Idaho Steel, a company in Idaho Falls that manufactures food processing equipment, has the worlds largest drum dryer. Jon Christensen, the companys sales and marketing director, tells EastIdahoNews.com the drum dryer is an 8-foot by 21-foot tube filled with steam that prepares potatoes for dehydration.
It receives mashed potato from the rest of the processing line and applies a very thin layer a smaller applicator (then) rolls on the surface of the drum. As that comes around, it comes to a sharp knife that will cut that off into sheets of potato flakes. It almost looks like sheets of paper, Christensen says.
The drum dryer then grinds the sheets down into flakes sized according to the customers specifications. Once the flakes are fully dehydrated, its packaged for sale in stores or used to make other products like chips, french fries or hash browns.
The better we can transfer the heat of the steam to the potato, the quicker we can dry and the higher the capacity, says Christensen. This is a new design with some new technology in it that is doing some amazing things. Its the holy grail of drum dryers right now.
The drum dryer is part of a complete potato production line consisting of sorting, peeling, cutting, blanching, cooling and cooking equipment. Though other companies use drum dryers to process potatoes, Idaho Steel owns the largest one in the world and uses it to serve clients and customers across the globe.
Kiremko builds some of the machines and we build some, but our machines (are) complementary. So by intermingling their machines with ours, we could (offer the full production process from start to finish), says Christensen.
China is starting to process more and more potatoes. They currently have a lot of rice, but (the production process is harder and more expensive), so they are changing from rice to potatoes, he says. At this moment, we are seeing an increase of sending machines to China, and we use machines from Idaho Steel to set up in China.
Idaho Steel celebrated its 100th year of business last year. In the early days, it only produced potato harvesting equipment but later grew to produce other food processing equipment. Today, Idaho Steel employs about 300 people.
Current environmental policies, which promote a more sustainable food sector, have boosted efforts to reduce energy demand during processing, and particularly during drying operations. One of the routes towards more sustainable and efficient drying processes is the design and implementation of optimal operational routines for the existing drying equipment. In the food industry, drum-dryers are typically employed for the production of food powders from viscous slurries (e.g. starchy slurries). Food powders are used in a wide range of applications in the food industry, from beverage powders (milk or cocoa), instant soups, spices or flours and flavours. In this framework, we propose a model-based optimisation routine for the operation of a double drum-dryer (product under atmospheric conditions) used in the manufacture of a breakfast cereal porridge. The problem defines optimal steam temperature and optimal rotation speed that minimises the energy demand of the dryer operation for a range of operating conditions that considered different: product formulation, final moisture contents, thickness and initial temperature of the wet slurry. Overall, this work demonstrates the potential of model-based approaches to the design and optimisation of more sustainable and efficient industrial drying technologies in the food sector, which can help in the achievement of short/medium-term energy reduction goals.
Many products that normally require cart rotation in a dry can now be batch-dried in the Super McKenzie - optimal results with minimal oversight. This dehydrator is quite a different beast than the regular McKenzie tunnel: the redesigned drying chamber is now slighter wider and slightly shorter, in order to best channel large quantities of hot air hot air that circulates first in one direction, then in a reverse flow. We submit that hot air flowing in two directions is better than hot air that just flows in one direction. Its better in terms of improved product flavor, texture, color, and product uniformity. And for our clients doing large-scale dehydrating its better for the bottom line, period.
A properly sized and tuned drum dryer system suited to your input volume is the key to planning an efficient system. Baker-Rullman's specialized engineers are dedicated to accomplishing these goals with each and every installation.
Our trunnion rollers are made from Class 50 cast iron with a minimum roller face hardness of 270 BHN. The inboard tapered roller bearings, which have a 'B-1-' life of 15 years, allow the roller to rotate around our stationary roller shaft supported by our hold-down pillow blocks. Baker-Rullman has proven this to be more reliable than the smaller diameter roller with an integral cast shaft system that is offered by our competition.
Baker-Rullman drum tires are designed and manufactured significantly different from those used by other vendors. Each tire is hot forged from a single billet of AISI 1025 steel, then finish machined. There is no weld seam on it, and the steel grain structure is oriented for greater wear resistance and strength. It is forged into a "T" cross-section instead of the usual rectangular bar cross-section other vendors generally supply using rolled and welded bar stock.
Baker-Rullman rotary drum dryers use less fuel per ton of product than many other drum dryers and do so in significantly less space. The triple-pass design provides approximately three feet of horizontal material travel for every foot of drum length. Precise electronic controls eliminate heat surges and fuel waste.
