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   发布的项目: 编号:8 (入库日期: 2005-2-14 ) 此记录目前共被浏览:2510 次
项目名称: 石油化工设备/工艺技术翻译
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具有5年以上石油化工技术翻译经验,熟悉化工静/动设备、化学工艺等相关专业知识。具有较强的语言文字表达能力,有高超的跨语言理解能力。勤奋敬业,认真细致,有充足时间和精力圆满完成每年80万字以上的翻译任务。

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源语种: 英语 目标语种: 简体中文
涉及行业: 化学/石油/化工 项目字数: 800,000
项目招标期: 2005-2-20 项目完成期: 2006-2-20
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   翻译样本:
Critical to the effectiveness of decomposition are temperature and evenness of the temperature profile, maintenance of steady waste feed rates, good atomisation of the waste feeds via spray nozzles, even distribution of the waste feeds, and a small but positive excess oxygen level. Furnace pressure must also be controlled at a slight vacuum, to ensure that noxious gases are contained. · Furnace Temperature Temperature is controlled in the furnace by varying the rate of fuel burning in the three furnace burners. · The prime control element is TC12021. This takes the middle value of three temperature readings, TE12021 A, B & C, from the exit of the vertical furnace section (the "throat temperature"). The temperature controller TC12021 provides an input to a "furnace load" controller (or kilowatt controller) within the DCS. This controller manages the increase or decrease of fuel required to control the temperature, and with it the air required for combustion. Changes in fuel are always made in such a way that the system will always be air rich. Hence, on increasing fuel demand, the air will be increased and the fuel will follow, and on reducing fuel demand, the fuel will decrease and the air will follow. There is also a feed-forward element to the temperature control from the waste feeds fed to the furnace, so that a change in feed will lead to a control response before the impact is seen fully on furnace temperature. Low furnace temperatures will lead to poor decomposition of the waste feeds. This can be the case for general low temperatures or simply as a result of cool zones in the furnace. Poor decomposition is the single most harmful effect on the long-term performance of the SAR plant, leading as it does to corrosion in the heat recovery section, and both acute and chronic fouling in the gas cleaning section and possibly downstream. Therefore, the furnace temperature is monitored at several places: TI12018 and TI12019 in the vertical section; TI12016 and TI12017 in the horizontal section; TI12023 and TI12024 in the exit duct to the waste heat boiler. All of these have low temperature alarms. High furnace temperatures can lead to damage to the furnace refractory system. · Fuel feed rates to the burners Control of fuel feeds is complicated by the fact that there are two possible main fuels (oil or gas), which could be in use either together or separately, and also there is a third fuel source, the MMA vent gas. The primary control on the MMA vent gas feed to the burners is the vent header pressure controller, 50PC20039, which is cascaded onto vent gas flow controller FC12157, acting on flow control valve FV12157. The intent is to consume all vent gas available, so this controller will normally dictate the feed rate of vent gas. However, there are limits on the vent gas rate, so that the main fuel must always be at or above its low fire setting, and must also account for at least 30% of the total furnace energy (kilowatt) demand is always burned as a priority, up to as much as is available. The furnace kilowatt controller works out the increase or decrease in main fuel rates required to maintain the desired temperature. To do this, it takes into account a notional heat value for each fuel (including the MMA vent gas). Fuel oil rate is controlled by flow controller FC12163, which acts onflow valve FV12163. Fuel gas rate is controlled by flow controller FC12154, acting on flow valve FV12154. MMA vent gas rates will continue to be dictated by MMA vent header pressure, subject only to satisfying the constraints mentioned above, so that it is the main fuels which vary to take up the changing demand. The ratio of the main fuels being fed, if both are in use at the same time, is maintained as the fuel rates are changed. The ratio of fuels can be changed at any time by the operator, by altering one of the fuels gradually in manual flow control, leaving the other to respond to changes in demand from the kilowatt controller. When switched back into auto, the kilowatt controller will control at the new ratio established. The fuel rate being controlled by the respective flow controller will be fed equally to all three furnace burners as they are fired up. If only two are fired up, then the fuel will be split between those two, etc. This does mean that a given burner could be over-fired in certain circumstances, although the burner limitations should restrict this. · Air flow control The rate of air flow to the furnace is measured in the common duct to the three furnace burners by flow controller FC11003. The flow is controlled by the speed of the Process Air Fan FN1102X, through flow controller FC11003. The set point for the flow controller is generated by the furnace kilowatt controller, so that there is always sufficient oxygen to meet the changes in fuel rate. The changes in waste feed rate are also used to provide an element of feed forward control to the air rate in the same way as to the fuel rate. The air flow controller set-point is also affected by the extra demand for oxygen arising from the furnace oxygen controller. This is discussed below. This oxygen value provides a trim control to the air flow controller FC11003. Note that, in furnace heat-up mode, before waste feeds are applied and while the converter is being preheated, the air supply to the furnace is drawn in under vacuum through FV12002 in the start up airduct, which tees into the main burner air feed duct between the preheaters and the decomposition furnace burners. The motive force for the air flow at that point is suction from the start-up fan, FN1301, located after the boiler/superheater package, rather than from the main plant blower, which is used instead for converter heat-up. This arrangement is described in greater detail in a separate document of preheat controls. · Oxygen control Oxygen in the furnace gases is measured in three analysers located at the end of the horizontal furnace, AI12027A, B & C. The lowest of these is used as the input to furnace oxygen controller AC12027, which provides a trim signal to airflow controller FC11003, as above. Control of furnace oxygen is critical to the process. If oxygen falls to zero, the SO2 in the gas stream can be reduced back to elemental sulphur, which will sublime (condense directly into a solid form) from the gas stream as it cools. This will lead to major fouling with sulphur in the heat recovery and gas cleaning sections, and possibly beyond, and will cause a major outage to clean up. If furnace oxygen is too high, the equilibrium between SO2 and SO3 in the furnace will shift towards SO3, leading to wasted sulphur species (and hence increased fresh acid purchase) and also to high weak acid effluent treatment costs. While this is undesirable, it is in the end only a cost issue, and is easily preferable to the consequences of low oxygen. For this reason, it is better to err on the side of high oxygen levels, and oxygen levels are normally increased above the usual target levels when any significant change is being made on the furnace. For this reason also, there is an interlock sequence in the DCS which will remove feeds in a stepwise fashion, with the higher oxygen consumers first, if a low oxygen level exist. Eventually, if the low level persists, all feeds will be cut off, leaving just the furnace burners operating. The oxygen analysers require a lot of maintenance attention to keep them working reliably. Because of this, each analyser has a "maintenance" setting, which effectively takes the analyser out of the control loop when it is being maintained or calibrated. Because of this inherent unreliability, to avoid too many spurious interlock actions, the low oxygen interlock operates on a two-out-of-three system to initiate it.