文献翻译-蒸发器能源公告

中英文翻译 英文原文 Energy Bulletin on EVAPORATORS ADB Energy Efficiency Support Project The Government of India and the Government of Netherlands have jointly launched a project entitled “Energy Efficiency Support Project (EESP)”to promote and accelerate the energy and environmental activities pertaining to the Indian industry. The project is sponsored by the Asian Development Bank (ADB) and ICICI Ltd. Confederation of Indian Industry (CII), an apex industrial association, is one of the executing agency for the project and is responsible for carrying out promotional activities with the support of Energy Management Centre (EMC) and Tata Energy Research Institute (TERI). Under this promotional activity, CII will publish energy bulletins periodically and circulate among the industry. This bulletin will cover the energy conservation aspects in evaporators, specific to the sugar industry. Introduction Evaporation is the process of removal of volatile solvent by vaporization, from an aqueous solution consisting of non-volatile solute. In majority of the cases of evaporation, the solvent is water. Evaporation plays a major role in the manufacture of a variety of products in chemical process industries, including food processing, pulp & paper, pharmaceuticals, fertilizers etc. However, this bulletin will focus only on the evaporator applications in the sugar (food processing) industry. Of the various types of evaporators available, the most commonly used type of evaporator in a sugar industry, for the concentration of treated juice, are the short tube vertical evaporators. Classification of evaporators Short tube vertical evaporators These are natural circulation evaporators and are commonly referred to as calandria or standard evaporators. These consist of short tubes, 4 - 6 ft long and 2 - 4 diameter , set between two horizontal tubesheets , arranged within the evaporator body. The tube bundle contains a large circular downcomer , which returns the concentrated juice from above the top tubesheet, to below the bottom tubesheet, for final product withdrawal. The driving force for flow of juice through the tubes is the difference in density between the liquid in the downcomer and the two-phase mixture in the tubes. Short tube vertical evaporator Advantages These evaporators can be used even with liquids that have a tendency to scale, since evaporation takes place inside the tubes, which are accessible for cleaning, fairly high heat transfer coefficients are obtained with thin liquors (i.e., dilute solutions of 1-5 c P ) and they are relatively inexpensive, provided that they are made of carbon steel or cast iron. Disadvantages A large heating area is required, since the units are broad, heat transfer coefficients are sensitive to the temperature difference and liquor viscosity ,due to the large liquid hold-up, these evaporators cannot be used with heat sensitive materials and such evaporators are unsuitable for crystalline products , unless agitation is provided to produce forced circulation. Industrial applications : These short tube vertical evaporators are suitable for non-corrosive, clear and non-crystallising liquors, such as sugarcane juice. Rising film evaporators The rising film evaporators are more commonly referred in the sugar industry parlance as Kestner type evaporator. Steam condenses on the outside surfaces of vertical tubes. The liquid inside the tubes is brought to a boil, with the vapour generated occupying the core of the tube. As the fluid move sup the tube, more vapour is formed, resulting in a high core velocity. This forces the remaining liquid to the tube wall. This leads to a thinner and more rapidly moving liquid film. As the film moves more rapidly, heat transfer coefficients increase and residence time drops. Advantages Since feed enters at the bottom, the feed liquor is distributed evenly to all tubes, as a large heat transfer area can be packed into a given body , they occupy less floor space and heat transfer