Baker-Rullman triple-pass rotary drum dryer to achieve efficiencies better than 1,500 BTUs per pound of water evaporated. This is the result of better heat utilization created by longer residence times, robust temperature control, and superior drum insulation.
Our triple pass dryer design protects your product from under or over drying. Heavier, wetter product moves slower than fine particles, giving uniform drying to all particles. That's why our rotary dryers have long been known for protecting the protein value of food by-products and the integrity of all types of material.
V.O.C. (Volatile Organic Compounds) emissions can cause pollution problems and restrict your production rates. Heat utilization in a Baker-Rullman system is superior to that of the other rotary drum dryers by virtue of the triple-pass rotary dryer design, eliminating unnecessary V.O.C. emissions.
Banana is one of the most widely consumed fruits in the world. It is produced in 135 countries and territories across the tropics and subtropics. India ranks first in the production, next are China, the Philippines, Ecuador, Brazil, and Indonesia. The fruit comes in a different size, with delicious, sweet and creamy flesh covered with an outer peel which may be green, yellow, red, purple, or brown when ripe.
Bananas are highly perishable due to their high moisture content and therefore very susceptible to postharvest losses during handling, transportation, and storage. Thus, it is of great importance to use an appropriate process method to reduce the losses. The drying process is one of the alternative ways to preserve food quality and increase its value. The objective is the removal of water to a level which prevents deterioration. The major motives are an extension of shelf life and reduction in volume. Drying process of banana is a process involving simultaneous heat and mass transfer. During the banana drying process, moisture in bananas diffuses from the internal to the surface and evaporates into the air stream; meanwhile, heat is transferred from the air to bananas. When moisture is removed, the volume of bananas decreases.
Traditional sun drying takes place by laying the banana under direct sunlight. Sun drying is cheap, but the product obtained is often of inferior quality due to contamination by dust, insects, animals, and rain. Also, direct exposure to sunlight causes the loss of vitamins and unacceptable color changes.
Using solar energy for food drying is environmentally friendly and economically feasible. Compared with sun-drying, solar dryers generate higher air temperatures and lower relative humidity, which results in shorter drying time and lower product moisture content. The method also protects the banana from contamination due to the higher temperature and enclosed structure. The finished product is of better quality.
Hot air drying is the most commonly used drying method for food preservation and has been widely applied for drying bananas. However, due to the low thermal conductivity of banana, this method always results in low efficiency of heat transfer, which renders low energy efficiency and long drying time. The quality of the dried product is often reduced in terms of color, rehydration ratio, texture, and other characteristics.
Vacuum enables moisture contained in the food to evaporate at a lower temperature, which gives better product quality, especially for foods which are heat-sensitive in nature. In addition, vacuum drying can help prevent oxidation since there is no air in the environment. Products dried by vacuum driers sustains better color, texture, and aroma compared to those that were air-dried.
For freeze-drying, the absence of liquid water and low temperature render a finished product of excellent quality with minimal reduction of volume. However, freeze drying is expensive and time-consuming for manufacturing dehydrated products.
Under the microwave field, microwave energy is mainly adsorbed by water polar molecules inside the food material. The polar water molecules tend to align themselves according to the electric field as they alternate at very high frequencies. Heat is produced due to friction between oscillating molecules, which results in rapid evaporation of water. Compared to conventional hot air drying, microwave drying results in high thermal efficiency, shorter drying time and improved quality of the finished product.
Osmotic dehydration is initially started with partial removal of water by immersing in a concentrated solution of osmotic agents such as sugar and salt. Water/solutes diffuse from and into the material through a semi-permeable cell membrane, which allows water to pass through them more rapidly than sugar. The fruit is subsequently dehydrated in the air drier where moisture content is further decreased. Osmotic dehydration minimizes heat damage to the flavor, aroma and nutritional content of the product, prevents color changes and reduces the loss of volatile compounds.
Spray drying process by spray drying machine is mainly used for drying banana fruit to produce the banana powder. During spray-drying, the feeding flow of the particulate fluids is sprayed into hot air to produce dried particles. This method features rapid drying speed. By drum drying, the banana pulp is dried into flakes by applying in thin layers onto the outer surface of drum which is heated by steam, and then further dried in a tunnel or cabinet dryer to 2% moisture content. The flakes are then pulverized to make powder. Drum dryers normally have high energy efficiency.
