Showing papers in "Chemical Engineering in 2006"

How to Estimate Utility Costs

Abstract: ypical process utilities include electricity, process steam, refrigerants, compressed air, cooling water, heated water, hot oil, process water, demineralized water, municipal water, and river, lake, or ocean water. For preliminary cost estimates, waste disposal cost can also be treated like a utility expense. Unlike capital, labor, and other expenses, utility prices do not correlate simply with conventional inflationary indexes, because basic energy costs vary erratically, independent of capital and labor. In essence, utility price is linked to two separate variables — inflation and energy cost. Elements of manufacturing expense that depend on labor and capital follow inflationary metrics like the CE Plant Cost Index (CE PCI). Energy cost, such as that for fuel in an electrical or steam generating plant, is like a raw material whose price can vary widely and erratically. To reflect this dual dependence, we need a two-factor utility cost equation such as the following: CS,u = a (CE PCI) + b (CS,f) (1) where CS,u is the price of the utility, a and b are utility cost coefficients, CS,f is the price of fuel in $/GJ, and CE PCI is an inflation parameter for projects in the U.S.1 Deriving the coefficients To derive Coefficients a and b, a manufacturing cost analysis must be prepared for a given utility.2 Electric power price, for instance, includes raw material costs, labor, supervision, maintenance, overhead, and a number of other items that determine total manufacturing expense and, ultimately, selling price. In such a list, individual cost items can be divided into two categories, those dependent on normal inflation and those dependent Feature Report

Study on leaching kinetics of pyrite cinder

Abstract: The leaching kinetics of pyrite cinder and sulfuric acid reaction was studied.The study results show that Fe_3O_4 is more reactive than Fe_2O_3 when cinders react with H_2SO_4;the leaching rate of iron is decided by the(reaction) rate of Fe_2O_3 and H_2SO_4;the reaction between Fe_2O_3 and H_2SO_4 is controlled by diffusion,and the(reaction) is applicable to the shrinking core model.The activation energy of the reaction is 6.936 kJ/mol.The(leaching) rate of iron is increased from 19.5% to 45% when the agitation rate is increased from 0 to 400 r/min,the mass fraction of sulfuric acid is 43%,the dosage of sulfuric acid is the theoretic dosage,the reaction(temperature) is 80 ℃,and the reaction time is 2 h.

Numerical simulation of flow behavior and mass transfer in internal airlift-loop reactor

Abstract: A mathematical model of airlift-loop reactor(ALR) was developed with the two-fluid model and the(kinetic) theory of two-phase flow.The model for predicting the local liquid volumetric mass transfer coefficient was set up based on penetration theory and isotropic turbulence theory.The calculated results based on Fluent(reasonably) explained the gas and liquid flow mechanism and mass transfer in ALR and the coincidence with literature(experimental) results has validated the accuracy and applicability of the model.

Mixing systems: design and scale up: many options are available to meet the mixing challenges confronted by the CPI. Both theoretical and empirical methods can help the engineer to fit the right system to the task

Abstract: undamental to the chemical process industries (CPI) — whether specialty or bulk chemicals, pharmaceuticals, food products, minerals processing, environmental protection or other products or activities — is the need for mixing. The wide variety and complexity of mixing tasks encountered in industrial applications require careful design and scale up to ensure that effective mixing is achieved efficiently. Designs based on a small range of traditional agitators are no longer economically acceptable. Modern impellers and the use of physical or computer modeling can greatly enhance performance and reduce costs. Mixing tasks fall into six main categories: 1. blending of miscible liquids; 2. blending of mixtures with \" difficult \" rheologies (such as non-Newtonian properties); 3. suspension of solids; 4. liquid-liquid dispersions; 5. heat transfer; and 6. gas-liquid dispersion. Different mixing behaviors and rules govern each basic mixing task. To optimize a design, or to scale-up reliably, these behaviors and rules need to be understood and defined. Complex tasks that involve two or more of the above categories require special attention. The controlling task must be identified to determine the design and scale-up rules to be applied. This article addresses the first five mixing tasks that are listed above. Gas-liquid dispersion is a complex subject in itself and has had many significant advances in recent years. Rather than give a very abbreviated summary here, we refer the reader to Reference [2] for this topic. In addition to agitator design and power requirements, which are fundamental to mixing systems, many other considerations also play a part in maximizing performance. These considerations include mechanical aspects, seal selection, materials of construction and surface finishes to prevent fouling or aid cleaning. Figure 2 outlines the process and factors involved in designing a suitable system. During processing, inhomogeneities of concentration or temperature often arise. This typically happens during process steps such as addition of chemicals, mass transfer, heat transfer and chemical reaction. Inhomoge-neities lead to non-uniform processing and can negatively impact product quality. The objective of blending is to maintain the required degree of homo-geneity. The homogeneity at a given time, M(t), is given by the change in concentration of a component from c 0 to c(t) with time: M t c c t c c () () = − − ∞ 0 0 (1) where c  is the concentration after an infinite period of time. The same relation also holds for temperature homo-geneity. A standard …