coefficients are high and are especially suited for foaming or frothing liquors. Disadvantages Heat transfer is difficult to predict, the hydrostatic head requirement may create a problem with heat sensitive products, pressure drop is higher than for falling film types and there is a tendency to scale. Rising film evaporator Industrial applications : Major applications include concentration of black liquor in paper plants ,concentrating nitrates, spin-bath liquors, electrolytic tinning liquors etc. Falling film evaporators In this type, the feed liquor is introduced at the top tube sheet and flows down the tube wall as a thin film. Since the film moves by gravity, a thinner and faster moving film forms. This results in higher heat transfer coefficients and reduced contact times. In a typical sugar industry evaporator, the average contact time between juice and steam is about 30 seconds, as against 3 minutes in the Kestner type evaporator and 6 - 8 minutes in the conventional short tube vertical evaporators. This offers an excellent opportunity for using high temperature and pressure steam, as the risk of caramelization of steam syrup is avoided/ reduced. Hence, 1.5 kg/cm at a 2temperature of 120C can be used in the I- effect of the evaporator. Advantages Heat transfer coefficients are high, there is no elevation in boiling point, due to the absence of hydrostatic pressure, satisfactory operation at low temperature driving forces, concentration of heat sensitive products can be achieved, due to the very short contact time of about 30 seconds, temperature driving force is not limiting and a broader range of applications is possible and vapour bubble obstruction is avoided, as the vapour is entrained with the juice filling the interior of the tube. Falling film evaporator Disadvantages Heat transfer is difficult to predict, there is a tendency to scale at higher concentrations and uniform feed distribution is a major problem Industrial applications : These evaporators are finding increasing use in the sugar industry. In addition , they are used for concentration of urea, phosphoric acid in fertiliser industries and black liquor in paper industries. They are used, especially, for applications handling foaming or frothing liquors. Evaporator arrangements Most evaporators are heated by steam condensing on the outer surface of tubes and nearly always the material to be evaporated flows inside the tubes. Usually, the steam is at a low pressure and the boiling liquid is under moderate vacuum. Reducing the boiling temperature of the liquid, increases the temperature difference between the steam and the boiling liquid, thereby increasing the heat transfer rate. Single effect evaporators : Evaporation by heating with steam in a single vessel is called evaporation in a single effect. They are used when the required capacity is small, steam is cheap and are operated in batch, semi-batch or continuous modes. This method of operation is rarely used, since it requires that the body be large enough to hold the entire charge of feed. Multiple effect evaporators: If the vapour from the first evaporator is taken for heating in a second evaporator, we have a double effect. The heat in the original steam is reused in the second effect. The evaporation achieved by a unit mass of steam fed to the first effect is approximately doubled. Additional effects can be added in the same manner. Thus, with three vessels, we have a triple effect and so on like a quadruple, quintuple or a sextuple effect. There are thus as many evaporator vessels as the effects. The most common evaporators encountered in practise are the triple, quadruple and quintuple effects. Steam economy Evaporator performance is rated on the basis of steam economy. Steam economy is defined as the kilograms of the solvent evaporated per kilogram of steam used. The greatest increase in steam economy is achieved in a multiple effect evaporator, by using the vapour from one effect as the heating medium