Rules Of Thumb : Conveyors For Particulate Solids

Part 1

1. Screw conveyors are used to transport even sticky and abrasive solids up inclines of 208 or so. They are limited to distances of 150 ft or so because of shaft torque strength. A 12 in. dia conveyor can handle 1000–3000 cuft/hr, at speeds ranging from 40 to 60 rpm
2. Belt conveyors are for high capacity and long distances (a mile or more, but only several hundred feet in a plant), up inclines of 308 maximum. A 24 in. wide belt can carry 3000 cuft/hr at a speed of 100 ft/min, but speeds up to 600 ft/min are suited for some materials. The number of turns is limited and the maximum incline is 30 degrees. Power consumption is relatively low.
3. Bucket elevators are used for vertical transport of sticky and abrasive materials. With buckets 20 Â 20 in. capacity can reach 1000 cuft/hr at a speed of 100 ft/min, but speeds to 300 ft/min are
   used.
4. Drag-type conveyors (Redler) are suited for short distances in any direction and are completely enclosed. Units range in size from 3 in. square to 19 in. square and may travel from 30 ft/min (fly ash) to 250 ft/min (grains). Power requirements are high.
5. Pneumatic conveyors are for high capacity, short distance (400 ft) transport simultaneously from several sources to several destinations. Either vacuum or low pressure (6–12 psig) is employed with a range of air velocities from 35 to 120 ft/sec depending on the material and pressure. Air requirements are from 1 to 7 cuft/cuft of solid transferred.
   
   

Rules Of Thumb : Compressors And Vacuum Pumps

Although experienced engineers know where to find information and how to make accurate computations, they also keep a mini mum body of information readily available, made largely of shortcuts and rules of thumb. This compilation is such a body of information from the material in this book and is, in a sense, a digest of the book.

Rules of thumb, also known as heuristics, are statements of known facts. The word heuristics is derived from Greek, to discover or to invent, so these rules are known or discovered through use and practice but may not be able to be theoretically proven. In practice, they work and are most safely applied by engineers who are familiar with the topics. Such rules are of value for approximate design and preliminary cost estimation, and should provide even the inexperienced engineer with perspective and whereby the reasonableness of detailed and computer-aided design can be appraised quickly, especially on short notice, such as a conference.

Everyday activities are frequently governed by rules of thumb. They serve us when we wish to take a course of action but we may not be in a position to find the best course of action. Much more can be stated in adequate fashion about some topics than others, which accounts, in part, for the spottiness of the present coverage. Also, the spottiness is due to the ignorance and oversights on the part of the authors. Therefore, every engineer undoubtedly will supplement or modify this material (Walas, 1988).

1. Fans are used to raise the pressure about 3% (12 in. water), blowers raise to less than 40 psig, and compressors to higher pressures, although the blower range commonly is included in the compressor range.
2. Vacuum pumps: reciprocating piston type decrease the pressure to 1 Torr; rotary piston down to 0.001 Torr, two-lobe rotary down to 0.0001 Torr; steam jet ejectors, one stage down to 100 Torr, three stage down to 1 Torr, five stage down to 0.05 Torr.
3. A three-stage ejector needs 100 lb steam/lb air to maintain a pressure of 1 Torr.
4. In-leakage of air to evacuated equipment depends on the absolute pressure, Torr, and the volume of the equipment, V cuft, according to w 1⁄4 kV 2=3 lb/hr, with k 1⁄4 0:2 when P is more than 90 Torr, 0.08 between 3 and 20 Torr, and 0.025 at less than 1 Torr.
5. Theoretical adiabatic horsepower (THP) 1⁄4 [(SCFM)T1 /8130a] [(P2 =P1 Þa À 1], where T1 is inlet temperature in 8F þ 460 and a 1⁄4 (k À 1)=k,k 1⁄4 Cp =Cv .
6. Outlet temperature T2 1⁄4 T1 (P2 =P1 )a
7. To compress air from 1008F, k 1⁄4 1:4, compression ratio 1⁄4 3 theoretical power required 1⁄4 62 HP/million cuft/day, outlet temperature 3068F.
8. Exit temperature should not exceed 350–4008F; for diatomic gases (Cp =Cv 1⁄4 1:4) this corresponds to a compression ratio of about 4.
9. Compression ratio should be about the same in each stage of a multistage unit, ratio 1⁄4 (Pn =P1 )1=n , with n stages.
10. Efficiencies of fans vary from 60–80% and efficiencies of blowers are in the range of 70–85%.
11. Efficiencies of reciprocating compressors: 65–70% at compression ratio of 1.5, 75–80% at 2.0, and 80–85% at 3–6.
12. Efficiencies of large centrifugal compressors, 6000–100,000 ACFM at suction, are 76–78%.
13. Rotary compressors have efficiencies of 70–78%, except liquid liner type which have 50%.
14. Axial flow compressor efficiencies are in the range of 81–83%.
    

Introduction to Biocatalysis (2)

Applications of Biocatalysis in Industry

Chemical Industry of the Future: Environmentally Benign Manufacturing, Green Chemistry, Sustainable Development in the Future

Owing to two very strong and important driving forces the chemical industry of the future will look considerably different from today’s version:

• cost and margin pressure resulting from competition in an increasingly open market-oriented economy, and
• operation of the industry in a societal framework which puts emphasis on a clean (or at least less polluted) environment

Processing with a view towards this new set of conditions focuses on the development of production routes with fewer processing steps, with higher yields on each step, to save material and energy costs. Less waste is generated, and treatment and disposal costs go down. Both pressures come together in the cases of environmental compliance costs.