Hot air oven is for hot air drying of various materials including banana. The cabinet dryer uses steam or electricity as heat sources and axial flow fan for forced ventilation. Foods are placed in the trays and the trays are put on the trolley, then push into the drying room for drying. The circulation system is fully closed, most air circulates in the oven, having high thermal efficiency and saving energy. Forced ventilation combining with adjustable air distribution plates achieves temperature balance in the oven, enabling the foods to be dried evenly.
Microwave drying machine adopts microwave to dry the foods, having rapid drying speed and uniform drying effect. Thermal effect and non-thermal effect works together, achieving sterilization at low temperature and short time, the flavor and nutritional components of food are retained to the maximum. Microwave works directly on the food, there is almost no other heat loss, having high thermal efficiency and saving energy. The machine is highly automatic and easy to control.
Meet the Morus, a tiny, tabletop vacuum dryer that works with stunning efficiency to completely dry and de-wrinkle your clothes in mere minutes. Rather than relying on centrifugal force to dry your clothes, Morus uses a combination of heat and a vacuum to extract every drop of water from your clothes giving you perfectly dry garments you can immediately take out and wear! The technology is a little new-fangled, but to uncomplicate how it works the Morus uses heat to turn water into vapor (not steam), and generates a vacuum to reduce the pressure to just below the vapor pressure of water (0.0313 atm). This basically accelerates the drying process, extracting every bit of water from your clothes so that theyre 100% dry when they come out. A spinning drum on the Morus ensures that every corner of the clothes you put in is exposed to the heat and the vacuum for the highest efficiency, and a reverse-tumble feature makes sure your clothes dont get crumpled or wrinkled in the process. To top everything off, the Morus even UV sterilizes your clothes before giving them to you, so not only are they perfectly dry, theyre safe and disinfected too!
Morus gets a lot of things right, from its innovative technique, to its small size, and even energy footprint. The vacuum dehydration technology consumes 40% less energy than conventional dryers, while taking the same amount of time to dry clothes. This method of drying even protects clothes from shrinkage or damage and works exceptionally well with sensitive fabrics. Fitting everything into a small form factor, the Morus can sit right on top of your front-load washing machine, or anywhere in your laundry room, allowing you to quickly dry clothes immediately after washing them so you can wear them once theyre done with the wash (Ive always wanted to do that).
The key difference between drying and dehydration is that the drying refers to the removal of solvent from a solid, semi-solid or a liquid whereas dehydration refers to the removal of water from the water-containing compound.
Both terms drying and dehydration refers to the removal of solvent from a solution, thereby leaving only the solute. Therefore, both these processes are mass transfer processes. Moreover, these processes will leave a solid residue at the end.
Drying is the process of removal of solvent from a solid, semi-solid or a liquid. Hence, it is a mass transfer process because the solvent mass in the solution moves from the solution to the atmosphere via drying. Here, the solvent can be water or any other solvent such as organic solvents. Also, this mass transfer occurs via evaporation. Often, we use this process as the final step before the packaging of some products. The final product of the drying process is always solid. It can be in continuous sheet form, in long pieces, particles or as a powder.
Usually, we use heat energy for the evaporation and for drying, we need an agent that can remove the solvent vapour produced from the evaporation. Desiccation, on the other hand, is a synonym for drying, but sometimes we consider it as an extreme of drying.
Moreover, the applications of drying process are in the food industry, the pharmaceutical industry, etc. we can dry food items in order to inhibit microbial growth and thereby to preserve the food. Other than that, it also reduces the volume and the mass of the item. In addition to that, we dry non-food items such as wood, paper, washing powder, etc.
Dehydration is the removal of water from the water-containing compound. This compound can be an aqueous solution, solid, etc. At the end of the dehydration process, water forms as an essential byproduct. The end product of the process is always solid. Moreover, unlike the drying process, we use specific processes with controlled temperature and humidity conditions. In contrast, hydration is the addition of water molecules to a compound.
Drying is the process of removal of solvent from a solid, semi-solid or a liquid whereas dehydration is the removal of water from the water-containing compound. Therefore, this is the fundamental difference between drying and dehydration. Another important difference between drying and dehydration is that drying process produces water or any other solvent as the byproduct while dehydration produces water as an essential byproduct. Apart from that, we can use mild conditions without any control for drying purposes. But we have to control the conditions such as humidity and temperature for the dehydration purpose.
Both drying and dehydration processes are mass transfer processes. They involve in the removal of a solvent from a compound. They differ from each other according to what they are going to remove. Therefore, the key difference between drying and dehydration is that drying refers to the removal of solvent from a solid, semi-solid or a liquid whereas dehydration refers to the removal of water from the water-containing compound.
