainablepart of the thermal fluid system (mostly the total contents of the system)3 ECONOMISERAn economiser recuperates heat from the exhaust gases of the main engine bycooling these gasses. The economiser is built up from concentric coils; the hotexhaust gases of the engine flow between these coils and transfer their heat to thethermal fluid.When the main engine is not running, the economiser will not heat up the thermalfluid and the fired heater will start automatically.When the main engine is running with a reduced output, the exhaust gas quantity isalso reduced and the produced heat capacity of the economiser will be reduced aswell. In case the heat demand of the heat consumers is more than the heat productionof the economiser, the oil fired heater will start automatically.When the heat production of the economiser is more than the heat demand of theheat consumers, the thermal fluid will be heated up beyond the supply temperatureto the system. There are two possibilities to cool the surplus of heat, to prevent thethermal fluid from overheatingvia a dumpcooler;via a bypass damper section in the economiser.3.1 DumpcoolerIn case of an execution with a dumpcooler, the dumpcooler will be installed in thethermal fluid supply line just behind the economiser.The dumpcooler is connected to the engine cooling water system on the cooling sideto cool the possible surplus of heat present in the thermal fluid.In some cases seawater is used in the cooler.The next diagram is a typical diagram for:container vessels;heavy lift vessels;reefers;fishing vessels;multi-purpose vessels;gas tankers;pipe laying vessel;live stock vessel.3.2 Bypass damper section in the economiser.The other possibility is to reduce the surplus heat generated by the economiser is by using a bypass damper section in the economiser.Depending on the heat demand the flue gasses are bypassed or guided through the heating surface of the economiser.Differences between the system execution with dumpcooler and double damper economiser:Double damper economisers DumpcoolerLonger gives additional leakage possibilities Bigger in diameter Simpler design of the economiserintegrated dampers in the main engine exhaust gas piping more accurate control of thermal fluid temperatureonly applicable in case of main enginesup to 10,000 kW;more thermal fluid pressure lossmore partsIn general a thermal fluid system with a double damper economiser is a more expensive but technically more advanced than a dumpcooler version.various economisers and the thermal fluid is heated up parallel.After the economisers the thermal flow is united again and guided through the fired heater.This next diagram is a typical diagram system for:ro-ro vessel;dredgers;passenger ferries;push boats and tow boat.4 BITUMEN TANKERSIn general the cargo for bitumen tankers must be kept on a high temperature, usuallybetween 200°250° C. This means that the thermal fluid supply temperature must bevery high as well, between 280° – 300° C.However, it is not allowed to feed the engine room heat consumers with these hightemperatures. So, in a typical bitumen tanker system the engine room heatconsumers are included in a separate “low temperature system” (i.e. 190° – 140° C).This low temperature system is heated either by the economiser(s) or by the “hightemperature system”, which is heated by the fired heater. The temperature of the lowtemperature system is connected to the high temperature system by a temperaturecontrolled mixed-injection system.5 CHEMICAL TANKERS5.1 Inter-medium heaterThermal fluid heating system for chemical tankers must be executed with aseparation between the cargo heating part and the heat production part. This meansthat a heat exchanger (inter-medium heater) must be installed between these twoparts.Because of this separation the secondary (cargo) system needs its own expansionvessel, pumps and other system accessories.The heating medium in the secondary part can be thermal fluid (160° – 120° C.) orhot water (150°-120° C.). To keep the heating surface (= price) of this intermediateheater limited, we raise the temperature of the heat production part to for example to260° C.This means that for the engine room heat consumers the same separate lowtemperature system with a mix-injection is needed as described above for bitumentankers.5.2 Tank-washA tank-wash heater can be installed in the system for tank-wash purposes. Theheater is temperature controlled by a two-way valve.。