In many cases, such as high-fructose corn syrup, or biotechnology and biocatalysis offer technology options and solutions that are not available through any other technology; in such situations such as acrylamide, nicotinamide or intermediates for antibiotics, biotechnology and biocatalysis act as “enabling technologies”. In the remaining situations, biotechnology and biocatalysis offer one solution among several others, which all have to be evaluated according to criteria developed in Chapter 2: yield to product, selectivity, productivity, (bio)catalyst stability, and space–time-yield.

In this context, the three terms in the title are to a good extent synonymous; nevertheless, they have been developed in a slightly different context:

• environmentally benign manufacturing is a movement towards manufacturing systems that are both economically and environmentally sound;
• sustainable development is a worldwide Chemical Industry movement and represents a set of guidelines on how to manage resources such that non-renewables are minimized as much as possible;
• green chemistry is the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances.

“Green chemistry is an overarching approach that is applicable to all aspects of chemistry” (Anastas, 2002). Green chemistry methodologies can be viewed through the framework of the “Twelve Principles of Green Chemistry” (Anastas, 1998):

1. It is better to prevent waste than to treat or clean up waste after it is formed.
2. Synthetic methods should be designed to maximize the incorporation of all
3. materials used in the process into the final product. Wherever practicable, synthetic methodologies should be designed to use and generate substances that possess little or no toxicity towards human health and the environment.
   
4. Chemical products should be designed to preserve efficacy of function while reducing toxicity.
5. The use of auxiliary substances (e.g., solvents, separation agents, etc.) should be made unnecessary wherever possible, and should be innocuous when used.
6. Energy requirements should be recognized for their environmental and economic impacts and should be minimized. Synthetic methods should be conducted at ambient temperatures and pressures.
7. A raw material or feedstock should be renewable rather than depleting wherever technically and economically practicable.
8. Unnecessary derivatization (blocking group, protection/deprotection, temporary modification of physical/chemical processes) should be avoided wherever possible.
9. Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.
10. Chemical products should be designed so that at the end of their function they do not persist in the environment and they do break down into innocuous degradation products.
11. Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances.
12. Substances and the form of a substance used in a chemical process should be selected so as to minimize the potential for chemical accidents, including releases, explosions, and fires.

Catalysis offers numerous advantages for achieving green chemistry goals: novel, high-yield, shorter process routes; increased selectivity; and lower temperatures and pressures. Biocatalysis combines the goals of all three topics above. Biocatalysts, as well as many of the raw materials, especially those for fermentations, are themselves completely renewable and for the most part do not pose any harm to humans or animals. Through the avoidance of high temperatures and pressures and of large consumptions of metals and organic solvents, the generation of waste per unit of product is drastically reduced.

Introduction to Biocatalysis (1)

Summary

Over the last 20 years, many reservations with respect to biocatalysis have been voiced, contending that: (i) enzymes only feature limited substrate specificity; (ii) there is only limited availability of enzymes; (iii) only a limited number of enzymes exist; (iv) protein catalyst stability is limited; (v) enzyme reactions are saddled with limited space–time yield; and (vi) enzymes require complicated cosubstrates such as cofactors.

Driven by the discovery of many novel enzymes, by recombinant DNA technology which allows both more efficient production and targeted or combinatorial alterations of individual enzymes, and by process development towards higher stability and volumetric productivity, synthesis routes in which one or all of the steps are biocatalytic have advanced dramatically in recent years. Design rules for improved biocatalysts are increasingly precise and easy to use.

Biocatalysts do not operate by different scientific principles from organic catalysts. The existence of a multitude of enzyme models including oligopeptidic or polypeptidic catalysts proves that all enzyme action can be explained by rational chemical and physical principles. However, enzymes can create unusual and superior reaction conditions such as extremely low pKa values or a high positive potential for a redox metal ion. Enzymes increasingly have been found to catalyze almost any reaction of organic chemistry.

Biotechnology and biocatalysis differ from conventional processes not only by featuring a different type of catalyst; they also constitute a new technology base. The raw materials base of a biologically-based process is built on sugar, lignin, or animal or plant wastes; in biotechnology, unit operations such as membrane processes, chromatography, or biocatalysis are prevalent, and the product range of biotechnological processes often encompasses chiral molecules or biopolymers such as proteins, nucleic acids or carbohydrates.

Cost and margin pressure from less expensive competitors and operation with emphasis on a clean (or less polluted) environment are two major developments. Fewer processing steps, with higher yields at each step, lower material and energy costs, and less waste are the goals. Biotechnology and biocatalysis often offer unique technology options and solutions, they act as enabling technologies; in other cases, biocatalysis has to outperform competing technologies to gain access. In the phar-maceutical industry, the reason for the drive for enantiomeric purity is that the vast majority of novel drugs are chiral targets, favoring biocatalysis as the technology with the best selectivity performance.

Biocatalytic processes increasingly penetrate the chemical industry. In a recent study, 134 industrial-scale biotransformations, on a scale of > 100 kg with whole cells or enzymes starting from a precursor other than a C-source, were analyzed. Hydrolases (44%), followed by oxido-reductases (30%), dominate industrial biocatalytic applications. Average performance data for fine chemicals (not pharmaceuticals) applications are 78% yield, a final product concentration of 108 g L, and a volumetric productivity of 372 g (L · d)

Biocatalysis. Andreas S. Bommarius and Bettina R. Riebel
Copyright © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ISBN: 3-527-30344-8

Advanced Control Engineering

BURNS, Roland S. (2001):
Advanced Control Engineering.
Oxford, UK: Butterworth-Heinemann. A division of Reed Educational and Professional Publishing Ltd.
ISBN: 0-7506-5100-8. 464p

Download

Ziddu