Madhu is a graduate in Biological Sciences with BSc (Honours) Degree and currently persuing a Masters Degree in Industrial and Environmental Chemistry. With a mind rooted firmly to basic principals of chemistry and passion for ever evolving field of industrial chemistry, she is keenly interested to be a true companion for those who seek knowledge in the subject of chemistry.
Molecular sieve technology is widely used for the simultaneous removal of water and mercaptans from both gas and liquid feed streams. However, a better understanding of the design principles and the operation of molecular sieve units is needed. For economic reasons, it is important not to overdesign the molecular sieve unit. At the same time, it is essential to ensure that the unit does not become the bottleneck of the gas processing plant at the sieves end-of-run condition.
Details of the design and operation of molecular sieve units used for natural gas dehydration are discussed here. The application of expert know-how and practical recommendations can provide an effective way to maximize molecular sieve lifetime and performance. Part 1 focuses on the design principles and practices of molecular sieve units.
Molecular sieves background. When treating a gas or liquid stream so that it can be processed by a specific unit, one of the commonly used treating units is an adsorption unit. These units are commonly used to remove water from a feed stream, but they can also remove additional contaminants (e.g., mercaptans). Specifically, when deep removal is required (below 1 ppmv), molecular sievesan adsorbent composed of a zeolite and, typically, a clay binderare the preferred adsorbent.
Adsorption units are capable of reaching extremely low specifications, which makes them viable pieces of equipment for incorporation into a process lineup. A major advantage of molecular sieves is that they can be regenerated, which reduces the required amount of molecular sieve to economically feasible quantities.
This article examines the use of molecular sieve units for natural gas dehydration, as they are critical components in the operation of an LNG or gas processing plant (typically combined with NGL extraction by cryogenic separation), and any limitation or loss in capacity of this unit can have a significant effect on overall plant economics.1,2
An adsorption unit used for water removal is called a dehydration unit (DHU). A DHU often consists of two or more vessels, filled with molecular sieves, that adsorb water during an adsorption period and are subsequently regenerated using a heated stream of treated gas. A sketch of a typical molecular sieve DHU is shown in Fig. 1.
The high temperature during regeneration causes water to desorb from the molecular sieve, a process called temperature swing adsorption (TSA). Although TSA is a discontinuous process, the overall DHU behaves like a continuous process because one or more vessels are always in adsorption mode, while another vessel(s) is in regeneration mode.
In a typical DHU, the regeneration gas used is a side (slip) stream of the product stream (typically approximately 10%). Downstream of the adsorber vessel, the wet regeneration gas is cooled, and water is condensed and subsequently removed in a knockout (KO) drum. When a molecular sieve unit is used for dehydration, it is possible to send the regeneration gas back to the feed after compression is performed to negate the pressure drop. Sending the regeneration gas back to the feed minimizes valuable product losses. Note: This type of lineup is possible only for DHUs designed for water removal, as knocking out the water in the regeneration KO drum provides a drain from the system. Components that cannot be removed from the loop in such a manner (e.g., sulfur species, such as mercaptans) will build up in the regeneration gas loop. Consequently, in such a lineup, the regeneration gas must first be treated by an appropriate absorption unit before it can be reinjected in the feed gas.
Basic design rules and operational requirements. As mentioned previously, an adsorption unit is a discontinuous process, since adsorption is essentially a batch process. One of the most important design parameters of an adsorption vessel is the available water uptake capacity of the molecular sieve bed. However, a few factors make this important design parameter less straightforward.
In adsorption, gas usually flows from top to bottom. During the adsorption period, the amount of water that can be adsorbed on the molecular sieve is dictated by both the capacity that can be reached in the limit of reaching equilibrium, and the capacity that results from the competition between adsorption kinetics and the flow of gas past a molecular sieve pellet.
In the adsorbing bed, two zones can be identified. The capacity-limited portion is situated at the top. It is saturated with water under the feed conditions of temperature, pressure and water concentration, and is referred to as the saturation zone (SZ). The part of the bed below the SZ that is engaged in dehydrating the gas from feed water concentration (wet) to effluent water concentration (dry) is called the mass-transfer zone (MTZ) (Fig. 2). During adsorption, the MTZ migrates from the top of the bed to the bottom of the bed, thereby lengthening the SZ. Once the MTZ leaves the bed, breakthrough occurs and the bed must be taken offline for regeneration.3,4,5
Another important parameter to take into account is that the capacity of the adsorbent decreases over time as a function of the number of regeneration cycles; therefore, end-of-run (EOR) capacity must be used when considering the required amount of adsorbent. When the capacity of the adsorbent falls below the level where all water in the feed can be adsorbed during the minimum adsorption time, then the adsorbent must be replaced (Fig. 3).
