【正文】 s post pile. The microanisms in the medium depose the pollutants in the exhaust, similar to the action that breaks down posted leaves and grass clippings into a soil conditioner. The biofiter39。s misconception that the emissions are polluting the surrounding environment. In many applications, both material and thermal pollution of air and water is founded such as hot dirty air or water streams. 4. Air pollution prevention from VOCs Volatile anic pounds (VOCs) are precursors (when bined with NOx) to the ozone problem. Some of the VOCs (or effluent contaminants and odor) are: anic solvents, phenols, aldehydes, oil mists, phthalic anhydride, sulphides, mercaptans, odors, and sewage gases. Some of the applications in which VOCs generated are as follows: general 23 manufacturing (wire enameling facilities, paint bake ovens, glass 174。 and regenerators (rotary and fixedmatrix type) and recuperators (prime surface, platefin, tubefin type) for flue gas and other polluted gas applications that do not have heavy fouling. When the aforementioned conventional exchangers are used for pollution prevention/mitigation applications, they do not require any additional special construction/design features in general. However, heat exchangers for high temperature applications, for corrosive environment, and having dual function of catalytic action and heat transfer need to be developed for pollution prevention applications. For further details on the construction features, design methodology and operating problems for heat exchangers, see Ref. [3]. 21 3. Environmental pollution Environmental Pollution is the release of any substance into air, water or land that is detrimental to the quality of life. Air Pollution is the release of any potentially harmful substances into the atmosphere, which endanger human health or the environment. Air pollutants can be gases, liquid droplets, particles or fibers. The role of heat exchangers to prevent or minimize air pollution from industrial processes will be discussed in this paper in more detail. Water Pollution is the release of potentially harmful chemical, physical, or biological substances into surface water (lakes, streams and estuaries), groundwater and oceans. Land Pollution is the release of potentially harmful solid or liquid substances into the soil. Thermal Pollution of water is the discharge of heated water from industrial processes that can kill or injure aquatic anisms. Most thermal pollution e from the hot cooling water discharges from electric power plants, followed by that from cooling operations of 22 industrial facilities such as metal smelters, processing mills, petroleum refineries and chemical manufacturing plants. Heated wastewater can harm the environment in two ways: first by raising the temperature of the receiving stream or bodyofwater above the range that can support the aquatic habitat。 [1]. The concept of Sustainable Development recognizes that economic growth and environmental protection are inextricably linked — goods and services must be provided in an ecoefficient manner— while progressively reducing environmental impact and resource intensity throughout their life cycle. Heat exchangers can help reduce the energy intensity of goods and services. Heat exchangers allow for the utilization of waste heat, processes to be integrated to reduce energy requirements, and energy to be exchanged between processes [2]. 2. Heat exchanger types A heat exchanger is a device that is used for transfer of thermal energy (enthalpy) between two or more fluids at different temperatures and in thermal contact. Typical applications involve heating or cooling of a fluid stream of concern, evaporation or condensation of a single or multiponent fluid stream, and heat recovery or heat rejection from a system. In some heat exchangers, the fluids exchanging heat are in direct contact. In other heat exchangers, heat transfer between fluids takes place through a separating wall or into and out of a wall in a transient manner. In most heat exchangers, the fluids are separated by a heat transfer surface, and ideally they do not mix. Such exchangers are referred to as direct transfer type, or simply recuperators. In contrast, exchangers in which there is an intermittent heat exchange between the hot and col d fluids — via thermal energy storage and rejection through the exchanger surface or matrix — are referred to as indirect transfer type, or simply and chemical 20 reaction may take place in the process in which heat exchangers are used such as in boilers, fired heaters, and fluidized bed exchangers. Mechanical devices may be used in some exchangers such as in the scraped surface exchangers, agitated vessels and stirred tank reactors [3]. Heat exchangers could be classified in many different ways such as according to transfer processes, number of fluids, surface pactness, flow arrangements, heat transfer mechanisms, type of fluids (gas— gas, gas— liquid, liquid— liquid, gas— twophase, liquid— twophase, etc.) and industry. Refer to Shah and Mueller [4] for further details. The most monly used heat exchangers for pollution prevention and mitigation are as follows: shellandtube for liquids, vaporization and condensation applications, and also for gases at high pressures and temperatures。 pollution control equipment because they help minimize operating costs. In the recent years, heat exchangers have bee important in implementing the concept of Pollution Prevention. The prevention approach is preferred because it is a longterm solution to pollution problems. For Pollution Prevention, the preferred hierarchy for waste management consists of four steps: (1) generation prevention, (2) recovery and recycling, (3) treatment to reduce volume and toxicity, and (4) proper disposal of a