Thermal analysis of low temperature seawater multi-effect distillation system

Abstract: Mathematical model and thermal analysis were performed for the low temperature multi-effect distillation system combined with thermal vapor compression(LT-MED-TVC).The variation in temperature loss as a function of effect number was carried out and the effects of the top brine temperature,the number of the evaporator′s effects and the motive steam pressure on grained output ratio(GOR) and specific heat transfer area were also studied.The results indicate that temperature losses increase significantly in the last effect evaporator.The thermal performance of LT-MED-TVC is much better than that of LT-MED.Better performance is obtained by increasing the top brine temperature,the number of the effects and the motive steam pressure for the operation of the system.

Flow rate characteristics of internal-mixing twin-fluid atomizers

Abstract: According to correlative theories,water,lubricating oil and Sodium Lauryl Sulfate solutions were used to investigate the influence of operational parameters(gas / liquid ratio) and liquid properties(viscosity,surface tension) on flow rate characteristics of a typical internal-mixing twin-fluid atomizer.Some important conclusions were drawn by experimental data analysis.For example,with the increase of liquid viscosity,the gas pressure and the liquid pressure increase,however,with the increase of liquid surface tension,the pressures of which are basically kept unchanged.On the basis of the investigation,empirical formula of atomizer fluid flow rate was regressed from the analysis of a great deal of experimental data.

Experimental investigation on apparent viscosity of heavy oil-water emulsions

Abstract: The relationships of apparent viscosity of heavy water-in-oil emulsion to the droplet size,the volume fraction of water and temperature were experimentally studied.The experiment shows that the viscosity decreases with the increase of the droplet size;and being different from light water-in-oil emulsion,the heavy water-in-oil emulsion presents a strong shear-thinning behavior even in lower water content;temperature change affects obviously the viscosity of concentrated water-in-oil emulsion,but it has a little impact on the relative viscosity.The predicted model for relative viscosity of Pal(1989) fits the experimental data well by taking into account the shear rate.

Experimental research of self-preventing fouling technology for the self-rotating twisted tape in heat exchangers

Abstract: The contrast experimental researches on the adhesive velocity of fouling,the dynamic thermal resistance of fouling,the abrasion velocity of the tube wall for the heat exchangers between smooth tubes and tubes with the self-cleaning plastic twisted-tape were carried out.The results indicate that the average adhesive velocity of fouling for the tubes with inserted twisted tape is only 54% that of the smooth tubes,the average dynamic thermal(resistance) of fouling is 30% smaller than that of the smooth tube,the abrasion velocity of the tube wall is very small.These investigation results will provide experimental support for the industry applications and popularization of self-cleaning twisted tape in heat exchangers.

Using carbide slag as desulfurater in dry flue gas desulfurization system

Abstract: Carbide slag used as desulfurizer instead of quicklime or white lime is an effective way to reduce the(operation) cost of dry flue gas desulfurization(DFGD) system.Experiments on dry flue gas desulfurization system of 75 t/h were performed by using carbide slag as desulfurizer.The experiment shows that because of the poor purity and activity,the carbide slag may concrete and block the nozzles when the mass fraction is higher than 15%,which affects the performance of the whole DFGD system.In consideration of both operation cost and desulfurization(efficiency,) a new kind of desulfurizer mixed with carbide slag and limestone was used.The result indicates that the desulfurization efficiency is about 80% when the mass ratio of carbide slag to limestone is 2 ∶1 and Ca/S mol ratio is 1.3.