Another important design parameter is the ability to predict the rate of deactivation. It is important to understand the main factors contributing to the deactivation of the molecular sieve. In general, these contributing factors are consequences of the thermal regeneration process.6
During regeneration of the water-saturated molecular sieve, hot dry gas is passed upward through the molecular sieve bed, and water desorbs. If the beginning of the regeneration cycle were started with dry gas at the maximum temperature, then water would first desorb from the bottom portion of the bed, using much of the heat of the gas. Subsequently, water that desorbed from the bottom portion of the bed would be carried to the top portion, which would not yet have been heated by the regeneration gas. The top portion of the bed would still be cold and saturated with water, so the desorbed water from the bottom portion of the bed could condense to form liquid water. The formation of hot liquid water in the bed could cause the clay binder of the molecular sieve to dissolve, subsequently forming cake during the regeneration step.2,512
Caking due to hot liquid water formation during regeneration can be avoided by using a well-designed heating profile during the regeneration cycle. If the temperature of the regeneration gas entering the bed is slowly increased, then the top portion of the bed can be preheated before much water desorbs from the bottom portion of the bed. Preheating the top portion of the bed prevents condensation of liquid water when the water from the bottom portion of the bed is finally desorbed. If a non-ideal temperature profile is used during regeneration, then degradation of the molecular sieve might still occur without the formation of a large solid cake.
The characteristics of the temperature profile required to avoid liquid water formation depend on a number of factors. The flowrate and composition of the regeneration gas dictate how much heat is delivered to the molecular sieve bed. The diameter and materials of the vessel determine how much heat is transferred to the vessel, and at what rate, as opposed to the amount of heat that is transferred to the molecular sieve. Furthermore, the amount of water adsorbed on the molecular sieve, taking into account the MTZ, dictates the gas-phase concentration profile of water moving upward through the bed.
Another form of molecular sieve deactivation is through coke deposition on the molecular sieve. If the feed to the unit is heavy, then the heavier hydrocarbons can be adsorbed onto the molecular sieve binder during adsorption. A portion of the hydrocarbons will be desorbed during regeneration, but the residual will remain on the binder, decompose and irreversibly form coke under hot regeneration conditions, which can lead to pore blocking that results in a lower water uptake capacity.
The least contributing factor is the effect that continual thermal cycling has on the molecular sieve. Some thermal degradation, and the subsequent loss in water removal capacity of the molecular sieve, will occur. The extent of this degradation and loss is dependent on the thermal stability of the molecular sieve. The regeneration process also causes degradation of the binder material. The expansion and contraction experienced during thermal swings lead to dust production and an increase in pressure drop that is detrimental to LNG production.
As the capacity of an adsorbent is limited and the vessels become more expensive as the diameter (i.e., the required wall thickness) increases, a significant economic driver exists to keep the vessels as small as possible. One way to achieve this is to operate at high pressures (typically 60 bara), as the mass flow to be treated is then compressed in a smaller volume. Another way is to reduce the amount of water deposited on the bed by cooling the feed stream and knocking out excess water in the feed KO drum. The temperature reduction is limited by the hydrate formation temperature, and the operating temperature is chosen for safe operation above that temperature.1 Another reason to operate at a low temperature is that the uptake capacity of the molecular sieve is higher.
Not yet discussed is the type of molecular sieve to be used.2,5,7,13 For dehydration, and especially for molecular sieve units used in LNG application, type 4A is used. As previously mentioned, a molecular sieve is composed of a zeolite and a binder, typically clay. The binder is used as a glue to strengthen the particles. The type of zeolite typically used for dehydration is the Linde Type A (LTA). A refers to Angstrom, indicating the diameter of the zeolite channels where the water is adsorbed; i.e., 4A refers to a zeolite with a channel diameter of 4 Angstrom. Apart from 4A, 3A LTA and 5A LTA sieves are also used. In these sieves, the type of cation determines the channel diameter (K+ for 3A, Na+ for 4A and Ca2+ for 5A).
