milan efficient medium coal industrial dryer

milan efficient medium coal industrial dryer

Low-rank coals such as lignites are without doubt one of the most abundant fossil fuel sources worldwide. Due to their usually high moisture content and low heating value, the combustion of low-rank coals leads to higher specific CO2 emissions compared to the combustion of other fuels like natural gas. Nevertheless, by using state of the art technology to reach the highest possible plant efficiency, specific CO2 emissions can be considerably reduced, even when utilizing low-rank coals of extremely poor quality. Moreover by implementing state of the art Air Quality Control Systems flue gas emissions including CO, NOx, SO2, and dust are reduced, so that the strictest European environmental limitations can be kept. In this sense, using state of the art technologies for the utilization of low-rank coals may contribute to an affordable, cost competitive, and environmentally friendly electricity production for every type of low-rank coal to be utilized

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Small scale solar drying technology is relatively well established with a considerable amount of r & d activities having been undertaken for a considerable number of years. Larger scale solar drying techniques and systems, using equipment to facilitate and enhance the drying process, as opposed to using natural sun drying, are used in some industrialized countries

As to solar cooking, technologies have been developed in the past which operate to a greater or lesser degree of effectiveness. The sociological and cultural factors dominate this field, as well as the availability of solar radiation at the time when the preparation of food is required. As approximately 80% of the basic energy needs of many of the communities in developing areas is the provision of cooking energy, the serious implications of the deforestation, and subsequent soil erosion, pollution, and the lack of recycling of natural fertilizers have a significant effect on the overall productivities of these areas. Technologies exist today which can alleviate the demand for cooking fuel using solar energy

drying technology - an overview | sciencedirect topics

Typical direct coal drying technologies involve contacting the wet coal stream with heated gases such as combustion gases/air mixtures. The energy required for evaporation of the water is transferred mainly by convection, and the vaporised water almost invariably exits the drying stage contaminated with fine particles. Such dryers therefore include some mechanism of particle capture before venting the water vapour and combustion gases

A typical direct contact rotary dryer is illustrated by Fig. 15.39 (after Mular et al., 2002), which consists of three main sections. The first section heats the air by burning the fuel, which then passes to the second section where the wet coal enters and is dried in the rotary unit. The dried coal exits from the bottom of the end hood, while the vapour/gas stream passes to the third section. This is a bag-house which captures much of the fine particulate material before exhausting to atmosphere. Figure 15.39 depicts a co-current design, and counter-current units are also available where solids and hot air pass in opposite directions

A vertical fluidised bed is another form of direct drying system, shown schematically by Fig. 15.40, in which the hot combustion gases are used to fluidise the wet coal material. In this case, a cyclone is used to recover entrained coarser particles before passing the exhaust gases through a bag-house

Figure 15.41 shows two variations on an alternative fluidised bed dryer design in which a vibrating horizontal mechanism is used. These designs also show cool air inlets that enable additional control for possible overheating events

drying technology - an overview | sciencedirect topics

Figure 15.43 depicts a flash drying unit in which wet coal is added to a hot gas stream at a sufficient velocity so as to entrain all particles and carry them up the flash tube. The intimate contact between the gas and the wet solids facilitates very quick drying. In this arrangement, the cyclone is again used in conjunction with the bag-house to recover the dried coal particles. There is also an option to recycle product to achieve lower final moisture levels

Freeze drying is a third generation drying technology, which has four distinct stages: freezing, vacuum, sublimation and condensing. It has been shown to overcome issues of structural damage to the end product (Karel, 1975; Dalgleish, 1990) and the absence of air prevents oxidative deterioration, and there is no possibility of heat damage. Freeze drying is approximately 4–8 times more expensive than air drying (Ratti, 2001) and therefore the process is more commonly used for smaller scale applications producing very high value products. Lin Hsu et al. (2003) compared hot air, drum and freeze drying of yam flours and found antioxidants were more preserved in freeze dried samples, but otherwise little difference was observed between the drying technologies

The combination of spray drying and fluid bed drying technologies is also called multistage drying (from GEANiro, or integrated spray drying. Through the process, it is possible to produce coarse, agglomerated, free-flowing dustless powder. Feed material is sprayed into a fluidized drying chamber, where it is dried to single particles, which pass to the fluid bed. The smallest particles are swept along by the current and recirculated to the bottom of the drying chamber and to the fluid bed agglomerator (Fig. 10.5). The new single particles sprayed collide with these recycled small ones to form agglomerates, allowed by the stickiness of the drying particles

drying technology - an overview | sciencedirect topics

RWE Power in Germany has also developed a fluidized-bed drying technology for lignite. The technology concept developed by RWE is called Wirbelschichttrocknung mit interner Abwärmenutzung (WTA) technology (English: Fluidized-bed drying with internal waste heat utilization), which is arguably the most advanced superheated steam drying technique [13]