Biosynthesis of astaxanthin in Haematococcus pluvialis caused by suppression on nitrogen and carbon metabolisms

Abstract: To study the synthetic mechanism of astaxanthin in Haematococcus pluvialis,the changes of nitrogen and carbon metabolisms in the algal cells growing under different inducing conditions were investigated.It showed that high light,acetate-supplementation,nitrogen and phosphate depletion all affected ribulose-1,5-bisphosphate carboxylase(Rubisco) and nitrate reductase(NR) either directly or indirectly,resulting in ultimate decrease of enzyme activities.The biosynthesis of astaxanthin in H.pluvialis occurred only when Rubisco and NR activities fell to rather low levels.By contrast,in control(CK) both enzyme activities maintained high levels under normal condition,but astaxanthin synthesis did not take place at all.These results strongly suggest that astaxanthin formation in H.pluvialis is caused by suppression on nitrogen and carbon metabolisms.

Study on vapor-liquid flow states of hanging downcomer bottom-orifices

Abstract: At hanging downcomer bottom-orifices,there exist three fluid flow states: only liquid flowing downwards through orifices(called "descending");only vapor flowing upwards through orifices(called "bubbling");neither of vapor-liquid phases flowing through orifices(called "bridging").The experiment was carried out in a(300 mm×)200 mm simulator of organic glass in air-water system.Using a multi-path conductometer,the three types of fluid flow states were successfully measured with ingenious layout of conductometric probes.The results indicate that the bridging exists really,its area fraction is 0.4-1.8 times bubbling area fraction.Hence,not only bubbling but also bridging shall be restricted for the seal criterion of hanging downcomer.

Analysis on cumulative exergy of two ethanol production processes

Abstract: The resource consumption of ethanol production by ethylene hydration method and maize zymosis method was analyzed by means of cumulative exergy analysis,which is based on life cycle consideration.The results were compared with those from the traditional energy and exergy analysis.It shows that for the system of ethanol(production,)although the energy and exergy consumption of the hydration method is less than that of maize zymosis method,its cumulative exergy consumption is higher than that of maize zymosis method.Therefore,the maize(zymosis) method is better in a view of the sustainability.

Assess your plant's true water-savings potential

Abstract: For companies in the chemical process industries, water is an indispensable utility. But the growing scarcity of quality industrial water, combined with stricter environmental regulations and the rising cost of wastewater treatment, have encouraged the conservation of water as a key utility in process plants. Concurrently, the development of systematic techniques for water reduction has made significant progress.

Flow resistance researches for SK static mixer tube of turbulent flow

Abstract: In order to acquire turbulent flow resistance rule in SK static mixer, a new numerical model of fluid resistance was put forward.Under the precondition of incompressible flow,fluid spiral motion in SK static mixer tube was resolved into axial beeline motion and circumferential rotation motion.With the theories of hydromechanics,the fluid resistance expressions of the two motions under the state of turbulent flow were obtained individually.After that,by reduplicating them,the calculating formula of SK static mixer for flow resistance was drawn.With water as experimental fluid,the turbulent fluid resistance in the SK static mixer was measured and the experimental formula was regressed by this experiment.By comparing and analyzing the theoretical results and experimental conclusions,a linear relationship between fluid friction factor and negative one fourth power of Renault number was concluded.

Technique of dyeing in supercritical CO_2

Abstract: The technique for dyeing in supercritical CO_2 was studied.The water-free dyeing facility with automatic computer control was designed based on supercritical CO_2 characteristics.The basic structure and operating principle of the facility were elucidated.The fabrics were dyed with disperse dyeing under supercritical CO_2,and the results of modifying and dyeing were measured by electronic scanning microscopy and infrared spectrometric analyzer.The dyeing parameters such as pressure,temperature and CO_2 flux were analyzed,which influenced the dyeing to a large extent.The modification on fabrics improves the rate of dye-uptake and the degree of homogeneity.The better dyeing effect can be achieved by controlling reasonably the dyeing pressure,temperature and CO_2 flux.