Water is the molecule that is adsorbed the strongest; consequently, water will displace all other adsorbed molecules. For LNG applications, a 4A sieve is more stable and has higher water uptake capacity than a 3A sieve, and less coadsorption will occur compared to a 5A sieve. However, in gas processing plants that process pipeline gas, a 3A sieve is typically used. The reason is that if methanol is added to the feed gas to prevent hydrate formation, it will pass the 3A sieve bed, since methanol does not fit into the pores. The methanol can be recovered downstream of the beds in the part of the lineup where heavier hydrocarbons (e.g., propane and butane) are separated from the natural gas. Furthermore, coadsorption of methanol on larger-pore sieves will adversely affect the effectiveness of the molecular sieve with regard to water removal.
The question of why molecular sieves are best suited for deep dehydration is illustrated in Fig. 4, where typical isotherms of adsorbents used for dehydration are shown.2,13,14 Although molecular sieves have a lower saturation capacity than alumina or silica gel, that capacity is much less dependent on the partial water pressure, which enables deeper specifications to be reached (< 0.1 ppmv H2O).
This characteristic also results in a shorter MTZ, enabling more efficient use of the adsorbent bed. In this context, it should be noted that the length of the MTZ is also determined by the particle size. For that reason, molecular sieve beds are typically layered, with the larger particles (e.g., 18 in.) used in the top layers to minimize the overall bed pressure drop and the smaller particles (e.g., 116 in.) in the bottom layer.
Another reason to select molecular sieves for dehydration is that the water uptake capacity is less dependent on feed temperature in comparison to silica gel and alumina. Furthermore, in contrast to molecular sieves, alumina and silica gel are large-pore adsorbents and, therefore, more co-adsorption of hydrocarbons will occur. Similar to molecular sieves, water will displace the coadsorbed components since it adsorbs stronger to the adsorbent; however, co-adsorption will also influence the length of the MTZ. More importantly, when regenerating the adsorbents, these co-adsorbed species will leave the adsorbent as peaks. If the regeneration gas must be treated, then the treating unit must be sized such that it can process these peaks. This factor significantly increases the cost of such a unit.
The majority of topics discussed to this point are related to the chemistry involved in the process. However, other factors are equally important from a design point of viewmore specifically, those determined by process engineering and economics.
In gas processing, a plant is typically designed and operated with a single purpose: to process natural gas so that the maximum amount of condensates can be recovered, and so that produced gas adheres to certain specifications. In general, the gas is produced for use in the natural gas grid or for liquefaction and transport to markets. The economic aim for such a lineup is to minimize the number and size of vessels, process steps and plot space. From an engineers point of view, that means safely pushing as much mass flow as possible through the smallest possible vessels. The total amount of gas and liquids to be processed is the economic basis of such a project. The design of the vessel must adhere to maximum flow and minimum flow criteria.
In gas phase systems, gas flow during adsorption moves downward to prevent fluidization of the bed under abnormal flow conditions. The diameter of the bed can be calculated once the superficial velocity is determined.1 The superficial velocity must be chosen so that the following criteria are met:
Some of these criteria are of importance to the main process flow, but they should also apply to the regeneration gas flow (in each stage of the temperature profile), which, for gas processing vessels, is typically upflow. Apart from these criteria, the regeneration gas flow must carry enough heat into the system to ensure that the beds are properly regenerated. Sufficient flow will ensure the stripping efficiency of the desorbed molecules, and the beds should be cooled within the time frame available.
Within these constraints, the objective is to secure a regeneration gas flow that is as small as possibletypically around 10% of the feed flow. Particularly when the regeneration gas is sent back to the feed, a minimum regeneration flow ensures minimum-size regeneration loop equipment and, even more importantly, helps reduce the size of the adsorber vessels. For lineups such as those shown in Fig. 1, the flow passing through the main process line units is the feed flow combined with the regeneration flow. As the regeneration flow is upflow, another important design constraint is to avoid fluidization of the bed.
The length (L) and diameter (D) of the beds are limited mainly for practical and economic reasons. One important limitation is the strength of the adsorbent particles, especially those at the bottom of the bed. These should be sufficiently strong to withstand the sum of the pressure drop over the bed, the weight of the bed above them when saturated with water, and the weight of the pressurized gas.
A more practical observation is that bed heights of more than 10 m are rarely observed. In such cases, the adsorber vessels tend to become the highest units at the site. Minimizing the diameter is an important economic constraint. A larger diameter is associated with greater wall thickness, which will increase the cost of the vessel. A rule of thumb that is often applied in vessel sizing is the L/D > 2 criterion. With a lower ratio, the result is often a so-called pancake reactor. In this type of reactor construction, most of the steel (i.e., cost) used for the vessel ends up in the top and bottom domes, where the curvature is more or less fixed.