for the next effect, in which boiling takes place at a lower temperature and pressure. The steam economy of a multiple effect evaporator will increase in proportion to the number of effects. Evaporator performance The evaporator is the major steam consumer in a sugar plant. The evaporator concentrates the juice from a level of 14 16 Brix to a level of 60 65 Brix. The exhaust steam is used for this purpose as it offers the leas steam consumption. Steam economies of 3 to 5 can be achieved, depending on the number of effects. Several types of evaporators are used in the sugar industry. The commonly used are the quadruple and quintuple effect evaporators. Typically, the steam enters the first effect at a pressure 1.1 kg/cm and a temperature of 105 C. The vacuum in 2the last effect is maintained around 650 mm Hg. The installation of a falling film evaporator (FFE) can be considered for the first three effects of a multiple effect evaporator system. FFE cannot be used for the IV- effect and V- effects, as the possibility of thick and sticky scale formation is high with thickened sulphited juice. This type of configuration has possibilities for extensive vapour bleeding, with only marginal vapour going to the condenser. The vapour bleeding can be as shown below: Such a configuration will offer the maximum steam savings in the evaporator system (up to 36% reduction can be achieved). Another very important aspect, which needs to be taken care of in an evaporator, is the effective utilisation of the area available in the evaporator. It is recommended to raise the clear juice temperature, very close to the boiling point, at the pressure prevailing in the first effect. The heating can be done by use of exhaust steam in a plate-type heat exchanger. Condensate recovery The recovery of the condensate from the evaporator section is very important, for attaining higher levels of thermal efficiency of the system. Generally, among the Indian sugar plants, the exhaust condensate is directly taken to the boiler house and reused as boiler feed water. On the other hand, the later effect condensate (vapour-condensate) is utilised as hot water for imbibition , cleaning, centrifuge washing etc.). Conclusion Evaporator is a major steam consuming equipment in a sugar industry. The evaporator performance has a direct bearing on the steam consumption of the sugar plant. The installation of falling film evaporators for the first few effects, combined with the practice of extensive vapor bleeding, can result in major reduction of steam consumption. 中文翻译 蒸发器能源公告 亚行支持能源效率项目，印度政府和荷兰政府的联合发起了一个题为“能源效率项目支持（ eesp） ”来推动和加快属于印度工业的能源和环境的活动。该项目是由亚洲开发银行（ ADB）和印度公司赞助 印度工业联盟（ CII） ，顶点工业协会，是项目的执行机构，负责与能源管理中心的支持开展促销活动（ EMC）和塔塔能源研究所（特里） 。 这次促销活动下， CII 将发布能源公报定期和产业间的循环。本公告将在蒸发器的节能方面，具体到制糖工业。 景区简介 蒸发是通过蒸发去除溶剂的挥发过程中，从水溶液组成的非挥发性溶质。在大多数情况下，蒸发的溶剂是水。 蒸发的化学过程工业中的各种产品的生产中起着重要的作用，包括食品加工，造纸，医药，化肥等。然而，本公告将只集中在糖蒸发器（食品）行业的应用。 可用各种类型的蒸发器，蒸发器在制糖工业中最常用的类型，治疗汁浓度，是短管立式蒸发器。 蒸发器的分类 短管立式蒸发器 这些都是自然循环蒸发器通常被称为排管或标准式蒸发器。这些由短管， 4 - 6 英尺长和 2 - 4“直径，设置两个水平管板之间，设置在蒸发器体。 管束包含一个大的圆管，它返回的浓缩果汁从上面到下面的管板，管板的底部，最终产品退出。驱动力的流汁通过管之间的液体密度的差异在降液管和两相混合物在管。 垂直短管蒸发器 优势 蒸发器可即便有倾向于规模的液体，由于发生蒸发管内，并易于清洗，相当高的传热系数与薄的酒获得的（即，稀 1-5 C P 解决方案） ，他们是相对便宜，但它们是由碳钢或铸铁。 缺点 加热面积大是必需的，因为单位是广阔的，传热系数的温度差和白酒类的粘度变化比较敏感，由于大的持液率，蒸发器不能用于热敏感材料，这种蒸发器不适合结晶的产品，除非搅拌以产生强制循环。 工业应用：这些短管立式蒸发器适用于非腐蚀性的，明确的和非结晶的酒，如甘蔗汁。 升膜蒸发器 升膜蒸发器通常在制糖工业中的说法是凯斯特纳式蒸发器。蒸汽凝结在垂直管外表面。管道内的液体煮沸，用蒸汽产生的占管的核心。当流体移动支撑管，形成更多的蒸汽，导致在一个较高的核心速度。这迫使剩余的液体的管壁。这导致了一个更薄、更快速移动的液体膜。作为电影的动作更为迅速，传热系数增加，停留时间下降。 优势 由于饲料进入底部的饲料，白酒类均匀分布的所有管，作为一个大的传热面积可以装入一个特定的身体，他们占用地面空间小、传热系数高，特别适合于发泡或发泡酒。 缺点 传热是很难预测的，静水压头的要求可能会造成与热敏感产品的问题，压力降比降膜类型，有一种倾向量表。 升膜蒸发器 工业应用：主要应用包括 浓度的黑白酒类在造纸厂，浓缩硝酸盐，自旋浴溶液，电解镀锡液等。 降膜蒸发器 在这种类型的饲料，白酒类介绍在顶部管板和流管壁作为薄膜。由于重力的动作片，更薄和更快的移动的电影形式。这导致更高的传热系数，减少接触时间。 在一个典型的糖业蒸发器，果汁和蒸汽之间的平均接触时间约为 30 秒，在 3 分钟的凯斯特纳式蒸发器和 6 在常规的 8 分钟 在一个典型的糖业蒸发器，果汁和蒸汽之间的平均接触时间约为 30 秒，在3 分钟的凯斯特纳式蒸发器和 6 在常规短管立式蒸发器 8 分钟。这提供了使用高温高压蒸汽的一个极好的机会，作为蒸汽糖浆，焦糖化避免 /减少。因此，1.5 公斤 /厘米 120的温度可以用在我的蒸发器的影响。 优势 传热系数高，有没有在沸点升高，由于静水压力的缺失，在较低温度下的驱动力，令人满意的