In the scheme of this very sophisticated system (Fig. 3.12), the lignite is first milled to a fine size by hammer mills that are placed in series with a two-stage FBD. The dried material exiting the bed is separated from the continuous phase and mixed with coarser particles from the bed bottom and directly injected into the boiler. The heat demands are provided by external steam originating from the turbine and transferred to the fuel particles inside the bed through tube bundles

A slightly modified design of the WTA process (Fig. 3.13) includes (1) an FBD using superheated steam, (2) a vapor compression step for recovering the latent heat from the process, and (3) the supply of energy to the drying solids. It is estimated that this specific system can provide drying of the raw material by reducing the moisture content by 48% (from 60% to 12%) using steam at 110°C and 50 mbar. A part of the steam at higher temperature is used for indirect heating of the fluidizing bed through submerged tube bundles [15]

drying technology - an overview | sciencedirect topics

Dehydration technologies have a long history in food processing and preservation. Seven well-known conventional drying technologies, from low-cost solar drying to high-cost freeze-drying, are considered in contrast to microwave techniques. In the scientific literature, and industry to some extent, microwave energy has been combined with several older drying techniques, usually in an attempt to accelerate drying rates. Fundamentals of microwave heating are examined including dielectric properties, microwave penetration, dielectric breakdown, and microwave-applicator designs. Microwave-assisted dehydration is discussed in convection, fluidized-bed, vacuum and freeze-dryers with a focus on limitations and benefits. Finally, live probiotics and other food cultures have been examined as examples of recent developments in microwave-assisted dehydration of challenging materials

An appropriate technology to minimize the post-harvest losses of dried agricultural commodities using the simple sun-drying technology is needed. The post-harvest losses include both quantity and quality losses; it seems that great tonnages of low quality sun-dried commodities were introduced to the market in developing countries in the past few years due to improper drying conditions. As living standards slowly rise in developing countries, it appears that there is a need to improve the manufacturing process for the supply of higher quality products to the consumer

Because of energy cost escalation and the decline of availability of certain fuels, solar energy was considered as a promising renewable energy source which can replace, either partially or completely, other energy resources in the development of sun-drying process. Extensive survey of the quality of sun-dried commodities showed that they have higher moisture content than recommended for safe storage and, therefore, they are easily infested by moulds and bacteria. There is also evidence of the presence of aflatoxins in such products, and low vitamin content of groups A, B, and C

drying technology - an overview | sciencedirect topics

The facility used to dehydrate agricultural commodities was designed according to the results of a questionnaire with reference to the market acceptability, consumer preference, harvesting time, fraction of harvest usually dried, and agriculture production in the country. Also, baseline data on climatic conditions, solar availability and drying operations were collected. The solar dryer used consists of a flat-plate collector with a surface of 24 m2, a drying chamber of a volume 2.5 × 2 × 2 m3 and a centrifugal fan of 2 hp to supply 800 m3 air/h. A chimney was installed to equalize the pressure inside the drying chamber to 10–15 cm water. Drying experiments were conducted during August, October, February, and March. Some agricultural commodities showed a wide market acceptability from the questionnaire. The drying temperature used was, on average, 60°C to remove about 70% moisture from commodities containing from 80–86% moisture initially. Ambient air temperature out and inside the drying chamber was recorded via thermocouples located in strategic points and connected to a potentiometer. Hygrometers were used to measure moisture content of the air entering and leaving the drying chamber. Drying time was recorded and samples were analyzed for their nutritive quality. Dried commodities showed long storage life and higher quality compared to sun dried products. The techno-economical evaluation showed a profit of 65.7%

The moisture content remaining after mechanical dewatering can be removed by thermal means. For a cofiring setup, it may be advantageous to use low grade waste heat to carry out thermal drying of the biomass. There are several types of dryers with varying sizes, configurations, and flows that can be used for this purpose