A sketch of a typical adsorber vessel is shown in Fig. 5.7 A certain distance between the bottom of the inlet distributor and the top of the bed is required to ensure pressure and flow equalization. The flow is reversed during regeneration, and the same requirement applies to the bottom portion of the bed. A careful observer will notice that the difference in size between the ceramic ball layers never exceeds a factor of 2. This ratio is preserved to lower the probability that smaller particles will migrate between larger particles.
In a worst-case scenario, such migration could lead to a small depression in the top of the bed, thereby creating a preferential flow path due to the lower pressure difference in the part of the bed referred to as a channel. If a channel is created in a bed, then the mole sieve in and around that path will be depleted much more quickly than the surroundings, since a larger part of the flow moves through it. This depletion will ultimately result in an early breakthrough of the bed.
As the capacity of a molecular sieve bed is limited and declines as a function of the number of regeneration cycles, an important design criterion is the required lifetime (i.e., how long the bed must last before a changeout of the inventory is required). That depends somewhat on the application; in general, molecular sieve beds are changed out during a major shutdown of the plant. Major turnarounds are planned every 2 yr3 yr, as various pieces of kit require maintenance.
For an LNG site, turbine and compressor maintenance needs determine when a major shutdown occurs. For most sites, the timing is every 4 yr. Although this timing provides the process engineer with a time frame for designing a molecular sieve bed, a translation to the number of cycles that fits into that period is required because the beds must retain sufficient water uptake capacity at the end of the 4-yr period.
An adsorption cycle comprises several steps. The major steps are adsorption and regeneration, whereby the regeneration step can be subdivided in heating, cooling and standby steps.2,5,9,12,15 The highest temperature to which the molecular sieve can be exposed during regeneration is determined by the thermal stability of the molecular sieve. For a 4A sieve, the temperature limit is 320C.
Although regeneration can take place at lower temperatures, the consequence is that more water will remain on the molecular sieve, thereby reducing the effective water uptake capacity. A typical regeneration profile is shown in Fig. 6. The step during ramp-up is inserted to prevent an overly rapid heating, which can result in hot water formation.
A typical adsorption time is 16 hr. Although TSA is a discontinuous process, the overall DHU behaves like a continuous process because one or more vessels are in adsorption mode, while another vessel(s) is in regeneration mode. Consequently, there is a limit to the time available for regeneration. With an adsorption time of 16 hr, in a 1+1 lineup, 16 hr are available for regeneration (cycle time is 32 hr), while in a 2+1 lineup (Fig. 1), only 8 hr are available for regeneration (cycle time is 24 hr). A cycle time sequence for a 2+1 lineup is depicted in Fig. 7.
The timing in a cycle time sequence is critical, as the transfer of beds from adsorption to regeneration must happen flawlessly. A mistake in the timing could result where one bed is coming out of the adsorption step while the bed being regenerated is still in the heating step, thereby creating a forced shutdown. Most sites work with fixed cycle times, which means that when the beds are fresh, excess capacity is available as the bed heights are designed for end-of-run conditions.
It is possible to minimize this effect by applying a variable cycling design, where the cycle time is adjusted at regular intervals in such a manner that these changes roughly follow the deactivation profile shown in Fig. 8. In this way, smaller beds can be designed, or the lifetime of the beds can be somewhat extended by reducing the overall number of cycles during troubleshooting or debottlenecking, thereby slowing the deactivation rate of the adsorbent.
As a consequence of this mode of operation, the minimum required capacity illustrated in Fig. 8 is essentially determined by the minimum time needed for regenerationi.e., the fastest time heating and cooling can be achieved while ensuring that the beds are fully regenerated.
Additional comments. Only the main design elements were discussed for a fairly typical molecular sieve unit. Not discussed are the various other permutations possiblefor example, the number of vessels deployed (e.g., 1+1, 3+1, 3+2, 4+2 lineups), the choice and the routing of the regeneration gas, regeneration gas heating options, regeneration at lower pressures, external or internal insulation of the vessels, etc. Although these options will influence vessel sizing and the total cost of the unit, the basic design elements discussed here will be the same.
Takeaway. The main design elements required for designing and operating a molecular sieve DHU are well understood. When taking these elements into account, it is possible to design molecular sieve units that are reliable, that deliver on specification and with required lifetime, and that require relatively little operational attention. GP
Ruud H. M. Herold was formerly a Senior Process Engineer at Shell Global Solutions International BV in Amsterdam, The Netherlands. He joined the company in 1986 and began working in the gas processing group in 2001, where he specialized in adsorption and catalytic processes used in gas and liquids treating. Mr. Herold holds an MSc degree in chemical engineering from the University of Amsterdam.
Saeid Mokhatab is one of the most recognizable names in the natural gas processing industry. He has been actively involved in the design and operation of several gas processing plants around the world, and has contributed to gas processing technology improvements through 300 technical papers and two well-known handbooks (published by Elsevier in the US). He founded Elseviers Journal of Natural Gas Science & Engineering, and has given invited lectures on gas processing technologies worldwide. As a result of his work, Mr. Mokhatab has received a number of international awards and medals, and has been listed in prestigious biographical directories.
Many processes within oil and gas pipelines and processing plants depend on maintaining specific temperatures and pressures at which the process fluids are liquids or gases. In addition, anytime water is a component in the process fluid hydrates can form and plug piping and vessels. Learn how Sensias Throughput optimization solution allows operators, and control systems to see inside the process in real time to understand where the facility is operating with respect to critical physical constants, including the phase envelope and hydrate temperature. This insight allows for more stable operation, reduced energy expenditure and associated emissions, and greater facility throughput. Case studies will include controlling methanol injection, managing heaters, virtual sensors for sulfur recovery units and more.
Dehydration, in food processing, means by which many types of food can be preserved for indefinite periods by extracting the moisture, thereby inhibiting the growth of microorganisms. Dehydration is one of the oldest methods of food preservation and was used by prehistoric peoples in sun-drying seeds. The North American Indians preserved meat by sun-drying slices, the Chinese dried eggs, and the Japanese dried fish and rice.
Hot-air dehydration was developed in France in 1795, enabling the commercial production of dehydrated food products, particularly spaghetti and other starch products. Modern dehydration techniques have been largely stimulated by the advantages dehydration gives in compactness; on the average, dehydrated food has about 1/15 the bulk of the original or reconstituted product. The need to transport large shipments of food over great distances during World War II provided much of the stimulus to perfect dehydration processes. The advantages of reduced bulk later came to be appreciated by campers and backpackers and also by relief agencies that provide food in times of emergency and disaster.
Dehydration equipment varies in form with different food products and includes tunnel driers, kiln driers, cabinet driers, vacuum driers, and other forms. Compact equipment suitable for home use is also available. A basic aim of design is to shorten the drying time, which helps retain the basic character of the food product. Drying under vacuum is especially beneficial to fruits and vegetables. Freeze-drying benefits heat-sensitive products by dehydrating in the frozen state without intermediate thaw. Freeze-drying of meat yields a product of excellent stability, which on rehydration closely resembles fresh meat.
The dairy industry is one of the largest processors of dehydrated food, producing quantities of whole milk, skim milk, buttermilk, and eggs. Many dairy products are spray driedthat is, atomized into a fine mist that is brought into contact with hot air, causing an almost instant removal of moisture content. See also food preservation.
Weve built a reputation on building the best rotary dryers in the industry. All of our dryers are custom designed to suit the unique processing needs of your material. Whether you require low or high inlet temperatures, short or long residence times, counter current or co-current flow, FEECOs design team can design a rotary drum dryer for your application.
Rotary dryers are a highly efficient industrial drying option for bulk solids. They are often chosen for their robust processing capabilities and their ability to produce uniform results despite variance in feedstock.
The drum is positioned at a slight horizontal slope to allow gravity to assist in moving material through the drum. As the drum rotates, lifting flights pick up the material and drop it through the air stream in order to maximize heat transfer efficiency. When working with agglomerates, the tumbling action imparted by the dryer offers the added benefit of further rounding and polishing the granules.
All FEECO equipment and process systems can be outfitted with the latest in automation controls from Rockwell Automation. The unique combination of proprietary Rockwell Automation controls and software, combined with our extensive experience in process design and enhancements with hundreds of materials provides an unparalleled experience for customers seeking innovative process solutions and equipment.
Rotary dryers are known as the workhorse of industrial dryers. They are able to process a wide variety of materials, and can lend a hand in nearly any industry requiring industrial drying solutions. Some of the most common industries and materials in which rotary dryers are employed include:
Unlike direct dryers, indirect dryers do not rely on direct contact between the material and process gas to dry the material. Instead, the rotating drum is enclosed in a furnace, which is externally heated. Contact with the heated drum shell is what dries the material.
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Our rotary dryers are built to the highest quality standards, with longevity in mind. The best part about buying a FEECO rotary dryer, is that you get the security of knowing your equipment is backed by over 60 years of experience, material and process knowledge, and a proven track record.