Flash (pneumatic) dryers: These are typically employed for rapid drying of particles suspended in a pneumatic medium, that also serves to transport these particles. However, these dryers are limited in their application for drying powders, cakes, granules, flakes, pastes, gels, and slurries, and cannot be applied to fibrous solids like biomass that cannot be dispersed (or fluidized) uniformly

drying technology - an overview | sciencedirect topics

Convective dryers: Are used with different convective heating media like flue gases, air, or superheated steam, and can be applied to drying a wide variety of types of solids. The dryers may either facilitate continuous or batch processing with the modes of gas-solid contact including: fixed/moving beds (conveyors), fluidized beds, and rotary dryers (tumbling dryers/kilns)

Conductive dryers: Conduction-based drying can use high temperature jacketing, externally wall firing, or the use of heated cartridges/inserts. Most commonly used configurations include drum dryers, paddle dryers, and jacketed kilns. These types of dryers are often used for applications like drying slurries, when there is a predominance of a liquid phase. For solids drying, these reactors suffer from low solid heat transfer coefficients, leading to higher temperatures requirements for the heating surfaces. Scaling up of these reactors is also difficult due to the limited volume-to-surface ratio

Radiative dryers: These dryers typically the involve the use of microwaves and infrared radiation in several reactor configurations. The advantage of these reactors is that the input energy can be used over a well-defined and targeted drying zone. Microwaves specifically have high penetration and can effectively target the moisture contained in the bulk of the biomass

drying technology - an overview | sciencedirect topics

However, the primary energy source for these dryers is electricity, leading to questions of affordability with processing very large quantities of a relatively low value product in a power production process. Even as thermal drying can lead to a complete removal of moisture, biomass has the potential to reabsorb water from the surrounding air up until it reaches its equilibrium moisture content. Reabsorption can be limited to an extent by pelletization. However, contact with liquid water must still be prevented leading to the requirement of indoor storage

A remarkable (but catastrophic) consequence of liquid water reabsorption was experienced in combating accidental fires in biomass storage silos. Attempts to quench the silo fire with water led to the stored wood pellets reabsorbing a large quantity of water. This resulted in a large increase in the weight of the fuel, resulting in structural damage to the silo. Hence, the design of firefighting measures employed for wood pellet silos must take this factor into account (Fig. 2.7)

Much attention has been made to upgrading technology of low-rank coals. This technology is largely divided into drying and stabilization technologies. The drying technology uses unused energy such as combustion flue gases or steam from on-site power plants to dry coal. The stabilization technology prevents spontaneous combustion from occurring in the process of stockpiling or transporting of coal after drying it

drying technology - an overview | sciencedirect topics

Many countries around the world have recently developed coal drying technologies by using waste heat. Among them, DryFining technology and WTA (Wirbelschichttrocknung mit interner Abwärmenutzung) technology are commercialized. What they have in common is that they both use fluidized-bed technology. The DryFining technology uses air fluidized-bed drying technology, and the WTA technology uses steam fluidized-bed drying technology (Fig. 4.6 [12])

The DryFining technology uses air fluidized-bed drying technology. It collects heat from a cooling tower and increases air temperature to 43°C and uses it as a fluidizing medium. It is reported that this technology has reduced moisture in coal by 9% from 37% to 28%, the use of coal to 14%, increased generating efficiency to 2%–4%, and significantly reduced SOx, NOx, and CO2

The WTA technology uses steam fluidized-bed drying technology. It uses waste steam from power plants. This technology reduced moisture in lignite from 50% to 12%, increasing lignite combustion boiler efficiency by 4%, from 43% to 47%. When it is used for a 1000 MW power plant, it can reduce approximately 1 million tons of CO2 annually

drying technology - an overview | sciencedirect topics

COMBDry technology is a hybrid technology combining the advantages of fluidized-bed drying technology and flash drying technology. It uses a vertical column to bring into contact coal and a drying medium through counter current. Several baffle plates attached within the column disrupt drying medium flow, forming turbulent flow, and increasing contact efficiency (Fig. 4.7). It is reported that this technology has drying efficiency of more than 70% with relatively short residence time (3–5 minutes) at a relatively low temperature (<150°C)

The reason why the COMBDry technology has high efficiency with relatively short residence time at a relatively low temperature is that it keeps driving force during drying period (Fig. 4.8). Low-temperature coal particles are injected from the upper part of the column while high-temperature drying media are injected from the lower part of the column. The temperature of coal particles increases gradually as the particles move down through the column while the temperature of the drying media decreases as it moves up through the column. As a result, surface moisture, which is removed at low temperatures, is removed at the upper part of the column and inherent moisture, which is removed at high temperatures, is removed at the lower part of the column

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